An anemometer is an instrument used to measure the speed of the wind, which is a common weather station instrument or to calculate any form of current gas. The term is derived from the Greek word anemos meaning wind which was first explained by Leon Battista Alberti who was an Italian artist and an architect in the year 1450. He used a mechanical anemometer which was placed perpendicular to the wind direction such that the wind velocity as indicated by the angle of inclination of the disc. Some early versions had a ball attached to a swinging arm that travelled up a curved scale according to the strength of the wind. Most anemometers consist of three or more cups mounted on arms that spin around a pole. Inside the pole, a mechanism records the number of rotations in a certain period of time. The speed is usually given in kilometres or miles per hour, although marine anemometers may give the speed in knots.
Types Of Anemometers
The basic classification of anemometers depends on the measurement of the velocity of wind and measurement of pressure of the wind. The 5 major types of anemometer are:
Cup anemometer: This consists of four hemispherical cups that are mounted on one end of the horizontal arms at equal angles on a vertical shaft. The positioning of the cups is such that the air passes through them in the horizontal direction making the cups rotate such that it is proportional to the speed of the wind. By calculating the turns of the cups over a period of time, the average speed of the wind is found. These are used by researchers, meteorologists, and educational institutions for research and commercial activities.
Hotwire anemometer: This consists of thin wire which is heated up to a certain temperature slightly more than atmospheric temperature. The wire cools as the air flows past the wire. To calculate the velocity, the relation between the resistance of the wire and the velocity of the wind must be obtained as most metal’s resistance depends on the temperature of the metal. These find applications in HVAC (heating, ventilating and air conditioning) businesses measuring the airflow through the building ducts.
Windmill anemometer: This is a mechanical device similar to the regular windmill used to calculate the velocity of the wind. It consists of the axis of rotation running parallel to the direction of the wind. It also has an aerovane as the direction of the wind is not constant helping the axis change the direction. The aerovane consists of a propeller and a tail to obtain precise wind speed and direction measurements.
Laser Doppler anemometer: A beam of light is used which is further split into two beams. The velocity is determined by calculating the amount of light that has been reflected off by the moving air particles when one of the two beams is made to enter the anemometer. These find applications in high-tech jet engines and also in river hydrology.
Sonic anemometer: Sound waves are used to obtain the speed of the wind. These waves are made to pass through the transducer. These find applications in aircraft and scientific wind turbines.
Uses Of Anemometer
Other than measuring the speed of the wind, the anemometer is used for the following purposes:
- To measure the wind pressure
- To measure the flow of the wind
- To measure the direction of the wind
- It is used by the drone users or RC plane users to check the weather conditions before testing their devices
- Also used by long range shooters and pilots
- Used by skydivers to evaluate wind velocity before they leap into the abyss
- Used in aerodynamics to measure the airspeed
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