US1478086A - Telephone-exchange system - Google Patents

Description

Dec. 1,8, l923 31,478,086

s. B. WILLIAMS, JR

TELEPHONE EXCHAGE SYSTEM Filed @pril 1 191s .7 sheets-sheet 1 n@ @NN @2mm /iffy Dec. 18,1923. v Lf 4 S. B. WILLIAMS, JR 1 TELEPHONE EXCHANGE SYSTEM Original Filed April 17, 1918 7 Sheets-Sheet 2 y @www mi,

Dec. 18., 1923. L f 11,478,086

s. B. WILLIAMS, JR y TELEPHONE EXCHANGE SYSTEM Original -Filed April 17. 1918 7 Sheets-Sheet '3` l //7 Ven for:

Dec.' 18, 1923. www@ f S. B. WILLIAMS, JR

V TELEPHONE EXCHANGE SYSTEM Filed April 17, 1918 7 Sheets-Sheep 4 /m/e/Waf.' Samva/; lfi/f//fd/md/ .y

RMwMA/fy MWSAJS@ Dec. 18, 1923.

s. yla; WILLIAMS, JR-

`TELEPI'IONE EXCHANGE SYSTEM Original Filed April 17. 1918 7 Sheets-Sheet 5 R, Mme@ Am Dec. i8 i923.

S. B. WILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM 7 sheets-shea 6 Original Filed April- 17. 1918 Dec. 18,1923. www@ S. B. WIILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM original Filed April 17, 1918 7 sheets-sheet 7 fav; I

Patented Dec. 18, 1923.

tirarse r nr rica.

SAMUEL B. WILLIAMS, JRmDF BROOKLYN,

NEW YORK, ASSIGNOR TO W'ESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NRV7 YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Original application filed April 17, 1918, Serial No. 229,035. Patent No. 1,400,120, dated December 13, 1921. Divided and this application led May 14, 1921. Serial No. 469,493.

To @ZZ whom t may concern.'

Be it known that I, SAMUEL B. WIL- Lmrrs, Jr., a citizen of the United States, residing at Brooklyn, in the county of Kings, State of N ew York, have invented certain new and useful Improvements in Telephone-Exchange Systems, oi' .which the following is a ull, clear, concise, and eXact description.

This invention relates to improvements in telephone exchange systems and has particular reieienceto systems ofthe type employing automatic switches for distributing calls .from telephone lines to the connecting circuits oi operators positions.

rlhe invention herein described and claimed is a division of Patent No. 1,400,120, issued December 13, 1921.

An object oi the invention is to provide a system wherein an operator has means for applying current to a connecting circuit for operatingl toll devices associated with calling lines, only when said circuit is connected to said lines and wherein lone toll-device-operating key is arranged to effect the actuation of the toll device and then cause disconnection oi thecalling line, while another key is arranged to operate the toll device and maintain connection with the calling line.

Other objects to which the .invention is directed will appear lin the course of the following description when taken in connection with the accompanying drawings which illustrate what is now believed to be a preferred embodiment of the inventive idea.

In the drawings, Figs. 1 to `7', inclusive, taken together, and arranged side by side in the manner indicated by the lines that eX tend to the margins of the drawings illustrate as much ot the complete organization of the system as is necessary to enable the construction and mode of operation to be understood. y

Two telephone lines are indicated in each ot the two groups LG and LG shown in Fig. 1, it being understood-that each group may comprise a number of such lines. The ordinary practice is to give the finderswitch br-ushes access to the terminals of 500 lines, these lines being divided into ten groups of 5G lines each. Each of the groups of lines have associated vwith it a distributor .switch 13.0 to the stationary contact terminals oit' which the lines of that group eX- tend, the brushes oi the distributor switch being connected with group apparatus which is actuated by the passage of the brushes over the terminals of a calling line. For a more complete understanding of the switch 130, reference is made to the abovementioned pending application. Each of the lines has associated with it at the central oilice, a connection register 92 or a resistance coil 91. Each line is also provided with one or more spring-jacks 14 by means ot which connection be made with the line when it is called. 4The lines represented as calling lines in Fig. 1 and the line indicated as a called line in Fig. 7, may be lines ot the same sort, similarly equipped and located at the same exchange; or the lines may be located at different oihces. Each oi' the lines of the various groups is connected with a class-of-service interrupter 170,

which may be common to the exchange; and

each of the lines also has connection with and is represented by a lamp on a common lamp board 15.

The groups ot lines have access to groups of connecting circuits through the medium of iinder circuits F, F and F 2. These finder circuits terminate upon the brushes of pairs ot' finder and selector switches, of which,y two sets, LF and CS and LF' and CS', are shown. The starting oi the finder switches to 5nd the calling lines is effected by the distributor-switch apparatus through the medium of starting apparatus, including the relays 20, 23 andQ-, which is common to all of the line groups and to all of the finder circuits having access to the lines of these groups. Each of the groups of connecting circuits, to which the lines of the various groups have access by way of the finder circuits F, F and F2, is associated with a particular operators position. The apparatus of only one position is shown, the others being similarly equipped. Each operators position is provided with a number of plug-terminated connecting circuits eX- tending to multipled groups of terminals upon the cord selector switches; and the brushes of each cord selector switch are given access to the terminals of a number of such groups of connecting circuits. Only one of the 'connecting circuits is Shown com operators positions.

plete, the other' connecting circuits in the associated group and in the other groups be ing similarly organized and connected. The multiple connection of the connecting ciruit with the terminals of the cordV selector switches are shown in the caseof the connecting circuit that is ccmpletely illustrated and in the case ot a single connecting circuit that is indicated in another group; and in ike manner the multiple connections ot' the telephone line with the terminalsY of the 5 line-inder switches are shown in the case oit the lines that extend from stations A and A. rlhe .multiple connections that exist be tween corresponding sets of switch terminais in the case oi the other connecting circuits and telephone lines are omitted in order to simplify the drawing. v

A number ofV groups ot cord-selector switches, like the group illustrated in Fig. 3,' may have access to the same groups of connecting circuits and their corresponding This is indicated in Fig. 3. Each of the groups of cord-selector switches has associated withl it certain selection-controlling apparatus, that lassocia-ted with the cord selectors shown in Fig.

3, appearing under the caption Frame 2, and that associated with another group of cord-selector switches appearing under the caption Frame 1. The selection-control-Y ling apparatus foreach frame or group ot cordfselector switches comprises a pair of relays 77 and 93 for each group of connecting circuits or` operators position, to which the cord selector has access, anda group ot relays 61, 63, 64;, 66 and 67 common to all ot the hist-mentioned groups.

Each of the operators positions is provided with apparatus which is common to all of the connecting circuits ot that. vposition, and which may be brought into association with any of the connecting circuits either automatically in the extension of a call toone of the connecting circuits,or at the will of the operator in thecourse of her supervisory operations. The operators rommon or position apparatus is illustrated on Fig. 5 and Fig. 6, and each of the connecting circuits withwhich the operators position Vis equipped may have connectionwith the position apparatus in the same way in which ythe connecting circuit illustrated in Fig.v 4

isshownto have connection with thisapparatus. Y Y

The line linder switches LF and LF and the cord selector switches GS and CS may be substantially like the switchillustrated and described in Patent No. 1,177,044 to James L. McQuarrie, issued MarchfQS, 1916. The line finder and Vcord selector switches are alike in allsubstantial respects. Eac'h comprises a longitudinally movable shaft 1, carrying as manysets of brushes 2 as there are groups'of stationary terminals to be engag'ed. To move the shaftV up, an extension at the lower end of the shaft is brought into engagement with the constantly rotating power member 3 by means of an idler wheel' operated by the up-drive magruetr 32;V and to move the shaft down, the extension is brought into engagement with the power member 4. byV means of an idler wheel oper ated by the. down-drive magnet 62. Normally, the brushes ot each ot the sets 2 are held af'part so as to clear the vassociated terminals by means of a separating cam 5 located between the innermost brushes otthe set.l The camV 5 is rotatably mounted, and when rotated in onerdirection, releases the brushes and permits them to engage the associated terminals. kThe tripping or releasing of' the brushes is controlled by a number of trip magents,`as V16 and'17. `Each ot these when'energized, rotates an associated trip rodv 6v thatextends transversely tothe switch shaft-s1 andcarries as many trip yokes 7 as there are finder switches or selector switchesin the group. The trip Vrod in. rotating brings all of its Atrip yokes 7 into position to operate the brush-controlling cams 5 of the corresponding sets ofbrushesv on all of theswitches, so that whichever ot the finder switches is caused to move up, has that-set ofV brushes tripped that Vcorresponds with the particulartrip magnet 16, 17, that is at the time energized. When the finder switch that has been in use is returned to its normal position, any of 'the-associated controlling cams 5 'that has been tripped, is engaged and rotated in a reversedirection toV separate its switch springs again Vand thus render them inactive. Each of the line finder and cord selector switches has associated. withit, a commutator S which comw prises a number of stationary commutator segments and a set of movable brushes carried at the top of the switchshait 1 and cooperating with the stationary segments. ThisV commutator serves to make and break a number of the controlling circuits in the various stages of the yupward movementot the switch shaft. Y

"For controlling the circuitsof the organilZation, there are employed a number of se quence switches which are shown at dierent points andy designated 200, 300, Z and d500 respectively.' These sequence switches Each consists of an Y thosel associated'with each offrit-he, sequence A switches 300 are designated 301 to in elusive; those associated withvea'oh of these quen'ce switches `400 are designated 1:01V to l1,21 inclusive andthose associated with each of the sequence switches 500 are designated 501 to 507 inclusive. To each of the c on-i`l tacts associated with the varioussequence switch, cams "are applied certain numerals. These numerals in the case of the cams 201, 301, 401 and 501 indicate theonlykpositions of the associated sequence switch in whichv these particular contacts are open; the numerals applied to all of the other contacts of each sequence switch indicate the only positions of the particular sequence switchy in which the associated v,contacts are closed. vThe resting positionsof the diiferent se quence switches, and the stagesof operationV with which these positions are associated, are as followszf Finder seguente switch. Q00.

Normal. A

.l-waiting starting circuit.

Hunting. v

Awaiting selector sequence switch.

rlallringlg.` i

Finder switch return.

Selector sequence switch 300.

` listen-fing 7663/ sequence switch. 400.

1 Normal.

2 Awaiting 6 Listening 8 Listening finder circuit. w

1n. out.

fl/Ning cowl sequence 'switch 500.

1 Normal. V

2 Awaiting connection.

1G Talking. Y V

rEhe class-of-service interrupter comprises a number ot sets Voft switch springs voperated by the cams 171 and 177, inclusive. Each of the i switch springsqassociatedwith 01 cams 1:, to 176, inclusive, consists of two springs the contacts or" which are normally in engagement.. Eachofthe two sets associated with the cams 171 and 177j consists of two springs the. contacts .of which are normally open. The; cams -172 to-176, inclusivaare so formed as to cause. one, two, three. four. andve breaks per revolution respectively in the normally closed circuits Controlled. by the associated. of switch springs. The cams 171 and 177 are so formed as to cause one closure per revolution and six closures per revolution, respectively, inthe circuits controlled by the associated switch springs. The cam 171 and its associated switch springs control the production of the pick-up impulses, the cam 17 7 and its associated switch springs control the production of the reset impulses, and the cams 172 to 176 and their associated switch springs control the production ci" the classof-service impulses, as will be .described hereinafter.

For a complete description and understanding of the class-of-service switch shown diagrammatically in the lower right hand corner of Fig. 5, reference is made to the above-mentioned parent application.

In outline, the operation of the system in the embodiment disclosed is as Jfollows Vhen a subscriber calls, the passage of the brushes of the distributor switch 130 over the terminals of the calling line records the call in the distributor apparatus or" the associated group, and this recorded call causes the closing of the starting circuit common to all of the distributor groups and to all of the lineinder switches that serve these groups, and also causes the energization of the :Finder switch trip magnet corresponding to the groups of lines in which the calling line is located. Itthe starting circuit is at the time being used by some other calling linethe recorded call is held until the starting circuit is freed. As soon as the call is discharged into the starting circuit, the distributor apparatus is released and made available for recording ano-ther call in the same group.

Thel finder switches each have as many sets of brushes as there are groups of lines. The closing of the starting circuit causes a preselected one of the iinder switches to move its brushes, and the energization ot the trip magnet makes active the set of brushes corresponding with the group in which the calling line is located. T he apparatus which brings about the energization of the trip magnet opera-tes to prevent temporarily the trip magnets ot other groups of lines from being energized by calls that may atthe time be initiated in the other groups.

As soon as the brushes of the finder switch are tripped another finder switch is brought into operative relation with the startingl circuit, and the starting circuit is released and made available for the use of calling lines in groups other than the group in which the rstementioned calling line is located. When the new nder switch is connectedwith the starting circuit, any other finder switch is prevented from being brought into operative relation with the starting circuit, so that the starting circuit has control over only one finder switch at a time.

When the brushes of the` started finder switch complete connection with the terminals of the calling line, the finder circuit operates certain apparatus that determines to which of a number of operators positions the connection of the calling line is to be extended.V The selection of the operators position is effected through the mediumV ofl selection-controlling apparatus that is common to the cord selector switches upon which the finder circuits terminate', and to the operators7 positions to which these cord selec- V torswitches are designed to extend calls. The

' selection-controlling apparatus is continuously under the control of the operators pi vsitions,and keeps a path prepared for ener'- lector 'switch is started.

ators position, and immediately thereafterV the common solecti'on-controlling apparatus is released and made available for controlling theV selection of other operators positions by other cord selector switches and finder circuits. During this selecting operation,the setting of the selection-controlling apparatus is maintained, so that the tripping impulse is prevented fromV passing to the trip .magnet of some other position which Y in the interval may have become available.

lf all of the operators positions should'be unavailable at the moment Athe finder circuit is ready to eXtend the connection, the finder circuit is held and the availability of the operators position is periodically tested by Y the selection-controlling apparatus until one of the positions becomes accessible, when the operation is proceededwith.

After the set of cord selector brushes has been tripped, it ,continues its upward movement, successively engaging the terminals of the connecting circuits locatedat the operatosposition that has been selected, and

steps uponY the terminals of the first connecting circuit encountered that is idle and available for use. If for any reason, the

y brushes should Vfail to be stopped upon the Yterminals of a connecting circuit, the cord selector switch is returned toits normal p ositiontV and the selecting operation is then repeated. Y

' Prior to the extension ofthe. connection to the connecting circuit. and atV the instant that the operators lposition is selected and the Vcorresponding trip magnet energized, a signalis displayed at the operators position which notifies the Operator that bei" resitca paresse has been` selected. and. that a `@all seomins- At thesanie falli, abbi-path' iS' Closed. that puts. the. Greater immediately "int telephon'c Communication with the calling subscriber, andthe listening-iii-keys associated with all of the connecting cords of the position-ere rendered, inoperative SQ that the Operator'cannotinterfeifewith the coming call by listening in on' afcord circuit afterthe position.. hasbeeri selected and before the call arrives. The operators position at the saine time lisfmade inaccessibleto otherincoming calls; I

When the cord selector switch stops on the terminals of the selected connecting circuit, it lights a lamp associated with thatY circuit attlie operators position, and Asubstitutes a direct path to the operators telephone for the by-path that was closed when the position was selected. At the same` time, impulses pass from the subscribers line to class-of-service signal mechanism at the operators position, Which mechanism is thus operated to inform theoperator of the class of service which the calling line is adapted to receive. When the class-of-service signal is displayed, the calling signal, that first notified the operatorthat her position had been selected, is Withdrawn, and means for enabling the operator to inform herself of theidentity of-the calling line is made operative. The operators control over the-listening keys has in the meanwhile been restored' so thatshe may, if she desires, listen in on any other connection.

Vhen the operator VhasV received the calling subscribers instructions sheV tests the line that is called for and, if it is free, inserts the calling plug into the called line spring-jack. This act automatically brings about the disconnectionl of the Voperators telephone-apparatus from the circuit and the restoration of the class-of-service signal ico mechanism, the operators` positionrvbeing rendered unsele'ctablel and the class-of-service mechanism being prevented fromV being brought into operative relation vwith anyV connecting circuitwhile the restoration is being effected.V When the subscri Kers 'have finished their conversation, the operator effects disconnection by ypressing the disconnect key and withdrawing calling plug. If the calling line is a' measured service line, the operator pressesy a 1key whichv registers the call on4 the line register and the position register upon the depression of the'ley and releases the connectionupon the Yrelease of the key. Thislrey is effectiveY to applyregister operating, current to the connecting circuit only callingline. the calling subscriber wishes a second connection, the operator presses an- Vwhen the connecting circuit is extended to a other registers the-call on theline V resistentes@ est einer' neet the calling line from the connecting circuit. Before performing the `disconnecting lor registering operations referred to above,

the operator supervises by pressing her listeningin liey, which act connects her telephone with the circuit and at the same time again actuates the class-of-service mechanism lto guide her in making the charge or registration.

lt the operator is unable for any reason to give the calling subscriber connection with the called line, she presses a holding key which maintains the connecting circuit in connection with the calling line, but withdraws the busy test from the line so that it may call and be called. 'By listening in on a called line thus held, the operator is given a busy test ii" the line is in use, the class-of service signal mechanism under these circumstances not being operated. li the line is tree when the operator listens in on the held connection, she may restore the holding key and proceed with the establishmentot the connection in the usual way.

The features oi the operation that have been set forth in outline in the foregoing, together with other features present in the system, will be fully explained in the detailed description that follows. V

lt will be assumed that the subscriber at station A takes his receiver from its switchhook. The brushes 131, 132 and 133 of the distributor switch 130 are constantly rotating, and thus are successively bringing the cut-in relay 11 and the te'lst relay 12 into temporary association with the various lines of the line group LG which the distributor switch 130 serves. Ii a line is in use either as a calling line or as a called line, its sleeve conductor 53 is connected through relatively low resistance with battery of the same potential as that to which the winding o' the cut-in relay 11 is connected, as will hereinafter be explained. Consequently, when the distributor brush 133 engages the sleeve terminal of such line, the cut-in relay 11 remains inert. But when the distributor brush engages the sleeve terminal of a line that is not in use, an energizing path is closed for cut-in relay 11 by way of the brush 133 and the sleeve resistance 91, or the message register 92 associated with that line. The test relay 12, therefore, is connected with the two line conductors 38 and 39 orf each line that is not in use, and when it is thus connected with thc conductors of the line extending to station A, at which the telephone receiver has been removed' from its switchhook, the test relay 12 attracts itsy armature and closes a circuit that. extends from battery through the winding of relay 9 to ground by way of the iront contact and armature of relay 12. Relay 9, in operating, closes a lockingr circuit or itself by wayroi' its left-hand front Contact and armature and Ythe left-hand back contact. and armature of relay 10. The distributor brushes do not stop upon the terminals ot thecalling line, but continue their rotation, the eiiect of their engagement with the calling line termina-ls being in effect to record the call by energizing` and locking up the relay 9.

The effect of recording the call upon the relay 9 is'to cause the starting of one ot the finder switches LF, LF", etc., which serve the lines ot this and the associated line groups. This is accomplished throughthe medium of a starting circuit, two of the conductors 57 and 58 of which are extended to the relays 19 of the various line groups LG, LG', etc. Assuming that the starting vcircuit is not in use at the time the call is recorded on the relay 9 of the line group LG, the operation of this relay closes a circuit that extends from battery through the left-hand armature and back contact 01"' relay 23, right-hand armature and back con tact of relay 24, conductor 57, right-hand resting contact and switch spring relay 19 of group LG, the windings of relay 19 and the associated trip magnet 17 in parallel, left-hand switch spring and resting contact of relay 19, right-hand winding of relay 1S, and right-hand front contact and armature of relay 9 to ground. rlhe closure o'l this circuit causes relay 18 to operate; and in operating relay 18 closes at its lett-hand front contact and armature a shunt path by way of its lett-hand low resistance winding to ground that sutliciently increases the current low in the circuit to bring about the operation of the relay 19 and its associated trip magnet 17 the relatively high resistance of the right-hand .winding of the relay 18 preventing the relay 19 and its associated trip magnet from being operated at the initial closure. of the circ-uit. Relay 19, in operating closes a circuit that extends from batteryby way o1c the left-hand arma-tureY and back contact of relay 23, winding of the starting relay 24, conductor 58, the right-hand armatures and resting contacts of other relays 19 in the series, right-hand armature and switch spring of the relay 19 of group LG, the windings of relay 19 and associated trip magnet 17 in parallel, and the left-hand switch spring and armature of relay 19 to ground. The closure ot this circuit operates relay 24 and the trip magnet of line group LG to start a line-finder switch and trip the brushes oi' that switch correspond with the line group in which the calling line is located, as will hereinafter be described. This circuit is maintained and the trip magnet 17, starting relay 24, and group relay 19 held energized until the relay 23 is actuated at a later stage of the operation, as will be described.

When the recorded call has thus brought about the energization of the starting and llO vso

brush-tripping circuit, the call recording apparatus including the relays 18, 9 and 10 is disconnected from thestarting circuit and the record obliterated by the releasincr and return of these relays to their norma condition. W hen the recording apparatus obtains access to the starting circuit, the operation of the relay 18 not only brings about the energization of the starting and tripping circuit by closing at its left-hand `front contact and armature the low resistance path to ground; but it also closes a circuit that extends from battery through the winding of relay-10, and the right-hand front contact and armature of relay 18 to ground The closure of the circuit causes relay 10 to open, at its lett-hand back contact and armature, the locking circuit of the relay '9. Relay 9 in releasing opens at its right-'hand front contact and armature, the path to ground by way of the right-hand or Ahigh resistance winding ot the relay 18. Relay 19, in operating, has opened at its left-hand switch spring and resting contact', the main energizing circuit of the relay 18, Relay 18, therefore, releases, and in doing so, opens at its right-hand lfront contact and armature, the energizing circuit of the re. lay 10, which relay thereupon releases.

Thus the relay 18,9 and 10 of the recording apparatus are returned to normal and are in readiness to respond to Aanother calling line.

It will be observedthat when the yrelay 10 operates, it closes a locking circuit for itself that extends by Way of its right-.hand fron't contact and armature, right-hand winding of relay 18, and right-hand `front contact and armature of relay 9 to ground.. This iis for the purpose of inserting a continued vinterruption of the locking path for relay V9, at the left-hand back contact and yarmature ot' relay 10, until the relay 9 is released. Otherwise it might happen that if the mo vmentary operation ot 4the relay 18 which operates relay 10, had occurred .betore the distributor lbrushes hadpassed beyond the calling line terminals and thus opened the initial energizing circuit ot the recording relay 9, the recording relay would remain locked up and again energize the starting and tripping circuit as soon as that circuit again beca-me available.

As the distributor switch'brushes leave the terminals of the calling1 line, the test relay 12 is released. It' in the `meanwhile the call Vhas been transferred to the starting circuit,

Whose 'terminals immediately adjoin the terminals of "the line 'to which the apparatus has just responded. In this case therecording relay 9 is again locked up by the response ot the test relay 12 as -soon as the terminals ofthe second calling line are en-V gaged, and remains locked up to bring about l call in eifcct is stored in the recording relay 9, and is made effective to start a finder switch 4as soon as the availability ot the starting circuit is restored. Y

`As has 4been described, the appropriation of 'the .starting circuit by Van incoming call is accompanied bythe Voperation of the relay 24, and thc relay 24, in operating, disconnects .the-conductor 57 from ground. .As it is over this path to `vground that the initial energization ot anyY of the relays 19 is effected, the calling lines of the other groups are deprived ot' control over their associated relay 19 and trip magnets until the starting relay 24 is returned to normal. li a line in another group,say Agroup LG, calls while the starting relay 24 is serving the calling line ot group LG, the recording relay 9 of that other group is locked up' and holdsy closed a path to ground from conductor 57 that includes the windings of the associated relay 19 and .trip magnet 16 in parallel and the rightlhand winding oat=theassociated relay 18. /Vhen the starting relay 221 has performed its function in connection withrthe calling line of group .LG `and releasesV its armatures, the ipath by way .ot conductor 5T is completed for' the energization oft the relays 18, 19 vand 110 and the trip magnet 18 of group LG', in the manner that has been described in connection with .the operation of these parts in group LG. 'A

It calling lines *in several groups are awaiting fthe starting relay, the recording relay-s 9 of .these ygroups being locked .up

as aresultot the .momentary `operation o'i the associated relays l2 asthedistributor switch brushes .pass over the terminals ot` the callinglines, the group, which is closest electrically to thestarting relayt, will have its trip magnet operated and will talre possession of the starting circuit. The reason for this is that the conductor 58 that includes the winding of the starting relay Q41,

and over which the continued .energizationof the relay 19 and associated trip `magnet is eitected, passes serially through the righthand Varmature and resting contact ot each ofthe relays 19, so Athat the relay 19 that isV closest electrically tothe relay 251. interrupts. the path of the conductor 58 to theimere remote relays of the series. Y

When the relay 19 of a group is energized by its seizure of the starting relay 24, it releases the associated relay 9, as has been described, and thus again renders the relay 9 subject to the momentary operation of the test relay 12 as the brushes of the distributor switch 130 pass over the terminals of the lines of that group. In order to prevent the calling line from starting more than one line iinder switch, the time required for the distributor brushes to complete a cycle ot their rotation is so regulated that the calling line will have been seized by a finder switch, and `thus deprived of its power to control the test relay 12, before the distributor brushes have again moved into position to engage the terminals of that line. v

The starting of a line finder switch when the common starting relay 24 is energized is effected by the closure of a circuit that extends from battery by way of the updrive magnet 32 of whichever'of the line finder switches LF, LF', etc., is next in order to be started, conductor 59, line finder sequence switch contact 213 (2 to 2), line nder sequence switch contact 217 (2), conductor 29, and left-hand armature and front contact of the starting relay 24 to ground. At the same time another circuit is completed from battery by way of the cord selector sequence switch contact 320 (l to 4) winding of relay 30, selector sequence switchcontact 309 (1 to 8), nder sequence switch contact 217 (2), and thence to ground by wayV of; conductor 29 and the left-hand armature and front contact of starting relay 24. Relay 30, in operating, closes a circuit that extends Jfrom battery through the motorV magnet and contact 203 (2) of the finder sequence switch, and right-hand front contact and armature of relay 30 to ground. The closure of this circuit moves the finder sequence switch 200 out ofposition 2. Relay 30, in operating, alsocloses a locking circuit for itself that extends from battery by way of selector sequence switch contact 320 (1 to 4), winding of relay 30, selector sequence switch contact 309 (1 to 8), left-hand front contact and armature of relay 30, selector switch contact 317 (1), nder se# quence switch contact 216 (2 to 3), conductor 25 and the right-hand back contact and armature of relay 23 to ground.

Vhen the finder sequence switch moves from position 2 to position 3, it closes a circuit from battery through the winding of updrive magnet 32, conductor 59, nder sequence switch contact 213 (2!2n to 3) andthe left-hand back contact and armature of test relay 37 to ground, that places the continued energization of the updrive magnet 32 under the control of the test relay 37. The test relay 37 is energized to open the circuit of the updrive magnet 32 and stop the upward movement of the finder switch brusheswhen the terminals of the calling theelevator rod 1 ot the line-linder switch f as a result of the energizat-ion of the updrive Vmagnet 32, all of the brush trip levers are moved past the corresponding1 trip yoles 7.

VThe only trip magnet that is energized in this case is the maonet 17 which corresponds with the group Ltr in which the calling line is located; and consequently the only trip yoke -in position to engage a trip lever on the elevator rod is the one which controls the brushes 40, 41, 42 and 43 that are adapted to engage the terminals of that particular group of lines. This set ot brushes, therefore, is released and made operative, and the other sets are held clear off their associated line terminals.

As soon as the set ot' brushes corresponding with the group in which the calling line is located is tripped, the group apparatus, by means of which the lines control the brush tripping and line iinder starting' operations, may be returned to its normal position. This is eii'ected by the closure of a circuit which extends i'rom battery by way of the winding out relay 23, conductor 26,

finder sequence switch Contact 212 to 3), V

conductor 68, and segment G ot the linefinder commutator and its corresponding brush to ground. As aV result the closure ot this circuit which is timed to occur an instant after the brushes are tripped, and before they engage the line terminals in the upward movement of the elevator rod, relay 23 is energized to open, at its left-hand armature and back contact, the circuit by way of conductor 58 been holding the starting relay 24 and the trip manet 17 and associated relay 19 energized. rWhen, an instant later, the relay 23 is deenergized by the ground brush disengaging the commut-ator segment G, the group or starting circuits are again rendered rei sponsive toa calling line.

When relay 23 operates it also interrupts at its right-hand armature and back contact the previouslytraced circuit that has maintained relay 30 of the finder circuit energized. That relay, in releasing its armatures, closes a circuit for moving the finder sequence switch 200 of some other finder circuit `from its normal or first position to pol sition 2 where it is in readiness to respond to the neXt operation of the starting relay 24. Assuming that the finder circuit F', which maybe assumed to be similar to the finder circuit F in its equipment, has its parts in their normal condition, this circuit may be traced from battery through the motor magnet 200 and contact 204 (l) or" the finder circuit F", finder sequence switch contacts 204 (4to 18) ot other finder circuits that up to this time has silnilar tofthe circu-itsgF and ,Ff'inetheirw equipment,xwhich.may be assumed tov bep-,1 busy, and therefore t0 have their sequences,

switches in; sonneY i position between position 4 and position-18 inclusive, finder-sequence p ance- 91 Ato; grounddn4 the case of certa-in switohfcontactq22l ofY finderecireuit F, lettehand backcontact and arma-ture 0f re lay 30,' selector sequencezswitch' contactrl (1)nder sequence switchlcontaet-f216 .(2f tov3), conductor 25, and,right-handgbaelf contactfand armature of relay 23,-to ground. Thus the passin, ;0f Y upward :movement c of fthe .started finder switch restores the `group '1 and, starting cire r cuits', releases relay 301! vof the aS,-,50,ci ated` finder Vcircuit, and moves f seop1ence\switch` 2000i anotherf lfinder circuit :into position 2 j inzreadiness to respond tothefnext actuation:,

of the starting re1ay24.y

Provision is niadeltcr moving the {indersequence swtchotcne `ot thernder, circuits into position 2,- -tand -thus rendering ythe. associated circuit. responsiveV tot the-.stanteV` ing, relay, when-allot ,the` nderscircuitsff 'areidle'` and have their findery sequence` switches standing ini-,position l,or-,when all of themareybusy and oneisreleased-tog, permit its finder sequence-switchsto returns toposition 1 whilethe sequence-switches, 'ofi 'all oit ithe Vothers are inA sornkefpesitionn between-4 andlS'inclusive. T his, is accom@ plished through the medium ofl-ythe, relay; 20,; which has itsy energizing;circuit-i corn-l pleted byway ot conductorn28 andithelseries, of' finder sequence. switch contacts H214., (4,3

to1)'to ground at theendot-A theser-iesv,

When this; conditionr` of the series-pt iinderp sequence switches exists, relay 2 0` y1s.; enen gized and closes ya, circuit: y,that extendsfreun-` hel204 camfseriesot' all-ot thefinder-,ses quence:switchesy to ground by, way .offconyv ductor 27 andithetrontfcontact and ar n1a.;A tureot frelay 20n The vclosure Vofnthis paths to ground energizes, the motor. niagnet-of' one of ther/linden sequence switches,2QO: by vway otthev-carn204ll) off the assoclted Y sequence switch to move that isWitch,-to.posi, i tion 2;

The condition that now, assumed to; exist t lis one inriwhich ,the-line,-1nderi-sw1tchLE* is Inovingup withditsset of fbrushesfcorre-f spondlngl with .line group- LG `tripped* 1n.`

vWhich thetrip `magnet 17,' and relay lgof-j that line E group and the l common startingi 'rer lay 24"'havebeen returnedto their -norinalfV condition, and 1n which the findersequence switch ot anothertinder'circuitfllf has beeniv moved to pos1t1on-2 in readinesstorespond, to the next operation of thegstartingfrelay `As the tripped. brushesrise theycolne ,inte

engagement consecutivelyA withwthe setsgot terminals corresponding with the differentlines of the group.A At the; instant offen;V gagernent of theebrush 42 with thecorrefy sponding line terminal 46 of each fline, a cir--`Y the@ ,segmentinthey Y Y tlal lbatter-.y exists Yfromconductor y 53, as

mense? switch Acontact'. 209 ",(2 `to 3) ,p conductorV ,50, y

brush, 42, line terminal ,46, conductor 53, and

wndingspfrmessage i register 92- Vor resistofthe lines orlbyy Way of. windings of rnespotential battery .in the case of other of the lines. I i

Incase a l ine isbusy either as `a. calling line,l or` as ,a Y called line, a path to low potenture ,and front Contact otrelay 52,sequence switch contact20 3 (2 to 3), conductor 49, brush41 liner,A terminal 45,conductor 39 tomonegtlimht ,telephoneffline, thence by ,wayot thepath controlled in contacts o'lathei substation,switchhook to. the l other limb of nthmewline, 4 conductor 38terrninal 44,

brush"4() conductor 48,1 sequence switch Y contaete2tl7, '(2 to. 3), ,outer front contact and; armature Lotgthfe. relayV 52, and right: handswinding, ofgtherelay 37 to ground. The -cincuitr ,traced ahoyeA is not :completed untilthe finder switch brushesengagevthe terminalsfot Y the calling, line, v,as i the calling linegis the -onlylinelthat has its telephone receiyenoff; the hook, and1;atthe same time isnot.connectedwith either some other v lineninder or@ by a; conneetingcircuit callmet,

Italsocompletesa circuit that extendstroin loettery` through` the, motor. `magnet and contactil 20G.; ofithe, finder sequence switch, and. left-handgtront Contact and armature offrelay 37 .togground Thevclosure, otthis circuitrnoves thefnder sequence :switch out Ofc, position: 3l

Proyisionfris made or` preyenting. the,Y

plugt, The,LcQrnpletion'Aofthisv circuit Y ener Azesthearelfaygi' andvcausesthat re-y layrgtcinterrupt =at tslghtrhand becktcohtant, the circuihby wayr-nzf the finder vsemovement ot the sequence switches 20() oitl more thanone finder circuit into the 2 or waiting position in case an intermediate finder circuit returns to its normal position before the started iinder circuit has tound the calling line and moved sequence switch 200 out oit position has been described, the passing` ot the G- segment, by energ'iying,` and then releasing relay 23, applies ground by way oi conductor 25, finder Quence switch contact 216 (2 to 3), selector sequence switch Contact 31T (1), letthand armature and back Contact oit relay SO, and iinder sequence switch Contact 221 'tor moving' out ot its normal or 1 position the tinder sequence switch ot the next finder circuit in the series which is standing in that position. Let it be assumed that the iinder sequence switch, which is thus mover out of position 1, is that which is associated with iinder circuit F2, the intermediate finder circuit F1 being;I in use at the time and its iinder sequenceA switch in some position between 41 and 18. Let it further be assumed that before the line finder switch ot .inder circuit F has found the callino line,

and while its sequence switch 200 is still resting` in position the iinder circuit F is treed and its sequence switch 200 returned to normal. It under these circumstances the ground from the back contact ot relay S siould still be applied by way ot the back contact of relay and tinder sequence switch contact 221 ot the finder circuit that is hunting' tor the callin0 iinder sequence switch of tinder circuit li" would also be moved out oi position 1 as v soon as it was returned thereto,` so that the finder sequence switch Contact 217 finder sequence switches ot circuits F and F2 would both be resting` in their 2 or waitingipositions, and the line finder switches ot both circuits would be started in response to the next call. To prevent thisT a common conductor 75 is provided, this conductor having' a branch which connects with the finder sequence switch contacts 218 (L11) and 21.7 ot' each ot the iindcr circuits ot the group. As a result, when the sequence switch 200 ot finder circuit F2 is moved out ot position 1 in response to the passing ot the G segment ot finder circuit F as the line finder switch starts up, it closes a circuit that extends from battery through selector sequence switch contact 320 (1 to 4) of iinder circuit il?. winding of relay 30, selector sequence. switch contact 309 (1 to 8),

, conductor 75, and finder sequence switch contact 218 ot finder circuit F2 to ground. Relay 30 operates and locks up by way oit the path which extends through its lefthand front contactand armature, selector sequence switch contact 317 (1), finder sequence switch contact 216 (2 to 3), conductor 25, and the right-hand back contact and line, the

armature ot relay 23 to ground. Relay 30, therefore, breaks at its left-hand armature and baclr contact, the path over which ground from the back contact ot relay 23 would otherwise be applied by way of finder sequence switch contact 221 (3) to move the sequence switch 200 ot finder circuit F outl of position 1 as soon as the sequence switch of that circuit should return to that position. Relay 30 remains locked up to hold this'path open until its locking` circuit is broken at tinder sequence switch Contact 216 (2 to 3) by the movement ot' the iinder switch out ot position 3 upon the finding of the calling' line. This same movement ot the finder sequence switch also interrupts. at sequence switch contact 221 (3), the path for moving` the inder sequence switch ot' any other iinder circuit out ot position 1. Therefore, the grounding oit conductor 75 when any finder sequence switch is moved out ot position 1, prevents the movement out ot position 1 of any intermediate findersequence switch whose linder circuit may be released while the finder sequence switch ot the started tinder circuit is resting in position 3.

In moving to position 41- upon the finder of the calling` line, the finder sequence switch closes a circuit that extends from battery, by way ot resistance coil 54 and sequence switch contact 210 (il to 41;), to the sleeve conductor oi the finder circuit, and thence by way or" the finder switch to the sleeve conductor 53 of the calling' sub- `scriloers line. This creates anelectrical condition upon the line that prevents it thereafter from affecting the distributor test magnets 11 and 12, and that prevents it from being connected with by any other line. In moving` to position 4 the finder sequence switch also closes a circuit that eX- tends from battery through the motor magnet and Contact (1) of the selector sequence switch, contact 220 (f1) or the finder sequence switch, and right-hand back ccntactand armature ot relay 37 to ground. The closure of this circuit moves the selector sequence switch out ot position 1 and into position 2.

rEhe next stages ot the operation of the system have to do with the selection by the finder circuit of an availableoperators position. The selection or" the operators position is etliected through the medium of an operators select-ing` circuit that is Icommon to all of the group ot finder circuits of which the finder circuit F is one. Before the finder circuit F is given access to the operators selecting circuit, it is necessary that the circuit shall have been set tree by any other one of the group of finder circuits which may have been employing it.

The circuit that controls the movement of the selector sequence switch 3.00 out .of position 2 extends from battery, through the motor magnetand contacts 303 (2) and 313 (2) of the selector sequence switch, and thence by way of conductor 7 6 and the lettn hand. back contacts and armatures of the relays 61 and 63 of the operators selecting circuit in series to ground. As will hereinafter be described, one or the other of the relays 61 and 63 is energized from the instant'a iinder circuit ot the group obtains possession of the operator-s selecting` circuit until the selecting circuit has performed its function and has been released. Therefore, if the operators selecting` circuit is not in use by some other finder circuit of the y group, the path traced above is closed, and

as a result the selector sequence switch 300 of the finder circuit F moves out of position 2 and comes to rest yon position 3.

ltY will be noted that the path to ground by way of conductor 76 and the resting contacts ot relays 61 and 63, for moving` the selector sequence switch out ot position 2, is continued through the selector sequence switch contactsV 303 (6 to 1) of all of the finder circuits in series. As a result, any of the selector sequence lswitches in moving into position 2 breaks, at its sequenceswitch contact 313 (6 to 1), the path of the conductor 76 to all of the selector sequence switch contacts beyond it in the series. Gonsequently, if there should happen to be two finder'circuits awaiting access to the operators selecting circuit, only the one closer electrically to the controlling relays 61 and 63 would be moved out ot position 2 when the selecting' circuit was released and the armatures of relays 61 and 63 retracted, the more remote finder circuit in the electrical series being obliged to wait until its energizing circuit is closed by the movement to position 6 of the selector sequence switch ahead of it in the series.

When the iinder circuit F obtains access 'to the operators selecting` circuit by the. vinovement of the selector sequence switch 300 into position 3, a circuit is closed that extends from battery through the winding of relay 61, the left-hand switch-spring and resting contact of that relay. conductor 73, and selector sequence switch contact 1311 (22E to 3) to ground. The relay 61 in operating closes a holding' circuit for itself by way of its lett-hand switch-spring and armature and the left-hand back contact and armature of relay 63 .to ground. rl`he relay 61 at the same time closes, at its right-hand Y switchspring; and armature, a circuit that i co brings about the selection ot one of the operators positions which happens at the time tombe available, and the energization ot the selector-switch trip magnet corresponding y to that position.

The availability or unavailability of each oi' the various operators positions is determined by the condition of the relay 77 associated with that operators position in the operators selecting circuit; and that in turn is determined by the condition of operators position apparatus that marks whether or not the operator is at her position and in readiness to receive a call. .The particular conditions upon which the energization or deenergization of the relay 77 depends will be described hereinafter. Forthe present, it will be suliicient to say that if the operator is not at her position, a circuit is completed that extends from battery through the left .hand winding' or' the associated relay 77 of the operators selecting circuit, the righthand back contact and armature of the associated relay 93, conductor 82, switch spring 197 and resting; contact of the operators telephone jack 195 to ground. It the operator is at her position, and the selecting apparatus has just operated to assign a call to that position,the path to ground for en ergizing the associated relay 77 is completed byway or" conductor 82, switch spring 197 and alternate contact of the operators telephone jack 195v and the right-hand front contact and armature of relay 148. lf the operator is at her position, and the call assigned to that position has reached one Vot the connecting cord circuits, thenthe path to ground for the energizationof the asso ciated relay 77 is completed by way of switch spring 197 and alternate Contact of the operators telephone jack 195,V conductor 241 and cont-act 411 (2 to 6) of the listening key sequence switch.

When the relay 61 of the operators selecting` circuit is operated, in the manner hereinbetore described, the attraction of its right-hand armature extends the conductor 141 to groundby way of the resting contact and armature of relay 67. The conductor 141 includes contacts of the entire series of rela-ys 77 associated with the various operators positions in the operators selecting circuit.v The arrangement is such that each relayv 77 when unenergized eX- tends the conductor 141 to the winding of the associated relay 93, 'and when energized Y Jtact of relay 147, conductor 33, lett-hand.

back contact and switch spring of relay 93, winding of that relay, back Contact 1 and armature of associated relay 77, conductor 141, right-hand armature and switch spring of relay 61 and back contact and armature of relay 67 to `aground. Relay 93 operates as a result of the closure of this ot relay circuit, and in attracting its lett-hand armature substitutes for the energizing path by way or" the upper armature and back contact 1&7." and conductor 88, a branch energizing path that extends by way of the winding of relay lei-7 and conductor Sei to the lett-hand armature and switch spring of relay 93, and thence through the'winding or" relay 93 and to ground as already traced. Relay 147, in operating, opens at its upper armature and bacl Contact, the paththat extends in multiple branches from conductor 83 to the relays 93 associated with this particular operators position upon the different switch trames, Frame 1, Frame 2, etc., that have access to this position. is the initial energization ,oiI the relays 93 associated with a particular operators position on the various Ytrames must be effected through the medium y ot the common conductor 83, the openingot this conductor at the upper back contact and armature or relay 147 instantly renders the position unselectable at any other cord selector trame. Also, the series relation that exists between the relays 93 of any operators position with respect to the permanent energizing path Se* of these relays, assures that only one ot the relays 93 will be permanently energized in case it is assumed that two calls originating in different frames attempt to access to the operators position at the same instant. lnV such a case, the operation of the relay 93 oi the 'trarne closer electrically to the relay 1427 opens the path or the energizing conductor Se to the relay 93 or' the more remote frame.

YWhen. the relay 147 is energized as a result or' the selection ot the associated operators position, in the manner described above, it closes a circuit that extends from battery through the winding of relay 156, upper back Contact and armature of relay 157, and lower front contact and armature or" relay 147 to ground. TheI relay 156, in operating, closes at its lower iront Contact and armature, a circuit that causes the lighting ot the operators position lamp 167, and the lighting ot this lamprnotiiies the operator that her position has been selected and that a call is being extended to one of her connect-ing cord circuits, the particular circuit that has been selected being indicated a tew moments later by the lighting of the lamp Bil-1 associated with that particular circuit, as will hereinafter be described. llelay 147, in operating, upon the selection ot the operators position, also closes circuit that extends trom battery through the lett-hand arma-ture and back contact or relay 159, winding ot relay 148 and lower front contact and armature of relay lei-7 to ground.

l/Vhen the relay 148 operates, it closes circuit that extends from battery through the winrfting ot relay 6fl (see Fig. E), the winding;- ot trip magnet 22 associated with the selected operators position on the selector switch, right-hand front contact and armature of relay 93, conductor S2, switch spring 197 and alternate contact o1 the operators telephone jack 195, and right-hand front Contact and armature ot relay to ground. The closure of this circuit energljizes the trip magnet 22; and also operates 'relay 6ft to close a Circuit that extends trom battery through the motor magnet and contact 308 or the cord select-or sequence switch (see F 2), conductor T2. and 'the iront contact and armature of reh to ground. The closure ot this circuit moves the sequence switch 300 out oi' position When the selector sequence switch reaches position 4, a circuit is completed that extends trom battery through the motor magnet and contact B01-1(4) of the selector sequence switch and the right-hand baci: contact and armature of relay 30 to ground, and a s a result ol' the closure of this circuit the sequence switch is moved to position 5. Vhen the sequence switch reaches position 5, a circuit is closed that extends from battery through the winding of the updrive magnet 34, conductor 89, selector sequence switch contact 516 (5 to 6) and right-hand bach contact and armature of relay 30 to ground. The updrive magnet 84. in attracting its armature starts the upward movement ot the switch brushes. At the outset'. of the upward movement of the brushes the tripping levers of all of the sets of brushes move into position te engage the tripping yolres 7 at the Various levels corresponding with the various operators positions. In the present instance, it is assumed that the trip magnet 22 is energized, and as a result the tripping yoke corresponding with that magnet is in position to engage the trippingleyerot the corresponding set olfA brushes and that set ot brushes is tripped and made operative.

immediately after the lnush-tripping position is passed in the upward movement of the switch, and before the brushes engage the connecting cord terminals of the corresponding bank, the c'ommutator segment is engaged by the associated grounded cominutator brush. This closes a circuit that extends from battery through contact 306 (5) of the selector sequence switch, the low resistance left-hand winning and high resistance right-hand winding ot relay 56 in series, contacts 315 (5) ot the selector sequence switch, contact 312 ot that switch, conductor 80, and to ground by way of the G segment and corresponding brush of the cord selector commutator. Relay 56, in operating, closes a locking circuit for itself that extends to ground by way ot contact 315 (5) of the cord selector sequence switch, right-hand front contact and armature of relay 56, and Y selector sequence f. switch, and left-hand switch spring and armature of relay 56 to ground. rlhis causes the movement of the selector sequence switch out of position 5 and into position 6.

When the cord selector brushes have been tripped, the operators selection is completed, and the operators selecting circuit may be released to become available for performing its function in connection With the extension of another call. Therefore, as the grounded brush engages the CT segment of the cord selector commutator a circuit is completed that extends from battery through the Winding of relay 63 of the operators selecting circuit, conductor 74, contact 312 (5) of the selector sequence switch, conductor 80, and G segment and corresponding brush of the cord selector commutator to ground. Relay 63, in operating, closes at its right-hand front contact and armature a locking circuit for itself that extends by Way of the right-hand armature and ,switch spring of relay 61, Vand the back contact .an armature of relay 67 to ground. Relay 63 also opens, at its lefthand armature and back contact, the circuit which, from the moment relay 6l Was first operated, has been maintaining that relay energized. Consequently, relay 61 releases its armat-ures and in doing so, opens the locking 'circuit for relay V63, which relay in turn is deenergized and released. The restoration of both the relays 61 and 63 again completes the connection of conductor 76 to ground, so that this path is again available for moving out of position 2, the selector sequence switch of any other finder circuit thatmay be awaiting access to the operators selecting circuit.

Relay 61, in releasing, also opens at its right-hand armature and switch spring, the

path to ground over which the relay 93 of the operators selecting circuit and relay 147 of the operators position circuit have been held energized. Relay 93, in releasing, opens the energizing circuit that extends from battery through left-hand Winding of the relay 77 right-hand back contact and armature of relay 93, conductor 82V, switch spring 197 and alternate contact of the operators telephone jack 195, and to ground by the divided path one branch Vof Which extends by Way of the right-hand front contact and armature of relay 148 and the other of Which extends by Way of contact 411 (2 to 6) of the listening key sequence vswitch 400 when that sequence switch is moved out of position 1, as will subsequently be described. Relay 77 therefore becomes energized, and remains energized as long as the operator is at her position and one or the other of the above-mentioned branch paths to ground is closed. Consequently, the selectorV lead 141 of the operators selecting circuit is extended yby Way of the armature and outer right-hand front contact of relay 77 of this position to the relay 77 of the next operators position in the series, so thatl When ground is next appliedto the selecting lead 141 by the movement of aselector sequence switch of another finder circuit into position3, the busy operators position will be passed by and another operators position selected.

It will be observed that a branch path from battery including the v right-liant Winding of each of the relays 77 is closed to the selecting conductor 141 by VWay of the inner right-hand front contact of the relay 77 When that relayis operated. The object of this is,l to insure that Veach of the reassociated with an unavailable operators position Will remain energized, and thus prevent any alteration of the series path by Way of conductor 141 through the relays 77 While the operators selecting apparatus is performing its selecting function. lf, for instance, the iirst operatorsposition in the series is busy and the corresponding relay 77 is energized, while the second operators position is available and the associated relay 77 deenergized when therelay 61 operates to ground the selecting lead 141, then the ground applied to the conductor 141 is effective to operate relay 93 associated With the second operators position, and through it to energize the associated trip magnet 21. lf at this moment the irst operators position should again become available, theV Vaccompanying release of the associated relay 77, if provision were not made for preventing it, Would disconnect the selecting conductor 141 from the relays 77 and 93 of the second operators position and connect that conductor instead to the relay- 93 of the irst operators position with the result that both of the trip magnets and 22 might be operated and cause the selection of tvvo operators positions by a single call. By the provision of the right-hand locl-:ing Winding of the relay 77, each relay 77 that happens to be energized when Vrelay 61 operates to ground the selecting lead 141 is held energized until the relay 61 releases, regardless of Whether the corresponding operators position becomesl available inthe meanwhile or not.

Under heavy traffic conditions it is possible that all of the operators positions may be busy and all of the corresponding relays 77 energized when an incoming call causes the operation of the starting relay 61 of the operators selecting circuit. Under these circumstances, the grounding of the select- Y la s 77 that is enero'ized as a Aresult of beinv iio ari-races comes availableV in the meanwhile or not.

Vio

To prevent such a condition from tying up the operators selecting circuit by thus indefinitely maintaining all the positions unselectable. the conductor 141 after passing through the armature and upper front contacts ot' all of the relays 77 inseries, is continued to battery by way ot the winding ot relay 66; and the relay 66, when it operates, closes the energizing circuit oiE the rela-y 67, which, in turn, interrupts at its back contact the path to ground of vthe conductor 141 closed by the operation of relay 61. rllhe alternate energization and deenergization of the reciprocally controlled relays 66 and 67 that results from the completion of this circuit causes an intermittent interruption of thelocking path to ground of the relays 77. Consequently, when one oi' the operators positions becomes available and opens the energizing path by way of the left-hand winding of the associated relay 77, that relay, at the next interruption of the locking path by way of conductor 141 and the back contact of relay 67, releases its armature and permits the selecting conductor 141 to be extended to the associated relay 93. This brings about the energization ot' the associated trip magnet and the operation of the common relay 64 for moving the selector sequence switch of the awaiting finder circuit out of position 3, in the manner hereinbefore described.

In the foregoing, the progress ot the call has been described up to the point whereV the selector sequence switch 300 has been moved to position 6, andthe cord selector brushes Corresponding with the selected 'operators position have been tripped and are moving over the terminals of the cord circuits associated with that position. When connecting cord circuit is notin use, battery is connected with the-corresponding terminal 118 onV the selector switch by way ot resistance 126 (see F ig. 4), right-hand back contact and armature of relay 95, switch spring 161 and resting contact of the disconnect ley 160, and conductor 88. When the corresponding brush 114 engages the contact terminal 118 olfsuch a connecting circuit, the circuit is completed by way ot brushv 114, conductor 99, selector sequence' switch contact 305 to 6), windings of relay 30, and selector sequence switch contact 320 (4 to 6) to ground. .Relay 30, in operating opens the previously traced circuit through updrivemagnet 34 of the cord se* seector switch, conductor 89, contact 316 (5 to 6) ot the selector sequence switch and right-hand back Contact and armature Off relay 30 to ground. The opening of this circuitstops the selector switch with its brushes in engagement with the terminals ot the non-busy connecting cord circuit. Relay 30, in operating, closes a circuit that extends from battery through the motor magnet and contact 302 (6) of the selector sequence switch, and righthand front contact and armature of relay 30 to ground. rllhis moves the selector sequence switch outot position 6. To insure the continued closure of this circuit until the sequence switch is moved out of position 6, the relay 30, in operating, also closes a locking circuit for itself that extends from battery by way of the resistance 55, selector sequence switch contact 317 (5 to 6), lett-hand armature and front contact of relay 30, contact 309 (1 to 8) or the selector sequence-switch, winding of relay 30, and contact 320 (5 to- 6) of the selector sequence switch to ground. This Vlocking path is opened and the relay 30 released as soon as the selector sequence switch moves out of position 6.

lhen the selector sequence switch reaches position 7, it closes a circuit that extends trom battery by way of the motor magnet and Contact 410 (1) of the listening key sequence switch 400 (see Fig. 4), leit-hand armature and bach contact ot' relay 95, lefthand back contact and armature of relay 13, left-hand baclr contact and switch spring ot relay 81,*sleeve conductor 87, selector switch contact 117, brush 113, Aconductor 98, and contact 307 (7) of the selector sequence switch to ground. llfhis causes the listening key sequence switch to move from position 1 to position 2. In position 2, a circuit is closed that extends from battery through the winding ot relay 13, contact 412 (2 to 6 oi' the listening' lrey sequence switch, lefthand back contact and switch spring o1c relay 81, sleeve conductor 87, and to ground at contact 307 (7) of the selector sequence switch over the path already traced. Relay 13, in operating, closes a locking circuit by `way otl its left-hand front contact and armature that maintains the relay energized independently of the initial energizing path through listening key sequence switch contact 412 (2 to 6).

As soon asthe listening key sequence switch reaches position 2, a circuit is closed that extends from battery through the motor magnet and contact 502 (1&14 to 1) or' the callin-g cord sequence switch (see F ig. T), conductor 255, contact 418 (2 to 6) oi the listening key sequence switch, lett-hand back cont-act and armature of relay 125, resting contact and switch spring 146 of holding key 140, contact 407 (1 to 4) o' the listening key sequence switch, and resting contact and switch spring 154 of the register and disconnect key '150 to ground.

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