craig.cahillane@LIGO.ORG - posted 15:50, Wednesday 29 August 2018 - last comment - 04:41, Thursday 30 August 2018(43733)
IMC OLG
UGF = 37.5 kHz Phase Margin = 46 degrees
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Craig measured this because we have been having difficulty staying locked today, and we have been suspicious of a problem with CARM.
It seems like we were loosing lock due to some very fast transients within a few minutes of switching to ANALOG CARM. We took the CARM boost out of the guardian and we are now staying locked for longer.
One concern is that there seems to be some changes on the PSL since yesterdays work. Tomorrow morning Peter King is going to look into why the ISS 1st loop noise has increased a lot.
Yesterday I noticed that even with the second loop ISS disabled but with its output enabled, that this caused the large variations in the diffracted power. With the output disabled, the first loop ISS seemed to behave as usual. Not sure why this would be the case, other than there is a lot of gain in the second loop. However it might be that the second and third loops have a set point that needs to be reset somewhere (I unfortunately do not know where it is, if true).