Applying the tuning recipes for level loops can lead to pitfalls, especially because of their integrating response, and the philosophies normally applied. With the PID tuning software the best the best responses for both strict and smooth level control are achieved. Find out more here.
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
When we work with PID controllers, we always assume that the control valve’s flow characteristic is linear. PID controllers cannot handle nonlinear responses properly. However, most of the time valves are nonlinear and we have to deal with them when tuning a loop.
Process units that change their operating window regularly, have the tendency to affect the performance of the PID controllers. As a DCS engineer, probably this had happened to you before. It had happened to me and it is really frustrating!
As an example, when you finally tune properly a simple PID loop such as a flow controller at 100% of the load and operators are pleased with your work; the planning department requests to cut the load to 50% and the problems begin! Typically, you are called to check the tuning of the flow controller, which according to operators now seems to be sluggish and cannot keep the flow at its setpoint. After cutting the load, the output of the flow controller dropped significantly to a lower operating range.
You start all over again: put the PID loop in MANUAL, perform a short step test, collect the data, identify the model using the open loop data and tune the controller with INCA PID Tuner. Operators are pleased again!
After a couple of days, planning department calls again and request to increase the load back to 100%. The flow controller starts to oscillate, and operators put it in MANUAL. Operators blame you! What can I do? This seems to be an endless story! How do I tune it?
As mentioned before, this had happened to me. However, there is an answer! It is possible to tune a PID controller to have a good performance on a large operating window of a process unit. And that is what I will explain in this blog.
The first step is to identify from process data the flow characteristics. By plotting in an X-Y chart the valve opening (output of the flow controller) against the flow (PV of the flow controller), you can easily identify the valve’s flow characteristics as can be seen in the figure below.
From furnace or boiler efficiency point of view, excess air control is very important to be set up correctly. When there is too much air in the combustion process, additional fuel is being burned to raise the temperature of this excess air to the combustion temperature. Excess air absorbs the heat that goes up the stack, rather than in the process. To control the excess air to its minimum level, it is required to control it tightly in a “safe way”. If there is not enough air being introduced into the combustion process, all fuel will not be burned and, consequently, it will be lost up the stack in the form of combustibles. Not only does this result in an obvious waste of valuable energy, safety and pollution hazards are created.
When the grass root plant starts production, 70% to 80% of the PID loops are in default mode. There is nothing wrong with default settings. However, when time passes and alarms occur, the production manager will complain about spending too much time on controlling the plant. You need to check all the PID loops to make sure the plant will run smoothly. In this blog, you will read 5 of the most common mistakes made by DCS engineers in PID tuning. And more importantly, how you can avoid those mistakes.
Tuning of PID controllers has shown to improve plant performance and increase stability and safety. Very often, single control loops are tuned with the focus only on that specific loop, without regard for process interaction with other control loops. Depending on the nature of the process, this interaction can lead to a destabilizing effect where the control loops fight each other instead of working together in harmony. Discovery how to analyze and tune interacting loops in this blog.
In most of the chemical and metallurgical industries a furnace or heater is the most common and important thermal equipment used. Some control schemes have been recognized for automatic control of furnace outlet temperature, cascade control of temperature with fuel, control of fuel to air mixture ratio, and excess oxygen control content in flue gas. The design of a control scheme is very important, and it may vary as per the process and plant requirement. The final control performs well only if the underlying PID loops are designed and tuned correctly. Without robust and safe PID tuning parameters, tight and safe control of the furnace outlet temperature is not possible. Picking the correct temperature control scheme design and tuning the PID loops in it properly are equally important. In this blog you'll learn about PID tuning of a furnace.
Your ultimate goal as a DCS engineer is to get the most out of your plant operations. Over the years you’ve developed your own rules of thumb and used your gut-feeling to tune your PID loops. Most of the time this works well. But what if I told you PID loops can be tuned the first time right? INCATools — a set of PID tuning and process control tools — enables this. It is developed to overcome the challenges you face everyday. In this blog, I tell you about the top 5 reasons to use INCATools to tune PID controllers.
Topics: PID tuning