An Anemometer is an instrument with which the wind can be determined.
Windmill with hemispheres
This instrument was introduced in 1846 by the Irish astronomer Thomas Romney Robinson (1792-1882). This instrument is a rotating windmill with three or four hemispheres (cups) with a rotating shaft rods to be confirmed. The axis is approximately perpendicular to the direction of the wind measurement. The hemispheres are hollow inside. If there are only three hemispheres then they are present prepared at 120° apart. The windmill will rotate because the wind on the concave side exerts more than on the convex side. The motion of the rotating balls through the ashes transform into a dynamo with an electrical voltage signal. The rotation speed of the wind speed are derived. This wind speed is expressed in meters per second or kilometers per hour.
Another form of an anemometer is used to measure the speed of the air (mine shafts, air conditioning) in buildings. With this type of windmill has blades in the wing shape or consists of a wheel with blades. The shaft is parallel to the direction of the wind. The weather puts a dynamo coupled motion into electrical voltage.
These motionless sensor is based on the principle that the propagation speed of sound changes with the wind speed. The direction of the wind can be lead and peaks can be measured.
This consists of two heated Pt100 measuring sensors, which are kept constantly in temperature differences. By passing air, the sensors can cooling off. The electric power which is necessary in order to maintain the temperature difference is measured and is a measure of the airspeed.
This type is similar to the classic hot wire anemometer, where the cooling is a measurement of the flow rate of the wind. The cooling effect, for example, a temperature sensitive resistance (NTC) in an electronic circuit, ensures that the wind speed is converted into a voltage or power difference.
Laser Doppler anemometer
Light scattering by particles in the flowing air can also be used as a measure of wind speed. Returning light has twice undergone a Doppler effect, from which speed can be found.
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