Observing system

Since the introduction of the sequencer we have had occasions where the detector control software programme BIAS apparently ignores exposure commands from the sequencer. This has been seen to happen only for NOTCam, not for the other instruments. After a certain timeout, the sequencer gives up and the prompt comes back without any warning. If this happen when running a script, the script continues with its next command, causing any dither script to skip one or more exposures in the sequence.

This spring an extra loop was added to the end of all NOTCam template scripts to check whether the expected number of files had been saved. This at least warns the user that files are missing and additional files can/should be taken if needed. This checking of files is not added to scripts made with the script generator.

Due to the intermittent nature of the problem, extensive test runs were made to investigate it. The problem seems to have become worse over time, but may depend on the occasion, and there is a strong correlation with the exposure time, which is not at all understood. A modification in BIAS was eventually made to do a ``retry'' of the exposure command if it times out. This works well for the most typical exposure times, but fails for the longer ones. We are looking in to making the work around also functioning for longer exposure times. This work-around at least makes sure that the exposure eventually is made, though at the cost of some extra overheads.