US1579236A - Telephone-exchange system - Google Patents

Description

LF36 y H. EN. NWL A TELEPHONE EXCHANGE SYSTEM Fild Sept. '7, 1922 5 Sheets-Sheet 1 n u? Si y; 53 EI-@Qa Ama ma L@ H. wa QNEM, A

ELEPHONE EXCHANGE SYSTEM Filed sem. v, 1922 5 Sheets-'Sheet 5 Patented Aprov 6, 1926 I" l irren i? li i arci HENRY vW. ONEILL, OF BROOKLYN, NEW YORK, ASSIGNOR TO YVES/ BERN ELECTRC GOlfIPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.'

TELEPHONE-EXCHANGE SYSTEM.

Application iled September 7, 1922. Serial No. 586,616.

To @ZZ whomz' may concern.' Y

Bc it known that l, HENRY lV. QNniLL, a

citizen of the United States, residing at Brooklyn, in the county ot' Kings, State ot New York, have invented certain new and useful Improvements in Telephone-EX- change Systems, ci which the following is a full, clear, concise, and exact description. i rlhis vinvention relates to telephone systems, and more particularly to systems in which connections may be established by means oi' so--called machine switching equipinent.`

lt is the general object of this invention in connection with systems ot this nature, to provide an improved system whereby the varionsl operations t'or establishingand supervising' connections may be accomplished and carried out in an expeditious and reliable manner over-any torni ot physical or phantom telephone circuit, including toll or long distance linesot great length which may be equipped :tor superposed telegraph working or with telephone repeaters, and to avoid the l necessity ot composite ringer equipments on such circuits.

Other objects and features ot the invention will be set forth in thetollowing description and claims, and although the present embodiment ot the invention is shown and will be described in connection with telephone systems, it will be understood that features ot the invention may readily be applied to advantage in@ other situations oit signal operation or remote control.

ln thehandling oi' toll telephone traiiic, it is well understood that the attention ot au operator is required in order to insure a ticket record from which toll lcharges may he entered and collections made, relative to such use of the telephone plant. It has been tound in practice that a single operatorinay be relied upon for such records. Therefore, in situations where machine switching equipinent may be employed tor local service in the areas of toil centers, the provision ot equipment whereby an originating operator may complete connections without assistance troni operatorsY or other attendants at distantswitching peints or toll centers, will rcsult .ininaterially increasing the number ot connections which may be handled during` a given period overa toll line circuit, thereby improving the service while effecting through which, switchin 0' economies in operation as well as in the telephone plant. 4

For convenience in the descriptions presently to he given, toll tratiic concerned more particularly with connections over intermediate distances and between widely separated points where service .is commonly referred to as long haul connections will be considered, as it then will be obvious that the present system may readilyY be applied `to the handling' of any desired short-haul or local-service trai'lic. lt will be pointedfout that in general, service over intermediate distances is commonlyreferred to as two- .nnmber tratiic under which calls maybe handled by an operator usually reached by a calling party over a so-called two-number .recording trunk circuit. This operator in addition to recording a call, also may serve as an outward line operator to complete, supervise and iinally to dispose of a call or connection. For long, haul connections, a calling subscriber usually reaches a recording operator over a trunk circuit commonly referred to as a single-ticket recordin' trunk. This operator writes the details or the call on a form ticket which is then forwarded by means ot' a vacuum tube ticket distributing systeml or otherwise, to reach an outward long distance line'operator. ln either case, it is the common'. practice for the toll operator to work back over a circuit commonly referred to as a toll switching trunk in taking up the line ot a calling party, betere proceedingl to work out over a toll line for ther purpose ot reaching the party wanted in the area ot a distant toll center, all as well understood in thek art.

ln carrying out the present invention, coordination ot devices .and equipment has been ciiected whereby a pliuality of alternatingl currents ot frequencies best suited to eiiicient transmission over telephone circuits may control sensitive receiving devices,

operations, supervisory signal control, and operations tor the breaking down et a connection may-be Acar-` ried out entirely under` the control ot a single originating operator. Notwithstanding the tact that the sensitive re eiving 'devices may be included with the main conductors ot a circuit during talking periods, neither voice nor other similar currents may become effective to set up translations through these de- CII Veo

`an impulse'formed of a plurality of alternating currents may traversethe line and at the inward end of the circuit, be translated through suitable receiving devices to condition switches for reception of selective or switching' impulses. On the instant the inl ward switehin(Y rlevices have been so condin LA tioned, an impulse formed ot a plurality et alternating currents will be caused to revert over the linecircuit and eect display of the dialing` signal and also render the dialingequipment at the distant outward or controllingl operators position operative. Following' this signal, the operator may proceed to dial the code or number of the distant station wanted.

rlhisV system further lprovides that notwithstanding; the fact that a direct current loop circuit at the inward end of a toll line will be controlled by selective impulses ot alternating currents originating at the distant' outward end or" the line, no revertive effects will take place relative to the sending of alternating` current impulses from the inward to the outwardy end of the'toll line.r during the reception of such impulses of alternating currents. However, in case this same direct current loop may be controlled locally as `by a trunks busy, line busy, by switchhook manipulation etleets at a called station, or by effects due to switching` through at successive switches, impulses ot alternating' currents will be sent back over the toll line to be manifested in either of the several dilferent ways already described. t will also be pointed out that at the inward end of a circuit sensitive receiving devices whichserve the various functions ot conditioning' the equipmentior the reception of selective impulses, also serve for the translation ot animpulse to break down a connection and further for the control of a line signal when the distant end ot the circuit may be taken for use on a manual basis. ln connection'with the control of the line sig'- nal, thesereeeiving devices also apply a socalled busy test condition to the various manual jacks in association with the toll line, cause visual busy signals to` be displayed, and also establish a busy condition on the test terminals ot bank contacts where` by a toll line may, except 'for such busy condition, be seized by an automatic switch.

'.l`he toll line equipment also provides that at various points on a switchboard a circuit may be taken i'or automatically controlling* the completion eta connection. Associated means is also provided whereby a circuit may he taken tor manual operation, while at other points on the saine or adjacent switch-boards a line may be taken for use ou a manual basis or may be seized for use through au automatic switch. Switching devices are also provided whereby these dit'- lerent respective points 'tor the taking ot a toll line may automatically be disconnected one from another with respect to the main or talking conductors oi a line circuit, in a manner to exclude all points or access except such point as may at any time, have right oli way through precedence oit seizure.

ln order to eliect the breaking' down ot an automatically established connection, the releasing` et the circuit by an originating operator results in an inverse response of the switching devices already referred to whereby an impulse formed ot a plurality ot alternating' currents is impressed over the line circuit when Vthe line is taken, such inverse response et' the devices ei'lect application of an impulse formed or" a plurality ot alternating' currents, to the line circuit in atiecting' the receiving devices already described, whereby the equipment at the diS- tant end et' the circuit will be restored automatically to its normal condition.

rl'his invention is illustrated diagrammatically in the accon'ipanying drawings, and by positiomlng the several sheets from left to right in the order of the numbering oit the Figs. l to l, there will be presented a complete arrangement for the handling` of telephone tratiie in accordance withl the 'features or this system.

Fig. l shows equipment in association with a first toll center including a subscribers station A, an operators cord circuit C, equipment T associated with toll line circuit L. ritt the point E, equipment similar to the equipment E2 (Fig. Q.) may be pres' ent.

Fig. 2 shows equipment which may be located at a second toll center and comprises devices T1, which may be in duplicate or' the equipment T shown in Fig. l, equipment E2 orinward or outward working on the line L, and devices R for associating the equipment EL directly with a selector switch such as S (.F 3). ln Fig. 2^, there is shown a primary liuc switch PL and a secondary line switch SL which may be used in substitution ofthe devices R otl Fig. 2, in joining the equipment E2 oi the toll line L with a first selector switch as the switch .S already mentioned. he devices indicated by the reference character MS within the dotted rectangle shown in the lower portion of Fig'. 2A et the drawings, represent such portions ot convimtional master switches in association with the primary and secondary line switch PL and Sli may be necessary to an'miderstandiug of the associated circuits. ln lligr. 2B is shown an alternate arrangement oi" a plurality of relays relative to reception and translation or impulses Vtermed ot alternating currents. i

ln Fig'. 3, is shown a selector switehS joined to a trunk circuit L1 connec'tively accessible to a repeater equipment TS :trom which a truuk circuit lig extends, while in iio Fig. t a selector switch S2 which serves tor terminating the trunk circuit lf ias access to a connector switch K which n f engage equipment to reach a subscribers ion D.

ln a Vfurther and more. detailed description ot the present system, operations i'or extending a connection troni the station A (Fig. to the station l (Fig. l), on the basis that machine switching equipment is provided in the respective exchange areas in which theI lines ot these stations terminate, will now be considered. 'l`o this cud, let it ,first be assumed that a ticket covering such a call originating at the station It, has reached an outward line operator at a toll position having access to the cord circuit C and the associated equipment. lu order to insure that the calling party may readily be ayailable when the called station may have been reached. the toll operator inserts a plug Q ot the cord circuit (l into a jack l, then operates a combined splitting and dialing key (il which may be ot locking type, thereby disconnecting the right-hand portion ot the cord circuit and connecting a relay 5() which responds over an obvious local circuit to connect av dialing device D with the lett-hand end ot the cord circuit now joined with the jack l. This jack may he assumed as terminating a toll switching trunk circuit ot common battery, automatic type, and that direct current ilrom a source (not shown) on this trunk circuit may now be established through the pulsing contacts 5 ot the dial D by way ot obvious circuit through the alternate contacts ot the relay and the main contacts ot the key 64.-. As well understood in the art, it will be clear that the operation of the dial D may result in equipment, which may be assumed as present at the point AE on the trunk circuit, functioning to establish the desired connection with the station A. During these operations the oil-normal contacts S9 ot' the dial, are rendered inetllective, principally due to a second dialing key it beingl in its norial position, thereby disassociatiug grounded battery relative to control ot a relay l5 and a signal ll which serve in association with dialing` operations when carried out over the toll line L, as presently will be described.

On completion ot the dialing operations, the key (it may be, restored thereby permitting direct current 'from the trunk circuit to traverse the main conductors ot the cord in closing circuit over a. bridge path thereon which may be traced through the winding ot a lirst alternating current relay SO, the r'gnthand winding ot a supervisory control relay TT. and the winding` ot` a second alternating current relay Sl. Y(While direct current through thi:`l circuit may be ineffective in the alternating current relays SO and S1, the relay TT may, however, respond and apply ground potential through a resistance 29, the normal contacts of a marginal relay 35, a supervisory signal ST, thence to grounded battery through the contacts S5 ol a talking key ll). lt will be pointed out that on the present connection, the marginal relay 35 continues inert duc to the comparatively high resistance ot the sleeve circuit at. the toll switching trunk jack l. 'l`lierctore, the sig ial S? may continue energized 'so long as direct current may tlow troni the truuk circuit over the bridge path already trai-cd. lt may be assumed in the present connection, that the trunk circuit is ot any well i-:nown type ot common battery circuit in which battery current will be present on the main conductors o'l' the trunk so long as the rcceivcr may be on its switchhook at a connected station, as the station A, while removal et' the receiver 'troni its 'switchhook will result in disconnection ot the direct current Vtrom the trunk circuit. lt will theretore be readily understood thatthe relay TT under control ot direct current through its right-haunt winding, may atleet the signal 8T in unison with operations ot the switchhook at the station A.

During the present connection, the lefthand locking winding oit the relay TT will be idle, this winding being cllective only in situations where the plug 2 may be inserted in the jack oit a trunk or toll line circuit, usually ot the ring-down type, on which the resistance of the sleeve circuit may he low as compared with the resistance ot the sleeve circuit ot a toll switching trunk, thereby permitting lliow ot sullicient current. through the relay Irl-5 to ellect its operation. Such a connection will be described iurther Proceeding with the present assumed connection, the operator may actuate the sccond con'ibined dialing and split-ting key il to isolate the lett-hand portion ot the cord circuit C in associating the dial D and associated equipment with a plug in which now may be inserted in a jack l ot the toll line L. This permits a local circuit to be traced :from -grounded battery, through the normal contacts S5 of the talking key l0, the lett-hand normal contacts ot a rciay 5S, the lowermost normal contacts ot a ringing key 55, by way ot the parallel connected local contacts ot the two alternating current relays SO and Si, the arn'lature and lowermostcontact stop ot a polar relay f), winding 13 ot this relay, the winding ot marginal relay S, the sleeve ot plug` 3 and `iack l, normal contacts 2T otl a relay Q2 and the winding ot a. relay l0 to ground. 'the lett-hand contacts et the relay 5S which responds at this time substitute grounded battery at this relay 'tor the grounded battery at the key 1Q. The response ot` the relay l0 etl'ects at its uppermost contacts, switching ot the conductors of the toll line L from the equipment E to receive alternating currents at 700 and 1100 cycles per second from the sources 20 and 21 respectively, by way ot the uppermost normal contacts otl the relay 22. Closure oit the lower-most contacts ot the relay 10 connects the winding ot the relay 22 in parallel with the winding ot the relay 10. The. actuation ot the relay 22 switches the line L from the sourcesI ot alternating current 20 and 21 to the tip and ring conductors of the jacke. A further circuit may new -be traced from grounded battery, through contacts 60 of a relay 62, resistance 61, contacts 23 of the relay 22 to ground through the winding of the relay 10. llVhen the relay 22 has fully operated, its contacts 27 and 28 will'have substituted the circuit last traced through the contacts of the relay 62 for the sleeve circuit or the connection in retaining the -relay 10 energized, while the lowermost contacts of the relay 10 maintain relay 22 under control-ot the sleeeve circuit. rllhe inner transfer contacts of the relay 22 disconnect a lead 63 and apply ground to a lead 43 r-elative'to a busy lead 53 in associated equipment which may be assumed as' present but not shown, at the point E. This will be rendered clear in connection with description of duplicate equipment E2 of Fig. 2, in which the leads 243, 253 and 263 respectively correspond with the leads 43, 53 and 63.

The relay 10 is of a quiclr-to-operate but slow-to-release type, while the relay 22 is of a slow-to-operate but quick-to-release type. Therefore, the diilerence intime ot operation of the two relays may represent an interval during which the alternating currents may be included with the toll line circuit. The difference in time of response in either direction of these relays is further augmented due to the tact that the relay 22 may respond and release only by way of contacts of the relay 10, and in addition to this, the'current resistance drop in potential on the windings of the relays 22 and 10 during the time they may be in parallel, one. with the other, in receiving current over the sleeve path of the connection as routed through the relay 9 and the relay 53 further insures sluggishness in the initial or starting movement of the relay 22 ywhen energized. Further features relative to inverse or releasing movement ot the relays whereby an impulse of current from the same current sources 20 and 21 will be applied to the line circuit L when the connection is taken down, is also brought about by the interconnective relation of the relays 22`aud 10, as will ippear further on in this description.

It will be obvious that the impulse of alternating currents jiust described applied to the line L when this circuitywas taken, will beefective in loop er metallic relation over the conductors of the toll line at the inward endot which (llig. the circuit extends through the uppermost sets of nornial contacts ot a relay 215, the lowermost sets of normal contacts of a relay 220, then-:fe over the sets of normal contacts ot a relay 225 to energize two alternating current relays and 24:0 connected in bridge on the extension conductm's of 'the line circuit L. -lVhile these alternating current relays may be of any suitable type, they preferably may be o't' the mechanically tuned typeI shown in my copending application, Serial No. 52t,152, tiled December 31, 1921. As iudicated in the drawing, the relays 230 and 241.0 may respond respectively to alternating currents at 1100 and 700 cycles per second, whereupon their normally closed contacts will be caused to separate. Therefore, ar-

rival or the present assumed impulse ot alternating currents will disable a circuit which may be traced from `grounded battery, through `the winding ota-` slow-to-re lease relay 250 R, Fig. 2), normal contacts o1" relay 255, whence the ci cuit divides,

one path extending to ground through the contacts of the relay 240 while the other path includes the contacts of the relay 230 and the left-hand winding of a line signal relay 260 to ground.

As shown in the drawing, the relay 250 is normally energized, the. duration or length oi the present incoming impulse of alternating` currents is sullicient, however, to permit this relay to release and connect grounded battery current over an obvious circuit to the uppermost winding of the relay 255. The response of the relay 255switches the relay 250 to a release conductor 263, and places a pulsing relay 270 under Control of the alternating current relays 230 and 240. Cessation ofthe incoming impulse of alternating currents, due to operation of the distant relay 22, as described, results in the restoring of the relays 230 and 24:0, thereby applying ground potential over an obvious circuit to eilect operation of the relay 270. Closure of the right-hand contacts of this relay places a relay 280 in bridge on the main conductors oit a trunk cireuit- L1, joined through blocking condensers 2115 over the extension conductors already traced to the line L. The opposite end ot' this trunk circuit extends to a first selector switch S (Fig. where it is routed through the uppermost normal contact pairs of a switching relay 310, `trom whence one conductor extends through the right-hand winding et a pulsing relay 300 -to grounded battery, while the other conductor extends through the lett-hand winding ot the l atter relay to ground at the normal right-hand contacts ot a release relay 303. At this time, the response ci the relay 280 is an idle operation (the purpose of this relay will be titl described later on). while the response ot the relay 800 closes an obvious circuit to cause the operation ot the slo\.\'-to-reease relay 308. At the right-hand contacts ot the latter relay. the ground side ot the trunl; circuit L1 is switched through the lowermest normal contacts ot an otllnornial switch l. QN. and the Secondary windings ot transformers to ground at that point'. Sources ot alternating currents and having periods of TOO and 900 cycles per second, respectively, as indicated in the thawing.I may energize the transformers during periods corresponding with responses ot a relay 335 as controlled by an interruptor 33S. Resulting impulses et these alternating' currents t 'averse the trunk circuit L1, thence over the toll line L to result in the energization ot the distant dialing signel Ltl, as presently ivill appear. ln its operated position. the lett-hand contacts of the relay 5302 apply ground potential to the lead 263. thereby connecting grounded battery through the lovverlnost vcinding ot the relay to retain this relay opt ated. A. relay QT responds to current troni grounded battery, through its right-hand winding, thence by way ot the right-hand normal contacts ot a relay 222, which corresponds to thc relay 22 in Fig. l, to the conductor Q63. rlhe relay Q also responds orer an obvious circuit. to the ground potential on the conductor Q63, thereby disconnecting,` the circuit through the uppermostA winding of the relay Q which will now be retained by the current through its lowerinost Winding. At the right-hand contacts ot the relay T, a line signal 26T is disconnected. while grounded battery through the ulvpermostnormal contacts o't the relay 220 is applied to a conductor 253. in energizing a busy signal 2511i, and through condensers 28S. Qtql and Q82 to etiiect a soalled clicl: busy test condition on the sleeves ot` the .iaclr Qtltl. 'Zot and respectively. t. the le'it -hand contactsI ot they relay itt-fi a priyate or test segment litt ot" baul; contacts lll is switched from the relay 9,20 to ground potential. thereby establishing a busy condition for the bank contztcts. yvhile ground, also connected to torni a shunt path on the lett-hand Winding ot the relay Q60, in order that a Zero resistance ground connection may be present for the local contacts ot ther relay Qltl as normally present through the local contacts ot they relay Ql-O. during the reception ot selectiye impulses as ivill presently be described. lt will be understood that between the bus)v signal lot and the ground connection. other similar busy signals. as may be retpiired in association with the` various lis each one ot which may represent a single liacl ot respectively associated 1nut tiples may be connected. its yvell understood in the art, the busy conditions just It will be pointed out that althougl the current at TOO cycles per second alrtaidy described as impressed on the main comluctfnx: at the selector iq., may etl'ect responses ot' tbc relay Q40, no ett'ect will thereby be set up t this point: since the pulsing relay zit) will continue ei'iergized through he local con tact's of the 1100 cycle relay Jill. which continues inert.

At the. cord circuit C. the operated pesition ot the liey ,li mnnects grounded bat tery through a resistance unitV Slt. the local contacts ot an alternating current relay itl. the normal contacts ot a relay fle. and the upper normal contacts ot the relay l5 to ground. u'hile a second path 'trom the :2a ne battery extends through the winding' o t a relay #t2 and the normal cout` .i inst mentioned ot the relay l5 to ground.

l linerg '1: tion ot the relay l2 disconnects the sourcesv ot alternating currents (itl and TS) trom the cord circuit and establishes the winding ot the alternatingcurrent relayv lo by yvay o t the niain nialre contacts olIV the key .l-l. in bridge ot the right-hand end ol the cord circuit. lt will be noted that the contacts ot the relay 4-0 normally shunt the relay 41S which therefore continues inert. u'hile the normal contacts ot the latter relay. in turn. shunt the signal itl.

)it the dial D. it will he noted that the pulsing contacts 5 are normally shouted by the ground connection already traced through the contacts o't the relay l5. rthere- 'tore, in Iase the dial may be moyed u'hilo the relay Vt-S may be deenergixed. the otnormal contacts 5&9 ot the dial \vill apply grounded battery trom the hey llVV to ener gize au alarm or warning signal tt connected to ground through the lou'er normal eontiacts ot the relay l5. while the shunt path on the dial contactsl 5 render this device inellective to establish impulses ot' current with the toll line li.

Assuming non' that'. incoming alternatin; |j cnrents Ytrom the .selector switch ti arrive and complete a circuit through they relaiv llt. its contacts 'l5 rfill separate. thereby reinoving the shunt trom the winding ol'lhe rela. tis which may then respond and disconnect the contacts ol' the relay lttl thereby render ing` these members in"apable ot' shouting the relay i8. so long as the latter r. av univ be in its operated position. llnring intel-run tionsI ol the alternating currents as ell'ected by t'he.di;'-tant interrupter .No each re.-tor:t tion ot the relay `ttl elects application ot Current through the dialing .signal Ll-,t which therefore vill be caused to tlash in unison i'ith such interruptions of the impulses of altel'nating currents. ln moving the dial l) in response to this signal the contacts Si) `apply current from ,grounded battery at thekey 44 through the winding' of the relay 15, the alternate' contacts of the relay l-S, upper normal contacts of relaytl, thence to ground throughther pulsingl contacts 5 of the dial and the lower normal contacts of the relay 50. The response of the relay 15 opens the circuit of the signal 11 and the shunt path normally present on the pulsing contacts 5 of the dial. On release of the dial, each separation of its contacts 5 during its return movement, effects deenergiZat-ion of the relay 42 which switches the. main conductors of the connection lof the toll lino L, from the relay e0 to the current sources G9 and 79 of TOO and 1100 cycles per second, respectively. In this manner, it will be readily understood, that a series of selective impulses formed of alternating currents may be impressed over the line circuit L. rlhe contacts 89 of the dial continue closed u ntil the dial has returned to its normal position, thereby 'holding relay 15 operated during;

Vthe olf-normal condition of the dial.

In response to the first separation of the pulsing' contacts 5 of the dial at the beginning` of its return motion, in addition to cnergization of the relay 42, the relay 1S will be Vreleased to extinguish the signal 41 and also to reestablish the shunt path through the contacts of the relay 40 whereby the relay t8 is normally shunted. It will be clear from the drawing` that although the guard relay 15 initially may respond Vthrough the forward contacts of the relay 48, it may thereafter be retained through its self locking contacts until the contacts 89 may separate at the moment the dial yarrives at its normal position. Following such release of the relay 15 the pulsing contacts 5 will again be disabled and the warning signal 11 conditioned to respond in case the dial may be moved before reception of an incoming impulse of alternating currents to effect response of the relay 4:8 and energization of the signal i-1, as already described.

The alternating` current relay l0 may be y of the type already mentioned as preferable for the relays 230 and 240, and may be tuned to respond to either one of the incoming` alternating` currents, 700 or 900 cycles per second. Either one orthe other of these currents may accordingly be idly present during: moments the relay 4l() may bo under operation. The principal reason for the emixiloyment of the two currents for the rcvcr-tire impulses over the toll line is to insure joint response of the supervisory control relays 80 and 81 to actuate a signal 75, in case the key lit may not be in its operated position, due to inadvertence or to the fact that the operators attention may be required 'peremptorily on another connection which may necessitate the restoring of the lioy lil. Detailed description of the operations whereby the sign al T5 may be controlled will be given further on.

Referring now to the arrival at the inward end of the line L of the incoming impulses of alternating currents as controlled by the dial D, the alternating; current relays 23() and 2l() respond in unison to these impulses, thereby effecting corresponding responses of the relay 270 which, in turn, effects successive interruptions of the loop circuit through the trunk L1. At the first selector switch El, the pulse relay 300 in responding* to such interruptions, successively completes a circuit from grounded battery through a primary magnet 390, a slow-to-release relay 309, the contacts of the release relay 30S and the normal contacts of the pulse relay 300 (during each release of this relay) to ground through the next contacts 313 of the switching` relay 310. The switch S may be 0f a well known type in which the first response of the magnet 390 will effect transfer of the oli-normal switch P. O.l N. as well as movement of the brushes. The response of interruptor relay 320 to grounded battery by way of the contacts E30-l of the switch P. 0. N., the alternate contacts of the relay 309 to ground through the left-hand contacts of the relay 303, prepares a circuit for' secondary magnet 325.

lll hen operated, the relay 320 establishes a self lockingl circuit which is independent of the relay 309. This circuit extends through the contacts of the magnet 325, outer right-hand-contacts of the relay 820 to ,ground through the contacts 313 of the relay 300. At tne switch l). O. N. the transfer contacts switch the ground side of the trunk L1 from the transfer ners 324 to ground through the lowermost normal contacts of an lalltrimhs-busy switch 306 of this selector, thereby discontinuing the application of thc reyertiye alternating currents over the toll line L. lt may be mentioned that although currents from the sources 388 and may have been present on the main conductors of the connection jointly with the first incoming' impulse of alternating;l currents as released by the dialD, the 700 cycle currents of such impulses may meet and combine in effecting' response of the relay 240, while the 1100 cycle current of the dial controlled impulse only, may effect response of the relay 230. Therefore, proper and unmutilated reception of the lirst selective impulse will be had irrespective of the presence of the currents from the selector S. Pause of the distant dial following' the first series or train of impulses, permits the relay 309 at the switch S to restore and complete to ground at the left-hand contacts of the relay 308, 'the circuit prepared by the relay 320 for the magnet 325. The first response of this tit) :equipment TS. rlie lirst response magnet will more the hruslies of the switch S in a secondary direction in seeking` outlet through an idle trunl; repeater circuit as the ot the inaegiiet also d'sconnects the relay 320 which releases, therehy disconnectingl magnet 325. group may he'husy, a prirate wiper 331 ot the hrusli ;roup will encounter ground potential which may lie traced haelt through the lowcrniost coiitactsot the relay 310, the normal contacts ot the magnet 825 (now deenergizcdl, thence to grounded battery through the contacts F30-,tf et' the switch P. O )l and the winding' ot the interruptor re ay 132'). The response ot this relay rgaiii cstahlishf l its felt-locking' circuit to render it independent ot the husy ground'assuinegl. as encountered hy the hiusl B531, while this re'- lay 320 also rcestahlishcs'the circuit 'lor the nur Vmet This cycle ot operations relatirc to altcrnatire responses of the relay 320 and the iiiapgnct 2: will automatically continue until t c hi'us hes 5395 and 23%' arrire at the contacts ot an idle repeater. Such idle condition will he characterized h j,v absence ot ground on a prirate secfi'nent as the seilinent 5320 ot a haul( 'contact K-i'oup B2 oiZ the repeater TF4 Assuming' now'that the hrushes hare arrired at an( respectirely engaged the segments o't the lianlr contacts ot the repeater, ahsenee ot ground at the segment 3550 prerents the sluintiiig' of the relay 310,

theretoi'e, current through the low resistance relay S20 orer the path already traced as common to the lirnsli 39d may he traced orer a circuit through the hipgh resistance winding ot the switching; relay El() to ground throueli the uppermost normal contacts of the switch fltlt and tlie'oiiter lett-hand contacts ot the release relay SOS'. This effects response ot the relay 310, while the relay l'lt) which is ot the marginal type continues inert. under the sinall current permitted hy the hie'h resl ice ot the relay 310. rThe two uppermost sets ot contacts the latter relay switch the trunk circuit Ll Atroni the hattery supply at this selectoi-YS to the hrushes lfli and f'ltltl which now Vciieaee ilie corresponding segments ot the hanl ,'ronp lig. whence luittery and `ground connections extend thro li the contacts 5353 and 951 olf a rerersinev ielay 'li; and the winding' ot a hattery supply or pulsing relay 350. The latterrelaiv now resginnds to current through the loop toi-ined hy the trunk circuit lil, and

e orer an ohrious circuit ctliccts response ot a slmr-to-release relay lot. rThe rig'g'lithand contacts S35 the latter relay apply :round potential lr; way ot the segment 'll and the lowerinost alternate contacts otV lltl to the rel: release conductor 263. iu sulistitution oi" the Aground siiliscqiiently disconnected hy rel ase of the relay 303 following,` disconnection of the relay 300 at the inthisV ln case Vthe first repeater ot a (l. hruslr C il,

contacts ot the i lays 'ltli) :ind ltltr) to the contacts `l` ,'now separated, ot the relaj,Y n1 i ln case all ot the trunlzs or repe; ters in a siilwlrroiip, which inclu( the repeater TS, iuay hare heen husy, the niag'net l'would l are adianced the liiushcs and Vllt heyond the haul; contacts ot' the last repeater i the group, Yat, which point dcrices (not shown) may etl'ect operation et the switch lflti, iii the inaniier rell known in the art. rhe uppermost contacts ot' this switch dis connect the relay ill() to insure that the 'cuit Ll will continue energized selector, while the transt'er oon- :,tlt extend the ground circuit Llrrto ground secoiuiary windings o'l transrelay 325 under control of 1' .Lier ll controls the application et alternatinev currents `tioin the sources 38S and 39,0. to these, transformers. whence re- Vnel interrupter and the resulting' ditlcrence in the ra e ot llashinp; oi" theylistant siegril will serre as Van indication to the ooerator as to what condition has heen encountered. i

Y Returning to the, iuomeiit Vwhen the re peat r T5 was seized in the present assumed conuectioi as :iVV result, o't which the relays fla-lr were operated, signal and chain control relay 372 is energized hy the cui rent an ohiious loop path through a y tltl o't the selector S2, the sets ot" normal contacts ot a re 'itl, trunk circuit if to tac repeater TS, where a liridgi'e path niay'llic traced trom the conductor tltitl otl this trunk hy way ot'the outer right-hand contacts ol the release relay itil, the normal. contat td' ot a shunting relay lfit, the lett-lI d winding otan electro-polarixcd superrisorj.' control relay lltl. conta ftsr'll ol' Vthe relay il. he righthand'wiiulinfe ot' a signal and chain circuit cuitrol relay STL and the, rielitdiand pulse contacts ot the relay 3.70 to the conductor -Etl ot theI trunk circuit l?. Yrlhile the relay ST2 responds to curi-ent through the path just traced, the relay BTO continrcs inert due to the 'tact that current is also present lOl) i lt) lill) over an obvious circuitthrough its righthand Winding to ground at the contacts 3279 of the relay d is in opposition or ditl'eren-r tial relation with respect to the current through 'the lettehand Winding. The reason for this feature or' the relay.370 Will appear further on.

U be closed in establishing the loop circuit or the trunk L1, 1n advance of closure o't the left-hand contacts through cuit of' the trunk L1.

which ground potential, When present through the contacts ot the alternating current relays 230 and 2li() may become effective with the contacts ot the relay 280, and in versely, that during release ot the relay 270 its lett-hand contacts separate to open the grounding Acircuit to the contacts of the relay 280 in advance of the separation of the right-hand contacts to open the loop cir- 'lhe relay 280 may respond Libstantially in unison with such control ot the trunk circuit loop, therefore, during' such control ot' the loop circuit by the relay 2?() in response to incoming impulses ot selective current-s, responses ot the relay 230 may be 'coiisidered as idle operations and therefore noneii'ective with the relay 225. lt may Jfurther be pointed out that the object in connecting the contacts ot the rela; 280 to receive ground potential through the contacts ot the alternating curront relays 230 and 240 is to taire advantage ot the tact that no ground will be present during the intervals alternating currents in the term ci an impulse may be present in the latter relays. This etl'ect in itselic constitutes a complete guard during instants the. relay 270 may be dcenergized under such impulses, and therefore the relay 280 Yis in this additional manner rendered ineffective l From the foregoing it will at cn tin be envious that during absence of incominr; impulses and during such times as the relay 270mm Vbe steadily retained in its operated position, while the relavs 23() and 24:0 will be inert, ground potential will be enent at the contacts of the relay 280. retorc, any interruption or" the loop'cir4 the trunlr L1 or reversals of current pclaritvtherein as n ay beset up through operations as already described, at subsequent switches, may effect response of the relay v280 whereby the relay 225 Will, in turn, be caused to respond in applying alternating. currents to the toll line L. 'l

The selector Se is substantially ofy the 'same type as the selector S and a detailed description ot the progress of the present connection through this switch S2 is not deemed necessary.

At the instant the relay 372 of the repeater TS responded as described, its lefthand contacts applied ground potential present through the normal contacts 366 of the relay 356 to4 effect response of the reversing relay 352. The contacts of the relay 37 2 as shown, render it clear that this circuit tor the relay 352 may be closed during the interval corresponding With the time the three contact elements may be in engagement, one With the others While the .relay may be under actual movement. Therefore, when the relay 372 may either be fully operated or fully restored, the relay 352 will be disconnected relative to the present described circuit for its momentary control. rEhe momentary operation of the relay 352 etlects a corresponding reversal ot current polarity in the loop of the trunk circuit L1. At the relay 280 this results in what may be described as a first momentary release followed by reoperation or a tendency to reoperate, then a second release or a tendency to release, and a iinal reoperation ot this relay 280. These etlects result in the three Contact elements ot' the relay 230 continuing in engagement, or in successively reengaging in a rapid manner, one with the other, during an appreciable length ot time, depending on the so-called follow eilect adjustment ot the contact elements and the time-constant ot operation characteristics of the relay 280. During such interval an obvious circuit itor energization of the relay 225 will therefore be completed through the Contact of the relay 280 as joined to ground over the lett-hand contacts of the relay 2T() and the contacts ot the alternating' current relays 23() and 240. A condenser 24e shown in bridge on the Winding oit the relay 225 vmay be eniployed for prolonging the energization of this relay, as in supplying energy during instants the contacts of the relay 280 may actually separate during rapid to and tro movements as described under the effects ot current reversal in the loop circuit L1. Burino' such predetermined energizations of the relayV 225, the loop circuit ci the line L will be switched from the trunk circuit L1 to receive alternating currents from sources 208 and 218, at 700 and 900 cycles per second, respectively, 'for controlling either one of the signals on the distant cord circuit C as already described in connection with currents sent back from-the selector S tor the same purpose as the present assumed impulse relative to closing the circuits of the dial D and also :tor indicating that the dial may now be operated.

The next series of impulses released by ,the dial D, when received by the relays 23@ loo lill

and Qltf eli'ect interruptions of the trunk circuit loop L1, as already described, and now may set up correspond'ng responses of the pulsing relay 350 o'j the repeater TS. IThe lirst release of this relay closes an obvious circuit Jlor the "esponse of the relay 356. the right-hand transfer c n acts of unich disconnect the path already traced through the left-hand Winding' of the relay STO, and the right-hand winding ot the relay 237' and connect a zero-resistance path bv ray oli tue right-haul contacts ot the pulsing' relay 350 to torni a bridge on the trunk circuit L2. rEhe lett-hand contacts ot' the relay 356 substitrte at this time "for the right-hand contacts of the relay 372 in closing a circuit CR commonly referred to as a chain relay circuit tor displayine` a signal (not ,f-hoivn) when all ot the trunk circuits of a sub-group may be busy. Separation o't the contacts 3GB of the relay in advance ot sepa 'ation of the contacts 367 render the relay 372 ineffective ivith the relay at the instant the relay 372 released due to response of the relay 356. Under the arriving' impulses, the relay will etiect corresponding; interruptions of the trunk circuit L2. thereby causing the pulsing' relay OO o1" the second selector S2 to etllect energizations of a primary magnet 40S under vchich the brushes llt), all and vvill be advanced to a predetermined point` dependine' on the number oit impulses received.

ce ition ot these impulses a series rola 109 ot this selector may release, tollovvine' ivhich a secondary motion magnet 40T, under the control ot' an interrupter relay AOG, ma).v automatically advance the brushes llo, -lll and l2 in a secondary direction in seeking; an idle connector sivitch as the connector K.

In describing' operations which may take place in case all ot the connectors of a sub- `e'i'oup to vfhich the selector S2 has access have been found busy, the magnet Ll-OT ivill advance the brushes 410, lll and i12 bevond the last trunk ot such group at which point mechanical means (not shown) vill cause operation ot the trunks-busy sivitch 'll-ue uppermost contacts of this switch the switching relay 430 to in t 'unir circuit if may continuo i S2, while the reak type contacts of this r the ground side o'f the trunk teitial ground to ground ,Y ding of a relay 02. vRee ot the i ter relay to current in the op circuit ot the trunk L1, connects the `econdary windings of transformers 40st in l; mi the battery supply leads which extent through the normal contacts of the lil@ to the main conductors ot the trunk. )i relay controlled by an interrupter i238 controls the application of all A l the vvin ternating currents at TUO and. flott cycles per second, respectively, from the sources ll and Si to the transformers lOl. Accord irw u, impulses 'formed of these currents` may traverse the connection to the toll line i and thereover be mani'tested by flashing' o't the distant dialiugi- ,"gnal kll, or the supervisory signal T5, as an indication to the operator that all trunks ot the selected `group are busy.

4lssuinine' non' that the last movement ol' the switch ll brouo' t the brushes lill. -tll and lh? iito engagementI with terminals ll'l. #Li-ll i i -l-li rtspectivcly ol the connector l( ivl ich may he idle` such idle condition ivill be churn'r erixed by absence oll ground on the terminal llo thereby pci.'- niitting grounded battery through the lou' resistance narginal relay 40G ot the lector S2 to complete a circuit through the hich resistance winding' ot the switching' relay 130 which may respond to disconnect the trunk circuit lf trom the battery supply circuits of the .selector fig and exten-l the trunk circuit L2 through to the brushes ll. all and 15. The trunk circuit lf may no be energized by grounded battery .supplied through a pulsing' relay l1() and the contacts l-Qtl and -l-'l ol. a bach-bridge relay 425.

The momentary interruption ol the triml: circuit lf etl'ected bj.' operation ot the 'clay 'fl-l() in extending' the truul; circuit' thri'nrh the switch S2, results in momentary release followed by reoperation ot the relay Il?! atl the repeater TS. The lett-hand contactsy ot the relay ST2 accordingly establish the circuit already described through the, relay thereby etl'ectina' inoim-ntary response ot the atter relay to cause a momentary rcversal ot current polarity in the trunk circuit L in response to which the relav 2S() ivill ell'ect momentary response ot' therchiy in applying an impulse ot alternating currents over the toll line circuit to displa' the dialing' sie'nal and to render the dial at the distant operatons position etl'ectivc for sending; another series ot selective impulses,

ist the repeater TS the relation ott thc right-hand group ot contacts on the relay 355 as shoivn, is such that in response to cn- 'ration` the .normal contacts ito will sep alato in advance ot the separation of the adjacent normal contacts Ilo?, and inversely. on deenergization ot this relay. the contacts SGT will close in advance ot closure ot the contacts 5386. las already described` the contacts 366 extend ground potential to the lettliand contacts olE the relay "Pfl oi.- to render thisy relay ell'cctii'e in setting up momentary energizations ot the relay 352 during' actua movement of the relay ft2 ifhile the contacts 36T normally prepare the circuit throueh the leftfblllfl Wlflillg Of the relay lou Il l) and the right-hand winding of the relay previously traced as including,` the ight-hand contacts of the relays 350 and 54 in completing av lirect current path energized by cu from over the trunk circuit L2. Therefore, movement ot the relay 372 in either direction, when h movement may be due to action of the relay 356 will be ineffective with the relay and theV relaySO accordingly will not be ali'ected and no impulse ot alternating, currents will be sent to the line L by the relay 225 at such times. Frein the foregoing it will be obvious that the lett-hand contacts ol the relay 372 may be rendered eiliective with the relay at such times only the relay 356 may be at rest in its ineit position, and since the latter relay may be @under eiiergization during periods corresponding only with the actual reception oi a train or series ot' impulses for controlling .subsequent switches as the selector S2 or the connector K in the present drawings, it will he obvious that the relay 372 may be rendered etlective to cause the relay 225 to send a revertive impulse of alternating currents over the line L only at the instant the repeater-TS may have been seized and at such other times asl when the relay may momentarily respond to the cutting` throu'h ot trunk circuits atl subsequent .switches or to other operations as will presently appear. To insure proper responses at such times, the time constant of operation ot the relay 872 is to be within-the time interval present. between the. separation of the normal contacts and the closure of the forward contacts on subsequent switching` relays7 as the relay 430 of the selector S2, in the connection now being traced. The importance ot the relation between the relays -6 and 372 relative to control of the relay 35% may further be emphasized by pointing out that except for the arrange nient just described. a revertive impulse orp alternating' currents would become effective at the distant cord circuit to display the dialing signal 41 and to render effective the dial l), immediately following' the reception ot tirst series of impulses through the repeater for advancin'r the brushes ot the lector switch S12 to a predetermined primary direction. Therefore. .nd releasing` of the distant dial would be premature as no tiniewculd have been' allowed for completion oft the movement oiC the brushes 410, 411 and 412 in a secondary direction as already described as ellected through automatic control by the magnet 407 in conjunction with the interruptei relay 406, whereby either an idle third selector switch (not shown) or an idle connector switch, as the connector l, may have been reached and seized `for use. t similar condition would also be presented relative to dialingthrough each one ot any subsequent selector switches which may be present in situations well understood in the arts where suoli switches may be required following the selector switch S2.

At the connector l the energized position of the pulsing relay 416 and the re- '2. :it the instant the relay 4127 responded, IAs right-hand contacts, during the interval tl ree contact members were in enone tacts 01"' two alternating current relays 484 d 485 and the lowerinost or lockingv winding oi" a ringing relay 451 to ground at the contacts ot the relay 417. @n response ot the relay 451 its seltlocking or next lower moet contacts establish the circuit already traced through its lowerinost winding, thence over another lead to ground by way of the right-hand alternate contacts ot the relay 417. The cont-acts 452 and 465 of the reay 451 disconnect a rinfgiiigjw equipment 450 and at the present time idly7 connect the main conductors through to the contacts ot u brnsh disconnect relay 440 of the connector. rhe object in retaining the relay 451 energized at his time is to insure that ringing` current may not be applied to a called station except under control ot the originating opci'at r, as presently will appear.' In response to the next train ot incoming impulses comprising` the first iinpulses for moving the connector l, the pulsing relay 416, during` moments it may be in its cle-energized position, completes a circuit troni ground potential by way of the contacts 433 of the re ay 41'? and the contacts 484.01? an olie-normal switch 4535, the wind-I ing` ot a slow-to-release relay 418 and a primary niaonet 419 to grounded battery. rillie first' energization et the magnet 419 in addi" .i to advanc'lig the brushes 460. 461 and 447Y also eitects actuation oi"- th ott-normal switch 455,` and due t tion of the relay 41 i i9 w`ll new e4 c. alwriiate 'contacts ot thcoiitacts 486 o the swi ot the relayY 41"!w to i i normal contacts. oit tllc pulsing re a'` 416. The present series ot impulses serve to adnormal contacts o'l the pulsing relay 416.

t the instant the relay ilireleased. its inaledii"re-brealt right-hand contacts monientarilj.' applied around potential as present tl ouah the lovverinost contacts ot the sn'itcli'fm, to roumled battery through thersu'itch lo? to'lmvermost winding ot the reversin; r relay 425. The moinentaryrrespouse, ot the latter relay to current in this circuit e'ltects momentary reversal ot current polarity thi-'ouch Y the trunk circuit L2. "it the repeater TS, the lett-hand Winding ot the relay 2% 741 beine" in series with the trunl; loop.'tliis reversal ot' current renders the current ellfect in the tivo -.vindin{.s ot the relay BTO cumulative, therefore. this relay ivill momeutin'ily respond and at Vits outer light-haiul contacts apply ground potential o etl'crt similar response ot the relayv 352. AYtnouel1 the relay at the repeater T5 will also momentarily release at this time due to Vreversal ot current polarity in the trunl; circuit if. its e'ltects relativerto theI relay V12 ivill'be substantially an overlappineY operation with the, ette-cts established by the relay BTO. The relay 3.72 in turn, inocurrent polarityv in the 1 n: iich will be effective with an by the relays 280 and 225 in apilvina an impulse ot'alternating currents to display; the distant dialing` signal 4i and to render the dial D operative. The object in supplyi ground potential through tor- 1yard contJ ts on the ot normal switch 455 Glu-hand contacts ot the relay 418 r these contacts ineffective i'vith 'ehr j) on response ot the relay 41S at the begjinning` o't' the first series ot' impulses to th's connector. but to render these tive with the relay 425 dur-inerelease ot' ne relay 41S onY cessation ot such incoming impulses.

Under the next and lastseries of impulses -lor completing the prcsentsassumed connection, the relay 416 may actuate the magnet 4S() in advancing the brushes 460, 461 and 44 into engagement With the bank terminals 463 and 445 respectively of the line circuit to the station B. vDuring such travel ot the brushes 45t), 461 and 447 the bank contacts ot intervening line circuits Will be passed over. and the private Wiper 447 may idly encounter either battery potential or groundpotential respectively depending' on Whether an intervening line may be idle or busy. To insure that the brush disconnect relay 440 may not be prematurely operated due to battery beingl encountered on the bank contact of an idle line, a slow-to-release relay 442 is connected te be. energas@ in allel with the magnet 480. Under operation. the lett hand armature ot the relay 442 svvitches the private brush 44T' Ylrom the uppermost or operating` Winding ot the relay 440 to the busy relay -l'lll over a path through the louermost contacts ot the relay 440 and the winding' o't the relay 43) to grounded battery. It' will be obvious that the relay 4.239 may respond each time the brush 44T may pass over and receive ground )otential trom the private segment ot a busy line, andin order that the outer right-hand normal contacts ot their-clay 439 may not disconnect the magnet i-SO at such time, thc right-hantl contacts ot the relay 442 are connected to Ytorm a by-path around these contacts ot the relay 439.

Assuming` that the brushes 460, l-Gl and 44T have completed their travel and are non' at rest in engagement ivith the respcctive' serments 463 and 445 ot the bank terminals, and assuming further as a first illustration, that the line circuit oit thc station B is busy, as a resulto'lI which laround potential ivill be present on the segment 445, through means not Vsho-.vn but Well understood in the art, the relay 'lfltl may initially respond overthc circuit` already traced b v Way ot the contacts 44S ot the relay 442. thenceV over the brush 44T to the assumed around at the. segment Immediately AFollowing` this. release ot the relay 442 ivill tale place due to theiiliulsing relay 410 non' beine: retained in its operated position as a result ot cessation ot the last series ot im-Y pulses. Although the contacts 4T@ ot the relay 442 reconnect the brush 44T to the uppermost Winding ot the relay 440 the opposite end ot this winding' will now stand open at the contactsrl' ot the busy relay 4919. ivhilc the 1nahe-betorelneali ell`ect at the left-hand contacts ot the relay 442 permit the conta-ets 432 to close and substitute 'tor the `around potential supplied by Way of the brush 447, a circuit through the Winding' ol: a relay 49T and the right-hand innermost alternate contacts or" the relay 43,. thence to ground through the outer lett-hand contacts ot the release relay 41T. in this self-locked circuit of the relay 430. response ot the relay 49T connects aV battery interruptor 49S by Way ot the inner lett-band alternate contacts ot the'rclay'ell with the uppermost main conductor lead trom which a path may be traced throng-rh the upper ivindinfr ot the relay 425 to Iaround. lt will be obvious that the latter relay may respond to the interrupter 49S in effecting' successive reversals ot current polarity in the trunlt circuit if. As already described such reversals may be translated through the preceding switches and etuiipinentV to apply alternating' currents over the line circuit- L to flash eitherthe distant dialing signal 4i, the supervisory signal 75 or to be manifested as tone in the rel engaged its terminals.

trunk circuit L1.

ceiVer of the operators set, depending on the position of the keys in the cord circuit C. During the sending back ot a busy signal the outer lett-hand contacts of the relay 439 join a busy tone transformer 493 with the niain circuit ot the connection. This serves in situations Where a connector may also be employed :tor completing local as Well as toll connections, and is not essential to toll traltic.

Let it now be assuniedas a second illustration, that instead ot the line et station B l'iaving'been found busy'this line Was idle at the inoinent the brushes of the connector Under such co-ndition battery potential by tray of cut-oill relay 446 for clearing the line et station l of asociated equipment (not shown), the segnient 445, brush 447, contacts 47 6 of the relay 442, uppermost winding of the relay 440, thence to ground through nornial contacts 475 ot the relay .439 and the outer lettliand contacts ot the release relay 417 et tects response ot the relay 440. This closes a rcircuit freni grounded battery through the lowerinost locking ory retaining winding ot the relay 440, its sell-locking contacts 444, thence to ground through the right-hand alternate contacts oi the release relay 417. Other circuit changes eilected by response et' the relayT 440 niay be described as separation ot its louferniost contacts to disconnect the busy relay 489, disconnection ot' the inagnet 488 attlie third lowerinost contacts 441, WhileV during inoyenient ofthe third lowerinest inalre-betorebreak contacts, ground potential is momentarily applied through theV winding of a relay 487, thence to grounded battery through the parallel connected contacts of the two alternating current relays 484 nd 485. Response ot the relay 487 eltablishes its selr"locli1ig circuit through its right-hand contacts to ground at switch `While the left-hand contacts of this lay join a grounding interruptor 488 to the uppermost inain conductor energized by current troni grounded battery, through the lett-hand Wind-ing ot the relay 416, contacts 49.0 or" the relay During each instant this current niay flow to ground through the interrupter 488 although the battery supply relay 416 Will continue energized, cessation ot current in the loop circuit ot the trunk L2 will result. In response to this release of the relay 372 at the repeater TS will result in nionientary response ot the relay to correspondingly set up a reversal of current polarity through the loop of the In a niaiiner siinilar to that already described, the relays 280 and 225 Will translate such reversal ol polarity into an impulse ot alternating currents (700 and 900 cycles) lover the line li to be nianitested o-ii either the distant dialing signal 41,

the supervisory signal 75 or as 'a tone indi-- this relay f cation in the receiver of the operators telephone set, depending on the position ot the leys ot the cord circuit. The speed of the interruptor 488 inay be such that resulting successive responses ot the relay 872 will serve to flash the distant signal in a charac teri'stic niaiiner readily distinguishable troni the dialing, trunlrs busy or the line busy signals already described. To this end, irregularity in the lashings may be controlled by the interrupter 488 in certain situations in a manner to elliect a predetermined nuniber ot rapid flashes followed by an interval of rest. This distinctive signal is tor the purpose ot indicating to the controlling operator that the connection has been extended to the line o't the station Wanted, and that ringing iiiay be proceeded with, relative to calling this station.

Further switching effects resulting troni the opeated position et the` relay 440 niay be described as steady ground applied over the contacts to prepare a path by Way et the louferniost alternate contacts 443` ot the ringing relay 451 and the lowerniost noinial contacts ot the relay 425 troni which a lead 457 extends to equipment (not shown) for energizinp` an attendants signal in case ringing oi the called line does not ta ze place within a. predetermined time. Such an arrangeinent iiiiglit take the torni ot the deyice shown iii the patent to Sperry, No. 1,406,288, granted February 14, 1922, in which the lead troni the right-hand ernia.- ture oi relay G corresponds to the present lead 457 and the signal G is he signal hereu` inbetore mentioned. The contacts 449 et the relay 44:0` apply ground potential to establish and continue a busy test condition by Way oi" the brush 447 With the segment 445 et the line oil station B, and also to etilect shunting oi" the uppermost Winding ot l. While the contacts 453 and et this relay join the niain conductors et the connector through to the inain ce. ducto-rs of the line circuit ot station B.

ln order to ring the station B the operator niay inoinentarily operate the non-loching ringing key of the cord circuit C, thereby applying ringing currents 700 and 900 cycles per second troni sources and 71 to the niain co l s of the present connection. These tra. rse

the line L' and the di tant c non ei:- teiided through the trunk circuits L1 and lf to coin lete circuit tl'irouoli the two serialli i y l n e connected. relays 484 and 48o joined in brido'e across ine niain conductors at the y 1 connector l.- bese relays inay be of the type alreadgi,7 reterred to as preferable tor the relaysQS() and 240 and under etliect ci the ranging currents se oaration ot their o d. l 1 ,i 1 contacts rsu-.lts iiitne deerfergisation or the relays' 451aiid 484. The relay 451 switches KVthe iiiain conductors as now joined to the llO line circuit ot the station B Jfreni connection with the toll line L to receive ringing current lroin the ringing system 450. Restoration ot' the relay JVS( disconnects the derived circuit liroin the upper conductor of the trunk circuit L2 through the interrupter L88, thereby discontinuing the reyertiye inipulse effects described as indicating that the connection has been completed to the station B.

Coincident with starting ot the ringing operation, it is arrangeci that an energized condition oi' the supervisory' signal [5 on the cord cir it C will be assured. To this end, they operated position ot' the ringing key 55 at its lowern'iost or side conta switches the` circuit troni grounded battery as present through the lett-hand alternate contacts ot the relay 5S (non` operated) 'troni the path to the armature ot the relay il to a path which entends through the right-hand alternate contacts oi the relay 58 to the loncrrnost. Winding ol the relay Sl. This insures that the armature ot' the latter relay will take up its lon'er bias, while the relay (i will be shunted, thereby assuring that the relay T inay be energized to disconnect the relay (5 and display the signal T5. The inaliebe'tore-breal; relation of the lorferniost set ot' transfer contacts on thc ltey insures that i'ollouing release or" this ringing key the signal 'if' will continue energized and therevtore may be extinguished only on response troni the station B as will non' be described.

During the ringing period the condenser LIDG shown joined from the upper one o't the main conductors by way of' the norinal lefthand contacts ot' the relay 439 to the saine niain conductor ot the connection at a point to the lett-hand side ot the ringing relay 51, is tor the purpose ot affording .so-called ring back induction Which inay traverse the connection over the toll line and serre as an audible signal in indicating to the outward operator that ringing current is actually being applied to the line circuit of' the station wanted.

As Well understood in the art, removal ot' the receiyer from its switchhoolr at the station I3 in response to this call Will result in the direct current coniponent troni the ring ing systein t5() by way ot the uppermost Winding or' the relay al effecting so-called tripping or initial response ol this relay, tollowing which it will be retained as selt' locked under control of the relays 481i, S5 and Llli'. This switches the circuit of the line to the station B from the ringing sy"- tem 450 to the connection as joined to the toll line L.

In describing supervisory control Whereby the signal of the cord circuit C will be retired due to response at the station B, talking battery supplied through the baclr bridge relay 425 to the station B energizes this relay to reverse the polarity of the battery current through the truul; circuit L2, and also to shunt the relays Si and At the repeater TS this rerersal ot' current through the lett-hand winding ot the relay BTO establishes a euniulatiye action with the current present in the right-hand Winding of this relay to eli'ect its' response and at its right-hand contacts ground potential is applied over an obvious circuit through theI winding of the relay 3.32v to grounded battery. Response ot the latter relay eit'ects reyersal ol current through the trunk circuit L1, thereby eli'ceting nion'ientary release. ot the relay 280 to elicct response of the relay whereby an impulse o'- alternating currents at itl() and SGU cycles per second will be applied over the line circuit L. A t the cord circuit C the dialing key haring been restored, arriyal ot the described impulse ot alternating currents eli'ects operation ci' the relays Fo and bl connected in bridge on the main coiuluctors of the cord circuit. .i condenser' 95% joined across the right-hand winding` of the relay 77 serres as a by-pass tor these relatirely high 'frequency alternating currents with respect to this windingl ot the relay 7T as connected in series with the relays r1.1.) and 81. Under energization, the relays su and 8l separate their parallel connected contacts to disconnect the circuit troni `rounded battery as connected to the armature ol'V the relay 9. now on its lower contact. stop l5. This disconnection ot current from the lower Winding et the relay permits current present through the upper winding ol this relay over the circuit through the relay 7, to eltect opposite bias olf this relay Therefore, on cessation ot the incoming inipulse of alternating currents, restoration ol the relays 80 and 8l will re-establish the full potential et the grounded battery by way of the armature ot' the relay 9, its` upper contact stop GS and upper winding to :he sleeve path ot the connection. In this condition olL thel circuits and position o'l the relay Si. il will be obvious that the winding ot the relay 7 will be shunted and the resultingl release ol' this relay will disconnect. the signal T5 and apply current 'troni grounded battery through the winding of the relay (i and the lower Winding 01"' the relay t) over the sleeve path of the connection. The circuits ot the supervisory signal 75 Inay continue in the present described deenergized condition during convversation between the station A and the station B.

In case the. subscriber at the calling or hoine station A inay flash during this period. the signal ST will be atl'ected as already described, and in the eyent that the party at the station B niay Hash the switchhool: al that point, the signal 75 will be controlled as Jfollows:

In the operation ot hashing, the first dellt) disconnect the relay 352, thereby reversing i the polarity of the current through the trunk circuit L1. rllhis reversal translated through the relays 280 and results in the application or" currents at TOO and 900 cycles per second to the toll line L. rit-the cordcircuit C this iinpulse eects joint response ot the relays 8O and Sl'to disconnect grounded battery from the armature ot the relay 9 as connected by way of its upper Contact stop G8 and upper winding to the sleeve circuit ci the connection. Due to absence ot current in this upper winding of the relay 9 the cur rent present through the normal contacts ot the relay 7, the yinding ot the relay 6 and the lower winding of the relay 9 to the sleevestrand of the connection will result in op posite biasing ot this relay. @n cessation of the incoming impulse o 't' alternating cui rents, the circuit will be established from grounded battery by way of the arniatnrc, lower contact stop 65 and lower winding ot' the relay 9 over the sleeve circuit. Presence of grounded battery at full potential on the lower contact stop of the relay 9 results in shunting down the relay 6 which thereupon may release and apply grounded battery through the winding of the relay 7 and the upper winding of the relay 9 to the sleeve circuit. Response ot the relay 7 disconnects the relay 6 and applies grounded battery to energize the signal 7 5. V i

lThe release of the switchhoolr at the sta.- tion B as the second inoveinent in the flashing operation, results in reversals et current polarity in the trunlr circuits L2 and L1 as already described, whereby another impulse of alternating curents will revert over the line L and effect response of the relays 8O and 8l on thc cord circuit C. 0p-Y crations similar to those iirst described will then take place to result in the armature of the relay 9 being` inoved to its upper bias, while the relay 7 will be released to extinguish the signal and to connect grounded battery through the circuit of the relay ln this manner it will he clear that irrespective ot the nuinber of tinies the switchhool; at the station B may be manipulated in a flashing ooeration the si :nal 75 will be il' shed in response to the inovenients ci the si l'chhoolr, and finally, that this signal may either be displayed or retired, depending on whether the receiver has been lett on or lett oil1 its switchhoolr at the conclusion of the flashing operations.

lt will be pointed out that the arniature lof the relay 9Ais to be provided with suitable biasing means which may be in the forni ci a spring 36 shown in the drawing. T1 is biasing effect insures that under a no cu:- rent condition for this relay as when plug 3 inay not be in use, the armature will be inoved to and retained on its lower cotact stop thcposition in which it shown in the drawi is may be uni e stood troni the drawing, the two wim` or coils of the relay 9 are connected to be ener, d in dii. t

e rcntal relation, one with the other, and during actual transition or inovcnient of the armature, current will be present in one oi the coils only; and that on the side to which the armature inay be travelling.

Baring periods the armature inay be rest in either one ot its positions, current ot a predetermined inaxiinuin strength in the coil corresponding with the po on of the arinn ture will be elllectivc to rc n the arinatui f against counter ellect or current ot e. prcdetermined ininiinuin strength in the opposite winding. The low current strength condition for the upper coil is present when the winumg oi the relay T nu y be in series with his coil, while the lonY or ininiinuin current condition for thc lower coil is had during periods the winding ot the relay 6 nisy be in series with this coil.

ln general, daring the automatic setting" up ot a connection the dialing` key la will remain in its operated position, until the dialing operations have been completed therefor, no revertive current effects 'from over a toll line circuit inay becoine effective with the supervisory control relays and 8l, and the signal 75 may continue energized until extinguished as a result of response at the distant called station. ln the event, however, that as heretofore mentioned, the key le may have been tcnuoorarily restored betere completion of the dialing operations and revertive inipulses due to eiifects resultingl from the extending of a connection through a distant switch may have retired the supervisory signal 75, this signal will be displayed due to operation et the ringing' key 55 in calling the distant station, as previously described.

Referring to the condition of the circuits at the repeater TS during the talking period, additional condensers 322- and 373 under control ot the reversing relay 852 are ioined in parallel with condensers 374i and 375 respectively, permanently wired in the main conductors' or the connection. rlhe additional capacity will be present during talle ing periods in order to better the telephonie transmission, while disconnection of the additional capacity during the tiine a connection is being built up through the repeater serves to guard against interference with the operation oit the pulsing relay 3o() as otherwise may occur due to reactive or surge currents troni condensers of higher capacity during the reception orn selective iinpulses.

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