Patent GB-831714-A (GB)
Title: Error detecting system for telegraph transmission
IPC: H04L1/00
Filed: 1958-08-08
Abstract: 831,714. Code telegraphy. STANDARD TELEPHONES & CABLES Ltd. Aug. 8, 1958 [Aug. 9, 1957], No. 25511/58. Class 40 (3). In an error-detecting system for telegraphy by code combinations of elements of one or the other of two kinds, e.g. mark and space, a different computational value is assigned to the occurrence of elements of one kind, e.g. marks, in the different positions of the elements in the code combinations, and the total value of a number, or group, of signals is obtained and used to send as a checking signal, whilst at the receiving station, the said incoming signals as received are utilized to form a check signal corresponding to the total value of the number of signals, and the check signals are compared to ascertain whether correct or faulty transmission has taken place. Transmitting arrangement, Figs. 1, 2, 3.-The sensing of the perforated tape by the pins of a transmitter XTR passes corresponding pulses over conductors 1 ... 5 to segments 1 ... 5 of a distributer TD from which they are applied over a conductor 38 to a computing device, Fig. 3, and also over the ring A of the distributer to the grids of a double triode 31 which conducts on space elements and operates the line relay LR to its contact S, marks being sent to the line L by the operation of the relay LR to contact M by its biasing. winding. The code combinations derived from the tape are also passed to a gating circuit 25 which detects the carriage return (CR) signal to provide a positive potential at 111 and to control the checking operation. Normally, a pulse also passes from segment S of the ring C to operate a magnet SM for stepping the tape, and current flowing through both windings of a relay R6 holds it unoperated. When the CR signal is detected, valve 112 conducts, relay R1 operates and causes operation of relay R6, which locks up over its contact 2 and prevents the operation of the stepping magnet SM, and the feeler pins are not retracted from the tape. The impulses at the inputs to the gate circuit 25 are also applied over a conductor 40 to a coupling circuit, Fig. 2, to effect the application of pulses corresponding to the. marking elements of the code combinations to the computing circuit of Fig. 3. During each revolution of the distributer TD, a pulse from segment 3 of the ring F operates a relay R7 which connects a positively charged capacitor C1 to conductor 56 controlling a valve 41 to initiate the operation of a one-shot multivibrator 42 having a period slightly greater than the length of a code element and operative to cut off valves 43 ... 46. When the multivibrator 42 restores, the valves 43 ... 46 are permitted to conduct at sequential instants determined by capacitors C2 ... C5 of different values, so that valves 48 ... 51 are cut off in sequence, whilst the valve 47 is cut off when the multivibrator restores. The valve 47, and the valves 60 ... 61 coupled to valves 48 ... 51 provide pulses to prime five valves 70 for conduction, and selective occurrence of marking elements on the leads 1 ... 5 render the associated valves 70 conducting. The plate circuits of the valves 70 are connected by conductors 80, 81 ... 84 to stages I ... V of an eight-stage binary computing (adding) circuit I ... VIII, which can store a total of 256 in the binary notation. Each stage comprises an Eccles-Jordon flip-flop circuit 92, the stages I ... VIII being connected and the output of stage V controlling the additional stages VI to VIII, and for the " 1 " condition the left-hand section of a circuit 92 is conducting so that the corresponding output valve 93 ... 100 is non-conducting, and the impulses transmitted will be complementary to those set up on the stages I ... VIII. When the total recorded on the circuits 92 is to be transmitted by the complementary digits, from the valves 93 ... 96 and subsequently valves 97..100, the detection of the CR signal operates the relay R1 preventing further tape feed. Also the relay R1 at contact R3 prepares the circuit of relay R2 which operates from the R segment of the ring F. At its upper contact 1 it connects ground to conductor 114 passing through cable 38 to the cathodes of the four valves 93, 94, 95, 96, and to a diode 115 and the anodes of these valves are connected to segments 1, 2 ... 4, 5 of distributer ring B, so that those valves which are conducting connect ground to the corresponding segment to send mark, whilst the non-conducting valves pass positive voltage to the associated segment and control the output relay LR to space. The diode 115 connects ground to the third segment so that the third element is always a mark. Relay R2 prepares a circuit for relay R3 which is operated by segment 4 of the ring 5, and at contact 3 prepares a circuit for R4 which operates from the segment R of the ring F. The operation of relay R4 disconnects ground from the conductor 114 and transfers it to the conductor 116 leading to the cathodes of the valves 97 ... 100 so that those which are conducting apply ground to the corresponding segments to provide marking elements and a grounded diode 115<1> provides a mark for the third element of the code combination representing the second part of the computed total. Relay R5, operated from segment 5 of the ring F opens the contact 3, the holding ciruit of relay R1 which releases and effects the release of relays R2, R3. R4 and R5 in sequence and at the released contact of relay R5 a pulse is passed from capacitor C8 over conductor 105 to restore all the trigger circuits 92 to their normal or zero condition. Receiving and checking arrangement, Figs. 6, 7, 8, 9.-The signals received over the line L<1> are recorded by a reperforator 118 and the perforated tape t is passed to a transmitter XTR2 from which the sensed output passes to a gate circuit 122 to detect the CR signal and also via conductors 1, 2, 4, 5 directly to the conductor 120 and from conductor 3 over the contacts 2 of normally de-energized relay R11 to the conductor 120. The pulses on the conductor 120 are passed to control circuits, Fig. 8, comprising valves 142 ... 150 applying pulses over the leads 160 ... 167 to the 8-stage computer and adder of Fig. 9. During the computing of the received signals, pulses are passed over conductors 160 ... 164 which control stages I ... V of the computer, the remaining stages VI ... VIII being controlled by the output of stage V. The pulses for conditioning the control valves 47<1> and 601 ... 631 of Fig. 7 are obtained from a multivibrator 128 set into operation by the actuation of a switch 130 and permitting when it returns to its initial condition at the end of each cycle the sequential operation of valves 43<1> ... 46<1>. The operation of the multivibrator 128 to make valve 46<1> conducting cuts off valve 200 to provide a pulse for operating valve 198 to control the magnet SM to step the tape t and the return of the multivibrator to its normal condition operates valve 196 to cut off the valve 198. The valve 200 also passes a positive pulse over conductor 182. During the computation process, the marks of the five-unit signals passed over conductors 1 ... 5 allow the valves 142 ... 146 to be correspondingly conducting and over leads 160 ... 164 to operate the stages I ... V of the computer circuit, Fig. 9. When the CR signal is detected, a positive potential at point 125 of the gate 122 renders valve 124 conducting to operate relay Rl which at contact 2 disconnects the lead 3 from the conductor 120 and the input to the computer. As the released contact of relay R12 applies a positive potential on the conductor 155, the valve 147 ... 150 of the coupling circuit, Fig. 8, are ineffective and the first part of the checking signal represented by elements 1, 2, 4, 5 are passed to the stages I to IV of the computer. At the beginning of the next cycle of the multivibrator 128 a positive pulse over conductor 182 causes the valve 190 to conduct and operates relay R12 which at contact 3 prepares a circuit for relay R13 and at contact 1 applies a positive potential to conductor 154 so that the valves 142 ... 145 of the coupling circuit are prevented from operating, and the second part of the checking signal is passed over leads 1, 2, 4, 5 to the valves 147 ... 150 controlling the stages V to VIII of the computer. The next impulse from the multivibrator operates via conductor 182, the valve 192 and relay R13 preparing a circuit for relay R14 and closing the circuit of an alarm 202 indicating that a checking process is taking place. Relay R13 opens the circuit of valve 196 so that the stepping magnet is held operated. If the transmitted signals have been correctly received and since the transmitted check signal is the complement of the check signal derived from the incoming signals, all the stages I ... VIII will be in the " 1 " condition, and a positive pulse over conductor 212 in conjunction with a positive pulse over conductor 182 will fire the valve 194 and operate relay R14. A positive pulse over conductor 134 resets all the computer stages I ... VIII to their normal condition, and the actuation of contact 3 of relay R14 opens the circuit of relay R11 effecting the sequential release of relays R12, R13 and R14. The release of relay R13 opens the circuit of the alarm device 202 indicating that reception has not been faulty and allows valve 196 to cut off the valve 198. In a modification, described in connection with Fig. 13 (not shown), the checking operation is effected by the comparison of the transmitted check signal corresponding to the actual total set up in the stages I ... VIII of the computer at the transmitter and the total derived from the signals as received and registered on the stages I ... VIII of computer at the receiving station.