Patent GB-190909055-A (GB)
Title: Improvements in Semi-automatic Telephone Exchanges.
Filed: 1909-04-16
Granted: 1910-04-18
Abstract: 9055. Siemens Bros. & Co., [Siemens & Halske Akt.- Ges.]. April 16. S e m i - automatic exchange systems. - In a semi-automatic exchange telephone system, or in a manual exchange system in process of transformation into a purely automatic system, a calling subscriber is connected by a preliminary selector to a selector or connector the leads of which are brought into connexion with an operator's station by means of an automatic switching-device, and are retained in connexion only during the time occupied by the operator in ascertaining the desired connexion and in transmitting the necessary sequence of impulses to select the subscriber wanted, t h e remaining operations such as testing, ringing, &c. being performed automatically by the selector in the usual way. The invention is described as applied to a system for one hundred subscribers in which each subscriber has at the exchange a preliminary selector, Fig. 1, which automatically selects the leads a<1>, b<1>, c<1> of an idle connector of the Strowger type. The leads of the various connectors are connected to the fixed contacts of the service-selector DW, Fig. 3, which, as soon as a connector is engaged by a calling-line, connects that connector to an operator's station Z, provided with a telephone set n, an annunciator q, and an impulse-sender represented by the keys T<a>, T<b>, and switch h. Preliminary selector. When a subscriber No. 33 removes his receiver, current passes through the normally-closed contacts of the cut-off relay T<33> and both windings of the call-relay R<33>, which closes the circuit of the actuating-magnet D<33> through an interrupter U', Fig. 3. After the first movement of the switch VW<33>, the contact i<33> brings the magnet D<33> into another circuit over the normal contact of spring t<3>, the magnet being thus independent of the call-relay R<33>. The stepby-step rotation of the selector continues until the leads of an idle connector are reached, whereupon current passes from the middle of the battery G through the lead m, contact r', winding v of cut-off relay T<33>, test lead c', resistance w<1>, Fig. 2, contact b<4>, and interrupter U' to earth, the excitation of the relay T<33> disconnecting the relay R<38> and the magnet D<33>. A holding-on circuit for the relay T<33> is also completed from the positive terminal of the battery G through the contact i<33>, spring t<3>, winding v, test lead c', resistance w<1>, Fig. 2, and contact b<5> of the relay B, now energized, to earth. As this circuit includes' the whole of the battery G, the potential in the test lead c<1> is such as to prevent the excitation of the cut - off relay of any other preliminary selector when its test-wiper engages the lead c'. Connector. As soon as the auxiliary switch rests on the contacts of an idle connector, current flows from the positive pole of the battery G, Fig. 3, through the relay A, Fig. 2, winding q<1> of a differential relay X, lead a<1>, contacts of switch VW<33> and of relay T<33>, sub-station apparatus, lead b<1>, winding q<2> of relay X, and relay B to earth. The relays A, B remain energized throughout the connexion, but the relay X is not energized at this stage. The relay B completes a circuit from the battery G through the interrupter U', Fig. 3, over the contact b<4> of relay B, contact f<1>, closed when the switch w is at zero, lead g, and the magnet D' back to the battery. The selector DW is thus stepped round until its third wiper engages the lead c<1> of the connector LW<1>, whereupon current flows from the battery G over contact f<2>, closed when the switch w is at zero, contact a<4> of relay A, contacts u<1>, x<1>, shunting the relay U, and lead c', to ground through the relay V, which at once cuts off the magnet D<2>, bringing the service selector to rest, and continues the leads a<1>, b<1> through the magnets A', B' to the operating station Z. The operator's station and the connector are now connected in parallel to the calling-station. In response to the call-signal q, the operator turns the switch h to contact 2, ascertains the desired connexion, and then moves the switch h to contact 3. This closes a new circuit, by which current passes from the battery G through the relay A, winding q<1>, lead a', contact v<1>, magnet A', and switch h to earth, thereby increasing the current through the winding q<1> and simultaneously decreasing that through the winding q<2>, so that the relay X is energized and closes at x<2> a circuit from the positive pole of the battery through the resistance w<2> and from this point (1) over relay B to earth and (2) over winding q<2>, lead b<1>, contact v<2>, relay B', lead bz, signal q and contact 3 to earth. By opening the contact x<1>, the relay X brings the relay U, hitherto short-circuited by the contacts x<1>, u<1>, into the existing circuit of the relay U. The excitation of relay U (1) throws over contact u<1> so that the battery is connected directly to the relay U, thus rendering. the circuit of the relays U, V independent of the contacts f<2>, a<4>; and (2) opens the contacts u<3>, u<4> so at the calling-station is cut off from the connector, which is now connected only to the operators station. The desired subscriber is selected by depressing the key T<a> so as to raise the connector w, opening and closing the contact 3, and then again depressing the key T<a> to rotate the connector Finally, the service-selector is disconnected from the connector leads by the depression of the key T<b>, opening the circuit of the relay B<1>, which breaks the circuit of the relays U, V. Specifications 6875/10 and 6964/10 are referred to.