OMEGACAM: Shutter test
The OmegaCAM shutter test is executed roughly every 90 days. It
consists of four dome flats of 10 and 0.1 seconds with the shutter
travelling in one direction, and the second dome flat pair (again 10
and 0.1 second exposures) is made with the shutter blades travelling
in the other direction (up and down). The pipeline divides each long
exposure by its corresponding short exposure, normalizes the result,
and then averages along the row direction (i.e. perpendicular to the
direction of shutter travel along the axis of the 8 OmegaCAM CCDs)
resulting in two fits table files with the average flux level in each
of 16,384 row pixels. Any differences in the two dome flat ratios can
be attributed to an inhomogeneity in the travel speed of the shutter
The pipeline creates two output frames from its shutter test recipe
(omega_shutter): a 1 x 16,384 pixel row average of the shutter travel
direction SHUTTER_UP (OC_PSHU_<DATE>_1_1_normal_normal.fits) and a 1 x
16,384 pixel row average of the shutter travel direction SHUTTER_DOWN
No health check plots are created for the shutter QC parameters.
Trending and Issues
Any inhomogeneity in the shutter travel in either direction will
result in a ratio of the row averages (black line in QC report) having
a significant slope. Furthermore, the comparison with the reference
traces will be apparent. Shutter timing homogeneity must be better
than +/-0.2% at exposures of 1 second.
The OmegaCAM shutter timing has been very stable and homogeneous.