AILEIKE Pressure Switch Measurement Calibration and Operational Testing Procedures – Pressure Controller

Pressure switches are vital pressure-control components in industrial automatic control systems; their operation and reset behaviour, as well as pressure accuracy, affect the stability of equipment operation and performance. It is therefore particularly crucial to carry out regular calibration, testing and measurement. These procedures utilise the ALKT9803 hydraulic calibration bench and the ALKC400E digital pressure calibrator to perform pressure switch calibration. During the procedure, strict control was exercised over on-site environmental conditions, and standardised procedures were followed for piping connections, medium filling and electrical wiring. Pressure ramp-up and ramp-down tests were carried out smoothly, with the normally open and normally closed operating states of the switches tested separately. The actuation and reset values were precisely measured and the data recorded. Operational guidelines were adhered to throughout, and requirements for periodic verification and routine maintenance of the equipment were implemented. Through standardised testing and calibration, the sensitivity of the pressure switches’ operation and the accuracy of their readings were ensured, thereby meeting industrial and metrological standards.

I. Tools for Calibrating Pressure Switches

Name	Hydraulic calibration bench	Digital Pressure Calibrator	Pressure switches
Model	ALKT9803	ALKC400E	Various models
Technical Specifications	Pressurisation method: Manual Pressure range: 0–60 MPa Medium: Purified water or calibration oil Outlets: 3 Connection: M20×1.5 (F) Net weight: 7.3 kg Product dimensions: 415 × 360 × 170 mm	Pressure: 0–60 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: 0–60 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 external thread Net Weight: 0.6 kg Dimensions: 110×50×185 mm
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. Filling, pressurising and connecting the hydraulic test bench to the tool

• Prepare the pressure-transmitting medium (purified water or calibration oil).

• First, unscrew the vent knob on the ALKT9803 reservoir and fill the reservoir with the medium, ensuring it is filled to at least two-thirds capacity. Once filling is complete, screw the knob back on tightly.

• Next, purge any excess air from the hydraulic test bench. First, unscrew the plugs from the three outlet ports, then loosen the knob on the filling port, open the shut-off valve (loosening it by half a turn is sufficient), turn the fine-adjustment knob anti-clockwise to the appropriate position, and close the relief valve. Then, use the hand-operated pressure rod to apply pressure, directing the fluid to the three outlet ports to expel any excess air.

3. Tool Connection

• Connect the pressure switch and the ALKC400E digital pressure calibrator to the outlet ports of the ALKT9803 hydraulic calibration bench using sealed connections; leave one port sealed with a plug.

• 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 30 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 value to the target pressure of 30 MPa. Once calibration is complete, secure the knob in its current position.

1. Testing the pressure switch’s make and break functions whilst in the normally open state

• Use the hand-operated pressure rod to apply pressure gradually, stopping at approximately 5–10 MPa. Close the shut-off valve, then use the fine-adjustment knob to turn clockwise to the upper cut-off value (actuation pressure) of 30 MPa. Upon hearing 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 counter-clockwise using the fine-adjustment knob until the lower cut-off value (reset value) of 27 MPa is reached. You will again hear a ‘beep’ from the instrument, the contact status will change, the display on the standard gauge will revert from ‘--’ 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 and the shut-off valve in sequence to gradually release the pressure within the pipeline. When the pressure has been fully relieved to 0, the measurement is complete.

2. Test procedure for closing and opening the 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.

• Turn the fine-adjustment knob anti-clockwise to the appropriate position and close the relief valve. Using the hand-operated pressure rod, slowly increase the pressure until it reaches approximately 5–10 MPa, then stop. Close the shut-off valve, and use the fine-tuning knob to turn clockwise until the upper cut-off value (actuation value) of 30 MPa is reached. You will hear a ‘beep’ from the instrument, the contact status will change, the standard 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 by turning it anti-clockwise until the pressure reaches the lower cut-off value (reset value) of 27 MPa. 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 and the shut-off valve in sequence to gradually release the pressure in the pipeline. When the pressure has been fully relieved to 0, the measurement is complete.

III. Precautions

Proper Use

• The pressure-transmitting medium must be clean and free from impurities to prevent blockages in the pipework and damage to the hydraulic test bench and pressure gauge.

• Operations must be carried out in accordance with standard procedures; when pressurising or depressurising the ALKT9803 hydraulic calibration bench, do so gradually to avoid pressure surges.

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

• At calibration points, readings must be taken only after the value on the standard gauge has stabilised, ensuring accurate real-time recording.

• Upon completion of the test, slowly relieve the pressure to zero and ensure there is no residual pressure before removing the instrument under test.

Maintenance and Calibration Intervals

• The ALKC400E digital pressure calibrator must undergo periodic metrological verification (recommended once a year) to ensure measurement accuracy meets standards.

• Switch off the power supply when the pressure gauge is not in use; if not used for an extended period, recharge the battery once every three months.

• If the hydraulic test bench is not to be used for an extended period, depressurise it before storage, empty the fluid from the reservoir cup, and cover it with a cloth cover to prevent dust from entering the instrument.

IV. Conclusion

Through standardised procedures, precisely calibrate the actuation and reset values of pressure switches and verify the reliability of switching between normally open and normally closed states. By utilising the ALKT9803 hydraulic test bench in conjunction with the ALKC400E calibrator, whilst strictly controlling temperature and humidity, managing clean media and employing step-by-step pressurisation, measurement errors are minimised. Data is recorded in real time to identify deviations and potential contact failures. Regular calibration, combined with annual metrological verification and equipment maintenance, ensures parameter accuracy and stable response, in compliance with industry metrological standards.