Patent GB-200217-A (GB)
Abstract: 200,217. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. April 10, 1922. Automatic exchange systems.-In private branch exchange and like systems in which access to a subscriber may be had over more than one line, all the lines are tested simultaneously when the subscriber's number is called, and connection is established over the first idle line. This is effected by a relay switching arrangement associated with the test leads of the P.B.X. lines. In one modification, the P.B.X. lines may be distributed indiscriminately to any line equipment in any line group. The invention is described as applied to a system in which a temporarily used impulse responder marks the wanted line, which is connected by relays and link circuits to the incoming trunk. Connection of ordinary called line to incoming trunk, Figs. 2 and 3. Five subscribers' lines SL21 - - SL25, four link circuits L11, L12, L13, L14, four outgoing trunks OT, and four incoming trunks IT1, IT2, IT3, IT4 are shown. A calling line is connected in the usual way through an idle outgoing trunk to an impulse-responder, which selects the wanted line by energizing a group relay ITT and earthing one of the marking wires M in that group. If the wanted line SL21, say, is an ordinary line, the connection T shown in dotted lines is made and earth is applied over circuit 2 to the connecting relays LC211, LC212 &c. The group relay ITT also closes a circuit 4 to select an idle incoming trunk IT4, say, associated with an idle link, relays ITC4, LM1 energizing in this circuit. Relay LM1 completes circuit 2 for the connecting-relay LC211, thus connecting line SL21 over link L11 to incoming trunk IT4. Relays ITC4, LC211 lock up in a holding circuit 5. Connection to P.B.X. line, Figs. 2 and 3. If the lines SL21 - - SL24 are P.B.X. lines, the dotted connections T are removed, and the test circuits connected over wires A21 - . A24 to the relays shown in Fig. 3. When the marking wire 2a correspondineto line SL21 is earthed by the impulse-responder, relay C energizes the relay HR1 of line SL21, if this is free, over a circuit 7 which corresponds to the circuit 2 previously described. If line SL21 is busy, its relay F is energized and opens the circuit of relay HR1, so that the relav HR2 or IIR3 of the first idle line is energized over circuit 7<a>. The energization of relay HR1, say, brings relay LR1 into circuit, thus reducing the resistance sufficiently to energize the connecting-relay LC211. In this system any line in the group of ten served by the marking relay ITT can be used as a P.B.X. line. Connection of ordinary called line to incoming trunk, Fig. 4. In the system shown in Figs. 2 and 3, the group marking relay ITT serves also to select an idle incoming trunk. By arranging that the test wire individual to a particular line controls the completion of the test circuit of the incoming trunks in the group of lines to which the individual line belongs, it is possible to distribute the P.B.X. lines into any group irrespective of their designation number. When an ordinary line SL49, Fig. 4, is marked, circuit 2 is completed over the test wire, line relay L, and common relay D. Relays L, D jointly closes a circuit 3 for the incoming test relay ITT1, which closes a circuit 4 over relays ITC4, LM1 of an idle link circuit, relays LM1, L jointly closing a circuit 5 for the connecting relay LC491, which extends the wanted line to the link circuit and thence over the contacts of relav ITC4 to the incoming trunk. The connection is maintained by a circuit 6, including the cut-off relay CO which energizes a guard relay F. Connection to P.B.X. line, Fig. 4. The test leads of a group of P.B.X. lines are connected through relays AR1 - - AR5 to a circuit controlled by a relay C which is in the common test circuit of the group. When the group is called, the relay C closes a circuit 7 through the relays AR1, L21, say, of the first idle line. which is connected to an incoming trunk in the same way as when an ordinary line is called. One or more lines may be in an independent group as is indicated by the circuit for line SL21e through relay AR4. Specifications 149,800 and 181,116 are referred to.