Patent GB-190610600-A (GB)
Title: Improvements relating to Telephone Exchange Systems.
Filed: 1906-05-05
Granted: 1907-05-04
Abstract: 10,600. Lake, H. H., [Stromberg-Carlson Telephone Manufacturing Co.]. May 5. Telephone systems; telephone calls.-Relates to the ringing-arrangements in exchange telephone systems, whereby, after depression, the ringing-key is automatically locked in its depressed position, and the ringing-current is automatically maintained in connexion with the called line, until the subscriber answers, whereupon the ringing-current is disconnected, and the depressed key is released. The ringing-current is periodically interrupted, and other interrupter means are associated with the ringing-relay in the cord circuit, whereby the called line will be grounded during a short interval immediately before and after each periodical application of the ringing-current, thus preventing any damage to the cord-circuit apparatus due to the capacity discharges of the line and sub-station apparatus after each disconnexion of the ringing- current. The invention is described in connexion with a party-line system, in which the call bell of each subscriber responds to currents of a particular frequency only. Fig. 2 shows the operator's listening and ringing key combined in one structure with the keys for a party-line having four subscribers. The stems of these keys are provided with cams 72 which can just pass through apertures 71 in a locking-plate 70, mechanically connected with the armature of the locking relay 51. The depression of any key completes the circuit of the relay, which moves the locking-plate to the right, thus locking the depressed key until the relay is de-energized. The armature of the relay also control the actuating-springs 75, 76 of the ringing-key. Fig. 1 shows the general arrangement of the system. The subscriber at A calls by removing his receiver, thus energizing the line relay 6, and lighting the call lamp 17. The operator then inserts the answering-plug 18, closing two circuits-(a) from the battery S through the wires 78, 82, winding 23 of the supervisory relay, plug sleeve, and cut-off relay 3 to the ground ; (b) from the battery S through the winding 23 as before, plug sleeve, line b, sub-station apparatus, line a, plug, tip, winding 22 of the supervisory relay, and wires 83, 84 to ground. The calling subscriber's supervisory relay has two windings 22, 23 and two armatures 24, 28, and when both windings are energized, contact-springs 25, 26 are out of contact, but when the subscriber's receiver is on the hook, the winding 23 only receives current and attracts its armature 28, thus allowing the armature 24 to fall, and the springs 25, 26 to complete the circuit of the supervisory lamp 29. The supervisory relay of the called subscriber is similar, but is provided with additional contact-springs 37, 38. Having ascertained that a connexion is required with the first subscriber at B' on the party-line, the operator inserts the calling-plug 19, and depresses the key 45', associated with the generator 46', supplying current to which the bell of subscriber at B' alone responds. The depression of the key 45<1> completes a circuit from the spring 50', through the contact 53', wire 54, springs 33, 34, wires 86', 84, battery S, wire 78, and locking-relay 51, back to the spring 50'. The energizing of the relay 51 locks the key 45<1> in its depressed position and also closes a contact 69, 75, completing the circuit of the ringing - relay 49 from the negative side of the battery S, through the wires 78, 77, relay 49, contacts 75, 69, to the interrupter 59 and ground. The relay 49 is, however, only energized during the time that the segment 66, Figs. 1 and 5, is in contact with the conductor 68 to establish the ground connexion through the segment 66, and contact-ring 62. Mounted on the shaft of the interrupter 59 are other interrupters 56<1>, 56<2>, 56<3>, 56<4> associated with the various generators 46<1> &c., and adapted periodically to interrupt the ringing- current, which flows over the following circuit : from the generator 46', through the contact-ring 63, segment 64, contact 55<1>, spring 47<1>, contact 48, armature 80, plug tip, subscriber's bell 10', plug sleeve, armature 79, contact 58, and back to the generator 46<1>. The length of the grounded segment 66 of the interrupter 59 is a little greater than that of the segment 64 of the other interrupters, as shown in Figs. 5 and 6, the result being that the relay 49 is energized and connects the called line to the conductors leading to the ringing- generator slightly before the ringing-circuit is closed by the contact segment 64. In the same way, the ringing-current is cut off slightly before the relay 49 is de-energized. In this way, the line circuit is earthed through the interrupter 56<1> and contact-ring 60 immediately before and immediately after each application of ringing - current, thus relieving the line of all static charges which might otherwise effect the cord-circuit apparatus. When the called subscriber replies by removing his receiver, a circuit is closed from the battery S through the wires 78, 85, winding 31 of the supervisory relay, plug sleeve, sub-station apparatus, plug tip, contacts 80, 81, contacts 37, 39, wire 87, winding 30, and wires 86', 84 to the battery. The excitation of the winding 30 breaks the circuit of the supervisory lamp 40 and at the same time breaks the contact 33, 34 included in the circuit of the locking-relay 51, which is therefore de-energized, and releases the depressed key 45', simultaneously permanently breaking the circuit of the ringing- relay 49 at the contact 69, 75. The supply of ringing-current is thus automatically cut off when the called subscriber raises his receiver. To enable the operator to make a "busy test," a test winding 92 is associated with the operator's induction coil and is connected to the spring 89 of the listening- key, and thence, when the key is depressed, through the spring 88, wire 90, contacts 38, 37, contacts 81, 80 to the tip of the calling-plug. The other terminal of the test winding is connected by wires 93, 86', 84 to ground. The test is made in the usual way. The spring 41, although shown detached from the springs 42, 44, is one of the springs of the listening-key.