Introduction of 4 common anemometers
1 hot wire anemometer. A metal wire heated by an electric current, the flowing air makes it dissipate heat, and the heat dissipation rate is linearly related to the square root of the wind speed, and then linearized by an electronic circuit (for easy calibration and reading), a hot wire anemometer can be made. There are two types of hot-wire anemometer: side heating type and direct heating type. The heating wire of side heating type is generally manganese copper wire, its temperature coefficient of resistance is close to zero, and a temperature measuring element is installed on its surface. The hot wire of the direct heating type is mostly platinum wire, which can directly measure the temperature of the hot wire itself while measuring the wind speed. The hot wire anemometer has high sensitivity at small wind speeds and is suitable for small wind speed measurements. With a time constant of only a few hundredths of a second, it is an important tool for atmospheric turbulence and agrometeorological measurements.
2 wind cup anemometer. It is the most common type of anemometer. The rotating cup anemometer was first invented by Robinson in England. At that time, there were four cups, and then three cups were used. The three parabolic or hemispherical empty cups fixed on the frame are all along one side, and the whole frame together with the wind cup is mounted on a shaft that can rotate freely. Under the action of wind force, the wind cup rotates around its axis, and its rotational speed is proportional to the wind speed. The speed can be recorded by electrical contacts, tachogenerators or photoelectric counters.
3 acoustic anemometer. The wind speed component in the sound wave propagation direction will increase (or decrease) the sound wave propagation speed, and the acoustic anemometer made by using this characteristic can be used to measure the wind speed component. Acoustic anemometers have at least two pairs of sensing elements, each pair consisting of a sounder and a receiver. Make the propagation directions of the sound waves of the two sounders opposite. If one group of sound waves propagates along the wind speed component and the other group happens to travel against the wind, the time difference between the two receivers receiving the sound pulse will be proportional to the wind speed component. If two pairs of components are installed in the horizontal and vertical directions at the same time, the horizontal wind speed, wind direction and vertical wind speed can be calculated respectively. Because ultrasonic waves have the advantages of anti-interference and good directivity, the frequency of sound waves emitted by acoustic anemometers is mostly in the ultrasonic band.
4 propeller anemometers. It is an anemometer with a set of three or four bladed propellers rotating around a horizontal axis. The propeller is mounted on the front of a weathervane so that its plane of rotation is always facing the direction of the wind, and its rotational speed is proportional to the wind speed.
