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Entry  Wed Jan 14 19:27:09 2015, ericq, Update, LSC, UGF servo now linear again 
    Reply  Thu Jan 15 03:18:11 2015, diego, Update, LSC, UGF servo now linear again 
       Reply  Fri Jan 16 04:14:05 2015, diego, Update, LSC, UGF servo now linear again 
          Reply  Fri Jan 16 20:37:52 2015, diego, Update, LSC, UGF servo now linear again 
Message ID: 10902     Entry time: Thu Jan 15 03:18:11 2015     In reply to: 10901     Reply to this: 10911
Author: diego 
Type: Update 
Category: LSC 
Subject: UGF servo now linear again 

The UGF servos were recommissioned today:

  • suitable values of frequency, excitation, phases and gain were found;
  • the phases were chosen in order to maximize the I signal and suppress the Q one;
  • the servos seemed sufficiently stable when in a quiet state, but they didn't performed well in other cases;
  • I also found out that DARM & CARM and MICH & PRCL are maybe too much coupled, but that could be actually due to the main loops rather than the UGF ones;
  • however, after some weird rampings with no apparent reasons, and after some quite bad and glitchy step responses, I found out that the effect of the chosen phases vanished: the I and Q signals were of the same order of magnitude again, probably causing the bad performance;
  • Jenne and I tried to increase che SINGAINs and COSGAINs (but keeping them equal to each other): this has the good effect of separating more the I and Q signals, but it's just a zoom effect: there still are mixing effects and, more important, some zero-crossings into negative values that cause the signal going into the servo to go crazy.

Our idea is that we need with some thinking about these servos and most of all try to figure out all this phase thing before we can start to trust the servos to be used for locking.

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