Patent GB-406274-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1932-08-20
Abstract: 406,274. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, BAKER, G. T., Blackbrook, Caerphilly, Glamorgan, and BELAS, F. T., 26. Arlescourt Road, West Derby, Liverpool. Aug. 20, 1932, No. 17161/33. Divided on 406,270, [Class 40 (iv).] In a system employing register-controllers selected by A-digit switches, a calling party obtains direct access to an operator over an A-digit switch in response to a particular single digit. If the calling party requires assistance in setting up a connection, the operator takes into use a second A-digit switch which she connects over her circuit to the outlet of the first A-digit switch. The calling party is instructed to dial the wanted number, whereupon the connection is set up over the originally seized first code selector by the registercontroller taken into use by the second A-digit switch, these operations being supervised by the operator. The first code selector, Figs. 1 to 3, first A-digit switch, Figs. 4 and 5, and register-controller (not shown) normally operate as described in Specification 406,270. The operator is signalled from the first code selector if the calling party is not entitled to full service. The A-digit switch, Figs. 4 and 5, seizes an idle operator's circuit, Figs. 6 and 7, in response to digit O whereupon 3L pulls up over the calling loop, 3B pulls up and locks, and service discriminating relay 3DR is connected to the forced release wire FR. Relay 3RZ pulls up to light lamp CLP and connect tone from GNR over the negative wire to the calling party. Relay 3BA also pulls up. The first code selectors are in two groups, one accessible to subscribers entitled to full service and one accessible to lines, e.g. call box lines, not so entitled. The restricted service group has ground over strapped terminals 30, 31, Fig. 1, on the barred trunk wire BT and when the A-switch connects through, this ground is momentarily connected to 3DR (lower) which locks up and flickers the calling lamp. When the operator plugs in, sleeve and relief relays 3S, 3SS pull up and 3DR falls back. If information or the supervisor is required, this is attended to, and when the calling party replaces his receiver 3L falls back and short circuits 3S (lower) to light the cord lamp. If assisted service is required, the operator throws a key to operate 3RR over the tip and this relay completes hunting circuits for a switch 1ADF which seizes a further A-digit switch. The in, out, forced release and holding wires from the first A-switch are now connected by 3K, 3KA over the assistance set to the second A-switch. 3L falls back followed by 3B, 3RR and 3KR, 3DR pull up to hold 3RZ. The calling party is now instructed to dial, the listening circuit being completed over condensers 3QC, 3QD. The first code selector and subsequent switches are set by the registercontroller seized by the second A-switch and when sending is complete, 3K, 3KA release but 3KR, 3BA, 3DR, 3RZ remain operated. The switch train is held over bridging retard 3IB and battery is fed to the calling party over 3L, conversation with the called party taking place over the assistance set. When the operator is satisfied as to the connection, she withdraws, whereupon 3S, 3SS fall back and disconnect battery from the holding wire during the cumulative release periods of 3RZ, 3BA, 3KR and 3DR. The first A-switch is therefore released and relay 3K, 3KA in the first code selector fall back to switch the connection directly through. If a wrong connection has been made, the operator again energizes RR which opens the in and out conductors to release the register-controller if still held. Relays 3K, 3KA, 3KR, 3RR fall back and ground is connected to conductor FR which ground, after the relapse of 3DR, is connected over 3RZ to the negative out conductor. This is the forced release signal and 3RZ remains operated in series with the release magnet of the first code selector until this switch is restored. The calling party may be advised to make a second attempt or the operator may set up the connection herself.