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Entry  Fri Apr 10 17:05:45 2015, ericq, Update, LSC, Relative ETM calibration (Rough MC2 calibration) quickCal.png
    Reply  Fri Apr 10 18:39:39 2015, ericq, Update, LSC, Relative ETM calibration (Rough MC2 calibration) betterCal.png
       Reply  Mon Apr 13 19:34:02 2015, ericq, Update, IOO, Modulation Frequency Tuned to IMC Length fMod_tuning.pdf
Message ID: 11215     Entry time: Fri Apr 10 18:39:39 2015     In reply to: 11214     Reply to this: 11216
Author: ericq 
Type: Update 
Category: LSC 
Subject: Relative ETM calibration (Rough MC2 calibration) 

I didn't verify that the loop gain was low enough at the excitation frequencies. blush

I put a 1kHz ELP in both arm servos, and got cleaner data for both. The ETM numbers are pretty much consistent with the previously posted ones, and the MC2 data now is consistent across frequencies. However, the MC2 numbers derived from each arm are not consistent.

Now:

  • ETMX / ITMX: 2.831 +- 0.043
  • MC2 / ITMX: 3.260 +- 0.062
  • ETMY / ITMY: 2.916 +- 0.041
  • MC2 / ITMY: 3.014 +- 0.036

With the data from ELOG 8242, this implies:

  • ETMX: 13.31 +- 0.21 x 10-9 / f2 m/counts
  • ETMY: 13.59 +- 0.20 x 10-9 / f2 m/counts
  • MC2 in Xarm meters : 15.32 +- 0.30 x 10-9 / f2 m/counts
  • MC2 in Yarm meters : 14.04 +- 0.18 x 10-9 / f2 m/counts
This is, of course, pretty fishy. Each arm sees the same frequency fluctuation of the light coming out of the IMC, especially given that the MC2 to arm data was taken simultaneously for both arms. Now, one possible source of this kind of mismatch would be a mismatch of the arm lengths, but there is no way they differ by 10%, as they would have to in order to explain the above numbers. To me, it seems more likely that the ITM calibrations are off. 
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