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In this paper, multi-frequency eddy current testing methods, the temperature of the metal plates and metal and measured the distance between the detection coil is studied.Eddy current testing, the impact of the workpiece detected coil impedance (or induced voltage) a number of factors, such as metal workpiece material, conductivity, magnetic permeability and the detection of the probe lift-off of the rock and have an impact on the eddy current signals. Detection according to different tasks, some of these parameters must be detected and calculated, while others are regarded as interference signals, must be given to remove. In order to reach this goal, in the eddy current testing on the need to increase the identification of means to get more experimental variables, a variety of interference suppression factors, improve the identification of the resolution and reliability, make the right of the measured part of the evaluation.This article first introduced the development of eddy current testing, an analysis from various angles of the principle of eddy current testing, eddy current testing in the equivalent circuit based on the analysis to explore the multi-frequency eddy current testing system, the feasibility of the application, the text also discussed in detail the design of eddy current sensors and eddy current sensor in the subject to choose parameters. And according to the mathematical model of the coil impedance, combined with the characteristics of value, using the least square method, BP neural network has been the temperature of metal and metal and the distance between coil and signal characteristics of the value of the non-linear relationship, with satisfactory results. In addition, through experimental study of the hardware of the multi-frequency eddy current testing technology, from the data found in the thickness of metal, metal and coil temperature and the distance and the correlation between voltage sensors and the use of BP neural network method of data fitting and verification, achieved some results of the study.
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