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.
The Ziegler-Nichols PID tuning method explained
Ziegler-Nichols is an often applied rule-based method that assumes a certain process response to obtain easy mathematical formulas for PID tuning. It typically results in aggressive control performance. The process characteristics are derived from simple experiments and used to calculate the PID parameters. The Ziegler-Nichols tuning method provides two different methods (the step response method and the frequency response method) and you might end up with undesired overshoot.In general Ziegler-Nichols leads to fast, sometimes too aggressive tuning, including overshoot.
Ziegler-Nichols method only guarantees a quarter amplitude decay damping ratio (height of the second overshoot peak to the first overshoot peak).
- You can only apply the Ziegler-Nichols step response method on stable processes. It requires open-loop tests to estimate process characteristics.
- You can only work with the Ziegler-Nichols frequency response method in a closed-loop PID controller. The aim is to push the controller to its stability limits in order to obtain estimated process characteristics.
The Ziegler-Nichols PID tuning method is simple and intuitive
Basically, Ziegler-Nichols works well enough when the dead time is small compared to the time constant of the process. It’s also simple, intuitive and it obtains reasonable performance for simple loops. DCS engineers often use this method when they need to tune new loops. New loops get always first a set of default tuning parameters. When this works well enough, there is no reason to retune the loop. When the loop needs to be retuned it might be smart to use a tuning rule such as Ziegler-Nichols. This method is also applicable to existing loops. When a closed-loop becomes active and doesn’t work properly, you might not know where to start. It can be helpful to use the Ziegler-Nichols method to reach an initial estimation of the tuning rules followed by manual tweaking of the parameters.
The assumptions of Ziegler-Nichols lead to shortcomings
A different PID tuning method for robustness
Model-based tuning leads to a safer plant
Do you like to know what INCATools PID tuning software can offer you?
Request your demo here.
