M. Ball, S. Dwyer

Just before beginning our extra maintenance today, we tried enabling the L2A filters for the PUM drive align through a re-routed signal as described in LHO alog 49825. We maintained lock during this test, something that may not have occurred under the old route.

Attached are plots of some of the control signals and seismic signals for ITMY before and after this test. Timestamps are as follows:

Reference taken at 14:40:00 UTC.

L2P activated at 14:45:48 UTC.

L2Y activated at 14:51:37 UTC.

We see slight reductions in the control signals below 0.1Hz on nearly all of these channels but larger drives in both soft and hard pitch ASC signals between 4 and 7Hz. Since the DARM feedback signal saw little to no variation in this frequency range, but the drivealign signals did. This agrees with a prior theory that the L2A digital filter is inaccurate in this frequency region. After the drivealign, the increase in the length signal was consistent with increase in the aforementioned ASC pitch signals.

Unexpectedly, turning on the L2P filter influenced pitch signals but not yaw signals; however, turning on the L2Y filter influenced both pitch and yaw signals.