Evan, Sheila, Jeff B Ed

Earlier today we were knocked out of lock by a 5.2 in New Zealand, the kind of thing that we would like to be able to ride out.  The lockloss plot is attached, we saturated M3 of the SRM before the lockloss and PRM M3 was also close to saturating.  

While LLO was down, we spent a little time on the offloading, basically the changes described in alog 21084.  This offloading scheme worked fine in full lock for PRM, however we ran into trouble using it durring the acquisiton sequence.  Twice we lost lock on the transition to DRMI, and twice we lost lock when the PRM coil state swtiched in DRMI on POP.  Hpwever, we can acquire lock with the new filter in the top stage of PRM and SRM, but the old low gain (-0.02).  We've been able to turn the gain up by a factor of 2 in full lock twice, so I've left the guardian so that it will turn of the gain in M2 (before the intergrator) in the noise tunings step. 

If anyone decides they need to undo this change overnight, they can comment out lines 344-347 and  2508-2514 of the ISC_LOCK guardian. 

Before we started this, the PRM top mass damping was using 10000 cnts rms at frequencies above a few hundred Hz, because of problems in the OSEMS (alog 21060 ).  Evan put some low passes at 200 Hz in RT and SD OSEMINF which reduces this to 2000 cnts rms. Jeff B accepted this change in SDF.  

 The second attached screenshot shows the PRM drives, the references are in the minutes before the earthquake dropped us out of lock.  The red and blue curves show the current drives, with the high frequency reduction in M1 due to Evan's low pass, and the new offloading on.  The last attached screenshot shows SRM drives with the new offloading.