On 27th of July, it was reported that arm 5 of the solid attenuator did not stay in 'out' position when retracted, but moved in immediately again.

Reason was, that the limit switch for the 'out'-position did not trigger, and thus the actuator was in error state. Default for error state is 'in'. In order to keep the arm removed, the default was changed on PLC level for the time being.

Today, 30th of July, we did ZZ to investigate the issue. It was found that the bar that accommodates the upper and lower limit switches had become loose and the limit switches were pressed out of the way by the motion, rather than being triggered.

The reason for the bar becoming loose, probably is a not ideal alignment of pneumatic actuator, guiding rod and limit switch bar, which resulted in a small relative motion between the three. This was fixed and limit switches were again aligned and trigger in both 'in' and 'out' position.

We believe, this will remain stable until WMP, but should be investigated more thoroughly, as we could not reach very well all connections in situ.