An Ultrasonic Anemometer Design

Several implementation methods of the anemometer have been introduced in this paper. The principles, advantages and disadvantages of theses wind speed measuring methods based on the ultrasonic have been discussed, and the factors which influence the measurement accuracy are also discussed. The current research status of the ultrasonic anemometer at home and abroad has been presented.The relationship among the measurement accuracy of the resonance frequency of ultrasonic transduction and the arriving time, the ultrasonic propagation attenuation characteristic, and the transmit signal directivity has been analyzed, and the suitable operating frequency has been chosen. The transducer structure, piezoelectric material, design of the acoustical impedance matching layers, substrate material and the process flow have been discussed. The design methods of two types of ultrasonic transducers have been analyzed. The first one is the single-frequency piezoelectric ultrasonic transducer operated at the radial vibration mode; and the second one is the broad-band transducer which is implemented through the coupling of the radial vibration mode and the longitudinal vibration mode by use of the equivalence of the two vibration modes in the cylindrical piezoelectric material. The space topology structure of multiple transducer arrays has important influence on the measurement accuracy of the vector wind speed. The straight-through structure and the reflecting structure have been analyzed. An ultrasonic probe topology structure combining with these two structures has been proposed and the computational fluid dynamics(CFD) has been used to simulate it in this work. Thus the wind speed measuring range of single ultrasonic probe can be broadened.The excitation modulation signal generator has been designed by use of the phase-locked loop inside FPGA, and the driving circuit has been implemented by use of MOSFET circuit. The output detected signals amplitude of the ultrasonic probe at the receiver is very small, which contains large amount of noise signals introduced by the acoustic interference and electrical interference. A multi-stage amplification and filtering structure has been designed in this work. Thus the noise signals can be suppressed very well while the signals are amplified. The amplified analog signal is converted to digital signal by a ADC circuit and sent to FPGA for signal processing. The ultrasonic signal propagation time measurement has been realized by use of VHDL language. Three ultrasonic signal arriving time measurement methods of zero-crossing detection, phase detection and relevant detection have been discussed and compared.The design of a 2-D anemometer has been carried out in this work. By use of the ultrasonic probe combining with the straight-through structure and the reflecting structure, the measurement accuracy of the anemometer is better than 5% at the wind speed of 0~150m/s.