Detector

As noted above, an upgrade to the detector controller will take longer. This also means the controller still does not provide the data of the temperature and pressure sensors. There is a temporary telemetry controller for the temperatures so we can at least read them by eye, and we now have found a way to read this data electronically. In the near future we plan to connect this to our network so the values can be read by the computer and entered in our data base. This will then allow us to add this to our monitoring system that warns when a dewar is heating up and should be filled. This is especially relevant for the ALFOSC detector as with the new controller the holding time has been reduced to 15-18 hrs, i.e., it needs to be filled more than once a day.

There have been some issues with the bias level varying, depending on the order in which commands are given. A post-processing programme has been made that calculates the bias level and the dispersion (as measure of the read-out noise) using the over-scan in the serial and parallel directions on the CCD whenever available and shows the results overlaid on the displayed image.

With the old data acquisition program a parameter existed to corrected the requested exposure time for relative delays in opening and closing the shutter such that the effective exposure time of an exposure taken with the CCD corresponds to the requested exposure time. This correction was found to be $\sim$+0.1 sec, i.e., the effective exposure time is slightly shorter than the request exposure time. This value is actually significant for short exposure times of a few seconds (e.g., used for standard star observations). However, the new system does not include such a parameter and will need to be added. In particular, the requested exposure time send to the CCD controller will be the value corrected for this `shutter error', while the header giving the exposure time in the resulting images should given the requested exposure (which in principle should correspond to the effective exposure time). A separate header will be created to show the `shutter error' in use at the time the exposure was taking.