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 Specifications... 5 Qualification... 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 Amplifier... 12 Current Amplifier... 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
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: This symbol identifies information about practices or circumstances 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. 2
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 specific gravity changes in vessels; flow of liquids and gases through orifice plates, nozzles or venturis; pressure drop across filters 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 equipment. 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 filled 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) 3
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 specified 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 field adjustments exceeding ±5% of the factory 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. 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. 4
Model 752 and 752A Differential Pressure Transmitters Section 1 Span Control When a transmitter leaves the factory, it has a fixed 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. 20 50 ELECTRONIC SIGNAL ma 4 OR 10 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. Specifications 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 field adjustments are limited to ±5% of factory-calibrated span. See Zero Suppression 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) 5
Section 1 Model 752 and 752A Differential Pressure Transmitters Specifications (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 terminals (external junction box optional) *Note: Turndown has a directly proportional effect on the indicated specifications. Zero or span field 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 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. See also EMI/RFI Shielding, page 17. An optional EMI/RFI filter system is available upon request. 6
Model 752 and 752A Differential Pressure Transmitters Section 1 Qualification The Model 752 and 752A transmitters have been subjected to IEEE-344 qualification 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. 7
Section 1 Model 752 and 752A Differential Pressure Transmitters 8
Model 752 and 752A Differential Pressure Transmitters Section 2 Section 2 Theory of Operation Basic Components Differential Pressure Unit (DPU) Valve Stem HP Housing LP Housing HP Bellows 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 fill liquid in the bellows, protecting the unit from damage or shift in calibration. Since the fill fluid 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. 9
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 fill liquid caused by ambient temperature changes. These extra convolutions are connected to the measuring bellows by a passageway to permit the fill 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 specifically 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 Beam & Strain Gage Assembly Figure 2.2 Strain gage assembly 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 specific bellows fill fluid used. The number of springs and their rate depends on the differential range desired. 10
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 flow 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 flows through the current amplifier 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 amplifier. The current is then returned to the loop. The total loop current flows 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 amplifier stage, and provides stabilized voltage for bridge excitation and power for the signal amplifier. 11
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 Amplifier The signal amplifier is an integrated circuit operational amplifier which provides amplification of the strain gage bridge network output voltage. Current Amplifier The current amplifier circuit converts the signal amplifier 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 field without voiding the qualifications certification. 12
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 field 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 amplification 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. 13
Section 3 Model 752 and 752A Differential Pressure Transmitters Piping Guidelines Observe the following practices when piping for flow 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 applications 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 flow 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 configurations. 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. 14
Model 752 and 752A Differential Pressure Transmitter Section 3 Perform the following steps to complete field 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 16, for reference. The total loop resistance must be less than the maximum calculated value. Table 3.1, page 16, 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. Model 752/752A GND + + Junction Box Power Supply + Receiver Load Resistor Figure 3.1 Typical field wiring connections for Model 752 and 752A with junction box + Model 752 / 752A + Power Supply + Receiver Load Resistor Figure 3.2 Typical field wiring connections for Model 752 and 752A without junction box 15
Section 3 Model 752 and 752A Differential Pressure Transmitters Table 3.1 Cable Specifications Loop Resistance/1000 ft (ohms @ 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 1160 2900 70 60 Power Supply Range (Volts) 50 40 30 20 10 10-50 ma 4-20 ma Any voltage or resistance within the shaded area for the respective transmitter output is acceptable. 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 Total Loop Resistance (Ohms) (Load Transmission Line) Figure 3.3 Power supply and loop resistance Care must be exercised when calculating the power supply output voltage. A power supply specified 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 R T = R Line + R Load + R Ext is correct. Loop Resistance Calculations Use the following method to calculate the loop resistance value. Total Loop Resistance (R T ) = R Line + R Load + R Ext Power Supply Voltage = V DC (70 V max. for 4-20 ma or 10-50 ma Systems) Maximum Transmitter Voltage = T VDC (70 V for both 4-20 ma and 10-50 ma Systems) Minimum Transmitter Voltage = T VDC (12 V for both 4-20 ma and 10-50 ma Systems) Transmitter Current = I DC (20 ma or 50 ma) R T = V DC - T VDC I DC 16
Model 752 and 752A Differential Pressure Transmitter Section 3 Maximum Loop Resistance Example 1: (Maximum loop resistance for 10-50 ma system): V DC = 70 Vdc T VDC = 12 Vdc I DC = 50 ma 70-12 R T = = 1160 Ohms 0.05 Example 2: (Maximum loop resistance for 4-20 ma system): V DC = 70 Vdc T VDC = 12 Vdc I DC = 20 ma 70-12 R T = = 2,900 Ohms 0.02 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): V DC = 40 Vdc T VDC = 12 Vdc I DC = 50 ma 40-12 R T = = 560 Ohms 0.05 I DC = 20 ma 40-12 R T = 0.02 = 1400 Ohms EMI/RFI Shielding IMPORTANT: The 752 and 752A transmitters have 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 filter 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 diagrams in Appendix A, page A-1, 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 isolating the pressure lines (process being monitored) from the monitoring instruments. 2. Configure the test manifold s control valves to connect the input pressure ports of the DPU to the appropriate pressure lines (process being 17
Section 3 Model 752 and 752A Differential Pressure Transmitters monitored). Follow the guidelines in Appendix A that are specific to your piping configuration. 3. Open the block valves if applicable (recommended for liquid service, but not for gas). NOTE: For gas service, it is recommended that a zero check be performed with both block valves closed. If the gas flow is pulsating, there may be a standing wave effect in the process line which can displace the indicator and appear as a zero error. 4. Apply electrical power to the transmitter loop. 5. Check the transmitter calibration across all checkpoints, using the instructions provided in Calibration, page 19. If re-adjustment of the zero and/or span is necessary, perform all 12 steps described in the Calibration Procedure, page 21. 6. Check the manifold and piping for leaks as follows: a. Open the bypass valve(s), then open one shutoff valve to pressurize the instrument. b. Close the shutoff valve and the bypass valve. c. Any leakage will be indicated by a change (increase or decrease) in the transmitter output. NOTE: Be careful not to subject the DPU to unnecessary shock or overrange pressure during operations. Shutdown Procedure To shut down operations, perform the following steps. See the installation diagrams in Appendix A, page A-1, for typical valve locations. 1. Remove electrical power from the transmitter loop. 2. Close the transmitter shut-off valves. 3. Close the main block valves at the process connections. 4. Open the transmitter drain valves and remove all pressure from the unit. 18
Model 752 and 752A Differential Pressure Transmitters Section 4 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 calibration. See Calibration below for details. Differential Pressure Unit (DPU) The field maintenance schedule for the DPU will depend on the purpose for which it is used. Periodic cleaning of the DPU is required if the instrument is used in a system where solids or semi-solids can accumulate in the DPU housings. Follow the guidelines in DPU Inspection and Cleaning, page 22, and take the necessary safety precautions to avoid damage to the bellows. Calibration Each transmitter is calibrated at the factory prior to shipment. A 9-point calibration check is recommended upon receipt, and again before the transmitter is operated for the first time. If "as found" values are not within the specified 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 20. For calibrating instruments, the pressure source should have at least 4 times the accuracy of the instrument being tested. In the event equipment is substituted that does not meet these requirements, the accuracy of the recalibrated transmitter must be derated accordingly. 19
Section 4 Model 752 and 752A Differential Pressure Transmitters Equipment Digital Voltmeter Power Supply Table 4.1 Calibration Equipment Requirements ±0.05% of reading accuracy at 10 VDC scale 12-70 Vdc, 60 ma minimum, regulation 3%, ripple 1% (see Electrical Connections, page 14) 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. Model 752/752A GND + Milliammeter (optional) + + Power Supply + Precision DC Voltmeter Load Resistor 500 ohms, 4-20 ma systems 200 ohms, 10-50 ma systems 20 Figure 4.1 Electrical connections for calibration Flexible cable is recommended for electrical connections to the instrument. Perform the following steps to complete field 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 16, for reference. The total loop resistance must be less than the maximum calculated value. Table 3.1, page 16, provides loop resistance values for various cable wire sizes.
Model 752 and 752A Differential Pressure Transmitters Section 4 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 tolerances 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 effects 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 specified in Table 4.2, perform all 12 steps. 1. Verify that the transmitter is installed in accordance with the mounting guidelines on, page 13 and the piping guidelines on page 14. 2. Locate the block valves and make sure they are closed. The block valves are normally installed at the facility for the purpose of isolating the pro- 21
Section 4 Model 752 and 752A Differential Pressure Transmitters cess being monitored from the monitoring instruments. 3. Configure the test manifold control valve to connect the output of the test pressure source to the high port of the DPU and vent the low side of the DPU to atmosphere. 4. Verify that all electrical connections are properly installed (see electrical connections in Figure 3.1, page 15. 5. Apply the appropriate power supply voltage to the transmitter. (To determine this voltage, see Power Supply, page 4.) 6. Exercise the transmitter by applying 0% and 100% calibration pressures (specified in Table 4.2, page 21) three times. If performing a calibration check only, proceed to step 10. 7. Apply the calibration pressure for the 0% checkpoint (as specified in Table 4.2, page 21). Adjust the zero control potentiometer as required to produce the recommended output level. 8. Apply the calibration pressure for the 100% checkpoint (as specified in Table 4.2, page 21). Adjust the span control potentiometer as required to produce the recommended output level. 9. Repeat steps 7 and 8 until no further refinements can be made. 10. Apply the calibration pressures referred to in Table 4.2, page 21, starting 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. Note: If correct readings cannot be obtained, refer to the troubleshooting suggestions in Tables 4.3 and 4.4, or return the unit to the manufacturer for repair and calibration. DPU Inspection and Cleaning To inspect and clean the DPU, perform the following steps. 1. Remove the instrument from service and remove pressure housing bolts. 2. Carefully remove the pressure housings. Note: If accumulation of material is extensive, rapid removal of the housings may damage the bellows convolutions. 3. Remove accumulation from between bellows convolutions and housings using a solvent, if possible. Note: Do not use sharp instrument to clean between bellows convolutions. 22
Model 752 and 752A Differential Pressure Transmitters Section 4 4. Replace the housings (new O-rings are recommended) and 3/8" CRES head bolts. 5. Apply Molycoat G paste or similar lubricant to threads and under heads (bearing surface) of bolts. Do not use silicone oil or grease. 6. Torque the head bolts to 45 ft-lb to a rotation of up to 135 degrees nominal using a torque wrench. The rotation of the bolt is measured after the bolt is "snug" with approximately 2 ft-lb torque. Note: Do not exceed the specified rotation. If a bolt fails to reach the specified torque within the rotation limit, reject the bolt. Troubleshooting Refer to Tables 4.3 and 4.4, pages 21 through 23, for troubleshooting information and Section 5 for part location. Note: If the sensor assembly is determined to be faulty, the transmitter should be returned to the factory for repair or replacement. Problem Low or No Output Possible Source Primary Element or DP Source Piping from Primary Element to Transmitter Bellows Unit Table 4.3 DPU Troubleshooting Probable Cause Orifice installed backwards or oversized; Flow blocked upstream from run; Density changes in process media or ref. leg Pressure tap holes or piping plugged; Bypass valve open or leaks; Liquids or gases trapped in pipe; Block or shutoff valves closed; Piping leaks, high pressure side Housing filled with solids restricting bellows movement; Gas trapped in housing in liquid service or liquid trapped in housing in gas service; HP housing gasket leaks; Body tampered with Corrective Action Replace orifice; Clean out run or open valve; Refill reference leg with same density liquid as process Clean out piping; Close bypass valve; Vent piping; Open block or shutoff valves; Repair leaks Clean out housing; Vent housing; Replace gasket; Return unit for repair 23
Section 4 Model 752 and 752A Differential Pressure Transmitters Table 4.3 DPU Troubleshooting Problem Possible Source Probable Cause Corrective Action High Output Primary Element Orifice partially restricted or too small; Loss of liquid in reference leg (liquid level) Clean out or replace; Refill reference leg Piping from Primary Element to Transmitter Leak in LP side piping Repair Bellows Unit Gas trapped in LP housing in liquid service or liquid trapped in gas service; LP housing gasket leaks; Range spring broken or body tampered with Vent housing; Replace gasket; Return unit for repair Erratic or Intermittent Operation Primary Element Flow pulsating Install dampening device upstream of meter run Piping from Primary Element to Transmitter Liquid trapped in gas piping or gas bubble in liquid piping; Vapor generator installed wrong; Reference leg gassy or liquid vaporizing Remove trapped liquid or gas bubble; Repipe; See piping instructions Bellows Unit Obstructed bellows travel; Gas trapped in HP or LP housing See DPU Inspection and Cleaning, page 22. Remove trapped gas Out of Calibration Bellows Unit Dirt in bellows; Damaged bellows Clean external bellows surface or return damaged DPU for repair 24
Model 752 and 752A Differential Pressure Transmitters Section 4 Problem No Output Transmitter "zeros" but cannot get full output Out of Calibration Erratic or Intermittent Operation Excess Output (will not "zero") Possible Source Power Source Transmission Cable Receiver (or load) Transmitter Power Source Load Resistance Transmission Cable Electronic Module Amplifier Table 4.4 Transmitter Troubleshooting Probable Cause Blown fuse, faulty component Loose terminal connection Blown fuse, faulty component Loose terminal, reversed power connection, faulty component Low voltage Resistance too high Resistance or length of cable in excess of specifications Loss of gain Corrective Action Replace fuse, repair power supply Tighten terminal connection; locate and replace broken wire Replace fuse; repair or replace receiver or load Tighten terminal, reverse power connection, return to factory for repair Repair power source Replace load resistance or repair as required Measure cable loop resistance and bring within specifications Return to factory for repair. Electronic Component value shifted Recalibrate or return to factory for repair Terminal Connections Electronic Component Loose or dirty Defective component Tighten and/or clean as required Return to factory for repair Strain Gages Physical damage Return to factory for repair Transmitter Defective component Return to factory for repair 25
Section 4 Model 752 and 752A Differential Pressure Transmitters 26
Model 752 and 752A Differential Pressure Transmitters Section 5 Section 5 Assembly Drawing and Parts List Figure 5.1 Model 752 and 752A, front view 27
Section 5 Model 752 and 752A Differential Pressure Transmitters 43! WARNING: Items marked with an asterisk (*) below may be replaced without loss of instrument qualification. No other field repairs or component replacements are authorized if instrument qualification is to be maintained. Table 5.1 752 and 752A Parts List ITEM DESCRIPTION PART NO. PER UNIT 1* Enclosure cover (gray) 9A-C0039-1045C 1 Model 752 circuit board assembly, 4 to 20 ma (replacements no longer available) 9A-C0752-1056B 2 Model 752 circuit board assembly, 10 to 50 ma (replacements no longer available) 9A-C0752-1070B 1 Model 752A circuit board assembly, 4 to 20 ma 9A-C0752-1269B Model 752A circuit board assembly, 10 to 50 ma 9A-C0752-1270B 4* Shaft and spring assembly 9A-C0752-1100B 2 6* O-ring, EPT, E740-75, 3/8 x 1/2 9A-C0001-1051R 2 7* Mounting bracket 9A-C0273-0001C 2 9 Pan head screw, 6-32 x 3/16, Model 752 9A-C0119-1006J Pan head screw, 6-32 x 1/4, Model 752A 9A-C0119-0016J 2 10* Bead chain 9A-C0076-0007T 2 11* Retaining ring 9A-C0087-0040T 4 28
Model 752 and 752A Differential Pressure Transmitters Section 5 Table 5.1 752 and 752A Parts List ITEM DESCRIPTION PART NO. PER UNIT 12* Cap 9A-C0752-1004C 2 14* Junction box 9A-C0752-1114C 1 15 Data plate 9C-C0752-1172G 1 16 I.D. plate, span adjust 9A-C0752-1121C 1 17 I.D. plate, zero adjust 9A-C0752-1122C 1 18* Silicone grease 9A-C0002-1003U A/R 19 Drive screw, 00 9A-C0600-1001J 4 20 Drive screw, #2 9C-C0600-1004J 4 23* Adapter 9A-C0752-1111C 2 24 Lock washer, #6 9A-C0003-0070K 2 25* Lock washer, 1/4 9A-C0003-0037K 8 26* Flat washer, 1/4 9A-C0003-1049K 8 29 Tag (not shown) 9A-C0199-0125C 1 30* O-ring, EPT, E740-75, 11/16 x 13/16 9A-C0001-1130R 2 31* Terminal bracket 9A-C0752-1112C 1 32* Pan head screw, 8-32 x 1/4 SST 9A-C0119-0006J 2 33* Marker strip 9A-C0752-1113C 1 34* Terminal block 9A-C0038-1170T 1 35* Pan head screw, 8-32 x 1/2 SST 9A-C0119-0005J 2 36* Conduit hub 9A-C0024-1006T 2 37* Drain plug 9A-C0186-0001T 1 38* Wire assembly, black 9A-C0752-1120B 1 39* Wire assembly, red 9A-C0752-1119B 1 40* Port plug, 1/2-in. NPT 9A-C0199-0215C 2 41 DC-550 silicone oil 9A-C0003-1002U A/R 42* Hex head bolt, 1/4-28 x 5/8 (8 ft-lb Torque) 9A-C0116-1007J 4 43* O-ring, cover, EPT 9A-C0001-1105R 1 44 Washer, flat, #6, SST 9A-C0003-0040K 1 45* Housing O-ring, EPT, E740-75, 1-3/4 X 1-7/8 9A-C0001-1054R 2 46* Housing, 1/2 1/4 NPT Ports 9A-C0764-1025C 2 47* Housing Cap Screws; 3/8-24 1-1/2 SST (40 ft-lb Torque) 9A-C0220-1028J 8 29
Section 5 Model 752 and 752A Differential Pressure Transmitters 30
Model 752 and 752A Differential Pressure Transmitters Section 6 Section 6 Dimensional Drawings Figure 6.1 Model 752 and 752A transmitters with junction box, front view Figure 6.2 Model 752 and 752A transmitters with junction box, side view 31
Section 6 Model 752 and 752A Differential Pressure Transmitters Figure 6.3 Model 752 and 752A transmitters, rear view 32
Model 752 and 752A Differential Pressure Transmitters Appendix A Appendix A Safety Precautions Suggested piping diagrams and startup instructions for typical and special flow applications are presented on the following pages. WARNING HIGH-PRESSURE HAZARD. TO PREVENT PERSONAL INJURY OR DAMAGE TO EQUIPMENT, DIRECT ALL PIPING AWAY FROM THE OPERATOR WHILE CONNECTING THE DPU TO THE SYSTEM PIPING. WARNING EXPLOSION HAZARD. NO ORGANIC COMPOUNDS, OIL, GREASE, DIRT, OR SCALE OF ANY KIND CAN BE TOLERATED IN AN OXYGEN INSTALLATION. Flow Application Important: Assure that the DPU high-pressure housing is connected to the upstream tap of the primary device. Note: To prevent overheating the DPU during blowdown, monitor the temperature by placing your hands on the pipe between the DPU and the manifold pipe containing the vent valves. Liquid Level Applications The process media may be used as a reference leg seal fluid when it is of a type that will condense in the reference leg under all conditions. If the process or process media characteristics are such that the above conditions cannot be met, a special reference leg seal fluid will be required. The special seal fluid must not be volatile and must not be miscible with the process media. Also, the difference in the densities of the special seal fluid and the process media will require compensation in calculating the differential pressure range of the DPU. A-1
Appendix A Model 752 and 752A Differential Pressure Transmitters Typical Piping/Startup Examples Diagrams for typical and special flow applications are presented on the following pages. Use the diagram best suited for the application as a guide for piping configuration. Gas Flow, DPU Above Run The following steps are recommended for applications in which hydrates are NOT present. 1. Open the bypass valve(s) and close the vent valve. 2. Open both shutoff valves and one block valve to pressurize DPU, then close the block valve. 3. Close one bypass valve and check the system for leaks. If output travels upscale, check for low-pressure piping leaks. If output travels downscale, check for high-pressure piping leaks. 4. Repair piping if necessary and repeat steps 1 through 3 until output remains stable at zero. 5. Close both shutoff valves and open the bypass valve(s). 6. Open both block valves and slowly open both shutoff valves. 7. Close the bypass valves, and if two bypass valves are used, open the vent valve. DPU STATIC PRESSURE CONNECTION (USE ONLY ONE) BYPASS VALVES SHUT-OFF VALVES VENT VALVE BLOCK VALVES PRIMARY DEVICE Figure A.1 Gas Flow, DPU Above Run A-2
Model 752 and 752A Differential Pressure Transmitters Appendix A Gas Flow, DPU Below Run The following steps are recommended only for applications that require the DPU to be mounted below the run. Drip pots are required when wet gas is present. 1. Open the bypass valve(s) and close the vent valve. 2. Open both shutoff valves and one block valve to pressurize DPU, then close the block valve. 3. Close one bypass valve and check the system for leaks. If output travels upscale, check for low-pressure piping leaks. If output travels downscale, check for high-pressure piping leaks. 4. Repair piping if necessary and repeat steps 1 through 3 until output remains stable at zero. 5. Close both shutoff valves and open the bypass valve(s). 6. Open both block valves and slowly open both shutoff valves. 7. Close the bypass valves, and if two bypass valves are used, open the vent valve. 8. If drip pots are used, open the drip valves and blow out accumulated liquid. BLOCK VALVES VENT VALVE PRIMARY DEVICE SHUT-OFF VALVES BYPASS VALVES STATIC PRESSURE CONNECTION (USE ONLY ONE) DPU DRIP POTS Figure A.2 Gas Flow, DPU Below Run A-3
Appendix A Model 752 and 752A Differential Pressure Transmitters Gas Flow, Hydrates Present The following steps are recommended for applications in which hydrates or heavy solids are present, and piping and shutoff valves are not less than 1/2-inch in diameter. Bypass the manifold above to isolate the meter from connecting piping. Drip pots prevent plugging. 1. Open the bypass valve(s) and close the vent valve. 2. Open both shutoff valves and one block valve to pressurize the DPU, then close the block valve. 3. Close one bypass valve and check the system for leaks. If output travels upscale, check for low-pressure piping leaks. If output travels downscale, check for high-pressure piping leaks. 4. Repair piping if necessary and repeat steps 1 through 3 until output remains stable at zero. 5. Close the bypass valves. If two bypass valves are used, open the vent valve. 6. Drain the drip pots of hydrates at regular intervals. VENT VALVE STATIC PRESSURE CONNECTION (USE ONLY ONE) BYPASS VALVES DPU BLOCK VALVES SHUT-OFF VALVES DRIP POTS PRIMARY DEVICE Figure A.3 Gas Flow, Hydrates Present A-4
Model 752 and 752A Differential Pressure Transmitters Appendix A Steam Flow, DPU Below Run For this application, condensing reservoirs and piping to orifice taps must be level. Assure that the reservoir and steam lines are at the same level. Two-inch pipe crosses may be used as seal pots. 1. Close the vent valves, if used, and open the bypass and shutoff valves. 2. Remove the condensing reservoir side and fill plugs. 3. Pour water into both reservoirs until the piping and the DPU housings are filled. Piping and housing chambers shall be free of bubbles. The pointer should rest at zero (or output will be 4 ma or 10 ma as applicable) when the instrument and piping are completely filled. 4. Install the side and fill plugs in the reservoirs. 5. Close the shutoff valves and open the block valves. 6. Slowly open both shutoff valves simultaneously and check for leaks. 7. Close the bypass valve. NOTE: Assure that plugs are used on the DPU. Valves should never be used on the DPU. PRIMARY DEVICE PLUGS BLOCK VALVES CONDENSING RESERVOIR SHUT-OFF VALVES VENT VALVES (OPTIONAL) DPU Figure A.4 Steam Flow, DPU Below Run A-5
Appendix A Model 752 and 752A Differential Pressure Transmitters Liquid Flow, DPU Above Run The following steps are recommended for applications in which sediments may be present. Inspect piping periodically. Not recommended for hot or gassy liquids. 1. Close both shutoff valves and open both block valves. 2. Open the bypass valve. Crack the vent valves or loosen the plugs from the top ports of the DPU body housings. 3. Crack and close the shutoff valves alternately until liquid is free of bubbles and spills out of both upper DPU body ports. 4. Close the vent valves or tighten the plugs. Close the block valves and open the shutoff valves. 5. The pointer should rest at zero (or output will be 4 ma or 10 ma as applicable). If it does not and no leaks are detected, the housing and/or piping are not completely filled with liquid. Repeat steps 1 through 4 until output remains stable at the lowest value. 6. Slowly open both block valves and close the bypass valve. BYPASS VALVE DPU SHUT-OFF VALVES PRIMARY DEVICE BLOCK VALVES Figure A.5 Liquid Flow, DPU Above Run A-6