Patent GB-235578-A (GB)
Title: Improved system for transmitting electrical impulses particularly for use in automatic telephone systems
IPC: H04Q1/32
Filed: 1925-06-10
Abstract: 235,578. Barnay, A. June 11, 1924, [Convention date]. Automatic exchange systems.-Impulse transmission over two-wire trunks such as interexchange trunks is effected by utilizing one line conductor only for impulses whilst the other conductor is employed for maintaining and controlling the impulse circuit. The repeaters usually associated with the outgoing ends of inter-exchange, trunks are therefore unnecessary. The impulsing and holding circuits are controlled by the line relay of the first group selector which relay repeats the successive series of impulses over one line conductor to movement-controlling relays in each of the numerical selectors. The holding circuit over the other line. conductor includes a special relay at the first group selector and a similar relay in series therewith at the incoming selector of each exchange involved in the connection. The holding circuit is maintained throughout the establishment of the connection but is disconnected to complete the talking-circuit as soon as the wanted line has been reached. In the system shown in Fig. 1, the connection involves a first group selector S1, an incoming selector S2 at a second exchange, a third selector S3 and a final selector S4. In a modification, Fig. 2, either of the line conductors 74, 75 beyond the incoming selector S<1>3 may be used for impulsing and the remaining one for holding, the choice of the particular conductors so employed being determined by a relay 60 which is or is not energized according to the value of a digit received by the selector S<1>3. The particular conductor employed also serves to effect wiper-selection in a final selector S<1>4 having two sets of wipers. In a further modification, Fig. 4, the choosing of the impulsing conductor by a preceding digit as in the previous modification also serves to control a relay 101 which determines whether the call shall be extended over a preselecting line switch CT to a further exchange or shall be completed locally over a selector S. First system, Fig. 1. The line relay 2 of the first selector S1 energizes release relay 10 which in turn operates holding relay 12. The impulses of the first digit are repeated over contacts 17, 15, 18 to relay 16 which controls the setting of the selector in any known manner. When an idle trunk 23, 25 is found, switching relay 21 operates, extends the impulse circuit over conductor 25 to relay 28 of the incoming selector S2 at the distant exchange, and extends the locking circuit of relay 12 over conductor 23 and in series with relay 26 to earth at contact 27. Relay 26 energizes release relay 43. The next series of impulses is repeated over conductor 52 to relay 28 and, when the selector has fully operated, switching relay 31 extends the impulsing and holding circuits to the selector S3. When the selector S4 has been set on to the wanted line, the operation of relay 21-31 removes earth from the holding circuit so that relay 12 de-energizes and completes the talking circuit. The release of relay 26 in the incoming selector S2 operates relay 45 which connects relay 56 across the called end of the line and relay 49 across the calling end in series with supervisory relay 42. Relay 49 operates to maintain slow-release relay 43 energized. When the called subscriber replies, relay 56 operates and short-circuits the high-resistance upper winding of relay 49 so that supervisory relay 42 now energizes and operates a meter or gives supervision. Modification, Fig. 2, employing selectors having two sets of wipers. The selector S<1>3 is an incoming selector (similar to selector S2, Fig. 1) at a 4000-line office in which the final selectors S<1>4 are of 200-line capacity. The selector S<1>3 receives two digits, one selecting a group, the second selecting one of five sub-groups within the selected group and also, according to the value of the digit, controlling the operation or non- operation of a relay 60. Relay 60 controls wiper selection at the selector S<1>4 which selector then responds to the two final digits of the wanted number. If relay 60 is operated, the holding circuit from relay 12 is extended over conductors 65, 75 to relay 68 which locks up and connects up the lower wiper set 85, 86, whilst the impulse circuit is extended over conductor 74 and contacts 69, 82 to relay 16-28. On the other hand, if relay 60 is not operated, relay 67 operates in the holding circuit over conductor 74 and connects up the upper wiper set 78, 79, whilst impulses are transmitted to relay 16-28 over the circuit 66, 62, 75, 80, 73. Modification, Fig. 4, involving a tandem exchange. The apparatus shown in Fig. 4 is reached from a selector similar to S'3, Fig. 2, at a distant exchange, in which a relay 60 determines which of the conductors 74, 75 is to be used for impulsing. If the digit which controls relay 60 denotes a connection to a further distant exchange reached over the wiper of a pre-selecting non-numerical switch CT, the holding circuit is extended over conductor 75 and includes relay 87 which operates relav 101 to connect up the trunk pre-selected by the switch CT. Relay 87 locks up over the earthed upper conductor of the out-going trunk, and succeeding impulses pass straight through to the distant exchange. If, on the other hand, the holding circuit is extended over conductor 74, relay 96 operates and the impulse circuit from conductor 75 is extended over contacts 91, 110, 98, 99 to the impulse relay 16-28 of the local selector S.