ITAS-18

Main Menu - Tracking Control

    Selecting this item out of the Main Menu will bring up an additional menu that looks like

    Tracking Control

  1. Reset Track
  2. Stoptrack
  3. Inc Pulse Number
  4. Dec Pulse Number
  5. Increment FACTOR
  6. Decrement FACTOR
  7. Increment DECFAC
  8. Decrement DECFAC

    Items one and two are complimentary functions which you may never use in normal operation. The transmission to the telescope electronics is checked character by character for accuracy. Should you find it necessary to turn off the main power switch on the rack, you will interrupt this process. The solution is item one. Item two is used less frequently, and then mostly for testing. If you ever find need of it, remember that the sky keeps turning, even if the telescope does not track. Once tracking is reestablished, automatic moves (such as the move to HOME) will not bring the telescope to the expected position.

    Items three and four change the number of pulses issued during a tracking command. Recall that the tracking command looks like YM-40! = . The "40" in the string is the number that is affected by items three and four. The main bottleneck in the transmission is the string processing time in the telescope electronics. In principle by lowering this number (item four) initial handle paddle response should improve, i.e., in switching from track to hand paddle. In practice using numbers less than 40 produce an audible gap in the sound of the tracking operation, meaning that the commands are timed too far apart. However, the "40" was empirically determined, and may need either changing or improving, thus the purpose of these menu items.

    Items five and six affect a program variable called FACTOR. As was explained earlier, the telescope motions (except for slew) work in a way similar to the tracking operation. A rate is selected using the three position switch on the hand paddle. The command "pulse at external rate" is issued when a button is pushed. This command will pulse the stepping motor(s) at half the applied frequency for a specified number of pulses. The variable FACTOR is used to compute the number of pulses issued. The number of pulses is (drive rate) * (FACTOR). If you consider the number of pulses to be the angular distance moved by the drive disk, and the drive rate to be the angular velocity, then FACTOR performs the function of time.

    Items seven and eight change the value of a variable called DECFAC, which is an extra factor in the computation of the number of motor pulses issued when both right ascension and declination motors are asked to run simultaneously. It takes longer for the telescope microprocessor to interpret and act on two axes of motion, so DECFAC allows each motor to run longer, thus preserving the impression of continuous motion.