We saw a large glitch in the RF AM monitors with high coherence with DARM at around 16:13 UTC on Sept 22nd, while the IFO was locked and maintence was happening. There werw people in the LVEA (though not near the PSL) and people in the CER but they were near the SEI and SUS racks, not the ISC racks. The first attached plot shows this on a 5 hour time scale, the second plot has 5 days. This can be compared to Evan's plots of the last 3 weeks (21766)
Starting around 2015-09-22 17:51:00 Z we had a few minutes or what appeared to be full-on instability of the RFAM stabilization servo. The control signal spectrum was >10× the typical value from 10 to 100 Hz. [Edit: actually, it looks like glitching; see below.]
I tried turning the modulation index down by as much as 1.5 dB, but there was no clear effect.
I've attached time series as a zipped DTT xml for the driver channls (control signal, error signal, OOL sensor) during such a glitchy period.
In the control signal, all the glitches I looked at have the same characteristic shape (see the screenshot with the zoomed time series): an upward spike, a slight decay, a downward spike, and then a slower decay back to the nominal control signal level.
The control signal during the Γ-reduction attempts seems quite smooth; the 0.2-dB steps do not produce glitches.
