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Mechanical pressure switches: How does one set the switch point?

Mechanical pressure switches are usually given a factory-set switch point. Nevertheless, some users want to make this configuration themselves, as, for instance, the pressure conditions in the application can change. In the case of pressure switches with a measuring aspect in a bellows, diaphragm or piston design, the manual setting of the switch point, reset point or hysteresis (with respect to the model) requires a certain amount of effort. Nonetheless it?s not witchcraft. This short article explains, step by step, how to do it.
Users need the next equipment: a pressure source (e.g. a dead-weight tester), a control pressure gauge, a continuity tester or a control lamp in addition to a tool for the adjustment screw (by the way, WIKA supplies the appropriate Allen key using its instruments; a conventional screwdriver is sufficient for setting the hysteresis).
Setting ไดอะแฟรม ซีล for the model PSM02 mechanical pressure switch from WIKA. The pin assignment 1 and 3 (small picture) corresponds to the switching function ?normally closed?, the assignment 2 and 3 would be for ?normally open?.
Setting of the switch point
First, screw the pressure switch in to the pressure source connection and connect its electrical connections to the continuity tester or control lamp.
Turn the adjustment screw for the switch point in completely. This sets the switch point to optimum value.
Now apply the required switching pressure to the pressure switch before control pressure gauge indicates the value.
From then on, turn the adjustment screw out before instrument switches and the continuity tester or the control lamp reacts.
Then lower the pressure until the pressure switch switches back and then increase it again to check on the switch point. If necessary, the switch point must be corrected by turning the adjustment screw. Repeat the task until the desired switch point is reached.
Setting of the reset point
In a few applications, the reset point is defined instead of the switch point, e.g. for minimum pressure monitoring. Here the task is similar to the switch point, but without turning in the adjustment screw.
Increase the pressure before instrument switches.
Then lower the pressure until the instrument switches back and adjust the positioning of the adjustment screw accordingly. The rule of thumb here is:
Set point < Actual value: Turn the screw out
Set point > Actual value: Turn the screw in
Setting of the hysteresis (not with all models)
To do this, first set the switch point and check the reset point (see above). With respect to the reset point, the hysteresis screw is turned in or out. The switch point must then be checked, as changes to the hysteresis screw also affect the switch point.
Note
An overview of the many mechanical pressure switches and also further technical information can be found on the WIKA website. In case you have any questions, your contact will gladly help you.
Also read our articles
Mechanical vs. electronic pressure switches: Functionality
Mechanical vs electronic pressure switches: Application areas
Pressure switches in booster pumps
SIL pressure switch: Safety in tyre manufacturing

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