Patent GB-190718163-A (GB)
Title: Improvements in Automatic Telephone Exchanges
Filed: 1907-08-10
Granted: 1908-08-10
Abstract: 18,163. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Aug. 10. Telephone systems.-In automatic - exchange telephone systems of the kind in which each subscriber has at the exchange an auxiliary switch which automatically selects an idle selector switch, separate holding-on windings are provided for the line-relay, the auxiliary switch, and the selector-magnets. The windings are energized during a conversation between two subscribers, and serve, in the case of the switches, instead of release-magnets, the switches being automatically returned to zero when the holding-on windings are deprived of current by the holding-up of the calling subscriber's receiver. The circuits of the holding-on windings are completed by damped switches during the pause following the rapid impulses which set the selectors, and these damped switches may also connect the speaking lines of one selector with those of the following selector only after the first selector has ceased working. In the final selector or connector switch, the damped switches which connect the speaking lines may first traverse test contacts, and also contacts which connect the called subscriber with a ringing generator. Fig. 1 shows the arrangements for a very small exchange. When the calling subscriber removes his receiver, current flows through both the calling relays 1<a>, 1<b>, which close a circuit from the battery 5 through the magnet 6 of the auxiliary switch 7 and the interrupting contact 9. The switch arms 10, 10<a>, 10<b> are thus automatically rotated until the arm 10 engages the earthed contact c<3> of an idle selector 12, thus completing a permanent circuit through the magnet 6, and preventing further actuation of the switch 7. The prolonged actuation of the armature 8 closes the contacts 6<c>, 6<d> of the damped switch 6<a>, thus connecting the magnet 6 directly to ground, so that the switch 7 is not affected by a subsequent movement of the switch 11. The subscriber's impulse sender 14 is so constructed that, whire the circuit of the a - line is interrupted to send the selecting impulses, the b-line is directly earthed until the switch arm 15 has again connected the a-line to the telephone &c. The selecting impulses pass over the a-line and through the arm 10<a>, contact d<3>, and magnet 17 of the selector, which thus brings the arms 19<a>, 19<b> on the contacts of the desired subscriber. Actuation of the magnet 6 by the interruption of the current through the relay 1<a> is prevented by the continued excitation of the relay 1<b>. During conversation, a holding-on current flows through the magnet 17 and relays 1<a>, 1<b>, and when this current is interrupted by the hanging-up of the receiver, the selector 12 returns to zero. Fig. 2 shows a larger installation for about one hundred subscribers. When the calling subscriber T<1> removes his receiver, current flows from the grounded contact c<o> through the arm 10, battery 25, magnet 26, subscriber's apparatus, relay 27, and the battery 28 to ground. The magnet 26 attracts its armature 29, moving the switch arms 10, 10<a>, 10<b> of the auxiliary switch 7 through one step. The switches 11 of the selectors 36 which are in use are connected as shown to the interrupter 37, so that the circuit of the magnet 26 is repeatedly interrupted until the arm 10 rests on the grounded contact of an idle selector. The prolonged attraction of the armature then allows the damped switch arm 33 to engage the contact 34, thus completing a circuit from the earthed battery 28 through the contact 34, 33, winding 32, and contact 31 (closed by the relay 27) to ground. The holding - on winding keeps the armature 29 attracted, and prevents further actuation of the auxiliary switch by the a-line impulses for operating the group selector 36. The calling subscriber then earths bis a-line a number of times corresponding to the tens' numeral of the desired subscriber, the resulting impulses energizing the magnet 39 and stepping round the arms 48<a>, 48<b>. The relay 42 is continuously energized by the grounding of the b-line. During the pause that follows these impulses, the prolonged attraction of the armature 40 allows the damped switch 50 to close contacts 51, 52 in the circuit of the bolding-on winding 46, and also contacts 53, 54 and 55, 56 completing the connexion of the speaking lines a', b<1> to the switch arms 48<a>, 48<b>. The selection of the units' numeral of the desired number is effected by the individual selector in the same manner as the tens' numeral is selected by the selector 36. During conversation, the magnets 26, 39 and the relays 27, 42 remain in circuit, but when the receivers are hung-up these circuits, and those of the holding-on windings, are broken and the switches return to their zero position. Fig. 3 shows the first selector of an installation for ten thousand subscribers, in which the first selectors consist of switches of the Strowger type, such as is described in Specification No. 2499, A.D. 1907. Assuming that the arm 10 of the auxiliary switch 7 has found an idle selector, the calling subscriber earths his a-line a number of times equal to the thousands' digit of the required subscriber, the construction of his impulse sender being such that his b line is continuously earthed. The magnet 76 is thus repeatedly energized and raises the wipers 75<a>, 75<b>, 75<c> to the desired horizontal row of contacts. During this movement, the current over the b-line energizes the relay 84 and opens the contact 86, but when the a-line impulses are over, the impulse-sender is arranged to earth the a-line for a short time, the b-line being at this time disconnected from earth. Under these circumstances, the magnet 76 locks-up through the contact of a damped switch not shown in Fig. 3, and completes at contact 81 the circuit of the rotary-magnet 87, which moves the testing-wiper 75<c> on to the first contact in the selected row. If the corresponding selector is engaged, its test contact is earthed through the interrupter 37, and the magnet 87 is thus intermittently energized until the wiper 75<c> engages the directly-earthed contact of an idle selector. The magnet 87 is then energized sufficiently long to close a holding-on circuit by means of a damped switch not shown in Fig. 3, but similar to that shown in Fig. 2. Fig. 4 shows the means for rendering the test-line of an engaged subscriber busy, and also the means for testing and ringing-up a desired subscriber. The calling subscriber is assumed to have been connected by the auxiliary switch or group selector to the individual selector 97. When the calling subscriber lifts his receiver or operates his impulse-sender, current passes through the winding 92 or 93 of a balanced relay, which attracts its armature 94, thus earthing the subscriber's test line 95. The a-line impulses energize the magnet 76 and move the wipers 75<b>, 75<b>, 75<c> to the desired contact. As soon as the magnet 76 has ceased acting, the three damped switch-arms 98, 99, 99 begin to move towards the contacts 100, 101, 102, 103. If the subscriber T<2> is disengaged, the arm 98 engages the contact 101, thus grounding the test line 95, and at the same time completing a circuit through the winding 105 of the balanced relay of the subscriber T<2>. The winding 105 being more powerful than the windings 92, 93, the subscriber T<2> is prevented from calling any other station. In the meantime, the arms 99 have passed over the long contacts 102, thus connecting the ringing generator 106 to line, and finally have completed the speaking circuits through contacts 103. If the subscriber T<2> is engaged, his test line 95 is earthed, and the arm 98, passing over the contact 100, completes the circuit of the cut-out magnet 108, which operates the switch arms 110 to disconnect the magnet 76 and at the same time connects a buzzer 111 to the calling subscriber's leads. The movement of the switch 110 also completes the circuit of the switch 116, the armature of which prevents the return of the switch 110, thus maintaining the connexion of the buzzer to line until the calling subscriber hangs up his receiver. The attraction of the armature 109 closes a holding- on circuit for the magnet 108 through the switch 113, which is grounded until the selector 97 has almost returned to zero.