Relay Based Identification of Systems

In this paper, describing functions (DF) of relay with hysteresis is used for identification of systems. Describing function analysis is widely adopted in relay feedback-based identification methods because of the ease of computation involved and the general usefulness of the method. In process control systems, the noises come from measuring devices, control valves or the process itself. Dur ing the relay feedback experiments, amplitude of the limit cycle output is often corrupted with noises which may even fail the test. To overcome the possible failure, a relay with hysteresis is considered in the proposed identification method. Both off -line and on-line identification methods are presented to show the advantages of the online identification. The identification method is developed for a first order plus time delay (FOPDT) system although the method can be extended for higher order systems in a straightforward manner. A Simulation example is included to illustrate the use of the proposed method for both off-line and on-line identification. Index Terms – Describing function, FOPDT, Hysteresis, Identification, Off-line, On-line, Relay. ————————————————————