Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Instrumentation & PLC symbol combinations

Instrumentation & PLC symbol combinations

Instrumentation & PLC symbol combinations

My job primarily is working with P&IDs. I'm trying to put together a list of PLCs that typically go with different instruments. And possibly what types of equipment they would go on.
For examples: If I have a LT = Level Transmitter, my P&ID is calling for a LIT = Level Indicating Transmitter. What might go with a LS = Level Switch?
If my P&ID calls for a SC = Speed Control on a conveyor, for the PLC I have 3 choices. SIC = Speed Indicating Control, SIT = Speed Indicating Transmitter or SS = Speed Switch.
I know these are questions one of our engineers or clients will answer.

I'm hoping to create a document that will help my drafters and myself learn more and cut out some markups before hand. I haven't been able to find resources to guide me. Any help you can provide would be helpful. Thank you in advance.

RE: Instrumentation & PLC symbol combinations

ISA 5.1 (2009 or later) is "the bible" for definitions and rules for P&ID instrumentation lettering.

RE: Instrumentation & PLC symbol combinations

I don't think you can put together a list that will not be modified by the instrument engineer. The representation of a PLC and other instrumentationon a P&ID will be custom determined for every project as depending on what is required, where PLC is located, who is the instrument engineer, and what PLC manufacturer is used.

I as a mechanical engineer prepared P&ID's with input from instrument engineer. I gave first shot based on copy of previous project P&ID's but in all cases the instrument engineer modified it for the specific project. For instance for a speed controlled VFD motor the P&ID would show the VFD with some instrument symbols inside and also some outside going to maybe a DCS or a PLC and also in-between and to the pump motor itself. With a VFD motor most of the control is buiilt into the VFD panel but auxiliary functions such as monitoring and changing setpoints, or interlocks with other equipment may be in a remote PLC or DCS. This is all project specific.

It may be benificial though to collect P&ID's of previous projects and to discuss up front with mechanical and instrument engineer what is the closest P&ID to the one they envision they will configure the system on this project to. I always started a P&ID by copying an existing P&ID from a previous project most closest to the one at hand, and modify rather than drawing from scratch which saved a lot of drafting time.

However some things are more simple like the instruments themselves. For instance there is always certain instruments associated with any instrumentation loop. For instance for level there is always a level sensor (LE) of many different possible types, a level tranmitter (LT or LIT) which transmits the sensor signal to a remote controller, and a contoller (LC or LIC) which recieves the signal and sends its own signal to operate the final control element such as a control valve (LCV). Each of these items will be represented by individual instrument bubbles on the P&ID. But when you get in to PLC and DCS or other special equipment displays they are all custom for project.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close