Abstract: 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 f.sub.1, f.sub.2, 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.

Abstract: At least two groups of scanning coils are arranged with respect to the surface of metal parts to be tested at different angles. Means are further provided for oscillating at least one group of scanning coils in a direction generally perpendicular to the normal direction of travel of the scanning coil. Optionally, the exciter windings are rectangular, circular or oval.

Abstract: An eddy current coil test assembly comprises a printed circuit board having respective conductors which form the excitation coil winding, the sensing coil winding, the input transformer winding, the output transformer winding and the connections between these respective elements. Pot core type transformers are mounted in close proximity to said windings. The printed transformer windings constitute respectively the secondary winding of the input transformer and the primary winding of the output transformer.