| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 90 === In this thesis, a high accurate ultrasonic system is used to measure the distance and temperature. At first, a high accurate multiple-frequency continuous wave (MFCW) ultrasonic range-measuring system for use in air is described. The proposed system uses a method heretofore applied to RF distance measurement but not to air-based ultrasonic systems. The method presented here is based upon the comparative phase shifts generated by three continuous ultrasonic waves of different but closely-spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40-kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual frequencies are transmitted serially, each generating its own phase shift. For any given frequency, the transmitter/receiver distance modulates the phase shift between the transmitted and received signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A single-chip microcomputer-based MFCW generator and phase detector was designed to record and compute the phase shift information and the resulting distance, which is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which can be run independently after calibration. Experiments were conducted to test the performance of the whole system. Experimentally, ranging accuracy was found to be within ±0.05mm, with a range of over 1.5m. The main advantages of this ultrasonic range measurement system are high resolution, low cost, narrow bandwidth requirements and ease of implementation.
In addition, we develop a new ultrasonic measurement method based on the speed of sound to measure the temperature. The average temperature of the air between the pair of ultrasonic T/R transducers is positively associated with the speed of sound. The method presented here is based upon the comparative phase shifts generated by two continuous ultrasonic waves with different but closely spaced frequencies. In the infant incubator, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Two frequencies are transmitted serially, each generating its own phase shift. Comparison of the phase shifts allows a highly accurate evaluation of the ultrasonic velocity when the distance between the transmitter and receiver is fixed. Ultrasonic velocity measurement system can provide a quick and precise monitoring of the temperature in an infant incubator. A single-chip microcomputer-based two-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting temperature, which is then sent to PC. The PC is used for calibrating the system and recording or controlling the temperature in an infant incubator. Theoretically, the resolution of temperature was found to be within ±0.2℃ when the distance between the transmitter and receiver is 1 m. But the temperature can be only verified by with an accuracy of ±1℃ by our laboratory prototype. The main advantages of this ultrasonic temperature measurement system are high resolution, low cost, and ease of implementation.
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