Patent GB-818491-A (GB)
Title: Connector and circuit arrangement for automatic telecommunication exchange system
Inventor: JOHNSON BENJAMIN BERTIE
IPC: H04Q3/00
Filed: 1955-10-25
Abstract: 818,491. Automatic exchange systems. TELEPHONE MANUFACTURING CO. Ltd. Oct. 15, 1956 [Oct. 25, 1955], No. 30515/55. Addition to 703,931. Class 40 (4). The parent Specification relates to the use of a pair of selective relay units, of the type described in Specification 689,735, in a connector responsive to a single digit. The disclosure in the parent Specification is now modified to make the connector responsive to either one or two digits. First embodiment, Fig. 1. Single digit 1-9. Closure of the loop energizes A, B and RF in sequence. At the first impulse A falls back to energize finger magnet FMA1 in the first selective relay unit unit SRA. FMA1 interposes its finger between the main armature AA and the contact card CA1. The main operating magnet EMA then pulls up over contacts rf2 and a1 to close the first set of contacts in SRA. At the end of the impulse A re-energizes to operate SW and restore FMA1, finger magnet FMB1 pulling up over the first contacts in level LAG which are held closed by EMA. At successive impulses the finger magnets of one or other unit SRA, SRB are thus operated in succession with alternate operation of main magnet EMA or EMB. At the end of the train A remains operated to maintain B so that CD falls back slowly to restore RF. If the wanted line is free its test conductor presents battery to level LAE or LBE to operate H. Contacts h2, h3 connect up the ringing circuit. When the called subscriber answers F energizes to cut off the ringing and connect up the speech path. Release is effected when both parties hang up. Calling a two-digit number. The first digit of a two-digit number is 0. The tenth impulse actuates the fifth bank of contacts in SRB. Circuit is made over level LBG to operate CH which switches the incoming line from levels LAA, LAC, LAE to levels LAB, LAD, LAF. The second digit 1-9 then selects a subscriber's line 01-09 in a manner similar to that described for lines 1-9. Second embodiment. The circuit shown in Fig. 1 can be converted to that shown in Fig. 2 which makes use of a third selective relay unit SRC and can handle calls to any one of 28 lines. A single digit 1-7 or 9 produces progressive energization of finger magnets and alternate energization of main magnets EMA, EMB in the manner described in connection with Fig. 1. At each closure of a bank of contacts in SRA or SRB so level LAH or LBH operates the corresponding finger magnet FMC1-FMC5. At the end of the train when CD restores the main magnet EMC of the third selective relay unit SRC operates to close the selected bank of contacts in SRC, selection of the levels LCA, LCC and LCE or LCB, LCD and LCF being determined by the condition of relay CH according to whether the digit is odd or even. Connection is then established as in Fig. 1. Calling a two-digit number. The first digit is 8 or 0. This is transferred to SRC as in the manner described above and as the number is even CH operates. The first impulse of the second digit reoperates finger magnet FMA1 over contact 8 or 0 in level LCG. The second digit is therefore registered on SRA or SRB to select the wanted line 81-80 or 01-00. Specification 767,730, [Group XXVI], also is referred to.