Digital eddy current apparatus for sensing and analyzing metallurgical characteristics of an electrically conductive material

• US 4,059,795 A
• Filed: 06/03/1976
• Issued: 11/22/1977
• Est. Priority Date: 06/03/1976
• Status: Expired due to Term

• Current Assignee: Sensor Corporation
• Original Assignee: Sensor Corporation
• Inventors: Mordwinkin, George
• Primary Examiner(s): Corcoran, Robert J.
• Application Number:
  US05/692,481
• Time in Patent Office: 537 Days
• Field of Search: 324/40, 324/37
• US Class Current: 324/233
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/9046 by analysing electrical signals
• CPC Class Codes: G01V 3/102 by measuring amplitude

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.

Claims

1. A digital eddy current apparatus for sensing and analzying metallurgical characteristics of an electrically conductive material comprising:

a. driving means supplying a square wave which is used as a reference;

b. a resonating means coupled to the driving means, the resonating means having a sensing element with an impedance which varies depending upon an eddy current characteristic of the electricity conductive material, the resonating means changes the square wave to a sinusoidal waveform which is a function of the impedance of the sensing element;

c. converting means coupled to the resonating means and converting the sinusoidal waveform produced by the resonating means into a rectangular pulse output, which pulse, when the resonating means is at a resonance condition, when referenced to the square wave pulse would be positioned in the center of one-half of the square wave, when the resonating means is magnetically coupled to the conductive material, the amplitude and phase of the sinusoidal waveform will be affected by the material characteristics, and the width and phase of the rectangular pulse will also be affected, the width of the rectangular pulse is a direct function of the amplitude of the sinusoidal waveform, movement of the rectangular pulse from its referenced position in the center of one-half of the square wave is a function of phase shift of the sinusoidal waveform; and

d. means for monitoring the width and position of the rectangular pulse with respect to the reference square wave as a direct function of the electrically conductive material'"'"'s metallurgical characteristics.

2. An apparatus as recited in claim 1 wherein the means for monitoring includes:

reference means responsive to the square wave for providing a rectangular pulse reference output which represents a known eddy current characteristic of a known electrically conductive material and

b. comparing means coupled to the reference means output and the output of the converting means "for comparing the width and position of the rectangular pulse to the rectangular pulse reference", if the pulse reference output from the reference means and the rectangular pulse output of the converter means are substantially identical then no signal output will be produced by the comparing means, if the pulse reference output from the reference means and the rectangular pulse output of the converter means are different then the comparing means will produce a rectangular pulse output which corresponds to the difference between the two input pulses to the comparing means.

3. An apparatus as recited in claim 1 wherein the means for monitoring includes a means coupled to the converting means for digitally measuring the width of the converting means output pulse thereby providing digital signals which correspond to the amplitude variations caused by the metallurgical characteristics of the electrically conductive material.

4. An apparatus as recited in claim 1 wherein the means for monitoring includes means coupled to the converting means output for digitally measuring the phase of the converting means output pulse relative to the reference square wave and thereby providing digital signals which correspond to the phase variations caused by the metallurgical characteristics of the electrically conductive material.

5. Apparatus as recited in claim 1 wherein the means for monitoring includes a means coupled to the output of the converting means for digitally decoding position of the leading and trailing edges of the rectangular pulse output from the converting means within a semicycle of the square wave from the driving means.

6. Apparatus as recited in claim 2 including a pulse width tolerance discriminator means coupled to the output of the comparing means, the pulse width tolerance discriminator means produces a rectangular pulse output which has a width equal to the pulse output of the comparing means minus tolerance pulse width which is set by the pulse width tolerance discriminator means.

7. Apparatus as recited in claim 6 wherein the pulse width tolerance discriminator means comprises:

a. a resistor and capacitor which provides an RC network; and

b. a threshold detector circuit variably taped from the resistor.

8. Apparatus as recited in claim 7 including a pulse-to-DC converter means having an input coupled to an output of the threshold detector circuit, the pulse-to-DC-converter means provides a reject signal when there is an input pulse to the pulse-to-DC-converter means input and provides an accept signal output when there is no pulse to the pulse-to-DC-converter means input.