This afternoon we performed a few tests on the OMC shutter with the ITF in NI single bounce in order to find a solution to the problem of OMC shutter getting stuck at the opening.
Fig.1 shows a test when sent a MOVETOLIMIT command via VPM to open the shutter. In this case the shutter motor get stuck, and we stopped it by sending the STOP MOTION command.
We have tested the opening of the shutter by sending some MOVEREL commands with a defined number of steps. We have found that with about 36000 steps the power on B1s reaches a plateau. Adding a bit of margin, we decided to perform 42000 steps to open the shutter. This is tested on Fig.2. We can see that it takes about 65 seconds to accomplish this motion.
We have then replaced the MOVETOLIMIT command by the MOVEREL command for the opening of the shutter in the class SHUTTER_OPENING of DET_MAIN. In the DET_MAIN.ini file, we have added the parameter nominal_open_steps = 42000, and we have updated the opening_duration to 80 seconds.
The opening and then closing of the shutter are tested with the automation on Fig.3. The closing is still performed with the MOVETOLIMIT command in order to be sure that we always start opening the shutter from the same position.
It was then possible to relock the ITF in Low Noise 3 at first trial.