Study On Water Intrusion Detection Of EMU Connector Based On Ultrasonic Technology

There are a number of line connectors of displacement sensor at the bottom of EMU train.For various reasons,there is water vapor intrusion.And water vapor will accumulate in connectors.When the water reaches a critical value and it will cause short circuit which will affect the operation of the train.So it is extremely necessary to detect the water level in the connector.In this thesis,ultrasonic detection method was used to study.Ultrasonic testing method has advantages of high sensitivity,fast speed detection and short detection time.It can detect the water level in the connector quickly and easily to guide the workers to drain away water and reduce labor workload.The specific work of this thesis is as follows:Firstly,based on the structure and condition of the connector,the pulse reflection method is selected.Based on the theory of propagation of sound waves in solid and liquid,the sound pressure and energy reflection coefficient at interface between the connector and water(air)are deduced.It is concluded that the ultrasonic energy is the reference value of ultrasonic detection.Secondly,the finite element model of the connector is established and the echo waveform is obtained by simulating the full water level,semi-water level and anhydrous.The energy of the echo signal is calculated and compared.The correctness of the theoretical calculation is verified.And the finite element model is applied to different ultrasonic frequencies.The echo waveform characteristics at different frequencies are compared.The ultrasonic detection frequency for the connector is selected.In addition,the expression of the sound field of the circular probe in the solid is deduced by the Gaussian beam model.Based on MATLAB programming,the sound field distribution of ultrasonic probe of the different frequency and different diameter are calculated and the calculation result is visualized.The influence of the excitation frequency and diameter of the probe on the beam directivity and near field length is summarized.According to the simulation results and the size of the connector,the appropriate ultrasonic probe diameter is selected。Finally,full water level,3/4 water level,half water level,1/4 water level,anhydrous state test are designed.Using the pocket-AE device to transmit different frequency ultrasonic pulses,collect the echo signal data,calculate the echo signal energy value.The difference of different water level echo signal energy value is compared.It is concluded that the ultrasonic testing method can detect the water level in the connector successfully.