US2337433A - Telephone system - Google Patents

Description

Dec. 21, 1943.

J. G. WALSH TELEPHONE SYSTEM 14 Sheets-Sheet 1 Filed April 2, 1942 m UFx lA/VENTOR J. a. MLSH ATTORNEY Dec. 21, 1943. J. G. WALSH TELEPHONE SYSTEM- l4 Sheets-Sheet 2 Filed April 2, 1942 A v VVV mRN lNl/ENTOR J G. WALSH ATTORNEY Dec. 21, 1943. J.'G. WALSH .r 2,337,433

TELEPHONE SYSTEM I Filed April-2, 1942 4 l4 Sheets-Sheet 3.

. ATTORNEY Dec. 21, 1943.

J. G. WALSH TELEPHONE sYslT EM 14 Sheets-Sheet 4 Filed April 2; 1942 was 8b.

21, 1943. J. G. WALSQH 2,337,433

TELEPHONE SYSTEM Filed April 2, 1942 14 Sheets-Sheet 5 FIGS lNVENTOR J. a. WALSH Dec. 21, 1943. J, GJW 2,337,433

TELEPHONE SYSTEM Fild April 2, 1942 14 Sheets-Sheet e POL AR/ZED POLARIZED lNVEA/TOR J G. MLSH ATTnDA/FY Dec. 21, 1943. J. G. WALSH 2,337,433

TELEPHONE SYSTEM Filed April 2, 1942 14 Sheets-Sheet 7 /Nl/EN7'0R J. G. MASH.

AT TORNEV Dec. 21, 1943. J G, WALSH 2,337,433

TELEPHONE SYSTEM Filed April 2; 1942 14 Sheets- Sheet 8 POLARIZED kcq MARC/[VAL lNVE/VTOR By 'J. a, mus 1 ATTORNEY Dec. 21, 1943. .1. s. WALSH TELEPHONE SYSTEM Filed April 2, 1 942 14 Sheets-Sheet 9 ATTORNEY):

FIG. /0

Dec. 21, 1943. Y J. G.WALSH 2,337,433

TELEPHONE SYSTEM Filed April' 2, 1942 14 Sheets-Sheet l0 POLAR/2L? INVENTOR- J. G. WALSH ATTORNEY Dec. 21, 1943. J. G. WALSH 2 3 7,

TELEPHONE SYSTEM Filed April 2, 1942 14 Sheets-Sheet 11 Dec. 21, 1943. J. G. WALSH 2, 7,433 TELEPHONE SYSTEM Filed April 2, 1942 I 14 Sheets-Sheet '12 POLARIZED m M "nu-"um wvawrop By J. G. HML 5H 4&9.

Dec. 21, 1943.

J. G. WALSH TELEPHONE SYSTEM 14 Sheets-Sheet 13 Filed April 2, 1942 NVQ INVENTOR J. G. MLSH er ATTORNEY Dec. 215, 1943. J, G, WALSH 2,337,433

TELEPHONE SYSTE'M Filed April 2, 1942 IIHF' m;

l4 Sheets-Sheet 14 HANG/AMI.

MARC/N41.

mam/r09 J. G. I444LSH .to the character of the selected level to control the operation of aweceding trunk circuit and to eiiect the-absorbin Patented Dec. 21, 1943 UNIT2ED STATES PATENT John G.Walsh; Newark, N.

Telephone Laborator York,- N. Y., aicorpora ies, tion of' -New York J., assignor to Bell incorporated, 1 New Application April 2, 1942'; Serial No: 4373398 tof aidigit; the selection of one or. more 'ofi'the levels" in..which the terminals are connectedv to '12 Claims.

This invention relates to telephone systems'and particularly to systems comprising impulse controlled selector switches for establishing "connections between calling and called lines.

Objects of the invention are an increase in the efliciency of the switching apparatus and trunking arrangements of automatic'and semiautomatic telephone systems and particularlyanincrease in the capability and efficiency of. selector switches used. in establishing intertoll connections.

This invention is a selector switch adapted for use in establishing connections under the control of directive impulses and having access .totrunk circuit of different kinds, normal post springs being provided for operation-on the various levels according to the character of the trunks connected to the terminals in a selected level to control theoperation of a preceding trunk circuit and to enable the transmission of stop and start 'dial signals if the character of the trunks connected to terminals in the selected level is of. a'character requiring the transmission of such. signals.

According to a feature. of the invention a' group selector which is operatively controlled'bydirec- .tiveirnpulses to select a desired trunk group. is

provided with normal post springs forjoperation on any level in which the terminals are connected to trunks over which reverse battery supervisory signals are transmitted, thereby to effect the in-. sertion of a repeating coil in the talking connection and enable response to reverse battery signals. A further feature is the provision of means for varying the impedance of the repeating coil thus inserted in a talking connection according to the impedance of the trunk through which .the connection is extended.

According to another feature of the invention a two-motion group selector switch adapted for. use

in establishing connections under the control'ofv directive impulses is provided with normal post springs for operation on desired levels accordin to the character of the trunks connected to the terminals in a selected level to control the operation of a preceding trunk circuit and with 'nor-.,

mal post springs for operation on desired levels to effect the absorbing of a digit.

According to another feature of the invention a two-motion group selector switch adapted for use in establishing connections under the control of,

directive impulses is provided with normal post springs for operation on various levels according trunks connected to. a

trunks? requiring the" transmission of .stop' iand .start' dial. 'signalstbeing efiective to restore .the brushes of' the selector to normal" if selected .re-

'sponsive to aifirstitra'inbf impulses incoming. to

. "thesele'ctor.

'A'cle'ar and complete understanding of the invention will 'belfacilitated'by considering. a system in'whichlthe .various features 'of.'the invention .are embodied, one such system beingshown in the "drawings which form apart of this specivfication. 'The invention is, however, -not' tlimited in its 'applicationitothe' particular system shown but is generally. applicable to systems comprising impulse'controlledswitches.

l Reierrin'gto'the'drawings: Fig'..1"shows,"in' a first toll ofiice', anj operators position comprising a cord 'CD I, telephone "and cuit OT I. anda signaling. circuit "CSI connecting .dial, aja'ck. J l terminating an outgoing .trunk cirthe outgoing :trunk' circuit "OI'l with a 'toll line Fig. 2 shows a; signal circuit CS2, an associated outgoing trunk circuitOTZ terminating in a jack "J2, atwoeway trunk circuitlTWTZ, and. a toll seylector' "TSZ all associated -with'the. tol1:..line.'"ILl 1.. in a'secondit'oll office;

.Fig'. 3 "showsanvinterswitch: trunk.,circuitIST3 connected-to a'setiof terminals in theba'nkiof "the intertoll firSt 'seIectOriTSZ;

Fig. 4- :shows an ,.intertoll selector "PS4 .associated:with"the'trunkiIST3;

Fig; 5"sh'ows a? trunkrcircuitlRDT5 associated 5I'With airing-downtoll linei'RDU connected "'to a setofnterminals inithe.bankci theintertoll selector T54;

",Fi s: '6 and '1 show 'atrunk. circuit CDTI., as

.sociated with a. trunkCDT- to a communityiadial office and .connected. to a set ot terminals inILthe bankof intertoll selector..TS4;

. 'Fig. 8-'shows' atrunkJcircuitFCDTIin a-com 1 :munityf dial "ofiice. associated with the trunk. CDT; shows allineifinderi'LFl' and selector'St-forause "in" connecting .a callingline to a trunk circuit 1..'CDTZ""0I1 a: call"toitheltollfofiiceg and-shows a "trunk'rlnder "TF," incoming. selector 'IS and con- .nectorfCLfOr'use in completingcalls incoming over a: trunk .CDTlfroml the toll. oflice;

Fig. 9' shows an intertolltsecond selectorl circuit .TS9 assoclatedwith. a. s'et of .terminalslin' the .bank ofiintertollnrstselector:TSZ;

1 Fig. 10 shows-an intermediate'tolroperator's pOSi'lZiOIi comprising a cord? CD1 flgetelephone and dial,v an.incoming'trunki-circuit-.112 lfl. terminating k jack J and an intermediate dialing trunk associatedwith the intertoll trunk circuit ITIZ;

v Fig. 14 shows a. connector circuit LC in a local step-by-step dial ofiice; and

Fig. 15 shows the relative position in which Figs. 1 to 14, inclusive, are to be an operative arrangement.v V

The system represented in the drawings includes a plurality of tool ofiices', each of which placed to form I, i; reverse battery supervisory signals.

comprises a toll board with operators positions and cords for answering calls incoming from local manual or dial ofiices, from toll subscribers lines, from community dial offices or from other toll ofilces; and for connecting calling intertoll trunks with switching trunks leading to called manual or dial local ofiices, to called toll subscribers lines, to trunksto community dial ofiices, and to intertoll trunks to other toll offices. Outgoing jacks are connected to switching trunks, toll lines, trunks to community dial ofiices and intertoll trunks; answering jacks areconnected to recordingtrunksftoll subscribers lines, trunks'frcm community dial oifices and intertoll trunks. Intertoll first selectors and intertoll second selec- .,tors are provided for use on calls incoming over "intertoll trunks to establish connections with other toll, local or community dial ofiices. The ""o'perators positions are provided With dials for use in controlling the operation of intertoll selectors in other toll ofiices and for controlling the operation of selector and connector switches in 'localor community dial ofiices.

While not shown in "the drawings, the operators positions may be provided with key-setsin placeof dials, in. which case senders are associated with the outgoing trunks to register the key-set impulsesand control the selectors.

' *Reference may be had toth'e patent to R. E. King et a1. 2,208,765, granted July 23, 1940, fora detailed disclosure of the cord and operators position circuits provided in each of the twotoll f" oflices for interconnecting calling and called lines and trunks and for controlling the completion of toll calls. The outgoing trunk'circuits OTI and 0T2, signaling circuits" CSI and CS2, two-way trunk circuit TWT2, intertoll first selector circuit TSZ, interswitch trunk circuit IST3, ring-down trunk, circuit RDT5, andcommunity dialtrunk circuits CDTIand CDT2 are all siinilarto corresponding circuits disclosed in the aforementioned f King et al. patent or in the King et al. Patent 2,209,777,granted July'30, 1940. The intertoll trunk circuits T44 I, T942, TI m, and TI I42 may also be two-.way trunk circuits, similar to two- Way trunk circuitTWTZ." The trunk, circuits T94I and TI34Imay be similar to trunk circuit .CDTI. The toll connector circuit TC is similar to the "toll connector disclosed in the patent to E. D. Butz, No. 2,021,286, granted November 19, 1935. Although not shown in the drawings, one or more intermediateselectors may be provided in the step-by-step ofiice for establishing connections with called lines.

The incoming trunk circuit ITII] is similar to the trunk circuit 1T2 shown and described in detail 'in' the aforementioned King et a1. patent.

The intermediate dialing trunk circuit IDfl-flllis similar to the intermediatedialing trunk circuit repeating coil to be connected in the talking circuit, the operation of relay I22! depending upon the character of the trunk selected by the associated selector TSI3.

The intertoll selector TS4, associated with trunk circuit IST3, is of the well-known twomotion, step-by-step type and comprises a set of brushes 43I, 432, 433 and 434, a terminal bank which is represented by three sets of terminals MI, 442 and 443, a line relay 4| I, a release relay 4 I 2, a switching relay 4| 6, vertical stepping magnet 4 I 1, rotary stepping magnet 4 I 8, release magnet 4I9, vertical off-normal springs 42I and eleventh-rotary-step springs 422. The selector T84 also includes normal post-springs 425 and 426 which are independently actuated on desired a the transmission of a ring-down signal over the associated ring-down intertoll trunk RDL. The normal post springs 425 are actuated upon selection of a level in which the terminals are connected to trunks to a community dial oiiice and it is necessary to give the calling operator a start dialing signal when the switching apparatus in the community dial ofiice is ready to receive directive impulses, such a level being represented bythe terminals 442 connected to trunk circuit CDTi.

Each of the intertoll selectors T89, TSI I and TSI3 is similar to the intertoll selector T84, like elements having reference characters with the same tens and units digits. Each of selectors T89 and TSI I includes an additional relay 9I4 or I I I4, for controlling the absorbing of the first train of dial impulses received if this digit is of such a numerical value as to indicate that the first digit is to be absorbed; in such a case the left-hand set of normal post springs are actuated to operate the release magnet of the selector. The right-hand set of normal post springs of selector T59 are actuated upon selection of a level giving access to trunks requiring the transmission of a stop dial signal to the calling operator, such a level being represented by the terminals 94I connected to trunk circuit T94I associated witha trunk to a community dial ofiice. The'righthand set of normal post springs of selector TSII are actuated upon selection of a level in which the terminals are connected to through trunks to render a rering signal from the calling operator ineifective to cause the release of selector TSI I, a level giving access to through trunks being reptrunk circuit TII42 and a level giving access'to connected to a trunk T83 oifice.

- 21d, winding-of relay the winding of relay I lay 288 of toll selector T52 is thereby operated m Operating circuit of' relay lay is v I '-="nection of ground to conductor 283 during the response of relays "215 and-28810- dialimpulsesfi:

topaz-i433 ceived, such a level being represented by terminals I342 connected to a trunk Tl3 to a local selector or connector in a step-by-step dial oflice;

and the left-hand set of normal post springs are 1 actuated on levels in which the terminals are connected'to trunks requiring the tran'smissionof a stop dial signal to the Calling operator, such a level being represented .by the terminals 134! 4! to a community dial Assumenow that theplug P2 of the cordCDl is inserted in iack'J Iof the outgoing trunk circuit O'I'i thereby closing a circuit for-operating relay it lay Hi1 as described'in' the aforementionedliiing 'et al patent and closes a circuit for operatively energizing the upper winding of signaling relay Hi0. signaling battery through conductor 4. Relay Hi l-effects theoperation of reltil connects 64, retard coil I59, middle winding of composite signaling relay il'il, upper winding of retard coil upper conductor of toll line TLE,

The operation of relay 1 upper winding of retard coil 256 of signaling circuit CS2 in the second toll office, to the windings of composite signaling relay 219. Relay an: operates, closing a circuit throughconductor 263, back contact of relay 25E! of outgoing trunkcircuit 0T2, back contact of relay 214 of twc way trunk circuit TWT2,-back contact of relay Ell, through the winding of relay 2T3. Relay 2'53 operates, connecting ground to conductor 253 to guard the toll line TLI from seizure in the second toll office. Relay 213 closes a circuit for operating relay 2l5, from ground through the front contact of signaling relay 210, conductor 263, back contact of relay 2H], back contact of relay 215, a front contact of relay 2l3, thence in simplex through both windings of retard coil 260, back contacts of relay 238, conductors 2H and 212,.inner front contacts of relay 213, conductors 28! and 232, back contacts of relay 290, resistors 285,186- and'ZSl, and through 288 to battery. The line reseries with relay 2150f the two-way trunk circuit TWTZ. Relay 2T5 closes a'circuit through resistor 216 for holding relay 273 and closes a circuit for operating the slow-to-release relay 211. Relay 211 also closes a holding circuit for relay 2% and connects ground potential to conductor 283 to hold the selector TS2 and any succeeding switches or trunks through which a connection may be established. W'hen'the calling operator operates the dialing key (not shown) the upper winding of relay Hlil is controlled'by the impulse contact of the dial. Each release and reoperation' of relay 149 in response to the 1 dialing of the first opens and closes the circuit through 'con uctor'-.. I64 and the upperconductor of toll line TLI,

digit of the called number causing a corresponding release and reoperation of relay 270 of signaling circuit TSZ. Relay 210 repeats these dial impulses to relay 215 of twoway trunk'circuit TWTZ and to relay-2&8 of se-;;

lector T32. Each release of relay 215 opens'the 27?; but since this reslow in releasing, it maintains the con- .The alternate release and reoperation f relay F5288 zcauses the' brushes oi selector 3 TS2 to he :stepped up to :the level correspondin'g to the digit dialed. At the end of the train: of impulses; the

' brushes-295,292, 293 and'fifl l areadvancedstepby-step in the selected level to hunt for ands'eize a set of terminals connected to an idle trunk. When an unguarded set of terminals is 'found, re-

.ilay'29il is operated to disconnect relay- 288xand connect-toll line TLL'through brushes- 29l--and 292 and the engaged terminals, to the next line,

. trunk or selector through which the desired connection is being established For a detailed 'de- 'scription of the operationof selector T32; reference may be had to the aforementioned pat- I ents to King etal.

Calls completed through selector T54 Assume first that'the leveliselected' by z the "brushes of switch TSZ is a'level in whi'ch' the terminals are connected to interswit'chtrunk "circuits, such a level being representediby the both windings'of retardlcoil 26 conductors' fiil and 262, back'contacts of relay 230, conductors 2H and 212, front contacts'of're1ay 2l3, conductors 28! and 282, front contacts of relay' ZQE, through brushes 29! and 292 .and'engaged'terminals of terminal'set 296, through'conductors 3D! and 352 of trunk circuit IST3', conductors 40! to-release relay l 5 2.

through a back contact of relay 4 I 8 to the alarm and 4532 of selector 'IS, back contacts ofrelay M6, through resistors' itl, dd?) and M9 and the winding of relay iii to battery. Relay MI is therebyenergized in series withtrelayZlii of the two-way trunk circuit TWTZ. The'operation of relay All closes a circuit for operating .theslow- Relay M2 connects ground circuit 49!! to initiate an alarm operation in case the selector T85 is seized but no"directive"impulses are received within a predetermined. in-

'terval of time. Relay M2 also connects ground to conductor 4-93,; this being without effect. since conductor 53 is connected thrcughconductor 303 and brush 2% of switch T82 to' ground at a from contact of relay Ell of two-way trunk .circuit TWT2.

No further operation takes'tplace until the calling operator dials the nextidigit of the called toll route code number. Each release and reoperation of relay 219, in response 00 13118 impulses transmitted by the dialing of the next digit, causes a ccrresponding'release and re'operation of relays 2l5and t! l. The first'releasebf relay 4H closes a circuit from ground iatzthe back contact of relay ME, through the back contact of relay All, a front contact-of relay 4l2,

winding of relay M3 and through the winding of vertical stepping magnet t i l to battery. "Relay 413 and stepping magnet Gil are thereby eperated, the operation of magnet ii! beingefiective to step the brushes of selector Ts i up to the first level of the terminal bank. The release of relay 4 at the end of the first impulse causes the release of vertical stepping magnet d i but :relay M3 is slow to release and remains operated. until all of the impulses in the train have beenirelease and remains operated whilerelay Ml isiresponding to dial impulses. The. vertical ofinormal springs 42I, are actuated as soon as the shaft on which the brushes are mounted moves front contactof relay 4I3 to ground at'alfront contact of release relay M2. The release and re- ,operation of relay MI in response to each succeeding impulse of the train effects a corresponding operation and release of the vertical stepping magnet 4I1 thereby advancing the brushes of switch T84 to the level corresponding t the digit dialed. When relay 4| 3 releases at the end of the train of impulses, it opens the operating circuit of relay 4 I5, but relay 4I5 isheld operated under control of springs 42I and rotary stepping magnet 4I8. The release of relay 4I3 closes a circuit for operating the rotary stepping magnet 4 I 8, this circuit being traced through the upper front contact of relay M5 and the upper back contact of relay M3, to ground at the uppermost front contact of relay 4 I 2. The operation of stepping magnet 4I8 advances the brushes of switch TS4 into engagement with the first set of terminals in the selected level. The operation of stepping magnet 4I8 also causes the release of relay M5; and the release of relay 4I5 causes the release of stepping magnet 4 I 8. When stepping magnet 4 I8 releases, it closes a circuit from battery through the winding of relay 415 through the upper front contact of vertical off-normal springs 42I, back contact of stepping magnet 4I8, middle lower back contact of relay 4I6, through test brush 433 to the test terminal engaged thereby. If the selector or trunk circuit connected to the engaged set of terminals is busy, brush 433 encounters a busy ground potential which causes the reoperation of relay M5. The reoperation of relay 4I5 causes the reoperation of stepping magnet M8 to advance the brushes of selector 'IS4 into engagement with the next set of terminals in the selected level. If the test terminal of this next set of terminals is also connected to ground, relay M5 is again operated to continue the advance of the brushes of selector TS4. When the brushes engage a set of terminals connected to an idle trunk or selector, relay 4I5 does notreoperate since the terminal engaged by brush 433 is free of ground potential; and relay M6 is operated by the current in a circuit traced from battery through the winding of relay 4I5, upper contact of vertical ofi-normal springs 42I, back contact of rotary stepping magnet 4I8, winding of relay 4IB, lower contacts of the eleventh-rotary-step springs 422, to ground at the uppermost front contact of relay 412. Relay M5 is marginal and .does not reoperate in series with the winding of relay 4I6. Relay 4I6 disconnects the winding of relay 4 from conductors MI and 402 and connects these conductors through the brushes 43I and 432 to the talking conductors of the trunk connected to the engaged set of terminals. The release of relay 4| I, when its winding'is disconnected from conductors 40I and 402, causes the release of relay 4I2. Relay 4I2 disconnects ground from conductor 403'but relay M6 .is' held operated since conductor 403 is connected through conductor 303 of interswitch trunk circuit IST3, the terminal engaged by brush 293 of selector T82, and through conductor 283 to ground at the front contact of relay 211 of twoway trunk circuit TWT2. 1

If the selector TS4 finds all of the terminals in the selected level busy, the brushes .43I; 11014.34,

inclusive, are advanced to the eleventh rotary position in which position springs 422 are actuated to disconnect the winding of relay.4IIi from conductor 403 and to connect the interrupter 423 to conductor 404, thence through a back contact of relay 3I3 of interswitch trunk circuit IST3,

back contact of relay 320, through conductor 304,

terminal and brush 294 of switch T82, lowermost front contact of relay 290, to the winding of relay 219 of two-way trunk circuit TWT2. Each time that ground is connected to the brush of interrupter 423, relay 219 is operated thereby closing a circuit from signaling battery through the front contact of relay 219, back contact of relay 218, back contact of relay 240 of out oing trunk circuit 0T2, through retard coil 269, middle Winding of relay 210, upper winding of retard coil 266, upper conductor of toll line TLI, thence through the upper winding of retard coil I66 and windings of signaling relay I10 to effect the operation of signal relay I10. The alternate operation and release of relay I10, under control of relay 219 and interrupter 423, causes the intermittent operation of relay I05 thereby alternately opening and closing a circuit through the lower, low resistance winding of relay I04 to flash the lamp SL associated with plug P2 of the calling operators cord CDI to indicate an all-trunks-busy condition. When the plug P2 is disconnected from lack J I, relays I04 and I are released thereby disconnecting signaling battery from conductor I64 to cause the release of relay 210 of signaling circuit CS2. The release of relay 210 disconnects ground from conductor 263 to cause the release of relays 215 and M I. The release of relay M I causes the release of relay M2; and the release of relay 215 causes the release of relay 211. With both'of relays 211 and M2 released, ground is disconnected from conductors 403 and 283 thereby causing the release of relay 290 Of selector circuit TSZ to cause this selector to be restored to normal in the manner described in the aforementioned patent to R. E. King et al. With both of relays 4H and M2 released, a circuit is closed from battery through the winding of release magnet 4I9 of selector TS4, lower front contact of vertical off-normal springs 42I, through back contacts of relays M2 and M I, to ground at the back contact of relay IIB. The operation of release magnet 4I9 causes the return of the shaft and brushes of switch TS4 to normal. When the shaft reaches normal. position, the vertical 01T- normal springs 42I are restored to normal thereby opening the circuit for operating the release magnet 4I9.

Assume now that the selector TS4 has selected the level represented by terminals 442, the terminals in this level being connected to trunks to a community dial oflice, and that the trunk circuit CDTI which is connected to terminals 442 is the first idle trunk circuit in the group. When relay 4I6 operates, a circuit is closed for operatively energizing the line relays 6I0 and BI I of trunk circuit CDTI. This circuit is traced from ground, through the front contact of relay 210 of signaling circuit TS2, conductor 263, back contact of relay 2 I0, back contact of relay 214, Winding of relay 215, uppermost front contact of relay 213, thence in simplex through both windings of retard coil 260 of outgoing trunk circuit 0T2, back contacts 'of relay 230, conductors 21I and 212, inner' front contacts of relay 213, conductors 28I and 282, front contacts of relay 290 of selector 'TSZ, through brushes 29I and 2 2 and I I l engaged terminals of terminal set 296, through conductors 3M and 302 of trunk circuit 'ISTS, conductors 40! and4il2 of selector TS l, front contacts of relay MB, brushes 43l and 432 of selector TS l, through conductors 60! and 602 of trunk circuit CDTI, both windings'of retard coil 600, thence through conductor 639,- a winding of relay 6H) and a winding of relay 6 to battery. Since the trunk circuit CDTI is associated with the trunk CDT to a community dial ofiice in which it is necessary to connect the trunk circuit to an idle selector before the calling operator dials the next digit of the called subscribers number, the left-hand normal post springs s25 of selector T84 are actuated upon selection of the level in which the terminals 442 are located to connect ground-to conductor 4134 as a stop dial signal. This connection is traced from ground at a front contact of relay M2, through the front contact of normal post springs 425, lower back contact of relay M3, upper back contact of the eleventhrotary-step springs 422, through conductor 494, back contacts of relays 3 l3 and 32!} of interswitch trunk circuit IST3, conductor 394, through brush 294 of selector T52, front contact of relay 293, and through conductor 284 to the winding of relay 219 of two-Way trunk circuit TWT2. Relay 219 is thereby operated to connect signaling battery through back contacts of relays Z'lS-and 245, conductor 264, retard coil 269, middle winding of relay 21B, upper winding of retard coil265, to the upper conductor of toll line TLI to effect the operation of relay I'll! of signaling circuit CS! in the toll office at which the calling operator is located. The operation of relay no causes the operation of supervisory relay lfit'thereby dis connecting ground from the lower, low resistance winding of relay HMto extinguish the dial pilot lamp (not shown) at the calling operators position, in the manner set forth in'aforementioned King et al patent. Since the calling operator has not completed dialing of the callednumber, the extinguishing of the dial pilot lamp indicates that no further digits should be dialed until this is again lighted as a start dial signal. After relay M2 releases due to the operation of relay 4 l 6, conductor .604 is connected through the upper back contact of springs 422, a front contact of relay 416, through brush 434 to conductor 684 of trunk circuit CDTi, thence through a back contact of relay 62! to ground at the back contact of relay Slfi. The aforementioned operation of relay 6H3 closes circuits for operating relays 6l2,'6l4 and 615. Relay E52 closesa circuit for lighting the busy lamps, such. as BLii, associated withoutgoing jacks to which trunk circuit CDTI is connectedv and connects battery through resistor 611 and the upper winding of relay 538 to thesleeve of the associated jacks at the toll board to mark the trunk CDTI busy. Relay 6!.4 looks through its upper Winding, conductor 5%, brush 433 of selector T54, a front contact of relay M5, conductor 453, conductor 3% of trunk circuit IST3, brush 293 of selector TSZ, a front contact of relay 29!],and through conductor 283 to ground at a front contact of relay 21? of two-way trunk circuit TWT2. Relay 6M disconnects ground from the lower Winding of relay 639 -to prevent operation of this relay if an operator should disregard the busy indication and plug intoa jack to which trunk circuit CDTI is connected. Relay 6 l 4 also disconnects the winding of relay 6%! from conductor Gi so as to prevent false operation of relay MI; and short circuits the upper windlamp 6E5 looks through its upper winding to ground 5 on sleeve conductor 603 and disconnects this conductor from the contacts of relays 612, 63! and 633. The lower contacts of relay 5E5 facilitate testing of this relay.

While the trunk CDT between the toll omce 10 and the community dial office is idle, there is a closed circuit through the windings of line relay 83! of trunk circuit CDT2 in the community dial office in series with the left windings of repeating coil RC8, conductors B5! and 652 of trunk CDT, right windings of repeating .coil RC6 of trunk circuit CDTi in th toll oiiice'and'both1 Relay 629 is polarized and doesnot operate since the current in this,

windings of relay 62c.

normally closed circuit is in the non-operating direction. Relay Sill is marginal and does not operate since the upper winding of relay 620 has a.

high resistance. When the upper windingof relay B26 is short circuited by the above-mentioned operation of relay Bi l, the current through trunk conductors E55! and 652 is increased sufficiently to cause theoperation of relay Bail in the community dial ofi'ice. Relay 813i closes a circuit for operating the slow-to-release relay 8%. Relay 892 closes a circuit for operating relay 863, cone 30 .nects ground to conductor 85?; to mark trunk circuit CDT2 as busy in the banks of selectors Si having access thereto, connects the winding of relay 869 to conductor 8-33 to mark the terminals of trunk CDTZ in the banks of trunk finders TF having access thereto, and closes a circuit for operating group relay tit. With relays Bill and 883 operated, the Winding of polarized relay Wi lis bridged across conductors 83.! and 832. The operation of group relay EH8, which is common to the lines connected to one level of terminals in the banks of a group of trunk finders TF, connects ground to the start vconductor 8H to start the first idle finder in the group, and connects ground to conductor 8l2 to mark the level of the banks in Which the terminals of trunk circuit CDTI. are located. For a disclosure of a finder circuit and its operation resulting from connection of ground to the start conductor, reference may be had to the patent to R. L. Stokely, No. 1,799,654, granted April 7, 1931.

When the brushes of the trunk finder TF engage f the terminals to which conductors 83!, 832, and v 833 are connected, a circuit is closed through conductor 833 for operating relay 839 and for operating a relay in the trunk finder circuit to stop the finder switch TF. Rela 899 closes circuits for operating relays 89'! and 853. The operation of relay 867 causes a reversal of the current oyer trunk CDT and through the windings of polarized relay B26. Relay 8% opens the circuit for operating relay 891 but relay 898 is slow in operating so that relay 8d? remains operated for an interval long enough to cause the operation of polarized relay 62d of trunk circuit CDT! to indicate selector IS. through the upper brushes of finder TF to the windings of the line relay, not shown, of the associated incoming selector IS. Relay 854 does not operate since it is polarized and the current is in the non-operating direction. The selector Si and IS and connector C may be two-motion step by-stepv'switches and reference may be had to pages 53*to 65 of the second edition Automatic Telephony by Smith and Campbell for a comthat a finder has connected the trunk CDT to a Relay 8% is thereby connected plet description of the structure and operation of such switches when used as selectors and connectors. The operation of relay 620 causes the operationof relay G2I. Relay 62I locks under control of relay 6I2, disconnects conductors 60I and 602 from the repeating coil R06 to prevent the transmission of dialtone from selector IS in the community dial oflice to the calling operator, disconnects conductor '504 from the ground at the backcontact of relay BIG and connects this conductor to ground at the front contact of relay 620. Since calls to trunk circuit CDT may come from intertoll trunks arranged for voice frequency signaling, the dial tone is not transmitted because it would interfere with th receiving of dial impulses. When relay 620 releases due to the release of relay 801, it disconnects ground from conductor 604 causing the release of relay 219; and the release of relay 279 causes the successive reelase of relays I10 and I05 thereby again connecting ground to the low resistance winding of relay I 04 to cause the lighting of the dial pilot lamp at the calling operators position as a signal to the calling operator that dialing may be resumed.

The calling'operator now dials the digits of the called subscribers number, the dial impulses being successively repeated by relays I40 and 210 to cause the alternate release of relay -BIO and Iill of trunk circuit CDTI. The release of relay BM in response to the first impulse of a digit operates relay 6I3. Relay 6I3 being slow in releasing remains operated until all of the impulses of a digit have been received by relay (H0; and, during each such interval, relay 6I3 short circuits the windings of relay 620 and the right windings of repeating coil RC. The operation of relay 6I3 upon receipt of the first dial impulse of the first digit also closes a circuit through the lower winding of relay SIS. Relay BIS operates and it locks through its upper winding under the sole control of relay BIZ. When relay 6| 3 releases at the end of the first digit it closes a short circuit around the winding of relay 62I, causing the release of relay 6 2I. Since relay BI 6 is operated, the release of relay 62I does not reconnect ground to conductor 604. Being slow in releasing, relay 6I2 remains operated during the response of relay 6I0 to dial impulses. Relay 6II repeats the dial impulses over trunk circuit CDT, to relay 80I of trunk circuit CDTZ. The release of relay 80I in response to the first impulse of each digit closes a circuit for operating relay 805. Being slow in releasing, relay 805 remains operated until all of the impulses of the digit have been received; and, during this interval, relay 805 short circuits the winding of relay 804 and the windings of repeating coil RC8. Relay -80I repeats the impulses through conductors 83I and 832, the first train being effective to directively operate the selector IS. The last two trains of impulses control the operation of a connector C to establish connection with the called line. Ringing is automatically started by the connector; and, when the called subscriber answers, a relay in the connector (which relay is not shown in the drawings) is operated to reverse the current through conductor 83I and 832 to cause the operation of polarized relay 8 04. Relay 804 closes a circuit for operating relay 801; and relay 801 reverses the current over trunk CDT to 0prelay 620. The operation of relay 820 connects ground to conductor 6I9, thence through the lowermost front contact of relay 6| 6, and middle upper front contact of relay GM, to conductor 604 to reoperate relay 219 of two-way trunk circuit TWT2. The operation of relay 219 causes the successive operation of relays I70 and I05. The opening of the circuit through the low resistance winding of relay I40 causes the lamp SL to be extinguished; and, since dialing has been completed, this indicates to the calling operator that the call has been answered by the called a subscriber.

When the called subscriber replaces the re ceiver, the reversal of current from connector 0 causes the release of relay 804 and the release of relay 804 causes the successive release of relays V relays 215 and 271 of the two-Way trunk circuit and M2 of trunk circuit CDTI.

TWT2 and the successive release of relays 8 I 0, 6| I Relays H6, H4 and 6| 5 are held operated through conductors 603, 403, 303 and 283 until relay 271 of two-Way trunk circuit TWT2 releases. The selector T82 is restored to normal as described inthe aforementioned King et al. patent. The selector T84 is restored to normal due to the release of relay 4I6 when ground is disconnected from conductor 403, in the manner hereinbefore described. The release of relays (H4 and 6I5 restores trunk circuit CDTI to normal. .The aforementioned release of relay BII causes the release of relay I of trunk circuit CDT2.. The release of relay 80I causes the release of relays 802, 803, 808 and 809. The release of relay 80I opens the loop across conductors 83I and 832 releasing the finder, selector 7 and connector switches in the community dial ofi'ice in the usual and well-known manner.

Assume next that the selector TS4 is operated under the, control of the impulses created by the dialing of the second digit by the calling operator in the first toll ofiice to select the level represented by the terminal 443, the terminals in this from; contact of normal post springs 426 and a front contact of relay 6 tov conductor 405 to operate relay 3I3 of interswitch trunk circuit IST3. Relay 3I3 connects conductor 404 to the winding of relay 320 and connects the winding of relay 3 to the windings of retard coil 3I0, thence through conductors 30I and 302 thence to ground at the front contact of signaling relay 210 as hereinbefore described. Relay 3H operates, closing a circuit for operating relay 3I4. Relay 3I4 closes a circuit through conductor 339 for operating the start relay 340 of the common timing circuit TC. As soon thereafter as ground is connected through interrupter A to conductor 34I, relay 3I5 operates. Relay 3I5 locks under conprepare for the con-

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