No abstract

The relay autotuner for PID control is based on the simple idea of investigating process dynamics by the oscillation obtained when the PID controller is replaced by a relay function. In this paper an asymmetric relay function is used, which provides an equation for the static gain of the process. A method to find the normalized time delay is proposed and the benefits of this is discussed. Ways to find low-order models from the experiment are described. Considerations of how to choose the relay parameters are made and some examples are given.

Abstract-This paper demonstrates how second-order timedelayed models adequate for PID controller synthesis can be identified from significantly shorter relay experiments, than used in previous publications to obtain first-order time-delayed models. Apart from having good noise robustness properties, the proposed method explicitly addresses non-stationary initial states of the dynamics to be identified, and handles constant load disturbances.

Abstract-The relay autotuner provides a simple way of finding PID controllers of sufficient performance. By using an asymmetric relay function the excitation of the process is improved. This gives better models, and hence a better tuning, without increasing the time consumption or complexity of the experiment. Some processes demand more accurate modeling and tuning to obtain controllers of sufficient performance. These processes can be singled out by their normalized time delays and be subject to further modeling efforts. The autotuner proposed in this paper provides a simple way of finding the normalized time delay from the experiment, and uses it for model and controller selection. The autotuner has been implemented and evaluated both in a simulation environment and by industrial experiments.

Abstract-In this paper two novel autotuners are compared with two industrially available ones. The aim is to see if the research frontline can improve the industry standard of today. Experiments are made on three laboratory processes with different characteristics. Two lag-dominated processes of which one is a level control problem with fast dynamics, and one a temperature control problem with slow dynamics, as well as one delay-dominated level control process. Both the experiments and the obtained controller performances are evaluated and discussed. The results show that the performance of the stateof-the-art industrial autotuners can be significantly improved.