Krishna, Michael

We took a look at the noise of BRSX with damping forced on and off now that the new damper is installed. For context, the previous damper injected lots of broadband noise which made the BRS unusable during damping. The first plot in the attachment shows that with the new damper we get comparable tilt subtraction whether the damping is on or off. The second plot is a more broadband view of the BRS noise and shows that the damping rings up the torsional mode (~3 Hz) and some other higher frequency modes but doesn't change the broadband noise. The wind picked up right when we forced the damping on so there's an overall increase in low frequency motion.

After taking the measurements with the damping forced on (~1 hr), we found that the BRS had started drifting rapidly which decreased the ability to subtract tilt. This is due to the heat generated by the stepper motor that drives the turntable. In normal operating conditions, the damper shouldn't ever need to run for this long and thus shouldn't create such a large of a drift.

The take away from this is that the BRSX sensor correction need not be turned off if damping does trigger. The tilt subtraction might not be very effective shortly after damping but it should still be useable.