Research On Data Processing Technology Of Electromagnet Ultrasonic Thickness Measurement System

Metal plates and pipes are widely used in industrial production,construction,oil transportation and other industries.In the process of sheet metal production,thickness is an important production index,while in the process of oil pipeline use,the thickness detection is not in place,which is prone to crude oil leakage and even explosion,endangering people’s property and life safety.Since the development of thickness nondestructive testing methods,there are many methods such as eddy current,laser,ray and ultrasonic testing.With its many advantages,ultrasonic testing is widely used in the field of industrial nondestructive thickness measurement,mainly including piezoelectric ultrasonic and electromagnetic ultrasonic testing.Piezoelectric ultrasonic thickness measurement is relatively mature,but it is limited to the need to use coupling agent,the surface of the object to be measured should be smooth,and the operation is difficult and high cost at high temperature.Electromagnetic ultrasonic thickness measurement not only does not need coupling agent,but also has simple operation,which has become a new research direction.However,due to the low energy conversion efficiency of electromagnetic ultrasonic transducer,the echo signal is doped with a lot of noise and interference,and the signal-to-noise ratio is low.Reasonably designing the algorithm to extract the effective signal and solve the accurate thickness measurement value is of great significance for the application of electromagnetic ultrasonic thickness measurement.Aiming at the problem of thickness feature extraction of electromagnet electromagnetic ultrasonic thickness measurement system using pulse electromagnet to provide bias magnetic field,based on the electromagnetic ultrasonic energy exchange mechanism,electromagnetic ultrasonic thickness measurement principle and echo signal thickness value calculation method,considering the poor signal-to-noise ratio of echo signal and large amount of data,it is difficult to extract thickness feature directly,and analyze the noise in the original echo signal,The preprocessing algorithm is designed to preliminarily reduce the noise of the data.The average filtering algorithm is proposed to suppress the random noise,the general digital filter to filter the low-frequency and high-frequency noise,and the wavelet hard threshold method to suppress the medium and high-frequency noise.The Gaussian multi echo parameter model is introduced to verify the effectiveness of the preprocessing algorithm.The preprocessing algorithm can preliminarily improve the signal-to-noise ratio and reduce the pressure of subsequent data processing.Considering the residual noise after pretreatment,the improved adaptive variational modal decomposition method is used to further suppress the noise,including determining K and quadratic penalty term by central frequency method ɑDetermination of signal SNR relationship ɑ,The Pearson correlation coefficient between the decomposed signal and the original signal determines the reconstructed mode.After the signal is processed by the above algorithm,the peak trough difference method is used to extract the thickness feature after signal noise reduction.Build an experimental platform to obtain the experimental data of electromagnet electromagnetic ultrasonic thickness measurement of steel plate and aluminum plate samples with different nominal thickness,and use this algorithm and other traditional algorithms for processing.The experimental results show that this algorithm has higher thickness measurement accuracy than other algorithms.The thickness calculation error of 24 mm thick steel plate is 1.53%,while that of 30 mm thick aluminum plate is 1.43%.Finally,in order to make the algorithm more convenient in engineering application,the upper computer for thickness feature extraction is compiled in the form of joint programming of Lab VIEW and MATLAB.Combined with the data acquisition card,the functions of data acquisition,data processing and thickness value display of electromagnet electromagnetic ultrasonic thickness measurement system are realized.