A schematic diagram of the SpectroCam-10 control system is shown in Figure 1.4. Riding with the dewar in the Cass. cage is a set of hard-wired electronics to control the detector and an IBM-compatible PC which provides for real-time control of these electronics. The PC is connected to a Sun Ultra-2 in the data room via a thin-wire ethernet line.
Figure 1.4:
SpectroCam-10 Control System
The very high level of background radiation in the thermal infrared requires that the detector be read out up to a few hundred times per second. The detector is therefore controlled by a set of high-speed electronics which provide DC and clocking voltages, and preamplify, digitize and coadd the output signals. The PC receives co-added data at the rate of one frame every several seconds, which it can either display or pass on to the data room computer.
The clocking patterns required to run the array are stored in EPROMs, and several different software-selectable tables are provided to read out different subframes of the detector (64x64 pixels for camera mode and 64x128 pixels for spectrograph mode, for example). The operator can select the desired table as well as the overall clocking speed through the control software. The default set of tables should be sufficient for most projects, but custom EPROM tables can be programmed with plenty of advance notice.
An important element of the control system is the hardware co-adder, which reads data from the detector at up to a few hundred frames per second and co-adds up to several thousand frames at a time. The co-adding is split between two sections of memory synchronized to the chopping secondary position. At intervals of about 2 to 20 seconds, the co-adder memory is read out by the PC, and the operator sees two frames as the end result (one for each half of the chop cycle). Note that this mode of operation is signficantly different from optical and near-infrared arrays, where an on-chip integration time of up to several minutes leads to one frame of data.
The PC runs under the DOS operating system, and a menu-driven program called PSYS provides for direct, real-time control of the detector electronics, filter and slit wheel stepper motors, and grating scan mechanism. It can display data in a simple ``Continuous Acquisition'' mode which is sufficient for checking the instrument's operation. When observing, the PC operates under the remote control of the data room SparcStation, to which it passes data for more detailed display and analysis.
The SparcStation runs Unix, and a set of custom control programs runs under Sun's CDE Windows environment. The programs are menu-driven and we feel that if you are a Windows, Icons, and Mouse person (WIMP), you can learn to run the instrument fairly easily. Data received from the PC can be displayed, analyzed, and graphed in several different modes, and is saved to the workstation's hard disk in FITS format for later processing. An Exabyte tape drive is available for data backup and transport.