US777544A - Telephone system. - Google Patents

Description

4 0 9 1 om 1 Q E D D E m N E T A P J. G. ROBERTS.

TELEPHONE SYSTEM.

APPLICATION FILED FEB, 24, 1902.

Z SHEETSSHEBT 1.

N0 MODEL PATENTED 111111. 13, 1904.

J. G, ROBERTS.

TELEPHONE SYSTEM.

APPLICATION 111.31) 131124, 11102.

2 SHEETS-SHEET 2.

NO MODEL.

' Swan/MM? UNITED STATES Patented December 13, 1904.

PATENT OEEIcE.

SVVITCI'IBOARD AND SUPPLY COMPANY, OF

CORPORATION OF ILLINOIS.

CHICAGO, ILLINOIS, A

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No.

Original application filed December 15, 1899,

777,544., dated Decernbc 13, 1904:.

Serial No. 740,395. Divided and this application filed February 24, 1902. Serial No. 95,155. (No model.)

To all whom it may concern:

Be it known that 1, JOHN G. RoBnR'rs, a citizen of the United States of America, and a resident of Detroit, county of Wayne, and State 5 of Michigan, have invented a certain new and useful Improvement in Telephone Systems, of which the following is a specification.

This application is a division oi my application filed December 15, 1899, Serial No. 740,395, renewed February 23, 1901, Serial The subject-matter of the present application relates more particularly to the supervisory features of a telephone system and the parts cooperating therewith, the object of the invention being to provide a supervisory system that is positive and e'l'licient in operation, that is simple in construction and ar rangement, and one that consists of but few and inexpensive parts.

In the accompanying drawings, forming a part of this specification, in which the preferred form of the invention is illustrated and in which the same reference characters des- 2 5 ignate like parts throughout the several views, Figure 1 a diagram of the system embodying the subject-matter of this application. Fig. 2 is a simplified diagram of the talkingcircuit of ig. 1. Fig. 3 is a diagram in a simplified form of the system of Fig. 1, but with only one battery at the central oliice; and Fig. A is a simplified diagram of the talking-circuit of Fig. 3.

Referring to Fig. 1, two subscribers lines 3 5 L and L are shown extending from their respective substations B and D to the central oiiice C. The limbs 2 and 3 of the subscribers lines are permanently connected together at the substations through the call-bell 4 and 4 the condenser 5, the latter being adapted to permit the passage of alternating or ringing current and to prevent the passage of steady current. A bridge normally open through the telephone-hook 6 extends between the two limbs and includes the receiver 7 and transmitter 8. At the central oiiice these lines center in a switchboard, where they are fitted with switch-sockets, connection terminals or jacks J iT J, the tip conductor 3 terminating in the tip-spring 'of the answering-jack J 5 and is multiplied through the several corresponding contact-terminals of the multiple jacks J and J the conductor 9 serving to connect them to the limb 3. The other conductor or limb, 2, of the telephone-line, which corresponds to the sleeve side of the line, is connected at the central oilice with the ground Or. The tip-spring y' of the answering-jack normally engages a contact-anvil 10, which is connected, by means of a conductor 11, to one 0 side of the winding of the line-relay R and thence to the normal or back contact oi. the cut-oil relay R. The armature oi the said cut ofl relay R is connected, by means of conductor 141, to the point 15, from whence the conductor 16 extends to the common wire I), connected with one pole of the direct-current generator A. The opposite pole of the generator A is connected to the ground Or. The sleeve contact or ring j 01 the answeringjack J is connected, by means of conductors 17 and 18, through the winding of the cutoff relay R to the point 19 upon one side 01'' the line-signal S, which is preferably a small incandescent lamp. The corresponding con tactsof the multiple jacks J J are connected,

by means of like branches 17and a conductor 20, to the branch 17 of the answering-jack J and conductor 18.

From the points 15 and 19, respectively, 0 conductors 21 and 22 extend to the back contact and armature of the line-relay R and comprise when closed together at the said armature and back contacta shunt of the signal S. The "Forward contact of the line-relay R 5 is connected, by means of a conductor 23, with the common lead or conductor I) from one side of the direct-current generator R the other pole oi. which is in connection with the like pole of the generator A.

The cord-circuit, which is adapted to form an operative union between any two circuits of the system, includes the ai'iswering-plug P and the coiinecting-plug P, each having tip and sleeve contacts j) and p adapted to engage, respectively, with corresponding contact-surfaces 7' and f of the jacks when the plugs are inserted therein. The tip-contacts of the two plugs are joined by the strands t and t and the interposed condenser 0. From the tip-strand t of the answering-plug P a conductor 25 extends to the winding of a supervisory relay r and thence to the common Wire D and to one pole of the generator A. The corresponding sleeve-strand s is extended, by means of a conductor 27, through the Winding of a supervisory relay r and thence to the lead D and to one pole of the generator B The armature of the supervisory relay is connected, by means of a conductor 29, with the conductor 25, and its back contactis connected to a conductor 30, which includes the supervisory signal or lamp S, the circuit of said lamp being completed through the forward contact and armature 26 of supervisory relay 9* and the conductor 31 to the conductor 27. Similar supervisory relays 1' and 0' are provided in connection with the tip and sleeve strands and s? of the connecting-plug P and a similar supervisory lamp S has its circuit jointly controlled through the armatures and contacts of said relays. The operators receiver it in conductor 34 is connected by any suitable listening-key 35 and conductor 36 with the strand 6 of the cord-circuit on one side and through the secondary winding 28 and conductor 32 with the live pole of generator A. Her transmitter 33 is included in a local circuit with the primary winding of the induction-coil and a suitable current source. A ringing generator C of usual type is grounded at one pole and is adapted to be connected by conductor 45 and the ringing-key 75, of any usual or desired type, with the tipstrand 5 of the said cord-circuit.

Referring to Fig. 1, the operation of the system will now be described. The subscriber B desiring a connection takes up his receiver and completes the bridge between the limbs 2 and 8 of the line and provides a circuit for current from the generator A over the following path: from the positive pole of the gen erator A, lead D, conductor 16, point 15, conductor 14:, armature and back contact of cutl off relayR', conductor 12, the winding of the line-relay R, conductor 11, tip-contact j of the answering-jack J, line conductor 3, through the substation devices, to the sleeve conductor 2, and back to ground and the negative pole of generator at the central ofiice. This causes the operation of the line-relay R,which attracts its armature and closes a local circuit including the line-lamp S to the generator B which may be traced from the positive pole of the said generator, over lead D*, to the conductor 16, lamp S, conductor 22, armature and forward contact of line-relay R, and back to the generator over the conductor 23 and lead D Upon noticing the signal the operator inserts the answering-plug P of her cord-circuit in the jack J of the subscribers line. In so doing the tip-spring of the jack is lifted from its normal contact, thus opening the circuit of the line-relay R and permitting its armature to close the shunt about the lamp S to extinguish said lamp and remove its resistance from the circuit. At the same time a local circuit through the sleeve-contacts of the plug and jack is established, said circuit including the sleeve-contacts, conductors 17 and 18, the winding of the cut-off relay R, the shunt 22 21 about the lamp S, branch 16, and lead D* to one pole of the generator B the circuit being completed from the opposite pole of the generator through the lead D conductor 27, including supervisory relay 7, 'to the strand 8 of the cord-circuit. The closure of this local circuit causes the operation of the cut-oif relay R to maintain the circuit of the line-relay R open during the established connection. The insertion of the plug also serves to complete a circuit from the generator A, over lead Di and through the wire 25, including relay 1', to the tip-strand t of plug P, thence over the tip side 3 of the telephoneline, through the substation transmitter and receiver, and back to the generator A over the other line conductor, 2, and ground-wire Gr. The supervisory lamp S has its circuit closed through the armature and front contact of the relay 7', but remains inert on account of the opening of its circuit through the armature and back contact of the supervisory relay r. The circuit of this lamp, it is evident, includes the generator B lead Di conductors 25, 29, 30, 31, and 27, and lead D Immediately upon the insertion of the plug P, as stated, the operator depresses the listeningkey 35 to connect her instrument with the cord-circuit to receive the order of the calling subscriber. Upon ascertaining the number of the subscriber wanted the operator proceeds to test the condition of the line wanted. This is effected by touching the tip of her calling-plug, such as P, to the test-ring of the jack of the said line. If such line has just called the central otfice and an operator has not had time to connect therewith, it will be seen from the previously-described operation that the test-rings of the several jacks of the line are connected, by means of conductors 17 20 18 22, the armature and front contact of the line-relay R of that line, the conductor 23, and lead D with the negative pole of the generator B As the tip of the calling-plug P used for testing is connected, through the conductor 36, key 35, and conductors 34 and 32, to the opposite pole of the generator B it is apparent that a circuit will be completed through the operators telephone when the line is so tested and that she will receive a click to inform her of the busy condition of the line. In case a connection has been established with the Wanted line by means of a cord-circuit similar to that shown in the ligure the test-rings of the jacks are connected with the negative pole of the generator B through the sleeve-strand of the inserted cord-circuit and the cond uctor 27 or 27*,and a testing-circuit is therefore again completed to the other pole of the said generator through the tip-strand of the testing-plug and the operators instrument. Upon finding the wanted line idle the calling" plug P is inserted in one of the multiple jacks in the usual manner. The insertion of this plug accomplishes several results: First, the local circuit through the cut-off relay R is established from the positive pole of the generator B", lead D, conductor 16, the short circuit of the line-lamp S, including conductors 21 and 22, the winding of the cutoff relay 1%, the conductors 18 and 20, and the branch 17 of the proper multiple jack to the sleeve-contact of the inserted plug, from whence a circult is extended by the sleeve-cord s" and conductor 27 through the relay-winding to the opposite pole of the generator B. Actuating the relay R prevents the operation of the line-relayR when the subscriber responds, and thus retains the line-signal S in inert condition. The energization of supervisory relay r closes the circuit to the supervisory lamp S. On account of the subscribers telephone not being off its hook the line-circuit is open to steady currents at the substation, and the supervisory relay r which is under the control of the subscriber after the inser-' tion of the plug, is not operated. The supervisory lamp 8 therefore lights over a circuit from the positive pole of the generator B conductors 25 and 29*, armature and back contact of relay r through the lamp S the armature 26 and front contact of relay r conductors 31 and 27, to the opposite pole of the generator B. This light remains active until the response of the called subscriber, when it is rendered inert, as will be hereinafter described. The operator now depresses the ringing-key to connect the ringing-generator C with the cord-circuit to call the wanted subscriber. The said key opens the strand 6 to prevent the ringing-current from passing back over the cord-circuit and making a noise in the waiting-subscribers receiver. The ringingcurrent finds a path from the live pole of the generator over conductor 45, key 75, strand 2?, tip-contacts of the plug and jack, conductor 9, limb 3, through the condenser 5 and bell at at the substation and operating the bell, and thence back over line-limb 2 to ground at the central oifice and the other pole of the ringing-generator. When the subscriber responds, the tip supervisory relay r is operated by current over the line-circuit and the supervisory lamp is extinguished. The subscribers are new in communication. During conversation the supervisory signals S and S are inert by reason of the actuation of the supervisory relays r and r associated wlth the plugs. Current for talking purposes is fed out to the substations from the generator A, which is a :lirect-current generator and may be called the charging-generator, through the supervisory relays r and r which are designed to present suflicient impedance to the passage of voice-currents to prevent short circuiting the same, the said currents being repeated through the condenser c from one end of the strand of the cord-circuit to the other, and thereby from one line to the other. At the termination of the conversation the subscribers return their receivers to the hooks, and thereby open the line-circuits for steady current between the two line wires. This causes the deenergization of the supervisory relays r and w, which close the circuits of the supervisory signals S and S through their armatures and back contacts, the circuit for lamp S including the generator B conductors D, 25, 29, 30, 31, 27, and D while the circuit of lamp S includes said generator, conductors D", 25, 29, 30, 31*, 27, and l). The signals being exposed, the operator is notified that the conversation is terminated and the plugs are with drawn, thus restoring all parts to normal position. In case a reconnection is desired by either subscriber or the attention of the operator is wanted while the plugs are still in the jacks the hooks at the substations may be vibrated to alternately energize and deenergize the corresponding relays r and a" to expose and e'l'lace the supervisory signals.

When a connection is established, the charging-generator A and the relays r or r are in a bridge of the talking-circuit, and the said relays are under the control of the respective subscribers and are energized over the talking-circuit, including the telephone lines. The cooperating relays r and r are under the control of the operator and in the specific arrangement shown are energized over local circuits. Both sets of relays, it may also be observed, are in the path of current from said generators to the contacts of the jack and may also be said to be connected between the cord.- strands of the cord-circuit.

The generator B may be of lower electromotive force than the generator A to save wire on the relays and make the resistance of the local circuits lower. It not, however, necessary that it be a separate generator from A. It may, in fact, be entirely dispensed with, in which case the lead or common line I) from the negative pole of the said generator B is connected with or forms a part of the ground-line or common ground Gr. Such an arrangement is shown in Fig. 3 of the drawings, in which the generator A only is used, the only change required being to extend the branches which formerly connected with the common wire D to the ground-wire G- or to ground them direct, for it will be understood that the line G is indicative of the &

common ground connection of the central office, which is usually shown in drawings of this character by merely indicating an earth connection for each branch. Instead, therefore, of bringing all branches to a common ground-line, such as G, each branch may be grounded separately in the common and wellunderstood manner. In said figure, therefore, I have shown some one way and some the other. In this figure I have also sought to indicate the apparatus at central by a simpler and more usual type of diagram, the strands of the cord-circuit being spread apart to show between their cooperating relays. The same reference characters are used as in connection with Fig. 1. This figure, as stated, shows the system using simply the main generator A. The wires 23 are shown directly grounded, or they may be extended to the ground G or to the conductors 2, leading to ground G. In

practice they are all connected to the common oflice-ground or common ofiice-return. The line 27 is carried to the grounded pole of the battery, although it might have been directly grounded, as in the case of lines 23. It will be clearly seen by tracing the operation with reference to this figure that the system is fully operative with only the single generator A. The subscriber in initiating a call operates the linerelay R from the main generator A in the same manner as in the previous figure. The line-signal, however, is operated from the main generator A instead of the auxiliary generator B the circuit of said signal being from ground at the generator, through the generator, over conductors D and 16, through the lamp S, over conductors 22 and 23, to ground or common office-return. The operator, seeing the signal,inserts the answering-plug P, as before, and in so doing closes a local circuit through the sleeve-contacts of the plug and jack containing the cut-ofi relay R and the supervisory relay 1 said circuit being traceable from the positive pole of the generator A, over conductors D 16, 21, and 22, through the winding of relay It, conductors 18 and 17, the sleeve-contacts of the jack and plug, sleeve-strand s, conductor 27 containing the winding of the relay r, and conductor 27, to the negative pole of the said generator. This causes the operation of the cut-ofi relay R to open the circuit of the line-relay R, thus rendering the line-signal inoperative during the remainder of the connection.

The actuation of supervisory relay 1" closes the local circut of the supervisory lamp S; but the said circuit is opened through the armature of the cooperating supervisory relay 0', which is now in a bridge of the talkingcircuit, together with the generator A, said bridge being extended from the tip-strand t of the cord-circuit, through the conductors 25 and 25, to the generator A and from the opposite pole of the generator to the line 2 or ground. The listening-key 35 serves to connect the operators telephone with the cordcircuit, as heretofore explained, whereby she is enabled to immediately talk with the subscriber B as soon as the answering-plug P is inserted.

Upon ascertaining the number of the party wanted, the subscriber-line is tested in the usual way, and if found idle the plug is inserted. The insertion of this plug operates the relay 1' over a local circuit similar to that specified in connection with the relay 9", and as the subscribers telephone is upon its hook the relay r is not yet operated and the supervisory lamp S is lighted. The circuit of this lamp S may be traced from the positive pole of the generator A, over the conductors 25, 25, and 29, armature and back contact of relay 0- conductor 30*, containing the lamp S armature 26 and front contact of relay r conductors 31*, 27 and 27, back to the opposite pole of the generator A. When the subscriber responds, the relay r is actuated over a circuit from the generator A including the telephone-line, which relay opens the circuit of the signaling-lamp S to indicate the subscribers response to the operator.

In Fig. 2 I show in simple diagram two connected lineswith special reference to the supervisory relays and their connections at such times, the two generators being employed as in Fig. 1 and all ringing and operators-tele-' phone apparatus being omitted. The local circuits established when the plugs are inserted in the jacks are here clearly shown. The one on the left includes the generator B conductor 16, cut-ofi relay R, conductor 18, sleeve-contacts of plug and jack, strands, wire 27, and supervisory relay r to the opposite pole of the generator 13. A similar local circuit is established for the other connected line. These circuits remain intact as long as the plugs are inserted and are therefore under the control of the operator. The relay 1' is in circuit with the generator A, said circuit including the telephone-line and adapted to be opened at the hook of the substation. This relay may therefore be said to be under the control of the subscriber. The relay 1* and generator A are connected in a bridge of the talking-circuit, said bridge starting from strand 6 and including conductor 25, containing the winding of relay 7', the generator A, and the common connection from the negative pole of the generator to the line-wires 2. The relay r is likewise in a bridge. The talking-circuit is shown in rectangular form and is apparent from the figure. The relays r and 7", broadly considered, are in a path of current from their respective generators to contacts of the jack, and the former may be stated to be in the path of current from the charging-generator A to one line conductor.

Fig. 4: shows the same kind of a diagram with but one generator. Here the local circuits, as well as the line-circuits, are supplied with current from the generator A. The local circuits include one the cut-ofi relay R and supervisory relay r and the other the cut-off relay R and supervisory relay r. The relay '2' or r is in a bridge of the talkingcircuit with the generator A, as before described. The only difference in the connections of the two systems is to omit generator B and connect the wires 27 and 27 to the grounded pole of the generator A. In this diagram it is apparent that of each pair of relays jointly controlling the signals one is under the control of the operator and the other is under the control of the subscriber. It is further apparent that said relays are in the path of current from said generator to the tip and sleeve contacts of the jack. They are also connected upon the opposite sides of the generator A between the cord-strands of each end of the cord-circuit, one relay being in addition in a bridge of the talking-circuit with generator A.

The lines are free from constant grounds at. the substations and are thereby distin-- guished from some systems wherein party lines are provided with ground branches at the several stations some one of which branches is always completed to earth. It is apparent, however, that the invention is not to be so limited in all respects, since it is capable of'use with many types of lines. The sleeve-relay and associated ti p-relay serve to entirely control the exposure and non-exposure of the supervisory signal, though other arrangements may in some respects fall within the scope of the invention.

1 claim- 1. In a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof, a second relay and means for energizing it, a switch at the substation and a switch at the central station for controlling the circuit through said relays, and a signal controlled by the conjoint action of said relays, substantially as described.

2. 1n a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof, a second relay and means for energizing it, a switch at the substation for controlling one of said relays and a switch at the central office for controlling the other of said relays, and a signal controlled by the conjoint action of said relays, substantially as described.

3. In a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof, a second relay and means for energizing it, a switch at the substation for controlling said bridged relay and a switch at the central oflice for controlling said other relay, and a signal controlled by the conjoint action of said relays, substantially as described.

4,. In a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof at the central ol'lice, a second relay in a local circuit at the central station, and a signal controlled by the conjoint action of said relays, substantially as described.

5. In a telephone system, the combination with a i'ielephoneline, of a source of current and a relay bridged between the two limbs of the talkingcircuit thereof, a second relay in an auxiliary circuit closed in registering contacts of the plug and jack, and a signal controlled by the conjoint action of said relays, substantially as described.

6. In a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof at the central station, a second relay in a local circuit closed in registering contacts of the plug and jack, and a signal controlled by the conjoint action of said relays, substantially as described.

7. In a telephone system, the combination with a telephone-line, of a source of current and a relay bridged between the two limbs of the talking-circuit thereof, a second relay and means for energizing it, a switch at the substation and a switch at the central station for controlling the circuit through said relays, and a signal in a local circuit completed through the contacts of said relays, substantially as described.

8. In a telephone system, the combination with a telephone line free from constant grounds at the substation, of a ehargi ng source of electricity, a pair of relays at the central office, one of said relays being under the control of a subscriber and the other under the control of the operator, and a signal in the local circuit including the contacts of both said relays, substantially as described.

9. In a telephone system, the combination with a telephone-line free from constant grounds at the substation, of a chargingsource of electricity and a pair of relays at the central otlice, one of said relays being under the control of the subscriber and the other under the control of the operator, and a signal entirely controlled by said relays, substantially as described.

10. In a telephone system, the combination with a telephone-line free from constant grounds outside of the central oiiice, of a charging sourceof electricity, an operators plug, a pair of relays, one of said relays being in a bridge of the talking-circuit at the central oflice and energized as long as the subscribers telephone is in use, and the other relay in an auxiliary circuit and energized aslong as the operators plug is connected with the line, and asignal controlled by said relays, substantially as described.

11. In a telephone system, the combination 'ith a telephone-line, of a relay and a source of current in a bridge at the central oflice, a second relay at the central ofiice, and means for energizing it, said relay being in a local circuit, and means for controlling a signal jointly by said relays, substantially as described.

12. In a telephone system, the combination with a telephone-line of a charging source of electricity and a relay connected with the tipstrand of the cord-circuit whereby the same is adapted to be operated over the telephoneline, a second relay at the central office connected with the sleeve-strand of the cord-circuit and adapted to be closed in a local circuit during conversation, whereby the same is operated as long as the plug is in the jack, and a signal in a local circuit including the contacts of both said relays, substantially as described.

13. In a telephone system, the combination with a cord-circuit at the central ofiice, of two relays associated therewith and adapted to control a supervisory signal, one of said relays being arranged to open the circuit of said signal when energized and the other being adapted to close the circuit of said signal when energized, substantially as described.

14:. In an operators cord-circuit, a pair of relays and a supervisory signal having its circuit controlled by the contacts of both said relays, one of said relays being adapted to normally close the circuit and to be energized over the telephoneline when the line is in use, whereby the signal is at that time rendered inert, and the other relay being adaptedto normally open the circuit, whereby when the cord-circuit is not connected with the line the signal is inert and when connected with a line not in use the signal is displayed, substantially as described.

15. In a telephone system the combination with a telephone-line and a cord-circuit, of a pair of relays associated with each end of the circuit and adapted jointly to control an associated supervisory signal, one of said relays being adapted to normally open the circuit of the signal and to be energized upon the insertion of a plug in the subscribers jack, and the other being adapted to close the signal-circuit when deenergized and to be actuated over the subscribers line when the same is in use for talking, substantially as described.

16. In a telephone system, the combination with a telephone line free from constant grounds at the substation, of a charging source of electricity, a pair of relays adapted to be energized from said source, a switch at the substation and a switch at the central station for controlling the circuit through said relays, a local circuit controlled by contacts of both said relays, and a signal controlled by said circuit, substantially as described.

17. The combination with a telephone-line free from continual grounds at the substation, of a charging source of electricity, a pair of relays adapted to be energized from said source, an operators plug, a switch at the substation for controlling one of said relays, means for controlling the other relay through the agency of the operators plug at the central station, and asignal-circuit including contacts of both said relays, substantially as described.

18. In a telephone system, the combination with a telephone line free from constant grounds at the substation, of a charging source of electricity, a pair of relays adapted to be simultaneously energized from said source, one of said relays being under the control of the subscriber andthe other under the control of the operator, and a signal adapted to be controlled by the conjoint action of said relays, substantially as described.

19. In a telephone system, the combination with a telephone line free from constant grounds at the substation, of a charging source of electricity, an operators plug, a pair of relays adapted to be energized from said source, one of said relays being energized as long as the subscribers telephone is in use and the other relay being energized as long as the operators plug is connected with the line and a signal controlled by said relays, substantially as described.

20. In a telephone system, the combination with a metallic telephone-line free from permanent grounds outside the central oiiice, of a charging-current source, a third conductor a pair or relays, one of said relays being energized over the telephone-line and the other over acircuit including the third conductor and a signal controlled by said relays substantially as described.

21. In a telephone system, the combination with a metallic telephone-line insulated from ground away from the central ofiice when used for talking, of acharging-eurrent source, a third conductor, a pair of relays adapted to be energized from said source, a switch at the substation controlling one of said relays over the telephone-line, and a switch at the central ofiice controlling the other relay over a local circuit including the third conductor and a signal controlled by said relays, substantially as described.

22-. In a telephone system, the combination withatelephone-line, of a source of electricity at the central ofiice, an operators plug and a pair of relays associated therewith, one of said relays being energized from the said source of electricity as long as the said operators plug is connected with the said line, and the other relay being energized as long as the said operators plug is connected with the said line and the subscribers telephone is in usefand asignal whose actuation is controlled solely by the said two relays, substantially as described.

23. In a telephone system, the combination with a telephone-line, of a source of electricity at the central olliee, an operators plug and a pair of relays associated therewith, one of said relays being energized from the said source of electricity as long as the said operators plug is connected with the said line and the other relay being energized as long as the said operators plug is connected with the said line and when the subscribers telephone is in use, and a signal associated with said pair of relays, the circuit of said signal being established by the operation of the first of said relays and said signal being rendered inoperative by the operation of the second of said relays, substantially as described.

24. In a telephone system, the combination with a telephone-line, of asource of electricity at the central ollice, an operators plug and a pair of electromagnets associated therewith, a supervisory signal, one of said magnets be ing energized from the said source of electricity as long as the said operators plug is connected with the said line to operate the said signal, and the other magnet being energized as long as the said operators plug is connected with the said line and when the subscribers telephone is in use to prevent the operation of said signal, substantially as described.

25. In a telephone system, the combination with a telephone-line, of a cord-circuit and a source of electricity associated therewith at the central oliice, a pair of relays associated witlrthe cord-circuit, one of said relays being connected with one strand of the cord-circuit whereby the same is operated over the telephone-line and the second relay being connected with the other strand of the cord-cireuit and a local circuit in which the said second relay is adapted to be closed during a eonnection whereby the same is operated as long as the plug is in the jack, and. a signal Whose exposure depends upon the energization of one of said relays and whose non-exposure is controlled by the other of said relays, sub stantially as described.

26. In a telephone system, the combination with a telephone-line, of a source of current at the central ofiice, an operators plug and comiecting-circuit, a supervisory signal, two supervisory electromagnet-windings associated .with said plug and circuit, one of said windings being energized from said source of current as long as the operators plug is connected with the line to operate said signal and the other winding being energized as long as the operators plug is connected with the line and the subscribers telephone is in use to prevent said signal operating, substantially as de" scribed.

27. In a telephone system, the combination with a telephone-line, of a source of current at the central ol'lice, an operators plug and connecting-circuit, a supervisory signal, two supervisory electromagnet windings associated with said plug and circuit, one of said windings being energized from said. source of current as long as the operators plug is connected with the line and serving to place said signal in condition to operate and the other winding being energized as long as the oper ators plug is connected with the line and the subscribers telephone is in use to render the said signal inoperative, substantially as described.

28. In a telephone system, the combination with a telephone-line, of a source of electricity at the central oilice, an operators plug and a pair of electromagnets associated therewith, a supervisory signal, one of said magnets being energized from the said source of electricity as long as the said operators plug is connected with the said line and serving when energized alone to operate said signal, and the other magnet being energized as long as the said operators plug is connected with the said line and when the subscribers telephone is in use and serving when energized to render the signal inoperative, substantially as described. 1

29. In a telephone system, the combination with a telephone line, of a source of current and an electromagnet bridged between the two limbs of the talking-circuit thereof, a second electromagnet and means for energizing it, a switch at the substation and a switch at the central station for controlling" the circuit through said electroinagnets, and a supervisory signal controlled by the joint action of said electroniagnets, substantially as described.

30. In a telephone system, the combination with a telephone-line, a cut-ell relay, a cordcircuit and source of current associated with the line, of a supervisory signal associated with said cord-circuit, said cordcircuit having only two strands, one of which forms a part of the busy-testing circuit, and means for establishing a path for current over one strand of said cord-circuit to operate said cut-oti relay and said supervisory signal, and a relay adapted to render the said signal inoperative and having its winding in a path for current over the other strand of said cord-circuit and telephone-line, said relay being controlled by the subscriber, substantially as described.

31. In a telephone system, the combination with a telephonedine and cord-circuit adapted to connect with said line, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, of a supervisory signal associated with said cord-circuit and adapted to be operated by current passed over one strand of said cord-circuit when connected with the line, and means controlled by the subscriber for rendering said signal inoperative by currcntpassed over the line-circuit and other strand, substantially asdescribed.

32. In a telephone system, the combination with a telephone-line and cord-circuit adapted to connect with said line, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, of a supervisory signal associated with said cord-circuit and adapted to be operated when a connection exists by current passed over one strand of said cord-circuit and over a suitable officereturn and not under the control of the subscriber, and means under the control of the subscriber for rendering said signal inoperative by current passed over the line-circuit and other strand, substantially as described.

33. In a telephone system, the combination with a telephone-line and cord-circuit adapted to connect with said line, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, of a supervisory signal associated with said cord-circuit and adapted when a connection exists to be operated over a local circuit including one of said strands and not under the control of the subscriber, and means under the control of the subscriber for rendering the said signal inoperative by current passed over the linecircuit and other strand, substantially as described.

34:. In a telephone system, the combination with a telephone-line, a cut-off relay for the line, and a cord-circuit adapted to connect with said line, said cord-circuit having only two strands, one of which forms a part of the busytesting circuit, of a supervisory signal associated with said cord-circuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, said local circuit including the actuatingwinding of said cut-off relay and one of said strands, and means under the control of the subscriber for rendering the said supervisory signal inoperative by current passed over the line-circuit and other strand, substantially as described.

35. In a telephone system, the combination with a pair of telephone-lines, a cut-off relay and source of current for each line, a cordcircuit adapted to connect said lines together for conversation, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, a supervisory signal associated with each end of said cord-circuit, and means for establishing a path for current over one strand of one end of said cord-circuit to operate the cut-off relay and supervisory signal associated therewith, and a relay associated with each end of the cord-circuit and adapted to render the said signal inoperative and having its winding in a path of current over the other strand of said cord-circuit and corresponding telephone-line, said relays being controlled by the subscribers, substantially as described.

36. In a telephone system, the combination with a pair of telephone-lines, a cord-circuit to connect said lines together for conversat1on,sa1d cord-circuithaving only two strands,

circuit, a supervisory signal associated with each end of the cord-circuit and adapted to be operated by current passing over one strand of the cord-circuit when connection is established with the line, and means controlled by the subscribers response for rendering said signals inoperative by current passing over the line-circuits and other strands, substantially as described.

87. In a telephone system, the combination with a pair of telephone-lines and a cord-circuit to connect them together for conversation,said cord-circuithaving only two strands, one of which forms a part of the busy-testing circuit, a supervisory signal associated with each end of the cord-circuit and adapted to be operated when a connection exists with the line by current passing over one strand of said cord-circuit and over a suitable office-return and not under the control of the subscriber, and means under the control of the subscribers for rendering said signals inoperative by current passing over the line-circuits and other strands, substantially as described.

38. In a telephone system, the combination with a pair of telephone-lines and a cord-circuit adapted to connect the lines together for conversation, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, of a supervisory signal associated with each end of the cord-circuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, said local circuit including the actuating-winding of said cut-off relay and one of said strands, and means under the control of the subscribers for rendering the said supervisory signals inoperative by current passing over the line-circuit and other strand, substantially asdescribed.

39. In a telephone system, the combination with a telephone-line and a cut-off relay therefor, of a cord-circuit adapted to be connected with said line, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, a supervisory signal associated with said cord-circuit and adapted to be operated by current passing over one strand of said cord-circuit when connected with the line, the actuating-winding of the cut-off relay being included in the path of said current whereby it is operated, and means controlled by the subscriber for rendering said signal inoperative by current passing over the linecircuit and other strand, substantially as described.

40. In a telephone system, the combination with a telephone-line and cut-off relay therefor, of a cord-circuit adapted to connect with said line, said cord-circuit having only two 1 strands, one of which forms a part of the l busy-testing circuit, of a supervisory signal one of which forms a part of the busy-testingassociated with saidline-circuit and adapted to be operated when a connection exists by current passing over one strand of said cordcircuit and over a suitable oiiice-return and not under the control of the subscriber, the actuating-winding of said cut-ofl' relay being also included in the path of said current, and means under the control of the subscriber for rendering said signal inoperative by current passing over the line-circuit and other strand, substantially as described.

41. In a telephone system, the combination withatelephone-line, and a cut-off relay there for, of a cord-circuit adapted to connect with the said line, said cord-circuit having only two strands, one of which forms a part of the busy-testing circuit, a supervisory signal associated with said line-circuit and adapted when a connection exists to be controlled over a local circuit not under the control of thesubscriber, the actuating" winding of said cut-oll relay and one of said strands being included in said local circuit, and means under the control of the subscriber for rendering the signal inoperative by current passing over the line-circuit and other strand, substantially as described.

42. In a telephone system, the combination with a subscribers telephone and line-circuit normally discontinuous or open to direct currents at the subscribers station, of a mainline terminal consisting of two normally open contact-pieces at the central oilice, a cord-circuit consisting of two strands and with contact-terminals adapted to connect with the contact-terminals of the line when the line is connected for conversation, one of said strands being adapted to be included in the busy-testing circuit, a source of currentassociated with said cord-circuit and adapted to send current over the telephone-line to feed the subscriberss transmitter, a supervisory signal associated with said cord-circuit and adapted to be operated over one strand of said cord-circuit when connected with the line, the circuit for operating said signal being completed over a local circuit at the central office, and means under the control of the subscriber to render said signal inoperative by closing the line-circuit at the subscribers station to form a path for current over the line-circuit and the other strand, substantially as described.

43. In a telephone system, the combination with a mainline normally open or discontinuous at the subscribers station, of a callingsignal normally associated with the line at the central office, a cut-off relay at the central office adapted to render the calling-signal inoperative when connection is made with the line, a line-terminal for the said line, a cordcircuit consisting of two conductors only and adapted to be placed in connection with the said linerterminals, one of said conductors forming a part of the busy testing-circuit, a source of current associated with said cordcircuit and adapted to send current over the line-circuit for energizing the subscribers transmitterduringconversation,asupervisory signal associated with said cord-circuit and adapted to be operated when connection is made with said line by current flowing in a localcircuit including one of said conductors and the cut-off relay or clectromagnet, said circuit not including the subscribers instrument, and means controlled by the subscriber for rendering the said supervisory signal inoperative by current from the said source located in the cord-circuit and sent over the line and other strand, substantially as described.

44. The combination with atelephone-line, of a snbscribers station, a line-tern1inal at the central oflice associated with said line, a cord-circuit consisting of two conductors and adapted to be united to the said line-circuit by means of registering contacts in the lineterminal and cord-terminal, a source of cur rent and a supervisory signal associated with said cord-circuit, an electromagnet to operate said signal and operated over a circuit established by the connection of the cord-circuit withthe line-circuit, said circuit being local and including one of said conductors and not completed through the subscribers instru ment, and means under the control of the subscriber for rendering inoperative the said signal by current passed over the line-circuit and other conductor, substantially as described.

45. In a telephone system, the combination with a telephone-line, a cut-ofl relay, a cordcircuit and source of current associated with the line, of a supervisory signal associated with said cord-circuit, and means for establishing a path for current over one side of said cord-circuit to operate said cut-oil relay and to cause the operation of said supervisory signal, and a relay adapted to render the said signal inoperative and having its winding in a path for current over the other side of said cord-circuit and telephone-line, said relay beingcontrollcd by the subscriber, substantially as described.

46. In a telephone system, the combination with a telephor'ie-lineand a cord-circuitadapted to connect with said line, of a supervisory signal associated with said cord-circuit and having its operation caused by current passed over one side of said cord-circuit when the cord-circuit is connected with the line, and means controlled by the subscriber for rendering said signal inoperative during conversation by current passed over the line-circuit, substantially as described.

4'7. In a telephone system, the combination with a telephone-line and a cord-circuit adapted to connect with said line, of a supervisory signal associated with said cord-circuit and made operative when a connection exists by current passed over one side of said cord-circuit and over a suitable oliice-return and not under the control of the subscriber, and means under the control of the subscriber for rendering said signal inoperative by current passed over the line circuit, substantially as described.

48. In a telephone system, the combination with a telephone-line and a cord-circuit adapted to connect with said line, of a supervisory magnet associated with said cord-circuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, a supervisory signal caused to operate by said magnet when energized, and means under the control of the subscriber for rendering the said signal inoperative by current passed over the line-circuit, substantially as described.

49. In a telephone system, the combination with a telephone-line, a cut-0H relay and cordcircuit adapted to connect with said line, of a supervisory magnet associated with said cordcircuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, said local circuit including the actuating-winding of said cut-ofi' relay, a supervisory signal operated by said magnet when energized, and means under the control of the subscriber for rendering the said supervisory signal inoperative by current passed over the line-circuit, substantially as described.

50. In a telephone system, the combination with a pair of telephone-lines, a cut-ofi relay and source of current for each line, a cord-circuit adapted to connect said lines together for conversation, a supervisory signal associated with each end of said cord-circuit, and means for establishing a path for current over one side of one end of said cord-circuit to operate the cut-offrelay and to cause the operation of the supervisory signal associated therewith, and a relay associated with each end of the cord-circuit and adapted to render the said signal inoperative and having its winding in a path of current over the other side of said cord-circuit and corresponding telephone-line, said relay being controlled by the subscriber, substantially as described.

51. In a telephone system, the combination with a pair of telephone-lines, of a cord-circuit to connect said lines together for conversation, a supervisory signal associated with each end of the cord-circuit and caused to operate by current passing over one side of the corresponding end of the cord-circuit when said end is connected with the line, and means controlled by each subscriber for rendering the supervisory signal associated with his line inoperative by current passing over his linecircuit, substantially as described.

52. In a telephone system, the combination with a pair of telephone-lines and a cord-circuit to connect them together for conversation, a supervisory signal associated with each end of the cord-circuit and caused to operate when a connection exists with the line by current passing over one side of said cord-circuit and over a suitable office-return and not under the control of the subscribers, and means under the control of the subscribers for rendering said signals inoperative by current passing over the line-circuits, substantially as described.

53. In a telephone system, the combination with a pair of telephone-lines and a cord-circuit adapted to connect the lines together for conversation, a cut-01f relay for the line, a supervisory magnet associated with each end of the cord-circuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, said local circuit including the actuating-winding of said cut-oif relay, a supervisory signal operated by said magnet when energized, and means under the control of the subscribers for rendering the said supervisory signals inoperative by current passing over the line-circuit, substantially as described.

54. In a telephone system, the combination with a telephone-line and acut-ofi relay therefor, of a cord-circuit adapted to be connected with said line, a supervisory signal associated with said cord-circuit and placed in condition to operate by current passing over one side of said cord-circuit when connected with the line, the actuating-winding of the cut-oi? relay being included in the path of said current whereby it is operated, and means controlled by the subscriber for rendering said signal inoperative by current passing over the line-circuit, substantially as described.

55. In a telephone system, the combination with a telephone-line and cut-off relay therefor, of a cord-circuit adapted to connect with said line, of a supervisory signal associated with said line-circuit and placed in condition to operate when a connection exists by current passing over one side of said cord-circuit and over a suitable ofiice-return and not under the control of the subscriber, the actuating-winding of said cut-off relay being also included in the path of said current, and means under the control of the subscriber for rendering said signal inoperative by current passing over the line-circuit, substantially as described.

56. In a telephone system, the combination with a telephone-line and a cut-off relay therefor, of a cord-circuit adapted to connect with the said line, a supervisory relay associated with said line-circuit and adapted when a connection exists to be operated over a local circuit not under the control of the subscriber, the actuating-winding of said cut-off relay being included in said local circuit, a supervisory signal having its circuit closed by said supervisory relay, and means under the control of the subscriber for rendering the signal inoperative by current passing over the line-circuit, substantially as described.

line at the central oflice, a cut-ofl relay at the central ofiice adapted to render the callingsignal inoperative when connection is made with the line, a line-terminal for the said line, a cord-circuit consisting of two conductors and adapted to be placed in connection with v the said line-terminal, a source of current associated With said cord-circuit and adapted to send current over the line-circuit for energizing the subscribers transmitter during conversation, a supervisory signal associated with said cord-circuit, a magnet adapted to be operated when connection is made with said line over a local circuit including the cutoff relay, saidicircuit not including the subscribers instrument, said magnet serving to operate said supervisory signal, and. means controlled by the subscriber for rendering the said supervisory signal inoperative by current from the said source located in the cordcircuit and sent over the line, substantially as described.

58. In a telephone system, the combination with a line-circuit, of a subscribers telephone, a line-terminal at the central ottice consisting of two contacts registering with two contacts in a cord-circuit when connection is made with the line, said cord-circuit including a source of current for energizing the subscribers transmitter, a supervisory signal associated with said cord-circuit and caused to operate by current passed over one side of the cord-circuit when connection is made with the line, said circuit being local and not under the control of the subscriber, and means for rendering the said signal inoperative'by current sent over the main line, said flow of current being under the control of the subscriber, substantially as described.

59. The combination with a telephone-line, of a cord-circuit having two st *andsto establish connections with the line for conversational purposes, a source of current associated with the cord-circuitand adapted to send current over both sides thereof during conversation, two electromagnets associated with the cord-circuit one in the path of current from said source over each said strand, a supervisory signal, one of said magnets serving when energized to operate the signal and the other serving when energized to render the signal inert, substantially as described.

Signed by me at Chicago, county of Cook, State of Illinois, this 11th day of January,

JOHN G. ROBERTS. Witnesses:

Rosana. LEWIS AMns, M. R. Roouronn.

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