So I checked time series and spectrum for checking when this problem started and which frequency has large RMS, respectively.
According to the time series plot, it's occurred when IFO lock was recovered around 10:33. Precisely, it occurs ~5 second after LSC_LOCK guardian entered OVSERVING_WITHOUT_LINES.
By checking the spectrum of PZT feedback, RMS comes from the 2400Hz (and sideband?) series.
Because of the today's maintenance work, I need to postpone the investigation of this issue.
If someone can takeover, please check it more detail.
TTFSS gain seems to be fine (~9dB for both common and fast gains).
So it's not a same problem as klog#31662, at least.
Is it related to the sound of a bell inside the PSL room because of today's fire drill? I guess that 10:33 is just the time to push the warning button.
Yes. Technical staff would turn the bell off after the end of the fire drill. So the off of bell could be after 11:00 or so. How is the present situation of the spectrum ??
It looks fine, and Miyoki-san's prediction that the alert bell was the cause of this issue seems to be correct.
Figure 1 shows some signals from 9:00 JST to 21:00 JST yesterday.
Large RMS cannot be seen after finishing maintenance work (around t=-3h)
Because sampling rate of DQ channels for PMC feedback and microphone is lower than 4kHz, they cannot detect this issue (left panels in Fig.1). Only error signal (MIXER_MON_OUT_DQ) detected because its sampling rate was 16kHz. On the other hand EPICS channels without Anti-Aliasing detected as a aliasing noise (right panels). This fact means there is unfortunately no witness to see time series waveform of this disturbance.
Figure 2 shows the zoom up around 10:30 - 12:20. According to the EPICS channels of microphone signals, external disturbance disappeared around 11:44. Even if there is no enough sampling rate, EPICS channels without anti-aliasing is enough for checking just timing coincidence. PMC control was disengaged around 11:41 for the maintenance work. This is reason why the large RMS disappears on PMC control signals faster than on microphones.
