US930512A - Telephone-exchange system. - Google Patents

Description

H. GrWEBSTER. TELEPHONE EXGHA NGE SYSTEM. APPLICATION FILED AUG. 4, 1904.

930,512. Patented Aug. 10,1909.

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H. G. WEBSTER. TELEPHONE EXGHANGE SYSTEM.

APPLICATION 'IILBD AUG. 4, 1904.

Patented Aug. 10, 1909.

2 SHEETS-SHEBT 2.

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HARRY G. WEBSTER, OF ;OHIOAGO, ILLINOISIZASSIGNOR TO MILO G..KELLO G G, OF CHICAGO,

. ILLINOIS.

Specification ofgLetters Patent.

TELEPHONE-EXCHANGE SYSTEM.

Patented Aug. 10, 1909.

Application filed Augusta, 1909.. Seri.a1;No..21.9,l3.

. Improvements in lelephone-Exchange Systems, of-which the following is a full, clear,

concise, and exact description,reference being had to the accompanying drawings, forming a part of this specification.

My invention relates'to central battery systems in which subscribers lines extend from sub-stations to an exchange, and are.

there associated wit-licord connecting apparatus, the said connecting apparatus including a supervisory signal or signals, which are controlled throughthe manipulations of the operator, andthe actuation of the subscribers hook switch jointly. Systems of this character have been devised in which the supervisory signal is a .small incandescent lamp, its circuit being controlled by a diiierentially wound relay having its two windings included inthe two talking strands of the cord circuit. In such "systems it-is necessary that. the line wire leading from one side of thc central battery be normally connected to ground'througha contact associated with the subscribers hook switch, the ground connection being automatically broken whenthe telephone-is taken for c011- versaticn. In other systems which have gone into use, the-use of a ground at the subscribers station isavoidcd by using two relays, one'for each of the talking strands of the cord circuit. in such-systems the supervisory signal is in alocal circuit controlled by the joint action of the two relays.

The object of myinvention is to provide means by which the ground atthe subscribers-station is rendered unnecessary, and-to simplify, the cord connecting apparatus. This is accomplished by associating with the cord circuit a relayhavingcontacts which have two operative positions (besides the normal one) controllingthe local circuit of the supervisory signal. Relays of this type are characterized by having two ,armatures with springatension adjustment, or-having two armatures one being of greater magnetic permeability than the other, or having a single armature arranged to'assuine two operative positions, (as distinguished from its normal position) determined by the {degree of-energ-ization oi' the relay inagnet,-and I- line.

eludes an answering plug 16 anda calling do notwish to limit-myself to any particular construction in such -a relay.

In the accompanying drawings illustrating a preferred form of myinvention I have shown diagrammatically,-in Figure 1, two complete line circuitsoi the three wire type in association with cord connecting apparatus utilizing the special relay, and indicating the two operative positions of the relay contacts Fig. 2 indicates the'normal position of the relay contacts. Fig. 3 is a diagram of-a' well known two wire line circuit using a line-relay and a cut-oii relay.

Fig. 4 isthat of a two wire line circuit in which the line and cut-0H relays are replaced by a single relay, and Fig. 5 shows diagrammaticallycord connecting apparatus adapted for association with either line circuit, thusillustrating-two modifications of my invention. Fig. -6 illustrates the mechanical arrangement of one type of cord relay which may be'usedin my invention.

Similar'characters refer to corresponding parts in the various drawings.

Referring to Fig. -1 the subscribers stations A and B are providedwith the usual apparatus adapted preferably for use with a central source of current supply and/coinprising a-transmitter t, an induction coil 2' and receiver 1" in a circuit which stands normally open at'the-hook switch 7L, the bell o and condenser cbeing in circuit with the line when the hook switch is depressed. Undeimnormal conditions limbs l and 2 of the line extend to the central oiilce and are there connected to the jacks 7-7 limb 1 being also carried through contacts 3-10 of thecut-ofi' relay 5, and the winding 01" relay.1l,-'to.the active side of the central battery 12; and limb 2 is carried through contact i of the cut-off relay to the ground or return sideof battery 12. The winding of the cut-off relay is of comparatively high resistance and is interposed between the test pieces or thimbles 6-6 of the jacks, and the ground G; and'the thimbles 66 are so arrangedthat upon the insertion of a plug into aLline jack an electrical connection is established between the thimbles 6 and sleeve springs 9 of the jacks associated with the The cord connecting apparatus inplu-g 17,-the'plug tips 18-19 being united by'strands 2O and21 and condenser a6; and the plugsleeves22-23 by strands 24c-25 and condenser 27 and the usual listening-in key 28, ringing key 32, calling generator 33 and operators set 29 are provided. A supervisory relay 34 is associated with the answering plug and controls the circuit of the supervisory signal lamp 403' and the supervisory relay 41 is associated with the calling plugl? and controls the circuit of supervisory lamp 47 as well as certain connections concerned in the busy test, which will be explained later. The supervisory relay 34 is so adjusted that when energized to a limited extent contact 3'7 will engage contact 38, but will not bring it out of engagement with contact 39, the normal position of this relay being indicated in Fig. 2. Relay 41 is so arranged and adjusted that when energized to a limited extent contact 44 will engage contact 45, but contact 45 will still remain in engagement with contact 46. Contacts 48-49 of this relay will also be brought into engagement when the relay is partially energized. When either relay is energized to a greater extent the contacts 3839 or 45-46 will be separated by the further movement of the armature contact 37 or 44 respectively.

Subscriber A in calling moves his receiver from its hook switch completing a circuit of relay l1 and lighting the lamp 14 in the usual manner. Upon the insertion of the answering plug 16, current flows from battery 12 through windin of relay 34 and thence through the wine ing of cut-off relay 5, causing the actuation of relay 5 and thereby disconnecting line relay 11, extinguishing the lamp 14, and removing the normal ground of the line at contact 4. At the same time current. is supplied to the subscribers instrument through windings 3536 of re layr34, causing the complete actuation of the relay 34 and leaving the lamp 4O unlighted,

' as shown in the drawing. After ascertaining the. line desired for connection (in this case that of subscriber B) the operator tests in the usual manner by touching the tip 19 to thimble 6. Contacts 4849 of the calling supervisory relay 41 stand normally open in order that a test of a busy line may not produce an excessive click in the receivers of the connected subscribers. In case the line tested is busy, current will flow from the thimble of the line tested through tip 19, strand 21, the operators receiver and induction coil winding and impedance coil 31 to the ground. or ofiice return, producing a click in the receiver, in the well known manner. In case the line is idle the operator hearing no click inserts her plug into the jack and rings the subscriber, the current from generator 33 serving to energize relay 5 at this time. Upon the restoration of the ringing key a circuit is completed from bat tery 12 through winding 43, strand 25, plug sleeve 23, thimble 6 and relay 5, causing the continued energization of relay 5. On account, however, of the comparatively high resistance of this circuit and of the arrangement and adj ustment of relay 41 the current which now flows through winding 43 is only suflicient to partially energize relay 41, bringing its contacts into the relation indicated in the drawing. The engagement of contacts 48 and 49 serves to short circuit contacts 50 of the listening-in key 28, so that in case the operator listens in on the connection aft r ringing, the winding 42 will not be disconnected as it is during the making of a busy test. The engagement of contacts 4445 completes the circuit of lamp 47 causing its illumination. When subscriber B removes his receiver in answering, the circuit thus completed is of comparatively low resistance and includes both windings of relay 41; the relay is thus completely energized and the circuit of lamp 47 opened at contacts 454G. lVhcn a subscriber replaces his receiver after conversation, current ceases to flow through line limbs 1-2 and relay winding 36 or 42 and the contacts return to their intern'iediate position, conipleting the circuit of the associated supervisory signal as shown in the case of relay 41. Both lamps when lighted constitute a. signal for disconnection and upon the removal of both plugs all parts assume their normal condition.

In Fig. 3 is illustrated a line circuit differing from that of Fig. 1 in that the bell b and condenser are in a permanent bridge of the line at the sub-station, and the jacks j j at the exchange have but two contact pieces. The thimbles 5t-57 of the jacks serve normally as testing terminals for the line, but when the line is switched for conversation they also constitute connection terminals for the sleeve side of the line.

I ig. 5 indicates a modification of the cord circuit of Fig. 1 adapted for use with the line circuit of Fig. 3 and when associated with this line circuit presents a modification of my invention, the operation of the structure thus indicated being as follows: The subscriber calls in the usual manner by removing his receiver and thus closing a circuit or" battery C through line relay 11 lighting the calling signal lamp 14. ()n the insertion of answering plug 16 the relay 51 is energized by a current from battery C flowing through winding 35 of relay 34, plug and jack contact 2257 and the winding of relay 51 to the return side of the battery. This energizes relay 51 causing the contacts and 55-56 to become separated, thus removing the normal connections of the line with relay 11 and battery C. The actuation of the relay 51 causes contacts 5455 to engage, thus completing a second circuit from contact 57 of the jack through limbs 1 and 9. of the line and winding 36 of relay 34,

causing the complete energization of *relay 34 and preventin'g the illumination of lamp 40, as was described with regard to Fig. l. The calling supervisory relay 69 is similar to relay 3 L, difie-ring in this respect from the calling supervisory relay 4101f Fig. 1. E lie operator tests, plugs inand rings in the usual manner. During' theactuation of the ringing lrey, relay 51 is energized by-current from battery C flowing 'through the resistance 72. The circuit=ot the ringing generator 33 is trom' the {ground or battery return, through plug and jacl =contact 1956, line limbs -21, relay contacts55'54, plug and jack contacts 57- 23, resistance 7 2 andthence through the common circuits of battery C to ground. Uponthe-restoration ol the ringing hey relay 51 is :energized by current through winding 70'of re1ay 69, but as in the systeniof Fig. 1 this current being relatively weak as compared with that which flows when the circuit of the line limbs is closed at thesub-station, the relay 69 is only energized to'a limited extent, causing only theengagement ofcontacts 4L ll5,-thus cl0sing-the circuit of lamp 47, causing its illumination. When the subscriber answers an increased current now flowsthrough winding 70 and through winding 71-of relay'69, causing a'greater energization which serves to separate contacts 454;6, extinguishing the lamp. "Nheneithersubscriber hangs up, the low resistance circuit through the line limbs and winding 36 or -71 being broken the relay isthen energized to a limited extent-only and its contacts-assume the intermediate position, causing the illumination of the lamp to or 47 associated therewith.

Both lamos when'lighted'constitute the signal for disconnection, andupon the removal of the plugs-allapparatus assumes the normalcondition shown in the drawing.

When the cord circuit of 'Fig. 5 isassociated with the line circuit illustrated in Fig. 4- the-operation of thecord circuit apparatus is substantially the same as when associated with Fig.-3. The'line circuit, however, is one in which a single relay 58 is associated with the line instead of the two separate relays 51 and 11 of Fig. 3. This relay 53 has an energizing winding 59 of comparatively low eiliciency, and when the circuit of battery 0 isclosed therethrough (as when the subscriberremoveshis receiver fromthe switch hook) the circuit being completecbthrough contacts 6FG8, limbs 12 and contacts 67-.64E to thereturn side of the battery,-the relayis-only energized to alimited extent and only actuats contact 61, bringing itinto engagement withcontact 62 thus completing a circuit of 7 battery C t irough lamp 1%, which includescontacts 6667 (it, causing the illumination of the lamp. Winding GOof this relay is ofcomparatively high efliciency and resistance.

-i-Vl1en a connecting plug as 16 is inserted,

acircuit 'thus being completed from battery C through winding 35 of relay 3%, plug and jack contacts 22-57 and winding to ground, relay 58 is then energized to a greater extent and causes the separatlon of contacts 67-66-'6 -l,thus opening the 'circuit of lamp l' land 'removingthe normal ground from line limb 2, 'and also causes the separation of contacts '68, 'thus disconnectlng winding 59 "from line limb 1. The greater energization of the relay also brings into engagement contacts 63-67, thus completing a'direct connection from jackcontact 57 t0 limb 2 of the line. If the-sub stationcircuit is openat this time relay 3l'is energized to a limited extent only,-cornpleting the --circuit oflamp' 40through'contaots 37 38--39, causing its illumination. lWhen the circuit is closed at the-sub-station the increasedfiow of current through winding ofrelay 34 and also through winding 36, causes the greater energiz'ati'on ofthe'relay 3 1 to separate contact 38-39, thus extinguishing the lamp. When plugging in to 'calla subscriber the circuit completed through winding 70 of relay 69 and winding-60 of relay 58, being of comparatively high resistance, relay =69 is only partially energized, while relay 58 is completely actuated as previously described. The test is secured in the usual manner, plug tip 19 and jack contact 57 being of the same potential as long as no connection exists with a jack *of the line tested. Vhile ringing, the relay 58 is completely actuated by current :or battery C flowing throughresistance 72 and winding 60.

Fig. 6 indicates the mechanical arrangement of one type of relay corresponding to that indicated as relay 34- orrelay 69. The armature 'a'resting upon the knife edge d is held in place by the pin and nut 77, and is shown in its normal position. The piece 7 6 is a continuation of the relay core. The springs 373-8-39 corres ond'tothe similarly numbered contacts 0 relay 34L; spring 37 normally rests upon the shoulder of the insulating'piece =75;'when the relay is partially energized the armature a is-sufiiciently attracted to'thepole piece fto bring spring 37 into engagement with the contact of spring 38, but the tension of spring 38 is so adjusted by screw 73 orby other obvious means that this limited energization of the relaym'agnet -is not suiiicient to cause a further movement of its armature. lVhen'the relay istenergizedto azgreater extentas by an increased flow of current through its winding or by current through an additional winding, the final movement of the armature cient energizing capacity to cause the re quired increase in energization of its respective magnet when the corresponding line circuit is closed and that the presence of the supplementary windings 36, a2 and Tl upon the same cores as windings 35, 48 and respectively, is not essential to the operation of my invention; the requirement being merely that the windings, which are in cluded on said cores, shall be suiiicient to secure the intermediate and final positions of the armatures or contacts associated therewith.

To recapitulate I have indicated in the Various drawings structures in which the insertion of a plug into the jack of an idle line causes the supervisory relay associated therewith to be energized to a limited extent to complete the circuit of its supervisory signal, and in which the completion of the circuit through the line limbs causes a greater energization of the supervisory relay to again efface the signal.

Where the term, operative earth connection is used in the following claims, it is to be understood as meaning a ground or third conductor connection, required for the proper operation of the supervisory signal.

While I have indicated in Figs. 3, 4: and 5 separate batteries CCC it will be obvious to those skilled in the art that these may be one and the same battery; also that the various grounds shown indicate the return side of the central oflice battery or batteries;

/Vherever in the following claims I have referred to the non use of a line, it is to be understood that I am referring to that condition in which the telephone of the as sociated line is not in use, rather than to the condition of a connection being established with said line at the central office.

Wherever in the following claims I refer to the use of a line, it is to be understood that I am referring to the conversational circuit being established.

It will be understood that although I have illustrated a cord circuit directly uniting two subscribers circuits without any intermediate or trunk connecting link, yet my invention is not limited to such a direct connection between subscribers in a single switchboard or in the same central oflice.

Wherever in the following claims I refer to a telephone line, it will be understood that said term is not limited to a line extending from a subscribers station and terminating at a central oilfice.

It will also be obvious to those skilled in the art that my invention is not confined in its application to switch board systems of the character illustrated in the drawings, but that it may be applied to and utilized in other telephone exchange systems and in signaling systems in general, and I therefore do not limit myself to the precise structures or circuit arrangements illustrated in the accompanying drawings but I claim:

1. A telephone exchange system including telephone lines extending to a central oiiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring ack, to connect one of said line conductors with one strand of its associated link circuit, and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relay magnet winding included in a relatively high resistance connection extending between said third conductor and a return conductor maintained at a potential different from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet will be energized to destroy the substation control of its associated line signal, a supervisory signal, and a unitary supervisory magnet for exercising sole control over said supervisory signal.

2. A telephone exchange system including telephone lines extending to a central ofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated link circuit, and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relatively high resistance relay magnet connected between said third coiiductor" and areturn conductor maintained at a potential different from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet will be energized to destroy the substation control of its associated line signal, a supervisory signal, and a unitary supervisory magnet for exercising sole control over said supervisory signal.

telephone lines extending to a central oliice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link cir cuits at said switchboard tor uniting said lines for conversation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapt-ed, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated link circuit and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relay magnet winding included ina relatively high resistance connection extending between said third conductor and a return conductor maintained at a potential difierent from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relayvmagnet will be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor through a signal producing device to the testing contact piece of a plug whereby when said testing contact piece of the plug is engaged with said third contact piece of a spring jack of a line, a flow of current will result through said test circuit it another plug be inserted intoanother spring jack of the same line, and whereby, it no connection exists with said line, no test indication will result, a supervisory signal, and a unitary supervisory magnet for exercising sole con trol over said supervisory signal.

l. A telephone exchange system including telephone lines extending to a central ofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for. extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation,- spring jacks for said 3 lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with athird conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack,

to connectone of said line conductors with one strand of its associated link circuit, and

a a to connect the other line conductor with the 3. A telephone exchange system including other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relatively high resistance relay magnet connected between said third conductor and a return conductor maintained at a potential different from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet will be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor through a signal producing device to the testing contact piece of a plug whereby, when said testing contact piece of the plug is engaged with saidthird contact piece of a spring jack of a line, a flow of current will result through said test circuit if another plug be inserted into another spring jack of the same line, and whereby, it no connection exists with said line, no test indication will result, a supervisory signal, and a unitary supervisory magnet for exercising sole control over said supervisory signal.

5. A telephone exchange system including telephone lines extending to a central ofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard tor uniting said lines forcoi-i versation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated link circuit, and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish. current overthe metallic circuit of said line, a relay magnetwinding included in a relatively high resistance connection extending between said third conductor and a return conductor maintained at a potential diiierent from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet will be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor through a signal producing device to the testing contact piece of a plug whereby, when said testing contact piece of the plug is engaged with said third contact piece of a spring jack of a line, a flow of current will result through said test circuit if another plug be inserted into another spring jack of the same line, and whereby, if no connection exists with said line, no test indication will result, a winding of a signal controlling electromagnet associated with said link circuit and adapted to be included in circuit with said source of current and with said relatively high resistance connection when said link circuit is connected with the line, whereby said signal controlling electromagnet is caused to display its signal and a second winding on said electromagnet under the control of the substation switch for causing the effaceinent of said signal by causing a flow of current over the line circuit and through said second winding.

6. A telephone exchange system including telephone lines extending to a central ofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected with a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated link circuit, and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relatively high resistance relay magnet connected between said third conductor and a return conductor maintained at a potential different from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet will be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor through a signal producing device to the testing contactpiece of a plug, whereby when said testing contact piece of the plug is engaged with said third contact piece of a spring jack of a line, a flow of current will result through said test circuit it another plug be inserted into another spring jack of the same line, and whereby, it no connection exists with said line, no test indication will result, a winding of a signal controlling elect-romagnet associated with said link circuit and adapted to be included in circuit with said source of current and with said relatively high resistance relay magnet when said link circuit is connected with the line, whereby said signal controlling electromagnet is caused to display its signal, and asecond winding on said electroinagnet under the control of the substation switch for causing the efl'acement of said signal by causing a flow of current over the line circuit and through said second winding.

7. A telephone exchange system including telephone lines extending to a central ofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation, spring jacks for said lines, each provided with three contact pieces, two connected with their associated line conductors and the third connected *ith a third conductor normally disconnected from said line conductors, connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated link circuit, and to connect the other line conductor with the other strand of its link circuit and with said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relay magnet winding included in a relatively high resistance connect-ion extending between said third conductor and a return conductor maintained at a potential different from that pole of the source of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relay magnet vill be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor through a signal producing device to the testing contact piece of a plug, whereby, when said testing contact piece of the plngvis engaged with said third contact piece of a spring jack of a line, a flow of current will result through said test circuit if another plug be inserted into another spring jack of the same line, and whereby,

ate-by the energization of said relay winding over said circuit and a second winding on said-relay for causing the efiacenient of said signal by a flow of current over the hue circuit under the control of the substation switch.

8. A telephone exchange systein=including telephone lines extendinglto a centralofiice, call signals associated with said lines and adapted to be operated by current over said lines, line conductors for extending said telephone lines to the switchboard, link circuits at said switchboard for uniting said lines for conversation, spring :jacks for said lines, each provided with :three contact pieces, two connected with their associated line conductors andthe third connected with a third conductor normally disconnected from said line conductors,connecting plugs each provided with two contact pieces, adapted, when inserted into a spring jack, to connect one of said line conductors with one strand of its associated linkcircuit, and to connect the other 'line conductor with the other strand of its link circuit andwith said third conductor, a source of current associated with said link circuit and having its two poles connected respectively with the two strands of said link circuit to furnish current over the metallic circuit of said line, a relatively high resistance relay magnetconnect-ed between said third conductor and a returnconductor maintained at a potentialdiii'erent fromthat-pole of thesource of current connected with said third conductor when a link circuit is connected with the line conductors, whereby said relaymagnet will be energized to destroy the substation control of its associated line signal, a test circuit extending from said return conductor-through signal producing device to thetesting contact piece of aplug, whereby, when said testing contact piece of the plug is engaged with said third contact piece of a spring jack of a line, a flowot' current will result through said test circuit if another plug be inserted into another spring jack ofthe same line, and whereby, it no connection exists with said line, no test indication will result, a relay winding associated with said'link circuit and adapted to be included in circuit with said source of cu rent and with said relatively high resistanc relay magnet when said link circuit is connected with a line, a signal associated with said relay winding and caused to operate by the energization of said relay winding over-said circuit and; a second winding-on said relay for causlngthe eftacement ,ofisaid signal ;by a fiow of currentoverthe line circuit under the control of the substation switch.

9. A telephone exchange-system comprising -a two-limb telephone line, a jack for said line having two talking contacts corresponding to the line limbs and a third contact normally disconnected from the other two contacts,;a coiiperatingplug havnig two c'ontacts,one-to engagea talking contact of said jack and the other 'to engage the other two jackcontacts whenever said plug is in position in said jack, a link-circuit having talking strands terininating insaid plug contacts, a .line relay, means normally controlledover said line'to actuate said line-relay, means for disconnecting said hue relay from the line todestroysaid control by the completlon of a circuit through one of said plug contacts, one of said talking strands and the third contact ofsaid ack, a super zvisory signal, and a unitary supervisory re lay for solely controlling said supervisory signal, associated vith said link-circuit.

10. A telephone exchange system comprising a telephone line extending in two limbs from a substationtotheexchange, a line signal at the exchange, a line relay and a source of current normally in circuit with said line,

means *at the substation for closing said circurt 'to display said line signal, a ack for said line having two talklng contacts corresponding to the line limbs and a third contact normally disconnected from the other twoicontacts, a cut-off relay .for destroying thenormal control of said line signal, a con nection from said third. contact of said jack through said cut-ofirelay to one pole of said source of current, a cooperating plug having twocontacts, one to engage a talking contact of said jack and the other to engage the otheritwo jack contacts whenever said plug is in position in said jack, a link-circuit having twotalking strands terminating in said plug contacts, a connection from that plug contact which is adapted toengage the third jackcontact, to that pole of said source of current opposite that :to which said cut-oft 1 relay is connected, a supervisory signal, and a unitary supervisory relay vfor solely controlling said supervisory signal, associated with said link-circuit.

11. A telephone exchange system comprising a telephone line extending in two limbs from a substation to the exchange, a source -ofcnrrent,a line signal, a line relay nor mally connected betweenone liinb ofsaid line and one pole of said source, a normal connection between the other limb of said line and the other pole of said source, means at the substation :for conductively unlting said limbs normally to actuate said line relay to display said line signal, a jack for said source of current, a cooperating plug line and one pole of said source, a normal said line having tip and sleeve talking contacts and an extra sleeve contact normally disconnected from the other two contacts, a cut-0fl relay for destroying the normal substation control of said line signal, a connection from said extra sleeve contact of said jack through said cut-ofl relay to one pole of having atip contact for engaging the tip contact of said jack and a sleeve contact for engaging the two sleeve contacts of said jack whenever said plug is in position in said jack, a linkcircuit having two talking strands terminating in said plug contacts, a supervisory signal, and a unitary supervisory relay for solely controlling said supervisory signal having a winding connected between the sleeve side of said link-circuit and that pole of the source of current opposite to that to which said cut-off relay is connected.

12. A telephone exchange system comprising a telephone line extending in two limbs from a substation to the exchange, a source of current, a line signal, a line relay normally connected between one limb of said line and one pole of said source, a normal connection between the other limb of said line and the other pole of said source, means at the substation for conductively uniting said limbs normally to actuate said line relay to display said line signal, a jack for said line having tip and sleeve talking contacts and an extra sleeve contact normally disconnected from the other two contacts, a cutoff relay for destroying the normal sub station control of said line signal, a connection from said extra sleeve contact of said jack through said cut-elf relay to one pole of said source of current, a cooperating plug having a tip contact for engaging the tip contact of said jack and a sleeve contact for engaging the two sleeve contacts of said jack whenever said plug is in position in said jack, a linkcircuit having two talking strands terminating in said plug contacts, a supervisory signal, and a unitary supervisory relay for solely controlling said supervisory signal having a winding connected between the sleeve side of said link-circuit and that pole of the source of current opposite to that in which said cut-off relay is connected and a winding connected between the tip side of said link-circuit and that pole of said source to which said cut-ofi' relay is connected.

18. A telephone exchange system comprising a telephone line extending in two limbs from a substation to the exchange, a source of current, a. line signal, a line relay nor- 1 mally connected between one limb of said connection between the other limb of said line and another pole of said source, means at the substation for conductively uniting said limbs normally to actuate said line relay to display said line signal, a jack for said line having two talking contacts and an extra contact normally disconnected from the other two contacts, a cut-off relay for destroying the normal substation control of said line signal, a connection from said extra contact of said jack through said eut-oii' relay to one pole of said source of current, a cooperating plug having a contact for engagingone talking contact of said jack, and a second contactfor engaging the two other contacts of said jack whenever said plug is in position in said jack, a link-circuit having two talking strands terminating in said plug contacts, a supervisory signal, and a unitary supervisory relay for solely controlling said supervisory signal having a winding connected between the said second contact of said plug and that pole of the source of current opposite to that to which said cut-off relay is connected.

let. A telephone exchange system comprising a telephone line extending in two limbs from a substation to the exchange, a source of current, a line signal, a line relay normally connected between one limb of said line and one pole of said source, a normal connection between the other limb of said line and the other pole of said source, means at the substation for conductively uniting said limbs normally to actuate said line relay to display said line signal, a jack for said line having two talking contacts and an extra contact normally disconnected from the other two contacts, a cut-oil relay for destroying the normal substation control of said line signal, a connection from said extra contact of said jack through said cut-oft relay to one pole of said source of current, a cooperating plug having a contact for engaging one talking contact of said jack, and a second contact for engaging the two other contacts of said jack whenever said plug is in position in said jack, a link-circuit having two talking strands terminating in said plug contacts, a supervisory signal, and a unitary supervisory relay for solely controlling said supervisory signal having a winding connected between the said second contact of said plug and that pole of the source of current opposite to that to which said cut-off relay is connected and a winding connected between said first-mentioned contact of said plug and that pole of said source to which said cut-off relay is connected.

In witness whereof, I hereunto subscribe my name this 2nd day of August, A. D. 1904;.

HARRY G. WEBSTER.

\Vitnesses FLORENCE WIOKLIN, LUELLA Mnnnrrr.

It is hereby certified that in Letters Patent No. 980,512, granted August 10, 1909, upon the application of Harry G. Webster, of Chicago, Illinois, for an improvement in TelephoneExchange Systems, an error appears in the printed specification requiring correction, as follows: In line 52, page 8, the WOlt and that the said Letters Patent should be read with this correction therein, that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 5th day of October, D., 1909.

[SEAL] C. C. BILLINGS, 7

Acting Commissioner of Patents.

in should read to;

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