US2131572A - Telephone system - Google Patents

Description

Sept. 27, 1938. N. H. SNJNIDERSv TELEPHONE SYSTEM Filed April 5, 1937 2 Sheets-Sheet l ATTORNEYJ` Sept. 27, 1938. N. H. sAuNDERs TELEPHONE SYSTEM 2 4sheets-sheet 2 Filed April 5, 1937,

INVENTOR. NORMAN H. sAuNDERs 5TM; 7, am@ Jima,

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AT ToRNEwi Patented Sept. 27, 1938 UNITED STATES TELEPHONE SYSTEM Norman H. Saunders, Homewood, lll., assigner to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application April 5, 1937, Serial No. 134,998`

Claims.

The present invention relates to telephone systems and more particularly to such systems of the automatic step-by-step type having embodied therein apparatus automatically operable to permit the tracing of incoming calls to any desired predetermined subscribers telephone.

Systems of the type mentioned conventionally comprise switch trains including step-by-step selector and connector switches for setting up and releasing connections between any pair of telephones in the system. In such systems, as well as in other systems of similar character, the need has long been recognized for means operable to assist an attendant in the tracing of incoming calls to particular telephones. This need arises in connection with repeated annoyance calls to certain telephones, in police work, and in rendering other services ordinarily required yof a public exchange system. Various expedients have been resorted to in the past for providing this form of service. These expedients, however, leave something to be desired with respect to the simplicity of the apparatus involved and also with respect to the faithfulness of the operation thereof.

It is an object of the present invention, therefore, to provide an improved and exceedingly simple circuit arrangement, applicable to practically any of the various modifications of the step-by-step automatic telephone system, for assisting an attendant in tracing calls to any desired telephone embodied in the system.

It is another object of the invention to provide an arrangement of the above character which utilizes to the fullest extent the switching equipment normally provided for rendering ordinary telephone service.

More specifically, it is an object of the invention to provide an arrangement of the above character which is operable to assist an attendant in tracing calls to a single telephone on a party line from telephone lines terminating at any one of two or more exchanges included in the system.

rlhe invention as described in detail hereinafter is illustrated as being embodied in an automatic system including two Yexchanges interconnected by two-way trunk lines and wherein stepby-step line, selector and connector switches, op-

erable in the order named, are provided in eachv exchange for establishing a connection between a first or calling line toa second or called line. Such a connection vmay be regarded as comprising a talking loop between the two telephones, the loop being completed when the call is answered at the second or called telephone. I

In general, the objects asset forth above are realized in accordance with the present invention by providing meansv automatically operable as soon as ithe line associated with theptelephone Vparticular telephone on a party line.

to be observed is seized by a connector switch of the switching equipment for preventing the established connection from being released in response to any possible operation which the calling party may perform at the calling telephone, and more particularly in response to the interruption of the talking loop at the calling telephone. More specifically, this means comprises a plurality of interrelated relays associated with the line leading to the telephone to be observed, one of which operates in response to the application of ringing current to this line, to prevent the selector switch, preceding the operated connector switch, from being released when the call- Ving party interrupts the talking loop at his telephone by hanging up his receiver. By holding this selector switch operated after the calling party hangs up, it is possible for the called party to inform an attendant at the central exchange that a call is to be traced, whereupon the attendant may, by observing the condition ofthe aforementioned selector switch or switches and the line switch which has caused the operation thereof, determine the line on which the call was initiated. Additional means, comprising certain of the relays of the connector switch in use, are provided which are operable in case a talking loop is not completed at the observed telephone to cause the restoration of the above-mentioned means so that theconnection may be released in the conventional manner when the calling party hangs up. As pointed out in detail hereinafter, the aforementioned relays are under the control of `the answering party at the observed telephone and function to hold a predetermined potential, namely, ground potential, on the control conductor of the. operated selector switch after the'party at the calling telephone hangs up, whereby the portionv of the switch train preceding the, operated connector switch is held operated. K Y

The present arrangement is of particular utility in assisting an attendant to trace calls to a As is well known,rsuch lines are identified byhaving thereo n a plurality of'telephones, each vof which has associated therewith a signal device. In those cases where selective harmonicvringing is relied upon for signaling a particular telephone, each specifically,` therelaiy associated with the party line to which the telephone under observation is `connected and forming a part of the means for holding the switch train operated, is connected and arranged to be responsive only to the application of current to the line of the particular frequency to which the signal device associated with the telephone under observation is responsive.

In certain instances it is desirable that incoming calls to a particular telephone be traced even though the calls originate on lines extending to an exchange different from that to which the lineassociated with the telephone under observation extends. The 'switch train or means for establishing this type of connection conventionally comprises a rst selector switch, a repeater, a second selector switch and a connector switch, connected in tandem and operable in the order named, 4the connection itself extending over a trunk line interconnecting the two ofces. In accordance with a further feature of this invention, means lare provided Voperable substantially simultane'ouslyV with thecompletion of such a connection for holding -the entire switch train operated so that attendants 'in the respective exchanges may make the necessary observations and exchange the information necessary to a determination of the line on which the call originated. Thismeans, more specifically described hereinafter, comprises means included in the repeater andresponsive to the operation of the battery reversing relay of the connector switch for applying a predetermined potential, namely, ground potential to the control conductor of the first selector 'switch independently of the hold relay of the repeater, it being understood that the lastmentioned relay normally holds ground potential on the control conductorjof the rst selector and isie'sponsiveto an'operation, namely, the hangingup of the receiver at the calling telephone, to 'removeground therefrom, thereby to release the portionnf the switch train preceding the repeater. The portion of the switch train following the selector is held operated by the means briey referred to above. The elements of the various means l'referred to vabove are arranged in an exceptionally simple manner suchthat the control relays normally provided in the various switches arentilized to the fullest extent in 'faithfully providing the form of service noted. Y

The'novelfeatures believed to be characteristic ofthe invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further vobjects and advantages thereof,A will best be understood by reference to the specification taken in connection with the accompanyingY drawings, in which Figs. 1 and 2 taken togetherillustrate in partially schematic form a telephone system of the type mentioned, having embodied therein means constructed and arrangedinsaccordance with the present invention for assisting an operator to trace calls to 'any desired telephone or telephones included in the system. Y n

*Referring now -to the drawings, there is illustrated, 'for the purposeof describingthe invention, anautomatictelephone systempf conventional formc'ornprising rtwo exchanges, one of which issh'own in Fig. ll and theothe'r of which is shown infFigJ V2 These two exchanges are interconnected byifa-'pluality ofitrunk lines such, for

example, as the line 86, 8l, and each thereof has embodied therein impulse responsive step-by-step switchesY for setting up and releasing connections between any pair lof telephone lines included in the system. In generaL'the system 'comprises a plurality of telephones or subscribers substations, four of which areshown at A, B, C, and D, adapt- "ed to be interconnected by means including their respective associated subscribers lines I0, II and I2 and switch trains including the aforementioned step-by-step switches. It will be observed that the line I2 `is of the party line variety having a plurality of telephones thereon, two of which are shown at C and D. The switch trains, when established, may individually comprise the usual lineswitch associated Vwitheachy subscribers line, one or more -tandem connected intermediate selector switches, the first of which is accessible to the line switch corresponding to the calling subscribers line, and a connector switch accessible to the finally operated selector switch and having vbank contacts in which the called subscribers line terminates. Thus, in the system show n, the lines Il), II and I2 terminate at line switchesV I-3, I4 and I5, respectively, the rst two of which have access to a group of selector switches, one'of which is shown at I0 included in the rst exchange, and the last of which has access to a group of selector switches, one of -whichisjshown at I8 included in the second exchange. These selector switches, in turn, have access to groups of connector switches, each connector switch of each group having its bank contacts multipled to the bank contacts of the other switches inv the same group and connected to serve a corresponding group of subscribers lines in the system. Thus, the selector switch I has access to a-,group of connector switches, one of which is shown at 1I, in the bank contacts of which a group of subscribers lines of the first exchange terminate. Similarly, the selector switch I8 has access Vtoa group of connector switches, one of whichis shown in detail at I'I, in the bank contacts of which agroup of subscribers lines of the second exchange terminate. In order to establish connections between the subscribers lines of the first exchange and the'subscribers lines of the second exchange, there is provided one or-more'two-way trunk lines which terminate at -either end at a two-way repeater. Thus, the trunk 4line 86, 8-1 Yterminates at a repeater 16 in the first exchange `and a repeater 8'I` in the second exchange. The repeaters in the iirst exchange similar to and including the repeater I6 are accessible-to the selector switches, such, for example, as the switch 10, and, similarly, the repeaters of the second exchange are accessible to the group of selector'switches of which only the switch I8 is shown. lIn the arrangement illustrated individualfselector switches I6 and 12 are provided for gaining access to the connector switches included in the respective exchanges on incoming calls-thereto, routed by way of the trunk lines such,'for example, as the line 86, 8T. `It-iswell known that by this arrangement, any subscriber may,by proper manipulation of the-impulsing device "at his substation, establish a connection between his line and any other subscribers line in the system.

Each ofV the linexswitches included inthe system, such, for example, 'as the line switches I3 told-inclusive, may be lof 'any desired commercialcons'tr'uction, although 'preferably is of the welliknown rotary type 'having three sets of bank contacts,v wipers corresponding tothe three contact sets, a ratchet and pawl mechanism for driving the wipers, an operating magnet for actuating the ratchet and pawl mechanism, and control means whereby the operating magnet operates when a call is initiated on the line associated with the corresponding line switch andV its operation is arrested when the wipers are rotated into engagement with a set of contacts corresponding to the i-lrst idle selector switch available. Similarly, each of the selector switches included in the system may be of any desired form, although preferably is of the well-known Strowger type comprising bank contacts arranged in levels, each level corresponding to a particular group of conector switches, wipers for engaging the bank contacts, ratchet and pawl mechanisms for imparting translatory and rotary movements to the wipers, vertical and rotary magnets for driving the respective ratchet and pawl mechanisms and control means whereby, when a selector'switch is first seized, it is automatically conditioned to be responsive to the first digit dialed at the calling substation, the dialing of the first digit causes the vertical magnet to step the wipers upward opposite the level of bank contacts corresponding to the number of impulses in the digit dialed and the wipers are automatically rotated by the rotary magnet and associated ratchet and pawl mechanism into engagement with the set of contacts corresponding to the rst idle connector in the group of connectors to which the called line` extends.

The various connector switches, like the selector switches, are preferably of the Strowger type and may be identical with that illustrated at i1. In brief, the switch i1 comprises two banks of contacts arranged in levels, the individual contact sets connected to the various subscribers lines being multipled to the corresponding contact sets of other similar connector switches included in the same group. Thus, the switch |1 comprises a contact 45 in the control Contact bank, which contact is connected to the control or C conductor lI9 leading to the line switch l associated with the party line |2. The corresponding line contacts 43 and 44 for the line conductors 20 and 2l of the line I2 are included in the line contact bank. The connector switch l1 also includes wipers 40, 4| and 42 for engaging the various contact sets in the two contact banks, such, for example, as the contacts 43, 44 and 45, a ratchet and pawl mechanism, not shown, for translating these wipers vertically opposite any desired contact level, a vertical magnet 25 for actuating this ratchet and pawl mechanism, a second ratchet and pawl mechanism, not shown for thereafter actuating the enumerated wipers into engagement with the particular contact set corresponding to the called subscribers line and a rotary magnet |2'n` for driving this second ratchet and pawl mechanism. The switch also includes a release magnet |69 for actuating the two ratchet mechanisms to permit the wipers to be restored to normal, a minor switch |01 for selectively applying ringing current of a particular frequency to a line seized by the switch |1, and control means comprising a plurality of inter-related relays |00, H0, |20, |30, |40, |50, |60 and |10, their control and controlled circuits and oir-normal springs |41 and |48, for controlling the operation of the vertical, rotary and release magnets and for performing the various other functions normally required in this type of switch. The switch |01 comprises a. ratchet and pawl mechanism,Y not shown, a motor magnet ||1 for actuating the ratchet andpawl mechanism, a release magnet ||6 for permitting the switch |01 to restore to normal, and off-normal springs 65. More specically, the last-mentioned control means comprises the relays |00 and ||0, oper-y ative in the order named to condition the vertical magnet |25 for operation; the relay |20 for preventing the impulses of the second digit, dialed at the calling substation, from being transmitted to the rotary magnet |26; the line relay |00 for interrupting the circuit of the vertical magnet 125m accordance with the impulses of the second digit; the relays ||0' and |20 for conditioning, at the end of the second digit, the rotary magnet |25 to be responsive to the impulses comprising the third digit dialed at the calling substation; the relay |00 for interrupting the circuit of the rotary magnet in accordance with the impulses cf the third digit; the relay |40 for partially completing the connection to the called line, for applying ringing current thereto and for applying, in case the called line is found idle, ring back current to the incompleted talking loop extending back to the calling subscribers substation; the relay |50 for applying busy tone to this loop, for-'interrupting the circuit of the motor magnet H1 and for preventing the calling line from being connected to the called line, all in the event the called line is found busy; the relay |60 for completing the connection between the call- Y ing and called lines, for interrupting the application of ringing current to the called subscribers line and the application of ring back current to the calling subscribers line; vand the relay |10 for reversing battery back over the loop extending to the calling subscribers line when. the called party answers.

As pointed out in .detail hereinafter, the relay l l0, whenoperated to one of its two positions, inl lector switch I6 when the talking loop is inter- A rupted at the calling partys telephone.

Each of the two-way repeaters included in the system may be identical with that shown generally at 15 as comprising primary'windings 11 and 13 normally connected across the line conductors 13 and 15 by a condenser 19 and secondary coils 80 and 8| connected in series across the line conductors 83 and-84 by a condenser 02. The control meansfor this repeater comprises the relays 200, 2|0, 220,A 230, 240,y 250 andv 258 and their respective control and controlled circuits. l

Neglecting for the present the details of the connector switch I1 and the means associated therewith-for assisting an attendant to trace calls to a predetermined subscribers telephone or telephones, the system as described above is entirely conventional in form and its operation is Well understood in the art. In brief, when a subscriber such, vfor example, as the subscriber at the telephone A initiates a call over the line I0 to asecond subscribers telephone in the Vsame exchange such, for example, as the telephone B,

by liftinghis receiver from its hook, the line switch I3 associated with the calling subscribers .linezoperates to select .an idle `selectorswitch Aand to Acondition the same to be responsive to impulses transmitted from the impulsing device at the telephone A. VAs noted above, `Aeach of the Vselectorswitches has :access :to yone or more connecto'rswitches in which :any'subscribers line .of .the system terminates. Thus, if the selector ;switchrl.,or'examplens seizedby the line switch LIS, .it .operates in response `Lto the dialing of the Afirst digit at thersubstation A to translate its :wipers y,vertically to a contact level corresponding rto the `group of Yconnector switches `at which the .called line II terminates, following which .it automatically rotates its wipers into engagement with 'a `set of contacts correspondingto the iirst Vidle .connector switch in this group. Thereafter, and kassuming the connector switch II is seized vby the Yselector switch l), the connector switch, in response to the dialingnof the second digit, and through the operation of its vertical magnet and the associated pawl and ratchet mechanism, translates its wipers vertically `to positions opposite thefcontact levels in which the conductors of the called subscribers line II terminate. Withthe switch train in this condition and when the third digit is dialed, the rotary magnet of vthe connector switch, in ycooperation with its associated ratchet and pawl mechanism, operates to drive its wipers into engagement with the contacts corresponding to the called 'line II.

vThe system conventionally includes means whereby ringing current and ring back tone are automatically transmitted, respectively, to the substations of called and lcalling parties in case 'the called line is idle and upon the connector wipers coming into engagement with the bank contacts at which the called subscribers line terminates. Also, in accordance with conventional practice, means are provided whereby, in the event the called line is found-busy, the calling line is -not lconnected 'thereto and `busy tone is transmitted back over the established loop to the calling party to indicate the busy condition rof the called line.

In the event the vcalled :line is found idle and the-called `party answers, battery isreversed back over the loop when the called party lifts his receiver from its hook to connect abridge across .the conductors of the called line. With the systern in'this condition, a talking connection Vis established'betweenthe calling 'and called parties which obtains until the conversation is terminated and one of the parties hangs up.

VThe arrangement is such that, Ywhen the'calling party is the rst lto `interrupt the talking loop by hanging up, the switch train leading-to the connector switch II and including vthe selecvtor switch andthe line switch I3 is normally released. The connector switch is,`however, held in Vits operated position until the called party hangs up to remove the bridge from across the conductors of his line. In the event the called party is the first to interrupt the talking loop, the entire Aswitch train is maintained operated until the calling partyhangs up.l

The method by which the apparatus included in the second exchange, shown in Fig. 2,voperatesto establish and releasea connection between two telephones, both of which-are on subscribers lines extending to this exchange, is exactly the same as that described above and is, therefore, omitted in the `interests oi simplifying the description.

In the operation ofthe system on a call from rvthe telephone A connected to a line of the `iirst exchange, tothe telephone C, connected to a line of the second exchange, the line switch I3 operates to seize an idle selector switch, such, for example, as the .switch 1.0, in the exact manner described above. In response to the dialing of the firstdigit, this selector switch seizes an idle Ytrunk line, which will be assumed to be the line 86, 81, extending to the second exchange. When the second digit lis Ydialed theselector switch I6 'l' seized by the 'line 86,;81 steps its wipers to a level corresponding to the contact level in which the conductors of thegroup of connector switches serving the called line terminate and automatically-seizes an idle connector switch in this group. Assuming the connector switch II is seized, this switch, in Yresponse to the dialing of the third and fourth digits, actuates its wipers linto engagement with the bank contacts at which the called lline :I2 terminates. When the fth digit is dialed, ringing current of the proper :frequency to cause `operation of only .the signal device at the desired telephone is applied to the :line I-2. When the .called telephone Vis answered battery is reversed backover the trunk line con- 4tductors, causing the relays 220 and 20,0 to operate and `complete the connection. It will be seen that the `switch atrainor Ameans employed in establishing this connection includes the selector switch .10, the repeater 76, the selector switch I6', and the connector switch I7, connected in vtandem and operable in the order named. As

pointed out in detail hereinafter, the arrange- -rnent is Ysuch that, -when -the calling party hangs Aup first, :the ventire'switch vtrain excluding the connector switch I'I iis normally released, this `latter switch being held operated until the called party hangs up. Alternatively, Aif Vthe :called party hangs up first, the entire switch -train is held operated luntil the-connection iscleared out at the telephone A.

The modeof'operation of the system on a call from `a telephone .connected `toa subscribers line ofthe second exchange to a ltelephone connected to a subscribers line ofthe 4iirst exchange is deemed toibo-obvious in view of the-description in the'preceding paragraph and for that reason is omitted.

Referring rnow moreparticularlyto the operation of the repeater `I6 inthe sequence of -operations just described, when the selector switch 'Ill L extends the calling loop tothe line conductors A'I3 anda-15a circuit is completed for 4energizing the line =re1ay 24D. This vcircuit extends from groundat the upper rwinding of the relay 240,

through this winding, over the conductor 9|,

through the upper winding ofthe -relay'2I-IJ, the repeaterwinding l-'I,=the -armatures 20,3 -and 202, oVer'lthe .side vof the calling loop including the line conductor 13, through the 'bridge at `the telephone A `Ioack over vthe-other -side of the calling loop including the conductor '15, through the armatures 20S-and 12.99, .the repeater winding 18, `the 'lower winding of the 'relay2I.0,over the conductor-92 and through the lower winding of the relay 240 tobattery. 'I'herelay 240 thereupon operates tocomplete, vat :its'armature 24|, an obvious energizing circuit 'for lthe Vhold relay 250 and Vto Vprepare, at fits armature 242 'andassocivated contact 244, a loop extending by way of the trunk line conductors 86 and.8-l to the second exchange. VWhen the'slow-to-release hold relay 250 operates'it applies ground at its armature 25! to ythe control or C conductor 14, thereby to hold, in

a well-:known manner, the switch'trainpreceding the repeater 16 operated. The relay 250, upon operating, completes an obvious circuit for energizing the relay 260, which latter relay, in turn, operates to complete, at its armatures 26| and 264 and their respective associated contacts 253 and 265, the loop extending to the second exchange. Completion of this loop causes the line relay in the selector switch I5 to operate and initiate the conditioning of this switch to be responsive to the impulses comprising the second digit dialed at the callingv telephone A. During impulsing the loop is alternately interrupted and completed by the operation and restoration of the armature 242 of the line relay 240.

When ground is applied to the control conductor 14, the right-hand winding of the relay 220 is energized. This relay is of the polarized type such that it will not operate when only its right-hand or polarizing winding is energized when the current through the left-hand winding is normal. When, however, the called party answers and the current is reversed over the loop including the windings 80 and 8|, the left-hand winding of the relay 220 is properly energized to cause the operation thereof. At its armature 22|, the relay 1220, upon operating, completes a circuit including "the conductor 93, for energizing the relay 200. The last-mentioned relay, in turn, operates to short-circuit, at its armatures 205 and 206, the windings of the relay 2|0 and, at its armatures 20|, 202 and 201, 208, to reverse battery back over the loop extending to the calling telephone.

The release of the repeater 16 is primarily under the control of the calling party in so far as the apparatus just described is concerned. Thus, when the called party hangs up and battery is reversed back over the loop to the repeater 16, only the relays 220 and 200 restore, ground being retained on the control conductor 14 by Virtue of the operated condition of the relays 240 and-2150. When the calling party hangs up, however, to interrupt the previously traced operating circuit for the line relay 240, this relay restores and causes the relays 250 and 260 to restore. The relay 250, upon falling back, removes ground potential from the control conductor 14 at its armature 25|, thereby initiating the release of the selector switch 10 and the line switch |3 in the usual manner. Thereafter, the relays 220 and 200 restore and the repeater is in its idle or normal condition.

Fom the foregoing description it will be apparent that the selector switch 10 is normally releasable in responseA to an operation performed at the calling telephone, namely, the operation of hanging up the receiver to cause the sequential restoration of the relays 240, 250 and 200. More particularly, it will be apparent that so long as a predetermined potential, namely, ground potential is maintained on the control conductor 14 which extends to the control conductor of the' selector switch, the switch is held operated, and that when the control means comprising the hold relay 250 restores in response to the calling partys hanging up, this potential is removed from the control conductor and the switch is released.

Referring now more particularly to the operation of the connector switch |1, when the selector switch S6 seizes this connector switch a bridge is connected across the line conductors and 3| at the repeater 16, this bridge comprising the repeater windings 80 and 8| and the left-hand winding of the polarized relay 220. When this bridge is closed, a circuit is completed for energizing the relay |00. This circuit extends from ground at the lower winding of the relay-noted, through this winding, by way of the armatures |14 and |14 of the relay |10, the conductor 29, the conductor 3|, through the bridge across the conductors 30 and 3|, over the conductors 30 and 28, and through the armatures |13 and |13"'a n`d the upper winding of therelay |00 Ato battery. When energized over the above-traced circuit, the relay |00 operates to complete, at its armature 0| and associated contact |03, a circuit or ener,- gizing the slow-to-release hold relay H0; The last-mentioned relay in turn operates to connect, at its armature ground to the control or C conductor 22, to prepare, at its armature ||2, holding circuits for the relays |40 and y|00 and to prepare, at its armature I|3 and associated contact H4, a circuit for the series connected vertical magnet |25 and the relay |20. With the hold relay ||0 in its operated position, the ground applied to the control conductor- 2 2 at the armature holds the selector switch Iii-"preceding the connector switch in its operated position. With the control means of the connector switch l1 in this condition, the vertical magnet |25 is conditicned to be responsive to impulses transmitted from the impulsing device at the calling subscribers telephone A. At the beginning of the i'lrst impulse of the third digit, the bridge across the line conductors 30 and 3| is interrupted, thereby to open the previously traced operating circuit for the line relay |00, permitting this relay to restore and complete, at its armature |0|, the previously prepared circuit for energizing the relay |20 and thevertical magnet |25 in series. The last-mentioned circuit vextends from ground at the armature 0| and its associated contact |02, through the armature ||3 and associated contact H4, the contacts |28 and |21 of the on normal springs |41, the winding of the relay |20, and through the winding of the vertical magnet |25 to battery. When the slow-to-release relay |20 operates, it prepares, at its armature |2| and associated contact |22, an obvious multiple energizing circuit for itself and the vertical magnet |25. At the beginning of the rst impulse when the line relay |00 operates to complete the operating circuit of the vertical magnetv |25, the ratchet and pawl mechanism associated with-the Vertical magnet causesnthe wipers 40, 4| and 42 to be translated 'one step `vertically.- This rst step of the switch also causes the off-normal'contacts |41 and |48 to be operated so that'thecontacts |28 and |21 are opened, the contacts |24 and |28 are closed and the contacts |29 and |49 are closed. Closure of the last-mentioned contacts prepares an obvious circuit for energizing the release magnet |69, and closure of the offnormal contacts |24'and 28 completesrrthe previously prepared multiple circuit for energizing the relay |20 and the vertical magnet |25. 'Ihe completion of the last-mentio-ned multiple circuit permits the vertical magnet alternately to be energized and de-'energized in accordance with the operation and restoration of the line relay |00 corresponding to succeeding impulses of the digit being dialed.v Thus, the wipers 40 to 42, inclusive, are stepped vertically'to a position oppositethe level in which the called line terminates and corresponding to the impulses of the dialed digit.

At the end of the digit diaied, the circuit for energizing the line relay |00 is closed, so that the previously tracedcircuit for the relay |20 and the vertical magnet |25 is interrupted at the armature Accordingly, the relay '|20 restores after an interval, opening, at its armature |2| and associatedcontact |22, the previously mentioned multiple circuit for itself and preparing, at the same armature and its associated contact |23, a circuit extending by way of the conductor 31, the armature |54 and the armature |45 for energizing the rotary magnet |26- and the slow-to-release relay |30 in parallel. At the beginning of the rst impulse of. the next digit, the line relay |00 again restores, to complete, at its armature |0|, the prepared circuit for energizing the rotary magnet |26 and the relay |30. In response to such energization, the relay |33 operates to interrupt, at its armature |3|, a point in the circuit for energizing thelower winding of the relay |40 and to connect, at this same armature, the directing` orY control wiper1 42 to the upper terminal of the winding of the relay |50 over a path extending by way of the armatures |3| and |33, the armature |42 and the conductor 35. At its armature |35, the relay |30 closes a shunt around the armature |54 of the relay |50. During succeeding impulses of the digit being dialed, the operatingrcircuit for the relay |30 and the rotary magnet |26 is alternately interrupted and completed at the armature HH of the line relay |00, in accordance with the impulses of this digit, whereby the rotary magnet causes its associated ratchet and pawl mechanism to step the wipers 40 to 42, inclusive, into engagement with the bank contacts 43 to 45, inclusive, to which the line conductors of the called line l2 are connected. During these impulses, the relay |30, due to its slow-to-release characteristic, remainsloperated. In the course of this stepping operation and each time the directing wiper 42 engages a contact corresponding to a busy line, the relay |50 operates, but withoutr effect at this time since its armature |54 is shunted by the operated armature |35. At the conclusion of the series` of impulses comprising the dialed digit, the relay |00 remains in its operated position so that the circuit for energizing the relay |30 and the rotary magnet |26 is interrupted. As a consequence, and providing the called line |'2 is idle, the vrelay |30 falls back after an interval to again prepare, at its armature |3| and associated contact |132, a circuit for energizing the'lower winding of the relay |40.

If the called line is idle and whenthe relay |30 restores, a circuit is completed forpartially energizing the relay |40, this circuitextending from battery at the cut-off relay in the line switch associatedwi-th the called line I2 over the contro-1 conductor |9, through the contact 45, the wiper 42,` the armature |3| and associated contact |32, over the conductor 38, through the lower winding of the relay |40, over' the conductor 36, through the contact |52 and associated armature I5 tof the relayV |56, and, over therelease'or trunk control conductor 22 to groundA at the armature The relay-'|40 partially operates in response to its partial energization, as described above, to complete, atits armature |44, its previously prepared locking circuit extending by way, of the conductor 25 to' ground at the armature ||2, thereby to cause thel Vfull operation thereof. When this occurs, the-linecircuit to the called line is partially completed at the armatures |.4| and |46, direct ground is connected to the control conductor I9I at the armature |41, ground is connected to the ringing interrupter start conductor 23 at the armature |43, the circuit for energizing the relay |50 is interrupted at the armature |42', the circuit for energizing therotary magnet |26 is interrupted at the armature |45, and a circuit is'prepared for energizing the motor magnet ||1 of the minor switch |01 at the armature- |45 and its associated lupper contact. Y

In response to thedialing of the final digit at the calling telephone, the motor magnet ||1 in cooperation with its associated ratchet and pawl mechanism steps the Wiper |08 into engagement with the contact leading to the ringing current generator having arr output frequency to which only the signal device at the called telephone C is responsive. At the beginningof the first impulse of the nal digit and' before the wiper |08' takes its first step, the-slow-to-releasefrelay |05 operates to interrupt at its armature |06 the path of the ringing current. This relay, dueto its slow-to-release characteristics remainsV operated during further impulses of the final digit and restores after an interval following the'final im pulse. When the switch |01 takes its r'st step at the end of the rst impulse, the olf-normal contacts 65 are closed' to prepare an obvious circuit for energizing the release magnet H6.

Shortly after the conclusion of the nal digit, the relay |05 restores, and ringing current is transmitted to the bell at the called substation C over a circuit extending from the ringing generator by way of the wiper |08', the conductor 46, the armatures |68, |06 and' |46, the Wiper 40 and associated contact 43, the line conductor 2|, the bridged bell and condenser atY the called partys substation, the conductor 20, the contact 44 and associated wiper 4 I, the armatures |4| and |6|, the conductor 3,4, and through the Vlower Winding of the relay |60 and battery to ground. Due to the alternating nature of' this ringing current, a voltage of the same frequency is induced in the upper winding of the relay |60. This Voltage is impressed across the terminals of the receiver at the calling substation over a path which includes the conductor 66', the lower winding ofV the relay |10v and the line conductor 3|. Due to the slow-to-operate characteristic of the relay |60, this relay does not operate during the ringing operation. In this manner, the calling party isnotied that the called line is idle, and only the called substation on the party line I2 is signaled.

When the called party at the telephone C answers the call by liftinghis telephone receiver from its hook, a direct current circuit is completed for the lower Winding of the relay |60, this circuit extending from thev grounded terminal of the ringing current source, over the conductor 46,

through the armatures |68, |06 and |46, through the wiper 40 and associated contact 43, the conducto-r 2|, through the bridge at the called substation, over the line conductor 20, through the contact 44, the wiper 4|, the two armatures |4| and |6|, and the lower winding of the relay |60 to battery. 'Ihe relay |60 now operates to close an obvious locking circuit for itself at its armature |61, to prepare the talking loop between the calling and called substations at its armatures |6| and |68, to interrupt its original energizing circuit at its armature |6| and associated contact |62, to interrupt, at its armature |65 and associated contact |64, the circuit for the ringing interrupter, to interrupt, at its armature |68 andassociated lower contact the circuit for applying ringing current to the calledline, thereby to discontinuev the application of ringingvand ring'- back tone to the loops extending to the called and calling parties, respectively, and to complete,

at its armature |65 and associated contact |66, a circuit for lighting the supervisory lamp No. I. When the relay |60 operates, a circuit is completed fcr energizing the battery reversing relay |10, this circuit extending from ground at the armature I2, through the armature |61 and the lower winding of this relay, by way of the conductor 21, over one side of the completed loop to the called telephone, through the bridge across the line conductors at this telephone, back over the other side of the loop and the conductor 26, and through the upper winding of the relay to battery. When the relay I 10 operates, it interrupts, at its armature |1I, the previously completed circuit for energizing the supervisory lamp No. I, interrupts, at its armature |16, the previously prepared circuit for the release magnet |69, prepares, at the armature |16, a circuit for energizing the supervisory lamp No. 2 and, at its armatures |12 and |15 and their respective associated contacts |13 and |14, reverses battery back over the completed loo-p extending to the repeater 16 for the purpose of causing the operation of the polarized relay 220 in the manner previously described. The operation of the armature I1| also completes a multiple locking circuit for the relays |40, |60 and |10, this circuit extending from ground at the'armature |43 by way of the conductor 36, the armature |65, the conductor 24 and through the armature I'll to theconductor 25 where the circuit divides into three branches, one for each of the windings kof the three enumerated relays.

Before describing the release of the connection as established in the above manner, it will be assumed that, instead of being idle, the called substation C is found busy at the time the wipers 40 to 42, inclusive, are stepped into engagement with the contacts 43 to 45, inclusive, corresponding to the conductors of the called line. When this occurs, ground is present on the releaseconductor I9 so that, the wiper 42, upon engaging the contact 45, completes an obvious circuit for energizing the relay |50. This relay operates to prepare, at its armature I5 I, a locking circuit for itself', which circuit is completed when the relay |30v restores after an interval, following the end of the fourth impulse digit. This circuit extends from ground at the armature III by way of the control conductor 22, the armature I5I and associated contact |53, the contact |34 and its associated armature |33, the armature |42, the conductor 35, and through the winding of the relay |50 to battery. In its operated position, the relay |50 holds open, at its armature |54, the original circuit for energizing the relay I 30 and the rotary magnet |26 and, at its armature I 55, applies busy tone to the lower line conductor 3| to notify the calling subscriber A that the called line C is busy. It is to be observed that the circuit for venergizing the motor magnet I I1 and the relay |05 is held open at the armatures |54 and |45 when the called line is busy, so that the dialing of the final ldigit has no effect thereon.

Continuing now with the operations which occur during the release of the established connection, when the conversation is concluded and the calling party A replaces his telephone receiver on its hook, the closed loop from the repeater 'I6 holding the line relay |00 operated, is opened at the armature 242 andassociated contact 244 of the relay 240 when the latter relay restores. As a terval, also restores. -When' the Vvrelay I|0 falls back, it interrupts, at its armature I I2, the original holding circuit for the'relay |60, prepares, at its armature II3, a circuitv for energizing therelease'magnet |60, completesat its armature II6 the 'circuit for energizing the release magnet II6, and at its armaturel I, removes ground from the controlconductor 22. The release magnet II6, upon operating, permits its wiper |08 to restore toY normal, in which position the off-normal springs 65 are opened Vand the operating circuit of the'release magnet ||6 is interrupted. The relay |00,'upon restoring and before the relay I I0 falls back, completes, at its armature I0| and associated contact |02, the previously traced circuit for energizing the relay |30. When the relay |30 operates, it removes, atit'sarmature |32, the multiple ground from: the control trunk conductor 22, which ground extends by way of the armature |41, the conductor'y38, the lower winding of the relay.Y |40 and the conductor 39. By removing this multiple ground from the conductor 2.2, the release of the switch train preceding the connector switch I1 is placed under the control of the relay IIO. Thus, when the relay "I I0 restores, following the operation of the slow-toreleaserelay |30, it completely removes, atvits armature III, ground from the conductor 22 for an interval, thereby permitting the selector switch I6 to be released in a manner well understood in the art. y f

When the relay III) restores,` shortly afterfthe restoration of the relay|00, it not only effects the release of the selector switch I6, but interrupts, at

its armature I I3, the circuit forenergizing the re VV lay |30, permitting this relay to restore, which it does after an interval, thereby to return ground to the control conductor 22 from the wiper 42.0f

.the connector switch and thus mark the switch I1 as busy in the selectorswitch contact banks f until the connection is cleared out at the called substation. Restoration of the relay ||0 also completes an obvious circuit'for energizingthe supervisory lamp No. 2, which circuit extends from ground at the armature I0| and its associated contact |02, through the armature |`|3 and associated contact I 5, the armature |16, and the supervisory lamp tovbattery. Although the original locking circuit for the relays .and |40 is opened, at the armature ||2, these relays are retainedl operated over the previously traced multiple locking `circuit extending from ground at the armature |43. It is to be observed at this point that the connector switch I1 is still vheld in its operated position by virtue of the fact that the by way of the armatures II3 and |16, the closed off-normal contacts |48, and through the winding of the relay |69 to battery. The release magnet thereupon, in a well-known manner, actuates its associated ratchet'to permit the wipers 40 to 42, inclusive, to be restored to normal. When the wipers reach their normal or home positions, the off-normal springs |41 and |48 are restored to normal in a well-known manner. Restoration of the relay |10 also causes the multiple locking cir,-

cuit for `the. lrelays |40 and .|60 to v'be opened .at the'armature |'|I, whereby these relays are permitted to restore. Thus, the control equipment included .in the connector switch is restored to normal `and the switch is ready for further use. `In the vevent the talking `loop is interrupted at the called substationC before the calling `party at the substation A hangs up, the battery reversing -relay is the first to fall back. This relay thereupon interrupts. at its armature HI, the multiple locking circuit for the relays |40 and '|50 and prepares, at 'its armature |75, a circuit for energizing the release magnet |59. Under .the conditions stated, theentire switch train preceding the 'connector Il is held in its operated condition until the talking loop is interrupted at the calling lsubstation A. When this occurs, the 'relay lHill restores to cause .the reoperatio-n of the relay |35 and to interrupt the 'circuit for the holding relay H0. The relay |39, upon reoperating, removes .multiple groundfrom the control conductor 22 so that, when the relay IIE) restores its armature H-I, the selector switch II-is released and automatically restores to normal. The steps which followxthe restoration of the relays 'I00 and II@ are from this point on exactly .the same as thoseldescribed in the preceding paragraphs.

As pointed out above, occasions arise when it is extremelydesirable to be able to trace calls to a particular telephone on a party line included inthe system. YIn accordance with the present invention, means are provided, operable in response tothe application of ringing current of the frequency to which the signal device is responsive, for preventing the -means comprising the relay '|.I'0 from initiating the release of an operated selector switch preceding the switch I'I in the above described manner. operated is maintained operated so'long 'as the established' talking loop is not interrupted at-the called telephone; More specically, this means comprises the relay 5180 for causing the operation of the `relay |90, which latter relay, when opera'tcd, prevents the relay I IIJ from removing ground from the control conductor 22 to release the operated selector switch preceding the seized connector fswitch. The winding of the relay |80 is connected in series with a condenser |09 across the line Dconductors 20' and 2| of vthe subscribers line l2, to which line is connected the telephone C it is desired to observe. It will be understood .that this line is ymultipled to the bank contacts of each of 'the group of connector switches at which fthe line I2 terminates, -so that, in the event any of these connector'switches is seized on an incoming call to the line |2, the relay |80 is connected thereacross. The relay I 80 is an alternating Ycurrent relay `designed to be responsive only to current of the ,particular4 frequency to which the signal device at the telephone C is responsive. There are several well-known relays'of this type now commercially available, any one of which is adaptable for use in this particular application. When the relay |80 operates, it completes, at its armature |8|, a circuit for energizing the relay |90. The last-mentioned relay has a number of armatures, including an armature |95 4for closing a locking circuit for itself independently of the relay |80 and an armature for each of the connector switches in which the conductors of the line |2 are multipled. Each of .the armatures |9|, |92, |93, etc., extends to thecontrol conductor of its associated connector switch,'and fthe .respective contacts associated This means when once,

aren-5172 with these :armatures are individually connected to the respective hold conductors of the corresponding connector switches. Thus, the armature |9| is connected by means of a conductor E9 to the control conductor 22 and the contact associated fwith the armature |9| is connected over a conductor 6| to the hold conductor 25. If desired, an additional armature left and associated contact may be embodied in the relay |00 for closing a circuit for energizing an alarm such, for example, as a bell.l Such an alarm is schematically indicated at 52. In `order that an attendant mayhold the switch train operated independently of the condition of the telephone C, i

under observation, there is provided another relay !85 adapted to have its winding bridged across the line conductors 25 and 2| by a key switch 66. It lwill be understood that the winding of this relay, `when connected across the conductors and 2|, functions to maintain the battery reversing relay |19 operated independently of the bridge formed by the telephone at the substation C. y

With the above arrangement it is to be observed that the relay I I G when in one of its two positions, namely, its operatedv position, applies a predetermined potential, i. e., ground potential to the conrol conductor 22 to hold the selector switch I6 operated. In the other of its two positions, or its restored position, this relayy removes ground potential from the control conductor 22 to release the selector switch. It will further be apparent that the conductors 60 and -SI comprise a normally uncompleted path for applying this same predetermined potential. to the control conductor independently of the relay H9, this path being closed and extending from ground at the armature |43, through the armatures |55 and Ill, over the conductors 25 and 6 through the armature I 9| and over the conductor 59.

In the operation of the above-described arrangement and assuming that it is desired to observe incoming calls to the telephone C on the line I2, immediately upon the application of ringing current toy this lineof the frequency to which the signal device at the substation C is responsive, the alternating current relay |80 operates to complete a circuit for energizing the relay |90, this circuit extending from ground at the armature |41 through the wiper 42, the contact 45, the control conductor I9 associated with the called line I2, the armature |8| and through the winding of the relay |90 to battery. The last-mentioned relay operates to complete at its armature |95, a locking circuit for itself and to close all of its armatures -|9I, |92, |93, |94, etc., to their respective associated contacts. Closure of the armature |94 to its associated contact initiates the operation of the alarm device 62, thereby indicating to an attendant in the exchange wherein the connector switch II is located that a call is being made to the telephone under observation. If the called line is answered, the attendant may, by connecting an operators telephone across the conductors 20 and 2| at the jack 51, converse with the-called party and determine whether or not the call is to be traced. If the call is to be traced, the attendant may, by observing the con- .dition of the selector switch I5, determine the line extending to the second exchange on which the call was initiated. By operating the key switch -66 to its locked OIT-normal position, the attendant may. place a bridge across the line conductors 20 and 2| comprising the winding of the .relay to hold the battery reversing relay 7.5

|10 operated. When this is done, the called party at the telephone C may hang up immediately after conversing with the attendant and before the call is traced.

It is the function of the means comprising the relays |10, |80 and |90 to prevent theselector switch I6 from being released in case the calling party interrupts the talking connection lmmediately after its completion and before the attendant can receive instructions as to whether or not the call should be traced. Thus, let it be assumed that the calling party hangs up shortly after the call is answered at the called substation. When this occurs, multiple ground is removed from the control conductor 22 at the armature I3I of the relay |30, and the relay` IIO restores as described above. When the relay IIO restores, it removes ground from the control conductor 22 at its armature III and normally this last operation would permit the selector switch I 6 to be released. As noted above, however, when the relay |90 is locked operated at the armature |95, the previously traced path including the conductors 60 and 6| is completed so that groundy is maintained on the control conductor independently of the relay IIO. The operated selector switch, preceding the connector switch I1 is, therefore, held in its operated condition until such time as the call is cleared out at the called substation or the operator removes the bridge across the conductors and 2| by operating the switch 66 to open the contacts thereof. Also, and as described previously, the relays |10, |40 and |50 are held operated by virtue of the multiple locking circuit extending from ground at the armature |43, until such time as the bridge across the loop comprising the line conductors 20 and 2| is removed. With the system in this condition and when the loop is interrupted at the called substation or at the switch 66, the relays |10, |60 and |40 restore, in the order named, and the release magnet |69 operates. The first-mentioned relay upon falling back interrupts, at its armature I1I and the associated lower contact, the previously traced alternative path from ground to the control conductor 22, so that when the relay I 40 restores, ground is completely removed from the control conductors 22 and I9. Thereupon, the relay |90 restores to interrupt, at its armature |95, its locking circuit and to open, at its armature I9I, a further point in the alternative path including the conductors 60 and I I. Removal of ground from the conductor 22 permits the operated selector switch to release and thus this switch and the connector switch I1 are restored to normal.

It will be evident that, in an instance when the line to a telephone under observation is seized by a connector switch but the call is not answered, the switch train comprising the operated connector switch and the selector switch preceding the same should be subject to release when the connection is interrupted at the telephone of the calling party. That this :'mode of operation is provided is evident from the fact that the battery reversing relay is only operated when the talking loop is completed to the telephone under observation. Thus, when this condition prevails, the battery reversing relay |10 is not operated and, consequently, the above-traced alternative path for applying ground potential to the control conductor 22 is not completed. Hence, when the relay IIIl restores its armature I I I, following the interruption of the loop at the calling telephone, ground is completely removed lease magnet |69 so that the wipers 40 to 42,`

inclusive, of the connector switch are permitted to return to their respective normal positions and ground is removed from the control conductor I9 associated with the called line I2.

Upon removal of ground potential from the conductor I9, the above-traced locking circuit for the relay |90 is interrupted and thisr relay restores, thereby returning the equipment to its normal condition.

Although the operation described in the pre,-

ceding paragraph is that which will ordinarily" occur in the event the call is not answered at the called telephone, it is pointed out that an attendant may hold up the switch train leading to the called line independently of whether` orI not the call is answered at the telephone under observation. Thus, when the alarm 62 Starts to operate, immediately upon the application lof ringing current to the line I2, the attendant may,

by actuating the key switch 66, place the bridgek comprising thewinding of the relay |85 across the line conductors 20 and2| to cause theoperation of the battery reversing relay |10. When this is done, the condition of the connector switch is exactly the same as that which prevails whenV the called telephone is answered. In other words,`

the switch train comprising the operated selector switch and the connector switch I1 is held operated following the interuption of the loop at the calling substation.

As pointed out previously, the arrangement of the system is such that, when the line leading to the Vtelephone to be observed is seized by any one of the group of connector switches in the bank contacts to which this line is multipled, groundis present on the control conductor of this line and the relay |90 is operated'. Hence, all of the armatures I9I, |92, |93, etc., are closed to their respective associated contacts, and the paths for applying ground potential to'the respective control conductors of the connector switches included in the group, independently of their respective hold relays, such, for example,

v as the relay IIO, are partially completed. Since,

however, these paths are only fully completed when the corresponding battery reversing relays,v

such, for example, as the relay |10, are operated,

, a switch train set up in an attempt to establish a connection to the observed telephone when the associated line is busy, is not held operated 'when the calling party hangs up and until the connection which created the busy kcondition of the line is cleared out.

Thus, in the sequence of operations just described, and if the line I2 is busy, the calling party receives busy tone and hangs up, where' upon the relays included in the connector switch restore to permit the release of the operated selector switch in the exact manne-r described above. This is possible because the battery reversing relay |10 is not operated when the lineV I2 is found busy and, hence, the path for applying ground by way of the conductors 60 and 6| to the control conductor 22, independently of the contacts associated with the armature III, is held open at the armature I1I and its associated lower contact.

As pointed out in the introductory portion of this specication, means are provided whereby the entire switch train leading to the telephone C may be held operated even though a call to this line is initiated on a subscribers line of the rst exchange shown in Figure l. This means comprises, in addition tothe apparatus already described for holding the selector switch in the second exchange operated, the relays 230 andY 2B!) in the repeater 16. The release of this repeater and the portion of the switch train preceding the same is normally under the control of the party at the calling substation. Thus, the

Vcalling party may, at any time before or after a connection to the called telephone is established, hang up his receiver and thereby interrupt the previously traced operating circuit for the line relay 24B. 'This relay, upon restoring, normally opens the circuit holding the hold relay 250 operatedwhich latter relay in turn, upon restoring, removes, at its armature 25|, ground potential from the control conductor 14 to initiate the release of the selector switch 10 and the line switch leading to this selector switch. Thus, it

, will be seen that the line relay 240 comprises con- Thus, when the connectionis established to the called line |2 and the telephone at the substation C is answered, the battery reversing relay |10 operates as described above to reverse battery back over the vline conductors 30 and 3| for energizing the relay 238, this circuit extendwhich are connected, respectively,'to the trunk line, conductors 86 and 81. Thereafter, and when the calling party hangs up to cause the restoration of the line relay 240, a circuit is completed ing from battery at the upper winding of the'relay |00, through the armatures |15 and |14 of the relay |10, over the conductors 3| and 81, through the operated armature 264, the restored armature 242 andthe winding of the relay 230 to ground.

-The relay 230 upon operating completes, at its armature 23|, a multiple circuit for holding the relay 200 operated. The latter relay, in its operated position, retains, at its armature 204,

` ground on the conductor 90 and thereby maintains the hold relay 250 in its operated position. The relay 250 in turn maintains, at its armature 25|, ground on the control conductor 14 to hold the p ortion of the switch train precedingY the repeater 16 in its operated condition.

It will be evident in View of the foregoing description that, so long as the battery reversing relay |10 is maintained operated, the switch train leading to and including the repeater 16 is not permitted to release. Consequently, and when the attendant in the second exchange determines that the selector switch I6 is operated, he may,

65 by conversing with an attendant in the rst eX- changeover another trunk line, instruct the latter attendant to trace the connection leading to the trunk line 86, 81. The attendant in the first exchange may do this by observing the condition of the operated selector switch 1D and the line switch I3.

When the connection is finally cleared out at Y the telephone under observation or at the switch 66, the battery reversing relay |10 restores to interrupt the previously traced circuit holding the lrelay 23|)A operated. This'relay'upon frestoringopens, at its armature 23|, the multiple circuit for the relay 20D, thereby to initiatev the sequential restoration of the relays 25D, 25|! and 260. g

When the relay 250 restores, it removes, at its armature 25|, ground from the control conductor 1'4 and permits the switch trainV leading to the repeater 1B to release.

From the foregoing description it will be apparent that, underany conditions following theI 'completion of a talking loop between a calling substation and the telephone under observation, it is possible to traceaY call to the latter telephone, and this is true irrespective of whether" the call is initiated on` a line extending to the' same exchange as the line ofthe telephone under observation, or is initiated on a line extending to an exchange different from lhat' of lthe line associated with the telephone under, observation. It will further be evident that the means provided for this purposel is selectively responsiveto the application of ringing current Y,cf-a particular character to the line of the telephone under observation and that, as a result,A` calls to a particular telephone connected to a party line may be traced.

While there has been described what is at present considered to bev the preferred embodiment ofthe invention, it will be understood thatl various modifications may be made therein, and it is contemplated in theV appended claims to cover all such modications as fall within the true spirit and scopevof the invention.

I claim:

1. In a telephone system, a irstline, a second :A

line, a first telephone on said `iirst line, a second telephone on said second line, means for establishing a connection between said lines on a call from said iirst telephonerto said second telephone, said means normally being releasable ing response to an operation performed at said rst telephone, means operative during the establishing of said connection for applying ringing current to said second,lineand means including means. responsive to the application of ringing current to said second line for preventing the release of said first-named means in response to an operation performed at said rst telephone,

whereby calls to said second telephone may be v traced byan attendant.

2. In a telephone system, a first line, .a second 1 line, a rst telephone .on said first line, a second telephone on said second line, means for establishing a connection between said lines onM a call from said rst telephone to said second' telephone, said means normally being releasable in response to an operation performed at said first telephone, means operative during the establishing of `said connection for applying ringing',

,current 4to vsaid vsecond line, a relay associated with said second line and operable in response to the application of ringing current thereto, and means `including means responsive to the operation of said. relay for preventing the release of s aid first-named means in response to an voperation performed at said rst telephone.

3. In a telephone system, a rst line, a second line including a control conductor, a rst telephone on said first line, a second telephone on said second line, means for establishing a connection between said lines on a call from said rst telephone to said second telephone, said means including means for applying a predetermined potential to said control conductor and normallyA being releasable in response to an operation performed at said rst telephone, means operative during the establishing of said connection for applying ringing current to said second line, a relay associated with said secondline and operable in response to the application of ringing current thereto, means including a second relay operable in response to the Operation of said first-named relay for preventingl the release of said rst-named means, and a circuit for maintaining said second relay operated independently of said first-named relay and so long as said predetermined potential is maintained on said control conductor, said circuit being completed upon the operation of said second relay.

4. In a telephone system, a rst line, a second line, a first telephone on said first line, a plurality of telephones on said second line, each of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive to ringing current of a character diierent than that of the current to which each of the other signal devices is-responsive, means for establishing a connection between said lines on a call from said first telephone to one of said plurality of telephones, said means normally being releasable in response to an operation performed at said iirst telephone, means operative during the establishing of said connection for applying ringing current to said second line, said current being of the character to which only the signal device associated with said one telephone is responsive, and means including means responsive to the application of ringing current to said second line of the character to which only the signal device associated with said one telephone is responsive for preventing the release of said first-named means, whereby calls to said one telephone may be traced by an attendant. Y

5. In a telephone system, a first line, a second line, a rst telephone on said first line, a plurality of telephones on said second line, each of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive to ringing current of a character different than that of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on a call from said rst telephone to one of said plurality of telephones, said means normally being releasable in response to an operation performed at said first telephone, means operative during the establishing of said connection for applying ringing current to said second line, said current being of the character to `which only the signal device associated with said one telephone is responsive, means including means responsive to the application of ringing current ifo said second line of the character to which only the signal device associated with said one telephone is responsive for preventing the release of said first-named means, whereby calls to said o-ne telephone may be traced by an attendant, and means for preventing said last-named means from operating in the event said second line'is busy at the time said call is initiated.

6. In a telephone system, a iirst line, `a second line, a rst telephone on said rst line, a plurality of telephones on said second line, each of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive to ringing current of a character diierent than that of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on rality of telephones, said means normally being releasable in response to an operation performed at said'rst telephone, means operative during the establishing of said connection for applying ringing current to said second line, said current being of the character to which only the signal device associated with said one telephone'is responsive, means including means responsiveto the application of ringing current tosaid second line of the character to which only the lsignal device associated with said one telephone is responsive for preventing the release of said first-named means, whereby calls to said one telephone may be traced by an attendant, and means' for V preventing the application of ringing current to isaid a call from said first telephone to one'of said 'plusecond line in the event said second line is busy at the time said call is "initiated, whereby said lastnamed means is prevented from operating.

'7. In a telephone system,-a first line, a second ralityof telephones on saidfsecondline, eachof said plurality vof telephones having associated therewith a signal device, each of said signal devices being responsive toI ringing current of 'a character different than that of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on a call from said rst telephone to one of said plurality of telephones, said means normally being releasable in response to an operation performed at said rst telephone', means operative during'the establishing of said connection for applying ringing current to said second line,

the signal device associated with said one telephone is responsive, a relay associated with said v` tionof said relay for preventing the release of said first-named means.

8. In a telephone system, a first line, a second 45 line, a first telephone on said first line, a plurality of telephones on said second line, each `of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive to ringing current of-a character different than that of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on a call from said first telephone to one of said plurality of telephones, said means normally being releasable in response vto an operation performed at said first telephone, means operative during the establishing of said connection for applying ringing current to said second line, said current being of the character to which only the signal device associated with-said one telephone is responsive, a relay associated with said second line and operative only in responseto the application of ringing current to said second line of the character to which the signal device associated with said one telephone is responsive, and means including means operable in response to the operation of said relay for preventing-the release of said rst-named means, said last-named means being maintained operated independently of said relay following the operation thereof." e

9. In a telephone system, a rst line, a second line including a control conductor, a first telephone on said rst line, a plurality of' telephones ,connection for applying ringing current to said second line, said current being of the character to whichV only'the signal device associated with saidone telephone is responsive, a relay associated With said second line Vand operative in response to l,the application of ringing current to said second line oftheV character towhich the signal device associated with said one telephone is responsive, means including a second relay operative in respense to the operation of said first-named relay for preventing the release of said first-named means, and a circuit for maintaining said second relay operated independently of said first-named relay and so long as said predetermined potential `is maintained on said -control conductor, said circuit being completed upon operation of said secfond relay.

10. In a telephone system, a first line, a second line, a first telephone on said first line, a plurality of telephones on said second line, each of said plurality of telephones having associated therewith a signaldevice, each of said signal devices being responsive to alternating ringing current of a frequency different from the frequency of the curyrent to which each of the other signal devices is responsive, means for establishing a connection be- -tween said lines on a call from said first telephone to one of said plurality of telephones, said means normally being releasable in response-to ,an operation performed at said first telephone, means operative during the establishing of said connection for applying ringing current to said second line,

-said current being of the frequency to which only .the signal device associated with said one telephone is responsive, and means Vincluding means responsive to the application of ringingcurrent to said second line of the frequency-to whichthe signal device associated with said one telephone is responsive for preventing the release of said firstnamed means, whereby calls to said one telephone may be traced by an attendant.

11. In a telephone system, a first line, a second line, a first telephone on said first line, a plurality of telephones on said second line, each of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive to alternating ringing current of a frequency different from the frequency of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on a call from said first telephone to one of said plurality of telephones, said means normally being releasable in response to an operation performed at said first telephone, means operativeduring the establishing of said ,connection for applying ringing current to said second line, said current being of the frequency to which only the signal device associated with saidone telephone is responsive, a relay associated `with Ysaid second line and operative only in rcsponse to the application of ringing current to saidsecond line of the frequency to which the signal deviceassociated with said one telephone is responsive, and means :includingrmeans responsive to the operationrof said relayA for preventing the release of said iirst-namedmeans.

, l2, In a telephone system, a first line, a sec- Vond line-including a control conductor, a first telephone on said lfirst line, a plurality of telephones onsaid second line, each of said plurality of telephones having associated therewith a signal device, each of said signal devices being responsive toA alternating ringing current of a frequency different from that of the current to which each of the other signal devices is responsive, means for establishing a connection between said lines on a call from said first telephone to said second telephone, said means including means for applying apredetermined potential to said control conductor and normally being releasable in response to an operation performed at said first telephone, means operative during the establishing of said connection for applying ringing currentvto said second line, said current being of the frequency to which only the signal device associated with said one telephone is responsive, a relay associated with said second line and operative in response to the application of iTg5 ringing current to saidy second line of the frequency to which the signal device associated with said one telephone is responsive, means including a second relay operative in response to the oper-- ation of said first-named relay for preventing the 3Q release of said first-named means, and a circuit for maintaining said second relay operated independently of said first-named relay and so longas said predetermined potential is maintained on said control conductor, said circuit being com- 3 5 pleted upon operation of said second relay.

13. In a telephone system, a first line, a second line, a first telephone on said rst line, a

second telephone on said second line, means including a selector switch and a connector switch, 4 0

4operable in the order named, for establishing a connection between said lines on a call from said first telephone to 'said second telephone, said selector switch including a control conductor adapted during the establishing of said connection, said selector switch being maintained operated so long as said predetermined potential is maintained on `said kconductor and being released when said potoV have a predetermined potential applied thereto ,4:5

tential is removed from said conductor, controlla) means in said connector switch for holding said" predetermined potential on said conductor and for normally removing said predetermined potential therefrom in response to an operation performed at said first telephone, means operative during the7 55 of said control means, means responsive to the ap-,go

for partially completing said path, and means responsive to the completion of a talking connection between said telephones for completing said path.

Yline,.a first telephoneon said first line, a plurality of telephones on said second line, each of said pluralityof telephones having associated there- -plication of ringing current to said second line Y T265 14. In atelephone system, a first line, a second with a signal device, each of said devices beingfqo responsive to ringing current of. a character different from that of the current to which each of the other signal devices is responsive, means includinga selector switch and a connector switch,

` operable, in the order named, for establishing a,v '(5 connection between said lines on a call from said rst telephone to one of said plurality of telephones, said selector switch including a control conductor adapted to have a predetermined potential applied thereto during the establishing of said connection, said selector switch being maintained operated so long as said predetermined potential is maintained on said control conductor and being released when said potential is removed from said conductor, control means in said connector switch for holding said predetermined potential on said conductor and for normallyremoving said potential therefrom in response to an operation performed at said rst telephone, means operative during the establishing of said connection for applying ringing current to said second line, said current being of the characterto which the signal device associated with said one telephone is responsive, and means responsive to the application of ringing current to said second line of the character to which only the signal device associated with said one telephone is responsive for applying said predetermined potential to said control conductor independently of said control means.

15. In a telephone system, a rst telephone, asecond telephone, means including a first selector switch, a second selector switch and a connector switch, connected in tandem and operable in the order named, for establishing a connection between said telephones on a call from said first telephone to said second telephone, said selector switches normally being releasable in response to an operation performed at said rst telephone, means operable during the establishing of said connection for preventing the release of said second selector switch, an alarm device, means included in said connector switch and operable during the establishing of said connection for causing the operation of said alarm device, and means operable substantially simultaneously with the completion of said connection for preventing the release of said first selector switch in response to an operation performed at said first telephone, whereby calls to said second telephone may be traced by an attendant.

16. In a telephone system, a rst telephone, a second telephone, means including a first selector switch, a second selector and a connector switch, connected in tandem and operable in the order named, for establishing a connection between said telephones on a call from said first telephone to said second telephone, said first selector switch normally being releasable in response to an operation performed at said first telephone, a relay in said connector switch operatedwhen said call is answered at said second telephone, an alarm device, means included in said connector switch and operable during the establishing of said connection for causing the operation of said alarm device, and means responsive to the operation of said relay for preventing the release of said rst selector switch in response to an operation performed at said rst telephone, whereby calls to said second telephone may be traced by an attendant.

17. In a telephone system, a rst telephone, a second telephone, means including a selector switch, a repeater, and a connector switch, connected in tandem and operable in the order named, for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said selector switch normally being releasable in response to an operation pernamed, for establishing a connection between saidV telephones on a call from said rst telephone to said second telephone, said selectorv switch normally being releasable in response to an operation performed at said first telephone, a relay in said connector switch operated when said call is answered at said second telephone, and means included in said repeater and responsive to the operation of said relay for preventing the release of said selector switch in response to an operationl performed at said first telephone, whereby calls to said second telephone may be traced by an attendant.

19. In a telephone system, a first telephone, a second telephone, means including a selector switch, a repeater and a connector switch, connected in tandem and operable in the order named for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said selector switch including a control conductor adapted to have a predetermined potential applied thereto during the establishing of said connection, said selector switch being held operated so long as said potential is maintained on said conductor and being released when said potential is removed therefrom, control means included in said repeater for maintaining said potential on said conductor and for normally removing said potential from said conductor in response to an operation performed Y at said first telephone, a relay in said connector switch operated when said call is answered at said second telephone, and means included in said repeater andresponsive to the operation of said relay for maintaining said predetermined potential on said conductor independently of said control means.

20. In a telephone system, a first telephone, a second telephone, means including a selector switch, a repeater and a connector switch, connected in tandem and operable in the order named, for establishing a connection between said telephones on a call from said first telephone to said second telephone, said selector switch including a control conductor adapted to have a predetermined potential applied ther-etc during the establishing of said connection, said selector switch being held operated so long as said potential is maintained on said conductor and being released when said potential is removed therefrom, control means included in said repeater for maintaining said potential on said conductor and for normally removing said potential from said conductor in response to an operation performed at said rst telephone, a vbattery reversing relay in said connector switch operated when said call is answered at said second telephone, and means including a relay in said repeater operated in re-V sponse to the operation'of said battery reversing relay for maintaining said predetermined potential on said conductor independently of said control conductor.

NORMAN H. SAUNDERS.

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