Patent GB-152702-A (GB)
Title: An improved automatic telephone system
IPC: H04Q1/18
Filed: 1919-04-23
Abstract: 152,702. Lenaghan, T. April 23, 1919. Automatic and semi-automatic exchange systems.-Groups of trunks and individual lines are selected by establishing a balance of electrical conditions, instead of by the customary use of numerical sets of impulses. In the system described, the calling subscriber cuts a variable amount of resistance into his line circuit for each digit of the wanted number, these amounts being recorded on registers at the exchange, and the selectors hunt under control of a differential relay, one winding of which is energized through a register resistance while the other is connected to the selector test circuit, so that the relay is de-energized and stops the selector when a trunk or line is found having a corresponding resistance in its test-circuit. Alternatively, however, the balancing-means may consist of inductances, the balancing-relay in this case comprising a reed which stops vibrating when high-frequency currents in the two circuits are in phase, or capacities may be used, the balancing-relay comprising a double coil suspended in a magnetic field so as not to be deflected when equal discharges flow through both coils. The invention is applicable to semi-automatic systems. Subordinate features of the system described include (1) means for operating the calling subscriber's meter a variable number of times, according to the exchange to which the called subscriber belongs; (2) selective means for the supply of ringing-current to party lines; (3) means for releasing an uncompleted or unanswered call after a certain time-interval; and (4) means for opening the connexion after a certain interval from the commencement of conversation. Construction of selectors. From the nature of the selective principle on which the system is based, the selectors may be constructed merely as hunting-switches. The selectors of each group are arranged side-by-side at front and back of a panel of terminals. Each selector comprises a power-driven worm-spindle M, Fig. 12, adapted to operate two or more wiper-sets G which are spaced apart so that each serves a row of 100 terminals, a selected wiper-set being put in circuit by a separate switch or relay. The wormspindle may extend the whole height of the panel, operating all the wiper-sets directly, or it may extend .only for the length of travel of the bottom wiper-set, the other sets being actuated by a rod Y which connects the carriers H<2>. When a selector is to be operated a shaft X is clutched to a primary power shaft and the wipers G rise over the terminals J owing to the engagement of a pin T in the worm. When the wipers reach a selectable set of terminals a magnet M4 is energized which disconnects the clutch 6. On the termination of the connection the magnet M<4> is deenergized, and the clutch 6 is re-engaged and continues the movement of the wipers until they reach the upward limit of their travel, when a bar N depresses a lug P under a catch Q, tilting a carriage H pivoted at H<1> on the carrier H<2> so as to lift the wipers G away from the terminals J, and allowing a spring U to disengage the pin T from the worm. The wiper-sets now fall by gravity to their bottom position, in which a pin V releases the catch Q, restoring the carriage H and re-engaging the pin T with the worm. The carriages H of the upper wiper-sets are tilted and restored in unison with that of the bottom wiperset by a rod Y<1>. The carriers H<2> move between guides K, which also carry conductors for supplying current to the wipers. The terminals J are formed with up-curved ends, as shown in Fig. 13, and with stamped holding-lugs J<2>, and are multiplied by cross-strips J. A rocker F<3>, under joint control of the magnet M<4> and pin V, operates a contact G<1>, which, in conjunction with a contact operated directly by the magnet M<4>, controls a relay for disconnecting the wipers during the release of the selector. The construction of the selectors and the method (described in the following paragraph) of keeping them ready for service at different levels of the panel, forms the subjectmatter of Specification 153,238. Method of starting the different selectors of a panel in rotation from their bottom position. When a connexion is to be made through a particular panel, a starting-relay 4, Fig. 14, is energized in series with the clutch magnets M<4> of all the selectors which are in their bottom position, and the magnets M<4> are de-energized in rotation by a commutator RG' geared to the driving-shaft. By this means the clutches of the different selectors are engaged in rotation and the wipers of the different sectors (except those engaged in existing connexions) are kept uniformly distributed over different levels of the panel, so that any set of terminals can be selected in a minimum time. Subscribers' number-sender. The numbersender, shown at the left of Fig. 6, is of the fingerdial type, with means for cutting variable amounts of a resistance 85 into the line circuit. The line circuit is normally closed (when the receiver is off its hook) through the contact-arm 29, contact 84, and stop 28<a>, and while the dial is being turned this short-circuit is maintained, the arm 29 being turned by the stop 28<a>. When the dial is released it is restored by a spring, opening the contact 84, 29, but the arm 29 is held by the pawl 31, and the line circuit is closed through a part of the resistance 85, arm 29, ratchet 30, and pawl 31. When the dial regains its normal position it trips the pawl 31, and the line circuit is opened until the arm 29 also has returned to normal. Operation of system shown in Figs. 6, 6<A>, 7, 7<A>, 8, and 9. A calling subscriber 20, Fig. 6, is connected bv a finding-switch WS1, HR<0>, &c., Figs. 6 and 8, to the register-controller shown in Fig. 8, and by a finding-switch TRLH to an idle first selector, consisting of a panel switch 12, Fig. 6<A>, and a switch WS3 for choosing a particular set of wipers of the panel switch. (The switch 1-2 shown at the right of Fig. 6 is for completing incoming calls.) The register controller first adjusts the balancing circuits by means of switches RE1, RE2, adding resistance to the calling line circuit until it comes up to a standard value, and then records the successive digits, as they are dialled, on resistance registers RE4, RE5, &c. These registers are mechanically connected with switches RE4A, RE5A, &c. which control the operations of the selectors. The switch RE4A controls the switch WS3, Fig. 6<A>, to select a set of wipers serving the exchange to which the wanted subscriber belongs, and the switch RE5A controls the switch 12, Fig. 6<A>, to move the selected wipers to an idle trunk of a selected subgroup of the trunks to this exchange. The twowire inter-exchange trunk is shown extending from Fig. 6<A> to Fig. 7<A> and terminates in a selector WS5, 14. A register controller, Fig. 9, at the distant exchange is now connected to this trunk by a switch WS4, RS6, Figs. 7<A> and 9, and the records RE6A, RE7A, &c. of the remaining digits are transferred over the two-wire trunk to registers RPC, RPD, &c., the trunk circuit having first been balanced by switches RPA, RPB operating similarly to the switches RE1, RE2, Fig. 8. The registers RPC, RPD, &c. are mechanically connected with switches RPCA, RPDA, &c. which control the operations of the selectors at the second exchange. The switch RPCA controls the switch WS5, Fig. 7<A>, to select one of the wiper-sets of the selector 14, and the selected wipers are moved under control of the switches RPDA, RPDB, &c. to find an idle trunk of a selected group of trunks. The connector 1-2, Fig. 7, in which this trunk terminates is then operated, under joint control of the switches RPEB, RPEC, &c. and RPFB to find the wanted line. The switches RPEA, RPFA, &c. are provided in case the connexion must be extended to a third exchange, in which case the records of these switches are transferred in the same way as between the first and second exchanges. For party-line working, selected harmonic ringing-current is supplied by the register switch RPGB. When the call is answered, the calling subscriber's meter is variably operated under control of the register switch RE4B, Fig. 8, and the registercontrollers, Figs. 8 and 9, at the two exchanges are then released. It should be noted that the selectors TRLH, Fig. 6, and 1-2, Fig. 7, have only two sets of wipers, one or other of which is put in circuit by the energization or non-energization of relays M5, M33, so that wiper-selecting switches are not needed for these selectors. The circuits of the register-controller, Fig. 8, are changed, from stage to stage of its operation, by a pilot switch CSC, CSD, &c., and those of the register-controller, Fig. 9, by a similar switch RSA, RSB, &c. A fuller description will now be given of the operation of the system shown in these Figures. Connexion of calling line, Fig. 6, to registercontroller, Fig. 8. The energization of the line relay M1 energizes a group relay M3, which energizes M49, Fig. 8, to start the finding switch HR‹ &c., and puts a selectable potential on terminal 48 of switch WS1, so that M37 is energized when this terminal is reached and arrests the switch WS1. When the switch HR‹ &c. finds the calling line, M39 is energized over the wiper H and stops the switch by energizing M38, at the same time short-circuiting part of its winding to render the calling line non-selectable to other register-controllers, and energizes M40, which locks M37 and energizes M2, Fig. 6, which disconnects the line relay M1 from line but keeps it locked. Balancing the calling, line. The two windings of the differential relay M50, Fig.. 8, are now energized, one through a standard resistance R16, exceeding the highest line resistance, and the other through the switch RE1 and the calling line, and a magnet M46 is energized to rotate the switch RE1. When