aLIGO LHO Logbook

H1 SEI (DetChar)

jeffrey.kissel@LIGO.ORG - posted 16:27, Tuesday 14 April 2015 - last comment - 20:24, Tuesday 14 April 2015(17872)

BRS Gravitational Damper Disabled

J. Kissel, J. Warner

We noticed that the wind / tilt at EX was so large that the peak-to-peak amplitude of tilt as measured by the BRS was surpassing the level at which the BRS's gravitational damper turns on. Since we're trying to get data in these high wind conditions, we've gone to the X end and and turned OFF the gravitational damper from the laptop software.
Will turn on again some time soon when it's less windy.

Comments related to this report

jeffrey.kissel@LIGO.ORG - 20:24, Tuesday 14 April 2015 (17880)

Link

Just a reminder (mostly to myself) -- turning off the gravitational damper, by commenting out its drive signal computation in the laptop's software and then restarting the software, renders the BRS useless for an hour or more because of impulse response of the 1 [mHz] high-pass that's applied to the analog signal.

I.e. If you're trying to use the BRS quickly after a software restart -- don't count on it!

Post email checking edit: Krishna reminds me that one can reduce the impulse by setting the DC offset compensation to the value record just before killing the software. We (Jim and I) consciously decided that the offset was too small to need updating in the software. We were wrong!