Patent GB-317070-A (GB)
Title: Improvements in or relating to methods of and apparatus for detecting flaws in electrical conductors
IPC: G01N27/83
Filed: 1929-07-03
Abstract: 317,070. Sperry Development Co., (Assignees of Sperry, E. A.). Aug. 10, 1928, [Convention date]. Magnetic tests: detecting, indicating, and locating faults.-Flaws in electric conductors are detected by passing a current through the conductor, cutting the magnetic field produced thereby around the conductor by moving a second conductor relatively thereto, and detecting variations in the electromotive force induced in this second conductor. As shown diagrammatically in Fig. 5, two oppositely wound coils 6, 7, preferably wound on a core 6<1> of alloy of high permeability. are moved relatively to a rail 1 through which current is passed between brushes 21, 22. When the coils 6, 7 are adjacent to a sound portion of the rail, the electromotive forces induced are equal and opposite, giving no sound in a telephone 5, but if a flaw 2 is present, the current is unequally distributed over the section of the conductor 1 at this point, causing a difference in the electromotive forces induced in the coils 6, 7 and producing a consequent sound in the telephone receiver 5. Fig. 1 shows a construction suitable for testing rails on a laid track. A sled 10 is supported beneath a test car 8 by rods 29 and is pressed against the track by springs 30. Housed within the sled are two armatures rotated through a pinion 15 and flexible shaft 14 from a motor 13 on the car body. Each armature is provided with unwound pole shoes of high permeability so as to direct a maximum number of lines of force through the armature. The armatures are oppositely connected and are in series with relay coils or indicator devices. The sled may be raised and lowered by means of linkwork 27, 31, 32, and has end extensions carrying the main supply brushes 21, 22 and auxiliary brushes 23, 231 which are connected in series with a relay for breaking the indicator circuit when passing over a rail joint. The relay may also operate a rail-counting device. In a modification, Fig. 8, two pairs of cross-connected coils 6, 7 and 6<1>, 7<1> are connected through amplifying valves 140, 100, 101, 104 to a series of relays 105, 106, 107 of different sensitivities so as to differentiate between flaws of different magnitudes. A relatively insensitive relay 108, connected to amplying valves 109, 110. controls a rail-joint marking pen magnet 114. The relays 105, 106, 107 control pen magnets 111, 112, 113. The pens mark on a chart advanced in accordance with the movement of the test car. A modification for testing wire as it passes through the rolling mills is shown in Fig. 10. Current is supplied to the wire 50, which moves rapidly in the direction of the arrow, by brushes 53, 54, between which is situated a pair of spaced detector coils 55, 56 which partly surround the wire. A second pair of coils 55<1>, 56<1> surround a portion of the wire 50 which is not traversed by current and therefore are only influenced by residual magnetism in the wire, enabling the presence of hard spots, crystallization, &c. to be detected. The coils 55, 56, 55<1>, 56' are formed in halves and are carried on frames 58, 59 hinged together at 60, Fig. 12, and normally kept open by a spring 63. The coils are closed around the wire 50 by links 65, 65<1> operated from a shaft 89<1>. Resting on and revolved by the wire 50 is a wheel 70 operating a linear measuring device 73 and a speed indicator 74. The wheel 70 is journaled on a bell-crank lever 75 pivoted on a shaft 76. When the end of the wire passes from under the wheel 70 this drops and causes the arm 77 of the bell-crank lever to open a switch 78 in the main circuit. At the same time the shaft 89<1> is rotated through bevel gear 71. operating link gear for opening the coils 55, 56, 55<1>, 56<1> and also cam gear for moving the brushes 53, 54 radially away from the wire 50, so as to prevent damage to the coils or brushes by the end of the wire. The speed indicator 74 may operate a rheostat 40 so as to increase the main current as the speed of the wire increases.