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Entry  Wed Nov 23 17:48:16 2016, rana, koji, Update, IOO, How bad is the McWFS? 
    Reply  Sat Nov 26 19:16:28 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_response.pdfWFS_demod_noise.pdfWFS_demod_noise_plan.pdfScreen_shot_2011-07-01_at_11.13.01_AM.png
       Reply  Tue Nov 29 17:45:06 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis demod.pdfWFS_demod_response.pdfWFS_demod_noise.pdf
          Reply  Tue Nov 29 18:35:32 2016, rana, Update, IOO, IMC WFS Demod board measurement & analysis 
             Reply  Fri Dec 2 18:02:37 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_noise_orig.pdfWFS_demod_noise_mod.pdf
                Reply  Sat Dec 3 13:27:35 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_noise.pdfdemod.pdf
                   Reply  Tue Dec 6 13:37:02 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis demod.pdfWFS_error_noise.pdf
                      Reply  Tue Dec 6 16:47:40 2016, Koji, Update, IOO, IMC WFS whitening filter investigation D990196-C.pdf
                         Reply  Tue Dec 6 17:54:08 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 34.png
                            Reply  Tue Dec 6 22:41:49 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 
                               Reply  Tue Dec 13 17:26:42 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 
                                  Reply  Thu Dec 15 03:46:19 2016, rana, Update, IOO, IMC WFS whitening filter investigation 
Message ID: 12661     Entry time: Fri Dec 2 18:02:37 2016     In reply to: 12647     Reply to this: 12662
Author: Koji 
Type: Update 
Category: IOO 
Subject: IMC WFS Demod board measurement & analysis 

ELOG of the Wednesday work.

It turned out that the IMC WFS demod boards have the PCB board that has a different pattern for each of 8ch.
In addition, AD831 has a quite narrow leg pitch with legs that are not easily accessible.
Because of these, we (Koji and Rana) decided to leave the demodulator chip untouched.

I have plugged in the board with the WFS2-Q1 channel modified in order to check the significance of the modification.

WFS performance before the modification

Attachment 1 shows the PSD of WFS2-I1_OUT calibrated to be referred to the demodulator output. (i.e. Measured PSDs (cnt/rtHz) were divided by 8.9*2^16/20)
There are three curves: One is the output with the MC locked (WFS servos not engaged). The second is the PSD with the PSL beam blocked (i.e. dark noise). The third is the electronics noise with the RF input terminated and the nominal LO supplied.

This tells us that the measured PSD was dominated by the demodulator noise in the dark condition. And the WFS signal was also dominated by the demod noise below 0.1Hz and above 20Hz. There are annoying features at 0.7, 1.4, 2.1, ... Hz. They basically impose these noise peaks on the stabilized mirror motion.

WFS performance after the modification

Attachment 2 shows the PSD of WFS2-Q1_OUT calibrated to be referred to the demodulator output. (i.e. Measured PSDs (cnt/rtHz) were divided by 21.4*2^16/20)
There are three same curves as the other plot. In addition to these, the PSD of WFS2-I1_OUT with the MC locked is also shown as a red curve for comparison.

This figure tells us that the measured PSD below 20Hz was dominated by the demodulator noise in the dark condition. And the WFS signal is no longer dominated by the electronics noise. However, there still are the peaks at the harmonics of 0.7, 1.4, 2.1, ... Hz. I need further inspection of the FWS demod and whtening boards to track down the cause of these peaks.

Attachment 1: WFS_demod_noise_orig.pdf  843 kB  | Hide | Hide all
WFS_demod_noise_orig.pdf
Attachment 2: WFS_demod_noise_mod.pdf  924 kB  | Hide | Hide all
WFS_demod_noise_mod.pdf
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