Krishna

The low-frequency (<0.1 Hz) noise in c-BRS looked much higher (~10X) than normal and we also noticed that the frequency and Q of the system were lower than that measured at UW. We suspected that the flexures suspending the beam-balance might have been damaged. Therefore, today I replaced them with spares that are fairly close to the original ones in size.

As a consequence of the flexure replacement, the mass distribution of the beam-balance has changed, hence the 'd' value is likely to be much larger than the previous value (~ 3 micrometers). The balance has currently been tuned to ~50 mHz frequency, which is close to the original resonance frequency. As is normal after a new flexure replacement, the mean angular position is drifting in one direction and will likely settle in 1-2 days.

If the low-frequency noise improves, I will likley measure a tilt transfer function tomorrow and try to improve the 'd' value, if needed.