AILEIKE 100 MPa High-Pressure Switch Calibration Procedure and Metrological Testing Specifications

Pressure switches are key control and protection components in industrial high-pressure automatic control systems; their actuation and reset accuracy affect equipment operation and production stability, and therefore require regular standardised calibration. For this calibration, an ALKT804 hydraulic calibration bench and an ALKC400A digital pressure calibrator were utilised, whilst strictly adhering to environmental temperature and humidity specifications. Standardised procedures were followed for fluid filling and venting, pipe connections and electrical wiring. With a set pressure of 50 MPa, the switches were tested under both normally open and normally closed conditions to precisely determine the actuation and reset values. During the operation, pressure was adjusted smoothly to avoid pressure surges, wiring was carried out in accordance with regulations, and data was accurately recorded. At the same time, instruments were periodically verified and equipment maintenance was carried out to ensure that the pressure switches responded sensitively, met the required parameters, and complied with relevant industrial operation and metrology standards.

I. Tools for Calibrating Pressure Switches

Name	Hydraulic calibration bench	Digital Pressure Calibrator	Pressure switches
Model	ALKT804	ALKC400A	Various models
Technical Specifications	Pressurisation method: Manual Pressure range: 0–100 MPa Medium: Purified water or calibration oil Outlets: 3 Connection: M20×1.5 (F) Net weight: 14 kg Product dimensions: 410×410×180 mm	Pressure: 0–100 MPa Accuracy: 0.02% FS Temperature compensation: With temperature compensation Current measurement: ±25.0000 mA Voltage measurement: ±50.0000 V DC output: 24 V DC Communication interface: RS-232/RS-485 Power supply: Built-in rechargeable battery Connection: M20×1.5(M) Net weight: 1 kg Dimensions: 156×47×239 mm	Pressure switch: 0–100 MPa Set point: 50 MPa Contact type: Normally open/normally closed switch Wetted parts material: Stainless steel Mounting thread: M20×1.5 (default)
Product Dimensions

The entire verification process must be carried out in strict accordance with current metrological technical specifications. The main references include:JJG 544-2011 ‘Pressure Controllers’, which applies to the initial verification, subsequent verification and in-service inspections of pressure, vacuum and pressure-vacuum controllers (including mechanical and electronic types); these are pressure control devices that operate without an external power supply and rely on pressure changes to directly drive mechanical components to close or open contacts.

II. Detailed Explanation of the Operational Process

(1) Preliminary Preparations

1. Environmental requirements

The temperature should be maintained at (20±2) °C, with relative humidity ≤85% RH and no condensation; ensure that the site is free from vibration, dust and corrosive gases.

2. Filling, Pressurisation and Pressure-Testing of the Hydraulic Bench

• Prepare the pressure-transmitting medium (deionised water or calibration oil) and a syringe.

• First, unscrew the pressure relief valve on the ALKT804 hydraulic calibration bench. Use the syringe to draw up the medium and inject it into the reservoir cup, ensuring it is filled to at least two-thirds capacity. Once filling is complete, reattach and tighten the pressure relief valve.

• Next, purge any excess air from the hydraulic bench. First, unscrew the plugs from the three outlet ports, open the pressure-regulating valve, relief valve and overpressure shut-off valve, turn the fine-adjustment valve anti-clockwise to the appropriate position, and close the relief valve. Then, use the lever to pressurise the system, directing the pressure to the three outlet ports.

3. Connecting the Equipment

• Connect the pressure switch and the ALKC400A digital pressure calibrator to the outlet of the ALKT804 hydraulic calibration bench using sealed connections. Press the Switch/Peak button on the ALKC400A to switch to pressure switch measurement mode.

• Pressure switch pre-adjustment: Open the protective cover of the adjustment knob on top of the pressure switch, have the adjustment tool ready, and allow sufficient travel for clockwise (increase) and anti-clockwise (decrease) rotation to set the pressure switch setpoint.

• Wiring instructions:

(1) Connect the red test lead of the ALKC400A to the 24V output terminal of the standard meter, and the black test lead to the measurement terminal of the pressure switch.

(2) Clip the red crocodile clip to the common terminal (COM) of the pressure switch, and the black crocodile clip to the normally open (NC) or normally closed (NO) terminal.

(3) Now, first clip the black crocodile clip to the normally open (NC) terminal. At this point, the ALKC400A pressure switch on the standard meter will display the word ‘Open’, confirming that the pressure switch is in the normal open (disconnected) state and that the wiring is correct.

(2) Operating Procedure

Key calibration steps: Set the target pressure to 50 MPa. Rotate the pressure switch adjustment knob slightly (clockwise to increase pressure, anti-clockwise to decrease pressure), whilst applying pressure using the calibration bench to fine-tune the pressure switch’s actuation point precisely to the target pressure of 50 MPa. Once calibration is complete, lock the knob in position.

1. Testing the closing and opening of a pressure switch in the normally open state

• Apply pressure using the ALKT804 lever; stop when the pressure reaches approximately 5–10 MPa. Close the pressure-regulating valve and the overpressure shut-off valve, then use the fine-adjustment knob to turn clockwise until the upper threshold (actuation pressure) for closing the switch is reached at 50 MPa. A ‘beep’ from the instrument will sound, and the contact status will change. the standard gauge pressure switch changes from ‘open’ to ‘closed’, and the pressure switch switches from the open state to the closed state; record the actuation pressure value.

• Continue to reduce the pressure by turning the fine-adjustment knob anti-clockwise until the lower cut-off value (reset value) of 47.5 MPa is reached. Again, a ‘beep’ from the instrument will sound, the contact status will change, the standard gauge interface switch will change from ‘closed’ to ‘open’, and the pressure switch will switch from the closed state to the open state; record the reset pressure value.

• The test is complete. Open the pressure relief valve, pressure-regulating valve and overpressure shut-off valve in sequence until the pressure is reduced to 0; the measurement is now complete.

2. Testing the closing and opening of a pressure switch in the normally closed state

• First, clip the black alligator clip onto the normally open (NO) terminal; you will then see that the pressure switch is in the normally open state, and the ALKC400A pressure switch test display will show the word ‘Open’.

• Open the pressure-regulating valve, the relief valve and the overpressure shut-off valve; turn the fine-adjustment valve anti-clockwise to the appropriate position, then close the relief valve.

• Apply pressure using the lever, stopping at approximately 5–10 MPa. Close the pressure-regulating valve and the overpressure shut-off valve, then use the fine-adjustment valve to turn clockwise to the upper cut-off value (set point) of 50 MPa at which the switch opens. You will hear a ‘beep’ from the instrument’s buzzer, the contact status will change, and the switch test on the standard gauge interface will change from ‘Open’ to ‘Closed’. the pressure switch switches from the closed state to the open state; record the actuation pressure value.

• Continue to use the fine-adjustment knob to reduce the pressure anti-clockwise until it reaches the lower cut-off value (reset value) of 47.5 MPa. You will again hear a ‘beep’ from the instrument, the contact status will change, and the switch test on the standard gauge faceplate will change from ‘open’ to ‘closed’; the pressure switch will switch from the open state to the closed state. Record the reset pressure value.

• Once the test is complete, open the pressure relief valve, pressure-regulating valve and overpressure shut-off valve in sequence to reduce the pressure to 0; the measurement is then complete.

III. Precautions

Proper Use

• Operations must be carried out in accordance with standard procedures. Pressure must be increased and decreased gradually on the ALKT804 hydraulic calibration stand to avoid pressure surges.

• The wiring of the ALKC400A digital pressure calibrator must be clearly identified; take great care to prevent reverse connections.

• Readings at calibration points must be taken only after the value on the standard gauge has stabilised, ensuring that records are accurate and up-to-date.

• Upon completion of the test, first slowly depressurise the system to zero; the instrument under test may only be removed once all residual pressure has been released.

Maintenance and Calibration Intervals

• The ALKC400A digital pressure calibrator 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.

• If the hydraulic test bench is to be stored for an extended period, it must be depressurised before storage; empty the liquid from the reservoir cup and cover it with a cloth cover to prevent dust from entering the instrument.

IV. Conclusion

This project utilised the AILEIKE ALKT804 hydraulic calibration bench and the ALKC400A digital pressure calibrator to complete standardised calibration of normally open and normally closed pressure switches under all operating conditions. Throughout the process, we strictly adhered to regulations, adjusted pressure smoothly, and followed standard wiring procedures to avoid pressure surges, thereby ensuring the accuracy and reliability of the calibration data. Conducting regular specialised calibrations of pressure switches can effectively identify and address potential faults such as pressure drift and contact failure. Combined with annual instrument verification and routine equipment maintenance, this approach ensures sustained calibration accuracy, stabilises the operational performance of pressure switches, eliminates potential operational hazards, and provides robust support for the long-term, stable operation of industrial high-pressure systems.