What is the principle of the wind meter?
An anemometer is an instrument used to measure wind speed. There are many types. The commonly used wind cup anemometer in meteorological stations.
It consists of three parabolic conical empty cups fixed to each other on a bracket at 120 °.
The entire sensing section is installed on the vertical rotation axis. Under the action of the wind, the wind cup rotates around its axis at a speed proportional to the wind speed.
The basic principle of an anemometer is to place a thin metal wire in a fluid and heat the wire with an electric current to raise it above the temperature of the fluid. Therefore, anemometers are called "hotlines".
When the fluid flows through the metal wire in a vertical direction, it will take away some of the heat from the wire and lower its temperature.
According to the theory of forced convection heat transfer, it can be inferred that there is a relationship between the heat loss Q of the hot wire and the velocity v of the fluid.
The standard hot wire probe includes two brackets that are tightened with short thin wires. Metal wires are typically made of platinum, rhodium, tungsten, and other metals with high melting points and good ductility.
The commonly used wire diameter is 5 μ m and the length is 2mm; The small probe has a diameter of only 1 μ m and a length of 0.2mm. According to different purposes, hot wire probes can also be made into double, three, and diagonal wires, V-shaped, X-shaped, etc.
In order to improve strength, metal film is sometimes used instead of metal wire, and a layer of metal film is usually sprayed on the insulation substrate, which is called a hot film probe.
The hot wire probe must be calibrated before use. Static calibration is carried out in a special standard wind tunnel.
Measure the relationship between flow rate and output voltage and plot it as a standard curve.
Dynamic calibration is performed in a known pulsating flow field or added to the heating circuit of an anemometer.
The pulsating electrical signal is used to verify the frequency response of the hot wire anemometer. If the frequency response is not good, it can be improved by using corresponding compensation circuits.
