A PID controller is designed by dominant poles placement method for an
unstable first order plus time delay system. The robustness of the pr
oposed controller is evaluated for perturbations in time delay, time c
onstant and gain. The performance of the proposed controller is compar
ed with that of the PID controller settings given by DePaor and O'Mall
ey (1989). The robustness of the control system is theoretically also
evaluated by Kharitonov's method (1978).