principle and the measuring range of anemometer

anemometer its basic principle is a thin metal wire in a fluid, the flow of electricity heating wire, make its temperature is higher than the temperature of the fluid, so the wire is called the hotline.

when the fluid flows through the wire along the vertical direction, will take away the wire part of quantity of heat, temperature drops make wire. Been derived according to the theory of forced convection heat transfer, the hotline dissipating heat Q and the relation between velocity v of the fluid. Two supporting tension standard hotline probe by a short, thin metal wire. Wire normally with platinum, rhodium, high melting point, good ductility, such as tungsten metal.

common wire diameter is 5 & mu; M, to 2 mm long; The smallest probe diameter only 1 & mu; M, length is zero. 2mm。 According to different purposes, hotline probe is made double wire, three wire, wire and V, X, etc. In order to increase the strength, sometimes with a metal film instead of metal wire, usually on a thermal insulating substrate coating a layer of thin metal film, called the hot film probe.

hotline sensor must be calibrated before use. Static calibration was conducted in the specialized standard wind tunnel, measuring the velocity and the relationship between the output voltage and drawing standard curve; Dynamic calibration is done in pulsating flow field known, or in the anemometer heated circuit and a pulse signal, check the frequency response of hot wire anemometer, if poor frequency response available corresponding compensation circuit to improve them.

0 to 100 m/s of velocity measurement range can be divided into three sections: low speed: 0 to 5 m/s; Medium: 5 to 40 m/s; High speed: 40 to 100 m/s. Anemometer thermal probe used in the precise measurement of the 0 to 5 m/s; Anemometer turn wheel probe measurement 5 to 40 m/s the velocity effect of the ideal; While using pitot tube can be within the scope of the high speed to get the best results. Correct selection of the flow rate of the anemometer is an additional standard temperature of the probe, the use of thermal sensors usually anemometer temperature of about + - 70C。 Special anemometer wheel probe of up to 350 c. Pitot tube is used for more than + 350 c.