Last year we found that a problem with the H1 GS13 was causing a .375hz feature in the motion of the table which showed up in the filter cavity. The root issue was a GS13 having a low gain compared to the other sensors. I was able to compensate by adding a digital gain of 2. During the vent, this gain got reverted at some point and the sdf accepted. I didn't fix this when I found it because it didn't seem to be causing the same issue, but it seems the feature has now returned. Doesn't seem to be causing problems for the filter cavity that I've heard of, but the ISI and SUS definitely see this feature.
First image are the side osems for FC2 while the IFO was locked, the crosshair is at .375hz, similar to what we saw in the past.
Second image is the HAM8 summary page for today, the .375hz feature is clearly visible while the ISI is isolated.
Third image are l2l tfs for each co-located gs13/cps pair, the red trace shows the magnitude of this tf is almost exactly half the other 2 gs13/cps pairs, above 1 hz.
I will try to fix this next Tuesday, but if the filter cavity is having problems, caput H1:ISI-HAM8_GS13INF_H1_GAIN 2 in a terminal and then accepting the sdf diff should fix the issue.
The filter cavity has been having locking issues, the operators were tieing sometimes to high wind 85169 or low green power 85395:
- 31st July 86113
- 18th July 85858
- 9th July 85664, 85660
- 4th July 85550
- More in June and July that I won't list....
After running calibration sweeps this evening and while H1 was still out of observing, I updated the GS13 gain as Jim describes above. The filter cavity saw some motion after I did this, but after a minute or two, things settled back out. I then accepted the SDF diff (screenshot attached) and took H1 back to observing.
