(Reference alog 37923 and its comments) FRS 8666

In the past two evenings H1 was taken out of observation mode by a transient SDF difference on SUSITMX. Conlog reports that the channel being changed is H1:SUS-ITMX_HWWD_STATE (I had previously incorrectly said conlog did not see any change, but my query was in error).

Trending the ITMX_HWWD_STATE does show it flashing an LED error once in a while, which has been a known issue from before O2 and presumed related to the longer monitor cable in the corner station between the HWWD unit in the CER and the satellite-amp box in the Biergarten. No such transients are seen in EY where the cable run is shorter. Trends show the HWWD-LED glitching every day at a rate of 5-10 per day. So my first questions was: why has this not taking H1 out of observation-mode before? Here is the answer:

We know the LED monitor voltage dips below the trip level during loss-of-lock and lock-acquisition when the DAC outputs are being driven more aggressively. Trends show that prior to this week all the HWWD glitches had occurred when H1 did not have a range, an indication it is not in observation mode (an example 24 hour trend is the bottom plot of attachment).

On Monday and Tuesday evening this week the HWWD LED glitched for 3 seconds each time when the DACs were relatively quiet. Top plot of attachment shows Tuesday's event, middle plot shows Monday's event. This could be an indicator that this signal is slowly degrading. Why it only happened once per day, and on each day between the local times of 5pm and 6pm, we can only assume this is a coincidence.

On reflection, the SDF should not be monitoring these HWWD STATE channels. With Vern's approval I have taken them out of the OBSERVE.snap for the four quad suspensions (these are the only systems with HWWD units). 

Attached are three 24 hour minute trend plots. In each plot, upper channel is the H1 range, lower is the ITMX HWWD STATE (0=good, 8=LED error). Bottom plot is a normal situation where there are no HWWD diffs when the IFO is in observation mode. Top plot shows Tuesday loss-of-observation-mode (spike near left margin), middle plot shows Monday loss-of-observation-mode (second spike in from left).

Here are the SDF changes to the OBSERVE.snap files:

-H1:SUS-ETMY_HWWD_STATE 1 0.000000000000000e+00 1
+H1:SUS-ETMY_HWWD_STATE 1 0.000000000000000e+00 0

-H1:SUS-ETMX_HWWD_STATE 1 0.000000000000000e+00 1
+H1:SUS-ETMX_HWWD_STATE 1 0.000000000000000e+00 0

-H1:SUS-ITMX_HWWD_STATE 1 0.000000000000000e+00 1
+H1:SUS-ITMX_HWWD_STATE 1 0.000000000000000e+00 0

-H1:SUS-ITMY_HWWD_STATE 1 0.000000000000000e+00 1
+H1:SUS-ITMY_HWWD_STATE 1 0.000000000000000e+00 0