Observing overheads

The NOTCam observations have significant overheads. Both the telescope dither overhead and the data acquisition related overheads are well understood but the overheads in readout, on the other hand, are not well understood and have increased from 2006 to 2008. During the remote summer school in June 2010 it was found that substantial load on the NOTCam data acquisition computer was taken up by the observing system ``talker'' log and the electronic observers log. A new talker was written, and in December 2010 both the talker and the obslog were moved from marissa to dedicated computer. From two observing nights in February we measured overheads and found that we were back to the nominal (2006) overheads.

Still the nominal overheads are not small, and in principle we are waiting for the new controller to shorten the too long readout-time. In the mean time, a special exposure command for NOTCam was suggested in which the dither overhead can be folded into the readout and file storage overhead. Depending on the type of NOTCam observations being made, this can save a very significant amount of time per night. For the exposure command, which now has $\sim$13 seconds overhead, it is expected that this work-around would lower the overhead to around 6-7 seconds per exposure, quite an impact for short exposures. This has been given the highest priority.

Thomas Augusteijn 2012-02-21