Patent GB-640033-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/60
Filed: 1947-08-07
Abstract: 640,033. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Aug. 7, 1947, No. 21771. Convention date, Dec. 1, 1938. [Class 40 (iv)] In an exchange in which calls between incoming and outgoing junctions are set up by automatic switches, forward signals between the junctions are repeated over the simplex of the speech conductors and pad switching is controlled according to their state of balance or unbalance. During the setting up of the connection, however, pad control is effected over the fourth wire which is subsequently used for repeating backward supervisory signals. Different controls may be affected according to the direction of unbalance, e.g. if the resistance of a given conductor is greater than that of the other, control of pad switching may be effected, whereas if the resistance of the given conductor is less than that of the other a control may be effected which switches out the impulse repeating means when two V.F. signalling junctions are connected together. Call over D.C. signalling junction. When an operator of the 1st exchange, Figs. 1 ... 5, inserts her calling plug into outgoing jack J1 and operates the talk and dial keys TK, DK, relays 10 and 20, 21 ... 28, operate 21 and 22 (which lights the cord supervisory lamp FL) in series with 54 in the sleeve circuit. Relay 25 lights the dial lamp DP. Relay 28 de-energizes the slow release relay 26. In the outgoing junction circuit 54 is followed by 68 and 58 which lights busy lamps BL1 and puts guarding earth on conductor 93. Relay 58 is followed by 64, 69, 70, 76, 60 and 61, which holds pad control relay 83 operated to retain the pads P1, P2 inserted in the outgoing junction. Relay 115 also operates to disconnect the relays 100 and 101 in the incoming impulse receiving circuit. Signalling relay 70 operates 190 over the upper conductor of the junction and earth return, compensation for earth currents being effected by connection of the lower oppositely poled coil of 190 in a series circuit over the lower conductor which is earthed at each end. Slow release relay 69 and slow-to-operate relay 69 prevent accidental release of relay 70 during the insertion of the plug FP into the jack. When 26 releases 29 operates in series with 78 over the tip conductor. Relays 31 and 32 connect the dial to the ring conductor, 79 connects the impulse repeating relay 70 to the ring conductor and 76 releases to place 70 solely under control of the dial contacts to repeat the impulses over the junction to 190. During dialling 37 operates to hold 31, 32 independent of the dial key. Restoration of the dial key releases the dial circuit, 24 reconnecting the plug FP to the operator's telephone. Supervisory signals over the sleeve control 22 which in turn controls the lamp FL. Relay 32 releases 78 which operates switching relay 66, the pad control relay 83 then being controlled over the simplex of the speech conductors. Thus while TK is still operated, 83 remains operated to battery at 11, 12 to keep the pads in circuit. When TK is restored pad switching depends on the type of circuit to which plug RP is connected. The supervisory lamp FL is now controlled directly over the sleeve circuit. In the second exchange, Figs. 6 ... 8, when impulse repeating relay 190 first operates, 200 operates, putting guarding earth on conductor 193; 156 puts battery on the sleeve of outgoing jacks to provide operator's busy test, and 160 lights busy lamps BL5. Relay 200 completes a circuit over the simplex from the front contact of 190 to operate 201 in the both-way junction circuit TWT2 and impulsing relay 225 in the incoming selector TS2. Slow release relays 202, 226 put holding earth on conductor 223. The first digit sets selector TS2 and the second digit AS2 in the usual way. If AS2 is set to an incoming junction circuit IT2, 251 operates over the simplex to revert ringing tone and to light the calling lamp AL7 and marginal relay 207 operates in series with 256 and the normallyoperated relay 219 over conductor 224, the first leaving pad-control relay 183 under control of 205. If jack J7 is connected over the cord C2 to a local circuit or to an operator's telephone, battery over the simplex operates 271 which unbalances the incoming speech conductors and differential relay 205 operates followed by 183 which switches in the pads. Relay 272 operates over the sleeve, followed by 273, which disconnects the repeater termination 276, 277. Relay 274 extinguishes the calling lamp AL7, disconnects the ringing tone and connects earth to conductor 244 so releasing 219, the said earth then being extended to operate the answering supervisory 211 which brings up 90 in the originating exchange followed by 55 which takes the low resistance winding of 54 out of the sleeve circuit to extinguish the calling supervisory lamp FL. Recall signals. If the calling operator operates key RK, 63 operates over the tip, followed by 59. On release of RK, during the slow release of 59, relay 70 releases momentarily to give a recall signal which is repeated by 190 and 251 and during the consequent operation and slow release of 252, 254 operates and locks and connects the interrupter I to 257 which intermittently disconnects 254 from the sleeve to flash the cord supervisory lamp. If the called operator operates her ringing key relay 270 releases 211 to release 90 and 55 at the calling exchange and bring up the cord supervisory lamp. Clearing down. If the answering operator disconnects first the calling operator may set up a fresh call over the trunk without first withdrawing and reinserting her plug. When the answering operator takes down her plug 272, 273 and 211 release and 255 operates to bring up marginal relay 206 in the simplex circuit. Relay 216 then operates to remove the holding ground from 223 and thereby release the selectors TS2, AS2. Relays 211, 256, 274 operate and 201, 205, 206 release followed by 202, 216, 211. Relay 216 causes 201, 205, 225 and 202 to re-operate as before and the selector TS2 is ready to set up another call. Relay 211 has meanwhile brought up lamp FL in the originating exchange. If the operator reoperates her talk and dial keys relays 10, 20 ... 28 operate as before. When 26 releases 29, 31, 32 operate and 27 releases to bring up 77 over the ring conductor. Switching relay 66 is thereby released, 78 operates over the tip and 70 is now under control of the dial as before. If the calling operator disconnects first, release of sleeve relay 54 initiates release of the outgoing junction circuit OT1, relay 70 releasing 190 which restores the both-way junction circuit TWT2 to normal thereby releasing selectors TS2, AS2. In the incoming junction circuit IT2, 256, 274, and 251 release, the latter operating 252 to bring up the cord supervisory lamp until 272, 273 are released by withdrawal of the plug. All trunks busy condition. 11th-step springs on TS2 connect an interrupter to conductor 224 and consequent intermittent operation of 211 is repeated by 90 and 55 to flash DP. If the selector is arranged to " camp " on a busy level the rate of interruption is different and 55 operates 57 which locks and prevents release of 70 should the dial be further operated. When the dial and talk keys are restored 78 releases 66, 76 operates to hold 70 operated and 57 releases. When an idle trunk is available the rate of flashing changes and the operator operates TK, DK, to reconnect the dial as before, dials 1 to initiate the hunting of the selector and then dials the remaining digits. Connection between D.C. signalling junctions. When a connection is established from junction T3 through selectors TS3, AS2 to the junction T1, relays 215, 156 operate to ground extended from circuit TWT3 over conductor 193 and 160 follows to light the busy lamps BL5. Relay 210 operates over the simplex to ground at the front contact of the impulse repeating relay controlled over junction T3. Relay 217 operates .to ground extended over 194. Relay 210 at the tandem exchange brings up 90 at the called exchange and 100 follows to put guarding earth on conductor 93. Relay 101 operates over the simplex in series with the impulsing relay in TS1 and holding relay 102 follows. Relay 60 lights busy lamps BL1. At the tandem exchange 217 operates 183 to cut pads P3, P4 out. When the call is answered at the distant exchange, 190 operates followed by 218 which locks up and extends the front contact of 190 over 194 to operate the supervisory relay in the both-way junction circuit TWT3 which repeats the signal over T3. Call from junction T1 to subscriber. A subscriber's line circuit does not contain arelaysuch as 256 in IT2-and 219 releases immediately AS2 seizes the circuit so that conductor 224 is connected immediately to the supervisory relay 211 which operates when the called subscriber answers. Relay 207 does not operate on such a call and 183 is held operated to retain the pads P3, P4 in the junction. Incoming call from V.F.-signalling junction. Fig. 9 shows a signalling circuit SC5 and bothway junction circuit TWT5 associated with a V.F. signalling junction T5 arranged for connection to the outgoing junction circuit OT2 and incoming selector circuits TS2, Fig. 7, which should be placed on its right. An incoming seizing pulse of V.F. current operates 390 ; 385 follows and 300 operates and locks while slow-to-operate relay 386 is pulling up. Relay 320 then releases and 301 and impulse relay 225 operate over the simplex. Holding relay 302 operates before the cessation of the V.F. pulse and brings up 325. Relay 390 repeats incoming V.F. dialling impulses over the simplex to set selectors TS2, AS2. If the call is extended to an operator's trunk circuit IT2 marginal relay 307 operates to leave pad control relay 383 under control of 305. When the call is answered 319 releases to bring up the answering supervisory 311 and 387 operates 389 during the operating period of 388 to send an answering supervisory V.F. signal o