Patent GB-238644-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q1/446
Filed: 1924-06-05
Abstract: 238,644. Automatic Telephone Manufacturing Co., Ltd., and Saville, W., (Automatic Electric Co.). June 5, 1924. Automatic exchange systems.-A tone current, particularly useful for applying to a subscriber's line if he fails to replace his receiver after conversation, is automatically varied in intensity in any desired manner, preferably from a minimum to a maximum value. Two modifications are described in which a periodically varying tone current is applied to a subscriber's line from a test clerk's position, the tone current always being at its minimum intensity when initially connected up. In the arrangement shown in Fig. 1, two leads 45, 46 from a test clerk's howler key K, are connected to the line of the subscriber who has failed to hang up. On the operation of the key K, a circuit is closed over the secondary windings of a transformer R and the subscriber's line for a relay 3, which energizes a self-interrupting relay 2, closes the tone currents circuit over the arm 33, 34 of a stepping switch C and the primary winding of the transformer R, and completes a circuit from an interrupter I to the stepping magnet 5 of the switch C. The tone circuit, which initially includes all the series resistances 24 - - 29, is interrupted at the armature 10 of the buzzer relay 2, and a tone current of minimum intensity is induced in the secondary winding of the transformer R and transmitted over the subscriber's line. The switch C is stepped round under the action of the interrupter I, and at every fifth contact one of the resistances 24 - - 29 is cut out of the tone circuit, thereby gradually increasing the intensity of the signal. When the subscriber hangs up, relay 3 relapses, closes the circuit of a supervisory lamp L, and opens the tone circuit and the stepping circuit of the switch C. If the switch C is not in the normal position, a relay 4 energizes over its upper winding and arm 22, 23, locks up over its lower winding, and closes a restoring circuit 18, 16, 22, 12 for the switch C. When the test clerk releases the key K, all the apparatus is restored to normal. If the subscriber fails to replace his receiver after a reasonable time, the test clerk may restore the key K, thereby de-energizing relay 3, which disconnects the tone and brings about the restoration of the apparatus as before. In the modified arrangement shown in Fig. 2, the test clerk inserts one plug P<1> of a double-ended cord into a jack J<1> associated with the first selector S to which the subscriber it is desired to warn is connected, and the other plug P into a jack J connected to the toneproducing apparatus. Since the calling subscriber's receiver is off its hook, the line and slow release relays A<1>, B<1>, are energized, and a relay A is energized over the grounded test wire 100. The relay A (1) locks up over armature 108, (2) connects the secondary winding of a tone transformer R<1> to the calling line, (3) energizes relay B which locks up and closes a point in the circuit of a supervisory lamp L<1>, (4) closes a circuit for the polarized howler buzzer HB, and (5) completes a stepping circuit for the magnet. DM of the switch C<1> from the interrupter I<1>. When the tone is first applied to the line all the resistances r - - r<4> are in circuit, but as the switch C<1> is advanced these resistances are cut out and the intensity of the tone rises to a maximum. When the wiper 138 reaches contact 139 the circuit of the magnet DM is opened and maximum tone remains on the line until the subscriber replaces his receiver, when the relays A<1>, B<1>, A de-energizes, the relay A disconnecting the tone. lighting the lamp L<1>, and closing a restoring circuit, for the switch C<1>. The test clerk removes the plugs P, P<1>, and all the apparatus restores to normal.