Operational Procedures for the Calibration and Testing of Pressure Switches Based on the Aileko ALKT9603 and ALKC400E

Pressure switches are core electrical components in industrial pressure control systems; their response, reset and contact make/break performance are critical to the stability of the equipment, making it essential to carry out standardised calibration, testing and measurement on a regular basis. To standardise operational procedures and verify equipment performance, this procedure was conducted using the ALKT9603 pneumatic calibration bench and the ALKC400E digital pressure calibrator under standard temperature and humidity conditions. Through standardised wiring and pressure-application and pressure-release tests, the normally open and normally closed states of the pressure switch were verified, and the actuation value of 2 MPa and the reset value of 1.9 MPa were precisely calibrated. The following section details the full process for the calibration and testing of pressure switches, covering calibration tools, preparatory work, the complete operational procedure and precautions, to ensure the accuracy of measurement data and the reliability of calibration results.

I. Tools for Calibrating Pressure Switches

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 outlet of the ALKT9603 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 shut-off valve on the ALKT9603, then turn the fine-adjustment knob anti-clockwise to a suitable position and close the relief valve.

• Apply pressure using the hand-operated pressure rod; stop when the pressure reaches approximately the test point. Then, use the fine-adjustment knob to turn clockwise until the required upper cut-in value (actuation value) of 2 MPa for closing the switch is reached. You will hear a ‘beep’ from the instrument, the contact status will change, and the display on the standard gauge will change from ‘-/-’ to ‘--’. 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 back 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 relief valve to gradually release the pressure in 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.

• Apply pressure using the hand-operated pressure rod; stop when the pressure reaches approximately the test point. 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 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 gauge, 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 relief valve 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

• Operations must be carried out in accordance with standard procedures. Pressure must be increased and decreased gradually on the ALKT9603 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 supply 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

Precise calibration, testing and measurement of pressure switches are essential for the stable operation of industrial pressure systems. This procedure, utilising ALKC calibration equipment and strictly adhering to standardised operating procedures, involved environmental control, standardised wiring, and step-by-step pressurisation and depressurisation tests to accurately verify the actuation and reset values of the pressure switches, whilst comprehensively testing the response performance of their normally open and normally closed contacts. Standardised testing procedures effectively mitigate operational issues such as pressure surges and wiring errors, ensuring the authenticity and accuracy of measurement data, and enabling the effective identification of potential equipment faults. Conducting regular calibration and testing of pressure switches ensures that equipment remains responsive and performs reliably, thereby preventing production failures caused by switch malfunctions and underpinning industrial production through standardised measurement and calibration practices.