Patent GB-772366-A (GB)
Title: Improvements in or relating to coded track circuits for railways
IPC: B61L1/18
Filed: 1954-07-29
Abstract: 772,366. Coded railway track circuits. GENERAL RAILWAY SIGNAL CO. July 29, 1954 [Aug. 27, 1953], No. 22172/54. Class 105. In a coded track circuit for a stretch of railway track, code pulses having a normal predetermined rate and of shorter duration than the spaces between them are transmitted from either end and received at the other end to effect transmission of a pulse from the receiving end immediately on termination of the received pulse with similar action at the original transmitting end. Such to and fro transmission of " dependent " code pulses goes on indefinitely in the absence of traffic from the stretch and provides inherently protection against brokendown joint'insulation between the track sections which would cause false and dangerous signal indications and these dependent code pulses are at a rate faster than the " independent " or " driven" " code pulses which are chosen in accordance with traffic conditions to provide distinctive signal indications. Each end of a section is provided with a track relay connectable to the rails for energization by a code pulse received from the other end, a code transmitting relay arranged, when the track relay is deenergized, to be energized and render active a timing circuit which immediately de-energizes the code transmitting relay to terminate the pulse and maintain it de-energized for a time longer than that for which it was energized, the timing circuit being effective only while the track relay remains de-energized. The invention is described as applied to an A.P.B. signalling system providing protection against opposing train movements over a single track stretch between headblock signals at the opposite ends of the stretch but permits following train movements within such single track stretch with block spacing protection with overlap control of the signals, i.e. a stop signal in the rear of the train with the preceding signal at caution, dependent coding being used both for the track sections associated with the sidings and for the single track stretches which include several track insulated sections involving repeats of the code pulses from one track section to the next. The codes are distinguished by their respective polarities including a quick shift from one polarity to the other during the same pulse transmitting period. All signals are normally at clear for both directions of traffic but only leaving signals at the headblock locations are actually illuminated and approach lighting is provided for other signals. Tumble-down control is effected through a single track stretch by stopping the " dependent " coding and putting to " stop " all opposing signals in the stretch at substantially the same time, the code pulses being repeated from section to section independently of the signal response except in so far as the polarity of the pulses is determined by the then existing condition of the associated signal. The timing of the pulses is effected by a relay and an associated capacitor-resistor organization, so that the changeover from driven or independent coding to dependent coding can be effected by elimination of the condenser-resistor control on the relay. The decoding means employs the home and distant signal control relays Hand D respectively arranged to pull up for the reception at the associated section end of negative and positive pulses and to be maintained up during pulse reception. Both relays are picked up for codes of both polarities (-/+). All apparatus is shown in the drawings in the normal state, that is with no traffic on the stretch of track. Assuming that the code transmitting relay 7CP, Fig. 3D, which may be a double winding polarized relay with a single double-acting armature or two single armatures, and is assumed to be the latter, with armatures N and P which operate to transmit a negative and positive pulse respectively, has just been energized to operate armature P to apply a positive pulse to the track section 6-7T. A positive pulse results from positive battery potential (+) on the upper track rail and a negative battery potential (-) on the lower track rail and a negative pulse results from the reversed condition of polarities on the track rails. It is also assumed that at the other end of the stretch a code pulse has been applied and then removed so that the pulse-timing relay 2PT, Fig. 3A, is still picked up by reason of its timing characteristics awaiting the reception of a code pulse before applying the next dependent code pulse. The energizing circuit of relay 7CP for a positive pulse is from (+) including #.c. 150-2SR (front contact 150 of relay 2SR), b.c. 151-P-7TR (back contacts 151 of armature P of track relay 7TR), b.c. 152-N- 7TR (back contacts 152 of armature N of track relay 7TR), b.c. 153-7TRP (track repeating relay), b.c. 154-7PT (pulse timing relay), f.c. 155-8DP (decoding repeater relay), upper winding of relay 7CP to (-). Armature P of relay 7CP on operation closes#.c. 156 and 157- 7CP to apply the positive code pulse to the rails of section 6-7T and at f.c. 158-7CP relay 7PT is energized over circuit from (+) and including f.c. 150-2SR, b.c. 151-P-7TR, b.c. 152-N-7TR, b.c. 153-7TRP winding of relay 7PT,#.c. 158-N- 7CP to (-). At #.c. 159-7PT the associated capacitor and resistance timing circuit is connected across the winding of relay 7PT to perform a timing operation when relay 7CP drops immediately armature P because b.c. 154-7PT is opened. Relay 7PT remains up for a period determined by the timing circuit, or until a dependent pulse is received by relay 7TR. The pulse transmitted by relay 7CP is received at the end of the track section 6-7T by track relay 6TR, Fig. 3c, over b.c. 160 and 161-N-6CP and causes this relay to operate its positive armature P to pick up track repeater relay 6TRP over f.c. 162-P-6TR. On picking up relay 6TRP at #.c. 163 closes a circuit for the upper winding of code transmitting relay 5CP over b.c. 164, 165, 166, this latter of a directional stick relay 6WS which is picked up and held for west-going traffic, b.c. 167 of a similar relay 6ES held up for east-going traffic, f.c. 163-6TRP, b.c. 168- 6H (6H being a decoding stick relay held on receipt of negative code pulses), #.e. 189-6D (6D being a decoding stick relay picked up and held on receipt of positive code pulses) upper winding of relay 5CP to (-). Relay 5CP operates its positive armature P to transmit a positive pulse to the section 4-5T through f.c. 169, 170 and this pulse is received by track relay 4TR, Fig. 3B, at the other end of the section and which, being a positive pulse, causes relay 4TR to operate its positive armature P to complete, over b.c. 176-N-4TR an energizing circuit over the lower winding of code transmitting relay 3CP, and including b.c. 173- 3TRP, b.c. 174-3WS, b.c. 175-4ES, b.c. 176-N- 4TR, f.c. 177-P-4TR, to actuate the armature N of this polarized relay 3CP to apply a negative pulse to the track rails of section 2-3T over #.c. 178 and 179. When this armature N picks up, at #.c. 180 it completes an energizing circuit for a polarity shift slow release relay 3PS, over f.c. 181-4D and b.c. 182-4ES. Upon release of armature N of relay 3CP at b.c. 187 it completes an energizing circuit for the upper winding of relay 3CP to operate its positive armature P to apply a positive pulse to the track rails over #c. 183, 184. Both negative pulse and positive pulse are received by track relay 2TR in the track section 2-3T, Fig. 3A, over b.c. 190, 191 of code transmitting relay 2CP to operate first its negative armature N and then its positive armature P and both decoding relays 2D and 2H are picked up and held by the repeated energizations that they receive due to this double character (-/+) type of pulse. The track repeater relay 2TRP receives an energizing pulse on the reception of both the positive and negative components of the double character pulse, but is slightly slow releasing and thus behaves as though responding to a single character pulse and the dependent positive code pulse is only transmitted when the relay 2TRP drops away. Relay 2PT is normally held by its stick circuit when the code pulse (-/+) is received; but the opening of b.c. 195-2TRP opens the holding time circuit across the winding of relay 2PT so that this relay releases immediately in readiness for the transmission of the dependent code pulse as soon as b.c. 195- 2TRP closes. This positive dependent code pulse transmitted over rails of track section 2-3T is picked up by track relay 3TR, Fig. 3B, over b.c. 178 and 183, this relay operating to cause a positive pulse to be applied to the track section rails 4-5T by the code transmitting relay 4CP. This positive pulse is received by track relay 5TR, Fig. 3C, over b.c. 169 and 204 of relay 5CP to cause a code of double character (-/+) to be applied to track rails 6-7T and is received by the track relay 7TR, Fig. 3D, which operates to cause a dependent code pulse applied by the operation of code transmitting relay 7CP, to the track 6-7T for transmission to the left. The decoding relays 7D and 7H are both picked up and held on account of the double character of the received pulse, so that f.c. 215, 216 are both closed to complete a circuit for a slow operating thermal relay 7TM which on operation closes f.c. 271 to energize the " green " repeater control relay 7GR which on operation at f.c. 217 provides a stick circuit for itself through the thermal relay 7TM, thereby maintaining f.c. 218 closed for energizing the green lamp G of signal SIG7, but the energy through the thermal relay is insufficient to hold it operated and f.c. 271 opens. If a positive pulse only is received, relay 7D is held and relay 7H drops away, a circuit thus being completed over b.c. 218 and b.c. 270 for the red stop lamp. If a negative pulse only is received relay 7H is held operated and relay 7D is dropped away, a circuit being completed over b.c. 218, and f.c. 2