Patent GB-366669-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1930-12-24
Abstract: 366,669. Automatic exchange systems. SIEMENS BROS & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. Dec. 24, 1930, No. 38879. [Class 40 (iv).] A switch having two sets of wipers acts over one set AF1 .. AF3 as a call-finder and over the other set AS1 .. AS3 as a group selector. Two such switches AF1 .. AS3, BF1 .. BS3, mav be associated to form a link circuit in which either switch may act as a finder the other then acting as a group selector. The two switches have access to different groups of calling lines and to different groups of outgoing trunks, the selection of the particular switch which is to act as the call-finder being determined by the group in which a calling line appears. In the system shown, the switches are of Strowger-type and their operation is controlled from a common control circuit, Fig. 2, of which two are provided for a group of link circuits, one control circuit being normally used for calls from one group of calling lines and the other for calls from the other group but each capable of use, when the other circuit is busy, for calls from either group. Operation of switch AF1 .. AS3 as finder. A call in the A-group of lines grounds a starting wire SWA, marking a level in the bank ANP and energizing relay A. Relay T operates over contacts of a normally-energized relay PX and operates a relay AS which connects up the circuits of the control circuit in such a way that the switch AF1 . AS3 acts as a finder. (If a call is made in group B and the other control circuit is busy, the starting wire SWB is extended to relay B in the control circuit shown, and relay BS is operated to cause the switch BF1 .. BS3 to operate as the callfinder.) Relay AS closes a circuit over wiper PA5 for the vertical magnet AV of the A-switch in the preselected link circuit, the magnet in turn at its contacts av closing a circuit for relay G(i) which interrupts the magnet circuit Vertical stepping continues until the marked level is reached when relay G holds over its winding (ii) and wiper PB8, and slow-acting relay RD, gets time to operate. The rotary magnet AR is now connected up over wiper PA4 and stepping occurs in a similar manner under the control of relay G until the calling line is reached when relay H operates over wipers PA7, AF3. Operation of switch BF1 .. BS3 as group selector. Relay AC operates over wipers PB3, PB5, and the calling loop, operating relays BC, CC. Impulses are repeated by AC over wiper PA6 to vertical magnet BV of the B-switch, relay CD operating at the first impulse to transfer the circuit of CC to a back contact of AC so that at the end of the impulses, relay CC relapses and completes a circuit over wiper PB2 for rotary magnet BR. Rotary stepping occurs under the control of relay G which operates over off-normal contacts an2 as long as the test wiper BS3 finds ground. When an idle trunk is reached relay HC(i) operates over wiper PB8 and off-normal contacts bn3 completing a circuit over wiper PA5 and rotary off-normal contacts anr1 for switching relay HB. If no idle trunk is found, the switch moves to 11 th terminals at which relay G is held operated over springs bs and slow acting relay BT operates over winding (i) and connects up busy tone BTL. If no impulses are received by relay AC within a predetermined time, relays TY, TZ successively operate to disconnect relay AC and release the control circuit The B-switch is moved to 11th contacts in the first level and a busy tone is given as before. At the end of conversation relay HB releases but both switches remain off-normal until the link is preselected for another call. Preselection of idle link. Release of relays AC, BC, T completes a circuit for the righthand winding of relay SP which operates relay G and gives an impulse to magnet PADM of switch PA. If the next link is busy relay SP operates again over wipe:r PA7 or PA8 and stepping occurs under the control of relay G until an idle link is reached. Relay BT now operates over winding (i) and locks over winding (ii) and wiper PA3 thus connecting ground to release magnets AZ, BZ of the switches in the selected link. In order to move switch PB to the position to which PA has moved, banks PA1, PB1 are connected together with a slip of one as shown. When relay BT operates magnet PBDM is energized over its contacts pbdm until a position one in rear of PA is reached when contacts pbdm are shunted. Relay PX operates and locks and when relay BT releases the wipers of switch PB take a further step. Statistical metering. If both control circuits are busy when a call is made, an overflow meter OM is operated.