GB216135A - Improvements in and relating to methods and apparatus for testing magnetic material - Google Patents

Abstract

216,135. British Thomson-Houston Co., Ltd., (Assignees of Gokhale, S. L.). May 15, 1923, [Convention date]. Magnetic tests and measurements.-The saturation value of magnetic material is determined by saturating a sample of the material, producing an electromotive force in a measuring-circuit proportional to the flux density, opposing this electromotive force by a second electromotive force proportional to the magnetizing-force, and measuring the difference between the opposing forces. Fig. 2 is a diagram of connections in which the specimen 2 is surrounded by a magnetizing-coil 3 which can be connected by switches 20, 21 in series with the primary winding 13 of a variable mutual inductance, an ammeter A, variable resistances 14, 15, and a source of continuous current. A test coil 12 also surrounds the centre of the sample 2, and is connected in series with the secondary winding 22 of the mutual inductance and with a galvanometer G, resistances 23, 24 being provided for calibration. The magnetizing-coil 3 is wound on a spool 4, Fig. 1, and is held in place between the ends of a magnetic yoke 1 by non-magnetic straps 5. Cradles 6 provided with pads 7 to prevent abrasion of the wire are interposed between the coil 31 and the base. The side pieces 8 of the base are of wood or other non-magnetic material, and carry the terminals 9 of the magnetizing- coil 3 and also the terminals 10 of the test coil. The magnetic circuit of the yoke 1 is completed by the sample 2, which passes through the centre of the coil 3. In order to secure good magnetic contact between the sample 2 and the yoke 1, the upright ends of the yoke are forked or provided with openings and each is provided with a keeper 11 and a thumbscrew 12 which clamps the sample in place. In order to carry out a test, it is ascertained that the electromotive forces generated in the coils 12, 22 oppose one another by connecting the coils 3, 13 separately in the circuit by means of the switches 20, 21, and noting the direction of the deflection on breaking the circuit. The mutual inductance between the coils 13. 22 is then adjusted to equality with that between the coils 3, 12 by connecting the coils 3, 13 in series and adjusting the mutual inductance until no deflection is given on the galvanometer when the exciting current is changed, there being either no sample or a saturated sample within the coil 3. The sample is then inserted and raised to saturation by closing the switch 17 and adjusting the resistance 14. To ascertain that the sample is saturated, the magnetizing-current is raised by closing the switch 18, when no deflection should be given on the galvonometer. The exciting- current is then reversed by means of the switch 19 and the galvanometer deflection noted, from which the saturation value can be calculated.