Patent GB-786540-A (GB)
Title: Method and device for measuring magnetostriction
IPC: G01B7/02
Filed: 1955-10-04
Abstract: 786,540. Electric indicating systems. ALLISCHALMERS MANUFACTURING CO. Oct. 4, 1955 [Oct. 19, 1954], No. 28264/55. Class 40(1). Magiietostriction of a specimen is measured by causing the end of the specimen to form, with a fixed reference plate, a condenser, and measuring the changes of capacity of the condenser. As shown (Fig. 1), hollow posts 11 filled with a viscous sound energy absorbing material have clamped to them brackets 18 which support magnetizing coil 28. The coil is clamped by brackets 38 against a backing member 37 and a terminal board 39. The specimen is freely suspended in the coil by clamping jaws 23 adjustable by screw 24, the jaws also being mounted in a bracket supported on posts 11. The coil is provided with extra winding 20 near its ends to produce a uniform field over the length of the specimen and a neutralizing coil 29 is for compensating for stray D.C. fields, and pick-up coils 31, 32, 33 for monitoring the flux intensity are also provided. The strip extends below the coil and has a plane surface 21 and co-operates with a conductor plate 48 having a mirror-like plane metallic finish. Conductor plate 48 is supported by an insulating member 52 of acrylic resin to which it is secured by conductive bolt 53. Insulating member 52 is supported by a metallized box 55 through an opening in which plate 48 is positioned. The portion of the housing surrounding the plate acts as a guard ring. Housing 55 is mounted on a table 50 and is vertically adjustable by a screw 61 so as to vary the spacing of the end of the specimen from the plate. In a modified arrangement (Figs. 6 and 9, not shown), the specimen is clamped at its centre of mass, since for the specimen shown, this coincides with the natural nodal plane for the magnetostrictive variations. The electric conductor plate 48 and guard ring arrangement already described may be replaced, in order to reduce vibration, by a rectangular block of non- conductive material having a low dielectric constant and coated with a thin metallic film. The circuit, Fig. 10.-A circuit measuring the spacing of the specimen and reference plate consists of multigrid converter tube 71, grids 77 and 78 of which are so coupled to tuned circuits 80, 83 or to constitute a triode oscillator while coupled between earth and grid 75 is a tuned circuit constituted by the condenser formed by the specimens and the fixed plate and inductance 73. As the plate spacing of the capacitor varies the apparent resistance of tube 71 changes resulting in a change of plate current. The signal developed across load resistor 103 in the anode circuit, which also includes an H.F. filter 99, is fed to an indicator 212 through switch 216. A voltmeter 114 is also connected to load resistor 103 and its other side is connected to a reference voltage derived from voltage divider circuit 110. A null indication on the voltmeter indicates a correct initial setting for the conductor plate. The current in the magnetizing coil 28 is maintained by means of a series resistor 179 the voltage developed across which may be fed to indicator 212. Switches 214, 215, 216, 217 may by selection of suitable combinations cause to be indicated on device 212, the condenser spacing, the current is coil 28, or the rate of change of flux in the various test coils 31, 32, 33 and the outputs of the test coils may be integrated by valve 220 and its associated circuits and the value of the flux indicated directly.