Patent GB-191219249-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-08-22
Granted: 1913-09-22
Abstract: 19,249. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Aug. 22 Semi-automatic exchange systems. - In a system in which subscribers are connected through an operator's cord-circuit and through automatic switches controlled by the operator, a signal 226, Fig. 2, for supervising the condition of the called subscriber's line is controlled at the connector I, Fig. 4, by means which vary the resistance in a two-wire trunk circuit 181, 180, the control being transferred to the third wire of the selector trunks F, E, Fig. 3, by a relay-set H, which serves primarily for repeating the impulses which control the switch I. The automatic switches E, F, I are of the type which are operated by sets of currentinterruptions in a metallic circuit. The suhstations A, A' are assumed to belong to manual and automatic sub-exchanges connected by twowire trunks to a main exchange. Line switch C, Fig. 1, and call signal. The line switch C and master - switch D are of the general type described in Specification 26,301/06, and the circuits are the same as in Specification 1418/10. When the subscriber A lifts down his receiver, the switch C extends his line to a trunk 98, 99 leading to a jack j, Fig. 2, thus energizing the relays 95, Fig. 1, and 106, Fig. 2. The relay 106 lights the call lamp 107. The operator inserts the plug p of a cord O in the jack and throws the key K to the left to connect her instruments S to enquire the wanted number. The connexion of the trunk 98, 99 to the jack j is completed by the relay 119, which is energized, together with the supervisory cord relays 28, 29, when the plug p is inserted. First and second selectors E, F, Fig. 3. The operator, having ascertained the wanted number, inserts the plug p<1> in the jack j<1> of a first selector E, and having thrown the key K to the right to connect her instruments to the trunk wires 130, 124, operates the impulsesender 140 to extend the connexion through the first selector E and a second selector F (the circuits of which are slightly simplified from those described in Specification 1298/10) to a two-wire trunk 181, 180 leading to a connector I serving the wanted subscriber. The line relay 55 of an impulse repeater H, which is connected in the outgoing end of this trunk, is energized and closes a circuit for the slowrelease relay 56, which connects ground G<15> to the third-wire circuit through the test-wipers 165, 38 of the selectors F, E and the sleeve of the plug p<1>. The selector release-relays 50, 153, which are branched from this circuit, are thus maintained energized. Impulse repeater H, Fig. 3, and connector I, Fig. 4. The energization of the relay 55 also completes a circuit through the relay 57 in series with a relay 68, Fig. 4, and the connector line relay 64, which energizes the slowrelease relay 187. The succeeding line-interruptions due to the operator's sender 140 deenergize the repeater 64, which energizes the private magnet relay 195 and vertical magnet 64<a>. As long as the impulses are passing the repeater relay 57 is short-circuited by a slowrelease relay 58. The vertical magnet 64<a> raises the wipers 61, 62, 63 to the required level, and the relay 195 and the private magnet 200 which it controls are then de-energized, and the side-switch moves to its second position. The final set of line-interruptions causes the energization of the rotary magnet 65<a>, which rotates the wipers to the terminals of the wanted subscriber A', and if the line 81, 82 is disengaged, the side-switch moves to its third position. Busy signal and release. If the line 81, 82 had been already engaged, there would be a ground connexion to the test-terminal 63, and the private magnet 200 would, upon the deenergization of the relay 195, be held energized over a circuit including a relay 208. The relay 208 in this case connects up the busy signal M to notify the operator, and closes a locking-circuit for itself and for the magnet 200, which locks the side-switch in its second position. The operator then notifies the calling subscriber and releases the switches by withdrawing the plug p<1>. Supply of ringing current. Assuming the wanted subscriber to be idle, and the sideswitch to have moved into its third position, the following changes take place (1) Ground G<20> is connected over the test-wiper 63 to energize the cut-off relay 220<a> of the line switch C<1>. (2) A circuit is closed through the sideswitch arm 196, ringer relay 67, springs of the back-bridge relay 65, and an interrupter 221, so that the relay 67 intermittently connects the ringing-generator L to the line 81, 82. (3) The circuit of the relays 64, Fig. 4, and 57, Fig. 3, is cut off by the side-switch arm 220 from the relay 68, and is continued only through the winding of a high-resistance relay 66, which was previously short-circuited by the relay 68. The relay 66 becomes energized. but its high resistance causes the deenergization of the relays 64, 57. The springs of the relay 66 provide a fresh circuit for the relay 187 to prevent its de-energization when the relay 64 falls back. When the subscriber A<1> lifts down his receiver, the back-bridge relay 65 is energized and cuts out the ringerrelay 67. The springs of the relay 65 also connect a resistance 236 in parallel with the high-resistance relay 66, in the circuit of the relays 64, Fig. 4, and 57, Fig. 3. The relay 64 is thus re-energized and now closes, through its own springs and those of the relay 65, a direct circuit through its own windings and through the relay 57, which also becomes reenergized. Supervisory signals. When the calling subscriber hangs up his receiver, the cord relay 28, Fig. 2, becomes de-energized, but the relays 29, 119 remain energized in series and the lamp 30 is thus lighted. The supervisory lamp 226 of the called subscriber is controlled by the cord relays 33, 34. The relay 33 is energized in series with the repeater relay 55, Fig. 3, when the key K is restored at the conclusion of the impulse-sending operations. The relay 34 is connected to the sleeve circuit 139, which extends through the selector test-wipers 38, 165, and from which the selector release relays 50, 153 are branched to battery. This circuit is connected to ground G<15> at the repeater H, either directly or through a resistance 175, according to whether the relay 57 is energized or not, and in this way the condition of the relay 34, and consequently of the supervisory lamp 226, is made dependent on the relay 57, the relay 34 being short-circuited when the relay 57 is de-energized. It has been shown in the preceeding paragraph that the relay 57 is deenergized when the connector side-switch moves into its third position (thus lighting the lamp 226) and re-energized when the called subscriber replies (thus extinguishing the lamp 226). When finally, the called subscriber hangs up his receiver, the back-bridge relay 65 is de-energized and cuts the high-resistance relay 66 again into circuit with the relays 64, 57, thus de-energizing these relays and causing the re-appearance of the signal 226. Release. The line-switch C, Fig. 1, is released in known manner when the calling subscriber hangs up his receiver. The release of the switches E, F, Fig. 3, and I, Fig. 4, ensues when the operator removes the plug p<1>, the consequent de-energization of the repeater relays 55, 56 serving to cut off ground G<15> from the test-wipers, 165, 38 and release relays 153, 50, and to open the trunk 180, 181, whereby the relay 66 and release relay 187 are deenergized. Trouble signals. The relay 68, Fig. 4, is common to a number of connectors and is in circuit with the line relays 64 as long as the side-switches are in first or second position. Normally it is only intermittently energized, but if trunk wires such as 180, 181 should become crossed, it is energized continuously, a fact which is notified to the attendant bv the continued glowing of a lamp 185.