Abstract: The apparatus comprises a parallel coil and a capacitance, the coil having an air gap in which an unknown specimen is inserted, a source of alternating voltage applied to the coil-capacitance combination, scanning means for automatically varying the value of the capacitance in steps, thus varying the phase of the voltage across the coil, means for digitizing the phase of the voltage corresponding to each capacitance value, a memory in which those digitized phase values are stored, a reference memory containing digitized phase values for known specimens, and means for comparing the digitized phase values of the unknown specimen with those of known specimens. A digital tolerance control circuit is also provided which accommodates deviations between the reference and the known phase values, up to predetermined amounts, and means are provided for displaying the generic name or grade of the stored phase values which match the phase values of the unknown specimen.

Abstract: A digital eddy current apparatus for sensing and analyzing metallurgical characteristics of an electrically conductive material. A square wave is supplied to a resonating circuit which includes a coil used as a sensing element for the conductive material. The resonating circuit produces a sinusoidal wave which is converted into a rectangular pulse which, when the resonating means is at resonance condition if superimposed upon the square wave pulse it would be positioned in the center of one-half of the square wave. The width of the rectangular pulse is a direct function of the amplitude of the sinusoidal wave and phase shift of the sinusoidal waveform is detected by movement of the rectangular pulse from the center position within the square wave. The width and position of the rectangular pulse is a direct function of the metallurgical characteristics of the conductive material.