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Entry  Fri Sep 18 13:33:17 2015, ericq, Update, LSC, Fast ALS troubles - Noise at 36kHz IRlock_noises.pdf
    Reply  Fri Sep 18 16:08:41 2015, ericq, Update, LSC, Fast ALS troubles - Noise at 36kHz PRMIlock_REFLspectra.pdfIMCspectrum.pdf
       Reply  Fri Sep 18 19:15:35 2015, rana, Update, LSC, Fast ALS troubles - Noise at 36kHz 
    Reply  Tue Sep 29 16:52:49 2015, ericq, Update, LSC, Fast ALS troubles - unknown zero OLG_fastALS.pdf
       Reply  Tue Sep 29 18:03:11 2015, rana, Update, LSC, use LISO Screen_Shot_2015-09-29_at_5.55.34_PM.png
          Reply  Wed Sep 30 10:00:02 2015, ericq, Update, LSC, used LISO 
       Reply  Fri Oct 2 03:29:16 2015, ericq, Update, LSC, Fast ALS progress - AO path crossed over, but no high BW crossedover.pdf
          Reply  Fri Oct 9 13:31:21 2015, ericq, Update, LSC, ALS plant shape xarm_plantTFs.pdf
             Reply  Fri Oct 9 14:50:18 2015, Koji, Update, LSC, ALS plant shape 
                Reply  Fri Oct 9 16:23:25 2015, ericq, Update, LSC, ALS plant shape 
                   Reply  Tue Oct 13 16:28:21 2015, ericq, Update, LSC, Fast ALS pomona liso_lp.zip2LPfit.pdf
Message ID: 11686     Entry time: Tue Oct 13 16:28:21 2015     In reply to: 11681
Author: ericq 
Type: Update 
Category: LSC 
Subject: Fast ALS pomona 

I've made a cascaded passive 2-pole pomona box for fast ALS use, using LISO to check that it'll give the right shape when hooked up to the CM board's input stage. 

First stage is a 133Ohm + 10uF cap for ~120Hz LP, second is 1.15kOhm + 47nF cap for ~3.8kHz LP. The DC gain is ~0.75, which is much better than what I was doing before. The second stage would normally make a 2.9kHz LPF on its own, but the loading of the input stage moves the corner up. 

It seems the 133 Ohm resistor is a reasonable load on the output AD829 of the ALS demod board (short-circuit output current of 32mA and a series output resistor of 499Ohm). To be able to use the digitized ALSX I and the lowpassed analog version simultaneously, I had to buffer the signal with a SR560 before the pomona box, otherwise the signals looked distorted. This isn't a good long-term solution. Maybe I can used the further-buffered differential output to drive the LPF+CM board. 

The LISO files used to model the filter and CM board input stage, and fit the pole frequencies are attached. 

I made some attempts to get the AO path going today, but I suspect this daytime noise is just too much; the PC drive seems too irritable

Attachment 1: liso_lp.zip  67 kB
Attachment 2: 2LPfit.pdf  16 kB  | Hide | Hide all
2LPfit.pdf
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