Patent GB-258775-A (GB)
Title: Improvements in automatic telephone exchange systems
IPC: H04Q3/00
Filed: 1925-03-25
Abstract: 258,775. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd. ),(Deakin, G., and Polinkowsky, L.). March 25, 1925. Automatic exchange systems ; metering .-In an unattended office, if a subscriber's line or a tie line, that is a two-way trunk to a similar office, remains calling for a pre-determined time before dialling or after the called party has hung up, a hunting switch operates a disabling relay individual to the calling line or trunk and all the apparatus seized is released. The disabling relay locks up over the loop (or fault) and marks the line busy. In the case of the trunk the disabling relay at the incoming, end sends a signal to force the calling line (if any) to release the outgoing end and also to create a calling condition at that end. If the trunk itself is non-faulty it is made free as soon as the calling line is disconnected, but if it is faulty the permanent call causes the operation of a hunting switch which operates a disabling relay at the (originally) outgoing end. Means are provided for signalling over a conversation trunk to the main exchange (an existing call being broken down if necessary) when a fuse blows or the ringing generator fails. The invention is described with reference to a rural office in which connections are set up with the aid of connecting circuits resembling those described in Specification 197,797 but modified to include a sequence switch. These comprise a connector in which one of two double wiper switches with two starting positions responds to the tens digit, the setting determining which switch shall respond to the units digit and also which starting position and which set of wipers shall be used. Certain tens digits are reserved for trunk calls and calls to an operator, and when the connector is set to these it starts a group of finders corresponding to the number and when the line is found the local connecting circuit is released. According to the Provisional Specification, the existence of a faulty tie line may be signalled to the main office in the same way as the blowing of a fuse &c. Alternatively a spare terminal on the local connectors is associated with the disabling relays and the maintenance staff dials this number occasionally to find out whether one of these is operated. Call-finder. Line relay Lr energizes the common relays Zr, Cr to start the stepping magnets SM of a group of finders. When the line is found, the test relay Tr stops the stepping magnet by cutting into its circuit the switching relay Sr. Cut off relay Cor pulls up and line and starting relays fall back, relay Sr remaining locked up over relay Nr. In response to the switch-through, impulse relay Ir and release relay Dr pull up, and also relay Br controlling the sequence switch stepping magnet SSM. Magnet SSM and relay Br interact, the switch being moved by half steps at each relapse of magnet SSM to position 2 in which the circuit of relay Br is broken at A. Dialling tone. In position 2, relay UR pulls up over B, C, Tsr. Relay Tsr causes the interrupter Btr to generate tone currents which are sent back over TC. Operation of connector by impulses. Relay Ir repeats the impulses to relays Fr, Ar in series. Relay Ar remains energized during a digit and energizes the sequence switch stepping relay Br and relay Fr repeats the impulses. The tens digit is repeated to the stepping magnet SM1. At each energization, relay Fr locks itself and relay Ar in a circuit over an additional winding of the release relay including interrupter contacts of the stepping magnet to make the operation more or less independent of the character of the line impulses. At the end of the digit, relay Ar releases relay Br, and the sequence switch moves to 3¢ under control of cam A. If the first digit was 3, 4 or 9, relay Vr pulls up in 2¢ over e, e<2>, G, Pr and locks itself over C, B. If it was 3, 4, 5 or 6, relays Xr pulls up over D, g<2>, g, C, B and locks up. If it was 4, 6, 8 or 9 wiper changing relay Kr pulls up in 3 over Pr, H, f<2> f, Kr, C, B and locks up. First digits 1, 2, 0 are used for setting up special calls as described below under " Inter-office working." In position 3¢, except in the case of digits 3 and 4, a self-interrupting circuit is made for magnet SM1 or SM2 according as Xr is energized or not. This circuit is broken by relay Jr in the case of digits 5, 6 when switch SM2 reaches its second starting position N1, in the case of 7, 8 when SM1 reaches position N1 and in the case of 9 when SM1 reaches its normal position N. In the case of digits 3 and 4 relay Jr is energized as soon as the sequence switch reaches 3¢. Relay Jr by energizing relay Br causes the advance of the sequence switch to 4 in which the units digit is repeated to magnet SM1 or SM2. At the end of the digit, the relapse of relay Ar releases relays Br to allow the sequence switch to leave 4 from which it moves straight into 10 under control of cam A. Test of wanted line. Relay Vr which is unlocked in position 4 is re-energized in position 4¢ over its left hand winding and in position 5 its right hand winding is connected to the operative. test wiper g (&c.). If the line is busy, Vr is held over its right hand winding and the relay Tr of the other cord after its left hand winding is disconnected at 6, but if it is idle, relay Vr falls back and energizes the wanted cut off relay over Tr, E, g (&.c.). P.B.X. groups. All the lines but the last of a P.B.X. group have the modified line circuit shown in Fig. 6 with resistances in the test circuit arranged to increase the potential of the test terminals and if the called line is one of these and is busy, relay Jr pulls up over E, g (&c.) in position 5¢, energizing magnet SM1 (or SM2) and is released in position. 6¢ allowing the wipers to take a step. If this line is busy relay Jr causes a further step in 8 and another if necessary in 9¢. Supply and control of ringing current. If relay Vr is de-energized when the sequence switch reaches 10, relay Jr is energized over H, Pr and moves the sequence, switch to 10¢ from which it moves under control of cam A to 11, relay Jr being released. In this position a circuit Pr, G is made for relay Rsr in the common ringing equipment, Fig. 2, which energizes relay Dr<1>. Relay Rir as described in Specification 208.073 connects up at intervals the relays Gr, Fr<1> Er<1> which generate ringing current in known manner. These relays are duplicated, the second set being switched in by a key ORK. The ringing circuit includes relay Rr, and relays Jr, Pr in parallel. The connection of relay Pr allows the calling party to hear a ringing signal. When the called party replies, relay Jr moves the sequence switch out of the ringing position. If some of the lines have resistances of about 1000 ohms, relay Jr may not respond and its duty is taken by relay Rr, butwhere there are no such lines, relay Rr may be omitted. The sequence switch on leaving position 11 moves automatically to the talking position 15. Relay Pr is connected to the two sides of the called loop to provide talking battery. Normal release after conversation. The calling party releases relay Ir and therefore relays Dr, Tr, Sr, Nr. Relay Br pulls up over a back contact of Sr and the sequence switch moves to position 16 in which relay Vr is energized. Relay Xr is energized on the relapse of relay Nr and makes a self-interrupting circuit for SM2, this circuit being broken by the energization of relav Jr when. SM2 reaches its normal terminals. Relay Jr causes the sequence switch to move to 17 and relays Kr, Xr fall back, followed by relay Jr which controls the restoration, of SM1 and drives the sequence switch to position 1. The talking wipers are disconnected during release since relay Nr is de-energized. Busy signal. If the line is busy, relay Vr is energized and Jr being disconnected the. sequence switch is unable to leave position 10. Ground from B is extended over an individual resistance to relay Ar<1> in the common tone equipment, Fig. 2. Relay Ar<1> pulls up slowly owing to a shunt over its back contact and energizes relay Br<1> which also pulls up slowly followed by relays Cr<1>, Cr, which have contacts for each cord, and one of which completes a circuit B, Ur, Tsr. Relay Tsr energizes the buzzer Btr and' relay Ur connects the tone transformer TC to the line. Relay Cr1 also short circuits relay Ar1 which falls back slowly followed by Br<1>, and Cr1, Ur, Tsr. Relay Ar<1> is then re-energized and the cycle is repeated. A duplicate buzzer EBtr may be cut in bv key OTK. With this arrangement the busy signal is an intermittent tone of the same frequency as the steady dialling signal but a separate busy tone may be provided. Number unobtainable tone. If a dead number (e.g. 70) is dialled, ringing cut off relay Rr pulls up over wiper f (the batteries connected to its ends being of different strengths) and the sequence switch moves straight from the ringing to the talking position in which relay Pr is connected to the high resistance relay Hr, Fig. 2. Relay Pr does not pull up. Relay Hr energizes relay Ir<1> which short circuits relay Hr. These relays interact to give about 7 clicks per second, the variations in potential of the a-wire producing an audible signal at the calling substation. Metering local calls. The circuits shown in Fig. 1 are altered as indicated by the dotted lines and crosses. Relay Mr, energized in position 11¢, makes a new circuit for relay Tr to guard against its being momentarily unlocked and connects booster battery over Or and the c-wiper to the meter MS which cuts in an opposing winding to make itself quick releasing. Relay Or disconnects the starting relays Cr of all the finders. In case of premature release, e.g. after busy signal, the metering circuit is opened by Nr. Forced release. When the sequence switch reaches position 2 and again when the called party hangs up, relay Er pulls up to battery at a, a<1> over one of the no