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Entry  Mon Jan 19 18:27:16 2015, ericq, Update, ASC, QPD ASC saga continues.  oplevPlant.pdfloopDesignComparison.pdfJan16_newLoops_offOn.png
    Reply  Tue Jan 20 02:39:49 2015, ericq, Update, ASC, QPD ASC saga continues.  
    Reply  Tue Feb 10 18:37:17 2015, ericq, Update, ASC, QPD ASC ready to go Feb10_loops_offOn.pngFeb10_newLoops_offOn.xml.zip
       Reply  Tue Feb 24 18:54:26 2015, ericq, Update, ASC, Single arm QPD ASC stability trend.png
Message ID: 11061     Entry time: Tue Feb 24 18:54:26 2015     In reply to: 10997
Author: ericq 
Type: Update 
Category: ASC 
Subject: Single arm QPD ASC stability 

I've lowered the UGFs for the transmission QPD servos to ~1-2Hz, and made it just an integrator. I left the arms locked with the QPD servos on for a few hours during the daytime today, and they succesfully prevented the Y arm from losing power from alignment drift for ~4 hours. Turning the servo off caused TRY to drop to ~0.6 or so. 

The X arm was only held for 2 hours or so, because after some unlock/drift event the power was below the servo trigger threshold. However, after gently nudging ETMX to get the transmission above the threshold, the servo kicked in, and brought it right back to TRX=1.0

Unfortunately, daqd was dead for much of the day, so I don't have much data to show; the trend was inferred from the wall striptool. 

It is not proven that there aren't further issues that prevent this from working with higher / more dynamic arm powers, but this is at least a point in favor of it working. 

EDIT: Here's a screenshot of the wall StripTool. Brown is TRY, blue is TRX. The downturn at the very end is me deactivating the servos. 

There is no scientific justifcation for the 0.9 threshold. Really, I should look at the noise/SNR again, now that there is some ND filtering on the QPDs. 

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