热场式风速仪风向标的测量方法

EOLOS thermo electric anemometer
The EOLOS is a thermo electric anemometer including the measurement of the wind direction. This means that the sensor is used to measure the wind speed as well as the wind direction. Basically the sensor works in the same way as our finger that is stretched out to feel the wind. The finger is cooled by the air that is flowing around it. The amount of cooling can give a subjective impression of how strong the wind is, and the finger side at which the cooling is the strongest gives away the direction. EOLOS does just the same thing in an objective and more precise way. The way this works, is described in the following. The measuring principle used in the EOLOS Anemometer is also known as hot-wire air mass flow measurement, hot-surface mass flow measurement, thermal dispersion mass flow measurement, hot wire anemometry, hot-surface anemometry or thermal dispersion anemometry and is used in nearly all modern automobile engines to measure the mass flow of air going into the engine.
Convection The thermal dispersion anemometry uses the effect of cooling that a hot surface encounters when a cooler flow of a medium passes it. In the EOLOS sensor this hot surface is a small tube and the medium flowing around it is air. The dispersion of heat from the tube to the air is known as forced convection. Convection is generally a heat transfer by movement of molecules. In the forced convection the movement is forced by wind or other outside sources as opposed to “natural” convection that occurs when the air heats up at the surface of the tube and than rises caused by the lower density of the warm air. Together with the forced convection there is always a small amount of natural convection which can be neglected here. The amount of dispersed heat by the forced convection depends mainly on the changing values of air flow, pressure (density) and the temperature difference between the tube and the medium (air).
Measurement In a hot-surface or hot-wire anemometer a surface or wire is heated by an electrical current that flows through it. The used materials have a temperature dependant electrical resistance that rises with the temperature (PTC). The electrically imparted heat is partially dispersed away by the flow of air. This heat loss rises with the flow rate of the air. Because of this the electric power can be used to measure the flow rate. To measure this flow rate dependant heat loss there are two established measurement principals: The Constant Current Anemometry (CCA) and the Constant Temperature Anemometry (CTA). CCA - Constant Current Anemometry With Constant Current Anemometry the electric current used to heat the probe is held constant and the voltage drop at the resistance is measured. This voltage is proportional to the temperature of the probe. With a rising flow rate the probe is cooled down and the voltage drops. A Constant Current Anemometer is very simple and is good at measuring small flow rates, but the sensibility drops fast with higher flow rates.
23062011
1