Patent GB-118382-A (GB)
Title: Improvements in and relating to Railway Signalling.
IPC: B61L3/22
Filed: 1918-01-23
Abstract: 118,382. McKenzie, Holland, & Westinghouse Power Signal Co., (Union Switch & Signal Co.). Jan. 23, 1918. Electrical Systems, automatic; t r a c k apparatus actuating signals on trains and for stopping trains.- Signals at the side of the track or on trains are controlled by alternating currents supplied to the track rails, which are divided into insulated sections, the frequencies of the two currents supplied being such that a resultant current of periodically varying amplitude is produced by means of which one signal-controlling relay is energized, a second signalcontrolling relay being energized by current of the frequency of one of the currents supplied to the track rails. In the systems shown in Figs. 1 and 5, current of one frequency is supplied through permanent connexions, whilst current of the other frequency is supplied through contacts which are controlled in accordance with the condition of the sections in advance. Fig. 1 shows a track with insulated rail sections, which are connected by inductance bonds 3, 3a, serving also as coils of transformers by which current is supplied to the track rails and thence to the devices controlling the track signals. High frequency current is generated by a battery 10 in circuit with a transformer winding 12 and the filament 6 and plate 8 enclosed in a vacuum tube K. Across the terminals of the coil 12 there is connected a tuned circuit including a condenser 13 and the coil 11 which serves as primary winding to the bond 3, through which the track rails are energized. The frequency depends upon the tuning of the resonant circuit comprising the transformer coil 14 and the condenser 15, one pole of which is connected to the grid 7 in the tube K. Current of a slightly lower frequency is supplied by a similar arrangement with suitably tuned circuits, the circuit of the battery 10<a> of which is closed only when the relay R, connected across the rails of the advance section, is energized, that is, when the advance section is unoccupied. Under this condition, the transformer winding 19 receives currents of both frequencies. The circuit of the coil 16 and condenser 20 is tuned broadly to these frequencies. The circuit of the secondary 22 and condenser 21 is tuned to the higher frequency and is connected by way of the grid and filament of the vacuum tube device K<111> to transformer 27, which supplies the relay R. The condenser 20 is connected to the filament of another vacuum tube device K<11> and by way of the condenser 23, shunted by a non-inductive resistance 24, to the grid of this tube. The grid is thus subjected to a single fluctuation of E.M.F. corresponding to each periodic variation in amplitude of the current in the coil 19 due to the two signalling currents impressed on the track, and the transformer 28 supplies alternating current of this " beat " frequency to the relay R<1> which is designed to respond to this frequency. When a train occupies the section, both relays R, R<1> are de-energized, and no current of the lower frequency is supplied to the section in rear. Hence, in that section, the relay R alone is energized and current of both frequencies is supplied to the next section, the two relays of which are energized. The armature contacts 29, 36 of the relays are arranged to illuminate one of the signal lamps X, Y, Z according to their positions. Fig. 5 shows a section of track to which signalling currents are supplied from central generators and line wires. The generator G supplies current at low frequency, say, 60 cycles per second to the line wires 38 and to the track rails through transformers T and 44, and a reversing switch N connected to the three-position semaphore F<1>. The semaphores are controlled by induction relays S, of which the coil 41 is fed from transformer T and the coil 40 from the track-rails. The armature, therefore, is moved to right or left of its neutral position according to the position of the semaphore in the advance section, and the operating circuits of the semaphore are closed thereby. For actuation of train-carried apparatus a current of high frequency, say, 20,000 cycles per second, is supplied to the track from generator G<1> through line wires 37 and transformer T<1>. The core of this transformer is wound with a third coil J which is supplied with low frequency current through the contact 43 while the relay S is energized; this coil saturates the core t<1> thus causing periodic variations in the amplitude of the high frequency current supplied to the track rails. A choking-coil L prevents passage of the high-frequency current into the low-frequency transformer 44. Apparatus on the train may be energized from the track rails inductively or by direct contact. Vacuum tube devices are employed to control the energization of either or both relays P, P<1> according to the frequency of current received. These relays control signals as shown in Fig. 1 or may, singly or in conjunction with speed-controlled devices, control train-stopping apparatus. Fig. 1 shows an induction coil 30 carried by the train, connected to a tuned condenser 20<d> and to the condenser 23<d> shunted bv the resistance 24<d> and to the vacuum tube K<iv>. The relay P is connected to the plate circuit in series wtih a transformer 28<d>. The circuits are so tuned that the relay P is energized by a direct current of high frequency and the relay P<1> by alternating current of " beat " frequency. An alternative arrangement of train apparatus corresponds closely with the arrangement of apparatus for controlling signals on the track shown in Fig. 1, the transformer 16 and condenser 20 being, in this case, supplied with current induced in a train-carried coil. In another modification, the relay P is connected in series with the resistance 24d of Fig. 1 instead of in series with the transformer 28<d>.