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Entry  Fri Jan 30 02:57:03 2015, Jenne, Update, Modern Control, First try with PRCL ASC Wiener filtering 9x
    Reply  Tue Mar 31 22:27:43 2015, Jenne, Update, Modern Control, Preliminary PRMI angular Wiener results PRMI_31Mar2015.pdf
       Reply  Sat Apr 4 17:54:03 2015, rana, Update, Modern Control, Preliminary PRMI angular Wiener results 
       Reply  Tue Apr 21 01:17:13 2015, Jenne, Update, Modern Control, T-240 self-noise propagated through stack and pendulum T240selfnoise.pngLimits.tar.gz
Message ID: 11229     Entry time: Tue Apr 21 01:17:13 2015     In reply to: 11186
Author: Jenne 
Type: Update 
Category: Modern Control 
Subject: T-240 self-noise propagated through stack and pendulum 

Going back to Wiener filtering for a moment, I took a look at what the T-240 noise level looks like in terms of pitch motion on one of our SOS optics (eg. PRM).

The self-noise of the T-240 (PSD, in dB referenced to 1m^2/s^4/Hz) was taken by pulling numbers from the Users Guide.  This is the ideal noise floor, if our installation was perfect.  I'm not sure where Kissel got the numbers from, but on page 13 of G1200556 he shows higher "measured" noise values for a T-240, although his numbers are already transformed to m/rtHz.

To get the noise numbers to meters, I use:  \left[ \frac{\rm m}{\sqrt{\rm Hz}} \right] = \frac{\sqrt{10^{\frac{[\rm dB/\sqrt{Hz}]}{10}}}}{(2 \pi f)^2}.  The top of that fraction is (a) getting to magnitude from power-dB and (b) getting to asd units from psd units.  The bottom of the fraction is getting rid of the extra 1/s^2.

 

Next I propagate this seismometer noise (in units of m/rtHz) to effective pendulum pitch motion, by propagating through the stacks and the transfer function for pos motion at the anchor point of the pendulum to pitch motion of the mirror (see eq 63 of T000134 for the calculation of this TF).   This gives me radians/rtHz of mirror motion, caused by the ground motion:

.

I have not actually calibrated the POP QPD, so I will need to do that in order to compare this seismometer noise to my Wiener filter results.

 

Attachment 1: T240selfnoise.png  252 kB  | Show | Hide all | Show all
Attachment 2: Limits.tar.gz  213 kB
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