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Eddy currents are electromagnetic nondestructive testing methods that provide nearly instantaneous low-cost mass inspection of components. They are applicable in quantitative measurements of materials properties and sorting of components by dimensions. In production lines, they are used to test moving parts as they scanned by moving probes or pass through test coils.
Eddy current methods are based on the flow of periodic, alternating or pulsating, electrical currents in probes closely placed to the surface of the test components. Electrical currents induced in the test components, known as eddy currents, are generated within the component. If the probes are small and do not encircle the test component, only the areas close to the surface are examined. This test method is applicable, for example, to the inspection of welds. Some systems employ coils energized with ac current at a fixed frequency that completely envelop the test component, allowing, for example, the inspection of the entire circumference of a pipe.
The magnitude of the eddy currents depends on the conductivity and magnetic permeability of the material. Frequency range selection is key to each application according to the depth of eddy current penetration. Thus compositional, metallurgical, and dimensional changes are detectable from the changes in electromagnetic response that they produce. Further, the effects of corrosion damage and material discontinuities, such as cracks, pits and voids, can be monitored in service.
Eddy current output signal amplitude and phase angle are measured in real time with high precision, eliminating human error and delays in data processing and decision-making. Our instrumentation consists of two Nortec Scopes plus probes.
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