LLO noted a 10 Hz comb that was attributed to the IRIG B monitor channel at the end station connected to the PEM chassis. (https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=71217)
LHO has agreed to remove this signal for a week to see how it impacts our DARM signal.
EX and EY cables have been disconnected.
Disconnection times
| EX | GPS 1400946722 | 15:51:44 Tue 28 May 2024 UTC |
| EY | GPS 1400947702 | 16:08:04 Tue 28 May 2024 UTC |
I checked H1:CAL-PCALX_IRIGB_DQ at gps=1400946722 and H1:CAL-PCALY_IRIGB_DQ at gps=1400947702. From 10 seconds prior to the cable disconnection to 1 sec before the cable disconnection, IRIG-B code in these channels agreed with the time stamp after taking into account the leap second offset (18 sec currently).
Note that the offset is there because the IRIG-B output from the CNS-II witness GPS clock ignores leap seconds.
I fixed things in https://svn.ligo.caltech.edu/svn/aligocalibration/trunk/Common/Scripts/Timing/ so that they run in the control room with modern gpstime package and also the offset is not hard coded. I committed the changes.
Please reconnect the cable soon so we have independent witness signals of the time stamp. There could be a better implementation but we need the current ones until a proper fix is proposed, approved and implemented.
I have checked the weekly Fscans to look for similar 1 Hz and 10 Hz combs in the H1 data (which we haven't see in the H1 O4 data thus far), or any obvious changes in the H1 spectral artifacts occurring due to the configuration change May 28. I do not see any changes due to this configuration change. This may be because the coupling from the timing IRIG-B signal may be lower at LHO than it is at LLO. I do notice that there is some change around the beginning of May 2024 that the number of line artifacts seems to increase; this should be investigated further. Attached are two figures showing the trend of 1 Hz and 10 Hz comb, where the black points are the average comb power and colored points are the individual comb frequency power values; color of the individual points indicates the frequency. Note that there is no change in the last black data point (the only full-1-week Fscan so far).
The IRIGB cables at EX and EY have been reconnected (PEM AA Chassis CH31).