Patent GB-181117-A (GB)
Abstract: 181,117. Relay Automatic Telephone Co., Ltd., and Ward, F. M. March 7, 1921. Automatic exchange systems; party-line systems.-In a party-line system of the kind in which the party-line substation bells are connected to earth from opposite sides of the line, the relative connections of the line wires are reversed when connection is required to one party, but not reversed when connection is required to the other party. As the relative connections of the line wires are reversed only when a call is made, and then preferably only during signalling periods, the use is permitted of coin-collecting party-line stations which require the reversal of the talking current to render the calling station inoperative until a coin is inserted. The invention is described as applied to a system using relays throughout, in which an impulse-recording device and a " marker " are temporarilv associated with a calling line to establish a marking circuit particular to an individual line, connection to which is thereupon extended by a relay switching organisation as described in Specification 181,120. The ringing set shown in Fig. 1 is inserted. in the incoming trunk, which is connected to the called line over an idle link circuit, Fig. 2, in the manner described in the above-mentioned Specification, after a selective marking circuit 50 or 74 has been completed. The Figures 1, 2, 3, and 4 should be placed above one another, Fig. 3 above Fig. 4, Fig. 2 above Fig. 3, &c. Normally one marking or test wire is allotted to each subscriber's line, but in the case of a two-party line two test wires t, Fig. 2, and 74, Fig. 3, corresponding to the two numbers allotted to the parties X, Y, are assigned to the line at the exchange. When the party line is marked as the wanted line over the test wire t, ringing current is supplied to the party X over the A wire, but when the line is marked as wanted over the second test wire 74, a relay PLM energizes in series with the line relav LE<2>, and reverses relative connections of the line wires A, B, causing ringing current to be supplied to the party Y over the B wire. The relay PLM is deenergized when the wanted party answers and restores the connections. The operations when the parties X and Y are called will now be described in greater detail. When the subscriber X is called, a selective marking circuit 50 is completed over the wire t, and on the energization of the incomirg trunk busy relay ITB, as described in Specification 181,120, the marking relay ITM relapses and completes circuits 70, 70a for the ringing relay RG and an attendant's lamp L, respectively. The relay RG alternately connects ringing and direct current over the circuits 71. 71<a> to the called line, the ringing current passing through the bell at the substation X. When the subscriber answers, the circuit 71<a> is completed through his instruments, the ringing trip relav RT is energized, and a short-circuit is removed from the relay RTX, which cuts off the ringing current and prepares the talking circuit 73. This circuit is completed when the ringing relay RG (now held over circuit 72) de-energizes on battery being disconnected from the A wire at an earlier switching stage. The operation when the party Y is called is similar to the foregoing with the exception that the completion of the marking circuit 74 a so energizes the relay PLM, Fig. 3, which locks up over circuit 75 and reverses the relative connections of the line wires. When the ringing relay RG is energized, ringing current is thereby supplied to the bell at the station Y over a circuit 76. The response of the relay RTX, when the called party answers, breaks the holding circuit 75 of the relay PLM, which de-energizes and restores the line connections. An individual line is rung in the same manner as the party X.