Needle-probe techniques for local magnetic flux measurements

Abstract

Numerical two-dimensional field investigations in the cross section of laminated nonoriented electrical steel sheet are performed in order to verify the possibilities and limitations of the two needle-probe technique for the measurement of local magnetic flux near the cutting edge. If one of the needles approaches the lamination edge or when inhomogeneities are present in the flux distribution along the strip width due to magnetic properties altered by the cutting procedure, then the signal from the needle probes no longer represents the flux through a rectangular surface under the needles because of E-field components perpendicular to the lamination surface. The flux calculated from the needles is compared to the actual flux passing through the rectangular surface under the needles and corresponding correction factors as a function of the needle position away from the cutting edge are computed. Depending on the positioning method, the needle probes can give an under- or overestimation of the actual flux. Corrections from 15% to 80% are necessary if distances of about the lamination thickness are considered. This work suggests an iterative numerical procedure for the interpretation of experimental data obtained from local flux needle-probe measurements.