Patent GB-186713-A (GB)
Abstract: 186,713. Siemens Bros. & Co., Ltd., and Christian, D. A. July 6, 1921. Semi-automatic exchange systems; metering systems.-In systems in which an operator extends a call through automatic switches, a current transmitted from the manual position over one of the speaking wires effects such changes in the automatic switches that if the called line is busy an intermittent current is sent back to the operator's position to actuate a flashing busy signal. Fig. 1 shows the invention applied to a system in which a manual operator plugs into a jack 2 leading to an idle group selector GSJ, and after throwing her dialling key K operates the impulse sender D to extend connection to a wanted automatic subscriber in known manner over a junction line repeater JC and a connector FS. During the setting-up of the connection battery is supplied to the a wire over a resistance 4, and when an idle junction is found, a. relay RL in the repeater JC is energized and closes a circuit, over retardation coil RC1 and contact 9, for a relay RL1 in the connector FS, the relay RL1 locking up over its left-hand winding and short-circuiting a condenser 6 inserted in the busy tone lead. When the key K is restored, relay RL relapses and at contact 9 prepares the circuit of the answering relay Y. If the wanted line is engaged, the contacts 5, 10 are closed in known manner, and intermittent current is supplied to the answering relay Y at the repeater JC. thereby closing a flashing circuit, over retardation coil RC<2> and contact Y', for the operator's supervisory relay SR. If no junction with its repeater JC is inserted between the group selector GSJ and the connector FS, the relay RL1 causes flashing current to be sent directly over the a wire, whereas if more than one junction intervenes, each repeater set is provided with relays similar to the relays RL and Y. A modified arrangement is described as applied to a system in which an automatic subscriber X, Fig. 2, has access to a connector FS over a preliminary selector PS, a group selector GS, and a junction line and repeater JC, connection from a manual position being made to an idle junction and repeater over a jack-ended group selector GSJ. In this modification no condenser is inserted in the flashing current lead' which is connected to the b wire, but in order that when a call is made from an automatic subscriber X and the wanted line is busy the answering relay Y3 shall not be energized by the flashing current and the call metered, the answering relay Y3 is connected to the a wire. When a call is made from the operator's position, after the dialling key K is restored, current is supplied to the a junction wire over a retardation coil RC, thereby energizing a relay RV, which locks up over its contact J, and at armatures 2, 3 connects the answering relay Y3 to the b wire, and battery (over retardation coil) to the a wire. If now the wanted line is engaged, the relay Y, is intermittently energized over the flashing current wire, and intermittently bridges the impulse relay A3 across the junction line at contact 13. thereby closing a flashing circuit for the operator's super-- visory relay SR. If further repeating stages areinserted, relays similar to the relay RV are provided thereat for the retransmission of the forward operating current and of the flashing current. Where both a manual position and antomatic subscribers have access to another distant manual position over switching stages such as the repeater JC and connector FS, Fig. 2, since the standard cord circuit at the distant manual position has the supervisory relay on the answering side connected to the a lead and battery to the b lead, then to operate the metering relay Y of a connection from an automatic subscriber the a and b leads are crossed at the incoming junction jack at the distant manual position, the cross being removed to get through supervision, when a call is made from the other manual position, by means of an additional reversing relay situated at the incoming junction jack and energized by the operating current sent forward from the calling manual position.