One of the other forms of mechanical velocity anemometer is the vane anemometer. Three-cup anemometers are currently the industry standard for wind resource assessment studies and practice. Wind direction is calculated from these cyclical changes in speed, while wind speed is determined from the average cupwheel speed. He added a tag to one cup, causing the cupwheel speed to increase and decrease as the tag moved alternately with and against the wind. Derek Weston in 1991 to also measure wind direction. The three-cup anemometer was further modified by Australian Dr. The three-cup anemometer also had a more constant torque and responded more quickly to gusts than the four-cup anemometer.
Patterson found that each cup produced maximum torque when it was at 45° to the wind flow. The three-cup anemometer developed by Canadian John Patterson in 1926, and subsequent cup improvements by Brevoort & Joiner of the United States in 1935, led to a cupwheel design with a nearly linear response and an error of less than 3% up to 60 mph (97 km/h). Once the error was discovered, all previous experiment involving anemometers had to be repeated. Instead, the ratio of the speed of the wind and that of the cups, the anemometer factor, depends on the dimensions of the cups and arms, and can have a value between two and a little over three. This was apparently confirmed by some early independent experiments, but it was incorrect. When Robinson first designed his anemometer, he asserted that the cups moved one-third of the speed of the wind, unaffected by cup size or arm length.
However, in practice, other factors influence the rotational speed, including turbulence produced by the apparatus, increasing drag in opposition to the torque produced by the cups and support arms, and friction on the mount point. Theoretically, the anemometer's speed of rotation should be proportional to the wind speed because the force produced on an object is proportional to the speed of the gas or fluid flowing past it. Because of this asymmetrical force, torque is generated on the anemometer's axis, causing it to spin. 38 on the spherical side and 1.42 on the hollow side, more force is generated on the cup that presenting its hollow side to the wind. Since a hollow hemisphere has a drag coefficient of. With a four-cup anemometer, the wind always has the hollow of one cup presented to it, and is blowing on the back of the opposing cup. This type of instrument is also called a rotational anemometer. Therefore, counting the shaft's revolutions over a set time interval produced a value proportional to the average wind speed for a wide range of speeds. The air flow past the cups in any horizontal direction turned the shaft at a rate roughly proportional to the wind's speed. It consisted of four hemispherical cups on horizontal arms mounted on a vertical shaft. Velocity anemometers Cup anemometersĪ simple type of anemometer was invented in 1845 by Rev Dr John Thomas Romney Robinson of Armagh Observatory. In 1994, Andreas Pflitsch developed the sonic anemometer. In 1991, Derek Weston added the ability to measure wind direction. In 1926, Canadian meteorologist John Patterson (1872–1956) developed a three-cup anemometer, which was improved by Brevoort and Joiner in 1935. In 1846, John Thomas Romney Robinson (1792–1882) improved the design by using four hemispherical cups and mechanical wheels. (1635–1703), developed their own versions, with some mistakenly credited as its inventor. In the ensuing centuries numerous others, including Robert Hooke Alberti is said to have invented it around 1450. The anemometer has changed little since its development in the 15th century.
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