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Bandwidth, Gain and Phase Margin in Servo Systems: What is Amplitude Gain Margin?
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| 2 minute read
Amplitude gain margin is a measurement in the frequency domain, taken from a Bode plot, that takes the amplitude below 0 dB at the lowest frequency point that the phase reaches -180 degrees (phase crossover frequency). Amplitude gain margin is an indicator of servo stability - the further below 0 dB, the better the stability. The gain margin refers to the amount of gain adjustment available before the system becomes unstable.
Higher gains in a servo system improve responsiveness, up to the point at which the actual gain equals the available gain margin. Changes in the mechanical stiffness caused by wear can reduce the measured gain margin over time, causing an otherwise stable system to become unstable.