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Entry  Thu Nov 14 23:56:18 2019, rana, Update, LSC, off the bad Violin filters out.pdf
    Reply  Fri Nov 15 11:58:12 2019, gautam, Update, LSC, off the bad Violin filters violinFix.pdfnewViolinConfig.png
    Reply  Mon Mar 1 16:27:17 2021, gautam, Update, LSC, PRM violin filter excessive? violins.pdfPRviolin.pdf
       Reply  Tue Mar 2 13:39:31 2021, rana, Update, LSC, PRM violin filter excessive? 
Message ID: 15853     Entry time: Mon Mar 1 16:27:17 2021     In reply to: 15026     Reply to this: 15854
Author: gautam 
Type: Update 
Category: LSC 
Subject: PRM violin filter excessive? 

The PRM violin filter seems very suboptimal - the gain peaking shows up in the MICH OLTF, presumably due to the MICH-->PRM LSC output matrix. I plot the one used for the BS in comparison in Attachment #1, seems much more reasonable. Why does the PRM need so many notches? Is this meant to cover some violin modes of PR2/PR3 as well? Do we really need that? Are the PR2/PR3 violin modes really so close in frequency to that for the 3" SOS? I suppose it could be since the suspension wire is thinner and the mass is lighter, and the two effects nearly cancel, but we don't actuate on PR2/PR3? According to the earlier elog in this thread, this particular filter wasn't deemed offensive and was left on.

Indeed, as shown in Attachment #2, I can realize a much healthier UGF for the MICH loop with just a single frequency notch (black reference trace) rather than using the existing "PRvio1,2" filter (FM2), (live red trace). The PR violins are eating so much phase at ~600 Hz.

Quote:

We turned off many excessive violin mode bandstop filters in the LSC.

Attachment 1: violins.pdf  14 kB  | Show | Show all
Attachment 2: PRviolin.pdf  18 kB  Uploaded Mon Mar 1 20:02:19 2021  | Show | Show all
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