Emergency Shutdown Circuit Monitoring

[markcraig]

Hi all,
I have an issue with design of an emergency shutdown circuit that can be monitored for open circuit and short circuit. Normally i would do this using UV trip coils but in this instance it is required that i use a NDE (normally De Energized) circuit as a failure of the shut down circuit must not stop the plant. Failure of the shutdown circuit is to bring up an alarm at the control panel.
Now i have seen a circuit used in this instance before where a small current is continually running through the system via some resistors and diodes. I just can't rememeber the configuration to save my life. I am thinking along the lines of a voltage divider. Am i even on the right path?
The shunt trip coils are 24V DC and i am not sure of the resistance at this time.

Any basic circuit would be greatly appreciated.

Thanks In Advance

Mark Craig
Electrical Engineer
Frontier Drilling

 

[ScottyUK]

Look for 'trip circuit supervision' relays. They are used in most medium and large switchgear where the final tripping circuit is energise-to-trip. The principle is more or less as you describe. Have a look at Areva's MVAX series for a typical design.


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If we learn from our mistakes I'm getting a great education!

 

[markcraig]

Thanks for that it is what i was after. I have spent days looking up shut down monitoring and all sorts of things like that I never thought of trip circuit supervision.


Mark

 

[Laplacian]

Here is a device you can wire up to for this purpose:

http://www.e-maxinstruments.com/applications/rawapp.html