Facts About Anemometers
Anemometers are meteorological instruments used to measure wind speed. There are two types of anemometers: pressure and velocity. However, since an increase in pressure means an increase of velocity, both types of anemometers can give you information about either factor.
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Pressure Plate Anemometer
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The pressure plate anemometer was invented by Robert Hook in 1667. It is a metal plate that is free to swing in the vertical. The pressure of the wind pushes on the plate, forcing the plate to move to a specific angle. The wind speed is then read from a scale attached to the instrument.
The Cup Anemometer
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The cup anemometer was invented by John Thomas Romney Robinson in 1846. Three or four cups are mounted on a vertical shaft. The difference in air pressure on one side of the cups causes them to spin. The velocity at which they spin can be translated by gears onto a dial indicating wind velocity.
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Calculation for Cup Anemometer
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Some cup anemometers do not have a dial to indicate wind velocity. In these cases, one of the cups is painted a different color. To find the wind speed in miles per hour, count rotations of the colored cup in 30 seconds. Multiply the number of rotations by the diameter in inches and divide by 168. To find the wind speed in kilometers per hour, count the rotations of the colored cup in 30 seconds. Multiply the number of rotations by the diameter in centimeters and divide by 265.
Laser Doppler Anemometer
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A laser Doppler anemometer has a laser beam that is split into two separate beams. One of the two beams is transmitted out from the center of the anemometer. Movement in the air causes a Doppler shift in the laser light. Scientists analyze the Doppler shift to calculate wind speed.
Windmill Anemometer
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A windmill anemometer has its axis of rotation parallel to the wind. The velocity of the windmill is translated into wind speed. Windmill anemometers can indicate wind direction and wind velocity.
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