IS barriers in Safety Instrumented Systems


Thread Starter

Sergio Diaz

I was wondering how can IS barriers affect safety functions on a SIS. I would assume that the failure rates of the barrier need to be included in the loop analysis to determine the integrity level (SIL). However I wonder if there is any preference or recommendation between using active barrier rather than passive barriers on a de-energized to trip system. If it is possible to use active barrier for analog transmitters, does anybody know of a logic solver that support connection of 4-wire devices? (I think that from point of view of the logic solver, an active barrier looks like a 4-wire device)



D Turner - MTL instruments UK

Zener barriers can be used in SIL rated systems and although we do not have any approved barriers we have a document justifying figures that can be used in the SIL estimation. Zener barriers (passive) would tend to have the better figures as they are the simpler, less components, devices.

Not sure I understand you 4-wire transmitter and Logic Solver. Can you tell me more?

Dave Turner