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Anemometers

An anemometer is usually an instrument that measures the particular velocity of air. There are several types of it. Probably the most commonly used wind glass anemometer at meteorological stations may be the sensing part of about three parabolic cones and empty cups fixed for a support at 120° both. The concave surfaces of the empty cups all experience one direction. The whole sensing part is installed on a vertical rotating shaft. Beneath the action of breeze, the wind cup rotates across the shaft at a speed proportional towards the wind speed.
The basic principle of the anemometer is to set a thin metal wire while in the fluid, and apply current in order to heat the metal wire for making the temperature higher versus the temperature of the substance. Therefore, the wire anemometer is termed the "hot wire". Should the fluid flows through the metal wire inside vertical direction, it will take away an element of the heat of the particular metal wire, so the temperature of the material wire will drop. Reported by the theory of obligated convection heat exchange, it can be derived that there may be a relationship between the heat Q lost by the heating wire and the velocity v belonging to the fluid. The standard hot wire probe features a short and slim metal wire tensioned by two brackets. Metal wires usually are made of metals using high melting point and good ductility just like platinum, rhodium and tungsten. The common wire has a diameter of 5 μm as well as a length of 2 mm; the littlest probe has a diameter of just one μm and a span of 0. 2 mm. In accordance with different purposes, the hot wire probe can even be made into double insert, triple wire, oblique line, V-shaped, X-shaped, etc. So that you can increase the strength, sometimes the metal film must be used instead of the metal wire, and a thin metal film will likely be sprayed on a thermally insulating substrate, which is labeled a thermal film probe. The hot wire probe needs to be calibrated before use. Static calibration is accomplished in a special typical wind tunnel. The relationship between movement rate and output voltage can be measured and drawn suitable standard curve; dynamic calibration is done in a known pulsating pass field, or in the heating circuit from the anemometer Check the frequency response on the hot wire anemometer using the last pulsating electrical signal. If the frequency response isn't good, the corresponding compensation circuit can be used to improve it. The flow velocity measurement consist of 0 to 100m/s is usually divided into three parts: low speed: 0 that will 5m/s; medium speed: SOME to 40m/s; high swiftness: 40 to 100m/s. The thermal probe belonging to the anemometer is used regarding accurate measurement of 0 for you to 5m/s; the wheel probe in the anemometer measures the flow velocity of 5 to 40m/s, the best result; and the use of pitot tube will get the best in the actual high-speed range result. A different criterion for the correct number of the flow sensor in the anemometer is temperature. Usually the temperature on the thermal sensor of the anemometer is going +-70C. The wheel probe in the special anemometer can reach 350C. Pitot tubes are employed above +350C.
Anemometers have several benefits, the following are some of the more important ones:
1. Small size, little interference to the flow field;
2. Wide application range. It are available not only for gas but for liquid, and can be utilized in subsonic, transonic plus supersonic flow of propane;
3. High measurement correctness and good repeatability. The disadvantage of that hot wire anemometer would be that the probe has a certain interference to the flow field, and the hot wire is easy to break.
4. Along with measuring average speed, it might also measure pulsation and turbulence; in addition to be able to measuring unidirectional motion, it can also assess velocity components in multiple directions while doing so.
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