I looked at past data from two weeks ago in which we were locking the Y arm without recycling.
Two weeks ago, the Y arm was as lossy as it is now, .
A good data set was found in Nov-21 08:44:55 - Nov-21 8:59:54. According to conlog, this is the last time when we changed the normalization factor for TRY to set it to 1. Here are the values for ASAIR_LF:
Compared with the data from yesterday (alog 15432), which gave a ratio of 0.82 at ASAIR_A, I don't see a big difference. Also, a plot from dataviwer is attached. Note that TRY dropped in the middle of the locking because we set the TRY digital gain such that it becomes 1 (although the one shown in the plot is without the PSL normalization which is 10.
Apart from this past data, I found another good data set from approximately two months ago in Oct-3 23:35:44 - Oct-4 02:34:44 when Sheila and Alexa were working on the Y arm IR WFS (alog 14296). However. I am having difficulty in getting the relevant data in second trend or full rate for some reason. I could get minute trend, but they were not helpful.
I managed to find the missing data frames on the Caltech cluster. The results for a lock on 3 Oct 2014 at around 23:18 UTC (1096413500) are very much the same:
H1:LSC-ASAIR_A_LF_OUT_DQ
locked = 1057.0
unlocked = 1226.4
ratio = 0.86
H1:LSC-ASAIR_B_LF_OUT_DQ
locked = 303.2
unlocked = 357.5
ratio = 0.85
A plot of the channels is attached (the x-axis is seconds). So, it seems the y-arm losses have not significantly changed in the past two months.