Patent GB-1223885-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: BROWELL LESLIE JAMES
IPC: H04Q3/00
Filed: 1968-05-20
Abstract: 1,223,885. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 27 March, 1969 [20 May, 1968], No. 23988/68. Heading H4K. A cross-bar switch with select magnets, auxiliary select magnets, and bridge magnets, has its outlets divided into groups with discrimination applied depending on which group of outlets is subject to marking of available paths so that the marking wires of that group may be connected to the respectively associated select magnets, operation of such a select magnet in respone to marking providing a circuit which allows the marking to operate the appropriate auxiliary select magnet. The switch is 10 x 12 arranged for triple group working as described in Specification 890,237, and may be employed in an exchange using the self-steering principle and of the kind described in Specification 890,235. A switch in the first stage A of a routing selector is described with reference to Figs. 1 to 4, not shown. Discriminating relays (RA), (RB) operated from a trunk relay group indicate whether markings will be applied on outlets associated with odd numbered or even numbered select magnets. If a 26th possible outlet is employed, the ninth magnet is common to both groups and becomes an exception. Offnormal contacts of the select magnets provide a break-out priority chain for a single magnet, and provide paths to the auxiliary magnets so that the one appropriate to the selected marking is operated. When both an auxiliary and a select magnet are operated a marking disconnect relay (MK) operates to leave the select magnet held over an auxiliary select magnet off-normal contact while the auxiliary magnet is held by the marking of available paths in the outlet group. A route controller (RC), acquainted with the readiness of the switch, operates the bridge magnet of an inlet connected to the trunk relay group. Switches in the B-stage of the router are similar to A-stage switches, three outlets being associated with each select magnet and being subject to further selection by three auxiliary magnets; only one outlet of each such set of three being marked at any one time and markings being applied to outlets associated with odd select magnets, or for even select magnets, but not for both at the same time. Break-out priority chains of off-normal contacts allow for one magnet to be selected in the odd and even series, and provide paths to the auxiliary magnets for that one to be operated appropriate to the marked outlet selected. With an auxiliary magnet operated a marking disconnect relay (MK) operates and brings up a marking relay (M) which for each idle bridge of the switch marks two wires to the accessible pair of outlets in the A-stage of the router. When, with the A-stage suitably prepared as described above, the P- wire is connected over an A-stage switch, the bridge magnet of the selected inlet of the B- stage switch operates. Off-normal contacts of the bridge magnet remove the marking to the A-stage outlets thereby releasing the auxiliary and select magnets and restoring the A-stage switch for further service. The B-stage switch is similarly restored with removal of marking, the bridge magnet busying the links over offnormal contacts. A-stage switches may be busied out by operating the marking disconnect relay (MK) over a chain of off-normal contacts of all the select magnets. Application of earth to one end of the chain operates the relay (MK) once the switch is in a restored state with all select magnets deenergized. With (MK) operated all marking wires are disconnected from the outlets and all bridges are busied forward to the trunk relay group.