US1523998A - Telephone system - Google Patents

Description

Jan. 20. 1925. 1,523,998

W. L. DODGE TELEPHONE SYSTEM Filed Dec. 22 1920 7 Sheets-Sheet l 0 F/yz orrucr: u

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Application filed December W211. I

To all whom it may-concern Be it known that l, WILL K131i L. Donon, a citizen of the United States, residing at Maplewood, in the county of Essex, State of New derseyyhave invented certain new and useful Improvements inlelephone Systems, of Which the follovvingis a full, clear, concise, and exact description.

This invention relates to improvements in switching systems wherein means are pro vided for controlling the transmission of current impulses for a plurality of trunk lines extending between Widely separated ofiices, and has particular reference to such means as applied to telephone systems.

in systems of this character, it has been proposed to employ, at opposite ends of the common path, sending means :tor trans initting thereover codes oi current impulses characteristic of the individual trunks and determined by the trunk line which is temporarily associated with the path for signaling purposes.

it is often desirable to extend connection from an originating ohice to -distant office through an intermediate or tandem olhce by means of a sectionaliaed trunk, line, the sections oi which are connected at the intermediate office.

An object oi t'liisfinventio'o is to provide a system of this nature orig nating operator at one office r t only selectively and automatically eat, a connect it. to terminate at a second but also selectively and automatically such connection through the second of terminate at a third office. 1th the selecting and operating out t impulses are transmitted between adgaccnt otfices over a common signaling path for the trunk lines interconnecting such otlices.

it is also an object of the invention to provide means controlled over the common signaling path wherelo an idle one of a plurality of trunks lea ing from the intermediate to any one of a plurality of terminsting offices may be automatically selected and connected to the selected trunk leading from the originating ofice.

v It is also an object to provide such a system wherein the originating operator maintains complete control of a connection extending through an intermediate oilice and the originating and terminating operators receive all supervisory signals occurring producing any signals rnnnrieionn s'a's'rnitt E'eriel lilo.

cuit leading to an adjacent ol'fice, a plurality of terminals also being provided thereat of each of the trunk line circuits leading to other oiiiccs. [any of the terminals when selected for use causes the automatic asso ciation of the trunk with the common apparatus for transmitting codes of current 1m pulses over the common signaling pr Lh leading to another oliice to select the end oi the sel ,ciied trunk terminating thereat. he charactu' of the codes of iinplnses is also dependent upon the individualterminal of the trunk selected at the originating ofiice and causes the selection of apparatus associated With the trunlt at the second oilice which thereupoi .LrlllC'hlOllS either to display a signal before e operator, for a connection terminating liereat, or to find an idle trunk circuit l ding to a selected one of a o li'ii*a.lit ot er odices and to automatically connect ch trunk to the selected trunk as detern red lay the connecting terminal employed v the originating hperator.

lln accordance with another feature of the invention the trii l circuit heing employed is temporarily asso ted with the common signaling iatli joir. the adjacent oilices interconnected in this manner for the purpose of transmitting code, impulses of current to control the supervisory signals associated with, the originating and terminating ends oi thesectionalised trunk circuit Without at the intermediate ofiices.

In accordance With a further feature of the invention the apparatus at theintermediate ofice, whichselects the trunk leading to the terminating oilicc in response to the selecting impulses received over the common signaling path from the originating office,

also introduces a repeater set associated with the trunk from-the originatlng ofiice -between such trunk and the trunk leading to the selected terminating office and simultaneously connects the balacing net-work of the latter trunk with the repeater set.

These and other features of the invention, not specifically mentioned above, will clearly appear from the following specification and the accompanying drawings, Figs. 1 to 7, 1nclusive, of which, when arranged in accord ance with Figs. 9 and 10, show an embodiment thereof in a telephone trunking system and Fig. 8 shows in schematic form the arrangement of the various oflices in such a system.

Referring to the drawings, there 15 shown a toll trunk line L1 comprising two talking conductors extending from a central office U to a central office V. A similar toll trunk extends from the ofiice V to the office 7. At the central office U an ordinary toll cord circuit 0 is located by means of which connection is established with the trunk line L1. The trunk line L1 terminating at ofiice V or ofl'ice W may be used to connect with the toll switching trunk circuit Q, extending from the terminating position of the central office W to the trunking position where it may connect with a regular subscribers line T. While only one toll cord circuit, one toll trunk line, one toll switching trunk and one subscribers line circuit is shown, it is understood that this is for the purpose of convenience only and that many such circuits and lines may be and usually are provided in actual service.

At the oflice U the trunk line L1 is provided with threejacks 10, 20 and 30. The insertion of theplug 1 of the toll cord 0 into jack 10 causes the transmission of a code of signaling current impulses over the common signaling path P, extending .from office U to office V, to produce a guard signal at the office V associated with the line L1, thereby notifying the operator thereat that a connection has been made with such line. In such a case the call would be extended through the medium of a toll switching trunk circuit Q of the usual type to a subscribers line such as line T terminating at office V. The insertion of the plug 1 of the toll cord 0 in the jack 20 causes another code of impulses to be transmitted over the common signaling path P to the office V, howover such code selects other apparatus associated with the line L1 at the ofiice V which functions to display the guard signal associated with the line L1 at a distant office, such as office \V. In such a case the call is extended at the office W by means of.

the toll switching trunk Q to a subscribers line circuit, such as T, terminating thereat.

'The insertion ofthe plug l of the to". cord 0 into the jack 30 at office U causes :1

different code signal to be sent over the common signaling path P to the ofiice V where it is received by still different apparatus, causing the line L1 to be extended to another office, such as otfice Y, as shown in Fig. 8. Similarly the call will be extended from ofiice Y to the subscribers line circuit T, terminating thereat, by means of a toll switching trunk, such as Q. Also, with additional jacks provided at ofiice U, calls may be extended to other oiiices similar to and Y. In any case, the viso-ry signals are transmitted over the com mon signaling paths from one of'licc to another so that the originating operator has complete control of the local lines interconnecting adjacent otlices or the through toll lines interconnecting widely separated oflices and passing through intermediate offices.

The signals for the various terminals of each line, as well as the various line circuits, are controlled over a signaling path or conductor 1 common to the trunk lines, and having a ground return. The signaling conductor is arranged in a Wellknown manner for the usual duplex operation, there being the usual artificial balancing lines AL and the differential polarized relays 335 and 335 provided at the ends of such path. A commutator is also provided at either end of the path for receiving and sending code signals. Thcsc connnutators are preferably of the well-known start-type of distributors employed in connection with printing telegraph systems, and it-will be understood, are provided with some wellknown means (not shown) for maintaining synchronism there-between. The commutator at oilice U comprises a sending distributor S for transmitting sig nals over the path P to the otlicc V and a receiving distributor It for receiving the signals transmitted over the path P from the ofiicc V. Siniilarly, the commutator at the oliice V comprises a sending distributor S and a receiving distributor 11 for transmitting the signals to and receiving the signals from the ollice U over the path P. These commutators comprise sending and receiving distributors and are of the same construction. 'lhereforc, a description of one is thought to be sullicicnt. For convcnicncc, the construction of the sending and receiving distributors S and ll, will be described. The sending and receiving distributors each comprise a series of stationary rings. some of which are continuous and others of which are segmented. A. shaft common to the sending and receiving distributors at one otiice. is provided. upon which are mounted the brush arms 319 and use normalh held against rotation by the respective ,armatnrcs ot' two separately controlled ltltlSQ magnets SRM and RR.

various super- The outer end of each brush arm. is insulated from the inner end so that each brush on the arm controls two separate groups of circuits. Between the common shaft and each brush arm a friction clutch mechanism (not shown) is provided by means of which the constantly rotating shaft causes the rotation of each lorush arm when released. The face of the sending distributor S is stationary and is provided with a common sending ring 814-, a restoring segment 1", a start segment a and individual segments 301 to 306 inclusive for controlling the character of the signals transmitted over the signaling path P. ll common ring 3-15 is also provided and segments 316, 317 and 318 are cn'iploycd for controlling localcirouits. The face of the receiving distributor it is also stationary and is provided with a common. receiving ring and individual receiving segments 361 to 386 inclusive, for selecting circuits according'to the codes of signals received over the signaling path P. The segments 350 to 354 are also provided for contrclling the local circuits and the circuits of the release magnet. i

it the cities U the common signaling path or conductor P is connected to the common sending segment 31%, while the alternate contact of the differential polarized relay 3 35 there-at is connected with a receiving segment 352 in such a manner that when the relay 2-335 is operatively energized, the release magnet REM is energized to release the brush 356. At the central ollice V, the conn'uon conductor P is connected with the common sending segment 314, while the normal contact of the differential polarized relay thereat is connected with a common receiving segment 368 of the receiving distributor R. The alternate contact of the relay 335 is connected with the segment 352, so that when the relay 335 is operatively energized the release magnet ll/RM is energized to release the brush 356.

The signals transmitted over the common coi'uhictor P by the sending distributors S and S, are determined by the polarity of current connected with the individual send iug segments of the respective sending distributors S and S, These polarities are determined by the position of the brushes of the various levels of the automatic selector switches SS and SS, provided at the respective otlices U and V. These automatic selector switches, which are common to a plurality of trunk lines, are similar in structure, the automatic selector switch SS being provided with eight banks of con tarts and corresponding brushes (1. Z and iril to 5326 inclusive 'llhe brushes are mounted upon a sii'igle shaft which is driven by a motor magnet initially controlled by start relay. 330, which is con lWCtCCl to start conductor X, common to simplification.

(0 is connected with one winding of rela v- 382 which controls the stopping of the motor magnet l llll and the energization the release magnet Sl tM-of the sending distributor Brush Z) is connected with a contact of slow releasing relay 333 for the purpose of assisting in the control of the switch, as will appear more fully hereinafter, A release relay 334 is also associated with the switch and is controlled by the sending distributor S, as will appear fully in the following description.

A plurality of contacts equal to twice the number of trunk line terminals to which the automatic selector switch SS is common may be associated with each brush. contacts associated with the different brushes are mounted at different levels in position to be engaged by the respective brushes as they are rotated by the motor magnet Mill. 'lwo correspondingly positioned contacts of all levels are allotted to each trunk line terminal, for example, the first two trunk line terminals may be allotted to the jack 10 of the line L1; the second two contacts to the jack of the line L1, and the third two to the jack of the line L1. Similarly, the corresponding (connecting) terminals of the succeeding lines associated with the common signaling path P will be allotted terminals (not shown) on the selector banks. lhus each line will require siic terminals on the various contact banks, but only one set of such contacts is shown for the'sake of clearncss. The two contacts of the levels a and b allotted to each trunk line terminal are connected with relays individual to and associated with such terminals. As shown, relays individual to the outgoing end of the trunk line L1 are connected by means of individual signal control leads A10, C10, A520. C20 and A30, C30, and common restoring leads l3 and D. These signal control leads A10 and C10 are shown as connected with the first two terminals of the level associated with the switch a, and the other signal control leads AQOQAFBO. C20 and (T30 would be associated with the following contacts on the same level. However, they are not shown continuous for the purpose of The conductors B and l) individual to the trunk line and common to the various terminals thereof are connected. with the contacts shown for the level I) in alternate manner so that both conductors are provided for each of the variousterluiuals of the trunk line L1.

The automatic selector switch SS located at the oflice V is lihc the switch SS in structure and is associated in a similar The.

manner with the sending distributor s. A

similarstartin relay 330", motor magnet MM and stopping relays 332, 333 and 334 are also provided. This selector switch is associated with the incoming ends of the trunlrlines at the'olfice V by means of in' dividual signal control leads AlO, ClO, A'20, C20, AEBO and (1'30 and the restoring lead BDl, as well as the common start lead X. Individually controlled leads are connected with the contacts of the level a and the other contacts are connected with the switch in a. manner similar to the corresponding leads at oflice 'U. Y

In order that signals transmitted from the otfice U by the sending distributor S and received at the oflice V, may be utilized, there are provided at the latter office six locking relays 371 to 376' inclusive, having energizing windings connected with the respective individual receiving segments 361 to 366" of the receiving distributor R When a signal of negative polarity is transmitted from the particular individual sending segment, the locking relay connected with the corresponding individual receiving segment *will be energized and locked. The locking relays control a plurality of receiving and selecting relays 380 to 391 inclusive, which cooperate with locking relays 371 to 37 5' to select the signal control conductor individual to a desired trunk line or trunk line terminal, while locking relay 376' controls the polarity of the current connected to such conductor. The individual signal control circuits or conductors are connected with the various contacts of relays 387 to 394 inclusive. Similar equipment is provided for the receiving distributor at the ofiice U for utilizing signals transmitted from the oilices V and W or Y respectively. Having in mind this brief description of the apparatus of the system shown in the drawings, it is thought that the invention will be more thoroughly compre- J hended from the description of the operation of the system shown.

( oomeotion of a cord circuit with jack 10 of trunk line L].

The operator at .ofiice U, desiring to establish a connection with a. telephone line,

vsuch as T, terminating at office V, inserts the calling lug 1 of the toll'cord 0 into the jack 10 of t e trunk line L1. Relays 11 and 25 thereupon operate over a circuit established from battery throu h the winding of relay 6, sleeve contacts of plug 1 and jack 10, and the windin s of relays 11- and 25 in series to ground. Relay 6, being marginal, does not operate in this circuit and supervisory lamp-T fails to light at this time. The operation of relay 25 causes the operation of the busy signaling device 4:, over an obvious circuit to indicate that the line circuit L1 is bein used. Relay 25 also, in opening its rig t-hand normal contact, prevents the line L1 from being selected upon a call incoming to ofiice U from another ofiice such as ofiice V which is not shown. The operation of relay 11 causes the operation of relay 14 over a circuit extending from battery, through the inner right-hand nolmal contact of relay 24, the alternative contact of relay 11, the winding of relay 1 1 and the left-hand normal conhand contact of relay 14, the left-hand normal contacts of relays 15 and 17 and the right-hand normal contacts of relays 18 and 22. A ground is also connected to the common start lead X over a circuit extending from ground through the outer righthand alternate contacts of relays 16 and 14, the right-hand contact of relay 15, and the right-hand normal contact of relay 17. The connection of the ground to the common start lead X causes the operation of start relay 330, which closes an operating circuit for the motor magnet MM, associated with the selector switch SS. The various arms of such selector switch advance stcp-lrwstep under the control of the lnotor magnet until the contact associated with the individual signaling conductor AlOis reached, whereupon, due to the previously traced ground connection for such lead, relay 332 operates through its left-hand winding, and by opening its left-hand normal contact, opens a circuit and stops theoperation of motor magnet MM. Relay 332, in operating. locks up through its right hand winding to battery at the contact of relay 334 and closes a circuit for the release magnet SRM ol the sending distributor S, which extends from battery through the common ring 315. the brush arm 319, the segment 316, the outer right-hand alternate contact of ielay 3232 and the winding of release magnet SRM to round. The attraction of the armature of the release magnet SRM, upon its energization, releases the brush arm 319, which is thereupon rotated through a complete cycle at the end of which the brush arm is stopped in its normal position, as shown. The brush arm 319, in being rotated, first engages the start segment 8. therebyconnecting positive battery with the common signaling conductor P. The brush then moves out of engagement with the segment 316, openmg the energizing circuit of and causing the deenergization of release magnet SRM, restoring its armature to the normal position for engagement with the arm 319 u on the 001m pletion' of its cycle. With tie automatic selecting switch SS in engagement with the first of the two contacts allotted to the jack 10 of the trunk line L1, positive current is connected to the first, second, fourth, fifth and sixth levels, associated with the brushes 321 to 326; while negative current is .connected with the first contact of the third level only. When the brush arm 319 engages the segment 317, a circuit is completed for relay 333. which. extends from. battery, through the ring 315, brush arm 319, segment 317 and the winding of relay 333 to ground. The operation of relay 333 establishes a circuit for relay'17 extending from battery through the contacts of relays 334 and 333, the brush arm I) and the contact associated therewith, the restoring conductor B connected to such contact, winding of relay 17, the right-hand contact of relay 15, theouter right-hand alternate contact of relay l-fl; and the outer right-hand alternate contact of relay 16 to ground. The openingof the normal contacts of relay 17 removes ground from the common start conductor X and the individual signaling conductor A10. Relay 17, in operating, also locks over a circuit extending from battery through the alternate contact and winding of relay 17 and from thence over the previously traced energizing circuit therefor. As the brush 319 successively engages the individual sending segments 301 to 306 inclusive, currents of the polarity connected with such ments through the contacts and brush arms of the selector switch SS, are successively connected with the common signaling con-- ductor P. When the brush 319 moves out of engagement with the segment 317, the

energizing circuit of slow-release relay 333 isopen and when the brush engages'segment 318 a circuit is formed for the energization the contact of relay 334. As the brush arm 319 disengages the segment 318, release rclay 334: is again deenergized. When the brush arm 319 engages the restoring segment 7", negative current is connected with the sig-. naling conductor P. The switch SS is now in position to be seized by another trunk line. or trunk line terminal. since the trunk line terminal of jack 10 is disconnected therefrom and the sending distributor is conductor P, bothwindings of the dilieren tial polarized relay 335 and the artificial line to ground. The operation of relay 335' causes the operation of release magnet R RM associated-withthe receiving distributor R at office V. The circuit for such magnet may be traced from battery through the alternate contact of relay 335, the segment 352, the brush arm 356, the segment 353 and the winding of release magnet RRM to ground. .The attraction of the armature of such release magnet releases the brush arm 356 which is thereupon rotated' through a complete cycle at the end of which it is stopped in its normal position, as shown on the drawing. As'the brush arm 356 moves out of engagement with the segments 352 and 353, the release magnet- RRM is'deenergized, thereby permitting the restoration of its armature to the normal position inorder to stop the brush 356 when it completes its rotation. When the brush arm 356 engages the segment 369 a circuit is'completed for relay 367, extending from battery through the ring 355, the brush arm 356. the segment 369 and the winding of relay 367 to ground. The closure of the contact of relay 367 prepares thelocking circuits for the various locking relays 371 to 376 inclusive. The

armatureof the differentially polarized relay 335' remains in its alternateposition as long as the positive current is connected with the other end of the conductor P, and is restored to its normal position whenever negative current is connected with the other end of such conductor. The brush arms 319 and 356 are being rotated at the same time and in synchronism so that while the brush arm 319 is engaged with the individual sending segment 303, the armature of the re- 1:1 "335 is restored to its normal position and brush 356 engages the individual receiving segment 363". A circuit is there upon completed, which extends from battery through the normal contact of relay 335', the common receiving segment 368, the brush arm 356, the individual receiving segment 363 and the lower winding of relay 37 3 to ground. The latter mentioned relay before the termination of the impulse which operates due to this circuit and locks over an obvious circuit due to the operation of relay 367. The closure of the lower contact of relay 373' causes the operation of relays 381' and 382' over a circuit extending from battery, through the windings of relays 382 and 381 in series and the lower contact of relay 373' to ground. Vhen the brusharm 356 engages segments 350 and 351, the

signal receiving relay 171 (Fig. 2) operates over a circuit from negative battery 377 through the normal contact of relay 376, the segment 350', the brush arm 356, the segment 351, the normal contact of relay 375, the lower normal contact of relay 380, the lower alternate contact of relay 381', the upper normal contact of relay 383,

- and upper normal contact of relay 388, the

ing frombattery through the right-hand alternate contact of relay 171, left-hand alter- .nate contact-of relay 173, and the winding of relay 167 to ground. Relay 167 being slow-to-operate and release, will not have sufficient time to close its alternate contacts energizes relay 173. Hence, the operation of relay 173 at this time has no efi'ect'upon the circuit. The relay 167 and a similar relay 267 (Fig. 4) are indicated as slow-tooperate and release by arrows intersecting their armatures and pointing in the direction that the armatures are slow tomovc.

Relay 171, in operating. causes the illumination of lamp 180 over a circuit extending from battery through the right-hand alternate contact of relay 171. the right-hand normal contact of relay 156. and lamp 180 to ground. The closure of the left-hand alternate conta't of relay 171 connects the supervisory relay 158 in bridge of the talking conductors of the trunk L1, extending toward the plug 151. When the brush arm 356' disengage's segments 368' and 366', the energizing circuit of relays 171and 173 is opened. causing the deenergization of relay 17 3. Slow release relay 170 is then energized over a circuit extending from battery through the righthand alternate contact of relay 171, the normal contact of relay 173, and the winding of relay 170 to ground. When the brush arm 356 engages-the segments 352 and 353' the'armature of relay 335' is in its normal position since the brush arm 319 is connected with restoring segment 7-. A negative current is, therefore, connected with the common signaling path or conductor P, so that the energizing circuit of release magnet R'RM is opened. The disengagement of the brush arm 356' from the segment 369' and engagement with segment 354' causes therelease of relay 367. Therefore, the locking circuit of relay 373 is opened, allowing the release of such relay and causing the deenergization of relays 381 and 382. All ap aratus associated with the automatic selectlng switch SS, the sending distributor S, the receiving distributor R and the receiving circuit at office V, is now in normal condition so that it may be employed in connection with any other trunk line. The lighting of the lamp 180 serves as a guard signal to the operator at the ofiice V indicating that the operator at. the office U has connected the toll cord circuit O with the trunk line circuit L1.

Connection of toll switching trunk circuit Q with telephone line circuit T.

The operator at office V ascertains from the operator at ofiice U the number of the desired line and then communicates with the toll switching operator at the office V before whom the telephone line circuit T terminates. An order wire (not shown) of the usual type is used for this purpose. The toll switching operator at the ofiice V informs the incoming or receiving operator at the same ofiice that the toll switching trunk Q, leading between the positions of the two 0 erators at the oflice V, should be employe for extending the connection to the wanted line circuit T. Immediately upon assigning the trunk Q, for this purpose the toll switching o erator inserts the plug 89 of the toll switc ing trunk Q into the jack 90 of the desired "line circuit T. The cut-oft relay 91 of the line circuit and the sleeve relay 88 of the toll switching trunk circuit Q thereupon operate over a circuit traceable from battery through the winding of relay 88, the sleeve contacts of plug 89 and jack 90, through the winding of cut-ofi relay 91, to ground. The operation of the cutoff relay 91 performs its usual function in rcn'ioving the line relay 92 from association with the line conductors, thereby preventing the display of the line signal 93 upon the answer of the called party. The opening of the right-hand normal contact of relay 88 disconnects the trunk operators" telephone set testing lead, with which a test has been made, on the line circuit T before the insertion of the plug 89 into the jack 90. The closure of the righthand alternate contact of relay 88 completes the continuity of the tip conductor of the trunk circuit, while the closure of the lefthand alternate contact of such relay causes the illumination of lamp 87 over a circuit extending from battery through. the lamp 87, the left-hand alternate contact of relay 88, the resistance 94, and the normal contact of relay 86 to ground.

Connection. of the trunk Zine circuit L1 with the toll switching trunk circuit Q.

The closure of the left-hand alternate contact of relay 156, completes the tip conductor of the trunk line L1, while the opening of the left-hand normal contact disconnects the operators telephone testing lead from such conductor. y

The supervisory relay 158 of the trunk line L1 and relay 86 of the toll-switching trunk Q operate over a circuit extending from battery through the left-handwinding of relay 86, the left-hand normal contact of relay 84;, the ring contacts of jack 80 and plug 151, the right-hand normal contact of relay 155, the right-hand normal contact of relay 154:, the left-hand alternate contact of relay 171, thewinding'of relay 158, the right-hand normal contact of relay 157, the left-hand normal contacts of relays 154 and 155, the left-hand alternate contact of relay 156, the tip contacts of plug 151 and jack 80, the right-hand normal contact of relay '84: and the right-hand Winding of relay 86 to ground. The energization of relay 86 extinguishes the lamp 87.

'lhe energization of supervisory relay 158 causes the energization oi relays 159, 160 and 161. the energizing circuit for relay 159 extending. from battery through the winding of relay 159 and the alternate contact of relay 158 to ground. The circuit for relay 160 may be traced from battery through the winding of relay 330. the common start conductor X, the inner right-hand normal contact of relay 16). the windingand right-hand normal contact of relay 160. the normal contact oi relay 161. the left-hand contact of relay 16:"). the outer left-hand contact of relay 169 and the righthand alternate contact o'l'- relay 158 to ground. .The relay 161 energizes in the yes circuit extending from battery through the winding and right-hand normal contact of relay 161 and from thence'in parallel over the energizing circuit of relay 160. Relay .ping the switch SS in that position.

160 in energizing is locked over an obvious circuit including the conductor X and relay 161 completes a locking circuit for itself from battery through the winding and right-hand alternate contact of relay 161, the right-hand normal contact of relay 162. the left-hand normal contact of relay 169 and the alternate contact of relay 158 to ground. The closure of the left-hand alternate contact of relay 160 establishes a circuit extending from ground through said contact. the normal contact of relay 161, the winding of relay 166, the normal contact of relay 157 and the right-hand alternate contact of relay 171 to battery. Re-

lay 166 encrgizes and looks through its winding and contact, the winding of relay 161 to ground at the inner normal contact of relay 169. Relay 164 is not energized in this locking circuit during the operation of relay 160,since relay 161 isshort-circuited by the ground at the lefthand alternate contact of relay 1.60 and the inner normal contact of relay 169. Re-

lay 160,- in closing its outer right-hand alternate contact, grounds the signal con- ;trol conductor AlO connected with the first of the two contacts on the level associated with brush a of the automatic selecting switchv allotted to the trunk'terminal 10 of line L1. Start magnet 330 is energized in the circuit through its winding. above described, and completes an operating circuit for motor magnet MM associated with the selector switch SS. This motor magnet. which is of the self-interrupting type. well known in the art. thereupon advances the brushes of the switch step by step until the brush a engages the. contact to which the signal control conductor Alfi is connected. whereupon relay 32-32 is operated over a circuit extending from battery through the right-hand winding of relay 332, the brush arm a and the contact associated therewith, the signal control conductor AlO, and the right-hand alternate contact of relay 160 to ground. The relay 382, in operating. opens the circuit of motor magnet MM, thereby step; A locking circuit is provided for the relay 332, which extends from battery through the contact of relay 334, the inner lefthand alternate contact and left-hand winding of relay 332 to ground. The-sending distributor S thereupon functions to successively connect with the common signaling conductor P currents of the polarities connected with the individual sending segments 301 to 306 of this distributor. To the restoring segment r negative current is permanently connected. while positive cur tive current is connected with segments 301,

302, 304, 305' and 306; while negative current is connected with segment 303. While brush arm'31 9 is making a complete cycle, the release magnet SRM is deenergized when said arm moves out of engagement with the segment 316'. The circuit of slow-releasing relay 333' is closed during the time the brush is in engagement with segment 317, and the release relay 33 1' is energized during the'time the brush engages segment 318. When relay 333' energizes a circuit is established for relay 1.65 extending from battery through the con tacts of relays 334' and 333', brush arm 6-, conductor B'Dl and the winding of relay 165 to ground. The operation of relay 165 opens the locking circuit and causes the release of relay 160, thereby removing ground from the conductor A'lO. Relay 165 also disconnects battery from the start conductor and upon the release of relay 160, the short circuit is removed from the winding of relay 164 and said relay then operates in the locking circuit for relay 166. The operation of relay 164 has no eflect at this time.- The apparatus associated with the sending distributor S and the automatic selecting switch SS now functionsin the I same manner as that associated with the sending distributor S and the automatic selecting switch SS. Relay 165 becomes deenergized upon the release of relay 333 which follows the disengagement of the brush arm 319 from the segment 317 The differentially polarized relay 335, connected with the common signaling conductor P at the office U, operates when the brush arm 319' engages the start se ent s, whereupon the release magnet RR of the receiving'distributor R at the office U is energized to release the brush arm 356. When the brush arm 319 engages the sending segment 303', the relay 335 is deenergized,

.whereupon relay 373 operates over a circuit extending from battery through the normal contact of relay 335, th segment 368, the segment 363 and the lower winding of relay of relay 373 to ground. When the arm 356 engages segments 350 and 351, battery is connected in circuit with relay 25 over a path which may be traced as follows: from 7 battery 377 through the lower normal contact of relay 376, segment 350, arm 356 and segment 351 of the receiving distributor R, the normal contact of relay 375, the lower normal contact of relay 380, the lower alternate contact of relay 381, the upper normal contact of relay 383. the upper normal contact of relay 388, the signal-receivin conductor E10, and the left-hand Winding of relay 26 to ground. Relay 26 thereupon operates and locks through its right-hand winding, the alternate contact of relay 11 and thence to battery through the inner right-hand normal contact of relay 24. At the time of the energization of relay 11, a circuit was established for relay 32 extending from ground at relay 26 through the winding of relay 32 and from thence over the locking circuit just described for relay 26. The cnergization of relay 32 prevents the operation of relay 33 when relay 26 is energized. The closure of the left-hand alternate contact otrclay 26 completes a circuit from battery through the winding of relay 6 of the toll cord circuit 0, the sleeve contacts of plug 1 and jack 10, the left-hand normal contacts of relays 19 and 23, the resistance 35. the right-hand normal contact of relay 241. the left-hand alternate contact of relay 26, and the left-hand normal contact of relay 33 to ground. The resistance of this circuit is such that the marginal relay 6 operates to cause the lighting of the supervisory lamp 7 over an obvious circuit, thereby notifying the operator that the connec- -tion has been established with the desired line circuit T and that such circuit is in condition for signaling the substation on the line.

The operator at ofiice U actua-tes the ringi/ng key.

The operator at ofiice U, upon observing the lighted condition of the su ervisory lamp 7, may actuate the ringing key 2, which connects the source of ringing current with the talking conductors of the cord circuit 0 and the associated trunk line L1. Ringingresponse relay 13 is operated, thereby causing the energization of relay 15 over a circuit extending frombattery through the winding of relay 15 and the contact of relay 13 to ground. Relay 17 is thereupon deenergized by the opening of its locking circuit and the conductor X is disconnected from ground by the operation of relay 15.

Operator at ofice U releases the ringing key.

Upon the restoration of the ringing key 2 of the cord circuit 0 to its normal position, relay 13 releases causing the deenergization of relay 15, which in deenergizing connects groun to conductor A10, which may be traced from ground throu h the outer left-hand alternate contact 0 relay 16, the outer left-hand alternate contact of relay 14, the left-hand normal contacts of relays and -17, and the right-hand normal contacts of relays 18 and 22. At the same time conductor X is grounded in the same manner, as previously described. Relay 330 thereupon operates to cause the operation of the motor magnet MM of the selector switch SS, whereupon the same sequence of operations of the selector switch SS occur as previously described in connection with the transmission of the guard signal from the station U to the station V.

In a similar manner the sending distributor S and the receiving distributor R function as described and the receiving conductor ElO is selected as previously mentioned. Relay 171 is unaffected by the, polarity of current flowing over the selected leadeupon the transmission of the final impulse over such lead, since the polarity of such current is such as to maintain said relay in an operated condition. However, relay 17 3 is operated over a circuit traced in parallel with that of the left-hand winding of relay 171, and relay 173 is thereupon momentarily'locked over a circuit ex- 'tending from battery through the righthand winding and right-hand alternate contact of relay 173 and the contact of relay 17 O to ground. Upon the operation of relay 173, all the apparatus associated with the sending distributor S and receiving distributor R is restored to normal as previously mentioned. left-hand alternate contact of relay 173 causes the operation of relay 1.67 over a circuit extending from battery through the right-hand alternate contact of relay 171, the left-hand alternate contact of relay 17 3 and the winding of relay 167 to ground. Relay 167 has sufficient time to close its contacts in this instance since relay 17 3 is held operated by the slowrelease relay 170 for a longer period of time than the duration of the impulse received over the conductor E'10. The closure of the left-hand contact of slow-operate and release relay 167 completes a circuit for ringing relay 155, which extends from battery through the winding of relay 155, and the left-hand contactof relay 167. Slow release relay 168 is also operated over an obvious circuit by the closure of the left-hand contact of relay 167. The. closure of the right-hand contacts of relays 167 and 168 also connect ground to the winding of relay 159 which is already energized under the controlof relay] 158. Relay 155, in operating, closes a circuit extending from thesource of ringing The closure of the alternate contact of relay 155 to ground.

Relay 81 thereupon operates during the conwinding of relay 84, the winding of relay 85 and the contact of relay 81 to ground. The operation of relay 84. maintains the relay 86 energized. 'Relay 85, in operating, causes the completion of a circu1t extending from a source of alternating current through the right-hand alternate contact of relay 85, the ring contacts of plug 89 and jack 90, the subscribers station on the line circuit T, the tip contacts of jack 90 and plug 89, the right-hand alternate contact of relay 88 and the left-hand alter-l nate contact of relay 85 to ground. The} bell 'at the subscribers station is thereupon operated to notify the subscriber that a call awaits his answer. i

As soon as slow-release relay 170 has fully restored. to normal, relay 173 is released due to the opening of the locking circuit, previously traced therefor, whereupon the release of relays 167 and 168 breaks two connections to ground for the windin l'of relay 159, this relay is not deenergize as a third ground connection is still maintained at the contacts of relay 158. Upon the cessation of such ringing current, ringing response relay 81 releases, causing the subsequent release of relay 84 and ringing relay 85 of the trunk circuit Q to remove the ringing current from the line circuit '1 and to restore the apparatus of the toll switching trunk circuit to. the condition in which it appeared prior to the sending of the ringing signal from the station U. The apparatus associated with the trunk line L1 is also restored to the same condition as before. Thus each time the ringing key of the cord circuit 0 at the station U is actuated and released, .the same series of operations occur and as a consequence the Signaling bell at the substation on the linecircuit T is actuated for an interval.

Subscriber at the station onthe telephone line circuit T removes the receiver from the switch/wok.

The subscriber at the station on the telephone line circuit T, when responding to the operation of the signal, removes the receiver from the switchhook, thereby causing the operation of the supervisory relay 83 over a circuit extending from battery through the winding of relay 83, the upper right-hand winding of repeating coil 95, the right-hand normal contact of ringin relay 85., the ring contacts of plug 89 and jack 90, the apparatus at the station on the line circuit T, the tip contacts of jack 90 and. plug 89, the'right-hand alternate contact of relay 88, the' left-hand normal con tact of relay 85 and the lower right-hand winding of the repeating coil to ground. Supervisory relay 83, in operating, causes the energization of relay 84 over a circuit 5 winding of relay 86 and the left-hand alter-' nate contact of relay 84 to ground. Relay 84 in operating, also causesthe deenergization of thesupervisory relay 158, due to the opening of the circuit thereof. Relay 158,

n opening its alternate contact, opens the energizing circuit of slow-release relay 159 and; the locking circuit of relay 161. Relay 159 is slow in releasing so that before it releases its armature, relay 163 is o erated over a circuit extending from attery through the winding of relay 163, the alternatecontact of relay 159 and the normal contact of relay 158 to ground. However, the operation of relay 163 performs no useful function at this time. Upon the closure of the normal contact of relay 159, relay 169 operates over a circuit extending from battery through the winding of start relay 330', the starting conductor X, the outer righthand normal contact of relay 165, the wind ing of relay, 169, the left-hand normal contact of relay 160, the right-hand alternate contact of relay 164 which is now operated due to the release of relay 160, the normal contact of relay 159,.and the normal contact of relay 158 to ground. Relay 169, in operating, locks through its winding and left-hand alternate contact to ground. The operation of relay 169 causes the release of relays 164 and 166. The closure of the righthand alternate contact of relay 169 grounds the signal control conductor ClO'which is connected to the second of the two contacts on the level a of the selector switch SS, whichare allotted to the jack 1 O, of the trunk line L1, extending from the station U to the station V. The energization of the start relay 330 causes the operation of motor magnet MM of the selector switch SS,

whereupon the switch advances step by step until the brush a engages the contact to which the signal control conductor is connected. Relay 332 thereupon operates over an obvious circuit and locks in the manner previously described to stop the motor magnet MM.

The brushes of the selector switch SS. engaging the second set of contacts allotted to the jack 10, connects a current of positive polarity with the individual sending segments 301, 302, 304 and 305 and connects current of negative polarity to the individual sending segments 303 and 306. The energization of relay 332 energizes release magnet SR-M' associated with the sending distributor S, whereby the brush 319 is released and makes a complete revolution to transmit over the common signaling conductor P a combination of impulses or code signals determined by the polarities connected with the individual segments of the sending distributor, as controlled by the position of the arms of the selector switch SS. \Vhen the brush arm 319' engages segment 317, relay 333 energizes and relay 165 thereupon operates over the previously described cireuit therefor. The operation of relay 165 deenergizes relay 169. \Vhen the combination of impulses has been transmitted in the manner described in the previous instance, the sending distributor S and the automatic selector switch SS, as well as all other associated sending apparatus, are restored to normal and the relay 165 is released. These transmitted impulses, being received at ofiice U, cause the energization I This current is of such polarity as to dif ferentialize and thus cause the release of relay 26 when it flows through the left-hand 'winding of such relay. The relation of the number of turns of the two windings of signal receiving relay 26 is such that when positive polarity traverses the left-hand or energizing windingv at the same time that current of a different polarity traverses the looking or right-hand winding. the relay is diflerentialized and releases its arlnatures. The opening of the left-hand alternate contact of relay 26 disconnects resistance 35 from its parallel relation with the winding of relay 11, whereupon the marginal relay 6 of the cord circuit 0 releases its armature and estinguishes the supervisory lamp 7, whereupon the apparatus at the ofiice U is restored to the, same condition as existed prior to the insertion of the plug 1 into the jack 10. The extinguishment of the lamp 7 serves as a signal to the operator at the ofiice that the desired subscriber has responded to the call.

Subscriber restores the receiver to s-we'tchhooh'.

At the conclusion of the conversation, the subscriber at the station on the telephone line circuit T restores the receiver to the switchhook, thereby releasing supervisory relay 83,- which opens the circuit of the release relay 84. Belay 86 is thereupon connected in circuit'with supervisory relay 158 to cause the energization of the latter relay. Prior to the energization of supervisory relay 158, all of the relays individual to the trunk line L1 at "station V which are conrelay trolled by such supervisory relay, are deenergized. The energization of supervisory relay 158 causes the operationot relays 159, 160 and 161 in the manner before described, to thereby cause the movement of the automatic selector switch SS until its brush a engages the grounded signal control conductor AlO, and the sending distributor S transmits over the conductor P the same combination of impulses as when the plug 1:11 was inserted into the jack of the toll switching trunk circuit Q. The operation of relay 160 also causes the operation of 166 and the short-circuiting of relay 164 as before described. Relay 165 operates when relay 333 is energized and releases relay 160. Following the release of relay 160, relay 164 operates in series with relay 166. Upon the return of the sending distributor S tonormal position and the release of relay 160, the automatic selector switch SS and .the sending distributor S are removed from their operative association with the trunk line L1 and may thereafter be temporarily associated with any other trunk line or terminal thereof. The transmitted combination of impulses; when received at the ofiice U through the action of differentially polarized relay 335 and the receiving distributor R, thereby causes the energization of relays 373, 381, and 382, as

previously mentioned, as well as the energization and the locking of, signal receiving rela 26, inthe manner previously described in etail. Resistance 35 is again connected in parallel with the winding of relay 11 to permit the operation of marginal relay 6 and the consequent dis lay of a-disconnect signal by the illumination of lamp 7. F01- lowing the energization of the signal-receiv ing relay 26, the brush 356 of the receiving distributor R is stopped in its normal position and relay 367 is released to cause the release of relays 3'73, 381 and 382;

Operator at ofiice U disengages the toll cowl circuit 0 from the jack 10 of the trunk line L]. v

cuit of and extinguishes the supervisory lamp 7 The release of relay 14 causes the energization of the start magnet 330 over a circuit extending from battery through the winding of start magnet 330, the start conductor X, the outer right-hand normal contact of relay 14 and the outer right-hand alternate contact of relay 16 to ground. The deenergization of relay 14 also grounds the signal control conductor C10 over a connection which may be traced from ground through the outer left-hand alternate contact of relay 16, and the left-hand normal contacts of relays 14, 18 and 22. Thus the second .of the two contacts of the level a. of the selector switch S3 allotted to the jack 10 of the trunk line L1 is grounded. Motor magnet MM thereupon functions when start relay 330 is energized over the circuit previously traced therefor, to advance all of its brushes until the brush a engages the contact to which the signal control conductor C10 is connected, whereupon rela 332 operates and locks as well as opens t e circuit of the motor magnet and stops the operation of the switch SS. The brushes 321. 322, 324 and 325 of the selector switch SS now connect positive current with the indi vidual sending segments 301, 302, 304 and 305 of the sending distributor S, while brushes 323 and 326 connect current of negative polarity to the sending segments 303 and 306 respectively of the sending distributor S. The closure of the outer righthand alternate contact of relay 332 energizes the release magnet SRM of the sendrelay 333 is operated. A circuit is thereupon completed from battery through the contacts of relays 334 and 333, the brush b, the restoring conductor D and the inner right-hand alternate contact and ri lit-hand winding of relay 16 to ground. T is relay thereupon becomes diilerentialized and releases its armatures. The impulses trans I mitted by the distributor are received at the office V. by the differential polarized relay 335 and the receiving distributor R to cause the energization and locking of relays 373 and 376, as well as the operation of relay 367. Relays 381 and 382 operate upon the energization of relay 373 so that when brush 356 engages the segments 350 and 351', the signal receiving relay 171 is difi'erentialized due to the character of the current flowing through its left-hand winding, as previously described in connection with the releasing of relay 26 at the station U. The circuit for causing the release of relay 171 may be traced from positive battery 378' through the lower alternate contact of relay 376, segments 350 and 351', the brush arm 356' of the receiving distributor R, the lower normal contact of relay 375', the lower normalcontact of relay 380., the lower alternate contact of relay 381, the upper normal contact of relay 383',

. the upper. normal contact of relay 888, the

receiving conductor ElO and the left-hand winding of relay 171 to ground. Relay 171 thereupon releases its armatures, and the opening of its right-hand alternate contact causes the release otrelays 166 and 164,

while the closure of the'right-hand normal contact of relay 171 causes the illumination of lamp 180 over a circuit extending from battery through the normal contact of relay 171, the right-hand alternate contact of relay 156 and the lamp 180 to ground. The lighting of the lamp 180 serves as a disconnectsignal to the operator at the office V.

The opening of the left-hand alternate contact of relay 171 opens the circuit including the supervisory relay 158 of the trunk line L1 and the relay 86 of the toll switching trunk circuit Q, whereupon both of these relays release. The opening of the alternate contact of supervisory relay 158 restores rev lays 159 and 161 to normal condition. Relay 163 is energized after the release of relay 158 and before the release of relay 159, but is deenergized when slow-release relay 159 is completely deenergized. The energization of relay 163 does not, at this time, perform any useful, function. The release of relay 86 of the toll switching trunk Q, causes the lighting of lamp 87 over a circuit extending from battery through the lamp 87, 1

the left-hand alternate contact of relay 88,

the resistance 94, and the normal contact of relay 86 to ground. The lighting of the lamp '87 now serves as a disconnect signal to the toll switching operator at whose posi tion the toll switching trunk circuit Q terminates. The terminating operator and the toll switching trunk operator at oflice V may, upon observing the lighted condition of the respective supervisory lamps 180 and 87, withdraw the plugs 151' and 89 from the jacks and 90 respectively, thereby restoring all apparatus to its normal condition.

Subscriber at the station on. the telephone line T terminating at ofifce V recalls the operator at ofiice U.

.From the previous description it is evident that while the receiver at the station on the line circuit T is removed from .the switchhook so that the switchhook contact thereat is closed, supervisory relay 158 and all relays 159 to 166 and 169, controlled by such supervisory relay, are deenergized. All the other .relays associated with the incoming end of the trunk line LL at the olfice V, the signal receiving relay 171 and slow release relay 170 andmelay 156 are energized, while the signal-receiving relay 173, the ringing relay 155 and the slow releasing relays 167 and 168 are deenergized. Relay 159 is made slow in releasing so that its alternate contact will be maintained in a closed condition during the short periods when the alternate contact of the supervisory relay 158 is opened during the eriod that the subscriber at the station on t e line circuit T is repeatedly opening and closing the switchhook contact thereat to signal the operator at the office U. Similarly, relay 163 is made slow in releasing so that it is maintained operated during the short period when the normal contact of the supervisory relay 158 is opened. Relays 162, 166 and 164 are also made slow in releasing to assist in the control of the recall signal before the operator at the ofiice U, when the subscriber at the station on the telephone line T is recalling the operator thereat.

Upon the first opening of the switchhook contact the supervisory relay 158 is energized, thereby energizing the relays 159, 160, 161 and 166, as previously described; also the automatic selector switch SS advances until the brush a engages the contact to which the individual signal control conductor A'lO, temporarily grounded. is connected, when relay 332 operates. The operation of relay,332 energizes release magnet SRM', whereuponthesending distributor S transmits over the common conductorP a combination of impulses deteraaaees mined by the polarities connected with the individual sending-segments 301' to 306 respectively. During the operation of the cord circuit then operates to cause the illumination of the supervisory lamp 7 and relay 32 is deenergized upon the operation of the signal-receiving relay 26 The closure of the switchhook contac shortly after the opening thereof, causes the deenergization of the supervisory relay 158, which causes the immediate deenergization of relay 161 and the energization of relay 163. The subsequent energization of the supervisory relay 158 in response to the next opening of the switchhook contact, causes relays 160 and 161 to operate in the order named, as previously described. Upon the operation of relay 160, relay 162 is energized over a circuit from battery through the right-hand alternate contact oi signal-receiving relay 171, the left-hand normal contact of relay 157, the winding and inner right-hand normal contact of relay 162, the left-hand alternate contact (if relay 164 which was energized when relay 160 released during the transmission oi the first series of impulses which resulted in the lighting of the lamp 7, and the inner left-hand alternate contact of relay 160 to ground. Relay 162 immediately looks through its inner right-hand alternate con tact and the inner left-hand normal contact otrel'ay 169 to ground. Upon the energizationof relay 162, relay 161 is locked over a circuit which may be traced from battery through thewinding and alternate contact of relay 161, the outer right-hand alternate contact of relay 162 and from thence to ground at the inner normal contact of relay 169, whereby relay 161 is removed from the control of the supervisory relay 158 during the rapid actuations thereof, while the switchhook contact is being rapidly opened and closed to signal the operator at the oflice ,U. The energization of relay 160 causes the automatic selector switch SS to start the sending distributor S, which transmits over the common signal- The reception of these impulses by the relay 335 at otlice U causes the receiving distributor R to function to cause the temporary energization of relay 367 and the temporary energization of relays 373, 381 and 382 as before. lVhen the brush 356 engages segments 350 and 351. signal-receiving relay operates over a circuit from negative battery 377, the segments 850 and in cooperation with the arm 356 otthe receiving distributor it, the lower normal contact of relay 375, the lower normal conta t of relay 380, the lower alternate contact of relay 381, the upper normal contact of relay 383, the upper normal contact of relay the signal-receiving conductor E10, the normal contact of relay 32, and the left-hand Winding of signal-receiving relay to ground. Relay 33, in operating, completes a locking circuit for itself extending from battery through the inner right-hand normal contact of relay 24, the' alternate contact of relay l1 and the right-hand winding and right-hand alternate contact of relay 33 to ground. The closure of the left-hand alternate contact of relay 33 connects interrupter 34 in series with the left-hand alternate contact of relay 26 and the resistance 35, thereby furnishing a grounded circuit through such resistance which is in parallel relation with the winding of relay 11. The alternate shunting of the winding of relay 11, caused by the intermittent ground turnislied through the interrupter 3 1, causes the intermittent operation and deenergization of marginal relay 6 to flash the supervisory lamp '7 at a predetermined rate, depending upon the speed at which the interrupter 34 operates. The intermittent lighting of the lamp 7 serves to indicate that the subscriber at the station on the line circuit T desires to recall the operator at the ofiice U. This recall signal is repeated after the second opening of the switchhook contact. of the station on the line circuit T. No more signals are transmitted over the signaling path during the continued opening and closing of the switchhook contact. The signal is produced at a constant rate and is easily observed by the operator. However, it is necessary to continue to open andclose the switchhook contact to maintain the signal in connection with the interrupter 3 1.

If, after repeatedly opening and closing the switchhook contact to signal the operator at the ofiice- U, the subscriber at the station of the telephone line circuit T should leave the switchhook contact closed, then the supervisory relay 158 is deenergized. After the" comparatively extended deenergization of this relay, relays 159 and 163 release and. upon the closure of the normal contact of relay 163, relay 169 operates over a circuit through the left-hand Contact of

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