Patent GB-379370-A (GB)
Title: Improvements in telephone plants
IPC: H04Q3/42
Filed: 1931-05-29
Abstract: 379,370. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. May 29, 1931, No. 15810. Convention date, May 31, 1930. [Class 40 (iv).] In a system employing link circuits terminating in call-finders AS and group selectors GV, the link circuits are divided into groups each served by a single register-controller RL, and an allotted call-finder in each group of which the register-controller is idle hunts for a calling line, the impulse circuit over the successful callfinder being extended to the appropriate registercontroller by a relay RN1. The first idle callfinder in each group is selected by a switch SS, and each starting circuit includes a contact of a relay ER which is closed as long as the registercontroller is idle. The switch SS also serves as the input control switch for the registercontroller. As described, the call-finders are of the around-and-in type. Circuit arrangements. Line relay LR connects up relay LGR which is common to the lines connected to the same terminal row of the finders, and the latter connects up start relay STR which closes a circuit to relays RR1, RR3 of each idle register-controller. If the first associated finder is idle, relay RR1 energizes over wiper A1 of the switch SS in series with relay SR and cuts off relay RR3, but if the first finder is engaged, relay RR3 energizes and connects relay RR2 to the starting circuits of all the associated finders, so that it pulls up provided there is any one idle and locks, disconnecting relay RR3 and closing a circuit over wiper A2 for magnet SM, which advances the switch SS in half-steps by means of an escapement D until an idle finder is reached, when relay RR1 energizes over wiper A1 and disconnects relay RR2. Relay SR in the finder energizes in series and connects up the primary magnet CVS to rotate the finder until wiper Kd engages the test terminal d of the appropriate row, when relay RS1 energizes and shortcircuits relay SR. The secondary magnet CRS now operates until wiper Kc engages the test terminal c of the calling line, whereupon relay RS2 energizes in series with cut-off relay BR, which however holds armature 2 initially attracted by line relay LR. Springs ORS are opened at the first radial movement of the finder. Relay RN1 energizes to extend the impulse circuit to the register-controller, in which relay RR4 operates and, connects up sluggish relay RR5 and relay ER which marks the register-controller busy by opening the circuit to relays RR1, RR3. The switch SS advances automatically to position 6, so that the first train of impulses are repeated by relay RR4 to the first register magnet RM1 over wiper A3. Sluggish relay RR6 operates during the train and then falls back, advancing the switch SS to position 7 to direct the next train of impulses to the second register magnet RM2, and so on. The setting of the selectors is effected in known manner, and relay RN2 then operates and disconnects relay RN1 to release the register-controller. Relays RR4, RR5 relapse in turn and relay RR6 energizes momentarily to advance the switch SS to normal.