SIGNALS EDDY CURRENT PROBES IN NON-DESTRUCTIVE TESTING ON THE HIGHER HARMONICS

Abstract

The method of harmonics for eddy current testing without the use of pre-prepared samples is developed. Methods of eddy current testing of objects with constant properties do not apply to objects with nonlinear properties. Numerical algorithm of non-destructive testing of ferromagnetic cylindrical objects in the throughcoil eddy-current probes was studied. This method is based on the high harmonics analysis increases the efficiency testing the structural state of steel objects and is designed, for example, for quality testing. Analysis of electromagnetic field through coil probe based on the nonlinear dependence of the magnetic induction of the magnetic field becomes relevant for the selection of operating modes non-destructive testing. For solutions we used numerical simulation using the sweep method. Checking the results of the selected calculation scheme carried out by comparison with the published results for the particular case of permanent magnetic properties. According to the selected method the effect of magnetic permeability and electrical conductivity was studied on the first and third harmonics of the magnetic flux in the cylindrical object, which determin on the probe signal. These dependencies allow determine the intensity of the exciting field under testing of ferromagnetic objects. It is shown the advantage of the third harmonic excitation on the frequencies of tens of hertz, suitable in terms of performance and to obtain sufficient amplitude of signals on the testing coil. Shown the results of the selection of testing modes for objects of structural steel. The recommendations on the choice of testing parameters using the third harmonic of the signal. Also given recommended frequency range and intensity of the exciting field in devices, operating according to the method of the higher harmonics.