Implementação de sistema PI para controle de temperatura utilizando o método da frequência de Ziegler-Nichols

Abstract

Industrial process controllers are increasingly needed, and the most used are the on-off controllers and the PID (proportional-integral-derivative), which are widely used in industrial processes. The general purpose of this article is to implement a prototype of a temperature control automation system with PID, reviewing tuning concepts and methods in order to compare the effectiveness with the on-off controller. The on-off type control has two fixed positions, on or off, since the PID corresponds to the relationship between the read variable and the setpoint. There are several methods of tuning this type of controller including empirical methods to the most refined; but that usually involves three steps: disturbing the process, analyzing and quantifying the system's response to the disturbance, and then tuning the controller parameters. The frequency method proposed by Ziegler-Nichols consists of determining the critical gain and the critical period to obtain the tuning parameters. The apparatus for the experiments consisted of a thermal box to simulate the environment, with a temperature sensor inside and an incandescent lamp to generate disturbance of the variable, a fan to blow air into the environment, and the embedded system containing an Arduino and an electrical circuit board. Applying the proposed method to the experiments, we obtained the results for the P, PI, PID and on-off controls. When analyzing these results, it was verified that for such conditions, the best controller was the PI type.