Patent GB-580365-A (GB)
Title: Improvements relating to railway signalling apparatus
IPC: B61L29/28
Filed: 1943-10-27
Abstract: 580,365. Railway signalling apparatus. WESTINGHOUSE. BRAKE & SIGNAL CO., Ltd. Oct. 27, 1943, No. 17726. Convention date, Jan. 9. [Class 105] An arrangement for detecting the presence of a train in a zone of a stretch of track, which zone may not coincide with a track section and may extend beyond a track section, e.g., for detecting the presence of a train within the approach length to a levelcrossing highway signal, or within the approach-locking zone of a passing siding points, the stretch possibly having a plurality of track sections each with a relay and electric energy supply, over the rails of the section, comprises a device responsive only to electric energy of a different characteristic supplied concurrently over the rails of the zone in question. Fig. 1 shows an arrangement for the control of a level-crossing highway signal XS located within a stretch of track wherein the track sections 4T, 5T, 6T for the control of the railway traffic signals are supplied with coded direct current in accordance with traffic conditions in sections ahead while the highway signal XS is brought into operation when a train reaches an insulated rail joint 20 defining the approach length to the level crossing. With section 6T unoccupied a code-transmitting relay 5CTM applies direct-current pulses to the rails of sections 5T from a track battery 5TB at the rate of 180 per minute where the code-following track relay 5TR operates a decoding transformer 5DT whereby relays 5H and 5J are energized, relay 5J responding only to code of 180 interruptions per minute. Thus the wayside signal 5S has its lamp G lit while front contact 25 of relay 5H effects the supply of 180- interruptions-per-minute code to the code transmitting relay 4CTM for section 4T. If a train enters section 5T the relays 5H and 5J are de-energized whereby lamp R of wayside signal 5S is lit while back contact 25 of relay 5H now effects the supply of 75-interruptions-perminute code to the code-transmitting relay 4CTM for section 4T. If section 5T had been supplied with 75-interruptions-per-minute code only relay 5H would have been energized whereby lamp Y of wayside signal 5S would have been lit and 180-interruptions-per-minute code would have been 'applied to section 4T. For the control of the level-crossing highway signal XS there is provided a relay arrangement including a cold-cathode controlled - ionization tube powered from an alternating current supply applied to rails of section 5T on entry of a train, the tube becoming de-energized when the train reaches the insulated rail joint 20 thereby to bring the highway signal into operation ; this control is duplicated to provid a highway warning for train movement in either direction in the section. When an eastbound train enters section 5T and so de-energizes the relay 5H a contact 26 thereof de-energizes a control relay CR whereby a back contact 35 closes the supply to a transformer ST which energizes a transformer T to feed alternating current to the rails ; this rail current passes through a gridcontrol transformer AGT bridging the rail joint 20 the secondary winding of which is connected to the grid 42 of the cold-cathode tube AT, the anode circuit of which includes a relay ATR and the secondary winding of a transformer ATT powered from the transformer ST ; a biassing voltage for the grid is obtained by a tapping to a resistance 44 placed across the secondary winding of the transformer ATT. The relay ATR receives energy only on the positive halfwaves but being slow releasing by reason of a condenser 55 maintains its contact 56 closed so to energize the lower winding of a two-winding relay E the upper winding of which was deenergized by the control relay CR opening its contact 28. When however the train reaches the insulated joint 20 the rail current is shunted from the grid-control transformer AGT whereby the tube no longer passes current and the relay ATR opens its contact 56 to de-energize relay E which in turn opens its contact 60 to deenergize the winding 30 of an interlocking relay XR which closes a back contact 32 to effect the operation of the highway signal XS. When the train passes an insulated joint 15 adjacent to the level crossing the tube BT, provided for the other approach side, is shunted and becomes non-conductive to de-energize corresponding relays BTR, W, and winding 31, but due to the mechanical features of the interlocking relay the contact 33 does not in these circumstances close and so when the rear end of the train passes the rail joint.15 at the level crossing the tube AT again becomes conductive to energize relays ATR, E and winding 30 which opens its contact 32 to stop operation of the level-crossing highway signal XS. It should be noted that the reactance 16 prevents shunting of the gridcontrol transformer AGT by the train when the rear of the train is at the right-hand side of joint 15. When the rear of the train passes joint 22 the tube BT again becomes conductive so that the relays BTR, W and winding 31 of the interlocking relay XR are energized. When the train vacates section 5T 75-interruptionsper-minute code is applied to the rails whereby the decoding relay 5H becomes energized and at its front contact 26 energizes the control relay CR which in turn energizes the relays E and W over its contacts 28, 27. It should be noted that the primary windings of the bridging transformers at the rail joints 20, 22 and a bridging reactance 16 at the level-crossing rail joint 15 are ineffective to block the coded direct current of 75 and 180 interruptions-per-minute. The reactance 16 prevents the control current for the tube of one approach length being shunted by a train in the other approach length and to this end the rail alternating current may be doubled in frequency by the transformer T being fed through a full-wave rectifier, Fig. 3 (not shown). An inductive loop 102, Fig. 10 (not shown), energized from the alternating current in the rails may be utilized for the energization of the grid-control transformer AGT instead of the arrangement of the primary winding bridging the insulated joint 20 as shown in Fig. 1. In the event of failure of the apparatus provided for detecting the entry of a train into the zone it will be seen that the level-crossing signal will still be put into operation by the normal track relay apparatus though at an earlier time. Moreover, the control by the relay CR may be omitted the apparatus for detecting the entry of the train into the zone then being continuously in concurrent operation instead of being put into concurrent operation by entry of a train into the section containing the zone. Where there are two level crossings in the stretch each with their own approach lengths the control alternating rail currents are of different frequencies with filters provided for the different frequencies, Figs. 11a, 11b (not shown) and in the case where an approach length extends into a different track section the supply of control alternating current to such length is effected only if a relay KH, Fig. 11b (not shown), normally energized by a feed-back code direct current during the " off " intervals of the main code, has dropped so indicating the entry of an approaching train into such different section. Alternating current (of different frequency) may be used for the track section Fig.12 (not shown) or superimposed for cab signalling Fig. 13 (not shown). Fig. 14 shows an arrangement in which a lock magnet SL for a passing siding points W can be energized by pressing a manual key SK provided that direct current track sections 1T, 2T, 3T are unoccupied to allow alternating current applied by a transformer T at section 1T to act, through transformers 124, 125 for the sections 2T, 3T, on the grid of a coldcathode tube WT having in its anode circuit a relay AR of which a contact 128, closes the circuit to the lock magnet SL.