Eddy current imaging apparatus and method using phase difference detection
First Claim
1. Apparatus for eddy current imaging using phase difference detection of an object, said apparatus comprising:
- a pair of coils, at least one of said coils being adapted to be disposed proximate to the object;
means for causing relative motion between the object and said coils;
an oscillator coupled to said coils for causing said at least one of said coils to create eddy currents in the object;
a pair of phase detectors coupled to said oscillator and to said coils, said oscillator providing signals having the same phase to both of said phase detectors; and
means for comparing the output signals from said phase detectors.
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Abstract
A phase-difference eddy current imaging system has a bridge circuit including a pair of coils with one or both coils disposed proximate an object that may contain one or more flaws. An oscillator is coupled to the bridge circuit and also to a pair of phase detectors that are coupled to the coils. A differential amplifier is coupled to the phase detectors for providing a comparison signal. A method for eddy current imaging using phase difference detection comprises providing relative movement between an object and at least one of a pair of coils, measuring the phase of the effective reactance in each of the coils, comparing the measured values, and formatting the compared values as a function of spatial position.
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Citations
18 Claims
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1. Apparatus for eddy current imaging using phase difference detection of an object, said apparatus comprising:
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a pair of coils, at least one of said coils being adapted to be disposed proximate to the object; means for causing relative motion between the object and said coils; an oscillator coupled to said coils for causing said at least one of said coils to create eddy currents in the object; a pair of phase detectors coupled to said oscillator and to said coils, said oscillator providing signals having the same phase to both of said phase detectors; and means for comparing the output signals from said phase detectors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Apparatus for eddy current imaging using phase difference detection of an object, said apparatus comprising:
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a bridge circuit including a pair of coils, at least one of said coils being adapted to be disposed proximate the object; an oscillator coupled to said bridge circuit for causing said at least one of said coils to create an eddy current in the object; a pair of phase detectors respectively coupled to said coils, each of said detectors being coupled to said oscillator to receive signals of the same phase; and a difference amplifier having a pair of inputs respectively coupled to said detectors.
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13. A method for eddy current imaging using phase difference detection of an object, said method comprising:
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supplying signals from an oscillator to a pair of coils, at least one of which creates an eddy current in the object; providing relative movement between the object and said at least one of the coils; measuring the effective reactance in each of said coils; and comparing measured reactance values. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification