Method for detecting defects in work pieces and facility and magnetic field measuring apparatus for implementing said method
First Claim
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1. A method of determining a depth of a ferromagnetic impurity in a workpiece of a nonmagnetic material, comprising the steps of:
- (a) magnetizing said ferromagnetic impurity uniformly by subjecting said workpiece at least in sections to a magnetic field;
(b) thereafter juxtaposing said workpiece and a magnetic field measuring sensor at a first distance from a surface of said workpiece to obtain a first signal measuring magnetic field strength deriving from said ferromagnetic impurity;
(c) then juxtaposing said workpiece and said magnetic field measuring sensor at a second distance from said surface of said workpiece different from said first distance to obtain a second signal measuring magnetic field strength deriving from said ferromagnetic impurity;
(d) forming a signal ratio of said first and second signals as a quotient of the magnetic field strengths at said first and second distances; and
(e) based upon said signal ratio, determining from a curve in which the dependency of the signal ratio is plotted against an impurity depth, a depth of the impurity in said workpiece from which the magnetic field strengths were measured.
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Abstract
A depth and other characteristics of a ferromagnetic impurity in a workpiece of nonmagnetic material can be determined after demagnetizing of the workpiece by magnetizing the workpiece in a uniform field, preferably to saturation, and thereafter taking measurements of the field strength from the impurity at two different distances, forming a quotient or ratio of the measured values and determining the depth from a curve in which the signal ratio or quotient is plotted against the depth.
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10 Claims
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1. A method of determining a depth of a ferromagnetic impurity in a workpiece of a nonmagnetic material, comprising the steps of:
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(a) magnetizing said ferromagnetic impurity uniformly by subjecting said workpiece at least in sections to a magnetic field;
(b) thereafter juxtaposing said workpiece and a magnetic field measuring sensor at a first distance from a surface of said workpiece to obtain a first signal measuring magnetic field strength deriving from said ferromagnetic impurity;
(c) then juxtaposing said workpiece and said magnetic field measuring sensor at a second distance from said surface of said workpiece different from said first distance to obtain a second signal measuring magnetic field strength deriving from said ferromagnetic impurity;
(d) forming a signal ratio of said first and second signals as a quotient of the magnetic field strengths at said first and second distances; and
(e) based upon said signal ratio, determining from a curve in which the dependency of the signal ratio is plotted against an impurity depth, a depth of the impurity in said workpiece from which the magnetic field strengths were measured. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for determining a depth of a ferromagnetic impurity in a workpiece of a nonmagnetic material comprising:
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means for magnetizing said ferromagnetic impurity uniformly by subjecting said workpiece at least in sections to a magnetic field;
a magnetic field sensor scannable over said workpiece and movable relative to a surface of said workpiece for juxtaposition with said workpiece at a first distance from said surface of said workpiece to obtain a first signal measuring magnetic field strength derived from said ferromagnetic impurity after said ferromagnetic impurity has been magnetized in said magnetic field, and at a second distance from said surface different from said first distance to obtain a second signal measuring magnetic field strength derived from said ferromagnetic impurity;
means for forming a signal ratio of said first and second signals as a quotient of said magnetic field strength at said first and second distances; and
means for determining from a curve in which the dependency of the signal ratio is plotted against impurity depth, based on said signal ratio of said first and second signals a depth of the impurity in the workpiece from which the magnetic field strengths were measured. - View Dependent Claims (9, 10)
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Specification