AILEIKE Guide to Testing the Performance and Metrological Calibration of Pressure Switches

Pressure switches are core components of industrial pressure control systems; their precise contact operation and pressure reset performance determine the operational stability of industrial equipment. Consequently, standardised calibration and performance testing must be carried out regularly. For this calibration, a test setup was constructed using the ALKB9651 micro-pressure calibration bench and the ALKC400E digital pressure calibrator. The testing environment was strictly controlled for temperature and humidity to eliminate external interference such as vibration and dust. The testing covered both the normally open and normally closed operating states of the pressure switches. Air circuit connections, electrical wiring, pressure calibration and pressure ramp-up/ramp-down tests were carried out in accordance with established procedures, with the switch actuation and reset values recorded with precision. Pressure was adjusted gradually throughout the process, and electrical wiring was carried out in accordance with standards to ensure the authenticity and accuracy of the test data.

I. Tools for Calibrating Pressure Switches

Name	Low-pressure calibration bench	Digital Pressure Calibrator	Pressure switch
Model	ALKB9651	ALKC400E	Various models
Technical Specifications	Pressurisation method: Manual Pressure range: 0–600 kPa Medium: Clean air Outlets: 2 Connection: M20×1.5(F) Net weight: 2.3 kg Product dimensions: 230 × 240 × 200 mm	Pressure: 0–600 kPa 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: 0–600 kPa Set point: 250 kPa 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 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 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 pressure switch and the ALKC400E digital pressure calibrator to the ALKB9651 outlet with a sealed connection. Press the ‘Electrical Measurement’ button on the ALKC400E standard gauge 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 250 kPa. 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 250 kPa. Once calibration is complete, secure the knob in its current position.

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

• First, turn the pressure adjustment handle anti-clockwise to a suitable position, then turn the fine-adjustment knob anti-clockwise to a suitable position, and finally close the relief valve.

• Use the pressure adjustment handle to turn clockwise to increase the pressure until it reaches approximately the calibration value. Then, use the fine-tuning knob to slowly adjust to the upper cut-off value (actuation value) of 250 kPa. When you 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.

• Turn the pressure adjustment knob anti-clockwise to reduce the pressure until it is approximately at the calibration value. Then, using the fine-tuning mechanism, slowly adjust the pressure to the lower cut-off value (reset value) of 240 kPa. 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 pressure relief valve to gradually release the pressure in the pipework 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 open state, with the standard pressure gauge displaying the ‘--’ symbol for a closed circuit.

• Turn the pressure adjustment knob anti-clockwise to the appropriate position to close the relief valve.

• Using the pressure adjustment knob, turn it clockwise slowly until the pressure is approximately at the calibration value, then use the fine-tuning knob to gradually increase the pressure to the upper cut-off value (actuation value) of 250 kPa. You will hear a ‘beep’ from the instrument, the contact status will change, the standard gauge display will change from ‘--’ to ‘-/-’, and the pressure switch will switch from the closed state to the open state. Record the actuation pressure value.

• Turn the pressure adjustment knob anti-clockwise to reduce the pressure until it is approximately at the calibration value, then use the fine-tuning knob to slowly increase the pressure to the lower cut-off value (reset value) of 240 kPa. 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 pressure relief valve to gradually release the pressure in the pipework 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 ALKB9651 micro-pressure calibration bench to avoid pressure surges.

• The wiring of the ALKC400E digital pressure calibrator must be clearly identified; take great care to prevent reverse connection.

• 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 low-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 calibration has completed the full-condition performance testing of the pressure switch, comprehensively verifying the accuracy and rapid response of contact operation and pressure reset. The entire testing process effectively minimised operational errors. Moving forward, metrological management requirements must be strictly adhered to, with annual verification of standard instruments carried out on schedule, alongside routine maintenance tasks such as charging, depressurisation and dust protection. We will continue to conduct regular testing and calibration of pressure switches to ensure the smooth operation of industrial pressure control systems.