Patent GB-190517380-A (GB)
Title: Improvements in Telephone Systems.
Inventor: JACOBS CHARLES MARK
Filed: 1905-08-28
Granted: 1906-08-23
Abstract: 17,380. Jacobs, C. M., and Nicholson, A. H. Aug. 28. Telephone systems.-Relates to automatic telephone exchange systems, and in particular to a combination of automatic with manual working of such a nature that certain groups of subscribers in constant need of intercommunication can effect the necessary connexions between one another by automatic means, each subscriber being also in a position to call the exchange operator if necessary. The selection at the exchange is effected by means of relays, which may be arranged as described in Specification No. 146, A.D. 1902, so as to respond selectively to certain combinations of positive and negative currents transmitted through the two line-wires and earth. For the purpose of transmitting the necessary combination of currents to the exchange, the subscriber may make use of switches such as are described in Specification No. 23,255, A.D. 1902. The Figure shows in incomplete diagrammatic form the connexions at the exchange of three subscribers A, B, C. The switch for transmitting the selecting-currents from station A is not shown, and the relays or groups of relays a, a<1>, a<2> associated with each subscriber's line are only indicated symbolically. The relay a<2> is employed for giving a signal to the exchange operator ; each of the remaining relays a, a<1>, &c. is employed for establishing the connexion between the calling subscriber and an individual one of the remaining subscribers. The operation of the system is as follows : Assuming that subscriber A is desirous of communicating with subscriber B, he transmits through the lines i and earth the combination of currents necessary to energize the relay a. The relay a closes a circuit from the main battery e through the contact f<5> of the line relay f of subscriber B and thence through the " suspense relay m, "local" " relay b, and cutout switch h. The tongue b<2> maintains the circuit of the battery e closed through the relay b and cutout switch h ; the tongues b<3>, b<4> connect the linewires i of the subscriber A directly with those of subscriber B ; the tongues b<1>, b<5> prepare two parallel circuits from the battery g through the two line relays f to earth, these circuits not being actually closed until the tongue of the suspense relay m falls back after the excitation of the selecting-relay a has ceased. The line relays f break the selecting relay circuits at f<5>, so that no other subscriber can call either of the connected subscribers ; moreover, the tongues f<1>, f<4> out off both the subcribers from all their own selecting-relays. The tongues f<1>, f<4> close parallel circuits from the battery g, each including one line-wire, the subscriber's instrument, the other line-wire, the cutout switch h, and earth. At the conclusion of the conversation, each subscriber reverses the current in the line by means of a magneto-machine, the electromotive force of which opposes the battery g, and thereby opens the holding circuit of the relay b at the cut-off switch and restores all the relays to the normal position. If the exchange operator is to be called, the relay a<2> is energized, the relay c being thereby excited and the circuit of tho lamp d closed through the relay itself. The lamp remains ignited until the operator inserts a plug in the jack k and energizes the relay f. The operator's speaking-lines are connected with those of the subscriber through the relay tongues f<2>, f<3>. The subscribers' calls are earth-connected high - resistance trembling bells l which are rung from the battery g at both stations as soon as the relays f are excited, and ring until the receivers are removed from the hooks. The suspense relays m may be dispensed with, and the relays a may directly operate the contact-tongues b<1>, b<2>, &c.