1. Current Telescope Control System Big Bear Solar Observatory Pointing and Tracking Guiding Light Beam Control

2. Introduction  Current telescope control system has evolved since 1969.  Very little of telescope is computer- controlled.  Light beam control system is unique to this telescope.

3. Pointing and Tracking  Equatorial mount: RA & Dec axes.  RA axis, ring gear, worm, transmission  Preload motor -- replaces weight  Slew motor.  Tracking motor -- originally synchronous motor, now stepper motor  Set / guide motor

5. Declination  Preload spring.  Slew motor.  Set / guide motor.

7. Computer Control System  High-level control: sundial.  Low-level control: pcguider, tracking motor controller.

9. Software languages, interface to hardware  Sundial: Tcl/Tk, C.  Pcguider: C.  Motor controller (internal).  Interface: serial ports.

12. Light Beam Control  Sundial also handles light beam control.  Interface to hardware LBC through digital I/O board (imitates old PDP11 DR11 cards).  Interface to cameras is either serial or TCP/IP socket interface

13. Other hardware  LBC system also controls some other hardware.  Zeiss H-alpha filter  Filterwheel(s)

14. PC Guider  Directly controls stepper motors for guider stages.  Communicates with telpos part of PDPRP on sundial.

15. Tracking motor control  LBC computer communicates directly to tracking motor controller to set RA tracking speed.  Needed primarily because of variable lunar motion (photoelectric guiders correct for solar variations).

16. Photoelectric guiders  Small telescope forms image of Sun on quad cell. Quad cell is on motor stage controlled by PC guider.  Quad cell generates error signals in RA, Dec.  Analog servo operates telescope guider motors to minimize error signal.