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Entry  Tue Sep 7 18:00:54 2021, Tega, Summary, Calibration, System Identification via line injection raw_timeseries.pdfdemod_signals.pdfcal_noise_asd.pdf
    Reply  Tue Sep 21 11:09:34 2021, Anchal, Summary, CDS, XARM YARM UGF Servo and Oscillators added 
       Reply  Wed Sep 22 12:40:04 2021, Anchal, Summary, CDS, XARM YARM UGF Servo and Oscillators shifted to OAF 
    Reply  Tue Sep 21 11:13:01 2021, Paco, Summary, Calibration, XARM calibration noise XARM_signal_asd.pdfXARM_demod_timeseries.pdfXARM_demod_asds.pdfXARM_cal_0921_timeseries.pdf
       Reply  Wed Sep 22 11:43:04 2021, rana, Summary, Calibration, XARM calibration noise 
          Reply  Tue Sep 28 16:31:52 2021, Paco, Summary, Calibration, XARM OLTF (calibration) at 55.511 Hz OLTF_Calibration_Scheme.jpgXARM_POX_Lock_Model_TF.pdfXARM_OLTF_Total_Model.pdfXARM_OLTF_55p511_Hz_timeseries.pdfGmag_55p511_Hz_ASD.pdf
             Reply  Thu Sep 30 18:04:31 2021, Paco, Summary, Calibration, XARM OLTF (calibration) with three lines XARM_OLTF_Model_and_Meas.pdfGmag_ASD_nb_withTRX.pdf
Message ID: 16363     Entry time: Tue Sep 28 16:31:52 2021     In reply to: 16353     Reply to this: 16369
Author: Paco 
Type: Summary 
Category: Calibration 
Subject: XARM OLTF (calibration) at 55.511 Hz 

[anchal, paco]

Here is a demonstration of the methods leading to the single (X)arm calibration with its budget uncertainty. The steps towards this measurement are the following:

  1. We put a single line excitation through the C1:SUS-ETMX_LSC_EXC at 55.511 Hz, amp = 1 counts, gain = 300 (ramptime=10 s).
  2. With the arm locked, we grab a long timeseries of the C1:LSC-XARM_IN1_DQ (error point) and C1:SUS-ETMX_LSC_OUT_DQ (control point) channels.
  3. We assume the single arm loop to have the four blocks shown in Attachment #1, A (actuator + sus), plant (mainly the cavity pole), D (detection + electronics), and K (digital control).
    1. At this point, Anchal made a model of the single arm loop including the appropriate filter coefficients and other parameters. See Attachments #2-3 for the split and total model TFs.
    2. Our line would actually probe a TF from point b (error point) to point d (control point). We multiplied our measurement with open loop TF from b to d from model to get complete OLTF.
    3. Our initial estimate from documents and elog made overall loop shape correct but it was off by an overall gain factor. This could be due to wrong assumption on RFPD transimpedance or analog gains of AA or whitening filters. We have corrected for this factor in the RFPD transimpedance, but this needs to be checked (if we really care).
  4. We demodulate decimated timeseries (final sampling rate ~ 2.048 kHz) and I & Q for both the b and d signals. From this and our model for K, we estimate the OLTF. Attachment #4 shows timeseries for magnitude and phase.
  5. Finally, we compute the ASD for the OLTF magnitude. We plot it in Attachment #5 together with the ASD of the XARM transmission (C1:LSC-TRX_OUT_DQ) times the OLTF to estimate the optical gain noise ASD (this last step was a quick attempt at budgeting the calibration noise).
    1. For each ASD we used N = 24 averages, from which we estimate rms (statistical) uncertainties which are depicted by error bands (\pm \sigma) around the lines.

** Note: We ran the same procedure using dtt (diaggui) to validate our estimates at every point, as well as check our SNR in b and d before taking the ~3.5 hours of data.

Attachment 1: OLTF_Calibration_Scheme.jpg  823 kB  Uploaded Tue Sep 28 18:05:08 2021  | Hide | Hide all
OLTF_Calibration_Scheme.jpg
Attachment 2: XARM_POX_Lock_Model_TF.pdf  31 kB  Uploaded Tue Sep 28 18:05:57 2021  | Hide | Hide all
XARM_POX_Lock_Model_TF.pdf
Attachment 3: XARM_OLTF_Total_Model.pdf  22 kB  Uploaded Tue Sep 28 18:06:39 2021  | Hide | Hide all
XARM_OLTF_Total_Model.pdf
Attachment 4: XARM_OLTF_55p511_Hz_timeseries.pdf  33 kB  Uploaded Tue Sep 28 18:13:20 2021  | Hide | Hide all
XARM_OLTF_55p511_Hz_timeseries.pdf
Attachment 5: Gmag_55p511_Hz_ASD.pdf  26 kB  Uploaded Tue Sep 28 18:17:22 2021  | Hide | Hide all
Gmag_55p511_Hz_ASD.pdf
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