Specifications for Full-Range Calibration, Testing and Performance Measurement of Differential Pressure Transmitters
Specifications for Full-Range Calibration, Testing and Performance Measurement of Differential Pressure Transmitters
Differential pressure transmitters are key measuring instruments for monitoring pressure differentials in industrial applications; measurement accuracy is of paramount importance, and therefore regular calibration, testing and performance measurements are required. In this instance, an ALKB201 micro-pressure pump, an ALKC400T precision digital pressure gauge (differential pressure type) and an ALK475TREX handheld programmer were used to carry out a full-range calibration of the ALK3051DP differential pressure transmitter. Environmental conditions were strictly controlled throughout the procedure, and piping and wiring connections were carried out in accordance with standard procedures. Pressure was applied and released in stages across both the positive and negative pressure ranges, whilst the pressure and current output values at each test point were verified. Deviations were corrected and hysteresis verified using the handheld programmer. The entire process was carried out in strict accordance with standards to ensure the instrument met accuracy requirements, guaranteeing the precision and validity of the measurement data and providing a reliable basis for stable industrial operations.
I. Tools for Calibrating Differential Pressure Transmitters
|
Name |
Micro-pressure Light Pump |
Precision Digital Pressure Gauge |
HART Handheld Terminal |
Digital Differential Pressure Transmitter |
|
Model |
ALKB201 |
ALKC400T(Differential pressure type) |
ALK475TREX(Chinese version) |
ALK3051DP |
|
Technical Specifications |
Pressurisation method: Manual Pressure range: ±6000 Pa Medium: Clean air Outlets: 2 Connection: M20×1.5(F) Hose: 680 mm Guide hose: 300 mm Guide connector: M10×1 to φ6 Net weight: 1.8 kg Product dimensions: 220×120×90 mm
|
Pressure: ±6000 Pa Accuracy: 0.05% FS Temperature compensation: With temperature compensation Current measurement: ±30.0000 mA Voltage measurement: ±30.0000 V DC output: 24 V DC Communication Interface: RS-232/RS-485 Power Supply: Built-in rechargeable battery Connection: M10×1 Net Weight: 0.85 kg Dimensions: 110×75×190 mm
|
Accuracy class: ±0.05% FS Communication: HART protocol Display: Monochrome screen Language: Chinese DC output: 24 V DC Power supply: Built-in rechargeable battery Net weight: 0.5 kg Dimensions: 230 × 130 × 45 mm
|
Pressure: ±6000 Pa Accuracy: 0.2% FS Output signal: 4–20 mA Power supply: 24 V DC Net weight: 3.5 kg
|
|
Product Dimensions |
|
|
|
|
The entire verification process must be carried out in strict accordance with current metrological technical specifications. The main references include:JJG 882-2019 ‘Pressure Transmitters’, which applies to the verification, periodic calibration and in-service inspection of pressure transmitters, and is used to standardise the indication error, hysteresis and repeatability of transmitters.
II. Detailed Explanation of the Operational Process
(1) Preliminary Preparations
1. Environmental Requirements
The temperature must be maintained at (20±2) °C, with relative humidity ≤ 85% RH and no condensation. The site must be free from vibration, dust and corrosive gases.
2. Connecting the Equipment
• Connect the ALK3051DP differential pressure transmitter and the ALKC400T precision digital pressure gauge (differential pressure type, hereinafter referred to as the ‘differential pressure gauge’) to the outlet of the ALKB201 micro-pressure pump, ensuring a sealed connection.
(1) Connect the high-range port of the differential pressure gauge to one of the ALKB201’s output ports.
(2) Connect the high-range port of the differential pressure transmitter to the other output port of the ALKB201.
• Wiring Method 1 (24 V power supply for the precision digital pressure gauge):
(1) Red test lead connection: Insert one end into the 24 V port of the standard gauge, and clip the other end to the positive terminal of the transmitter
(2) Connect the negative terminal of the transmitter to the 250 Ω resistor.
(3) Black test lead connection: Insert one end into the current interface of the standard gauge, and clip the other end to one side of the 250 Ω resistor.
(4) Handheld communicator cable connection: Insert one end into the communication interface of the handheld communicator, and clip the other end to both ends of the 250 Ω resistor.
(5) Once the wiring is complete, a closed circuit is formed.
Wiring Diagram (1)
• Wiring Method 2 (ALK475TREX Handheld Transmitter, 24V Power Supply):
(1) Red test lead connection: Insert one end into the standard meter’s current socket and clip the other end to the negative terminal of the transmitter
(2) Black test lead connection: Insert one end into the standard meter’s common terminal
(3) Handheld unit communication cable connection: Insert one end into the handheld unit’s communication port; clip the red clamp to the transmitter’s positive terminal, and clip the black clamp together with the clamp on the black test lead
(4) Once the connections are complete, forming a closed circuit, switch on the ALK475TREX handheld unit’s 24V switching power supply
Wiring Diagram (2)
• If the differential pressure transmitter does not read zero at the current atmospheric pressure, and the standard gauge indicates that the differential pressure transmitter’s current reading of 12 mA is inaccurate, use a HART handheld communicator to calibrate the transmitter’s zero point and current.
(2) Positive Pressure Calibration Procedure for Differential Pressure Transmitters
1. Pressure Increase Calibration Procedure
• First, turn the ALKB201 handle anti-clockwise until it stops, then turn the precision fine-adjustment knob anti-clockwise to the appropriate position, and close the pressure relief valve. then use the handle to slowly increase the pressure clockwise until it reaches approximately the calibration value, at which point stop. Next, use the fine-adjustment knob to turn clockwise until the reading deviates by 3000 Pa from the calibration value; the differential pressure gauge will also show a deviation in the transmitter’s current reading of 16 mA. Use the handheld calibrator to adjust the pressure and current values.
• Calibrating the transmitter’s pressure value:
Select either the low-range fine adjustment or the high-range fine adjustment. If the pressure value measured by the transmitter is below 3000 Pa, select the low-range fine adjustment; if the pressure value is above 3000 Pa, select the high-range fine adjustment. Then press the right button, enter the pressure value of 3000 Pa, and finally press the right button again to confirm. Both the pressure value and the current value will be successfully calibrated.
• Next, use the handwheel to slowly increase the pressure clockwise until it reaches approximately the calibration value, then stop. Use the fine-tuning function to adjust to the calibration value of 6000 Pa; the current value should be 20 mA. If there is an error, calibrate using the handheld calibrator (follow the procedure described above).
2. Depressurisation calibration procedure
• First, use the handle to slowly reduce the pressure in an anti-clockwise direction until it reaches approximately the calibration value, then stop. Next, use the fine-tuning mechanism to adjust to the calibration value of 3000 Pa. The current value measured by the differential pressure gauge should be 16 mA. If there is a deviation, use the handheld calibrator to calibrate the pressure and current values.
• Record the correspondence between pressure and current at each point, and verify that the hysteresis (the difference in current at the same point during pressure increase and decrease) meets the requirement (≤0.05% FS).
3. Pressure Relief Procedure
Open the pressure relief valve and gradually release the pressure within the pipework; once the pressure has been fully relieved to zero, the measurement is complete.
(3) Negative Pressure Calibration Procedure for Differential Pressure Transmitters
1. Pressure Increase Calibration Procedure
• First, turn the ALKB201 handle clockwise until it stops, then turn the precision fine-adjustment knob clockwise to the appropriate position, and close the pressure relief valve. then use the handle to create a negative pressure by turning it anti-clockwise; stop when the pressure reaches approximately the calibration value; next, use the fine-adjustment knob to turn it anti-clockwise to the calibration value minus 3000 Pa. If the pressure value measured by the differential pressure transmitter deviates from –3000 Pa, and the current value of 8 mA measured by the differential pressure gauge also deviates, use the handheld calibrator to calibrate the pressure and current values.
• Calibrating the transmitter’s pressure value:
Select either the low-range fine adjustment or the high-range fine adjustment. If the pressure value measured by the transmitter is below –3000 Pa, select the low-range fine adjustment; if the pressure value is above –3000 Pa, select the high-range fine adjustment. Then press the right button, enter the pressure value –3000 Pa, and finally press the right button again to confirm. The pressure value and current value will both be successfully calibrated.
• Next, use the handwheel to create a negative pressure by turning it anti-clockwise. Stop when the pressure reaches approximately the calibration value, then use the fine adjustment to set it to the calibration value of –6000 Pa. The current value should be 4 mA; if there is an error, calibrate using the handheld controller (follow the procedure described above).
2. Depressurisation calibration procedure
• First, use the handle to slowly reduce the pressure clockwise. Stop when the pressure is approximately at the calibration value, then use the fine-tuning knob to adjust to the calibration value minus 3000 Pa. The current value measured by the differential pressure gauge should be 8 mA. If there is a deviation, use the handheld calibrator to calibrate the pressure and current values.
• Record the correspondence between pressure and current at each point, and verify that the hysteresis (the difference in current at the same point during both pressure increase and decrease) meets the requirement (≤0.05% FS).
3. Pressure Relief Procedure
Open the relief valve to gradually release the pressure within the pipeline. Once the pressure has been relieved to 0, the measurement is complete.
III. Precautions
Proper Use
• Operations must be carried out in accordance with standard procedures. When using the ALKB201 precision pressure gauge, pressurisation and depressurisation must be performed slowly to avoid pressure surges.
• The wiring of the differential pressure gauge must be clearly identified; take great care to prevent reverse connection.
• Readings at the calibration point must be taken only after the differential pressure gauge reading has stabilised, ensuring that records are accurate and up-to-date.
• Upon completion of the test, first slowly depressurise the system to zero, ensuring there is no residual pressure, then switch off the power supply before removing the instrument under test.
Maintenance and Calibration Intervals
• The ALKC400T precision digital pressure gauge (differential pressure type) must undergo periodic metrological verification (recommended once a year) to ensure measurement accuracy meets standards.
• When the pressure gauge is not in use, the power supply should be switched off; if not used for an extended period, it should be recharged once every three months.
• The fine-pressure light pump should be depressurised before storage during prolonged periods of inactivity and covered with a cloth cover to prevent dust from entering the instrument.
IV. Conclusion
This project successfully completed full-range calibration, testing and performance measurement of the differential pressure transmitter. Multi-point testing was carried out across both positive and negative pressure ranges; zero-point and span deviations were corrected, and hysteresis was verified. All indicators met the accuracy requirements. Operating procedures were strictly adhered to throughout the process, effectively preventing issues such as pressure surges and wiring errors, thereby ensuring the authenticity and validity of each set of measurement data. As a critical monitoring instrument, the operational status of the differential pressure transmitter directly impacts the effectiveness of production control. Moving forward, in addition to conducting calibration and testing in strict accordance with established procedures, it is essential to implement regular verification and routine maintenance of the equipment. Through standardised management, we will maintain the stable performance of the instruments, minimise faults and measurement deviations, and ensure the smooth and efficient operation of industrial automation systems with reliable measurement results.
