What Are the Different Techniques for Wind Speed Measurement?

brief introduction

Anemometer measurement technology and selection guide

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brief introduction

Anemometer Probe Selection

The flow 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 anemometer's thermal probe is used for accurate measurement of 0 to 5m / s; the anemometer's rotary probe is best for measuring the velocity of 5 to 40m / s; and the use of a pitot tube can get the best in the high speed range result. An additional criterion for the proper selection of an anemometer's flow rate probe is temperature. Usually, the temperature of the anemometer's thermal sensor is about + -70C. Rotary probe of special anemometer can reach 350C. Pitot tube is used for + 350C and above.

Anemometer thermal probe

The working principle of the anemometer's thermal probe is based on the cold shock air flow to take away the heat from the hot element. With the help of an adjustment switch to keep the temperature constant, the adjustment current is proportional to the flow velocity. When using a thermal probe in turbulence, the airflow from all directions hits the thermal element at the same time, which will affect the accuracy of the measurement results. When measuring in turbulence, the display value of the thermal anemometer velocity sensor is often higher than that of the rotary probe. The above phenomenon can be observed during pipeline measurement. Depending on the design of the pipe turbulence, it can occur even at low speeds. Therefore, the anemometer measurement process should be performed on the straight part of the pipe. The starting point of the straight part should be at least 10 × D (D = pipe diameter, unit CM) before the measurement point; the end point should be at least 4 × D after the measurement point. The fluid cross section must not be obstructed. (Angles, resuspends, objects, etc.)

Anemometer rotary probe

The working principle of the anemometer rotary probe is based on converting the rotation into an electrical signal. It first passes a proximity sensor to start, "count" the rotation of the runner and generate a series of pulses. Get the speed value. The anemometer's large-diameter probes (60mm, 100mm) are suitable for measuring turbulence at medium and small flow rates (such as at the outlet of a pipe). The small-caliber anemometer of the anemometer is more suitable for measuring the airflow with the cross section of the pipeline more than 100 times larger than that of the exploration head.

Positioning of anemometer in air flow

The correct adjustment position of the rotary probe of the anemometer is that the airflow direction is parallel to the rotary axis. When the probe is gently rotated in the air flow, the displayed value will change accordingly. When the reading reaches the maximum value, the probe is in the correct measurement position. When measuring in a pipeline, the distance from the starting point of the straight part of the pipeline to the measurement point should be greater than 0XD. The effect of turbulence on the anemometer's thermal probe and pitot tube is relatively small.

Anemometer measurement of airflow velocity in pipes

Practice has proven that the 16mm probe of the anemometer is the most versatile. Its size not only guarantees good permeability, but also can withstand a velocity of up to 60m / s. As one of the feasible measurement methods, the measurement of air flow velocity in the pipeline, the indirect measurement procedure (grid measurement method) is suitable for air measurement.

VDI12080 provides the following procedures:

Square cross-section grid, measuring common specifications

Circular cross-section grid, measuring centroid axis specifications

Circular cross-section grid, linear range measurement

Measurement of anemometer in exhaust air

The vent will greatly change the relatively balanced distribution of airflow in the pipeline: high-speed areas are created on the surface of the free vents, and the remaining parts are low-speed areas, and vortices are generated on the grid. According to the different design methods of the grid, the airflow section is relatively stable at a certain distance (about 20 cm) in front of the grid. In this case, the caliber runner of a large anemometer is usually used for measurement. Because the larger caliber can average the uneven flow velocity and calculate its average value in a larger range.