From gonzalez@lsu.edu Fri Mar  3 13:00:49 2006
Date: Fri, 3 Mar 2006 12:00:49 -0600
From: Gabriela Gonzalez <gonzalez@lsu.edu>
To: Keith Riles <kriles@umich.edu>
Cc: Valery Frolov <vfrolov@ligo-la.caltech.edu>, Brian O'Reilly <irish@ligo-la.caltech.edu>, Michael Zucker <zucker_m@ligo.mit.edu>, Joseph A Giaime <jgiaime@ligo.phys.lsu.edu>

Hi Keith,

As you may remember, there was a problem in L1 during the days  
between Feb 18 and Feb 20, that affect segments L1-961 to L1-968  
(included). As best as it could be diagnosed (see Valera's entry on  
Feb 20, my entry the same day and other entries on Feb 18,19,20), it  
was due to a mass resonance shifting away from its notch in the  
control loops, the resonance in question getting excited and causing  
problems somewhere in the sensing chain. The consequence was a  
drastic change in sensing gain that was not tracked by optical power  
in arms or the recycling cavity, and thus it was not corrected by the  
"dynamic input matrix", making the loop gain vary wildly. In  
principle, since we follow the loop gain, the data could be used, but  
since the problem was in the analog sensing, I doubt very much we can  
trust the data. I am proposing we (you!) create a "bad sensing" L1 DQ  
flag that analysis groups can use to veto this data (and I'll  
recommend doing that at least to the inspiral group). I propose the  
flag to start at GPS 824394400, a minute before the first drastic  
change in gain, as measured by SenseMon loop gain coefficient (see  
"start" plot attached), which cuts 1311 seconds at the end of segment  
L1-961, and ends at GPS 824501400, 112 seconds before the start of  
the first good segment, L1-969. According to conlog, this would throw  
away 21500 sec ~ 6 hrs  of science data, some of which may be good,  
but I wouldn't know how to find...

I attach some plots that may remind you of the situation, admittedly  
a while ago and centuries ago in our memories.

Let me know what you tink (I am in an inspiral review telecon, I'm nt  
sure it will be over in time for me to join the Det Char telecon at  
12:30, but I can talk about this when I join if you nwat).

GAby.



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