Non-Contact Conductivity Measurements in Non-Ferromagnetic Pipes and Rods: The Choice of Working Frequency
Abstract:A simple and precise technique for the measurement of electrical conductivity in non-ferromagnetic pipes and rods at low frequencies is here explained. Results are easily achieved by means of the study of the induced currents when the sample is submitted to an axial harmonic magnetic field. The phase of eddy currents is analyzed by means of the induced voltage on a short coil located inside the pipe or around the rod while the sample under test is axially excited by a long primary coil. When operating at low frequencies the eddy-currents are essentially distributed over the whole depth of the sample in such a manner that we can appreciate any irregularity or flaw when the probe coil is displaced along the sample axis, as it occurs in a non-destructive testing technique. Due to the skin effect, at higher frequencies the current density is enhanced near the sample surface in such a manner that the measurements carry out information especially concerning to the boundaries of the tube or the rod.
Document Type: Research Article
Publication date: June 1, 2009
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