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Entry  Tue Sep 15 15:10:48 2015, gautam, ericq, rana, Summary, LSC, PRFPMI lock & various to-do's powerSpec0915.pdf
    Reply  Tue Sep 15 18:35:21 2015, ericq, Summary, LSC, some further notes 
       Reply  Tue Sep 15 20:44:13 2015, gautam, Summary, LSC, Checking the delay line phase shifter DS050339 IMG_20150915_193100.jpgCalibration.pdf
       Reply  Thu Sep 17 03:48:10 2015, ericq, Summary, LSC, some further notes 
          Reply  Thu Sep 17 13:06:05 2015, ericq, Summary, LSC, Low input impedance on CM board 
Message ID: 11601     Entry time: Tue Sep 15 18:35:21 2015     In reply to: 11599     Reply to this: 11603   11609
Author: ericq 
Type: Summary 
Category: LSC 
Subject: some further notes 

About the analog CARM control with ALS:

We're looking at using a Sigg designed remotely switchable delay line box on the currently undelayed side of the ALS DFD beat. For a beat frequency of 50MHz, one cycle is 20ns, this thing has 24ns total delay capability, so we should be able to get pretty close to a zero crossing of the analog I or Q outputs of the demod board. This can be used as IN2 for the common mode board. 

Gautam is testing the functionality of the delay and switching, and should post a link to the DCC page of the schematic. Rana and Koji have been discussing the implementation of the remote switching (RCG vs. VME). 

I spent some time this afternoon trying to lock the X arm in this way, but instead of at IR resonance, just wherever the I output of the DFD had a zero crossing. However, I didn't give enough thought to the loop shapes; Koji helped me think it through. Tomorrow, I'll make a little pomona box to go before the CM IN2 that will give the ALS loop shape a pole where we expect the CARM coupled cavity pole to be (~120Hz), so that the REFL11 and ALS signals have a similar shape when we're trying to transition. 

The common mode board does have a filter for this kind of thing for single arm tests, but puts in a zero as well, as it expects the single arm pole, which isn't present in the ALS sensing, so maybe I'll whip up something appropriate for this, too. 

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