Pressure Switch Calibration Procedure
Pressure switch calibration verifies that a pressure switch changes its electrical contact state at the required pressure and resets at the specified pressure. In process industries, pressure switches are used for alarms, equipment interlocks, pump protection, compressor protection, and selected shutdown functions.
A typical calibration uses a suitable pressure source, a calibrated pressure reference, and a multimeter to monitor contact operation. The technician records the pressure at which the switch operates during increasing pressure and the pressure at which it resets during decreasing pressure. The difference between these values is the switching differential, commonly called deadband.
This guide explains the equipment required, safety precautions, calibration setup, rising and falling pressure tests, set point adjustment, deadband and repeatability calculations, troubleshooting, and calibration report preparation.
Equipment Required for Pressure Switch Calibration
| Equipment | Purpose |
| Hand pressure pump or suitable pressure controller | Applies controlled increasing and decreasing pressure |
| Calibrated pressure gauge or digital pressure calibrator | Provides the reference pressure reading |
| Digital multimeter | Monitors contact continuity and changeover |
| Suitable pressure fittings and tubing | Connects the pressure source safely to the switch |
| Manufacturer datasheet | Provides set point, reset point, allowable differential, range, and pressure limits |
| Calibration report | Records as found and as left readings and the final result |
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The device contains a micro switch, connected to a mechanical lever and set pressure spring. The contacts get actuated when process pressure reaches the set pressure of the spring. In this session calibration of pressure switch is covered.
- It can be used for alarming or interlocking purposes, on actuation.
- It can be used for high / high-high or low /low-low actuation of pressure in the process. The set range can be adjusted within the switch range.
- The sensing element may be a Diaphragm or a piston
Isolate the Pressure Switch and Review Its Settings
Identify the instrument tag, switch type, pressure range, required trip point, reset point or differential, contact configuration, and process connection. Obtain authorization before testing any switch associated with an alarm, interlock, or shutdown function.
Connect the Pressure Source and Contact Monitor
Safely isolate and depressurize the switch. Connect the pressure source and calibrated reference to the correct port. Connect the multimeter to the designated common and NO or NC terminals according to the wiring diagram.
Verify the Initial Contact State
With the switch at its specified initial pressure condition, check the contact state using the multimeter. Record the state of the relevant contacts and verify that it matches the switch wiring diagram and expected operating logic.
Measure the Rising Pressure Trip Point
Increase pressure gradually while monitoring the contacts. When the contact state changes, record the reference pressure as the rising trip point. Approach the switching point slowly enough to avoid overshooting it.
Measure the Falling Pressure Reset Point
Reduce pressure gradually and record the pressure at which the contacts return to their reset state. Do not exceed the maximum allowable pressure simply to perform this test. Follow the manufacturer’s procedure and specified test limits.
Calculate Deadband and Check Repeatability
Calculate the difference between the rising trip point and falling reset point. Repeat the test under consistent conditions and compare the readings with the manufacturer’s specifications and approved acceptance criteria.
Adjust the Pressure Switch if Required
If the as found results do not meet the specified requirements, inspect the setup and switch condition before adjustment. Adjust the set point or differential only when the switch design permits it, following the manufacturer’s instructions. Repeat the tests after adjustment.
Restore the Switch and Complete the Calibration Report
Safely remove the test pressure, reconnect the process connection and electrical wiring, check for leaks, restore authorized bypasses, and confirm normal operation. Record as found and as left readings, acceptance criteria, adjustments, and the final result.
Pressure Switch Calibration Test Results
| Test cycle | Rising trip pressure | Falling reset pressure | Deadband |
| 1 | 8.00 bar | 7.20 bar | 0.80 bar |
| 2 | 8.05 bar | 7.25 bar | 0.80 bar |
| 3 | 8.00 bar | 7.20 bar | 0.80 bar |
Common Pressure Switch Calibration Problems and Solutions
| Problem | Possible cause | Recommended action |
| Switch does not change state | Incorrect terminals, damaged contacts, insufficient pressure, or faulty mechanism | Verify the wiring diagram, contact continuity, pressure source, and switch condition |
| Trip pressure is too high | Incorrect setting, wrong pressure reference, or mechanical drift | Verify the reference equipment and configured set point before adjusting |
| Reset pressure is inconsistent | Unstable pressure source, friction, or switch mechanism wear | Apply pressure slowly and repeat the test under consistent conditions |
| Deadband is greater than specified | Incorrect differential setting, wear, or damaged mechanism | Check the manufacturer’s adjustment method and permitted differential |
| Trip point changes between tests | Pressure overshoot, inadequate stabilization, or mechanical instability | Improve pressure control and repeat the test |
| NO and NC states appear reversed | Incorrect terminal identification or misunderstanding of the normal state | Check the terminal diagram and confirm the specified initial pressure condition |
| Switch fails after reinstallation | Incorrect wiring, leakage, incorrect installation, or process connection issue | Verify wiring, connection integrity, and operation under the approved return to service procedure |
Safety Precautions During Pressure Switch Calibration
- Isolate the switch from process pressure and verify that stored pressure has been safely released.
- Confirm the test pressure source, gauge, fittings, tubing, and adapters are rated for the intended pressure.
- Use suitable protective measures when testing high pressure, hydraulic, toxic, corrosive, or flammable process services.
- Do not disconnect or test energized electrical contacts unless the approved procedure and hazardous area requirements permit it.
- For switches used in safety instrumented functions or critical trips, obtain authorization and apply the approved bypass, impairment, and restoration procedure.
- Confirm the correct contact state and process response before returning the switch to service.
Pressure Switch Calibration Report Format
| Report field | Information to record |
| Instrument identification | Tag number, location, manufacturer, model, and serial number |
| Switch configuration | Rising or falling trip, NO and NC terminal identification |
| Required settings | Specified trip point, reset point, and allowable deadband |
| Reference equipment | Pressure calibrator identification, range, and calibration due date |
| As found results | Initial trip point, reset point, deadband, and contact state |
| Adjustment details | Adjustment performed, if any, and reason |
| As left results | Final trip point, reset point, deadband, and contact state |
| Acceptance criteria | Required limits and source of the limits |
| Final status | Pass or fail, technician, date, and remarks |
Frequently Asked Questions About Pressure Switch Calibration
What is pressure switch calibration?
Pressure switch calibration verifies that the switch operates and resets at the specified pressures. It also checks contact operation and switching differential.
What is the difference between trip pressure and reset pressure?
Trip pressure is the pressure at which the switch changes state in the specified direction. Reset pressure is where the switch returns to its previous state.
How do you calculate pressure switch deadband?
For a rising pressure trip and falling pressure reset, subtract the reset pressure from the trip pressure. Compare the result with the manufacturer’s specified differential.
What equipment is required for pressure switch calibration?
Typical equipment includes a suitable pressure source, calibrated pressure reference, digital multimeter, compatible fittings, and the manufacturer’s datasheet.
How do you calibrate a low pressure switch?
Use a pressure source and reference suitable for the low pressure range. Increase and decrease pressure slowly while recording the contact changeover points.
Why is pressure switch repeatability important?
Repeatability indicates how consistently the switch operates under the same test conditions. Poor repeatability may indicate instability, mechanical wear, or problems with the test setup.
Should a pressure switch always be adjusted during calibration?
No. Record the as found results first and compare them with the specified acceptance criteria. Adjust the switch only when required and permitted by the manufacturer.
What should a pressure switch calibration report include?
Record the instrument tag, specified settings, reference equipment, trip and reset pressures, deadband, as found and as left results, acceptance criteria, and final status.
