5 Undisputed Steps to Implement Automatic Process Control (PID)

The sequence or method for learning any subject is very “important”It will definitely save you time, money, and a LOT of headaches (remember how bad stress is). In my 12 years of experience, I have followed many…“methods”"and many "“steps”"of many"“people”"to learn Automatic Process Control (specifically PID Control).".

Many methods were a bit “bad”", others "“terrible”"," and some "very, very good." Good or bad, you learn from everything; it's a great advantage to learn what "not" to do and what actually works.

In this article I want to give you a "nibble" of the 5 "big" steps that you absolutely must learn if you want to“really”"To be a benchmark in Automatic Process Control. These 5"“big”"The steps mark the path you must follow, and then you must delve deeper into each one (in each step there is so much to learn that you will probably need to take a course to learn each one).".

Okay, ready? Let's start your journey.“to an excellent professional career”"in the world of Automatic Process Control.".

Step 1. Learn ALL about the Process. 

Come on, if you're currently a PLC programmer, DCS programmer, or you configure any other automated system, you should know that if you DON'T know about the industrial process that will interact with or be automated by your PLC, DCS, etc., you're LOST. 

So, particularly if you want to implement a whole PID control strategy, do an excellent configuration, and test your “method”"of tuning that always works for you, and you want to be the "“king of the dance”"When your entire implementation works perfectly!, then you must and have to know the PROCESS.

In my opinion, understanding the process means two minimum things (but there can be more):

a. Have you studied how the final product of the industrial process is produced?, That is, you know from start to finish how the raw materials are transformed and what the final product is. This means you've studied the Operating Manual, you have a general understanding of the flows, pressures, temperatures, etc., required for the process to function, and what actions the operator takes, what interlocks are involved, and so on.
Then you should have studied the Process Flow Diagrams (PFDs) and P&IDs in detail. You know exactly how the "process" moves, what changes occur at each stage, and which instruments and control loops are involved in each part of the process. You should even know the size of the pipes, the volume of the tanks, where the equipment is located, the types of instruments and valves, the tags of the equipment and instruments, typical speeds, typical power ratings, etc. It's very important to understand all this information holistically. And yes, much of this information will help you configure and control your control loop (if you've been asked to configure and tune it). If you're designing or tuning an entire system within a process, or something larger, and you don't know this, you'll be "lost." It had to be said, and it was!.

b. Define the characteristics and model of the Process. I know you're afraid of running tests on a process (of disturbing it), especially if you don't know it well (which is why the above is vital). However, your best friend here is the operator. That person who has probably been operating the plant for years and years, and for whom changing a temperature or pressure value is as routine as saying hello in the morning (a daily occurrence). Ask when and by how much you could move the variables of interest to run some tests and develop the process model. Yes, you need to know the process gain (Kp), the dead time (DT), the process time constant (Tau), whether it's first or second order (or higher), if it has noise and how much? What type of process is it? Is it linear or not? What action does it have? How do the valves behave and what are their characteristics? What disturbances are the most common and which ones affect the process the most? And many other questions.
And that's because, how are you going to CHECK Something you don't know in depth. If you want to be an expert in Automatic Process Control, then you need to know all this and more about the process. Nobody said it would be easy, but with the right method, you can save yourself a lot of trouble.

Passed 2. Learn how you will control the process, and learn it well! 

By now you're a master of the process and the operators are your best friends. Well, since you already have everything…“clear”With the process underway, it's time to use a "controller" to manage it. Which one, or what type? Generally, it's a PID controller (yes, our beloved controller), but for much more complex tasks, we must choose another type (that's a story for another time). While the PID controller is "“simple”From a technical and mathematical standpoint, there are many variations, versions, types, etc., which can make implementation and configuration difficult. To begin, you must have a general understanding of what a PID controller is, why and how its three components are used, and how to clearly interpret the effect of each component and/or the combined effect and movement of the three actions (their impact on the process). You must also understand the strengths and weaknesses of each action and how to use them to your advantage, the physical or hardware format in which they are embedded, and how and when to use each one. What equations are available and why are they used?…etc.

Okay, after this, you'll generally be using whatever PID controller is available in a PLC, DCS, or field controller, etc. You're not going to say, "I want to use this specific piece of equipment or PID controller" (or you'll very rarely have that opportunity). So, since you already have the PID controller to use (whatever equipment is available), you must study its structure, units, and features in detail. This is extremely critical. In my experience, all PID controllers (from each brand) are always different. Some have more tools, others fewer; some use these units, others use different ones, and so on. A lot to learn? Absolutely, but it's necessary if you want to do an excellent job. Avoid being like me, who, while learning, has stopped the process "a few times," damaged some equipment, and ruined an entire day's production. That's why I'm telling you all this, okay?

Step 3. The famous controller tuning

This "step" is not insignificant, and in fact, the foundation for successful tuning lies in the two previous steps. If you skip any of them and rush through them (don't learn them and execute them correctly), believe me, it can all end in disaster. Tuning a PID controller is said to be an art, and it truly is. I've seen many professionals lose their minds trying to work with a PID controller (hahaha, no joke, I'm one of them :D). The situations and process variations are so varied that a simple procedure isn't enough. We need a clear method or step-by-step guide to lead us to success (and prevent us from getting lost along the way). Sometimes, I've literally had to spend days tuning a control loop, mainly because I didn't have a clear procedure or method.

There are also many questions you need to answer, such as what to do before tuning? Are the instrumentation and valves okay? Is the process operating under normal conditions? What is the most dangerous thing that could happen? Within what range can I manipulate the variables? Which tuning method should I use? Trial and error? Which formal method is best? What initial tuning values should I set? Is the plant's physical layout adequate? How should I document this process? What tools should I use? Which PID combinations should I use for each process? When and where should I use each tuning method? Why isn't a tuning method working? And much more…

And perhaps the most important question is: What is the operational objective of this control loop? Again, hard work, yes, but with a proper and serious procedure or "method," this could be a piece of cake.

Step 4. Monitor the performance of the control loop.

We've tuned it, and the process variable is responding well! Excellent! You show the operator the response, and he's happy with how the process is responding. Great, let's go home! Wrong. Always dedicate one or two days to monitoring the loop and its performance. The truth is, you might "succeed" in tuning the control loop for just a moment, and then the process changes, and your tuning is literally "in the trash." Therefore, it's important to clearly identify the most common operating range the process will use, properly validate any physical changes that may have occurred (changes in pipe size, valves, etc.), what type of production and product were present when you tuned it? Was it a special occasion? Has the operator who tuned the loop changed? Have production rates increased? Did you tune the loop too close to stability? Have the operating procedures changed? Are there other parts of the process that have started interacting with your loop? etc., etc.

Step 5. Accompany and improve your control loop, use advanced strategies.

The next step would be to complement the PID controller with a defined control strategy to improve and significantly enhance its performance. I'm talking about using well-known configurations such as Cascade Control, Ratio Control, Feedforward Control, Nonlinear Process Control and Programmable Gain, Characterization Curves, Loop Decoupling, Override Control, Split-Range Control, Dead-Time Compensation, and so on. Note: only if necessary.

Automatic process control is a cyclical process; you must constantly be alert to any changes in the process or equipment (and anything else) and re-evaluate steps 1 through 5, and their interactions. You must view Automatic Process Control as a whole, not as individual control loops.

Later I will go into more detail about each step and each question; it's a broad topic, so let's take it one step at a time.

Okay, does that seem like a lot? Again, a “procedure”" either "“method”" either "“step by step”"Doing it correctly will make this less difficult and allow you to become a true Specialist in Automatic Process Control. For my part, I will be writing more details about my “method”"that I have learned over many years and after several "falls" and "successes.".

If this article helped you or you liked it, COMMENT y SHARE With your friends. Knowing your opinion is very important to me.

Finally, if you are determined to learn Automatic Process Control (PID Control) and its Tuning, our Premium courses might interest you (where I show my "method" in full):
– PID Controllers Master Class – 100% practical
– PID Tuning Ultimate: The Definitive Course for Tuning
– The Ultimate Process Control Formula (All-inclusive: PID Control, Tuning, and Modeling)

Until next time.