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Entry  Tue Feb 18 23:55:33 2014, Jenne, Update, LSC, ALS locked with LSC! 
    Reply  Wed Feb 19 00:35:23 2014, Koji, Update, LSC, ALS locked with LSC! 
       Reply  Wed Feb 19 01:33:03 2014, Jenne, Update, LSC, ALS locked with LSC! ALS_XARM_LockingFilters.pdfALSvsLSC_AllLockingFilters.pdfLSC_XARM_LockingFilters.pdf
          Reply  Wed Feb 19 03:07:22 2014, Jenne, Update, LSC, ALS locked with LSC! 
Message ID: 9651     Entry time: Wed Feb 19 01:33:03 2014     In reply to: 9650     Reply to this: 9652
Author: Jenne 
Type: Update 
Category: LSC 
Subject: ALS locked with LSC! 

I am also not able to lock the ALS using the 'regular' LSC filters.  To figure out what filters were doing what, I made several comparison plots from Foton.

The first one is the progression of ALS locking, using the filters from ALS-XARM.  FM5 is always engaged, then FMs 2, 3, 6, 7, and 8, and finally FM 10 (the low frequency boost) is engaged.


The next plot is a comparison between the ALS version of the filters, and the LSC-XARM equivalents. 


Finally, just so I remember which LSC filters do what, I made an equivalent of the first plot, but for the LSC filters.


When I try to lock the Xarm ALS using the regular LSC filters, I'm getting an oscillation somewhere, that grows and eventually knocks me out of lock.  It looks from dataviewer to be in the ~few Hz range, but it's hard to see it in DTT, since I don't stay locked all that long once the oscillation starts.  (If I catch it, I can back off the gain and turn off the servo without losing lock, but if I don't turn off the servo, I inevitably push the ETM too hard and lose green lock to the arm.)  I tried engaging the 3.2 Hz resonant gain filter, and it just makes things oscillate sooner, so that's not a solution with the current filter designs. 

Also, I'm not able to lock the IR using the ALS version of the XARM filters.  I'll have to meditate more on the situation, but the filters seem to be different enough that there's no crossover at this point.

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