Implementation and testing of an advanced relay auto-tuner

In this paper, an advanced relay feedback auto-tuner for single-loop controllers is presented. The tuner combines an improved relay feedback process frequency response identification method and a multiple-point frequency response fitting controller design method. In process identification, multiple accurate points on the frequency response curve of a process are obtained in one single relay feedback test. A controller is then designed based on these estimated points using frequency response fitting methodology. The auto-tuner was implemented on a personal computer with AD/DA card. The software was developed on a commercial real-time control platform. The algorithms were written in C++ and compiled as a Dynamic Link Library. The auto-tuner has been tested on a dual-process simulator which can be easily configured as various typical processes, and on pilot coupled-tank and heat exchanger. The testing results show that the tuner gives significant performance improvement over the standard relay auto-tuner.