Contactless Measurement of Sheet Metal Resistivity at High Temperatures

A previously developed contactless method to measure the resistivity of metals at high temperatures has been extended for metal sheets. The theoretical basis of the method has been augmented by solving the problem of power input to a sample in the form of a thin-walled cylinder under inductive heating. Essentially, the method consists in measuring electromotive forces (EMFs) induced by a high-frequency electromagnetic field in two circular loops with different diameters that are arranged coaxially to the cylindrical sample. The formula derived for the power introduced into a thin-walled cylinder has made it possible to find a relationship between the resistivity of the sample and EMF. From the experimental values of the EMF, the resistivity of the sample and, accordingly, the power input to the sample have been determined. This has allowed us to determine the integral hemispherical emissivity factor of the sample. Data for experimentally checking the method using a thin-walled niobium cylinder are presented. They agree with those obtained by other authors to within 3%, which makes this method promising for practical application. Techniques for conducting necessary experiments and processing experimental data are exemplified.