Patent GB-265732-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/42
Filed: 1925-12-10
Abstract: 265,732. Siemens Bros. & Co., Ltd., and Humphries, H. E. Dec. 10, 1925. Semi-automatic exchange systems.-A sender, Fig. 3, connected to a junction, Fig. 2, to an automatic exchange is controlled from an operator's key-set, Fig. 1, by code currents over the three-wire connection between the operator's cord circuit and the junction. The key-set is associated with the cord by the ringing-key RK, or by a relay controlled thereby, the ringing- trip-relay TR being energized at once when the operator plugs into the junction. Nine values of a digit are accounted for by connecting ground or battery or neither to the awire and to the b-wire, and the tenth by the non-closure of a circuit which is closed for all other values over the c-wire. Each digit register comprises relays W, X, Y, Z, Fig. 3. The a-circuit energizes relay W or X or neither and the b-circuit energizes Y or Z or neither, while the non-closure of the c-circuit in conjunction with battery on the a-circuit energizes Y and Z. The use of polarized relays in the registers is avoided by connecting the relays W, X for example in series in a local self-interrupting circuit, thus setting up a condition of flutter which is terminated in favour of one relay or the other by + or - potential on the a-wire. Operator's circuits; seizure of idle sender. The operator plugs into the junction, throws the key RK, awaits dialling tone, presses four keys in succession and restores the key RK. The sleeve relay S, Fig. 2, is energized, locks itself, and starts the switch SF, and when an idle sender is found relav T is energized over wire 13 in series with relay N, Fig. 3, and energizes relay B. Relay TR, Fig. 1, is energized in a circuit from contact x4, Fig. 3, and is disconnected by relay RS which locks itself over c4, na4, ll2, rs2, RK and the b-wire to x4. Dialling tone is sent back from the incoming selector in a circuit which passes through the sender, or from the sender at DDT, or from the junction at b2. Relay C or NA or both are energized when any key is depressed and energizes relay L, which energizes relay LL continuously until keying is finished. The locking circuit of relay SR is disconnected from the b-wire at each key-depression at c4, na4, but the relay is kept energized at c3, na3, ll1 until keying is finished, when ground is no longer connected to the b-wire at the sender. A modified circuit is described in which the operator gets a buzzing signal if she keys before throwing the key RK. Registering the number keyed by the operator. The keys control relays PA, NA, PB, NB to connect. ground or battery or neither to the a and b-wires, while any key except 7 also energizes relay C to connect battery to the c-wire. Relay V, Fig. 3, is energized in the c-circuit when any key but 7 is depressed and closes a local circuit through relays W, X and a back contact w1, x1 of each, so that these relays flutter their sensitive armatures w1, x1 without moving their other armatures, but if the a-circuit 12 which is connected over wiper 23 to an intermediate point of this local circuit, is connected to ground or battery, relay W or X is steadily energized, locks itself and cuts out the other. Relays Y (i), Z (i) are controlled in the same way over the b-circuit. Relay J, energized in series with V over the c-circuit, controls the back-stroke magnet ICM to advance the switch IC as soon as the key is let up. When key No. 7 is depressed, relays V, J are not energized, but battery is connected to the a-circuit to energize relay X (which however does not lock itself as contact v2 is open) and ground is connected to the b-circuit to energize (over 24, v3, x4) the relays Y (2), Z (2), which lock over their first windings. In this case the stopping-magnet ICM is energized over contacts x2, v5 to advance the switch IC. In the second and further positions of this switch subsequent depressions of keys control similar relay registers (not shown) Sending operations. A relay U4 energized over wiper 22 as soon as the registering operations are completed connects an interrupter 27 to backstroke magnet OCM to drive the switch OC to its 2nd position, connecting the interrupter 27 over p2, 32 to magnet CSM to drive the counting switch CS. When the wiper 42 of this switch reaches its 7th terminal it connects the interrupter 27 over wiper 33 to magnet OCM to drive OC to 3rd position, removing at 30 a short-circuit from the coupled interrupter 29, which now transmits impulses over circuit 11 to the junction b-wire. When the wiper 43 reaches the terminal marked by the first digit register, it closes an interrupter circuit through wiper 34 and magnet OCM to drive OC to its 4th position, in which interrupter 29 is again short-circuited and magnet CSM is connected over wipers 32, 41 and its own self-interrupting contact csm. The switch CS races to its next normal position, in which the wiper 41 opens this self-interrupting circuit and closes a circuit csm, 41, ocm. 33, OCM to drive OC to its 5th position, from which a similar cycle of operations begins for sending the second digit under control of the second relay register, and so on. A pause between digits is ensured by the 7 idle steps taken by the switch CS from each normal position. For digits up to 5 the switch CS moves through a quadrant from normal to normal, but for higher digits through a semicircle. In the latter case a self-interrupting circuit is closed for magnet CSM in the mid-way normal position to step it rapidly through. Specification 230,291 is referred to in the Provisional Specification. Release of sender. After all digits have been sent the switch OC reaches its 13th position, and is driven through its last three positions to normal by a circuit 28<a>. In passing it energizes relay E which operates a statistical meter SM and unlocks relay N, which is not again connected to the incoming test circuit until all units are restored to normal. Relay N unlocks all energized relays, and a self-interrupting circuit is closed through wipers 40, 31 (in normal positions) and 21 (off-normal) to drive the switch IC to normal. Relay T, Fig. 2, in series with N is de-energized and switches through to the junction. Premature release. If the operator withdraws the plug while sending is in progress, the relapse of relay N energizes relay P (over 31 off-normal and 40 normal) which opens contact p2 to prevent operation of the switch OS and commons the terminals of the bank 33 to provide a self-interrupting circuit to drive OC to normal. Delay signal. Battery is connected to wires 35, 36, Fig. 3, at alternate intervals so that if the complete number is not registered within a certain period relay ZA becomes locked up and connects tone and flash current to the a-circuit.