Standardised Operating Procedure for the Verification, Testing and Measurement of Pressure Gauges Using the AILEILE ALKD12AGY Electric Pressure Calibration Bench

In order to implement the operational standards for the metrological verification of pressure gauges, ensure the accuracy and reliability of process pressure monitoring data, and meet production metrological control requirements, a full-range metrological performance verification programme was organised for the Y-100BF stainless steel pressure gauge. This calibration utilised the AILEIKE ALKD12AGY electric pressure calibration bench to provide a standard pressure source, in conjunction with the ALKC400D precision digital pressure gauge as the standard measuring instrument, to carry out multi-point reading verification covering the instrument’s positive pressure range. The verification was carried out in strict accordance with metrological specifications. Pressure increase and decrease tests were completed under controlled environmental conditions, following standard procedures for pressure stabilisation and standstill, reading recording, and gentle tapping of the dial. Parameters such as indication error and variation were assessed. The specific operational steps and risk precautions are as follows.

I. Pressure Gauge Calibration Tools

Name	Electric Pressure Calibration Bench	Precision Digital Pressure Gauge	Stainless steel pressure gauge
Model	ALKD12AGY	ALKC400D	Y-100BF
Technical Specifications	Pressure range: -0.1 to 25 MPa Medium: Clean air Outlets: 4 Connection: M20×1.5 female Power consumption: <500 VA Power supply: AC 220±10%, 50 Hz Weight: 30 kg Dimensions: 800×442×330 mm	Pressure: -0.1–1 MPa / 0–25 MPa Accuracy: Class 0.05 Temperature compensation: With temperature compensation Power supply: Built-in rechargeable battery Connection: M20×1.5(M) Net weight: 0.6 kg Dimensions: 110×50×185 mm	Pressure: -0.1 to 0 MPa / 0 to 25 MPa Accuracy: Class 1.6 Material: Stainless steel Dial diameter: φ100 mm Connection: M20×1.5 (M) Net weight: 0.35 kg Product dimensions: 100 × 42 × 140 mm
Product Dimensions

The entire verification process must be carried out in strict accordance with current metrological technical specifications. The main references include:JJG52-2013 ‘General Pressure Gauges, Pressure-Vacuum Gauges and Vacuum Gauges with Elastic Elements’, which applies to the initial verification, periodic verification and in-service inspections of general pressure gauges, pressure-vacuum gauges and vacuum gauges with elastic elements, and covers on-site indicating pressure measuring instruments commonly used in industry.

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 electric pressure calibration unit to a 220V power supply and switch it on.

• Connect the standard gauge ALKC400D and the pressure gauge under test (Y-100BF) to the output ports of the ALKD12AGY, ensuring a tight seal; secure any unused output ports with plugs.

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(2) Pressure Gauge Calibration Procedure

1. Pressure Build-up Procedure

• First, open the ALKD12AGY pressure shut-off valve, then turn the manual fine-adjustment pump anti-clockwise to the appropriate position, and close the return valve.

• At this point, press the pressure increase button to build up pressure to the required value. When approaching the target pressure, release the button, then use the fine-adjustment pump to turn clockwise to the calibration value of 5 MPa. Once the pressure has stabilised and the standard reading no longer fluctuates, check the pressure reading on the pressure gauge under test. Then, gently tap the side of the pressure gauge’s casing with your finger (tapping the glass or striking it forcefully is strictly prohibited), observe the position of the pointer, and record the reading once it has stabilised after tapping. Use the reading after tapping as the actual calibration reading for that pressure point, and calculate the error.

• Continue pressing the air pressure boost button to increase the pressure; stop when the pressure is approximately at the calibration value, then use the fine-adjustment pump to adjust to the calibration value of 10 MPa. Check the pressure reading on the pressure gauge under test, tap the pressure gauge, and record the reading once it has stabilised after tapping.

• Repeat the same procedure to adjust the pressure to the calibration points of 15 MPa, 20 MPa and 25 MPa. Check the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised. (Note: If the reading is found to drop gradually during pressurisation (indicating a slight leak), close the air shut-off valve.)

2. Pressure Reduction Procedure

• First, slowly open the return valve to reduce the pressure; stop when the pressure reaches approximately the calibration value, then close the return valve. Next, use the fine-adjustment pump to set the pressure to the calibration value of 20 MPa. Check the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised after tapping.

• Repeat the same procedure to adjust the pressure to the calibration values of 15 MPa, 10 MPa and 5 MPa. Observe the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised.

3. Pressure Relief Procedure

Open the return valve and the gas pressure shut-off valve in sequence to gradually release the pressure within the pipework. Once the pressure has been relieved to 0, the test is complete.

(3) Vacuum Calibration Procedure for Pressure Gauges

1. Pressure-up Process

• First, remove the standard gauge for measuring positive pressure and the gauge under test, then fit the standard gauge for measuring negative pressure and the gauge under test. Adjust the fine-tuning pump clockwise to the appropriate position and close the return valve.

• Press the vacuum pressurisation button to create a vacuum; stop when the vacuum reaches approximately the calibration value, then use the fine-adjustment pump to adjust the vacuum to –0.02 MPa. Check the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised.

• Continue to use the vacuum-to-pressure button to create a vacuum, stopping when the vacuum is approximately at the verification value. Then, use the fine-adjustment pump to adjust the vacuum to the verification value minus 0.04 MPa. Observe the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised.

• Repeat the procedure to set the test points to –0.06 MPa, –0.08 MPa and –0.1 MPa. Observe the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised after tapping. (Note: If the reading is found to drop gradually during pressurisation (indicating a slight leak), close the vacuum shut-off valve.)

2. Depressurisation Process

• First, slowly open the return valve to reduce the pressure; stop when the pressure reaches approximately the calibration value, then close the return valve. Next, use the fine-adjustment pump to set the vacuum to -0.08 MPa, check the reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised after tapping.

• Repeat the same procedure to adjust the vacuum to -0.06 MPa, -0.04 MPa and -0.02 MPa. Observe the pressure reading on the pressure gauge under test, tap the gauge, and record the reading once it has stabilised.

3. Depressurisation Procedure

Open the test return valve and the vacuum shut-off valve in sequence to gradually release the pressure within the pipework. Once the pressure has been reduced to 0, the test is complete.

III. Precautions

Proper Use

• When measuring positive pressure, press only the ‘Air Pressure’ button (do not press the ‘Vacuum’ button); when measuring negative pressure, press only the ‘Vacuum’ button (do not press the ‘Air Pressure’ button). The pressure/vacuum conversion must be carried out under unpressurised conditions.

• During calibration, ensure that the permissible error of the reference gauge is less than that of the gauge under test to guarantee accurate and reliable results that comply with metrological standards.

• Connect the electric pressure calibration bench to a 220V power supply; do not connect it incorrectly.

• Operations must follow standard procedures. Pressurisation and depressurisation of the ALKD12AGY electric pressure calibration stand must be carried out slowly to avoid pressure surges.

• Pressurise to the calibration point and record the reading once the standard gauge’s reading has stabilised; for the pressure gauge under test, once the pressure has stabilised, tap the case lightly and take the reading immediately after the tap to ensure accuracy.

• Upon completion of the test, first slowly depressurise to zero; only when there is no residual pressure should the instrument under test be removed.

Maintenance and Calibration Intervals

• The ALKC400D precision digital pressure gauge should 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 lubricating oil in the electric pressure calibration stand should generally be checked and replaced every six months or after 500 hours of operation.

• Without the appropriate testing skills and equipment, do not open the cover to carry out maintenance; under no circumstances should components be adjusted or replaced.

• If the electric pressure calibration stand is to be stored for an extended period, it must be depressurised before storage and covered with a cloth cover to prevent dust from entering the instrument.

IV. Conclusion

Strict adherence to these operating procedures ensures the standardised completion of full-range signal acquisition and metrological performance verification for pressure transmitters, enabling the calculation of output errors and hysteresis errors at each calibration point, and guaranteeing the accuracy and validity of the traceability of measurement data. Routine calibration must strictly follow operational guidelines, with appropriate switching between pressure increase and decrease control modes, and the implementation of regular verification of standard instruments and routine inspection and maintenance of calibration equipment, to ensure the continuous and stable operation of the entire pressure calibration system.