Control-system design for minimum bandwidth

THIS digest discusses a method of designing feedback control systems so that for a specified performance their bandwidth is a minimum. Not infrequently, engineers have designed control systems with the objective of minimizing errors; with attention focused on the problem of minimizing errors there is a tendency to use bandwidth inefficiently so that he manufactures increased difficulties. He may open up the bandwidth of the control system to the point where he has undue transmission of noise. In the case of mechanical systems, he may increase the bandwidth to the point where elastances in gear boxes and supporting structure will cause severe stability problems. As the result of large bandwidth, he may encounter a saturation problem in one of the components toward the output end that would not otherwise exist. Expanding the bandwidth of a control system may require him to use more expensive components than are really necessary. For these and many other reasons he should strive to keep the bandwidth requirements of a feedback control system as low as possible.