Sheila, Varun, Jenne

This morning I found that IFO had relocked and lost lock at engage ASC 10 times in a row (some of those where while people were here last night, several more after they left).

• Stopped at PREP_ASC, where the very rung up 1kHz violin modes caused pum WD trips for both ITMX and ITMY. I sat there for about an hour manually damping serveral modes and made some changes to the violin mode guardian:
  • waiting 160 seconds after the monitors are cleared, before moving on.  This should give the monitors a chance to settle before we check them to decide if a mode is rung up and needs low gain (or if the mode doesn't need to be damped while we are on RF at all).
  • Tried not clearning the monitor history to see if this would help the monitors settle faster.  (This was much slower than clearing and waiting for the impulse from clearing the history). 
  • lowered the threshold for when we consider a mode rung up based on its monitor, which should be possible since we wait longer for the monitor to be cleared. 
  • When a mode is rung up, engage it with 1/100th of the normal damping gain.  We used to do a calcaultion which would scale the gain with the monitor, but this simpler approach should be fine and maybe less likely to set the gains too high. 
  • While we are damping on RF, checks for PUM WD trips and turns off damping for that suspension if it is tripped.
  • Operator request:  It would be nice to add something to the OPS overview that would indicate when one of the PUM watchdogs is tripped...
• It looks like the ASC problems from last night and this morning are mostly due to CHARD Y being away from it's error point (as Dan wrote), even though our initial alignment looks good and we are arriving in lock with a good recycling gain.  This is similar to problems we were having with ASC towards the end of O3a.
  • We lowered the CHARD Y gain used for engagement from 2.5 to 0.5, and added a line after the convergence checker (when the soft limiters get turned off) to increase it to 2.5.  (This has been undone)
  • We have elimintated the INP1 soft limiter, since INP1 is a loop that has trouble keeping up with the other loops during engagement it doesn't seem to make sense to limit it. (This has been undone)
  • Jenne reduced the smoothing in the smooth limiters. 
  • We re-ran initial alignment
  • We found that the ASC REFL B whitening was changed yesterday after our last lock. This happened after our last sucsessfull lock, and before 22 locklosses whlie engaging ASC, so we are un-doing it. 
  • We found that the AS AIR 45 whitening gain was increased by 6dB yesterday afternoon, also after our last lock.  Jenne manually set the digital gains down and we tried engaging the ASC, this also didn't work, similar lockloss.  
  • We re-set the AS45 whitening gain in analog.  Yesterday morning I had re-engaged the second stage of AS_C whitening, which had been on in O3a but was turned off sometime durring the vent.  We believe this is OK, and we did lock once this way yesterday, but I've reset it to only one stage of whitening for AS_C.
  • By doing various things, we were able to get through parts of the ASC engagement, but never to get it fully engaged.  Sometimes we lost it by engaging SRC1Y, sometimes when turning off the offsets in AS_36Q.  The furthest we've gotten so far is by engaging everything in the ENGAGE_ASC state except SRC1 Y, allowing ADS3 (PRM) to converge slowly while the power recycling gain recovered.  We lost this when we turned off the AS36Q offsets.