379,671. Automatic exchange systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, U.S.A. May 27, 1931, No. 15575. Convention date, May 7. [Class 40 (iv).] A register-sender, Figs. 4 and 5, transmits impulses over the outgoing a-wire directly to the magnets of two-directional group and final selectors, change-over and other control being effected over the b-wire. During each digit, the normal battery and earth connections to the outgoing wires are reversed, and an interrupter produces impulses in the a-wire. The successive connection of the final selector magnets to the a-wire is controlled by a side-switch SE, Fig. 3, which is further advanced by impulses from the register-sender after the final selector has been set, to make successive tests as regards the busy, idle, or disconnected condition of the called line. The register-sender responds in accordance with the condition found, transmitting corresponding signals to the relay group PU, Fig. 1, at which a distinctive tone is connected up and the register-sender is released. In the case of inter-exchange calls, the incoming selector THS, Fig. 2, comprises a repeater having two oppositely-polarized relays 201,202, bridged in series across the incoming junction loop, one being normally energized to hold the connection and the other responding to impulses to control the succeeding switches. Calls to an information-operator's circuit TC are made by dialling a single digit O and for such calls a metallic circuit is automatically completed through the relay group PU. The selectors OS, HS, comprise two relays only, a two-step change-over relay and a switching relay, the former operating through its first step when the selector is taken into use to open a point in the circuit of the release magnet. If a group selector finds all trunks in a selected level busy, it is released and again set by the same digit, this operation being repeated if necessary a predetermined number of times under the control of a counting switch RC in the register-sender, after which the connection is released and a special tone-signal given. Setting of register-sender ; translation. Line relay 111 connects magnet 151 to test wiper 155 causing switch DS to select an idle registersender. Relay 116 then operates in series with magnet 151 connecting release relay 112 over wiper 155 to be held by ground in the registersender. The six digits dialled are repeated over relay 404 and distributed over wiper 425 to registers A-T, B-U, TH, H, A-T, B-U, respectively, the first two being released by relay 483 in position 4 of wiper 423 in readiness to be used a second time. In position 3 of wiper 424 a circuit is completed over wiper 510 for magnet 535 of translating switch TS. The magnet on operating removes a short-circuit from a parallel-connected relay 534 which then energizes to open the magnet circuit. Stepping thus takes place until the contacts 538 corresponding to the two code digits (45) are reached when relay 533 operates over wipers 517, 1 and 2 of TS, 512, 510, 424. Control of office selector OS. Relav 533 grounds start conductor 457 causing interrupter 413 to operate two-step relay 412 which then connects the interrupter to magnet 541 of the counting switch CS. Relays 411, 408, operate connecting interrupter 414 over conductors 165, 124, to the vertical magnet 178. Impulses are thus sent synchronously to switches OS, CS, until wiper 544 reaches the contact jumpered to the contact engaged by wiper 3 of switch TS. Relay 410 then operates completing a restoring circuit for switch CS and releasing relays 408, 412. Relay 171, which had previously been partially operated by current through its upper winding from conductor 125, to open a point in the circuit of the release magnet 175, now operates fully over conductor 164 in series with relay 407, completing a selfinterrupting circuit for the rotary magnet 174. When an idle junction 185, 187, is found, relay 172 operates and switches through, disconnecting relays 171, 407. In the register-sender, when switch CS reaches normal, relay 411 releases and back-stroke magnet 501 advances output-control switch OCS to position 2. Assuming one routing digit only is required, the terminals engaged by wipers 4 .. 8 of switch TS are jumpered to lead 464 so that switch OCS steps over its interrupter contacts to position 7 in which ground is again connected to start conductor 457 provided that the hundreds register H is off-normal. Selectors THS, HS. Polarized relays 201, 202, are connected in series with resistance 207 over conductors 185, 187, and when the junction is seized relay 201 operates energizing relay 204. When relay 408 energizes preparatory to the transmission of the thousands digit, the direction of current over the junction is reversed so that relay 201 releases and at each impulse from interrupter 414 relay 202 operates and transmits an impulse to vertical magnet 212, relay 205 operating at the first impulse and connecting relay 204 in parallel with the magnet. At the end of the digit relay 201 operates again, connecting up the lower winding of relay 203 which operates over resistance 215 to shortcircuit resistance 207 thus causing the operation of relay 407. Belay 203 also connects up rotary magnet 213 and when an idle selector HS is found, relay 206 operates, disconnecting relay 203 and releasing relay 407. Relay 206 by short circuiting its upper winding effects the operation of the upper armature of relay 271. Control of selector HS now takes place in a similar manner to that of selectors OS, THS, impulses being repeated to magnet 278 by relay 202. Final selector C. The tens impulses are repeated by relay 202 over the upper talking conductor to vertical magnet 304. At the end of the digit, a circuit is completed over the lower winding of relay 203 and the lower talking conductor for side-switch magnet 311 which advances the side-switch SE to position 2 so that the units impulses pass to the rotary magnet 305. Called line busy. In position 3 of the sideswitch, if the called line is busy, test relay 302 operates over wiper 313 short-circuiting resistance 318 over w:.per 310 so that relay 203 operates, in turn short-circuiting resistance 207 to effect the operation of relay 407. Since the switch OCS is now in position 11, ground is connected over wiper 505, resistance 525, leads 465, 161, to relays 114, 113, the latter of which operates, releasing relay 116 and the registersender, disconnecting conductor 125 to release the operated switches, and connecting up busy tone from lead 167. Dead-number call. If the called line does not test busy, an impulse from interrupter 414 is transmitted to relay 201 and repeated to magnet 311 to advance the side-switch SE to position 4, the operation of relay 409 which occurred in position 10 of OCS connecting up stop relay 410 to interrupter 413 so that a pause occurs after a single impulse. If the test wiper 316 finds a disconnected contact, relay 302 does not operate, and resistance 318 is again shortcircuited so that relay 407 is energized to ground lead 161 as for a busy call. This ground connection, however, does not include resistance 525 since OCS is not in position 12, so that relay 114 also operates and a " verification tone " is transmitted from lead 168. The calling subscriber should now verify the wanted number in the directory and. if necessary may call a verification operator. Called line idle ; ringing. If the called line is idle relay 302 energizes over its lower winding and battery on the called-subscriber's cut-off relay. Relays 203, 407, are therefore not operated, but a further impulse is transmitted from the register-controller to magnet 311 advancing switch SE to position 5 in which ringing-current is supplied over cam-operated contacts 312, 314, to the called line. In the register-sender, in position 13 of switch OCS, ground is connected over resistance 526 and lead 163 to operate relay 114 which connects up ring-back-tone 166, and releases relay 116 and the register-sender. When the called party replies, relay 303 operates, relay 203 energizes over the called loop to short-circuit resistance 207, and relay 117 operates over the junction 185, 187 and relays 201, 202. Relay 117 energizes relay 110 which switches through. Release. If the called party hangs up first, relay 203 falls back, inserting resistance 207 to release relay 117. When the calling party hangs up, relays 111, 112 release, and ground is removed from the conductor 125. The release of relay 172 energizes release magnet 175 which opens the test circuit until release is complete. In selector THS, relays 201, 204 release, energizing release magnet 214 and unlocking relays 272, 301 which similarly release switches HS, C. If the calling party hangs up first, the final selector is held off-normal until the called party hangs up by a locking circuit for relay 303 completed over the called loop. All trunks busy. Relay 407 is operated in series with relay 171 as long as the selector OS is hunting and maintains magnet 501 energized. If all trunks are busy, 11th step springs 176 operate the release magnet 175 to restore the selector to normal. When relay 410 falls back, relay 406 operates to advance a switch RC one step, and to close a further holding circuit for magnet 501 so that when relay 411 operates again the previous digit is repeated. After three such unsuccessful hunts, switch RC grounds lead 161 to release the register-controller and connect up the " verification tone." A similar operation occurs if switches THS or HS encounter a busy condition. Call to information operator. If digit O is dialled, magnet 535 of switch TS is operated over wipers 510, 424, at the end of this digit, and relay 533 operates over a terminal N connected to the normal terminal of register B-U. The switch OS is raised to its third level to seize a trunk circuit TC, after which switch OCS