The TV is fixed to an adjustable focus plate on the carriage which allows for re-focusing if the TV is changed or another instument is mounted at CASS which requires a different focus. The TV is nominally focused on the slit jaws of the IDS. A filter wheel is available for the TV camera allowing up to four choices of filters.
To acquire an object, the TV acquistion probe; which is fitted with a FLIP MIRROR, can be in one of two positions:
Guide stars are selected these days from X-Y data supplied by the Guide
Star Server (GSS).
In front of the integrating sphere output port are two filters wheels known as AFARC and BFARC. The commands that move these being: compfilta and compfiltb respectively. These can be moved either individually or together and provide a range of neutral density filtering. When taking arc exposures, the COMPARISION MIRROR mirror moves into the field and directs light from the output port of the integrating sphere onto the slit jaws of the IDS.
The lamps are driven from circuit boards mounted in a small box on the
side of the A&G box. A meter (with a 3 position switch) allows the
lamp currents to be measured or adjusted. Depending on the lamps in use,
a preset pot on the edge of the board allows the current to be changed.
The current of an arc lamp is nominally between 5 and 15mA. A lamp on/off
toggle signal (which works when lamp current is sensed) is sent to the
All mechanisms that use stepper motors are controlled by double height eurocard boards (one for each motor) which contains the motor coil phase switching and power (4 power transistors) circuits. A 6821 PIA chip handles the input signals from the mechanism's associated position sensors (Hettich slotted inductive switches) and limit switches and also provides the direction and speed TTL toggles to drive the motor circuits. The ramp up/down of the stepper motors is done using a hardware circuit.
Serial communications to the 6850 ACIA board in the MMS is via an RS232 link (9600 7E1). There are two ports, one for engineering the other for computer control. Generally only the computer port is used. The RS232 connection runs to a panel mounted on the CASS electronics rack where control can be switched between two ports on a PORTSERVER, port 13 which the ICS computer accesses over the network, or port 11 which a Virtual PC accesses over the network for engineering use. This Virtual PC is a Linux machine running on taurus with a dosbox running the CDSAI Engineering software. The Virtual PC can be accesed by starting a VNCViewer session on your computer, then connect to: idsconsole:1 with the password: ******** A small box mounted on the panel fitted with a switch selects to where the comms line is routed. See the picture below or Cassegrain Interconnections drawing for more details.
n.b. Although only full I/O control with the Virtual PC is enabled with the switch in the ENG position. When control is in the ICS position, the Virtual PC can still read incoming data and will show if a mechanism has moved. A useful diagnostic.
Here is an image of the Engineering software user interface:
In case you see the DOS C: prompt instead of the above screen, you can start the program by typing: cdsai <return>. If the screen is present but not updating and no data scrolling then call someone from the CFG group to restart the virtual machine idsconsole:1 (126.96.36.199). If the screen is present but the Error Status Window says that there is no respons and there is no data scrolling in the Data Flow Window, the instrument is switched off. This can be switched on remotely by entering the INT Cass APC webserver.
The original instructions on howto operate the instrument with the CDSAI program can be found here , this document is a scanned version in pdf format, as the original document was lost.
Refer to the INT Technical Manuals, nos: 41
42 43 44 for full details and circuit drawings
for the A&G box.
Refer to the INT Technical Manuals: 54 and 55 for the circuit drawings for MMS boards.