Patent GB-563852-A (GB)
Title: Improvements relating to railway traffic controlling apparatus
IPC: B61L3/22
Filed: 1941-07-03
Abstract: 563,852. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. July 3, 1941, No. 8398. Convention date, Dec. 31, 1940. [Class 105] In a railway traffic control system using train-carried control apparatus responsive to coded track current, the train-carried apparatus comprises an inductor mounted over each rail and a code-following relay receiving energy from the two inductors through an amplifying device, the amplifying device being arranged so that the output current therefrom is insufficient to operate the relay unless the currents from the inductors are supplied to the amplifier substantially simultaneously and in phase. The arrangement, inter alia, minimizes the risk of improper relay operation by " magnetic spots" in the rails, and gives satisfactory " broken rail " protection where long track-sections (11,000 ft. mentioned) are used with high-speed traffic, allowing the use of a low-frequency A.C. supply (20 cycles per second described) for the coded current, or of coded D.C. Fig. 1 shows an insulated track section DE supplied at its exit end over transformer TD with current coded at the usual 75 or 180 frequency code (selected in known way by contact of relay HD in accordance with traffic conditions in the next section ahead) by coding device CT of known kind. The entranceend is' bridged by a transformer-rectifier ER and code-following track relay ETR released when the section is occupied by a vehicle TV. Contacts of relay ETR control the relay HD of the next section to the rear. Current of the particular code frequency supplied to the track when occupied by vehicle TV passes round a track circuit completed between the rails by the vehicle wheels and is picked up by the inductor coils 9, 10 mounted ahead of the leading wheels. Coded energy from coil 9 is passed through transformer T1 and is applied between control grid 15 and cathode 17 of an electron tube amplifier VT1, the grid being negatively biassed by battery 16. The primary and secondary circuits of transformer T1 have condensers 12, 13 respectively for tuning the circuits to the frequency of the A.C. code-current source BX, CX (viz., 20 cycles per second). Coded energy from coil 10 is passed through a separate channel via transformer T2 (with tuning condensers 22, 23) to the grid 25 and cathode 27 of an electron tube amplifier VT2, with biassing unit 26. The output of this amplifier passes through the primary winding 34 of a transformer T3 included in the circuit between plate 28 and cathode 27. The secondary winding 36 is included in the circuit between the screen grid 19 and cathode 17 of amplifier VT1. The output circuit of amplifier VT1 includes the primary winding 40 of a transformer T4 between plate 18 and cathode 17. The secondary winding 42 of transformer T4 is included in circuit with grid 44 and cathode 46 of a further amplifier VT3 which includes the primary winding 49 of transformer T5 in circuit with its plate 47 and cathode 46. Secondary winding 50 supplies current to the code-following polar relay MR, the contact 51 operating with code frequency and connecting a low voltage source having terminals B32, N32 with the halfwindings of transformer AT primary winding 54 alternately. Secondary winding 55 supplies coded current through a decoding unit DU of known kind to relays A, L, relay A picking up only with 180 code and relay L only with 75 code. With 180 code relay A picks up and relay L releases, as shown, lighting the " clear " signal lamp 57 of cab signal CS. With 75 code relay A releases and relay L picks up to light " approach " signal lamp 60. With both relays A, L released " slow speed " lamp 62 is lit. The negative bias provided by battery 16 is high enough to ensure no current normally flowing in the plate circuit of amplifier VT1, and also to ensure that no current, or at least insufficient current to cause operation of relay MR, shall flow in the plate circuit when the grids 15, 19 are positively driven either singly or out of phase. With the grids driven positively and substantially simultaneously and in phase, a condition unlikely to be caused by " magnetic spots " in the rails, sufficient current flows in the plate circuit to cause operation of relay MR. The Specification gives E.M.F. diagrams illustrating the action. Source B32, N32 supplies energy to the signal lamps, to the indirect-heating filaments 20, 29, 48 of the amplifiers, in parallel, and also to the motor 31 of a motor-generator MG, the generator 32 of which, with terminals B300, N300, supplies high-voltage current to the plate circuits of the amplifier.