| 摘要 |
The invention relates to a apparatus for non-destructive testing by eddy currents of long metal products in motion, of the type comprising a cylindrical emitter coil (2) arranged coaxially around the metal product to be tested and two identical cylindrical receiver coils (3, 4) arranged inside the emitter coil (2), coaxially with the metal product (1) to be tested, these two receiver coils (3, 4) being arranged symmetrically with respect to the transverse mid-plane (6) of the emitter coil (2), the two receiver coils (3, 4) being mounted in differential mode, the measurement signal corresponding to the difference between the two signals produced by the two coils, characterised in that it comprises a cylindrical ring (5) made of an electrically conducting material, arranged at least partially inside the emitter coil (2), coaxially with the metal product (1) to be tested. Advantageously, the said ring (5) is made of a non-magnetic material. <IMAGE>
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