Oli, Sheila, Jim, Camilla
We've been having trouble keeping the ALS X arm locked, so Oli put the request for the X arm guardian to "UNLOCKED" which means that it asks the PLL to lock and nothing else. We've been sitting here for 15 minutes and see that the PLL can't stay locked in this configuration where the ground motion doesn't matter and the laser should easily stay locked.
The second two attachments show how much the fiber beatnote depends on outdoor temperature, it is now varying by more than 20dBm, while last summer with similar temperature swings it would only vary by 4dBm. This year the problem seems to be coming and going, for about a week at a time the temperature dependence seems to go away.
We won't be able to lock the IFO while the PLL is not staying locked like this, this problem seems to be coming and going recently, so it may explain a lot of IFO downtime.
At 20:03 I noticed that the PLL hadn't unlocked in 25 minutes, so I tried relocking the ifo and was able to get through to where we stop using ALS
20:45 UTC NOMINAL_LOW_NOISE
20:48 UTC Observing
TJ, Sheila
We looked at the PLL logic. When we are in observing, the PLL is requested to be locked. We see times when the logic stops trying to lock it, with H1:ALS-X_FIBR_LOCK_ERROR_CODE = 262144 = 2^18.
Looking at the attached medm screen, counting the error codes starting with 0, the 18th one is beatnote strength. This checks out because the beatnote momentarily dipped below -10dBm at this time, and the limit is -10dBm. TJ looked and the Y arm limit is -20dBm, so TJ changed the X arm limit to match and accepted that in SDF.
There is still an issue with the fiber beatnote having this strong temperature dependence that needs investigation, but this will stop it from preventing locking when it is on the edge for now.
