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Control System Damping

Closed loop control systems don't always work as well as they ought to.

The problems are caused by electronic and more often by mechanical inertia and delays.

These graphs show some of the problems.

Graph B shows an over damped system. It takes too long to reach a steady state.

Graph D shows a critically damped control system. It reaches a steady state in the shortest possible time without overshooting.

Graph A shows an under damped system. This one overshoots before eventually settling down.

Graph C is the worst. In this case it overshoots and never settles. This is called hunting.

Often the critically damped case is the best choice. Graph A, under damped, can be better if the goal is to get the control system to within, say, 20% of the target as fast as possible and some overshoot and oscillation can be tolerated.