Cameron Barton 752 User manual

BARTON®MODEL 752 & 752A
DIFFERENTIAL PRESSURE
TRANSMITTERS
For Nuclear Service
User Manual
Part No. 9A-C10820, Rev. 02
November 2015
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
Specications ............................................................................................... 5
Qualication............................................................................................... 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 Amplier........................................................................................ 12
Current Amplier...................................................................................... 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

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 affect instrument operation or
may lead to an instrument response that is not planned.
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............................................................................................................
A-11

3
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 trans-
mits it to remote receiving, control, or readout devices. Sources of differential
pressure include liquid level and specic gravity changes in vessels; ow of
liquids and gases through orice 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 compat-
ible 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 con-
nections 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 internally-
connected bellows, a center block, overrange valves, a temperature compen-
sator, 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)

4
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 out-
put 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 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 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
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.
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-
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.

5
Model 752 and 752A Differential Pressure Transmitters Section 1
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 10-
50 mA. This output is linear with the measured variable, as shown in Figure
1.2.
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 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.
Specications
Input Range.................................... 0-30 inches (water column) to 0-500 psid
(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 effects 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. Minimum
span is 30” w.c
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
maximum)
10-50 mA..................................... 12 VDC plus 5 VDC per 100-ohms load (to 70 VDC
maximum)

6
Section 1 Model 752 and 752A Differential Pressure Transmitters
Specications(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
maximum)
10-50 mA..................................... 20 ohms per volt above 12 VDC (to 1160 ohms
maximum)
Load Effect*
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
Power Supply Effect*
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 Effect*(combined effect
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)
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
damage to unit
Process Connections...................... 1/4" and 1/2" NPT (female) on both high and low
pressure sides
Weight ............................................ 8 lb (basic)
Electrical Interface.......................... 1/2 inch conduit connections to internal screw termi-
nals (external junction box optional)
*Note: Turndown has a directly proportional effect on the indicated specications. 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-
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.

7
Model 752 and 752A Differential Pressure Transmitters Section 1
Qualication
The Model 752 and 752A transmitters have been subjected to IEEE-344
qualication 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.

8
Section 1 Model 752 and 752A Differential Pressure Transmitters

9
Model 752 and 752A Differential Pressure Transmitters Section 2
Section 2—Theory of Operation
Basic Components
Differential Pressure Unit (DPU)
HP Housing
Valve Stem
HP Bellows
LP Housing
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 ap-
plied 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 sili-
cone strain gage beam, which is actuated directly by the valve stem connect-
ing 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 sup-
ported 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.

10
Section 2 Model 752 and 752A Differential Pressure Transmitters
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 specically 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 or-
der 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 con-
necting 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
Beam & Strain Gage Assembly
Figure 2.2—Strain gage assembly
Range Springs. The range springs act with the bellows to balance the differ-
ential pressure applied to the unit. The springs are fabricated of a material that
is compatible with the specic bellows ll uid used. The number of springs
and their rate depends on the differential range desired.