Cloud Sensor

revised (12/06/97)

A thermoelectric module is sandwiched between two aluminum plates and mounted outside the observatory, one side pointing toward the sky and the other toward the ground. The module will generate a small voltage directly related to the temperature difference across the thermoelectric module. The voltage is amplified by a high gain instrumentation amplifier whose output is fed to a voltage controlled oscillator. The output of the oscillator is run to an input line of the computer printer port which counts the pulses. The number of pulses can then be calibrated to indicate the cloud cover. A clear sky will "look colder" in relation to the ground temperature than a cloudy sky. This technique gives fairly reliable results but sometimes gives erroneous readings during extreme weather conditions such as rain, high winds, or very rapid temperature changes.

The peltier module is sandwiched between the 2 AL plates with nylon screws. White heat sink compound was used on each side of the Peltier module. A one inch wooden dowell was slotted and a nylon screw was put through the dowell and AL plates to facilitate mounted on the south side of the observatory. A one inch hole was drilled in the observatory side to mount the dowell. A hole was then drilled through the dowell lengthwise where the two wires from the Peltier module are run into the observatory.

The Peltier Thermo Electric Module was purchased from Herbach and Rademan for $24.95 USD.