Fault location in ferromagnetic rods - uses alternating field for additional axial magnetisation without later demagnetisation

摘要

A method and device is used for fault location in elongated ferromagnetic test material (2). It uses a magnetic flux to detect faults on or beneath the material surface causing flux variations outside the surface which are detected and converted into electrical fault signal voltages. The device obviates the later demagnetisation of the test without using the advantage of additional magnetisation in the axial direction. The additional magnetisation is produced by an alternating magnetic field whose frequency is lower than that of the primary field and whose amplitude reaches a sufficient level for additional magnetisation during part of the field cycle. Parts of the signal voltage winding with field null transitions are suppressed.