The detector controller for ALFOSC does not include the detector temperature control, and a separate temperature controller is used but this has no connection to our computer system, i.e., the temperature is available only from the controller display. Unfortunately, the temperature controller cable can have a bad connection to the dewar causing the heater (of the detector) being switched on continuously. This gives a high dark current and in one case this caused some problem especially affecting long spectroscopic exposures. It was noted that from a bias exposure it is easy to see there is a problem as there is a clear slope in the read direction in the data. An automatic procedure is being made that checks this and detects any changes as soon as possible.
Quality control of the ALFOSC detector indicates that with the current controller there is less readout noise when using amplifier B than amplifier A. The plan is to change to Amplifier B being default. However, is was found that the controller software does not provide for the option of windowing when using amplifier B. Some work-arounds can be used to still being able to use amplifier B at all times, but this needs to be fully implemented before we can offer this option to the users.
Thomas Augusteijn 2013-05-10