US1168894A - Telephone-exchange trunking system. - Google Patents

Description

F.'LUBBERGER.

TELEPHONE EXCHANGE muuxme SYSTEM.

' APPLICATION FILED NOV. 29, 1909.- I

Patented Jm.18,1916.

aka mam fvw/wzfov:

' F. LUBBERGER.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

' APPLICATIQN man NOV. 29, 1909.

1,168,894. r Patented Ja11.18,1916.

5 SHEET$-SHEET 3.

F. LUBB ERGER.

TELEPHONE- EXCHANGE TRUNKING SYSTEM.

VAPPUCATION FILED NOV. 29. 11909.

' 1,168,894. Patented Jan. 18, 1916.

5 SHEETS-SHEET 4.

l IWTZCW} F. LUBBERGER.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

' APPLICATION FILED NOV. 29,1909.

Patented Jan. 18, 1916.

5 SHEETS-"SHEET 5.

QHKmG mw um w . To all whom it may concern:

UNITED STATES PATENT onrron FRITZ LUBBERGER, OF CHICAGO, ILLINOIS, ASSIGNOR T0 AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE TRUNKING SYSTEM.

" Specification of Letters Yatent.

Application filed November 29, 1909. Serial No. 530,400.

,Be it known that I, Fnrrz for automatic lead to another board in the same exchange,

or to another exchange, depending upon the character of the system. At the other board, or at the other exchange, another operator then completes the connection to the line of the called subscriber. It has been found, however, that the trunks between the difierent boards, or between the difierent exchanges, are liable to be made busy longer than necessary by reason of the fact that the operators do not always promptly withdraw the plugs from the trunk jacks as soon as the subscribers are through talking. With the arrangements employed previous to my invention the releasing of the trunks was entirely dependent upon the withdrawal of the plugs from the trunk jacks, and if this was not done the trunks were, made busy and were not available for other calls.

An object of my invention is, therefore,

the provision of animproved construction. and arrangement whereby a trunk brought into use by -a manual board operator, either automatically or otherwise, is not dependent upon the withdrawal of the plug from the jack, or upon any other act of the manual board operator, but may be released and restored to normal condition by simply hanging up the telephone atom of the two connected. substations, whereby the release of a trunk thus brought into use by a, manual board operator is under substation control, and whereby the failure of the manual board operator to wit-hdraw the plug from the trunk jack, or to-perform any other act, is of no particular consequence, and is not neces- LnnBERonn, a subject of the Emperor of Germany, and

of that kind in line switchthat is to say, an

within the contemplation of my invention, is

the provision of means whereby a trunk Patented Jan. 18, 1916.

which extends between the boards of A and '7 B operators, or between difierent exchanges or stations, and which has been selected and i brought into use (either automatically OI otherwise) by the manual switchboard oper ator, maybe restored to normal condition by the calling subscriber or by the called subscriber, or by both, whereby the said trunk is then available for use inmaking other calls.

Another object is the provision ofan arrangement whereby a, manual board operator may know which one of several trunks is idle, consisting of a'signal adapted to be displayed for the idle trunk responsive to someact on the part of the manual board operator, such as the operation ofa push button or other switch, whereby a positive signal is presented for only one trunk, to-wit,

the idle trunk which is at that time available for extending the connection to the called telephone line.

Another object is the provision of an automatic trunk-selecting switch" for automatically selecting idle trunks, and a signaling apparatus adapted to cooperate with said auto matic trunk-selecting switch, whereby a manual switchboard operator may, by operating a push button orother similar switch, receive a signal indicating the idle trunk selected by the said switch, and whereby the operator may then employ the said automatically selected trunk as a medium for reaching and operating an automatic switch, or as at medium for reaching and communicating with any other kind of switchboard apparatus.

Another object is the provision of a nonnumerical trunking switch for selecting idle trunks, subject to control by a manual switchboard operator, and means controllable froma substation (which may be that of either a calling subscriber or a called subscriber) for releasing the said switch, and for thereby restoring the automatically selected trunk to normal condition in case the manual switchboard operator fails to take down the connection by means of which control was exercised over the said switch,

Another object is .the provision of an arrangement whereby substation control may be'exercised over an automatic "witch to dis- .connect the same from a trun that termi- 'nates in a plug, which substation may be that of the called subscriber, and v which automatic switch may be one over which a .manual switchboard operator exercised control in the establishment ofthe calling con- 7 l 4 a .C, a device Rfor indicatin idle trunks,

' and a subscribers substation in a system embodying the principles' of my invention. Fig. 2 shows a trunk line switch D and its master switch E of said system Fig. 3 shows another trunk line switchiF with its master switch H of said system. Fig. 4 shows a subscribers substationP', .a 'B-op: erators cord circuit C and telephone set I of said system. Fig. 5 is a diagrammatic representation of two manual swltchboards, an A-board and a B-board, showing themrangement of trunks-between them in the 1 system disclosed herein.

In the various figures several batteries B are shown with one pole (preferably the -positive)*connectedqto ground G. There.

may, however, be but one battery, or there .may be one battery in-each exchange.

The subscribers substation P, as shown in 1, is of the usual common battery type and comprises a receiver 2, transmitter 3,

"switch. hook 4, ringer 5, condenser 6 and impedance coil 7. Allotted to the line of sub-," station P at the central office are the line and .ut-ofi' relays 8 and 9, line lamp 10 and answering jack -11. The A-operators cord circuit C is very similar to the usual circuits used for the same purpose in manual switchboards, but is somewhat modified in *order to bring about the release of .the line switches D and F when the subscribers hang up their receivers. The circuit comprises I the usual supervisory relays 75, 151, 7 6' and .92, lamps 159 and 161 and operators telephone set e.

. The device R for indicating idle trunks comprises two bank levels L and M which are engaged by the wipers 12 and 13 a motor magnet 14 for operating the ratchet wheel 16, which latter is designed for operat- ,;:ing the wipers 12 and 13, and a relay 17 for [controlling the energizing -circuit of the motor magnet 14. The bank levels L and: ,M each consist of a common segment 18 and 19 and a set of individual contacts a and a. The number of individualcontacts in each level corresponds tothe number of trunks allotted to the A-board. The wipers l2 'and 13 are adapted to keep one contact in each level in electrical connection with the common segment of that level. The motor mag I net 14 is provided with an armature'20 upon the ,end of which is mounted a pawl 21..

When thG magnet 14 energizes, the pawl '21 operates the ratchet wheel 16, which inturn causes the wipers 12 and .13 to rotate over the bank contacts by means of asuitable mechanical connection .(not shown). To,

. each trunk is allotted a relay 22 which, when the plug 72 isinserted into the jack J ofthe' trunk corresponding to the contact 23 upon which the wiper 13 is resting,., operates to close an energizing circuit through the re: lay 17. The relay 17 in turn operates to energize the motor magnet 14, which operates the ratchet wheel 16 to move the'wipers 12 and 13 to the contacts of the next idle trunk. To each jack on the A-board is allotted a signallamp 6 which indicates to the operator (when the button 24 -is' pressedyupon what contact the wiper 12 1s resting, andtherefore signifying that the corresponding trunk is to be used-in com- .pleting the connection.

The'trunk line-switch D (Fig. 2) is of the same'general formas that disclosed in the,

Amefican Telephone Journal of June 6,. 1908, page 528. The switch- D is provided with a magnet 25 that performs not only the additional function whichthe release magfunction of a released magnet, but; also an net in the said Telephone J ourmzl does not. I i

performf The magnet 25 serves bothasa trlp magnet and release magnet, and is designed to remain energized while the switch is in operation. When the magnet 25 is energized the armature 26 is so attracted as to v move the plunger 'arm 27 about its pivot point 28 and thrust the plunger 29 into the bank Q. Now, when the magnet deenergizes,

the plunger is restored to normal by meansthrough the medium of the spring 30. Thus,

of the magnet 25 the plunger 29 is thrust into the bank Q and then withdrawn. The armature 26 vis pivotally secured to' the switch frame (not shown) at the ,point 31 l and at the other end the arm 32 is in turn pivotally secured to the plunger iarm 27 at the point 34, the said arm being arranged-to rotate about the pin 28. The P11111156! arm 27 -is provided with a finger 35 whic ,ti hen the plunger is thrust into the bankjjshifts the spring 36 out of engagement with the spring 37 and into engagement with the spring 38. By this operation the magnet 25 is disconnected from battery d il'ect and is connected to thebattery lead 39-through the resistance 40. The said line switch is also. provided with a bank of terminals,

normal position the notch is designed to engage the flange or web on the plunger shaft 51, so that when a plunger operates the shaft may more the idle plungers opposite another bank terminal.

The general operation of the switch is as follows: The magnet 25 is energized whengan A-op'erator inserts a plug in the jack J (Fig. 1) and the armature 26 is attracted against the magnet cores. Upon thus operating, the armature 26 moves the plunger arm 27 about the pivot point 28 land thrusts the plunger 29 into the bank Q. The magnet 25 remains energized as long as conversation is being carried on, but as soon as one of the parties hangs up his receiver the said magnet deenergizes and allows the plunger 29 to restore to normal position. Also, when the plunger enters thebank the plunger shaft 51 is rotated by means of the master switch E and carries all idle plungers that are in locked engagement with it opposite the next idle bank terminal. Now, when the plunger is restored the web on the plunger shaft has moved away so that the notch 50 does not engage it again, but the web slides along the fan-like tail-piece of the plunger, without moving said plunger, until the plunger shaft returns to the position from which the plunger was released. Vl hen the shaft ,reaches this position the notch 50 again engages the web and the plunger is then again in locked engagement wlth the shaft. If,

after being withdrawn from the bank Q, the

plunger 29 should. be operated again before it has become engaged with the shaft 51 it would again enter the same bank Q.

The masts switch E, which may be of any suitable or approved type, is provided for operating the plunger shaft 51, and for controlling certain circuits that will be disclosed hereinafter. It comprises the following details: The motor magnet 52 for operating the ratchet wheel 53, which latter is designed for operating the plunger shaft 51, a relay 54 for controlling the circuit of-the motor magnet and a relay 55 which con trols the circuit of the releasemagnet 25 under certain conditions, as will appear hereinafter. The master switch also has a bank 0 comprising a set of contacts 0 and a common metallic egment 56. T hewiper 57 is adapted to remain in constant engagement with the bank O and to maintain one of the conta 10 in electrical connection with the common segment 56. The motor magnet 52 is provided with an armature 58 upon the end of which is mounted a pawl 59. When the magnet 52 energizes the pawl 59 engages the ratchet wheel 53, causing it to rotate and thus more theplunger shaft'.

The line switch F and master switch H are similar to those just described, with the addition of the winding 167 on the motor magnet relay 16S and the master switch bank level (Fig.

The operators cord circuit C (Fig. 4:) is

,very similar to anordinary cord used in manual service, being modified slightly in order that the hanging up of the receiver of the called party will cause the release of the trunk l1ne switches. The cord comprises .the repeating coil N. supervisory relays 60,

61 and 62, lamps 63, (it and 65 and plug seat- I switch h.

A clearer understanding of my invention may be had. from an explanation of its operation when one subscriber calls another.

Suppose,- for example, that the subscriber at substation P desires to speak with the subscriber at substation P, the line of'which terminates in another exchange. When the subscriber at substation P removes his receiver from the switch hook an energizing circuit is established through the line relay 8, said circuit extending from battery B- through the line relay 8, contact point 72,

and armature 71 to the line conductor 70,

then through the substation P, over the line conductor 69, armature 68 and contact point 67 to ground G. The line relay 8 thereupon energizes and closes a circuit through the line lamp 10. The operator then inserts the plug p into the answering jack 11, whereupon a circuit is closed through the cut-off relay 9. This circuit extends from ground G through the cut-off relay 9, through the sleeve of the jack 11 and sleeve of plug p, through the relay 76, thence through battery B to ground G The cutolf relay 9 thereupon energizes and attracts its armature 68 and 71 away from the contact points 67 and 72 and into engagement with the points 73 and 74. This operation breaks the circuit through the line relay 8, which latter deenergizes and extinguishes the lamp 10.-

the operator presses the push button 24 to find what trunk she shall use in completing the connection. 'When the button 24 is ressed the lamp-'b is lighted, thus indicatng that the jack J is the one to be used.

- The circuit through the lamp '6", extends from ground G through the contact point 80, push button spring '81, through the .lamps b, etc., in multiple (there being one lamp on each operatorfs' position for each trunk) to the condilhtoffiil, through the individual contact 831of the bank L, wiper 12, common segment 18, and over conductor. 84, contact point 85 and armature 86- to bat-.

tery B. The operator now operates the key k to connect her telephone set to the order wires .87 and 88, and repeats the number of the desired' lineto the B-operator. Whenlv the B-operator is ready to complete theieonnection she noti es: the 'A-joperator, who then inserts'the' plug 72' into the jacksJ- When signal lamp 65. When the lamp "65 is dis- Isa 'When the armatu e I 162 engagesthe .t'act. point 163;. a 'circuit'us l'established wth'roughthe lamp 161. This circuit extends 45 from ground G through the; armature154,

* the plug p enters the jack J the line switches D and F- operate to extend the connection to the cord clrcuit C (Fig. 4) and light the played the B-operator removes the plu p of the desired. line: The operation of fthe various apparatus involved in this connection will now be explained. When'the-plug enters the jack J anene'rgizing' circuit is established through the relay 22, said cir} Icuit xtendin from ground 'Gi through the relay 22 to t e trunk conductor89, thence through the sleeve of the condu orslof the jack J and plug pand,relay 9 ,to battery B. The relays 92 and 22'enerig1ze andattract their respective armatures con- .contactpoint 155, armature Q1 62, .contact :point. 163' and lamp 161 tob'atte'ry B. y The x a engagement of the armature 123 with the contact point 152 extends the-connection 'to- 6b the conductors and 89. The en agement of the armature 93' with the contac -point 91 G through the contact point 91', armature .93, individual contact point 23 of the bank. level,.M,- wiper 13, common segment 19,, -over conductor 94 and through relay 17 to battery B. The motormagnetrelay 17 upon energizing attracts its armature 86 away from the; contact point 85 br'nging it into engagement with the contact p mt 95,- thereby closin an energizing ircuit through the me or magnet 14. This circuit extends from ground Gr through the magnet 14, interrupter" springs 96 and 97 contact point 95 and armature 86 to battery B and" '20, being provided'with the interrupter buzzer to give the ratchet Wheel a con- -ofi the contact 23, thereby opening the cir- I I cuit through themotor magnet relay 17,

circuit through the motor magnet.

with the wiper l3 ,and alwaysrests upon a the lamps d, 11. em, from its seat and lnserts 1t into the ja J ?-ttra cts its armature 20, the pawl 21 engag-' ng'a tooth of thef'ratchet wheel 16 which irotatesthe wipers -12 and 13. The armature" springs 96 and 97 opens and closes the circhit through the magnet 14, "causing it to operate in a manner similar to that ofa tinuous motion until" the wiper 13 is carried Whichin turn denergizes and breaks the trunk corresponding to -the next contact'is If the: I g 1 so :busy, however, the relay Willremam energized until the wiper 1 3 finds a contact:-

which is not grounded. The wiper 12 moves contact correspondingto the same trunk as that upon which the wiper 12 is resting.

:Whenever the relay 17 is energized,- and,

therefore, the rotary magnet is operating, a circuit is closed hroughthe lamps d, d

: etc., there being one of these lamps on each ,operators position. JThe circuit through :these lamps extends fr'oxF ground Gr through 'nmultiple, contact to battery B, and thence to grolfipd G. i'l he lighting of these lamps then in cate's, to the operator that the wipers "12- and 13 are rotating and no conpoint 95, armature 86 naction should be made until the lights are extinguished. L all the trunks are busy the lamps d, d,'etc.,' will remain lighted. until 'o'ne off the trunks is- -freed. Whenthe plug 7 7) enters thejack J yacitcuit is also closed through the relay-98, said circuit extending but it has such a high resistance that'sufiie I cient current does not :fiov'v to energize the re-- I the contact point 104, thereby closing an enerzmg c1rcu1t through the magnet 25 of the neswitch I), causing it to attract its armahecircuit'through the magnet 25 exf from ground G through the relay 98, 'relay; 3 99, trunk conductor 89,sleeve conductors of, the jack J and 'plu g p? and relay 92 to bat-f Q'ter'y B.: The relay 98 thereupon energizes,

nd'thrust the plunger 29 into the bank .115- closes a circuit throughthe motg'r magnet? {:T

a relay 17. This circuit extends from ground .t'en s from ground Gr through the contacti point 1 ,.armature 101, contact point 102,

armatur 103, contact point 104, armature 105, through the magnet 25, springs 36' and When ture 26 the spring 36 isshifted out of engagement with the spring 37 and into en- 1205i .37 and springs 106 and107 t6 the battery jf lead/ 39,-thence through battery B to ground f G the magnet 25 attracts its armae gagement withthe spring 38,. whereby a new f circuit isestablished through the magnet 25. This circuit extends from ground Gr through ,'the magnet 25 to the spring 36, as 1 previously traced, thence through, the spring 1o 29 also forces the This circuit extends from ground G 38 and resistance coil to battery lead 39. This circuit maintains the magnet 25 in an energized condition and holds the plunger 29 in the bank Q. lVhen the plunger 29 enters the bank Q, the springs 13 and 15 are pressed into engagement with the springs 4:2 and 1 1, respectively, thereby extending the conductors 89 and 90 through to the trunk conductors 108 and 109. The plunger spring 16 into engagement with the spring 17, whereby an energizing circuit is closed through the motor magnet relay 5% of the master switch E. This circuit extends from ground G through the springs 46 and 17 to the individual contact 110, through the wiper 57, common segment 56 and relay 5% to the battery lead 39, thence through battery B to ground G. The relay 5& upon energizing closes the springs 11 and 113 in contact,tl1us completing an energizing circuit through the motor magnet 52. and ground G13 through the magnet 52 and relay 55 to the interrupter springs 111 and 112, thence through the springs 113 and 11 T to the battery lead 39, and through battery I B to ground G. "The motor magnet now 0pcrates to advance all idle plungers' which are in locked engagement with the shaft 51 to a position opposite the next idle bank Tsiniilar to the terminal Q.

Before the motor magnet begins to 0perate, the spring 116 rests upon the top of a tooth of the toothed wheel 117, but as soon as the ratchet wheel 53 is moved one step by the pawl 59 the spring 116 slips off the tooth and engages the spring 115, whereby the circuit through the motor magnet is maintained, regardless of the springs 113 and 111, until the ratchet wheel has advanced far enough for the spring 115 to drop down into the next notch of the wheel 117 By this time the wiper 57 will have moved off. the contact point 110 and onto the next one, allowing the relay 51 to deenergize and open the contact between the springs 113 and 111. If, however, the next trunk is busy the wiper will find ground on the next contact, the relay 5% will not be deenergized and the shaft will continue to rotate until the plungers come opposite an idle trunk. As previously mentioned, the relay 55 is energized at the same time as the motor magnet 52, and being a slow-acting relay it remains in an energized condition as long as the motor magnet is in opera- 'jtion,

thus cutting 0E battery current at the :springsJ OG and 107 from the release mag- ,nets of all the idle line switches to which H r the master switch E is allotted. Thus it its will be seen, that it is impossibleto operate ny of the line switches whiletheir plungers are being moved from one bank terminal to another.

' As soon 35th conductors -tea 9.0 are ;seat springs 135 and 136, and through battery extended to the trunk conductors 108 and 109 an energizing circuit is established through the relay 118, causing it to attract its armature 119 into engagement with the contact point 120, thereby closing an energizing circuit through the magnet 121 of the line switch F. The circuit through the re lay 1.18 extends from ground G through the relay 151, contact point 152, armature 123, tip of plug 79, conductor 90, relay 150, springs 4:3 and 42, conductor 109, relay 118, conductor 108, springs 11 and 45, relay 99, conductor 89, sleeve of plug 79' and relay 92 to battery B. The relay 118has a resistance sufiiciently high so that enough current does not flow to energize the relays 150, 99 and 151. When the circuit through the magnet 121 is closed the said switch operates in a manner similar to that described for the line switch D. The plunger 125 is forced into the bank S, the conductors 108 and 109 are extended through the springs 126 and 127, and 128 and 129 to the conductors 130 and 131, the idle plungers are moved opposite the next idle trunk, and the master switch wipers 132 and 133 are moved to the bank contacts corresponding to that trunk. Also, when the plunger enters the bank S an energizing circuit is closed through the supervisory lamp and relay 61 of the cord circuit C. This circuit extends from ground G through the springs 169 and 170 to the conductor 134:, thence-through the relay 61 to battery B; also, from conductor 134: a branch ex'tends through the lamp 65, plug 136 to the battery B, thence to ground G. The relay 61 upon energizing attracts the armature 137 away from the spring 138. When the B-operator sees the signal lamp 65 light she removes the plug 7) from lts seat and inserts it into the jack J 2 corresponding to the line asked for by the A-operator. When the lu '9 is removed from its seat the s rin l 2 l a:

136 is shifted out of contact with the spring 135 and into contact with the spring 171, whereby the circuit through the lamp 65 is broken and a circuit is the lamp 63. This circuit extends from ground G through the armature 172, contact oint 139, lamp 63, springs 171 and B to ground G. When the plug 12 is inserted into the jack 2 an energizing circuit is established through tion P and relay 62 of the cord circuit C. This circuit extends from ground G through the relay 14:0, sleeve conductors of the jack 2 and plug 72 and relay 62 to battery B, thence through battery B to groun G. These two relays'u on energizing complete a circuit from t e re eating coil N through the plug 79 and jac: j to the line conductors 141 and 142. Th substation may now be signaled by any suitableor ap the cut-off relay 1 10 of the substa-- established through proved means, as, for instance, by. operating the key 9, whereby the trunk is cut oil from the line and a ringer generator bridged across the line.

'5 When the subscriber at substation P removes his receiver from the hook an energizing circuit is established through the' relay 60, said circuit extending from ground G flrelay 60, contact point 143, armature 10 1.44, tip of plug and jack to the conductor 142, transmitter 145, switch hook 146, impedance coil 147, line conductor 141, sleeve of the plug and jack and relay 62 to battery B thence through battery B to groundG.

1c The relay 60 upon energizing attracts its armature 172 away from the contact point 139 and closes contact between the armature 148 and contact point 149. The opening of v the contact between armature 172 and contact point 139 extinguishes or retires the lamp 63, thus signifying to the operator that the subscriber has answered. 'When the contact between the armature 148 and contact point 149 is closed the relay 118 is bridged bythe windings 174 and 173 of the repeating coil N. When this occurs sufficient current then flows through the relays '150, 99 and the manner described, and the called sub scriber has answered, then as soon as either 0 party hangs up his receiver the line switches;

- vD and F immediately release and leave the trunk lines 108'a'nd 109 between the two eX- changes ready for another connection, re- I ,gardless of the length of time the plugs remain in the jacks. It will first be explained how the line switches release when the subscriber at substation P restores his receiver to the switch hook before the subscriber at substation P has hung up. When.

the receiver is hung up at substation P the energizing circuit of the relay is broken, allowing the armatures 78 'and 79 to fall back into engagement with their respective contact points. The relay 76, however, does not deenergize, its holding circuit ex- .tending from ground G through the cutoff relay 9, sleeve of the plug p and relay 76 to battery B. When the 'armature 79 engages the contactpoint 158 a circuit is established through. the supervisory lamp '159. This circuit extends from ground G through the lamp 159, contact point 158, armature 79, oontact'point 157 and armature 77 to battery B. The lighting of the lamp 159 therefore indicates to the A-operator ductors 131 and 1.30 is maintained at the gers are rotated onto the next trunk.

157 and armature 77 back to battery. When the contact between the contact point 152 and armature 123 is broken the relay. 151 de-. energizes and removes the short-circuit from the relay 92, which again energizes, but at"80' the same time the relay 92 denergizes the line switch D (Fig. 2) releases and opens the trunk, so that the relay 151 does not again energize when the relay 92 energizes. When the relay 92 energizes this second time a circuit is closed through the supervisory lamp 161, which indicates to the operator that the switch D has released. The circuit through the lamp 161 extends from ground G through armature 154, armature 162, contact point 163, lamp 161 to the non grounded pole of the battery B.

The release of the line switch D takes place as follows: When the relay 92 decnergizes, the circuit through the relay 150 95 and relay 118 is opened, whereupon the armature 103 falls out of engagement with the grounded contact point, the magnet 25 de'elnergizes and the plunger 29 -is'withdrawn from thebank Q. The relay 99, after being once energized, will be maintained in that condition by the circuit through the relay 98, so that the said relay 99 remains energized during the release of the switch D. When the plunger 29 re- 105 stores to normal the trunk connection is broken between the springs 42 and 43, and

44 and 45. When the circuit throughthe relay 118 is broken said relay de'e'nergizes and opens the circuit through the magnet 1. 0 121 of the line switch F. The switch F thereupon releases and the trunk conductors 108 and 109 are available for another'connection. A guarding potential for the concontact point 165 of the bank of the master switch H as long as the plug 79 remains up, so that. after the switch F releases, these conductors cannot again be seized before the operator has had time to remove the plug. This guarding potential extends from the battery B through: thesprings 136 and 171, conductor 166 to the contact point 165. If, now, the wiper 133 passes onto this contact the winding 167 of the motor magnet relay 168 becomes energized, and the plun-- When the line switch .F releases and opens the contact between the springs 169 and 170, the A ground is removed from the relay 61 and 3 ,said relay deenergizes and establishes a circuit through the lamp 64-, thus giving the B-operator the disconnect signal. lVhen the plug is removed from the jaclc and restored to its seat all relays restore to normal, and the guarding potential is removed from the master switch bank.

if the subscriber at substation P hangs up his receiver first, the line switches D and F also immediately release as follows: hen the receiver at substation P is restored to the hook the energizing circuit through the relay (i0 is opened. The. armature H8 falls out of engagement with the contact point 1 :9, which opens the energizing circuit through the relay 150 (Fig. '2), causing the release of the switch D, which is followed by the release of the switch F, as before explained. When the armature 1T2 engages the contact point 139 a circuit is established through the lamp 63, signifying to the B- operator that the subscriber has hung up his receiver. The lighting or displaying of this lamp, together with the lighting of the lamp G l, which signifies that the switches D and F have released, notifies the operator that the connection may be removed. The release of the switches D and F is also made known to the A-operator by the lighting of the lamp 161, which takes place as follows: When the switches release, the energizing circuit of the relay 151 is destroyed and the armature 15% engages the contact point 155, thus establishing a circuit through the said lamp 161. This circuit extends from ground G through the armature 154 and contact point 155, armature 162, contact point 163 and lamp 161 to the nongrounded pole of the battery B. lVhen the receiver at substation P is restored the lamp 159 is lighted in the same manner as when the receiver at substation P is first restored. The glowing of the two lamps 159 and 161 indicatesto the operator that the connection may be taken. down. The busy back iackd is provided at the B-otlice, said jack being connected to a source of busy-signaling current. Vi hen the B-operator tests a desired line and finds it busy, she inserts the plug 79 in the jack J and thus connects the calling subscriber to the busy signal.

From the foregoing it will be seen that I provide a system of automatic trunking between different switchboards, or between different exchanges, which automatic trunking is controlled by manual switchboard operators. It will also be seen that, in a systern of this kind. I provide means for automaticallv selecting idle trunks leading to the automatic switches for selecting .d e trunks between the diilerent switchboa; or he-' tween the different exchanges. In l way,

and by reason of thesignaling a provided in conjunction with the salt matic trunk-selecting apparatus. the n idle trunks ahead of the calls, toge tending connection from one board to another. 1 donot.

switchboard operator at whbse board the call originates, or to whose board the call is transmitted before .it is extended to the other exchange, may know which trunk jack to use, as when she presses a button or other switch a. signal is immediately given or displayed for the purpose of indicating which trunk jack is idle. Thus means are pro vided for automatically selecting trunks, and additional means are then provided for enabling a manual switchboard operator, by simply operating a push button or other device, to know which is the idle trunk that has been automatically selected for he nextcall. Upon extending connection to thisidle trunk the ope 'ator thereby causes another switch to automatically extend connection to another preselected trunk, which latter trunk may lead to another switchboard or to another exchange, depending upon the character of the. system. The trunk extending between the two boards, or between the two exchanges, is then automatically released and restored to normal condition when the receiver is hung up at either the calling or called substation. this way the release or restoration of the trunks between the A and B boards, or between different exchanges, is not dependent upon the withdrawal of the plugs from the trunk jacks. nor upon any acts of the manual switchboard operators, such release or restoration being under the control of the subscribers, themselves. Consequently the retention of a plug in a trunk jack after the subscribers are through talking not result in making a trunk busy longer than is necessary, inasmuch as the trunl: between. the different switchboards, or between different exchanges, which was brought into I use as the result of the-insertion of the plug in the trunk jack, is restored to a. non-bu y or idle condition as soon as eith r of the 'o connected subscribers hangs up his receiver at the substation thereof. Broadly stated, therefore, I provide means for enaoling a subscriber to release and restore to a nonbusy or idle condition the trunk that was brought into use by a manual switchboard operator. More specifically considered, this is a trunk for-extending connection one lmanual switchboard to another. broadly considered, 1 provide a trunks which terminate at a. main 7 board, 1nd means for automatically th itc means for enabling the manual sw operator to know which idle trunlt selected for the next call. More considered, these trunksare f myself to tli'ewuse of the diff tures and conihn'iations in exact character shown What I claim as my invention is 1. In a telephone system, a calling line,- a trunk, means including a manual SW1tOhboard for extending a connection from said line to said trunk includingalso automatic means controlled at said board for bringing said trunk into ,use, and substation-com trolled means for restoring said trunk to non-busy or idle 'condition.

2.111 a telephone system, a calllng line, a trunk, means including a manual swltchboard for extending connection from said line to said trunk inc uding also automatic means controlled at said board for bringing said trunk into use, calling substationcontrolled means for restoring said trunk to non-busy or idle condition, and automatic means for giving a signal when the trunk is necting.said'last mentioned boardwith the released.

3. In a telephone system, a subscribers line, a trunk, means including a manual switchboard for extending a connection from said line .to said trunk including also,

means controlled at said board for bringin said trunk into use, substation-controlle means for restoring said trunk to non-busy or idle condition," another manual board to which said trunkleads, and means for concalled line. 3 v

4. In a telephone system, a calling line, a

trunk, means including a manual switch-' board for extending a connection from said line to said trunk mcluding also automatlc means-controlled at said'board forbringing" said trunk into use, calling substationcontrolled means for restoring said trunk-to non-busy or idle condition, another manual board to which said tru'nk'leads, and means for connecting said last-mentioned board with the called line.

5. In a telephone system, a subscribers line, a trunk, means including a manual switchboard for extending a connection from said line to said trunk including also" means controlled at said board for bringing I said trunk into use, substation-controlled means for restoring said trunk tonon-busy or idle conditionfa set of switchboard cords, and an automatic switch for said trunk adapted to automatically select idle cords.

1 6. In a telephone system, acalling line, a

trunk, means including a manual switcn board for extending a connection from said line to said trunkincluding also automatic means controlled at said board for bringing.

said trunk into use, calling substation-v controlled means for restoring said trunk ton'on-busy or idle condition,'a set of'switchboard cords,'and an automatic switch for said trunk adapted to automatically select idle cords.

7. Ina telephone system, a subscribers line, a trunk, means including a manual switchboard for extending a connectionmeans'for restoring said trunk to non-busy or idle condition, a manual trunk, andmeans for connecting said first-mentioned trunk with said manual trunk.

i 8. In-a telephone system, a calling line, a

trunk, and means for connecting said firstmentioned trunk with said manual-trunk.

' from line to said trunk including also means controlled at said board for bringing said trunk into use, substation-controlled 9. In a telephone system, a calling line, a i

trunk, means including av manual switchboard for extending a connection from said line to said trunk including also automatic means controlled at said board for bringing said I trunk into use, calling substationcontrolled means for restoring, said trunk to non-busy or idle condition, and metallic line circuits over which said restoring means are controlled, each line circuit including the two sides ofaline in series.

7 10. In a'telephone system, a calling line, a trunk, means including a manual switchboard for extending a connect on from said line to said trunk includingwalso automatic means controlled'at said/board for bringing said trunk into use, means for extending a connection from Said trunkto a called line,

calling substation-controlled means/for restoring-said trunk to non-busy or'idle condition, and common battery,mans for supplying talking currentjtosubstations con.- nected through the medium of said trunk.

11.?In a telephone system, calling and called subscribers lines, means for establishing a connection betweensaid lines, said means including a trunk, a manual switch-, board, automatic means controlled at said)" IOU board for bringing said trunk into use, sub

station-controlled means for restoring/said the medium of saidtrunkf" )7 i 12. Ina telephone'system, a'plurality of trunks, an operators automatic switch, and signaling means, responsive to said switch for indicating which is the next'trunk to be used in extending a call......

ing current to substations connected through trunk to non-busy or idle conditioIi,-,.-arid common battery means for supplying'lzalk-K 13. In a telephone system,.-'a' plurality of i trunks, means for automatically selecting idle trunks ahead of the calls, and means on a manual switchboard for indicating the preselected trunk to the operator. 14. In a telephone system, a plurality of trunks, an operators switch, signaling means responsive to said switch for indicating which is ,the next trunk to be used in extending a call, and automatic switches in which said trunks terminate for connecting therefrom.

15. In a telephone system, a plurality of trunks, means for automatically selecting idle trunks ahead of the calls, means on a manual switchboard for indicating the preselected trunk to the operator, and automatic switches in which said trunks terminate for connecting therefrom.

16. In a telephone system, a plurality of trunks, an operators automatic switch, signaling means responsive to said switch for indicating which is the next trunk to be used in extending a call, and means including a manual switchboard for completing calls from said trunks to the lines of the called subscribers.

17. In a telephone system, a plurality of trunks, means for automatically selecting idle trunks ahead of the calls, means on a manual switchboard for indicating the preselected trunk to the operator, and means including a manualswitchboard for completing calls from said trunks to the lines of the called subscribers.

18. In a telephone system, a calling line, a plurality of trunks, means including an operators switch for extending a connection from said line to one of said trunks, signaling means responsive to said switch for indicating which is the next trunk to be used in extending a call, other trunks for connection with said first-mentioned trunks, and substation-controlled means for restoring said other trunks to a non-busy or idle' condition.

' 19. In a telephone system, a calling line, a plurality of trunks extending to a manual switchboard, means for automatically selecting idle trunks ahead of the calls, means on said manual switchboard for indicating the preselected trunk to the operator, other trunks for connection with said first-men tioned trunks, and substation-controlled means for restoring said other trunks to a non-busy or idle condition. I

20. In a telephone system, a plurality of trunks, an operators automatic switch, signaling means responsive to said switch for indicating which is the next trunk to be used in extending a call, and means for manually extending connection to said trunks in response to calling subscribers.

21. In a telephone system, a plurality of trunks, means for automatically selecting idle trunks ahead of the calls, means on a manual switchboard for indicating the preselected trunk to the operator, and means for manually extending connection to said trunks in response to calling subscribers.

22. In a telephone system, a plurality of trunks, an operators automatic switch, signaling means responsive to said switch for indicating which is the next trunk to be visory signals for the manual operators.

23. In a telephone system, a plurality of trunks, means fol automatically selecting idle trunks ahead of the calls, means on a -manual switchboard for indicating the preselected trunk to the operator, subscribers lines, means for manually including said trunks in talking circuits with said lines,

line signals for said subscribers lines, and

supervisory signals for the manual operators,

24. In a telephone system, a plurality of trunks, an operators automatic switch, signaling means responsive to said switch for indicating which is the next trunk to be used in extending a call, devices for bringing the said selected trunk into use between calling and called substations, and common battery means for supplying current to said substations for talking and operating purposes.

25. In a telephone system, a. plurality of trunks, means for automatically selecting idle trunks ahead of the calls, means on a manual switchboard for indicating the preselected trunk to the operator, devices for bringing the said selected trunk into use between calling and called substations, and common battery means for supplying current to said substations for talking and operating purposes.

26. In a telephone system, a trunk, a manual-switchbard, means controlled at said board for bringing said trunk into use, a relay at said switch-board, means for energizing said relay, and means to shortcircuit said relay to restore said trunk to non-busy or idle condition.

27. In a. telephone system, a calling line, a trunk, means including a manual-switchboard for extending a connection from said line to said trunk including also means controlled at said board for bringing said trunk into use, a relay at said switchboard, means for energizing said relay, and substationcontrolled means to short-circuit said relay to restore said trunk to non-busy or idle condition.

28. In a telephone system, a trunk, a manual switchboard, automatic means controlled at said board for bringing said trunk into use, a relay at said switchboard, means for energizing said relay, and means to shortcircuit said relay to restore said trunk to non-busy or idle condition.

29. In a telephone system, a sub scribers line, a trunk, means including a manual switchboard for extending a connection from said line to said trunk including also automatic means controlled at said board for bringing said trunk into use, a relay at said switchboard, means for energizing said relay, and substation-controlled means to short-circuit said relay to restore said trunk to non-busy or idle condition.

30. In a telephone system, a trunk, a

trunk into use, a pair of relays at said manual switchboard, one of said relays controlling the circuit of the other, means for energizing said first relay, and substation-controlled means to deenergize said first relay to restore said trunk to non-busy or idle condition.

32.- In a telephone system, a trunk, a manual switchboard, automatic means controlled at said board for bringing said trunk into'use, a pair of relays at said manual switchboard, one of said relays controlling the circuit of the other, means for energiz ing said first relay, and means to deenergize said first relay to restoresaid trunk to nonbusy or idle condition.

33. In a telephone system, a subscribers I line, a trunk, means including a manual switchboard for extending a connection from said line to said trunk including also automatic means controlled at said 'board for bringing said trunk into use, a pair of relays at said manual switchboard, one of said relays controlling the circuit of theother, and substation-controlled means to deenergize said first relay to restore said trunk to non-busyv or idle condition.

34. In a telephone system, a cord circuit, a pair of relays in said cord circuit, means for energizing said relays, one of said relays controlling the energizing circuit of the sec 0nd, and a short-circuit around the first relay controlled by the second.

35. In a telephone system, subscribers lines, and means for establishing a talking connection between said lines, including 'a manual switchboard, a trunk circuit, automatic switching means controlled over said trunk circuitfor establishing a connection thereover, a relay in a talking conductor of said'trunk, and means controlled by said relay to restore said trunk to non-busy or idle condition.

36. In a telephone system, a subscribers' line, a trunk circuit, means including a man ual switchboard for extending a connection '5 ,from said line to said trunk, automatic said means switching means controlled over said trunk circuit for establishing a connection thereover, a relay in said trunk, and substationc'ontrolled means controlled through said relay to restore said trunk to non-busy or idle condition.

37. In a telephone system, a, manual switchboard, a trunk circuit, automatic switching means controlled over said trunk circuit for establishing a connection there-.

over, a relay in said trunk controlling, the

continuity of thesame, and means operative;

through the deenergization of said relay-to restore said trunk to non-busy or idle-condition.

' 38. In a telephone system, a subscribers.

line, a trunk circuit, means including a'manual switchboard for extending a connection from said line to said trunk; automatic switching means controlled over said trunk circuit. for establishing a connection thereover, a relay in said trunk controlling the continuity of the same, and substationcontrolled means operative through the deenergization of said relay. to restore Said 1 trunk to non-busy or idle condition.

39. In a telephone system, a trunkline, an automatic switch, another line terminah ing in said switch, means for operating said switch over two sides of said other line in series to seize said trunk, means for rendering said trunk-busy to prevent a second switch from seizing said trunk when the same has been seized by said first-mentioned switch, and means for maintaining said trunk busy after said first switch has been disconnected from said trunk.

40. In a telephone system, a trunk line, a group of line switches, a master switch controlling said line switches, crating one of said line switches to seize said trunk, means associated with said trunk for rendering said trunk busy to prevent a sec-- 0nd line switch from establishing connection with said trunk after. said first line switch has been operated, and means for maintaining said busy condition after said first-mentioned line switch has been released to disconnect from said trunk.

said first-mentioned switch has been released:

from said trunk.

42. In a'telephone system, an operators board, a trunk line terminating therein, means including an automatic switch for extending a connection to said contrplled by said operator for extending? saidcon'nection from said board, means as means for optrunk, means.

common to said circuits,

secutively whereby the nals may be operated in 55. In a telephone system, an operators board, a plurality of trunks. terminating in said board, a signal for each trunk, a circuit for each signa, said circuits uniting in a common conductor, a source ofcurrent for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means whereby said mechanism may be operated to select said circuits consecutively to prepare them consecutively whereby nals may be operated in the and means under the control for operating the signal of the circuit which as been so prepared whereby the next idle trunk to be used is indicated.

56. In a telephone system, an operators boarll, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism means whereby said mechanism maybe operated to select said circuits consecutively to prepare them-com secutively whereby the corresponding signals may be operated in the same manner, means under the control of an operator for operating the signal of the circuit which has been so prepared whereby the next idle runk to be used is indicated, and a cord circuit for seizing the trunk indicated and for operatin the said mechanism to prepare the circuit 0 the next trunk to be used.

57. In a telephone system, board, a plurality of trunks terminating in said board, a signal for'each trunk, a circuit same manner,

- for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic pro gressively movable switching mechanism common to said circuits, and means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order.

58. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in. a common conductor, a source of current for operating said si nals, an automatic progressively movab e switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them'concorresponding sigthe same order, and

meanswsnder the control of the operator for operatin the signal of the circuit which has been prepared whereby the next idle trunk to be 'used is indicated. 7 v

the corresponding Sig-.

of an operator an operators vmon to said circuits,

secutively whereby 59. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor,

an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch. may select the said circuits of the idle trunks consecutively a source of current for 7 operating said signals,

of the circuit which has 30 common conductor, a source of current for 9 operating said signals, an automatic progressively movable switching mechanism common to said circuits, means whereby said mechanism may be operatedto select saidcircuits consecutively to prepare them consecutively "whereby the corresponding signals may be operated in the same manner, and a busy test circuit for each trunk, said means inc uding said busy test circuit.

61. In a telephone'system, board, a plurality of trunks terminating in said board, a signal foreach trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism commeans whereby said mechanism may be operated to selectsaid circuits consecutively to prepare them consecutively whereby the may be operated in the same manner, a busy test circuit for each trunk, said means including said busy test circuit, and means under the control of an operator for operat ing the signal of the so prepared whereby be used is indicated.

62. In a telephone system, an operators board, a plurality of trunks terminating in the next idle trunk to said board, a signal for each trunk, a circuit-1 0 for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, mechanism. may be operated to select szzid circuits consecutively to the corresponding signals may be operated in the same manner, a busy test circuit for each trunk, said means inl prepare them ccnan operators 100 corresponding signals circuit which has been means whereby said 3.

'signals'may be operated in the same order, a. busy test circuit for each trunk, said eluding said busy test circuit, means under the control of an operator for operating the signal of the circuit which has been so prepared whereby the next idle trunk to be used is indicated, and a cord circuit for seizing the trunk indicated and for operating 'the said mechanism to prepare the circuit of the next idle trunk to be used.

63. In a telephone .system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a -circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order, and a busy test circuit for each trunk, said means including said busy test circuit.

64. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, 'an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding means including said busy test circuit, and means under the control of an operator for operating the signal of the circuit which has been so prepared whereby the next idle trunk to be used is indicated.

65. Ina telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order, a busy test circuit for each trunk, said means including said busy test circuit, means under the control of an operator for operating the signal of the circuit which has been so prepared whereby the next idle trunk to be used is indicated, and a cord circuit for seizing the trunk indicated and for operating the said mechanism to prepare the cir cuit of the next trunk to be used.

66. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each ,trunk, a circuit said circuits consecutively toprepare them consecutively whereby the corresponding signals may be operated, and means under the control of a plurality of operators for operating the signal, the circuit of which has been so prepared.

67. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechar 1 common to said circuits, means whereh mechanism may be operated to select said circuits consecutively to prepare them consecutively whereby the correspondii nals may be operated in the same 1 means under the control of a plural I operators for operating the signal, circuit of which has been so prepared, and a cord circuit for seizing the trunk indicated,

and for operating the said mechanism to.

prepare the circuit of the next trunk to be used.

68. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said mechanism may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order, and means under the control or a plurality of operators for operating the signal, the circuit of which has been so prepared.

69. In a telephone system, an operators board, a plurality of trunks terminating in said board, a signal for each trunk, acircuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said mechanism may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order, means under the control of a plurality of operators for operating the signal, the circuit of which has been so prepared,

and a cord circuit for seizing the trunk in dicated and for operating said mechanism to presare the circuit of the next trunk to be use v I 70. In a telephone system, an operators board, a plurality of trunks, terminating in said board, a signal for each trunk, a circuit for each signal, said circuitsuniting 'in' a common conductor, a source of current for operating said signal, an automatic progressively movable switching mechanism common to said circuits', ,i means whereby said mechanism may be operatedto select said circuits consecutively to prepare them consecutively whereby the correspondingfsignalslmay be operated in the. same manner,

a busy test circuit for each trunk, said means including said busy test circuit, and means under the control of a plurality ofoperators for o crating the signal, the circuit b which has n so prepared. v

71. In a telephone system, an operators board, a pluralitybf trunks terminating in said-board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic, progressively movable gswitchin g' mechanism,

common to said circuits, means-whereby said the control of a plurality of operators-for operating the signal, the, circuit of which seizing the trunk indicated and foroperat ing the said mechanism to prepare the circult ofthe next trunk to be used.

72. In a-telephone system, an operators board, a plurality of i trunks terminating in consecutively signals may said-board, a signal for each trunk, acircuit for each signal, said circuits unitingin a common conductor, a source of current for operating said signals, an automatic progressively movab e switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare them consecutively whereby the corresponding signals may be operated in the same order, a busy test circuit for each trunk, said means including said busy test circuit, and means 4 under the control of a plurality of operators for operating the signal, the circuit of which has -been so prepared. g

.73. In a telephone system, an operators board, a plurality oftrunks terminating in said-board, a signal for each trunk, a circuit for each signal, said circuits uniting in a common conductor, a source of current for operating said signals, an automatic progressively movable switching mechanism common to said circuits, means for making some of said trunks busy and whereby said switch may select the said circuits of the idle trunks consecutively to prepare. them whereby the corresponding including said busy test circuit, means under the: control of a plurality of operators for operating the signal, thercircuit of which has-been so prepared, and a cord circuit for seizing the trunk indicated and for operating the said mechanism to prepare the cir- I cult of. the next trunk to-be used. has been so-prepared ,'and' a cord circuit for p Illinois, this 26th day of November,

S1gned by me at Chicago, Cook county,

' FRITZ LUBBERGER.

Witnesses:

EDWARD D. Finns, ARTHUR J. RAY.

p be operated in the same order, -a busy test circuit for each trunk, said means

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