Patent GB-717152-A (GB)
Title: Improvements relating to code communication systems for centralised railway traffic control
IPC: B61L7/08
Filed: 1952-07-22
Abstract: 717,152. Centralized traffic control systems. GENERAL RAILWAY SIGNAL CO. July 22, 1952, [Aug. 3, 1951.] No. 18536/52. Class 105. In a code communication system for centralized railway traffic control for transmitting from a plurality of field stations to the central control office indications of the conditions of apparatus at respective stations, the group of code elements allotted to identify the respective stations effect operation, in a sequence corresponding to the characters of the code elements, of relays in a bank of station relays located at the central office and including one relay for each station so that after operation of the first relay selectively in accordance with the character of the first code element the succeeding relays are selectively energized by the immediately preceding operated relay in accordance with the respective characters of the corresponding code elements to cause said preceding relay to drop away whereby the only station relay remaining energized on completion of the identifying code is the relay for the station identified by that code. In a circuit organization utilizing marks and spaces as code elements, two station relays are assigned to be selectively energized by the first code element. Two other station relays are assigned to be energized selectively in response to the second code element, one or the other of these relays being energized in dependence upon the selected relay of the first two and on the character of the second element. Thus the selection progresses step by step each additional step having a number of station relays comparable to the number of station relays that has been associated with all preceding steps, the third step having, in the case stated, four station relays. Figs. 2A and 2B placed side by side illustrate the circuit organization at the central control office for receiving indications utilizing marks and spaces of equal durations as code elements, from a field station represented by the broken line rectangle in the top right hand corner of Fig. 2B and containing only the line relay Li and the code transmitter relay C1 which operates its contact 27 to transmit the code elements by placing positive potential on the line between the field and control stations to represent a "mark"; the absence of potential representing a "space." The code transmission apparatus located at the field station is assumed to be as disclosed in Specification 717,142. The symbols (+) and (-) indicate connections to the respective positive and negative terminals of a direct current source and B(+) and B(-) indicate connections to respective positive and negative terminals of a split battery with centre tap CN. The relay contacts of relays identified by letter reference characters but with no circuit shown for the windings of the relays are contacts of relays bearing similar reference characters provided at the control office having their operations and control circuits as described in the Specification 717,142. In the description the contacts of the various relays will be identified by prefixing the letter f or b to denote whether the contact is a front or back contact respectively and adding the relay reference. Thus the front contact 27 of relay Ci is denoted by f27C1. To select one of the station relays 1ST-8ST by a code transmitted from the field station an identifying code of three code elements is required at the control office. Each communication channel has a magnetic stick relay at the central office as, e.g. RGK, LGK,.2TK, each of which is conditioned in accordance with the code elements received through the respective channels and each of which has associated therewith an indication-lamp RGE, LGE or TE. As described in the said Specification the reception channels at the control office are cyclically conditioned each to receive one code element by means of a code oscillator CT, Fig. 2B, which determines the period during which each communication channel is effective and, incidentally the duration of each code element, during an indication communication cycle. The initial opening of contact f27C1 at the commencement of a communication cycle causes line relay L at the control office to drop away and at contact f28L opens a retaining circuit of the oscillator CT which is released to oscillate thereby initiating the operation of the bank of stepping relays 1V-4V which are dropped away in turn from their normally energized positions in numerical order with a partial repeat of the dropping away of relays 1V-3V for the second time to form steps 5, 6 and 7. Thus relay 1V is picked up again on dropping away of relay 3V and relay 2V is picked up again on dropping away of relay 4V and relay 3V is picked up again on dropping away of relay 1V for the second time. Oscillator contacts 32, 33 are closed when the oscillator is retained at rest and on its first half-swing or step period, contacts 38, 39 close and likewise for each odd step, contacts 32, 33 closing during the even steps. The first stepping period is reserved for lock out purposes between the control office and field station transmissions and a "space" is transmitted during this period so that the first element of the identifying code is transmitted during the second step of the transmission operation. Thus if relay C1 is energized for the transmission of a "mark," contact f27C1 is closed and the line circuit is energized over contacts f30C and b31, 2V. Contact b124, 4V connected in parallel with b31, 2V ensures continuity of the line circuit throughout the stepping operation. Even-step mark relay EM is picked up over oscillator contacts 32, 33, b34LCS, f35L, f36, 3V and b37, 2V and this circuit is opened on initiation of the third step at contact f36, 3V, but relay EM is held during the third step over contacts f41EM, b40LCS and oscillator contacts 38, 39. Reception of the first code element as a mark causes relay 2ST to pick up over contacts f24EM, b42LCS, f43, 4V, b44, 3V, f45CP, wire 21 and contact f26EM, and this relay is held over a circuit including contacts f50, 2ST; b49, 4ST; b48, 6ST; stick circuit wire 47, and contact f46CSP. Relay CSP having been picked up on initiation of the cycle, is maintained picked up throughout the cycle except for a momentary de-energization at the midpoint of the cycle prior to repeat of the relay stepping. operation at which time contact f51CPP functions for f46CSP. If the first code element is a "space," relay EM is not energized and relay 1ST then pulls up over contacts b24EM, b42LC2, f43, 4V; b44, 3V; f45, CP; wire 21 and contact b26EM and the relay is held energized over wire 47 and contacts b52, 5ST; b53, 3ST; and f54, 1ST. If the second code element is a "mark" the odd-step mark relay OM is picked up over contact fingers 38, 39, contacts b40LCS, f55L, b56, 2V;f57, 4V; b58, 3V; and this relay is held during the fourth step over a circuit including oscillator contacts 32, 33; contacts b34LCS, f59CSP, f60OM. At contact b25OM positive potential is applied to wire 22 over contacts b61LCS, b61a, 4V, f62, 1V and f63CP. If relay 2ST has been picked up (first code element being a "mark") relay 4ST is picked up over wire 22, contacts b64, 1ST and b65, 3ST and establishes a stick circuit over contacts f67, 4ST; b66, 8ST; and wire 47. At contact b49, 4ST the stick circuit of relay 2ST is opened and at contact b68, 4ST the energizing circuit of relay 3ST is opened. If relay 1ST has been picked up (first code elementa "space") relay 3ST is picked up over contacts b69, 2ST and b68, 4ST; the energizing circuit for relay 4ST being open at b64, 1ST. Relay 3ST is held and opens the holding circuit for relay 1ST at contact b53, 3ST, and opens the energizing circuit of relay 4ST at b65, 3ST. If the third code element is a "mark," the relay EM is picked up during the fourth step over contact fingers 32, 33, contacts b34LCS; f35L; b36, 3V; f70, 1V; b71, 4V; and sticks over contact f41EM during the fifth step and (B+) is applied to wire 23 at contact f24EM. If at this time relay 1ST is held operated as the result of the first two code elements relay 5ST picks up over wire 23, contacts b77, 4ST; b78, 3ST; b79, 2ST; b80, 6ST; b81, 7ST; b82, 8ST; and is held over its front contact and stick circuit wire 47 and opens the stick circuit of relay iST at contact b52, 5ST and opens the energizing circuits of relays 6ST, 7ST and 8ST at contacts b83, 5ST; b84, 5ST; and b85, 5ST; respectively. If relay 2ST is held after the first two code elements the reception, of a mark as the third element results in relay 6ST being picked up and held to release relay 2ST at contact b48, 6ST, and to open the pickup circuits of relays 5ST, 7ST and 8ST. If relay 3ST is held after the first two code elements relay 7ST is picked up in response to the reception of a "mark" third code element, and held to release relay 3ST at contact b94, 7ST and open the pickup circuits of relays 5ST, 6ST and 8ST. Similarly if relay 4ST is held after reception of the first two code elements, on reception of a "mark" third element relay 8ST is picked up and held to open the stick circuit of relay 4ST at contact b66, 8ST and to open the pick up circuits of relays 5ST, 6ST and 7ST. When the third element of the indication code is a "space" relay EM is not picked up during the fourth step and whichever one of the relays 1ST-4ST is held picked up as the result of the first two code elements, is held also during the fifth and sixth steps. The fourth code element received during the fifth step gives the indication of the condition of an apparatus, e.g. whose identity code is three spaces, S.S.S. and hence relay iST would be held operated during the fourth and fifth steps. Assuming a "mark" is received during the fifth step, then relay OM is operated and held during the sixth step and at contact f25, OM, positive battery (B+) is applied to wire 101 over contacts b61LCS, b61a, 4V; b62, 1V; b97, 2V; f98, 3V; b99, 4V; f100CP; and an energi