Patent GB-396704-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/42
Filed: 1932-02-05
Abstract: 396,704. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., HARTLEY, G. C., and SNELL, M. S., Connaught House, Aldwych, London. Feb. 5, 1932, No. 3454. [Class 40 (iv).] Connections are established over two switches F1, each available for both incoming and outgoing calls, and an intermediate link circuit PC comprising hunting switches F2, S, the operations of all the switches being controlled by a common control circuit BP of bye-path type. When a call is initiated, switches GF of two control circuits hunt for idle switches F1 serving the calling group and these then hunt for the calling line. The first (hundreds) digit is received by switch R1 to mark a group of contacts in the bank of switch R2 which then hunts for an idle switch F1 serving the wanted hundreds group. The tens digit is also received by R1 to mark a group of contacts in a third switch R3 which then directly responds to the units digit to mark the wanted line. The switch R1 is further operated to select an idle link circuit PC, the switches F2, S, of which are then set by marking under the control of switches GF, R2, respectively. Each subscriber's line circuit has a combined line and cut-off relay which is operated through its second step by current over the b-wire. Detailed operations. Two-step relay LK operates partially over a resistance RE in the b-wire closing its contact l to energize a group relay SA and a common start relay SS which completes circuits for relays ST in idle control circuits. Relay ST connects up magnet GFM and when an idle switch F1 serving the calling group is found, relay N operates over wipers gfm 7, gfm 6, and contact hs 5, and energizes NN. Relay HA also operates and when a similar relay HB has also operated the starting circuit is opened. In each of the allotted switches F1, magnet FM1 is operated over wiper gfm 4 and when the calling line is reached relay K operates over wipers gfm 10 and fm 14. Relays PX, KK, HS, operate, and earth is connected over wipers gfm 9, fm 12, to energize LK fully, operating its contacts k. Relay A operates over the calling loop, energizing B, BB, and impulses of the first digit are repeated to magnet RM1 over relay C. As soon as R1 moves off normal, magnet RM2 is operated over wipers rm 20, rm 15, to advance R2 to the beginning of the group marked by Rl when M operates over wipers rm 21, rm 10. The relapse of relay CC at the end of the digit energizes relay EH followed by E. Switch R1 now advances to its 11th contacts under the control of relay T in preparation for the second digit, whilst switch R2 hunts for an idle switch F1 in the marked group over wiper rm 24 or rm 25 according as the hundreds digit was odd or even. When this is found relays P, H operate. During the second digit, relay CE is operated and magnet RM3 energized to hunt for the group marked by R1 when relay M operates and on the relapse of relay CC, relay TE switches over the impulse circuit to magnet RM3 for the final digit. If the tens digit is even relay JA operates and in conjunction with relay JB selects one of four marking levels of R3. Relay TE releases relay T so that switch R1 advances again in search of an idle link circuit. The operation of relays T, TT, when this is found completes circuits over wipers rm 16, rm 18, for magnets FM2, SM, to advance switches F2, S, to the contacts marked by GF, R2, under the .control of relays FN, M, respectively. When both have operated relay K energizes followed by TX which completes a driving circuit over wipers rm 26 for magnet FM1 of the switch F1 serving as the final selector. (Relay K which operates over one of two multiple battery connections according to the position of armature jb 2 is marginal and cannot operate in parallel with a similar relay, thus ensuring that only one control circuit can mark over each half of the field at once.) When F1 reaches the wanted line marked over one of wipers rm 35 .. rm 38, relay R operates over wipers rm 28, fm 15. Relays U, RR, are now operated, releasing relay B and operating relays BS, BBS, in the link circuit. If the wanted line is free, relay P operates over wipers rm 17, sm 2, fm 13, completing a circuit over wiper rm 14 for relays JS, GS. The latter connects up ringing- current to the outgoing b-wire and ringing-tone through AS to the calling subscriber. Relay GS also operates relay HS, and the called party's relay LK is operated through both steps over the b-wire, wiper rm 17, and relay P. When the wanted subscriber replies, relay FS operates followed by FFS which switches through. The control circuit is released by the removal of earth from wiper rm 12 when BBS operates, causing the release of relays T, TT, BB, and the return of switches R1 .. R3 to normal. If the wanted line is busy, relays P, GS, do not operate and busy tone BT is sent back. Call to operator. If the digit 0 is dialled relay O operates over wiper rm 18. Switch R2 hunts for an idle outlet as before but switch R1 is not stopped in position 11 but goes on to select an idle link circuit of which the switches F2, S, are then set, the latter to a trunk leading to an operator's position. Relay OS operates over wiper rm 19 to cut out the feed and remains locked over wiper sm 3 to earth at the operator's position. P.B.X. hunting. If the contact selected by switch R3 after the third digit is the first of a group, and the corresponding line is busy, relay V operates over one of the wipers rm, 31 .. rm 34, and earth on the contact, relay PX being operated after the first digit if the hundreds group selected contains P.B.X. groups. Relay V causes switch R3 to advance without hunting to the last line of the group when relay N operates to battery on the corresponding contact. Magnet FM 1 of the final selector is now operated over wiper rm 26 and contacts r2, el, n2, and the switch F1 hunts for an idle line with relay P testing over wipers rm 17, sm 2, fm 13. If no idle line is found, relay R operates when the last line is reached and busy tone is sent as before. Outgoing junction call. If the digit 1 is dialled, relay JA operates over wiper rm 17 and R2 hunts for an idle outgoing junction. The operation of H, when this is found energizes relays OG, O, and the connection proceeds as for a call to an operator. Metering. Relays GS, JS are released in succession by DS when a called subscriber replies and a metering impulse is transmitted over wipers fm 24, fm 14, to meter MR. In the case of a call to an operator, relay JS is not energized and metering does not take place. For an outgoing junction call, booster battery over wiper sm 3 operates JS over a rectifier causing a metering impulse to be transmitted over wipers fm 24, fm 14. Coin-box subscribers. The line circuit of a coin-box subscriber has batterv over a resistance SP connected to the contact of wiper fm 13. For a call from such a line to an operator relay CB operates over wipers gfm 9, fm 13, and connects earth over wiper rm 26 to actuate a relay which gives a flashing signal to the operator. Specification 397,174, [Group XXXVII], is referred to.