Measurement Methods and Applications of Anemometers and Thermal Anemometers
An instrument for measuring the flow rate of air. There are many types of it, and the commonly used one for meteorological stations is a wind cup anemometer. It consists of three parabolic cone empty cups fixed on a bracket at an angle of 120 ° to each other, forming an induction part. The concave surface of the empty cup is in the same direction. The entire sensing part is installed on a vertical rotating axis, and under the action of wind, the wind cup rotates around the axis at a speed proportional to the wind speed. Another type of rotary anemometer is a propeller type anemometer, which consists of a three or four blade propeller as an induction component and is installed at the front end of a wind vane to align it with the direction of the wind at any time. The blades rotate around the horizontal axis at a speed proportional to the wind speed. The commonly used types of anemometers include: anemometers made using the principle of correlation between the heat dissipation rate of the heated object and wind speed; An ultrasonic anemometer is made using the principle of increasing and decreasing the speed of sound waves due to the influence of wind speed.
Selection of anemometer probes
The measurement range of flow velocity 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 sensitive probe of the anemometer is used for measurements from 0 to 5m/s; The rotary probe of the anemometer has the most ideal effect in measuring flow velocities ranging from 5 to 40m/s; And using a pitot tube can achieve the best results in the high-speed range. An additional standard for selecting the flow rate probe of an anemometer correctly is temperature, which is typically used by the thermal sensor of the anemometer at temperatures of approximately+-70C. The rotor probe of the specially designed anemometer can reach 350C. Pitot tubes are used for temperatures above+350C. The specific details are as follows:
1. Thermosensitive probe of anemometer
The working principle of the thermal sensitive probe of the anemometer is based on the cold impact airflow taking away the heat on the thermal element. With the help of a regulating switch, the temperature is kept constant, and the regulating current is proportional to the flow rate. When using a thermosensitive probe in turbulence, airflow from all directions simultaneously impacts the thermal element, which can affect the accuracy of the measurement results. When measuring in turbulence, the reading of the flow velocity sensor of the thermal anemometer is often higher than that of the rotary probe. The above phenomena can be observed during pipeline measurement. According to different designs for managing pipeline turbulence, it can even occur at low speeds. Therefore, the anemometer measurement process should be carried out on the straight section of the pipeline. The starting point of the straight section should be at least 10 times before the measurement point × D (D=pipeline diameter, in CM); The endpoint should be at least 4 after the measurement point × Location D. The fluid cross-section must not have any obstruction. (edges, overhangs, objects, etc.)
2. Rotary probe of anemometer
The working principle of the rotary probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensing start to "count" the rotation of the rotary wheel and generate a pulse series. Then, it is converted and processed by the detector to obtain the speed value. The large-diameter probe of the anemometer (60mm, 100mm) is suitable for measuring turbulence at medium and small flow rates (such as at pipeline outlets). The small caliber probe of the anemometer is more suitable for measuring airflow with a cross-sectional area greater than 100 times that of the exploration head
