| 摘要 |
PROBLEM TO BE SOLVED: To rapidly derive distance and thickness of layers from values of inductance measured by generating AC magnetic field for an ferrous material, a nonferrous metal material, conductive fluid or the like. SOLUTION: Alternating current with multiple frequencies is supplied to an exiting coil, and multi-frequency magnetic field is applied to an object to be measured, and induced voltage of a detecting coil is measured, and the inductance of the coil at each frequency is measured in the lump. That is, the device is composed of the exiting coil being opposed to a flat plate-like conductive material to be measured or containing a conductive material to be measured with a circular cross section, an exiting coil driver which supplies alternating current to the coil, an induced voltage detecting coil which is arranged parallel to the exiting coil, a pre-amplifier which detects the induced voltage of the coil, and a digital signal processing section which processes voltage data. Multi- frequency inductance is calculated from the voltage data with multiple frequencies using the discrete Fourier transform, and the thickness of layer is derived from the measured value of multi-frequency inductance using the regressive calculation on the basis of solution from a theoretical model of the conductive material to be measured.
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