Patent GB-366143-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-11-01
Abstract: 366,143. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool, and MASON, J. A., 52, Belgrave Street, Liscard, Wallasey, Cheshire. Nov. 1, 1930, No. 32939. [Class 40 (iv).] The normal finders of a group are directly connected to first selectors while the overflow finders are connected to the terminals of second finders. The normal finders are divided into A- and B- half-groups, the overflow finders being taken into use only when the normal finders of both half-groups are busy. In the system described, the normal finders are of the 200-point up-and-around type with all the control relays but the switching relays in the allotter circuit. The overflow finders are connected up so that no two finders of the same overflow group shall have access to the same group of overflow selectors. The invention may be used for reducing the number of discriminating selector repeaters in satellite offices. Operation of normal finders. In response to the operation of line relay L and start relay ST, a test is made of the preselected finder by wiper 2a which, if it fails to find battery to energize LK and short circuit G, allows the latter to interact with the driving magnet of the allotter. In the case of a normal finder wires 20, 21 are connected together by a strap at 17, 18. The operation of LK is therefore followed by that of SF which shunts the highresistance winding of LK to mark the finder busy and energizes the vertical magnet VM and series relay C. VR then pulls up, locks itself and energizes G, which then interacts with the vertical magnet until the level is found and with the rotary magnet (on the relapse of C) until the line is found whereupon SC (or FC) pulls up in series with the line and cut-off relays LK, SC (or FC) locks up in series with CO and energizes the appropriate switching relay HB (or HA). Metal rectifiers MRC in series with the test relays prevent their operation if booster battery is encountered during the hunt. If SC and FC pull up together, only HB is operated. Earth sent back from the first selector when the finder switches through shunts out LK and ST falls back followed by VR, whereupon G and ADM interact until a new finder is allotted. Overflow arrangements. When LK falls after the last of the regular finders of the " A " sub-group has been taken into use, YA falls and energizes YB which transfers the starting lead to the " B " half-group and causes the roles of the banks 2a, 3a to be inter-changed, the test wires of the overflow finders appearing in bank 3a. If now all the regular finders in the " B " half-group also become busy the start lead is re-transferred to the "A halfgroup, and the next call is extended by one of the special overflow finders. When LK pulls up to confirm the allotment of one of these, a circuit is made for DK in the secondary allotter over 20 and a circuit in the preselected secondary finder. DK associates the stepping relay GG of the allotter with the driving magnet SNM of the secondary finder which then hunts with its wiper 4c for the terminal connected by LK to battery over SF. When this is found, GG is shunted out by the low resistance of SF, SK, and FK pulls up shunting its high-resistance winding to enable SF, SK to pull up. SK switches the secondary finder through and SF starts the primary finder which hunts in the manner described in the preceding paragraph for the calling line. When the last secondary finder of a group is taken into use, OB falls back to prevent continuous drive of the secondary allotter and to ground the wire 20 to mark the corresponding primary finders non-selectable in the bank 4a of the primary allotters which are thus stepped on if necessary. Metal rectifier MRC3 prevents the operation of LK when 4b of the secondary allotter passes booster battery. ZA, ZB operates for the overflow finders of the "A" halfgroup in the same way as YA, YB for the regular finders to transfer the start lead to the "B" half-group when the "A" half-group is busy. When all finders in both half-groups are busy the start leads are diverted to OF which operates a traffic meter. Release. The release magnets are energized from a ground in the allotter circuit instead of from the selector. Faults. If the start relay of the "A" halfgroup remains operated for (say) 3 seconds, S and Z relays TA, TB operate alarms (not shown) and disconnect YA, ZA which cause the start circuit to be switched over to the "B" half-group. Routine testing. When the springs RTA, RTB are operated, the finders hunt in turn to the eleventh terminals in the tenth level.