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Eddy currents produce a secondary field that cancels a part of the external field and causes some of the external flux to avoid the conductor. French physicist Léon Foucault (1819–1868) is credited with having discovered eddy currents. In September 1855, he discovered that the force required for the rotation of a copper disc becomes greater ...
In the traditional version of eddy current testing an alternating (AC) magnetic field is used to induce eddy currents inside the material to be investigated. If the material contains a crack or flaw which make the spatial distribution of the electrical conductivity nonuniform, the path of the eddy currents is perturbed and the impedance of the ...
These are called eddy currents. On the lefthand side nearest to the other wire (1) the eddy current is in the opposite direction to the main current (big pink arrow) in the wire, so it subtracts from the main current, reducing it. On the righthand side (2) the eddy current is in the same direction as the main current so it adds to it ...
The direction of the circulation of eddy-currents is always such as to tend to oppose the relative motion. The eddy-current in the part receding from the poles tends to attract the poles forward or to drag this part of the disk backwards. The eddy-current in the part advancing toward the poles tends to repel those poles and to be repelled by them.
The energy in these currents is dissipated as heat in the electrical resistance of the conductor, so they are a cause of energy loss. Since the magnet's iron core is conductive, and most of the magnetic field is concentrated there, eddy currents in the core are the major problem. Eddy currents are closed loops of current that flow in planes ...
In 1956 Don left Rocketdyne and began experimenting with eddy-current sensing technology and formed Bently Scientific Company. He manufactured and sold eddy-current products via mail-order out of his garage in Berkeley, California. [20] In 1960 he bought land in Douglas County, Nevada. In 1961, Bently relocated his company to Minden, Nevada ...
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A notable advance in the art of dynamo construction was made by Samuel Alfred Varley in 1866 [113] and by Siemens and Charles Wheatstone, [114] who independently discovered that when a coil of wire, or armature, of the dynamo machine is rotated between the poles (or in the "field") of an electromagnet, a weak current is set up in the coil due ...