Anemometer

In meteorology, an anemometer (from Ancient Greek άνεμος (ánemos) 'wind' and μέτρον (métron) 'measure') is a device that measures wind speed and direction.

In the ensuing centuries numerous others, including Robert Hooke (1635–1703), developed their own versions, with some mistakenly credited as its inventor.

In 1926, Canadian meteorologist John Patterson (1872–1956) developed a three-cup anemometer, which was improved by Brevoort and Joiner in 1935.

The air flow past the cups in any horizontal direction turned the shaft at a rate roughly proportional to the wind's speed.

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).

The three-cup anemometer was further modified by Australian Dr. Derek Weston in 1991 to also measure wind direction.

Three-cup anemometers are currently the industry standard for wind resource assessment studies and practice.

A vane anemometer thus combines a propeller and a tail on the same axis to obtain accurate and precise wind speed and direction measurements from the same instrument.

[3] The speed of the fan is measured by a revolution counter and converted to a windspeed by an electronic chip.

Hot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest.

An industrial version of the fine-wire anemometer is the thermal flow meter, which follows the same concept, but uses two pins or strings to monitor the variation in temperature.

They measure wind speed based on the time of flight of sonic pulses between pairs of transducers.

[7] The time that a sonic pulse takes to travel from one transducer to its pair is inversely proportionate to the speed of sound in air plus the wind velocity in the same direction:

Their main disadvantage is the distortion of the air flow by the structure supporting the transducers, which requires a correction based upon wind tunnel measurements to minimize the effect.

Since the speed of sound varies with temperature, and is virtually stable with pressure change, ultrasonic anemometers are also used as thermometers.

As wind passes through the cavity, a change in the wave's property occurs (phase shift).

The small size of acoustic resonance anemometers makes them physically strong and easy to heat, and therefore resistant to icing.

This combination of features means that they achieve high levels of data availability and are well suited to wind turbine control and to other uses that require small robust sensors such as battlefield meteorology.

In 1450, the Italian art architect Leon Battista Alberti invented the first such mechanical anemometer;[10] in 1663 it was re-invented by Robert Hooke.

The compression of the spring determines the actual force which the wind is exerting on the plate, and this is either read off on a suitable gauge, or on a recorder.

James Lind's anemometer of 1775 consisted of a vertically mounted glass U tube containing a liquid manometer (pressure gauge), with one end bent out in a horizontal direction to face the wind flow and the other vertical end capped.

If the wind blows into the mouth of a tube, it causes an increase of pressure on one side of the manometer.

The wind over the open end of a vertical tube causes little change in pressure on the other side of the manometer.

Since the pressure difference determines the vertical position of the float this is a measure of the wind speed.

The pitot port measures the dynamic pressure of the open mouth of a tube with pointed head facing the wind, and the static port measures the static pressure from small holes along the side on that tube.

Measuring the angle between the string-ball apparatus and the vertical gives an estimate of the wind speed.

This type of anemometer is mostly used for middle-school level instruction, which most students make on their own, but a similar device was also flown on the Phoenix Mars Lander.

Approximately 1.5% (1.6% above 6,000 feet) should be added to the velocity recorded by a tube anemometer for each 1000 ft (5% for each kilometer) above sea-level.

At airports, it is essential to have accurate wind data under all conditions, including freezing precipitation.

Anemometry is also required in monitoring and controlling the operation of wind turbines, which in cold environments are prone to in-cloud icing.