Design And Implementation Of High Precision Ultrasonic Anemometer Measuring System

The measurement of wind speed is one of the bases of aerodynamics and related research.There are many kinds of anemometers in use,and their working principles and performances are also different.The correlation between wind speed and temperature is strong,and temperature is particularly difficult to measure accurately.The ultrasonic jet lag method can eliminate the influence of temperature in the air.This paper aims to design and implement a measurement system for measuring wind speed and direction by ultrasonic time difference method.The hardware circuit of ultrasonic anemometer mainly includes three parts: main control module,transmission driver module and echo conditioning module.The main control module adopts DSP+FPGA architecture.DSP is responsible for time difference extraction,measurement control,communication with upper computer,etc.FPGA works with DSP to control square wave excitation,channel selection,acquisition control and data storage,etc.,and 12-bit high-precision ADC is used for digital acquisition.After the transmission driver module switches the square wave signal through the channel and selects the chip,the voltage is boosted to 300 Vpp to stimulate the transducer to emit ultrasonic signal.The echo conditioning module uses a charge amplifier to transform the charge signal of the transducer into a weak voltage signal,which is amplified by a program-controlled amplifier for digital acquisition.The sensor distance can be adjusted according to the actual demand.The mathematical model of wind speed and direction is established according to the structure.The time difference extraction algorithm is designed.According to the properties of the echo signal,an echo time arrival algorithm based on variable threshold zero-crossing detection is proposed.The main program of the measurement system and the communication protocol with the upper computer are designed in detail.This paper also analyzes the error sources of ultrasonic anemometer and designs different error correction algorithms according to different error classifications.The matrix fitting correction algorithm is derived by combining structural machining and installation error.In this thesis,a prototype of ultrasonic anemometer based on time difference method is developed,and a measuring experimental platform is built.The wind speed and direction were measured in laboratory and wind tunnel,and compared with TSI hot-wire instrument.The experimental results show that ultrasonic prototype under the condition of low wind speed,measurement accuracy is higher,the wind speed measuring precision is 0.1 m/s,a resolution of 0.01 m/s,the wind measurement precision is 1 °;Compared with the TSI hot-wire instrument,the mean value of the measured results was the same,but the standard deviation was larger.