Sensor structure and principle of anemometer
Anemometers can provide the most original recorded wind speed and direction data in hydrographic stations, environmental protection, agriculture, forestry, power plants, islands, transportation, mines and other industries.
The anemometer sensor adopts a traditional two-cup rotating frame structure. It converts the wind speed into the rotational speed of the rotating frame.
In order to reduce the starting wind speed, a lightweight wind cup made of special materials and a jewel bearing support are used. After being detected by the sensor, the device fixed on the rotating frame transmits the signal to the host for measurement.
The microcontroller in the anemometer samples, corrects, and calculates the output signal of the wind sensor;
Finally, the instrument outputs five parameters: instantaneous wind speed/one-minute average wind speed/instantaneous wind level/one-minute average wind level/wave height corresponding to the average wind level.
The measured parameters are directly displayed digitally on the LCD display of the instrument.
In order to reduce the power consumption of the instrument, the sensors and microcontrollers in the instrument have taken a series of special measures to reduce power consumption.
In order to ensure the reliability of the data, when the power supply voltage is too low, the battery mark at the bottom of the display shows lack of power, prompting the user that the power supply voltage is too low and the data is no longer reliable, and the battery needs to be replaced in time.
How an anemometer works
The basic principle of an anemometer is to place a thin metal wire in a fluid and pass an electric current to heat the wire so that its temperature is higher than the temperature of the fluid, so the wire anemometer is called a "hot wire". When the fluid flows through the wire in the vertical direction, it will take away part of the heat from the wire, causing the temperature of the wire to drop. According to the forced convection heat exchange theory, it can be derived that there is a relationship between the heat Q lost by the hot wire and the velocity v of the fluid. A standard hot-wire probe consists of two brackets stretching a short, thin metal wire, as shown in Figure 2.1. Metal wire is usually made of metals with high melting points and good ductility such as platinum, rhodium, and tungsten. Commonly used wires have a diameter of 5 μm and a length of 2 mm; the smallest probe has a diameter of only 1 μm and a length of 0.2 mm. According to different uses, hot wire probes are also made into double wires, triple wires, oblique wires, V shapes, X shapes, etc. In order to increase the strength, a metal film is sometimes used instead of a metal wire. A thin metal film is usually sprayed on a thermally insulating substrate, which is called a hot film probe, as shown in Figure 2.2. Hot wire probes must be calibrated before use. Static calibration is carried out in a special standard wind tunnel, and the relationship between flow velocity and output voltage is measured and drawn into a standard curve; dynamic calibration is carried out in a known pulsating flow field, or by adding a heating circuit to the anemometer. The last pulsating electrical signal is used to verify the frequency response of the hot-wire anemometer. If the frequency response is not good, the corresponding compensation circuit can be used to improve it.
The flow velocity measurement range of 0 to 100m/s can be divided into three sections: low speed: 0 to 5m/s; medium speed: 5 to 40m/s; high speed: 40 to 100m/s. The thermal probe of the anemometer is used for accurate measurement from 0 to 5m/s; the wheel probe of the anemometer is ideal for measuring flow rates from 5 to 40m/s; and the pitot tube is used to obtain the best results in the high-speed range. result. An additional criterion for the correct selection of the flow velocity probe of an anemometer is the temperature. Usually the operating temperature of the thermal sensor of an anemometer is about +-70C. The wheel probe of the special anemometer can reach 350C. Pitot tube is used above +350C.
