The primary function of the autoguider is to compensate for imperfections in the telescope tracking caused by pointing model inaccuracy and gear errors. This is accomplished by measuring the position of the centroid of a bright guide star in the field of view. The change in position from the original Fiducial point is sent to the TCS, which will correct the position of the telescope accordingly. Secondary functions include providing displays of pointing errors, seeing, magnitude, relative transparency and of course displaying the CCD image. With the advent of the AutoFib-2 fibre positioning system, the autoguider can be used to report positions of stars in the field of view of its camera. This facility is used to calibrate the distortion map of the instrument in order to place fibres more accurately.
Make sure that all of the Boards in the system are present and that there is at least one CCD controller set up. Make sure that the serial comand link to the controller is present and that there is a fibre optic link back to a FOX chassis which is connected to the VME rack.
Switch on power; or press the reset switch ( left most card bottom
switch on the VME rack ); or enter
On reset or power-up, the basic Forth Kernel is loaded from on-board Eproms,
this gives the system the ability to talk to serial ports and SCSI discs.
Then the default hard disc block 9 is loaded. The system is currently runing code from version 3 of the operating system. As block 9 is interpreted, a test is made to see if the system has loaded version 4 yet. If it has, the reload is skipped.
The system then does a RELOAD, which loads a new kernel from a kernel image on disc. Block 0, word 0 is read which points to the start of the kernel image on disc. Normal Forth practice puts this image at a default block address of 10,000. The autoguider system has 2 different images at 2000 and 2100. These differ only in that the system at 2000 will reload again from either Quantum or INSITE floptical drives.
The reloaed kernel is a Forth V4.2 kernel, which is the latest release. The next stage is to oad block 10 from the disc which defines the block numbers for the software modules which make up the rest of the normal Forth Version 4.2 system. These elective modules are loaded by block 9 to make a normal Forth system. The syatem has now loaded all necessary blocks from 0 to 1000.
The rest of the basic image Forth system is then loaded. This includes the image display and DICI drivers, and the Network Interface layer. Any other modules are loaded here, except those for the actual Autoguider application.
The last main part of the system to be loaded is the Autoguider application itself. It contains the CCD drivers with the commands the autoguider uses, and the ability to support more than one CCD controller. The window graphics, configuration and centroiding code is here. Once the autoguider application has loaded, the autoguider system has a set of commands which will operate the system in its normal fashion. This Common command set is what the Network or User Interface manipulate.
The Network to Autoguider interface is loaded, which allows the Network software to see the command set and status variables necesary to operate the system. The User interface is loaded last, which provides parameter checking and command line parsing on a limited set of Forth words normally available to the operator.
At this point, the system prompts the user to enter todays configuration and then the system initialises all necessary systems ready for use.