Applications Of Fractional Fourier Transform On Improved Ultrasonic Level Measurement

Ultrasonic distance measurement is an effective non-contact measuring method which is advantaged by high precision, cleanness, easy installation, high adaptability to working environment. So far, such method has been widely applied in various occasions that require to measure liquid levels, such as river levels, food processing, chemical engineering and sewage treatment. The working principle of ultrasonic liquid level meter is determining distance through calculating the time of ultrasonic transmitting and receiving and multiplying by speed of sound. However, transmitting signals are applied in most ultrasonic liquid level meters in domestic and foreign countries as constant-frequency signals. Consequently, the dead zone becomes bigger and the anti-interference ability becomes poorer. Moreover,it is impossible for traditional filtering methods to solve the coupling between non-stationary signals and noise. Therefore, it is significant to develop an ultrasonic liquid level meter featured with high precision, small dead zone and stable reading.After referring to and reviewing a great deal of relevant technical documents and literature, the author presented a detailed introduction to linear frequency modulation signal and analyzed the characteristics and advantages of the non-stationary signal as well as the generation method.After that, this paper has made a systematic introduction to fractional Fourier transform, including: first, fractional Fourier transform is defined from several different perspectives for revealing the relationship between fractional Fourier transform and traditional Fourier transform and introducing the nature of fractional Fourier transform as well as fractional Fourier transforms of some common functions;secondly, the method for non-stationary signals to filter in fractional Fourier domain is proposed, steps of the filtering method are introduced in details and a simulationresult is attained.Finally, this paper has introduced designs of hardware and software of the ultrasonic liquid level meter in details. The ultrasonic liquid level meter designed in this research is cored on MSP430 serial single chip microcomputer. In general, the meter is consisting of an ultrasonic transmitting module, an ultrasonic receiving module, a displaying and button module and a temperature compensation module.Furthermore, the software part has functions like data collection, data calculation,filtering algorithm and logical judgment of the control.Through analyzing and calculating the experimental data, the author has designed a system that can achieve precise measurement and basically meet design requirements.