During maintenance we made some checks to the software that allows to optimize the injection of the green transmitted by the arm cavities into the fiber that brings them to the beating box. There are two ways of doing this:

1) Dithering: there is a loop that uses mechanical dithering to generate alignment error signals, and tries to minimize them. In order to turn this loop on, it is necessary to push three buttons on Acl: ENABLE (which allows the lines and the spiral to start), Ramp Set and LOCK (which engages the control filter).

Once we are happy with the working point set by the loop, we need to push the button KEEP, which will keep memory of the new working point. Then we can open the loop by pushing UNLOCK, Ramp Unset and DISABLE.

2) Manually: in order to change the setpoint of the PZT, the first step is to push the button RELEASE. Otherwise, the working point will not change because the memory of the last point will be kept. Then we can change the working point of the PZT by using the button SET X/Y. Once we are happy with the new working point, we need to push the button KEEP, in order to update the position memory.

(Notice that if you haven't push UNLOCK, Ramp Unset and DISABLE, even if you push RELEASE, you will not be able to change the working point manually, it is necessary to open the control for doing this.)

During this test we noticed though, that a change on the PZT value, didn't change at all the power in the photodiodes. After some investigation Alain realized tha the line that was sending data to the DAC, was commented since october, so the current was not being sent to the PZTs. We restored the communication and tested the loops today, clearly seeing the effect. So the loops are back working properly.