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Phase Margin and Gain Margin

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Newbie level 6
Feb 9, 2006
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gain margin

Dear all,

Anyone could explain to myself what's the meaning of PHASE MARGIN and GAIN MARGIN in Control Engineering System.

Hope to hear from you all soon.

Thanks & best regards,
Sie Kiam

gain margin phase margin

Look at this recent post for an explanation of phase margin
phase margin gain margin

how far or what extent the value of gain of a system can be increased is called as gain margin..if you increasing beyond that system will start to oscillate or simply it become unstable...
gain margin and phase margin

Gain margin is the amount you can increase the gain of a system before achieve the 0 dB gain, and phase margin is the amount of phase the system can lag before achieve the 180° phase lag.
In conclusion the gain and phase margins are a measure of how far from instability a system is.

phase margin and gain margin

Both margins are used to measure how stable the system is.

For phase margin it is the phase difference to 180 degree when the gain is 1

for gain margin, it is the gain when the phase shift reach 180 degree.

so it is two faces of the same coin.

just rememebr when you have 180 degree phase shift, if your loop gain is >= 1, then you have oscillation. That is why you want either one of two cases: 1. when gain is 1, you have certain phase margin; 2. when the phase shift is 180, you want the loop gain less than 1.

you also should note the difference between open loop gain, close loop gain and loop gain.
gain margin vs phase margin

refined form of Barkhausen criteria for oscilltors,,
or a boundary condition if violated ..leads positive feedback consequently oscillation and stability phenomenon

gain and phase margin

Phase margin is the difference in degrees from -180deg (or 360) when the loop gain is 0dB.

Gain margin is the gain in dB at the point where the phase is -180deg (or 360).

phase and gain margin

phase margin is the phase at gain crossover frequency and gain margin is the gain at the phase crossover frequency
importance of gain margin and phase margin

Consider a negative feedback system, if the feedback signal has same magnitude and 180deg phase, the resultant signal will be unstable. To get a stable feedback system, either the signal magnitude must be smaller (gain margin) or the phase delay must be smaller (phase margin).

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