| In today’s industrial society,gas pressure vessels are not only vital to social and economic development,but also inseparable from people’s lives.Due to factors such as external corrosion and the defects of the container itself,it is very likely that the container will be damaged and gas leakage will occur.In the field of pressure vessel gas leak detection,acoustic emission method has gradually become a research hotspot due to its advantages of non-invasiveness,fast response and low cost.In the early contact acoustic wave detection method,the occurrence of gas leakage was judged by analyzing and comparing the frequency spectrum before and after the leakage.In the later non-contact ultrasonic testing method,the leakage ultrasonic spectrum is analyzed to avoid the interference of environmental noise on the results,and the occurrence and intensity of leakage are judged according to the amplitude of a specific ultrasonic frequency.However,when the internal pressure of the pressure vessel is small,the acoustic signal generated during leakage will be very weak,and the signal noise of the collected signal will be low,which will greatly affect the detection accuracy and accuracy.In order to solve this problem,a tiny leak detection method based on lock-in amplification algorithm is proposed in this thesis.The lock-in amplification algorithm is mainly used to extract the target signal from the strong noise.The algorithm first multiplies the reference signal and the input signal to perform phase-sensitive detection,and moves the target frequency to the DC component.Then low-pass filtering is performed to filter out the high-frequency noise after phase-sensitive detection,and finally the amplitude of the target signal is calculated through the retained DC component.The lock-in amplification algorithm has a strong ability to suppress noise and can effectively improve the signal-to-noise ratio of the micro-leakage signal.This thesis firstly introduces the difference between traditional lock-in amplifier and quadrature lock-in amplifier,discusses the influence of different reference signals on the DC component after phase-sensitive detection,and conducts simulation calculations for sine reference signal and square wave reference signal respectively.Then,the influence of different data lengths on the results and the filtering effect of the filter order on the noise are analyzed.Finally,a leak detection system is designed and an experimental platform is built to detect and analyze tiny leaks with different distances and pressures,which proves that the lock-in amplification algorithm has a good detection effect on tiny leaks with low signal-to-noise ratio. |
