Patent GB-248869-A (GB)
Title: Improvements in telephone exchange systems
IPC: H04Q3/00
Filed: 1924-12-22
Abstract: 248,869. Western Electric Co., Ltd., (Western Electric Co., Inc.). Dec. 22, 1924. Semi - automatic and manual exchange systems. -A toll call is set up by a toll operator by means of alternating current impulses compounded of two (or three) frequencies which control tuned relays at the distant end of the toll trunk. Similar impulses are employed to operate supervisory, dialling, and busy signals and to initiate ringing of the wanted subscriber. Alternatively, the desired connection may be set up by an operator at the distant end of the trunk, and in this case the calling and supervisory signals are controlled by A.C. impulses. The toll trunk may also be seized over automatic switches. Toll call completed automatically by the the toll operator. Connection to the calling subscriber A and the toll trunk L. When the ticket covering the call reaches the toll operator, she inserts plug 2 of the cord circuit C in the jack 1 of a toll switching trunk, and throws a splitting and dialling key 64, energizing relay 50 to connect the dial D to plug 2. Automatic equipment AE is then controlled to make connection with the calling line A, the off-normal springs 89 being ineffective since key 44 is not operated. When key 64 is restored, a bridge circuit is closed through A.C. relays 80, 81 and a supervisory control relay 77, which is energized by battery on the toll-switching trunk as long as the calling subscriber's receiver is on its hook to light a lamp 87. Relay 35 is inoperative owing to the. resistance of the sleeve circuit. The plug 3 is inserted in the jack 4 of the toll trunk L, and the dialling key 44 is thrown to associate the dial therewith. The sleeve circuit is closed over the talking key 19, ringing key 55, lower winding of polarized relay 9, marginal relay 58, and switching relay 10. Relay 58 energizes and locks, while relay 10 energizes, connects the trunk L to A.C. sources 20, 21, and connects up relay 22 in parallel with itself. Relay 22 disconnects the A.C. sources 20, 21 and connects the trunk L to the jack 4, and closes an independent holding circuit for relay 10 over contacts of relay 62. Wire 43 is grounded to set up a busy condition in the equipment E associated with the trunk L and similar to the equipment E2, Fig. 2. Relay 10 is slow to release while relay 22 is slow to operate to allow the alternating currents of frequencies 700 and 1100 to operate tuned relays 230, 240. Fig. 2, at the incoming end of the trunk. A normally operated relay 250 is thereby released, allowing relay 255 to energize connecting relay 250 to the test wire 263 and placing impulse relay 270 under control of A.C. relays 230, 240, so that it energizes when the alternating currents are cut off and bridges relay 280 across the outgoing trunk L1. Line relay 300 and release relay 303 at the selector S energize, grounding the test wire 263 to lock relay 255 and operate relays 250, 275. Busy relay 275 energizes a busy signal 254, applies a busy test click to jacks 200, 251, 299 through condensers, grounds the test terminal 226 in the switch bank B1 and shunts left winding of relay 260 to lower the resistance of the impulse circuit. Control of switches and completion of the connection. Release relay 303, Fig. 3, switches the lower trunk wire to ground through a transformer 324, over which A.C. impulses of frequencies 900 and 700 are sent back from sources 398, 388 under control of an interrupter 338. These impulses are received by an A.C. relay 40 tuned to either frequency and connected to the trunk L over operated contacts of relay 42. This relay removes a shunt around relay 46 and causes a dialling lamp 41 to flash. The impulse springs 5 of the dial D are normally short-circuited, and if the dial is operated before the dialling lamp is flashed, an alarm lamp 11 is lighted over the. off-normal spring 89. At the first movement of the dial at this time, however, relay 15 energizes over the off-normal springs and contacts of relay 46. locks and removes the short-circuit from the impulse springs. The dialled impulses are repeated over the trunk L by relay 42 in the form of A.C. impulses of frequencies 700 and 1100 from sources 69, 79. These are received by relavs 230, 240. Fig. 2, which control the impulse relay 270 to transmit impulses to the selector S. which is of the Strowger type, and performs a hunting movement upon the cessation of impulses to find an idle outgoing trunk L2 with an associated repeater TS. The dialling signal transformer 324 is cut out at the off-normal contacts. Relay 372 energizes over its right winding over the trunk L2 in series with line relay 400 at the second selector S2 and the left winding of polarized relay 370, which is inoperative since a circuit is also closed over its right winding. Reversing relay 352 pulls up momentarily over the make and break contacts of relay 372, causing bridge relay 280, Fig. 2, to be twice shortcircuited at its make and break contacts. Relay 280 controls relay 225, and these relays are adjusted to produce a single response of relay 225 to send back an A.C. impulse of frequencies 700 and 900 over the trunk L from sources 208, 218 to repeat the dialling signal and free the dial. The next set of impulses are repeated as before over the trunks L, L1 to line relay 350, and thence over the trunk L2 to the second selector S2, which subsequently performs a hunting movement to make connection with an idle connector K. Relay 356, Fig. 3, is energized during impulsing to cut out relay 372 and close a direct bridge across the trunk L2. Energization of switching relay 430 effects a momentary relapse of relay 372, sending back a dialling signal as before through reversing relay 352. Release relay 417 at the connector K upon energization at its make and break contacts connects up ring- ing relay 451, which locks to prevent automatic ringing of the wanted subscriber. Series relay 418 upon release at the end of the vertical movement of the connector momentarily energizes reversing relay 425 to send back a dialling signal through polarized relay 370 which controls reversing relay 352. Sluggish relay 442 is energized during the last set of impulses to connect busy relay 439 to the test wiper in place of switching relay 440. If the wanted line B is idle, switching relay 440 energizes, and at its make and break contacts momentarily connects up relav 487, which locks and applies intermittent ground to the upper line wire over interrupter 488. Relay 372, Fig. 3, responds, and impulses are sent back to operate the dialling lamp 41, supervisory lamp 75, or the operator's receiver, according to the position of the keys in the cord circuit. This signal may take the form of rapid flashes followed by a rest period. Relay 440 also grounds 457 to give an alarm signal if ringing does not take place within a given time. Operation of the ringing key 55 connects A.C. sources 70, 71 of frequencies 700 and 900 to the line wires to energize relays 484, 485 at the connector. Relays 451, 487 accordingly relapse, and the former connects up the ringing apparatus 450. To ensure that lamp 75 is lighted, key 55 closes a shunt circuit for relay 6 through the lower winding of relay 9 and operated contacts of relay 58, thereby maintaining relay 7 energized. Ring back tone is fed through a condenser 496, Fig. 4, and upon reply of the called subscriber, ring cut-off relay 451 energizes and locks. Back bridge relay 425 energizes and reverses the current over the incoming line, so that polarized relay 370 responds and causes reversing relay 352 to operate, sending back an A.C. impulse which energizes relays 80, 81, Fig. 1, the dialling kev 44 being restored. The lower winding of relay 9 is thus disconnected, and the armature moves to its upper position under the influence of the upper winding, which is in series with relav 7. At the end of the impulse, relays 80, 81 fall back and shunt relay 7 to cut out the supervisory lamp 75, while relay 6 energizes over the sleeve circuit in series with the lower winding of relay 9. The lamp 75 remains under control of the called subscriber : when he moves his switch hook relays 80, 81 receive an A.C. impulse, and open the circuit through the upper winding of relay 9, so that its armature moves to its lower position to shunt relay 6 and relight lamp 75. At the repeater TS, additional condensers 372, 373 are introduced in the talking circuit by relay 352, and relay 370 establishes shunt circuits about contacts of relays 350, 356 to guard against movement of the dial or switchhook at the calling station. Busy signals. If the first selector S fails to find an idle trunk, contacts 306 are operated, connecting the lower incoming trunk wire to a transformer 334 to send back A.C. impulses from sources 388, 398 to flash lamp 41 or 75 or to give a tone signal under control of an interrupter 348, which differs in period from the dialling signal interrupter 338. If the second selector S2 fails to find an idle connector, relay 402 energizes over contacts 401 and sends back A.C. impulses in a similar way. If the wanted line is busy, busy relay 439 energizes over the test wiper and locks when sluggish relav 442 falls back in series with relay 497, which connects an interrupter 498 to back bridge relay 425 so that impulses are sent back to give a busy signal. Relay 439 controls the usual busy tone. Release. Removal of plug 3 releases relay 22, which connects A.C. sources 20, 21 to the trunk L momentarily before relay 10 falls back. Relays 230, 240, Fig. 2, respond and release impulse relay 270, which opens the bridge across the trunk L1, so that line relay 350 and release relay 354 at the repeater TS relapse. Relay 255 is disconnected, but relay 250 remains energized over restored contacts of relays 230, 240. Switching relay 310 at the selector S is disconnected at the test wire, and this switch restores. Line relay 416 and release