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#1 Quimarah


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Posted 25 November 2023 - 10:45 AM

Hello everyone!

I'm working on a P&ID and i'm unsure on the approach i have to take.

Is there any bibliography that describes the selection of instruments.

I mean if it should be Discrete local, discrete primary front or back, Computer local, computer local front or back, logic local, pilot local, etc.

Thanks in advance

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#2 breizh


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Posted 25 November 2023 - 07:08 PM


Let you Google PID instrument tags.


You will find plenty of information.


Note : as a Process Engineer working with operation team, you need to mention to your E&I Engineer what you want, this guy will update the P&ID accordingly. Let say on field (meaning local), on DCS/PLC, meaning control room. Most of the time data are continuous, meaning with trend on DCS/PLC. Important to indicate alarms with feedback to support the board operators and safety interlocks (safety matrix) with actions.

In other words, let you describe in words what you need (scope).

Good luck


#3 Quimarah


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Posted 26 November 2023 - 07:18 AM

Thank you for your help!

#4 shvet1


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Posted 26 November 2023 - 11:23 PM

Issues you have described refer to a local practice. You should combine local practices&requirements from opearting team, engineering team (process engineer + instrument engineer), management team (project manager, project consultant), and suppliers.


The same control principles may be solved opposite ways depending on local conditions.


E.g. I have encountered such option - a large distillation tower (~4x40m) had one level gauge on bottom and one hand-operated control valve on pump discharge to control liquid level in tower. An operator sits in a shed next to LG and does nothing other than 24/7/365 looking at LG and occasionally runing from LG to CV to open/close that. On the same application I have encountered 1 LG + 3 LT ESD + 1 LT DCS + Honneywell.


Good start for a newcomer is



Edited by shvet1, 27 November 2023 - 12:07 AM.

#5 Quimarah


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Posted 27 November 2023 - 06:57 AM

Thank you!