Mid-West Instrument offers Form A (Single Pole Single Throw Normally Open), Form B (Single Pole Single Throw Normally Closed) and Form C (Single Pole Single Double Throw break before make) reed switch options.
The Form C (SPDT) switch offers the most flexible configuration from a functional standpoint. If you are not sure if you need the normally closed or normally open contact for your application, the SPDT switch offers both.
The use of the Normally Closed contact helps in self-test logic. The designer can determine that the differential pressure switch is connected by monitoring the NC contact. Unless you create a scenario to operate the Normally Open switch, there is no way of knowing if the switch is present or connected in the system.
Switch functionality identified in our literature is defined at 0 differential pressure.