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I
PROCESS NEIGHING
GUIDE
e
i_ I
TABLE OF CONTENTS --INTRODUCTION 3
TYPES OF PROCESS TANK WEIGHING LOAD CELLS 4
TENSION LOAD CELLS 5
Tension Hardware 6
Model 60001 S-Beam 7
COMPRESSION LOAD CELLS 8
Mounting Variations 9
Support Structures for Compression Load Cells 10
Vessel Mechanical Restrictions 11
Compression Load Cell Hardware 12
Determining Quality of compression Load Cells 13
Determining Capacity of Compression Load Cells 14
Model 65016 TWA 15
Model 65059 TWA 16-17
PROCESS WEIGHING INSTRUMENTATION 18-19
J-Box 20
Controller 21
INSTALLATION 22-25
SYSTEM CALIBRATION 26-28
ENVIRONMENTAL CONSiDERATION 29
WEIGHING SYSTEMS IN HAZARDOUS AREAS 30-31
LOAD CELL TROUBLESHOOTING 32-33
General 32
Physical Inspection 32
Zero Balance 32 -Leakage Resistance 33
APPLICATION DATA FORM 35-38
Copyright 1991 Sensortronics Inc
INTRODUCTION
PLANNING YOUR PROCESS TANK SENSORTRONICS PROCESS WEIGHING SYSTEM WEIGHING EQUIPMENT
The purpose of this guide is to give you an Sensortronics has been the leading overview of process tank weighing manufacturer of industrial weighing equipment procedures and to assist you in planning the for over twenty years Our quality control and most efficient and effective system for your severe-environment test procedures are specific requirements second to none
Applications vary considerably so it would Virtually all of our equipment is designed and
be impossible to cover all of the variations in built to withstand the most demanding
this guide Therefore before you finalize your industrial conditions
plans we suggest that you fill out an Application Data Form in the back of the
At Sensortronics were proud of ourguide and return it to our Application and
weighing equipment but were just as proudEngineering Department One of our Appli shy
of our people Theyre friendly and know~cations Specialists will then call you to
ledgeable And theyre committed to review it
providing you exactly what you need when If at any time during the planning stages you you need it have any questions please feel free to call us for assistance So when youre considering process tank
weighing equipment if you consider the state-of-the-art and personal service youll decide on Sensortronics
UBCUNIFORM
BUILDING CODE
I SEISMIC ZONE 4 I Approved
3
TYPES OF PROCESS TANK WEIGHING LOAD CELLS
There are two different types of load cells used to transmit the weight of process materials to weighing elements shyCompression Type (Figure 1) and Tension Type (Figure 2)
Several factors will determine whether a compression or a tension load cell will best suit your requirements
CAPACITY
Compression load cells allow vessel capacities up to and including 1000000 pounds Whereas tension load cells are usually limited to gross weight capacities of 25000 pounds
FLOOR SPACE
By elevating vessels above floor level valuable space can be conserved with tension load cells In addition batch process vessels can easily be fed by ingredient tanks suspended above them
ACCURACY
Systems using compression load cells are sometimes more accurate because vessels which are mounted to a solid foundation are more stable Tension cells can be adversely affected by vessel swinging which is induced by vessel agitation or centrifugal force Vessel stops can be used to minimize this effect With proper equipment selection and installation accuracies of 1 and better can be expected from either method
VESSEL RESTRAINTS
Use of compression tank weighing assemblies usually eliminates any need for check rods Tension cells may need vessel stops to eliminate vessel swinging
4
Figure 1
Figure 2
TENSION LOAD CELLS
SMALL CAPACITIES (Figure 3)
Small capacity weigh vessels are the ideal candidates for this type of load cell When designing this method of vessel weighing consideration must be given to vessel agitation center of gravity and vibrations set up by vessel contents
LOW CENTER OF GRAVITY (Figure 4)
When a small weigh vessel has a low center of gravity and contains liquid a single tension cell if located directly over the center of the weigh vessel can provide an inexpensive method of determining vessel weight
e CYLINDRICAL AND RECTANGULAR VESSELS (Figures 5 and 6)
Vessels supported by tension load cells will usually fall into one of two main categories Cylindrical vessels which can be supported by three tension cells (Figure 5) Rectangular or square vessels which will require four tension cells (Figure 6)
With the use of a three or four tension cell arrangement it is important to have equal stiffness of all support beams and strucshytures Use of support beams with different stiffness may cause load to shift to adjacent tension cells and overload the cells
Figure 5
Figure 3
Figure 4
Figure 6 5
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
TABLE OF CONTENTS --INTRODUCTION 3
TYPES OF PROCESS TANK WEIGHING LOAD CELLS 4
TENSION LOAD CELLS 5
Tension Hardware 6
Model 60001 S-Beam 7
COMPRESSION LOAD CELLS 8
Mounting Variations 9
Support Structures for Compression Load Cells 10
Vessel Mechanical Restrictions 11
Compression Load Cell Hardware 12
Determining Quality of compression Load Cells 13
Determining Capacity of Compression Load Cells 14
Model 65016 TWA 15
Model 65059 TWA 16-17
PROCESS WEIGHING INSTRUMENTATION 18-19
J-Box 20
Controller 21
INSTALLATION 22-25
SYSTEM CALIBRATION 26-28
ENVIRONMENTAL CONSiDERATION 29
WEIGHING SYSTEMS IN HAZARDOUS AREAS 30-31
LOAD CELL TROUBLESHOOTING 32-33
General 32
Physical Inspection 32
Zero Balance 32 -Leakage Resistance 33
APPLICATION DATA FORM 35-38
Copyright 1991 Sensortronics Inc
INTRODUCTION
PLANNING YOUR PROCESS TANK SENSORTRONICS PROCESS WEIGHING SYSTEM WEIGHING EQUIPMENT
The purpose of this guide is to give you an Sensortronics has been the leading overview of process tank weighing manufacturer of industrial weighing equipment procedures and to assist you in planning the for over twenty years Our quality control and most efficient and effective system for your severe-environment test procedures are specific requirements second to none
Applications vary considerably so it would Virtually all of our equipment is designed and
be impossible to cover all of the variations in built to withstand the most demanding
this guide Therefore before you finalize your industrial conditions
plans we suggest that you fill out an Application Data Form in the back of the
At Sensortronics were proud of ourguide and return it to our Application and
weighing equipment but were just as proudEngineering Department One of our Appli shy
of our people Theyre friendly and know~cations Specialists will then call you to
ledgeable And theyre committed to review it
providing you exactly what you need when If at any time during the planning stages you you need it have any questions please feel free to call us for assistance So when youre considering process tank
weighing equipment if you consider the state-of-the-art and personal service youll decide on Sensortronics
UBCUNIFORM
BUILDING CODE
I SEISMIC ZONE 4 I Approved
3
TYPES OF PROCESS TANK WEIGHING LOAD CELLS
There are two different types of load cells used to transmit the weight of process materials to weighing elements shyCompression Type (Figure 1) and Tension Type (Figure 2)
Several factors will determine whether a compression or a tension load cell will best suit your requirements
CAPACITY
Compression load cells allow vessel capacities up to and including 1000000 pounds Whereas tension load cells are usually limited to gross weight capacities of 25000 pounds
FLOOR SPACE
By elevating vessels above floor level valuable space can be conserved with tension load cells In addition batch process vessels can easily be fed by ingredient tanks suspended above them
ACCURACY
Systems using compression load cells are sometimes more accurate because vessels which are mounted to a solid foundation are more stable Tension cells can be adversely affected by vessel swinging which is induced by vessel agitation or centrifugal force Vessel stops can be used to minimize this effect With proper equipment selection and installation accuracies of 1 and better can be expected from either method
VESSEL RESTRAINTS
Use of compression tank weighing assemblies usually eliminates any need for check rods Tension cells may need vessel stops to eliminate vessel swinging
4
Figure 1
Figure 2
TENSION LOAD CELLS
SMALL CAPACITIES (Figure 3)
Small capacity weigh vessels are the ideal candidates for this type of load cell When designing this method of vessel weighing consideration must be given to vessel agitation center of gravity and vibrations set up by vessel contents
LOW CENTER OF GRAVITY (Figure 4)
When a small weigh vessel has a low center of gravity and contains liquid a single tension cell if located directly over the center of the weigh vessel can provide an inexpensive method of determining vessel weight
e CYLINDRICAL AND RECTANGULAR VESSELS (Figures 5 and 6)
Vessels supported by tension load cells will usually fall into one of two main categories Cylindrical vessels which can be supported by three tension cells (Figure 5) Rectangular or square vessels which will require four tension cells (Figure 6)
With the use of a three or four tension cell arrangement it is important to have equal stiffness of all support beams and strucshytures Use of support beams with different stiffness may cause load to shift to adjacent tension cells and overload the cells
Figure 5
Figure 3
Figure 4
Figure 6 5
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
INTRODUCTION
PLANNING YOUR PROCESS TANK SENSORTRONICS PROCESS WEIGHING SYSTEM WEIGHING EQUIPMENT
The purpose of this guide is to give you an Sensortronics has been the leading overview of process tank weighing manufacturer of industrial weighing equipment procedures and to assist you in planning the for over twenty years Our quality control and most efficient and effective system for your severe-environment test procedures are specific requirements second to none
Applications vary considerably so it would Virtually all of our equipment is designed and
be impossible to cover all of the variations in built to withstand the most demanding
this guide Therefore before you finalize your industrial conditions
plans we suggest that you fill out an Application Data Form in the back of the
At Sensortronics were proud of ourguide and return it to our Application and
weighing equipment but were just as proudEngineering Department One of our Appli shy
of our people Theyre friendly and know~cations Specialists will then call you to
ledgeable And theyre committed to review it
providing you exactly what you need when If at any time during the planning stages you you need it have any questions please feel free to call us for assistance So when youre considering process tank
weighing equipment if you consider the state-of-the-art and personal service youll decide on Sensortronics
UBCUNIFORM
BUILDING CODE
I SEISMIC ZONE 4 I Approved
3
TYPES OF PROCESS TANK WEIGHING LOAD CELLS
There are two different types of load cells used to transmit the weight of process materials to weighing elements shyCompression Type (Figure 1) and Tension Type (Figure 2)
Several factors will determine whether a compression or a tension load cell will best suit your requirements
CAPACITY
Compression load cells allow vessel capacities up to and including 1000000 pounds Whereas tension load cells are usually limited to gross weight capacities of 25000 pounds
FLOOR SPACE
By elevating vessels above floor level valuable space can be conserved with tension load cells In addition batch process vessels can easily be fed by ingredient tanks suspended above them
ACCURACY
Systems using compression load cells are sometimes more accurate because vessels which are mounted to a solid foundation are more stable Tension cells can be adversely affected by vessel swinging which is induced by vessel agitation or centrifugal force Vessel stops can be used to minimize this effect With proper equipment selection and installation accuracies of 1 and better can be expected from either method
VESSEL RESTRAINTS
Use of compression tank weighing assemblies usually eliminates any need for check rods Tension cells may need vessel stops to eliminate vessel swinging
4
Figure 1
Figure 2
TENSION LOAD CELLS
SMALL CAPACITIES (Figure 3)
Small capacity weigh vessels are the ideal candidates for this type of load cell When designing this method of vessel weighing consideration must be given to vessel agitation center of gravity and vibrations set up by vessel contents
LOW CENTER OF GRAVITY (Figure 4)
When a small weigh vessel has a low center of gravity and contains liquid a single tension cell if located directly over the center of the weigh vessel can provide an inexpensive method of determining vessel weight
e CYLINDRICAL AND RECTANGULAR VESSELS (Figures 5 and 6)
Vessels supported by tension load cells will usually fall into one of two main categories Cylindrical vessels which can be supported by three tension cells (Figure 5) Rectangular or square vessels which will require four tension cells (Figure 6)
With the use of a three or four tension cell arrangement it is important to have equal stiffness of all support beams and strucshytures Use of support beams with different stiffness may cause load to shift to adjacent tension cells and overload the cells
Figure 5
Figure 3
Figure 4
Figure 6 5
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
TYPES OF PROCESS TANK WEIGHING LOAD CELLS
There are two different types of load cells used to transmit the weight of process materials to weighing elements shyCompression Type (Figure 1) and Tension Type (Figure 2)
Several factors will determine whether a compression or a tension load cell will best suit your requirements
CAPACITY
Compression load cells allow vessel capacities up to and including 1000000 pounds Whereas tension load cells are usually limited to gross weight capacities of 25000 pounds
FLOOR SPACE
By elevating vessels above floor level valuable space can be conserved with tension load cells In addition batch process vessels can easily be fed by ingredient tanks suspended above them
ACCURACY
Systems using compression load cells are sometimes more accurate because vessels which are mounted to a solid foundation are more stable Tension cells can be adversely affected by vessel swinging which is induced by vessel agitation or centrifugal force Vessel stops can be used to minimize this effect With proper equipment selection and installation accuracies of 1 and better can be expected from either method
VESSEL RESTRAINTS
Use of compression tank weighing assemblies usually eliminates any need for check rods Tension cells may need vessel stops to eliminate vessel swinging
4
Figure 1
Figure 2
TENSION LOAD CELLS
SMALL CAPACITIES (Figure 3)
Small capacity weigh vessels are the ideal candidates for this type of load cell When designing this method of vessel weighing consideration must be given to vessel agitation center of gravity and vibrations set up by vessel contents
LOW CENTER OF GRAVITY (Figure 4)
When a small weigh vessel has a low center of gravity and contains liquid a single tension cell if located directly over the center of the weigh vessel can provide an inexpensive method of determining vessel weight
e CYLINDRICAL AND RECTANGULAR VESSELS (Figures 5 and 6)
Vessels supported by tension load cells will usually fall into one of two main categories Cylindrical vessels which can be supported by three tension cells (Figure 5) Rectangular or square vessels which will require four tension cells (Figure 6)
With the use of a three or four tension cell arrangement it is important to have equal stiffness of all support beams and strucshytures Use of support beams with different stiffness may cause load to shift to adjacent tension cells and overload the cells
Figure 5
Figure 3
Figure 4
Figure 6 5
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
TENSION LOAD CELLS
SMALL CAPACITIES (Figure 3)
Small capacity weigh vessels are the ideal candidates for this type of load cell When designing this method of vessel weighing consideration must be given to vessel agitation center of gravity and vibrations set up by vessel contents
LOW CENTER OF GRAVITY (Figure 4)
When a small weigh vessel has a low center of gravity and contains liquid a single tension cell if located directly over the center of the weigh vessel can provide an inexpensive method of determining vessel weight
e CYLINDRICAL AND RECTANGULAR VESSELS (Figures 5 and 6)
Vessels supported by tension load cells will usually fall into one of two main categories Cylindrical vessels which can be supported by three tension cells (Figure 5) Rectangular or square vessels which will require four tension cells (Figure 6)
With the use of a three or four tension cell arrangement it is important to have equal stiffness of all support beams and strucshytures Use of support beams with different stiffness may cause load to shift to adjacent tension cells and overload the cells
Figure 5
Figure 3
Figure 4
Figure 6 5
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
TENSION HARDWARE
TENSION HARDWARE
Load transmission hardware for tension load cells (S Beams) comes in a variety of configurations
The hardware pictured Suspension string assemblies (Figure 7) and externally threaded rod ends (Figure 8) usually require either threaded flexure rods or wire rope to form a complete mounting package
When utilizing tension cells for vessel weighing care should be taken in the design phase to incorporate integral stops to limit process induced side forces It is also of prime importance to apply the force axially to the load cell
It is also important to equalize the load on the tension cells by adjusting the length of the wire rope or using adjusting nuts If a cell is not adjusted to carry its proportion of gross vessel weight the two cells immediately adjacent will assume its share of the load causing a possible overload condition
Figure 7
Figure 8
6
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
TENSION LOAD CELLS
MODEL 60001 S-BEAM PERFORMANCE SPECIFICATIONS
Rated Capacities (Ibs) 2S0 SOO 7S0 1K 1SK 2K 2SK 3K SK 10K 1SK and 20K
Safe Overload 1S0 FS
Full Scale Output (FS) 3 mV IV (nominal)
Zero Balance plusmn1FS
Rated Excitation 10 VDC (1S V maximum)
Non-Linearity lt 003 FS
Hysteresis lt 002 FS
Non-Repeatability lt 002 FS
Operating Temperature Range
Temperature Effect Output lt 00008 of reading 1degF Zero lt 0001S FSoF
Bridge Resistance 3S0 ohms (nominal)
Material and Finish Tool steel electroless nickel plated
FEATURES
bull Wide range of capacities bull Factory Mutual System Approved
bull Integral loading brackets bull Exceeds NIST H-44 Requirements
bull Stainless steel versions available bull NTEP certified load cells available for
bull Complete environmental protection class IIISOOO divisions and class IIILl10OOO divisions
8
I~JI I I
Wiring Tension (+) Red +Input4 CONDUCTOR
SHIELDED CABLE A Black -Input20 FEET
Green +Output White -Output SpeCificatIOns are sublect to change without notIce
Capacity A Thread B C 0 E
150300 38-24 75 50 200 300
50015K 12-20 100 75 200 300
2K4K 112-20
5K 34-16
75K10K 34-16
15K 1-14
20K 114middot12
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
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~ J en
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gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
Compression load cells are the most widely used method of weighing process vessels They utilize assemblies which have mounting hardware that transfer vessel load to a double or single ended shear beam in a compressive manner (Figure 9)
Most applications that use compression load cells have either three or four support locations depending on vessel geometry Vertical cylindrical vessels can utilize a three or four point support (Figure 10) Vertical rectangular or square vessels require a four pOint support
Here are some of the advantages compression type cells provide
bull Compact overall height
bull Self-checking capability so there is no need for check rods or stay rods
bull Capacities of up to 300000 pounds per load cell
bull Center of gravity of vessel has no effect so liquids or solids can be measured accurately
bull Horizontal cylindrical vessels can be accommodated with compression cells
bull Seismic rating up to and including Seismic Zone 4
bull Built-in provisions for thermal expansion and contraction
bull 150 of rated capacity overload protection 100 in any other direction
bull Rejection of side loads
I I I I I I I I I I I I I I I I I I I I I I I I
r--- I 1_--1 l 1 r -~~-1f-
I I LOAD I I LOAD
I I 4)4) I I I i I I I I I
r---J L---l l I I j -~~-F~
Figure 9
Figure 10
8
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
MOUNTING VARIATIONS
STRUCTURAL SUPPORTS (Figure 11)
bull Structural supports should not deflect more than 12 when vessel is filled to capacity
bull All structural supports on weigh vessel should deflect equally
bull Load cells should be level and plumb within one-half degree
CONCRETE FOUNDATION MOUNTING (Figure 12)
bull A solid concrete pier or foundation is preferred
bull If mounted on a concrete pad make sure the pad is level
bull Utilize shims grout etc as necessary to keep load cells level and plumb at both of the attachment locations (Le where the vessel support meets the top mounting plate and where the assembly meets the foundation)
HORIZONTAL VESSELS (Figure 13)
bull For the greatest accuracy load cells should be mounted under all supports
bull Orient load cells in the plane of maximum thermal expansion
bull For lower accuracy systemsload cells and flexure assemblies can be used
LEVEL AND PLUMB TO
+1120
l shyI I
I
-
---- shyFigure 11
Figure 12
Figure 13
9
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
l
COMPRESSION LOAD CELLS
SUPPORT STRUCTURES FOR COMPRESSION LOAD CELLS
When designing a support structure for vessel weighing consider the following as a minimum
bull Support structures should be rigid with low deflection A more flexible structure will have a low natural frequency and the vessel will respond accordingly (bounce) The weighing system will transshylate this into weight indicator instability (See Figure 14)
bull Non-uniform flooring under a tank support structure can cause a shift of the support structure (Figure 15) This also causes errors due to force shunts and other mechanical constraints such as installed piping A permanent shift in the support plane after load cell installashytion may cause an incorrect indication on the readout device This is due to cosine error where the load cells signal is reduced by
1
COS (of Angle) (Figure 16)
bull After following proper mechanical design and installation practices the weighing system must be calibrated to achieve maximum accuracy The various methods are discussed in the section entitled System Calibration on pages 26-28
10
CAUTION Supports 112 MAX
more than 12 under full vessel load
should deflect no
Figure 14
Figure 15
IncorrectCorrect I Beams on same plane Vessel tilts
~-------------
G==i
r
-
II I i
LJ Fjgure 16
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
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GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
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U5 I
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I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
VESSEL MECHANICAL RESTRICTIONS
To insure the highest possible weighing accuracy we suggest reviewing your design drawings with a Sensortronics Application Engineer Some of the items which have a direct affect on weighing accuracy are
PIPING TO AND FROM THE WEIGH VESSEL (Figure 17)
Basic considerations are
1 Flexible connections to and from vessel are always preferred for best weighing accuracy
2 Flexible connections should be installed in the horizontal run of piping For best performance these horizontal runs should have no bends and should occur before first pipe support
3 Do not use flexible connections to correct for piping misalignment This will eliminate their effectiveness
4 Pipe supports should be mounted to same structural support as weigh vessel
5 If system is vented pass inlet piping through oversized holes in vessel
6 In sealed systems piping must be designed with more care as the piping is liable to generate horizontal and vertical force shunts which will affect accuracy
OTHER CONNECTIONS TO WEIGH VESSEL (Figures 18 and 19)
Catwalks ladders shared structural supports and mechanical restrictions may cause interaction between weigh vessels and should be avoided or isolated as far as practical Our Application Engineers can provide recommendations to enhance performance
Figure 17
Figure 18
Figure 19
11
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
COMPRESSION LOAD CELL HARDWARE
The most important aspect of hardware is to transmit the applied load vertically to the load cell With Sensortronics Tank Weighing Assemblies this hardware is supplied as an integral part of the assembly and it will assure you excellent load transmission (Figure 20)
The correct hardware also limits movement of the weigh vessel Sensortronics selfshychecking design makes the weighing assembly an integral part of the vessel and eliminates the need for additional safety check rods or stay rods of any type This design allows for thermal expansion I contraction and it will successfully withshystand most seismic disturbances
The 65016 TWA complies with Zone 4 requirements as outlined in the 1988 edition of the Uniform Building Code For a detailed discussion of this self-checking capability request Sensortronics Engineering Report 1990 (ER-1990)
~ I I I
I I I I I I I I I I
Figure 20
12
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
DETERMINING QUANTITY OF COMPRESSION LOAD CELLS
To determine the required number of load cells the most important consideration is the size and shape of the weigh vessel Most vertical vessels fall into two categories cylindrical or squarel rectangular (Figure 21)
Vertical cylindrical vessels can easily distribute their weight over three support points Whereas a vertical rectangular or square vessel will require four or more support locations
Horizontal cylindrical vessels can utilize two compression cells and two flexure assemblies However due to the difficulty in achieving an accurate calibration it is recommended that four compression cells be used (Figure 22)
Other factors that affect the required number of support locations are wind loading large capacity and seismic considerations See Sensortronics Engineering Report No ER-1990 for detail on seismic considerations
I~
Figure 21
Figure 22
13
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
DETERMINING THE CAPACITY OF COMPRESSION LOAD CELLS
To determine the capacity requirements of compression load cells
1 Determine the empty load of the vessel (This is the weight of the tank when it is empty plus any permanent equipment such as motors agitators or piping)
2 If the vessel to be weighed has a double-shell Uacketed) be sure to include the weight of any fluids introduced into the jacket
3 Determine the live load of the vessel (This is the maximum capacity of the vessel not a normal or usual or working capacity) Consideration should also be given to shock loads
4 Add these two figures to obtain Gross Weight
Gross Weight is then divided by the number of structural support points The resultant number is the required capacity for your load cells
As a general rule if your requirement falls between two capacities choose the higher This conservative method of determining capacity helps take into account any unequal load distribution on the load cells caused by agitators mixing equipment or vessels with higher empty load weights than originally anticipated in the design of the vessel
EXAMPLE Vessel Empty Weight 10500 pounds Vessel Live Weight 85000 pounds Vessel Gross Weight 95500 pounds
n i I I
I i
i
(
VESSEL EMPTY
WEIGHT
10500 POUNDS
VESSEL LIVE
WEIGHT
85000 POUNDS
VESSEL GROSS WEIGHT
95500 POUNDS
Figure 23
95500 pounds -- 4 supports = 23875 pounds per load cell Choose a 25000 pound capacity load cell
14
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
AND JACKETED shy20 FT LONG
LOAD CELL
~ J
Typical for all Tank Weighing Assemblies
Wiring Red Black Green White
Compression (+) +Input -Input +Output -Output
15
COMPRESSION LOAD CELLS
MODEL 65016 TWA PERFORMANCE SPECIFICATIONS Rated Capacities (Ibs)
Safe Overload
Full Scale Output
Bridge Resistance
Rated Excitation
Non-Linearity
Hysteresis
Non-Repeatability
Zero Balance
System Accuracy
Operating Temperature Range
Temperature Effect Output Zero
Side Load Discrimination
Material and Finish Load Cell Mounting Assembly
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system Installation
CABLEshy4 CONDUCTOR 2 AWG SHIELDED
1K 1SK 2SK SK 10K 1SK 2SK SOK 7SK 100K 12SK
1S0 of Rated Capacity
3 MVIV plusmn 02S
700 ohms (nominal)
10VDC (2SV maximum)
lt003 FS
lt002 FS
lt001 FS
plusmn 1 FS
Better than 01
lt0008 of reading of lt0001S FSI of
SOO1
Tool Steel Electroless Nickel Plated
1K2SK - Cast Ductile Iron Zinc Plated
Higher Ranges - Welded Steel Zinc Plated
FEATURES
bull 1000 to 125000 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Built-in provisions for thermal expansion and contraction
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Approved for UBC-SS Seismic Zones 1-4
bull 150 compression overload protection 11 00 in any other direction
bull Factory Mutual System Approved bull Complete stainless steel assemblies available
CAPACIT
lK 5K
OK 25K
SOK 75K 930 1625 1200 1150 78100 -~
lOOK - 125K 11752350 1400 2000 1200 1000 800 112 1 50
For capacities to 300K consult factory
DENOTES FULL SCALE CAPACITY
ASSY
1605
1625
1650 -16125
NOTE
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
COMPRESSION LOAD CELLS
MODEL 65059 TWA PERFORMANCE SPECIFICATIONS Rated Capacities 5075100150250500
1K 15K 25K
Safe Overload 150 of Rated Capacity
Full Scale Output 3 MV IV plusmn 025
Bridge Resistance 350 ohms (nominal)
Rated Excitation 10VDC (15V maximum)
Non-Linearity lt003 FS
Hysteresis lt002 FS
Non-Repeatability lt001 FS
Zero Balance plusmn1FS
System Accuracy Better than 01
Operating Temperature Range
Temperature Effect Output lt00008 of readingoF Zero lt00015 FSoF
Side Load Discrimination 5001
Material and Finish Load Cell Tool Steel Electroless Nickel Plated
(Neoprene Boot on 50 to 250 lb units)
Mounting Assembly Steel Zinc Plated with Neoprene
Shock Mount in all Ranges
NOTE Performance specifications apply to the Shear Beam load cells
Dependent on satisfactory system installation
FEATURES
bull 50 to 2500 pounds capacities
bull Self-checking eliminates the requirement for checking devicesstay rod assemblies
bull Low profile design
bull Complete environmental protection
bull Load cells have standardized outputs for multi-cell systems
bull Stainless steel assemblies available in the higher ranges (500 to 2500 pounds)
bull 150 compression overload protection 150 side force protection
bull Provides shock absorption for high impact applications
bull Factory Mutual System Approved
OPTIONS AND ACCESSORIES
bull NTEP certified load cells available for ClasSlllL10000 divisions
bull Stainless steel load cells or complete assemblies
bull Load cell capacities up to 200000 pounds
bull Digital and analog control instrumentation
bull Junction Boxes and Intrinsic Safety Barriers
bull Load Equalizer Pads
bull Articulated Load Plate Interface
bull Integral conduit adaptors (1 4 NPT)
bull Electro-polished Sanitary versions
16
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
22 AWG SHIELDED AND JACKETED 20 FT LONG
NEOPRENE --J--_ ISOLATION
COMPRESSION MOUNT
COMPRESSION LOAD CELLS
MODEL 65059 TWA
550
(6 PLACES)
CABLE 4 CONDUCTOR CABLE shy
NEOPRENE ISOLATION COMPRESSION MOUNT
400
l--- 600 ---~
t 425
~~~--~---~r-50
rl ~4OO
412
15K 2K 25K CAPACITY
17
5075100150250 CAPACITIES
44 DIA (6 PLACES)
CABLE shy4 CONDUCTOR 22 AWG SHIELDED AND JACKETED 20 FT LONG
300
~~~--~-----rl-~50
rl I--shy 400
l--- 600 ----
lK CAPACITY
4 CONDUCTOR 22 AWG SHIELDED AND JACKETED ~====~===~i--t NEOPRENE
388
ISOLATION20 FT LONG
COMPRESSION
MOUNT
~
500 CAPACITY
See below for 1K fhru 25K Outlme Drawings
L~ -----1
56 DIA (2 PLACES)
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
Sensortronics offers a wide variety of process weighing instrumentashytion Here are just a few of the possible variations
INFORMATION ONLY
This system usually consists of a locally mounted electronics package with a digital display of vessel contents Often a remote display of the vessel contents or a printed report for manufacturing or accounting is generated (Figure 24)
RE-TRANSMISSION ONLY
This instrumentation variation uses a Blind Transmitter IJunction Box to provide load cell excitation output signal summing and an analog or digital signal proportional to vessel contents for input to a control system (Figure 25)
r-shy
shy
~ dllO ~ f ~B
--
v
~
J-BOX
J I
I I
I 1mJ111111mJ
REMOTE DISPLAY
Figure 24
4-20MA BLIND
TRANSMITTER
Figure 25
CONTROLLER
bullJ (=F
Lshy = PRINTER
CONTROL SYSTEM
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PROCESS WEIGHING INSTRUMENTATION
PROCESS WEIGHING INSTRUMENTATION
INFORMATION AND RE-TRANSMISSION
This system goes a step further and adds a re-transmission signal proportional to weight that is used to assist in a control scheme Its signal is normally a 4-20 MA DC or depending on control input requireshyments a digital signal such as RS232 485 etc (Figure 26)
INFORMATION RE-TRANSMISSION AND CONTROL
The addition of control to an instrumentation system can be as simple as contact closures at preshydetermined weight values For example you could use high level shut-ofts to batching systems which would control the entry and exit of various materials to the weigh vessel totalize these additions and deletions to the vessel and report to a supershyvisory device as to weigh vessel activity and history (Figure 27)
CONTROLLER
gt0shy4middot20 MA
JmiddotBOX RS 232422485
0middot10V DC ~---
Figure 26
CONTROLLER
J-BOX
4-20 MA RS23~2~4=22~~48~5-------
TioVoc SETPOINTS bull LC OR COMPUTER PRINTER SUPERVISORY CONTROL bull
Figure 27
19
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
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x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
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~ J en
I shyI S
Z cr (J
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LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PROCESS WEIGHING INSTRUMENTATION
JUNCTION BOXES (Figures 28 and 29)
Summing Junction Boxes (normally located adjacent to the weigh vessel) are designed to sum the electrical outputs of load cells used in process tank weighing applications Any capacity of tension or compression load cells can be accommoshydated but load cells of different types and capacities should never be mixed
FEATURES
bull Up to 4 load cell inputs with individual Figure 28 load cel trim pots
bull Up to 12 load cell inputs with section pots
bull 20 of output cable included
bull Remote sensing capability for cable lengths greater than 25
OPTIONS
bull Stainless steel NEMA 4 enclosure
bull Explosion proof enclosure
bull Lightning protection for load cell protection (surge arrestor)
o
o I I~I~~I~I~I TO WEIGHMETER
Figure 29
PROCESS WEIGHING INSTRUMENTATION
~
J ~I
MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
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U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PROCESS WEIGHING INSTRUMENTATION
~
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MODEL 2010 PROCESS WEIGHT CONTROLLER
DESCRIPTION (Figures 30 and 31)
The 2010 Process Weight Controller is a multi mode intelligent load cell interface compatible as a discrete multidrop or distributed control system component Flexibility reliable performance ease of operation and quality engineering make the 2010 the ideal solution for any weighing system control need
As a stand alone device the 2010 is capable of complete single loop control of a dedicated weighing process As part of a locally integrated network the 2010 provides single loop control and inteshygration to a local process control network Communication with a host computer system is possible via any of three available serial data links
FEATURES
bull Five Program Modes shyUser Programmable
Batch Controller Loss In Weight Controller Setpoint Controller Rate of Change Monitor Weighmeter
bull Display Range of plusmn 999950
bull 32 character alphanumeric LCD display (Backlit)
bull 18 key operator interface with tactile feel
bull 1610 capability
bull Digital Calibration
bull Digital Filtering
bull Programmable Security Access Codes
bull Display units (pounds ounces kiloshygrams grams tons and tonnes)
Figure 30
Model 2010 Process Weight Controller
o o
HINGE INPUT OUTPUT MODULES (1610 MODULES
ANALOG MAX) OUTPUT
AC INPUT LOAD CELL INPUT
SERIAL PORT 1 20 MA amp RS232
SERIAL PORT 3 ~ SERIAL PORT 2 RS232(RS485) RS232(RS422)
Figure 31
21
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
INSTALLATION
MODEL 65016 TWA
GENERAL RECOMMENDATIONS
1 Using Figure 32 determine proper mounting dimensions and bolt diameters for your particular TWA installation
2 Make sure that mating surfaces are level and smooth
3 Structural supports should be rigid
4 Align TWA as shown in Figure 33 This will allow for thermal expansion and contraction of the vessel with minimal weighing effect on weighment
5 Use flexible conduit when installing cable from TWA to summing junction box (See page 25 for further wiring information)
6 Although the TWA is a rugged device it can be damaged by shock loads If forklifts etc can hit the support structure at the installation pOint barriers or stops should be used
~---------- 8 --------~
C
CABLE - L--- D ------lt 4 CONDUCTOR 22 AWG SHIELDED
I
H DIA (8 PLACES)iGI f-- (TYP)
~ J
AND JACKETED-20 FT LONG
LOAD CELL
A
ASSY CAPACITY
1605 lK - 5K
1625
1650
16125 lOOK
A B C 0 E
513 935 500 625 375
800 750 600
30 1625 1200 1150 950
75 23 50 14 00 2000 1200
F
400
800
900
1000
G H J 275 56 50
600 78 75
650 78 100
800 112 150
c-- DENOTES FULL SCALE CAPACITY
65016-XXX - TWA
Typical for all Tank Weighing Assemblies
Wiring Compression (+) Red +Input Black -Input Green +Output White -Output
Figure 32
22
USE THIS ORIENTATION IN THE PLANE OF MAXIMUM EXPANSION
Figure 33
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
INSTALLATION
J PREPARING MOUNTING LOCATION
After determining the proper level and smooth location to mount the TWAs preparation of the intended area needs to be accomplished The TWA is easily installed on a metal beam or a concrete foundation or footing If your support structure is different from those outlined blow please contact Sensortronics for application assistance
CONCRETE FOOTING OR FLOOR (Figures 34A and 348)
A Install threaded rods in foundation as shown Make sure they line up with the holes in TWA mounting plates
B Install leveling nuts on threaded foundation rods (See Figure 34A)
J C Align TWA in plane of maximum
thermal expansion I contraction
D Loosely attach nuts to foundation rods Do not tighten nuts at this time (See Figure 34B)
E TWAs should be level and plumb (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
METAL STRUCTURE (Figures 35A amp 358)
A Position TWA on beam or support and use as template for hole patterns Be sure to center TWA with shear center of support beam (See Figure 35A)
B Remove TWA and drill holes
C Align TWA in plane of maximum thermal expansion I contraction
D Install bolts and nuts loosely Do NOT tighten at this time (See Figure 35B)
E TWAs should be level and plumb J (plusmn5deg)
F Repeat steps A thru E for each TWA
G See page 24 for shimming instructions
CONCRETE FOOTING OR FLOOR LEVELING NUTS
Figure 34A
NUTS
Figure 348
METAL STRUCTURE
Figure 35A
Figure 358 23
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
(J
U5 I
(J
U5 +
Cl J I (j)
Cl UJ cr
~ J en
I shyI S
Z cr (J
gtshycr (J
LC 3
x x (J (J Cl UJ UJ J
I U5 U5+ II + (j) MODEL 20034
I-Cl ~ Z gtshyUJ J I cr cr cr en S (J (J
Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
INSTALLATION
SHIMMING
After installation of the TWA and vessel but before tightening nuts shimming may need to be done to assure that the TWAs are level and plumb within plusmn5 0 and that the tank weight is equally distributed on the TWAs (See Figure 36 and 37)
1 After TWA and vessel installation physically inspect all TWAs and using normal force try to adjust the assembly If you can move either of the pins which connect the mechanical support assembly with the load cell STOP Shimming is necessary
2 Raise vessel slightly and insert shim (starting with shim material of approximately 0020) under the base of the TWA Repeat for each TWA as required Lower vessel and check to insure no manual adjustment to TWA can be made Figure 36
3 Another purpose of shimming is to equally distribute the tanks weight on the TWAs To check the distribution a) With excitation voltage applied to TWAs
measure signal output on the green (+)
and white (-) wires b) Signal output should not vary more than
plusmn25 from other TWAs c) If output does vary more than 25 repeat
shimming procedure on TWA d) Re-check signal outputs after shimming
NOTE If on your first attempt only one TWA requires shimming recheck all TWAs to assure that all are still level
(
FINAL SrEP
1 Tighten nuts to approximately 50 ft lib
2 Recheck all TWA signal readings to verify load distribution once again
3 Repeat steps 1 2 and 3 for all TWAs
Figure 37
24
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
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S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
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x UJ
I
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U5 I
(J
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I U5 U5+ II + (j) MODEL 20034
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Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
INSTALLATION
J ELECTRICAL CONNECTIONS FOR LOAD CELLS
In most TWA installations termination of the TWA integral cable will take place in a Junction Box such as the Sensortronics
Model 20034 A typicalJ Box and ~ndividual load cell connections are shown in Figure 38
J
RED +EX
2I
BLK -EX shyWHT -SIG 0
J 3 GRN +SIG 4 GRY SHLD 5
gtshycr (J
Cl J I (j)
GENERAL WIRING CONSIDERATIONS
1 DO NOT cut cable on the TWA Coil any excess cable within the J-Box
2 If cable lengths in excess of 25 are required order additional 4 or 6 conductor
cable from Sensortronics at 1-800shy722-0820 Use of remote sensing may be desirable
3 Use flexible conduit between the TWA and the Junction Box
4 A drip loop is recommended in either flexible or rigid conduit to prevent moisture from entering either the load cell or J Box
Z I- ~ Cl cr I UJJ
S en(J cr
(J (J X xU5 U5 UJ UJ + I I +
TO WEIGHMETER
15141312111 (j) (j) cr cr
I + TRIM POTS CLOCKWISE TO INCREASE SPAN
W sect)
20034-40
5 SHLD GRY
+SIG GRN
W 4
-t -SIG WHT3 02 J -EX BLK1 +EX RED
11121314151 11121314151 LC 2
x UJ +
x UJ
I
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U5 I
(J
U5 +
Cl J I (j)
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Figure 38
25
I
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
SYSTEM CALIBRATION
CALIBRATION PROCEDURES
There are five different methods that can be used to calibrate electronic weighing systems with strain gauge load cells These procedures are described in detail below
Two methods are based on simulation of the load cell signal and three are based upon using known weights
All five procedures assume that the digital weight indicator has been configured according to the specific procedures found in its Installation and Operation Manual and that the Summing Junction Box has been trimmed using one of the two methods described in the Junction Box Manual
METHOD I - ELECTRONIC CALIBRATION USING A LOAD CELL SIMULATOR
Load Cell Simulators are devices available from load cell manufacturers which electrically simulate the output of the load cells Simulators from one manufacturer can be used to calibrate a weighing system which uses another manufacturers load cells
The simulators consist of a Wheatstone bridge with a variable resistor that can be precisely set to simulate a particular level of output from the load cell Some models are continuously varishyable and some have certain fixed output pOints
Simulators are generally accurate to better than 1 part in 1000 making them very acceptable for calibrating process weighing systems shyparticularly large vessels for which it would be difficult to obtain sufficient calibration weights
The main limitation of a simulator is that it will not compensate for any weight variations caused by misalignments or mechanical connections to the weighing system
PROCEDURE
Connect the simulator in place of the load cells following the manufacturers instructions and wiring codes
With the simulator set at zero follow the instructions for the digital weight indicator to ZERO the indicator
Adjust the simulator to produce an output equal to full scale on the weighing system For instance if you have three 3000 mV IV load cells each with a capacity of 5000 pounds set the simulator to 200 mV IV to simulate 10000 pounds A 100 mV IV setting would simulate 5000 pounds and so on
Set the digital weight indicator SPAN to equal the weight represented by the simulator setting
Return the simulator to a zero setting then to settings representing several intermediate weights and check the zero and linearity of the instrument
Connect the load cells to the indicator and repeat the ZERO procedure to adjust for the weight of the scale vessel or platform
A VARIATION ON METHOD I
If you have an accurate digital voltmeter capable of reading to 001 millivolt or better you can calculate the expected load cell signal for any particular load and adjust the simulator until the calculated signal is measured between the Signal + and Signal connections
Measure the ACTUAL Excitation Voltage VExc and note the nominal mV IV rating of the load cells (use the minimum actual mV IV if the load cells were trimmed using the Excitation Trim method)
Millivolts (at any weight) = (VEXC) X (mV IV) X (Desired WeightScale Capacity)
Set the ZERO SPAN and intermediate weights as in the original procedure
METHOD II - ELECTRONIC CALIBRATION USING A MILLIVOLT SOURCE
Some manufacturers of instrument calibrators for thermocouples and other devices make precision adjustable millivolt sources which can be used to calibrate a weighing system (Transmation is one well-known manufacturer)
If you have a millivolt source capable of producing a signal accurate to 001 millivolt over a range of 000 to 3000 millivolts it can be used for calibration
The limitations are the same as for Method I
26
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PROCEDURE
Calculate the actual millivolt output signal of the load cells at zero and full scale using the formula and methods described in the Variation of Method I
Disconnect the Signal Leads ONLY from the digital weight indicator and attach the millivolt simulator leads to the indicator observing voltage polarity (Plus to Plus Minus to Minus)
Set the millivolt source to simulate the signal corresponding to a ZERO weight on the scale and ZERO the indicator following the manushyfacturers instructions
Change the millivolt source to simulate the signal corresponding to a full scale weight on the scale and set the SPAN on the indicator
Check the linearity and return to zero by setting the simulator to several intermediate millivolt levels METHOD III - DEAD WEIGHT CALIBRATION USING CALIBRATED MATERIAL TRANSFER
This method and the two methods which follow it use the addition of known amounts of weight to calibrate the weighing system
In calibrated material transfer an amount of material is weighed on nearby scales of known accuracy and transferred to the weighing system being calibrated
The accuracy of the method depends upon the care which is taken to make sure that all of the weighed material is transferred
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Transfer a known weight of material equal to approximately 80 to 100 of the scales rated capacity from a nearby scale Set the indicators SPAN to the known weight by following the manufacturers instructions
SYSTEM CALIBRATION
Remove the material and check the scales return to zero Rezero if necessary
Apply known weights of material in increments of approximately 10 of full scale to test the linearity and repeatability of the weighing system
METHOD IV - DEAD WEIGHT CALIBRATION USING CALIBRATED TEST WEIGHTS
This method is identical to Method III except that calibrated test weights are used instead of transferring material from a nearby scale
Since it is expensive to obtain large quantities of calibrated test weights this method is usually limited to scales of 15000 pound capacity or less
PROCEDURE
This procedure is identical to Method III except calibrated test weights are used instead of transferred material
METHOD V - DEAD WEIGHT CALIBRATION USING THE SUBSTITUTION METHOD
This method is used for high accuracy calibration where it is not possible to use calibrated weights equal to the full scale capacity of the weighing system
Ideally the calibrated weights should be equal to at least 5 of the weighing system capacity and they should be of the largest size which can be conveniently handled since they will have to be repeatedly applied to and removed from the weighing system
PROCEDURE
ZERO the digital weight indicator by following the manufacturers instructions
Apply all of the calibration weights and record the reading Set the indicators SPAN equal to the amount of weight applied
27
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
SYSTEM CALIBRATION
Remove the calibration weights and apply substitute material until the indicator has the same reading as when the calibration weights were applied
Re-apply the calibration weights and record the new reading
Substitute more material until the indicator shows the new reading
Repeat the addition of calibration weights and substitute material until the desired full scale weight of the system is reached
Note that the amount of material on the weighing system will be equal to the calishybration weights multiplied by the number of times the substitute material has been added The indicator may show a different weight due to accumulated errors
Adjust the indicators SPAN so that it agrees with the amount of material which has been added to the weighing system
If a large correction is required it may be necessary to repeat the substitution process to refine the calibration
Remove the material and calibration weights and check for return to zero
REQUIREMENTS OF LEGAL-FORshyTRADE WEIGHING SYSTEMS
If a weighing system is used to measure material for sale or for custody transfer it must be calibrated using approved methods by individuals authorized to calibrate legal-forshytrade weighing systems
Generally authorization is easy to obtain if an individual or company can demonstrate that they have an adequate quantity of certified calibration weights are knowledgable in appropriate calibration techniques and make application to the governing agency for authorization
Weighing systems used for process applications such as inventory control and batch formulation do not generally have to be calibrated as legal-for-trade
28
If you are not sure whether a weighing system must be legal-for-trade we recommend you contact the governing agency in your area concerning their requirements
BASIC TROUBLESHOOTING
Although troubleshooting is not the focus of this Technical Bulletin some basic troubleshooting skills are often helpful when calibrating weighing systems
When troubleshooting a weighing system remember this - electronic weighing systems are extremely accurate and predictable Most problems are caused by one of three things
1 Wiring errors
2 Incorrectly configured components
3 Unexpected or unnoticed effects from mechanical connections to the weighing system
Begin by double checking the load cell connections
Measure the excitation voltage starting at the indicator then moving to the junction box then to the individual load cells
Disconnect the signal wires one load cell at a time and measure the signal Is it approximately what you would expect given the load distribution on the weighing system
Recheck the configuration of the indicator following the manufacturers instructions stepshyby-step
Finally if you havent located the cause of the problem by this time then visually inspect the weighing system Is anything other than a load cell supporting a portion of the weight In particular check flex connections on piping and electrical connections Make sure the load cells and their mounts are properly installed and adjusted
NEVER trust your memory or make assumptions Verify everything and you should find the problem
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
ENVIRONMENTAL CONSIDERATIONS
J Sensortronfcs has supplied systems which have been used in the most severe environshyments imaginable Our application engineering staff can help you design weighing systems which meet your most demanding requirements
A Are there corrosive materials in an area where they could be spilled on the tank weighing system
B Does the presence of chemicals in the tank area create a potentially hazardous environment
C Will the tank weighing system see extremes in temperature or humidity
o Will the tank weighing system be located in an area with regular or periodic wash downs
The range of conditions which a weighing system is exposed to are as wide and varied as industry itself To assure you a long and dependable service life a number of questions should be answered Among the items to consider are
A
B
~ yen
c
oo bull
E
E Is the vessel subject to wind loading shock vibration or seismic activity
29
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
WEIGHING SYSTEMS IN HAZARDOUS AREAS
When weighing systems need to be located in areas classified by the National Electrical Code as hazardous due to gases flammable vapors or combustible dusts the use of intrinsic safety barriers assures safe operation of the weighing system
Sensortronics Tank Weighing Assemblies are FM approved for use in conjunction with Intrinsic Safety Barriers for Class I II amp III Divisions 1 amp 2 Groups A-G from various manufacturers A typical system layout using barrier assemblies is illustrated below (Figure 39)
Intrinsic safety is a technique that limits thermal and electrical energy below a level required to ignite a specific hazardous mixture The National Electrical Code states Intrinsically safe equipment and wiring shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific flammable or combustible atmosshypheric mixture in its most easily ignitable concentration
HAZARDOUS AREA
r NEMA BOX TO WEIGHMETER
65016 TWA (TYPl LOAD CELL 1
~~----
LOAD CELL 2
CLASS I II amp III DIV 1 amp 2
GROUP AmiddotG
J-BOX
I
LOAD CELL 3
TO J-BOX
Figure 39
NON-HAZARDOUS AREA
INTRINSIC SAFETY BARRIER
BOX
NEMA BOX
WEIGHMETERI CONTROLLER
ENCLOSURE
30
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
WEIGHING SYSTEMS IN HAZARDOUS AREAS Listed below is a compilation of the various classifications groups and divisions as defined by the National Electrical Code
CLASS 1 LOCATIONS
Potential for explosion or fire due to the presence in sufficient quantities of flammable gases or vapor in the atmosphere
CLASS 1 DIVISION 1 LOCATIONS
These are locations where either by normal operating conditions failure of storage containment systems or normal maintenance conditions hazardous concentrations of flammable gases or vapors exist either continuously or periodically These locations require that every precaution be taken to prevent ignition of the hazardous atmosphere
CLASS 1 DIVISION 2 LOCATIONS
These locations are ones which are immediately adjacent to Class 1 Division 1 locations and may have accumulations of gases and vapors from these locations unless ventilation systems and safeguards to protect these ventilation systems from failure are provided An area can also carry this desigshynation when (1) handling or processing flammable vapors or gases Under normal conditions these vapors and gases are within a sealed or closed system or container Only under accidental system or container breakdown or improper abnormal use of operation equipment will these flammable liquids or gases be present (2) when failure of ventilation equipment would allow concentrates of flammable vapors or gases to accumulate
CLASS 2 LOCATION
Class 2 locations are those which are hazardous due to the presence of combustible dust
CLASS 2 DIVISION 1
The locations are those that either continuously intermittently or periodically have combustible dust in suspension in the air in sufficient quantities in normal conditions to form exshyplosive or ignitable mixtures Another area which can carry this classification is an area with machinery malfunctions causing a hazardous area to exit while providing a simultaneous source of ignition due to electrical equipment failure
CLASS 2 DIVISION 2
This area is one which under normal operations combustible dust will not be in suspension in the air nor will it put dust in suspension However dust accumulation may interfere with heat dissipation from electrical equipment or accumulations near and around
electrical equipment and could be ignited by burning material or sparks from the equipment
GROUPSATMOSPHERES
Group A (Class 1) Atmospheres containing acetylene
Group B (Class 1) Atmospheres containing hydrogen or gases and vapors of equal hazard such as manufactured gases
Group C (Class 1) Atmospheres containing ethylene ethylether vapor or cyclo- propane
Group D (Class 1) Atmospheres containing solvents acetone butane alcohols propane gasoline petroleum naptha benzine or lacquer
Group E (Class 2) Atmospheres containing metal dust
Group F (Class 2) Atmospheres containing carbon black coal or coke dusts
Group G (Class 2) Atmospheres containing flour starch or grain dusts
31
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
LOAD CELL TROUBLESHOOTING
GENERAL
The most essential element in an electronic weighing system is the load cell There are basic field tests which can be performed on-site in the event a fault condition is recognized A good quality digital multi-meter with at least a four and one-half digit ohm meter range is essential The static field tests to be performed on the load cell consists of a physical inspection checking the zero balance of the load cells strain gage bridge verifying the integrity of the bridge resistance values and finally determining whether resistance leakage exists
PHYSICAL INSPECTION
If the load cell surface has rusted badly corroded or has become heavily oxidized there is a chance the strain gage areas have been compromised as well Look at specifics to verify their condition Do the sealed areas show signs of contamination Regarding the load cell element itself is there apparent physical damage corrosion or significant wear in the areas of load introduction load cell mounting or the flexure areas Also inspect the condition of the load cell cable to assure the integrity has not been compromised due to cuts abrasions or other physical damage It is a good idea to pay particular attention to the condition of the cable at the cable fitting Assure that no mechanical force shunts exist Be certain protective covers are not impeding the deflection of the load cell (particularly in the case of low capacity units with wrap around covers) It is imperative that no foreign materials are restricting the free movement of the load cell as it deflects under load
In the phYSical inspection stage pay close attention to the condition of any type of accompanying weighing assembly and ancillary weighing system components such as stay I check rods
In some instances where a mechanical overload potential exists it may be necessary to remove the load cell from the installation and check it for distortion on a surface which is absolutely flat In those cases where distortion is limited it may not be possible to detect a distorted load cell element However in more severe cases it will be quite evident Keep in mind that even
relatively small distortions can damage a load cell to the extent it cannot be used with satisfactory results
Cables should be free of cuts crimps and abrasions If the cable is damaged in a wet environment for instance a phenomenon called wicking can occur passing moisture within the cable jacket leading to a contaminated gaging area
ZERO BALANCE This test is effective to determine if a load cell has been subjected to physical or electrical overload such as shock loads metal fatigue or power surges Before beginning the test the load cell must be in a no load condition This means absolutely no weight can be placed on the load cell
Before verifying the load cell zero balance the bridge resistance should be checked Refer to the load cell specifications provided by the manufacturer for input (excitation) and output (signal) bridge resistance values Typically nominal values will be 350 ohms or 700 ohms It is normal for the input resistance to be somewhat higher than the nominal value as modulus circuits and calibration resistors are often located in this area of the bridge
Disconnect the load cell signal leads and measure the voltage between the H signal and the (+) signal lead The output should be within the manufacturers specifications for zero balance typically 1 of full scale output During the test the excitation leads should remain connected to a known voltage source such as a weight controller Itransmitter lindicator Ideally if the weight controller Itransmitter I indicator used with your weighing system has been verified for accuracy it is the best device to use for verifying zero balance
The usual value for a 1 shift in zero balance is 03 mV assuming 10 volts of excitation on a 3mV IV output load cell (02mV on a 2mV IV output load cell) Full scale output is 30 mV 1 is 03 mV When performing your field tests remember that load cells can shift up to 10 of full scale and still function properly If your tests indicate a shift of less than 10 you probably have a different problem If the test indicates a shift greater than 10 this is a good indication the load cell has been overloaded and should be replaced 32
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
LOAD CELL TROUBLESHOOTING
LEAKAGE RESISTANCE
If the load cell under test has met all the specified criteria to this point but still is not performing to specifications the load cell should be checked for electrical shorts Electrical leakage is almost always caused by water or some other form of contamination within the load cell or cable Early signs of electrical leakage typically include random signal drift and instability Keep in mind that we are dealing with extremely high resistance values and that fluids such as water are excellent conductors Therefore it follows that even a minor degree of contamination can affect load cell performance
Proper application of any load cell is paramount if satisfactory performance is to be achieved The improper application of the load cell is the leading cause of water contamination It is almost always the case that load cells which are environmentally protected to provide some degree of resistance to relative humidity are the subject of this type of failure This is often true because the assumption is made that such load cells can be applied to wash down or extremely high humidity situations where a load cell which is truly environmentally sealed should be utilized Many Sensortronics products are provided with a true environmental seal in their standard configuration Others are offered with this added protection when specified by the customer or dictated by the application If you have any questions as to whether or not your application requires this additional protection consult your Sensortronics representative or the Factory Applications Engineering staff
Another cause of leakage is a loose or broken solder connection inside the load call Poor
connections can cause an unstable reading if the load cell is jarred or experiences sufficient vibration to cause the connection to contact the load cell body Keep in mind this is a relatively rare situation but can occur in some instances A simple field test is to lightly tap on the load cell (exercise care when performing this test on low capacity load cells so as not to overload it in any way) If there is a problem of this nature the light tap should cause the signal to react NOTE Do not confuse the signal caused by the force you may be exerting on the load cell with instability as a result of a poor connection
An essential instrument is a low voltage megohm meter Be careful Do not excite the load cell bridge with a voltage greater than 50 volts Voltage in excess of 50 volts could potentially damage the load cell bridge circuitry
If the resulting measurement indicates a value of less than 1000 megohms there may be some degree of current leakage If the value is over 1000 megohms you can assume there is not a resistance leakage problem with the load cell
Once these tests have been completed you can be reasonably well-assured the load cells are in good working order if no problem is identified If your weighing system problem persists you may wish to continue your evaluation of the system by verifying the condition of the junction box (if one is used) and the system instrumentation
If a load cell fault is still suspected contact Sensortronics Application Engineering staff for further assistance or contact Sensortron ics Repair Coordinator to make arrangements to have your load cells or other weighing systems components evaluated at the factory
33
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
APPLICATION DATA FORM
COMPANY PHONE (
FAX (
ADDRESS CONTACT
CITY STATE IDENTIFICATION (User project name)
Tank Information (check one) 1 Vertical supports
Number of supports ___
Type of support and size o H or I Beam o Pipe o Tubing DAngles o Other (sketch
required) Support rests on
o Steel structure o Concrete floor pier
o flat o sloped
o Tile floor USE THIS AREA TO SKETCH YOUR TANK CONFIGURATION ATTACH ADDITIONAL SHEETS IF NECESSARY o flat
o sloped
2 Gussets on steel frame Number of gussets ___ (Please attach sketch of gusset dimensions and mounting hole size and centers)
3 Gussets on flooring Number of gussets ____ Type of floor -- shyAre there any tanks or processing equipment mounted near gusset 0 Yes 0 No
~--- -~-- ~~-If yes please explain --_ ----~------- ---- --
ADDITIONAL TANK INFORMATION
4 Vibration 0 none o heavy o moderate
5 Piping Connection 0 fixed o flexible (indicate connections on above sketch)
6 Agitated Vessel 0 yes 0 no If yes give agitator details on placement rpm weight etc --------------------~
7 Jacketed vessel 0 yes 0 no If yes detail jacket temperature jacket capacity jacket condition during weighment
8 Tank location in area o general purpose o sanitary o hazardous o indoors o outdoors Class ____ Division ____
Group ___________
9 Seismic zone Dyes Zone__ o no
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet
PRODUCT AND PROCESS INFORMATION
Check (1) all that apply
PRODUCT TO BE WEIGHED
Productname _____________________________________ ~_____________________________
Type o Liquid o Solid o Slurry o Powder o Granular
Temperature range ____to
Product characteristics o Abrasive o Hazardous o Corrosive Classification _________________
o Viscous
Any other information about your process which would effect the performance of the weighing system_ ____
ELECTRONIC REQUIREMENTS
Outputs required (check all that apply)
o Digital display o RS 422 o 4-20 MA o 0-10 VDC o RS 232 o 20 MA Loop o RS 485 o Setpoints How many _
Power available o 115VAC o 230 VAC o 24 VDC
Electrical Enclosure Rating
o NEMA 1213 o Other (specify) _____ ----------------------------- shyo NEMA 4 o NEMA 4X o NEMA 4X Stainless Steel
Distance between Tank Weighing Assembly and
____ feetJ-8ox
J-8ox and Controller ____ feet