Restricted structure controller tuning and performance assessment

A typical process plant includes hundreds of PID controllers and many of these require tuning. The economic operation of process plant and machinery controls depends upon the controller structure and the choice of tuning variables. The problem of defining a benchmark cost, which relates to financial requirements and involves realistic control activity, is considered. The computation of the cost, for an existing PID controller and the best-tuned restricted structure controller, is discussed. The use of these benchmark figures of merit for controller re-tuning is considered.