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Entry  Fri Aug 1 12:49:06 2014, Koji, Summary, IOO, MC servo analysis MC_OLTF.pdfMC_Error_Common.pdfMC_Crossover.pdfMC_CLTF_Fast.pdf
    Reply  Thu Aug 7 11:57:59 2014, Koji, Summary, IOO, MC servo analysis MC_OLTF_Fit.pdfIMC_OLTF.zipMC_OLTF_estimated.pdf
       Reply  Fri Aug 8 12:39:19 2014, ericq, Summary, IOO, MC servo analysis mcLoopAug8.zipMCloopAug8.pdf
          Reply  Fri Aug 8 15:57:29 2014, ericq, Summary, IOO, MC servo analysis OLTFs.pdfCLTFs.pdfmcLoopAug8.zip
             Reply  Fri Aug 8 18:08:12 2014, Koji, Summary, IOO, MC servo analysis 
             Reply  Sat Aug 9 14:35:28 2014, Koji, Summary, IOO, MC servo analysis MC_OLTF_Fit.pdfliso.zipMC_CLTF_Fit.pdfMC_CLTF_new.pdfMC_OLTF_new.pdf
Message ID: 10359     Entry time: Sat Aug 9 14:35:28 2014     In reply to: 10354
Author: Koji 
Type: Summary 
Category: IOO 
Subject: MC servo analysis 

Eric's OLTF turned out consistent with the AO path TF that has been measured by me on Jul 31 (entry 10322).

Attachment 1:
Updated empirical fit of the open loop TF by LISO.
In this fit, I gave some of the poles/zeros associated with the boost manually set so that I can use them for the servo design.
LISO itself can make better fitting if all of the variables are moved.

Atatchment 2:
The OLTF data and LISO source for the fitting.

Attachment 3:
Comparison of the AO path TFs. The red one was measured directly on Jul 31. The TF is normalized at the low frequency.
The blue was estimated from the OLTF model given above. They are well consistent now.

Attachment 4:
Now some servo design was tried. In the new design (blue), zeros of the super boost frequency was moved from 20kHz to 30kHz
with the hope of having flatter AO response. The improvement is very little while costing costing above 100kHz. Note that the vertical
axis is intentionally in a linear scale. In fact, the AO response is much improved compared to the one before the MC UGF was increased
(shown in magenta). We have a flatter response both in magnitude and phase.
Therefore I think there is no need to tweak the boost frequency for the AO path.
I'd rather recommend to inspect the high frequency LPFs to earn more gain margin at 1MHz as
explained in entry 10322.

Attachment 5:
This figure shows the comparison of the TFs for the current and new design trial, just in case someone is interested in to see.


Attachment 1: MC_OLTF_Fit.pdf  234 kB  Uploaded Sat Aug 9 15:40:16 2014  | Hide | Hide all
Attachment 2: liso.zip  372 kB  Uploaded Sat Aug 9 15:40:40 2014
Attachment 3: MC_CLTF_Fit.pdf  54 kB  Uploaded Sat Aug 9 15:41:10 2014  | Hide | Hide all
Attachment 4: MC_CLTF_new.pdf  82 kB  Uploaded Sat Aug 9 15:42:57 2014  | Hide | Hide all
Attachment 5: MC_OLTF_new.pdf  101 kB  Uploaded Sat Aug 9 15:43:21 2014  | Hide | Hide all
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