The main part of the control system

The main part of the control systems are still the PID regulators. Control theory deals with defining their parameters. The starting point of the PID regulator constants calculation is a simple experiment apart from the algebraic approach. A simplified system model is created on the basis of the experiment. The PID regulator constants are calculated from parameters of the identified system model. The idea of the automation of this process is evident and the most of the PID controllers are equipped by some self tuning algorithm (self tuner). There are several methods for tuning PID controllers. Generally it can be distinguished between model based self tuner and none model based self tuner. The controlled system is generally identified as three or four parameters model (a first-order system with delay time or a second order system with delay time) and the constants of the controller are calculated according to the identified model in the case of the model based self tuner. The constants of the controller are directly edited according to the parameters of the measured responses in the case of non-model based self tuner. The following text in this chapter describes the most used self tuning methods and their implementation in the commercial PLCs. Methods based on step response are primarily used for the systems with slow response (e.g. temperature systems) and are based on measurement and evaluation of the step response of the controlled system as the reaction on the set point change. The controlled system is identified as three or four parameters model.