Features

 

  • Microcontroller based unit.
  • Firmware is user upgradeable via a serial port.
  • 4 PWM controlled heater outputs, with over current protection.
  • 2 PWM controlled fan outputs, with fuse protection
  • 2 User controlled outputs, opto isolated, unfused.
  • Over current protection on the 4 heater outputs.
  • 4 Temperature sensors, 1 measuring the ambient temperature, 2 for measuring the temperature of heated surfaces, one for measuring main mirror temperature.
  • LM335Z temperature sensors.
  • Honeywell HCH-1000 capacitive humidity sensor.
  • Humidity sensor used to calculate the dew point.
  • Usb connection to PC application software.
  • Uses an external 12V power source.
  • Monitors battery voltage and disables unit when battery is running flat.
  • User set parameters are stored in internal EEPROM.
  • PC software can plot humidity, air temperature, heater temperatures and battery voltage to visualise unit efficiency.

 

Heater Outputs

  • Tracks dew point temperature, outputs 1 and 2 only.
  • Tracks ambient temperature, outputs 1 and 2 only.
  • Preset temperature, outputs 1 and 2 only.
  • User set duty cycle, outputs 1 to 4.

Two of the heaters can be connected to it’s own dedicated temperature sensor. This allows these outputs to be controlled by the dew point, air temperature or a user set temperature.

The last two outputs are manually controlled by a duty cycle set by the user. Outputs one and two can also be set in this mode.

The PWM outputs are grouped in pairs and are phase shifted by 50%, this spreads the battery load and decreases the peak current drawn from the battery supply. The PWM frequency is 30Hz.

The four heaters are continually monitored for an over current condition and the corresponding output is then disabled.

Fan Outputs

Fan number one can have a temperature sensor connected to automatically control the fan speed to cool down the mirror.

The speed of both fans can be user controlled via the pc software. The maximum current for each fan is 1A.

Auxillary Outputs

There are opto-isolated outputs that can be switched on and off from the pc software. These outputs can be used to switch externally connected relays. The maximum current that can be drawn by the relays switching coil is 50ma. Solid state relays are probably the best choice. These outputs can be used to switch on and off observatory lights etc. These outputs are not fused.

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