Researches And Experiments Of Water Pipe Leakage Detection And Positioning Methods Based On Principle Of Acoustic Emission

The cross-correlation detection and positioning technology based on the principle of acoustic emission has the characteristics of high detection efficiency,and is widely used in positioning the water pipe leakage.The speed of the leaked acoustic emission signal along the pipe wall(sound speed)and the propagation time difference between the leakage signal spread to both ends of the two piezoelectric sensor are the two key parameters to achieve the leak location.Therefore,the sound speed and propagation time difference measurement methods are studied,the water pipe leak detection and positioning system is developed,the experimental platform is set up,and the sound speed percussion experiment and leakage point positioning experiments are carried out to verify the effectiveness of the studied methods and the developed system.The method based on short-term energy and linear fitting is proposed to measure the speed of sound.According to the characteristics of the percussion signal,two pairs of percussion signals picked up by two piezoelectric sensors are filtered and normalized.The square of the preprocessed signal is calculated,and the short-term energy is obtained.According to the short-term energy curve,the threshold value is set to determine the starting points of two percussion signals.The time difference corresponding to the starting point is utilized,and the propagation time difference between the two sensors is calculated so as to obtain the true sound speed of the water pipe.The performance indexes are presented to evaluate this method qualitatively and quantitatively.The method can remove the interference of spike burr noise,so it has stronger anti-interference ability compared with direct threshold method.The generalized cross correlation method is used to measure the propagation time difference of the leakage signal.Since the advantages and disadvantages of the three propagation time difference measurement methods are compared,i.e.,the cross correlation,adaptive and cepstrum,the generalized cross correlation method is chosen to deal with the leakage signal.The main distribution band of the leakage signal is determined through experiments.According to the characteristics of the leakage signal,the fourth-order Butterworth band-pass filter is used to preprocess the two leakage signals for enhancing the signal-to-noise ratio of the leakage signal.The two-way leakage signals after the pretreatment are cross-correlated in order to improve the measurement accuracy of the propagation time difference.The water pipe leakage detection and positioning system is developed to implement the above signal processing methods.The system consists of two slaves,a wireless receiver and a PC.The two slaves are designed with MSP430F5529 ultra-low power microcontrollers,which use battery-powered,and solve the problem of no external power supply.The GPS module nanosecond level synchronization timing function is utilized to solve the problem of synchronous sampling between different places.The 2.4G wireless communication is adopted to solve the problem that the distance between the two slaves is limited during the leak location.The MATLAB language is used to develop the GUI(graphical user interface)software in the PC for achieving the above data processing methods,the amount of computation is not restricted,and good results are obtained.The experimental platform is built in our laboratory,and the sound speed percussion experiment and the leak point positioning experiment are conducted to verify the effectiveness of the above signal processing methods and systems.The experimental results show that the measured sound speed is 1623.9m/s,and the maximum relative error of the leakage point is controlled within 6.6%,for the galvanized pipe with outer diameter of 25 mm.