Patent GB-766496-A (GB)
Title: Improvements relating to code communication systems
IPC: B61L7/08
Filed: 1954-12-10
Abstract: 766,496. Railway traffic control systems. GENERAL RAILWAY SIGNAL CO. Dec. 10, 1954 [Dec. 11, 1953], No. 35843/54. Class 105. [Also in Groups XIX and XXXVIII] A code communication system, e.g. a Centralized Traffic Control System for Railways, of the kind in which indications from a plurality of field stations to a central office are transmitted by shunting a pair of line wires, comprises at the central office coding means for applying a series of spaced pulses to the line wires as a cycle code, each pulse and each intervening space constituting respective cycle steps, a relay binary counter at each field station to count the steps in a code cycle and to govern the application of an indication shunt so that such shunt can only be applied on a designated step for that station and a relay binary counter at the central office to count the cycle steps and to transfer a received indication to registration means appertaining to the sending field station as determined by the receiving cycle step so that the field stations are scanned each cycle to ascertain the conditions obtaining thereat. In the embodiment described each binary counter comprises digital relays passing through a sequence of permutations of their conditions (picked up or dropped down) in accordance with a binary code requiring a change of only one digit and so of only one relay to register each cycle step, the changing relay in response to any one step being selected by virtue of the existing conditions of the relays at the time of that step, a relay on change, remaining in the new condition until its reversion is required in reponse to a subsequent cycle step. Using (n + 1) relays of which one changes conditions on each input step, the number of distinct steps which may be counted is (2n-1) not counting the conditions when all the relays are de-energized and dropped down, i.e. in the " at rest " condition. Figs. 2A and 2B placed side by side with Fig. 2A on the left represent the central office, Fig. 2A, and a typical field station, Fig. 2B, connected by two line wires 10, 11 which, in the " at rest " condition of the system are energized with positive potential on wire 11 and negative potential on wire 10 from the battery 12 at the central office. A code cycle is initiated by a line shunt applied at a field station in response to a change in conditions at such field station, as by the occupation of a track section by a train. Such shunt is detected at the central office by increased current through the upper winding of the shunt detecting relay OL which causes the initiation of a code cycle, viz. a series of polarity reversals in the line wires 10, 11 and the binary counters at the central office and at all field stations are set in motion, each station being assigned one or more designated steps in the cycle during which its short-circuiting of the line wires is appropriately routed by the counter at the central office to registration means such as the display lamps. TE. On entrance of a train into a track section the normally energized track relays 1T, 2T, &c., Fig. 2B, are released and in the case of relay 1T, for example, dropping its armature 24 to pick up repeater relay 1TP, which during the change-over of its contact 17 opens the holding circuit of the normally held change relay CH which drops away opening its holding circuit at fc19CH (front contact 19 of relay CH) and at bc20CH (back contact 20 of relay CH) closes a point in the energizing circuit of relay IV1 of the binary counter group of relays IV1-IV6. This circuit is from battery positive pole (x) bc37L (relay L being, in the at-rest condition of the system, in the droppedaway condition by virtue of the rectifier 16 being oppositely poled to the potential on the wires 10, 11) bc38FTP (relay FTP being normally energized but dropped away when fc27CH is opened), bc20CH, lower windings of relay IV1, back contacts 39 to 43 of relays IV2 to IV6 respectively to negative pole of battery (-) atfc27CH the stick circuit over the upper winding of relay BTP and fc91BTP, fc28-ITP is opened and relay BTP drops away, and at fc30BTP opens the pick-up circuit of relay FTP. Each counting relay IV1-IV6 has two windings oppositely poled with respect to the direct current applied to them and energization of the upper winding alone picks up the relay which is then held but energization of both windings causes the relay to drop away. At fc26-IV1 relay CH is picked up over its upper winding and held over fc19CH, bc18-2TP, bc17-ITP. Although bc20CH is now open, relay IV1 is held over fc22-IV1. In these conditions a cycle-initiating shunt is placed across line wires 10, 11 from wire 11, rectifier 44, bc45BTP, bc46FTP, fc47-IV1 to line wire 10. As the result of such shunt the current through relay OL, Fig. 2A, is increased to beyond operation point through its upper winding and on picking up the relay is held at fc136-OL from (+) on bc54CR2 over the lower winding. At fc56-OL slow release relay OZ is picked up and is held over bc53CR2 and fc84-OZ. At fc86-OZ a further energizing circuit is provided for relay OL from wires 10, 11 even through bc150ZP be opened. At fc65-OZ energizing circuits for relay V1 are closed over bc66CR1 and over the upper winding of relay V1 and over the lower winding of relay V1, bc67CR1, bc68-72 of relays V2 to V6 respectively and the relay VI remains in its dropped-away condition. At fc58-OZ relay CR1 is picked up over bc59CR2 and held over fc35CR1 and bc59CR2. At bc66CR1 and bc67CR1 the two energizing circuits of relay V1 are opened and at fc66CR1 relay V6 is picked up over its upper winding and fc65OZ, bc73 to 76 of relays V1 to V4 respectively. At fc83V6 an alternative stick circuit for relay OZ is completed over fc84OZ so that this relay OZ is held over fc49-52 as the counting relays pass through their various permutations of conditions during a cycle of operation. At fc78V6 slow release relay OZP is picked up over fc79CR1, fc80-OZ, and is held over fc79CR1 and fc81-OZP or, when relay CR2 is picked up, over fc53CR2. Since relays CR1 and CR2 are both simultaneously in released conditions for only very brief intervals relay OZP remains picked up throughout a code cycle. At fc82-OZP relay CR2 is picked up over fc55CR1 to start the code stepping by interaction with relay CR1 which is deenergized at bc59CR2 and after a slow release period drops away and at fc55CR1 de-energizes relay CR2 which after a slow release period drops away to pick up relay CR1 at bc59-CR2 relay CR1 picking up relay CR2 again at fc55CR1. During the short period when relay CR1 is dropped away and relay CR2 is still picked up the holding circuit of relay OL is opened and this relay drops away. Atfc13- and 14-CR1, the polarities of the line wires 10, 11 are reversed, and when wire 10 is positive the pulse is designed as a positive pulse. It is assumed that the step in the cycle during which the indication of track occupancy resulting in the dropping away of track relay IT is transmitted by shunting the line wires 10, 11 is the second cycle step. During this second step the counter circuit organization is such that relays IV2-IV5 are dropped away while relay IV6 is picked up and on this step a shunt circuit, viz. the indication shunt, exists between the wires 10, 11 over rectifire 44, fc45BTP, bc125L, fc126-ITP, bc127 to 130 of relays IV2 to IV5 and fc131-IV6. Similar circuits may exist on other even steps at other field stations for indication shunts. The reversal of the polarity on the wires 10, 11 causes relay L at the field stations to pick up over the rectifier 16 and at bc125L the indication shunt is removed from the line. At bc14CR1 the energizing circuit for the upper winding of relay OL is opened but this latter relay is held over fc135CR1 and fc136-OL. At the field station initiating the cycle of operation, i.e. Fig. 2B, relay IV1 is in its picked-up condition when relay L is picked up on the first impulse of the code cycle and at bc37L the lower winding energizing circuit of relay IV is opened and this relay drops away and at bc26-IV1 completes the energizing circuit for the upper winding of relay BTP over bc60-64 of relays IV2-IV6,< >fc27CH, fc28-1TP or fc145-2TP, bc90FTP. On picking up, relay BTP is held over fc91BTP. At fc95BTP, (+) is connected to wire 98 over bc96FTP and fc97L so that as relay L is alternately picked up and dropped away in unison with the code pulses on the wires 10, 11, energy is alternately applied to wires 98 and 99 by contact 97 of relay L. Also at fc37L positive battery potential (+) is applied alternately to wire 101 over fc100BTP and to wire 102 over bc38FTP and fc21BTP. According to the scheme adopted in the example the upper and lower windings of each relay are energized only if they are in series with a front contact of the relay of the immediately preceding digit and with back contacts of relays of all the other preceding digits. Whether the relay operates depends upon the lower windings being in the de-energized condition and to this end the lower winding is in series also with front contacts of an odd number of relays for succeeding digits in the picked-up condition. If the relay in question is to be dropped away by energization of the lower winding, this winding must be in series with front contacts of an even number of relays for succeeding digits in pickedup condition. Thus when relay L picks up for the first time energy is applied to wire 98 and over bc103 to 106 of relays IV1 to IV4 respectively to energize the upper winding of relay IV6. At the same time energy is applied to wire 101 but fc111-IV5 is open preventing the energization of the lower winding of relay IV6 so that this relay picks up. The upper winding of relay IV1 is energized at bc97L each time relay L drops away and at bc37L wire 102 is energized over bc21BTP. When relay L drops away for the first time an odd number of the relays for the succeeding digits a