Gain Margin Rule of Thumb

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Gain Margin Rule of Thumb
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1 Gain Margin Rule of Thumb

The gain margin is one of the robustness measures of a closed loop system under control. A low gain margin can cause instability. Specifically, no measurement is perfect and therfore no model is perfect. When creating a LTI model from measured data there are always gain variations that are ignored as inconsequential. However, the lower the gain margin the more consequential those gain variations become.

The gain margin can be determined from a:

  • Bode Plot of the open loop transfer function - magnitude at the frequency where the phase crosses -180 deg
  • Nichols Plot of the open loop transfer function - magnitude at the points where the phase crosses -180 dB

1.1 Minimum Recommended Gain Margin

A good rule of thumb for the gain margin is

Table 1: Minimum Phase Margin Recommendations
Application Minimum Phase Margin (20*log10 dB)

Tracking

6

Please feel free to add the recommended minimum phase margin for the applications you are familiar with.