A three-stage automatic PID tuning system

This paper proposes a three-phase methodology to PID auto tuning in commercial digital regulators. The methodology is composed of three distinct steps. A pre-tuning phase is intended to tune a temporal PID, which is able to stabilise the process. A relay auto-tuning phase improves it according to the frequency characteristic of the process, giving an optimal setting on the ISTE criterion sense. The last step involves the operator in deciding how control should be improved according to some qualitative response features. This is accomplished with a fuzzy rule-based system. Desin Instruments company will implement it altogether in a commercial regulator.