Hi

From the pid diagrams we have to make loop diagrams..Loop Drawings: Loop drawings used to show terminations for wires from the field

device through junction boxes, multi-core cables and marshalling cabinets to the

terminations for a controller.

They will need to show all the

devices on a segment, where the power is introduced, where IS barriers are

positioned, if used, and where terminators are located. How long is the home run

cable? How long is each drop? What types of wires are used? Are there any “rules”

violated? Which devices are backup link masters and which are basic? What are the

addresses of each device?

 
ISA S5.4 is what you need. "Control System Documentation" by R. Mulley, published by the ISA also has similar information. ISBN 1-55617-490-X.

For those that don't know, a loop diagram is just about the most useful piece of paper you can have when trouble shooting instrument loops.
 
jemes said:
From the pid diagrams we have to make loop diagrams..Loop Drawings: Loop drawings used to show terminations for wires from the field

device through junction boxes, multi-core cables and marshalling cabinets to the

terminations for a controller.

They will need to show all the

devices on a segment, where the power is introduced, where IS barriers are

positioned, if used, and where terminators are located. How long is the home run

cable? How long is each drop? What types of wires are used? Are there any “rules”

violated? Which devices are backup link masters and which are basic? What are the

addresses of each device?
Click to expand...

Sounds like a schematic to me. In the Navy we had the wiring diagram which was basically a ladder type drawing. Then we had the schematic (mostly of controllers) which showed how the wires were bent around inside and where they terminated to. Very very handy.

Dan Bentler
 
AutomaticLeigh said:
ISA S5.4 is what you need. "Control System Documentation" by R. Mulley, published by the ISA also has similar information. ISBN 1-55617-490-X.

For those that don't know, a loop diagram is just about the most useful piece of paper you can have when trouble shooting instrument loops.
Click to expand...

They are also known as ILD's (Instrument Loop Diagrams).

Yes they are extrmely helpful and in most of my work pretty much essential. They document the connection of a single instrument all the way from the field back to the control system. This is pretty important in somewhere like an oil refinery where there are literally 10's of thousands of loops that may or may not interact.

I think ISA is a good place to start though that only gives general guidelines. You are better off trying to find someone that will give you actual completed examples.
 
Also known as P&ID, Piping & Insturment Drawing/diagram, not to be confused with PID (Proportional, Integral & Derivative) control.
It is a schematic of sorts, that is oriented to piping and control than it is to just electrical.

ISA members can download standards for free, so the $85(?) membership cost pays for one standard download.

Most instrumentation text books mention the symbols, show the most common, and a sample loop diagram or two.

The most extensive treatment of loop drawings is in "Instrumnentation & Process Control for steamfitter, Pipefitter, Journeyman and Apprentices", published by NJS-PAC (National Joint Steamfitter Pipefitter Apprenticeship Committee, now out-of-print. My copy is 1980, paperback, and has about 13 pages on the basics of P&ID's, more oriented towards the interpretation and understanding, than the actual production of a P&ID.

When the book was published, P&ID's were done by hand, with sharp pencils, by draftsman on drafting tables. Of the software tools mentioned above, CAD, is probably the most common used in engineering groups, but anyone can crank out basic shapes & lines in Power Point & Paint.

Dan
 
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danw said:
Also known as P&ID, Piping & Insturment Drawing/diagram, not to be confused with PID (Proportional, Integral & Derivative) control.
It is a schematic of sorts, that is oriented to piping and control than it is to just electrical.

ISA members can download standards for free, so the $85(?) membership cost pays for one standard download.

Most instrumentation text books mention the symbols, show the most common, and a sample loop diagram or two.

The most extensive treatment of loop drawings is in "Instrumnentation & Process Control for steamfitter, Pipefitter, Journeyman and Apprentices", published by NJS-PAC (National Joint Steamfitter Pipefitter Apprenticeship Committee, now out-of-print. My copy is 1980, paperback, and has about 13 pages on the basics of P&ID's, more oriented towards the interpretation and understanding, than the actual production of a P&ID.

When the book was published, P&ID's were done by hand, with sharp pencils, by draftsman on drafting tables. Of the software tools mentioned above, CAD, is probably the most common used in engineering groups, but anyone can crank out basic shapes & lines in Power Point & Paint.

Dan
Click to expand...

In my experience P&IDs and Loop Sheets are completely different.

A P&ID covers a fair chunk of actual plant, showing vessels, piping, pumps, exchangers and instrumentation in a broad overview kind of way. A loop sheet deals with a single loop, from field instrument through the various electrical terminations back to the control system, plus any internal soft connections in the control scheme the loop may be part of.

Totally different in my view.....
 
SLCintegrator,

You are absolutely correct in your observation, and jemes explains how he makes a loop diagram from a P&ID.

But the I&M techs in the lime plant I was in today used the two terms interchangeably, and I've tired of trying to convert the world to the technically correct definitions.

Given the nature of the forum as instructional to many readers who don't post, I gave into the temptation to throw it out there.

You're right. I'm wrong.

Dan
 
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