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
Calibration Procedure of the Pressure Switch
Connect the pressure switch to a hand pressure regulator and test gauge, as shown in the diagram above.
With a Multimeter, set to the continuity range to check and verify that the switch contacts are as indicated: NO (Normally open) and NC (Normally close).
Connect the Ohmmeter or DMM between the normally open contacts (NO) and the common terminal (C) of the switch. The meter should read “open circuit”. Adjust the hand pressure regulator to increase the pressure to the set point of the pressure switch until the contacts change over. The meter should now read “short circuit”. Note the pressure reading and write it down. This pressure is the switch set point for a “rising” pressure.
Increase the pressure to the switch to its maximum rating. Slowly reduce the pressure to the switch until the switch changes over from closed to normally open again. Note and write down this pressure reading. This pressure is the switch setting for a “falling” pressure.
When error found, adjust set point by screw adjustment and repeat until desired value obtained
From the readings you have taken work out the pressure difference between the rising and falling pressure settings. This is called the “dead band” of the switch. The dead-band calculated should be equal to or less than the manufacturers’ dead-band. The maximum dead-band is usually stated by the manufacturer.