peter.king@LIGO.ORG - posted 10:37, Wednesday 21 November 2018 - last comment - 11:28, Wednesday 21 November 2018(45446)
ISS work
Looking over trend data from O2, the second loop ISS seemed to have operated with ~2.5% diffracted light.
This morning I adjusted the offset slider to diffract ~2.5% and re-adjusted the light level on the ISS
photodiodes. This should be okay for the second loop now. MEDM still indicates more than 50 W as the
output of the pre-modecleaner with the ISS on.
The transfer function was recorded for slider settings of 8.0 dB and 15.0 dB (ISSG8.jpg and ISSG15.jpg
respectively). When the slider is increased beyond the ~10 dB, there is a large increase in the noise
spectrum from ~80 kHz upwards (gains.png).
Images attached to this report
Comments related to this report
With the gain slider at 15dB, you ahve onlt 10 degrees of phase margin, so the increase of noise in the 80kHz region is likely due to gain peaking.
Looking at the open loop transfer function, the optimal UGF should be about 30 kHz, as in the first SR785 screenshot