Patent GB-191229355-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-22
Abstract: 29,355. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Automatic exchange systems. - Relates to means for signalling exchange attendants in case of trouble in the circuits, and especially for signalling a main-exchange attendant in case of trouble at a sub-exchange or district office. Separate signals are provided for serious and minor troubles. The main-exchange attendant is also provided with means for testing the efficacy of the ringing-generator at the subexchange. The invention is described in connexion with a system in which selective switches of Strowger type are controlled by impulses which pass from ground at the sub-station over one or other of the subscribers' line wires. Each sub-exchange is equipped with line-switches C, Fig. 2, controlled by a master-switch E, and connectors H, Fig. 4, and the main exchange comprises first and second selectors D, F, Fig. 3. The operations by which a subscriber A, Fig. 2, connects himself to a subscriber A<1>, Fig. 4, will first be described, and then, in the final paragraph, the signalling and testing arrangements. Subscriber's impulse transmitter. This is the same as that described in Specification 1420/10. When the dial is operated, it first sends an impulse over the ' rotary ' wire 35 to operate the subscriber's line switch; then, as it returns, it sends a pre-determined number of impulses over the ' vertical ' wire 34, to give the selector shaft the desired degree of movement; and finally it sends another impulse over the ' rotary ' wire 35 to trip the selector side-switch to its next position. Line-switch C, and master-switch E, Fig. 2. These operate generally in the manner described in Specifications 26,301/06 and 1420/10. The preliminary impulse over the line 35 passes through the trip-magnet 44, which trips the line-switch plunger to close the contacts 63, 69, 68. 65, connecting the line 34, 35 to the preselected idle trunk 93, 94. (The master-switch magnet 71 is included in the circuit of the trip-magnet 44, but owing to its low resistance is not energized.) The closure of the contact 69 completes a circuit through the release magnet 45, the master-switch bank-contact individual to the trunk 93, 94, and the lower winding of a relay 73. The magnet 45 being of low resistance is not affected, but the relay 73 responds and closes the circuit of the self-interrupting masterswitch magnet 71, which moves the plungers of the untripped line-switches until they come opposite to the terminals of the next idle trunk, whereupon the relay 73 de-energizes. First selector D, and second selector F, Fig. 3. The vertical impulses representing the first digit pass over the wires 34, 93 to the relay 113, which controls the vertical magnet 99, which steps up the shaft wipers 109, 110, 111 to the desired level. The succeeding rotary impulse over the wires 35, 94 energizes the relay 114, and the private magnet 102 controlled by the relay 114 trips the side-switch to its second position. The wiper 105 now closes a circuit through the self-interrupting rotary magnet 100, which presses down the armature of the private magnet 102 and rotates the shaft wipers 109, 110, 111 to the first set of terminals. If the first trunk is busy, so that the terminal on to which the test wiper 111 moves is grounded, a circuit is closed through the release relay 120 (which, being of low resistance, does not respond) and through the side-switch wiper 106 to the private magnet 102, the armature of which is therefore held in its forward position when the rotary magnet de-energizes, whereby the side-switch is prevented from tripping to its third position. The circuit of the rotary magnet 100 is therefore maintained over the wiper 105, and the shaft wipers are rotated a second step, the above test process being then repeated. Finally, when the ungrounded testterminal of an idle trunk is reached, the magnet 102 de-energizes and trips the side-switch to its third position, cutting out the rotary magnet, connecting ground through the low-resistance release relay 120 to the test wiper 111, and extending the connexion to the second selector F. The selector F operates, in response to the impulses representing the second digit, in exactly the same way as the selector D, and extends the connexion to the trunk 260, 261, which terminates in the connector H, Fig. 4, at the sub-exchange to which the wanted subscriber belongs. Connector H, Fig. 4. The impulses for the third digit pass through the relay 141, controlling the vertical magnet 143, which steps up the shaft wipers 138, 139, 140 to the desired level, and the succeeding rotary impulse energizes the relay 142, controlling the private magnet 145, which trips the side-switch to its second position. (The relay 153, energized in series with the line relays 141, 142, serves only in effecting the release of the connexion, and is without effect at this stage.) The rotary magnet 144 is now connected in place of the vertical magnet 143 by the side-switch wiper 149, so that the impulses for the fourth digit cause the shaft wipers 138, 139, 140 to be rotated to the terminals of the wanted subscriber. The succeeding rotary impulse energizes, as before, the rotary relay 142, the relay 153, and the private magnet 145. Busy test, signal, and release. If the wanted subscriber's line is engaged, a circuit is closed from his grounded test-terminal, through the shaft wiper 140, side-switch wiper 150, springs 319, 318, release magnet 146, and springs 286, 287 to battery, and the connector is released. In this case, when the calling subscriber presses the ringing-button 38, the vertical relay and magnet are energized and the shaft is raised a step so as to close the off-normal contact 164, whereby a busy-signalling device I is connected back to the calling line. The calling subscriber then hangs up his receiver, releasing the connexion as described hereafter. Supply of ringing-current. If the wanted subscriber's line is idle, the side-switch trips to its third position as soon as the concluding rotary impulse has ceased. The calling subscriber intermittently presses the ringing-button 38, which grounds the vertical side of the line so as to energize the relays 141, 153, which now control the ringing-relay 157, the side-switch wiper 149 being in its third position, and the relay 157 connects the ringing-generator K to the selected line. In the first non-ringing interval after the called subscriber has lifted down his receiver, the back-bridge relay 156 becomes energized and cuts back a supply of microphone current to the calling line by transferring the lower winding of the relay 153 from battery to ground. The relays 141, 142 are now energized, but the relay 153 is not energized, the effects of its two windings being opposed. Release. When the calling subscriber hangs up his receiver, both sides of his line are momentarily grounded at the springs 7, 8, 9, thus maintaining a circuit through the relay 141 and the upper winding of the relay 153 but short-circuiting the relay 142 and the lower winding of the relay 153. The relay 153 therefore becomes energized and open-circuits the back-bridge relay 156, the de-energization of which results in the lower winding of the relay 153 being transferred back from ground to battery. Current is thus re-established through the relay 142 and the lower winding of the relay 153 (but not now in such a direction as to oppose the effect of the upper winding), and for a moment all three relays 141, 142, 153 are energized, so that a release circuit is closed from battery, through the springs 287, 286, release magnet 146, springs 306, 305, wire 308, and the release relay 135 of the second selector F. The relay 135 closes a circuit through the release magnet 130 of the selector F and the release relay 120 of the selector D. The relay 120 energizes the release magnet 101, which in turn connects ground to the circuit 255 to energize the relay 256 controlling the magnet 45, which resets the line switch. When the springs 7, 8, 9 disengage, the various release magnets are de-energized and release the switches. Trouble signals and testing - arrangements. Trouble at a sub-exchange is signalled to the main exchange over a wire 177, which is connected to a point between two relays 175, 176, Fig. 3, which are connected in series across the main battery so as to be normally energized. In cases of serious trouble, due to the failure of circuits common to a number of subscribers, a relay 183, Fig. 2, at the sub-exchange is deenergized and connects ground to the wire 177, thereby short-circuiting the relay 176, which closes the circuit of a generator 167 through a red lamp 170 and an alarm 196. A local alarm 198, Fig. 2, is also energized. Minor troubles, affecting only a single line or trunk circuit, are signalled by the energization of a relay 215, Fig. 2, which connects the wire 177 through its own low-resistance winding to battery, virtually short-circuiting the relay 175, Fig. 3, which de-energizes and connects up a white lamp 174 and an alarm 221. The " serious trouble" relay 183 may be de-energized by the blowing of the main fuse 166, or of a fuse in a circuit serving a group of subscribers. For instance, the blowing of the fuse 168, in the supply circuit 180 of the cut-off relays 55 cuts into circuit a relay 206, which energizes a local signal 210 and a relay 209, which opencircuits the relay 183. Every time the masterswitch magnet 71 opens its springs a relay 200 is energized and connects ground to the wire 177. In normal operation this causes only an occasional flashing of the red lamp 170, but if the armature of the magnet 71 sticks in its attracted position the lamp 170 glows continuously. A local signal 204 gives a corresponding indication. The " minor-trouble " relay 215 is energized by the operation of either of the heat-coils 171, 172 in the subscriber's line wires or of the heat