You've all probably been in a similar situation - you became aware of an underperforming PID loop, took immediate action, tuned the loop and at the end of the day the PID loop was still performing well. The next day the operator complains; the loop had been oscillating all night and is now in manual mode. The first thing you need to do is check the PID parameters and tune the loop again, the operator isn't happy, and neither are you. You could prevent this if you calculated the robustness of the controller. Learn in this blog how to consider robustness by looking at your PID parameters in your PID tuning.
It’s no secret that well-tuned PID loops contribute to a stable and healthy plant. Once optimally tuned, only critical PID loops that cause too many alarms tend to be tuned again. Underperforming loops are often ignored. But if you frequently analyze all your PID loops you can enhance total efficiency, have less wear and tear, more overall stability, and fewer operator interventions. Read in this blog why it is essential to monitor your PID’s and how to perform monitoring most cost-effectively.
More than a hundred years ago, Sperry Corporation invented automatic pilot control in airplanes. It was magical and scary at the same time. Nowadays, they can anticipate the exact arrival time, other planes nearby, and the weather forecast. It became unimaginable that our planes would fly without it. Model-based Predictive Control in an APC (Advanced Process Control) project is the automatic pilot in plants. APC projects can maximize your performance and plant's profit. For decades, the chemical process industry has been working with it. It can benefit smaller plants considerably as well. However, proper PID tuning is the first step in an APC project. It is the foundation for your automatic plant pilot, learn in this blog why.
It's no secret that proper PID tuning will contribute to a stable plant with fewer variations and fluctuations. Optimal and stable operations are the ultimate goal. This can result in several percentages of extra throughput and several percentages reduction of specific energy consumption. Additional throughput is highly desired in high market conditions, while the specific energy consumption might be more interesting when selling prices are low and energy prices high. In all cases, more stability results in fewer alarms and fewer operator interventions.
In this blog, you will learn why PID tuning improves process performance and how to accomplish this technical result of PID tuning.
In this blog we are going to compare different tuning techniques used to tune the level loops in a distillation column. The tuning methods under consideration are Lambda, the Zak Friedman tuning rules and AptiTune. The idea is to obtain a tuning based on engineering specifications like maximum deviations, minimal gain and dead-time margin.
The following distillation column example illustrates the tuning strategies that can be applied when designing the controller for level loops. A debutaniser is used to separate the C4 (isobutane, n-butane) from a natural gas liquids stream (NGL). In this example, there are 4 cascade loops, for the column pressure, the top temperature, and the column bottom and reflux drum levels. There are also single loops for the feed and steam flow. The piping and instrumentation diagram is presented the figure below:
Topics: PID tuning
You reviewed all important PID loops on your process, and they all seem to work well. You selected some of the loops and followed the tuning procedure to update the PID parameters and with proper tests and models, you managed to apply the known tuning rules so the fast response to SP changes could be achieved. So, there is nothing else to worry about, right? You might have unnoticed some of the loops.
Even though this recipe could be adequate for many of the loops, provided other important criteria are also taken into account, as process objectives, restrictions, and characteristics of actuators, this is not always true, especially for level loops. Two different types of strategies can be distinguished depending on the control objective:
Topics: PID tuning
At most plants, the biggest challenge in tuning PID controllers is to reject process disturbances. However, in many PID controller’s information regarding process disturbances is missing in the PID algorithms which drastically affects PID performance. Do you need to understand how to add that information in PID controllers? Check out this blog, about the benefits in feedforward in PID controllers.
The key objective for a DCS engineer is to make sure automated operations run as smoothly and as safely as possible. You want to keep the operators as happy as possible - which means keeping the alarms to a minimum and prevent operator interventions. The impact of optimal PID tuning on smooth and safe operations and the number of operator interventions, cannot be overestimated. With a fully-booked schedule, PID tuning is often something that has a lesser priority.
In this blog, we want to explain the impact of the PID tuning on the operator interventions. The first objective of this blog is to put PID tuning higher on the priority list. The second aim is to provide you a way to achieve better tuning within a minimum of time and on a first-time-right principle.
Many tuning methods are proposed for PID controllers, of which trial and error is the best known and used method. Despite its popularity, the biggest downside is that it’s time-consuming and it doesn’t guarantee a robust and stable solution. The Ziegler-Nichols method is a good alternative but doesn’t always provide optimal performance. In this blog, you will read why Ziegler-Nichols isn’t always the right choice to achieve stable and robust control loops.
Topics: PID tuning
The period before a plant’s launch is a stressful time. There is a possibility you will face mechanical problems, errors in the instrumentation and DCS configurations, safety issues and even last minute changes in control designs.
When a plant is commissioned, all the equipment and all safety and control systems are tested. However, this doesn’t mean that, at this stage, the plant is tuned to generate the most optimal results. In this blog, you will read why it’s important to start with PID tuning in a plant’s commissioning phase.
Topics: PID tuning