The Study Of Gas Sensor Experiment System Based On Acoustic Relaxation

Gas detection has a lot of applications in the actual production and life.First,the real-time gas monitoring of the environment provides a guarantee for the industry and military fields,such as petrochemical industry,aerospace and so on.At the same time,with more attention being given to environmental protection,the detection of atmosphere has become more and more important.The development of the acoustic theory and the proposal of ultrasonic parameters which is suitable for the practical application make it possible for us to use sound spectrum?sound attenuation spectrum and sound velocity spectrum?to realize fast and accurate gas detection in complex gas environment.The gas acoustic relaxation sensing experiment system not only can measure the sound spectrum in different gas and verify the theoretical model,moreover,it will become the basis of future intelligent ultrasonic detector which is sure to have a great practical application.The experimental system based on gas acoustic relaxation and ultrasonic sensor is designed and implemented in this thesis.It can be used to measure sound attenuation spectrum and sound speed dispersion spectrum under wide frequency range.We use 7fixed frequency ultrasonic transducers and a experimental cavity that can provide0.1atm-3atm gas environment to cover the frequency range of 8KHz-4MHz.A singlechip and a waveform generator are used to produce the sine wave at a specific frequency.A pair of ultrasonic transducers are used to transmit and receive ultrasonic waves and the distance between the two transducers is changed by the stepper motor system.At the same time,a data acquisition and control system based on LabVIEW is designed to realize automatic control and measurement.Using this software system,we can control the stepper motor,collect the temperature and humidity data and the signals at the transmitting end and the receiving end.Then after denoising and calculating,the required acoustic parameters will be obtained.After the completion of the system,we first carried out a functional test,and then used the experimental system to measure the acoustic attenuation coefficient and sound velocity in pure CO₂ and 50%CO₂-50%N₂.Compared with the experimental device?the prototype 1?of our laboratory,this system can cover a frequency range of acoustic relaxational processes,furthermore,it can be used to measure the dispersion of sound velocity.Comparing the experimental results with the acoustic spectra obtained from the theoretical reconstruction,the stability and reliability of the experimental system are verified.For the measurement of sound attenuation coefficient,we improved the accuracy of measurement compared with prototype 1.