Patent GB-433956-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1934-02-23
Abstract: 433,956. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. Feb. 23, 1934, No. 5990. Convention date, Feb. 24, 1933. [Class 40 (iv)] In. an arrangement whereby selectors are set by alternating-current impulses controlled by subscribers, the alternating-current source is associated with a link circuit which is non- numerically connected to the subscriber's line on receipt of a call signal from a current source (magneto) at the sub-station. The alternating-current source is normally disconnected from the link circuit but is connected, when non-numerical selection is completed, to provide dial tone. It is disconnected when a wanted line tests idle, but if a busy condition is encountered, remains connected to provide a busy signal. The same source is also used to force release under standstill conditions. The source and the impulse-responding relay are connected across the line in parallel, but the shunting effect of subscriber's loop prevents the relay from operating until the loop is opened by the dial. The Specification as open to inspection under Sect. 91, comprises also an arrangement in which the impulse - responding relay is connected in series in the line. This subjectmatter does not appear in the Specification as accepted. Calling subscriber A2 rings with magneto H2 to operate relay R1 which holds over its lower winding and energizes R2 which starts pendulum armature 54 vibrating. R3 pulls up and opens the operating circuit of R2 which holds until the pendulum armature stops and then falls back to operate start relay R4. Relay R5 in idle finder-connector links pulls up over a normal contact in the connector and connects interrupter 83 to magnet ASM, and when the calling line is found, R6 pulls up in series with the cut-off relay R7 which holds armatures 51, 53 common to itself and relay R1. Relay 5 remains held to a further contact in the connector so that R8 pulls up and connects an A.C. source V2 to the line over adjustable resistance M1 and also connects across the line an impulse relay assembly comprising D.C. relay R9 and a bridge of rectifiers, resistance M3 and condenser C1 being connected in the relay circuit to make it quick to operate and release. The calling party has, in the meantime, removed his receiver so that the A.C. serves as dialling tone, but the shunting effect of the line prevents impulse relay R9 from operating. On dialling, R9 responds to the breaks and repeats impulses to dialling relay R10 and the connector magnet LVM in parallel. R10 operates relay R11 which, after the relapse of R10, fails to hold over the test wiper if the wanted line is idle, so that cut-off relay R12 pulls up in series with relay R15 which completes the ringing circuit and by releasing R8, disconnects the A.C. impulsing source V2 and impulse relay R9 from the line. When the called party replies ring-tripping relay R17 operates, locks, completes the speaking circuit, and operates meter RR. Wanted line busy. When dialling relay R10 relapses, R11 holds in parallel with the operated cut-off relay of the wanted line so that common relays R13, R14 interact and the calling line is intermittently short-circuited at 79 to give a busy signal, the A.C. generator V2 being still connected to the line. When the calling party replaces his receiver, impulse relay R9 pulls up and R5 falls back followed by R7, R6, R8. The A.C. source V2 is now disconnected and interrupter 83 is connected to magnet LVM which homes the connector so that R11 falls back and relays R13, R14 cease to function. Release, normal and forced. The upper winding of R16 is connected across the line during conversation so that when either party gives the clearing signal, R16 pulls up and releases R5 with results as described in the preceding paragraph, switching relay R15 being also released. If both parties fail to give the clearing signal, the connection is released by common equipment shown at the foot of Fig. 2. Relay R18 operates when switching relay R15 pulls up and completes circuits for a relay PR2 and the magnet KVM of a stepping switch KV. PR2 releases R18 and the switch takes a step but PR2 maintains itself for a period over a vibrating armature 103 and ultimately relapses to re-operate R18 and start a fresh cycle. Switch KV is ultimately stepped to a position in which R8 is operated to connect the A.C. source V2 and impulse relay R9 to the calling side of the line. As it is assumed that the calling party has replaced his receiver without clearing, his bell is of sufficiently high impedance to permit impulse relay R9 to operate and close a circuit for the lower winding of R16 which brings about release in the normal manner. If the calling party replaces his receiver before the connection is completed R9 pulls up to release R5 which releases the partially set up connection. If a subscriber's line is so faulty as to prevent impulsing although the calling signal is effective or if dialling is delayed, thermal relay TK completes a circuit for R16 (lower) which releases the equipment as previously described.