Cup anenometers are used to measure wind speed, or as in the case of of our anemometer, is used to totalize the amount of wind that has passed over a surface (referred to as a totalizing cup anemometer). Some cup anemometers measure wind pressure, but wind pressure is a function of speed, so speed is often the desired data.
Often confused with providing wind velocity, the cup anemometer is unable to determine wind direction (velocity is a function of BOTH speed AND direction). Though, in 1991, Australian inventor, Derek Weston invented a cup anemometer capable of determining both wind speed and direction by adding a tag to one cup to increase its drag; cyclical changes in the cups’ spin rate allowed for calculations of direction, though these days the more advanced weather stations use sonic sensors that measure air particle velocities and have no moving parts!
Though other types of anemometers have been invented as early as 1450 by the Italian Renaissance humanist polymath, Leon Battista Alberti, the cup anemometer itself was the invention of Irish astronomer & physicist, John Thomas Romney Robinson’s nearly 400 years later in 1843. His design was a 4 cup design (seen in the illustration on the right); the 3 cup design was created by Canadian John Patterson in 1926, with further improvements in design in 1935 by Americans, Brevoort & Joiner.
The word anemometer comes from the Greek root, anemos, meaning “wind”, and most anemometers sole function is to measure the speed of wind in one of the following most commonly used units of measure:
- miles per hour
- feet per minute
- feet per second
- kilometers per hour
- meters per minute
- meters per second
All these units can be easily converted over to numbers on the Beufort Scale.
Cup anemometers have either 3 or 4 hemispherical cups mounted at the end of metal or plastic arms. Each cup is mounted at equal angles to each other on a vertical central shaft supported by a base clamped or bolted immovably tight. Because each cup is mounted at equal angles, it does not matter from which direction the wind blows, a cup will ‘capture’ the wind and be pushed causing the next cup to be blown into its former position where that cup is now ‘pushed’ and so on and so forth. The result is spinning cups atop the vertical shaft. The rate of spin is proportional to the speed of the wind, and can be recorded on either an electronic datalogger or some mechanical or digital display.
Modern cup anemometers have a coned back to increase the aerodynamics of the cup unit itself (lessen drag) in order to give us more accurate readings.
Our totalizing cup anemometer is located just above water level on the wooden frame supporting the Evaporation Pan.
Our cup anemometer measures amount of wind which passes over water surface in the evaporation pan. An odometer near the base of the anemometer records amount of wind occurrence in miles.
The cup anemometer is located on south side of pan near the Six’s Thermometers and its data helps us determine evaporation rates.
~ Steve Woodruff and Devin Lussier