Control of processes with time delays

The need to control processes with time delays can be found in many aspects of the metallurgical industry from refining to rolling mills. When the time delay becomes long compared with the system time constant, or when the time delay varies, then control of the process becomes difficult using classical control methods. Three controllers are evaluated for their applicability to this problem: the classic proportional-integral (P-I) controller; the Smith linear predictor; and the Clarke-Gawthrop self-tuning controller. Each of the controllers is implemented on an example process which is first-order with a long time delay. All three control strategies are evaluated for their response to step reference changes, step load disturbances, and variations in the process time delay. No one control strategy has the perfect solution, so the advantages and limitations of each strategy are presented and discussed