RELAY-BASED ESTIMATION OF MULTIPLE POINTS ON PROCESS FREQUENCY-RESPONSE

In this paper, a new technique for process frequency-response identifi cation is proposed, which can identify multiple points on a process fr equency response from a single relay feedback test. A modified relay i s proposed and it can effectively excite a process not only at the pro cess critical frequency omega(c) but also at 0.5 omega(c) and 1.5 omeg a(c). As a result, the process frequency responses at multiple frequen cies around omega(c) can be accurately estimated from one relay test u sing the FFT algorithm. The technique has been tested on various proce sses in real-time. The results show that the method is insensitive to noise and steplike load disturbance. The technique can also be easily extended to identify other frequency-response points of interest. (C) 1997 Elsevier Science Ltd.