SIS Instrument Designation on P&IDs
SIS Instrument Designation on P&IDs
(OP)
i'm working on a process plant where there will be a Safety Integrated System (SIS) designed for the process.
It occurred to me that it would be helpful to designate the instrument "bubbles" on the drawings if they are components of this system.
I'm curious to know from others if anyone has developed a symbol for this designation. Years ago we had a safety system that we indicated by adding little solid five pointed stars next to the instrument bubbles. Anyone have a better designation?
It occurred to me that it would be helpful to designate the instrument "bubbles" on the drawings if they are components of this system.
I'm curious to know from others if anyone has developed a symbol for this designation. Years ago we had a safety system that we indicated by adding little solid five pointed stars next to the instrument bubbles. Anyone have a better designation?





RE: SIS Instrument Designation on P&IDs
In my opinion, the meanings of these existing symbols should have never been changed as existing drawings that rely on the old definitions creating possible confusion among people who only know the new meanings, and new drawings that rely on the new definitions might confuse people who only know the old meanings. They should have created new symbols for the new meanings.
xnuke
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RE: SIS Instrument Designation on P&IDs
The company I currently work for seemed to have created their own instrument standard symbols for P&IDs. Been that way for 40 years. I would love to change it to match ISA5.1, but if everyone is already use to what we have, doesn't make sense to change now.
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RE: SIS Instrument Designation on P&IDs
RE: SIS Instrument Designation on P&IDs
When you draw the P&IDs, do you know which of the interlocks are SIS?
Or is this a symbol you add later once the system has been evaluated?
We usually show this information on a different document.
RE: SIS Instrument Designation on P&IDs
The new ISA Standard does call out the diamond within square symbol for SIS but it isn't practical since the arrangement doesn't leave enough room for tags themselves especially when the sequence part of the tag often uses 4 digits.
And so I'm back to wondering what anyone else has used...
RE: SIS Instrument Designation on P&IDs
RE: SIS Instrument Designation on P&IDs
Since I posted this question I've read the latest ISA 5.1 on the subject and see that ISA's recommended approach seems to be by changing the nomenclature of the instrument tag and not the symbol itself. They add a "Z" after the first letter of the tag for an SIS item. FT-xxxx would become FZT-xxxx if it is to be a part of the SIS system.
Loopee
RE: SIS Instrument Designation on P&IDs
I've was at a company with DCS, PLCs and SIS systems and it makes it even more difficult. DCS was traditional circle in a square, PLC was Hexagon, SIS was circle in a square with SIS written outside of one corner.
My preference would be to keep symbols similar. So for an instrument going to a DCS would be the circle in a square. Instrument to a SIS would be a circle in a square, but thicker line width on the symbol (BOLD).
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RE: SIS Instrument Designation on P&IDs
About the Z: yes, ZZS would be a limit switch in a SIS loop.
And hey, I dont know about it either..but it is what the new S5.1 calls for.
The bold is a good idea...I once thought I would make the "ears" a solid black on the circle circumscribed by the square. That would have showed up well but the CAD people didnt like it.
You just can't have everything!!
Anyway thanks for your idea, that may be the best thing.