Design of An Ultrasonic Air Temperature Measurement System with Self-Correction Function for Humidity
| Autor: | Wen-Yuan Tsai, 蔡文元 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 This dissertation will present an ultrasonic air temperature measurement system with self-correction function for humidity. This highly accurate system can measure the average air temperature. This system consists of a pair of 40kHz ultrasonic transducers with single-pass operation. That is one transducer used as transmitter and the other as receiver. First we will discuss the effect to sound speed by environmental elements including temperature, humidity and the combination of temperature and humidity and their correction methods. This system calculates the average air temperature by the changes of sound speed in the air. But because the propagation speed of ultrasonic wave can be easily effected by humidity, the accuracy of the air temperature measurement system will be effected too. Therefore to achieve high accuracy in measurement, correction will be needed according to different environment humidity. This dissertation will implement the ultrasonic air temperature measurement system with humidity correction suitable for all kinds environment humidity and this measurement system will achieve high accuracy. We use the combination of the ultrasonic techniques of time-of-flight and phase shift. The ultrasonic wave that we adopt here is binary frequency shift-keyed(BFSK). This type of ultrasonic technique is a highly efficient algorithm with the advantages of both time-of-flight method and phase shift method with which we can get higher accuracy compared with the time-of-flight method and larger range measurement than the phase shift method. In addition, this dissertation will propose the technique of ultrasonic air temperature measurement with multiple-frequency continuous wave(MFCW). This technique makes use of three continuous ultrasonic wave of different but closely-spaced frequencies and under the condition of constant distance between transmitter and receiver three different phase shift can be acquired to measure the temperature. This technique can be applied to larger range of measurement than single-frequency continuous wave. This temperature measurement system is single-chip microcomputer-based with a relative humidity/water vapour pressure meter, generators of binary frequency shift-keyed wave and multiple-frequency continuous wave, a frequency detector, and a digital phase meter to record the data of time-of-flight and phase shift and to calculate the temperature measured. Eventually the measured temperature will be displayed on LCD or PC. PC is necessary only for calibration of the system. Experiments are conducted in a temperature/humidity-controlled chamber using BFSK with the frequencies of 40 and 42 kHz. Resolution is 0.05% and the length of air propagation path is 100 cm. The error of the measurement is ±0.4 ℃. The main advantages of this ultrasonic temperature measurement system are high resolution, using narrow-bandwidth ultrasonic transducer of low cost and and ease of implementation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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