Device for defect testing of non-ferromagnetic test samples and for ferromagnetic inclusions
First Claim
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1. A device for defect testing of non-ferromagnetic test samples and for the presence of ferromagnetic inclusions in said test samples, comprising:
- means for inducing alternating eddy currents in the test samples including a coil arrangement energized by a selectively variable alternating current generator;
a permanent magnet yoke of such strength as to produce magnetic saturation of ferromagnetic samples for inducing a constant D.C field in the test samples at the same time as the alternating eddy currents;
receiver coil means including two spaced apart differentially connected receiver coils coupled to the test samples for developing a first signal corresponding to the reaction of alternating eddy currents with the non-ferromagnetic test samples and a second signal corresponding to a reaction of the D.C. field in the test samples with a ferromagnetic inclusion, said first and second signals existing in composite form;
a first thresholded circuit connected to the receiver coil means for producing a third signal responsive to the first signal indicating the presence of a physical defect in the non-ferromagnetic test sample;
a second thresholded circuit including a low-pass filter connected to the receiver coil means for preventing passage of the first signal and for producing a fourth signal responsive to the second signal to indicate the presence of a ferromagnetic inclusion in the test samples, said low-pass filter being variable in common with the current generator;
a preamplifier interconnected between the receiver coil means and the first and second circuits;
a logic circuit fed by both the third and fourth signals for producing a fifth signal indicating the presence of both the third and fourth signals; and
means responsive to said third, fourth and fifth signals for providing sixth, seventh and eighth signals indicative of, respectively, the existence of a defect only in a material separation or inhomogeneity of the surface of the sample not in the presence of a ferromagneetic inclusion, the existence of a ferromagnetic inclusion underneath the sample surface, and the existence of a ferromagnetic inclusion with surface contact.
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Abstract
Detection of both surface defects of a non-ferromagnetic test body as wells the presence of ferromagnetic particles in the test body by inducing eddy currents and D.C. fields in the body. The resulting signal voltages are filtered and separately examined.
51 Citations
1 Claim
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1. A device for defect testing of non-ferromagnetic test samples and for the presence of ferromagnetic inclusions in said test samples, comprising:
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means for inducing alternating eddy currents in the test samples including a coil arrangement energized by a selectively variable alternating current generator; a permanent magnet yoke of such strength as to produce magnetic saturation of ferromagnetic samples for inducing a constant D.C field in the test samples at the same time as the alternating eddy currents; receiver coil means including two spaced apart differentially connected receiver coils coupled to the test samples for developing a first signal corresponding to the reaction of alternating eddy currents with the non-ferromagnetic test samples and a second signal corresponding to a reaction of the D.C. field in the test samples with a ferromagnetic inclusion, said first and second signals existing in composite form; a first thresholded circuit connected to the receiver coil means for producing a third signal responsive to the first signal indicating the presence of a physical defect in the non-ferromagnetic test sample; a second thresholded circuit including a low-pass filter connected to the receiver coil means for preventing passage of the first signal and for producing a fourth signal responsive to the second signal to indicate the presence of a ferromagnetic inclusion in the test samples, said low-pass filter being variable in common with the current generator; a preamplifier interconnected between the receiver coil means and the first and second circuits; a logic circuit fed by both the third and fourth signals for producing a fifth signal indicating the presence of both the third and fourth signals; and means responsive to said third, fourth and fifth signals for providing sixth, seventh and eighth signals indicative of, respectively, the existence of a defect only in a material separation or inhomogeneity of the surface of the sample not in the presence of a ferromagneetic inclusion, the existence of a ferromagnetic inclusion underneath the sample surface, and the existence of a ferromagnetic inclusion with surface contact.
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Specification
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Current AssigneeInstitut Dr Friedrich Forster Pruferatebau GmbH & Company KG
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Original AssigneeInstitut Dr Friedrich Forster Pruferatebau GmbH & Company KG
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InventorsWorkley, James, Haug, Fritz, Klopfer, Walter, Gabauer, Dale
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Primary Examiner(s)Strecker, Gerard R.
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Application NumberUS07/282,450Time in Patent Office634 DaysField of Search324/227, 324/232, 324/239-243US Class Current324/232CPC Class CodesG01N 27/9046 by analysing electrical sig...
