Magnetic test (search, exploring) coil arrangement for scanning flat and curved surfaces from electrically conductive test specimens in conjunction with the application of the eddy-current method

摘要

In the case of the application of the pulsed eddy-current method in nondestructive testing, in accordance with the prior art use is made, for the purpose of localised scanning of test specimens and of generating the signals, of coil systems in which the principal axes of the field-exciting coil and of two measuring coils are arranged in parallel and are perpendicular to the test surface. Because of the unavoidable irregularities in the two windings, there are difficulties in practice in bringing about a balance between the signal voltages connected in series when there is no disturbance of the eddy-current field - e.g. due to a material defect. The essential feature of the coil arrangement according to the invention is a field-exciting coil whose axis is likewise perpendicular to the surface of the test specimen, and a measuring coil whose axis is arranged parallel to said surface. The measuring coil in this arrangement is laterally displaced and tangentially aligned with respect to the excitation coil (see sketch). Components of the exciting magnetic field coincide only to a slight extent with the direction of the principal axis of the measuring coil, with the result that balancing is substantially facilitated. IMAGE