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F system IO modules and IS barriers

Created by: John Locke at: 8/21/2008 11:46 AM (3 Replies)

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8/21/2008 11:46 AM	Rate (0)
John Locke Posts: 28 Rating: (0)	Hi, Can anyone clarify the correct usage of IS barries within SIL rated loops when using F modules. I relise you need to use SIL rated barriers, however how does the barrier impact the inbuiltfeatures of the F modules. eg. Example 1: DO module configured for SIL 2 through a barrier, the module performs light/dark tests and monitors for open circuit etc. This is checking the link to the barrier and not the final element, so does this mean you cannot claim SIL 2 for the SIF? Example 2: AI module configured for SIL 2 through a barrier, the module supplies a monitored sensor voltage etc. Thisis monitoring the barrier and not the transmitter, so does this mean you cannot claim SIL 2 for the SIF? Which parts of the module diagnostics need to be functioning correctly in order to satisfy the SIL, im guessing a way round would be use a diagnostic barrier with monitoring and use that signal as a DI back to the safety system. I'd be greatful to hear from anyone whos dealt with these issues. Thanks in advance.
John Locke Posts: 28 Rating: (0)
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8/21/2008 3:38 PM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, I do not have an answer here, but only some points to think about. Forexample 1) failsafe DO. Let's consider that you use aZener barrier as IS barrier. - the barrier has only passive components. I believe that it does not add any power, does not load itself with energy over time, ... Soit could be considered as any wiring terminal from the safety point of view, andwould not require a SIL certificate as such. -why would aZener barrier block the testpulses?I don't see a reason why thesepulses would not reach the effectieve load at the end? And if the barrierreschapes or blocksthe pulses, the system will trip. So, I guess that the answer will depend onthe exact type ofIS barrier you use, as I tried to explain above. To be checked with the validating administration in your country.
	Last edited by: edr at: 8/21/2008 3:41 PM Best regards jklm Suggestion was helpful? Feel free to rate it.
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9/9/2008 11:01 AM	Rate (0)
PeteB Posts: 16 Rating: (2)	John, Here are some of my basic experiences! Basically if your barriers "isolate" the controlside of the circuit from the fieldside then you will have to make sure/prove thatthe field side of your circuit is suitable for SIL2. This would probably require a specific SIL2 rated barrier and SIL2 rated field device(s). If you use a "Zener" barrier then the field signal and the testing signals supplied by the F-SM (failsafe signal modules)can pass through to the field side of your circuit thereby maintaining a single safety loop. You would need to check the the "Zener" barrier failure modes but the chances are the F-SM will successfully detect most and "failsafe". You would need to make sure that the Zener barrier you selected keeps the loop within the technical specification's of the F-SM and that the barrier allows the F-SM to maintain its testing routine. For example if you use a "Zener" barrier with only a single diode to the earth connection, i.e. the 0V side is tied to the earth, then a F-DO (failsafe digitial output) module wouldn't pass its self tests. The F-DO modules needs to see the current return to the M side of the card otherwise it thinks there is a short in the field. Hope that helps. Pete
PeteB Posts: 16 Rating: (2)
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4/7/2014 12:34 PM	Rate (0)
CS Moderator Moderator Joined: 9/1/2005 Last visit: 11/14/2024 Posts: 4113 Rating: (195)	follow up question published by Marc.Kneiberis split to a seperate thread with the subject need to install an IS barrier using F ANALOG INPUT HART Module. Best regards CS Moderator
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards CS Moderator
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