Relay based estimation of process model parameters

A set of general expressions is derived from a single symmetrical relay feedback test for estimation of model parameters of lower-order processes. Using the expressions the exact parameters of open loop stable and unstable first order plus time delay (FOPDT) and second order plus time delay (SOPDT) transfer function models may be obtained from simple measurements made on the limit cycle. Further, the expressions can be used to estimate lower-order models of a higher order process with great accuracy when the steady state gain of the process is known a priori. Examples are given to illustrate the novelty of the proposed relay feedback based identification method.