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Entry  Mon Sep 9 20:46:28 2013, Masayuki, Update, LSC, MICH calbration 
    Reply  Tue Sep 10 17:35:50 2013, Masayuki, Manasa, Update, LSC, MICH calbration MICH_calib_loops.pngOLTF_MICHDC.pngMICH_DC_resp.pngMICH_RF_resp.pngMICH_free_noise.png
       Reply  Thu Sep 12 23:36:25 2013, Masayuki, Update, LSC, MICH calbration BSsus.PNGITMXsus.PNGITMY.PNGfree_running.PNG
          Reply  Fri Sep 13 19:22:01 2013, Masayuki, Update, LSC, MICH calbration noise.PNG
             Reply  Mon Sep 16 14:11:47 2013, rana, Update, LSC, MICH calbration Screen_Shot_2013-09-16_at_2.10.31_PM.pngScreen_Shot_2013-09-16_at_2.18.47_PM.png
                Reply  Tue Sep 17 00:50:42 2013, Masayuki, Update, LSC, MICH calbration noise.PNG
Message ID: 9134     Entry time: Tue Sep 17 00:50:42 2013     In reply to: 9131
Author: Masayuki 
Type: Update 
Category: LSC 
Subject: MICH calbration 

I found the bug in my calibration code, and I fixed it.

And I put the white Gaussian noise on the BS actuator, and calibrated to the differential length with my new code. We already know the efficiency of the actuator(elog#8242), so I could estimate how much I put the disturbance and compare the two values. The result is in attachment 1.  x_exc means the value of the disturbance. 

You can see the PSD of the differential motion decrease factor of 3 by decreasing the disturbance by factor of 3 (except for the region from 1 Hz to 5 Hz), and the value at lower frequency than resonant frequency of the suspension is comparable to the value estimated with the actuator efficiency. Also there is no dip when I put the larger disturbance than free running noise.

Between 1 Hz and 5 Hz there seems to be a resonance of something (seismic stack?). And also on resonance of the suspension there seems to be some other noise source. One possibility is the active damping of each suspension.

Actually still there seems to be a dip between 0.1 Hz and 1 Hz. But if you consider about those effect, I think this result doesn't seems to be so strange. But according to the documentation of LIGO document-T000058, which I found the seismic motion in 40 m Lab is written in, the seismic motion at 0.1 Hz is 10^-7. I'm not sure about this factor of 10 difference. One possibility is the geophone doesn't have good sensitivity at low frequency. I'm still not sure this result is really collect.



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