ALKY25A Portable Pressure Calibrator: Specifications for Pressure Transmitter Calibration and Measurement Operations

Pressure transmitters (HART protocol) are core pressure measurement instruments in industrial process measurement and control systems. Their measurement accuracy and output stability are of critical importance; conducting standardized calibration, testing, and measurement activities is key to ensuring the metrological performance of these instruments and the accurate transmission of measurement values. This work specification covers pressure transmitters (HART protocol), using the ALKY25A portable presasure calibrator and the ALK475TREX (Chinese version) HART handheld programmer as core tools. It encompasses environmental preparation, wiring connections, zero and span calibration, as well as the full process for pressure ramp-up/ depressurization verification under positive pressure and vacuum ranges, and hysteresis verification. It provides a standardized basis for field operations, ensuring that the transmitter’s measurement accuracy and output characteristics meet technical specifications.

I. Tools for Calibrating Pressure Transmitters (HART Protocol)

Name	Portable Pressure Calibrator	HART Handheld Programmer	Pressure Transmitters
Model	ALKY25A	ALK475TREX (Chinese Version)	Various Models
Technical Specifications	Pressure Range: -0.095 to 2.5 MPa Medium: Clean Air Pressure Connection: M20×1.5 Accuracy: Pressure: 0.05% F.S. Current: 0.05% ± 1d Resolution: Pressure: Min 10 Pa Current: Min 1 μA Current Measurement Range: 0 to 22 mA DC Output: 24 VDC DC Operating Time: ≥16 h Temperature Compensation: With temperature compensation Display: 4½-digit LCD, 5½-digit LCD; dual display for pressure and current Power Supply: 220 VAC, 50 Hz, 3 VA Weight: 5.6 kg (including aluminum case) Dimensions: 300 × 150 × 120 mm	Communication: HART Protocol Display: Black-and-white screen Language: Chinese DC Output: 24V DC Power Supply: Built-in rechargeable battery Net Weight: 0.5 kg Dimensions: 230 × 130 × 45 mm	Pressure: -0.1 to 2.5 MPa Accuracy: ±0.1% FS ±0.2% FS ±0.5% FS Output Signal: 4 to 20 mA + HART Power Supply: 24 VDC Connection: M20×1.5(M）
Product Dimensions

The entire verification process must strictly comply with current metrological technical specifications. The primary 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 standardize 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

• Make a sealed connection between the pressure transmitter (HART protocol) and the output port of the ALKY25A portable pressure calibrator: Connect the pressure output tube’s M10×1 threaded port to the calibrator’s output port, and connect the other threaded port (M20×1.5) to the pressure transmitter in a sealed manner.

• Wiring Method 1 (24V Power Supply for Portable Pressure Calibrator):

(1) Red test lead connection: Insert one end into the 24V port of the pressure calibrator, and clip the other end to the positive terminal of the transmitter

(2) Connect the transmitter’s negative terminal to the 250Ω resistor.

(3) Black test lead connection: Insert one end into the pressure calibrator’s current port, and clip the other end to one side of the 250Ω resistor.

(4) Handheld communicator cable connection: Insert one end into the handheld communicator’s communication port, and clip the other end to both ends of the 250Ω resistor.

(5) Complete the wiring to form a closed loop.

 

Wiring Diagram (1)

• Wiring Method 2 (ALK475TREX Handheld Unit with 24V Power Supply):

(1) Red test lead connection: Insert one end into the current port of the pressure calibrator; clip the other end to the negative terminal of the transmitter.

(2) Black test lead connection: Insert one end into the common port of the pressure calibrator.

(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 black test lead’s clamp from the calibration bench

(4) Once the connections are complete and a closed loop is formed, turn on the ALK475TREX handheld unit’s 24V switching power supply

 

Wiring Diagram (2)

• If the transmitter does not display 0 at the current atmospheric pressure, and the pressure calibrator detects a deviation in the transmitter’s 4 mA current value, use a HART handheld communicator to calibrate the transmitter’s zero point and current.

3. Specific Calibration Steps for the Handheld Programmer

(1) Calibrate the Transmitter Zero Point

Turn on the power to the handheld programmer; the handheld programmer has successfully established communication with the pressure transmitter.

 

(2) Calibrate the 4 mA or 20 mA current value measured by the pressure gauge from the transmitter

 

(2) Calibration Process for Pressure Transmitters (HART Protocol)

1. Pressure-Rise Calibration Process

• First, lift the switch valve on the ALKY25A portable pressure calibrator upward (do not switch while under pressure), then turn the fine-tuning knob counterclockwise to the appropriate position, and finally close the vent valve (pressure relief valve).

• Use the pressure-application handle to slowly increase the pressure until it reaches approximately the target calibration pressure, then stop. Next, use the fine-tuning handle to increase the pressure to 1.25 MPa. If the pressure reading from the transmitter deviates from 1.25 MPa, or if the 12 mA current reading from the pressure transmitter measured by the calibrator also deviates, use the handheld calibrator to adjust the pressure and current values.

• Calibrate the transmitter’s pressure value:

Select either the low-range fine-tuning or high-range fine-tuning mode. If the transmitter’s measured pressure is below 1.25 MPa, select low-range fine-tuning; if it is above 1.25 MPa, select high-range fine-tuning. Then press the right button, enter the pressure value of 1.25 MPa, and finally press the right button again to confirm. Both the pressure value and current value will be successfully calibrated.

• Continue using the pressure-application handle to slowly increase the pressure until it reaches approximately the target pressure, then use the fine-tuning handle to raise it to the calibration pressure of 2.5 MPa. If the pressure reading from the transmitter deviates from 2.5 MPa, the pressure calibrator should measure a current value of 20 mA from the transmitter. If there is an error, calibrate using the handheld calibrator (follow the same procedure as above).

2. Pressure Reduction Calibration Procedure

• First, slowly open the vent valve (pressure relief valve) to relieve pressure until it reaches approximately the target pressure value, then stop. Close the vent valve (pressure relief valve), and use the fine-tuning knob to increase the pressure to the calibration value of 1.25 MPa. If there is a deviation between the pressure value measured by the transmitter and 1.25 MPa, or if the current value of 12 mA measured by the pressure calibrator also deviates, 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 current difference at the same point during pressure increase and decrease) meets the requirement (≤0.05% FS).

3. Pressure Relief Process

Open the vent valve (pressure relief valve) to gradually release the pressure. When the pressure reaches 0, the measurement is complete.

(3) Vacuum Calibration Process for Pressure Transmitters (HART Protocol)

1. Pressure-Rise Calibration Process

• First, push the positive/negative pressure switch valve down (do not switch while under pressure), then turn the fine-tuning knob clockwise to the appropriate position, and finally close the vent valve (pressure relief valve).

• Use the pressure-application handle to slowly create a vacuum. Stop when the vacuum reaches approximately the value to be calibrated, then use the fine-tuning knob to adjust counterclockwise to a vacuum value of -0.06 MPa. If there is a deviation between the pressure value measured by the transmitter and -0.06 MPa, or if there is a deviation in the 9.9 mA current value measured by the pressure calibrator, use the handheld calibrator to calibrate the pressure and current values.

• Calibrate the transmitter’s pressure reading:

Select either “Low Range Fine-Tuning” or “High Range Fine-Tuning.” If the transmitter’s measured pressure is below -0.06 MPa, select “Low Range Fine-Tuning”; if the pressure is above -0.06 MPa, select “High Range Fine-Tuning.” Then press the right button, enter the pressure value -0.06 MPa, and finally press the right button again to confirm. Both the pressure and current values will be successfully calibrated.

• Continue using the pressure-application handle to slowly evacuate the system. Stop when the vacuum value is reached, then use the fine-tuning handle to adjust to the calibrated vacuum value of -0.095 MPa. If the pressure value measured by the transmitter deviates from -0.095, the pressure calibrator should measure a current value of 4 mA from the transmitter. If there is an error, calibrate using the handheld calibrator (follow the same procedure as above).

2. Decompression Calibration Process

• First, slowly open the vent valve (pressure relief valve) to relieve pressure until it reaches approximately the vacuum value, then stop. Close the vent valve (pressure relief valve) and use the fine-tuning handle to adjust the pressure to -0.06 MPa. If the pressure value measured by the transmitter deviates from -0.06 MPa, and the current value of 9.9 mA measured by the pressure calibrator also deviates, use the handheld calibrator to calibrate both the pressure and current values.

• Record the correspondence between pressure and current at each point, and verify that the hysteresis (the current difference at the same point during pressure increase and decrease) meets the requirement (≤0.05% FS).

3. Pressure Relief Process

Open the vent valve (pressure relief valve) and gradually release the pressure until it reaches 0; the measurement is then complete.

 

III. Precautions

Proper Use

• Stop charging the battery when the indicator light on the portable pressure calibrator’s external charger changes from red to green; prolonged charging can damage the battery. Use the standard 8.4V charger for charging.

• Follow standard operating procedures, increasing and decreasing pressure step by step to avoid pressure surges.

• Ensure that the communication cable between the pressure calibrator and the handheld controller, as well as the wiring to the pressure transmitter, are clearly identified to strictly prevent reverse connections.

• Readings at calibration points should be taken only after the pressure calibrator’s readings have stabilized to ensure real-time accuracy.

• Upon completion of the calibration, slowly depressurize the system to zero and ensure there is no residual pressure before turning off the device’s power; only then should the instrument under test be removed.

Maintenance and Calibration Schedule

• Perform periodic metrological verification on the portable pressure calibrator to ensure measurement accuracy meets standards.

• Turn off the power when the portable pressure calibrator is not in use; if not used for an extended period, recharge it once every three months.

• When storing the portable pressure calibrator for an extended period, depressurize it first and cover it with a cloth cover to prevent dust from entering the instrument.

IV. Conclusion

Based on AILEIKE calibration equipment, this specification establishes a standardized verification and testing system covering both positive pressure and vacuum operating conditions. Through full-range pressure increase, pressure reduction verification, and hysteresis verification—combined with HART communication to complete zero-point and span calibration—it can accurately correct deviations in pressure and current output. Strict adherence to this specification and the accompanying operation and maintenance requirements, along with regular equipment verification, ensures accurate and reliable traceability of measurement values and guarantees that transmitter measurement accuracy meets standards.