Method of measuring the thicknesses of magnetic metal plates

1,061,895. Measuring thickness of ferromagnetic plates, electrically. YAWATA IRON & STEEL CO. Ltd. March 2, 1964, No.8684/64. Heading G1N. In a method of measuring the thickness of a ferromagnetic plate 4 (Fig. 1) a yoke 1 is brought into proximity with the plate the yoke having a cross-sectional area whereby it is not saturated when current in a coil 2 thereon produces a flux which saturates the metal plate. The coil is excited successively by two fixed value saturating currents (e.g. 3 amps. and 2À7 amps.), the magnetic potential difference between the two legs of the yoke across the plate at each current value is determined by a coil or coils 3, wound on a non magnetic former, and in which a voltage is induced, representative of magnetic potential difference. The difference in magnitude of the two magnetic potential differences is taken as a measure of the plate thickness, being compared with characteristic curves representing plates of known thicknesses such as in Figs. 2 to 4 (not shown).