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Entry  Tue Feb 10 02:40:54 2015, Jenne, Update, LSC, Some locking thoughts on PRMI 
    Reply  Tue Feb 10 03:09:02 2015, ericq, Update, LSC, Some locking thoughts on PRMI 
       Reply  Tue Feb 10 13:48:58 2015, manasa, Update, LSC, Probable cause for headaches last night 
Message ID: 10992     Entry time: Tue Feb 10 02:40:54 2015     Reply to this: 10994
Author: Jenne 
Type: Update 
Category: LSC 
Subject: Some locking thoughts on PRMI 

[EricQ, Jenne]

We wanted to make the PRMI lock more stable tonight, which would hopefully allow us to hold lock much longer.  Some success, but nothing out-of-this-world.

We realized late last week that we haven't been using the whitening for the ASDC and POPDC signals, which are combined to make the MICH error signal.  ASDC whitening is on, and seems great.  POPDC whitening (even if turned on after lock is acquired) seems to make the PRMI lock more fussy.  I need to look at this tomorrow, to see if we're saturating anything when the whitening is engaged for POPDC.

One of the annoying things about losing the PRMI lock (when CARM and DARM have kept ALS lock) is that the UGF servos wander off, so you can't just reacquire the lock.  I have added triggering to the UGF servo input, so that if the cavity is unlocked (really, untriggered), the UGF servo input gets a zero, and so isn't integrating up to infinity.  It might need a brief "wait" in there, since any flashes allow signal through, and those can add up over time if it takes a while for the PRMI to relock.  UGF screens reflect this new change.

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