ibrahim.abouelfettouh@LIGO.ORG - posted 12:18, Sunday 17 November 2024 - last comment - 13:59, Sunday 17 November 2024(81319)
OPS Day Midshift Update
We had a lull in the heavy winds during which I was able to get an initial alignment in and then up to DRMI locked.
The wind is now back up to the 30s mph and the IMC glitch is happening quite frequently (both on the rocky start-up to DRMI and thereafter).
Thus, I will be staying in DOWN until conditions improve.
Meanwhile, the HAM6 SHUTTER red alert came on with guardian telling me not to power up due to SHUTTER_FAILURE. I am investigating this.
Fast shutter worked and is working. (I was worried that the mirror was broken off but that's not the case, the shutter still opens and closes without an issue.)
From the guardian log (attached), it failed because AS_B_DC_NSUM was 20.3 when the shutter was closed and the threshold is 15. AS_B was 0.28. Fundamentally, this is because I reduced the gain of this DC path by 20dB and digitally compensated in search for an existing sensor that won't rail when lock is lost, and the same fast shutter test failure was observed (see alog 79104). Back then, I wrote "I adjusted the dark offset while IMC was unlocked but we can probably increase the threshold to 30 or so if it continues to bother us."
The dark offset has drifted enough to bother us at times (i.e. it is about 12 counts or so on average now), so I told Ibrahim to increase the thresholds only for AS_B, i.e.
PdBDarkLo=-40 # dark level low
PdBDarkHi= 40 # dark level high
in FAST_SHUTTER.py.
Since we now have a dedicated diode to look at lock loss power spikes, we can turn down the analog gain of AS_B_DC by 20dB and turn off +20dB filter in FM4 of H1:ASC-AS_B_DC_SEG[1234] filter, and adjust the dark offset again on Tuesday.
The mirror is still attached to the fast shutter and is moving. It actually closed using HV (see GS13 signal) when the test failed (2nd attachment), and later when I opened/closed it with low voltage drive it responded correctly (3rd attachment).