With Terrence.

Simon came by the center area and helped us repair the damaged QPD stage for the BS LEN OL.

We changed the clamping of the OL breadboard to make room for the QPD (we removed a C-clamp from the -X,-Y corner and replaced it with a dog clamp on the underside) and reinstalled the QPD.

In the course of testing the new setup, Terrence noticed that there were signs of something touching: small increments of IP-L used to test the LEN OL was correlated with large TM-Y. We quickly realized that this was because we'd been tolerating a large constant IP-L of some +3300 µm. In fact Terrence had deliberately captured this extreme position as part of the ALIGN state because that's where the IP wanted to sit, and the DCCTRL loop didn't have the strength to get it all the way back to zero with the LVDT actuators. 

We tried to get the IP back to center with the FRs, but discovered that the IP is very close to unstable. The H2 LVDT varies particularly wildly, so probably IP leg 2 (at 11 o'clock looking towards +L, -X,+Y) is weak. After several attempts, the closest Terrence could get it to center without it falling over to the other side was L= 426 µm, T= -483 µm, Y = 331 µrad. The FR positions that gave this position were 20000, 23000 and 56000 counts. We redefined IP SET to hold it at that position and did some TFs with IM actuation to check that the payload was now fine, which it seems to be. 

However, this is not a good situation and we should probably remove the tank lid and remove a bit of weight from the IP to make it more stable.

The risk of not tweaking it is that if there's a disturbance (like a small earthquake or a big temperature change, or stresses from pumpdown) and if falls over, it takes a skilled operator to get it back close to center and it may not be possible to target the same point each time.