Summary: It works consistently without remeasuring the sensing matrix everyday and some other nonsense.

The current setup (which will change in the future) is this:

• QPD centering is turned off.
• WFS centering is turned on.
• WFS is fed back to PZT mirrors (i.e. the beam is aligned to the cavity).
• ITMY green camera centroid output is copied to the frontend over EPICS using /ligo/lho/scripts/cameracopyY script.
• ITMY centering error signal goes to ASC via ALS WFS_DOF1 (which is strangely named AWFS3 in the ASC MEDM).
• Centering error goes back to the ETM and ITM such that the ETMY beam position is not affected.
• ETMY beam position is uncontrolled, which is not good. Probably some change is necessary.

The screen shot shows the current settings.

Other things:

In the same screen shot, the strip tool shows that the demise of the WFS centering is the demise of this system. Blue trace is one of the outputs of the WFS centering, and as soon as it starts to hit the bottom rail everything becomes ratty and eventually it breaks lock. I'll change the table layout to get more juice out of the PZT mirror range.

When it unlocks, a large transient from the centroid thing hits both ETMY and ITMY, so you need to wait for maybe 30 seconds until it becomes possible to lock again.

You want to reset the WFS centering servo (which may or may not grab) and enable the WFS again, and most of the time it goes back to a good alignment. Sometimes WFS centering never recovers by this procedure. If that happens, you might want to zero the ASC output to the ETMY and ITMY and do it again.