Research On Distance\Thickness Of Metallic Layers From Pulsed Eddy-Current Nondestructive Measurements

This thesis mainly researches the methods which measure the mental thickness and the distance between the mental and the coil through adopting the technology of pulsed eddy current (PEC).In rolling mill, it is very important step which impact product quality that measure the thickness of mental after rolling. Now, there are many methods for measuring the thickness of mental. For example, the contact measurement, the radial measurement, the ultrasonic measurement, eddy current measurement, etc. But there are some problems in those ways. So used pulsed eddy current, not only it has highly precision, faster measurement, and non- contact, but also it overcomes some shortcoming in tradition measurements.This thesis, first, researches some tradition measurements in measured thickness of mental, and the advantage of pulsed eddy current measurement. Eddy current basis of theory of measurement is introduced, and brings forward impedance analytical method of eddy current. Second, on the base, an eddy current testing model of mufti-layered metal structure was presented in the light of the work of C.V.Dood, W.E.Deeds and others. Using Maxwell electromagnetic equations, by solving the boundary-value problem of magnetic vector potential, analytical expression to impedance increment of the solenoid coil in eddy current testing of the medium in half space was given. According as the impendence of coil, combining the method of feature of the signal, the nonlinear relation which is between the mental thicknesses, the distance between mental and coil and feature of the signal is get by using neural net. The result is satisfied. Otherwise,PEC is researched by hardware experiment. Relation between the thicknesses, the distance and induction signal is found from data, and the relation is estimated, then validated. From the result, good conclusion can be gained. Last, according as the technology data of corporation of ABB, it is researched relations which is between the mental thicknesses, the distance between mental and coil and induce signal. The conclusions are the foundation for the next step's research.