Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1998-06-22
2000-03-21
Snow, Walter E.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324236, G01B 706, G01B10100, G01B12102, G01R 3312
Patent
active
060406941
ABSTRACT:
The invention relates to a method according to the eddy-current testing principle, and to a device for determining the thickness of an electrically conductive protective layer which is applied to an electrically conductive base material. The electrical conductivities of the protective layer and of the base material are different from each other. An excitation coil through which a high-frequency electric current is passed is brought near to the protective layer, so that an electric eddy current is produced in the protective layer and possibly in the underlying base material. A parameter related to the impedance of a probe coil is determined and is used as a basis for determining the thickness of the protective layer, for example by comparison with known reference values. The frequency of the high-frequency electric current is selected in such a way that the thickness of the protective layer is determined unambiguously for a ratio of the electrical conductivities of between 0.7 and 1.5.
REFERENCES:
"Thickness and conductivity of metallic layers from eddy current measurements" (Moulder et al.), 8127 Review of Scientific Instruments, vol. 63, No. 6, New York 1992.
"Non-destructive testing of corrosion effect on high-temperature protective coatings" (Dibelius et al.), VGB Research Project No. 54, Nuclear Technology, vol. 70, No. 9, 1990.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Snow Walter E.
Stemer Werner H.
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