ABSTRACT
The role of the feedback controller is to produce a control action based on the set-point tracking error that, when implemented through the manipulated variable on the process, helps the controlled variable to approach the desired set-point. The most important feature of a feedback control system is the fact that it learns the process behavior through continuous measurements of the output and feeds the information back to the controller that commands certain change in the manipulated variable. Each element in feedback control loop should be considered as a physical system with an input–output pair. When the controller is switched from the manual mode to the automatic mode, the tracking error often forces the controller to produce a manipulated variable value that may be substantially different from its previous value. In general, there are several forms of the proportional–integral–derivative equation for practical purposes. Moreover, depending on the vendor, one may or may not have the ability to choose a specific form.
