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MI 020-328September 1988Instruction

Bubble Tube Installations

For Liquid Level, Density, and Interface Level Measurements

MI 020-328 – September 1988

Contents

Figures............................................................................................................................... v

Introduction ........................................................................................................................ 1Abbreviations ................................................................................................................. 1Principle of Operation .................................................................................................... 1Alternative to Bubble Tubes ........................................................................................... 2Reference Instructions .................................................................................................... 2Formulas for Specific Gravity Conversions ..................................................................... 3

For Liquids LIGHTER than Water ........................................................................... 3For Liquids HEAVIER than Water ............................................................................ 3For All Liquids ........................................................................................................... 3

Calibration ..................................................................................................................... 3

Calculations ........................................................................................................................ 4Liquid Level Calculations (Figure 2) ............................................................................... 4Interface Calculations (Figure 3 and Figure 4) ................................................................ 5

With Constant Tank Level (One Bubble Tube) ......................................................... 5With Varying Tank Level (Two Bubble Tubes) ......................................................... 5

Density Calculations (Figure 5 and Figure 6) ................................................................. 6With Constant Tank Level (One Bubble Tube) ......................................................... 6With Varying Tank Level (Two Bubble Tubes) ......................................................... 7

Installation .......................................................................................................................... 8Typical Piping Arrangements ......................................................................................... 8Determination of Length Difference (Dimension “H”) With a Pair of Tubes ................. 8Piping Parts List ............................................................................................................. 8Installation Notes ........................................................................................................... 9Typical Bubble Tube Installations (Figure 8 and Figure 9) ........................................... 10

Tank With One Bubble Tube .................................................................................. 10Tank With Two Bubble Tubes ................................................................................ 11

Typical Side-Connection Installations .......................................................................... 11Tank With One Bubble Connection At Side Of Tank ............................................. 11Tank With Two Bubble Connections At Side Of Tank ........................................... 12

Use of a Differential Pressure Regulator ........................................................................ 12B0107XY Differential Pressure Regulator (Figure 12) .............................................. 14B0107XX Differential Pressure Regulator (Figure 13) .............................................. 15

Pressure Drop in Air Lines ............................................................................................ 15

Operation ......................................................................................................................... 16Operating Notes ........................................................................................................... 16Putting into Operation ................................................................................................. 16

Formulas to Calculate Output and Pressure Loss .............................................................. 17Calculating Output for Any Input ................................................................................ 17

Liquid Level Formula ............................................................................................... 18

iii

MI 020-328 – September 1988 Contents

Density Formula ...................................................................................................... 18Interface Level Formula (Figure 14) ......................................................................... 19

Calculating Pressure Loss in Air Line ............................................................................ 20

Calibration ........................................................................................................................ 21

Maintenance ..................................................................................................................... 21

iv

Figures

1 Bubble Tube Functional Diagram ................................................................................ 2 2 Liquid Level Calculation .............................................................................................. 4 3 Interface Calculation - One Tube ................................................................................. 6 4 Interface Calculation - Two Tubes ............................................................................... 6 5 Density Calculation - One Tube .................................................................................. 7 6 Density Calculation - Two Tubes ................................................................................ 7 7 Bubble Tube Notch Details ......................................................................................... 9 8 Bubble Tube Installation - One Tube .......................................................................... 10 9 Bubble Tube Installation - Two Tubes ......................................................................... 11

10 Bubble Tube Installation - One Tube at Side of Tank ................................................. 11 11 Bubble Tube Installation - Two Tubes at Side of Tank ................................................ 12 12 B0107XY Differential Pressure Regulator and Bubble Tube Piping ............................. 14 13 B0107XX Differential Pressure Regulator and Bubble Tube Piping ............................. 15 14 Interface Level Calculation Calculating Output for any Input ...................................... 19 15 Bubble Tube Maintenance ........................................................................................... 21

v

MI 020-328 – September 1988 Figures

vi

IntroductionThe bubble tube principle of hydrostatic measurement is a convenient, low-cost method of measuring liquid level, density, or interface level in an open tank. It is particularly applicable for those installations where:

♦ Process liquid could crystallize in transmitter lines.

♦ Process temperature exceeds temperature limit of flange-mounted transmitter.

♦ Process tank does not have side connections for flange-mounted transmitter.

♦ Process liquid is corrosive and cannot have direct contact with transmitter.

AbbreviationsThe abbreviations below are used in this instruction.

Principle of OperationAir is passed through a restrictor to a tube partly immersed in a liquid. The lower end of the tube is at a fixed distance above the bottom of the tank (see Figure 1).

The pressure of the air supply is high enough to overcome the hydrostatic head on the tube, and the excess pressure appears as small bubbles coming out of the bottom of the tube. Thus, the back pressure in the tube is a measure of the pressure on the bottom of the tube due to the level of liquid. Since the position of the tube is fixed, any change in this back pressure is due to a change in the level of the liquid.

The back pressure is connected to the high-pressure side of the transmitter, and the low- pres-sure side is vented. Thus, the differential pressure measured by the transmitter is a measure of the level of the liquid.

If the level of the liquid is constant (continuous overflow), any change in the transmitter dif-ferential pressure must be due to a change in liquid density or interface level. Thus, density and interface level can also be measured. If the tank level varies, these measurements can still be made by using two different-length tubes connected to opposite sides of the transmitter; see Figure 4 and Figure 6.

ABBREVIATION MEANING

LRV Lower-range value (measurement that produces a 4 mA output)

URV Upper-range value (measurement that produces a 20 mA output)

Sp.G. Specific gravity (relative density) of a liquid. Specific gravity of water in both customary and SI systems is 1.00.

1

MI 020-328 – September 1988 Introduction

Figure 1. Bubble Tube Functional Diagram

Alternative to Bubble TubesIf it is impractical to immerse bubble tubes in the tank (because the tank has a mixer and/or baffles, or because the liquid is corrosive, etc.), the bubbles can be introduced through con-nections at the side of the tank. See Figure 10 and Figure 11 for details.

Reference Instructions

DESCRIPTIONDOCUMENT

NUMBER

Purge Rotameter MI 005-529 Purge Rotameter(Liq.Lev.) MI 010-153

Diff. Press. Regulator MI 011-170

13A,13H,15A Transmitters MI 022-345

823DP-I,-H, Transmitters MI 020-330

823DP-D Transmitter MI 020-345

843DP Transmitter MI 020-437E13DH/DL/DM Transmitter MI 020-140

Density Measurements TI 1-50a

Liquid Interface Level Measurement TI 001-051

Liquid Level Measurements TI 001-052

2

Introduction MI 020-328 – September 1988

Formulas for Specific Gravity Conversions

For Liquids LIGHTER than Water

For Liquids HEAVIER than Water

For All LiquidsDensity [lb/ft3] / 62.4 = Sp.G.

Density [kg/m3] / 1.00 = Sp.G.

CalibrationIf measurement range was specified in the sales order, the transmitter was calibrated in the fac-tory to these values, and these same values are stamped on the transmitter data plate.

If measurement range was not specified, transmitter was calibrated in the factory to maximum span for the particular sensor installed in the transmitter. In this case, the measurement range area of the data plate is left blank so that the user can mark the desired calibrated range (in terms of head of water) himself.

The transmitter must be calibrated to the desired range before putting it into operation. (If the transmitter was calibrated in factory, the calibration should be checked.) Use the applica-ble formula to determine the input pressures (in terms of head of water) corresponding to the desired measurement limits. Mark these input pressure limits in the applicable area on the transmitter data plate, and use these values as the calibrating input signals.

°Baumé:

°API:

°Baumé:

°Twaddell:

Sp.G.140

°Be′ 130+--------------------------=

Sp.G.141.5

°API 131.5+---------------------------------=

Sp.G.145

145 °Be′–--------------------------=

Sp.G.°Tw200----------- 1+=

3

MI 020-328 – September 1988 Calculations

CalculationsThe sections that follow show typical calculations for liquid level measurement, interface mea-surement, and density measurement. Interface and density measurements are shown with both a constant tank level and a varying tank level.

Note that the upper-range and lower-range values (URV and LRV) refer to the desired maxi-mum and minimum measurements, respectively. The Calibrated Span = URV - LRV. The value of the suppression is the output at LRV above 0%.

Liquid Level Calculations (Figure 2)

where:

EXAMPLE: A = 2.0 m, B = 0.2 m, GL = 0.8

Figure 2. Liquid Level Calculation

Span = (A)(GL)HW at LRV = (B)(GL) = Suppression

HW at URV = (A + B)(GL)

Calibrated Range = LRV to URV

GL = Sp.G. of Tank Liquid

HW = Equivalent Head of Water

Span = (2.0)(0.8) = 1.60 mH2OHW at LRV = (0.2)(0.8) = 0.16 mH2O = Suppression

HW at URV = (2.0 + 0.2)(0.8) = 1.76 mH2O

Calibrated Range = 0.16 to 1.76 mH2O

4

Calculations MI 020-328 – September 1988

Interface Calculations (Figure 3 and Figure 4)

With Constant Tank Level (One Bubble Tube)

where:

EXAMPLE: Liquid Sp.G. varies between 0.9 and 1.8; A = 50 inches and B = 10 inches

With Varying Tank Level (Two Bubble Tubes)

where:

EXAMPLE: Interface liquid Sp.G. varies between 1.0 and 1.7; and H = 40 inches.

Span = (A)(G2 - G1)

HW at LRV = (A)(G1) + (B)(G2) = Suppression

HW at URV = (A + B)(G2)


G1 = Sp.G. of Upper Liquid

G2 = Sp.G. of Lower LiquidHW = Equivalent Head of Water

Span = (50)(1.8 - 0.9) = 45 inH2OHw at LRV = (50)(0.9) + (10)(1.8) = 63 inH2O

Hw at URV = (50 + 10)(1.8) = 108 inH2O

Calibrated Range = 63 to 108 inH2O

Span = (H)(G2 - G1)

HW at LRV = (H)(G1) = Suppression

HW at URV = (H)(G2)


G1 = Sp.G. of upper liquid

G2 = Sp.G. of lower liquid

HW = equivalent head of water

Span = (40)(1.7 - 1.0) = 28 inH2O

HW at LRV = (40)(1.0) = 40 inH2O = SuppressionHW at URV = (40)(1.7) = 68 inH2O


5

MI 020-328 – September 1988 Calculations

Density Calculations (Figure 5 and Figure 6)

With Constant Tank Level (One Bubble Tube)

where:

EXAMPLE: Liquid Sp.G. varies between 1.0 and 1.8; and A = 40 inches.

Figure 3. Interface Calculation - One Tube Figure 4. Interface Calculation - Two Tubes

Span = (A)(G2 - G1)

HW at LRV = (A)(G1) = Suppression

HW at URV = (A)(G2)Calibrated Range = LRV to URV

G1 = Minimum Sp.G.

G2 = Maximum Sp.G.


Span = (40)(1.8 - 1.0) = 32 inH2O

HW at LRV = (40)(1.0) = 40 inH2O = Suppression

HW at URV = (40)(1.8) = 72 inH2O


6

Calculations MI 020-328 – September 1988

With Varying Tank Level (Two Bubble Tubes)

where:

EXAMPLE: Liquid Sp.G. varies between 1.2 and 2.0; and H = 40 inches.

Span = (H)(G2 - G1)

HW at LRV = (H)(G1) = Suppression

HW at URV = (H)(G2)Calibrated Range = LRV to URV

G1 = Minimum Sp.G.

G2 = Maximum Sp.G.


Span = (40)(2.0 - 1.2) = 32 inH2O

HW at LRV = (40)(1.2) = 48 inH2O = Suppression

HW at URV = (40)(2.0) = 80 inH2O


Figure 5. Density Calculation - One Tube Figure 6. Density Calculation - Two Tubes

7

MI 020-328 – September 1988 Installation

Installation

Typical Piping ArrangementsWith bubble tube installations, refer to either Figure 8 or Figure 9, as applicable. With side-connection installations, refer to either Figure 10 or Figure 11, as applicable.

Determination of Length Difference (Dimension “H”) With a Pair of TubesWith density measurement, the larger the length difference (dimension “H”) between tubes, the more accurate the measurement will be. With interface measurement, dimension “H” is the desired level measurement range.

Physical limitations are set by both the height of the tank and the amount of sludge in the bottom of the tank. The lower tube should have a minimum of 75 mm (3 in) of clear liquid below it.

Piping Parts ListTransmitter Piping:

Pipe: DN 8 or 1/4 in; or DN 10 or 3/8 inTubing: 10x1 mm or 0.25 in OD; or 10x1 mm or 0.375 in OD

Bubble Tubes:

Pipe: DN 8 or 1/4 in; or DN 10 or 3/8 in

Rotameter:

For control of purge rate and visual indication in a purge or bubble tube system. For additional details, refer to MI 005-529.

Suitable for gas or liquid purges up to 1.4 MPa (200 psi) at 70°C (160°F). See list below.

Suitable for gas or liquid purges up to 1.4 MPa (200 psi) 90°C (200°F). See list below.

Foxboro Part Description

D0105NX 0.2 to 30 scfh (Gas), or 0.1 to 5 gph (Liquid)

D0105PF 5 to 60 scfh (Gas)

D0105PB 4 to 40 gph (Liquid)

M0153YM 5 to 200 mL/s (Gas) or 0.1 to 5 mL/s (Liquid)

M0153YN 20 to 500 mL/s (Gas)

M0153YP 5 to 40 mL/s (Liquid)

D0127MF 0.2 to 30 scfh (Gas), or 0.1 to 5 gph (Liquid)

D0127ML 5 to 60 scfh (Gas)

D0127MK 4 to 40 gph (Liquid)

8

Installation MI 020-328 – September 1988

Snubbers:

For installation in the process line to reduce or eliminate any unwanted pressure pulsa-tions, 1/4 NPT at both ends.

For gases and thin liquids, see list below.

For oils and thick liquids, see list below.

Differential Pressure Regulator

Foxboro Type 62V (Part B0107XY), orFoxboro Type 63BD (Part B0107XX).

Installation Notes1. Bubble tube and transmitter piping is supplied by user.

2. There should be a minimum of 75 mm (3 inches) of clear liquid (no sediment) below the bottom of the tube. With two-tube installations, there should also be a minimum of 75 mm (3 inches) of liquid above the upper tube).

3. Bubble tube assembly should be located in area of representative liquid, and where liquid agitation is at a minimum.

4. Bubble tube assembly must be rigidly fixed in position.

5. Bottom of bubble tubes to be notched so that air comes out in a steady stream of small bubbles (rather than an intermittent stream of large bubbles, which could introduce errors). See Figure 7 for details of this notching. (Not applicable for side-connection installations.)

Figure 7. Bubble Tube Notch Details

0045162 Brass, 1500 psi (100 bar)0045163 303 ss, 5000 psi (340 bar)

0044596 Brass 1500 psi (100 bar)

0044597 303 ss, 5000 psi (340 bar)

9


6. Condition of air (temperature, moisture content, etc.) must be compatible with process liquid.

7. If air reacts with process liquid, an inert gas (such as nitrogen) can be used.

8. A differential pressure regulator may be desirable to limit use of air.

9. The rotameter needle valve should not be used for tight shut off. A hand valve should be installed upstream to permit servicing or for complete shut-off of purge medium when desired.

10. If purge supply is higher than the maximum rating of the rotameter or differential regulator, or the purge supply pressure varies greatly, install a pressure regulator downstream from the shut off valve.

Typical Bubble Tube Installations (Figure 8 and Figure 9)

Tank With One Bubble Tube (Liquid Level; Density or Interface with Constant Level)

Figure 8. Bubble Tube Installation - One Tube

10


Tank With Two Bubble Tubes (Density or Interface with Varying Level)

Figure 9. Bubble Tube Installation - Two Tubes

Typical Side-Connection Installations

Tank With One Bubble Connection At Side Of Tank(Liquid Level; Density or Interface with Constant Level)

Figure 10. Bubble Tube Installation - One Tube at Side of Tank

11


Tank With Two Bubble Connections At Side Of Tank(Density or Interface with Varying Level)

Figure 11. Bubble Tube Installation - Two Tubes at Side of Tank

Use of a Differential Pressure RegulatorIt may be desirable to use one or two differential pressure regulators in the piping to limit the use of air. The regulator maintains a fixed difference between the output pressure of the regu-lator and a varying lower pressure.

In a bubble tube measuring system, if the tank level is high, or if the ends of the bubble tubes tend to clog, the pressure delivered to the bubble tube may not be high enough to generate bubbles. Or, if the tank level falls, the pressure may be so high that large bubbles are produced and air is wasted. Thus, with both situations incorrect measurements can result.

However, if a differential pressure regulator is used, the bubble system supply pressure will automatically vary to adjust for changing tank conditions. Thus, desirable small bubbles are produced (with more accurate measurement readings), and purge air is minimized.

If two bubble tubes (or two side tank connections) are used, either one regulator can be used as a common regulated air supply, or a regulator can be used in each line for better bubble control and highest economy of air usage. See Figure 12 and Figure 13 for piping details.

12


The two regulators in the table below are available from Foxboro.

Parameter

Type And Part Number

Type 62V Type 63BD

BO107XY BO107XX

Differential Pressure (fixed) 10.3 kPa1.5 psi

20.7 kPa3.0 psi

Maximum Input Pressure 690 kPa 100 psi

1720 kPa250 psi

Exhaust Flow Rate (at standard conditions)

0.03 m3/h 0.9 ft3/h

NoneNone

Maximum Temperature 65°C150°F

80°C180°F

Liquid Purge No Yes

13


B0107XY Differential Pressure Regulator (Figure 12)

Figure 12. B0107XY Differential Pressure Regulator and Bubble Tube Piping

14


B0107XX Differential Pressure Regulator (Figure 13)

Figure 13. B0107XX Differential Pressure Regulator and Bubble Tube Piping

Pressure Drop in Air LinesIf the air must flow through a considerable length of pipe or tubing to the transmitter, or if the flow of air is excessive, there will be some pressure loss. Any pressure loss will cause incor-rect readings.

15

MI 020-328 – September 1988 Operation

One method to determine if a pressure loss exists is to install test gauges at each end of the line going to the transmitter, and compare readings. To calculate the loss in pressure, see “To Cal-culate Pressure Loss in Air Line” section that follows.

(With one-tube installations, a quick check for pressure loss is to momentarily turn off the air supply and note if there is any change in transmitter output.)

If a significant pressure loss exists, reduce the air flow, and/or use a larger size line, and/or move the transmitter nearer the bubble tube.

Operation

Operating Notes1. Function of restrictor is to control flow of air. This is accomplished with needle

valve on bottom of rotameter (except if Type 62V differential pressure regulator [B0107XY] is used). Use this needle valve to adjust air flow for optimum small bubble size.

If Type 62V regulator (B0107XY) is used, needle valve on regulator is used to adjust flow of air.

2. To prevent measurement errors, open ends of the tubes should always be covered with tank liquid.

3. With interface measurement, maximum level must be below open end of upper tube; minimum level must be above open end of lower tube.

4. If range is to be changed, transmitter must be recalibrated to new range. Dimen-sion “H” may require changing for new range.

5. Needle valve on rotameter should not be used as a system air shutoff; instead use upstream valve at air supply to system.

6. Do not allow level of liquid to fall below bottom of bubble tube (or tank connec-tion).

7. Check all connections for leaks.

Putting into OperationIf transmitter is not calibrated to the desired range, it must be calibrated before starting this procedure.

After system is installed, adjust the process liquid (level or density) so that the measurement is at some point on scale. Then complete this procedure before operating the system.

1. If transmitter is not equipped with the optional output indicator, connect an indicator in transmitter output loop to read output.

2. Turn on air supply and adjust flow of air as follows. (If system does not have a differential pressure regulator, tank liquid must be at URV.)

16

Formulas to Calculate Output and Pressure Loss MI 020-328 – September 1988

System With Type 62V Differential Pressure Regulator (Part B0107XY)

Fully open rotameter needle valve (at bottom of rotameter). Adjust regulator needle valve (at bottom of body) so that small bubbles come out of tube in a slow, steady stream.

All Other Systems

Adjust rotameter needle valve (at bottom of rotameter) so that small bubbles come out of tube in a slow, steady stream.

3. If, in Step 2, the bubbles are not visible (because of tank location, type of liq-uid, etc.), using the applicable air adjustments specified in Step 2, gradually increase flow of air while noting output of transmitter. Keep increasing air flow as long as output increases. At point where output stops increasing, increase air flow slightly.

4. With a one-tube installation, make the “pressure drop” test described in previ-ous section. If significant error exists, make necessary corrections.

If transmitter has been calibrated correctly, this completes the procedure; oth-erwise proceed to Steps 5, 6, and 7 (reference adjustment). Note that the accu-racy of the measuring device in Step 5, will probably be less than that of the transmitter; this may degrade the accuracy of the transmitter.

5. Using a suitable measuring device (such as a dipstick with level application or a hydrometer with density application), determine actual measurement of liq-uid.

6. Using applicable formula listed in the section that follows, calculate transmit-ter output corresponding to tank measurement.

7. Adjust transmitter zero to get correct output. If necessary, also adjust zero read-ing of receiver.

Formulas to Calculate Output and Pressure Loss

Calculating Output for Any InputThe formulas that follow are for various types of transmitters as listed in the table below.

TRANSMITTER OUTPUT VALUE OF “X” VALUE OF “Y”

4 to 20 mA 16 mA 4 mA

10 to 50 mA 40 mA 10 mA

3 to15 psi 12 psi 3 psi

20 to 100 kPa 80 kPa 20 kPa

17

MI 020-328 – September 1988 Formulas to Calculate Output and Pressure Loss

In using these formulas, the transmitter must already be calibrated to the desired range. If the transmitter has not been calibrated (or if the calibration is to be changed), complete the cali-bration first. Use the applicable formula to determine the input pressures (in terms of head of water) corresponding to the desired measurement limits. Mark these input pressure limits in the applicable areas on the transmitter data plate.

Liquid Level Formula

EXAMPLE: Transmitter with 4 to 20 mA Output and:

Therefore,

Density Formula

EXAMPLE: Transmitter with 10 to 50 mA Output and:

Therefore,

Actual Level = 30 linear inches above bubble tube

Min. Level = 10 linear inches above bubble tubeMax. Level = 90 linear inches above bubble tube

Actual Sp.G. = 1.0

Min. Sp.G. = 0.6Max. Sp.G. = 1.4

Output (X)Actual Level Min. Level–Max. Level Min. Level–--------------------------------------------------------------

Y+=

Output (16)30 10–90 10–------------------

4 8.0 mA=+=

Output (X)Actual Sp.G. Min. Sp.G.–Max. Sp.G. Min. Sp.G–

----------------------------------------------------------------- Y+=

Output (40)1.0

·0.6–

1.4 0.6–-----------------------

+ 10 30 mA==

18

Formulas to Calculate Output and Pressure Loss MI 020-328 – September 1988

Interface Level Formula (Figure 14)

EXAMPLE: Transmitter with 3 to 15 psi Output and:

Figure 14. Interface Level Calculation Calculating Output for any Input

A = 5 linear inches above lower tube

H = 20 linear inches

Output (X)Actual Interface Level

Maximum Interface Level--------------------------------------------------------------

Y+=

Output (12)5·

20------

+ 3 6 psi==

19

MI 020-328 – September 1988 Formulas to Calculate Output and Pressure Loss

Calculating Pressure Loss in Air LineThe pressure loss in a line varies with the flow, the ID of the line, and the length of the line. The equation to determine the pressure loss is:

P = (K)(F)(L)

where:

P = Pressure drop, inH2O (or mmH2O)

F = Flow, ft3/h (or m3h)

L = Length of Line/1000, feet (or m)

K = Constant

The following table combines the line ID and other factors into one overall constant, K.

If the ID of the actual pipe used is not listed in the table above, use the formula below to cal-culate the approximate value of K.

K = 1/(62)(ID)4 [with line ID in inches]

If the measurements are in the SI system (line ID in mm, line length in metres, and flow in m3/h), then use the following formula to calculate K.

KSI units = (65.9/ID)4

EXAMPLE 1: Determine pressure loss in a 20 foot length of 1/8 pipe due to an air flow of 4 scfh.

K = 3.0 for 1/8 in pipe (from the table)

P = (K)(F)(L) = (3.0)(4)(20/1000)

P = 0.24 inH2O

Type of Line Line Size Line ID

Value of K

ANSI Pipe 1/8 in 0.269 in 3.0

1/4 in 0.364 in 0.9

3/8 in 0.493 in 0.271/2 in 0.622 in 0.105

3/4 in 0.824 in 0.035

ANSI Tubing 1/8 in 0.125 in 70.0

3/16in 0.188 in 12.5

1/4 in 0.25 in 4.0

1/2 in 0.50 in 0.245

3/4 in 0.75 in 0.0501 in 1.0 in 0.016

20

Calibration MI 020-328 – September 1988

EXAMPLE 2: Determine pressure loss in a 10 metre length of 5 mm ID pipe due to an air flow of 0.1 m3/h.

KSI units = (65.9/ID)4 = (65.9/5)4 = 30176

P = (K)(F)(L) = (30176)(0.1)(10/1000)

P = 30 mmH2O

CalibrationIn general, follow the calibrating procedures outlined in the appropriate transmitter instruc-tions.

If desired, instead of using air pressures as calibrating signals, these signals can be generated by varying the level (or density) of the tank liquid to values at or near each end of the range. Use the calibrating values stamped on the data plate; or if the range is to be changed, calculate the new values. In this way, the transmitter can be calibrated without removing it from the pro-cess.

MaintenanceUse applicable reference instructions listed on page 2 when servicing the transmitter, rotameter, or differential pressure regulator.

If there is any tendency for solids to crystallize in the bubble tubes, or if dirt tends to collect there, remove the cleanout plugs and push a rod down through the tubes and/or flush with a suitable liquid. Perform as often as required.

Figure 15. Bubble Tube Maintenance

21

MI 020-328 – September 1988 Maintenance

.

ISSUE DATES JUN 1984 JAN 1988 SEP 1988

The Foxboro Company33 Commercial StreetFoxboro, MA 02035-2099United States of Americahttp://www.foxboro.comInside U.S.: 1-888-FOXBORO (1-888-369-2676)Outside U.S.: Contact your local Foxboro Representative.Facsimile: (508) 549-4992

Foxboro is a registered trademark of The Foxboro Company.Siebe is a registered trademark of Siebe, plc.

Copyright 1984-1988 by The Foxboro CompanyAll rights reserved

A Siebe Group Company MB 100 Printed in U.S.A 0988