Use of Programmable Controllers ( PC )
W. Müller (mueller@caha.es)
 

I am clever

The development of PC’s has had a very rapid progress in the last years. Where relay controls or circuits with processors used to be developed normally, today programmable controllers can be used in many cases.
However the possibilities that PC’s offer, are not yet sufficiently valuated. Therefore we give here a few use indications:

- The PC FX2N is very fast, since it takes only 0.08 µsec per logig instruction.
- It can work in floating point mode.
- Beside the basic computing capabilities, it can also work with trigonometric functions   and square roots.
- It can make code conversion like ASCII, HEX, BCD, Bin, Gray-Code.
- It can program a Closed Regulation Circuit (PID).
- Direct control of stepper motors.
- Generation of pulses with puls width modulation.
- Easy to use instructions set (subroutines, interrupt-programs, jumps within the   program).

We use the FX2N series from MITSUBISHI, that among others will control the following systems:
  • Dome rotation control.
  • Slit open/close control.
  • Dome autotracking.
  • Positions data acquisition.
  • Signal buffering in case of mains failure.
  • Emergency motor generator control.
  • Dome ventilation control.
  • Monitoring of supply voltages.
  • Liquid nitrogen production control.
  • Automatic drinking water filtering control.
  • Shut / Open of the Sky monitor hut.
  • System change run off control.
MITSUBISHI FX2N WITH INTERFACE
Programmable Controler MITSUBISHI FX2N with interface

There is a great deal of accessory modules available, for example:
    - Expansion modules.
    - A/D and D/A converters.
    - High speed counter modules.
    - Positioning mudules.
    - Ports interface modules (232, 422, Ethernet, Profibus).
    - I/O Link modules.
    - Analogic value modules.
PC’s are especially usefull to update old control systems. For instance, the old control system in the 2.2m telescope, used to have 80 relais with about 500 contacs and now, after update, we have just only one Programmable Controller.
Especially useful has shown up the Ports Interface Module, wich allow communication with computers. That way, a PC can control the automatic tracking of the 1.23m telescope, through a guider in a workstation.

We are preparing now another PC to control the dome automatic tracking for the 3.5m telescope and we have in mind another PC for automatic system change.

 

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