US1638295A - Telephone system - Google Patents

Description

Aug. 9, 1927.

- 1,638,295 G. R. EATON ET AL musrnoma SYSTEM Filed Nov. 13. 192-2 2 Sheets-Sheet 1 INVENTOES GEORGE KEA Y MICPAELB=STAZAK B ATTORNEY Aug. 9, 1927. ,638,295

. G. R. EATON ETYAL TELEPHONE SYSTEM I Filed Nov. 15. 1922 2 Sheets-Sheet 2 INVENTORS GEORGE R. EATON MICHAEL B. STAZAK BY ATTORNEY Patented Aug. 9, 1927.,

UNITED STATES PATENT OFFICE.

GEORGE E. EATON, OF OAK PARK, AND MICHAEL B.

ST'AZAK, OF CHICAGO, ILLINOIS,

ASSIGNOBS T0 KELLOGG SWITCHBOABID AND SUIEPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS. I

TELEPHONE SYSTEM.

Application filed November 13, 1922. Serial No. 600,554.

Our invention relates to telephone systems, and more particularly to systems in which a number of subscribers lines terminate in a private branch exchange and a number of other subscribers lines terminate in a main exchange of the manual type or of the automatic type of switchboard;

. An object of our invention isthe provision of an operators cord circuit at the pri vate branch exchange for interconnecting subscribers telephone lines, terminating therein, and also the provision of a two-way trunk circuit between the private branch exchange and main exchange, the said operators cord circuit of our invention adapted to operate in connection with said trunk circuit to interconnect asubscribers line at the private branch exchange with a subscribers line at the main exchange.

Another object of our invention is to provide battery for conversational purposes from the private branch exchange when our cord circuit is used for interconnecting subscribers lines terminating in the private branch exchange, but to provide battery for conversational purposes from the main exchange, instead of the private branch exchange, when connection is madebetween the cord circuit at the private branch exchange and the trunk circuit ofour invention.

Still another object of our invention is to place the supervisory signal at the main exchange. which notifies the operator thereat when conversation has terminated under the control of the subscriber at the private branch exchange, so that when the subscriber replaces his receiver upon its switchhook the said supervisory signal will light to indicate to the main exchange operator that the subscriber at the private branch exchange has replaced his receiver. We also place a supervisory signal at the private branch exchange under the control of the subscriber thereat so that when he replaces his receiver upon its switchh-ook the operator at the private branch exchange will be informed that the said subscriber has replaced his receiver at the same time the main exchange operator is notified of this fact. The features just set out above in this paragraph exist when the main exchange is a manually operated exchange, and should the main exchange be' an automatic exchange, the autoexchange in a trunk I private niatic switches are placed under the control of the subscriber at the private branch exchange, as is also the said supervisory signal at the private branch exchange.

A further object of our invention is the provision of means whereby the subscriber at the private branch exchange may send a series of current impulses to operate the switches at the automatic exchange or that the operator at the private branch exchange may send a series of current impulses to operate the automatic switches at the automatic exchange instead of-said subscriber.

Still another object of our invention is the provision of means whereby the private branch exchange operator may be signaled over the trunk circuit from themain exchange regardless of whether or not the said trunk circuit is engaged by a plug of a cord circuit at the private branch exchange.

Theabove features, as well as other features of our invention, will be more particularly pointed out in the following specification and. in the appended claims.

For a more complete understanding of our invention, reference may be had to the accompanying drawings, in which Fig. 1 illustrates the arrangement of our cord circuit, and

Fig. 2illustrates our trunk circuit having its one end terminating in the private branch jack and night jack, and its other end terminating in an automatic switch, and also terminating in a trunk jack at main manual exchange. In actual practice, however, it will be understood that a separate trunk circuit will extend to the automatic exchange and a separate trunk circuit will also extend to the main manual exchange. I

Referring now in general to our invention. in 1 we show a substation having an impulse-sending device D and terminating in a jack J with which is operatively as sociated a. line signal S. The cord circuit C oi? our inv ntion which is provided for the branch exchange, comprises a pair AP and GP interconnected bythe Y and Y, having the f plugs talking conductors condensers K and K interposed. In the answering end of the cord circuit C is pro vided a generator G and a ringback key RK and also a slow-acting sleeve relay SR, an answering supervisory relay AR and a supervisory signal AS. The sleeve relay SR is adapted to energize when AP is connected to a ack who e sleeve cont-act is connected to ground, and relay SR energizing places the supervisory signal AS under the control of the answering supervisory relay AB. The calling end of cord circuit C is provided with a slow acting sleeve relay SE, a calling supervisory relay CR and a supervisory signal G5, which is placed under the control of relay CR- when the sleeve relay SR is energized. An impulse-send ing device 0-D and a key DK are provided for connecting the said device OD in circuit with plug Cir, as is also provided a ringing generator G and a rin ing key BK for connecting said generator to the plug GP. A listening key LK is provided for connecting the operators telephone set O to the conductors Y and Y of cord circuit C. A slow-acting relay SCB is provided for con trolling the circuit of signal CS, said signal being either under the control of a subscriber at a substation terminating in the private branch exchange or by the operator at cord circuit C. I also provide the cord circuit C with relays BR, SGR and DR which will only operate when the cord circuit C is connected to a trunk circuit, but will not operate when the cord. circuit C is interconnecting subscribers lines at the private branch exchange. To the right of Fig. 1 we show a substation B provided with an impulse-sending device D and terminating in a jack terminal J which has associated with it a line signal S.

In Fig. 2 we show a trunk circuit TC terminating in a night jack NJ, which night jack NJ is used for the wellknown purpose in night service, and also terminating in a trunk jack TV} which is located at the private b 'anch exchange. Associated with the trunk jack TJ is a relay 27 which energizes when a plug of a. cord circuit at the branch exchange is inserted into the jack TJ, said relay 27 controlling the lighting of the supervisory signal TS. An alternating current relay AG is provided which is controlled from the main exchange for causing the signal TS to light to signal the private branch exchange operator even though a plug of a cord circuit is engaging the jack TJ. A relay BB is also provided for con trolling the circuit of relay 27 and operates when relays 27 and AC are energized. The other end of the trunk circuit TC terminates in a trunk jack TJ at a. main manual exchange, said trunk jack TJ having a cutoil relay CO and a line relay LR associated therewith for controlling a. supervisory signal SS. The answering end of a cord circuit C at the main manual exchange having an answering plug AP, a ringing key RK sleeve relay SR supervisory relay AR and signal AS for the usual wellknown purposes, is shown and is adapted to be connected to the trunk jack TJ. We also show the said other end of the trunk circuit TC terminating in a non numerical switch F S, but this is only for thsake of explanation, for in actual practice a separate trunk circuit T G will be provided be tween the private branch exchange and automatic exchange, and a separate trunk circuit will also be provided between the said private branch exchange and the main manual exchange. The switch FS operates automatically, when a plug is inserted into the jack TJ, to select an idle set of contacts 90, 91 and 92 leading to an idle selector switch. The said switch comprises an olinormal contact ON, a line relay LR and a cut-off relay CO, said relays Ll-land CO operating, when connection is made with the trunk jack TJ, to render the said trunk switch busy against being selected when in its oif-normal posit-ion, and to also close a circuit through the motor magnet M to'cause the same to more the wipers 87, 88 or 09 into engagement with an idle set of contacts 90, 91 and 92 leading to an idle selector switch.

and in case the switch FS is unable to select an idle selector switch. busy-back aicans BB are provided for notifying the calling sub scriber or operator at the private branch exchange of this fact.

Having referred to our invention in gen eral, we will now describe the same more in detail, and for aclearer understanding will first describe the manner in which a connection is established by our cord circuit between two subscribers at the private branch ex-' change. Assuming that the subscriber at substation A initiates a call. by removing his receiver from its switchhook, the calling 1, na] S appearing before the operator will light, over a circuit traced from battery. through the lamp S, normal contact 1 of jack J, line limb 2, through the now closed switohhook contacts of substation A, line limb 3, normal contact 4 of jack J to ground. The operator seeing the lighted lamp S will insert the answering plug AP into the ack J and then operate the listening key LK to connect her telephone set 0 in conversational circuit with the calling subscribers line, and will inquire the wants of the calling subscriber at substation A. When the plug AP is inserted into the jack J, an energizing cir cuitis established for the slow-acting sleeve relay SR, traced from battery, through the winding of relay SR, conductor 5. normal contact 6 of relay DR, conductor 7, sleeve contacts of plug AP and jack J to ground, and relay SR energizing over this circuit, closes an energizing circuit for the answering supervisory relay AR, traced from battery, through the lower winding of relay AR, alternate. contact 8 of relay SR, ring conductor of cord circuit 0, normal contact ill) * relay DB, conductors 9 of ringing key RX, ring contacts 01" plug AP and jack J, through the alternate switchhook contacts of substation A, tip contacts of jack J and plug AP, normal contact 10 of key BK, tip conductor and alternate contact 11 of relay SR, to ground through the upper winding of relay AR. Relay SR energizing closes a circuit for the answering supervisory signal A3 at its alternate contact 12,v but si nal AS will not light at this tion is idle, the operator will insert the calling plug GP into the jack J, whereupon a. circuit-is closed torthe slow-acting sleeve relay SR, traced rroin battery through the winding of relay SR normal contact 14: of

and 16, sleeve/contacts ot plug GP and jack J to ground. R elay SR energizing closes its alternate contacts 17, 18 and 19, which closes a circuit for the calling supervisory relay CR, but relay CR will not energize until the called subscriber responds. The calling supervisory signal CS will light over a circuit traced from battery, through the signal CS, alternate contact 18 of relay to ground at normal contact 20 of relay CR, and remain lighted until the called subscriber responds tonotify the operator when the called su-b scribe-r answers. lhe operator now operates the ringing key BK to ring the call bell at the called substation B, and ringing current may be traced from the generator G, alternate contact 21 of ringing key BK, tip con tacts of plug GP and jack J, through the call bell at substation B. ring; contacts of jack J" and plug P, alternate contact 22 to ground. When the called subscriber removes his receiver from its switchhook in response to the call bell and the key 3K is in its normal position, relay CR will energize and open its normal contact 20 in the circuit of signal CS, whereupon nal CS is etl'aced to notify the operator that the called party has responded and the operator will leave her ringing key BK in its normal position. The circuit for relay CR may be traced from battery through the lower winding oi relay CR. alternate contact 17 of relay SE, normal contact 23 of key DK, normal contact 22 of key BK, ring contacts of plug CP and jacl; J, through the now alternate contacts of the raised switchhook at subf ation B, tipcoiuacts of jack J and plug: Ci 7 l contact 21 of key Bl. normal contact 2-l of key DK, alternate contact 19 of relay SR, to

ground through the upper winding of relay CR. v

The subscribers at substations A and B are now in conversational circuit, which may be traced over the heavily marked conductors Y and Y of cord circuit C. When conversation is terminated, the subscribers replace their receiv rs upon their respective switchhooks, and the subscriber A replacing his receiver will open the circuit of relay AR, which relay, AR will de-energize and close the circuit for lamp AS, Whereupon lamp AS will light to notify the operator that the calling subscriber has replaced his receiver, and when the called subscriber B replaces his receiver, the circuit of relay CR will be. opened and relay CR will (ls-energize and close the circuit for the signal CS, causing said signal CS to light. The operator seeing the burning signals AS and CS, will know that conversation between subscribers A and B has terminated and will withdraw the plugs AP and CP from the jacks J and J. respectively, whereupon the cord circuit is restored to normal and the signals S and S are again placed under the control of the subscribers A and B, respectively.

Having described the operation of our cord circuit C in establishing a connection bet veen sul'iscribers at the private branch exchange, We will. now describe its operation. when connection is established between a subscriber at the private branch exchange and a subscriber at a manual main exchange.

Assuming now that the subscriber at substation A initiates a call and desires to converse with a subscriber the "main er:- change, the operator at cord circuit C will answer the call in the same manner as described above, and the cord circuit will operate likewise in the same manner. The operator learning that thecalling subscriber desires to converse with subscriber at the main exchange, will insert the plug GP in the trunk jack TOT, thereby closing normally open contact 26 of jack TJ by ineans of the plug OP, which clues a circuit for the slow-acting relay 27, traced from battery, through the winding of said relay 27, normal contact 28 of relay RR, conductor 29,.norma'l contact 30 oi" relay AC, conductors 3'1 and 32, alternate contact 26 at jacl-c Tel, to ground. Relay 2? over this circuit attracts its lower armature 33 to prevent the contact member 34 from closing a: circuit for the tunk supervisory signal TS at this time, and also closes its alternate contacts 35 and 36 to extend the tip and ring conductor of the trunk circuit TC through to the main exchange Where they terminate in the trunk jack TJ. The line relay LR in the line circuit at the main exchange will now operate over a circuit energizing traced from ground through the Winding of the line relay LR, normal contact 105 of the cut-off relay CO tip conductor 38 of the trunk, normal contact 40 of jack NJ, alternate contact 35 of relay 27, tip contacts of jack TJ and plug Cl normal con tact 21 of key BK, normal make-beforebreak contact 24 of key DK, normal con tact 19 oi? relay SR (the said relay SR does not energize when the plug CP is con nected to a trunk jack, as the sleeve of the jack TJ is free from ground and relay SR failing to energize relay OR- is prevented from energizing,) conductors 42 and 43, alternate make-betore-break contact 44 of relay SR, winding of relay BR, normal contact 45 of relay DR. conductor 46, alternate make-before-break contact 47 of relay SR, conductor 48, normal contact 17 of relay SR. normal make-betore liu'eak contact at? of key DK, normal contact 22 of key 12K. ring contacts of plug GP and trunk jacl. TJ, alternate contact 36 of relay 27, normal contact 41 of jack NJ, ring conductor 39, normal contact 106 of relay CO and to battery through the other winding of the line relay LR at the main exchange. The line relay LR operating closes a circuit for the supervisory signal SS to denote to the main exchange operator that a call is awaiting her attention on the trunk line, said circuit being traced trom battery through the signal SS. alternate contact 107 of relay LR to ground. Belay BR- will not energize over the circuit just traced due to the high resistance of the line relay LR, at the main exchange, and also due to the shunt circuit about relay BR which may be traced from point 82 in the above traced circuit, through resistance R, normal contact 64 of key LK, normal contact 45 of relay DR and to point 83. The operator at the main exchange noting the burning supervisory signal SS before her Will insert the answering plug AP of a cord circuit C provided for her. into the outgoing trunk jack TJ to answer the call. and upon the insertion ot said answering plug AP into said outgoing trunk ack T5, the sleeve relay SR Will operate and close its alternate contact 108, and the cut-oft relay C9 associated therewith will operate to cause the line relay LB to de-energize to el'tace the said burning signal SS in the wellknown manner. he battery now ted through the relay BR- ot cord circuit C, from the main exchange. through the windings of the supervisory relay AB in the cord circuit at the main exchange, said windings being of such resistance to permit the energization of relay BR, the circuit of relay BR being the same as traced above except as to the circuit at the main exchange, Which Will now be through the Winding of relay AR instead of relay LR,

and a further description of this is not deemed necessary. Relay AR energizing opens its normal contact 109 to prevent the premature lighting of lamp AS. Relay BR energizing closes a circuit for the relay DR, traced from battery through the upper Winding of relay DR, conductor 49, alt-ernate contact 50 of relay BR, sleeve contacts of plug AP and jack J to ground, and relay energizing closes a locking circuit for itself traced from battery through its upper Winding and alternate contact 6, conductor 7, and to ground through the sleeve contacts of plu AP and jack J. Relay DR energizing opens the energizing circuit of relay SE at normal contact 6 of relay DB, and relay SR deenergizing opens its alternate contacts 11 and 12, which ca ises relay AR to deenergize, and said relay SR tie-energizing also closes a circuit for the supervisory control relay SCR, said circuit traced from ground at the main exchange through the Winding of the supervisory relay AR, the tip conductor 38 of the trunk circuit, normal contact 40ot jack NJ, alternate contact 35 of relay 27, tip contacts of trunk jack TJ and plug GP, normal contact 21 of key 'RK, normal contact 24 of key DK, normal contact 19 of relay SR, alternate contact 53 of relay DR, Winding of relay SCR, normal contact 11 of re lay SR, conductor 55, normal inakebeforebreak contact 44 of relay SR, Winding of relay BR, alternate contact 56 of relay BR, normal contact 58 of relay SCR, conductor 46, normal makebefore-break contact 47 of relay SR, conductor 59, normal contact 8 of relay SR, conductor 48, normal Contact 17 of relay SR, normal contact 23 of key DK, normal contact 22 of key BK, ring contacts of plug GP and jack TJ, alternate contact 36 of relay 27, normal contact 41 of jack NJ, ring conductor 39 to battery through the other Winding of the supervisory relay AF. in the cord circuit at the main exchange. Relay SCR energizing over this circuit opens its normal contact 58, Which opens the circuit of relay BR, and relay BR restores, and relay SCR also opens its normal contact 60 to prevent the lighting of the supervisory signal CL. Relay BR de-energizing opens its alternate contact 56, there by opening the circuit of relay SCR, but relay SUB Will not restore, as a circuit is closed tor said relay SCR through the calling substantion A. The circuit may be traced as above described up to and including normal contact 11, Where it extends over conductor 61, normal contact 10 of key BK, tip contacts of plug AP and jack J, through the alternate SWltOllllOOlZ contacts of substation A, ring contacts 0t jack J and plug AP, normal contact 9 of relay BK, normal contact 8 of relay SR, conductor 48 and over the previously traced circuit. Thus, it

lUtl

all)

cord 'circuit from "the 1 1 g1 ounu,

is seen that the supervisory"signal CS at cord circuit (l and that'the supervisory .sig-

nal AS in the cord circuit .at the main ex change are contr l ed by the calling subscriber, and when the calling subscriber A replaces his receiver upon its switchhook, the lamp GS of cord circuit C and the super visory signal at the main exchange will light to notify the respective operators that the connection is no longer desired.

The above operation talres place upon the main eI-Ichange operator inserting the answering plug AP of the cord circuit into the outgoing trunk jack TJ of the trunk line TC. The operator at the main exchange is now in conversational circuit with the calling subscriber at substation A, which may be traced over the heavily marked conductors, talking battery being fed from the mainexchange, to the cord circuit C at the private branch exchange andcalling substation A and the main exchange pperator will inquire the wants or" the callihgsubscriber at substation A, and upon learning that he desires to converse with a subscriber at thev main exchange, she will establish connection with the called subscribers line and signal. him in the usual manner.

The calling subscriber and called sub scriber are now in conversational circuit and after conversation has terminated the subscribers rep-lace their receivers upon theii respective switchhoolrs. The calling sub scribcr at substation A havingreplaced his receiver upon its switchhoolr, the circuit for the relay SCR- in the cord circuit C is opened and the circuit for AR in the cord circuit at the main exchange is opened, and relay SCH restoring closes its normal contact 60., reby closing a circuit for the supervisory s1 l CS, traced from battery, through the 'uitl GS, normal contact '18 of rel SR, alternate contact Dlhto ground at normal contact of relay SCH; Said signal CS lighting .over tlns circuit notifies the private branch exclia1ige operator that conversation has terminated and that the calling subscriber has replaced hisreceiver, andishe will then withdraw'the plugs AP and P from jacks J and J, respectivelywhereupon .the cord circult C normal position. The superrela R at the mainexchange reimmediately upon the subscriber at substaion A replacing his receiver, closes u "for the. supervisory signal AS, traced itrom battery, through said signal AS, normal contact 109 of relay AR" to nd the main exchange operator observing this burni. 0* signal AS, willfknow that the calling sub. riber has replaced his receiver and will withdraw the plug of her he outgoing end jack the supervisory relay.

whereupon said relays restore,

54 of relay TJ of the trunk circuit TC at the main exchange.

It sometimes occurs that the calling subscriber notifies the operator at the private LK after learning the wants of the calling 7 subscriber, but leaves it in its operated po-' sition for the purpose of preventing a false disconnect signal to'be given to the main exchange operator. vVh'en the mainv exchange operator answers the call, a circuit is closed from ground through the winding of the supervisory relay AR at the main exchange, tip contacts of plug AP and jack TJ. trunk conductor '38, normal contact 40 of jack NJ, alternate contact 35 of relay .27, tip contacts ot jack TJ and plug GP,

normal contact 21 of key BK, normal contact 24 of key DK. normal contact 19 of relay SR, conductors l2 and 43, alternate contact 44 of relaySR, winding of relay BR, alternate contact (i iof listening key LK, conductor 46, alternate contact 4.7, conductor lSy'normal contact 17 ct relay SR, normal contact 23 of key DK, normal contact 22m" key RK, ring contacts of plug GP and jack TJ, alternate contact 36 of relay 2?, normal contact 1-1 of jack NJ, conductor 39. ring contacts of jack TJ and plug AP,

to battery through the other winding of the said supervisory relay A3 at the main exchange. The supervisory relay at the main exchange operates over this circuit to prelay DR energizing opens the circuit of re- SR, whereupon relay SR- restores as delay scribed above, but relay BR will not restore when relay D R energizes, due to the fact that make-betorebreak contacts ll and 47 do not leave their alternate position until after normal contacts 11 and 8 of relay SR are closed. whereby an operating circuit is maintained for the relay BR," said circuit being the same as described above. up to point 66loetween conductors 42 and43, the circuit from thispoint-Qbeing through alternate cont-act 53-ot relay DR,.-winding of relay S'GR. rormal contact 1. 1 of relay SR, conductor It 3, normal contact 4a of relay SR, winding o1 relay BR, alternate contact 64:

vent the lighting'ott the supervisory signal] i of listening key LK, conductor 46, normal contact 47 of relay SR, conductor 59, normal contact 8 of relay SR, conductor 48, and the remainder of the circuit is the same as traced above. Relay SCR operates over this circuit and opens its normal contacts 58 and 60, and the opening of contact 60 prevents the burning of the supervisory signal CS. The operator at the main exchange now converses with the private exchan e operator and upon being informed that connection is desired with a subscriber at the main exchange, the main exchange operator will make connection with the called-tor sul scribers line in the usual. way, and when. the called-tor subscriber responds the private exchange operator will request him to wait a moment until she rings the calling subscriber at substation A, which she does by operating the ring back key RE, which connects the ringing generator G to the calling line to ring the call bell at the substation A. The calling subscriber at substation A will now respond to his call bell by removing his receiver whereupon he will be in conversational circuit with the called-tor subscriber at the main exchange. The private exchange operator upon hearing the calling subscriber talk will restore her listening key LK which opens its alternate contact 6%, thereby opening the circuit of relay Bit, and the normal contact 58 of relay SCR being open, relay BR will restore, but relay SCR will not restore since a circuit is now closed through the alternate closed contacts Off the switchhook at substation A and is held energized over the same circuit as hereinbefore traced. When conversation has terminated and the subscribers hang up their rc ceivers, the supervisory signal CS at the private branch exchange and the supervisory signal AS at the main exchange will light to notify the respective operators that conversation has terminated, whereupon the operators will take down the;connect1on and the system will restore to normal in the same manner as pointed out above.

Assuming now that conversation has terminated and that the subscribers have replaced their receivers and that the private branch exchange operator fails to withdraw the plug GP from the trunk jack TJ and that the main, exchange operator de sires to use this trunk to signal the private branch exchange operator. she may do so even through the plug GP remains in the trunk jack TJ, and the manner in which it may be done will now be described.

The main exchange operator will operate the ringing key RK which will open normal contacts 110 and 111 and close alternate contacts 110 and 111 to connect ringing current to the tip and ring contacts of plug AP to bring about the operation of relay AG at the private branch exchange, over a 67, condenser C, through the winding of al ternating current relay AG, normal contact 41 of jack NJ, conductor 39, ring contacts of jack TJ and plug AP through ringing key RK to ringing generator and to ground.

Relay AG operates over this circuit and attracts its armature 68 to permit the contact member 84 to engage the ground contact 69 when relay 27 restores, said relay AC also closes its alternate contact 30, which closes a circuit for relay RR, traced from battery through the winding of relay RR, conductor 70, alternate contact 71 of relay 27, which relay 27 is energized since the plug OP is still in the jack TJ, alternate contact 30 of relay AC, conductors 31 and 32 to ground at alternate contact 26 of jack TJ. Relay RR energizing closes a locking circuit for itself, through its alternate contact 72, con ductor 32 and to ground at alternate contact 26 of jack TJ, and also opens the circuit of relay 27 at normal contact 28 of the said relay RR. Relay 27 now restores to permit the contact member 34 to engage the ground contact 69 to bring about the lighting of the trunk signal TS before the private branch exchange operator, over a circuit traced from battery through the lamp TS and to ground through the now closed contact member 34 and contact 69. The private branch oporator observing the lighted lamp TS will withdraw the plug OP from the jack TJ, which permits the spring contact 26 to re store, thereby opening the locking circuit of relay RE, which willrnow restore, and then insert the answering plug AP and throw her listening key LK to enable her to converse with the main exchange operator, thetalking battery being provided over the trunk circuit from the main exchange. When the plug AP was inserted into the trunk jack TJ a circuit was closed for relay 27, which relay 2? energizes to eiface the signal TS as described in the foregoing specification, and a circuit is also closed for relay BR, traced from ground throughthe winding of the supervisory relay AB, in the cord circuit at the main exchange, conductor 38, normal contact 10 and alternate contact 35, tip contacts of jack TJ and plug AP, normal contact 10, normal contact 414 of relay SR, winding of relay BR, normal contact 4 5 of relay DR, normal contact 47 of relay SR, normal contact 9, ring contacts of plug AP and jack TJ, alternate contact 36, normal contact 4-1, conductor 39 and through the winding of the said supervisory relay at the main exchange to battery. The supervisory relay AR at the main exchange energizes over this circuit to pre- Vent the premature lighting of the supervisory signal AS thereat, as before deto normal conta; ll of relay SB, whe

57 of relay BR, conductor 16, to ground,

through the sleeve contacts of plug GP and jack 5, and relay DR energizing closes a locking circuit for itsel1 through its alternate contact let and conductor 16 to ground at jack J. Relay DR energizes upon the insertion of the plug OP into the jack J before relay SR has time to energize, and relay DR energizing opens its normal con tact 14: which prevcntsrelay SE from enerizing. Relav SCR does not 0 aerate at this D time. The operator now operates the ring 1 ing key BK toapply ringing current to the call bell of the substation A and the subscriber in response to his call bell will remove his receiver from its switchhoolr, there by closing a circuit for relay SOB traced over the same ci *it as that relay i up cattery now flows through the winding of relay SUE, alternate contact 53 of relay DR, normal contact 19 of relay SR, normal contacts 2a and 21, tip contacts of plug Cl? and acl: J, through the alternate switchhool: contacts of substation A, ring contacts of jack J and plug GP, normal contacts 22 and 23, normal contact 1'? of relay SR, conductor 48, normal contact 8 of relay SR and over the viously traced circuit of relay BR. Relay operating opens its normal contact 58, thereby opening the holding circuit ofrelay and relay BR restores if the operator has restored her ringing key BK, but the supervisory relay at the main exchange held energized now in circuit with the relay SCH. During the time the operator is ringing the calledior subscriber at substation A, the supervisory signal GS will burn and when the lrey BK is restored and should the subscriber respond during this period, relay SCR will energize as just pointed out above, and will open its normal contact 60, where; by the signal CS is eli'aced, which will notify the operator that the subscriber has responded.

The subscriber at substation A and the operator at the main exchange are now in conversational circuit, talking battery being fed from the main exchange over the heav ly marked conductors, and when conversation has terminated the subscriber at substation A. replacing his receiver will open the circuit of the relay SCR in the cord circuit C and of the supervisory relay AR at the main exchange, thereby causing the lamp CS to light to notify-the operator at cord circuit C that conversation has terminated and the operator at cord circuit C will take down the connection, and after conversation has ninatcd the main exchange operator will raw the. plug AP from the jack: TJ, eupon the system restores to normal as described above. Should a subscriber at the main exchange desire to talk with the subscriber at substation A at the private branch,

exchange the main exchange operator will,

insert the calling end of her cord circuit C shown on the draw1n as 1t is not deemed necessary tor a clear understanding) into the jack TJ and apply ringing current to operate'relay AC to bring about the ll9'lltlllQ' of si nal TS as Jointed out above. In this instance the relays SCR and ill! will be energized by battery provided thro gh the supervisory relay in the calli end of the cord circuit C, and when U'scriber substation A replaces his r, the supervisory signal controlled by a (l relay in the said calling end will light to notify the main exchange operator that conversation has terminated, whereupon she will tal-:e down the connection, and theoperator at cord circuit will be notified of the termiinition of conversation as polntedout above.

From the above description of our invention, i is at once clear that the main exchange operator may use the trunk circuit to signal the operator at the private branch exchange, even though the plug of the cord circuit C remains 1n the trunk Jack TJ, and

further that the operator at cord circuit C.

and the operator at the main exchange will be notified that conversation has terminated iruiiecuatelyupon the subscrlber at substai n It; replacing his receiver upon its switch-' branch exchange with a called-for subscriber at an automatic exchange. v

Assuming that the calling subscriber at rue substation A of the private branch exchange-initiates a call, the private branch exc= nge operator will answer the call in the 'san'ie manner described in the foregoing specification, and upon learning that the calling suhsc iber desires to converse with a subscriber whose line terminates in an automatic er-rch ange. she will insert the calling plug OP (it th cord circuit G into the trunk jack TJ, it be. SSPil'iDlQfl now that the trunk circuit terminates in an automatic exchange instead of a manual main exchange as decribed above, whereupon relay 27 will energize to prevent the lighting of the super visory lamp TS, as was clearly pointed'out being had to this patent for a clearer understanding of the operation of the switches which. may not be understood from the en suing specification. When the alternate contacts and 36 of relay 27 are closed a circuit is established from battery through the winding of relay LR, wiper 89, normal contact or relay CO, conductor 39, normal contact 4-1 of jack NJ, alternate contact 36 of relay 2?, ring contacts of jack TJ and plug GP, normal contacts 22 and 23, normal contact 17 of relay SR, conductor 48, alternate contact 47 of relay SR, conductor 46, normal contact 45 of relay DR, through the winding of relay BR, alternate contact l t of relay 9ft, normal contact 19 of relay SR, normal contacts 24 and 21, tip contacts of plug GP and jack TJ, alternate contact 35 of relay 2?, normal contact 40 of jack Nil, conductor 38, normal contact 81 of relay CO, wiper 88 and to ground. Relay LR energizes over this circuit but relay BR does not energize over this circuit due to the high resistance of relay LR compared with that oi? relay BR, and also due to the shunt circuit about relay BR which may be traced from the point 82 in said circuit, through resistance R, normal contact 6a of listening key Lil: to point 83, and relay LR energizing closes its alternate contact 84 to place a ground upon the conductor 95 to render the switch FS busy to prevent the switch FS from being selected while busy, and also to establish an energizing circuit for outo'tl' relay CO through normal contact ON. Relays LR and CO being energized a circuit for motor magnet M is established through their alternate contacts 85 and 86, respectively, whereby said magnet M advances wipers S7, 88 and 89 into engagement with the first set of contacts 90, 91 and 92, which we will assume, leads to a busy first selector switch. Therefore, the test contact thereof is grounded due to the busy condition of the first selector switch, which may be more clearly understood by referring to the Winston Patent No. 1,197,989, referred to above, and a locking circuit for relay LB and is, therefore, established, which may be traced "from ground at the test contact 90, test wiper 87, and alternate contacts 93 and 94; and the windings of relay LR and CO, respectively. Relay CO thus maintains the circuit of driving magnet M closed, notwithstanding the opening of the circuit at 01]?- normal contacts Oll at the first step of the ductor another step and in tact continues such advancement until the test wiper 87 engages an idle test contact 90, which, we will assume, is the third one leading to a first selector switch. Assumin this is idle, as stated, it would be ungrounucd and theretore the locking circuit tor relays LR and CO is interrupted, but relay Llt being a slow-acting relay maintains its armature attracted until a locking circuit from the selected first selector switch is provided, in the manner well-known in the art, but relay CO being a quick-acting relay immediately releases its armature, opening its contact 89 in the circuit of driving magnet hill, thus rendering the switch wipers inert, thereby permitting them to remain in engagement with the contacts 0'1 the idle selector switch. W hen an idle selector switch is selccted,battery will be fed through the windings 01 an impulse relay in the selector switch to the contacts 91 and 92 engaged l the wipers 88 and 89, respectively, windings of said impulse relay being of such resistance as to permit the energization of the relay BR oyer the previously traced circuit, and relay BR energizing a circuit will be established for relay DR,

traced from battery through the upper winding of said relay DR, conductor 49, alternate contact 50 of relay Blt to ground through the sleeve contacts of plug AP and jack J. Relay DR energizing over this circuit will lock up through its alternate contact 6, con- 7 and to ground at the sleeve of jack J, and relay DR also opens the'energizing circuit of relay BR at norn'ial contact l5 and closes a circuit for relay SCR, said circuit being traced from the tip contacts of in the well-known manner, the

till

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the jack TJ and plug GP, which battery extends to said jack TJ from the wiper 88,

through the normal contacts 21, 24: and 1 alternate contact 53 of relay DR, winding of relay SCR, normal contact 11 of relay SR, said relay SR having restored when relay DR energized, normal contact 10, tip eontacts'ot plug Al? and jack 5, through the now closed alternate contacts of the switch hook at substation A, ring contacts of jack J and plug AP, normal contact 9, normal contact 8 01 relay SR, conductor d3, normal contact 17 of relay SR, normal con-l visory signal CS to prevent the same from lighting at this time. I

The operation of the finder-switch and the cord circuit C as ustdescribed above lielay OCR energizing f occurs immediately upon the insertion of the plug Cl into the jack TJ and before the calling subscriberhas time to Operate his impulse dial D. The calling subscriber at substation A now operates his dial to send impulses to operatethe automatic switches at the main exchange in the usual V6115.

known manner.

oeing from the Wiper 88, normal contacts 81 and 40, alternate contact 35 of relay 27, tip contacts of jack TJ and plug CP, normal contacts 21, 24 and i9, cOnduct' reQ, normal i contacts or jaclr ,J and plug AP, normal contacts or plug contact 36 of relay 27, normal contacts 41- Contact 9 or key RK, nor1nal contact 8 of relay SR cOnductOr, 48 normal contact 17 of relay SR normal contacts 23 and 22, ring CP and jack TJ, alternate and SQand' to the wiper 89, When the dial i o erat d this ircuit will be o ened and clos'echas is well know but relay SCR being slow-acting wilinot de-energize, as' the circuit is openedandclosed at such rapidity that the circuit will not; be opened sufficiently long to cause the de-energiz1ation of relay SCH, thus preventing the premature light ing or the signal CS. vAfter thev sending of the impulse and the called subscriber responds", it being assumed that the called sub scribers line was idle when called, the calling subscriber at substation A and the called subscriber at the automatic exchange are in conversational circuit, traced over the heavily marked conductors having the condensers K and K" nterposed, talking battery being fed from the automatic exchange.

After conversation has terminated, the subscribers replace their receiversupon their respective switchhooks, and the replacing of the receiver upon its switchho'ok at the sub station A Willopenthe circuit of relay SCR at the alternate switchhookcontacts of substation A, whereupon relay SCH Will restore and close its normal contact 60, thereby closing a circuit for the signal CS, traced from battery through the lamp CS, alternate contact 18 of relay SR, alternate contact 54 of relay DR to ground through horm'alcontact 60 of said relay SCR, YVhen the subscriber at substation A replaces his receiver, the holding circuit for the automatic switches at the automatic exchange was opened, whereupon said switches restore in the usual and well-known I manner, The private branch exchange operator seeing the burning signal CS will know that the conversation has terminated and thatthe calling subscriber has replaced hi s rece1ver upon its switchhoolr, and she will Withdraw the plugs Thec rcuit for the impulses v AP and CP from the jacks J and TJ, respeetivel whereupon relay DR restores and the signal CS is efia'ced and the cord circuit C is restoredto normal. Upon the removal of the plug CP hem the jack TJ, relay 27 restores as described in the foregoing specification, Now, as to the restoration of the switch FS,"this is effectedupon the restoration of the selector switch selected by said switch' F S, which opens the holding circuit of relay LR andcauses relay'LR to restore. Relay LR restoring, its normal contact 84 is closed, connecting ground through alternate contact ON and the winding of relay CO to battery. Thus, relay LR being de-energized and relay CO energized, the retaining pawls controlled by these [relays are disengaged from thifr associated ratchet, allowing the switch ES to restore, The restoration or the switch and the other switches at the automatic exchange may be understood more clearly by referring to theWinston patent n ioned a Reverting now to when the operator at cord circuit" answered the calling subscriber at substation A, and assuming that the calling subscriber thereat requested the operator to call the subscriber at the automatic exchange to call him b ck when the calledfor subscriber answers, the callingsubscriber in this instance will replace'his receiver, after informing the operator of his wants, and awaita call from the operator at cord circuit C v The operator willnot restore her listening key at this time but will leave itin itsoperatedj position to close its alternate contact 64; to close a circuit for the relay BR as her'einbef'ore described. The operator willnow insert the calling plug CP into the jack TJ, Whereuponan idleselector switch is selected by the switch FS in the same manner pointed out above, and when an i dle'select'or switch is selected an enerrgizing circuit is closed for relay BR, as

hereinbefore tracechand relay BR energizing closes a circuit t9 bring about the enerlz'ation 'f relay DR, and relay energizi'ng causes the restoration of relay SR as l ar y Poin d 1 1 abor e else the energizatjo of rel'ay SCH], the circuit for relay being the same as traced above up to normal contact ll where it now extends h o g orm l. when 4 o r y winding of relay B R alternate contact 64 of key LK', conductor 45, normal contact 8 of relay e cla e the previously traced cir- Quit-- Rela SQR energi ing opens its contact 58 in the holding circuit of relay BR,

rela BB does not restore since the listening key LK is thrown and its alternate contact Gels closed" to establish a holding circuit forrelayBR. Relay SCH energiz lag also prevents the eighties from lighti a i cam h er e? n w. pe-'- ates her dialing lay DK, ninety ripening the circuit of relays BB. and SCH, causing the same to restore, but whose restoration has no particular effect at this time, said key DK connecting the operators in'ipulse-sending device OD in circuit with the trunk conductors leading to the automatic switches in the automatic exchange. The operator will now operate the impulse dial OD to bring about the operation of the automatic switches at the automatic exchange to cause the same to connect to the called-tor subscribers line, and having sent the required number of impulses, she will restore her dialing key DK, whereupon relays BR and SCR will again energize, and upon hearing the response of the called-tor subscriber, will inform him to wait until she rings the calling subscriber at substation A, which she will do by operating her ringback key BK, as here nbefore described, and upon hearing the calling subscriber answer she will restore her listening key LK. The calling and called subscriber are now in conversational circuit. hen the listening key LK is restored relay BRde-energizes due to its circuit being opened at alternate contact 64: of said key LK, but relay SCR will not deenergize as it will now be heldv up over a circuit extending through the now closed alternate switchhook contacts at substation A, and signal CS will not light, as pointed out above.

hen the conversation has terminated and the subscribers replace their receivers, the holding circuit for the automatic switches will be opened to permit the same to restore and relay SCR will restore and the signal GS of cord circuit C will light to denote that the calling subscriber has replaced his receiver and the operator seeing this light will withdraw the plugs AP and GP, wliich will bring about the restoration of the system as set out above.

In connection with the finder switch FS, means are provided to indicate to the calling subscriber or the private branch operator at cord circuit C when such switch has not been able to find an idle trunk. For instance, if all of the trunks leading from contacts 90, 91 and 92 are busy, their test contacts 90 will be grounded, causing the switch to step to the last set of contacts 90, 91 and 92. There being no ground connected to terminal 90, relay CO immediately de-encrgizes but relay LR maintains its armature attracted due to its slow-acting construction, so that upon the closing of normal contacts 80 and Slot relay G0, a locking circuit LR is established from ground through busyback BB. terminal 91, wiper 88, normal contact 81. of relay CO, over the trunk conductor 38 to the calling substation A, if subscriber thereat has not replaced his receiver, or through the listening key LK and the iii in its operated position, returning over the trunk conductor 39, normal contact 80,

relay CO, wiper 89, contacts 92 and 90, .wiper 8. alternate contact 93 of relay LE to battery. A characteristic signal is thus transmitted from busyback signal BB over the path just described, whereby the subscriber at A or the operator at cord circuit C receiving such signal. knows that all of the trunks are busy and it received by the calling subscriber he will replace his receiver, whereupon lamp AS will light to give an indication to the operator at cord circuit C, and the operator seeing the burn ing lamp AS will withdraw the plug AP and GP from jacks J and TJ. The lamp AS lights when the subscriber at A replaces his receiver due to the fact that relay SR remains energized since no idle selector switch was selected and relay AR will restore, thereby closing an operating circuit for said signal AS. It the operator at cord circuit receives the signal due to the fact that she has her listening key operated when she is requested by the calling subscriber to call the called-for subscriber, she will recognize the busy condition and withdraw the plugs AP and GP, whereupon the switch FS will restore to normal in the same manner described above.

Assuming now that a subscriber terminating in the automatic exchange desires to signal the private branch exchange operator at cord circuit C, and that the plug OP of cord circuit C is still engaging the trunk jack TJ, which maintains the circuit of relay 2T closed, and that the switch FS is in its normal position, the said subscriber will operate his impulse sending device to cause a connector switch to engage contacts connected to the conductors 95, 96 and 97, whereupon an alternating current willv be sent from the connector switch over conductor 96, normal contact of jack NJ, conductor 67, condenser C, winding of re lay AC, normal contact ll of jack NJ, conductors 39 and 97 to the connector switch at the automatic exchange. The relay AG operates over this circuit and the relay 27 being energized due to the fact that plug OP is in ack TJ, a circuit is closed through relay which energizes and closes a look ing circuit for itself. said relay energizing opens the circuit ot relay 27 which will now restore to permit the lamp TS to light as hereinbet'ore clearly set out. The operator seeing the lighted lamp TS will take care of the call by removing the plug CP and inserting the answering plug AP into the jack TJ and will then extend the call as before described. Thus, it will be understood that the fact that the plug remains in the jack TJ after the conversation has termi- *sesess nated, does not prevent the trunk circuit TC from being used to signal the private branch exchange operator at cord circuit C.'

lVhile we have illustratedand described a particular arrangement of ourinvention, it is to be understood that We do not wish to be limited to the exact arrangement as shown and described, as modifications and changes will suggest themselves to those skilled in the art, but we intend to cover all that which comes within the spirit and scope of the appended claims. 7

Having described our invention what we claim as new and desire to secure by Letters Patent is: V

1. In a te ephone system including a private branch exchange, subscribers telephone lines terminating therein, a link Cir-- cuit for interconnecting said telephone lines inconversational circuit, a main exchange, a trunk circu t between said private branch exchange and said main exchange. said link circuit adapted to be connected to said trunk circuit to connect a subscribers line at the branch exchange with the main exchange, individual supervisory means at the main exchange and at the private branch exchange controlled over the said sub'scribei"s 'telephone line on either incoming or outgoing calls, to notify the operators at the private branch exchange and main exchange re-s spectively when conversation has terminated,

means whereby the'subscriber on said tele-' phone line may communicate his wants to the operator at the main eticl a'nge, or where- 4 by the operator at saidbranch exchange may conununicatc said subscribers wants to the mam exchange operator. means operative when said branch exchange operator .connnunicates the subscribers wants to the main exchange operator to prevent the said supervisory means operatingzto signal a false disconnection signal upon the replacement of the calling subscribers receiver upon its switchhooh while said subscriber is waiting for his call to be completed, means for p'ro vidi batter; for talking purposes from the int. i circuit to permit signalling of the branch exchange operator shouid said link circuit remain connected to said trunk circuit. I I

In a telephone system including a private branch exchange and a main ex i we. telephonelines terminating in said pri ate branch exchange, a trunk circuit beween said exchanges, a link circuit for interconnectine" said telephone lines and for connecting one of said telephone lines in circuit with said main esch'angeover said trnnl-r circuit, supervisory means at the main euchanee and at the private branch exchange controlled over said telephone line connected in circuit with said main exchange to indicate to the operator at saidrmain exchange and said private branch exchange when conchange may c'ommum "wants to the main exchange operator, means operative when said branch exchange opcrater communicates thesubscribers wants in exchange, and means for said trunk change, a linlr circ nectiori is no longer desired with said main eXchange on either incoming or outgoing 1 to the operator atthe' main exchange, or

whereby the operator at said branch eX "cate said subscribers to the main exchange operator to prevent the said supervisory means operating to signal a false disconnection signal upon the replacement of the calling subscribers receiver upon its switchhook while said subscriber is waiting for his call to be completed, and means for said trunk circuit for signaling the private bra'nchexchange operator over said trunk circuit regardless of whether or not the saidlink circuit is connected to said trunk circuit. I

3. In a telephone system including a private branch exchange having subscribers telephone lines terminating therein, a link circuit for interconnecting said lines, a main exchange, a trunk circuit terminating in said private branch exchange and said main exchange, said link circuit adapted to be con nected to said trunk circuit to connect a sub scriber on one of said telephone lines in conversational circuit with said main exchange,

supervisorymeans for said mainexcha'nge and said private branch exchange controlled over thesub'scrili efls line which is in conversa'tionalcircuit with the main exchange to notify the'private branch exchange operator and" main exchange operator when the conve'sational circuit is no longer desired on either incoming or outgoing calls, means wherebyth'e subscriber on said telephone line may communicate his wants to the operator atl'he main exchange, r whereby the operator at said branch exchange ma communicate said su'b's'cribers wants to the main exchange operator, means operative when said branch exchange operator communicates the subscribers wants to the main exchange operator to prevent the said supervisory means operating to signal a false disconnection signal upon, the TGPlRCQH'HEHtof the cal in; subscribers receiver upon its switchhook whilesaid' subscriber is waiting for his call to be completed, means for providing tall:- ing battery. from the main exchange, and

automatic means for said trunk circuit for signaling the private branch exchange op- 4. In a telephone system including main exchance a rivate branch exchange having subscribers telephone lines terininating;-

therein, a trunk circuit terminating in said private branch exchange and said main ex- I v U I H at the private branch exchange for'ccnnectmg one er said sub scribers" lines in circuit with said main exchange over said trunk circuit, individual supervisory means for said private branch exchange and said main exchange, and means controlled by the subscriber at the private branch exchange for controlling said individual supervisory means on either incoming or outgoing calls for signalling for a disconnection at both. exchanges, means whereby the subscriber on said telephone line may communicate his wants to the operator at the main exchange, or whereby the operator at said, branch exchange may communicate said subscribefls wants to the main exchange operator, means operative when said branch exchange operator communicates the subscriber s wants to the main exchange operator to prevent the said supervisory means operating to signal a false disconnection signal upon the replacement of the calling subscribers receiver upon its switchhook while said subscriber is waiting for his call to be completed, and means for said trunk circuit to permit the signalling oi the private branch exchange should said link circuit remain connected to said trunk circuit.

5. In a telephone system including a private branch exchange and a main exchange, a trunk circuit terminating in said branch exchange and said main exchange, a subscribers telephone line terminating in said branch exchange, a cord circuit for connecting said telephone line to said trunk circuit, individual supervisory signalling means for said main exchange and said private branch exchange, said means controlled by the subscriber at said private branch exchange on either incoming or outgoing calls for inclicating termination of conversation at both exchanges, means whereby the subscriber at said private branch exchange may commun-icatc his wants to the operator at the main exchange, or whereby the operator at said branch exchange may communicate the said subscribers wants to the main exchange operator, means operative when said branch exchange operator communicates the subscribers wants to the main exchange operator to prevent the said supervisory means operating to signal a false disconnection signal upon the replacement of the calling subscribefis receiver upon its switchhook while said subscriber is waiting for his call to be completed, and means for said trunk circuit for permitting the operator at said cord circuit to be signalled from said main exchange regardless of whether or not said cord-circuit is connected to said trunk circuit.

6. In a telephone system including a private branch exchange having subscribers telephone lines terminating therein, a main exchange, a trunk circuit between said private branch exchange and said main ex change, a cord circuit for interconnecting said telephone lines and also for connecting any one of said lines to said trunk circuit, means for providing talking battery from said main exchange, supervisory means for said cord circuit for indicating to the operator thereat when the subscriber has terminated conversation, supervisory means at said main exchange for indicating when said conversation has terminated, both of said supervisory means being controlled by the subscriber at the private branch exchange on either an incoming or an outgoing call, means whereby the subscriber at the private branch exchange may communicate his wants to the operator at the main exchange, or whereby the operator at the branch exchange may communicate to said subscribers wants to the main exchange operator, means operative when said operator communicates the wants of the subscriber to the main exchange operator to prevent the said supervisory means operating to signal a false disconnection signal upon the replacement of the calling subscribers receiver upon its switchhook while said subscriber is waiting for his call to be completed, and means for signalling the branch exchange operator from the main exchange prior to the disconnection of said cord circuitefrom said trunk circuit.

7. In a telephone system, a private branch exchange, a subscribers telephone line terminating therein, a main exchange, a trunk circuit for interconnecting said exchanges, a

cord circuit at the private branch exchange for connecting said telephone line to said trunk circuit, means whereby the subscriber on said telephone line may communicate his wants to the operator at the main exchange, or whereby the operator atsaid cord circuit may communicate said subscribers wants to the main exchange operator, means for recalling said subscriber when the main exchange operator fulfills the wants of said subscriber, means for providing talking battery from said main exchange, and supervisory means at the main exchange and at the private branch exchange controlled over said telephone line on either incoming or outgoing calls for notifying the respective operators thereat when the subscriber on said telephone line replaces his receiver upon its switchhook and to signal for a disconnection, means for rendering said supervisory means inoperative when the subscriber replaces his receiver upon its switchhook while waiting for the operator at the private branch exchange to communicate his wants to the main exchange operator, and means for said trunk circuit to permit the signalling of the branch exchange should said link circuit remain connected to said trunk circuit.

8, In a telephone system including a via a vate branch exchange, subscribers telephone lines terminating therein, a cord circuit for interconnecting said telephone lines, a main exchange, a trunk circuit for interconnecting said exchanges, said cord circuit adapted to be connected to said trunk circuit to extend a call from the private branch exchange to the main exchange, means whereby the subscriber at said telephone line may communicate his wants to the operator at the main exchange, or whereby the operator at said cord circuit may communicate said subscribers wants to the main exchange op erator, means for recalling the calling su scriber when the branch exchange operator effects the call to the main exchange, means for providing talking current'from the main exchange, individual supervisory means for said private branch exchange and said main exchange controlled by the subscriber at the private branch exchange on either incoming or outgoing calls for indicating to the operators at said exchanges when conversation has terminated, means operative when the operator at the private branch exchange er"- fects the subscribers call to the main exchange to prevent the supervisory means operating to signal a false disconnection signal when the subscriber replaces his receiver upon its switchhook while waiting for his call to be completed, and means for said trunk circuit to permit the signallng of the branch exchange should said link circuit remain connected to said trunk circuit.

Signed by us at Chicago, in the county of Cook and State of Illinois, this 9th day of November, 1922.

GEORGE R. EATON. MICHAEL B. STAZAK;

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