Method for detecting defects in work pieces and facility and magnetic field measuring apparatus for implementing said method

The invention relates to a process for determining ferromagnetic impurities in workpieces in nonmagnetic material, especially in wheel disks or shafts of gas turbines for aircraft or the like. It relates further to an apparatus for carrying out the process and a magnetic-field measuring device, especially as a part of this apparatus. A depth and other characteristics of a ferromagnetic impurity in a workpiece of nonmagnetic material can be determined after demagnetizing of the workpiece by magnetizing the workpiece in a uniform field, preferably to saturation, and thereafter taking measurements of the field strength from the impurity at two different distances, forming a quotient or ratio of the measured values and determining the depth from a curve in which the signal ratio or quotient is plotted against the depth.