Patent GB-382679-A (GB)
Title: Improvements relating to automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1931-08-07
Abstract: 382,679. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and PATTERSON, W. G., 68, Eltham Road, Lee, both in London. Aug. 7, 1931, No. 22402. [Class 40 (iv).] A group selector is adapted to change its circuits in response to backward signals over a fourth wire so that it may provide either (1) battery feed for the called party in local calls, (2) an outgoing loop in junction calls, or (3) a clean metallic circuit for calls to an operator. The fourth wire is also used on local calls for the transmission of signals to apply ringing current or busy tone at the group selector and may further be used for metering. The signals comprise currents of different strengths and polarity, and arrangements may be made to re-ring a calling party from the operator's position or from the group selector. As described, the selector normally presents an outgoing loop. On seizure, line, release, and dialling relays A, B, C pull up and dialling tone is returned over A(ii). The train of impulses is repeated to VM, the switch hunts for an idle outlet (absence of ground) by interaction of RM and G in known manner and H switches through. Succeeding trains of impulses are repeated at a2 in the outgoing loop, relay D and impedance I in the loop being short-circuited by C during impulsing. Call to another exchange ; metering. Ring- ing current and busy tone are connected at the distant exchange. Reversal of current over the junction on reply operates D so that DA pulls up to ground from an interrupter connected to DA(i), locks over DA(ii), and prepares a circuit for DA(iii) and DB(i) which is completed after an interval by ground from an interrupter connected to DB(i) which locks over DB(ii). DA falls back on termination of the pulse over DA(iii) and is prevented from reoperating by DB. During the period of operation of both DA and DB, the fourth wire circuit is completed and battery impulses sent back from a succeeding switch in accordance with the route taken pass to the called subscriber's meter. Local call, The final selector, at the termination of rotary movement, connects low resistance ground to the fourth wire to operate WB(i) which locks over (ii) and disconnects (i). Relay TB may operate momentarily in series with WB(i) or it may be made slow to operate. Relay WB replaces the outgoing loop by battery over I and ground WD. If the wanted line is busy, high resistance battery connected to the fourth wire by the final selector operates BT but not RG and busy tone is sent back over A(ii). The battery signal may be connected over back contacts of the final selector switching relay on relapse of a slow-release relay which provides a fleeting test period. If the line is free, the switching relay connects low-resistance batterv to the fourth wire to operate both BT and RG so that ringing current is connected up over F(i) and tone is sent back over A(ii). When ringing is tripped F locks over (ii), releases RG and BT so that WD energizes over the called loop and starts up the metering control relays DA, DB which connect up a single metering impulse over front contact f3. Call to toll or recording operator. The call proceeds as before but high resistance ground from the operator's position operates TB and not WB. Assuming the chain line connection made, the feed bridge is entirely cut out and relay A falls back but B is held by TB which also shunts the impulse contacts A2 in the loop. The operator can re-ring the calling party from her cord-circuit. If the dotted line connections are used instead of the chain lines, the signal from the operator's position to operate TB is only given momentarily when it is required to re-ring the calling party. TB then completes a re-ring circuit over F(i) which operates ineffectively on response of the calling party, the feed-bridge remaining in circuit during conversation. Metering does not take place since neither D or WD is operated. All outlets busy. When eleventh step springs S1, S2, S3 operate, G energizes and locks, s2 operates an overflow meter over the test wiper, and s3 operates BT to send back busy tone over A(ii).