Patent GB-250643-A (GB)
Title: Improvements in or relating to telephone exchange systems
IPC: H04M3/60
Filed: 1925-01-07
Abstract: 250,643. Western Electric Co., Ltd., (Deakin, G.). Jan. 7, 1925. Automatic and semi-automatic exchange. systems; metering.-In an exchange network in which calls to a number of distant exchanges may be made through an intermediate tandem exchange, a link circuit selects in accordance with the wanted exchange code a local circuit, which is picked up by an idle tandem trunk to the intermediate exchange and then sends impulses whereby a switch at the distant end of the tandem trunk selects an idle junction to the wanted exchange. The invention is described as applied to a system in which the exchange prefix is recorded on registers associated with a link circuit, Fig. 1, which operates as described in Specification 250,644, to extend the call to an idle one of a wanted group of outgoing junctions. In the case of a call through a tandem exchange, the link circuit seizes an idle local junction circuit LJC, Fig. 2, of a group particular to the wanted terminal exchange. Finders at the near end of idle tandem junctions then hunt until one of them, such as the finder TJO, engages the seized local junction LJC, an interrupter associated with which then transmits a series of impulses corresponding to the wanted exchange. These impulses are recorded on a register RJ, Fig. 3, associated with the tandem junction, the register marks a group of trunks leading direct to "B" operators at the wanted exchange, and a hunting switch TJ1 at the distant end of the tandem junction seeks an idle one of these trunks, such as the trunk ACO, Fig. 4. Describing such a call in greater detail, when an idle local junction circuit LJC, Fig. 2, is taken into use over a link circuit, Fig. 1, relay LJ energizes over the test wire c, marks the junction selectable in the banks of the finders at the near ends of the tandem circuits, starts the driving magnet RT of the interrupters INT.I, INT. A, INT.B, and energizes a common starting relay CS for the idle tandem circuit finders. When the junction LJC is picked up, test relay TJ1 opens the driving circuit and energizes a second test relay TJ2, which connects up the low resistance winding of the relay TJ1 to mark the junction busy to the finders. On the next closure of the interrupter INT. A, relay PI is energized, locks up, applies battery to the outgoing b wire, thereby energizing an impulse relay JS, Fig. 3, at the outgoing end of the tandem circuit, and closes a circuit for the impulse relay P2 from the interruptar INT.I. This interrupter now sends a series of impulses corresponding to the selected local junction LJC to the relay P2, which repeats them to the relay JS which in turn repeats them to the register R'. At the end of the impulse the train interrupter INT.B closes the circuit of relay P3, which locks up and opens the circuit of the impulse relay P2. At the same time the series relay JD, Fig. 3, relapses and energises relay JC, which removes a short-circuit from a high resistance relay JB. The relay JB now energizes and the relay JS relapses, closing a circuit for the driving magnet PT of the switch at the distant end of the tandem circuit, and marking the wanted group of junctions over wiper R of the register RJ. When the wanted group is engaged test relay JT1 is connected up, and on an idle junction to a " B " position, Fig. 4, being seized, energizes over the test wire c, arrests the switch, and energizes a relay JT2 which closes a circuit for a connecting relay JH and marks the engaged trunk non-selectable. Relay JH locks up and connects battery to the a wire through retardation coil RET, energizing relay S4, Fig. 2, which energizes cut-off relay CO, thereby opening the test circuit and de-energizing relays LJ, Fig. 2, JT1, JT2, Fig. 1. Relay CO de-energizes relay CS, which arrests the other hunting finders such as TJO. Relay S4 also releases relays TJ1, TJ2, Pl, P3, and closes the b wire, thereby connecting the supervisory relay S2, Fig. 1. of the link circuit in series with relays JS, JB, Fig. 3. Connecting relay JH also closes a circuit over the b wire for relays S5, Fig. 3, and JB1. JB2, Fig. 4, but only JB1 operates and lights the calling lamp CL. When the " B " operator plugs into the wanted line sleeve relay JC energizes, extinguishes the lamp CL, lights lamp S2L, and energizes relay JA, which disconnects battery from the test wire c and releases relays JA, which disconnects battery from the test wire c and releases relays JT1, JT2, Fig. 3. On the reply of the wanted party, relay S3 energizes, extinguishes lamp S2L, and short-circuits relay JB1, causing the response of relays S5, Fig. 3, and JB2, Fig. 4. Relay S5 shunts relay JB and the relays S2, Fig. 1, and JS, Fig. 3, respond, thereby preparing the metering circuit as described in Specification 250,644. At the end of conversation when the calling party hangs up, the link circuit, Fig. 1, releases and the call is metered as in the above Specification. Relays JS, SS, Fig. 3, relapse and cause the restoration of the register RJ, after which relays JH, JC are unlocked. The removal of battery from the a wire de-energizes relays S4, CO, and frees the local junction LJC, whilst the opening of the b wire de-energizes relay JB2 and lights the calling supervisory lamp SIL. When the called party hangs up the lamp S2L burns, as described in Specification 250,642, and upon the operator taking down the connection relay JA relapses and frees the junction to her position.