sheila.dwyer@LIGO.ORG - posted 20:16, Monday 12 September 2016 - last comment - 00:54, Tuesday 13 September 2016(29638)
CARM gain too high
Jenne, Evan, Sheila
Since Saturday (after RH settings were changed and we recovered from the power outage) we have been having sudden locklosses in the Analog CARM transition and the next few states. We measured the CARM open loop this afternoon and saw that the gain was too high leaving us with too little phase margin (blue trace in screenshot). We reduced the gain in the common mode summing junction by 8 dB (from 16dB to 8dB), green trace in the attachment. Both measurements in the attachment were taken at DC readout.
Evan's model of the CARM loop can be found at 22188
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Since lowering this gain we haven't had any more of the locklosses shortly after switching to analog carm.