An anemometer, first invented in 1450 by Italian architect Leon Battista Alberti, is an instrument that measures wind force, calculating the speed and direction of the wind. There are two types of anemometers: velocity anemometers which determine the velocity of the wind; and pressure anemometers which determine the pressure of the wind.
Velocity anemometers include cup anemometers, windmill anemometers, hot-wire anemometers, laser Doppler anemometers, and sonic anemometers. Pressure anemometers include plate anemometers and tube anemometers.
Cup anemometers are the simplest type of anemometers. The first of its kind was created in 1846 by Dr. John Thomas Romney Robinson. Robinson’s version of the cup anemometer featured four cups, each symmetrically mounted at the end of a horizontal arm. Robinson believed that his anemometer was perfectly designed and that the collected data would always be correct, regardless of the size of the cups or the length of the arms. However, his thesis was incorrect and his design was problematic; thus, the wind speeds recorded in the 19th century were also incorrect.
It was later discovered that the size of the cups in conjunction with their positions were vital, and a better version would calculate the wind speeds more accurately.
In 1926, Canadian John Patterson developed a more efficient three-cup anemometer. In 1935, the three-cup anemometer was advanced with a cupwheel design by Brevoort & Joiner of the United States; this version was advantageous and had an error of less than three percent. In 1991, the three-cup anemometer was again improved to measure both wind direction and wind speed by Australian Derek Weston (he added a tag to one cup).
Windmill anemometers, also called propeller anemometers, are quite different from the three-cup anemometer. Unlike the three-cup anemometer which is rotated vertically, the windmill anemometer must be parallel to the direction of the wind and rotate horizontally. Moreover, to get an appropriate result, a wind vane must be used since the wind changes its direction constantly. An example of the windmill anemometer is the aerovane, which looks like a toy airplane. This device has both a tail and a propeller on the same axis, which allows precise wind speed and direction calculations from the same device.
Hot-wire anemometers are delicate and occupy a very fine wire, either a tungsten or platinum, which is heated up to a fitting temperature above the surrounding area. When air passes through the exposed wire, it cools down the wire and thus determines the flow velocity by noting the convection that was taken away. In other words, the heat lost to flow convection determines the flow velocity. The heat lost can be obtained by measuring the change in wire temperature.
Laser Doppler anemometers employ a laser that is divided into two beams, with one transmitting light out of the anemometer toward the directed target to collect the reflected radiation, which determines the relative velocity of the object that was targeted in accordance with the original laser beam.
Sonic anemometers, classified as velocity anemometers similar to the ones mentioned above, determine the wind speed and wind direction by ultrasonic sound waves in one, two, or three axes. Occupied with transducers (device that converts energy), the sonic anemometer measures wind speed by transmitting and receiving sonic signals; thereafter, the device calculates the wind speed in three axes. This device is rather accurate and responds quickly to wind speed fluctuations since there are no moving parts that need to balance in accordance with the air flow; its steady stature makes it fitting for turbulence measurements.
Plate anemometers are pressure anemometers that are either circular or square with a flat plate; it is balanced by a spring which rests behind it. To measure the pressure of the wind, a wind vane keeps the plate directed against the wind and the force of the plate against the spring. Due to their fundamental design, plate anemometers are not able to record sudden fluctuations in wind pressure. In fact, they are inaccurate for high winds, respond slowly to variable winds, and fail to respond to light winds. Consequently, they are usually used to record average wind pressures.
Tube anemometers, also classified as pressure anemometers, employ a vessel at the top with an opening to record wind pressure. The pressure that occurs through the mouth of the opening causes changes to the internal pressure of the compartment, allowing the wind pressure to be calculated. The tube anemometers are very sturdy and can be mounted on a pole without any maintenance for many years.
In general, anemometers, which originated from the Greek word “anemos” (i.e., wind), are beneficial devices for collecting wind data. They are widely used and have great significance for many fields. Not only are these instruments used by weather stations, but they are used by NASA, airports, various branches of the military, beaches, civil engineers, normal citizens, and others alike. Most important, they can be lifesavers.
