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