1

Weight Measurement Technology

2

Definition of Terms

• Millivolt– 0.001 volts: the unit of measure of output

from sensors• PSI

– Pounds per Square Inch: Unit of measurement of stress used in the application of strain gage sensors

3

Definition of Terms

• Stress– Any action on a body that results in

deformation. Usually measured in pounds per square inch or Pascal's

• Thermal Stress–Two dimensional strain caused

by thermal heating (expansion)or cooling (contraction)

4

Definition of Terms

• Strain– Deformation of a body or structure as a result

of an applied force• Strain Gage

– A device that converts mechanical deflection to an electrical signal

5

Definition of TermsMechanics of a member in compression

• Compression – Stress by forces

pushing together• Tension

– Stress by forces causing extension (pulling)

WL

∆LAt Rest

Add Weight

Mechanics of a member in tension

Add Weight

W

L

∆L

At Rest

6

Definition of Terms

• Poisson’s Ratio– The ratio of transverse strain to

longitudinal strain -- The ratiofor carbon steel is .3

• Shear– The component of a horizontal

beam that is being measuredA D

Shear Area = A x D

7

Definition of Terms

• Live Load– The design capacity of a vessel

• Dead Load– The empty weight of a vessel

8

Definition of Terms

• Wheatstone Bridge– An electrical circuit used to

detect small resistance changes in strain gages

• Signal Lines– In half bridge systems, these

are the lines that return the signal to signal conditioners

+EXC

-EXC

SignalProcessor Transducer

Red

Black

White

OutputSignal

Rd

RcRa

Rb

Note: c dR and R are fixed resistors

9

Definition of Terms

• Sense Lines– In full bridge systems,

these are the lines that bring in the sensed voltage

Signal

+Sense+Excitation

-Sense-Excitation

10

Introduction

• Bolt-On – Transducers attached to existing vessel structural support

• Direct Support – Transducers are built into structural support elements

Both share a common platformSilicon Semiconductor Strain Gages

11

Introduction

• Silicon Semiconductor Strain Gage– Solid state resistors– Manufactured from a single-crystal boule– Acid –etched to require resistance– Glass fused to bending beam

12

Theory

+EXC

-EXC

SignalProcessor Transducer

Red

Black

White

OutputSignal

Rd

RcRa

Rb

Note: c dR and R are fixed resistors

• Wheatstone Bridge– An electrical circuit

used to detect small resistance changes in strain gages

13

Theory

• Compression and expansion.– Poisson’s Ratio.– .3 for carbon steel

14

Theory

• The Bolt-On weight transducer detects and amplifies this change in length and provides a resistance change that is proportional

• Vessel support experiences small strain (length) changes in direct proportion to the change in weight of material in vessel

15

Factors That AffectPerformance

• Rigid Piping Connections• Catwalk• Hidden Load Bearing Members• Vessel goes Through Roof• Tripper Conveyors or Deck Plating

16

Factors That AffectPerformance

• Poor Foundation• Flexible Structure• Uneven Loading

– Structure not level– Off-center loading– Wind– Equipment

Vibration

Side LoadSide load causestension on legs onthis side, whichcould be interpretedas decreased materialweight

Side load causescompression on legson this side, whichcould be interpretedas increased materialweight

Tension and compression equal but opposite; canceleach other if all legs instrumented with L-Cells.

17

Factors That AffectPerformance

• Shock Loads• Excessive electrical noise or heat

18

Bolt on Weight Measurement

19

Introduction

• Bolt-on provides continuous bulk material inventory

• Immune to material characteristics• Provides weight not level• Non-intrusive• Ideal for renovations or retrofits• Install without interrupting production

20

Microcell

• A half bridge strain gage device used to transform a mechanical motion into an electrical signal

21

L-Cell

• Dual axis strain gage device used to transform a mechanical motion into an electrical signal; minimizes environmental effects

22

Type of Legs

Channel Unequal Angle

Pipe Legs

Square Tubing

RectangularTubing

H or I Beam

EqualAngle

23

Type of Legs

• Pipe Legs

24

Leg Bending

25

Lateral Stain

26

Compression/Expansion

27

psi CalculationLegged Vessel

live load (working capacity)live load per leg =number of legs

live load per legload factor (psi) =

steel area calculation

B

A

C

D

B

C

A

C

T

B

AA

B

A

B

T

Area = 3.13 x D x TPipe Legs

Area = (2A + 2B) x TTubular Legs

Area = (A + B) x CAngle Legs

Area = 2 x B x C + {A - (2C)} x DH or I Beam Legs

28

Horizontal Location onVertical Legs

• Square tubing• Rectangular tubing• H & I beam• Channels• Angle with equal or unequal legs • Vertical pipe legs

29

Vessel Free Leg

30

Support Legs

N=2N=2N=0

N=0

With X-BracesWithout X-Braces

31

Leg Accuracy Chart

0123456789

0 1000

2000

3000

4000

5000

6000

7000

8000

9000

{Stress in PSI}

{± E

rror

%}

Outside N=0Outside N=1Outside N =2Inside N=0Inside N=1Inside N=2

32

psi Calculation HorizontalBeam Supported Vessels

live load (working capacity)live load per support point =

two times the number of support beams

live load per support pointload factor (psi) =

shear area calculation

A D

Shear Area = A x D

33

Horizontal BeamsLeft & Right Same Side of Web

supportpoint

loadpoint

supportpoint

34

Horizontal BeamsLeft & Right Opposite Side of Web

supportpoint

loadpoint

supportpoint

35

Horizontal BeamsLeft or Right Back-To Back

supportpoint

loadpoint

supportpoint

36

Horizontal BeamsLeft or Right Single L-Cell

supportpoint

loadpoint

supportpoint

37

Horizontal BeamsLeft & Right Back-to-Back

loadpoint

supportpoint

supportpoint

38

Horizontal BeamsExcitation Wiring

• L-Cell orientation is the determining factor for reversing the excitation wiring.– If the the L-Cell is

located to the right of the Load Point then the excitation is reversed.

• i.e. red to black and black to red

loadpoint

RevRed t

ersedo B

Ec

xcik &

aBtat

laionc

Wirino Re

gd

NorRed t

malR

Ee

xd

ciat&

atla

ioc

nk

Wo

iringBlao B t ck la k t

39

Horizontal Accuracy Chart

0

1

2

3

4

5

6

7

8

9

0 1000

2000

3000

4000

5000

6000

7000

8000

9000

{Stress in PSI}

± E

rror

%

4 Cells/Beam

2 Cells/Beam

1 Cell/Beam

40

Skirted SiloSilo Layouts

Legend:= L-Cell Set= Junction Box= Door

1516

14

13

12

11

1098

7

6

5

4

32

1

24' (7.3m) Diameter9'5" (2.9m)

L-Cell Spacing

21

3

4

5

6

7

89 10

11

12

13

14

15

1617

26' (7.9m) Diameter9'5" (2.9m)

L-Cell Spacing

12

3

4

5

6

7

8

910 11 12

13

14

15

16

17

1819

20

28' (8.5m) Diameter8'10" (2.7m)

L-Cell Spacing

123

4

5

67

8 910

11

12

13

14

21' (6.4m) Diameter9'5" (2.9m)

L-Cell Spacing

9' (2.7m) Diameter9'5" (2.9m)

L-Cell Spacing

1

4

62

53

12

3

4 56

7

8

12' (3.7m) Diameter9'5" (2.9m)

L-Cell Spacing

12

3

4

56

7

8

9

10

15' (4.6m) Diameter9'5" (2.9m)

L-Cell Spacing

12

3

4

5

6 7 8

9

10

11

12

18' (5.5m) Diameter9'5" (2.9m)

L-Cell Spacing

41

psi CalculationSkirted Silo

D

T

live load (working capacity)load factor (psi) =

3.14 x D x T

42

Skirted SiloL-Cell Sets

Cable routing through3/16" hole

43

Skirt Accuracy Chart

02468

1012141618

0 1000

2000

3000

4000

5000

6000

7000

8000

9000

{Skirt Stress in PSI}

{± E

rror

%}

Best CaseWorst Case

44

Bolt-On Weight Technology

• Evaluate customer data requirements• Level-by-weight and weight-by-level systems are at best

a 10% system• Bolt-on not affected by

– Angle of repose– Rat-holing– Bridging– Moisture content– Compaction– Vapors– Dust