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Entry  Wed Nov 21 21:06:13 2012, Ayaka, Update, LSC, calibration of arms 7x
    Reply  Sat Nov 24 13:58:07 2012, rana, Update, LSC, calibration of arms 
       Reply  Mon Nov 26 10:42:06 2012, Ayaka, Update, LSC, calibration of arms armcalib.zip
Message ID: 7738     Entry time: Wed Nov 21 21:06:13 2012     Reply to this: 7739
Author: Ayaka 
Type: Update 
Category: LSC 
Subject: calibration of arms 

Motivation

In order to estimate whether we can see acoustic coupling in arms or not, we have to calibrate signals to phase noise.

Method

I used the same method as Yuta and Jenne did (6834).
I switched from ETM locking to ITM locking since only ITM actuators are calibrated (5583), and measured the open loop transfer function and the transfer function from ITM excitation to POX/POY error signal. Then I can estimate the calibration value H [counts/m] from POY/POX error signal to displacement.

Results

Yarm; H = 9.51 x 1011 counts/m
  OL_y.pngerr_exc_y.pngPOY_disp_y.png

Xarm; H = 6.68 x 1011 counts/m
OL_x.pngerr_exc_x.pngPOX_disp_x.png

Phase noise in arms:
XY_phase.png
blue; Xarm, green; Yarm

 

Next Step

I will calibrate the acoustic signal and see if it is reasonable that we can see the acoustic coupling signal in the arms.
But I guess it is difficult. Actually I have not seen coherence between ETM feedback signals and acoustic sounds yet. (I measured acoustic noise near POX and in PSL table.)

If I find that it is hopeless, I will create some sounds and try to measure transfer function from acoustic sound to arm cavity signals.
I am interested in how the transfer function calculated by wiener filtering is different from the measured transfer function.

 

Note

I found that we do not have enough phase margin. This is why the arm locking is not so stable.

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