Patent GB-330339-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M19/06
Filed: 1929-04-04
Abstract: 330,339. Siemens Bros. & Co., Ltd., and Humphries, H. E. April 4, 1929. Automatic, and semi-automatic exchange systems. - In arrangements for charging a sub-exchange battery from a source, at the main exchange on closure of a key or the like thereat, a. preliminary test is made to determine whether the junction is sound or faulty, and, if sound, the charging source is connected up and different signals are given according as to whether sufficient charging current is flowing or not. If the proper charging current does not flow, the source is intermittently connected to the junction and a charge indicator flickers. Charging takes place over both junction wires in parallel the junction being also used for conversations in either direction, and arrangements are described for (1) gradually bringing the junction to charging potential, (2) disconnecting the charging source when the junction is seized for conversation (3) gradually lowering the potential of one of the wires when the junction is seized at the subexchange. The preliminary test is applied directly to one junction wire which, if sound, is disconnected at the sub-exchange by a relay which operates if the other wire is grounded. If the other wire is merely discontinuous, charging takes place over the first wire. The system described comprises operator's and charging control circuits, Fig. 1, and a repeater, Fig. 2, at the sub-exchange, incoming calls to which are extended over a finder D, Fig. 3. Charging sub-exchange battery. The operator at the main exchange, Fig. 1, throws key K which completes a circuit from the charging source S for A over the jack CJ. The charge indicator C1 momentarily operates and relay B(i) is energized over the junction a-wire in series with high resistance winding (ii) of polarized relay CC which remains inert. Relay B holds over winding (ii) and releases A so that the indicator CI is operated. Charging potential from S is applied to the a-wire over high resistance YD and b2, a1, A being slow to release, and the line condensers are charged slowly to prevent operation of relays by condenser surges. Relay C energizes and connects full charging potential over D(i) to the a-wire so that D and CC pull up, and charging potential is connected also to the b-wire. Relay E pulls up, opens the original holding circuit of B(ii) but this relay continues to hold as D is operated. If the difference of potential between the sub-exchange battery and the source S is not sufficiently great, D does not energize, and B falls back to release C and E. Relay A pulls up again and the above-described sequence of operations is repeated and the resulting intermittent operation of CI informs the operator that key K should be restored. At the sub-exchange, CC operates CP which connects the low resistance windings of CC to both junction wires to complete the charging circuit, and relay CQ operated by CP disconnects the high resistance windings of CC and locks itself to the b-wire. The connection of the source S to the b-wire was delayed in order that line relay L, Fig. 2, should first be disconnected therefrom by CP. Whenever the charging current drops below a certain value, D falls back, the indicator flickers as described above, and the a-wire is momentarily grounded over a1, b2, high resistance, B(i) to discharge the line condensers slowly. If the a-wire happened to be grounded or disconnected, relay B(i) would not operate and charging will not take place, while if the b-wire were grounded L, Fig. 2, would operate V to open the circuit of B(i) and prevent charging. If the b-wire is disconnected, charging takes place over the a-wire. if the charging circuit at the sub-exchange is open, the relays of Fig. 1 operate until the stage when D should pull up. As this does not happen, the charge indicator flickers as before. If during charging the source S fails, or if the junction wires become grounded, the reverse flow of current over CC releases this relay and the subexchange battery is disconnected from the junction, and, in the case of failure of the source, D falls back and the indicator circuit is opened. Call from main exchange. The insertion of the plug into jack CJ opens the circuit of key K so that if charging is proceeding, the operated relays in Fig. 1 fall back and the junction is connected to the jack. Slow-to-releasa relay F, operated during charging to short-circuit the tip and ring of the jack at f1, maintains the shortcircuit for sufficient time to prevent condenser discharges from affecting the operator. At the sub-exchange CC, CP, CQ fall back and is operated to ground over jacks DJ, CJ, loops the line a1, b1, and operates V. Line relay LA pulls up over the loop, completes the starting circuit over PG for a call finder, and connects battery over CO to the test bank. When the calling junction is found, CO releases LA and operates PG which opens the starting circuit. Dialled impulses sent over jack DJ are repeated by L to the sub-exchange selector, DD being operated during the train to short circuit one winding of the repeating coil and improve the impulse circuit. When the caller party responds, the D-wiper of the finder is grounded and JS pulls up to operate S, which locks up. At the end of conversation, JS falls back and Z pulls up to connect ringing current to the junction, and release S which, in turn, releases Z. Relay Z connects ground over v1, c1, to hold CO and ground the test terminal to busy the junction during ringing, and when Z.falls back CO releases and LA re-energizes over the loop, a busy marking being maintained during the release period PG. The ringing current operates a clearing indicator and the operator withdraws. If the operator does not clear, PL operated in series with CO, gives an alarm after a predetermined time. Call to main exchange. When the junction is seized by a connector, shown at the top of Fig. 3, FF and CO operate over wire c2 and the test wiper, and the circuit CP is opened at ff3 so that if charging is taking place the charging circuit is opened at cp1, cp2, and the initial circuit for relay B, Fig. 1, is opened at ff4. The operated relays of the charging control circuit, Fig. 1, fall back and A energizes to complete a condenserdischarge circuit through B(i) which does not operate. Ringing current from the connector operates indicator K1 and when the operator plugs in, ground is removed from K and connected to the b-wire to operate L the circuit of which has previously been held open by CQ which was locked to the charging source. Relay L loops the line to the connector, trips the ringing, and energizes V and S. When the calling party replaces his receiver, CO and FF fall back, and Z operates to give the clearing signal and busy the junction as described in the previous paragraph.