Cameron BARTON 753A User manual

BARTON®MODEL 753A
GAGE PRESSURE TRANSMITTER
User Manual
Part No. 9A-10840, Rev. 02
March 2020
Contents
Safety............................................................................................................ 2
Section 1—Introduction................................................................................. 3
General ......................................................................................................... 3
Product Description....................................................................................... 3
Gage Pressure Transducer ...................................................................... 3
Electronic Transmitter................................................................................ 3
Power Supply ............................................................................................ 4
Zero and Span Control.................................................................................. 4
Zero Control .............................................................................................. 4
Span Control ............................................................................................. 4
Specications ............................................................................................... 5
Section 2—Theory of Operation.................................................................... 7
Basic Components........................................................................................ 7
Gage Pressure Transducer ....................................................................... 7
Electronic Transmitter................................................................................ 7
Basic Operation ............................................................................................ 7
Surge Voltage Protection Circuit .............................................................. 8
Reverse Polarity Protection....................................................................... 8
Regulator................................................................................................... 8
Strain Gage Bridge Network ..................................................................... 8
Signal Amplier.......................................................................................... 9
Current Amplier........................................................................................ 9
Temperature Compensation.......................................................................... 9
Section 3—Installation, Startup, and Shutdown........................................ 10
Overview..................................................................................................... 10
Unpacking/Inspection.................................................................................. 10
Initial Calibration Check .............................................................................. 10
Mounting ..................................................................................................... 10
Wall or Rack Mounting ............................................................................ 10
Piping Guidelines.........................................................................................11
Electrical Connections ................................................................................11
Loop Resistance Calculations................................................................. 13
Maximum Loop Resistance..................................................................... 14

2
Safety
Before installing this product, become familiar with the installation instruc-
tions presented in Section 3 and all safety notes throughout.
!WARNING:Thissymbolidentiesinformationaboutpracticesorcircum-
stances that can lead to personal injury or death, property damage, or
economic loss.
CAUTION: Indicates actions or procedures which if not performed correctly
may lead to personal injury or incorrect function of the instrument
or connected equipment.
IMPORTANT: Indicates actions or procedures which may a󰀨ect instrument operation or
may lead to an instrument response that is not planned.
EMI/RFI Shielding.........................................................................................14
Startup Procedure.........................................................................................14
Shutdown Procedure....................................................................................15
Section 4—Calibration and Maintenance.....................................................16
General Field and Periodic Maintenance......................................................16
Electronic Transmitter................................................................................16
Calibration.....................................................................................................16
Test Equipment.............................................................................................16
Electrical Connections for Calibration.......................................................17
Calibration Checkpoints............................................................................18
Calibration Procedure................................................................................18
Troubleshooting............................................................................................20
Section 5-Assembly Drawing and Parts List...............................................21
Section 6-Dimensional Drawings..................................................................23
Appendix A.....................................................................................................25
Safety Precautions........................................................................................25
Flow Application........................................................................................25
Typical Piping/Startup Example....................................................................25
Gas Flow...................................................................................................25
Product Warranty............................................................................................26
Product Brand.................................................................................................26

3
Model 753A Gage Pressure Transmitter Section 1
Section 1—Introduction
General
The Model 753A Gage Pressure Transmitter provides a 4-20 mA or 10-50 mA
proportional-to-gage-pressure signal for transmission to remote receiving,
control, or readout devices. Sources of gage pressure include liquid and gas
ow through orice plates, nozzles or venturis; static line pressures, etc.
Product Description
The Model 753A utilizes a gage pressure transducer functioning in combina-
tion with an electronic circuit. The 4-20 mA or 10-50 mA output is compati-
ble with a wide range of electronic receiving, control, and readout equipment.
The instrument utilizes surface mount electronic components, electronic
circuits and a molecular-bonded strain gage sensing cantilever beam, actuated
directly by a Bourdon tube pressure sensing element. In many applications,
the electrical connections are contained within a junction box, as shown in
Figure 3.1, page 12. However, the junction box is optional.
Gage Pressure Transducer
The mechanical actuating device for the Model 753A transmitter is a C-type
Bourdon tube pressure sensing element enclosed in a pressure housing.
Figure 1.1—Gage pressure transducer assembly
Electronic Transmitter
The electronic transmitter supplies a 4-20 mA or 10-50 mA direct current
output signal that is proportional to the gage pressure sensed by the Bourdon
tube. The output signal is transmitted over two wires to remote receiving
devices.

4
Section 1 Model 753A Gage Pressure Transmitter
Power Supply
A regulated direct current (DC) power supply is required to operate the trans-
mitting loop. The voltage required will depend on the total loop resistance
(load resistor, cable wiring, and any other resistance in the loop) as shown in
Figure 3.3, page 13. Table 3.1, page 13 shows the resistances in ohms
per 1000 feet of wiring for the various cable wire sizes. Once the total loop
resistance has been determined, the power supply voltage can be calculated as
follows:
• For 4-20 mA output: VDC = 12 VDC + 2 VDC per 100-ohms load
• For 10-50 mA output: VDC = 12 VDC + 5 VDC per 100-ohms load
Exercise care when calculating the power supply voltage. A power supply
specied at 50 VDC ±1 volt must be considered a 49 VDC source to insure
the minimum required voltage at the transmitter. Use the actual value when
available. Otherwise, use the "worst case" value.
Power supply wiring connections are shown in Figures 3.1 and 3.2, page
12.
Zero and Span Control
The transmitter has two 10-turn potentiometers—one for zero adjustments,
the other for span control. With these two controls, measurement can be made
between any two points within the rated transmitter span. However, to ensure
a high level of accuracy, combined zero and span adjustments should never
exceed ±5% of the factory calibration.
IMPORTANT: Combined zero and/or span eld adjustments exceeding ±5% of the fac-
tory calibration can alter transmitter performance in direct proportion to
the changes to the factory calibration. For example, if combined adjust-
ments to zero and span change the factory calibration by a factor of 2,
transmitter performance may be decreased by a factor of 2.
Zero Control
During calibration, the zero control is used to adjust the instrument’s output
signal to 4 mA or 10 mA at the minimum pressure setting of the instrument.
Span Control
When a transmitter leaves the factory, it has a xed range of 0-200 psig,
0-2500 psig, etc. Typically the output from the transmitter varies from 4-20
mA or 10-50 mA. This output is linear with the measured variable, as shown
in Figure 1.2, page 5.

5
Model 753A Gage Pressure Transmitter Section 1
During calibration, the span control is used to adjust the instrument’s output
to 20 mA or 50 mA output signal at the maximum pressure setting of the
instrument.
10
50
OR
ELECTRONIC SIGNAL mA
4
20
20 40 60 80 100
% OF FULL SCALE DP RANGE
Figure 1.2—Output calibrated to upper limit of DP range
Specications
Input Range.................................... 0-108 psig to 0-4620 psig
(Consult factory for other ranges)
Output............................................. 4-20 mA or 10-50 mA, direct or reverse acting
Reference Accuracy*...................... ±0.5% of factory-calibrated span, including e󰀨ects of
non-linearity, hysteresis, and repeatability
(±0.25% accuracy optional)
Zero/Span Adjustments .................. Combined zero/span eld adjustments are limited to
±5% of factory-calibrated span. See Zero Suppres-
sion and Custom Span for additional options.
Zero Suppression ........................... Available as an option.
0% to 50% suppression of factory-calibrated span
Custom Span.................................. Available as an option.
20% to 100% of factory-calibrated span
Sensitivity*...................................... ±0.01% of factory-calibrated span
Power Requirements (see Figure 3.3, page 13)
4-20 mA....................................... 12 VDC plus 2 VDC per 100-ohms load (to 70 VDC
maximum)
10-50 mA..................................... 12 VDC plus 5 VDC per 100-ohms load (to 70 VDC
maximum)
Load Range
(includes line and receiver; see Figure 3.3, page 13)
4-20 mA....................................... 50 ohms per volt above 12 VDC (to 2900 ohms
maximum)
10-50 mA..................................... 20 ohms per volt above 12 VDC (to 1160 ohms
maximum)
Load E󰀨ect*
4-20 mA....................................... ±0.025% of factory-calibrated span per 100-ohms
change
10-50 mA..................................... ±0.05% of factory-calibrated span per 100-ohms
change

6
Section 1 Model 753A Gage Pressure Transmitter
Power Supply E󰀨ect*
4-20 mA....................................... ±0.025% of factory-calibrated span per 1 Volt
change
10-50 mA..................................... ±0.05% of factory-calibrated span per 1 Volt change
Noise*............................................. 0.2% (peak-to-peak) maximum of factory-calibrated
span
Thermal E󰀨ect*
(combined e󰀨ect on zero
and span)........................................ ±1.0% of factory-calibrated span per 100ºF change
within the operating temperature range selected
Operating Temperature................... 40ºF to 135ºF (standard), -15ºF to +135ºF (optional)
Overpressure limit .......................... 1.5 × factory calibrated range without damage to unit
Process Connections...................... 1/4" NPT (female)
Weight ............................................ 8 lb
Electrical Interface.......................... 1/2 inch conduit connections to internal screw termi-
nals (external junction box optional)
*Note: Turndown has a directly proportional e󰀨ect on the indicated specications. Zero
or span eld adjustments beyond ±5% may a󰀨ect indicated performance. Calibration is
by the end-point method with zero and full scale outputs held to ±0.5% of true calibrated
values.
IMPORTANT: The Model 753A transmitter has no integral electronic interference sup-
pression features. If an instrument is to be installed in an area containing
EMI/RFI sources and this interference cannot be tolerated, take precau-
tions to protect the transmitter signal. See also EMI/RFI Shielding, page
14. An optional EMI/RFI lter system is available upon request.

7
Model 753A Gage Pressure Transmitter Section 2
Section 2—Theory of Operation
Basic Components
Gage Pressure Transducer
The gage pressure sensing element is a C-type Bourdon tube. The C-type
Bourdon tube is an arc-shaped metal tube, elliptical in cross-section and open
at one end. The open end is attached to the pressure source. The closed end is
free to move. When pressure is applied to the inside of the tube through the
open end, the tube loses its circular shape and the sensing element is actuated.
The gage pressure transducer range is determined by the force required to
move the C-type Bourdon tube bellows through its normal range of travel. To
provide for various ranges, tubes are designed with dierent wall thicknesses
and degrees of tube cross-section distortion.
Strain Gage Assembly. The strain gage assembly consists of a strain gage
beam and a glass-to-metal seal feed-through assembly. Strain gages are
bonded to opposite sides of the strain gage beam. The end of the strain gage
beam is connected to the gage pressure sensing element. Any movement of
the sensor causes a corresponding linear movement of the strain gage beam
which acts upon the strain gages. Any action of the strain gages is monitored
by the electronic transmitter circuit.
Electronic Transmitter
The 753A transmitter senses the pressure applied at the input of the gage pres-
sure assembly and the electronic circuit converts to a 4-20 mA or 10-50 mA
output signal. The pressure causes the closed end of the C-type Bourdon tube
to move and the movement is mechanically transmitted to the strain gages by
the strain gage beam. Motion of the end of the strain gage beam applies ten-
sion to one gage and compression on the other. The gage in tension increases
in resistance, while the one under compression decreases in resistance. The
two gages are connected to form two active arms of a bridge circuit.
Basic Operation
The electronic transmitter is basically a loop current regulating device, where
loop current is controlled by an input of mechanical force or motion. The
block diagram (Figure 2.1, page 8) shows the relationships of the various
stages and the main ow of the electrical currents. As shown, the transmitter,
power supply, and load (line plus receiving device) are connected in series.
The current from the power supply enters the transmitter, passes through the
reverse polarity protecting diode, then divides into two separate paths. The

8
Section 2 Model 753A Gage Pressure Transmitter
main current ows through the current amplier stage and returns to the loop.
The remainder of the current passes through the electronic regulator where it
divides into two paths, through the bridge circuit and the voltage amplier.
The current is then returned to the loop. The total loop current ows through
the load and back to the power supply.
Surge Voltage Protection Circuit
Two gas discharge tubes and a Zener diode are placed in the input circuit to
prevent transient voltages from entering the transmitter circuit.
Reverse Polarity Protection
Reverse input polarity protection is provided by the forward-conducting
diode. In the event the polarity of the input is reversed, the diode blocks the
input and prevents the reversed input power from damaging the electronic
circuit components. The diode can accommodate a maximum of 80 Volts
without damage.
Regulator
This stage of the circuit regulates that portion of the loop current which is not
calibrated at the current amplier stage, and provides stabilized voltage for
bridge excitation and power for the signal amplier.
Figure 2.1—Operational block diagram
Strain Gage Bridge Network
The strain gage bridge network consists of two silicone piezo-resistive strain
sensors, the zero adjusting potentiometer, bridge completion resistors, and the
temperature compensation components.

9
Model 753A Gage Pressure Transmitter Section 2
Signal Amplier
The signal amplier is an integrated circuit operational amplier which pro-
vides amplication of the strain gage bridge network output voltage.
Current Amplier
The current amplier circuit converts the signal amplier output voltage to
current. The amount of current is precisely regulated with the feedback net-
work to make it proportional to the bridge output.
Temperature Compensation
The Model 753A transmitter is temperature-compensated at the factory. Only
those repairs described in Section 4 of this manual may be performed in the
eld without voiding the certied performance.

10
Section 3 Model 753A Gage Pressure Transmitter
Section 3—Installation, Startup, and Shutdown
Overview
This section describes the steps required to install the instrument so that it
will perform to its original factory calibration condition. Installation tasks
include
•initial calibration check
• mounting the transmitter
• installing piping
•installing eld wiring
Unpacking/Inspection
The instrument should be inspected at the time of unpacking to detect any
damage that may have occurred during shipment.
IMPORTANT: The unit was checked for accuracy at the factory. Do not change any of
the settings during examination or accuracy will be a󰀨ected.
If the transmitter is Class II cleaned, it is shipped in a polyethylene bag to
protect the instrument from contamination. Remove this bag only in a clean
area.
Initial Calibration Check
The Model 753A transmitter is factory-calibrated. However, to ensure that the
calibration is intact following shipping, a calibration check is recommended
prior to operating the instrument. See Calibration, page 16, for step-by-step
instructions. Record the "as found" values and recalibrate, if necessary.
Mounting
Mount the transmitter so that the transmitter cover is facing the operator and
the controls are on the right side. Use mounting structures that are designed to
minimize vibration and prevent resonance. Support connected process tubing
and conduit using the same mounting as the instrument base to minimize rela-
tive motion of the instrument and connections.
Wall or Rack Mounting
1. Locate and drill four bracket mounting holes in the mounting surface.
2. Attach the instrument to the wall using 5/16" (8 mm) bolts, Grade 5 or
better, and torque to 10-20 ft-lb.

11
Model 753A Gage Pressure Transmitter Section 3
Piping Guidelines
Observe the following practices when piping for ow and liquid level ap-
plications.
1. Install the transmitter as near the primary metering device as possible,
and choose a piping diameter accordingly. For distances up to 50 feet,
use 1/4-inch pipe or tubing. For runs of 50 to 100 feet, use 1/2-inch pipe
or tubing.
IMPORTANT: Distances greater than 100 feet should be used only if an air purge or
blow-back system is installed.
2. Slope all piping at least one inch per linear foot to avoid liquid or gas
entrapment in the lines or the instrument.
• Slope all piping downward from the transmitter when used in gas
applications to prevent liquid entrapment.
• Slope all piping upward from the transmitter when used in liquid ap-
plications to prevent liquid entrapment.
3. If the process temperature exceeds 135ºF, provide a minimum of 2 feet
of uninsulated piping between the transmitter and the primary metering
device for each 100 degrees in excess of +135ºF.
4. Install a suitable pulsation dampening device upstream of the transmitter.
Where severe pulsation is present, the accuracy of the ow measurement
will be aected.
5. For ease of operation and maintenance, install manifolds to allow sens-
ing lines to be shut o while removing the instrument from the line or
performing a calibration. Appendix A, page 25, shows an example of a
typical installation conguration.
6. Locate all shuto valves so that they are readily accessible from the front
of the instrument. Locate block valves at the source of dierential pres-
sure lines.
7. Prevent leakage by using a suitable sealing compound on all joints. Mea-
surement errors can be caused by leaks in the piping.
Electrical Connections
!WARNING: Ensure that the condulet cover is secure before applying
power to instrument when used in hazardous areas. Failure to do this
may result in personal injury or property damage.
Flexible cable is recommended for electrical connections to the instrument.

12
Section 3 Model 753A Gage Pressure Transmitter
Perform the following steps to complete eld wiring.
1. Connect the power supply and the receiver to the transmitter as shown in
Figures 3.1 and 3.2.
2. Determine the total loop resistance required for the installation, using
Figure 3.3, page 13, for reference. The total loop resistance must be
less than the maximum calculated value. Table 3.1, page 13, provides
loop resistance values for various cable wire sizes.
3. Install a load resistor sized for the application.
!WARNING: Failure to properly calculate power supply DC output voltage
may result in inaccurate transmitter readings, possibly leading to safety
system performance degradation during design basis events. To avoid
equipment inaccuracy hazards, follow the examples and tables in this
section for determining the proper power supply DC output voltage.
Figure 3.1—Typical eld wiring connections for Model 753A with junction box
Figure 3.2—Typical eld wiring connections for Model 753A without junction box

13
Model 753A Gage Pressure Transmitter Section 3
Table3.1—CableSpecications
Loop Resistance/1000 ft
[ohms @ 68°F (20°C)]
Cable Wire Size
5.06 14 AWG, 2 Wires
8.04 16 AWG, 2 Wires
12.78 18 AWG, 2 Wires
20.30 20 AWG, 2 Wires
4-20 mA
10-50 mA
200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
2900
1160
70
60
50
40
30
20
10
Total Loop Resistance (Ohms) (Load Transmission Line)
Power Supply Range (Volts)
Any voltage or resistance within the
shaded area for the respective
transmitter output is acceptable.
Figure 3.3—Power supply and loop resistance
Care must be exercised when calculating the power supply output voltage. A
power supply specied as 50Vdc ±1 volt must be considered a 49Vdc source
to ensure the minimum required voltage at the transmitter. Use the actual
value when available; otherwise, use "worst case" value.
Use Figure 3.3 as a reference to determine if the maximum calculated value
of RT= RLine + RLoad + RExt is correct.
Loop Resistance Calculations
Use the following method to calculate the loop resistance value.
Transmitter Current = IDC (20 mA or 50 mA)
RT= VDC - TVDC
IDC
Total Loop Resistance (RT) = RLine + RLoad + RExt
Power Supply Voltage = VDC (70 V max. for 4-20 mA or 10-50 mA Systems)
Maximum Transmitter Voltage = TVDC (70 V for both 4-20 mA and 10-50 mA Systems)
Minimum Transmitter Voltage = TVDC (12 V for both 4-20 mA and 10-50 mA Systems)

14
Section 3 Model 753A Gage Pressure Transmitter
Maximum Loop Resistance
Example 1: (Maximum loop resistance for 10-50 mA system):
VDC = 70 Vdc TVDC = 12 Vdc
IDC = 50 mA RT= = 1160 Ohms
0.05
70-12
Example 2: (Maximum loop resistance for 4-20 mA system):
VDC = 70 Vdc TVDC = 12 Vdc
IDC = 20 mA RT= = 2,900 Ohms
0.02
70-12
Example 3: (Calculation to determine maximum loop resistance with
power supply ≥12 Vdc, but ≤ 70 Vdc for 10-50 mA and 4-20 mA systems):
VDC = 40 Vdc TVDC = 12 Vdc
IDC = 50 mA RT= = 560 Ohms
0.05
40-12
IDC = 20 mA RT= = 1400 Ohms
0.02
40-12
EMI/RFI Shielding
IMPORTANT: The 753A transmitter has no integral electronic interference suppression
features. If an instrument is to be installed in an area containing EMI/RFI
sources and this interference cannot be tolerated, take precautions to
protect the transmitter signal. An optional EMI/RFI lter is available upon
request. Contact the factory for information.
The following precautions are recommended to limit EMI/RFI interference:
1. Run signal wires in solid conduit or use high quality shielded cable to
connect the transmitter to the power equipment.
2. House the transmitter leads in solid conduit up to the junction box where
the shielded cable is connected to the leads.
3. Ground the electronic transmitter, junction box (including the cover),
conduit, and cable shield.
Startup Procedure
To operate the transmitter, perform the following steps. See the installation
diagram in Appendix A, page 25, for typical valve locations.
1. Locate the block valves and make sure they are closed.
NOTE: The block valve is normally installed at the facility for the purpose of iso-
lating the pressure lines (process being monitored) from the monitoring
instruments.
2. Congure the test manifold’s control valves to connect the input pres-
sure port of the gage pressure transducer to the appropriate pressure lines
(process being monitored). Follow the guidelines in Appendix A that are

15
Model 753A Gage Pressure Transmitter Section 3
specic to your piping conguration.
3. Open the block valve if applicable (recommended for liquid service, but
not for gas).
IMPORTANT: For gas service, it is recommended that a zero check be performed with
the block valve closed. If the gas ow is pulsating, there may be a stand-
ing wave e󰀨ect in the process line which can displace the indicator and
appear as a zero error.
4. Apply electrical power to the Model 753A transmitter.
5. Check the transmitter calibration across all checkpoints, using the in-
structions provided in Calibration, page 16. If re-adjustment of the zero
and/or span is necessary, perform all 12 steps described in the Calibration
Procedure, page 18.
6. Check the manifold and piping for leaks as follows:
a. Open the shuto valve to pressurize the instrument.
b. Close the shuto valve.
c. Check for a change (increase or decrease) in the transmitter output
that could indicate leakage.
IMPORTANT: Be careful not to subject the gage pressure transducer to unnecessary
shock or overrange pressure during operations.
Shutdown Procedure
To shut down operations, perform the following steps.
1. Remove electrical power from the Model 753A transmitter loop.
2. Close the shut-o valve.
3. Close the main block valve at the process connections.
4. Open the vent/drain valve to remove all pressure from the unit.

16
Section 4 Model 753A Gage Pressure Transmitter
Section 4—Calibration and Maintenance
General Field and Periodic Maintenance
Electronic Transmitter
The electronic transmitter circuits are basically maintenance-free and do not
require routine preventative maintenance other than a periodic check of cali-
bration. See Calibration below for details.
Calibration
Each transmitter is calibrated at the factory prior to shipment. A 9-point cali-
bration check is recommended upon receipt, and again before the transmitter
is operated for the rst time. If "as found" values are not within the specied
range, a full calibration should be performed.
The transmitter should be recalibrated at periodic intervals, determined
primarily by the usage of the transmitter, historical performance, the desired
accuracy of the output signal, or indications that the instrument may be out of
calibration. If a transmitter is installed after an extended period of storage, a
calibration test should be performed before operating the transmitter to ensure
correct performance.
Test Equipment
To perform the calibration procedure for an instrument with 0.5% accuracy,
the test equipment should meet or exceed the requirements listed in Table 4.1,
page 17. For calibrating instruments, the pressure source should have at
least 4 times the accuracy of the instrument being tested. In the event equip-
ment is substituted that does not meet these requirements, the accuracy of the
recalibrated transmitter must be derated accordingly.

17
Model 753A Gage Pressure Transmitter Section 4
Table 4.1—Calibration Equipment
Equipment Requirements
Digital Voltmeter ±0.05% of reading accuracy at 10 VDC scale
Power Supply 12-70 Vdc, 60 mA minimum, regulation 3%, ripple 1% (see Electrical
Connections, page 11)
Precision Load Resistor 200 ohms, ±0.05%, 1W (10-50 mA transmitter) 500 ohms, ±0.05%,
1W (4-20 mA transmitter)
Pressure Source Provides zero to full scale pressure (Accuracy: 4 times the accuracy
of the instrument under test)
Electrical Connections for Calibration
The electrical connections required for calibrating the transmitter are shown
in Figure 4.1.
!WARNING: Ensure that the condulet cover is secure before applying
power to instrument when used in hazardous areas. Failure to do this
may result in personal injury or property damage.
Figure 4.1—Electrical connections for calibration
Flexible cable is recommended for electrical connections to the instrument.
Perform the following steps to complete eld wiring.
1. Connect the power supply and the DC voltmeter to the transmitter as
shown in Figure 4.1.
2. Connect a milliammeter as shown, if desired.
3. Determine the total loop resistance required for the installation, using
Figure 3.3, page 13, for reference. The total loop resistance must be
less than the maximum calculated value. Table 3.1, page 13, provides

18
Section 4 Model 753A Gage Pressure Transmitter
loop resistance values for various cable wire sizes.
4. Install a load resistor sized for the application.
!WARNING: Failure to properly calculate power supply DC output voltage
may result in inaccurate transmitter readings, possibly leading to safety
system performance degradation during design basis events. To avoid
equipment inaccuracy hazards, follow the examples and tables in this
section for determining the proper power supply DC output voltage.
Calibration Checkpoints
Table 4.2 presents the transmitter output values in current and voltage, along
with the associated tolerance for instrument with 0.5% accuracy, for both the
4-20 mA and 10-50 mA variations. Instruments are held to the same toler-
ances during factory calibration. For calibrating instruments with 0.25%
accuracy, divide the tolerances shown by one-half.
Table 4.2—Calibration Checkpoints for Instrument with 0.5% Accuracy
Applied Calibration
Pressure Checkpoint
(% of Span)
Output*
4-20 mA Transmitter** 10-50 mA Transmitter***
Current
(±0.08 mA)
Voltage
(±0.04 Vdc)
Current
(±0.2 mA)
Voltage
(±0.04 Vdc)
0% 4 mA 2 Vdc 10 mA 2 Vdc
25% 8 mA 4 Vdc 20 mA 4 Vdc
50% 12 mA 6 Vdc 30 mA 6 Vdc
75% 16 mA 8 Vdc 40 mA 8 Vdc
100% 20 mA 10 Vdc 50 mA 10 Vdc
*This value includes the e󰀨ects of conformance (non-linearity), deadband, hysteresis, and repeatability.
**This value was obtained using a 500-ohms load resistor.
***This value was obtained using a 200-ohms load resistor.
Calibration Procedure
The following procedure can be used to obtain "as found" calibration values
or perform a full calibration.
•To obtain the “as found” calibration values (calibration check only),
perform steps 1 through 6 and steps 10 through 12, skipping steps 7
through 9.
• For periodic calibration or in cases where the “as found” calibration
values do not meet the tolerances specied in Table 4.2, perform all
12 steps.
1. Verify that the transmitter is installed in accordance with the mounting
guidelines on page 10 and the piping guidelines on page 11.
2. Locate the block valve and make sure it is closed. The block valve is nor-
mally installed at the facility to isolate the process being monitored from

19
Model 753A Gage Pressure Transmitter Section 4
the monitoring instruments.
3. Congure the test manifold control valve to connect the output of the test
pressure source to the input port of the gage pressure transducer.
4. Verify that all electrical connections are properly installed (see electrical
connections in Figure 3.1, page 12.
5. Apply the appropriate power supply voltage to the transmitter. (To deter-
mine this voltage, see Power Supply, page 4.)
6. Exercise the transmitter by applying 0% and 100% calibration pressures
(specied in Table 4.2, page 18) three times. If performing a calibra-
tion check only, proceed to step 10.
7. Apply the calibration pressure for the 0% checkpoint (as specied in
Table 4.2, page 18). Adjust the zero control potentiometer as required
to produce the recommended output level.
8. Apply the calibration pressure for the 100% checkpoint (as specied in
Table 4.2, page 18). Adjust the span control potentiometer as required
to produce the recommended output level.
9. Repeat steps 7 and 8 until no further renements can be made.
10. Apply the calibration pressures referred to in Table 4.2, page 18, start-
ing from 0% to 100%, and record the applied pressures and the output
levels at each measurement.
11. Repeat the calibration checks in descending order, from 75% to 0%, and
record the applied pressures and the output levels at each measurement.
12. Repeat steps 10 and 11 until you have completed three consecutive runs
and have recorded all relevant data.
IMPORTANT: If correct readings cannot be obtained, refer to the troubleshooting sug-
gestions in Table 4.3, page 20, or return the unit to the manufacturer
for repair and calibration.

20
Section 4 Model 753A Gage Pressure Transmitter
Troubleshooting
Refer to Table 4.3, page 20, for troubleshooting information and Section 5,
page 22, for part location.
Table 4.3—Transmitter Troubleshooting
Problem Possible
Source
Probable Cause Corrective Action
No Output Power
Source
Blown fuse, faulty
component
Replace fuse, repair
power supply
Transmission
Cable
Loose terminal connection Tighten terminal
connection; locate
and replace broken
wire
Receiver
(or load)
Blown fuse, faulty component Replace fuse; repair
or replace receiver
or load
Transmitter Loose terminal, reversed power
connection, faulty component
Tighten terminal,
reverse power con-
nection, return to
factory for repair
Transmitter
"zeros" but
cannot get
full output
Power
Source
Low voltage Repair power
source
Load
Resistance
Resistance too high Replace load resis-
tance or repair as
required
Transmission
Cable
Resistance or length of cable in
excess of
specications
Measure cable loop
resistance and bring
within specications
Electronic
Module
Amplier
Loss of gain Return to factory for
repair
Out of
Calibration
Electronic Component value shifted Recalibrate or return
to factory for repair
Erratic or
Intermit-
tent
Operation
Terminal
Connections
Loose or dirty Tighten and/or clean
as required
Electronic
Component
Defective component Return to factory for
repair
Strain Gages Physical damage Return to factory for
repair
Excess
Output (will
not "zero")
Transmitter Defective component Return to factory for
repair