Tuning of PID controllers has proved to improve plant performance and increase stability and safety. However, at most plants, the biggest enemy of PID tuning is time. As a DCS engineer, you are often a firefighter — supporting ad hoc work on a daily basis. As a result, you have no or too little time to tune PID control loops for temperature, pressure, flow, level, etc. Especially while the most complex PID controllers that often cause process oscillations and alarms require a lot of time due to their slow responses. That’s frustrating. The good news is that you can do your PID tuning first time right. How? That and what PID tuning exactly is I’ll explain in this blog.
What is PID tuning? Often a process of trial and error
In day-to-day operations, PID controllers are often in manual mode or, when in auto, cause process oscillations due to bad tuning or suboptimal control strategies. Many DCS engineers tune by intuition, fiddling their way to final tuning by a combination of trial-and-error and experience.
Trial and error is a “simple method” of tuning a PID controller. Once you get a clear understanding of what PID parameters do and you have a simple loop to tune, this method becomes relatively easy. The downside is you are still using an iterative workflow. You tune a PID controller and look at what happens when you changed the settings. It normally takes a couple of iterations to get the desired settings of a PID controller. And for more complex loops, that have a direct effect on product quality, energy consumption, and overall plant throughput, you might even settle with a malfunctioning loop causing frequent alarms. So, in the end, the trial and error method is a time-consuming process, while an operator expects you to solve problems with PID loops quickly, without any consequences for the production process. That’s frustrating.
Optimal PID tuning with a first-time-right approach
For the record, the trial and error method or tuning rules like Ziegler-Nichols, Lambda, Cohen-Coon, and Kappa-Tau give reasonable results in many (simple) cases. However, for complex PID controllers directly effecting plant throughput optimal tuning is essential. Because time is scarce, you preferably want to do it first time right to get a loop that is robust and will stay tuned for the long term. To do so, PID tuning software will help you accomplish this.
PID tuning tools can calculate the parameters you need for a stable process. However, before the software can make this calculation, it needs to know how the process responds eventually and how fast or how slow it gets there. That’s why you need to run a test on the process. Does it take ten minutes or one hour to respond and settle after the actuator adjustment? That’s the information the software needs to calculate the tuning. The reality is that for these slow loops you would have gone through multiple tuning iterations when using the trial-and-error method, so you would have spent more time in that case.
Do you have to retune all PID controllers? No, prioritize and look at the ones that cause many alarms and/or cause oscillations in the overall process.
PID tuning software gains time
Yes, it takes time to run tests on difficult PID controllers. But once the software can calculate the right parameters, you don’t have to look at it again. In the end, the software helps you achieve the desired result faster. It simplifies the process of improving the control of individual PID loops.
With a first-time-right approach — using PID tuning software — you reduce risks and get:
- A more stable production process and more efficient plant operations
- Increased product quality
- Reduced process oscillations resulting in less wear and tear of the equipment
- Fewer alarms and operator interventions
Do you want to learn more about or PID tuning software, how it stabilizes your plant and reduces alarms and operator interventions? Read the whitepaper: 7 reasons why to get INCATools PID tuner software
Do you like to know what INCATools PID tuning software can offer you?
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