Eddy current impedance solving method and device based on cross-correlation algorithm

Abstract

The invention discloses an eddy current impedance solving method and device based on a cross-correlation algorithm. On the basis of explaining a cross-correlation algorithm principle, digital design of a core assembly of the cross-correlation algorithm is given based on an Xilinx FPGA hardware platform, and the algorithm can be achieved only through a single-chip FPGA and a small number of interface devices, so that miniaturization and portability of detection equipment are facilitated; the result obtained through the cross-correlation algorithm is compared with the LCR test result, the error is kept within + / -0.5%, and the algorithm accuracy is high; the cross-correlation algorithm completes single workpiece sorting under eight groups of frequency responses in about 2.4 s, the algorithm real-time performance is high, and the method is suitable for online detection; the degree of in-phase and quadrature branch component output approaching the direct current is the reflection of the precision of a cross-correlation algorithm. The direct current output of the in-phase branch circuit still has low-frequency jitter, the development of subsequent work starts from introducing a moving average filtering algorithm after forming filtering, component data of more cycles participate in mean value operation, and the calculation accuracy of the direct current component is further predicted to be improved.

Description

technical field [0001] The invention relates to the technical field of eddy current impedance, and more specifically relates to a method and device for solving eddy current impedance based on a cross-correlation algorithm. Background technique [0002] When a conductive workpiece is placed in the magnetic field of the eddy current probe, a specific impedance value will be generated in the eddy current coil, and all samples made of the same material will have the same impedance in the probe. According to literature records, its impedance The change curve is a function of the properties of the measured object and the instrument characteristics of the detection instrument. The properties of the object to be measured include: 1) electrical conductivity; 2) size of the object to be inspected; 3) magnetic permeability; 4) workpiece defects, etc. The characteristics of the instrument include: 1) the frequency of the AC field in the detection coil; 2) the size and shape of the dete...

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Problems solved by technology

[0003] Some scholars have applied machine learning to feature extraction of eddy current testing. For example, Ge Liang used support vector machine (SVM) technology to realize feature extraction and defect identification of narrow lap weld eddy current signals, and the accuracy of defect discrimination reached more than 80%. The algorithm requires huge GPU overhead, real-time performance and cost cannot be well guaranteed, and for qualitative analysis, the accuracy rate is still lacking; Sasi B has studied the dual-frequency eddy current detection technology based on linear algebra, but the computational complexity of this method Larger, longer processing cycle, poor real-time performance; based on phase-sensitive detector (PSD) and low-pass filter (LPF) technology, Fan Mengbao separates the amplitude and phase from the impedance two-dimensional information, and gives a discrete element-based The schematic diagram of the X-R orthogonal decomposition circuit of the eddy current detection signal of the device lays the foundation for the quantitative analysis of the impedance signal, but the circuit is only for the extraction of characteristic information of single-frequency excitation, and it has great influence on the situation where multiple frequencies are required to reflect the characteristics of the test piece. Limitations: Gao Junzhe proposed an impedance information solution method based on a lock-in amplifier, using an analog multiplier and an analog low-pass filter to design a lock-in amplifier circuit, which is limited by the use of an 8th-order Butterworth filter as a low-pass in the implementation plan Filter, its -3dB cut-off frequency is only 30Hz, and the output amplitude has a jitter of about 33ms period, and the repeatability of the test results needs to be improved

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