Effect of dead time on closed-loop regulation

The steady-state performance of closed-loop regulation in the presence of random disturbance is found to be dependent on a crosspower term. Without dead time, this term is negative, resulting in good disturbance rejection. The presence of dead time will increase the crosspower term and may even reverse its sign, resulting in poorer performance. Furthermore, the closed-loop regulation may be worse than the open-loop, and a decrease in the controller gain may be needed to improve disturbance rejection.