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Entry  Mon Jul 27 16:47:53 2015, ericq, Update, IOO, MC2 -> MCL Actuator TF mc2_2_mcl.pngMC2_2_MCL_TF.txt.zip
    Reply  Thu Jul 30 02:06:20 2015, Ignacio, Update, IOO, MC2 <-> MCL Actuator TF fitted TF_BODE.pngMC2_2_MCL.pngTF_INV_BODE.pngMCL_2_MC2.png
    Reply  Wed Aug 12 22:33:36 2015, Ignacio, Update, IOO, Re-measured MC2 -> MCL TF bode_TF.pngCoherence.png
    Reply  Fri Aug 28 20:15:49 2015, rana, Update, IOO, MC2 -> MCL Actuator TF 
       Reply  Mon Aug 31 07:49:11 2015, ericq, Update, IOO, MC2 -> MCL Actuator TF 
          Reply  Mon Aug 31 14:15:23 2015, Ignacio, Update, IOO, Measured the MC_F whitening poles/zeroes Data.ziptf.png
Message ID: 11539     Entry time: Fri Aug 28 20:15:49 2015     In reply to: 11447     Reply to this: 11548
Author: rana 
Type: Update 
Category: IOO 
Subject: MC2 -> MCL Actuator TF 

I made a measurement of the MC2 actuator transfer function by injecting noise from 1-100Hz into LSC_MC2_EXC for about 15 minutes, then estimating the TF from MC2_OUT to IOO_MC_L with CSD/PSD. The inverse of this TF will be applied to their Wiener target data to give us the direct subtration filter we want.

I think what happened here is you forgot to undo the MC_F whitening filter which is the Generic Pentek Interface board next to the MC servo board. I suggest you guys measure this on Monday so you can correctly estimate the MC length noise. And then perhaps undo the whitening in the anti-whitening filter of this filter bank so that the signal which is recorded is in units of kHz.

This should allow your online subtraction filter to be more correct: roughly speaking, the phase shift below a pole or zero is going to be 45*(f/fp) deg. Since we expect there to be 2 zeros at 15 Hz, it would be 9 deg phase shift at 1.5 Hz and limit the subtraction to ~80%.

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