US1033877A - Telephone-exchange system. - Google Patents

Description

B. R. GORWIN.

TELEPHONE EXCHANGE SYSTEM.

APPLIGATION FILED 0012.12, 190s. RENEWBD APR. 29, 1911.

1,033,877. Patented July 30, 1912;.

l l J J M I By ELMER R. CORWIN, OF CHICAGO, ILLINOIS, l-ISSIGrNOBL T0V CORWIN TELEPHONE MANU;

FACTURING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS;

TELEPHONE-EXCIIANGE SYSTEM.y

Specification of Letters Patent.

Patented July 30,1912.

Application led October 12, 1908, Serial No. 457,195. Renewed April 29, 1911. Serial No. 624,143.

To ad w/Lom t may concern.'

Be it known that I, ELMER R. ConwIN, citizen oi' the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Telephone EX- change Systems, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to telephoneeX- change systems and its objects and advantages will fully appear by a description of one embodiment thereof shown in the accompanying drawing, in which- Figure 1 illustrates a multiple switchboard telephone exchange system to which the invention is adapted, though the invention is not to be limited in its application to multiple switch-board systems. F ig. 2 is a detail of plug and jack.

I have shown at A, B two telephone substations each including a receiver a, a transmitter Z), a switch-hook c, a call bell e, anda condenser ,t', the elements a Z) c being included in bridge of the telephone line, which bridge is open when the receiver is upon the switch-hook c and which bridge is closed by the switch-hook when relieved of the weight of t-he receiver. The elements e f are in another bridge permanently closed to alternating signaling currents but open to direct currents. The type of sub station outfit shown is one that I have selected for the purpose of illustrating the invention, but it is to be understood that I do not limit myself to the form of sub-station apparatus shown, for it will be obvious as the description of the invention is proceeded with, that the operation of the system does not depend upon the peculiar sub-station outfit shown. The stations A B are connected to the eX- change, in the form of the invention shown, by means of metallic circuits whose limbs g and it are connected, respectively, with line springs g1 and thimbles h1, constituting spring-jacks. A plurality of spring-jacks is shown in multiple relation with each line, the lowermost spring-jacks constituting the answering-jacks while the remaining jacks constitute line-jacks. The limbs g and of each telephone line also terminate in contacts of an armature switch, which switch is governed in its position by a cut-of`f relay z',

the limbs of each telephone line being normally connected by way of said armature switch and the contacts normally engaged thereby, with a line lamp or signal 76 and a battery 701 adapted to excite said lamp, when the circuit including the battery k1, the line signal 7:, the armature switch of the associate cut-ott relay z' and the line limbs g and 7L is closed by the removal of the telephone receiver at a calling station from its supporting switch-hook. The cut-olf relays are included in grounded limbs extending from contact portions of the answering jacks, preferably the line thimbles. As will more fully hereinafter appear, the cut-off relays are initially included in local circuits by the plugs, while, ultimately, the circuits for said cut-off relays depend upon the line conductors that are conduct-ively connected by the switch-hooks at t-he sub-stations. In order that the spring-jacks need not be provided with more than two contact element-s g1 k1, and in order to dispensewith line relays and contacts between the lines and the jacks, I employ the non-inductive resistances Z that connect a limb (71,) of each line with the contact /zl of such line that has connection with the cut-off relay z', these non-conductive resistances being permanently connected and in parallel with the cut-oft' relays and permitting the passage of voice currents to their associate spring-jack parts, while at the same time properly controlling the distribution of battery current to eifect the proper operation of the cut-oit relays z', all in a manner which will be understood, after I have described the form of cord circuit outt illustrated. For the cord circuit, I have shown an answering plug my, and a connecting plug nhavingtips and sleeves united respectively by the tip strand 0 and the sleeve strand p, with which strands t-he cord circuit apparatus of the form illustrated is connected. As I prefer to employ double supervision, the cord strands 0 p are separated, so far as the passage of straight current is concerned, by condense-rs g and 11, which, however, permit the passage of telephonie cur-rent. Upon the left of the condensers g and r, I have shown the calling subscribers supervisory relay s controlling an armature switch whose normal cont-act constitutes a terminal of a display signaling device, such as a lamp s1, the other terminal of said lamp being grounded through a batyratus associated with the called subscribers end of the cord circuit, and I will, t-herefore, simply rely upon the illustration of the called subscribers signaling apparatus to indicate its nature. There is also employed any sut-able form of operators telephone outfit t and calling or ringing outfit u whose .circuit relation with the co-rd circuit is well illustrated but need not be described.

Assuming that the calling subscriber A. has removed his receiver a from its' switchhook, circuit is established through the line lamp Za by way of the contacts of the armature switch of the associate cut-off relay z'. The operator, in response tothe signal conveyed by the lamp 7c, will place herself in communication with the calling subscriber, after having inserted the answering plug fmI into the jack of the calling` subscriber (the answering` jack, inasmuch as a multiple switch-board system has been selected for illustrating the invention). The sleeve or body of the answering plug mrst engages a contact part of the answering jack, namely, the partA 71.1, whereupon the cut-off relay z' of the calling-subscribers line is included in a circuit that may be traced from the grounded terminal of said cutoff relay, through the winding of said cutoH relay, the terminal h1, the sleeve or body of the engaged answering plug m, a part of the cord strand 7?, the armature switch of the supervisory relay s, the normal contact of said armature switch, the supervisory signal device S1, the battery s2, back to said cut-olf relay z'. The cut-off relay z' being energized, the line signal lamp 7c is placed in open circuit, so that the signal presented by said lamp is effaced. Upon the further movement of the answering plug m within the engaged jack, the tip of said answering plug is brought into engagement with the line spring g1, whereupon circuit is established through the supervisory relay .s that may be traced from the grounded battery s2, through the winding of said supervisory relay, the portion of the tip strand 0, the tip of the answering plug m, the line spring g1, the line limb g (of the calling subscriber), the switch-hook c, receiver a, transmitter b, line limb 7L (of the calling subscriber), to the grounded cut-off relay Z corresponding to the calling subscribers line, by way of non-inductive resistance Z. lNhen the relay s is energized, the supervisory signal displayed by the lamp s1 is effaced, so that the local circuit for the cut-off relay z' is broken at the armature switch of said supervisory relay, but the circuit of the cutort' relay of the calling subscribers line is still maintained, owing to the establishment of the circuit last traced through the resistance Z. This resistance Z, therefore, is an important feature of my present invention, for by its employment the telephonie connection between the contacts Ztl and the limb /L of each line is preserved, while at the same time the limbs of each line enter into the formation o-f an alternative circuit for the associate cut-off relay c' when the local circuit for said cut-off relay has been ruptured by the movement of the armature switch of the supervisory relay s from its normal Contact.

When the operator establishes connection with the called subscriber, the local circuit through the called subscribers cut-off relay z' is established, as had been the local circuit, through the calling subscribers cut-off relay, but the alternative circuit through the called subscribers line is, of course, not established until the called subscriber removes his telephone from the switch-hook.

lt goes without saying that the supervisory lamps s1 are caused to glow when the associate supervisory relays are in open circuit, which is the case when the corresponding receivers are upon their switch-hooks, and that such supervisory lamps are included in open circuit when said supervisory relays are energized, which occurs when the associate receivers are removed from their switch-hooks.

Another feature of my invention which has been generally described will now be specifically pointed out. lt consists in using for the cut-off relay circuits and the circuits for the supervisory signal devices s1, a portion of the cord strand p as well as a part of an associate line conductor intervening between the associate contact /Ll and the resistance Z. Said line conductor portion and cord circuit portion are included yin local circuit in order to operatethe signal device shown and the associatecut-off relay z', the cord strand then being incomplete for talking purposes, owing to the break in. the talking strand p at the armature switch of the supervisory relay s. Zhen the alternative circuit by way of the line for the cutolf relay z', has been established, and the supervisory signaling device s1 has been excluded from circuit, then the function of the conductor 79 as a signal circuit conductor has been discharged and its function as a part of the talking circuit is then brought about. It will be understood from the description that has been given that were it not for the interposition of each resistance Z between the associate line limb Z1. and the conductor uniting the'associate thimbles Ztl associated with said associate cnt-off relay z',

current from the battery s2 would be shunted by said cut-od' relay to the ground that must be provided in practice in connection with a battery and with which ground a terminal of the cut-off relay is connected.

It will be observed that the resistances Z are in parallel with the associate cut-o relays 2', in order that the function of said resistance may be accomplished.

It is obvious that changes may readily be made in the preferred embodiment of the invention herein shown and particularly described, without departing from the spirit of the invention, and I do not, therefore, wish to be limited to the precise features illustrated, but,

Having thus described my invention, l claim as new and desire to secure by Letters Patent l. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said metallic telephone lines for opening and closing circuit through said signal devices, cut-off relays at the exchange for excluding the aforesaid line signal devices from circuit, thereby e'acing the signals occasioned by said line signal devices, each cut-oft' relay and associate telephone line having a common ground, a local circuit for each cut-off relay including a line contact of an associate jack switch and a plug contact for engagement with said jack switch terminal and a grounded source of current, a resistance interposed between each cut-off relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-oft1 relay, whereby in establishing connection between a ack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but suiiicient current is forced to pass through the associate cut-olf relay to cause its energization, and thereby the effacement of the line signal.

2. A telephone exchange system including telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with t-he exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cutoftn relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug,

a source of current, and a circuit established by said plug when engaged with a jack and including said source of current and cut-ofi' relay, said resistance forcing the passage of sufficient current from said source through the cut-ofiz relay brought into association with said plug to cause the energization of said cut-ofi relay, and thereby the effacement of the line signal.

3. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal cont-act of a jack associated with said line, a cut-off relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, and a circuit established by said plug when engaged with a jack and including said source of current and cut-olf relay, said resistance forcing the passage of sufficient current from said source through the cut-off relay brought int-o association with said plug to cause the energization of said cut-olf relay, and thereby the eifacement of the line signal.

it. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, cut-off relays at the exchange for effacing the signals occasioned by said line signal devices, each cut-off relay and associate telephone line having a common ground, a local circuit for each cut-off relay including a line contact of an associate jack switch and a plug contact for engagement with said jack switch terminal and a grounded source of current, a relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-olf relay, whereby in establishing connection between a jack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but sufficient current is forced to pass through the associate cut-0E relay to cause its energization, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectivel ness of said alternate circuit.

sistance interposed between each cut-off re- 5. A telephone exchange system including telephone lines connected with jack switches at an exchange, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-offl relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of' current, a circuit established by said plug when engaged with a jack and including said source of current and cut-off relay, said resistance forcing the passage of sutlicient current from said source through the cut-off relay brought into association with said plug to cause the energization of' said cut-0H relay, and thereby the effacement of the line signal, a cord circuit relay under the contro-l of a telephone station, an alternate circuit for a cut-off relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit.

6. A telephone exchange system including metallic telephone lines connected with ack switches at an exchange, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-oil relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of current, a circuit established by said plug whenngaged with a jack and including said source of current and cut-off relay, said resistance forcing the passage of suflicient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-off' relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station,.an alternate circuit for a cut-oft1 relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit.

7. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, cut-oft1 relays at the exchange for eacing the signals occasioned by said line signal devices, each cut-off relay and associate telephone line having a common ground, a local circuit for each cut-off relay including a line contact of an associate jack switch and a plug contact for engagement with said ack switch terminal and a grounded source of current, a resistance interposed` between each cut-off relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-off relay, whereby in establishing connection between a jack switch and a plug, all of the current liowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but sutlicient current is forced to pass through the associate cut-olf relay to cause its energization, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cuto relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay.

S. A telephone exchange system including telephone lines connected with jack switches at an exchange, a resistance interposed between a side of' each telephone line and a line terminal contact of a jack associated' with said line, a cut-oftn relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-of relay, said resistance forcing the passage of suiiicient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-ofi' relay, and thereby the eli'acement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cutoff relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay.

9. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-olf relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-oft relay, said resist-ance forcing the passage of suiiicient current from said source through the cut-olf relay brought into association with said plug to cause the energization of said cut-off relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay.

10. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, cut-olf relays at the exchange for effacing the signals occasioned by said line signal devices, each cutoff relay and associate telephone line having a common ground, a local circuit for each cut-off relay including a line contact of an associate ack switch and a plug contact for engagement with said ack switch terminal and a grounded source of current, a resistance interposed between each cut-ntll relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-off relay, whereby in establishing connection between a jack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but sufficient current is forced to pass through the associate cut-off relay to cause its energization, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alter'- nate circuit for a cut-oftz relay, switching mechanism controlled by said cord circuit relay serving to govern the eifectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay and included in circuit with the cut-offl relay that is brought into association with a cord circuit plug and excluded from said circuit by said cord circuit relay upo-n the establishment of the alternative circuit for the cut-ofi1 relay.

l1. A telephone exchange system including telephone lines connected with jack switches at an exchange, a resistance interposed between a side of each telephone line and a line terminal Contact of a jack associated with said line, a cut-off relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a ack and including said source of current and cut-oii' relay, said resistance forcing the passage of sufficient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-oif relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone stat-ion, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the eectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit and included in circuit with the cut-off relay that is brought into association with a cord circuit plug and excluded from said circuit by said cord circuit relay upon the establishment of the alternative circuit for the cutoff relay.

12. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, a resistance interposed between a side of each telephone line and a line terminal conta-ct of a jack associated. with said line, a cut-olf relay in association with each telephone line and in parallel with the associate resistance, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-ntf relay, said resistance forcing the passage of suflicient current from said source through the cut-oif relay brought into association with said plug to cause the energization of said cut-off relay, and thereby the effacement of the linevsignal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay and included in circuit with the cut-o relay that is brought into association with a cord circuit plug and excluded from said circuit by said cord circuit relay upon the establishment of the alternative circuit for the cut-off relay.

18. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said metallic telephone lines for opening and closing circuit through said signal devices, cut-off relays at the exchange for excluding the aforesaid line signal devices from circuit, thereby eacing the signals occasioned by said line signal devices, each cut-off relay and associate telephone line having a common ground, a local circuit for each cut-oftl relay including a line contact of an associate jack switch and a plug contact ,for engagement with said ack switch terminal and a grounded source of current, a resistance interposed between each cut-off relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-off relay, whereby in establishing connection between a jack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but suflicient current is forced to pass through the associate cut-off relay to cause its energization, and thereby the eifacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit.

14. A telephone exchange system including telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-off relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-off relay, said resistance forcing t-he passage of suiiicient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-ofir1 relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cutoff relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit.

15. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal Contact of a jack associated with said line, a cut-oit relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuitincluding aplug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-off relay, said resistance forcing the passage of sufhcient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-oil1 relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, and switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit.

16. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected' with the exchange by said metallic telephone lines for opening and closing circuit through said signal devices, cut off relays at the exchange for excluding the aforesaid line signal devices from circuit, thereby effacing the signals occasioned by said line signal devices, each cut-off relay and associate telephone line having a common ground, a local circuit for each cut-off relay including a line contact of an associate jack switch and a plug cont-act for engagement with said jack switch terminal and a grounded source of current, a resistance interposed between each cut-off relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-oif relay, whereby in establishing connection between a jack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but sufcient current is forced to pass through the associate cut-off relay to cause its energization, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay.

17. A telephone exchange system including telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-off relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, a circuitestablished by said plug when engaged with a jack and including said source of current and cut-off relay, said resistance forcing the passage of sufficient current from said source through the cut-olf relay brought into association with said plug to cause the energization of said cut-off relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal rgoverned in its action by said cord circuit relay.

18. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resist-ance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-O relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesoid line signal devices from cir-- cuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-off relay, said resistance forcing the passage of sufficient current from said source through the cutoff relay brought into association with said plug to cause the energization of said cutoff relay, and thereby the elfacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-oft1 relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay.

19. A telephone exchange system including metallic telephone lines extending to jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said metallic telephone lines for opening and closing circuit through said signal devices, cut-off relays at the exchange for excluding the aforesaid line signal devices from circuit, thereby effacing the signals occasioned by said line signal devices, each cut-off relay and associate telephone line having a common ground, a local circuit for each cut-olf relay including a line contact of an associate jack switch and a plug contact for engagement with said jack switch terminal and a grounded source of current, a resistance interposed between each cut-0H relay and the associate line limb which is in connection with said jack terminal that is connected with said cut-o relay, whereby in establishing connection between a jack switch and a plug, all of the current flowing from said grounded source of current is not permitted to pass to the grounded connection of the associate telephone line, but suiiicient current is forced to pass through the associate cut-oftV1 relay to cause its energization, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-off relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay and included in circuit with the cut-off relay that is brought into association with a cord circuit plug and excluded from said circuit by said cord circuit relay upon the establishment of the alternative circuit for the cut-off relay.

20. A telephone exchange system including telephone lines connected with jaclr 1 switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated 'with said line, a cut-off relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to efface the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cutoli' relay, said resistance forcing the passage of suflicient current from said source through the cut-off relay brought into association with said plug to cause the energization of said cut-olf relay, and thereby the eacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-olf relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal. governed in its action by said cord circuit and included in circuit with the cut-off relay that is brought into association with a cord circuit plug and excluded from said circuit by said cord circuit relay upon the establishment of the alternative circuit for the cut-0E relay.

2l. A telephone exchange system including metallic telephone lines connected with jack switches at an exchange, line signal devices at the exchange, switching means at the stations that are connected with the exchange by said telephone lines for opening and closing circuit through said signal devices, a resistance interposed between a side of each telephone line and a line terminal contact of a jack associated with said line, a cut-olf relay in association with each telephone line and in parallel with the associate resistance for excluding the aforesaid line signal devices from circuit, thereby to eiace the line signals occasioned by said line signal devices, a cord circuit including a plug, a source of current, a circuit established by said plug when engaged with a jack and including said source of current and cut-01T relay, said resistance forcing the iso passage of sufficient current from said source through the cut-off relay brought into association With said plug to cause the energiZat-ion of said cut-ofi1 relay, and thereby the effacement of the line signal, a cord circuit relay under the control of a telephone station, an alternate circuit for a cut-ofi relay, switching mechanism controlled by said cord circuit relay serving to govern the effectiveness of said alternate circuit, and a supervisory signal governed in its action by said cord circuit relay and included in circuit With the cut-ofi' relay vthat is brought into association With a cord circuit plug and excluded from said circuit by said cord circuit relay upon the establishnient of the alternative circuit for the cutoi relay.

In Witness whereof, I hereunto subscribe my naine this tenth day of October A. D., 1908.

ELMER R. CORl/VIN.

Wvitnesses G. L. CROGG, L. Gr. STROH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C.

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