Identification and control of open-loop unstable processes by relay methods

This paper describes a reliable automatic PID tuning method for open-loop u nstable processes. Identification with low order models is performed by mea ns of two relay tests, one with an additional delay, which does not require a priori knowledge about the process, with the only necessary condition be ing that the process be gain stabilisable. This paper provides an overview of the method, states conditions that need to be satisfied for its successf ul implementation, and demonstrates its application on a number of examples . (C) 2001 Elsevier Science Ltd. All rights reserved.