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Thu Sep 4 14:43:58 2008
PMC Open Loop Gain
I have measured the PMC's open loop gain.
UGF is 629.7Hz, with a phase margin of 53 degrees.
I injected into FP2 on the front panel, and measured MixOut/Source from 100Hz to 100kHz using the SR785. I did this both when the loop was open, and when the loop was closed (open the loop by enabling FP1, which breaks the loop).
We have 2 transfer functions involved: The actual open loop gain of the PMC servo loop (G1), and the gain between FP2 and the MixerOut monitor point (G2). This gives us:
TF(closed loop) = G2*(1+G1)
TF(broken loop) = G2
G1 = TF(closed)/TF(broken) - 1
This G1 is the final open loop gain, and it is plotted below.