US999728A - Telephone system. - Google Patents

Description

F. B. ALLEN. TELEPHONE SYSTEM.

APPLICATION FILED NOV. 29, 1909.

Patented Aug. 8, 1911.

2 SHEETS-SHEET 1.

Irv/e076! Hunk Allen HI-.9 A/To'r-ney F. B. ALLEN. TELEPHONE SYSTEM. APPLICATION FILED NOV. 29, 1909.

Patented Aug. 8, 1911.

ZBHEETS-8HEET 2.

lnyenfo'r' Fmnk Allen filo Aim/"20y UNITED SA'ILES FRANK B. ALLEN, O F ELYRIA, OHIO, ASSIGNOR TO THE DEAN ELECTRIC COMPANY, OF

ELYRIA, OHIO, A CORPORATION OF OHIO.

TELEPHONE SYSTEM.

' To all whom it may concern;

and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled inthe art to which it appertains to make and use the same.

My invention relates to telephone systems, and more particularly to trunk circuits which are intended to connect telephone lines terminating at different exchanges, together, in circuits adapted for the carrying on of conversation between the connected stations. Circuits of this general nature are now well known in the art and are extensively used. In theiruse several operations are required, among them the connections between the trunk circuit proper, the other central station appliances, and the line wires. To facilitate these connections, it is necessary to signal the parties participating in them, and considerable apparatus is required to control the signals used. In the circuits now in use-it is customary to speak of the ex change at the call-initiating line as the A exchange, and the terminal at that end as the outgoing terminal of the trunk. The exchange at the other end of the trunk is called the'B operators position, and the terminal there, the incoming terminal.

The object of my invention is to produce a trunk circuit embodying a complete set of signals controlled for guiding the operators in making the connections. A mong other things, 'I produce apparatus for signaling the called or desired subscriber which is dependent upon the connections at both ends of the trunk circuit.

circuit, which is in turn controlled by a trunk relay which is connected to one end of the trunk, and a terminal relay connected to the other end. Each relay'is governed .by the switching. means at the end of the thereof, while its scope will be more particularly pointed out in the appended claims. I

Specification of Letters Patent.

Application filed November 29, 1909.

To accomplish this I provide a device governed over an electrlc Patented Aug. 8, 1911.

Serial No. 530,449.

Figure l is a diagram of a. telephone system showing two subscribers lines, a central cord circuit and a trunk circuitaccording to my invention. Fig. 2 is a modification of the trunk circuit of'Fig. 1.

Referring now to the drawings and the embodiments of my invention shown therein, in the upper left hand corner of Fig. 1

I show a diagram of a subscribers line upon which is the station of a single subscriber at A This includes the telephone transmitter T, the receiver '0, the bell Y and condenser K in bridge of the line. The line extends to multiple jacks at the A or main exchange station. The line and cut-01f relays are shown at R and R. The line lamp at L. At A I show a 3-conductor cord circuit terminating at P and P although I may use any other well known form' of cord circuit. The connections of the cord circuit are separated by condensers K and K interposed in the strandsv thereof. The tip'supervisory relays are shown at R and R The sleeve supervisory relays at It and B, At Z and Z I show retardation coils adapted to choke out the variations in the battery current, also the talking current. The supervisory lamps. are shown at L and L At J located in proximity to the plug P at the A station, I show'the terminal jack of the trunk circuit which leads to the B station. At the B position 'the trunk is divided into two sections which are conductively separate but inductively united by the induction coils I and I Between the windings of these induction coils are interposed the condensers K and K At It I show a relay controlled over the A end of the trunk and known asthe trunk relay. AtX I show a high noninductive resistancewhich is normally in circuit with this relay but adapted to be shunted out. At It I show a relay which is controlled over the called subscribers line and which is known 'as the subscribers relay. At R I show a relay having certain functions hereafter to be described, and which'is known as the control relay. This relay is self-locking. At R I show a relay which is controlled from the B end of the trunk and which is known as the terminal relay. At R3 I show a relay controlling the connection of the signaling current to the line and which is known. as-the signaling relay. At LKI show a signal which.

is known as a guard signal and which also performs the function of a disconnect signal; that is, it indicates in its guard capac--- .ity to the B operator the fact that the plug P has been inserted into the jack J in its disconnect capacity, that said plug has been withdrawn from said jack. At L I show a signal which indicates the combina- "tion of the appliances for signaling the erators position in multiple jacks J 2 which fare accessible to the B operator. R and R vare the cut-off and line relays respectT'n ely. on this line. L is a line lamp. At the B board the trunk terminates in' the plug P, ,which is adapted to be inserted into the'jacks of the called subscribers line.

The operation of my invention, which will best serve to describe the functions of the various pieces of apparatus, is as follows: Assuming that the subscriber at station A desires to communicate with the subscriber at station C, the subscriber at A removes the receiver 0 from the hook H which rises to close the switch 1-H. This completes a circuit through the relay R as follows: negative side of battery B R -.2-34H- 1T the \Vheatstone bridge at- A 5 678- to. positive side of battery B Condenser K in the bell bridge at the substation prevented the operation of the relay R before the removal of the receiver. The

relay R pulls up the armature 9 closing the i switch 910, lighting the lamp -L over the following circu1t: negative side of battery B9-10Ll1 to positive side of battery. The lamp L is before the A' operator,

and on observing its illumination, she inserts the plug P into the line jack J of'the'calling subscriber. The circuit is immediately completed throu h the sleeve supervisory relay R and the line relay R as follows: ground G battery B -12-R -13-l4'15R- 8- to ground at G. The relay R is energized, pulling up the armatures-3 and 6 cutting off the calling line through the line relay and extinguishing the lamp L. The relay R 'pulls up the armature 16, closing the switch 'l6-17 in the circuit of the lamp L This lamp is not lighted, however, as simultaneous with the energization of relay R, a circuiris closed through R as follows:

positive side of' B 18R -19- tip side. of cord 20.21=-225 substation appa-- ratus at A 4 23.-24. 25 26 Z 12 back to battery B The relay R pulls'up its armature 27 interrupting the circuit ofthe lamp L at 2728, and preventing the illumination of said lamp. The A operator now connects her telephone set (not"'shown) in circuit with the substation and ascertains that the subscriber at the substation C is wanted. She then calls and communicates that fact to-the B operator over a separate order wire circuit. The B operator informs the A operator of the trunk which is to be used, in this case the trunk W which is shown in the drawing. The A operator, who usually is waiting with the plug in her hand, immediately inserts the plug P into the jack J on this trunk. A circuit is completed through the relay R- as follows: ground G battery B -1230R 31- 3233-34 to ground at G The relay .R pulls up its armatures 3-5 and 36 cutting off the test at 37, closing the circuit of tlie lamp L at 35-38 and the circuit of the relay R at 3G39. The lamp L is immediately lighted over the following circuit: positive pole of battery B 18L 4O 41-4238353012 to negative pole of B A circuit is also completed through the tip supervisory relay R and the trunk relay R, the latter at the B exchange. This circuit is traced as follows: positive pole of B l8 R -43393G44:-4l54:6 4748-IXR 49I 50 51 52 53Z 12- to negative pole of battery 13. The current in this circuit is suflicient to energize the trunk relay R, but owing to the resistance X, is insutlicient to operate the relay R The relay R pulls up armature 54E, engaging its frontcontact 55 and completing a circuit through the guard lamp L as follows: -B 5l55565'758 L* to ground at G. The lamp L lights up and in its guarding capacity indicates to the B operator that the plug P is inserted in the jack of the trunk V. The B operator, then, after testing the called line and finding it idle, inserts the plug P? into the ack J of that line. The circuit through the relays R and R is completed as follows: ground at- G B R -6O6l-62R 63 to ground at G. R pulls up its armatures G4 and 65, cutting oif'the called line from the line relay and signal. The relay R pulls up the armature 58, interrupting the circuit of the guard lamp L and extinguishing the same. The armature 58 is drawn up to engage the front contact 59 in the second circuit of this lampto be described presently. The armature 66 is at-' tracted, interrupting the test at 67 and closing the switch 66-68. Thearmature 69 is attracted, closing the switch 6970 in the circuit of the relay R The B operator now closes the sw tch N of the generator M which we will assume is adapted to furnish current of a character to which the bell at substation C responds.

'Infthis actthe master spring Q, is closed to engage the contactsfil and 72. a A circuit is thus, closed through the relay. 3* as follows; ground G "2-, -Qj71 73-R-7 4j'70- 695-.-75,.76 -77, battery B* to ground G This energizestherelay R? which pulls .up armature '78, closing the switch. 7879 ringing lamp that-is itis illuminated during the stage between the first application ofthe ringing current and the response of the called subscriber to indicate to the B operator that the called station has not yet responded. The relay R also attracts its armature 82 closing the contacts in the circuit of the relay R which is' now. energizedover the following circuit: ground 72Q- ground at G. This circuit, it will be seen,

is directlycont-rolled by-the relay R which.

operates the switch S ltherein. This circuit is also controlled by the relay R acting through the relay R The relay R pulls up the armatures 84 and 8.5 to engage their front contacts 86 and 87.

cuit: ground G machine MN.90- 87-85888991--93. condenser K and bell -Y of the station C92-9495-96 8=L86- to ground G This circuit will be made each time the ringing switch N and master key Q, are operated. When the subscriber at station G responds byremoving the receiver 0 from the hook H a low resistance bridge through the substation apparatus is completed and the subscribers relay R energized over the following circuit: G" one winding of R"97 -68-6698 991008-'l:96 959l92 the substaa tion apparatus 9391--'-89-88-85 l01102103 lower winding of R ground G The relay R pulls up the armature 104, closing the switch Ell-105 and completing a shunt 106 around the ret sistance. The resistance X being thus removed from thecircu-it-of the relay R the current fiow therein is sufficient to energize R which pulls up its armature 41 breaking the circuit of the supervisory lamp L at 4041. The extinction of'this signal indicates to the A operator that the called station has answered. Relay R also httracts' the armature 77 breaking the circuit of relay R at '7677. This relay being deenergized, releases the armatures 78 and 82,.

the fornier interrupting the circuit of the lamp L and indicating to the operator the response of the called subscriber. The

interruption of the switch 8182 breaksthe- Signalingnow takes place through the following cir+ cation of the ringing current to the line and -the objectionable ringing in the called subscribers ear. The subscribers at A and C ow converse .over the following circuit:

from the transmitter Tl-H+23 induction. coils {I and I' 1-02-'10'1' s5+ 92 94 -95 -96'84100'-99 induction coils I and I 484746 45K-20 2l'-22-5 receiver O, and back to T. Current is supplied to one side of this circuit by battery 'B and to the other by battery B through the connections which are readily apparent without description. Upon the termination of the conversation each subscriber hangs up his receiver. The breaking of the switch 1H at substation A interrupts the circuit of relay R which has been described, allowing the armature 27 to fall back, closing the switch 2728 in the circuit of the lamp L which now lights up.- Upon observing this, the A operator pulls out plug P, restoring the apparatus at the'answering end of the cord to normal condition. The interruption .of the hook switch at station C breaks the circuit of relay R which becomes inert. The switch '1O 1105'in the shunt of'X is interrupted placing the resistance again in the path of the current through relay R and reducing the current therein to an amount insuflicient to operate said relay. The armature 41 falls back, closing the circuit of the lamp L which lights up. The A operator now pulls outpl'ug' P restoring the apparatus in the calling end of th cord to normal condition and breaking t" a circuit of the trunk relay R". The arr .ture 54 falls back upon the contact 110, :ompleting the following circuit: GB --54- 110-1115958L* G. This lights the lamp L which serving in its disconnect capacity, indicates to the B operator the disconnection of plug P from jack J. The B operator now pulls out plug P which interrupts the circuit of the relays R and R restoring the system to normal condition.

In Fig. 2 I show a slight modification in which the application of the ringing current, after the first operation, is done automatically. I show an interrupter connected in a ground leg. 121 which terminates in a back contact 120 of the master key spring Q- When it is desired to ring the called substation, the ringing key is depressed and locked down. After the energizations of relays R and R have taken place, as described above, the master spring Q, drops back uponv the contact 120 and a circuitthrough relay R is completed as follows: G V-12112O R808l8283 565554 battery B ground G*. The interrupter V which is constantly rotating,

' is constructed to complete this circuit through period of time and then broken for a certain.

certain intervals only; consequently, the circult ust traced will be made for a certain period of time during each revolution of the interrupter. This-continues until the called subscriber responds, when the circuit of relay R is broken, as previously described.

During each energization of relay R ringing current will be applied to the line as previously described. It will be readily apparent that the ringing relay It will be moperative to connect the signaling current to line until the'plug P 'isinserted into the jackv J, the plug P inserted-into the jack J ,-and the master switch Q closed. Moreover, the circuit of thisrelayis controlled directly by the trunk rels y and is not dependent upon any intervening apparatus,

I make the control'relay R self-locking,

thus dispensing with asecond relay for the performance of this function.

While I have shown these parts thus controlled and operated, I do not wish to be limited thereto, as it will be obvious to those skilled in the art that numerous and extensive departures from the form and details of the apparatus here shown maybe made without departing fron1 .the' spirit of this invention, the same being herein shown solely for the purpose of clearly illustrating specific embodiments of my invention- Iclaim: -'I". 1. In .a telephone system, a plurality of subscribers lines, a central station circuit, 'a trunk circuit adapted to be connected to the central station circuit and :1 called line,

. circuits, a source of signaling'current in the 'a relay in the trunk controlled 'over the trunk and central station circuit'and operated. when connection 18 made between said trunk, a signaling relay adapted to connect said source in circuit with a calledline, a

circuit for the signaling relay, a switch in said .circuit' controlled by. the first named relay, a controlling relay in saidtrunk, a second switch in the circuit of the signalingrelay controlled by said controlling relay, a

. circuit for the controlling relay, a terminal relay controlling the circuit of the controlling relay anda subscribersrelay adapted, when the called subscriber responds, to'interrupt the circuit of the controlling relay to disconnect said source of signaling current.

2. In a telephone system, a plurality of subscribers lines, a central station circuit, a trunk circuit adapted to be connected to the central station circuit and to a called .line, a-source of'signaling current in said trunk, a relay for connecting said source to a called line, a circuit for said relay, a con trolling relay adapted to operate switch contacts,.in the signaling relay' circuit-to comest plete the "same, a circuit for-the controlling relay,la terminal relay controlled by the connection of the trunk and called line, and

of signaling current insaid trunk, a .relay.

adapted to connect said source in circuit with a subscribers line, a circuit forsaid relay, a controlling relay independent of the talking circuit located in the trunk and controlling contacts in said circuit, a trunk relay' controlled over; the talking circuit controlling contacts in said circuit, said controlling relay under control of said sec- 0nd switch'and adapted when said switchis operated to be energized to o crate the contacts in the circuit of the signaling relay whereby said signaling relay is inoperative until bcthsa-id switches are closed,

4. In a telephone system, a plurality of subscribers lines, a-central station. circuit,

a trunk circuit, a switchto connect the trunk and central station circuit, a second switchto connect the trunk to 3, called line, a source of signaling current in said trunk, a relay adapted to connect said source in circuit with a subsoribers line, a ,circuit-f for said relay, a controlling relay-independent of the talking circuit located in theltru liandcon-' trolling contacts in said circuit, a trunk relaycontrolled over the talking circuit con-- trolling contacts in said circuit, said controlling relay under control of said second switch and. adapted when said switch is operated to be energized to operate the contacts in the circuit of thesignaling relay whereby said signaling relay is inoperative until both said switches are closed, and a subscribers relay under control of the called subscriber and adapted when said subscriber responds to interrupt the circuit governing the signaling relaywhereby said source is disconnected from the subscribers line.

1 5. In a telephone system, a plurality of subscribers lines, a central station circuit, a

trunk circuit, switching meansfor connecting the central station circuit and the-trunk, second switching means for connecting the trunk and the called subscribers line, :5- source of signaling current in said trunk, a relay in said trunk adapted to cninect said source in circuit with a subscribers line and a key in said trunk controllingsaid relay, said relay being inoperative until both said switclnng connections are made and sa d hey is operated.

6. In a telephone system, a plurality of subscribers lines, a central station circuit, af trim-k circuit, switching means for connecting th'e'l-central station circuit and the trunk, second switching. means for connectingfthe' trunk "and the. called subscribers line, assure-e of -signaling.current in said trunk, a relay in saidztrunk adapted to connect -saidsource in' circuit with a subscribers line, acircuit for. said relay over which the-same energized: and a key in said circuit,- said circuit'controlled by said key and both said switching connections.

7; In a telephone system, a plurality of subscribers lines; a central station circuit, a trunk circuit, switching means for con netting the'central stationcircuitand the trunk, second switching means for connect-- ing the" trunk and the called sribscribefls line, a source of signaling current in said trunk, a relay adapted to connect said source in circuitwith'asubscribers line anda key in said trunk, said relay being controlled by said key and both said switching connections. v

8. In a telephone system, a pluralityof subscriberslines, a central station circuit,

a trunk? circuit,-switcliing means for con-- .-necting the central station circuit and the trunln second switching means for connecting the trunk and the called subscribers ylinefa sourceof signaling current in said trunk, a relay in said. trunk adapted to conne'ctsaid source in circuit with a subscribers line, a circuit-for said relay, contacts in, said circuit controlled by said firstnamed switching. means, a key insaid trunk controlling contacts in said circuit and other. contacts in said circuit controlled by said second named switching means, said signaling relay being inoperative until both said switching means are operated to connect said trunk to said circuitsjand said key is operated.

9. Ina telephone system, a plurality of subscribers lines, a central station circuit, a trunk circuit, switching means for connecting the central station circuit and thetrunk,

second switching means for connecting the "trunk and the calledsubscribers line, a

source of si naling current in said trunk, a relay in said trunloadapted to connect said source in circuit with a. subscribers line, a

gcircuit for said relay, a trunk relay controlled by said first named switch connect-ions, contactsin said circuit controlled by .said; trunk circuit, acontrollingrelay con- -trolled' by said second switch connections,

other contacts in said signaling relay circuit under control of said controlling, relay and a key in said signaling relay circuit, said signaling relay being inoperative to connect.

said source to lineuntil said trunk is connectetl to the central station circuit and to the called line and said key is operated.

10. In a telephone system, a plurality of ,Ineans controlled by the called subscrio" subscribers lines, acentral station circuit, a trunk circuit, switching means for connecting the central station circuit and the trunk, second'switching means for-connecting the trunk and the called subscribers line, a source of-signaling current in' saidtrunk, a relay in said trunk adapted to con nect said source in circuit with sub-J trunk and the called subscribers line, a,

source of signaling current in saidtrilnk, a, relay in said-trunk adapted to connect saidsource in circuit with a subscribers line, a

circuit for' said relay over which the same is energized, a key in said circuit, said circuit controlled by said key and both said switching connections, and means controlled by the called subscriber for causing the disconnection of the source ofv signaling current from the line.

12. In atelephone system, a pluralityof subscribers lines, a central station circuit,

a trunk circuit, switching means for connectingthe central station circuit and the trunk, second switching means for connecting the trunk and the called subscribers line, a source of signaling current in said trunk, a relay adapted to connect said source in circuit with a subscribers line, a

key in said trunk, said relay being controlled by said key and both said switching connections, and means controlled by the called subscriber for causing the disconnection of-the source of signaling current from the line. v

13. In a telephone system, a plurality of subscribers lines, a central station circuit, a trunk circuit, switching means for connecting the central station circuit and the trunk,

second switching means for connecting the source of signaling current in said trunk, a relay in said trunk adapted to connect said.

source in circuit with a subscribcrs line, a

circuit for said relay, contacts in said circuit controlled by said first named switching means, a key in said trunk controlling contacts in said circuit, other contacts in said circuit controlled by-said second named trunk and the .called subscribers line, a

switching means, said signaling relay bea ing inoperative until both said switch ng said circuit, and said key is operated, and

means are operated to connect said trunltto for causing the disconnection of the source trolled by said first naiiied switch connec- 'tions, contacts in said circuit controlled by said trunk relay, a controlling relay con trolled by, said second switch connections, other contacts in said signaling relay circuit under control of said controlling relay, a key iii-said signaling relay circuit, said signaling relay being inoperative to connect said source to line until said trunk is con nected 'to' the central station circuit and to -the called line and said key is operated, and

means controlled by the called subscriber for causing the disconnection of the source of signaling current from the line.

. [-15. In a telephone system, a plurality of :isubscribers lines, a central station circuit, a

unk circuit, switching means for connectng said-trunk and central circuit, second switching means for connecting said trunk and a called line, a source of signaling current in said trunk-circuit, a signaling relay adapted to connect said signaling source in circuit with a called line, a circuit including saidsignaling relay and a source of current,"

a plurality of contacts in said circuit, a

trunk relay adapted to be operated when the first switching means is operated and controlling contacts in the circuit of-the signaling relay, a controlling relay controlling contacts in said circuit, a circuit therefor,

.said circuit under control of said second switchingcmeans and the called subscriber, and a key controlling contacts in said sig naling relay circuit.

.16. In a telephone system, a plurality of subscribers lines, a central station circuit, a trunk circuit, switching means for connecting said trunk and central circuit, second switching means forconnecting said trunk and a called line, a source of signaling current in said trunk circuit, a signaling relay adapted to connectsaid signaling source in circuit 'Wlilll'tl called line, an automatic signaling key associated with said trunk, aid;

ringing relaybeing controlled by said two switching means and said automatic key.

17. In a telephone system, a plurality of subscribers" lines, a central station circuit, a trunk circuit, switchingmeans for connecting said tr'unk and central circuit, secondv switching means for connecting said trunk and a called line, a source of signaling current in said trunk circuit, a s1 gnalm g relay adapted to connect said signaling source in 1 circuit with a called line, a circuit for said relay over which the same is energized and an automatic key in said circuit, said circuit controlled by said automatickey and both said switchconnections,' i

I 18. Iiia telephone system, a plurality of subscribers lines, a'central station-circuit, a trunk circuit, switching-means for connecting the centralstation circuit and the trunk, second switching means for connecting the trunk and the called subscribers line, a source of signaling current in said trunk, a relay in saidtrunk adaptedtoconnect said sourcein circuit with a subscribers line and an automatic key in said trunk, said relay beingcontrolled by'said key and bot-h said.

switching means.

19. In a telephone system, a plurality of subscribers lines, a' central stat-an circuit, a trunk circuit, switching means for connect ing the central ation circuit and the trunk, second switching means for connecting the trunk andjthe called subscribers line, a source of signaling current in said trunk, a

' relay in said trunk adapted to connect said source in circuit with a subscribers line, a circuit for said relay, contacts in said circuit controlled by said 'first named switching" means, an automatic key in said trunkcon trolling contacts in said circuit and other contacts in said circuit controlled by said.

second named switching means, said signaling relay being inoperative until both said switching means are operated to connect said trunk to said circuit, and said automatic key is operated. I

20. In a telephone system, a plurality of subscribers.-lines, a central station circuit, a

trunk circuit, switching means for connect-- ing the central station circuit and the trunk, second switching means for connecting the trunk and the called subscribers' line, a

source ofsignaling current in said trunk, a

relay in said trunk adapted to connect said source in circuit with a subscribers line, a circuit for said relay, a} trunk relay controlled by said first' named switch-connections, contacts in said circuit controlled by saidtrunk relay, a controlling relay controlled by said second switch connections,

other contacts in said signaling relay circuit under control of said controlling relay, and an automatic keyjin said signaling relay circuit, said signaling relay being inoperative to connect said source to line until said trunk is connected to the central stationcircuit and t0 the called line and-said automatic key is operated.

V 21. In a telephone system, a plurality of subscribers lines, a central station circuit, a t'runk circuit, switching means for connecting the central. station circuit an d tl ie trunk, second switching means for connecting the trunk and the. called subscribefls line, a

s automatic key in said trunk controlling said relay, said relay being inoperative until both eaegzaa source of signaling current in said trunk, a relay in sa1d trunk adapted to connect said source ]11' circuit with a subscribers line, an

- said switching connections are made and said automatic key is operated, and means controlled by the called subscriber for causmg the dlsconnection of the source of sig- -naling current from the line.

22 In a telephone-system, a plurality of subscribers lines, a central station circuit, a. trunk circuit, switching means for connecting. the central stationcircuit and the trunk, secondswitchingmeans for connecting the trunk and the called subscribers line, a source of. slgnallng current in said trunk, a relay in said trunk adapted to connect said source in circuit with a subscribers, hne, a circuit for said relay over which the.

' the source of signaling current from the line.

23. 'In a telephone system, a plurality of subscribers" lines, acentral station circuit, a

trunk circuit, switching means for connect ing the central station circuit and the trunk, second switchingmeans for connecting the trunk and the called subscribersline, a

source of'signaling current in said trunk, a

relay in said trunk adapted to connect said source in circuit with a subscribers line, a circuit for said relay, a trunk relay controlled by said first named switch connections, contacts in said circuit controlled. by

said trunk circuit, a controlling relay-controlled by said second switch connections, other contacts insaid signaling relay circuit under control of said controlling relay,

an automatic key in said signaling relay circuit, said signaling relay being inoperative to connect said source to line until said trunk is connected to the central station circuit' and to the'called line and said automatickey is operated, and means controlled.

by the called subscriber for causing the disconnection of the Source of signaling current from the line.

24. In a telephone system, the combination of 'a plurality of telephone lines, central station connecting means, a trunk circuit, means for connecting said central station connecting meansv and said trunk,

means Ior connecting the trunk to a called line, a trunlnrelay controlled bysaid first means, a source of signaling current for signaling a subscriber on--a calledline, means including a circuit for connecting said source to a telephone -line,-1contacts in said circuit controlled by said trunk relay and a key in said. circuit said last named means being inoperative to connect said signaling source-in circuit with the called line until said key and both said first named means are operated.

25. In a telephone system, the combination of a plurality of telephone lines, central station connecting means, a trunk circuit, means for connecting said central station connecting means and "said trunk, means 'for connecting the trunk to acalled line, a trunk relay, controlled by said first means, a source of signaling current for signaling a. subscribe r on a called line, means including a circuit for connecting said source to a telephone line, contacts in said circuit operated by said trunk relay, a key in said circuit,

said last named means being inoperative to connect said source to a called line until said key and both said first named means are operated and a subscribers relay adapted to interrupt the said circuit when the called subscriber responds.

26. In a telephone system, a central station,

telephone lines" terminating thereat, a connecting circuit thereat, a subcentral station, telephone lines terminating thereat,-a trunk circuit connecting said central stations, switching means for connecting the central station connecting means and the trunk circuit, switching means for connecting the trunk circuit to it called line, a trunk relay controlled over the central station end of the trunk, a source of signaling current adapted to be connected up to signal a called substation, means controlling the connection of said source, a circuit for said means, a switch in said circuit directly controlled by the trunk relay, a terminal relay controlled by the trunk-line switching means, a self-locking relay controlled by said terminal relay and a switch in the circuit of the signaling source controlling means governed by the I self-locking relay In testimony whereot I affiX my signature in presence of two witnesses.

, FRANK B. ALLEN. Witnesses C. B. Harrow, F. U. Rrcrrnr.

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