[Sudarshan K, Suresh D]

  We looked at the data to see if work associated with engaging the IMC WFS DC centering loops resulted in a shift of the IMC output beam pointing.    There was no evidence to support that conjecture.    The last known instance when ISS outerloop was reliably locked was on Dec 9th.   We could not trace the reason for the shift of the beam to any specific event other than that mentioned below.

  In the attached set of time series plots we see that the IM4_TRANS_QPD segments started saturating several weeks ago and three out of four segements were continuously saturated from Dec 27th onwards.  Therefore this QPD could not be used subsequently to determine if the beam moved during the IMC centering loop work (which commenced on Jan 4th)

 However we can see that there was a change in the DC values of the  ISS QPD pitch and yaw signals around 27th Dec.  We can see an associated change in the signals of the IM4 QPD segments as well.   It is most likely that the IMC output beam shifted around that time and was probably associated with the recovery from the power glitch on 26th.  I could not find any other logged activity around that time.

[suresh]

As early as 10th of Dec we can see from the 40 day trend (attached) that the segs 3 and 4 of IM4 QPD had started to saturate.   We could not therefore use this sensor to monitor the beam position since that time.

I have reduced the Whitening gain on the IM4 TRANS QPD ( from 36dB to 0 dB ) and  recentered the spot on the QPD by using the IM4 TRANS QPD picomotor.   We can monitor the beam motion from now onwards to see if there is any effect from the DC spot centering loops in the IMC ASC.