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Entry  Fri Apr 24 03:57:30 2009, Yoichi, Update, Locking, DARM demod phase 
    Reply  Fri Apr 24 04:38:49 2009, Yoichi, Update, Locking, DARM demod phase 
       Reply  Fri Apr 24 11:34:32 2009, rob, Update, Locking, DARM demod phase darm_phase_rotate.png
          Reply  Fri Apr 24 17:26:57 2009, Yoichi, Update, Locking, DARM demod phase 
Message ID: 1519     Entry time: Fri Apr 24 17:26:57 2009     In reply to: 1516
Author: Yoichi 
Type: Update 
Category: Locking 
Subject: DARM demod phase 

Quote:

There's actually code in place in the LSC to dynamically adjust the demod phase for AS1. I've never made much use of it, because it's possible to get around the problem with some gain tweaking if you start at the right phase, or because I did the DC readout handoff earlier.

Attached is a cartoon showing how the demod phase at the dark port changes as the CARM offset is decreased.


The cartoon is very nice.
I actually changed the demod phase continuously as the CARM offset was reduced to get up to arm power = 70.
As the CARM offset is changed, not only the DARM signal gain but also the phase margin around 100Hz changes if you use a fixed demodulation phase.
So it was necessary to change the demodulation phase to keep the DARM loop stable.
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