How does the anemometer work?
An anemometer is an instrument used to measure wind speed. There are many types. The commonly used meteorological station is a wind cup anemometer.
It consists of three parabolic conical cups fixed to each other at 120 ° on a bracket.
The entire sensing part is installed on a vertical rotation axis. Under the action of 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 it with an electric current to make it higher than the temperature of the fluid. Therefore, anemometers are called "hot wires".
When the fluid flows through a 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 convective 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 hotline probe consists of two brackets that are tightened with short thin wires. Metal wires are usually 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 diameter of the small probe is only 1 μ m, and the length is 0.2mm. Depending on the purpose, the hot wire probe can also be made into double wire, triple wire, diagonal, V-shaped, X-shaped, etc.
In order to improve strength, metal film is sometimes used instead of metal wire, and a thin 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 performed 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.
