APPS: TMR Concept - A Query

Tue Dec 9 21:16:39 EST 2008

==> Automation List post by Abhijit Goswami, Haldia...
To view or reply to this thread: http://www.control.com/thread/1228712876#1228798876

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Re: APPS: TMR Concept - A Query
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Hi Ritika,

Forget TMR, conventional design engineering prefers break to alarm/trip. Why so, when the problem is not in process but in system or associated hardware? Simply because, when the protection function is not in place, the preferred choice is shutting down the process. It may increase spurious trip rate but will drastically reduce dangerous failures which is catastrophic. Objective of design is to balance safety with availability.

Along with inbuilt diagnostics, voting in TMR provides additional level of validation through "threads of similarity", which allows the system to use in higher SIL rated applications.

If a TMR hardware is chosen for an application to eliminate nuisance trips only, simply you may follow 3-2-1-0 degradation as suggested by you. Otherwise by default it is 3-2-0 only, if it is not F&G application.

Hope above clarifies.

Regards.
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