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Entry  Thu May 1 03:15:03 2014, Jenne, Update, LSC, Yarm locking with CM board Yarm_CMlocking_spectra_30Apr2014_copy.pdfYarm_CMlocking_TFs_30Apr2014_copy.pdf
    Reply  Thu May 1 03:23:07 2014, ericq, Update, LSC, Yarm locking with CM board 
    Reply  Thu May 1 13:03:34 2014, Jenne, Update, LSC, MC board pulled for AC coupling 
       Reply  Thu May 1 14:45:44 2014, Jenne, Update, LSC, MC board back in IMG_1394.JPGIMG_1395.JPGIMG_1398.JPGIMG_1402.JPG
    Reply  Thu May 1 16:41:35 2014, ericq, Update, LSC, Yarm locking with CM board AOsignsSame.pdfAOsignsOpposite.pdfloopModeling.m
       Reply  Thu May 1 17:00:05 2014, rana, Update, LSC, Yarm locking with CM board 
Message ID: 9888     Entry time: Thu May 1 03:15:03 2014     Reply to this: 9889   9891   9893
Author: Jenne 
Type: Update 
Category: LSC 
Subject: Yarm locking with CM board 

[Rana, EricQ, Jenne]

We locked the Yarm by using the CM board this evening. 

POY is going from its demod board to the CM board, and then the slow output of that is going to the POY channel of the whitening, and then on to the ADC.  So, with no AO path engaged, this is basically like regular Yarm locking. 

First of all, Den and Koji back in December were concerned that they were seeing some EOM saturation in the fast path, but we don't think that's an issue.  We looked at the FSS PCDRIVE while we increased the AO gain.  In fact, it looks like the offset is coming from the MC board's IN2 slider.  Even with no input on that slider, increasing its value puts an offset into the MC.  To fix this, I am going to put a 6.8uF cap in series with R30 in the MC board, which is part of the crossbar switch where the IN1 and IN2 get summed.  This should AC-couple the output of the IN2 slider before the summing node.

We aren't sure which sign to use for the AO path of the CM board...Eric is doing some modelling to see if he can figure it out.  He's going to try to see which spectra (below) his model matches.

For the spectra, we have a reference trace with no AO path, a trace with "Plus" polarity on the CM board which started to show a peak when the value of the MC IN2 slider was at about -6 dB, and a trace with "Minus" polarity, which started to show a peak when the value of the MC IN2 slider was at about -16 dB. 

Yarm_CMlocking_spectra_30Apr2014_copy.pdf

We took loop measurements for each of the Plus and Minus cases. Something that seems a little weird is how shallow of a slope we have in both cases near our UGF.

Yarm_CMlocking_TFs_30Apr2014_copy.pdf

 

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