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Entry  Thu Aug 6 04:36:41 2015, ericq, Update, ASC, Reviving PRC angular feedforward 
    Reply  Tue Aug 11 02:26:46 2015, ericq, Update, ASC, PRC Angular FF Lives! fitExample.pngFFspectra.pngPITsub.pngYAWsub.png
Message ID: 11482     Entry time: Thu Aug 6 04:36:41 2015     Reply to this: 11489
Author: ericq 
Type: Update 
Category: ASC 
Subject: Reviving PRC angular feedforward 

Tonight, I've taken a bunch of data where the PRC is carrier locked and the ITM oplevs have the DC coupling FM turned on, as we use during locking. This is to inform new feedforward filters to stabilize the PRC angular motion, by using Wiener filtering with the POP QPD as the target, and local seismometers/accelerometers as witnesses. So far I've looked at the 1800 seconds leading up to GPS time 1122885600, but there has been plenty of locked time tonight if I need to retrieve more. 

I've also measured the PRM ASC output torque -> POP QPD spot motion with high (>0.95) coherence from 0.1Hz to 10Hz. 

Prefiltering so far consists of a 4th order elliptic LP at 5 Hz, with the target subtraction band being the 1-3Hz range. 

With offline FIR filtering, the RMS pitch motion is reduced by a factor of 3 just with the STS1_X data. IIR fitting remains to be done. 

The PRC yaw motion, which is marginally noisier, is a little more tangled up across X and Y. 

Plots / filters forthcoming pending more analysis. 

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