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

Mechanical pressure switches are often supplied with a factory-set switch point. Nevertheless, some users want to make this configuration themselves, as, for example, the pressure conditions in the application form can change. In the case of pressure switches with a measuring element in a bellows, diaphragm or piston design, the manual setting of the switch point, reset point or hysteresis (depending on the model) requires a certain amount of effort. Nonetheless 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 perhaps a control lamp as well as a tool for the adjustment screw (incidentally, WIKA supplies the appropriate Allen key with its instruments; a conventional screwdriver is enough 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 the highest possible value.
Now apply the desired switching pressure to the pressure switch until the 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 before pressure switch switches back and then increase it again to check the switch point. If necessary, the switch point should be corrected by turning the adjustment screw. Repeat the task until the desired switch point is reached.
Setting of the reset point
In some applications, the reset point is defined rather than the switch point, e.g. for minimum pressure monitoring. Here pressure gauge 10 bar is comparable to the switch point, but without turning in the adjustment screw.
Increase the pressure before instrument switches.
Then lower the pressure before 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 get this done, first set the switch point and then check the reset point (see above). Depending on 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 together with further technical information can be found on the WIKA website. If you have any questions, your contact will gladly assist you to.
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