Trip Concept

[dembous]

Hello all,

Could anyone tell me if Safety PLCs are exclusively designed to operate using a de-energize-to-trip concept?

Most SIS systems are designed using a de-energize-to-trip concept. I tried, in vain, through IEC 61508/511 to see if I could find any paragraph or so dealing with the issue. Coul anyone also help me on that?

Thanks for your help.

 

[JLSeagull]

It depends.

Fail safe design is normal for most process applications. However, some of the NFPA standards such as deluge systems use supervised circuits and energize outputs to open deluge valves, etc.

 

[Ashereng]

No. Safety PLCs are not designed to use de-ernergise to trip or energise to trip.

A safety PLC needs to be designed and configured to do what is the "safe sate" in case of a shutdown.

De-energise to trip is not always the "safe" state. Each case is different.



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[dembous]

Thanks a lot guys!!!
Have a nice weekend.