There are four types of anemometers:
1. The hot wire is a metal wire heated by an electric current, and the flowing air makes it dissipate heat. Using the linear relationship between the heat dissipation rate and the square root of the wind speed, and then linearizing it through the electronic circuit (for scale and reading), the hot wire wind speed can be made count. 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 in atmospheric turbulence and agriculture.
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. The wind speed component of the acoustic anemometer in the sound wave propagation direction will increase (or decrease) the sound wave propagation speed, and the acoustic anemometer made with 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 the acoustic anemometer is mostly in the ultrasonic band.
4. Propeller-type anemometer It is an anemometer with a group of three-bladed or four-bladed propellers rotating around the 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.
