Patent GB-767370-A (GB)
Title: An electric selecting device responsive to impulses
Inventor: FOSTER WILLIAM GORDON
IPC: H01H67/22
Filed: 1955-01-19
Abstract: 767,370. Electric selective signalling systems. TELEPHONE MANUFACTURING CO., Ltd. Jan. 19, 1955, No. 1666/55. Addition to 703,931. Class 40 (1). [Also in Group XXXIX] An electric selecting device comprises two electric selective. relay units of the type described in Specification 689,735, [Group XXXIX], and the parent Specification so arranged that each unit when operated energizes a finger magnet of the other to produce a progressive selection of work contacts of the device, and is characterized in that a first train of impulses selects a group of work contacts and a second train selects a particular work contact in the selected group. First embodiment, Fig. 1. Two digits are used to select 1 of 20 work contacts pco, pce. Relay A responds to impulses over a subscriber's line. Operation of A energizes B which holds up until the end of the digit. Contact b2 closes to energize the first finger magnet FMA1 in the first selective relay unit SRA. The first digit is either 1 or 2. The first impulse energizes relay C and the operating magnet SRA of the first selective relay unit. SRA energizes the first finger magnet FMB1 in the second selective relay unit SRB and restores FMA1. Relay SW energizes at the end of the impulse when the short-circuit to earth at a1 is removed. If the interdigital pause occurs after this first impulse then the release of C energizes SA and the group of contacts pco is selected. If, however, a further impulse occurs before the pause than SRB pulls up in parallel with SW to release FMB1 and SRA and operate FMA2. At the end of the impulse SW falls back. The end of the digit releases C to energize SA, relay CH also pulling up over contact srb1. Relay CH selects the lower level of work contacts pce. In both cases operation of SA restores SRB and energizes E so that the second digit can be received. FMA1 immediately energizes over contacts e2. The first impulse of the train energizes C to remove earth from the work contacts. Finger magnets energize in alternating selective relay units SRA, SRB until the end of the digit when C releases to earth the selected contact in the selected group of work contacts. Second embodiment, Fig..2. Forty-line system. Two additional selective relay units SRC, SRD are provided. If the first digit is 1 or 2, SA operates when C releases, while if the first digit is 3 or 4; SB operates. According to whether SA or SB operates, the second digit is effective on SRA and SRB or SRC and SRD. As in Fig. 1, CH distinguishes between odd and even first digits. Third embodiment, Fig. 3. Thirty-line system. The first digit is counted on selective relay units SRA, SRB acting as a pair. According to whether the first digit is 1, 2 or 3, so SA, SB or SC pulls up as soon as C falls back. The second digit is accordingly counted by units SRA and SRB or SRA and SRC or SRB and SRC to select a contact in group pcl, pc2 or pc3 respectively. Fourth embodiment. Sixty-line system. This system uses Fig. 3 as modified by the addition of the dotted lines, together with Fig. 4. Relay CH distinguishes between odd and even in the first digit, SA, SB or SC operating according to whether the digit is 1 or 2, 3 or 4, or 5 or 6, respectively.