Mechanical switches normally have a physical diaphragm which is in contact with the media such as nitrile, viton for example. The movement of the diaphragm is physically transferred to either a contact arrangement or microswitch. Normally the settings are at zero pressure, however the default differential pressure is adjustable. They can be pre-set at the factory or adjustable for the end-user .
Electrical switches are in essence part of the progress in volume pressure sensors. Normally the current is lower, but you will find the accuracy and repeatability is far superior to mechanical based switches.
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