How to Interpret DCS and PLC Symbols on a P&ID
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- Опубликовано: 7 июн 2020
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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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You might want to review 2 of our other videos called How to Read a P&ID (realpars.com/p-id/) and What is an HMI? (realpars.com/what-is-hmi/).
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Very well explained each time. Great job RealPars!
That's great to hear! Thanks for sharing and happy learning!
I am the one who likes your videos before watching it. It is always a helpful and informative video.
That is amazing! We are happy with such great support - feel free to reach out if you ever have any questions.
Happy learning!
Excellent quality and explanation of the video. Good job RealPars!!
Thank you! Much appreciated!
Helpfull as always. Thank you for the great content!
Great to hear that! Thank you.
Great explanation with proper animation.. great job
Thanks a lot!
Very useful for me . Thanks Realpars
Happy to hear - thanks for sharing!
Excellent..Thank You !!
Thanks real pars again with a good video!!
You are very welcome - happy learning, Shubham!
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
Hi Ashu,
Thanks for your comment, great to hear that you have been with us for such a time! We currently only provide our course videos in English, you are always able to turn on the English subtitles as that might make it a bit easier for you.
Our apologies for any inconvenience!
Happy learning!
Excellent video, very informative!
Glad it was helpful, Jim!
Expecting @realpars to explain the industry 4.0 concepts
Great video. Definitely going to forward this to my boss so more of our staff can get trained with this.
That's amazing to hear, Jacob! If you have any questions, feel free to contact us at any time.
Happy learning!
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Great information shared, pls keep making specially on valves,actuators,Transducers,converters related.
Thanks for your kind comment and your topic suggestion! I will happily go ahead and pass this along to our course developers.
Well explained... thanks for sharing. Greeting from Peru
Thanks for your support - great to hear that!
Thanks such nice and useful topics
Thanks for your support, Derin!
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?
ISA 5.1-2009 is the applicable standard to P&ID symbology.
thanks real pars
You're welcome!
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!
Hi Daniel. Thanks for your input. FCV actually stands for "Flow Control Valve". FV and FCV are used interchangeably and vary from one company to another. There are several P&ID's out there that use both terms to represent the exact same pneumatically controlled valve for example.
Daniel, you are correct. According to ISA 5.1, section 4.2 (23e) "The succeeding letters CV shall not be used for anything other than a self-actuated
control valve." The correct designation should be "FV".
@@dennislynch7492 Dennis, thank you for that ISA reference. After reviewing ISA 5.1, section 4.2 (23e), and to be absolutely correct, the valve should be labelled as FV501. As mentioned before, the acronyms FV and FCV are both used on P&ID's to depict an "FV", which certainly can cause confusion. Daniel, thanks for bringing that to our attention.
Hello everyone. I'm certainly aware of some companies using "FCV" for cases like this one. To be honest, in the company that I work for people keep using "FCV" everytime despite my efforts to correct them. It is a very common error, but it's still an error. I'm glad you guys have taken the time to provide references to the correct form of nomenclature and make clarifications. Please keep making these wonderful videos. Many thanks.
I'm of the same opinion with regard to the labelling. Usually less is more. A cliché, I know, but a good one.
As always before get starting am click LIKE button to thank you👍
You're the best!
Superb
Amaging helpful videos,keep it up.....
Thank you so much!
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.
Can you make a video on compressor control system (CCS)?
Hi Qatif!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!
Amazing
Thank you!
Thanks
Our pleasure!
@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.
I hear ya............. I remember an entire wall just behind the control panel.....full of clicking-clacking relays..... I'm guessing you know, but youngins might not, about burnishing contacts.
@@tedmortenson4036 Man, I had completely forgotten about the old rubber "sticks" that we would use to dresses up contacts.
Those, and the old soapstone bars we would use to clean up the commutator on DC motors. While they were running of course. :)
@@MrWaalkman Those certainly were "the good old days", but relays are still important today for the same reasons they were 40 years ago. I, too, started in a plant that was all relays and pneumatic control. It may seem "old fashioned", but these systems worked well and billions of tons of products were produced with quality and in quantity. Sure, we can do it more efficiently with PLC's and various logic programs, but relays are still required for circuit isolation and handling high-power switching.
@@realpars I don't know about the good old days, I was by that time quite comfortable chasing down faults in a PLC. But as a maintenance electrician prior to switching over to engineering, I am fine with finding faults with a meter as well.
As you know, some of the major problems with relays are:
a) Reliability. Relays wear out.
b) Latency. Relays take time to be pulled in, and usually more time to drop out. Usually this amounts to just having to hold down the start button a little longer. However, sometimes it has to be designed out of the system.
c) No "phantom diodes" in relay logic. In ladder logic, the logic flow follows a pre-defined path that never deviates from how the PLC is designed. *And it never reverses direction.* That's important since designers can, and have, managed to miss this, and you can have unexpected operation of the machine. I did an elevator install that because of an unaccounted for secondary path, the doors of the cab would open up while in operation. The factory rep swore up and down that I had a wiring error until I pointed out where they had made their mistake on his prints.
I'm working on upgrading an old lathe for a friend and I have spotted two places where the original has taken "advantage" of this "feature". We'll see how it goes.
d) Modification of the system. Gone (thankfully!) are the days of re-wiring a 60 foot long cabinet to accommodate a new product. The job is hard enough as it is. As a side note, while in one of these old plants I was shown an early "PLC" that was programmed by wirewrapping logic gates. It was a museum piece back in 1992. :)
Now I do miss the old Veederoot / Selsyn systems used for keeping the conveyors in sync. Selsyns are just cool (we used WWII Naval surplus ones), and a Veederoot is used to set the pace of the Paint shop conveyors. It is essentially the innards of an old-style gas pump, and it uses the price per gallon dials to set the rate.
God all these acronyms made me start laughing hysterically at how little I know
Nice but an instrument belongs to a process equipment usually the full instrument tag name with the equipment number will be populated in the PLC Tags DB.
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.
Hi there,
Thanks for your comment and feedback.
I'm sorry to hear that you were hoping for more Allen Bradley course videos. We do mostly focus our course videos on Siemens, with a small section devoted to Allen Bradley.
I will happily forward this feedback to our course developers for you.
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
As far as understand, Process Control System or PCS doesn't really specifies what kind of system you are talking about. I guess people may use "PCS" when it is unknown to them what kind of system is actually in place or there's simply no need to distinguish between the possibilities. A "DCS" is one specific type of Process Control System, such as SCADA systems or PLCs.
@@DanielSanchez-it1ki unclear your reply sir. Actually in the video, I can't distinguish the PLC and DCS. Is the PLC solve all the case of emergency?
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 .
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