SIS Instrument Designation on P&IDs 1

[Loopee]

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?

 

[xnuke]

2009 version of ISA 5.1 redesignated circle-in-square as either primary control system/basic process control system and diamond-in-square as either secondary control system/SIS and encouraged users to adopt these meanings for the symbols as soon as possible.

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
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[controlnovice]

What xnuke said!

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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[JLSeagull]

Is Loopee asking about differentiating the field instrument bubbles not the system bubbles? Restated, should a safety instrument designation be assigned to the SIS measurement instrument on the P&ID? The DCS signals may use instrument models that differ from the instruments suitable for the SIS.

 

[roydm]

A thought that springs to mind.
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.

 

[Loopee]

To Mr Seagull's point- I was thinking about the actual instrument but since the controls are part of the SIS loop, I suppose either the system side or the instrument side would work.
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...

 

[JLSeagull]

It is common for the instrument tag number to extend beyound the symbol on the P&ID's. Thus some require the P&ID group to cad with a break in the symbol so that the number is contiguous.

 

[Loopee]

Hi All,

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

 

[controlnovice]

Not sure about adding 'Z'. Per ISA 5.1, 'Z' means position. If you had a position switch as part of the SIS, that would be ZZS?

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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This is normally the space where people post something insightful.

 

[Loopee]

Thanks ControlNovice,

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.