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Message ID: 9635     Entry time: Thu Feb 13 22:27:54 2014
Author: Jenne 
Type: Update 
Category: LSC 
Subject: PRMI locked on REFL 33 I&Q 

[Jenne, Koji]

I was able to get the PRMI locked on REFL33 I&Q, but it wasn't overly stable, since there is so little separation between the MICH and PRCL signals in that PD. 

We have already adjusted the phase to maximize PRCL in the I-phase.  Since MICH is ~45 degrees separated from PRCL, there is some projection of MICH in the I-phase, and some in the Q-phase. 

To remove this MICH component, I locked the PRMI on REFL55, and drove MICH.  I looked at REFL33I at the CARM filter bank input (as just a dummy location to get a signal into DTT).  I then added REFL33Q to the CARM row of the input matrix, to try to get the MICH line minimized.  I then used these values for PRCL, and used just REFL33Q for MICH, and re-locked the PRMI.  The PRMI was much more stable and happy. 

The input matrix values that I used were:

MICH:  REFL33Q = -0.487, Servo Gain = -20.0

PRCL:  REFL33I = 1.556, REFL33Q = 1.8, Servo Gain = -0.020


Some locking notes:

The PRMI is very sensitive to alignment, and the PRM tends to drift away from optimal alignment on a ~1 hour timescale.  When the PRM was not well aligned, it looked like MICH had a locking offset (manifested as non-equally sized blobs at AS).  The MICH offset seemed to go away when we realigned the PRM. 

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