CASPIR operates within the environment common to all infrared instrumentation on the 2.3 m telescope. A schematic overview of the CASPIR system is shown in Figure 20. All mechanical functions are controlled from MOPRA through a DECNET link to the LSI-11/23 located in the Cassegrain Instrumentation Rack in the Nasmyth Lab, and from this to the instrument control subrack mounted on the Instrument Mounting Box (IMB). The detector array clocks, biases, and signal processing are performed by the SBRC Array Control Electronics (ACE2) also mounted on the IMB, close to the CASPIR dewar. The ACE2 is controlled directly by MOPRA through a 9600 baud RS-232 connection. Data from the four detector output channels are digitised in the ACE2 using four 16-bit, 500 kHz Burr-Brown ADCs, and serialised using four transputer Link Adaptors. The serial data are transmitted from the Cassegrain focus to the Nasmyth Lab where four T800 transputers receive the data and process it as necessary. When the requested integration sequence completes, the data are transferred to MOPRA through a transputer link to Q-bus interface and are displayed on the workstation screen and stored on disk. The detector array temperature is controlled by a commercial controller located in the Nasmyth Lab. MOPRA communicates with this controller through an RS-232 line.
The following describes each section of this chain in detail.
Figure 20: Overview of the CASPIR system showing connections between the dewar
and MOPRA via the SBRC ACE2 drive electronics, the transputer preprocessor,
the control subrack on the IMB, the LSI-11/23, and the Lakeshore temperature
controller.