Anemometer

What is Anemometer?

An anemometer is an instrument that is used for meteorological purposes like measuring the velocity of wind. It is used in the weather station and the name for this device is derived from the Greek word "anemos" which means, "Wind". There are various kinds of anemometers that have been developed from around the fifteenth century. Anemometers can be classified in two different sections. The first type of anemometer is that which measures the velocity of the wind and the second type is that which measure the pressure of wind. Though they have been classified as two different type if one gets a standard anemometer it can serve the purpose of measuring wind speed as well wind pressure.

Types of Anemometer and the way they work

The five major types of anemometers are as follows:

1. Cup Anemometer-This is the simplest kind of anemometer which consists of four hemispherical cups which are mounted on one end of the four horizontal arms which are also mounted at equal angles to each other on a vertical shaft. The cups are mounted in such a way that air passes across the cups in a horizontal direction and the cups are turned which is proportionate to the speed of the wind. To find the average speed of the wind, the turns of the cups over a period of time has to be counted. It seems the Cup anemometer is exposed to friction as a result of which they do not provide accurate results.
2. Windmill Anemometer- The windmill anemometer is also a mechanical device that helps in finding out the velocity of wind. It is very similar to the normal windmill in which the axis of rotation runs parallel to the direction of the wind thus making it horizontal. But the wind keeps on changing its direction therefore the axis has to change its direction so an aerovane is also combined in the device. An aerovane consists of a propeller and a tail so that precise wind speed and direction measurements can be obtained.
3. Hot wire Anemometer- In this type a very thin wire is used which is heated up to a temperature that is a little more than the atmospheric temperature and when air flows past the wire it cools it. The resistance of most metals towards electricity depends to an extent on the temperature of the metal thus the velocity can be obtained from the relation between resistance of the wire and the velocity of the wind.
4. Laser Doppler Anemometer- These types of anemometers use very high-end technology thus come out to be accurate. Here a beam of light is used which is split into two beams, one of these enter the anemometer and the velocity is determined on the basis of the amount of light that has been reflected off by the moving air particles.
5. Sonic Anemometer- In this type of anemometer the speed of wind is obtained by sending sound waves between a pair of transducers and calculating the way their speed is affected. This type is quite popular in aircrafts and scientific wind turbines. Since they also do not have many moving parts they can also be used in the automated weather stations.