Digital eddy current apparatus for generating metallurgical signatures and monitoring metallurgical contents of an electrically conductive material

Claim 1

Digital eddy current apparatus for identifying specimens of electrically conductive material of unknown composition comprising: (a) Driving means supplying a square wave which is used as reference; (b) Sensing means coupled to the driving means comprising an inductance, the impedance of which varies depending on eddy current characteristics of the specimen magnetically coupled thereto, and a capacitance connected with the inductance; (c) Scanning means for varying the value of said capacitance in steps over a range including the value which resonates with said inductance magnetically coupled to a specimen at the frequency of the driving means square wave and produces a voltage waveform thereacross which is in phase with the square wave, said range also including values of capacitance larger and smaller than the resonating value which produce voltage waveforms out of phase with the square wave; (d) Converting means coupled to the sensing means converting the voltage waveforms across the inductance corresponding to said values of capacitance connected therewith into rectangular pulse outputs, the rectangular pulse output corresponding to the resonating capacitance being positioned in the center of one-half the square wave, the rectangular pulses corresponding to other values of capacitance being offset from the center of one-half the square wave, said offsets being a function of the phase shift of the voltage waveforms; and (e) Means coupled with the converting means for monitoring the successive values of capacitance and the offsets of the waveforms corresponding to the respective capacitance values so as to provide a capacitance-offset relation which is a function of the metallurgical characteristics of the specimen.