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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: 11489     Entry time: Tue Aug 11 02:26:46 2015     In reply to: 11482
Author: ericq 
Type: Update 
Category: ASC 
Subject: PRC Angular FF Lives! 

PRC Angular FF is back in action!

Short and sweet of it:

  • Took witness (T240 channels) and target (POP QPD) with DC coupled oplevs on. About 25 minutes of nice stationary data.
  • Downsampled everything to 32Hz, since coherence suggests subtraction only really possible from 1-5Hz. 
  • Prefiltering done by detrending and ellip(3,3,40,5Hz)
  • 4 second FIR impulse time was enough
  • Filtered target by inverse actuator TF before sending to wiener code. The only difference between this and filtering the witnesses with the actuator TF directly is an effective RMS cost function, i.e. prefiltering. 
  • Spending time tweaking IIR fitting pays off. Divided out zpk(0, [p3, p3*],1), where p3 is some well fit stack/suspension resonance, so that vectfit fits remaining portion with equal numbers of poles and zeros, guaranteeing AC coupling and 1/f rolloff to prevent noise injection
  • Quack->foton->OAF all worked fine
  • All in all, seems to work well. POPDC RMS goes down by a factor of 2 yes

  • Code used lives in /users/ericq/2015-08-PRCFF and the NoiseCancellation github repo

Fit example:

Subtraction spectra

Subtraction prediction vs. reality (positive dB is good)

Attachment 1: fitExample.png  99 kB  | Hide | Hide all
Attachment 2: FFspectra.png  217 kB  | Hide | Hide all
Attachment 3: PITsub.png  126 kB  | Hide | Hide all
Attachment 4: YAWsub.png  130 kB  | Hide | Hide all
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