US1893691A - Multioffice telephone system - Google Patents

Description

Jan. 10, 1933. J. wlCKs MULTIOFFICE TELEPHONE SYSTEM 7 SheetsFSheet l Filed Mayy 29, 1931 .w H W mm M mm wm B u .1 un NQ FB Mw o IL l ivm@ J E x QEE uh QQ `1an. 10, 1933. W|KS 1,893,691

MULTIOFFICE TELEPHONE SYS TEM Filed May 29, 1931v 7 sheets-Sheet 2 Jan. 10, 1933. J. WICKS MULTIOFFICE TELEPHONE SYSTEM Filed May 29, 1951 7 Sheets-Sheet 5 N Nnmm wwmm v mmm,

Jan. l0, 1933. l J. wlcKs MULTIOFFICE TELEPHONE SYSTEM 7 sheets-sheet 4 Filed May 29, 1931 ...n Z111 winks' Jan. 10, 1933. J. WICKS MULTIOFFICE TELEHIONE SYSTEM Filed May 29, 1931 vusheets-sheet 5 SMH W Jn Z'm Hicks @Mx/ 7 Sheets-Sheet 7 Filed May 29, 1931 To Aura. ExcH. "5

lfm- JD 1m ink s m\ uw l w m kw m E bww a Ww WCW/ r l km. TF Il y Patented Jan. l0, 1933 UNITED STATES PATENT OFFICE JOHN WICKS, OF OAK PARK, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0

ASSOCIATED ELECTRIC LABORATORIES, INC., 0F CHICAGO, ILLINOIS, A CORPORA- TION OF DELAWARE MULTIOFFICE TELEPHONE SYSTEM This invention relates to multi-oliice telephone systems in general, but is concerned more particularly with such systems includings both automatic and manual exchanges and employing alternating current control over the inter-office trunk lines.

The invention has for its broad object the provision of new and improved circuits for effecting the control of inter-office connections by means of alternating current impulses transmitted over two-way trunk lines.

According to one feature of the invention, alternating current impulses of diiierent lengths are transmitted over the trunk lines and converted into the proper direct current signals at the respective ends of the trunk line to effect the operation of the switches and supervisory signals.

Another feature of the invention lies in the novel toll offering arrangement which includes a new and improved toll-offering connector switch and corresponding improvements inthe manual switchboard circuits.

The above and other features .of the invention will be more clearly understood from a perusal of the following specification when read in connection with the accompanying drawings, comprising Figs. 1 to 6, inclusive,`

which show by means of the usual schematic diagram sufficient portions of a multi-oliice telephone system to enable the present invention to be understood.

Fig. l is a trunking layout of the telephone system including a manual exchange and two automatic exchanges, A and B. The manual exchange is indicated at the left. of the drawings and comprises an operators posit-ion circuit PC, an operators cord circuit CC, and a trunk circuit TC which forms the manual end of two-way trunks extending to the'iirst automatic exchange A. Automatic exchanges A and B are three-digit exchanges including selectors and connectors. The twoway trunks from the manual exchange terminate at exchange A in repeaters, such as R1, and incoming selectors, such as ISl. These trunks are accessible to selectors from the 0 level. Automatic exchanges A and B are interconnected by two-way trunk lines terminating at exchange A in repeaters, suchp as R2, and incoming selectors, such as IS2, and at exchange B in repeaters, such as R3, and incoming selectors, such as IS3. Repeaters R2 and R3 are identical to the repeater R1 terminating the trunk from the manual exchange. The trunks extending to exchange B are accessible over the ninth level of the selectors in exchange A. The trunks extending to exchange A are accessible over the 0 level of the selectors in exchange B.

Fig. 2 discloses a cord circuit CG, which is one of a number of similar circuits of an operators position, and an operators position circuit PC and an operators telephone circuit OTC which are common to the cord circuits at the position.

Fig. 3 discloses the trunk circuit TC which is accessible at the manual board over jack J and terminates the two-way trunk line extending to automatic exchange A and comprising conductors 1 and 2. y

Fig. 4, comprising parts A and B, discloses the two-way repeater circuit R1 located in the automatic exchange A, and terminating the two-way trunk line comprising conductors l and 2, connecting exchange A to the manual exchange.

Fig. 5 disclosesan incoming selector circuit ISl, a local selector S1, and a subscribers substation T1 and the associated lineswitch LS1 having access to local selectors, such as S1. The banks of selectors ISI and S1 are multiplied and have access to the trunks extending to the Amanual exchange over the 0 level by way of a repeater, such as Rl, over conductors 24, 26, and 28. The incoming selector ISI is controlled by repeater Rl over conductors 25 and 27.

matic exchange B. Repeater R2 is in all respects identical to repeater R1 which is shown in detail in Fig. 4.

Referring now to the trunkin la out shown in Fig. 1 of the drawings, a rie description will irst be given of the manner which the various connections are set up 1n the multi-oiice system shown. Assuming first that the operator at the manual exchange has received a request for a connection with the subscriber at substation T3 in automatic exchange A. The operator inserts the calling end of the cord circuit CC into the jack J, associated with a trunk extendlng to exchan e A. When the plug of the cord is inserte in the jack, the trunk circuit TC operates to send a preliminary seizing impulse of alternating current over the trunk line. This impulse of alternating current is received by the repeater R1 in exchange A and prepares the repeater for operation on an incomlng call. The loop circuit to the incomlng selector ISl is also completed responsive to the preliminary impulse. The operator now proceeds to dial the telephone number of substation T3, whi-ch it will be assumed is 323. Responsive to the operation of the dial, the trunk circuit TC transmits corresponding impulses of alternating current over the trunk line which are received by the repeater R1, and are convertedinto direct current impulses to operate the incoming selector switch ISl and the connector switch C1. In case the called line is idle the connector C1 rings automatically and, when the called subscriber at substation T3 answers, reverses battery back to the repeater R1. Responsive to the reversal of current, repeater R1 transmits an alternating current impulse over the trunk line to trunk circuit TC to give answering supervision. Trunk circuit TG brings about the extinguishing ofthe supervisory lamp at the operators position to inform the operator that the called party has answered.

At the end of the conversation when the called subscriber hangs up his receiver the battery connections at connector C1 are again restored to normal. This causes the repeater R1 to transmit a disconnect impulse of alternating current over the trunk line, which Icauses the trunk circuit TC in the manual exchange to again light the supervisory lamp to show that the called subscriber has disconnected. When the operator removes the cord CC from jack J, the trunk circuit TC transmits a long impulse of alternating current over the trunk line. This long impulse of alternating current is received by repeater R1 and bringsvabout the release of the incoming selector switch IS1 and the connector switch Cl and also restores repeater R1 to normal. The apparatus has now completely restored to normal.

Assumin now that a subscriber, such as the subscri er at substation T1, in the automatic exchange A wishes to talk to a. sub-` scriber who can reached only through the manual exchan e. When the subscriber at substation T1 ifts his receiver, lineswitch LS1 is operated and searches for an idle trunk, such as that extendin to the local selector S1. The calling su scriber then dials the digit 0, whereupon selector S1 is operated to the tenth level and selects an idle trunk extending to the manual exchange, such as the one accessible by way of repeater R1. When repeater R1 is seized, it transmits a calling signal over the inter-oiiice trunk line which is received by the trunk circuit TC, and causes the lighting of the calling lamp at the operators position. On noting the lighted condition of the trunk lamp the operator inserts the answering plug of a cord circuit such as CC, into the associated jack, thereby causing the trunk circuit TC to transmit an alternating current im pulse over the trunk line to exchange A. Repeater R1 responds to this impulse and reverses the battery over the calling line to perform a meterin function in case metered service is used. he operator then completes the desired connection over the other end of cord CC. At the end of the conversation, when the calling subscriber releases, repeater R1 transmits an alternating current impulse over the trunk line to light the supervisory lamp at the operators position. When the operator removes the plug from the trunk jack, a release signal is transmitted over the trunk line to restore the equipment in the automatic exchange. A to normal.

In case the manual operator receives a call for a subscriber, such as the subscriber at substation T2, in the automatic exchange B, she inserts the plug of a cord, such as CC, into the ack J, thereby causing the trunk circuit' T to transmit an alternating current impulse over .the trunk line to prepare the switches in exchange A. Repeater R1 closes the loop to incoming selector ISl in the manner previously described. To call subscriber substation T2, the manual operator dials the number 9332. Responsive to the operation of the dial in accordance with the first digit 9, the trunk circuit TC transmits alternating current impulses over the trunk line which are converted into direct current impulses by repeater R1 to operate the incoming selector switch ISl to the ninth level. The switch automatically hunts in this level for an idle trunk extending to automatic exchange B by way of a repeater, such as R2. When repeater R2 is seized, it transmits a signalling impulseof alternating current over the trunk line which is received by repeater R3 and causes the repeater to close the loop to the incoming selector ISB. Responsive to the dialling of the remaining digits, trunk circuit TC transmits correspondingzkimpulses of lalternating current over the trunk line exby the repeater R1 and converted into direct current impulses.' The direct current impulses operate the repeater R2 which again converts the impulses into alternating current impulses for transmission over the trunk l1ne extending to the automatic exchange B. These alternating current impulses are received by repeater R3 which converts them into direct c'urrent impulses for operating the incoming selector switch IS3 and the connector switch C3 to esablish the connection to the subscriber at substation T2. Substation T2 is signalled automatically and when the subscriber answers, the reversal of battery in connector C3 causes repeater R3 to transmit an answering supervisory signal over the trunk line. This alternating cur rent signal is received by repeater R2 which reverses the battery through the incoming selector to repeater R1. Responsive to the reversal of battery, repeater R1 transmits an answering supervisory signal over the trunk line to the manual exchange which is received by the trunk circuit TC. The trunk circuit in turn extinguishes the supervisory lamp at the operators position to inform the operator that the called subscriber has answered.

At the end of the conversation, when the subscriber at substation T2 hangs up his receiver, the battery connections from the connector to repeater R3 are again reversed to normal and repeater R3 transmits a disconnect impulse of alternating current over the trunk line to the exchange A. Repeater R2 responds to this impulse and again reverses the battery connections to repeater Rl to normal. Repeater R1, responsive to the battery reversal, transmits a disconnect impulse of alternating current over the trunk line, which is received by trunk circuit TC and results in the lighting of the supervisory lamp to indicate to the operator that the called subscriber has hung up his receiver. When the operator pulls out the plug, a release impulse is transmitted over the trunk line by the trunk circuit TC. Responsive to this impulse, repeater R1 opens the loop extending through incoming selector ISl to repeater R2, causing this repeater to send a release pulse over the trunk line to automatic exchange B. Repeater R3 responds to this impulse to open the loop extending to the automatic switches in the exchange and thereby releasing the switches and also restoring repeater R3 to normal. All the equipment which was used in this connection has now been restored to normal position.

Subscribers in exchange B can call subscribers in exchange A by dialling the digit 0' and then the regular telephone number ot' the wanted subscriber. The dialling of the digit O operates the local selector, such as S2, to seize a repeater, such as R3, connected to a trunk line extending to exchange A. The reminates in an incoming selector, such as IS2,

and this selector and a connector, such as C1 Yor C2, respond to the regular telephone number of the wanted subscriber to extend the desired connection. In case the subscriber at substation T2 in exchange B wishes to estalish a connection which can be completed only by the manual operator, he dials the digit 0 thereby extending a connection to automatic exchange A and then dials a second digit 0 which operates the incoming selector TS2 to select an idle repeater, such as R1, terminating one of the trunk lines extendin to the manual exchange. The repeaters R1, 2, and R3 operate in these connections in a similar manner as previously explained for the other connections.

Having described the trunking layout of the exchanges in general, and having described generally the various connections which can be established within the system, the operation of the circuits will now be explained in detail with reference to Figs. 2 to 6, inclusive. These figures should be laid out in order from left to right with Fig. 2 at the extreme left.

Call from manual exchange to substation T3 n echcmge A A call from the manual exchange to substation T3 in the automatic exchange A will first be described. It will be assumed that the operator has received a call over a trunk line which may be in all respects similar to the trunk line terminating in the trunk circuit TC and that she has ansufered the call by inserting the plug P1 of cord circuit CC into the calling jack and operating key K to its left-hand position to connect her telephone circuit with the calling line. The operation of key K to its left-hand position completes a circuit for relay 200 in the cord circuit extending from battery, lower winding of relay 200, spring 21() and its make contact, conductor 227 armature 233 and its resting contact to ground. Relay 200 operates and closes a locking circuit for itself extending from battery, upper winding of relay 200, armature 204 and its working contact, working contacts of key spring 209 and said spring, conductor 226, winding of relay 232 to ground. Relay 232 operates in this circuit in series with relay 200 and at armature 233 and its resting contact opens the initial energizing circuit of the latter relay. At armature 235 and its resting contact it opens the circuit of the monitoring relay 238. Atarmatures 236 and 234 and their respective working contacts it connects the operators telephone circuit to the in exchange A. The operator thereu on inserts plug P of cord circuit CC into t e j ack J and proceeds to dial the desired number, which in this case is 323.

Responsive to the insertion of plug into jack J, the relay 303 in the trunk circuit operates in series with relay 274 in the common position circuit PC over the following circuit from ground, u per winding of relay 303, resting contact o armature 315 and sald armature, sleeve of jack J and `plug P, working contact of armature 203 and said armature, conductor 221, armature 270 and its resting contact, upper and lower windings 'of relay 274, to battery. Relay 274 in operating, at armature 275 and its working contact completes a circuit for relay 278. Relay 278 operates rand at armature 279 and its working contact completes a circuit for the supervisory lamp 215 extending from ground, armature 275 and its working contact, working contact of armature 279 and said armature, conductor 225, key spring 208 and its working Contact, supervisory lamp 215, to battery yand inl parallel therewith through resistance 217 to battery. In the trunk circuit TC, relay 303 operates and at armature 304 and its working contact, completes a circuit for relay 367 extending from ground, armature 304 and its working contact, resting contact of armature 328 and said armature, winding of relay 367 to battery. Relay 367 operates, and at armatures 368 and 369 connects the source of alternating current to the outgoing trunk line comprising conductors 1 and 2.

The alternating current used for signalling is obtained through a special frequency doubling transformer disclosed in the lower portion of Fig. 3. Leads 380 and 381 are connected to the commercial power source having a frequency of about 60 cycles. The frequencyv doubler consists of a transformer having a primary and a secondary winding with the primary winding divided into two sections. Lead 381 is connected to the center point of the primary winding while the outer terminals of this winding are con- I,

nected to two dry discs rectifiers 378 and 379, and the other lead 380 extending from the commercial power source is connected to the midpoint of these rectiiers. During one half-cycle of the alternating current, the current will be in such a direction that it will flow through rectifier 379 and upward through the lower half of the primary winding and .back over lead 381. During the other half-cycle of the current, current will flow over lead 381, upper section of the primary winding, rectifier 378, and back over lead 380. Thus it isfsen that the two opposite half cycles of alternating current fiow through portions of the primary winding in the same direction, thereby producing magnetic flux in the core of transformer 377 in accordance with two half cycles which are in the same direction through the core. Each of these half-cycle changes in the magnetic flux will produce a complete cycle of alternating current in the secondary winding of the transformer. Thus the output current of transformer 377 will have a frequency which is twice that of the commercial power source. This output current is taken through lamps 375 and 376 and connected to the trunk line at armatures 368 and 369, as previously explained.

Returning now to the point where relay 367 operated and connected the alternating current source to the trunk line, the relay also completes a circuit for relay 322 at armature 370 and its working contact. This circuit extends from ground, spring contact 300 on jack J which is closed as soon as the plug P is inserted into the jack, armature 312 and its resting contact, working contact of armature 370 and said armature, normally closed springs controlled by armature 327, winding of relay 322, to battery. The closure of jack sprinv 300 also completes a circuit for relay 360. 2Relay 360 is equipped with a weighted spring armature 361 and an appreciable interval of time elapses before this armature comes to rest in engagement with its working contact. Relay 362 is made slow-to-operate by a copper slug on the armature end of the core and will, therefore, not operate until its circuit remains permanently closed after armature spring 361 comes to rest in engagement with its working contact. When relay 362 operates, it completes a circuit for the busy visual 302 at armature 363 and its working contact, and at armature 364 and its working contact it closes a point in a second circuit for relay 367 extending from ground, armature 329 and its resting contact, armature 341 and its resting contact, armature 364 and its working contact, winding of relay 367, to battery.

Relay 322 is made slow-to-operate by a copper'slug on the armature end of its core and does not operate for a short time after its circuit is closed. at armature 370 of relay 367. lVhen relay 322 finally operates it completes a locking circuit for itself at armature 327 and its working contact, to ground at the jack springs 300. At armature 329 and its rest-ing contact and armature 328 and is resting contact it opens the two circuits previously described, for relay 367, allowing this relay to drop back and cut-off the alternating current from the trunk line thereby ending the preliminary pulse which was being transmitted over the trunk line extending to exchange A. At the double make contacts 323 and 325, relay 322 completes a circuit from grounded conductor 382, contacts 323 and 325, armature 334 and its resting contact, windin of relay 347, resistance 383 to battery. elay 347 operates and at armature 352 and its working contact completes a second circuit for the busy visual 302, and at armature 349 and its resting contact it opens a point in the circuit of relay 353.

Referring now to the repeater R1 shown in Figs. 4A--4B of the drawings, the preliminary impulse of alternating current which was transmitted over conductors 1 and 2 by the trunk circuit TC in the manner just described, operates relay 435 by way of armatures 424 and 425 and their respective resting contacts and the left-hand Windings of repeating coil 437. Relay 435 completes a circuit for relay 445 extending from ground, normally closed contacts controlled by armature 413 of relay 410, armature 436 and its working contact, conductor 11, normally closed springs controlled by armature 449, armature 469 and its resting contact, lower winding of relay 445, to battery. Relay 445 operates its amature 450, thereby preparing a locking circuit for itself over both of its windings but the upper winding 1s short-circuited over the abovetraced circuit until relay 435 releases at the end of the preliminary impulse. When relay 435 releases and opens the ground connection to relay 445 at armature 436, relay 445 .operates all of its armatures and locks operated in a circuit eX- tending from ground, normally closed springs controlled by armature 413, conductor 12, armature 450 and its working contact, upper and lower windings of relay 445, to battery.

At armatures 446 and 457 and their respective working contacts relay 445 completes a loop circuit extending to the 1ncoming selector TS1, Fig. 5, to prepare the selector for operation. This loop circult eX- tends from ground, lower winding of line relay 500 in selector-TS1, resting contact of armature 514 and said armature, conductor 27, Working contact of armature 457 and said armature, conductor 23, lower-right-hand winding of repeating coil 437 conductor 14, resting contact of armature 493 and said armature, lower winding of supervisory relay 471, working contact of armature 451 and said armature, conductor 13, upperright-hand winding of repeating coil 437, conductor 3, armature 446 and its working contact, conductor 25, armature 511 and its resting contact, upper winding of line relay i 500, to battery. Line relay 500 operates in this circuit and at armature 501 and its working contact completes arcircuit for rele-ase relay 502.

Relay 445 in operating, at armature 447 and its working .contact connects ground to the release conductor 26 in order to busy the repeater R1 in thebanks of local and incoming selectors, such' as S1 and ISL This lground is also connected to the upper winding of relay 471 energizing this winding, but relay 471 does not operate 'since the current through its lower winding is in such a direction as to oppose the current through its 'upper winding. At armature 449 and its cord circuit CC into the trunk jack J. As

soon as the operator turns the dial 282 from its normal position, preparatory to dialling the desired telephone number, a circuit is completed for relays 268 and 272 in series from ground at the dial oit-normal springs, key spring 266 and its resting contact, winding of relay 272, winding of relay 268, t0 battery. Relays 268 and 272 operate in this circuit. At armature 269 and its resting contact, relay 268 opens the ring conductor extending to plug P1, and at armature 270 and its resting contact it opens the circuit of the supervisory relay 274 and sleeve relay 303 and at the working contact of this armature completes a point in the dialling circuit. At armature 273 and its working contact, relay 272 connects battery through resistance 283 to the ring conductor over working contact of armature 273 and said armature, conductor 223, armature 206 and its working contact, ring of plug P and jack J, lowerleft-hand winding of repeating coil 318, winding of relay 314, upper winding of relay 310, resting contact of armature 304 and said armature, to ground. This circuit is completed as soon as relay 303 releases responsive to the opening of its circuit at armature 27 0 of relay 268. Relay 314 operates in this circuit but relay 310 is adjusted so that it will not operate in series with relay-314 and resistance 283. At armature 315 and its working contact, relay 314 connectsthe sleeve of jack J to ground at armature 311 and its resting contact. At armature 317I and its working contact itconnects' the tip of jack J to the winding ofthe impulse repeating relay 371. At armature 316 and its front contact it prepares a point in the energizing circuit of relay 367.

When 'relay 303 releases as previously described, a circuit is completed for relay 307 which operates without effect at this time.

The impulsing circuit to relay 371 has nowl ing contact of armature 271 and said armature, conductor 220, armature 202 and its y working contact, tip of plug P and jack J,

armature 317 and its working contact, winding of relay 371 to battery. Relay 371 operates in the circuit and at armatures 372 and 37 3 and their respective resting contacts opens points in the outgoing trunk conductors 1 and 2. At armature 374 and its Working Contact it completes a circuit from ground, working contact of armature 374 and said armature, working contact of armature 316 and said armature, winding of relay 367, to battery. Relay 367 operates in this circuit and at armatures 368 and 369 and their respective working contacts closes points in the circuit from the alternating current source to trunk conductors 1 and 2, but these conductors are now open at armatures 372 and 373. At armature 370 and its working contact, relay 367 completes an auxiliary locking circuit for itself extending from grounded conductor 382, armature 312 and its resting contact, working contact of armature 370 and said armature, working contact of armature 316 and said armature, winding of relay 367, to battery. This circuit maintains lthe relay 367 operated when its initial energizing circuit is opened at armature 37 4 during the repeating of the digit impulses. f y

When the dial 282is released and allowed to return to normal, the impulsing circuit to relay 371 is opened three times in accordance with the first digit. Each time the dial contacts are broken, relay 371 releases and at armatures 372 and 373 and their respective resting contacts the alternating current source is connected to conductors 1 and 2, whereby three short impulses of alternating current are transmitted over the trunk line to repeater R1 in exchange A. When the dial 282 has returned to normal, the circuit to relays 268 and 272 is broken and these relays release, again closing the circuit for the supervisory relays 27 4 and 278 and the sleeve relay l303'. These relays again operate and the supervisory lamp 215 is again lighted. At armature 273 of relay 272 the battery connection through resistance 283 is removed from the ring conductor and relay 314 again releases, completing the circuit for sleeve relay 303. Relay 314 opens the circuit of relay 367 which also releases.

The remaining digits, 2 and 3 are transmitted over the trunk lines in the same manner as described above for the first digit. Relays 274, 278, and 303 release when the dial is moved off-normal and relays 268, 27 2, 314, 371, and 367 are operated. When the dial 282 returns to normal after the last digit 3 has been transmitted, relays 314, 367, and 371 are released and the sleeve relay' 303 and supervisory relays 274 and 278 are again operated, and the supervisory lamp 215 remains lighted until the called subscriber answers.

Referring now to repeater R1 as shown in Fig. 4 of the drawings, the alternating current impulses transmitted over conductors 1 and 2 by the trunk circuit TC are received by relay 435 which is operated by each impulse. Each time relay 435 operates it completes a circuit from ground, normally clos/ed springs controlled by armature 413, armature 436 and its working contact, conductor 11, working contact of armature 449 and said armature, normally closed springs controlled by armature 444, Winding of relayv 488, to battery. Relays 488, 494, and 499 are impulse correcting relays which are provided so that the interruptions in the loop circuit extending to the automatic switch train in exchange A will be of the proper length. Relay 488 operates at the beginning of each impulse in the above traced circuit, and completes a locking circuit for itself from ground at the resting contact of armature 497 and said armature, armature 490 and its working contact, winding of relay 488 to battery. At armature 493 and its' resting contact it opens the loop circuit extending to the selector switch ISL At armature 491 and its working contact it completes a circuit for the upper winding of relay 499 over the normally closed contacts controlled by armature 496. Relay 499 operates and at armature 443 and its working Contact, completes a circuit for the upper winding of relay 494. At armature 442 and its resting contact it opens the shortcircuit around its lower Winding and at armature 444 and its working contact it transfers the impulsing circuit from relay 435 to its own winding so that relay 499 will not release until the end of the alternating current impulse. Relay 494 operates and at armature 497 and its resting Contact, opens the circuit of relay 488 allowing this relay to release and at armature 493 and its resting contact again close-the loop circuit to the incoming selector, thereby completing the first impulse to the switch. At armature 498, relay 494 opens the short-circuit of its lower winding.

At armature 496 andl its working contact it completes the above traced locking circuit from the impulse conductor 11 to the upper winding ofrelay 499.

Thus, relays 499 and 494 are locked operated until the end of the alternating current impulse, if this impulse has not already ended before the operation of relay 494. If the alternating current received was shorter than desired, the circuit of relay,499 is opened at armature 496 as soon as relay 494 operates. Relay 499, therefore, releases and at armature 443 opens the circuit of relay 494 and allows this relay to release. From the above explanation, it is apparent that the loop circuit extending to the incoming selector switch ISl is opened -for the same duration of time for each impulse, namely the time required for relays 499 and 494 to operate and for relay 488 to release. The outgoing impulses to the selector switch are uniform irrespective of the length of the alternating current impulses received. The first time relay 499 operated it completed a circuit from ground, armature 441 and its working contact, conductor 16, winding of relay 4 15 to battery. Relay 415 operates in this circuit and at armature 418 and its working contact short-circuits the upper-left-hand winding of repeating coil 437 to improve the' operation of the impulse-responding relay 435.

It might be Well to point out at this time that when relay 445 operated, when the repeater R1 was first seized and at armature 447 grounded conductor 6, relay 419 operated in a circuit from the grounded conductor, winding of relay 419, resistance 420 to battery, and relay 400 was operated 1n a circuit from the grounded conductor 6, winding of relay 400, resistance 434 to battery. Each time relay 499 operates responsive to the digit impulses, a circuit is completed from ground at armature 433 of relay 430 and the resting contact of said armature, conductor 22, armature 440 and its working contact, working contact of armature 455 and said. armature, conductor 20, to the lower terminal of the winding of relay 400. This ground shunts out the battery through resistance 434 and shunts the winding of relay 400, thereby making this relay sloW-to-release so that 1t will not release during the momentary shortcircuit of its winding when the dialling impulses are being received.

Referring now to Figs. 5 and 6 ofthe drawings, the circuit of line relay 500 of incoming selector ISl is opened each time relay 488 of the impulse correcting relays in repeater R1 is operated in accordance with the digit impulses, and at armature 501 and its resting contact relay 500 completes a circuitfroin ground, armature 513 and its resting contact, armature 501 and its resting contact, armature 504 and its working contact, winding of series relay 505, winding of vertical magnet 517 to battery. Since the first digit dialled was three, the shaft and wipers of selector IS1 will be raised to a position opposite the third level of the bank. Relay 505 operates in series with the vertical magnet and at armature 506 and its working contact completes a circuit from grouii'l at the working contact of armature 503 and said armature, armature 506 and its Working contact, oit-normal springs 519, interi upter springs of the rotary magnet, winding of rclay 507 to battery. Relay 507 operates and at armature 509 and its Working contact prepares the circuit to the rotary magnet. Vhen relay 505 deenergizes at the end of the vertical movement of the switch, a circuit is completed for the rotary magnet from ground at armature 503, armature 506 and its resting contact, armature 509 and its Working contact, windingv of rotary magnet 518 to battery. The rotary magnet operates and rotates the wipers into engagement with the first set of contacts in the bank. At the same time it opens its interrupter springs, thereby opening the energizing circuit of relay 507, allowing this relay to release and open the rotary magnet circuit. In case the first trunk in the third level is busy, test wiper 521 will encounter a grounded bank contact and relay 507 will be again operated in a circuit from ground on test wiper 521, armature 512 and its resting contact, oit-normal springs 519, interrupter springs of the rotary magnet 518, winding of relay 507 to battery. Relay 507 again operates to complete the rotary magnet circuit which energizes and. rotates the wipers into engagement with the second set of bank contacts. The operation of the rotary magnet again opens the circuit of relay 507 and allows this relay to release.

The above inter-action between stepping relay 507 and the rotary magnet 518 continues until test wiper 521 is rotated into engagement with a bank contact associated with an idle trunk. As soon as ground is removed from test wiper 521, relay 510, which has been shunted by this ground during the rotation of the shaft and wipers, operates in series with the stepping relay 507. At armatures 511 and 514 and their respective resting contacts it disconnects line relay 500 and at the working contacts of these armatures it switches through the incoming line to the line wipers 520 and 522. At armature 512 and its working contact a locking circuit is prepared for switching relay 510 and at armature 513 and its resting contact ground is removed from the armature of the line relay to prevent the release of the switch at this time. Relay 500 deenergizes and at armature 501 and its working contact opens the circuit of release relay 502. Relay 502 is slow-to-release and remains operated until ground has been returned over test wiper 521 to maintain relay 510 operated. Relay 502 then releases and at armature 503 and its working contact opens the initial energizing circuit of relay 510, and at armature 504 and its resting contact prepares a point in the release circuit of the switch.

It will be assumed that the connector C1 shown in Fig. 6 of the drawing was selected by the incoming selector ISl over bank contacts 552, 553, and 554. As soon as switching relay 510 of the selector is operated and switches through the incoming line, line relay 607 operates over the incoming loop and at armature 608 and its Working contact closes a circuit for release relay 609. Release relay 609 operates and at armature relay 510 of the selector. Relay 600 whic is included in the circuit of line relay 607' is a dilferential relay and does not operate at this time. At armature 611 and its working contact release relay 609 prepares the impulsing circuit and at armature 612 and its working contact it prepares a locking circuit for relays 615 and 631.

When the incoming loop is interrupted at armature 493 of relay 488 in repeater R1, line relay 607 releases and completes a circuit from ground, armature 608 and its resting contact, armature 611 and its Working contact, oH-normal contacts 643, winding of series relay 613, winding of vertical magnet 641 to battery. A t the first vertical step the olf-normal springs are operated and thereafter the impulsing circuit extends over oilnormal contacts 642 and armature 614 and its Working contact of the series relay 613 which operates in series with the vertical magnet at the first impulse. Since the second digit of the called telephone number was assumed to be 2, the shaft and wipers of the connector switch are raised opposite the sec ond level of the bank. When relay 607 remains energized at the end of this digit, series relay 613 releases and at armature 614 and its resting contact prepares the circuit for the rotary magnet. When relay 607 releases responsive to the first impulse ofthe last digit, a circuit is completed from ground, armature 608 and its resting Contact, armature 611 and its working contact, oi-normal springs 642, armature 614 and its resting contact, resting contact of armature 624 and said armature, armature 636 and its resting contact, winding of rotary magnet 644 to battery 45 and in parallel with the rotary magnety through the winding of relay 627 to battery. Relay 627 operates in this circuit and at armature 629 and its working contact completes a circuit for the rotary magnet independent of armature 624 of relay 619. The rotary magnet is energized in this circuit at each impulse of the last digit, which 1n this case was assumed to be 3, and rotates the wlpers of the switch into engagement with the third set kof bank contacts in the second level. At armature 628 and its working contact relay 627 prepares a test circuit to relay 6 19. -At armature 630 and its resting contact 1t opens a point in the energizing circuit of relay 615.

It will first be assumed that subscriber T3 is already engaged in a conversation when the wipers of connector C1 are operated into engagement with bank contacts 648, 649, and 650. In this case there will be a ground potential on test bank contact 649, and test .relay 619 will operate a circuit extending 'from grounded bank contact 649, test wiper 646, armature 628 and its workin contact, winding of relay 619 to battery. Relay 619 operates in this circuit and at armature 626 and its working contact connects up the busytone to the incoming line conductor 34 over conductor 652, resting contact of armature 637 and said armature, working contact of armature 626 and said armature, and through the line condenser to conductor 34. At armature 625 and its 'working contact an energizmg circuit is prepared for relay 615. At armature 620 and its working contact relay 619 prepares a locking circuit for itself which becomes effective as soqn as the slow-to-release relay 627 deenergizes. At armature 621 and its resting contact the circuit of the switching relay 631 is opened and at a1'- mature 623 and its resting contact a point is opened in the circuit oi the battery reversing relay 602.

When relay 627 releases it completes the locking circuit of relay 619 at the normally closed springs controlled by armature 628, and at armature 630 and its resting contact completes an energizing circuit for relay 615. Relay 615 operates and at armatures 616 and 618 and their respective resting contacts it opens the ringing circuit and at the working contacts of these armatures it closes points in the talking conductors. At armature 617 and its working contact it completes a locking circuit for itself to ground at armature 612 of release relay 609 by -way of armature 601 of the differential relay 600.

The busy tone is transmitted to the operator at the manual exchan e through repeating coil 437 of repeater R1, over the trunk line and through repeating coil 318 of thev -trunk circuit TC to the cord circuit CC and operators telephone circuit OTC. When the operator at the manual exchange hears this tone she knows that the wanted subscriber is already engaged in a telephone connection. In case she wishes to offer the call to the wanted subscriber, she momentarily operates the toll offering key 286, thereby completing a circuit from ground, key springs 277, windingsof relays 272 and 268 to battery. Relays 272 and 268 operate in this circuit and at armature 270 the circuit of the supervisory relays 274 and 278 and the sleeve relay 303 of the trunk circuit TC is opened, and these relays release. At armature, 273 and its Working the differential relay 310 also operates in this circuit from the battery feed through the resistances 284 and 285 in multiple. When sleeve relay 303 releasedthe slow-to-release relay 307 was operated from ground 4at the jack springs 300. At varmature 309 andlts working contact, relay 307 closes a locking circuit for the lower winding of relay 310, and at armature 308 and its working contact completes a circuit extending from ground, armature 311 and its working contact, working contact of armature 308 and said armature, winding of relay 367 to battery. Relay 367 operates'and at armatures 368 and 369 and their respective working. contacts connects the alternating current source to the trunk conductors 1 and 2. As soon as relay 310 operated it closed a shunting 'c1rcuit for the winding of relay 307 extending from Jack springs 300, armature 312' and its worlrmg contact, to the upper termlnal of the wmding of relay 307. Resistance 384 1s provided to prevent the short-circuitmg of the battery. Relay 307 is made slow-to-release by a copper slug on the heel end of its core and 1s further slow-to-release due to its short-cir- 'cuited winding and, therefore, an appreciable time elapses before this relay will release. When it finally releases it opens the locking circuit of relay 310 at armature 309 and its working contact and allows this relay to release, thereby reoperating sleeve relay 303 and the supervisory relays 274 and 278 in the position circuit. The release of relay 307 opens the circuit of the impulse sending relay 367 at armature 308 and its working contactl and relay 367 thereupon releases and at armatures 368 and 369 opens the connection Yof the alternating current source to the trunk line conductors 1 and 2. The length of the toll oiering impulse is, therefore, governedby the time required for the slow-to-release relay 307 and relay 367 to deenergize.

Referring now to repeater- R1 shown in Fig. 4 of the drawings, when the toll-Oifering alternating-current impulse is received over trunk conductors 1 and 2, relay 435 is operated and at armature 436 and its working contact completes a circuit from ground at the normally closed springs controlled by armature 413, armature 436 and its working contact, conductor 11, working contact of arc,

mature 449 and said armature, normally closed springs controlled by armature 444, winding of relay 488 to battery. Relay 488 operates and at armature 490 and its working contact completes a locking circuit for itself to ground at armature 497 of relay 494.

At armature 491 and its working contact it completes the circuit for the upper winding of relay 499. Relay 499 operates, at arma- `ture 443 and its working contact completes an energizing circuit for relay 494, and at armature 444 and .lts working contact prepares a locking circuit for itself. Relay 494.oper- 417 and its working'contact prepares a lockg 1n circuit for the slow-to-release relay 405.

Vhen relay 499 operated it completed a circuit at armature 440 extending from ground at armature 433 of relay 430, conductor 22, armature 440 and its working contact, working contact of armature 455 and said armature, conductor 20, to the lower terminal of the winding of relay 400 thereby shuntinglthis relay and allowing it to rei lease. en relay 400 releases it extends the ground on conductor' 20 through armature 401 and its resting contact to the lower terminal of the winding of relay 419, thereby shunting this relay. At armature 403 and its resting contact it completes an operating circuit for relay 405 from the grounded conductor 20. Relay 405 operates and at armature 406 and its working contact completes a locking circuit for itself to the grounded conductor 6, through armature l417 of'relay 415.

Relays 400 and 419 are so adjusted and the toll offering impulse is so timed that relay 499 remains operated a suiiicient length of time so that the shunted relay 400 will releaseand operate relay 405. The impulse ends before relay 419, which is shunted upon the release of relay 400, hashad time to deenergize. At the 'end of the toll offering impulse, relay 435 releases and at armature 436 and its working contact opens the locking circuit` of relay 499. Relay 499 releases and opens the circuit of rel-ay 494 at armature 443 and its working contact. At armature v441 andits working contact it opens the circuit of slow-to-release relay 415, and at armature 440 and its working contact it opens the shunting circuit of relays 400 and 419. Relay 400 again operates and opens the shunting circuit o relay 419 at armature 401 and its resting contact. At armature 404 and itsv normally closed springs controlled by armature 603, upper winding of line relay 607 to battery. The lower winding of relay 600 is thereby shunted and this relay energizes over its upper winding. Relay 600 operates and at armature 601 and its working contact it completes a circuit for switching relay 631 extending from ground at armature 612 of the release relay 609 and through the working contact of this armature, armature 601 and its working contact, lower winding of switching relay 631 to battery. Relay 631 operates and at armature 635 and its working contact completes a locking circuit for itself from ground at armature 612 of the release relay 609. At armature 637 and its resting contact it opens a point in the busy-tone circuit and at armatures 632 and 638 and their respective Working contacts it completes the talking circuit over wipers 645 and 647 and bank contacts 648 and 650 to the called subscribers line. At armature 634 and its Working contact it transfers the locking circuit of relay 619 to the ground potential which is present on test Wiper 646, due to the previously established connection.

Since relay 619 remains operated, it is apparent that the talking connection to the already established connection, in which subscriber T3 is engaged, is established by connector C1 without any battery connections to the line since the back-bridge relay 602 has been disconnected at armatures 626 and 623 by the operation of relay 619. Thus, the operator can cause the connector C1 to cut-in on the busy line Without any disagreeable noises and can offer the call to the wanted subscriber. The locking circuit of relay 619 is transferred to the ground potential which is present on bank contact 649 so that in effect the connector C1 will camp on the busy line and wait for the wanted subscriber to release the already established connection.

Referring now to the point where relay 400 again operated ,to complete the circuit for the ground connection to negative talking conductor, the duration of this ground connection is determined by the time required for the slow-to-release relay 415 and the slowto-release relay 405 to deenergize. When relay 499 releases it opens the operating circuit of relay 415 at armature 441 and its working contact. Relay 415 releases after an interval and at armature 417 and its working contact opens the locking circuit of relay 405. After an interval relay 405 releases and at armature 409 and its working contact opens the circuit over which ground was connected to the negative talking conductor as described above.

In case the subscriber at substation T3, when informed of the call which is waiting from the manual exchange, desires to continue with the present conversation and instructs the operator to release the other call, the operator at the manual exchange will remove the plug P from the jack J and bring about the release of rl the uipment which has been used in the establishment of the connection. The method in which the release of the equipment is brought about will be explained later. It will be assumed that subscriber at substation T3 wishes to accept the toll call from the manual board and hangs up his receiver to release the already established connection. As soon as ground is removed from test bank contact 649 by the release of the established connection, relay 619 is released and at armature 625 and its Working contact it opens the initial ener izing circuit of the ring-cut-of relay 615, ut this relay remains operated over its armature 617 from ground at armature 612 of release relay 609. At armatures 623 and 626 of relay 619, the back-bridge relay 602 is again connected to the line wipers and at armature 622 and its resting contact ground is connected to test wiper 646 to make the call line busy to other switches. When the established connection has been released, the called subscriber again lifts his receiver thereby completing a direct current path through his substation and allowing the back-bridge relay 602 to operate and reverse the battery connections to the incoming line. Relay 602 at armature 606 and its working contact also completes another point in the locking circuit of relays 631 and 615 so that these relays will not release in case the called subscriber does not replace his receiver after the operator has released the connection.

The reversal of the battery connections to the line at connector C1 reverses the current through the lower winding of relay 471 in repeater R1, and as the -two windings now! assist each other this relay operates. At armature 472 and its working contact, relay 471 completes a circuit from the grounded conductor 6, normally closed springs controlled by armature 431 of relay 430, conductor 4, working contact of armature 472 and said armature, winding of relay 473-to battery. Relay 473 operates and at armature 478 and its working contact shunts the impulsing springs on relay 488 to prevent the opening of the loop circuit to connector C1, at armature 477 and its working contact it prepares a circuit for relay 480, at armature 475 and its working cont-act it prepares a circuit for the impulse sending relay 423, and at armature 476 and its working contact it completes a circuit for relay 488 of the impulse correcting relays extending from ground, normally closed springs controlled by armature 413 of relay 410, armature 436 and its resting contact, conductor 10, amature 47 6 and its working contact, resting contact of armature 483 and said armature, normally closed springs controlled by armature 444, winding of relay 488 to battery.v Relay 488 operates and at armature 491 and its working ycontact completes a circuit for relay 499.

Relay 499 operates and at armature 443 and its working contact completes a circuit for relay 494. At armature 444 and its working for itself. Relay 494 operates 4and at armav ture 496 and its working contact, completes the locking circuit of relay 499 to the grounded conductor 10, at armature 497 and its rest` ing contact it opens the locking circuit of relay 488 allowing this relay to release. Relay 499 in operating also completes a circuit for relay 480 at armature 441 and its working contact extending over armature 477 of relay 473. Relay 480 operates and at armature 484 and its working contact locks itself to the grounded conductor 6. At armature 485 and its working contact it completes a second shunt circuit for the impulsing springs of relay 488. At armature 486 and its working contact it short-circuits the lower Winding of relay 494 and at armature 487 and its working contact short-circuits the lower winding of relay 499.

Vhen relay 488 operated responsive to the operation of relay 473, it completed a circuit from the grounded conductor l0, armature 475 and its working contact, working contact of armature 492 and said armature, conductor 9, upper winding of relay 423 to battery. Relay 423 operates and at armatures 424 and 125 and their respective working contacts it connects the alternating current source through the frequency doubling transformer 35 to the trunk conductors 1 and 2 to transmit an impulse of alternating current over the trunk line for answering supervision. When relay 480 operated it opened the locking circuit of relay 499 at armature 483 and its resting contact but the lower winding of this relay is short-circuited at armature 487 and the relay is, therefore, slow-to-release. Relay 499 releases after an interval and at armature 443 and its working contact it opens the energizing circuit of relay 494 which is also slow-to-release, due to its short-circuited lower winding. After a short interval relay 494 releases. The length of the alternating current impulse transmitted over the trun line to the manual exchange is, therefore, governed by the time required for relays 499 and 494 to operate and for relay 488 to release, since the circuit of the impulse transmitting rela 423 is opened at armature 492 and its working Contact as soon as relay 488 releases. The impulse correcting relays 488, 494, and 499 are now restored to normal and relays 471, 473, and 480 remain operated.

The alternating current impulse which was transmitted over the trunk line responsive to the answering of the called subscriber momentarily operates the alternating-current impulse-receiving relay 320 in the trunk circuit TC in Fig. 3 of the drawings. At armature 321 and its working contact relay 320 completes a circuit from groun working contact of armature 321 and said armature, armature 326 and its working contact, armature 338 and its resting contact, normally closed springs controlled by armature 346, upper winding of relay 343 to battery. Relay 343 operates and at armature 345 and its working contact completes a locking circuit for its two windings in series extending through resting contact ofv armature 355 and sald armature, to ground at jack springs 300. At armature 344 and its resting contact it removes ground from the low resistance winding of relay 303, thereby bringing about the release of relays 274 and 278 in the operators p osltlon circult and extinguishing the supervisory lamp 215 to inform the operator that the called subscriber has answered. At armature 346, relay 343 opens its initial energizing circuit and at the working contact of this armature transfers the ground from the impulse receiving relay to the upper terminal of the winding of relay 347. However, the answering supervisory impulse received is not of suficient length to release relay 347 and this shunting circuit is opened at armature 321 and its working contact by the cessation of the impulse before relay 347 releases. Upon noting the extinguishing of the lamp 215, the operator restores the key K to its normal position, thereby releasing relay 200. Relay 200 in releasing connects the talking conductors through from plug P1 to plug P and also releases the operators position circuit PC. The calling subscriber has-now been connectednto the desiredcalled 'subscriber and 'the conversation may take place, the talking circult including repeating coil 318 in trunk c1rcu1t TC and the repeating coil 437 in repeater R1.

Returning now to the point where the wipers of connector C1 were operated into engagement with bank contacts 648, 649, and 650, 1t w1ll now be assumed that the subscriber T3 1s not engaged in any telephone connection at this time. In this case there will be no ground potential present on bank contact 649 and the busy relay 619 will not be operated.

' A short interval after the cessation of the dialling impulses, relay 627 releases and at armature 628 and its resting contact completes a circuit from ground at the working Contact of armature 610 and said armature, resting. contact of armature 621l and said armature, upper winding of switching relay 631, resting contact of armature 628 and said armature, wiper 646 and bank contact, 649, to battery through the cut-olf relay of the called subscribers lineswitch. Relay 631 operates in this circuit in series with the cutof relay and at armature 635 and its working contact completes' a locking circuit for its lower winding. At armature 633 and its Working contact direct ground is connected to test wiper 646 to make the called line busy to other switches and also to maintain the cut-off relay of the lineswitch operated. At armature 636 and its resting contact relay 631 opens a point in the circuit to the rotary magnet, and at armatures 632 and 638 and their respective working contacts it completes the ringing circuit to the called line. This ringing circuit extends from the ringing lead 651, upper Winding of ring-cut-oiil relay 615, resting contact of armature 616 and said armature, Working contact of armature 632 and said armature, wiper 645, bank contact 648, line conductor extending to the called station, the bell and condenser at the called station, the second line conductor, bank contact 650, Wiper 647, armature 638 and its working contact, armature 618 and its resting contact to ground. Ringing current .is intermittently transmitted over this circuit until the called subscriber lifts his receiver, thereby shortcircuiting the bell and condenser at this station and completing a direct current path over the above traced circuit for the upper winding of ring-cut-off relay 615. Ring-cutoff relay 615 operates and at armature 617 and its working contact completes a locking circuit for its lower winding. At armatures 616 and 618 and their resting contacts it opens the ringing circuit and at the working contacts of these armatures it completes the talking circuit to the called station.

Responsive to the completion of the talking circuit, back-bridge relay 602 operates over the called subscribers loop and at armatures 603 and 604 reverses the battery connections to the incoming line conductors. At armature 605 and its resting contact a point is opened in the release circuit of the connector switch. The reversal of the battery connections to the incoming line conductor causes the repeater R1 to transmit a short impulse of alternating current over the trunk line to extinguish the supervisory lamp at the operators position, in the manner described above. The operator then releases the key K associated with her cord circuit and the talking connection between the'callin and called subscribers is established.

Vhen the called subscriber at substation T3 hangs up his receiver at the end of the conversation, back-bridge relay 602 releases and again restores the battery connections to the incoming line conductors to normal. The reversal of current through the lower winding of relay 471 in repeater R1 causes this relay to release, and at armature 472 and its working contact it opens the circuit of relay 473. Relay 473 releases and at armature 475 and its resting contact it completes a circuit for the impulse transmitting relay 423 extending from the grounded conductor 10, armature 475 and its resting contact, working contact of armature 481 and said armature, conductor 9, upper winding of relay 423 to battery. Relay 423 operates and at armatures 424 and 425 it connects the alternating current source to trunk conductors 1 and 2 extending to the manual exchange to transmit an alternating current impulse as a disconnect signal. At armature 476 and its resting contact, relay 473 completes a circuit from grounded conductor 10, armature 476 a locking circuit for itself. Relay 499 operates and at armature 443 and its working contact completes a circuit for relay 494. At armature 441 and its working contact it completes a circuit for relay 415. Relay 494 operates and at armature 495 and its working contact it completes a circuit extending from grounded conductor 10, armature 476 and its resting contact, armature 482 and its working contact, armature 495 and its Working contact, armature 465 and its resting contact, upper winding of relay 461 to battery. Relay 461 operates its armature 463 to complete a locking circut for itself from grounded conductor 6, but does not operate its remaining armatures until the ground is disconnected from the junction of its upper and lower windings. This same ground extends through armature 479 and its resting contact, armature 453 and its working contact, conductor 8, winding of relay 430 to battery. Relay 430 operates in this circuit and at armature 433 and its resting contact removes ground from conductor 22 to prevent the release of relays 400 and 419 and the operation of relay 405.

vAt armature 497 and its resting contact 494 opens the locking circuit of relay 488 and allows this relay to release. At the normally closed springs controlled by armature 496 it opens the energizing circuit of relay 499. Relay 499 has its lower winding short-circuited at armature 487 and its working contact and is, therefore, slow-to-release. When,

relay 499 releases it opens the circuit of relay 494 at armature 443 and its working contact, and at armature 441 it opens the circuit of relay 415. Relay 494 is also slowto-release, due to its lower winding being short-circuited at armature 486 and its working contact and a short interval is, therefore, required for this relay to release. When it releases, it removes the ground connection from the junction point of the two windings of relay 461 and allows this relay to operate in its second step and operate all of its armatures. At the back contact of armature 495 relay 494 again completes the circuit of relay 488 and this relay again operates in the. in

it prepared a circuit at armature 465 and its working contact for rela 458. When relay 494 is operated during t e second complete operation of the impulse correcting relays 488,494, and 499, it completes a, circuit from the grounded conductor 10, armature 476 and its resting contact, armature 482 and its working contact, armature 495 and its working contact, amature 465 and its working contact, conductor 19, armature 429 and its resting contact, conductor 18, winding of relay 458 to battery. Relay 458 operates in this circuit and at the normally closed sprin s controlled by armature 459 it opens the loc ing circuit of relay 480 and at the'normally closed springs controlled by armature 460 it opens the locking circuit of relay 461. Both of these relays, together with relay 458, remain operated over the circuit just described as long as relay 494 of the impulse correcting relays remains operated. When relay 494 again releases, the ground connection to relays 458, 461, and 480 is opened and these relays release. Relay 458 is made slow-tore lease to insure that relays 461 and 480 will release before relay 458 so that their locking circuit will not be again completed at the normally closed contacts controlled by armatures 459 and 460.

When relay 480 releases, as described above, it opens the circuit of the impulse sending relay 423 at armature 481 and its working contact, thereby terminating the impulse of alternating current which was being transmitted over the trunk line as a disconnect signal to the manual operator. At

armature 482 and its working contact itV opens the circuit to relay 488 to stop the operation of the impulse correcting relays. At armature 485 and its working contact it opens the second shunt around the impulse springs of relay 488, and at armatures 486 and 487 and their respective working contacts it opens the short-circuits around the lower windings of relays 494 and 499. Slowto-release relays 415 and 430 release .after an interval following the final release of relay 499. v

When the long alternating current im pulse for disconnect supervision transmitted in the manner just described is received at the trunk circuit TC, relay 320 operates and at armature 321 and its working contact it connects ground through armature` 326 and its working contact, armature 338 and its resting contact, working contact of armature 346 and said armature, to the upper terminal of the winding ofv relay 347. A resistance plrovided to prevent the short-circuitoft e battery. elay 347 ismade slow-tore ease by a copper slug on the heel end of its core and is now shunted by the round connected to the upper terminal of its winding. The disconnect pulse yis so timed that it is of suclent duration to maintain relay 347 shunted until it releases. When relay 347 releases it completes a circuit for relay 353 extending from ground at armature 344 of relay 343 and the working contact of this armature, armature 349 and its resting contact, armature 332 and its resting contact, upper wlndmg of relay 353 to battery. At armature350 and its working contact it opens its locking circuit and at armature 352 and its working contact it opens one point in the circult of the busy visual 302. The busy visual, however, is maintained operated from ground at armature 363 of relay 362.

j Relay 353 operates in the above traced circult and at armature 354 and its working contact it completes a locking circuit for its two windings in series from ground at armature 344 of relay 343. At armature 355 and 1ts resting contact it opens the locking circult of relay 343. The operation of the remainmg armatures is Without eilect at this time. I Relay 343 releases wheny its locking circuit is opened by relay 353 and at armature 344 and its working contact, opens the locking circuit of relay 353 and at the resting contact oi this armature it connects ground to the low resistance lower winding of sleeve recontact of armature `315 and said armature,

sleeve of jack J and plug P, normally closed springs controlled by armature 203, and to battery through supervisory lamp 215 and resistance 217, in multiple. Supervisory lamp 215 lights to inform the operator that the called subscriber has hung up his receiver. Relay 347 is released only momentarily and again operates as soon as relay 320 releases at the end of the disconnect signal.

When the operator notes the lighted condition of the supervisory lamp 215 she removes the plug P from a trunk jack J, thereby opening the circuit of the sleeve relay 303 and opening the jack springs 300. The opening of jack springs 300 removes ground from conductor 382, thereby opening the locking circuit of relay 322 and the circuit of relay 360.A Relay 322 releases and at the double contacts 323 and 325 it opens the circuit of relay 347. At armature 329 iand its resting contact itcompletes a circuit extending from ground, armature 329 and its resting contact, armature 341 and its resting co'ntact, armature 364 and its Working contact, winding of relay 367 to battery. Relay 367 operates and at armatures 368 and 369 and their respective working contactsv it connects the alternating current source to trunk conductors 1 and 2, thereby transmitting an alternating current

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