Sonic / Ultrasonic Anemometers
C = local speed of sound.
Then, Similarly, and, so, which gives us the wind component along one axis.
A pulse along an axis 90o horizontally to the previous one gives the component along its axis.
Consider:
Thermal Wind Devices
Changing current causes a voltage imbalance in a bridge circuit.
The relationship between current and the wind speed is given by: where A and B are usually determined during calibration of the instrument and are related to heat losses due to convection, radiation, wire support conduction. ìAî is the current in the wire when V = 0.
Wire used is typically platinum about .01 to .1 mm thick and about 1 mm long.
Advantages: Disadvantages
Hot-film anemometers use a thin film of platinum.
Kata Thermometer
PPT Slide
Quartz Crystal Anemometer
Resonance frequency is determined with heater off. Crystals at air temp.
For wind direction:
Vortex Anemometer
150 KHz stripped from signal at receiver leaving modulation signal.
Comparison of several anemometers
Email: alcorn@ariel.met.tamu.edu
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