Hand/Trip switch failure detection

[helpyou]

HI

Have a question on field hand/trip switches. Their failure in most of cases activates a trip function. My question is, how does the safety system know/detect that switch is faulty and how is it different between normally open and normally close switches?

Thank you

 

[razookm]

To explain this, Any unit is considered to be either in a safe-sate (normal operating ) or in a trip-state. Normally, Trip switches are configured using Fail-safe philosophy. Trip circuits are normally powered by a lower voltage and Fail-safe design means that power is required to maintain the system in a safe-state. To trip the system, this power needs to be interrupted. Trip switches are "normally closed" and when not actuated, it will ensure the power circuit is maintained. If the trip switch is actuated or any connection to the trip switch gets disconnected, the control power will be interrupted and the system will go to trip-state.