Dynamic model identification of a real-time simple level control system

Abstract

Using a relay feedback approach, mathematical expressions for identification of real-time level control system in transfer function form are proposed in this paper. An ideal relay with hysteresis is feedback to a simple level control system for the generation of sustained oscillations. Subsequently, limit cycle information is utilised in deduced expressions for the estimation of unknown system parameters. Using describing function analysis, the gain of an ideal relay with hysteresis is approximated to yield simple mathematical expressions. Typical examples from literature are considered to show the effectiveness of the proposed identification scheme. Yokogawa distributed control system: CENTUM CS 3000 is considered as a platform for the realisation of both relay feedback and Ziegler–Nichols (ZN) method. The accuracy of derived transfer function models is compared with a model derived from ZN method and thereafter demonstrated through frequency response plots which illustrate the experimental validation of the identified real-time process model.

Keywords:

• Describing function
• level control system
• limit cycle
• process identification and relay feedback

Acknowledgements

The authors would like to thank the Department of Electronics & Instrumentation Engineering, National Institute of Technology Agartala, Tripura(W), India, for providing the state of art laboratory facilities to carrying out experimental work. The authors also extend their sincere gratitude to the anonymous reviewers for their valuable comments and constructive suggestions with regard to this paper.

Notes

No potential conflict of interest was reported by the authors.