AILEIKE Pressure Switch/Pressure Controller Measurement Calibration and Operational Testing Procedure

A pressure switch is an electrical component commonly used in control systems. Its primary function is to monitor whether an object has reached a specific pressure and to convert this signal into an electrical signal for feedback control. The set point, reset hysteresis and contact make-and-break performance of a pressure switch directly affect the stability of equipment operation and operating conditions; therefore, regular calibration, testing and precise measurement are required. For this calibration, the ALKT702 pneumatic calibration bench and the ALKC400E digital pressure calibrator were utilised. Strict control was maintained over the temperature and humidity of the testing environment, and the work site was free from vibration, dust and corrosive gases. By ensuring proper sealing of piping connections and electrical wiring, calibration tests were conducted on both the normally open and normally closed operating modes of the pressure switch. The actuation pressure and reset pressure were precisely measured, and the sensitivity of the contact switching was verified. Standardised operating procedures were followed throughout the process to ensure the accuracy and reliability of the test data.

I. Tools for Calibrating Pressure Switches

Name	Air Pressure Calibration Bench	Digital Pressure Calibrator	Pressure switch
Model	ALKT702	ALKC400E	Various models
Technical Specifications	Pressurisation method: Manual Pressure range: 0–6 MPa Medium: Clean air Outlets: 2 Connection: M20×1.5 female Net weight: 10 kg Product dimensions: 400 × 320 × 185 mm	Pressure: 0–6 MPa Accuracy: 0.02% 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: M20×1.5 (M) Net Weight: 0.6 kg Dimensions: 110×50×185 mm	Pressure switch: 0–6 MPa Set point: 2 MPa Contact type: Normally open/normally closed switch Wetted parts material: Stainless steel Mounting connection: 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 inspection 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 not exceeding 85% RH and no condensation; ensure that the site is free from vibration, dust and corrosive gases.

2. Connecting the equipment

• Connect the pressure switch and the ALKC400E digital pressure calibrator to the outlet of the ALKT702 pneumatic calibration bench, ensuring a sealed connection. Press the ‘Electrical Measurement’ button on the ALKC400E 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) or anti-clockwise (decrease) rotation to set the pressure switch setpoint.

• Wiring instructions:

(1) Connect the red test lead of the ALKC400E to the 24V output terminal of the standard gauge, and the black test lead to the pressure switch measurement terminal.

(2) Clip the other end of the red alligator clip to the common terminal (COM) of the pressure switch, and the black alligator 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 ALKC400E pressure switch display will show the ‘-/-’ symbol, 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 2 MPa. Rotate the pressure switch adjustment knob slightly (clockwise to increase pressure, anti-clockwise to decrease pressure), and, whilst applying pressure using the calibration bench, precisely calibrate the pressure switch’s actuation point to the target pressure of 2 MPa. Once calibration is complete, lock the knob in position.

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

• First, open the ALKT702 pressure-regulating valve, turn the fine-adjustment knob anti-clockwise until it stops, then close the vent valve.

• Use the lever to apply pressure, stopping when the pressure reaches approximately the calibration value. Then, use the fine-adjustment knob to turn clockwise until the required upper cut-in value (actuation value) of 2 MPa is reached for the switch to close. You will hear a ‘beep’ from the instrument, the contact status will change, the display on the standard gauge will change from ‘-/-’ to ‘--’, and the pressure switch will switch from the open state to the closed state. Record the actuation pressure value.

• Continue to reduce the pressure using the fine-adjustment knob by turning it anti-clockwise until the pressure reaches the lower cut-off value (reset value) of 1.9 MPa. You will again hear a ‘beep’ from the instrument, the contact status will change, the display on the standard gauge will change from ‘--’ back to ‘-/-’, and the pressure switch will switch from the closed state to the open state. Record the reset pressure value.

• Once the test is complete, open the vent valve to gradually release the pressure in the pipeline until it reaches 0; the measurement is then complete.

 

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

• First, clip the black crocodile clip onto the normally open (NO) terminal; you will then see that the pressure switch is in the normally closed state, with the ALKC400E standard pressure switch displaying the ‘--’ closed symbol.

• First, open the pressure-regulating valve, turn the fine-adjustment knob anti-clockwise until it stops, and close the relief valve.

• Use the lever to apply pressure, stopping when the pressure reaches approximately the calibration value. Then, use the fine-tuning knob to turn clockwise until the required upper cut-off value (actuation value) of 2 MPa is reached, at which point the switch opens. You will hear a ‘beep’ from the instrument, the contact status will change, the standard gauge display will switch from ‘--’ to ‘-/-’, and the pressure switch will switch from the closed state to the open state. Record the actuation pressure value.

• Continue to reduce the pressure using the fine-adjustment knob in an anti-clockwise direction until the lower cut-off value (reset value) of 1.9 MPa is reached. You will again hear a ‘beep’ from the instrument, the contact status will change, the display on the standard gauge will change from ‘-/-’ to ‘--’, and the pressure switch will return from the open state to the closed state. Record the reset pressure value.

• Once the test is complete, open the vent valve and gradually release the pressure in the pipeline until it reaches 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 ALKT702 pneumatic calibration stand to avoid pressure surges.

• The wiring of the ALKC400E 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 ALKC400E 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 should be switched off; if not used for an extended period, it should be recharged once every three months.

• If the pressure test bench is not to be used 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

This project successfully completed the systematic calibration, testing and precise measurement of the pressure switch system. Through testing under both normally open and normally closed operating modes, the equipment was precisely calibrated to an actuation pressure of 2 MPa and a reset pressure of 1.9 MPa. Standardised testing was carried out using Aileko calibration equipment to precisely verify the pressure switch’s hysteresis accuracy, contact switching sensitivity and on-off stability. The entire testing process was conducted in accordance with standardised procedures, effectively minimising human error and ensuring the authenticity and accuracy of the test data. Conducting this testing on a regular basis ensures the sustained control accuracy of the pressure switch, providing reliable metrological data to support the stable operation of industrial pressure control systems and the management of production processes.