Though basic in construction, the cup anemometer introduced in 1846 is considered an industry standard in measuring wind speed. Modern variants of this technology use three cups that spin around a vertical axis. The torque generated by the movement of wind is proportional to the wind speed. Cup anemometers must be calibrated because the torque also depends on the geometry of the cups used and the length of the arms they are attached to. Cup anemometers are relatively inexpensive and simple to construct, making them a popular project for science fairs.
Hot wire anemometers exploit the electrical properties of metals to indirectly measure wind speed. The electrical conductivity of a metal wire is proportional to the temperature of the metal. A hot wire anemometer is essentially a fine metal wire that is heated above ambient temperatures. When wind blows, the wire is cooled, measurably reducing its conductivity. The degree to which the conductivity is reduced is proportional to the velocity of the wind. Hot wire anemometers are small and require electrical measurement equipment to use effectively.
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