Michael, Krishna
We did more sensor correction (SC) tests today with mildly windy conditions. This was similar to the tests reported in 26455. However, we had made one important mistake in that test - the CPS value reported was before the blend filter input which is measured after sensor correction. This was wrong, it needs to be measured before SC (using H1:ISI-ETMY_ST1_SCSUM_CPS_X_IN_DQ). This is a more accurate measure of the local table motion.
As before, the four configurations were: a) 90 mHz blends, b) 90 mHz blends and SC using BRS, c) 45 mHz blends, d) 45 mHz blends and SC using BRS and we also tested e) 90 mHz blends and SC without using BRS.
The two measurements for End Y (BRS-2) and End X (BRS-1) are shown in the attached pdfs. We saw very similar looking results in both.
The wind-speed varied between 5-20 mph with a rough average of ~12 mph for EY and ~9 mph for EX. First page shows the Stage 1 T240 motion and as before 45m+BRS_SC gives the best performance, with 45m, 90m+BRS_SC or 90m+SC configurations giving roughly the same performance. The next page shows the RMS of the CPS signals before the sensor correction. 90m has the least CPS motion with 90m+BRS_SC being the next best. SC using BRS and not using it (with or without tilt-subtraction), can be compared by using the blue and yellow/orange lines respectively. The third page shows the ground motion during each configuration and the corresponding tilt-subtracted signal.
Some comments:
1) The sensor correction filter used here (Mitt_SC) is a broadband filter going down to 30 mHz. We may want to tune it for 40-50 mHz instead, to reduce the low-frequency motion.
2) Based on the results so far, the best configuration for 0-10 mph wind-speeds (LOW wind) might be 45 mHz blends+BRS_SC which gives the best isolation (a factor of ~50-100 at the microseism!). And for winds above 10 mph (HIGH winds), 90 mHz +BRS_SC might be best. This is the same configuration that was followed for O1 but with the addition of SC using BRS.
This afternoon, we recentered the DC position of the beam-balance. Due to the process, the amplitude is very high so we are using this opporunity for a Q measurement.
