Krishna, Jim

This is a slight variation on an earlier duty cycle analysis by Jim. I'm trying to establish how the new ISI-Stage1 control scheme implemented in O2 at LHO benefited the interferometer. As a reminder, in O1, we only used feedback from the Stage 1 seismometer and switched between the 45/90 mHz blends to combat microseism/wind respectively. In O2 we used 'tilt-subtracted' feedforward at low-frequencies and 250 mHz blends as the nominal configuration on all platforms including the HAMs. The data lives in:  SeiSVN/seismic/Common/Data/LHO_O1_O2_duty_cycle_data

The first attachment shows plots for duty cycle versus wind for O1/O2. It uses the minute trends of ISC Lock State and the ETMY windspeed (max) signal. The first page simply shows the distribution of wind - fraction of time windspeeds were in a given bin (bins were ~2 mph) during O1 and O2. The second page shows the fraction of the time the interferometer was locked at a given windspeed. Not only is there a clear improvement in O2, but the curve looks flat up to a windspeed of ~30 mph unlike in O1. The overall duty cycle in O2 seems to have suffered a bit, possibly due to other reasons. Pages 3 and 4 show similar plots, but only comparing the 45 mHz blends used in O1, which are still the default configuration at LLO. Again, it is interesting to note the downward trend on page 4 for the 45 mHz blend, which suggests that even 10-20 mph winds would begin to impact the interferometer.

The second attachment has very similar plots for duty cycle versus microseism velocity, using the band-limited-rms ITMY_Z (max) signal in the microseism band. The O2 configuration looks better once again and there is a similar trend of nearly flat duty cycle up to ~1300 nm/s velocities in O2. The distribution of the velocities looks odd/different, partly because of the inclusion of Hanford summers in O2, which are very quiet in the microseism.