In our article Scilab Recipe 4: GUI Basics, we discuss the process of designing a simple GUI for our PID feedback simulation. The prime function of this PIDGUI window is to allow easy adjustment of the controller parameters and saturation limits, then update the corresponding variables in Scilab workspace. The actual simulation and response plots are performed in the Xcos model.

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Integrator windup in PID feedback control is well-known to control engineers. It happens when the integral term is used with some nonlinear saturation in the loop, such as when a physical variable reach its limit. When that happens, the feedback loop breaks, causing error accumulation in the integrator. This results in worse step and disturbance responses than the case of pure linear system.

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In our previous article Digital PID Controllers, we discussed some basics of PID controller implementation as software algorithm on a computer. In that article, we simplify the matter by omitting the effect of sampling period on the PID parameters. In practice, we may want to relate a chosen set of parameters in continuous-time, perhaps from simulation or some tuning rule, to its discrete-time representation. In this article we investigate such relationship on a commonly-used PID form.

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*Scilab-related articles are moved to our companion site: Scilab Ninja*

Scilab is a numerical computation software developed by Scilab Enterprises and has become my favorite choice for control engineering. Recently, so many posts on this site depend on this open-source software in some way. I now decide to construct another website Scilab Ninja specially for Scilab-related materials, including theRTSX (Robotic Tools for Scilab and Xcos). Some hightlights are Scilab Control Engineering Basics study modules that I use as supplement in my control design courses, and the use of scripts and Xcos models in certain control applications such as hardware-in-the-loop model development.

Our articles on PID control are scattered around related websites. Here we provide links to them, which will be updated periodically.

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