Method and apparatus for non-destructive testing of magnetically permeable bodies using a first flux to saturate the body and a second flux opposing the first flux to produce a measurable flux

摘要

The present invention relates to a method and apparatus for non- destructive comparative investigation of physical characteristics affecting the reluctance of different parts of a body having magnetic permeability. In accordance with the present invention a first saturating magnetic flux is induced in the body or a part thereof giving rise to a flux distribution pattern determined by the reluctance of the body or part thereof which in turn is determined by the physical character of the body or body part. A second magnetic flux is also induced generally opposing the first magnetic flux in a selected region of the flux distribution pattern, outside of the body or body part while maintaining substantial first flux saturation of the body or body part such that any resultant magnetic flux in that region is at a readily measureable flux level. Also provided is a detector for detecting along the body either variances from that flux level with the second magnetic flux being maintained substantially constant or variances of the second magnetic flux with the resultant magnetic flux being maintained substantially constant.