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Entry  Tue Feb 17 16:44:04 2015, Koji, Update, LSC, Delay line installed again 
    Reply  Tue Feb 17 19:49:51 2015, Koji, Update, LSC, Delay line un-installed again 
       Reply  Mon Feb 23 21:57:13 2015, Koji, Update, LSC, Delay line installed again (experiment, round 1) 
          Reply  Tue Feb 24 01:57:01 2015, Jenne, Update, LSC, Modelled effect of relative modulation phase ChangeInAngle_PRCLvsMICH.pngREFL33_MICH_SensMat_vsModulationOrder_vsModulationPhase.pngREFL33_SensMat_vsModulationPhase.pngREFL33_PRCL_nominalVsLoweredGamma.pngREFL33_MICH_nominalVsLoweredGamma.png
             Reply  Thu Feb 26 00:20:54 2015, ericq, Update, LSC, Modelled effect of relative modulation phase 33budget_canceled.png33budget_nominal.png2015-02-ModPhase.zip
                Reply  Thu Feb 26 01:51:39 2015, ericq, Update, LSC, Sideband HOMs C1_HOMcurves_PR.pngC1_HOMcurves_Y.pngC1_HOMcurves_X.pngC1_HOMlist.zip
                Reply  Thu Feb 26 01:53:35 2015, Koji, Update, LSC, Modelled effect of relative modulation phase 
       Reply  Tue Feb 24 23:39:16 2015, Jenne, Update, LSC, Delay line re-installed again 
          Reply  Wed Feb 25 04:59:47 2015, Jenne, Update, LSC, Delay line re-installed, measurements round 2 SensMat_PRMI_24Feb2015.pdf
             Reply  Wed Feb 25 12:16:27 2015, Koji, Update, LSC, Delay line re-installed, measurements round 2 
                Reply  Wed Feb 25 14:18:28 2015, rana, Update, LSC, Delay line re-installed, measurements round 2 
          Reply  Wed Feb 25 14:51:13 2015, Jenne, Update, LSC, Delay line un-installed again 
             Reply  Wed Feb 25 20:00:39 2015, Jenne, Update, LSC, Delay line un-installed again - sensing matrix comparisons 
                Reply  Wed Feb 25 23:48:57 2015, rana, Update, LSC, some thoughts 
                   Reply  Thu Feb 26 20:02:46 2015, Jenne, Update, LSC, re: some thoughts 
Message ID: 11070     Entry time: Wed Feb 25 20:00:39 2015     In reply to: 11069     Reply to this: 11071
Author: Jenne 
Type: Update 
Category: LSC 
Subject: Delay line un-installed again - sensing matrix comparisons 

I have measured the sensing matrix for the PRMI at the REFL photodiodes for both the nominal configuration and the 33MHz cancellation configuration.  The nominal configuration measurements do not compare well with those from November (http://nodus.ligo.caltech.edu:8080/40m/10701) which makes me unhappy no.  Both sets of nominal config reported below are from today, after tuning the demod phases and making sure the MICH and PRCL loops looked the same as yesterday (esp. overall gain).  The cancellation config data is from last night.

Note that the magnitude for each photodiode is referred to its own "PD counts".  Since the electronics are different for each PD, and that is not taken into account here, you cannot directly compare an element from one PD to an element from another PD.  What you can do (which is most of what we need right now) is compare all the different measurements for a single photodiode.

PRCL Sensing elements 33 MHz cancellation, REFL55 I&Q lock Nominal, REFL55I&Q lock Nominal, REFL33I&Q lock
  Mag [PD counts / m] Phase [deg] Mag [PD counts / m] Phase [deg] Mag[PD counts / m] Phase [deg]
REFL 11 3.0e13 0.05 4.2e13 0.1 2.9e13 0.1
REFL 33 1.1e11 3.4 1.8e12 0.25 1.2e12 0.3
REFL 55 1.8e10 2.1 1.4e11 4.8 9.3e10 4.1
REFL 165 7.0e9 15.5 6.3e11 0.5 4.2e11 0.9

 

MICH Sensing elements 33MHz cancellation, REFL55 I&Q lock Nominal, REFL55 I&Q lock Nominal, REFL33 I&Q lock
  Mag [PD counts / m] Phase [deg] Mag [PD counts / m] Phase [deg] Mag [PD counts / m] Phase [deg]
REFL 11 3.0e12 2.8 4.1e12 3.0 2.9e12 3.3
REFL 33 1.1e10 3.7 1.7e11 3.5 1.2e11 3.9
REFL 55 2.1e9 30.3 1.4e10 27.7 1.1e10 30.2
REFL165 6.4e8 24.4 6.3e10 21.0 4.5e10 23.0

So, what I'm apparently seeing is that the magnitudes of the sensing matrix signals that are made using 55MHz (i.e. everything but REFL11) change when we go into the cancellation configuration, but the phases of the sensing elements do not change significantly.  Also, I am apparently seeing that REFL11 and REFL33 only have about 3 degrees of separation between the MICH and PRCL signals no matter what configuration is used.  This doesn't make a lot of sense, since we know that we can lock robustly on REFL33I&Q (it's been sitting there happily as I write this elog), so it seems crazy that we could actually be so degenerate.  Also, at the bottom of the elog that I wrote in November 2014, I show a sensing matrix where both REFL11 and REFL33 have about 45 degrees of separation between the MICH and PRCL signals.

I don't think I'm doing anything too crazy here, particularly with the phase.  For a given PD and given DoF, I find the magnitude of the peaks of the I and Q signals, and just do atan2(Q-signal, I-signal)*180/pi, and those are the numbers that go in the phase columns above. 


Before taking my measurements, I tuned up the demod phases for the PRMI-only case.  I think REFL11 may have previously been tuned for CARM when the arms were held with ALS, but I don't really recall.  Anyhow, now all 4 REFL PDs are tuned for PRMI-only.

This was done while the PRMI was locked with REFL 55 I&Q. 

EDIT, 26Feb2015: Last night I mixed up the REFL11 and REFL33 new demod phases.  Bold are the corrected version.  Also, note that REFL33 was formerly tuned for PRCL in PRFPMI, which may be why it changed by ~10 degrees.

  Old demod phase [deg] New demod phase [deg]
REFL11 20 131.7 +/- 0.1   74.7 +/- 0.1
REFL33 142.2 74.7 +/- 0.1    131.7 +/- 0.1 
REFL55 19

15.3 +/- 0.3

REFL165 -172 -170.0 +/- 0.2

Here's the recipe for locking REFL 55 I&Q in the nominal modulation configuration.  It's the same as the REFL33 I&Q lock that I was using today, except that for the REFL33 version, the matrix elements are both unity.

PRMI REFL55 I&Q, nominal configuration MICH PRCL

Input Matrix

36*REFL55Q 12*REFL55I
Gain 5.0 -0.028
DoF trigger POP22I; 50 up, 0.5 down POP22I; 50 up, 0.5 down
FMs FM 4, 5 on FM 4, 5 on
FM trigger FM 2, 3, 6, 9; 50 up, 0.5 down, 5 second wait FM 1, 2, 6, 8, 9; 50 up, 0.5 down, 1 second wait
Normalization none none
Output matrix -1*ITMX, +1*ITMY 1*PRM

 

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