How to Interpret DCS and PLC Symbols on a P&ID

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In this video, we’re going to talk about how to correctly interpret PLC and DCS symbols on a P&ID.

Anybody such as Instrumentation & Control Engineers, technicians, and maintenance personnel working on industrial plant control systems depend heavily on P&ID’s.

A P&ID is like a road map telling us what the instruments and devices are, where they are located, and how they interact with the rest of the plant.

Original symbols and terminology for P&ID’s were created long before the introduction of PLC’s and DCS’s in-plant control.

Before computers came along, process control loops were stand-alone. In other words, each process had its own individual controller.
Control rooms were massive and had sprawling control panels with lots of controllers and other devices such as strip chart recorders and switches.

Today’s industrial processes are controlled by computerized systems using virtual controllers found in PLC’s and DCS’s.

New control rooms are filled with HMI’s and keyboards connected to a DCS or a PLC system. All of this computerization required that new P&ID symbols had to be developed.

If you recall, stand-alone instruments are indicated on a P&ID by a circle with a tag number.

The horizontal bar across the middle of the circle indicates the physical instrument resides in a primary location accessible to an operator on the main control panel.

If we take that same symbol and draw a box around it, it now means that it is no longer a physical instrument. It is now part of a shared display and shared control in a DCS.

PLC symbols don’t show up on P&ID’s nearly as often as DCS symbols. But, when they do show up, they are drawn as a diamond inside a box.
All you have to know is that the symbol represents a software instruction to perform some function in the plant.

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#P_and_ID #PLC #RealPars

[pravinpr]

I am the one who likes your videos before watching it. It is always a helpful and informative video.

[tolgun]

Very well explained each time. Great job RealPars!

[carhammer]

RealPars your videos are amazing and am following you for long time.the people in the industrial world have very limited source of knowledge and your channel is one of them.your videos are in english i would like to work with you to translate them in to Hindi and we can create a RealPars Hindi that i am sure will help millions

[-Blackpearl-]

Excellent quality and explanation of the video. Good job RealPars!!

[AliHasan-xpqv]

Great explanation with proper animation.. great job

[andresmarin]

Hi! excelent content Real Pars Team, I love your well-explainded videos. I have a question: Which is the standard that regulates the P&ID symbology?

[jacobcamenzind]

Great video. Definitely going to forward this to my boss so more of our staff can get trained with this.

[DanielSanchez-itki]

I've always wondered why would you refer to a valve as FCV and not just FV. To me, a FCV is a control valve that has a controller locally mounted on it, that is, the valve itself physically includes an element of control. Many old models from companies like Fisher fit into this description. But a valve that is just part of a flow control loop where the controller is actually part of the DCS, should be called just FV in my opinion. Calling it FCV may cause confusion. I actually know of many people that because of that confusion actually think that the valve performs the control action. I would like to hear anyone else's opinion on this. Very nice video!

[davebennett]

ARE YOU FOLLOWING ME? Seriously though, been digging into a gigantic new control project and trying to make sense of the client's P&ID was hard. They're process engineers and weren't aware of what the PLC was actually doing, so their diagram was inconsistent with symbols. I couldn't make sense of it. Now I can at least see what it SHOULD look like, so maybe we'll get somewhere.

[shubhamdubey]

Thanks real pars again with a good video!!

[xtehtastore]

Great information shared, pls keep making specially on valves, actuators, Transducers, converters related.

[QatifCarCare]

Can you make a video on compressor control system (CCS)?

[ХристоНеделчев-зг]

Helpfull as always. Thank you for the great content!

[prasanthjmohan]

Expecting @realpars to explain the industry 4.0 concepts

[thu-alfikarfalih]

As always before get starting am click LIKE button to thank you👍

[MrRockoman]

Well explained... thanks for sharing. Greeting from Peru

[AKBRONCOSFAN]

How much longer do we have to wait for Allen Bradley PLC training tutorials on realpars.com??? I've been patiently waiting for well over 2 years now, get with the program REALPARS.

[mohanr]

Really good explanation .try to take some controller types.actually I'm a student from process control department.if it is possible, try to upload some soft copy sir.it will be very helpful and useful.for me, it is very easy to understand the concepts from your videos.thanks for sharing your knowledge .

[MrWaalkman]

@1:04 "Old Control Room"? Hey! I cut my teeth in these installations. What are you trying to say here? :)

I spent many a day and night listening to the clacking of the relays. You could actually tell when things had gone south by a change (or more likely, a cessation) in the rhythm of the relays. That's when you would hope that it was only a field device that had gone bad, and not one of the million relay contacts in the panel.

Should it be an intermittent pair of contacts, the standard process was to tear off a little piece of tissue paper and roll it into a ball and place it in the cavities of the suspected relays while they were energized, where they would stay until the relay dropped out. Then wait for the next hiccup. Now look in your panel for the relays that were pulled in but no longer had the tissue ball in the cavity. That would be your prime suspects right there.

[tonnguyen]

Sir. The "DCS" and "PLC" you have talked in video is that the same with PCS: process controll system and ESD emergency shutdown system?.
Look at P&ID I can assume you maybe work in Oil and Gas Industry