| 摘要 |
1,200,146. Fluxgate magnetometers; flaw detecting. F.M.O. FORSTER. Aug.14, 1968 [Aug.17, 1967], No.38938/68. Heading G1N. Fluxgate magnetometers. A fluxgate magnetometer comprises an annular core 30, a primary winding 34 linking the core, and a secondary winding 42 extending diametrically across the core without linking it so that the signal induced in the secondary winding is the net result of opposing signals induced by flux changes in the two halves of the core. Two or more cores may be provided having a common primary winding Figs.4, 6, 7, (not shown) or parallel-connected primary windings Fig.9 (not shown), their secondary windings being connected in series to produce a net output only when the cores are in magnetic fields of different strengths. To provide a shift in operating characteristics, a permanent magnet 202 may be arranged with its axis on a core diameter perpendicular to the secondary winding and a rectifier 162 may be connected in series with the secondary winding. Flaw detecting. A workpiece 14 is tested for flaws by passing a current through it and scanning its surface with a fluxgate magnetometer described above. The secondary (or primary) winding of the fluxgate may be tuned with a capacitor 47 so that the frequency of the primary A.C. lies on the slope of the resonance curve thereby making the response to flaws insensitive to variations in the distance from the surface of the workpiece. To improve the signal to noise ratio, a plurality of fluxgates Fig. 9 (not shown) may be spaced in the direction of scanning with their secondary windings connected in series to a band pass filter tuned to the frequency which a flaw passing the fluxgates will produce. |
