Article

Process frequency response estimation from relay feedback

Department of Electrical Engineering, National University of Singapore, Singapore 119260
Control Engineering Practice (Impact Factor: 1.91). 09/1997; 5(9):1293-1302. DOI: 10.1016/S0967-0661(97)84368-7

ABSTRACT In this paper, a method for process frequency response identification is proposed, which can identify multiple points on process frequency response from a single relay feedback test. The process input and output transients resulting from a relay feedback cannot be directly converted to the frequency domain to obtain a process frequency response using FFT. A decay exponential is then proposed to modify the process input and output, so that the process frequency response can be identified with the help of FFT. Real-time testing of the method on various processes gives quite accurate process frequency responses, especially in the frequency range [0, ωc], which is important for control design and process modelling. The method inherits and extends the advantages of the original relay auto-tuning technique. It can be easily applied to PID auto-tuning and to transfer function modelling.

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