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MODULE - DPE
MODULE – DPE
DIFFERENTIAL PRESSURE MEASUREMENT ELECTRONIC METHODS
OBJECTIVE
On completion of this module you will be required to:-
a) Identify and name all parts of an electronic D/P Cell.
b) Calibr ate an Electronic D/P Cell for an output of 4mA to 20mA.
RESOURCES:
1.) Your training Officer
2.) Your Module DPE
Instrumentation : Document No. 10 Page 1 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
MODULE – DPE
DIFFERENTIAL PRESSURE MEASUREMENT ELECTRONIC METHODS
CONTENTS PAGE
1.) INTRODUCTION PAGE –3
2.) PRINCIPLE OF OPERATION PAGE – 3
3.) COMPONENT NAMES PAGE - 4
4.) PRECAUTIONS PAGE – 5
5.) INSTALLATIONS PAGE – 6
6.) CALIBRATION PAGE –7
7.) SELF TEST PAGE – 10
Instrumentation : Document No. 10 Page 2 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
MODULE – DPE
DIFFERENTIAL PRESSURE MEASUREMENT ELECTRONIC METHODS
INTRODUCTION
The Electronic D/P Cell is an instrument that continuously measures Differential
Pressure and transmits this measurement as a Proportional Current output signal
ranging between 4mA and 20mA.
The Differential Pressure Cell is a versatile instrument and is used in Flow, Liquid
Level and other Differential Pressure applications.
PRINCIPLE OF OPERATION
The Electronic D/P Cell consist of two major assemblies, one is the “Topworks
Housing”, which encloses the electronics module in one compartment and the
Field Termination Block in the other compartment.
The other major assembly includes the sensor assembly and the process covers
and is known as the pressure-detector section.
The high and low pressures are connected to opposite sides of the pressure-
detector section.
The resulting Differential Pressure in then converted to a proportional 4mA to
20mA output signal. Different manufacturers of Electronic D/P Cells use different
technologies to measure and convert the differential signals to the 4mA to 20mA
signal.The electronic signal is transmitted to a receiving instrument to record, indicate
and / or control.
Instrumentation : Document No. 10 Page 3 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
COMPONENT NAMES
Figure 1
A. – FIELD TERMINATION SIDE
A. – ELECTRONICS SIDE
Instrumentation : Document No. 10 Page 4 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
B. – SEAL
C. - ELECTRONICS MODULE
D. - SENSOR ASSEMBLY
E. - PROCESS COVER
F. - PROCESS SIGNAL LINE CONNECTION
G. – PROCESS COVER GASKET
PRECAUTIONS
1. During draining condensate of venting gas from the transmitter
pressure-detector section, take appropriate care to avoid contact
with the skin, eyes or body, or inhalation of vapors, the process
fluids or gasses may be toxic or harmful. Since draining condensate
of bleeding off of gas gives the pressure measurement a
disturbance, these operations should not be performed when the
loop is in operation.
2. If the process fluid or gas is toxic or harmful, take appropriate care
to avoid contact with the skin, eyes or body, or inhalation of vapors
when removing the instrument for maintenance.
3. As a general rule, maintenance to this device should only carried
out in a maintenance workshop that is equipped with the necessary
tools and equipment.
Instrumentation : Document No. 10 Page 5 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
4. Handling the CPU assembly. The CPU assembly contains
sensitive components that may be damaged by static electricity.
Take care not to touch the electronic components, electrical
contacts or printed circuit board patterns on the board.
It is best to use a grounded wrist strap assembly to avoid damage
caused by static electricity.
Always place the electronic module in a special plastic bag with an
antistatic coating when removing and transporting the module.
Note: CPU stands for Central Processor Unit
TYPICAL D/P CELL INSTALLATIONS
Instrumentation : Document No. 10 Page 6 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
FIGURE - 3
Liquid level measurement in an open tank
Instrumentation : Document No. 10 Page 7 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
FIGURE – 4
Liquid level measurement in an closed tank
Instrumentation : Document No. 10 Page 8 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
CALIBRATION
1. Connecting the Process input signal to the D/P Cell. Refer to Fig.
5. A typical process input signal would be 0 Kpa to 30 Kpa. This value
will however be determined by the actual application where the D/P
Cell is to be used.
Symbols “H” and “L” are shown on the capsule assembly to indicate
the high and low pressure connections on the capsule of the D/P Cell.
For calibration purposes, you must connect the pressure input signal to
the “H” side connection of the capsule.
FIGURE – 5
Instrumentation : Document No. 10 Page 9 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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2. Wiring the D/P Cell for Calibration. Connect a 24 VDC power supply
to the D/P Cell as shown in Figure – 6
POWER SUPPLY WIRING CONNECTION
Connect the power supply wiring to the SUPPLY + and - terminals
FIGURE – 6
Instrumentation : Document No. 10 Page 10 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
Connect a Milliamp Meter as shown in Figure – 7 or in series with the
positive supply lead as shown in Figure – 8
FIGURE - 7
Instrumentation : Document No. 10 Page 11 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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FITGURE – 8
CALIBRATION PROCEDURE
1. With no differential pressure applied to the capsule, adjust the
“ZERO” screw until a value of 4mA is displayed on the milliamp
meter.
2. Apply a regulated pressure equivalent to the upper range value to
the high-pressure connection. eg. 30 Kpa.
3. Adjust the “SPAN” screw until the output displayed on the milliamp
meter is 20 mA.
Instrumentation : Document No. 10 Page 12 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
4. Repeat steps 1, 2 and 3 until the ZERO and Upper Range values
are 4 mA and 20 mA respectively.
When you have completed the calibration, you must ask the Training Officer to
check your work.
If you have attained the required standard, you may proceed with the Criterion
Test.
Instrumentation : Document No. 10 Page 13 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
MODULE – DPE
DIFFERENTIAL PRESSURE MEASUREMENT ELECTRONICMETHODS
SELF TEST:
QUESTION – 1
Blank out the bottom of Page – 4 Figure – 1 and name all of the componets of
the D/P Cell
QUESTION –2
Calibrate the D/P Cell supplied to you for a range of 0 Kpa to 50 Kpa.
LEARNER TRAINING OFFICER
DATE:……………………………
SIGNED:…………………………
DATE:……………………………
SIGNED:…………………………
Instrumentation : Document No. 10 Page 14 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE - DPE
DPE
CRITERION TEST
DIFFERENTIAL PRESSURE CELL – ELECTRONIC
NAME
DATE
COMPANY NUMBER
SIGNATURE
ASSESSOR SIGNATURE
RESULT COMPETENT / NOT YET COMPETENT
Instrumentation : Document No. 10 Page 15 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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MODULE - DPE
QUESTION – 1
Label the attached diagram of an Electronic D/P Cell
Instrumentation : Document No. 10 Page 16 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
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QUESTION – 2
State the standard supply voltage for an Electronic D/P Cell
QUESTION – 3
State the standard output signal for an Electronic D/P Cell
Question – 4
Calibrate and Electronic Cell for a Range of 0 Kpa to 40 Kpa
Instrumentation : Document No. 10 Page 17 of 17
Created : 01 February 2003 Revision No: 01
Last Approved : March 2003 First Published : March 2003
R i d O L hi D t
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