US1574954A - Telephone-exchange system - Google Patents

Description

March 2 1926.

J. L. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed June 6, 1921 6 SheBt$-She8 l March 2,1926.

J. 1.. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed June 6, 1921 6 Sheets-Sheet 2 ANQTHEFR TRUNK .7 11 .6

March 2 1926. I

1 J. L. WR!GHT' TELEPHONE EXCHANGE SYSTEM Filed June 1921 e sheets-sheet s March 2,19%, 1,514,954

J. L. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed June 6, 1921 6 sheets- Sheet 4 March 2 1926. 1,574,954

7 J. L. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed June 6, 1921 6 Sheets-Sheet 6 Patented Mar. 2, 192%.

entree stares earner crates.

JOSEPH L. WRIGI-I'l, or CLEVELAND, OHIO, Assmnon or ONE-HALF T0 Poona SOUND TELEIHONE COMPANY, OF EVERETT, W'ASI-IIIYGTON, AND ONE-HALF TO INCQRZPORATED, OF NEW YORK, N. '55., A' COR- WESTERN ELECTRIC COMPANY, PORATION.

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Application filed June 6, 1921. Serial No. 475,224.

To all whom it may concern:

Be it known that JOSEPH L. \Ynnurr, a citizen of the United States, residing at Cleveland, in the county oit' Cuyahoga and State 0t Ohio, has invented certain new and useful Improvements in ielephone-Exchange Systems, of which the "following is a specification.

My invention relates to telephone exchange systems, and especially to systems employting operators in conjunction with automatic apparatus.

The object of my invention to produce a system which is rapid in operation and requiring but a minimum number of acts onpart of the operator at the central office to receive and establish connections.

My invention embraces such features as automatically associating a calling line with an idle operators cord circuit or trunk, to automatically connect the operators tele phone set to the calling line and at the same time render the operators position busy against other calls until the connection is established. In establishing connections the only duty performed by the operator isthat of placing the plug associated with the trunk or cord into the jack of the called subseribers line. The testing, ringing and automatic disconnect of the calling and called subscribers lines is performed automatically without any attention on part of the operator. 7

The calling lines are automatically connected to idle trunks or cord circuits by means of what are termed tens and units relays. These relays are formed into groups and operated in order to establish connections in the manner similar to corresponding relays of the following Clement patents: 1,105,490 of July 28, 1914; 939,188 of November 2, 1909; 1,107,146 of August 11, 1914,

and 1,107,152 of August 11, 1914.

In the present instance provision is made to prevent interference in case of simultaneous calls in the same or different groups of tens and units relays. Provision is also made for enabling a large number of what are termed primary trunks to be rapidly distributed among a large number of what are termed secondary trunks. These secondary-trunks terminate in cord circuits located at the various operators positions Arrangements are made so that in case a calling line is connected to one of the cord circuits and connection is desired to a sub scribers line located in another, exchange, the operator can cause the calling line to become disconnected from the cord circuit and to be automatically trunked to the de-' sired branch exchange in which the wanted line is located.

Other features of my invention. will pointed out in the detail description to' follow. V

My invention'is illustrated in the accompanying drawings, wherein:

Figure 1 shows a plurality of subscribers" line equipn'ients at the central oiii ce with a set of control relays for regulating the action of the tens and units relays. V

Figure 2 shows a primary trunk with its associated tens and units relays. c

Figure 3 shows the circuits and relays for controlling the tens and units relays associated with the secondary trunks.

Figure 4 shows a portion oi a secondary trunk with means for controlling individual groups or sets of trunks.

l igure 5 shows a secondary trunk terminating on a cord circuit at the operators position.

Figure 0 is the trunk circuit extending between exchanges Referring to Figures 1 and 2, relay 203 represents a tens relay associated with the prin'iary trunk, while relay 204; represents one of the units relays associated with this trunk. In practice. and as disclosed'in the Clement patents mentioned. there will be a bank or group of these relays associated with each primary trunk. Each tens relay will preferably contain contacts associated with ten subscribers lines. In case ten re lay-s are provided then each primary trunk is capable of serving one-hundred subscribers lines, Each trunkin this case will also be provided with ten units relays in. order to form the proper cross combinations with the tens relays.

Figure 1 shows the line and cut-oft relays designated as 111. 112 and 113.

ciated with the primary trunks. A similar group of relays numbered 1 to 10 of which only three are shown, serve to control. the action of the units relays associated with the primary trunks. Associated with each of therelays 1 to'10 is a master relay such as 101- which serves to connect" the units wires in a group oftten linerelaysso asto enable one or more relays of the group, 1 to 10 to be operated as the case maybe. is the contacts associated with relays 1 to 10 for controlling the master relays are in series relation it of course, follows that the operation of but one of these relays is effected. The series contacts are guardedby the portion 111 of the switch X. This switch X is a step-by-step switch provided with three sets of wipers and bank contacts This switch is caused to step once at each call originated and also in *ase any abnormal condition is created.

As only one master relay such as 101 is capable of being operated at the same instant it-follows'that calls can be originated at the same instant from a particular group of ten lines whose connections are controlled by'the operated relay 101. The operation of relay 101 serves to control the operation of the tens relay associated with the primary trunk. l lach master relay as 101 controls an individual tens relay of the group. Relay 102 is operated by any relayin the group'l to 10 and serves when so operated to sever the tens starting wires to prevent further operation of relays 1 to 10 The contacts of relays 1 to 10- which control the operation of the units relays of the n'imary trunks are also in series relation-so that but one units relay of-a group can be operated at the same time. These seriescontacts are guarded by means of the portion 112 of the switch X.

In case one of the series wires or contacts are broken preventing. the connection. frombeing established from the calling line to the primary trunk the switch X will automatically step thereby shifting the ground connections directly to contacts on relays of the sets 1 to 10 and 1 to 10. During this shifting. relay 109 will be operated to restore the control relays formerly-operated.

The portion :113 of-the switch X controls the starting wires to the various primary trunks; \Vlum however, conneetio'n is estahlishcd the starting wire isshifted to the next trunk in the series inorder to provide tonuniformuse of these trunks.

The starting conductor as shown in Figure 2 extends in series through the contacts of relays206'and'202 of each primaryt-runk. A tap orconnection is made to each primary trunk through the-contacts of the portion: 113 of the switch With this arrangement each primary trunk has an individual =starting circuit extending from a particular contact on the switch X. This series arrangement is the same as that of the s ries contacts of the sets of relays 1 to 10 and 1 to 10 When the switch, as shown in ure l is resting on the-first contact and should relays 10 and 10 beeperated then the circuitscontrolled by their series contact would extend through the contacts of all the lower relays in the series. This arrangement of wiring is made in order to guard against always starting from a certain point in the series.

Referring to Figure 3. a similar set of? control relays to that of Figure 1 are shown. The operation of these relays is similar to those of Figure 1 and need not be described in detail at this point. The shifting or emergency switch Y associated with this set of relays is, however, not steppedupon the origination of each call but is only operated in case of abnormal conditions.

Referring to Figure 4. the tens and units relays 404 and 405 of the secondary trunk are operated in the same manner as are similar relays of the primary trunk and the same number of these relays will preferably b allotted to each secondary trunk.

The starting wires leading from the portion 314- of the switch Y of Figure 3 instead of'leadingdirectly to the control relays such as 103, one of which is associated with each secondary trunk are connected in multiple to contacts of a set of relays such as 401. Each relay of this set has starting conductors associated with a particular set of seco1 dary trunks. The starting conductors are in series relation. In other words when one trunk of a group is busy a relay associated with that-trunk serves to shift the starting wire to thene xt trunk in the series:

In case all of thetrunks eta group controlled by relay 401 are busy then the switch Z will step to the next contact and thereby cause the operation of a relay as 4-01 associated with the next group of second'ary trunks.

Vith the foregoing arrangement it is possible to allow the interconnection of a large number of primary trunks with an equally larger'number of secondary trunks.

Referring to Figure 5, the secondary trunk-is show-n terminating in a plug P. This plug-is connected to a flexible conductinn cord of the usual type. Condensers 49 and-59 are inserted in the talking conductorsof the cord circuit in the usual manner. Relay 501 provided with two windings serves to supply talking current tothe calling subscriber whiletalking current is supplied to the called subscriber through the trim-ling of relay 504: and the winding of the relay 505.

Relay 5001sautomatically operated upon the origination of a call and serves to connect the operators telephone set to the trunk while lamp 512 is also lighted at the same time thus indicating to the operator upon which trunk or cord circuit the call is connected. Relays 502 and 509 are slow acting); relays, the :toriner serving to prevent accidental disconnect. ot the calling si'ilaecribefis line in case he should inadvertently operate his switch hoolt. Relay 510, 01 erated'in conjunction with the resistance coil 120, to control the action 01 the entail? relay of the called line. lVhcn the plug; is placed in' the jack .l such as shown in vFigure l, relay 5310 is placed in series with the cut-oil relay of the line associated with. the jack. When the windings of relay 510 and the cut-oil relay alone are placed in series they will both operate, but when the resistance coil 1.29 is inserted in series with the windings of these relays then relay 510 alone will remain operated and the cut-oil relay will restore.

Associated with the cord circuit is a ringing switch R for automatically supplying ringing current to the line oi the called sub scriber. Each cord circuit is provided with a tour-party ringing kex K oi the usual locking and indicating type. Each key isprovided with master springs 517 which are only operated when any one of the four but tons oi the set is in its "fully depressed position.

Figure 6 comprises a trunk jack 000 provided with tip and sleeve springs which are connected to the primary windings 001 of the ordinary repeating coil, thercenter point being grounded as illustrated.

'The third conductor of the jack 600 is connected to the winding of relay 603 which when energized bridges the secondary windruns 602- of the repeating; coil across the tipand'ring conductors extending to the secondary trunk control circuit in the distant oflice. v

Relay604t is the cut-off relay. i

It will be understood that the trunk shown in Figure 6 leads to a distant office where it is further extended by apparatus 009 similar to that shown in Figures 3, 4 and 5.

The operation of the system for a local call is as follows:

Subscriber No. 11 upon removing his receiver energ'izes the line relay associated with his line. The operation of this relay completes the circuit of relay 1 by the following path ground contacts of line relay, 16, contacts of relay 102, 17, winding of re lay 1 to battery B through the contacts of relay 109. The operation of relay 1 coinpletes the circuit of relay 102 and thereupon the initial energizing circuit for relay 1 is broken. The circuit of this relay is, however, maintained locked to ground over conductor 16.

The operation of relay 1 also completes the circuit of relay 101 by the t'ollowipg' path: ground portion 111 of the switch I 1.). contacts of relay 1*, 20, winding of relay 'The Cll'OUlt'OTi the control relay 200 of an idle primary trunk is completed as follows: ground, contacts of relay 1 d0, contacts of relay 500, 11, portion 113, of the switch X,

A12, contacts o'trelav 206, 43, winding of relay 200, to battery B. The operation of relay'200 allows the circuitv0t the tens relay 203 to be completed by the following path:

ground, contacts of relay 101, 3 1, contacts of relay 200, 35, winding of relay 203, to

battery B. The operation of relay 200 also allows the circuit of the units relay 204 to be completed by the following path: ground. portion 112 ot-the switch X, 27', contacts of relay 1 28, contacts of relay 200, 29, winding of relay 20 1, to battery B. The operation of relays 208 and 204 places relay 206 in series with the winding of the cut-oft relay associated with subscribers line N0. 11 by the following path 2 battery B, winding of relay206, .66, contacts of relay 204, 65, contacts of relay 203, 64, winding of the cut-off relay to ground.

The ope-ration of the 'cut-ott relay disconnects and causes the restoration of the line relay associated with subscribers line No. 11. The restoration of this relay removes ground'from the locking contacts of relays 1 and 1 The restoration of relay 1 releases relay 102 and also relay 101. The restoration of relay 1 releases relay 103 and also relay 200 (Figure 2).

The operation of relay 206 also servesto disconnect relay 200.

' While relay 200 is energized it completes the circuit to relay 202 which disconnects the starting wire'i leading tothe next trunk of' the series, thus preventing any possible interference with the relays of that trunk.

The operation of relay 200 also completes the circuit of relay 201 which thereafter has its circuit completed or maintained through its locking contact to ground and to battery B through the contacts of relay 205.

The operation of relay .206 when placed in series with the cut ofl' relay of the calling line disconnects the starting wire from relay 200 and continues it to the next trunk of theseries..

The circuits of relays 203 and 204 are both maintained locked to ground through the contactsof relay 201. Relay 204 has a resistance coil 31 included in its locking circuit while relay 203has a similar coil 37 pletes the circuit of relay 300 by the follow- 7 ing path: ground, contacts of- relay 201, 70,

contacts of relay 206,71, winding of relay 300 to battery B. The ope-ration of relay 300 completes-the circuit of relay 1 by the following path: ground, contacts of relay 300, '82, contacts ofrelay 308, 8'3, winding of relay-1 to battery B through the contacts of relay 304. The operation of relay 1 completes the circuit of relay 308. After the operation o't'relay 308 the circuit of reley 1 is maintained locked to ground over conductor 82. The operation of relay 1 also completes the circuit of relay 307 by the tollowin path: ground, portion 313 of the switch 1, 96,"contacts of relay 1", 97, winding of relay 307 to battery B. The operation-ofrelay 307 allows the circuit of relay 1 to be completed by the following path: ground, contacts of relay 300, 78, contacts of relay 307, 79, contacts of relay 310, 80, windingof relay l 81, to battery'B through the contactsof relay 304- The operation of relay 1 completes the circuit of relay 310 which opens the initial energizing circuit of-relay 1 which thereafter has its circuit maintained locked to ground over conductor 79.

The operation of-rela-y 1 also completes the" circuit of'relay 401 of a group of idle secondary trunks by the followin'g' path: ground, contacts of relay 1 98, portion 409 of the switch Z, 99, winding of relay 401 to battery 13. The operation of relay 401 allows the circuit of relay 403 associated with an idle secondary trunk to be completed by thefollowingzpath: ground, contacts of relay 1 104, winding of relay 309, 105, por tion 314of-the switch Y, 106-, contacts of relay 401, 107, contacts of relay 408, 108,

' contacts of relay 402, 109, contacts of relay 406. 110, winding of'relay 403 to battery B.

The operation of relay 403 allows the circuit of the tens relay 404 to be completed by the following path: ground, contacts of relay 307- (Figure' 3), 85, contacts of relay 403, 95, winding or relay 404 to battery B. Theoperatiouxof relay403 also allows the circuit of the units relay 405 to be completed by tl'IG fOIlOWlIIgpath: ground, contacts of relay 309,86, coil 87 88, portion'312:

of the switch Y, 89, contacts of relay 1, 90, contacts of relay 403, winding of relay 404, to battery B.

The operation of relays 405 and 404 connects the primary trunk to the secondary trunk whereupon relay 402, (Figure 4) is placed in series with relay 205 by the following path: battery B, winding of relay 402, 78, contacts of relay 405, 70, contacts of relay 404, 7 5, winding of relay 205, to ground.

Relay 405 after being energized has its circuit maintained to ground by the following path: battery B, winding of relay 405,

contacts of relay 405, coil 92, 93, contacts 0trelay 402, 112 to ground through the contacts of relay 509 (Figure Relay 404 after bein energized has its circuit maintained locked by the following path: battery B, winding of relay 404, contacts of relay 404, 94, winding of relay 406, 93, contacts of relay 402, 112 to ground through the contacts of relay 509. The operation of relay 402 which maintains the circuits of relays 405 and 404 energized in the manner just described also shifts the starting conductor 10? to the next trunk in the se ries or group. Relay 409 was energized at the first operation of relay 403 and serves to sever the starting circuit leading to the next trunk in the series or group to prevent interference.

The operation of relay 205 (Figure 2) re moves battery from the winding of relay 201 thereby causing its restoration. The restoration of this relay removes ground from the winding of relay 300 Figure 3) which upon restoring releases relays 1 and 1 The releasing of relay 1 causes the restoration of relay 308 and also the restoration of relay 307. The restoration of relay 1 causes the restoration of relay 310 and also relays 309, 401 and 403.

The operation of relay 402 and relay 406 completes the circuit of relay 500 (Figure 5) by the following path: ground, contacts of relay 509, 112. contact-s of relay 402, 113, contacts of relay 406. 114, winding of relay 500, 115, contacts of relay 510, 110 to battery B through the contacts of relay 508.

The operation of relay 500 connects the operators telephone set directly across the tip and sleeve conductors 48 and 58 allowing her to converse with the calling subscriber. The lamp 512 has its circuit completed in multiple with the winding of relay 500 thus indicating to the operator that a calling line is connected to the trunk or cord circuit.

The operation of relay 500 completes the circuit of relay 408 by the following path? battery B, contacts of relay 500, 117, winding of relay 408, to ground. The operation:

of relay 408 which is common to the'par' ticular operators position upon which a secondary call is received, serves to shift the starting wire ifOlll all oi the cord circuits associated with that position to preyent other calls being received thereon. I

ltelay 407 is also operated in multiple with relay -108. in case there are twenty-live cords or trunlas to an operators position, relay 108 in operating will render cords 1 to 13 unselectable while relay 407 will render cords 14 to 25 unselectable.

As soon as the primary trunk is connected to the secondary trunk then battery supply is furnished to the calling subscriber throughthe windings of relay 501 connected to tipand sleeve conductors l8 and respectively. The operation of relay 501 completes the circuit of the slow-acting relay 502 but at this time no ell'ect is produced by the operation of either of these two relays. a

The operator upon learning the number desired places the plug P into the jack of the called-for line. In making this connection the operator pays no attention to the condition of the line. The insertion of the plug places busy test relay 507 and the cutoli. relay of the called line in series. As the busy test relay 507 has its winding connected to the. grounded side of battery and as the winding of the cut-off relay also has its winding connected to the grounded side of battery no effect is produced in case the line is idle.

The operator disregarding the fact whether the called line is busy or idle presses one of the ringing buttons thereby connecting the proper character of generator current to the normally open contact of relay 522.- lVhen relay 522 is operated the generator current is connected to the tip por tion' of the plug P through the normally open contacts of relay 521. Relay 522 IS operated by the following path: ground, contacts 52 1 controlled by the rotating cam 523 winding of relay 521 winding of relay 522, 147, normally open contacts of relay 510, normally open contacts of relay 503, 145, contact of relay 509, 144, contacts of relay 505, contacts of relay 506, contacts of relay 510, to battery through the back contacts of relay 508. Relays 521 and 522 being opcrated intermittently connects generator current to the line of the called subscriber,

When the operator depressed the ringing button it caused the operation of the master contacts completing the circuit of relay 503 by the following path: battery B, contacts of relay 508, springs 517, 150, contacts of relay 502, winding of relay 503, resistance coil 136,135, contacts of relay 509 to ground. '1 he operation of relay 5 03 closes the tip and sleeve conductorsv and connects the winding of relay 10 in series-with the cut-off relay of the called line by the following path: battery B,-winding of relay1510, 130, contacts the of. relay 501, 131, contacts of relay 503,

sleeve of plug P, jack of the called line,

winding of cut-oil relay to ground.

'1 he operation of relay 510 disconnects the winding of relay 507.

ll'heu the called subscriber answers during a non-ringing interval, relays 504 and 505 are operated. The operation of relay 50a completes the circuit of relay. 506 by following path: battery 13, contacts of relay 508, contacts of relay 510, contacts of relay 50 1-, winding of relay 506, 135, contacts of relay 509, to ground. Ground is also supplied in multiple to conductor 135 through the normally open contacts of relay 50-1. This latter ground connection serves to maintain relay 500 energized in case relay 509 should be energized in case the calling subscriber should be the first to replace his receiver. After relay 506 is operated its circuit is maintained locked directly to battery through its associated locking contact.

l v hen the connection was established and relay 510 operated the circuitof relay 500 was disconnected thereby disassociating the operators telephone set.

The restoration of relay 500 opens the circuits of relays 407 and 408 thus allowing calls to be received upon the cord circuits associated with this particular operators position.

At the tern'iination-of the conversation the calling subscriber replacing his receiver causes the deenergization of relay 501 and consequently the deenergization of relay 502. The restoration of the latter, relay closes the circuit of relay 509 by the fol lowing path: battery B, contacts of relay 508, contacts of relay 510, contacts of relay 502, winding of relay 509 to ground. The operation of relay 509 removes ground from conductor 135 but as relay 504i is operated at this stage relay 503 will remain energized. The operation of relay 509 connects ground to the winding'of relay 402 by the following path: ground, contacts'of relay 509, 77, 78, winding of relay 4 02 battery B. As relays 4.02 and 205 are in series this direct ground connection serves to shunt and cause the restoration of relay 205. The restoration of relay 205 removes ground from the locking contacts of relays 203 and 20d thereby causing their restoration and to disconnect the line of the calling subscriber from the primary trunk. The restoration of relays 203 and 20% breaks the series connection between relays 206 and the cut-off relay of the calling line. The restoration of relay 206 restores the primary trunk to its normal position.

The called subscriber replacing his receiver causes the restorationof relays 501 and 505. Relay 505 when restoring connects battery to the winding of relay 503 by the following path: battery B, contacts of restore.

relay 508, contacts of relay 510, contacts of relay 502, contacts of relay 505,- contacts of relay 506 to the. winding of relay 503. The other terminal of relay 503 being connected to battery through its locking contact the relay will thereby beshunted and caused to The restoration of relay 503 severs the tip and sleeve conductors and allows the resistance coil 129 to be placed in series with the winding of relay 510. The insertion of this coil is between the winding of relay 510 and the winding 01 the cut-oil relay of the called line. This new series path is as tollows: battery B, Winding of relay 510, coil 129, contacts of relay 510, conductor of plug P, jack J, winding of the cut-oil relay to ground. The resistances and adjustments of the relays are such that relay 510 will remain energized but the cut-off relay of the called line will restore and thereby allow the line relay of that line to be replaced and in readiness to be operated in case the subscriber should originate a call while the plug remains in the jack.

The restoration of relayi l momentarily connects ground to the winding of relay 510 by the following path: ground, contacts of relayv504t, contacts of relay 501, 124, contacts ot'rclay 506, contacts of relay 503, contacts of relay 510, coil 129, Winding of relay 510 to battery B. The eilect of this momentary ground assists in causing the restoration of the cut-oil relay as its winding is also connected to ground. As relay 509 is energized and 504 deenergized at this period ground is; removed from conductor 135 allowing the restoration of relay 506.

.The operator is made aware of the fact when both subscribers have replaced their receivers due to the lighting of the signal lamp 133, whiclrhas its circuit completed by the following path: ground, contactsof relay 509, lamp 133, contacts of relay 505, contacts-of relay 502, contacts of relay 510, to battery B through the contacts of relay 508. The opera-tor upon receiving the disconnect signal removes the plug from the jack there-by breaking the circuit of relay 510. The restoration of this relay opens the circuit of relay 509 causing its restoration, thereupon the cord circuit is in condition for receiving other calls. Relay 509 in restoring also removes ground when the winding of relay 402 causing its restoration.

.In'case the called subscriber does not answer and the calling subscriber should replace his receiver the release of the connection is efiectedin the following manner: relay 501 restoring opens the circuit of relay 502. After the restoration of relay 502 ground is connected to the third conductor of the plug P by the following path: ground,

.ccntactsof relay 504-, contacts of relay 501,

cc ntacts of relay 506, contacts of relay 503 to the third conductor of the plug-P. This momentary ground connection serves to shunt the cutoff relay of the called line and the action of relay 509 after the complete restoration of relay 502'opens the circuit of relay 503 which upon restoring allows the resistance coil 129 to be included in series with the winding of relay 510 and the winding of the cut-oil relay ot' the called line.

From the foregoing description it will be noted that the cut-off relay of the called line is restored by the calling subscriber in case the called subscriber does not answer even though the plug remains in the jack. The same ellect is produced upon the cut-off relay of thecalled line in case the called Subscriber answers and afterward replaces his receiver.

In case the called-for line is busy when the plug is inserted in the jack, thenrelay 507 will be operated, due to battery B being supplied through'the winding of arelay 510 associatedwith another cord circuit. The operation of relay 507 under :these conditions completes the circuit of relay 508, theoperation of relay 1508' connectsa suitable busy tone signal to the tip conductor 4:8 .in series with the condenser 141/ thus notifying the calling subscriber that :the called line is busy.

The operator, of course, is-not aware that -the called line is busy and in attempting to ring the called line by pressing the proper ringing-buttonis unable to cause theoperation of relay 503. The operation of relay 50S-removes battery. from the mastercontacts 517 of the ringing key thus rendering the action of these contacts ineffective. As relay 503 is not operated it, of course, fol lows that relay 510 is not connected to the third conductor of the plug and consequently its operation is prevented.

Relay 508, can be provided with a signal lamp as shown thus indicating to the opera tor that the called line is busy.

The calling subscriber upon receiving the busy tone signal replaces his receiver, causing the restoration of relays 501 and 502. The restoration of these relays completes the circuitof relay 509 by the following path: batteryB, contacts of relay 508, 139, contacts of relay 502, w1nding of relay 509 to ground. The operationnof relay 509 conipletes the circuit of the disconnect lamp 133 and the operator observingthis'signal withdraws the plug from the-jack, allowing the restoration of relay 507, which-upon restoring opens the circuitof relay 509.

The selection of a group of secondary trunks is made in the following manner In case all the trunks in a group controlledby arelay-et0l (Figure 4:) which is operated are busy, it willnaturally follow that relay 309 whose winding is included in series with :thestarting circuit will not be operated in series. with some :trunksrelay suckers-403 (Figurefl'). Inca-Se all ofjthe trunks of a group are busy and relay 309call originates. The lamp or signal 133 fails to operate their the circuit of the stepping magnet 414 of the switch will be completed and cause the switch to step. Relay 410 is operated in n'niltiple with the winding of relay 401 and completes the circuit of relay 411. The operation of relay 411 completes thecircuit of relay 412. The operation of this latter relay allows the circuit of the stepping magnet 414 to be completed by the following path: back cont-acts of relay 309, 100, contacts of relay 311, 101, contacts of relay 412, contacts of relay 413, 103, winding of magnet 414 to battery B. The operation of the magnet completes the circuit of the vibrating relay 413 which in operating opens the circuit of the magnet itself. The action set up between the magnet 414 and the relay 413 is such that the switch Z steps until relay 309 is operated in series with the winding of some relay such as 403 of an idle secondary trunk.

Under normal conditions relay 309 will operate and restore, before the set of relays 410, 411 and 412 fully operate. Itwill also be noted that while relay 309 is energized it completes the circuit of a slow acting relay 311 which serves to open the circuit extending to the stepping magnet 414 to prevent its operation.

From the foregoing it will be noted that the switch Z will not step unless all of the secondary trunks of a particular group are busy whereupon it will step and connect the next set of trunks. This operation will be kept up until a group containing an idle trunk is reached.

The switch X of Figure 1 is caused to step at each incoming call in the following manner: lVhen any line relay operates it connects ground to the common conductor 25 thereby completing the circuit of relay 105 through the back contacts of relay" 104. The operation of relay 105 completes the circuit of relay 104 and relay 104 in operating opens the circuit of relay 105. Relay 105 restoring in advance of relay 104 completes the circuit of the stepping magnet 110. This stepping magnet has its circuit closed by ground supplied through the back contacts of relay 105 and the front contacts of relay 104.

Having described the mode of operation for local calls a description will now be given when the subscriber in one exchange calls for a subscriber in a different exchange.

The call when originated by the calling subscriber causes the circuits and apparatus to be operated in identically the same manner as outlined in connection with Figures 1, 2. 3, 4 and 5;

Figure 5 in the present instance illustrated one of a plurality of cord circuits before the operator at the exchange in which the Figure 0 is illuminated in the manner described in connection with a local call. The operator inquiring the number of the wanted line finding that it is for a subscriber located in a different exchange, instead of placing the plug P into the jack of a local subscriber-as described and pressing the ringing button, places the plug P into the trunk jack 600 Figure 6, leading to the desired exchange.

The insertion of the plug into the trunk jack 600 is followed by the operator depressing a special button 620 Figure 5. The operation of this button causes the operation of relays 503 and 506. Relay 503 is operated from ground. through the lower winding 601 of the repeating coil. Relay 505 which is connected to ground is not operated in this instance. This provision is made in order to give supervision to the first or originating operator. hen the plug is inserted in the jack 600 and the special button operated relay 603 is energized completing the circuit between the secondary winding of the repeating coil and the trunk extend ing to the other exchange. The completion of this circuit causes the operation of relay at the distant oiiice similar to. relay 300 which in turn causes the operation of the secondary control arrangement and the consequent operation of the proper tens and units relays to extend the call to an idle operators cord circuit. After the connec tion is extended to the cord circuit the operator at whose position the cord circuit is located receives the desired number from the originating operator as the special button 620 Figure 5 when depressed connects the operators telephone set directly aeross the tip and sleeve conductors of the plug P Figure 5. V I

The operator at the outlying or distant exchange completes the connection to the called subscriber in the manner outlined in describing the local connection.

When the calling subscriber replaces his receiver the originating or first operator receives the disconnect signal. due to the restoration of relay 501 which causes the circuit of lamp 133 to be closed as relay 505 is prevented from operating as its Winding is connected to ground and the primary winding of the repeating coil FigureG is also connected to ground at its middle point. The originating operator receiving the disconnect signal withdraws the plug P from the trunk jack600 and relay 603 '"is deenergized opening the circuit formerly existing between the secondary winding 602 of the repeating coil and the trunk conductors extending to the other exchange. The called subscriber replacing his receiver gives the operator at the distant exchange thedisconnect signal and the plug is then withdrawn from the jack of the called subscriber. p

It will be noted that the cord circuit of the originating operator when used for trunk calls is so arranged that supervision is given when the calling subscriber replaces his-receiver. In local calls the same circuit is arranged to give'supervision only when both the calling-and the called subscribers replace their receivers.

The cordcircuit at the distant exchange which is identical with-the crnd'circuit of the originating operator is arranged to give supervision or a disconnect signal to the distant operator only when the originating operator talzes down the connection and when the calledsubscriber replaces his receiver or fails tonnswer.

This application is a continuation in part of application Serial No. lldailtl, filed August-12, 1916. The application in question shows a telephone exchange system wherein the calls are conlincd to a single o'tlice while in the present application the system relates to what maybe termed a multi-o'tl'ice system.

Figures 1, 2, 3 and l are identical with corresponding figures of the co-pendingapplication while l igure 5 is anodified for multi-oliice work.

' In the present application as in the first application secondary trunks with their controlling circuitsare ar anged in groups.

In trunking from one .exchange to another exchange a group or groups of trunks 'ith theircontrolling circuits are arranged so that. inextending 'a call from the originating otlice to a distant ofiice or exchange the primary trunks of the'distant exchange are not utilized but the trunk calls terminate directly into groups of secondary trunks at the distant exchange thus eliminating the primary selection at the distant exchange.

Having thus-described my invention what I desiretosecure by Letters Patent is:

1. In a telephone exchange system, the combination of an exchange provided with operators cord circuits for extending calls trom calling to called lines in'that exchange, a second exchange provided with operators cord circuits for extending calls from calling to called lines in that exchange, means associated with the cord circuitsof each exchangecomprising a single supervisory signal controlled jointly by the calling and called subscriber when connection is edected between a calling and a called line in the same exchange, .means for placing the con trol of the supervisory signal under control otthe calling subscriber alone when a call is extended from a subscriber in one exchange to a subscriber in another exchange.

9;. In a telephone exchange system, the combination ol two exchanges, operators cordrircuits at each exchange, trunk'lincs extending between said exchanges, primary andsm-ondary relay switching means for extending calls to an operator's cord circuit at each exchange, primary and secondary means used at one exchange and secondary means alone at another exchange when. calls are extended over said trunk lines.

3. In a telephone exchange system, the combination ot two exchanges, operators link circuits at each exchange, primary and secom-lany relay switching means for connecting a calling line to an operators linlc unit at the exchange where'the call originates, trunk lines extending between said exchanges, primary and secondary means used at one exchange and secondary means only used at the other exchange when calls are extended over said trunk line.

4. ln a telephone exchange system, the combination of a plurality of exchanges, opmrators link circuits at each exchange, for extending local calls and trunk calls-trunk linescxtending between the exchanges, primary and secondary relay switches at each exchange tor completing local calls, primary and secondary means at one exchange and secondary means alone at another exchange tor completing trunk calls over said trunk lines.

5. In a telephone exchange system, the combination o't an operators cord circuit provided with a supervisory lamp, said lamp arranged to be controlled jointly by the calling and called subscribers, a trunk line extending "to a second operators cord circuit, means controlled by the calling subscriber alone for controlling the supervisory lamp when said trunk line extending to the second operators cord circuit is used.

(3. in a telephone exchange system, telephone exchanges and subscribers lines terminating therein, operatorscord circuits for extemling calling lines to called lines in a local exchange, primary and secondary means for automatically extending calling lines to said cord circuits, means including said cord circuits tor extending calling lines in one exchange to called lines in another exchange, a single supervisory signal associated with each cord circuit controlled jointly by the calling and called subscribers when connection is effected between a calling and it called line in the same exchange, and means for placing the super visory signal under the control of the calling subscriber a'lone'when a connection is extended fromia subscribers line in one exchange to a subscribers line in another exchange.

"ln'testimony whereof I affix my signaturev JOSE-PH L. WRIGHT.

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