Safety PLC - 2oo3 loop considerations for Boiler PLC as per NFPA85

Hi All,
I want to know about what NFPA 85 standard says regarding configuration of 2oo3 logic for a safety PLC.
Particularly, if there are 2 out of 3 transmitters/switches installed in a boiler for any tripping security (like furnace draft, inlet header pressure etc.), is it necessary to connect it to 3 different I/O cards in a Safety SIL-3 PLC? E.g if a digital input card in a safety PLC has a capacity of 16 inputs, and has TMR architecture with no single point of failure, is it still necessary to input the 3 input switches operating in 2oo3 configuration in 3 separate DI cards? Or can we connect all 3 switches in a single DI card?
Please inform in light of NFPA 85, or any other standard governing boiler safety control.

Thanks.
 
If you intend to operate any equipment at SIL3 you will have to refer both hardware and software designs through a Professional Consultancy. Personally I would go through the standard word-for-word.

We in Europe have European standards: I would guess the standard quoted wouldn't mention specific control system design or 2oo3 systems.


Even if the I/O cards were fault tolerant, for SIL3 applications 3 inputs span 3 input cards.
 
SWAZ...

NFPA-85, as well as 86 & 87, does not evaluate Voting-systems. But, it now recognizes SIS Voting Logic be included when considering Burner Management logic!

My company can provide M of N voting systems for applications similar to the one you described . One particular application was a 3 of 75 voting system to prevent thermal runaway of a hydrogen reactor.

Available in software or hardware, they also included options such as input-sensor fault detection, input bypass; output disable; and on-line testing features.

If you want additional details contact me on- or off-forum.

Regards, Phil Corso (cepsicon [at] aol [dot] com)
 
SWAZ...

NFPA-85, as well as 86 & 87, does not evaluate Voting-systems. But, it now recognizes SIS Voting Logic be included when considering Burner Management logic!

My company can provide M of N voting systems for applications similar to the one you described . One particular application was a 3 of 75 voting system to prevent thermal runaway of a hydrogen reactor.

Available in software or hardware, they also included options such as input-sensor fault detection, input bypass; output disable; and on-line testing features.

If you want additional details contact me on- or off-forum.

Regards, Phil Corso (cepsicon [at] aol [dot] com)
Dear PhilCorso,
3 of 75 ??? This is some overkill, or just a typo?
 
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