2015-07-23 00:56:48.936610  ISC_LOCK  NOMINAL_LOW_NOISE -> LOCKLOSS

This is similar to two types of locklosses we had (alog 18777).  AT that time, we thought there were two types, one in which SR3 slowly drifted away, and one in which we had a slow (20 second oscillation) that shows up in SRC ASC signals, and is seen in POP90.  We turned on the SR3 OpLev with DC coupling, and thought that took care of the slow run away.  We are still using this.  We thought that the slow oscillation was fixed by a change in the ASC matrix for AS 36 (alog 18923).   Since that time we have made many changes to the sensing matrix. 

 

The slow oscillation shows up in the SOFT loops, as well as the SRC ASC loops.

 

There is a simliar but more confusing event at 2015-07-23 03:57:49.960100  ISC_LOCK  INCREASE_POWER -> LOCKLOSS.  This one is more confusing for 2 reasons, the guardian was stuck at the lockloss time so it was recorded about 60 times in the log , and because we tried to lower the power at the end which makes the last few seconds unusual.