What is the principle of hot-wire anemometer?
One is the impeller anemometer. It goes without saying that the probe of the impeller anemometer rotates like a fan blade to measure wind speed, mainly measuring the wind speed on the wind speed surface;
The second is a hot wire anemometer, whose probe is a thin metal wire that heats up, so it is called a hot wire, mainly measuring the wind speed at clean low wind speed points;
The third is the differential pressure anemometer, which mainly measures wind speed based on the principle of differential pressure, mainly for measuring high wind speed and ultra-high wind speed;
The octopus anemometer/matrix anemometer for laminar flow measurement is used for surface wind speed measurement or pitot tube measurement inside pipelines, which is also a point wind speed measurement.
Here we mainly introduce the hot wire anemometer:
Hot wire anemometer is a speed measuring instrument that converts flow velocity signals into electrical signals and can also measure fluid temperature or density.
The principle is to place a thin metal wire (called a hot wire) heated by electricity in the airflow, and the heat dissipation of the hot wire in the airflow is related to the flow rate;
The heat dissipation causes a change in the temperature of the hot wire, resulting in a change in resistance, and the flow rate signal is converted into an electrical signal. It has two working modes:
① Constant current type.
The current through the hot wire remains constant, and when the temperature changes, the resistance of the hot wire changes, resulting in a change in the voltage at both ends, thus measuring the flow rate;
② Constant temperature type.
The temperature of the hotline remains constant, such as at 150 ℃, and the flow rate can be measured based on the required applied current.
Constant temperature type is more widely used than constant current type. The length of the hot wire is generally in the range of 0.5-2 millimeters, and the diameter is in the range of 1-10 micrometers. The material used is platinum, tungsten, or platinum rhodium alloy.
If a very thin (less than 0.1 microns thick) metal film is used instead of a metal wire, it is called a hot film anemometer, which functions similarly to a hot wire but is mostly used to measure liquid flow velocity.
