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Message ID: 7116     Entry time: Wed Aug 8 11:16:06 2012
Author: Sasha 
Type: Summary 
Category: Simulations 
Subject: SURF - Week 7 - Summary 

This week, I brought my c1lsp model online and fixed up some the medm screens for c1spx. Along the way, I ran into a few interesting problems (and learned a bit about bash scripting and emacs! :D). The screens for the main TM_RESP matrix are not generating automatically, and the medm screens don't want to link to the channels, for some reason. I don't have this problem with the other matrices (i.e. C2DOF and SEN_OUT), so I think it has something to do with TM_RESP being a filter matrix (which the others are not). In addition, the noise overview medm screens for c1spx are practically nonexistent - someone just copied the file for the SUS-ETMX screens into the master directory for c1spx, so they need a complete overhaul. I am willing to do this, but Jamie told me to focus my attentions elsewhere.

So I went back to noise generation. I've been using Matlab to figure out how to recreate the various noise sources (laser amplitude noise, local oscillator phase/amplitude noise, and 60 Hz/ADC. Frequency noise will be added some time this week and seismic noise should be already covered in Jamie's suspension model) in my c1lsp model. I'm doing it the way the RCG does it - by applying a filter to white noise. I'm generating white noise by just using a random number generator and pwelch-ing it to get the power spectral density.

For the filters themselves, I picked z, p, k such that it shaped the white noise PSD to look like the PSD of the noise in question. This was fairly straightforward once I figured out how zeroes and poles affected PSD. Once I'd picked zpk, I applied a bilinear transform to get a discrete zpk out, then converted to a second order section to make computation faster. I then applied that to the white noise (matlab has a convenient "sosfilt" function) and pwelch-ed/graphed it to get the result.

Attached is my attempt at filtering white noise to look like 60 Hz. noise. I can't seem to find a way to pick z and p such that the peak is more narrow (i.e. other than having two complex conjugated poles at 60 Hz.). I took the spectrum of 60 Hz. noise from a terminated ADC channel (Masha kindly let me borrow one of her GURALP channels).

EDIT: I also remembered that I've been looking for how to get a good power spectrum for the rest of the noises. Jenne referred me to Kiwamu's work on this, and I'm mostly going off elog #6133. If you have any other good elogs/data on noises, please feel free to send them my way.

I then measured the PSD of the sensors on the real suspended optics and a PSD of the suspension model. It looks like the OSEMs on the suspension model are only reading white noise, which probably means a lost connection somewhere (Attachment 2 is what the model SHOULD produce, Attachment 3 is what the model ACTUALLY produces). I perused Jamie's model, but couldn't find anything. Not sure where else to check, but I'll continue thinking about it/trying to fix it.

Attachment 1: Screen_Shot_2012-08-06_at_9.20.02_PM.png  33 kB  | Hide | Hide all
Attachment 2: Screen_Shot_2012-08-08_at_11.13.55_AM.png  32 kB  | Hide | Hide all
Attachment 3: Screen_Shot_2012-08-08_at_11.08.23_AM.png  31 kB  | Hide | Hide all
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