Cameron Barton 752, Barton 752A User Manual
BARTON® MODEL 752 & 752A
DIFFERENTIAL PRESSURE
TRANSMITTERS
For Nuclear Service
Part No. 9A-C10820, Rev. 02
Contents
Safety ............................................................................................................ 2
Section 1—Introduction ................................................................................. 3
General ......................................................................................................... 3
Product Description....................................................................................... 3
Differential Pressure Unit ......................................................................... 3
Electronic Transmitter................................................................................ 4
Power Supply ............................................................................................ 4
Zero and Span Control.................................................................................. 4
Zero Control .............................................................................................. 4
Span Control ............................................................................................. 5
Specications ............................................................................................... 5
Qualication............................................................................................... 7
Section 2—Theory of Operation .................................................................... 9
Basic Components ........................................................................................ 9
Differential Pressure Unit (DPU) ............................................................... 9
Electronic Transmitter...............................................................................11
Basic Operation ...........................................................................................11
Surge Voltage Protection Circuit .............................................................11
Reverse Polarity Protection ......................................................................11
Regulator ..................................................................................................11
Strain Gage Bridge Network ................................................................... 12
Signal Amplier........................................................................................ 12
Current Amplier...................................................................................... 12
Temperature Compensation........................................................................ 12
Section 3—Installation, Startup, and Shutdown ........................................ 13
Overview ..................................................................................................... 13
Unpacking/Inspection.................................................................................. 13
Initial Calibration Check .............................................................................. 13
Mounting ..................................................................................................... 13
Wall or Rack Mounting ............................................................................ 13
Piping Guidelines ........................................................................................ 14
Electrical Connections ............................................................................... 14
Loop Resistance Calculations ................................................................. 16
Maximum Loop Resistance ..................................................................... 17
EMI/RFI Shielding ....................................................................................... 17
November 2015
User Manual
Startup Procedure ....................................................................................... 17
Shutdown Procedure .................................................................................. 18
Section 4—Calibration and Maintenance ................................................... 19
General Field and Periodic Maintenance .................................................... 19
Electronic Transmitter.............................................................................. 19
Differential Pressure Unit (DPU) ............................................................. 19
Calibration .................................................................................................. 19
Electrical Connections for Calibration ..................................................... 20
Calibration Checkpoints .......................................................................... 21
Calibration Procedure ............................................................................ 21
DPU Inspection and Cleaning ..................................................................... 22
Troubleshooting .......................................................................................... 23
Section 5—Assembly Drawing and Parts List ........................................... 27
Section 6—Dimensional Drawings ............................................................. 31
Appendix A ...................................................................................................A-1
Safety Precautions .....................................................................................A-1
Flow Application .....................................................................................A-1
Liquid Level Applications ........................................................................ A-1
Typical Piping/Startup Examples ...............................................................A-2
Gas Flow, DPU Above Run ....................................................................A-2
Gas Flow, DPU Below Run ....................................................................A-3
Gas Flow, Hydrates Present...................................................................A-4
Steam Flow, DPU Below Run.................................................................A-5
Liquid Flow, DPU Above Run .................................................................A-6
Liquid Flow, DPU Below Run .................................................................A-7
DPU Below Tank with Reference Leg: Hot or Cool Liquids ....................A-8
DPU Level with Tank Bottom: Cool Liquids with Pressurized Tank ........A-9
DPU Below Tank Bottom: Cool Liquids with Pressurized Tank ............A-10
Product Warranty .....................................................................................A-11
Product Brand ............................................................................................................
Safety
A-11
Before installing this product, become familiar with the installation instructions presented in Section 3 and all safety notes throughout.
WARNING:Thissymbolidentiesinformationaboutpracticesorcircum-
!
stances that can lead to personal injury or death, property damage, or
economic loss.
CAUTION: Indicates actions or procedures which if not performed correctly
IMPORTANT: Indicates actions or procedures which may affect instrument operation or
2
may lead to personal injury or incorrect function of the instrument
or connected equipment.
may lead to an instrument response that is not planned.
Model 752 and 752A Differential Pressure Transmitters Section 1
Section 1—Introduction
General
The Model 752 and 752A Differential Pressure Transmitters provide a 4-20
mA or 10-50 mA signal that is proportional to differential pressure and transmits it to remote receiving, control, or readout devices. Sources of differential
pressure include liquid level and specic gravity changes in vessels; ow of
liquids and gases through orice plates, nozzles or venturis; pressure drop
across lters and static line pressures, etc.
Product Description
The Model 752 and 752A transmitters combine a differential pressure unit
(DPU) with an electronic circuit. The 4-20 mA or 10-50 mA output is compatible with a wide range of electronic receiving, control, and readout equip-
ment. The instrument utilizes miniaturized hybrid electronic circuits and a
molecular-bonded strain gage sensing cantilever beam, actuated directly by
the bellows' travel within the DPU. In many applications, the electrical connections are contained within a junction box, as shown in Figure 3.1, page 15.
However, the junction box is optional.
Differential Pressure Unit
The mechanical actuating device for the Model 752 and 752A transmitters
is a dual bellows assembly enclosed by a set of two pressure housings. The
assembly (Figure 1.1 below and Figure 2.1, page 9) consists of two internallyconnected bellows, a center block, overrange valves, a temperature compensator, a strain gage assembly, and range springs. The internal volume of the
bellows and center block is lled with a clean, non-corrosive, non-conductive
liquid with a low freezing point, and sealed. The motion-sensing cantilever
beam is also sealed within this environment.
Figure 1.1—Bellows unit assembly (BUA)
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Section 1 Model 752 and 752A Differential Pressure Transmitters
Electronic Transmitter
The electronic transmitter supplies a 4-20 mA or 10-50 mA direct current output signal that is proportional to the differential pressure sensed by the DPU.
The output signal is transmitted over a two-wire transmission line to remote
receiving devices.
Power Supply
A regulated direct current (DC) power supply is required to operate the transmitting 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 16. Table 3.1, page 16 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
specied 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.
For power supply wiring instructions, refer to the electrical connections
shown in Figures 3.1 and 3.2, page 15.
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-
Zero Control
tory calibration can alter transmitter performance in direct proportion to
the changes to the factory calibration. For example, if combined adjustments to zero and span change the factory calibration by a factor of 2,
transmitter performance may be decreased by a factor of 2.
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.
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Model 752 and 752A Differential Pressure Transmitters Section 1
ELECTRONIC SIGNAL mA
Span Control
When a transmitter leaves the factory, it has a xed range—0-120”w.c., 0-63
psi, etc. Typically the output from the transmitter varies from 4-20 mA or 1050 mA. This output is linear with the measured variable, as shown in Figure
1.2.
50
20
OR
10
4
20 40 60 80 100
% OF FULL SCALE DP RANGE
Figure 1.2—Output calibrated to upper limit of DPU range
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.
Specications
Input Range .................................... 0-30 inches (water column) to 0-500 psid
Output ............................................. 4-20 mA or 10-50 mA, direct or reverse acting
Reference Accuracy* ...................... ±0.5% of factory-calibrated span, including effects of
(±0.25% accuracy optional)
Zero/Span Adjustments .................. Combined zero/span eld adjustments are limited to
Zero Suppression ........................... Available as an option.
Custom Span .................................. Available as an option.
Sensitivity* ...................................... ±0.01% of factory-calibrated span
Power Requirements
(See Figure 3.3, page 16)
4-20 mA ....................................... 12 VDC plus 2 VDC per 100-ohms load (to 70 VDC
10-50 mA ..................................... 12 VDC plus 5 VDC per 100-ohms load (to 70 VDC
(Consult factory for other ranges)
non-linearity, hysteresis, and repeatability
±5% of factory-calibrated span. See Zero Suppression and Custom Span for additional options.
0% to 50% suppression of factory-calibrated span.
20% to 100% of factory-calibrated span. Minimum
span is 30” w.c
maximum)
maximum)
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Section 1 Model 752 and 752A Differential Pressure Transmitters
Specications(cont'd)
Load Range
(includes line and receiver; see Figure 3.3, page 16)
4-20 mA ....................................... 50 ohms per volt above 12 VDC (to 2900 ohms
10-50 mA ..................................... 20 ohms per volt above 12 VDC (to 1160 ohms
Load Effect*
4-20 mA ....................................... ±0.025% of factory-calibrated span per 100-ohms
10-50 mA ..................................... ±0.05% of factory-calibrated span per 100-ohms
Power Supply Effect*
4-20 mA ....................................... ±0.025% of factory-calibrated span per 1 Volt
10-50 mA ..................................... ±0.05% of factory-calibrated span per 1 Volt change
Noise* ............................................. 0.2% (peak-to-peak) maximum of factory-calibrated
Thermal Effect*(combined effect
on zero and span)........................... ±1.0% of factory-calibrated span per 100ºF change
Operating Temperature ................... 40ºF to 135ºF (standard), -15ºF to +135ºF (optional)
Max. Safe Working Pressure .......... 3000 psig
Static Pressure Effects*
1-30 psid range............................ ±0.2% of factory-calibrated span per 1000 psig
30-200 psid range........................ ±0.5% of factory-calibrated span per 1000 psig
200-500 psid range...................... ±1.0% of factory-calibrated span per 1000 psig
Overpressure Effects*
1-30 psid range............................ ±0.5% of factory-calibrated span per 1000 psig
30-200 psid range........................ ±1.5% of factory-calibrated span per 1000 psig
200-500 psig range...................... ±3.0% of factory-calibrated span per 1000 psig
Overpressure limit .......................... Up to 3000 psig on either side of DPU without
Process Connections...................... 1/4" and 1/2" NPT (female) on both high and low
Weight ............................................ 8 lb (basic)
Electrical Interface .......................... 1/2 inch conduit connections to internal screw termi-
maximum)
maximum)
change
change
change
span
within the operating temperature range selected
damage to unit
pressure sides
nals (external junction box optional)
*Note: Turndown has a directly proportional effect on the indicated specications. Zero
or span eld adjustments beyond ±5% may affect 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 752 and 752A transmitters have no integral electronic interfer-
6
ence 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. See also EMI/RFI
Shielding, page 17. An optional EMI/RFI lter system is available upon
request.
Model 752 and 752A Differential Pressure Transmitters Section 1
Qualication
The Model 752 and 752A transmitters have been subjected to IEEE-344
qualication testing that demonstrates that the unit will not lose its pressure
boundary or structural integrity when subjected to loadings associated with
seismic accelerations up to 12 Gs.
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Section 1 Model 752 and 752A Differential Pressure Transmitters
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Model 752 and 752A Differential Pressure Transmitters Section 2
HP Housing
Valve Stem
HP Bellows
LP Housing
Section 2—Theory of Operation
Basic Components
Differential Pressure Unit (DPU)
LP Bellows
Figure 2.1—DPU cutaway view
The differential pressure range of the dual-bellows type DPU is determined
by the force required to move the bellows through their normal range of
travel. To provide for various ranges, range springs are incorporated into the
Bellows Unit Assembly (BUA). The range springs, which are available in
various factory assemblies, accurately balance the differential pressure applied to the DPU.
In operation, the two bellows (which are connected by the valve stem shown
in Figure 2.1) move in proportion to the difference in pressure applied across
the BUA. The linear motion of the bellows is picked up by the tip of the silicone strain gage beam, which is actuated directly by the valve stem connecting the two bellows. If the bellows are subjected to a pressure greater than the
differential pressure range of the DPU, they will move through their normal
range of travel, plus a small additional amount of "overtravel," until the valve
on the stem shaft seals against its valve seat. As the valve closes on the seat, it
"traps" the ll liquid in the bellows, protecting the unit from damage or shift
in calibration.
Since the ll uid is essentially non-compressible, the bellows are fully supported and cannot rupture regardless of the over-pressure (up to the full rated
pressure of the instrument) applied to the unit. Furthermore, since the unit
contains opposed valves, protection against "overrange" in either direction is
provided.
Draining or Venting. Pressure connections on the top and bottom of the high
and low pressure DPU housings provide a drain when the unit is used in gas
installations, or a vent when the unit is used in liquid installations, when
installed in accordance with standard practices.
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Section 2 Model 752 and 752A Differential Pressure Transmitters
Beam & Strain Gage Assembly
Temperature Compensation. The high pressure side of the DPU has extra
bellows convolutions to provide for expansion and contraction of the ll
liquid caused by ambient temperature changes. These extra convolutions are
connected to the measuring bellows by a passageway to permit the ll liquid
to change volume without materially affecting the internal pressure or the
physical relationship of the measuring bellows.
Bellows. The bellows used in the DPU were specically developed for use
in sensing and measuring instruments. They are designed to provide exacting
linearity characteristics as well as long life, and to be free of the effects of
work hardening. Individual bellows diaphragms are stamped from special order Type 316 ELC (Extra Low Carbon) stainless steel sheets. The diaphragms
are assembled and seam welded to form the bellows.
Strain Gage Assembly. The strain gage assembly (Figure 2.2) 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 installed directly into a cutout in the valve stem connecting the two bellows of the DPU. Any movement of the bellows in either
direction 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.
Tension Strain Gage
Compression Strain Gage
Range Springs. The range springs act with the bellows to balance the differential pressure applied to the unit. The springs are fabricated of a material that
is compatible with the specic bellows ll uid used. The number of springs
and their rate depends on the differential range desired.
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Figure 2.2—Strain gage assembly
Model 752 and 752A Differential Pressure Transmitters Section 2
Electronic Transmitter
The DPU senses the difference in pressure applied across the bellows unit
assembly and the electronic circuit converts to a 4-20 mA or 10-50 mA output
signal. The pressure causes a linear motion of the bellows which is mechanically transmitted to the strain gages by the strain gage beam. Motion of the
end of the strain gage beam applies tension 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 2.3, page 12) 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
main current ows through the current amplier 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 amplier.
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 amplier stage, and provides stabilized voltage for
bridge excitation and power for the signal amplier.
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Section 2 Model 752 and 752A Differential Pressure Transmitters
Figure 2.3—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.
Signal Amplier
The signal amplier is an integrated circuit operational amplier which provides amplication of the strain gage bridge network output voltage.
Current Amplier
The current amplier circuit converts the signal amplier output voltage to
current. The amount of current is precisely regulated with the feedback network to make it proportional to the bridge output.
Temperature Compensation
The Model 752 and 752A are temperature-compensated at the factory. Only
those repairs described in Section 4 of this manual may be performed in the
eld without voiding the qualications certication.
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Model 752 and 752A Differential Pressure Transmitter Section 3
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 affected.
The transmitter 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 752 and 752A transmitters are 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 19,
for step-by-step instructions. Record the "as found" values and recalibrate, if
necessary.
Mounting
Mount the transmitter so that the pressure housings are in a horizontal position and when the operator is facing the transmitter cover, the controls are on
the right side. Use mounting structures that are designed to minimize vibration and avoid resonance and/or keep resulting amplication below 33 Hz.
Support connected process tubing and conduit using the same mounting as the
instrument base to minimize relative 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.
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Section 3 Model 752 and 752A Differential Pressure Transmitters
Piping Guidelines
Observe the following practices when piping for ow and liquid level applications.
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 affected.
5. For ease of operation and maintenance, install manifolds to allow sensing
lines to be shut off while removing the instrument from the line or performing a calibration. Appendix A shows examples of typical installation
congurations.
6. Locate all shutoff valves and bypass valves so that they are readily accessible from the front of the instrument. Locate block valves at the source
of differential pressure lines.
7. Prevent leakage by using a suitable sealing compound on all joints. Measurement 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.
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