Study On Temperature Measurement System In Gas Medium By Ultrasonic Amplitude Phase Modulation Method

The measurement of the temperature plays a crucial role in the online monitoring and the safe operation of the equipments of industrial process. It is a challenging problem to obtain accurate temperature measurement. Common temperature measurement methods can be divided into two categories, the invasive and non-invasive methods. The invasive methods benefit from the simplicity of the equipments and low price. However, the original temperature distribution of the measured object may be affected by the insertion of the probes due to the invasive measurement, leading to measurement errors. The non-invasive methods do not disturb the temperature distribution of the measured objects, and overcome the drawbacks of the invasive methods, which has attracted increasing attention. Owing to the distinct advantages of ultrasonic, such as good orientation, strong penetration ability, ability to obtain concentrated energy easily, the good adaptability to the specific conditions including the poor lighting conditions, the high-concentration dust, the poisonous and harmful gases, and the strong electromagnetic radiation environment, the ultrasonic method is widely used in the field of temperature measurement This dissertation studies the ultrasonic temperature measurement method.The main contributions of the thesis can be summarized as follows.(1) According to the basic law of ultrasonic wave propagation and the thermodynamic equations, the ultrasonic measurement principles are clarified, the relationship between the ultrasonic velocity and the media temperature is established, and the importance of the accurate time-of-flight (TOF) data to the ultrasonic temperature measurement is revealed.(2) The principle of TOF measurement methods are studied, besides the advantages and disadvantages. In order to avoid the delay time due to the receiving wave front part and overcome the disadvantages of the threshold method, the correlation method and the phase difference method, the amplitude and phase modulation method is presented which can measure the TOF in gas medium.(3) An ultrasonic temperature measurement system, including MCU STC as the hardware circuit control core, the ultrasonic transducer, the amplifying circuit, the multi-way switch, the Schmidt trigger, the host computer, the software of TOF measurement by MCU Timer, is designed to obtain the TOF data. The errors of the ultrasonic temperature measurement system is analyzed, including the main reasons and the influence of electrical errors, the TOF measurement method errors and environmental errors, which provide a foundation for further study on the ultrasonic temperature measurement in gas medium.(4) The experimental studies are carried out to be proved the rationality in design and accuracy in method of the ultrasonic temperature measurement system. The temperature measurement accuracy and the temperature range(35℃-90℃) are revealed. An modified amplitude and phase modulation waveform is proposed, which can improve the speed and efficiency of the measurement system.