Process frequency response estimation from relay feedback

Qing Guo Wang, Chang Chich Hang, Qiang Bi

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)


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,ω(c)], 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.

Original languageEnglish
Pages (from-to)1293-1302
Number of pages10
JournalControl Engineering Practice
Issue number9
Publication statusPublished - Sept 1997
Externally publishedYes


  • FFT
  • auto-tuning
  • frequency responses
  • identification
  • relay feedback

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Applied Mathematics


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