Patent GB-278839-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1926-08-13
Abstract: 278,839. Siemens Bros. & Co., Ltd., Long, D. P., and Wilkins, A. L. Aug. 13, 1926. Automatic exchange systems; party-line systems.-In an automatic telephone, system in which subscribers on a party line call each other directly by means of code-signal magnetos, exchange apparatus which is normally seized in making a call is released after a time interval when a revertive call is made or when dialling is unduly delayed. For incoming calls, code signalling from exchange apparatus is used. In exchanges comprising a large number of rural lines it is economical to use special pre-selectors and first selectors. When a first selector is seized in an outgoing call, a delayed release device, operates two relays in turn, the second of which removes battery from the incoming c-wire, so that the pre-selector steps on and releases the first selector. The result of dialling is that the circuits of both relays are opened so that the device can be cut out at either stage. The preselector steps on to its last contacts where it is held till release takes place. For calls incoming to a party-line, the connectors comprise two twocoordinate switches, one of which responds to the last two numerical digits to find the line, while the second or code switch is actuated by two extra code digits to pick out the code signals to call the required subscriber. In a second system, for exchanges having only a few rural lines, ordinary preselectors and first selectors are used, but each party line is provided with special apparatus connected to the preselector and to the connector multiple. The connectors used are of the type in which ringing is suppressed, as in Specification 278,840 for example. The apparatus comprises a two-coordinate switch having a special set of vertically-arranged contacts bridged by a wiper which partakes only of the vertical motion. In outgoing coils, the switch is stepped vertically at a slow rate by an interrupter, and after the first step the test circuit for the connectors is opened and a loop closed for the preselector which finds a first selector, and dialling tone is sent back. If the tenth or other predetermined set of contacts is reached before dialling takes place, a relay is operated which stops the movement of the switch and releases the preselector and first selector. For incoming calls, the switch is operated by two code digits and the required code-ringing signal sent over the line. The ringing signal is controlled by a codetransmitting cam and a control cam, which operates and locks a ringing-connecting relay for the duration of the ringing cycle. The cycle is repeated until the called subscriber answers when ringing ceases at the end of a cycle. The partylines are arranged for simplex dialling, while the special first selectors and special apparatus repeat the impulses in a loop signalling system. First system; special pre-seleotor.-When the subscriber lifts his receiver, earth on the a and b wires operates line relay R over its windings in parallel to battery over wiper D. Magnet DM is operated by interrupter I to step the switch until a free link is found, when battery over the wiper C energizes test relay T, so that relay R de-energizes. Earth is fed forward from wiper E over low resistance winding T (1) to mark the link busy. Special first selector. Relay A (1) operates over the c-wire when the selector is seized, followed by winding A (2) over the subscribers' loop. Relays V, D operate in turn, lamp PL is lighted, winding A (1) de-energized, and dialling tone connected up from wire DS. The first set of impulses are repeated to vertical magnet VM at contact a1, and off-normal contacts k1 - - k4 change over, so that relay L operates over contacts a2, d3, k2, v1, and locks up. cutting out lamp PL. Relay D is held by the vibrating contact a2 until 'the impulses cease, when rotary magnet RM is operated through its interrupter and contacts v3, k4, d1, t5 to find a free link. Test relay T now operates over its winding 1, locks up over its winding 2, breaks the stepping and switches the speaking wires through. The remaining sets of impulses are repeated at a3, and when the called subscriber lifts his receiver, supervisory relay Y operates, de-energizing relay L. Release. When the calling party hangs up, relay A releases, initiating release of the succeeding switches and relay V, T, and energizing the release magnet MM. Relay T of the pre-selector now de-energizes and the magnet DM steps the switch to normal. No impulses transmitted. Earth is applied in turn by cam-operated springs to leads 10, 11, Fig. 2. Earth on lead 10 operates relay S (1), which locks up over its winding 3. Earth is removed from lead 10 and applied to lead 11 when relay Z (1) operates and locks up over its winding 2, disconnects battery from the c-wire so that relay T of the pre-selector releases and breaks the locking circuit of relay S which de-energizes when earth is removed from lead 11. The preselector now steps by means of off-normal wiper E until the penultimate contact is reached when relay R operates over wiper D. Relay T energizes over wiper C when the last contact is reached, and the switch is stopped with relay R held over the A and B wipers. The first selector is therefore released. When the calling subscriber hangs up, relays R, T release in turn and the pre-selector returns to normal. Incoming call; final selector FS. When the preceding selector tests in, relay N (1) operates over the c-wire and relay A over the speaking leads. Relay D operates [battery, contacts t1, n2, relay D, contacts a1, k3, w1, earth]. The next impulse train operates the vertical magnet VM [battery, d2, a2, e2, g2, VM, earth], the off-normal contacts k1 - - k3 operating. Relay D holds over contacts a1, d3 until the end of the impulse train, when relay G operates [battery, t1, u2, relay G, d1, k3, w1, earth], completes at g5 a circuit for relay D similar to its original circuit, and locks up over contacts d1, g1. The units impulses are repeated to rotary magnet RM and off-normal contacts w1, w2 operate. At the end of the train therefore relays D, G release in turn, and relay E operates [battery, d2, ww2, E, w2, earth] and locks up, switching the impulsing circuit to the magnets of the code switch CS. Relay D again pulls up from battery at t1, to earth over contacts a1, g5, e5, kk3,ww1. The first code impulse train is repeated to magnet VM<1>, and contacts kk1 - - kk3 change over so that relay D releases at the end of the train, and relay G pulls up and completes another energizing circuit for relay D. The next impulse train actuates the magnet RM1 and contacts ww1, ww2 change over. Relays D, G release in turn, and in the interim relay T tests the called line. Ringing and completion of connection. Relay T operates [battery, d2, ww2, g3, T, n3, wiper C‹, to earth at called subscriber's cut-off relay] to connect battery at t1 over its low-resistance winding to busy the called line. Relay L now operates [battery d2, ww2, g3, L, e3, earth]. The motordriven code-ringing device is now running. When the nose of the cam C3 engages its springs, relay S (1) operates over wiper C1 and locks up over contacts s1 n4 when the nose of the cam leaves the springs. Cam C2 now sends the correct sequence of ringing impulses over the called subscribers' instrument, and a ringing signal is sent back from transformer RS [RS, wiper A1, t1, l1, calling subscriber's loop, l2, battery]. At the end of the ringing period, relay S releases owing to the depression in cam C3, and when the called subscriber replies relay L energizes, releasing relay E, which in turn releases relay L and disconnects the ringing signal from the calling line. Release of final selector. Removal of earth from the c wire releases relay N. Relay T releases, completing circuits for release magnets MM, MM<1> from earth at t1 so that the switches return to normal, when the selector is again selectable over contacts k1, kk2. Line busy. Relay T does not operate, but when relays D, G have released, busy signal transformer BS is connected to the calling line and the calling subscriber hangs up. Second system. Fig. 4; connection from party line subscriber. When the subscriber lifts his receiver, relay A operates over the a and b wires in parallel, and energizes relay L [battery, contact n6, L, contact a2, normal contact on bank VC, wiper vc, earth]. Relay L locks up and relay AA energizes over contacts co3, v4, l4, s3. The vertical magnet VM now operates, and the switch takes one step. The off-normal contacts k1 open the test circuit from the final selector bank FS. Relay V operates from earth over the wiper vc, connecting relay AA to the cam interrupter IM, and closing a loop to the preselector PS, which finds a selector, but the dialling tone is not repeated back owing to the repeater coils being short-circuited at contacts b2, al. The interrupter IM now acts to step the switch up slowly until the tenth or other predetermined level is reached, when relay CO operates to stop the switch. Call to ordinary exchange subscriber. Dialling begins before relay CO operates, impulses being repeated by relay A. Relay L immediately releases, so that relay V holds up over contact l3 when relay CO operates. When the calling subscriber clears relays A, V release to energize release magnet MM. Inter-party call. Operation of relay CO releases relay V at co6. At the end of the call. relays A, L release, energizing the release magnet MM. Call to party-line from exchange. The final selector SS tests in over wire c, and if the line is free the relays N, T operate in series with the test relay of FS; if the line were busy, a busy signal would be sent back from the final selector. Battery is disconnected from relay A and a lamp PL is lighted. Relay AA operates, [battery over b wire, n3, v4, co3, AA, earth] and completes a circuit fo