2
1.2
WIND VANE
The wind vane is coupled to a 20K ohm, ±20%, single turn potentiometer. The linearity of
the potentiometer is ±1%. Maximum power dissipation should be limited to 1/4 watt.
Resolution is infinite over potentiometer's 355 degree arc. There is a gap ("dead band")
of approximately 5 degrees between the ends of the resistive media. As the wind blows
past the vane, the design of the counter-weight and the tail fin align the point of the
counter-weight into the wind. Fluctuations in the wind direction are measured by the
sensor as the aerodynamics of the counter-weight and the tail try to keep aligned to the
path of the wind. The motion of the wind vane is translated to the potentiometer shaft
causing a change in the potentiometer's resistance. Connecting the potentiometer wires
to a voltage source allows easy measurement of the wind direction as a change in voltage.
1.3
TEMPERATURE
The ambient air temperature is measured by using a thermistor that is mounted inside the
protective shield located on the side of the sensor base. The thermistor exhibits rapid
changes in its resistance in response to temperature changes. The resistance change is
inversely proportional to the temperature. By using precision scaling and linearization
resistors in a bridge circuit, the resistance changes of the thermistor can be converted into
a voltage that can be easily calibrated and monitored. The thermistor's resistance vs.
temperature data can be found in Table 1.
2.0
SPECIFICATIONS
Anemometer:
Turning Radius:
3" to center of cup
Speed Threshold:
1.2 mph
Transducer Type:
Reed Switch, Magnet Activated
Speed Constant:
1.25 mph = 1 Hz
Measurement Range:
0-100 mph
Accuracy:
1 mph or ±3%
