Method and apparatus for testing a metallic workpiece by inducing eddy currents therein

摘要

A method for testing a metallic workpiece by eddy currents induced by a test coil in the workpiece, in which a measured variable that is a function of the test coil impedance serves as a measure for workpiece physical properties. The circuit includes an oscillator with an amplifier and two resonant circuits adjusted to neighboring frequencies f1, f2, the test coil impedance is at least part of the inductive component of one or both resonant circuits and a variable component influences the resonant frequency of one of the resonant circuits.