How does the anemometer work and how does the anemometer work?

1. Principle of anemometer:

The basic principle of the anemometer is that a thin metal wire is enclosed in a fluid and heated by an electric current, making its temperature higher than that of the fluid. Therefore, the wire anemometer is called “hot-wire”. When the fluid flows through the wire in a vertical direction, it will take part of the heat away from the wire and cause the wire temperature to clear. According to the forced convection heat exchange theory, the relation between the heat Q dissipated by the hot-wire and the velocity v of the fluid can be derived. Wire is usually constructed of platinum, rhodium, tungsten and other metals with high melting point and good ductility. Common wire diameter 5 m, length 2mm, minimum probe diameter 1 m, length 0.2mm. According to different USES, the hot wire probe is also made into double wire, triple wire, oblique wire and v-shaped, x-shaped, etc. In order to increase the strength, sometimes use metal film instead of metal wire, usually in a thermal insulation substrate coated with a thin metal film, known as hot film probe. The hot-wire probe must be adjusted 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 was conducted in the pulsating flow field is 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.

The velocity measurement range from 0 to 100m/s can be divided into three sections: low speed: 0 to 5m/s; Medium speed: 5 to 40m/s; High speed: 40 to 100m/s. The thermal probe of the anemometer is used for the accurate measurement of 0 to 5m/s, and the rotary probe of the anemometer is used for the optimal measurement of the velocity of 5 to 40m/s. The pitot tube gives the best results at high speeds. An additional criterion for the correct selection of anemometer velocity probes is temperature, usually the temperature of the thermal sensor of the anemometer is approximately + -70c. The spinner probe of the special anemometer can reach 350C. Pitot tubes are employed to +350C and above.

2. Anemometer usage:

1) observe whether the pointer of the electricity meter point to zero before use. If there is deviation, the mechanical adjustment screw of the electricity meter can be adjusted gently to return the pointer to zero.

2) put the correction switches in the broken position.

3) insert the measuring rod plug into the socket, the measuring rod is placed vertically upward, the screw plug is pressed to make the probe sealed, the “correction switch” is placed in the full position, and slowly adjust the “full adjustment” knob to make the meter pointer point to the full position.

4) place the “calibration switch” at the “zero position” and slowly adjust the “coarse adjustment” and “fine adjustment” knobs to make the meter pointer to the zero position.

5) after the above steps, gently pull the screw plug to expose the measuring rod probe (length can be selected according to the need), and make the red point on the probe face the wind direction, according to the meter reading, check the correction curve, you can find out the measured wind speed.

6), after measuring several minutes (about 10min), the above steps 3 and 4 must be repeated once to standardize the current in the meter.

7) after the test, the “calibration switch” shall be placed in the inoperative position.