Patent GB-812754-A (GB)
Title: Electronic code communication system
IPC: B61L7/08
Filed: 1956-02-01
Abstract: 812,754. Electric selective signalling. GENER.AL RAILWAY SIGNAL CO. Feb. 1, 1956 [Feb. 3, 1955], No. 3190/56. Class 40 (1). An electronic code communication system comprises means at the transmitting station for continuously transmitting a succession of groups of successive pulses each pulse of which represents a data item, the pulses being counted at the receiving station to render active successively a plurality of indicator means, the counter being reset by the synchronizing means after the transmission of each group of pulses. The system is described as applied to the transfer of information regarding the operated conditions of railway switches, signals, &c., and track occupancy conditions, to a central station from one or more remote field stations. General arrangement. As shown in Figs. 1 and 2 a plurality of field stations transmit their indications over a line 10 to the central office. Alternatively a radio link may be used. A 15 kc/s. pulse constitutes one type of character of the indication code and a 14.75 kc/s. pulse constitutes the other character. Timing pulses of 8 kc/s. are transmitted from the central office to the field stations and station call pulses are sent having a frequency of 7.75 kc/s. At the central office the 100 c.p.s. output of a multivibrator 15 keys the carrier transmitter 17 whereby five millisecond carrier pulses are applied via filter 13 to line 10. The output of multivibrator 15 is also applied to the divider and station-call pulse generator 18 which at every twelfth pulse causes the output of transmitter 17 to be slightly shifted in frequency for a pulse period to provide a station-call pulse. The interval between one station-call pulse and the next is a station period for a particular station in the system. Station counters 19 are driven from pulse generator 18 and gate on each station period a different bank of storage units 34 through storage unit gating and clear-out circuits 20. At the end of a cycle as determined by counters 19 the synchronizing circuit 16 is made effective to stop the multivibrator 15 for a short time, providing a period of " no signal" which is used to synchronize the system. The pulses received at each field station are passed by filter 14 to receiver 21 which provides separate outputs for each timing pulse and station-call pulse, the station-call pulses being applied to counter driving circuits 22 and counted at station counters 23 to determine when that particular field station should transmit its indication code, and also utilized to reset the step counter 24 to its initial condition in readiness for counting the pulse periods of the appropriate station period. Both outputs from receiver 21 are supplied to pulse combiner 25 whereby a pulse is applied to the counter driving circuits 22 for each timing pulse and station-call pulse received. The output from the pulse combiner controls the transmitter 27 through control amplifier 26, a space pulse being transmitted via filter 11 if no input is being applied over line 29 from indication contacts 28 and station counter 23, and a mark pulse being transmitted if line 29 is energized. The counter driving circuits 22 are gated by the station counters 23 and controlled by the pulse combiner 25 to operate the step counter 24 only in the station period for that station. The output pulses from pulse combiner 25 are also applied to synch. period detector 30, which at the end of a cycle, when no pulses are received produces an output pulse to reset the station counter .23. As the counter 24 is stepped it causes energy to be applied through the various indication contacts 28 to the transmitter control amplifier 26 to provide an indication of the condition of the contacts. The indication code received at the central office is passed via filter 12 to receiver 31 providing separate outputs corresponding respectively to marks and spaces which are combined at 32 and cause the step counter 33 to advance one step for each pulse and selectively gate the storage devices in the bank corresponding to that station, the appropriate bank being gated through its own gating and clear-out circuit by station counter 19. Consequently the mark pulses are routed via storage unit and gating clear-out circuits 20 to the proper bank of storage devices, space pulses having no effect on the storage devices. The gating and clear-out circuit associated with each bank of storage devices clears out all previously received indications prior to routing a new indication code to a bank. Circuit details. Central office timing and synchronizing circuits, Figs. 3A, 3B, 3C, 3D. The output pulses of the 100 c.p.s. multivibrator 15 are applied to the carrier transmiter 17 and via capacitor 44 and resistor 45 to a guide electrode of the twelve cathode cold cathode glow tube 46 to cause the glow to step from cathode to cathode. With the glow on cathode 51 the potential on line 53 is applied to valve 55 which is gated by pulses from multivibrator 15 and produces an output pulse for every twelve pulses from the 100 c.p.s. generator, and these negative-going pulses are applied to the transmitter 17 to transmit distinctive station call pulses, and to the grid of normally conducting valve 63 to cause it to be cut off. The output pulses from 63 are applied via pulse former 71 to the units station counter 74 and also via step counter reset 72 to step counter 33, both counters comprising cold-cathode gridcontrolled glow tubes. The counter 33 demarcates the pulse periods of an indication code, the various tubes being fired in succession in response to positive going pulses on line 83. The output from step counter reset 72 ensures that the counter 33 starts each station period with tube 75 of its step No. 0 fired. The pulses from 71, corresponding to the occurrence of a station call pulse in the transmitted code, cause successive firing of the tubes in the ring counter 74 which each time it is restored to its initial condition with stage No. 0 conductive, applies a pulse to the tens counter driver 88 via lead 87 to advance the tens counter a single step. The valve 156 is normally cut off and potential on lead 87 makes it momentarily conducting to apply a pulse via pulse-forming circuit 163 to the counter 90 to fire any tube which has its grid biased by a previously fired tube. Initially no tubes in counter 90 are fired but on operation of start push button 123 a potential is applied to the grid of tube 168 in stage No. 0 to cause it to fire. Push button 123 also applies an enabling bias to tube 84 in counter 74 to permit tube 84 to fire with the next pulse on lead 70. As shown, forty field stations may be accommodated in the system, and on the fortieth station period stage No. 9 of counter 74 and stage No. 3 of counter 90 are conductive resulting in positive gating voltages appearing on leads 91, 92, which via diodes 93, 94 cause valve 96 to become conductive and apply a pulse via capacitor 102 to the anode of valve 103 and via capacitor 104 to the grid of valve 43. Valves 43, 103 are connected as a one-shot multivibrator with valve 43 normally conducting but rendered non-conducting by the application of the pulse, the time constants being arranged to keep it so for a time equal to one station period. During this time the cathode of the valve 40 no longer has a lowimpedance path to earth and the 100 c.p.s. multivibrator 15 is inoperative. In this way the synchronizing " no signal " period in each cycle of operation is provided. When the synchronizing circuit 97 reverts to normal the station counters are also restored and a, new cycle begins. Field station apparatus, Figs. 4A, 4B, 4C. The pulses received over the line 10 at each station from the central office are applied via filter 14 to receiver 21 which provides a positivegoing pulse on lead 170 for each station call pulse received, and a positive-going pulse on lead 171 for each timing pulse, these pulses being applied to a one-shot multivibrator 25 which is thereby operated at 100 c.p.s. The output pulses from pulse combiner 25 are applied via pulse former 189 to the grid of a cold cathode tube 200 which fires at the instant it also receives an input from lead 170 via cold cathode tube 193. When tube 200 fires there is a drop in its anode voltage causing tube 193 to be extinguished followed by tube 200. Each positive-going trigger pulse from the cathode of tube 200 is applied over lead 212 to the input of the units station ring counter 220, and is applied via diode 213, lead 214 and capacitor 215 to the grid of tube 217 of the units station counter to advance the counter by one step. The station tens counter driver 223 receives an input from the cathode of tube 200 which causes the tube 226 to fire only when it is also receiving an input over lead 228 from step No. 9 of counter 220 whereby the next output pulse from 194 advances the units counter 220 and also steps the tens counter 227. At each field station connections are made to selected steps of the counters 220, 227, dependent upon the particular number of that station, the connections shown, i.e. leads 286, 287 being for station No. 2. The step counter drive 231 is gated so that it can provide output pulses to operate the step counter 135 only during the station period intended for that station, the junction of resistors 232, 233 in the grid circuit of tube 234 being connected via diodes 236, 237, to leads 286, 287 respectively. Tube 234 receives positive-going pulses via capacitor 245 and at the appropriate station period provides trigger pulses over lead 144 to operate step counter 135. At the beginning of each station period, to ensure correct operation of counter 135, resetting pulses are applied over leads 212, 255 from the station counter driver 194. The valve 360 of synch. period detector 30 receives an input from pulse combiner 25 via diode 363 which holds capacitor 367 positively charge