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 blades.

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 (OC_PSHD_<date>_1_1_normal_normal.fits)

QC1 Health Check Plots

No health check plots are created for the shutter QC parameters.

QC1 parameters (trended for each individual detector)

QC Reports for SHUTTER Frames

QC Report 1:
SHUTTER homogeneity QC report . . . for all detectors:
top: the average over all >16,000 pixels of the 8 row CCDs of the OmegaCAM array. The current row average is shown as blue (shutter travel: UP) and green (shutter travel: DOWN) lines. The reference row average is shown as red lines.
The ratio of the two shutter travel directions for the current frame is shown as a black line offset by 0.10. A homogeneous shutter travel time in either direction would result in this line being very flat.
Least-square fits to these lines and their ratios are indicated in the frame legend along with a measure of the computed shutter inhomogeneity (in percent).
bottom: a normalized histogram of the flux counts associated with the two shutter travel directions. The blue histogram is for the shutter UP travel, the green histogram for the shutter DOWN travel (both histograms should be very similar), and the black histogram is the ratio of the two (it should straddle 1.00).

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.

History

The OmegaCAM shutter timing has been very stable and homogeneous.