US2158945A - Telephone system - Google Patents

Description

E. S. PETERSON TELEPHONE SYSTEM Filed sept. 24, 1957 8 Sheets-Sheet l May 16, 1939.

May 16, 1939.

E. s. PETERSQN TELEPHONE SYSTEK Filed Sept. 24, 1937 8 Sheets-Sheet 2 mz3 :5 v1

INVENTOR. EDWARD s. PETER$0N BY MM ATTORNEYS.

May 16, 1939. E. s. PETERSON TELEPHONE SYSTEI Filed Sept. l24:, 1937 8 Sheets-Sheet 5 ATTORNEYS May 16, 1939.` E. s. PETERSON TELEPHONE SYSTEM Filed Sept. 24, 1937 8 Sheets-Sheet 4 My 16 l939- E. s. PETERsoN TELEPHONE sYs'rEn Filed Sept. 24, 1937 8 Sheets-Sheet 5 IUP-gw OPUmZZOU EDWARD s. PETERSON BYM/Q/.Mymm

ATTORNEYS.

8 Sheets-Sheet 6 mhmo l.. um.

NNS S #USUN w) cui; u m

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nmnu n Nmmu INVENTOR.

EDWARD S. PETERSON v BYd/v/v, If/247,

ATTORNEYS` 8 Sheets-Sheet 7 mhm Q0 v mwzss 65:8 com .vrou

lNvENToR EDWARD s. PETERSON www, MM

ATTORNEYS E. S. PETERSON May/16, 1939.

TELPHONE sYs'rEu Filed Sept. 24, 1937 8 Sheets-Sheet 8 OIL oww

INVENTOR. EDWARD S. PETERSON BY am,

ATTORNEYS.

Patented May 16, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application September 24v, 1937, Serial No. 165,472

25 Claims.

The present invention relates to telephone systems and more particularly to systems adapted to serve a small group of subscribers lines in a rural community.

In the early history of telephone operations, it was the practice in rural areas to provide a more or less independent telephone exchange for the rendition of telephone service to the small group of subscribers in each small community. These exchanges were of the manual type and each thereof required an operator for setting up desired connections between the various subscribers lines. In the usual case, the telephone traflic was so small as Yto take up only a small part of the operators time and as a consequence, the service was poor and the cost thereof relatively high. In order to obviate the above disadvantages, there has been developed what is known as a semiautomatic system wherein the setting up of connections between the subscribers lines terminating ati a small rural exchange is under the control of an operator located in a larger exchange remote from the small community exchange. By this arrangement it is possible for one operator in the central exchange to perform duties other than the supervision of calls emanating at t'he small rural exchange, with a consequent decrease in the cost of the service rendered and an increase in the quality of the service. Several forms of this type of system have been devised, one improved form being disclosed in United States Patent No. 2,010,372, granted August 6, 1935, to the present applicant The system of this patent comprises, in general, a control trunk line interconnecting the control and local exchanges, an operators station in the control exchange including an operators telephone and an impulsing device, a plurality of nderconnector links included in the local exchange for setting up conversational connections between the various subscribers lines terminating at this exchange, and allotter means arranged to assign,

in a deiinite order, the idle finder-connector links to calling subscribers lines. Control of the linder-connector links to set up the desired connections is achieved by transmitting impulses from the impulsing device at the operators telephone, by way of the control trunk line, to cause any seized link to perform it's line selecting functions and the usual auxiliary functions vnormally required in an automatic system. Various other features are incorporated in the circuit arrangement of this prior system which are designed to increase the operating eciency of the equipment in the local exchange and increase the standard of service rendered to the various subscribers.

It is an object of the present invention to provide an improved system of the general character noted which is of simple and economical arrangement, is thoroughly reliable in operation, and requires a minimum of maintenance.

More specifically it is an object of the invention to provide a system of the form described wherein relays are used exclusively in setting up desired connections to the various lines of the system and wherein the arrangement is such that the number of relays required for an exchange of a given line capacity is reduced to a minimum.

In general, the objects as set forth above are attained in accordance with the present invention by providing a system of the form just described wherein all-relay finder-connector links are exclusively utilized in the rural exchange for setting up connections between the various lines terminating at the exchange, and allotter means comprising a plurality of interrelated relays are provided for successively assigning idle ones of the links to successive calling lines. More particularly, the finder switch embodied in each of the finder-connector links comprises a plurality of group select relays so connected and arranged as sequentially to operate in response to the initiation of a call on one of the lines terminating at' the exchange to select a group of lines including the calling line, and a plurality of units relays so connected and arranged as sequentially to operate to select the calling line from the selected group of lines. Similarly, the connector end of each link includes a plurality of interrelated relays arranged to operate in a predetermined sequence in accordance with a series of impulses, transmitted from the central exchange operators impulsing device over the control trunk interconnecting the two exchanges, to select a group of lines including a called line, and a plurality of relays so connected and arranged as sequentially to operate in accordance with another series of impulses transmitted from the impulsing device over the control trunk to select the called line from the selected group of lines. Control of the links in their operation to set up connections between the various lines extending to the rural exchange is achieved by providing control apparatus associated with the control trunk and common to all of the links. In this apparatus are included a pair of impulse responsive relays so connected and arranged that one thereof operates at the beginning of each odd impulse transmitted from the central exchange operators impulsing device over the control trunk and restores at the beginning of each even impulse. This one relay is arranged to control the operation of the line selecting relays embodied in the connector portion of each link. Also embodied in the common apparatus are means whereby the control operator located in the control or central exchange may monitor any connect-ionfollowing its establishment and tmay control lthe application of ringing current to a called subscribers line to provide selective code ringing of those subscribers lines which are of the multi-party type. Means under control of the central exhangeoperator are further provided inthe common` e'qluipment for performing the usual auxiliary-ff-unctions of applying ring-back tone currentfor 'busy tone current, depending -upon the condition of the called line, to the controltrunk and -a loop extending to a calling subscribers line. A:For the vpurpose of controlling the operation of the common equipment 'in the 'remote exchange, there are' provided at the operators' station in the cenral exchange, in addition 'to 'the impulsin'g device 'noted above, a vplurality of `key switches, one'of Vwhich'is operable'to connect 'the -opera'torstelephone 'to 'the 'control "trunk 'and 'two others "of which are operable to veffect 'the ringing'of a called substation. .Asignal device is lalso located at 'the operators station vfor indicatingthe seizure 'of the .common apparatus duringthe initiation of a call on 'one 'of 'the subscriberslines. lVIea'ns are further provided 'whereby this signal device is energized 'when'all of 'the Ylinks becomebusy,`or when a' fault is present in the apparatus located at 'the remote exchange which 4renders this apparatus inoperative. The common control vapparatus also 'includes supervisory equipment whereby the conrol operator inthe central exchange may establish a connection 'to any one of "the 'finder-connector 'links 'to determine whether or not it is actually busy, and may release any linkthus'tested inthe event it is found to have been permanently appropriatedby the'failure of v aparty'to ring off following the use o'f vthelink.

'Ilhe novel vfeatures believed' to be characteristic 'of 'the invention are set'forth with particularity inthe appended claims. lThe inventi'onitself,

however, bothv as toits organization and' method 'of operation, together with Yfurther objects and advantages thereof, will best be understood by 'reference to the specification taken lin connection with the accompanying drawings, in whichFigure 'l illustrates the 'finder end of a'iinder-connector link, incorporated in the system Yof the present invention; Fig. 2 illustrates the vlink'. starting apparatus, 'which,"in combination with the allotter means illustrated 'inFig'L Acontrols the assignment of idle links to the calling lines; Fig. '3 illustrates the link' portion of the'iinder- 'connector link; lIEigJ illustrates the'oon'nector end'of the link; Figs. 4` and 6 illustrate "the 'control apparatus associated'with the control trunk and commonto'all of 'thelfnde'reconnec'tor links vembodied in the system; Fig."7 'illustrates vrthe supervisory'apparatus'referred to above; 'Fig'. 8 illustrates 'the equipment located' at theoperators "station in the 'control exchange; 'and Fig.""9 is a 'is villustrated 'in diagrammatic form, `"a"s`yst'e'm of the 'g'eneraltype describedin .the opening para- "graphs, 4vvhi'c'l'l diagrammatic Y'illu'strati'on is included for' the purpose'ofV facilitating a'n 'understanding of the features to which the invention more particularly pertain. In brief, the system comprises a Central or control exchange S which may have a number of subscribers lines, not shown, extending thereto, and which is interconnected with a second rural community exchange SID, remote from the exchange 900, by Lmeansfof :a two-way controltrunk line 443, and -a ytoll trunk line 4M. The second cnice has extending thereto a small number of subscribers lines, four of which are indicated at 9| I, 55, 9l3 and 9M, having connected respectively thereto subscribers substations A, B, C and D. Although Fa single fsubstationfhas been shown as being connected :to'-each ci the enumerated subscribers flines, litfwill :be understood that in an actual installation embodying the features of a system of "this character each of these lines will probably beiof the party line variety, i. e., each thereof will have more than one substation connected thereto "Embodied in `the rural exchange 910 are'a plurality of "finder-connector linksfor set- "tingupconnections between the various subscribers lines to establish conversational circuits thereover, allotter `rneans `for successively assign- "t'ionsof thefinder-connector links'during the establishin'g 'of desired'connections. lIncluded in the'central orcontrol exchange Sill!) is the operators 'equipment for controlling, "by way of the 'trunk linei4ll3,` the equipment for'performing the 'ahovel-noted incidental functions.

Neglecting for'the present the details of the "circuits 'involve'd'as shown more rparticularly in Figs. '1"to '8,inclusive, andconsidering the operation ofthe system generally, it is pointed out'that the'establishing of connections bfetween'any pair of "the 'various subscribers lines terminating at the'suboflice"9| is entirely'under the control of therur'al operator lccate'dat'the central exchange "900. Thus, on a call frornone of the suboice "subscriberslines to 'anotherof the subohce sub- Iscriberslines, such,'0r example, as a callfrom substation A'to'the lsubstation B, the party at 'the 'substation A removes his receiverfrom its ihook, and operates,`in a Well-known'manner, his *hand'generator to vapplyiringing current tothe lin'eilll'l 4'which current"sets 'in' operation an assigned *idle finder-connector link to Asearch `for andseiz'e -thecalling line. It will be understood "that the'al'lotment vof the finder-connector links is under'the control Aof the automatically operating allotter means referred to above and described more specifically hereinafter. When the calling ""line" is seized' bythe assigned link, itis connected to thetwo-waycontrol trunklMSby'way of lthe link, and the signal device'atthefoperators boar'd 'is-caused to operate to inform-the operator-'that r`a -callfawaitsl attention. |The operator mayf-then connect Aher telephone to ythe trunk line 4.43 to vestablish la conversational circuit extending by yway :of this trunk-line, the seized link, and Ithe callingsubscribers line to the callingsubscribers substation .Following receipt :of Athe .information ,as `to the .party desired by the calling party, the .operator actuates the impulsing device located at her telephone to cause the connector switch of .the seized finder-connector link to operate and select the called line. Two series of impulses are vrequired 'for such selection, the rst series caus- 'in'g'thehonnector sWitchto selecta group 'of lines includingthe calledlinefa'nd Vthe second series causing "the 'switch to se'lectthe particular 'called 'line from'the `selectedgroup of lines. Following the 'selection ofthecalled line, this line is automaticallytested to determine its idle or 'busy condition, "and, if found busy,'busy vtone hcurrent nis 'returnedto the op'eratorstelephone andthe calling subscriberstelephone. The 'operator or'the calling 'party 'may 'then cause th'epartially established connection to be cleared out. "In the Aevent ithe called line is foundto be idle,the operator, by actuating a'suitable ringing key, may cause ringing current Aproperly'to be appliedto the -line conductor or `conductors of the line extending to the called subscribers substation, and ring-'back tone current `to beapplied'tothe loop extending Avtothe calling subscribers substation. iIt will 'be understood that selective code ringing is employed'in those instances where the called subvscrib'ers substation is connectedto a party line. Whenthe called subscriber answers, a conversation'alcircuit is automatically set up between the 'calling and called substations. Following this, the operator may remain on the connection to monitorthe same, or shemay operate a key switch at her board to cause the control trunk andthe equipment inthe suboliice common'to the links "t'o'be released for further use.

'Atthe conclusion of the conversation between the calling and called parties, either ythereof may actuate the generator located at his substation to cause the 'release of (the link by way oi which "the connection is established. The projection of ringing'current over the loop connecting the two parties causes the sequential operation of relays fincluded inthe link to' initiate fthe ultimate release "thereof.

y"libeferrlng now to Figs. J1 to '8, inclusive, of the drawingswhereinthe circuits of the system described above are vshown in considerable detail, "and more particularly to Fig. .1, the finder .end of theflnder-connector link there illustrated includes 'a'circuit network whereby any one of the `plurality of subscribers lines terminating at the subo'flicefmaybe connected to the line conductors 'of the link. Thus, any one of the lines |06, |01,

nected to the conductors forming the "link line "|'89,"throug`h the operation of relays `R| 20, RI30,

"R143, R, R|60,R`|l0, R|'80,"R|'90, R|0 and R20 provided in the'flink. i Of the enumerated relays, Rl 20,`R`|40.and RI'60 comprise group select relays which are so connected and arranged as sequentially to operate lin 'response to .the initiation of la call on one of the lines noted to select a group of these lines including the calling line. Similarly, the relays R|80, R190 and R|`0 are so con- .nected and arranged as sequentially to operate to select a particular calling line from a group of .lines selected by one of the group select relays. The relays Rl, R|50andR|10 are line group switching relays and Aeach thereof corresponds to one of the group select relays. These switching relayS-IareIarranged to operate, in .the manner r'delscribed in detail hereafter, only when the corre- .spondinggroup select relay is operated and following theselectionof the calling line.

understood that thenumber of group select relays and `the number of units relays will depend en- "tirely upon the number of subscribers lines to which the link is to have access. In a link having access Lto one hundredy lines, ten group select relays and'ten units relays willbe required. For the .purpose of initiating the operation of the Ilinks, each o'f'the subscribers lineshas associated therewith a line rlay'w'hih operates when a`call 2link to the calling line.

It Will be is 'initiated on'the associated line. This relay for "the 1line"9-|-| is `indicated at-R|00 and, in cooperation with 'the start conductor vC-Bl, functions to cause 'the allottermeans indicated at 80 in Fig. l

"andf-th-e starting apparatus shown in Fig. 2 to as- -sign anid'le link to the line 9|| when a call is sini-tia'ted on this line, and to mark the group of 'lines vincluding the line j91| and also the line iSH Ifinf the marked group. Each of the subscribers lines-also has associated therewith a cutoff relay "the terminals `-embodied in three other similar relays are indicated at 8 l, 82 and 83, respectively. ylin order to control the operation of the aboveenumerated relays, there are provided the two relays R300 and R3 |0 shown in Fig. 3 and, as 'pointed out vin detail hereinafter, the rst of these vvrelays'operates following the completion of the line group yselecting operation of the iinder switch andinit-iates thesequential operation of the units relays to search for the calling line in the selected group, and R3|0 operates when the calling line is found-to cause the calling line to be connected tothe control trunk 443. The operation of the allotter relay correspondingto the nder-connector switch illustrated is undervthe control of R2@ and it is noted here that the latter relay operates to cause'the assignment of a new link to a calling subscribers line in the event the link illustrated searches for and fails to nd the calling line. f The starting apparatus shown in Fig. 2 is interconnected with the allotter means 80 and includes 'a plurality of relays R200, R2 |10, R220, R230, R240, R250,'R260,'R 2`|f0, R280and R290, which function 'to fcause xa signal to be transmitted to the central exchange operator when all of the links are busy and also to prevent a defective link from twice being assigned to a calling line. This apparatus also includes a timer 2|0 which, in combination with certain of the relays noted, initiates the releasef'of'a seized link in the event the link fails Ato n'd the calling line responsible for its operation within a predetermined time interval following the seizure of the link, and assigns a second The relays noted further operate in amanner such that, if the second assigned link fails to nd the calling line, 'an alarm signal is transmitted to the operators Jstation'to indicate the condition of the link and all of the apparatus in the rural exchange is prevented from further operation.

'Referring now more particularly to Fig. 3 of the drawings, the equipment vthere shown is individual `to `the link illustrated, and comprises a repeater1 `i305 at vwhich the line |89, leading to the nder end oi the link, normally terminates, and line conductors adapted to be connected to the line conductors C343 and C344 outgoing to the connector Aend vof the link. The last-mentioned conductors as well as the line conductors of the link line |89 are also adapted to be connected by a gang relay R390't'o the control equipment common to all of the links and illustrated in Figs. 4, 6 and 7. The repeater 'noted includes primary windings 306 and "309, connected in series across the line conduc- "tors C341 and 'C348 by means comprising a condenser i308, and secondary windings 3|8 [and 'e319 connected in series 'between the line conduc- 'torsC34'E and vC345 by means comprising a condenser 309. The control equipment in this` portion of the link includes, in addition to the relays R300 and R310 already mentioned, the gang relay R390 for associating the link with the common control equipment shown in Figs. 4 and 6, the relay R380 for selectively associating this control equipment with diierent ones of the control relays embodied in the connector end of the link, the line switching relays R320 and R330, and relays R340, R350, R360 and R310 which operate in the manner described in detail hereinafter to initiate the release of the link.

The connector end of the link as shown in Fig. 5 is somewhat similar to the nder end of the link in that a circuit network is provided whereby any desired called line may be connected to the link line 349 through the operation of group select, units, and group switching relays. Thus, the lines indicated at 521, 528, 529, 531, 538, 539, 911, 506, 515, 501, 508 and 509 may selectively be connected to the link line 340 through the operation of the relays R500, R510, R520, R530, R540, R550, R560, R510, R580, R590, R60 and R10. Of the enumerated relays, R10, R590,` R510 and R550 are group select relays which are so connected and arranged as sequentially to operate in the order named and in accordance with the impulses comprising a first series of impulses transmitted over the control trunk 443 from the impulsing device at the central exchange operators station, to select a group of lines including a desired called line. Similarly, the units relays R530, R520, R510 and R500 are so connected and arranged as sequentially to operate, in the order named and in accordance with a second series of vimpulses transmitted from the impulsing device bodied in the rural exchange is illustrated in Figs.

4 and 6 and includes two repeaters 454 and 616,v

and control relays R400, R420, R430, R440, R450, R460, R410, R480, R40, R50, R500, R610, R620, R630, R640, R650, R660, R610 and R690 for performing the various functions briefly outlined above and set forth in greater detail hereinafter. Of these relays, the relays R600 and R610 are impulse responsive relays for controlling the operation of the group select and units relays embodied in the connector switch illustrated in Fig. 5. These two relays are soconnected and arranged that one thereof, namely R600, operates at the beginning of each odd impulse transmitted from the impulsing device located at the operators station over the control trunk 443 and restores at the beginning of each even impulse transmitted from this device. The relays R630 and R640 are ringing current control relays and are selectively operative to apply ringing current to either line conductor of a called sub-scribers line, thereby to provide a means for selectively ringing the telephones connected to a party line. The relays R660 and R610 are provided for the purpose of controlling the operation of R380, embodied in the link proper, in a manner such that the impulsing relay R600 is successively connected to control the group select and units relays of the connector switch shown in Fig. 5. The relays R650 and R690 are the busy and switching through relays, re-

spectively, and are included in the means for testing the called line to determine its idle or busy condition, for preventing the calling line from being connected to the called line in case the latter is found busy, for transmitting a busy signal to the operator and the calling subscriber in the event the called line is found busy, and for connecting the calling line to the called line in the event the latter is found idle. The relay R620 is a monitor relay which is provided for the purpose of enabling the central exchange operator to set up a connection to a called subscribers line to the exclusion of a calling subscribers line. The remaining relays identified above and shown more particularly in Fig. 4, with the exception of R400 and R420, are primarily controlled from the central exchange operators apparatus and function to control the relays shown in Fig. 6. The relay R420 is operative to signal the central exchange operato-r when the common equipment is seized, when all of the finder-connector links become busy, or when a fault occurs in the rural exchange which renders the switching equipment therein inoperative.

A local control set 43 is also included in the common equipment, which may be used in emergencies by an operator located in the rural office, to control the establishing of connections between the various lines extending to the rural ofiice independently of the operator in the central exchange. In this connection, it is pointed out that the relay R400 is provided for selectively connecting the common equipment to the control trunk 443 or the emergency operators apparatus. For the purpose of enabling the central exchange operator to test the condition of the various links located in the rural ofce, the supervisory apparatus illustrated in Fig. '7 is provided. This apparatus is interconnected with the common equipment, shown in Figs. 4 and 6, and includes relays R100, R110, R120, R130, and R140, which are selectively arranged to be energized, in response to the dialing of predetermined digits at the central exchange operators station, to connect the operators telephone with the line conductors of any of the various links included in the suboilice.

Referring now more particularly to Fig. 8 of the drawings, the operators equipment included in the central exchange and associated with the control trunk 443 is illustrated as comprising an operators telephone 800, which is adapted to be connected by way of a key switch 810, and a repeater indicated generally at 840 to the trunk noted. Additional key switches 810 and 800 are provided, which are utilized in performing the ringing and monitoring functions noted above and described more particularly hereinafter` This apparatus also includes an impulsing device 860 and control means comprising two relays R820 and R830 which function in the manner pointed out specifically hereinafter in the detailed description of the operation of the system,

Operation of finder switch to find a calling Zine Referring now in greater detail to the operation of the apparatus brieily dscribed above to establish a connection between two subscribers substations, such, for example, as the substations A and B connected to lines terminating at the suboice, if the substation A is in the calling sub-- station, the call is initiated when the party at this substation actuates his hand generator to apply ringing current to the line 01, thereby to cause the operation of th line relay R100. The path of this current extends from one terminal of operated independently off its upper winding. At

RAI'IT I, the relay R100 interruptsfa point" in the' line circuit of the calling subscribers'line and, at

RAI 02, applies battery from theoutoirel'ay'RIv I 0" to the control conductor 029,. thereby to mark this line in the nder Switches toY whichA it ex'- tends; Upon: operation of' RAI 03; ground is" applied from RAII3 to theA startAv conductor C91',

which ground servesA` to mark" in theY finderA switches the' particular group of lines including the callingline 9|"I and'to start an idle one of" the switches searching for the calling line, assuming'A anA idle finder-connector link is avail"- able. Thus, when the relay`R| operates', a cir- -cuit is completed' for energizing the Slow=to release-'relayRZI 0 included in the starting apparatus shown-in Fig; 2; This circuit extend'sirom'4 ground' at RAI I3' by Way' of the elements' RAI03,

RAIN-, RCII05, C91', C93 and through the winding' of R2|0 totbattery.v The relay RZI'O; upon operating, completes, at RA2`I I', a circuit for initiating the operation of" the Vgroup selectv relays included in the nder switchof Fig; l, only in the event theV control equipment common to the various' finder-connector links of the suboilice is idle at` the time the calli'sinitiated. At its armatures RA2`I2; RA2'I3, RA2I4, R215, R2llY andy RA2'I'1', the relay R2| Dfinitiates--the operation'fof the start-- ing apparatus shown in Fig. 2 to assignl a new idle lnder-connector link to the callingv linein case the link'shown is-unsuccessful iniinding the line, and to transmit ari-alarm signal to the centralexcha-nge operator inthe eventl the-secor1dassigned linkf also fails to'nd the calli-ng line; allA in the manner described in detaillhereinafter.

Assuming thev control equipment common to all ofthe links. of thissuboice to-be-idle, all of the relays illustrated in Figs, 41, 6 and are in their restored positions as shown. When the relayRZItl operates, therefore, and assuming that the iinder-oonnectory linkillustrated isl the link assigned to thev calling lineV 9.I I, a circuit-is-'completed upon operation-Lof RZLI 0; for. energizing the iirst` group select relay R120, this circuit extend-- ing from groundpatfRA'49I3:by way of? thexelcments RA439;T,.C.2.04, RAMI.; RA2 I .I, RA23|.,C89., RA32, RC33. C18,Y RA3I 2, RC3I3,2, RABUI?, RC302, CTM, RAIBI, RC L62,y RA-M'Is, RC |42, RAI2I ,.RClsZT and through the winding ofA R|20fto1battery.'A They relay R,I,2|),upon,operating, completes, at RAME, aholdingcircuit foritself extendingzirom ground on 018i, interrupts.y ati RAIZI and' RCI2L its original operating circuit, completes at RA|2| andRC|23 a circuit for energizingRMI),v and .prepares at RA|24 a circuit, traced hereinafter,vv for energizing the group switching relay RI30. The above-noted circuit for energizingRI40-eXtends from ground on C'I8y by way of RA3l2, RC3 I3, RAMI RC302, C74, RAIS I, RCIGIZ, RAIII I, RCI42, RA.|2.| RC|23 andthrough the winding ofR|40 tobattery. At RAI 2.6, the relay RIZIl` connects the start conductor C92,to C19., which latter conductor is included in thecircuit, traced hereinafter, for energizing the lower winding of R300v Each of the start conductors CSI, C92, etc., corresponds to one group of subscribers. lines and the relays respectively associated with the lines of each groupall have circuits controlled thereby for applying. ground to the associated group start conductor. In the present case, the group of'linesi including the calling line is associatedwith the' start' conductor CBI and assuming there are no calling linesin the group'associatedwith the conductorCSZ; so that4 ground is not present thereon, R300 is'not' energized upon operation. of'RAI26. As a result, RI4'0` operates to. complete, at RAI'45', a locking circuit' for itself;l to interrupt, at RAI'IIB, the above-noted looking circuitV for' R120, and to interrupt, at RA'I'H" and' RCIZ; a point' in the original circuit for energizing R|20 The last-mentioned relay restores after an interval' and opens, at RAIN, aA point in thev preparedA circuit for energizing the group' switchingY relay R|30i Upon the restoration of RAI25, a further point is opened inthe lockingA circuit forv R|20" and, when RA'IZB/ falls` back, thestart conductor C92 is disconnected from C79' included in the circuit for energizing the' lower winding of R300; When RAMI is pulledintoY engagement with RCI43, a

circuit is completed, extending" fromr ground on- GT4', for energizing' the third group select relay, and'when'RAIM is operated a circut'is prepared forenergizingthe second group switching relay RMU: The: sequential operation of the group seliectrelays' Rl20, RMU', RISO, etc., continuesin the exactirnanner described above until the one of these" relaysl corresponding tothe group of lines including the calling` line 9|'I is' operated. In the present instance, wherein the callingy line is included in" the second line group, orl that group correspondingl to the group select relay R140 andthe start conductor'CSI, a circuit is completed upon operation'of R'I`40 for energizing the lower'windingofRSl This circuit extends i from ground at RAI13, by way of the elements RA|03 RAIN, RCI05 C9I, C96; RAM'I, C19; RA3|6 andthroughthe lower winding of R300- to battery. The relay R300-immediately operates to short-circuit, at RA305, its upper winding, thereby torend'er'itself slightly slow'to release. It is notedthat' both-the third group select relay and R30'0areenergizedsimultaneously with the oper'- ationrofr R140', but' R300 is much faster to operate thanany ofthe group select relays. The energizing circuit for the third group select relay is, therefore, opened at RA30 Iv and RC302before this relayr operates; Hence, theI third group select relay remains restored' and R-I40`remains locked up overA its'` holding'circuit extending by way of RAIGS to groundy on C78;

Each timer one of thev group select relays R|20, R140; RfIfG, etc., operates, itv prepares testing circuits for determining which line included in the associated group of lines is the calling line. Thus; the relayRI40', upon operating RAI48, RA-|49, RAMS", etc., prepares testing circuits for the lines-9| |f, |48, |49, etc., included-in the group corresponding to the group select relay R|401 and thestart conductor CSI. These prepared. testing circuitsenable, thel unitsrelays R|80', R|.90, RID, etc., to select the particular' calling line from the selected group of lines including the calling line. In thisk connection itv will be noted that RI 40.v upon operating applies, at RAI48, battery from. thecutoif relay RI I0v to CJIBY of the common linkline |56.

Following the operation of the nder switch to select the group of' lines including the calling line, the units relays are started into operation to select from' this selected group of lines the particular calling line as identiiied by the extension of' battery to the control conductor CI I6. Thus, when' R300 operates, a circuit is completed for energizing the first units relay R180, this circuit extending from ground on C18 by way of RA3I2, RC313, RA301, RC303, C15, RA185, RCI86, RAI94, RCI95, RAM, RCI and the 5 winding of R180 to battery. The relay R180 operates after an interval and completes, at RA188, a locking circuit for itself, which circuit extends from ground on C18 by way of RAI8, RA198, RA188, and through the winding of R180 to battery. At RCI81, a circuit is completed,

extending from ground on C15, for energizing the second units relay R190. At this same armature and its associated contact RCI86, the original circuit over which R180 was energized is interrupted, the last-mentioned relay being held operated for an interval over its holding circuit as described above. When R180 operates, it connects, at its armatures RAI8I, RA182, and RA183, the conductors of the common link line 156 to the conductors of the link line 189 extending to the repeater 305.

Disregarding for the present the operations which follow the operation of the armatures RAI8I to RAI83, inclusive, and considering further the sequential operation of the units relays, it will be seen that R190 operates shortly after the operation of R180 and prepares, at RAI94 and RC196, a circuit for energizing the next succeeding units relay. At its armature RA 191, the re- 80 lay R190 completes an obvious locking circuit for itself extending from ground on C18 and, at

`RA198, it opens a point in the above-noted holding circuit for the first units relay R180. The relay R180 immediately restores to complete, at

RA185 and RC'186, the previously prepared circuit for the units relay next succeeding R190, which latter relay, upon operating, interrupts the holding circuit for R190 and prepares a circuit for energizing the fourth units relay. This operation continues until the particular calling line in the selected group of lines is found.

As noted previously, the finding of the calling line is determined by the presence of battery potential on one of the control conductors, corresponding to C1 16, included in the common link lines 156, 159, 199, etc. In the present assumed case, wherein the calling line 911 is the first line in the second group of lines, this line is found immediately upon the operation of R180. Thus,

when RAI83 engages its associated contact, a circuit is completed for energizing the lower winding of R310, this circuit extending from battery at the cut-off relay R110 by way of RA102, C29, RA148, C116, RAI83, C119 and through the lower winding of R310 to battery. The relay R310, upon operating, closes its armature RA3I2 to the associated contact RC3II1 to complete a locking circuit for itself. This circuit includes the upper winding of R310 and extends from ground on 50 C18 to battery at the lower terminal of this winding. When RAB I 2 is disengaged from RC3 I3, ground is removed from C15 so that there is no longer a circuit prepared for energizing further 85 ones of the units relays R180, R190, R10, etc. Hence, the sequential operation of these relays is interrupted immediately upon the operation of R310. In this connection it is pointed out that the slow-to-operate characteristic of each of 70 the units relays prevents further sequential operation thereof following the finding of the calling line. For example, the relay R310 operates to interrupt the prepared circuit for R190 before sufficient time has elapsed to permit the latter 'I5 relay to operate. The closure of RA312 to RC3I4,

upon operation of R310, connects C18 to C16, thereby to complete a circuit for energizing the selected one of the group switching relays which, in the present case, is R150 associated with the group select relay R140. This circuit extends from ground on C18 by way of RA312, RC314, C16, RAUM and through the winding of R150 to battery. The relay R150 operates when energized over the above traced circuit and at its armatures RAIEI and RAI52 connects the conductors C29 and C25 of the subscribers line 9,11 through to the line conductors C341 and C348 leading to the control equipment common to all the links and illustrated in Figs. 4, 6 and 1. v

The relay R310, upon operating RA3I5, shortcircuits its lower winding to cause the energization of the cut-off relay R1 10 associated with the calling line 911 over a circuit extending directly from ground at RA3I51 by way of C119, RAI83, C116, RANB, C29, RA102 and through the winding of R110 to battery. At RA311 the relay 310 prepares a circuit, traced hereinafter, for holding the connector switch of Fig. 5 operated independently of the control equipment shown in Figs. 4, 6 and '1. At RA3I6, the relay R310 interrupts the operating circuit for R300 and at RA3I1 it completes a circuit, traced hereinafter, for energizing the gang relay R390. When R1 I0 operates RAI 13, it interrupts the holding circuit for the line relay R100 and removes ground from the start conductor C91. At RAI 12, the relay R1 I0 shunts the armature RAI02 to complete a holding circuit for itself and to maintain ground potential on the control conductor C26, thereby to hold the calling line marked as busy in the relays of the connector switches to which this line extends. At RAI I I, the relay R110 opens a point in the circuit over which the line relay R100 was originally energized, thereby to prevent the line relay R100 from being energized during the release of the connection. When R100 restores, it opens at RA103 a point in the path for applying ground to the start conductor C91 and a point in the circuit for energizing its lower winding. At RAII, it completes a point in the line circuit extending to the calling subscribers substation A and, at RAI02, it opens the shunt from around the operated armature RAI I2. When R300 restores shortly following the operation of R310 a circuit is completed at RA304 for energizing the upper winding of R20, this circuit extending from ground on C16 by way of RA304, C11 and the upper winding of R20 to battery. The relay R20, upon operating completes at RA2I and RA22 an obvious circuit for energizing the allotter relay R30 which latter relay operates, in turn, to condition the next succeeding idle finder-connector link to be seized by the next succeeding calling line; all in the manner described in detail hereinafter.

When ground is removed from the start conductor C91 at RAII3 of the cut-off relay R119, the above-traced operating circuit for the slowto-release relay R210 is opened and this relay restores to remove at RAZ I I, ground from the conductor C18. Before this occurs, however, multiple ground is applied to the conductor noted in response to the sequential operation of certain of the relays shown in Figure 3. Thus, immediately upon the operation of R310, a circuit is completed at RA3II for energizing the gang relay R390, this circuit extending frorn ground to RA351 by way of C331, RA3II, C338, RA336, C339, and the winding of R390 to battery. Upon ing and allotter appartus is released for further USS.

Extension of the confnectiofn,4 to. the control. er. change operators telephone.

Simultaneously with thev operation*of'ithe'gangy relay R390; circuitsarev completed-rforenergize ing the switchingrelay R380' andi.thesliawf-to*-` release relay R420.' Tlie'rst ofr tl-iese circuits.` extends from groundatfRABT-L by" way ofi' C364; RASBSZ, C354 andl through the'Windifngzofl'vt38l to battery. 'I'hefsecond'ementioned circuit; name'-A ly, thatvfor energizing-R420, extends from ground at RA398 by Way' ofC358? RA438'1and the Wind"- ing of R420to'battery.` When'tlie-switclziing-/rwlay 380 operates, it prepares `circuits,` tracedheree inafter, for energizing the-group selectrelaysl R70, R590', R510, R550; etc., in accordance with the impulsesJ transmitted duringv the rst digiti dialed at the opera-tors station in the central exchange. The relay R420; uponA operating, completes; at RA423; an-obviousi circuit for ener-- gizing the slow-to-operate relayf R400. At itsl armatures YRA42 land RA42 2"l and their' respectiver associated contacts RC'426-v and 11104258;- the relay R420 completes a circuit for energizing R830 ineluded in the control apparatus at the centraliexchange operators station. The-lastf-mentioned circuit extends from grouncilat REWE-byway ofy the elements R'A412I, RA`40Il, RC40'2; C444, the repeater' winding 8414i RPA81222' thellowerfwinding of R830,l the repeater' winding` 845i C4455 RCME, RA40'4", RA422; H6428; and-through the resistor 428" to battery Inrespcnse to its^energization over the above-traced' circuit, R880 operates to complete, at RA88F; an obvious circuit forenergizing the signal lamp` 890; At RA832, they relay R830`completes anobvi'ouslockL ing circuit for itself.

Shortly followingthev energ-ization" and operation of R830, `the-relay R400* operates tou in'- terrupt, at RA43'1and4 R'A438 the4 operating cir cuit for R420. At its armature Ril-43V, the ref lay R430" completes`- a locking circuit for' itself extending fromA ground at RA482-byway ofCGll1 and the Winding of R430/tobattery: AtRAlI-SS'; this relay'prepares an alternative locking-circuit for itself extending'fr'om' groundand lieldiopen at' RA482; At its` armaturesA RA48'I to RA434'; inclusive,v the relay R430" interrupts points yin` the impulsing circuits traced hereinaftergif'or' energizing the supervisory' relays R100? to RTI-0*, inclusive, thereby to prevent these'relays from be'- ing aiiectedl during the transmission of' impulses 'to the selecting relays'of theconnector'switcli;

Shortly following the' operation' of'lft4'31l7 and the consequent interruption of the operating cir cuit for R420, the'latterrelay restoresi'urtlier` to prepare, at its armaures'RA42'l andR`A422iand their associated contacts-RC425 and'RC4'2T,' re*- spectively, the loop extending'between therca-l'le ing subscribers substation A andthe operators telephone 200". The operator, upon witnessing the energized condition of the signal lamp 890, is informed that a. calli's present upon the line 443V which requires her attention:l By operating theA key switch 8 l 0=torits off-normal i position, sheA mayl complete the'talkingf loop between theftelephone-800;and the callingsub'scribers substation A-, andcondi'tionthe-common control equipment located-f in thesuboice to be responsive to impulses@transmitted1 theretof fromtheimpulsing device-86011 Thus, when-tliisArv key switchisoperated to its off-normal position, an obvious circuit is' completed"I at-V the# switch element" 8.41"! for* energizing R820, which relayf operates 'RA8231 to open= a pointin` the holdingV circuit forfR830f: 'Il're lastmentionedl relayV restoreslitsl amature RA832` to open a further point" inf-its holding circuit; and'itsarma-ture RA83I to interrupt thecircuitA for! energizing the'signallamp 88012 At its armatures-RAMI# and RA8242L the relay R820, upon-operating', completes circuits'for energizing' the'- relays R450; R460?, and-R410 embodied in the control equipment' at the1 distance exchange. The firsty of'A these circuitsextends froinground!- at` the-switchingelement B18-by wayofI the im pulsing springs 89|-rl and v86-2; thespringsV 812-1 and 813 of thekey switch-810,fC026; the springs` 8I2 andiV 8|'3f ofv tl1'e--key` switch- 810; RA-82'|;y RA-822, the-repeater Winding 844; C444, H0402-, RA40I, R`A42Ii RC425'1; C448, the repeater winding- 455; the lower windingof R440 and through thewind4` ing`of`R4550'tobattery. The seoond'of the abovenoted circuits, namely that forv energizing R460 and vrR4T0in-series, extends from ground at the switch spring 8| 8 of the key switch 8|0 by way of the impulsing-spring-s 86| and862, the springs 874 and` 81.51.o the key switch-8.10; the; springs 883and: 884 of thefkey switchy 880, C825, the springsfl 4'- andad 5i oI-the key switch 8 l 0i, RA824.- thef repeater-v winding.' 8.45,y C445, RC405, RA404, R'A422, RC42L C449,.the-lower.repeater Winding. 456 of the repeater 454,-theupper windingofy R440,. and throughj the `windings' of -R460 and R410- infseries;` to-'batte-ry. AlthoughA both ofV thewindingsoi. R440 are energized,v this relay does: not operate', the two windings :beingconnectedinopposition to permit-operation of the relayA onlyl wheny one thereof is-energized and the other is'deenergized'-,

When the relay R450? operates,` following-f its err-- ergization over; the above-traced circuit, it completes:-at'RA45'-I an obvious-circuit for energizingv the slow-to-releaserelay R480.. A-t itsarmature RA4-52, thexrelay R450 opensapoint in a circ-uit, tracedl hereinafter, for' energizing the-relays R40- and R600-in.parallel;and,- atits varmature 453.-, it opensI a point` inthe circuit foryenergizing the ringing currentv control relay R630.

The relayk R460, upon operating, interrupts, at 12A-46|, a point in the circuit, traced hereinafter, for energizing the monitorrelay 620. When R410 operates in response to itsenergizationin series with.R460',^. it preparen,A at its armature RA4H, a point in the above-noted circuit for energizing R460 completes, ati-its armatureRAMZ, a: multiple circuit furthe sloW-to-releaserelay R480 and interrupts; at` its .armature RA413,.a point in the circuit, traced. hereinafter, for. energizing. the ringing.-current. control relay` R640..

Shortly following, the operation of R450 to cornplete a circuit for. energizing R480, the last-mentioned relay operates to complete, at RA48`2` an obvious alternative holding circuit for maintainingl R430 energized independently of4 the slow-torelease relay R490Z At its armature RA4-63, the relay R480' interrupts a point' in the circuit; traced hereinafter, for. energizing R340 during therelease of the lindert-connector link by the central exchange operator. Ath its armature RA48I, the relay R480 completes an obvious circuit for energizing R490, and the latter relay operates, in turn, to prepare, at RA49I, a point in the circuits for energizing R40 and R50, to interrupt, at RA492, the original holding circuit for R460, and to prepare, at its armature RA493, a circuit, traced hereinafter, for energizing the switching relay R690, following the selection and testing of the called line. At its armature RA494, the relay R490 prepares a point in the above noted circuit for energizing R340 included in the control equipment of the iinder-connector link illustrated in Figures l, 3, and 5, and at its armature RA495 it opens a point in the circuit, traced hereinafter, for energizing R280 included in the starting apparatus illustrated in Figure 2. At its armature RA491, the relay R490 prepares a circuit, traced hereinafter, for energizing R140 and at RA496 it opens a point in the common portion of the circuits for initially energizing the group and units relays of the iinder switches, thereby to prevent a second link from starting to operate before the control equipment common to the links and shown in Figs. 4, 6 and 7 is released. With the control equipment included in the suboice and common to the links in this condition, it is prepared to respond to impulses transmitted from the impulsing device 860 located at the operators position in the central exchange thereby to cause the group and units relays or" the connector switch to select the called line 515.

Dialing the' called Zine As pointed out'above, immediately upon the operators actuation of the key switch 8I0 to its off-normal position, a conversational circuit is established between the operators telephone 800 and the calling subscribers substation A. This loop includes the calling subscribers line 9| I, the common link line |56, the link line |89, the line conductors C34? and C348, the link conductors C552 and C353, the line conductors C463 and C460, the repeater 454, the control trunk 443, the repeater 640 and the line conductors leading to the operators telephone. With this circuit completed the operator may converse with the calling party and obtain the necessary information for completing the connection to the desired substation. In the present case, wherein it is assumed that the calling party A desires to converse with a party at the substation B, the central exchange operator manipulates the impulsing device 860 in accordance with the number designating the line 55 to which the substation B is connected, thereby to cause the connector switch shown in Figure 5 to select this line. It will be observed from a consideration of Figure 5 that the telephone number of the called line 515 is 20 since this line is in the tenth line in the second group of ten lines.

At the Ybeginning of the rst impulse of the iirst digit dialed, the previously traced operating circuits for the relays R450, R460 and R410 are interrupted at the impulsing springs 06! and 062 of the impulsing device 860. The relay R460, upon falling back, prepares, at its armature RA40I, the above-mentioned circuit for energizing R620, a point in this circuit being simultaneously opened at RA41I of R410. At its armature RA4E9, the last-mentioned relay prepares a point in the circuit for energizing R640, this circuit being held open at the restored armature RA442 of the differential relay R440. At the two armatures RA45I and RA412, embodied respectively in R450 and R410, the operating circuit for R480 is opened. Due to its slow-to-release characteristic, however, the last-mentioned relay remains operated during impulsing. The relay R450, upon falling back, completes, at its armature RA452, a circuit for energizing the slow-to-release relay R40 and the lower winding of the impulsing relay R600 in parallel, this circuit extending from ground at RA44I by way of RA452 and RA49I to C208, where it divides, one branch extending through the winding of R40 to battery and the other branch extending by way of RABI I, RCBIE and the lower winding of R600 to battery. Both of the relays R40 and R600 operate, the first thereof to complete, at RA42, an obvious circuit for R50 and the second thereof to prepare, at its armature RA605, a circuit, traced hereinafter, for energizing the upper windings of R600 and R6I0 in parallel. The impulsing relay R600, upon operating, also prepares, at RA606, a` path for shortcircuiting the lower winding of R650, this path being completed upon operation of R50 and extending from ground at RA52 by way of C491, RA606, the lower winding of R6I0, RC6I2, RA6I I back to ground on C208. The relay R50 upon operating also prepares, at its armature RA54, a test circuit, traced hereinafter, for energizing the busy relay R650 in the event the called line ultimately selected is found busy. At its armature RA5I, the relay R50 completes a circuit extending by way of C489 and RA614 for energizing R660, which latter relay immediately operates to short-circuit, at RA66I and RC662, the winding of R610. This short-circuiting path extends from ground at RA5I by way of C489, RA614, the winding of R610, RC662, RA66I, C485, back to ground at RA493.

In addition to performing the functions described above, the impulse responsive relay R600, upon operating, completes, at RA004, a circuit for energizing the iirst group selec-t relay R10 included in the connector switch shown in Figure 5. This circuit extends from ground at RA3I1 by way of C369, RA553, RA513, RA593, C356', RC386, RA381, C361', RA395, C361, RA604, C368, RA396, C368', RA388, RC389, C358 and through the winding of R10 to battery. At its armature RA60I and associated contact RC603, the impulsing relay R600 prepares a circuit, traced hereinafter, for energizing the third group select relay R510, this circuit being held open at the restored armature RA594 of the second group select relay R590. The last-mentioned circuit is yfurther prepared at RA51 upon the operation of R50 at the beginning of the iirst pulse of the first digit. It will be understood that due to the slow-to-release characteristic of the relay R40, this relay and the relay R50 are held operated during any series of impulses comprising a particular dialed digit. With R40 operated, circuits, traced hereinafter, are opened at RA43 for applying busy tone current to the calling subscribers line` 9| I and the control trunk 443.

As noted previously, the two relays R600 and R6I0 are so connected and arranged that R600 operates at the beginning of each odd impulse, R6I0 operates at the end of each odd impulse, R600 restores at the beginning of each even impulse, and R6I0 restores at the end of each even impulse. Thus, and as pointed out above, R600 operates immediately upon the restoration of R450 at the beginning of the rst impulse of the rst digit. At the end of this pulse, when the impulsing springs 86| and 862 are again closed to cause the reenergization of R450, R460, and

R410, the above-traced short-clrcuiting path for the lower windingfof R6I0 is interruptedv at RA452'per1nitting this winding to be energized in series with the lower winding of R600. When .this occurs,'R600 stays operated and R610 oper- Vates to prepare, at RA6|| and RC6I3, the above- ,battery and the other branch extending by way of RA605 and the `upper winding of R600 to battery. The relay R6|0 remains operated, but the relay R600, being differentially wound, restores when its upper and lower windings are both energized. When RA605 falls back, the circuit for energizing the upper winding of R600 is opened and when RA606 falls back, a. second pointis opened in the circuit for energizing the lower winding of R600 and the llower winding of R6|0 in series. In order to render R600 fast to restore at the beginning of each even impulse, its

upper winding is constructed so that the ux produced thereby greatly predominates over that furnished by the lower winding. At the end of the second impulse when R450 again operates, the circuit holding R6|0 operated is interrupted yat RA452 and R6l0 restores its armature RA6|I to restore the two relays R600 and R6I0 to the condition which prevailed before the rst impulse was transmitted thereto. It will of course be understood that the sequential operation and restoration of these two relays as described above are repeated during each succeeding pair of impulses transmitted thereto.

Due vto the repeated operation and restoration of R600 in response to the impulses transmitted thereto, the group select'relays R10, R590, R510, and R550 are caused successively to energize and restore in accordance with these impulses. Thus,

it was pointed out above that R10 was energized and operated at the beginning of the first impulse of the first digit dialed. Ihis relay, upon operating, prepares, at RA1I, a circuit for energizing the group switching relay R60, the latter relay not being energized` at this time due to the fact r'that ground is Withheld from C363 at the restored armatures RA620 and RA691. At its armature RA12, the relay R10, upon operating, completes a locking circuit for itself extending from .ground at RA3I1 by way of C369, RA553, RA513,

RA593, RA12 and the winding of R10 to battery.

` At its armature RA13, the relay R10, upon operating prepares a circuit for energizing the second group select relay R590, this circuit being completed upon the restoration of the impulsing relay R600 at the beginning of the second impulse and extending from ground at RA51 by way of C469, RA60I, RC602, C366, RA394, C366', RA304, RC385, C354'RA13 and the winding of R590 to battery.

ywhich R590 is energized. At RA12, the relay R10 interrupts a further point in its locking circuit as traced above. Before R10 falls back and immediately upon operation of R590, a holding circuit is completed for the latter, which circuit extends from ground at RA3| 1, by way of C369, RA553, RA513, RA592 and the winding of R590 to battery. At RA59I, the relay R590 prepares a circuit for energizing R580 from ground on C363' and, at RA594, it prepares a circuit for energizing the third group select relay R510.

At the beginning of the third impulse, when the impulsing relay R600 again operates, the lastmentioned circuit is completed at RA60| and RC603 and extends from ground at RA51 by way of C469, RABl, RC603, C365, RA393, C365', RA38I, RC382, C352', RA594 and the winding of R510 to battery. The relay R510, upon operating, completes, at RA512, an obvious locking cir-l cuit for itself, interrupts, at RA513, the locking circuit for the preceding group select relay R590, prepares, at RA51I, a circuit for energizing the group switching relay R560, and prepares, at RA514, a circuit for energizing the next succeeding group select relay.

In view of the foregoing description, it will be apparent that each group select relay is energized at the beginning of the impulse to which it corresponds. For example, R10 is energized and operates at the beginning of the first impulse, R590 at the beginning of the second impulse, R510 at the beginning of the third impulse, etc. Each of these relays upon operating causes the restoration of the preceding group select relay and prepares a circuit for energizing the corresponding group switching relay and the next succeeding group select relay. Each of the group select relays further functions to prepare testing circuits for each of the lines in the group to which it cor- 5 9| I 506, 515, etc., included in the second group of lines corresponding to this group select relay.

It will be understood that in a finder-connector link, wherein the lines extending thereto are divided into ten groups, ten group select relays will be utilized which successively operate in accordance with a first digit of from 1 to 0 to select a group of lines including a desired calling line.

In the present instance, wherein the called liney 515 is included in the second group and the lrst digit comprises only two impulses, the group select relay R590 will be energized at the end of the digit so that a circuit is prepared for energizing the corresponding group switching relay R580. Since the digit comprises an even number of impulses, the two relays R600 and R610 are both restored.

At the end of the series of impulses comprising the first digit, the impulsing springs 86| and 862 are again closed to cause the reoperation of R450, R460 and R410 and remain closed for a suiiicient period of time to permit the sequential restoration of R40 and R50. Thus, when R450 operates, it interrupts, at RA452, the above-traced circuit over which R40 is energized. After an interval,

R40 falls back, to interrupt, at RA42, the opery ating circuit for R50. The relay R50, upon restoring, opens at RA5I, the shunt across the winding of R610 and, at RA51', interrupts a point in the circuit for energizing the respective lower windings of R600 and R6|0 in series. At RA51, the relay R50 opens a point in the common porwhich occur from thispoint on.. depend :upon the.

rned-iettelyiinterrupts',i atitsfarniature yRAS-I e lfioldingd4 circuit-fori`thev Second unit'sf'f'relayRSBi and'-com-pletes, iat-f RRS I 4, a i'holdingMcircuitfiforM itself. f At fits farmaturese RSfI Iii? BASI 2 5- and RAfI, thisithirdJ-unitsrelayeprepztres -a circuitfor 'testingth' condi-tion"A of "the" third line nfftlre e second'figroupfiand' at its*armature-#Rigid it prepares ea circuitvr for energizing-'trieV -fourth* units' *n* relayr' In; view-eff the irrimediiattiely-A 'precedingdescrip-rv 201; tionfit `-Will lie"'understoodthatthe unitsf'relays are1-successivelylenergzedin accordancewitnthei impulses efthsecend'dig'it'andthatyat the endr cf this' digityfV only f thef4 one `-of' these 'frel'ayseorren spending to' thenumbefr-of thelast impulsein im the esecondldigitf-"is energized-.-

Inthe'present assumecrease;wherein;the-called line-51 5"i's thev tenth'` `line in 'f 'the' second groupl of linesfthe second-digit, as has been-pointed out,` Williiomprise ten-inipulses"softhat;at `the:conclusion:of `lthis g Y digitfthe' tenthunits relay R5 00 isA energizedand they control Aconductor ,C559i'ilf the calledflirie 515' is connectedrby vWay of -the-'armatures RAEBVand, RA503 to the control' conductor C362of .the link line-3ll9;` .Itiwill'loe.observedxtnatthe operated vgroup'selectrelay YR590 wand the operated yunits relayiRSB'ar'e lockedrup ,over holding circuits-` including the" common' portionwxtending frnn ground at. RA3I1, which 'circuitsare held'om.. plet'ediindepen'dently',of'the control equipment common' `toall of .the links:`

At the conclusionr of l the second.. digit.` the'y ref lays R450',C R46il'ffand R41-01're-operate; and therelays. R40"nd Y'lft'l'llland theimpulsemesponsiize. relays, R0 00- and-R6] 0 'if .operatedrl restore; all in theflmannernescribed abovein 'connection Withl ftheoperations which "occur, following the 1: dialingwof thefrst digit at.. the .central h.exnharigee operators station. 'I'heisequence..ofoperations,.i

conditionlof ,the .ea-lled line las .identied.by. thej J potential existingonthecontrol conductor: therefv of. Asfnoted inlan earlierlportion- OLthedeSCripw tion,- vin :connections-with thex operation :of `the finden switch :shown in Figurefl .if the mailedJ 55 line .is rbusyl,its :contizol .conductor is markedwith I: groundpotentialQwhereasuif the `line. is -idlet-bata: tery, potential is present: :thereomy l.this potential-f beinga'applied tdfthez -controlw .conductor-1 from the, g. cuteoi relay,associated,.with` the lineandcorre=f`-o sponding gto., the ,.relafyf. RI I0 associated.withwthe calling line 9| .Il Y v Theoperations;resultifig whenz-.thical'ledllif is idle Assuming the' `cal-led; line :to "be: idle', the'` relays5 R40 land# R50 fupon" restoring," shortly jfol'lowing i theendA off-the second digit; `completen, eireuit forenergizing the-upper wvin'ding of-theiswitching relay `R690, this :circuit extend-ing- "from" battery u at the `cutoil?relaylassociatedWith'tl'le calledline S15-by Way-ofC559-=RA591y C518,"RA503'C362^3' RA399, C352, RAM: VRC5550484? thenpperl wind# ing of R690jC6 I 4^andxC4'85 -tdground at *RA'49'3 1 In responseto'the energizationofits' upperwindf-iq ing over` the above-traced circuit, R580 operates Y for energizing R340 and, at this same armature and RC695, it prepares a point inthe circuit for energizing R330. relay R690 closes ground to C353 to complete a circuit for energizing the selected group switching relay R580. This circuit extends from ground at RA691 by way of C363, RA39I, C363', RA59I and the winding of R580 to battery. When the group switching relay R580 operates, it connects, at its armatures RA58I to RA588, inclusive, the line conductors of the lines 9H, 506, 515, etc., comprising the group selected, to the common lines 5|1, 5| 8, 5|9, etc. This operation causes the called line 515 to be connected to the link line 349 to complete conversational circuits between the calling and called telephones and the central exchange operators telephone 800. With .the system in this condition the operator may listen in to determine whether or not the called line is being used by two parties each having his telephone conected thereto. If the called line is busy the operator may hold the connection until ythe previously established connection is cleared out, break in on the ensuing conversation, or release the connection in the manner described hereinafter. If, on the other hand, the called line is idle, the operator may proceed to ring the ydesired one of the substations connected thereto.

Ringing the called substation To this end and as pointed out above, provisions are made whereby ringing current may be transmitted over either line conductor of the rrepeated actuations of the key switch 880 to its off-normal ringing position. yEach time the springs 883 and 884 of this key switch are opened, ground at the spring 818 is removed from the positive trunk line conductor C445 to open the "operating circuit for the relays R460 and R410,

thereby to cause the deenergization of these relays and the upper winding of the differential relay R440. As a consequence, R440 operates to interrupt, at RA44I, a point in the circuit for `energizing R and R600 in parallel, and to prepare, at RA442, a circuit extending by way of C411 for energizing the ringing relay R640. The last-mentioned circuit is completed at RA413 upon the restoration of R410. 'I'he relay R640 upon operating prepares, at RA649, a circuit, held open at RA66I and RC663, for energizing the relay R320. At RA64I and RA645, the ringing relay R640 completes a path for applying ringing current to the line conductors of the called line.

`If the ringing device at the substation B is con- At its armature RA691, the

nected between the positive line conductor and ground, the path of this current is from one terminal of the ringing current generator by way of C609, RA645, C355, RA394, C344, RA502, RA508, C558 and through the ringing device to ground. If, on the other hand, the ringing device at the called substation B is bridged across the line conductors C551 and C558, this path instead of extending to ground at the ringing device is returned to the grounded side of the ringing current generator at RA64I, by way of C551, RA581, RAI, C343, RA393 and C354.

At its armatures RA642 and RA646 and their respective associated contacts RC644 and RC648, the ringing relay R640, upon operating, completes obvious paths for by-passing portions of the ringing current through the condensers 641 and 643 to the receiver of the operators telephone and the receiver of the calling partys telephone, thereby to indicate that the called substation is being rung. It will be understood that the ringing relay R640 is energized and deenergized repeatedly in accordance -with the coded ring identifying the called subscribers substation B and that the above-outlined operations take place during each interval when R640 is energized.

At the 'conclusion of the ringing operation as described above, the non-locking ringing key or switch 880 is restored to its normal position, thereby to 1re-complete the circuit for energizing the upper winding of R440 and the relays R460 and R410 in series. There results the restoraV tion of the ringing relay R640, thereby permanently to disconnect the ringing current generator from the called line and to re-establish the above-referred to conversational circuits between the operators telephone, the calling subscribers substation and the call subscribers substation.

In the event the ringing device at the called substation B is bridged between the negative line conductor of the called line 515 and ground, this device may be energized by the operators actuation of the ringing key 810 in accordance with the coded ring identifying the called substation B. Each time this switch is operated to its offnormal position, the above-traced circuit extending from ground at the spring 8|8 is interrupted at the switch springs 812 and 813, thereby to cause the'deenergization of R450 and the lower winding of the diierential relay R440. With its lower winding deenergized, R440 operates in the exact manner noted above to prepare, at RA442, a circuit for energizing the ringing relay R630, this circuit being completed, at RA453, upon the restoration of R450 and extending from ground at RA442 by way of RA 453, C416, and the winding of R630 to battery. When R630 operates, it prepares, at its armature RA639, a circuit for energizing R320 and, at its armatures RA63I and RA635 and their respective associated contacts RC633 and RC631, applies ringing current to the called subscribers line, thereby to energize a signal device bridged across the line conductors C551 and C558 or between the negative line conductor C551 and ground. If the ringing device is bridged across the line conductors, the path of the ringing current is exactly the same as that traced above and completed in response tothe energization of the ringing relay R640. If, on the other hand, this path is bridged between the negative line conductor C551 and ground, the path of this current extends from one terminal :of'ltheminging current Agenerator.Joy wayi of .:C6D&,1.RC.633,--RA63 l- C354RA3933 (S34-3fY RASUL, RASS-1; C551 andithr-oughgfthe ringing deff-A Vice atethessubstation .to` grpundf: A .por-tionof= rthis; cur-rentis .byfpassednth-rough; the icondensers r r SBM-andfGSSt-by 'WayQoffthe:loopwextendingto the f operators-"telephonetandfthe,receiveriofi,thisetelef phone to indicateltofthet operator that 'athefcalledm substation is fbeing At: thefendf ofethev `ringing operatiomwhenrthefkey-switch 81`isre1fstored. Ito' normal,- ther4 circuit; traced-.-above;forenergizing the lower fwrndinge ofi'RMitfand @the Winding of-R45 in'. series is Ireecornpletedrf, When RMG-and R45roperate, the1operating;circuit-fora interrupted and:therlatterfrelay--restores; permanently -,-to disconnect the ringing current f generatonrom.v the :line lconductors leading to :the calledsubscribers substationfand; toI re-establish the talking loops referred to above Iextending bet-f.- rtweenrthe `calling 1 and:` calledfsubstations; :and the e f o-perators telephone.: Y

With; .fthe` systemf-finfthisconditionafthef oper-i ator-,may, =by simply-retaining her=.,appa1atns the. condition whichtprevailst atethe :conclusion of.-= the -ringingffoperatiomemaintain henf telephone s connected;vto the connection-` existing :between-,theL` s calling and called lines to monitor the conviersa--=- tion which y,ensues-fafterethe t called i substation 'is answered. e. A1ternativelyf,. she .-rnaygoperatev rthe xkey or:z-sw-itch\.-81-0 to: the monitoring positiong: thereby nto establish-a conversational ,circuiti fbe. tween-herftelephonefandfche calleda telephoneto f theA exclusion vvof, thefcallingfparty. .As a further a alternative, 'she mayo operate.the fkey-switohf I il. sto its-:normal ;positionf,'therebyrto cause the frere leasesfof Y Tthe equipment common to' xalle-of `the linksfandprepareA the-,same for@furthenuseiin t connection @with :rothen :cal-ls initiated.` Y on@ lines J1- terminatingzat-ithe suleoiiicefJ 9 I |J.-

Monitoring In. :the event. the operatori, desires .tof-converse withthe called party to the' exclusion-ofthe119,11AY ing party, she .may operate thesWitCh 810'to the.. monitoring. ,position vvimmediately following there; conclusion of the ringingoperation. .Inlresponse` to thisloperatonrvthe -springs.,814.\ andn15u 'are openedio insert the resistor- 816i'n. the abo'vetraced. .circuit for energizing theupper Winding of R44- andrthewindingsrof,R460andR410`in series, The resistor-.416is 'soiproportionedthat,Y l, wheninserted in.A this circuit, 1on1-y ythe' marginal ,l relay R460is affected,V thediffe'rential relay R440' 2 remainingcrestored, .and R410.' "remaining operated.vl Thenmarginal relaxe5MM',(however, re` stores to-tcornpleter.atRAAB'HY a, circuitfortener-Y gizing,the .monitoring @relay .,REZD'; .this i circuit. extendingefrome ground atlRAlllil g by'- Way of RAM-I, RA4.l,`.C496and,the Winding of RBZDto battery, ,Wh'n energized over the above-traced circuit,'R620 'operates to open, at RABZT; a point in thel circuit;traced`hereinaften for energizing the" busy relay'RGSUfiand 'tof apply,-at'RA628,'" multiple'groundv` to the conductor C3635L At4x its armatures RAS'Z I and" RAS-2'4-i and theirrespee# tive:V associated; ontactsRCBMand 1RC625; th'ev relay R620 disconnects'th telephone located at.'- the calling:substation:A fro'mfthe iloop'extending; between: theoperatons telephonei andithe called` 1f suloscriber"s substatioms: Atnfthesevfsames iarma"'= turesf'and: their' :respective -associ'atedfcontacts i f RC623^randffRC 626,-ffa directametallic: circuitmis f completedv'between the line conductorsgC463 and C464 andf 1the lineconductors'CEB nand C55-"I, respect-ive1y,a ofithe.zcalledqsubscriberis line. -s Thusf. f

armem- Release-ofthe common control equipment'K In the usual operation. of-utheisystemgthe oper ator inthe central *exchange causes the equipe; mentcomrnonto the links and --located in the subloice 910 to-be restored to-,norrrial immediately,.- upon ascertaining :thatxthe'rca'llzis answered. 1 To this end,.:the operatonsimply `restoresjthe `keywml.

switch tlto its normaly position, Athereloy-to cause the deenergization of^R32l v-gr When ythis relay restoresits armaturesv RA82ltandRA824gM the above-traced operating circuits'for-.there-rr latter relays, upon restoring, yoperrthe operating circuit -forthe slowetoerelease IrelayeRtili.which restores,l after-,an.interval;1to interrupt :the oper- 1 ating lcircuitfrfor- -R4901.f

When -R48l gestores-Yitsarrnature RAME; -the -30-151.

holding circuit .forY R439.y is interrupted, permit ting the lastementioned1'elay-1to-irestore and -in.- terrupt,: at--RA438f=4 a furtherA point in its. holding: A- circuit.: At RA483,f-:the:"relay1R489yuponf rey storing,completcs a circuit lforuenergizing R330;35

upon' operating, :interrupte-T the operating circuitur i forthefgang relay R390; whichlatterr-relay re---. 60 stores all: of its armaturesto disconnect-=y the con@ trol .equipnicntv :associated r1 Withfv :the illustratedy: linkzfromzthe control=equipment cornrnontoallw` of the linksfandishownin-Figs. 4, 6 and 7. -The'- RA390$,-fmultiple:'ground f'rom'C16, interrupts, at RA-395', a pointvinrthesoperating circuit for R320-, f andz'interrupt's;atfwits armatures f\l`1.A39l-- to. RA39 61S; inclusive? pointssin l the :fcont-rol circuits forathe relays. includedfin the.conneetor switch 70 of Fig.

As Ypointed. out above; the ,relay 'R32 0, lupon v*restoring, Vits .f armatures;` completes an alternative.

loopt-between. the callinghand:called` substations,

and i withl the systemf in this oondtion, the con- 75

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