GB971302A - Improvements in or relating to electrical switching arrangements - Google Patents

Abstract

971,302. Magnetic amplifiers. WESTING- HOUSE BRAKE & SIGNAL CO. Ltd. May 24, 1961 [May 24, 1960], No. 18231/60. Heading H3B. An electrical switching arrangement comprises a transductor having two high permeability magnetizable cores, and A.C. and D.C. windings arranged so that a D.C. signal opens the transmission path of an A.C. signal through the arrangement, in which the A.C. winding comprises a relatively small number of spaced turns, and the D.C. winding comprises a relatively large number of turns, the A.C. and D.C. windings being spaced from each other. Two toroidal cores 1, 2 are provided with D.C. windings 3, 4 in series, and A.C. windings 5, 6 in series opposition, and the presence of a predetermined D.C. in windings 3, 4 allows A.C. to flow through load 12. Windings 3, 4 may be replaced by a single coil threading both cores and consisting of 400 turns of 36 S.W.G. wire on a bobbin, each A.C. winding comprising twelve turns of wire made up of nineteen strands of 36 S.W.G. wire covered with P.T.F.E. A railway signalling circuit is described which provides different outputs when the D.C. input is " on " and " off " (Fig. 6). The A.C. windings of a switching arrangement, 31, are connected to the primary winding 36 of a matching transformer 35, the secondary winding of which is connected through rectifiers 38, 39 and a centretap to output terminals 40, 41. An output is produced whenever a predetermined D.C. is present in winding 34. A further transductor arrangement 42 is provided which consists of two similar halves each including a D.C. winding 43, 44, an A.C. winding 45, 46, and a further winding 47, 48 connected through rectifiers 50, 51 to output terminals 52, 53. With no D.C. in windings 43, 44 a D.C. output is produced at 52, 53 by transformer action, and this output is reduced by increasing the D.C. input. A variable resistor 58 changes the gain of arrangement 42, relative to that of arrangement 35. The " off " output circuit consisting of transductor 42 may be omitted if a single output is required. A time delay is provided by the arrangement in Fig. 9, in which A.C. is applied to a matching transformer 71 and the output is half-wave rectified to give A.C. fundamental and ripple components superimposed on a steady D.C. The A.C. is passed by transformer 61 for rectification at 67 to give a D.C. control current for gate arrangement 68. On disconnection of the A.C. source from terminals 69, 70 the inductive windings 65, 66 cause the D.C. component to decay exponentially, thus delaying the operation of gate 68. A proving device in the form of a transductor 60 is provided to indicate correct operation of the D.C. circuits prior to it. All the circuits are stated to be fail-safe.