Patent GB-190929963-A (GB)
Title: Improvements in and relating to Automatic Telephone Systems.
Filed: 1909-12-22
Granted: 1910-12-22
Abstract: 29,963. American Automatic Telephone Co., and Goodrum, C. L. Dec. 22. Automatic exchange systems.-In systems of the kind in which groups of subscribers' lines are connected to the fixed contacts of one or more rotary switches or callfinders, the connexion between the wipers of the callfinder and the wipers of the associated selector or connector is broken during the operation of the callfinder by means of a relay associated with the operating- circuit of the latter. The subscribers' lines may be multipled to two callfinders in relatively reverse order in such a way that when a call is made both finders are started and cause their wipers to pass in reverse order over the line terminals, thus reducing the travel of the finder necessary to find a given line. The invention is described as applied to a system in which the selecting-impulses are sent over a complete metallic circuit, no earth connexions being used at the substation. Construction of switches. Fig. 3 shows a form of switch adapted to serve, with slight modifications, either as a callfinder or as a connector. A central shaft 7 carries a set of three or four wipers 10 having contact segments 10<a> engaged by a set of fixed brushes 10<b>. The wipers 10 are rotated over the fixed contacts 100 by a ratchetwheel 6 and a pawl 21 pivoted to the upper end of the armature lever 22. The pawl 21 has a projection 32 by means of which it and the detent 30 can be withdrawn from the ratchet 6 when the releasing-magnet 36 is energized. A pin 45 on the ratchet closes a contact 41-43 when the switch is in its normal position, contact 41-42 being closed at other times. Call-finder. Two sub-stations A, D are shown in Fig. 6 connected to the contacts, of the call-finder F, the wipers F<1>, F<2> of which are connected to the wires 4<A>, 5<A> leading to the wipers of a connector C, Fig. 7. When the subscriber A removes @@s receiver, his line-relay A<5> is energized over the contacts of his cut-off relay A<6> and thus earths the common starting-wire f at the same time removing the earth connexion from his terminal f <16> on the finder F. The grounding of the wire f<5> completes the initial circuit of the power magnet 27<F> through the contact f<43>, f<41> and also the circuit of the slowrelease relays F<3>, F<5>. The magnet 27<F> moves the wipers of the finder one step, thus opening the contact f<43>, f<41> and bringing the magnet 27<F> under the control of the wiper f<18>, its circuit including a wire f, armature f<13> of the relay F<5>, and the wire f<12>. By attracting its armature f<3>, the magnet 27<F> makes and breaks this circuit, and thus moves the wipers step by-step until the wiper f<18> engages the unearthed contact f<16> of the calling line, whereupon the circuit is permanent'y broken. The relays F<3>, F<5>, which are also dependent upon the wiper f<18>, are thus de energized, and the armature f<10> in falling back completes the circuit of the calling - subscriber's cut -off relay A<6>, which de-energizes the line-relay A<5> so as to prevent the arrest of other finders upon the terminals of the subscriber A. The armature f<23> prepares the circuit of the release magnet 36<F> as described later. The relay F<3> disconnects the wipers F<1>, F' from the leads 4<A>, 5<A> during the movement of the finder, thus preventing interference with other engaged lines, the multipled terminals of which are passed over by the wipers. The relay F<4>, connected in parallel with the release magnet 36<F> has a similar function during the return movement of the finder. Connector. When the armatures of the relay F<3> fall back, the relays 41<A>, 51<A>, Fig. 7, of the connector are brought into circuit over the leads 4<A>, 5<A>, wipers F<1>, F<2>, and the sub-station apparatus. The relay 51<A>, which is sluggish in action, by attracting its armatures c<4>, c<13> prepares the circuits of the actuating-magnet 27<c> and of the slowacting relay C<3>, the circuit of the latter being initially completed over the normally-closed contact c<43> and afterwards over the armatures c<18>, c<22>. When the impulse-transmitter A<4> is operated, the relay 51<A> is unaffected but the quick-acting relay 41<A> closes the circuit of the magnet 27<c>, thus moving the wipers to the contacts of the desired line. When the interruptions of the line-circuit cease, the circuit of the relay C<3> is permanently broken at c<21>, and its armature c<9> in falling back completes the circuit of the cut-off relay B<6> of the called subscriber. Microphone current is supplied to the calling subscriber through the relays 41<A>, 51<A>, and to the called subscriber through the coils 4<B>, 5<B>. Supply and control of ringing-current. The means for controlling the supply of ringing-current are shown in Fig. 9, in which several of the details of Fig. 7 are omitted for the sake of clearness. When the relay C<3> is finally de-energized, its armature c<45> completes the circuit of the ringing- relay C<8> over the interrupter C<9> and armatures c<410>, c<45>, and at the same time the armatures 60<a>, 70<a> connect the wipers to the armatures 48<a>, 58<a> of the relay C<8>. The ringing-generator C<7> is thus intermittently connected to the called line when the relay C<8> is de energized. When the called subscriber removes his recaiver, the coil 5<B> receives current when the relay C<8> is next excited, and by attracting its armature c<33> closes a circuit for the relay C<8> independent of the interrupter C<9>, thus cutting off the ringing-current. Release. The release of both call-finder and connector are dependant upon the calling subscriber, being controlled by the relay 51<A>, Fig. 7. When the subscriber hangs up his receiver, this relay is de-energized and its armature 136 completes the two release circuits :-(1) for the release magnet 36<c> through an interrupter c<6>, contact c<24>, wire c<30> and contact c<42>-c<41> ; (2) for the release magnet 36<F> through an interrupter F<6>, Fig. 6, wire c<26>, contact c<24>, wires c<30>, c<31>, armature f<25>, and contact f<41>, f<42>. The release magnets are thus set in action and their circuit is maintained until the switches reach their zero position when the contacts c<42>-c<41>, f<41>-f<42> are broken. The release circuits are such that a switch is automatically returned to its normal position, in case for any reason it should be moved out of position, or in case the finder switch should fail to find a calling line it would continue to operate until it passed off the last contact when it would return to normal position. Duplicate call finders. In order to reduce the time taken by the call finders to select a calling- line, the lines may be connected in reverse order to the contacts of two finders, so that the switch which first reaches the calling line would connect itself up, while the other switch or switches would continue in operation to the end of the bank of contacts when it would be returned to normal by the release circuit previously described. When a larger number of call finders are allotted to a group of calling-lines, the means described in Specification 12,614/10 may be used to select an idle call finder ; or a distributing-switch may be used for the same purpose. Sub-station apparatus. To illuminate the subscriber's apparatus, and to indicate the absence of a fault therein, an incandescent lamp A<9>, Fig. 6, may be inserted in the line-circuit as indicated.