Patent GB-190916643-A (GB)
Title: Improvements in Telephonic Sub-station Switching Systems.
IPC: H04M9/00
Filed: 1909-07-16
Granted: 1910-01-06
Abstract: 16,643. Aitken, W., and British Insulated & Helsby Cables. July 16. Intercommunication systems.-The selecting levers or keys are retained in their depressed position by means of a magnet, the circuit of which is broken when the receiver is hung up, so that the levers or keys return to their normal positions. The system is so organized that when a complete connexion is established the magnets at the calling and called stations are bridged across the talking- circuit and serve as impedances through which the microphones are supplied with current. Fig. 5 shows the invention applied to a system in which each station can obtain connexion with the exchange leads E<1>, E', the selecting-switches a, 2, 3, 4, and a<1>, 1, 3, 4 &c. being provided with additional sets of contacts for effecting the exchange connexions, besides the contacts 1, 2, 3, 4 for the other intercommunicating stations. When the selecting-switch is moved to connect up to the exchange contacts at the left-hand station in Fig. 5, the contacts 1-2, 3-4, &c. are opened but contacts 1-3,5-7, and 9-10 are closed. The other two stations are connected in parallel to the exchange leads so that the contacts 2, 6 are not required. If subscriber I wishes to call subscriber III, he removes his receiver f, depresses the battery reversing-key j, and closes the contact 3 of the selecting-switch a, 2, 3, 4, whereby a calling-circuit is established from the battery k through the key j, magnet a, contact 3, line-wire 33, contact 12-13 at station III, and bell h<4> shunted by the resistance h<5> back to the battery. In order to learn what station is calling him, the called subscriber removes his receiver and depresses a key m<5>, thereby temporarily completing a talking-circuit over the common service-wire 44 from the microphone d' at station III through the key m<5>, wire 44, key m (depressed by the calling subscriber), microphone d, inductive coil e, contacts 7-8, 3, wire 33, and contacts 12-11, 4-3, back to the microphone. After learning that he is being called by station I, subscriber III closes contact 1 of his selecting-switch a<2>, 1, 2, 4, thereby completing the talking circuit from the microphone d<2>, coil e<2>, contacts 7-8, 1, line-wire 11, contacts 2-1, 4-3, microphone d, coil e, contacts 7-8, 3, line wire 33, and contacts 12-11, 4-3, back to the microphone d<2>. The microphones are supplied with current through the magnets a, a<1> which serve as impedances and are bridged across the talking-circuit as shown in Fig. 3. The selecting- switches are released when the circuit of the magnets a, a<1> is broken by hanging up the receivers. If subscriber I wishes to call the exchange, be moves his selecting-switch to actuate the springs E, so that contacts 1-3 and 5-6 are closed as stated above, the talking-instruments being thus connected to the exchange-lines E', E<2>. The opening of contacts 1-2, 5-6 prevents other stations from calling the exchange, while the closing of contact 9-10 energizes indicators q, q<1>, q<2> at the other stations, thus denoting that the exchange line is engaged. The closing of contact 7-8 of the hook-switch and contact 10 11 of the selecting-switch completes a circuit for the magnet a, which holds the switch in the exchange-position until the receiver is hung-up. Calls from the exchange are received by the annunciator n at station II. The operator at this station moves his selecting-switch into the exchange-position, and after learning the subscriber wanted calls up that subscriber in the manner previously described, at the same time depressing the key p to short-circuit the condenser o, in order to prevent the ring-off signal being given at the exchange. The subscriber wanted then moves his switch into the exchange-position and is then connected to the exchange as before. In a modified system for exchange and local service, the selecting- switches shown in Fig. 5 are replaced by a selecting-lever adapted to be moved over the linecontacts without making contact therewith until it is depressed when an iron boss on the lever bridges the poles of an electro-magnet. The arm is thus retained in contact with the stud during conversation but is released when the circuit of the magnet is broken on hanging up the receiver. In this system, connexion with the exchange is obtained by means of an independent switch, which is returned to its normal position mechanically by the movement of the switch-hook when the receiver is hung up. The battery-reversing key j, Fig. 5, may be similarly released. An additional pair of springs associated with the hook-switch short, circuit the receiver when it is on the hook, thereby rendering it impossible for a subscriber to overhear another conversation by manipulating the switchhook very slightly. Specification 15,818/08 is referred to.