Patent GB-495802-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1937-05-21
Abstract: 495,802. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. May 21, 1937, No. 14196. Convention date, May 22, 1936. [Class 40 (iv)] In an inter-exchange system in which a seizing impulse is sent over a junction to take into use the incoming selector, an impulse of opposite polarity precedes the seizing impulse in the case of a toll call to allow breaking in on a local connection. The arrangement may be combined with discrimination by long and short impulses. The two-way junction FL between a main exchange S1 and a satellite exchange S2 is associated at each end with a polarized relay R1, R11 having two operative positions or, according to the Specification as open to inspection under Sect. 91, with a pair of relays in conjunction with rectifiers. Call from exchange S1 to exchange S2. Upon seizure of the junction FL, relay R9 energizes in the test circuit and connects battery and earth through polarized relay R1 to the junction, which at the exchange S2 is looped through polarized relay R11. These relays energize, and R1 closes contact a to operate R2, which connects up R8 and the latter in turn connects up RF1, RF2, so that after an interval the battery and earth connection to the junction is replaced by a loop connection. Relay R11 closes contact b to operate R14, R15, and the latter connects the junction to battery and earth through R14 and seizes the incoming selector. In the case of a toll call, however, RF3 is energized from the group selector GV1 at the time of seizure and reverses the junction connections so that an impulse of opposite polarity is first sent, and R11 closes contact a to operate R12, which locks. The subsequent operation of R2 short-circuits RF3, and the normal signalling current is sent, so that the conditions at exchange S2 differ only in that R12 is up and an additional signal is sent forward to the incoming selector. Dialled impulses are repeated by RIO over the junction loop, R7 being operated during each train, and are received and repeated forward by R14 at the exchange S2, where R17 is operated during each train. Relay RF13 energizes upon the reply of the called party and reverses the current over the junction, so that R1 closes contact b and connects up R3, which sends back a signal to the group selector GV1. Upon release by the calling party, R10 responds to a long current impulse and opens the loop for a sufficient period to allow the relapse of R15, which sends a release signal to the incoming selector. A momentary operation of RF11 guards the junction until the selectors have reached normal. The relapse of R9, R10 restores the relays at the exchange S1, and RF1 guards the junction pending release in the same way as RF11. Call from exchange S2 to exchange S1. As shown, there is no discrimination. Relay R19 connects battery and earth to the junction to operate R4, whereupon R5 energizes, seizes the incoming selector and connects battery and earth to the junction, which at the exchange S2 becomes looped by the operation of RF11, RF12, corresponding to RF1, RF2. Impulses repeated by R20 are received and repeated forward by R4. If the polarized relays R1, R11 are both normally connected to the junction, a relay similar to RF3 may be provided at the exchange S2 to send a discriminating impulse of opposite polarity. Faults. Relay R9 upon operation makes a circuit over a high resistance M3 for RF1, which is rendered sluggish by a condenser C8 and resistance M5. If, on account of the junction FL being defective, R2 has not operated when RF1 pulls up, R9 is disconnected, the junction is freed and an alarm is given. The armature of RF1 is mechanically locked until RF2 operates. Since these two relays operate simultaneously in a normal call, the armature of RF1 is not then locked. A fault at the exchange S2 closes contact 90 or 91 and thereby connects FR7 to the test circuit. This relay energizes in series with R19 if or when the junction is idle and connects up FR9, FR8 and a thermal relay TK. Relay FR8 locks and disconnects FR7, FR9, and TK upon operation releases FR8 by differential action, and the cycle of operations is repeated. The junction is connected through condensers to a second winding of FR9, so that the inductive impulses produced therein operate FR1, which is similarly connected at the exchange S1. This relay closes a circuit to a supervisory position through FR2, and the impulses are repeated inductively thereto by FR3.