Patent GB-213678-A (GB)
Abstract: 213,678. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. Jan. 5, 1923. Automatic exchange systems.-According to the nature or condition of the wanted line, dis tinctive potentials are placed on the A and B wires to control the subsequent operation to extend the connection or to send back signals to the calling subscriber. The invention is described with reference to a system in which the calling subscriber's unit, Fig. 1, is connected to the wanted line through a feed relay group, Fig. 2, a repeater, Fig. 4, at the wanted exchange, and a ringing group, Fig. 5. The wanted subscriber's marking wire is selected by a recorder, Fig. 3, which is temporarily associated with the repeater, Fig. 4. Examples are given of calling (1) a disengaged subscriber, (2) an unassigned number, (3) an engaged subscriber, and (4) an operator. The different potentials on the A and B wires are repeated back by the repeater, and variably operate relays IS, NU, BB, &c. in the feed relay group. Selection of the wanted line. Upon lifting of the subscriber's receiver, the line relay LE, Fig. 1, is energized, and the calling line is xetended, by means of relays LC, OTC to an idle feed relay group. Relays A, G, GX operate in turn, completing a circuit 4 for the holding wire H, whereupon relay CO energizes and relay LE de-energizes. An idle recorder is also seized provisionally, and relays BB, ND are energized. The recorder is prepared in the usual manner, and the calling subscriber dials the wanted number, which is assumed to be in another exchange, in which case the feed relay group is extended to a repeater either immediately as described in Specification 212,682, or after the transmission of one or more digits. A circuit 8 is thus closed over the trunk and differential relay IS for relay I, Fig. 4, which energizes and operates relays GR, BBR. Relay GR prepares a recorder at the distant exchange, and impulses are repeated thereto by relays A, I, whereupon the repeater is connected to the wanted line. (1) Calling a disengaged subscriber. Relay MCX of the recorder, Fig. 3, connects battery through the left-hand winding of relay SU to the marking wire UMW, which is connected to earth through the line relay of the wanted subscriber. The relay SU being differentially wound is not energized. While the called line is searching for the repeater to which the calling subscriber is connected, relay ITM, Fig. 5, is energized and operates relav RG, which disconnects the A wire and earths the B wire. Differential relay ISR, Fig. 4, is thus unbalanced and energizes. Relay ISCO, which extends earth on the B wire first to relay BBR, which is short-circuited, and then to relay RB2, which energizes and operates relay RICO over a circuit 17. Relay AIR is thus energized over a circuit 18. The B wire of the feed relay group being now earthed through relay AIR and the A wire being open, relay IS, Fig. 2, energizes and relay ICO operates in the same way as relay ISCO, and relay BB is short-circuited so that feed relay B<2> operates over circuit 19 and prevents energization of sluggish relay NU. When relay CO, Fig. 1, in the called subscriber's unit energizes in series with relay ITB, Fig. 5, over the holding circuit H, relay F operates and breaks the marking circuit over line relay LE. The connection is completed by the release of relay ITM. (2) Calling an unassigned number. The marking wire UMW is not connected to a line relay, so that differential relay SU, Fig. 3, becomes unbalanced and energizes, extending the B wire to the open wire z, while, the A wire is earthed over the inner right-hand contact of relay RH. Relay ISR energizes and operates relav ISCO, which locks, releases relays ISR, BBR, shortcircuits relay RB1 over the A wire and energizes sluggish relay NUR over circuit 12. Relay NUR disconnects the B wire of feed relay group from relay I, but the circuit over the A wire is maintained. Relays IS, ICO are accordingly energized, short-circuiting relay I by relav B<1> to release the repeater, operating sluggish relay NU over circuit 12" and releasing relay BB, so that a distinctive tone is sent to the calling subscriber over contact nu. (3) Calling an engaged subscriber. The marking wire UMW is connected to battery, so that relay SU is short-circuited over one winding and energizes, connecting the B wire to battery over wire z, the A wire being earthed. Relays ISR, ISCO, NUR operate as before, but relay BBR is held by battery on the B wire, so that the B wire of the feed relay group is connected to battery through relay RA2 over circuit 13. Relays IS, ICO, NU operate as before, but relay BB is held over the B wire, so that a busy tone is transmitted over contact bb. Relay I is shortcircuited over the feed relay B<1> and releases the repeater. (4) Calling an operator by dialling a special number. Relay MXO is energized over the marking circuit 91, so that battery is connected to the A wire over circuit 20 and earth to the B wire over circuit 21. Relays ISR, ISCO energize, operating relay RB1 over the A wire and relay RB2 over the B wire, relay BBR being short-circuited. Relay JRS energizes over circuit 22 and connects battery to the A wire of the connecting circuit, the B wire being earthed over relay I. Relays IS, ICO energize, operating relays B<1>, B<2> over the A and B wires, relay BB being short-circuited and relay ND being held. The holding wire H is thus earthed over circuit 25, and the calling line is released from the feed relay group, the holding relays being short-circuited. Relay CO falls back, and relay LE energizes over the calling line, locking sluggish relay F and lighting the calling lamp CL. When the operator plugs in, relay LE is released and relay CO energizes over the sleeve circuit, which serves as a test circuit.