US921321A - Telephone system. - Google Patents

Description

H. G. WEBSTER. TELEPHONE SYSTEM. APPLICATION FILED JULY 6, 1906.

Patented May 11, 1909.

2 SHEETSSHEET 1.

H. G. WEBSTER. TELEPHONE SYSTEM. APPLICATION FILED JULY 5, 1906.

2 SHBETS $HEET 2.

' l l l l l Hl Patented May 11, 1909.

UNITED STATFJETENT HARRY G. WEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO MILO G. KELLOGG, OF CHICAGO,

ILLINOIS.

TELEPHONE SYSTEM.

To all whom 'it may concern Be it known that I, HARRY G. lVnns'msR, a citizen of the United States, residing at Chicago, county of Cook, and State 0]": Illinois, have invented certain new and useful Improvements in Telephone Systems, of which the following is a specification.

My invention relates to telephone eX- change systems and particularly to those of the so-called two wire type, in which the spring-jacks or connection terminals have but two contactpieces, one contact-piece being utilized as both a talking terminal and a test terminal.

The object of my invention is to provide in such a structure improved means for securing a busy test without undue interference with a conversation which may be in progress over the circuit of the line tested.

In accordance with my invention, I associate with the cord-circuit or link-conductor special cont-acts controlled in the manipulation of the listening-key, whereby a proper test circuit is secured and other contacts controlled by a relay operated after the securing of a busy test, whereby a proper talking circuit is maintained during the progress of the conversation. During that period when a busy test is to be secured, I include in the testing circuitsuflicient resistance or impedance to prevent undue disturbance of the potential existing at the terminal of the line tested and thus avoid interference with an existing conversation.

The invention will be more fully understood from the accompanying drawings, in which- Figure 1 illustrates one form of my invention as embodied in a complete telephone system of a well known type; Fig. 2 illustrates other cord-connecting apparatus adapted for association with the same telephone system. embodying a modification of my invention; Fig. 3 illustrates a third cordcircuit apparatus adapted for the same system and embodying a further modification ot the invention; and Fig. 1 illustrates the invention as applied to a complete telephone exchange system of somewhat different character than that of Fig. 1.

Like characters refer to corresponding parts in the several figures.

Referring to Fig. 1, A and B designate two subscribers stations which are con- Specification of Letters Patent.

Application filed. July 5, 1906.

Patented May 1 1, 1909.

Serial No. 32 5846.

nected to a central battery C by suitable telephone lines. The equipment at substations A and B, which may be of any preferred type, is here shown as comprising a call-bell 7) in series with a condenser c in bridge of the telephone line, and a normally open bridge including the transmitter t and receiver 1-, which is closed at the upper contact of the switch-hook 72v when the receiver is removed therefrom. Assuming that subscriber A wishes to communicate with subscriber B, he removes his receiver from its switch-hook, thus closing circuit through limbs 1 and 2 and energizing relay 3 by current flowing from the upper terminal of battery C, through the winding of relay 3, the normally closed contacts of relay 5 and limbs 1 and 2 of the line to the return side of the battery. This energizes relay 3, and the consequent closing of its contacts causes the illumination of lamp at. Upon the insertion of an answering plug 0, current will flow from battery C, through relay 9, strand 1%, contact 30 of spring-jack 6, and relay 5 to the return side of the battery. This current energizes relay 9 and relay 5, and the energization of the latter relay removes limbs 1 and 2 from their normal battery connections and connects them to the two terminals 30 and 29 respectively of the spring-jack 6. Additional current then flows through relay 9 and strand 14:, through the line limbs, the

substation and through contact 29 of the spring-jack, strand 13 of the cord-circuit and relay 7 to the return side of the battery, energizing relay 7 and preventing the illumination of supervisory lamp 11. Under normal conditions, cord strand 15 (which is a talking strand and is connected with strand 13 at condenser 17) ias its circuit completed through ringing-key contacts 21 and 22 of relay 8, lever 24 and contact 25 of listening-key 7 and thence to the ground or lower terminal of battery C through the winding of relay 8. hen the operator actuates the listening-key in answering the call, this circuit is interrupted and may now be traced from the tip of plug P, through keyk, contacts 21--22, lever 24- of the listening-key and contact 26 to the winding of the test relay 23, this latter relay being of relatively high resistance or impedance. .Fhe operator, after learning the want of the calling subscriber in the usual manner, proceeds to test the line wanted by applying the tip of the plug P to the contact 30 of a spring-jack 6 of the desired line-in this case, that of sub scriber B. If the line be idle, the potential at the plug tip and spring-jack contact is the same and no current flow results. If, however, the line be connected at some other spring-jack, a difference of potential will exist and current will then flow from contact 30, through strand 15, key contacts 2122, lever 24 and contact 26 to ground through relay 23, energizing this relay and, by the closure of its contacts, completing a circuit of battery 0 through winding 27 of the operators induction coil and giving the required test. Assuming that the line be idle, the operator inserts the plug P into the spring-jack, releases the listening-key 7c and operates the ringing-key 7a'.. The operation of this latter key connects relay 5 in circuit with battery C, through resistance 28, which, by its energization, connects the line limbs to the spring-jack terminals and thus connects limb 2 to calling generator G, through jack contact 29 and strand 15 in the well known manner. Upon the release of the ringing-key, current flowing from battery C, through relay 10, strand 16 and contact 30, maintains the energization of relay 5, and the ensuing energization of relay 10 causes the illumination of supervisory lamp 12. When the subscriber answers, additional current flows from battery C, through relay 10, the substation and the line limbs and thence through strand 15, contacts 21 and 22, lever 24 and contact 25 and thence to ground through the winding of relay 8. The consequent attraction of armature 19 of relay 8 extinguishes lamp 12; and the attraction of armature 20, engaging contact 21, disconnects lever 24 from the cord strand at contact 22 and completes a connection from strand 15 to relay Sand condenser 17 which is independent of the connection previously existing through contact 22, lever 24, and contact 25. It is apparent, therefore, that if, during the progress of the conversation,

the operator actuates her listening-key, no interruption of the strand 15 will result, nor will test relay 23 be connected to the circuit. When subscriber B replaces his receiver at the conclusion of conversation, the conse quent deenergization of relay 8 restores the normal connection of the strand 15, and the circuit of the tip strand and relay 23 may be again controlled by the operation of the listening-key. The replacing of either receiver causes the illumination of the corresponding supervisory lamp, the illumination of both lamps constituting the usual disconnect signal; and upon the removal of the connecting plugs O and P, the apparatus returns to normal. 1

Fig. 2 shows a cord circuit apparatus similar in operation to that of Fig. 1 except for such changes as are involved in the modification of my invention, and adapted for a. ciation with the line circuits shown. in this structure, the strand 15 is provided with a resistance 33 which may be in the form of impedance, and this resistance is normally short circuited at contact 31 of listening-key It. When the listening-key is actuated for the purpose of answering and of securing a busy test, this short circuit is interrupted; and when the test is made, current will flow from the tip of the plug P, through strand 15, key in, resistance 33 and the winding of relay 8 to ground, and the consequent charge and discharge of the con denser 0 gives the required indication in the operators receiver 7". The listening-key is released upon the insertion of the plug 1?, the subscriber is called in the manner previously described and, when he answers, current flowing through strand 15, contact 31, key is and relay 8, causes the completion of a short circuit of resistance 33 at armature 20 and contact 32, which short circuit is independent of that controlled by the listening-key. A satisfactory talking c011- nection is thus provided for the tip strand, and this is not interfered with by a subsequent operation of the listening-key unless the subscriber has replaced his receiver upon its hook, in which case the relation of resistance 33 to strand 15 is controlled at the listening-key as before. In the structure of this figure, the resistance 33 is sufliciently high, or of suiiicient impedance, to prevent an undue disturbance of the potential of the tested line at the time of making the test.

In Fig. 3 is illustrated a further modification of my invention as appiicd to cord-connecting apparatus similar to that of Fig. 1 and Fig. 2. In this figure, the circuit of the tip strand 15 is normally as follows: from the tip of plug P, through strand 15, key it and contact 31 to condenser 17 and also through wire 50, the winding of relay 8, lever 24 and contact 25 of key is to the return side of the battery G, these being circuits adapted for conversation. Then the listening-key is operated to answer and test, a new condition results in which the circuit of strand 15 is interrupted; the condenser 17 then being connected to the operators set; and the strand being connected through key /c, wire 50, the winding of relay 8, lever 24 and contact 26 of key 70 and thence through the individual resistance 35 to ground through the winding of test relay 23, this latter circuit constituting the testing circuit which, in this structure, therefore, includes the winding of relay 8. The test relay 23 operates in the manner previously described when the busy test is made; and after the restoration of the listening-key, the response of the subscriber causes the energization of the relay 8, producing a new circuit condition. The attraction of armature 20 of relay 8, engaging contact 32, establishes a connection of the winding of relay 8, the condenser 17 and strand 15, which is independent of the contacts con-trolled by the listening-key; and the attraction of armature 19, engaging contact 36, establishes a connection from the winding of relay 8 to the return side of the battery independent of that controlled at lever 2t and contact It is therefore .apparent that a subsequent operation of the listening-key during conversation will not interfere with the conversational circuit or battery supply. Likewise, lever 21 being now connected directly to ground or oilice return at contact 26 and armature 19, the individual resistance 35 prevents interference with the operation of the test relay 23 through the engagement of lever 2i and contact 26, should listening-key 7." be left in its actuated position while the operator is making a test with another cord. Also, in this structure, the resistance and impedance of the winding of relay 8 may be utilized in whole or in part to prevent interference with the line tested, and the relay 23 may be of lower resistance than that indicated in Fig. 1 It is likewise apparent that whereas in Fig. 2 the connection of condenser 17 and relay 8 to strandlo are not actually broken, in Fig. 3 the condenser 17 is disconnected from strand 15 at the time of making the test, and in Fig. 1 the condenser 17 and the winding of relay 8 are both so disconnected.

In Fig. 4t, 1 have illustrated my invention as applied to a telephone exchange system of slightly dillerent character, in which the line relay windings are permanently connected to two limbs of the line and in which it is required that the tip and sleeve strands of the cord circuit be both connected to the active terminal of the battery after the busy test is secured. In this structure, the subscriber A calls in the usual manner, and the circuit thus closed energizes relay 3?. The consequent closing of its contacts completes the circuit of lamp 4: which includes contact 12 of the cut-oil relay 38, the cut-oil relay being included, by differential windings 39 and 10, in the normally open limbs of the line extending to contacts 29 and 30 of the spring-jack 6. Upon the insertion of the answering plug 0, current will flow from battery C, through relay 9, strand 14L, spring-jack contact 30, winding 10 and to the return side of the battery through winding of relay 37. Current will also flow from battery C through relay 7, strand 13, contact 29, winding 39 and thence in conjunction with the current now flowing througn winding 81 of relay 37, through limbs 1 and 2 to the return side of the battery, through winding 80. The currents through windings 39 and 40 being of unequal value, the relay 38 is sufficiently energized tointerrupt the circuit of lamp-4c at contact 42, and the simultaneous energization of relay-s 7 and 9 prevents the illumination of lamp 11. Normally, the circuit of strand 15 is as follows: from the tip contact of plug P, through strand 15, key is, to condenser 17, and through the Winding of relay 8, its contacts 21 and 22, lever 24- and contact of the listening-key and thence to the active terminal of battery C through the, protective resistance 11, this circuit being one adapted for signaling or talking purposes. When the listening-key I? is operated to answer and test, this normal battery connection of relay 8 is removed and the relay and tip strand are then connected to the ground or return side oil the battery through test relay 23 by the engagemen-t of lever 2% with contact 26. The re sistance or impedance of relay 8 may thus be utilized in whole or in part to prevent interference with the tested line. The test is made by touching the tip contact of plug P to jack contact 30 in the usual manner; This contact is connected to ground through the winding of relay 37 and no current will flow through relay 23, which is also ground ed, unless there be another connection or unless the subscriber has removed his receiver, in which case a potential will exist at contact 30 sufficient to cause the energization of relay 23 and the usual test indication; Upon the insertion of the plug P, current will flow from battery C, through the winding of relay 10, strand 16, contact 30, winding 40 of relay 38, and the winding 80 of relay 37 and while this current may be suflicient to energize relay 37, the simultaneous energization of relay 38 interrupts the circuit of lamp 4 at contact -12 and prevents its subsequent display. Relay 10 is at this time energized and causes the illumination of lamp 12. hen the subscriber answers, current will flow from battery C, through winding 81 of relay 3'7 and to limb 1, and also through resistance 11, contact 25-, lever 24L, contact 22, contact 21, relay 8 and strand 15, also to limb 1, and thence through the substation and limb 2 to ground through winding 80. Relay 8 is thus energized and the actuation of its contacts extinguishes lamp 12 and establishes a new circuit connection for strand 15, which may be traced from battery C, through resistance 41, armature 20, contact 21 and relay 8 to strand 15, thus preventing a subsequent operation of the listening-key, during conversation, from interrupting the battery connection of relay 8, or from connecting test relay 23 to the strand 15. In this structure, as distinguished from those previously described, the winding of relay 8 and; condenser 17 are permanently connected to strand 15, the battery connection of relay 8 alone being shifted, and the continuity of strand 15 is not disturbed by the manipulation of the listening-key.

It will be understood that the several batteries C and C may be one and the same and that the various earth connections indicated are connections to the return or grounded side of the battery or the ofiice return. It is also obvious that many alterations and modifications may be made in the matter herein disclosed without departing from the spirit of my invention, and I therefore do not wish to limit myself to the precise structures illustrated.

What I claim as new and novel and desire to cover by Letters Patent of the United States, is

1. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a tesL responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, a substation on said line,

means operated by current through said substation to prevent the inclusion of said resistance in circuit with said strand.

2. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, an impedance included in circuit with said strand and source by the operation of said switch, a substation hook switch, means operated by current controlled by said hook-switch to prevent the inclusion of said impedance in circuit with said strand.

3. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operated by current over a portion of the talking circuit to alter the circuit of said resistance so to preventthe switch control of the normal circuit.

4:. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, an impedance included in circuit with said strand and source by the operation of said switch, and means operated by current over a portion of the talking circuit to alter the normal circuit of said switch so to prevent the switch control of the normal circuit.

5. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to break the circuit thus established.

6. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a high resistance test relay included in circuit with said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to alter the circuit of said switch so to prevent the inclusion of said test relay in circuit with said strand.

7. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operated by current over a portion of the talking circuit to change the circuit of said switch to prevent the inclusion of said resistance in circuit with said source.

8. A telephone exchange system compris ing atelephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linkconductor, a source of current normally connected with said strand, a test responsive clevice associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operated by current over a portionof the talking circuit to alter thecircuit relation of said resistance so to prevent the switch control of the normal circuit.

9. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to break the circuit thus established.

10. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally con,- nected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a high resistance test relay included in circuitwith said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to break the circuit thus established.

11. A telephone exchange system comprising a telephone line having a testing contact, a linkconductor, a testing circuit completed over a talking strand of the link-con ductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a listening-key switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operated by current over i a portion of the talking circuit to alter the listening key circuit, so to prevent the inclusion of said resistance in circuit with said source and strand.

12. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linlrconductor, a source of current normally connected with said strand, a test responsive device associated withsaid circuit, a listening-key switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operated by current over a portion of the talking circuit to alter the circuit of said listening key to prevent the inclusion of said resistance in circuit with said source and strand so to prevent the switch control of the normal circuit.

13. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linkcondnctor, a source or current normally connected with said strand, a test responsive device associated with said circuit, a listening-key switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to break the circuit thus established.

l-i. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a listening-key switch normally con trolling the normal circuit of said strand and source, a high resistance test relay included in circuit with said strand and source by the operation of said switch, and a relay operated by current over a portion of the talking circuit to break the circuit thus established.

15. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linkconductor, a source of current normally connected with said s rand, a test responsive d vice associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by he operation of said switch, and means operating in response to current over the hue limbs to prevent the switch control of the normal circuit.

16. A telephone exchange system compris ing a telephone line having a testing contact, a linkconductor, a testing circuit completed over a. talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control of the normal circuit and to prevent the inclusion of said resistance in circuit with said source and strand.

1?. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linkco'nductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of tot said switch, and means operating in re said strand and source, an impedance included in circuit with said strand and source by the operation of said switch, and a relay operating in response to current over the line limbs to prevent the switch control of the normal circuit and to prevent the in clusion of said impedance in circuit with said source and strand.

18. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the linkconductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a test relay in cluded in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control of the normal circuit and to prevent the inclusion of said test relay in circuit with said source and strand.

19. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source 01"" current normally connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a high resistance test relay included in circuit with said strand and source by the operation of said switch, and a relay operating in response to current over the line limbs to prevent the switch control of the normal circuit and to prevent the inclusion of said high resistance test relay in circuit with said source and strand.

20. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over av talking strand of the link-conductor, a source of current normally connected with said strand, a test respimsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the inclusion of said resistance in circuit with said source and strand.

21. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current noinially connected with said strand, a test responsive device associated with said circuit, a switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation sponse to current over the line limbs to pre vent the inclusion of said relay in circuit with said source and strand.

A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over atalking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, aresistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control of the normal circuit.

23. A telephone exchange system comprising a telephone line having a testing contact, a lii'ik-conductor, testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control oi. the normal circuit and to prevent the inclusion of said resistance in circuit wit-h said strand.

'24. A telephone exchange system comprising a telephone line having a testing contact, a lii'ik-conductor, a testing circuit completed over a talking str, nd of the link-conductor, a source of current normally connected with said strand, a test.- responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the inclusion of said resistance in circuit with said strand.

A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over av talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a manually operated switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation of said switch, and a relay operating in response to current over the line limbs to prevent the inclusion of said relay in circuit with said source and strand.

26. A telephone exchange system comprising a telephone line havinga testing contact,

a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand a test responsive device associated with said circuit, a listening-key switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control of the normal circuit.

27. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a listeningkey switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the switch control of the normal circuit and to prevent the inclusion of said resistance in circuit with said strand.

28. A telephone exchange system comprising a telephone line having a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a listening -key switch normally controlling the normal circuit of said strand and source, a resistance included in circuit with said strand and source by the operation of said switch, and means operating in response to current over the line limbs to prevent the inclusion of said resistance in circuit with said source and strand.

29. A telephone exchange system comprising a telephone linehaving a testing contact, a link-conductor, a testing circuit completed over a talking strand of the link-conductor, a source of current normally connected with said strand, a test responsive device associated with said circuit, a listeningkey switch normally controlling the normal circuit of said strand and source, a test relay included in circuit with said strand and source by the operation of said switch, and a relay operating in response to current over the line limbs to prevent the inclusion of said. relay in circuit with said strand.

30. The combination with telephone lines having testing contacts, of a cord circuit, a test contact for the cord circuit, a test receiving device normally isolated therefrom, a supervisory relay for the cord circuit normally connected with the test contact of the cord and controlling contacts normally in the circuit of the test receiving device, said testing contact being disconnected from the coil of said supervisory relay and connected with the test receiving device during testing, substantially as described.

31. The combination with a telephone line having testing contacts at the central oiiice, ot' a cord circuit having a test conductor to connect with the contact of the line in making a test, a supervisory relay for the cord circuit having its coil normally connected with said test conductor, contacts of said relay normally in the circuitof said test con ductor, and means for disconnecting the coil of said relay from said test conductor during testing, substantially as described.

32. The combination with a telephone line having test contacts at the central office, of a cord circuithavin a normally complete tip strand, a central source of current, a supervisory relay connected between said strand and said source, a test circuit, said relay controlling contacts normally in said test circuit, said test circuit including a portion of the tip strand of the cord circuit, means for disconnecting the coil of said supervisory relay from the testing conductor during testing, and means for disconnecting said testing conductor from the tip strand of the cord circuit when the conversational connections are established, substantially as described.

The combination with a telephone line having test contacts at the central office, of a cord circuit having a normally complete tip'strand, an operators listening key for the cord circuit, contacts of said key normally completing the tip strand of the cord circuit, a source of current, a supervisory relay with its coil connected between said source and said tip strand, said relay being under the control. of the called subscriber when the cord is connected for use, the actuation of the listening key being adapted to sever the connection of said supervisory relay from the tip of the cord circuit, a testing conductor normally connected with the tip of the cord circuit through contacts of said supervisory relay, said relay being adapted by its actuation to sever the connection of said testing conductor from the tip of the cord circuit, and to complete a looking circuit for itself, whereby the actuation ofthe listening key will not again sever the connection of said supervisory relay from the tip of the cord circuit, substantially as described.

34. In a telephone system, the combination with a cord circuit having a normally complete tip strand, a listening key for the cord circuit having contacts normally in the circuit of said tip strand and adapted to be severed when the key is actuated, a testing device normally isolated from the cord circuit and connected therewith by the actuation of said key, a supervisory relay connected with said tip strand and controlling normally open contacts in said tip strand and normally closed contacts in the circuit of said testing device, said relay being under the control of the called subscriber when the cord is connected for use, the actuation of said relay being adapted to close its contacts in shunt of the contacts of said listening key, whereby a locking circuit is completed for said relay, and whereby the listening key may be actuated without severing the circuit of said supervisory relay, substantially as described.

35. In a telephone system, the combination with a telephone line having test contacts at the central office, of a cord circuit having a test contact to register with the test contacts of the line, an operators listening key for the cord circuit, series contacts of said listening key normally completing the tip strand of the cord circuit, the actuation of said listening key being adapted to sever the tip strand of the cord circuit, a testing conductor, a supervisory relay adapted to be actuated over the tip strand of the cord circuit and controlling contacts normally connecting said testing conductor with the tip strand of the cord circuit, the circuit of said relay being normally completed through contacts of said operators listening key and thereafter completed over a path in shunt of said contacts, and containing contacts of the relay itself, whereby the key may be actuated without severing the circuit of said supervisory relay, substantially as described.

36. A telephone exchange system comprising a telephone line having a testing c011- tact, a link conductor, a testing circuit completed over a talking strand of the link conductor, a source of current, a test responsive device associated with said circuit, a switch, a resistance included in circuit with said strand and source by the operation of said switch, a relay having a normal connection with said strand, and switch means operated by said relay serving to establish a circuit for said relay extending about said normal connection, said means also preventing operative inclusion of said resistance in circuit with said strand and source.

37. A telephone system comprising a telephone line having a testing contact, a link conductor, a test terminal therefor, a test re sponsive device associated with said conductor, a resistance, a switch for operatively associating said resistance with said conductor, a relay having a normal connection with said conductor, and switch means controlled thereby for establishing a, circuit for said relay in shunt of said normal connection and opening a contact between said switch and said conductor.

38. A telephone system comprising a telephone line, multiple terminals therefor, a link conductor having a test controlling cir-f cuit sensitive to the idle or busy condition of said terminals, a switch operable to connect said circuits with said conductor, a relay adapted to be energized responsive to current over said conductor, said relay having a. normally closed contact in the connection extended from said circuit to said conductor, and a normally open contact adapted to be traversed by current through said relay when energized.

39. A telephone system comprising a telephone line, multiple terminals therefor, a link conductor having a test controlling circuit sensitive to the idle or busy condition of said terminals, a switch operable to connect said circuit with said conductor, a relay adapted to be energized responsive to current over said conductor, and switching means actuated thereby, preventing reconnection of said circuit and conductor.

In witness whereof, I hereunto subscribe my name this 3rd day of July 1906.

HARRY G. WEBSTER.

lVitnesses Gno. E. MUELLER, H. C. OLMSTEAD.

It is hereby certified that Letters Patent No. 921,321, granted May 11, 1909, upon the application of Harry G. Webster, of Chicago, Illinois, for an improvement in Telephone Systems, errors appear in the printed specification requiring correction,

as follows: In line 4:, page 7, after the word strand, a comma should be inserted,

and in line 68, page 8, the Word circuits should read circuit; and that the said Letters Patent should be read With these corrections therein that the same nhay conform to the record of the case in the Patent Office.

Signed and sealed this 22d day of June, A. D., 1909.

[SEAL] O. O. BILLINGS,

Acting Commissioner of Patents.

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