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Entry  Wed Jan 29 14:49:48 2020, anchal, DailyProgress, BEAT, Beanote Spectrum vs FSS Gain Values Beatnote_vs_FSSGain.pdf
    Reply  Wed Jan 29 15:58:26 2020, anchal, DailyProgress, BEAT, Beanote Spectrum vs FSS Gain Values Beatnote_vs_FSSGain.pdf
       Reply  Fri Feb 7 09:57:32 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in NFSS and checked beatnote NFSS_Spanned_Beatnote_Variation.pdf
          Reply  Fri Feb 7 18:12:03 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in SFSS and checked beatnote SFSS_Spanned_Beatnote_Variation.pdf
             Reply  Mon Feb 10 11:07:33 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in PMCs and checked beatnote PMC_Spanned_Beatnote_Variation.pdf
                Reply  Thu Feb 13 15:27:18 2020, anchal, DailyProgress, BEAT, Further iterated back and forth to optimized FSS Gains. FSS_Gain_Span.pdf
Message ID: 2522     Entry time: Wed Jan 29 15:58:26 2020     In reply to: 2521     Reply to this: 2524
Author: anchal 
Type: DailyProgress 
Category: BEAT 
Subject: Beanote Spectrum vs FSS Gain Values 
Quote:
I'll repeat this measurement again to make sure this optimal gain setting region was not a coincidence due to some other parameter out of my control.

Measurement

  • Everything is almost the same as the last measurement.
  • This time, if you notice from orange to yellow curve, I had to manually lower down the gain on the south common path by 12 dB instead of 3 dB to ensure the south path doesn't go into oscillations.
  • From there onwards, the gains were reduced normally by 3 dB in each step/

Inference

  • The beatnote spectrum indeed drops down to lowest when the gains are 3 dB below the maximum gains where I keep the loops.
  • Maybe keeping a large gain margin is important. But I need help to understand this result.
  • Also, it is kind of clear that the laser noise starts showing up from the yellow curve onwards only. So in current gain settings, the noise floor is probably due to something else.
  • Another weird fact I saw was that the RMS of error signal taken at "Mixer" port which is the TP5 point in LIGO-D040105-C_CTN_North increases significantly only after the gain values of the loop is decreased by more than 15 dB (to -1 dB each on FAST and COM).
  • The same thing can't be said for the south path where I see a gradual increase in this error signal RMS value as the gains are reduced.
  • If someone has a better idea of understanding these results or has some suggestions on further tests or a combination of parameter changes I should do, please let me know.

Data

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