Abstract
The applicability of the basic relay tuning method is extended by a robust on-line method to tune proportional–integral controllers without breaking the closed-loop control. A relay is connected in parallel to the controller to induce self-oscillation and then simple measurements are made only on the half period of limit cycle output to obtain a first-order plus dead time model of the process dynamics. A non-iterative optimum tuning formulae is developed in order to reduce the control signal variations. The simulation and experimental studies are presented to validate the design method.
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