Options (SPST, SPDT)

At the forefront of differential pressure monitoring technology, Mid-West Instrument proudly provides a diverse array of switch options tailored to meet varying needs and applications. This flexibility in their product range is evident in the three distinct types of reed switch options they offer. Mid-West Instrument offers Form A (SPST Open), Form B (SPST Closed), and Form C (SPDT) reed switch options.

The first one is Form A, also known as “Single Pole Single Throw Normally Open” or SPST Open. In its normal state, the switch is open, meaning the circuit is incomplete. This configuration is ideal for applications that require the switch to complete the circuit only when certain conditions are met, thereby activating the connected device.

The second offering is the Form B or “Single Pole Single Throw Normally Closed” (SPST Closed). In this type of switch, the circuit is usually complete, and it only opens (breaks the circuit) when specific conditions occur. This type is often used in safety systems, where the device needs to be activated most of the time and only turned off under particular circumstances.

Lastly, Mid-West Instrument offers Form C, known as “Single Pole Single Double Throw break before make” or SPDT. This type of switch can alternate between two circuits, providing high flexibility. The ‘break before make’ term refers to breaking the connection with one circuit before making a connection with the other, ensuring that the two circuits are never connected simultaneously.

This comprehensive suite of reed switch options allows Mid-West Instrument to cater to a broad spectrum of customer requirements, offering the appropriate technology for different applications, and thereby demonstrating their commitment to customer satisfaction and industry excellence.

spdt switch

An important spotlight is the the Form C (SPDT) switch, which 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.