Not logged in
Fri Apr 24 03:57:30 2009, Yoichi, Update, Locking, DARM demod phase
Fri Apr 24 04:38:49 2009, Yoichi, Update, Locking, DARM demod phase
Fri Apr 24 11:34:32 2009, rob, Update, Locking, DARM demod phase
Fri Apr 24 17:26:57 2009, Yoichi, Update, Locking, DARM demod phase
Fri Apr 24 17:26:57 2009
In reply to:
DARM demod phase
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.