Mechanical pressure switches: So how exactly does one set the switch point?

Mechanical pressure switches are usually given a factory-set switch point. Nevertheless, some users want to get this to configuration themselves, as, for instance, the pressure conditions in the application form can change. Regarding 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 regards to the model) requires a certain amount of effort. But it?s not witchcraft. This article explains, step by step, how to do it.
Users need the following equipment: a pressure source (e.g. a dead-weight tester), a control pressure gauge, a continuity tester or a control lamp as well as a tool for the adjustment screw (incidentally, WIKA supplies the appropriate Allen key with its instruments; the standard screwdriver is sufficient for setting the hysteresis).
Setting plan view 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 into 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 indicate optimum value.
Now apply the desired switching pressure to the pressure switch before control pressure gauge indicates the worthiness.
After that, turn the adjustment screw out until the instrument switches and the continuity tester or the control lamp reacts.
Then lower the pressure until the pressure switch switches back and increase it again to check on the switch point. If necessary, the switch point should be corrected by turning the adjustment screw. Repeat the task before desired switch point is reached.
Setting of the reset point
In some applications, the reset point is defined instead of the switch point, e.g. for minimum pressure monitoring. Here the procedure is similar to the switch point, but without submiting the adjustment screw.
Increase the pressure until the instrument switches.
Then lower the pressure before instrument switches back and adjust the positioning of the adjustment screw accordingly. The guideline 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 get this done, first set the switch point and then check the reset point (see above). Based on the reset point, the hysteresis screw is turned in or out. Perspective must then be checked, as changes to the hysteresis screw also affect the switch point.
Note
An overview of the various mechanical pressure switches in addition to further technical information can be found on the WIKA website. Should you have any questions, your contact will gladly assist you to.
Also read Depraved : Functionality
Mechanical vs electronic pressure switches: Application areas
Pressure switches in booster pumps
SIL pressure switch: Safety in tyre manufacturing

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