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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: 10911     Entry time: Fri Jan 16 04:14:05 2015     In reply to: 10902     Reply to this: 10916
Author: diego 
Type: Update 
Category: LSC 
Subject: UGF servo now linear again 

UGF Servos' commissioning still going on, updates of today:

  • on Rana's suggestion, we don't use anymore the Q-signal rejection at the level of Phase 1 and Phase 2; instead, a proper complex division is made between those two signals (with a check in case of zero); then the resulting signal is demodulated with a new Phase 3, which is the one used to select the I signal while zeroing the Q one; changes to the model and the screens have been made;
  • a new evaluation of all the parameters for the four servos has been made; aside for the new phase, and the zeroing of the other phases (because they are not used anymore for the selection), the parameters are not dissimilar from the prevoius ones
  • the PRCL and MICH servos seem sufficiently stable;
  • CARM and DARM are stable only for a short amount of time; what usually happens is that one of the two starts drifting in one random direction, and usually the other one follows shortly after; it is not clear if there is a relation or if they stop being stable after a similar amount of time; I still noticed a few lowest limits appearing in the input signal, which should be avoided; I'll check the model again tomorrow;
  • the weird thing about CARM and DARM is that at the same time when one of them starts drifting, its I and Q signals begin to be comparable; when the servo is shut off, they resume their normal state;
  • an increase in the excitation gain improves the separation of I and Q and also reduces their variations, but a high peak in the loop due to this might not be a good idea.


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