GB936015A - Improvements in or relating to apparatus for testing of ferro-magnetic material - Google Patents

Abstract

936,015. Detecting flaws. CENTRAL ELECTRICITY GENERATING BOARD, J. E. T. WISEMAN, and P. D. HANSTEAD. April 30, 1962 [July 25, 1961], No. 26866/61. Addition to 866,570. Class 37. In an apparatus for testing ferromagnetic material by positioning a magnetizing coil in the vicinity of the sample, applying intermittent or continuous direct current to the coil, and measuring, by a magnetometer mounted with the coil to form a single probe unit, either the reinanence or permeability of the sample; the flux gate magnitometer arrangement of the parent is replaced by a Hall plate or a pair of Hall plates. Electrodes 21, Fig. 2, of the Hall plate are energized from a constant current source 20, which may be A.C. to facilitate amplification, and the output from electrodes 23, which is representative of the magnetic field in the sample, is measured by a voltmeter 22. A potentiometer 24 also across source 20 provides an opposing voltage to reduce to zero the output from the plate in a zero field. The voltmeter may include an amplifier and a range changing switch. The Hall plate 15 may be mounted perpendicular to the surface of the specimen and coupled to spaced points on the specimen by yokes on each side of the plate, as is described with reference to Fig. 3 (not shown), or two plates mounted parallel to the surface . of the specimen may have their surfaces opposite the specimen bridged by a yoke as in Fig. 4 (not shown). The arrangement may be used to measure remanence or permeability.