Design Of An Ultrasound Wind Velocity And Direction Measurement System Based On Time Difference Method And Phase Detection Method

In recent years,ultrasonic wind speed measurement technology is the most widely used technology in the field of wind speed measurement.However,the traditional ultrasonic wind speed measurement method based on time difference or phase detection principle can not take both measurement accuracy and measurement range into account.In this thesis,we proposed a method of ultrasonic wind speed measurement with a large range and high precision,which combines time difference method and phase detection method.A prototype of ultrasonic wind speed measurement system is built to achieve a large range and high precision ultrasonic measurement.The main research work is as follows:1.According to the requirement of wind speed environmental meteorological monitoring and low-speed wind tunnel experiment for a large range and high-precision measurement of anemometer,an ultrasonic anemometry model combining time difference method and phase detection method is established,the overall scheme of the system is designed,and the key technologies are analyzed.2.Aiming at the problem that the traditional ultrasonic time difference measurement method based on threshold method is not accurate due to the amplitude fluctuation of the signal,and the measurement accuracy of the traditional single frequency pulse time difference measurement method based on correlation operation is limited due to the low rejection ratio of the main and side lobes of the correlation results,three kinds of high-precision cross-correlation time difference measurement methods based on pulse combination signal,LFM signal and Costas coded signal are proposed.The main side lobe rejection ratio and timing accuracy of cross correlation results are greatly improved by the measurement method.According to the characteristics of narrow band of the existing ultrasonic transducer on the market,the measurement accuracy of three cross-correlation time difference measurement methods is compared and analyzed through experiments,and the optimal scheme for time difference measurement is determined.3.In order to solve the problem of low precision and limited range of traditional phase detection method,a ± 180 ° digital phase detection method is developed by constructing the whole period phase detection circuit model,which extends the linear phase detection range and improves the phase detection accuracy.Furthermore,in order to solve the problem of limited measurement range of phase detection method,the time difference method and phase discrimination method are combined in this paper to ensure the wind speed measurement range and improve the measurement accuracy,which realize a large range and high-precision ultrasonic wind speed measurement.4.Based on the principle of ultrasonic wind speed measurement,an ultrasonic transmitting and receiving system is designed.The signal generating module based on the look-up table method is designed to generate the single frequency pulse combination,frequency modulation and frequency hopping ultrasonic signals.According to the capacitive impedance characteristics and the attenuation characteristics of the transmitting signal of the ultrasonic transducer,a driving circuit with the functions of tuning matching,tail absorption and power amplification is designed,which improves the electroacoustic efficiency of the transducer and shortens the tail attenuation time of the output signal of the transducer.According to the principle of ultrasonic wind speed measurement combined with time difference method and phase detection method,the low-noise constant phase signal conditioning circuit,high-precision time difference measurement circuit and high-precision digital phase detection shaping circuit are designed.Based on FPGA,a large range and high precision measurement of wind speed is realized through time difference measurement and digital phase detection.5.The prototype of ultrasonic wind speed measurement system is built and the wind speed and direction measurement calibration experiment is designed.The experimental results show that the wind speed measurement range is 0?75m/s,the resolution is 0.05m/s,and the relative error of wind speed measurement is less than 3%of the measured value under the condition of wind speed less than 20m/s and better than 1% of full scale under the condition of wind speed greater than 20m/s;the measuring error of wind direction is less than 3°and the resolution is 0.1°.