Patent GB-191208997-A (GB)
Title: Telephone Exchange Systems.
Inventor: JOHNSON MORTON LEWIS
IPC: H04Q5/00
Filed: 1912-04-16
Granted: 1913-02-20
Abstract: 8997. Johnson, M. L. April 16. Automatic exchange systems; party-line syst e m s ; t e l e p h o n e s , mounting and supporting.-In a lock-out system for party lines, the stations are provided with magnets, which, under the influence of the current normally impressed on the line, permit the connexion of the telephone instruments to the line, s w i t c h i n g mechanism being provided at the exchange to limit the line, when in use, to current to which the magnets are not responsive. As described, the magnets are polarized, and when a party-line station calls, the connexion of the battery with the line is reversed; this reversal is not effected when the station is called, but the connexion of the telephone across the line so lowers the potential that it is insufficient to energize the other magnets. In connexion with automatic systems, harmonic ringing currents for reverting calls are obtained from special levels of contacts on the first selector, and the subscribers' ringing keys act to introduce a high resistance so as to allow the called station to answer. Fig. 1 shows the party-line. When the receiver is removed, the circuit of the polarized magnet 17 is closed at 16, and, if no other station is in use, the armature 19 is attracted, releasing the lever 12. The lever 12 then rises, closing the circuit of the instruments at 7, 8 and releasing the impulse transmitter 4. Fig. 2 shows automatic exchange circuits, which are of a known type. When a subscriber removes his receiver, the circuit closed through his magnet 17 passes from line wire 1 through a switchspring 25 to earth, and from the wire 2 through the switch-spring 24 and winding 23 of line switch to the battery 3. The armature 26 is then attracted, connecting the winding 28 to earth through the switch-spring 27, so attracting armatures 29, 30 moving switch - springs 24, 25 and closing contacts 31, 32, 38. The line wires 1, 2 are then connected through contacts 31, 32 and coils of relay 36 to the opposite poles of the battery 3, so that interference by other stations is prevented, since their magnets 17 will not be actuated if the receivers are removed. For reverting calls, four levels of bank contacts, 44<1>, 45<1>, 46<1>, 44<2>, 45<2>, 46<2>, &c., on the selector are arranged to furnish ringing currents of the proper frequencies, the selector wipers being shown engaging contacts 44<1>, 45<1>, 46<1>. When an idle set of contacts at the proper level has been found, relays 48, 49 are energized. When the calling subscriber presses his key 42, the introduction of the resistance 43 causes the relay 48 to release its armature, the relay 49 remaining energized, so that the circuit of the ringing relay 50 is prepared over the relay contacts 56, 53 and is intermittently closed at 51 by the cam 52. When the ringing relay 50 is energized, the circuit of the relays 54, 57 is maintained over a contact on that relay. As will be seen, the normal polarity of the lines is re-obtained in this case, as well as when a station is called, in order to allow the station to answer.