Patent GB-364875-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1931-01-29
Abstract: 364,875. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and ENGBLOM, J. F. T., Villa Tomoana, Elm Avenue, Beeston, Nottingham. Jan. 29, 1931, Nos. 2873 and 25357. [Class 40 (iv).] In a by-path system, the talking circuit is established by interacting devices which mutually control each other over the by-path. The interacting devices may be relay chains or stepping switches. In the system described, the figures being arranged as shown in Fig. 7, a calling party in one exchange is connected over line switch RLS and junction circuit J, Fig. 1, group selectors T, TD, Fig. 3, at a tandem office, group and final selectors NSA, NSB, FS, Fig. 4, at a third exchange, to the wanted line, whereupon the wanted subscriber's line switch WRLS, Fig. 5, is set on a junction circuit JY, similar to J, and relay chains, Figs. 2 and 6, or switches DS, Fig. 8, associated with the junction circuits interact to effect selection of an idle one of a group of direct junctions between the calling and wanted exchanges, the setting path being then released. As shown in Figs. 2 and 6, one relay chain is used at each exchange and the chains are synchronously run down three times in establishing a speaking connection. The synchronizing signals normally pass over the b wire of the setting path and each gives rise to a cycle of circuit changes in the junction circuits involving the operation of a relay in each chain. During the first operation of the chains, and at a point which varies with different exchanges, a signal is sent over the a wire from the wanted to the calling exchange, and the circuits perform a modified cycle during which a relay RA or RB, Fig. 2, selects a group of conversational junctions leading directly to the wanted exchange. A similar signal over the a wire is sent from the calling exchange during the second operation of the chains whereupon WRA or WRB, Fig. 6, at the wanted exchange selects the group of direct junctions to which the calling exchange has obtained access. During the third operation of the chains, relays RC-RE and WRCWRE are operated in varying combinations to connect up the junctions in turn, and when the calling exchange finds and seizes an idle one, a signal is sent over the a wire of the setting path to effect the seizure of the same junction at the wanted exchange. Separate chains at each exchange may be used for controlling the group selecting and hunting operations, and the chains may themselves make the actual connections to the direct junction. In the modification, Fig. 8, using stepping switches in place of relay chains, the three series of cycles corresponding to the triple operation of the chains are performed during one operation of the switch although a switch may be adapted to traverse its banks three times for this purpose. The switch gives access to different groups of junctions over different wiper sets. Assuming Fig. 8 to represent the switch at the calling exchange, it receives the exchange designating signal from the wanted exchange during its movement over terminals 2 to 5 to operate a wiper choosing relay PA .. PD ; it sends the corresponding signal to the wanted exchange during movement over terminals 7 to 10, e.g. by relay PX on terminal 8 ; and after passing terminal 11 it commences to hunt for an idle junction in the group. Alternatively, the switches may control other switches or relay sets for effecting the actual connection. The interacting devices may be common to a number of connecting devices. If all direct junctions are busy, the setting path is used for conversation. Local calls at the first exchange are similarly set up under the control of the tandem office. Connection over setting path. Line relay LR pulls up, RLS hunts for an idle junction circuit (absence of ground on wire P) and K switches through. Line relay LR falls back slowly and relays A, AA, B in the junction circuit operate. Junction switch JF hunts for an idle junction to the tandem office, and KS switches through, whereupon relays TA, DD pull up in series over the junction a wire and eleventh step springs TS3 at the incoming selector, dial tone being superposed on this circuit. When dialling commences, C, Fig. 1, pulls up, short-circuits AA and also DD to improve impulsing conditions, the impulses being repeated by A over the a wire to TA which repeats them to vertical magnet TV in series with TC which holds during the train. TB operated originally by TA also holds. Relay TG operates over off-normal springs TN1 and holds itself. At the end of the train change-over relay TC connects up rotary magnet TR which interacts with TG until an idle second group selector TD is found, whereupon TH operates in series with TG and switches through. Group selector TD is operated in similar manner to seize a repeater JR associated with an idle junction to the wanted exchange, JAA pulls up over the a wire in series with DD, Fig. 1, and energizes JB so that JDD operates over the outgoing a wire in series with the impulse relay at incoming selector NSA. Further trains of impulses are repeated by A and JAA to group selectors NSA, NSB and final selector FS. During impulsing, JC in the repeater short-circuits relay JDD. The group selectors operate in known manner and when the connection is extended to final selector FS, relay FSA operates over the a wire in series with JDD, and FSB pulls up. The tens digit is repeated to vertical magnet FSV in series with relay FSC which completes a circuit for FSV independent of off-normal springs FSN1. FSC falls back at the end of the train and the units digit is repeated to FSR in parallel with FSE which connects FSG to the test wiper and maintains a circuit for the rotary magnet if FSG momentarily operates on busy lines. At the end of the train the wanted line is tested during the release period of FSE, and if busy, FSG operates, locks, and connects busy tone to the b wire. If the wanted line is idle, FSH pulls up on relapse of FSE but WK and magnet WDM of the subscriber's line switch remain inert. The wanted line is not rung, but when FSH switches through, line relay WLR pulls up over the a wire and holds FSH over its lefthand winding. Completion of conversational path. The wanted subscriber's line switch WRLS seizes an idle junction circuit JW as in the case of a calling party but in the junction circuit, WAA pulls up over the a wire in series with JDD, Fig. 3, while WA remains unoperated although connected over the b wire to JD, Fig. 3. The junction switch WJF is therefore not started up but WQ and WQA pull up and operate WB, WBA. Relay JD operates JDA and connects JA to the b wire to operate D, Fig. 1, JA remaining inert. Relay D operates DA which locks up, disconnects DD and D from the a and b wires, and connects up NN and N instead, JA still remaining inert. M pulls up and locks, and CX, Fig. 2, operates over chain contacts of relays CA .. CF and energizes CA which energizes CN over its left-hand winding whereby the low resistance right-hand winding of N is connected to the b wire to allow JA, Fig. 3, to pull up. Relay JA repeats the signal forward by connecting a low resistance winding of JD to the b wire to operate WA, Fig. 5, so that WCX, WCA, WCN operate in turn. Relay WCN releases WA and JD, Fig. 3, and JD releases JA and N. Relay N releases CX and CN in turn, and relay WA releases the corresponding relays WCX, WCN, Fig. 5, WCN being slow-to-release owing to a short-circuited winding to ensure that CN, Fig. 1, has released before WA is reconnected to the b wire. A cycle of operations has thus been completed in which the first relays CA, WCA of the chains at the calling and called ends of the connection have been operated. During the next cycle it will be assumed that an exchange designating signal is sent back from the wanted exchange. Such signals are sent during different cycles depending on the exchange. On this cycle, the circuits at the calling and tandem exchanges operate in a similar manner to the first cycle up to and including the forward signal to operate WA, Fig. 5, except that the second relay CB of the chain is operated. At the wanted exchange WA, WCN and the second chain-relay WCB pull up but WA is not now released by WCN since WCB is operated. Relay WCB grounds the a wire to release JDD, Fig. 3, which repeats the signal to release NN, Fig. 1. Relays CA, CN are released by NN, and exchange designating relay RA pulls up, locks, and energizes Y, which releases N, JA so that low resistance winding of JD is removed from the b wire and WA, Fig. 5, releases. WCA, WCN also fall back, ground is removed from the a wire and JDD, Fig. 3, repeats the signal which permits NN to operate. Y releases and N is again connected to the b wire to complete the cycle. Cycles of operations similar to the first now follow until the last of the chainrelays CG, WCG are operated. During the next cycle, CZ, CN, Figs. 1 and 2, and the corresponding relays WCZ, WCN, Figs. 5 and 6, operate, CG, WCG release, and two-step relays CW, WCW operate their light armatures cw1, wcw1. At the wanted exchange WA is disconnected from the b wire, at the tandem exchange JD disconnects JA, and at the calling exchange N falls back and releases CZ to permit full operation of CW and release of CN, full operation of WCW at the wanted exchange being permitted by the release of WCZ which also releases WCN. The circuits of the relay chains are now in their normal condition, and a fresh series of cycles is performed, an exchange designating signal being sent from calling to called exchange at tne beginning of the fourth cycle. At this point chain-relays CC, WCC are operated and when N operates for the fourth cycle and CD, CN are energized, the low resistance winding of N is not connected to the b wire (since CW is also operated). In this case NN is disconnected from the a wire but is held over its left-hand winding, JAA falls back and releases WAA but JDD remains held