Ultrasonic Wind Speed and Wind Direction Anemometer for Wind Measurement

Traditional mechanical wind speed and direction sensors have rotating parts, which are prone to wear and tear. The mechanical structure may be damaged by bad weather, and sand dust and salt spray will also cause corrosion. At the same time, due to the existence of friction, the mechanical anemometer will not be able to drive the propeller or the wind cup to rotate when the starting wind speed is lower than the starting value. Therefore, the mechanical anemometer will not be able to measure the breeze below the starting wind speed. In order to overcome the inherent shortcomings of the traditional cup anemometer, the new ultrasonic anemometer came into being.

Ultrasonic wind speed and direction sensors have been widely used in industrial fields and scientific research due to their advantages such as fast response speed, high measurement accuracy, and easy maintenance and use. The ultrasonic wind direction sensor mainly uses the ultrasonic frequency difference emitted by four vertically placed ultrasonic sensors to calculate the wind speed and wind direction, and outputs the wind speed (m/s) and wind direction (°) through the sensor output.

Three ultrasonic velocimetry methods

Ultrasonic wind speed measurement mainly includes time difference method, frequency difference method, phase difference method and correlation method.

Time difference method

Jet lag is very common and works on the principle that in calm air, the speed of sound waves is changed by the flow of air in the direction of the wind. If the wind direction and the sound wave travel in the same direction, the speed of the sound wave will increase, otherwise it will decrease the speed of the sound wave.

When the ultrasonic wave propagates in the air, there is a speed difference between the downwind and the upwind direction. When it propagates a fixed distance, this speed difference reflects a time difference, and this time difference has a linear relationship with the wind speed to be measured. Therefore, the ultrasonic anemometer emits ultrasonic waves in sequence at a fixed frequency, and measures the arrival time of ultrasonic waves in two directions, thereby obtaining the propagation speed of the downwind and the propagation speed of the headwind, and the wind speed value can be obtained after processing and conversion.

Frequency difference method

The frequency difference method is a direct method with multiple cycles. The accuracy of this method is twice that of the time difference method. It is suitable for medium and small diameter pipes. .

Phase difference method

The phase difference method is to measure the wind speed by converting the time difference into phase.

Problems with ultrasonic anemometers

Wind direction angle transient problem: When analyzing the wind direction signal measured by the two-dimensional ultrasonic wind speed and wind direction sensor, the wind direction angle transient phenomenon generally exists in the wind direction data, that is, the wind direction angle appears extremely violent and large in a short period of time. fluctuation. The wind direction signal fluctuation characteristics during the wind direction angle transient period are obviously different from other periods. Only by deeply understanding the reasons for the wind direction angle transient phenomenon can we judge whether this phenomenon will affect the subsequent analysis of the wind direction signal fluctuation. If there is an adverse effect, appropriate methods should also be used to make reasonable corrections to the wind direction signal.

Ultrasonic anemometers are currently widely used in electric power safety monitoring, bridges and tunnels, urban environmental monitoring of sailing ships, road safety and other fields. The many advantages of the ultrasonic anemometer make it more and more widely used, and it will occupy the dominant position of the anemometer device in the future.

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