US1672088A - Automatic telephone system - Google Patents

Description

June 5, 1928. 1,672,088

A. J. RAY ET Al.

AUTOMATIC TELEPHONE SY-S TEM Original Filed Feb. 19, 1921 6 Sheets-Sheefl 1 EN jjB-lu lLf-l June 5, 1928. l 1,672,088

A. J. RAY ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 19. 1921 6 Sheets-Sheet 2 d/ Za. 24.44. fing:

A. J. RAY ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 19. 1921 6 Shee'S-Shee'c 3 June 5, 1928. 1,672,088

IITETL'L'P-s- Efhur Bag-Harlag E MElqea June 5, 1928.

A. J. RAY ET A1.

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 19. 1921 6 Sheets-Sheet 4 N @N @N .NNN RM mmm Rum Y vw. IMM Gwq mi v L E imm, A mil 8W Il Mmw. m E.

-Iwn DPsg-Harleg EMQEJEE A. J. RAY ET AL.

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 19, 1921 Efhur IEE ZW June 5, 1928.

June 5, 1928. 1,672,088 A. J. RAY ET A1.

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 19, ,1921 6 SheetS-Sheeb 6 atente .lune 5, 1928.

UNITED -STATES PATENT OFFICE.

ARTHUR J'. RAY AND HARLEY B. MCELYEA, vOF CHICAGO, ILIINOIS, ASSIGNORS, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., 0F CHICAGO, ILLINOIS, A

CORPORATION or' DLAWARE.

AUTOMATIC TELEPHQNE SYSTEM.

Application .Bled February 19, 1921, Serial No. 446,319. ARenewed Hay 11, 1925.

This invention relates in general to automatic telephone systems, but more particularly to such systems as comprise a number of more or less widely scattered automatic exchanges which may be of various sizes and classes and which are interconnected by toll or long distance lines, and the object of the invention in general is to provide new and improved circuit arrangements whereby a toll operator may establish connections between the various subscribers of the different exchanges, and whereby she can supervise the calls and make proper charges for the same while using a minimum of equipment.

Considered more in detail, an important feature o1c the invention consists in the provision of improved circuits whereby the toll operator may call a subscriber over a trunk line and then call a second subscriber over the same trunk line and whereby she is given complete supervision by each subscriber separately.

A further feature relates to toll or way stations which may be located at intermediate points on toll lines connecting two automatic exchanges. Novel circuit arrangements are shown providing for automatic calling to and from a station of this kind.

The foregoing and other improvements will be described fully hereinafter, reference being hadV to the accompanying drawings. Although as stated there maybe several automatic exchanges of differentsizes and variety in a system of this kind, it has been decided to illustrate the invention in connection with a system which includes a large automatic exchange at which there is a toll operator and two small community automatic exchanges. or C. A. Xes as they are abbreviated, neither ot which has an operator, that are so located that one is much nearer to the large exchange than the other and lies between the two since this arrange- Incnt atlords -an opportunity to described the various features to good advantage. In the drawings, comprising Figs. -1-6, inclusive, there is shown by means of the usual circuit diagrams suiicient of the apparatus in the above mentioned hypothetical system to enable the invention to be explained and understood.

Referring to Fig. 1, the apparatus shown at the left of the sheet is located in the large automatic exchange and includes the equipment individual to a single trunk line, of which there may be several between the automatic exchange in which the operator 1s located and the nearer community automatic exchange. The ring down drop 143 is provided for the purpose of signalling the operator when a subscriber obtains connection with the toll trunk line 131--132 at the distant end. The jacks J and J are provided for the purpose of answering calls and for calling out over the trunk line shown. The keys K and K2 are arranged to connect the calling device S in the associated control circuits at the proper times, as will be subsequently explained.L The key K is a release key and may be used in releaslng a connection while the calling device S is in the circuit. The jack J2 is provided for the sole purpose of calling the intermediate substation Q, Fig. 4, and 1s similar to jacks J and J with the exception -that the usual supervisory relay such as supervisory relay 140 associated with jack J is replaced by resistance R".

The equipment on the right of toll trunk l1ne 131-132, is in the nearer C. A. X. The relay group E momentarily projects generator out on toll line 131-132 to operate drop 143 when the toll line is called, and also provides a holding circuit for Whatever switch seizes it. The switching apparatus shown`in Figs. 2, 3, and 4, is also in the nearer C. A. X. while t-he switching apparatus shown in Figs. 5 and 6 is located in the farther C. A. X., and the substation Q (Fig. 4f) is a toll substation located on the toll line between the two C. A. Xes.

The telephone substations with the exception of the substation Q are of the usual automatic type. The substation A, for example, comprises the usual transmitter, receiver, and ringer, and the calling device S for controlling the automatic switches. The substation Q consists of the usual transmitter, receiver, and ringer and also has a local battery and an induction coil in accordance with the usual practice when common battery cannot be supplied. .The key Ka is provided or the purpose of switching the circuit to the proper condition for answering 10iv a call or making one as the case may be.

A and `A', respectivel known rotary ty preferably composed of dry cells.

The individual line switches, such as the line switches C and C Figs. 2 and 6, which are associated with the lines of substations are of the well ,inw 'ch the wipers have no normal position/and move in a forward direction onlyx These line switches are in l common use and their construction and function is well understood. .e

The selectors D, D', D", and D", Figs.' 2, 3, and 5, are ofthe usual Strowger vertical and rotary type having their bank contacts arranged in horizontal rows or levels, and are operated according to the well known two wire systemrof control. The circuits are shown complete in the drawings and will `be described hereinafter.

vThe connectors H and H', Fi 2 and 6, are mechanically the same as t e selectors D, D,.D2, and D". The circuit shown for connector' H, and likewise for connector H is a simple two wire circuit which is in com- H1011 use.

The selector repeaters G and G', and 5, which are associated with the posite ends of the toll line connecting t e two community a tomatic exchanges, are also of the same mechanical construction as the selectors D, D-, D2, and-D3, having s e- Figs. 4 two 01pv cial relays and circuitsadded, however, t 'at enables either of themto function as an ordina-ry repeater when seized locally, while either acts as a selector in response to the vfirst digit and thereafter as a repeater when operated from the Vtoll line.

The re ater F, Fig. 3, is operated over one vcon uctor of the toll line 131-132, while the repeater F is operated over the other. The function of each is to translate grounded impulses into ,two wire impulses and repeat them. to its associated selector D or D as the case may be. v

The relay group P, Fig. 4, is provided for the purpose of signalling the toll station Q which, as before stated, is located on a toll line between the two C. A. Xes. Access to the relay group P is obtained by the operator by callin a dill'erent di it than the one ordinarily called when it is esired to operate the switch G on the distant end of the toll line. v

' The apparatus having been described more or less in general will now be described in connection with a detailed description of its operation. c

' In general a call from one C. A. X. to another or to the ltoll station Q is completed as follows: When a subscriber in one C. A. X. wishes toobtain scribe;- iii) tle'ilther C. A. X. hedcalls the opera or ia in 0or00 de nin u n whether hisline teminates in Itlie negreiixer v ing subscriber to however, is energized,

connection with a subascertains the number of the calling" suby scriber and also the number vof the subscriber desired.

hang up his receiver and' when he does so he releases the connection.

She then instructs thegca/ll- Then she calls his. number to make sure that he has gven his own number and not another.

hen 'heanswers she tells him to wait on the line while, she dials the sub\ scriber wanted. When the called subscriber answers he can obviously converse with the calling subscriber while the operator may converse with either-or both, and all throug the connection she maintains damp supervision over both the calling and the called subscribers except when one of them is the subscriber atsubstation Q.

' It will now be assumed that the subscriber at substation A desires to obtain connection with the -subscriber at the toll station Q, which is located on the toll line between the two C. A. Xes. The number of substation A is assumed to be ..123 while the number at substation Q is assumed to be 3.

When the rece1ver is removed at the call- -includes the winding 'of the switching relay 14-.and the stepping magnet 16 in series; and at armature 17 connects test wiper 23 to the `above circuit at a point between the switchllng relay 14 and the stepping magnet 16.

The operation now depends upon whether the trunk linev with which the line switch wipers are associated is busy or idle. If the trunk line is busy there is a ground potential u on the test contact with which the test wlper 23 is in engagement; the switching relay 14 is short circuited and the stepping magnet 16, which interrupts its own circuit, operates in the manner of'a buzzer to advance the switch wipers in search of an idle trunk line. However, we may assume in the present case that when the call is initiated the trunk line upon which wipers of the line switch are standing is 1 e. line relay 15 is energized the switching relay 14 is not short circuited and the stepping ma net 16 is not operated because of the hig resistance of relay 14. The latter relay, )grounds the test wiper 23 at armature 20, and at armatures 19 and 21 disconnects the line conductors 11 and 13 from the winding of line relay 15 and from ground, respectively, and extends them by way ofwipers 22 and 24, bank contacts 25 and 27, trunk conductors 28 and 30, and armatures 49 and 52 and their resting contacts to the upper and lower windings, respectively, of line relay of the selector D. The line and release relays 35 Under these circumstances when the.

and 36 of selector D energize immediately and the latter grounds the release trunk .conductor 29 before the slow acting line relay 15 of the line switch C has time to deenergize, thereby establishing a holding circuit for switching relay 14 of line switch C as follows: from ground through the working contact of armature 41 and said armature of release relay 36, release trunk conductor 29, test contact 26, test wiper 23, armature 20 and its working contact, switching relay 14, and stepping magnet 16 to battery. By means of this ground potential on the multiples of test contact 26 the selector D is rendered busy to the other line switches `having access to it; and a branch of this holding circuit extends by way of private normal conductor 12, to test Contact 95 and its multiples in the banks of the connectors having access to the line of substation A, thereby protecting it hagainst intrusion in the usual manner.

The subscriber at substation A may nowl operate his calling device in accordance with the digit 0, which is the call number of the toll recording operator located in the large automatic exchange, and when he does so the line relay of selector D is deenergized ten times momentarily. Each time the line relay 35 of selector D is deenergized due to the opening of its circuit at the calling device S of the calling substation A, a circuit is closed at armature 40 for the vertical magnet 56 in series with the slow acting relay 37 as follows: from ground hrough the resting contact of armature fil'hind the said armature, armature 40 and its resting contact, armay tureI 42` and its working contact, relay 37,

and vertical magnet 56 to battery. By theoperation of the vertical magnet the switch shaft and wipers are raised step by step until the wipers stand opposite the tenth lcve: of bank contacts. Relay 37 energizes and retains its armature attracted throughout the vertical movement ot' the shalt, and upon the closure of the vertical oii` normal springs 44 completes a circuit for the stepping relav 38. Upon energizing, relay 38 prepares the circuit ot' the rotary magnet 58 at armature 47, and at armature 46 establishes a locking circuit for itself. At the end of the vertical movement the slow acting relay 37 deenergizes and completes a circuit for the rotary magnet 58 which thereupon energizes to advance the wipers 53-55, inclusive, into engagement With the first set ot` bank contacts in the level opposite which they are raised. The rotary magnet also breaks the circuit ot the stepping relay 38 at interrupter contacts 48. The stepping relay 38 immediately dcenergizes and breaks the circuit of the rotary magnet which thereupon deenergizes also and again closes the interruoter contacts. The operation'now depends upon whether the test contact with which the test wiper 54 is in engagement is busy or idle.v If the test contact is busy it has a ground potential on it and the stepping relay energizes again .and the same cycle of operation is repeated over and over until an idle or ungrounded test contact is reached. ('When an idle set of contacts is reached the switching relay 39 energizes in series with the stepping relay 38 over the following circuit: from grounded release trunk conductor 29, through switching relay 39, interrupter contacts 48 of rotary magnet 58, vertical oil normal springs 44, and stepping relay 38 to battery. Relaj.7 38, however, due to its relatively small num ber of turns does not energize over this circuit. lt is assumed that test contact 57 is the first one found idle. vIn this case the energization of relay 39 switches the connection through to the trunk line terminating in contacts 56 and 58, and comprising conductors 106 and 108. These conductors lead to and terminate in the line relay 120 of relay group E. vAs soon as the switching relay 39 operates it connects ground to test contact 57 by way ot' armature 50 in order to make the seized trunk busy immediately. In addition to making the seized trunk busy this ground extends by way ot' conductor 107, armature 282 and its resting contact, armature 209 and its resting contact, conductor 109, armature 126 and its resting contact, and slow acting relay 122 to battery. Slow acting relay 122, upon energizing, closes at armature 129 a circuit for slow acting relay 123. Upon energizing, relay 123 projects ringing current by way of armatures 129 and 130 onto the trunk line comprising conductors 131 and 132. This induces an alternating cnrrent in the secondary winding ot repeating coil T, thereby operating the drop 143 in front of the operator in the large automatic exchange. However, at the same time that the circuit is ,closed for slow acting relay 122 the extending of the. connection closes a circuit for line relay 120 as has been previously explained. The two relays 120 and 122 are operated practically simultaneously. When line relay 120 operates it closes a circuit at armature 124 for release relay 121 which energizes and opens the circuit of the slow acting relay 122 thus allowing it'to deenergize and open the circuit ot' slow acting relay 123 which later falls back and removes generator from toll line 131-132. Due to the combined slowness of relays 122 and 123 the drop 143 in front ot the operator is operated before generator is removed. Relay 121 in addition to opening the circuit of relay 122, grounds release trunk conductor 109 thereby completing a holding circuit that extends back by way of conductor 107 to selector D to hold it and line switch C in their respective operated positions. It is understood that this circuit is established before the slow acting release relay 36 of selector D has time to deliio to normal and inserts a the usual manner -and after being informed as to the subscriber desired and the number of the calling subscriber she instructs him to hang up h1s receiver and when he does so line relay 120 deenergizes with the resultthat release relay 121'deenergizes also and removes ground :from release trunk conductor 109, thereby allowing the switch C to assume normal circuit conditions and also allowing switch D to release.

The operator may be engaged with other duties and consequently' not have time to listen for a click or other noise to inform hr that the calling subscriber has hung up.- In this lamp 147 at intervals for when the release relay 121 of relay group E deenergizes it closes a circuit at armature 125 and its resting contact for supervisory relay 139 which operates armature 142 to close an illuminating circuit for lamp 147. The energizing circuit for supervisory relay 139 is as follows: from ground through line relay 204 of repeater F, resting contact of armature 212 and said armature, control conductor 163, upper winding 161 of double wound impedance coil I', resting contact of armature 125 and said armature, resting Vcontact of armature 129 and said armature, trunk conductor 131, upper winding 134 of double wound impedance coil I, spring 145 ofjack J and its working contact, normally closed springs controlled by spring 137 of key K, and supervisory relay 139 to battery. In addition to relay 139 line relay 204 of repeater F operates over the above traced circuit and at armature 216 closes a circuit for slow acting release relay 200. Release. relay 200, upon energizing, extends ground to `release trunk conductor 107 by way of the Working contact of armature 209 and said armature, and resting contact of armature 282 and said armature. This ground on release trunk conductor 107 guards the toll line 131-132 against intrusion at the automatic end thereof by preventing the seizure of said line by E. Relay 200, upon energizing, in addition 'to grounding the release trunk conductor as described also closes at armature 208 a circuit for the upper or polarizing winding of electro polarized relay 202. This Winding consists of few turns of high reslstance wire and consequentlycannot operate relay 202 until it is lower winding. Returning now to the line relay 204, that relay, upon energizing, not

case she need only observe the place, the calling device S 'way .of the relay group` assisted to by current in the only closes the circuit for rela 200 at arma? ture 216 as above described, ut also closes The operator upon seeingethe lighted con-4 dition of lamp, 147, as fore described, knows that the calling subscriber has hung up, thereby leaving the trunk free for her to proceed with the call, and she throws key K 1n the proper direction thereby operatmg sprin from the circuit, thereby extinguishing lamp 147, and inserts the ca ling device S in its being connected to batter through the low protecting resistan'ce The operator may now` operate the calling device Sf in accordance with the 137 which removes relay 139- first digit 1 of the number of substationA,

assumed to be 123. When the callin device S is operated in accordance with t e first digit 1 of the desired number, line relay 204 of repeater F is deenergized once momentarily. When the line relay 204 is deenergized, it closes a circuit extending from ground by way of armatures 216, 214, and 207 to slow acting relay 201'. Relay 201 operates and closes at armature 210 the brldge across conductors 225 and 226 by a more direct path excluding relays 202 and 206. When there are several impulses tobe transmitted, the slow acting relay 201 remains energized throughout and obviously deenergizes again upon This is the usual expedient made use of to obtain first class switch control. At this time, however, there is but one impulse to be transmitted and when line relay 204 deenergizes, as previously described, it repeats vat armature 217 the impulse to the line relay 227 of selector D which steps its wipers up to the lir'st level and rotates them in search of an idle trunk line. It will be understood that since the circuit tical Vwith the circuit their cessation.'

of selector D is idenof switch D thatthe operation of the former .need not be ex` in s of the double wound line relay 66. Wien the line is thus extended the line and release relays 66 and 65, respectively, of connector H energize and the latter prepares the switch for the vertical operation and grounds the release trunk conductor 259 in order to guard the trunk agalnst intrusion and also to hold the selector D in its operated position.

The operator may now operate her calling device S for the second digit of the desired number. lAs a result the line relay 204 of repeater F is deenergized twice momentarily and repeats the impulses to the line relay 66 of connector H which is also twice deencrgized. Each time the line relay 66 deenergizes armature 88 sends an impulse of current to the vertical magnet 69 in series with the slow acting relay 64 by way of the following circuit: i'rom ground through armature 88 and its resting contact, armature 85 'and its working contact, od normal spring 98, oli normal spring 87, relay 64, and vertical magnet 69 to battery. By the operation of the vertical magnet the wipers 91-93, inclusive, are raised step by step unt-il they stand opposite the second level ot' bank contacts. It is in this level that the line of substation A terminates. The slow acting series relayl 64 is energized in series with .the vertical magnet and by means of its armature 84 maintains the circuit of the vertical Y magnet intact after the operation of the off normal springs, which occurs at the end of the first vertical step. At the end of the vertical movement the slow acting relay 64 deenergizes and transfers the operating circuit to the rotary magnet 68.

The operator will now operate her calling device in accordance with the last digit 3 of the called number. Vhen the 'calling device is operated the line relay 66 respon s to the impulses repeated to it as before and sends three impulses to the rotary magnet 68 over the following circuit: 'from ground by way of previously traced circuit to spring 98 and thence by way 'of spring 97, armature 84 and its resting contact, rest-ing contact otl armature 77 and said armature, armature 74 and its resting contact, and rotary magnet 68 to battery. By the operation of the rotary magnet the wipers 91-93, inclusive, are rotated step by step until they come to rest on the third set of contacts in the level opposite which they were raised. These bank contacts are indicated in the drawing by the numerals 94,-96, inclusive, and are the bank contacts in which the line of substation A terminates. The slow acting relay 61 is. energized in multiple with the rotary magnetandretains its armatures attracted throughout the rotary movement. At arma- Kture 7 5,- relay 61 connects test relay 62 with test wiper 92, andat armature 76 the said relay 61 closes la shunt around armature 77 of test relay 62 and its resting contact. The latter operation is to prevent the test relay from opening the rotary magnet circult while the test Wiper is passing over busy test contacts.

It will be assumed first that for some reason the line of substation A has become busy since the subscriber thereat hung up after` callin the operator, as previously explained. Such eing the case, when the test wiper 92 arrives at test contact there is a ground potential thereon, the busy test relay 62 is energized, and when the slow acting relay 61 deenergizes at the end of the rotary movement a locking circuit is established for the test relay 62 as follows: from grounded release trunk conductor 259 through armature 78 and its working contact, normally closed contacts operated by armature 75, and test relay 62 to battery. Relay 62 opens the roti ry magnet circuit at armature 77, in order tc prevent further movement of the wipers 1f4l the calling device should be turned again, an] at armature 79 connects a lead from the busy signalling machine B to the lower heavy talking conductor. By this operation an audible slgnal is transmitted to the calllng operator and, being advised thereby that the called line is inaccessible for the time being, she will operate key K', Fig. 1, and thereby release the connection.

sume that the line of substation A is idle when called. In that case when the test wiper 92 arrives at test contact 95 the' latter is not grounded and the test relay 62 is not energized. When the slow acting relay 61 deenergizes at the end of the rotary movement it completes at armature 75 a circuit for the switching relay 60as follows: from grounded release trunk conductor 259 by way of armature 78 and its resting contact, upper windin of switching relay 60, resting contact o armature 75 and said armature, test wiper 92, test contact 95, normal conductor 12, switching relay 14 of line switch C, and stepping magnet 16 to battery. Switching relays 60 and 14 are operated 1n series over this circuit, and the latter clears the called line of its normal battery and ground connections in the line switch C. It may be stated here that due to an interlocking device (not shown) between the armatures of line relay* 15 and the armatures of switching relay 14 that the armatures of relay 14 are operated only about half way and consequently the wipers are not connected up at this time. In the connector H, when the switching relay 60 energizes, it establishes a lockino' circuit for itself at armature 73, grounts the test wiper 92 at armature 72, opens the circuit of the rotary magnet at armature 74, and at armatures 71 and 99 (completes the connection to the line wipers 91 and 92. v

Inthe present case, however, we may aslll The connection has now been completed to the desired called line and ringing current is intermittently projected out over the line conductors 11 and 13 to operate the bridged ringer at substation A. The ringing circuit is of the usual character and need not be described in detail. When the called subscriber-responds by removing his receiver from the hook, the ring cut off relay 63, the upper winding of which is included in the return circuit of the generator, operates and at armature 81 locks itself to ounded release trunk conductor 259. Re-

y 63 also breaks the ringing circuit at the l5 resting contacts of armatures 80 and 82 and at the working contacts of these same armatures completes the talking circuit. The transmitter at substation A 1s now sup lied with talking current through the win ings of the double wound back bridge .relay 67,

and this relay is accordingly energized withff the result that the incoming conductors 258 and 260 are reversed as re ards their connection with the windings o the line relay 66. It follows that the direction of current flow in the trunk line and the bridge at repeater F is reversed. The two windings of the electro polarized relay 202 of repeater F, which heretofore have opposed each other now assist each other in operating the said relay. Upon energizing, relay 202 closes at armature 211 the circuit of slow actin relay 203. Relay 203, upon energizing, c oses4 a shunt at armature 215 and its working contact around armature 217 and its working contact, closes a multiple point in the circuit of release rela 200 at armature 213, opens the circuit o? .relay 201, and at armature 212 transfers the operators control circuit conductor 163 from theline rela 204 to relay 205. Line relay 204 immedlately deenergizes but owing to the operation of relay 203, as previously explained, it does not have any eifect.

The control circuit has now been switched from the grounded lto the ungrounded pole of battery at the repeater F and the effect of this operation at the distant exchange will now be considered. Assuming that the operator restores her key K to normal while waiting for the called subscriber to answer, which will ordinarily be the case, the supervisory relay 139 o erates and lights the supervisory lamp 14 Now when the other end of the control circuit is switched from ground to batter no current flows over the said circuit an consequently the supervisory relay 139 deenergizes and extinguishes lamp 147. The operator, upon seeing lamp 147 become extinguished, knows that the called party has answered and she immediately associates her head set with the cord circuit in use.

The operator may now converse with` the called subscriber and 4upon ascertaining that tion Q and since a he is the one that desiresthe connection tells him to wait on the line 'while she calls the f desired subscriber, being in this case the one at substation Q. The operator now inserts the other plug wbelonging 'to the cordy circuit in use into jack J2, that being the proper jack to use when calling substation Q. It 1s easily seen that as soon as a plugis inserted into the jack J2 thatthe line rela 275 and therelease relay 276 of repeater I; operate in the same manner as thel line and release ^relays of the repeater F operated in the previous example, battery being fed out through resistance Re and sprin 170, and since the two repeaters are identical the result in this case as in the previous one is that the line relay closes a bridge across the trunk conductors 283 and 284 of the associated selector, which in this case is the selector D2, while the energization of the release relay makes the repeater ready to repeat impulses. Obviously, the closing of the bridge across the trunk conductors 283 and 284 energizes the line and release rela s 285 and 286 of the selector D2 and makes t e switch ready to operate.

The energizing circuit of the line relay 275 of repeat-er F is `as follows: from ground through line relay 275', resting contact of armature 175 and said armature control conductor 164, lower winding 162 of impedance coil I1, resting contact of armature 127 and said armature, resting contact` of armature 130 and said armature, trunk conductor 132, lower winding 135 of impedance coil I, spring 170 of jack J and its working contact, normally closed con` tacts controlled by spring 171 of key K2, and resistance Re to battery. p

The operator throws key K2, immediately after inserting the plug intov jack J2 and Athereby substitutes the calling device S together with the resistance R for resistance The operator may now operate the calling device S in accordancev with the digit 3 which is the number of the substation Q, Fig. 4, and when she does so three -momendtary interruptions are produced in the cir;` cuit of the line relay 275 of repeater F said relay repeating them to the line relay 285 of the selector D2. 'Line relay 285 is accordingly deenergized three times momentarily with the result that the selector D2 operates to step the wipers 288, 289 and 290 up to the third level of bank contacts and then rotates them in search of an idle trunk line. The operation of switch D2 is similar to the operations of switch D5 and consequently need not be explained in detail ex` cept as regards the giving of the busy signal. The digit 3 gives access to the 'substaperson desiring connection with substation Q wishes to. be ,connected with only-that particular substation )39 nevadas and nojother there is only one trunk line in the third level of D2, all the test contacts in the third level except the test contact 292 being grounded.

It will irst line on which the substation Q is located 1s busy when the call is made as above explained. In that case there is a ground potential on test contact 292 and accordingly when the test wiper 289 reaches test Contact 292 the wipers do not stop but continue to advance step by step until they pass off the last contact in that level and when they .do so the cam 238 secured to the switch shaft operates the springs 239 andl 274. The operation of spring 274 opens the circult of switching relay 287, while the operation of spring 239 connects the grounded busy lead 237 from the busy machine B, Fig. 2, to the lower winding of line relay 285 and removes direct ground therefrom. This latter operation serves to give the operator a busy signal to inform her that the line is inaccessible for the time being and she, upon hearing 1t operates key K and thereby releases the connection.

It will now be assumed that the trunk line terminating in contacts 291-293, 1nclusive, is idle when the call is attempted as previously explained, this being the case the arrival of test wiper 289 on test contact 292 is followed by the energization of switching relay 287 and the connection is extended by way of the bank contacts 291 and 293, trunk conductors 255 and 257, and the upper and lower left windings of the repeating coil T4 to the upper and lower windings, respectively, of line relay 376 of relay group P. The line and release relays 376 and 377 immediately energize and the latter grounds the release trunk conductor 256 at armature 381. This ground is placed on the release trunk before the slow acting release relay 286 of the selector D2 has time to release and serves to hold the selector in its operated position. By means of this ground potential on test contact 292 and its multiples the switch G and the relay group P are rendered busy to others. At the same time that the release relay 377 grounds the release trunk as before explained it extends the connection to the called substation at armatures 382 and 383 by way of armature 384 and normally closed contacts operated by armature 385, and conductors 386 and 387. Battery from impedance 375 immediately flows over the connection to substation Q and thence by way of springs 389 and 390 of key K3 and their resting contacts, trunk conductors 394 and 395, left hand windings of repeating coil T3, armature 440 and its resting contact, armature 435 and its resting contact, and the upper winding of line relay 407 to ground. Relay 407 ,energizes and at armature 434 closes the following circuit:

be assumed that the trunk from ground through armature 441 and its l contact, and release relay 402 to battery.

Release relay 402, upon energizing, connects ground to release -trunk conductor 450 at armature 418. vThis ground extends by way of the release trunk conductor 450 to the test contacts in the banks ofwall the switches having access to the selector repeater G and thereby protects the trunk line from intrusion at this end.

The connection has now been extended to tl1e"\called substation but the bell thereat has not been rung. In order to ring the bell at substation Q the operator operates the calling device S for the digit 0., for example. In response to the impulses repeated to it, linev relay 376 of relay group P deenergizes a plurality of times thereby operating slow relay 378 through the resting contact of armature 379. Relay 378 energizes and retains its armatures attracted throughout the series of impulses and at its armatures 384 and 385 divides the trunk into two sections and projects ringing currents from generator Gen. out on the section on which substation Q is located thereby ringing the bridged bell thereat. It is easily seen that when the trunk is divided by the energization of relay 378 that battery from4 impedance 375 can no longer flow over the distant end of the trunk to keep the switch associated therewith busy. In order that battery be not removed from the distant end of the trunk, battery is placed thereon by way of resistance R7 and armature 385 and its working contact before the trunk is completely divided thereby maintaining .the line and release relays of the switch G energized so that the latter will not remove ground from the associated release trunk. At the end of the series of impulses the slow relay 378 deenergzes and obviously removes ringing current from the trunk line and unites the two sections thereof. The operator may repeat the operation as many times as necessary in order to attract the attention of the subscriber at the called substation. When the subscriber at substation Q answers he throws the key K3 in the proper direction to operate the springs 392 and 393 and raises the receiver from the hook.

The talking circuit is now completed to the two substations and extends in either direction form the paired repeaters F and F', Fig. 3, which are coupled together through talking condensers, as shown. the transmitter at the called substation being supplied with current from the .local battery through the primary of the induction coil shown clearly in the drawing. The receiver is included in a bridge extending across the trunk as follows: from conductor 386 by way of spring 389V and its-resting contact, spring 392 and its working contact, up-

per or secondarywinding of lnduction'. coil 397, right working contact of the sw1tchhook and said switchhook and its left working contact, the receiver, working contact of spring 393 and said spring, and the restlng contact of spring 390 and sald spring to conductor 387. The required connection havlng lbeen established, the subscribers may now converse as desired. When the conversation is tinished both subscribers will hang up their receivers and the subscriber at substation Q also restores the key K3. When the receiver is replaced at substation A the circuit of vback bridge relay 67 is broken and when it deenergizes, relay 67 reverses the conductors 258 and 260as regards their connection with the windings of the line relay 66. This reverses the direction of current flow in conductors 258 and 260 and 1n the lbridge across conductors 225 and .226 in repeater F to normal. The two windin s of relay 202 now oppose each other; the said relay retracts its armature, and the circult of relay 203 is broken. Relay 203, upon deenergizing, opens the bridge across con ductors 225 and 226, disconnects the control circuit from battery through relay 205 at armature 212 and restores it to ground through line relay 204. Line relay 204 and the operators supervisory relay 139 immed1- ately energize in series over the operating circuit. The line relay 204, upon energizing, closes thebridge across the trunk conductors 225 and 226 before the connector H has time ,to release, and closes the circuit of release relay 200 again before it has time to deenergize. Supervisory vrelay 139 operates armature 142 and thereby lights the supervisory lamp 147.

W'hen the operator perceives the disconnect signal she pulls down the connection. When the plug visvremoved from the jack J spring 145 disconnects the control circuit from supervisory relay 139 and battery and connects it to 'impedance 159 and thence to ground, this being the normal condition of the circuit. Supervisory relay 139 upon deenergizing, eXtinguishes lamp 147. Line relay 204 of repeater F, being no llonger supv plied with battery, deenergizes and at armature 216 opens the circuit of release relay 200, and at armature 217 opens the bridge across conductors 225 and 226 thereby releasv ing the connection to substation A in the well known manner.. Upon deencrgizing, release relay 200 opens the circuit of the polarizing Winding of relay 202 at armature 208 and at armature 209 removes ground from the resting Contact of armature 282 so i that when the latter armature falls back ground' will be removed from release trunk conductor 107. v f

y, When the plug is pulled from the jack J 2 spring v170 disconnects the' control clrcuit from battery through resistance R and connects it to ground through s ring 146 and its resting contactlandim ance 160. When battery isA removedl from the control'circuit, as above explained, line relay 275 of repeater F deenergizes and releases the connection to substation Q in the same manner as the deenergization of the line relay of repeater F releases the connections to Asubstation A.

It will now be assumed that the subscriber at substationl Q desires to obtain connection with the subscriber at substation A whose number when called by a subscriber in the same C. A. X. is 345. When the subscriber at substation Q removes lhis receiverto make a call he also throws key K3 in such a direction that the springs 392 and 393 are operated. This allows him to listen in on the toll line and ascertain if it is in use or not. Assuming that the toll yline is found to be idle, he throws the key to the opposite or calling position and when he does so the springs 388-391, inclusive, are operated. Springs 389 and 390 disconnect the section of the toll line comprising conductors 386 and 387 from the section comprising conductors 4394 and 395 and connects 1t to a bridge that includes the upper or secondary winding of the induction coil 397 in series with the receiver. The spring 391 connects battery through resistance R to conductor 395 to operate the line relay 407 of selector repeater G which in turn operates the releasey relay 402 and thereby grounds thev release trunk 450 to make switch G test bus Spring 388connects batte through resistance R and calling device 2 by way of the switchhook springs, the bell coils in parallel, conductors 386 and 387, armature 384 and its resting contact and the normallyclosed contacts controlled by armature 385, armature's 382 and 383 and their resting contacts, conductors 368 and 369, right hand windings of repeating coil T2, armature 365 and its resting contact, armature 360 and its resting contact, and the upper winding of line relay 332 to ground. Line relay 332 immediately ener- -gizes and closes the following circuit for gizing, opens at armature 347 a point inthe circuit of release magnet 339 and prepares the circuit of vertical magnet 341 and grounds therelease trunk conductor 253 at armature 346 in order to make switch G and also relay group P busy. When the ground is placed'on release trunk conductor 2,53 the circuit of the winding of electro polarized relay 333 is Release relay 327, upon-ener-A upper or polarizinglill The switch G is now ready for operation,

lVhen the calling subscriber operates the.

calling device S2 1n accordance with the digit 0, or the number of the tll recording operator, the circuit of' line relay 332 is interrupted ten times. In response to the interruptions thus produced the line relay 332 is deenerglzed ten times momentarily and at each deenergization sends an impulse of current to the vertical magnet 341 over the following circuit: from ground through arlnature 366 and its resting contact, armature 359 and its resting contact, armature 347 and its working contact, armature 350 and its resting. contact, slow acting series relay 326, and vertical magnet 341 to battery. By the operation of the vertical magnet the switch shaft and wipers are raised shaft the slow acting Vance thQlWipcrs step by step until the wipers 336, 337 and 338 stand opposite the tent-h level (if bank contacts. The slow acting relay 326 -energizes in series with the vertical magnet and retains its armature attracted throughout the Vertical movement and upon the closure of off normal contacts 301 completes the circuit of the stepping relay 325. Upon energizing, relay 325 prepares the circuit of rotary magnet 340 at. armature 343 and at armature 342 prepares a locking clrcuit for itself in series with interrupter springs 304. At the end of the vertical movement of the and completes the circuit of the rotary magnet 340 which thereupon energizes to ad- 336-338, inclusive, into engagement with the first set of bank contacts in the level opposite which they are raised. The rotary magnet also breaks the P circuit of stepping relay 325. The said relay deenergizes and opens the circuit of' the rotary magnet, which thereupon deenergizes also and again closes its interrupter contacts. The operation now depends upon whether the first trunk is busy or idle. If the first trunk is busy there is a ground potential upon test wiper 337 is in engagement and the stepping relay is energized again and the' same cycle of operations is repeated over and over until an idle or ungrounded test contact is reached. lVhen an idle set of contacts is reached the switching relay 328 energizes in series with the stepping relay over the following circuit: from grounded` relay 326 deenergizes l the test contact with whichy relay 328 com letes the following circuit: from ground y way of ounded release trunk conductor A253, wor ing contact of armature 349 and said armature,ftest wiper 337, test contact 306, release trunk conductor 107, armature 282 of release relay .276 of4 repeater F and its resting contact, armature 20".) ofv relay 200 and its resting contact, conductor 109, armature 126 and lts resting contact, and slow acting relay 122 to battery'. Relay 1 22 energizes and closes the circuit of relay 123 which energizes and pro]ect s generator out over the trunk line 131-132 to operate drop 143. This all happens in the same manner as described in the previous case in which the subscriber at sub-A station A called the operator.

Returning now to the selector repeater the energization of switching relay 328 closes the following bridge across line wipers 336 and 338: from line wiper 338 by way of armature 352 and its working contact, lower armature, upper left winding of repeating coil T2, working contact of armature 308and said armature, the armature of release magnet 339 and its resting contact, and line Wiper 336. Over this bridge the line .relay 120 of relay group E energizes and operatesn the release relay 121 thereby opening the circuit of relay 122 which falls back and opens the circuit of relay 1.23. Relay 123 falls back later and removes generator from the trunk line. The electropolarized relay 333 included in the bridge across line wipers 336 and 338 does not energize at this time be- `cause the current in its lower winding oposes that flowing in its upper winding.

The operator upon observing the operated condition of drop 143 Vrestores it to normal and inserts a plug of an idle cord circuit into jack J and associates her head set with the cord circuit. After finding out who is calling and who he desires to be connected with, she tells him-to hang up his receiver. He does so and also returns key K3 to normal thereby releasing the connection and restoring the conditions on the associated trunk line to normal.

The release of switch G will now scribed in detail. lVhen the receiver is replaced at substation Q the circuit of line relay 332 of switch G is broken and the said relay accordingly deenergizes. At armature 359 line relay 332, upon falling back opens the circuit of release relay 327. Release relay 327, upon deenergizing, removes groun from release trunk conductor 253 at armature 346, and at armature 347 closes the following circuit for release magnet 339: from ground by way of armature 366 and its resting contact, armature 359 and its resting conbede' izo ` of` an idle trunk line.

latter reaches normal position` When the connectionl is released as de scribed the line and release relays 120 and 121 of relaygroup E deenergize and the latter restores the operators control circults to normal at armatures 125 and 127. Ihe 'supervisory rela 139 immediately energizes in series with l1ne relay 204 of repeater F over a previously traced circuit and attracts its armature 142 thereby lighting-superv1s ory lamp 147. The operator upon seemg the lighted condition of lamp 147 knows that the subscriber at substation Q has hung up his receiver andthat she may now proceed with the call.

To do this the operator removes the plug from jack J and inserts it into jack J 2 and proceeds to call thesubscriberat substation Q as she did in the previous example. `lNe shall assume that she obtainsconnectlon with relay groupsl? and that she operates er calling device in the usual manner to ringthe bridged bell at substation Q.

When the' subscriber at substation Q'answers, in response to the ringing of the bell thereat, he not only removes his recelver but also throws keyKa in Isuch a manner as to operate springs 392 and 393 thus completmg the talking circuit. After ascertalning that he is the person desiring the connectlon wlth the subscriber at substation A, the operator requests him to remain on the line while she calls the desired subscriber.

The opera or-now removes theplug from jack J 2 thereby releasing the establlshed' connection. She then inserts a plug lnto 'jack .T and when she-does so supervisory relay 139 and jline relay 204 of repeater F .energize in series over the control c1rcu1t 1n the usual manner. Line relay 204 closes the circuit of .release relay 200 `and also closes' the usual bridge across conductors 225 and 226, thereby making-the yselector D ready for the usual impulses. Release relay 200 of the repeater F energizes and prepares the repeater for repeating.properly' the usual impulses. The operator now throws the proper key and thereby includes the calling device in the control circuit. She-now ope'I-, ates her calling device in accordance with \the digit 2 which is the digit that gives access to the C. A. X. in which substation A is located, and when she does so the selector steps its wipers up to the second level of bank contactsvand rotates them in search W'e shall assume that the trunk line terminating in contacts 246-248` inclusive, is idle and 'consequent- 1y is selected since it is the only trunk line terminating inv that level.

magnet upon en-" arized relay 333.

ytends still further ductors 252 and' 254, upper That being the case'` the operation ofl switching relay, 221 switches the connection through vto the 'trunk line terminatingin bank contacts 246,247

and 248. A ground potential by way f armature 226'of release relay 228 an arma- ,ture 234 of switching relay 221 is limmediately sent forward to ground test contact 247 and its multiplesin order to makef the selected trunk busy immediately. This ground potential, in addition to making the selected trunk busy, extends by way of jumper 300, release trunk conductor 256, armature 381 of relay group P and vits resting contact,

-and release trunk conductor 253 to battery through the upper winding of electro-POL.

electro-polarized relay 333 is such that it cannot operate the relay until it is assisted by current in the lower winding as has been explained before.,

The ground potential exb'y way of armature 346 and its resting contact, ofi' normal contacts 303,' armature 362 and its resting contact, resting contact of armature 353 and said armature, to battery 330. Reversing relay 330 is wound large number of turns to make it slow to pull up, and consequent y it does not operate immediately. A further result .of the operation ofswitching relay 221 of switch D nection by and their working contacts, 242,

wipers 240 and bank contacts 246 and 248, trunkconand lower left windings of repeating coil T2, armatures 345 and 351 and their resting contacts, and normally closedcontacts of reversing relay 330 to the upper and lower windings of line relay 331. The line relay 331 immediately energizes and operatesrelea'se relay 335, atl

armature 358. Release relay 335, upon energizing, places ground on release trunk conductor 253 by way of armature 366 and its working contact, ott normal contact 303, and resting contact of armature 346 and said armature. This ground extends back by way ofthe resting contact of armature 381 and said armature, release trunk conductor 256, and jumper 300 to test contact 247 to maintain the switch D in its operated position.

The upper winding of through reversing relayV With a v and isgiven a stiff adjustment, the two features combinin is that it extends the conl way of armatures 233 and 236 Further results of the energization of '.re-

lease relay 335 are that the clrcuit ofslow relay 334 is prepared at armature 367 and the trunk `control circuit is -switched from its normal path to ground through the upper winding of relay 332, t0 battery by way of armature 365 and its working contact,

lower. winding of relay 329, working contact of armature 357A and said armature, and resistance R?. Relay 329 of switch G and line relay 407 of switch G immediately energize in series over the following circuit:

lao

from ground by way of line relay 407 of switch G', resting contact of armature 435 and said armature, resting contact of armature 440 and said armature, upper and lower left windings ofrepeatlng coll T3, trunk conductors 394 and 395, resting contacts of springs 389 and 390 of key I@ and said springs, trunk conductors 386 and 387 armature 384 and its resting contact and normally closed-contacts controlled by armature 385, armatures 382 and 383 and thelr restlnrr contacts, conductors 368 and 369, upper and lower right windings of repeating coil T2 and thence by way of previously -traced circuit to battery.l Since the circuits of switches G and G are identical the energization of the line relay 407 of yGr" is effective to energize the release relay 402 and .thus make the swltch busy and prepare it for the operating.,Y impulses in the same manner as the line and release relays 332 and 327 prepared switch Gr for operation when the subscriber at substation Q made the call previously described. I

In the switch G the only effect produced at this time by the energization of relay 329 is the opening of the circuit of reversing relay 330, at armature 353. This occurs before the slow to pull up reversing relay has had time to energize.

The operator may now operate her calhng device for the second digit 3 of the 4desired number. The repeater F repeats these impulses to the line relay 331 of switch G.

three times mome tarily and at armature 357 opens the circt't of line relay 407 of switch G three times momentarily. The effeet of this operation will be described later. Each time line relay 331 deenergizes it not only opens the controlling circuit at armature 357 as explained but also closes the circuit of slow relay 334 at armature 358. Re'- lay 334 operates and maintains its armatures attracted during the entire series of impulses. At armature 363 relay 334 closes a shunt around the lower winding of relay 329 so as to obtain a better impulsing circuit for line relay 407 of switch G', while at armature 362 it opens a point in the circuit of reversing relay 330 to prevent its operation at this time due to the deenergization of relay l329 when the shunt is placed around its lower winding. `When the impulses cease slow relay 334 falls back, removes the shunt from the lower winding of relay 329, and at the same time closes the circuit of reversing'relay 330 at armature' 362. Revers ing relay 330 being slow to energize does not have suflicient time to operate before relay 329 operates and opens its circuit at armature 353,

The operation of the selector repeater G The line relay 331 iccordingly deenergized on the distant end of the toll line will now be described in detail. Each time the line relay 407 deenergizes due to the opening of its circuit by armature 357 of the switch G,

armature 434 falls back and closes thefolf' lowing circuit: from ground by wayy of armature 441 and its resting contact,`arma ture 434 and its resting contact, armature 419 and its-working contact, armature 424 and its resting contact,slow acting series relay 401, and vertical magnet 412 to batlcuit of the rotary magnet at armature 414 and establishes a locking circuit for itself at armature 413 in series with the contacts 449 controlled by the rotary magnet 411.

At the end of the vertical movement of the shaft the slow actingl relay 401 deenergizes and completes a circuit for the rotary magnet 411 which thereupon energizes to advance the wipers 443-445, inclusive, into engagement with'the first set of contacts in the level opposite-which they `are raised, at the same time opening the lockingl circuit of stepping relay 400 at its interrupter contacts. Stepping relay 400 accordingly deenergizes and breaks the 4circuit of the rotary magnet which thereupon deenergizes also and again closes its interrupter contacts. The operation now depends Jipon whether the test contact with which the test wiper 444 is in engagement is busy or idle. If the test Contact is busy there is a ground potential on it and the stepping relay energizes again and the same cycle of operation is rcpeated over and over until an idle or ungrounded test contact is reached. Vhcn an idle set of contacts is reached the switching relay 403 energizes in series with the stepping relay 400 over the following circuit: from ground by way of working contact of armature 418 of release relay 402 and said arma-ture, switching relay 403, interruptcr contact 449, oil normal contact.Q 420. and stepping relay 400 to battery. Relay 400, however, due to its relatively small number of turns and. .comparatively stift' adjustment does not energize over this circuit. It is assumed that test contact 447 is the first one found idle. In this case the energization of the switching relay 403 closes a bridge across the trunk line comprising conductors 473 and 47.5 terminating in the contacts 446 and 448. This bridge may be traced as follows: from line wiper 445 by way of armature 433 and its working contact, lower right winding of repeat- IMI i so

closed reverslng contacts ing coil T,Iarmature 425 and its worlxing contact, lower winding of electro polarized relay 408, resistance R", working contact o.f

said' armature, upperright winding of repeating coil T3, armaarmature 417 and relay 479. The line and release relays of the connector H energize in the usual manner thus preparing the connector for the usual impulses. Since connector H' is identical with the connector H and the operation of the latter has already been described it is not thought necessary to describe the operation of the connector H in detail. It will suice to say that connector H operates in accordance wit-h the last two digits 4 and 5 to give access to the line of subst-ation A and that when the subscriber thereat responds to the ringing of his bell by removing his receiver he causes the usual operations to take placein the connector, which results in the energization of back bridge relay 479 and the consequent reversal of the connection of conductors 473 and 47 5 as regards the windings of line relay 476. The reversal of the conductors 473 and 475 results in the operation of the electro polarized relay 408 its two windings now assist each other.

When the elector polarized relay 408 operates it switches the control circuit from its normal path to ground through the upper winding of line relay 407, to battery by way of the upper winding of relay 404, and closes at armature 436 a locking circuit for the lower winding of line'relay 407. The condition now existlng is that the trunk line extending from switch G to switch G is connected to the live pole of battery at each end and consequently there is no flow of current over it. As a result relay 329 in the selector repeater G deenergizes and at armature 353 closes the circuit of reversing relay 330. The reversing relay 330, upon energizing, reverses the direction of, e current flow in the conductors 252 and 254 andI consequently in the bridge across the conductors 225 and 226 at repeater F. Electro polarized relay 2020i the repeater F accordingly energizes and, in a manner before explained, connects the live pole of battery to control conductor 163, allowing the supervisory relay.139 to deenergize and extinguish superviso lamp 147 in front of the operator to apprise her of the fact that the calledsubscriber has answered.

The called and calling subscribers'may of the back bridge d 1n the bridgev'thereo because causes the electropolarized relay 408 to deenergize and restore the control. circuit te its normal path to ound by way of the upper windin of re ay 407. This reoperates relay 329 o switch G. Relay 329, upon energizing, opens the circuit of reversing relay 330 at armature 353. Relay 330, upon eenergizing, reverses the current. flow in the conductors 252 and 254 to normal whereupon the electropolarized relay 202 in the repeater F is deenergized. This results finally in the switching of control conductor 163 back .to its normal ground by way of line relay 204. he supervisory relay 139 on the otherend of the control circuit is a ain energized and lamp 147 is again lighte to apprise the operator of the fact that conversation is'linished.

The operator upon noting the lighted condition of supervisory lamp 147 pulls down the connection; When the plug is removed from jackl J the control circuit is re stored to its normal path to ground through impedance 159. This results in the deenergization of supervisory relay 1 39 and also the line relay 204 of repeater F. As a result the supervisory lamp 147 is extinguished and the bridge across conductors 225 and 226 at repeaterF is opened. l This allows'line relay 331 of the switch G to ,deenergize and open the circuit of release lrelay 335. When relay 335 deenergizes, the control circuit extending to switch G is restored to its normal path to ground by way ath to of the upper winding of line rela 332.- This obviously results in the deenergization of line relay 407 of repeater G and the consequent deenergization of release relay 402. When release relay 402 deenergizes the following circuit is completed: from ground by way of armature 441 and'its resting contact, armature 434 and its resting contact, armature 419 and its resting contact, olf normal contacts 421, and. release magnet 415 to battery. Release magnet 415 energizes, and restores the switch shaft and wipers to normal position inthe usual manner. l The opening of the bridge across trunk conductors 473 and 475 usual release of connector H ingly need not be explained.

, t is seen that.A each of the 'two connections that -have' just been described 'includes the subscriber at substation Q, `either as a calling ory called subscriber, y As a matter of fact calls to and from the substation Q as compared to the total number of calls in the entire system will be very few indeed, the

and accordobviously results in the.

loc

we l

subscribers such as the subscriber at substation A and the subscriber at substation A. In a call to substation Q it will be noted also that there is provided no way for givsu rvision to the operator when the su scri r at substation Q answers or hangs up his receiver. Calls to substation Q are ve rare and it is not thought necessary to ma e any special or elaborate provisions to overcome this diiliculty.

' A call will now be described that will be typical of practically al the calls that are to be made from one exchange to another. For this purpose it will be assumed that the Asubf scriber at substation A desires to obtain connection with the subscriber at substation A. In order for the subscriber at substation A to obtain connection with the toll recordin operator he must dial two digits. The rst digit is 0 and gives connection to the C. A. X. that is nearer the operator. The second digit is also 0 and as explained before gives connection with the o erator. When the subscriber at substation A removes his receiver to initiate the call his line switch C operates in a manner similar to that described for the line switch eration of `calling device is again C to extend the calling line to an idle trunk line. We shall assume the trunk line leading to selector l)3 is the one selected. This being the case, the line and release relays 461 and 462 in the selector Da operate in the usual manner and perform the usual functions. In response to the digit 0 the selector D3 raises its wipers 464-466, inclusive, step by step until they stand opposite the tenth level of bank contacts. The wipers are then automatically rotated to piclr out an idle trunk line in the level opposite which they are raised. It will be assumed that the trunk line terminating in 468 and 471 is the first one found idle and consequently the one the case the energization of switching relay 463 switches the connection through by way of trunk conductors 449'and 451, upper and lower right windings of repeater coil T3, armatures 417 and 425 and their resting contacts, normally closed contacts controlled by reversing relay 405 to the upper and lower windings of line relay 406. 'It will be appreciated that this operation is substantial the same as the operation described in which the selector D was used to obtain connection to the switch G in a preceding exa'mple, the circuits of the two switches G and G being identical. This being the case it is not thought necessary lto describe the opswitch G in detail. However, it may be said that when the switch G' is seized-that it immediately closes the proper circuits in order to prepare thev switch G for receiving the usual impulses. When the turned the switch .G

A :,evaess the bank contacts 467,

selected. This being asus repeater and repeats the impulses received to the switch -G in the distant exchange. In response to the impulses thus received the switch G raises its wipersr336, 337, 338 ste by step until they stand opposite the tent level of bank contacts and rotates them in search of an idle trunk line. It will be assumed that the trunk line terminating in bank contacts 305-307, inclusive, is the first one found idle and conseuently the one selected. This being the case t e enei'gization` of switching relay 328 extends .the connection in the same manner as was described in the case in which the subscriber at substation `Q, called the operator. In response to the call thus received the operator will insert a plug into the jack lJ and ascertain from the calling subscriber his own number and the number with which he desires connection. After obtaining the `desired information the operator requests the calling subscriber to hang up his receiver and when he does so the connection just described is released. The operator then operates her calling device in the usual manner and thereby reestablishes connection with him in order to ascertain whether or not he has given the correct number. When the subscriber at substation A answers the final result is that supervisory lamp 147 in front of the operator is extinguished as before described. The operator upon seeing the lamp become extinguished knowsthat he has answered and takes the proper steps to converse with him and upon ascertaining that he is'the person that desires the connection she instructs him to wait on the line while she calls the numberhe wants. She then inserts a plug into the jack J and proceeds to call the subscriber at substation A.

phone is the one wanted and assuming that Y he is the subscribers may now converse with each other. 'When the conversation is finished the lsubscribers will hang up their receivers and the release will take place in the usual manner. When the two connections are released both supervisory lamps 147 and 148 become lighted and the operator upon seeing this will pull down the connection. If, however, yone subscriber hangs up and the 'other fails to do so'only the particular lamp associated with the connection to the' subscriber that has hung up will become lighted. However, this will not prevent the releasing of the connection for the operator upon removing' the plugs from the jacks lll " switch G other. In switch G the line relay 332,`

causes the-circuit conditions to be restored to normal. Assuming .that it is the subscriber at substation A that has'not hung up the removal of the plug from jack J will cause the control circuit to be switched to its normal path to ance 159. The other end of the control circuit in repeater F is connected at this time to battery by way of relay 205 and the result is that relay 205 energizes and at armature 218 opens the circuit of release relay 200. When release relay 200 deenergizes it opens the upper or polarizing winding of electro polarized relay 202 at armature 208 withl the resultthat relay 202 is deenergized for the lower winding alone cannot hold the relay operated. When relay 202 deenergizes it opens the circuit of relay 203. Relay 203 upon deenergizing, the conductors 225 and 226 at armature 215. The opening of the bridge allows the line relay 331 and release relay 335 of selector repeater'G toI deenergize. Release relay 335 upon deenergizing removes ground from release trunk conductor 253 at amature 366 thereby allowing selector D to restore to normal position, and at armature 365 restores the control circuit that extends to switch G to its normal path toground through the upper winding of line relay 332. Since the other end of the control circuit is connected to battery through" the upper winding of relay 404 of switch G the line relay 332 of switch G and relay 404 of energize in series` with each upon energizing, closes the circuit of release relay 327. Release relay 327 energizes and at armature 346 places ground on release trunk 253 thereby rendering the toll line busy for the time being. Inswitch G', relay 404 upon energizing opens the circuit of release relay 402 at armature 327 and upon the deenergization of release relay 402 completes the following circuit for release magnet 415: from ground by way of armature 441 and its resting contact, armature 434 and its working contact,armature 427 and its working contact, armature 419 'and its resting contact, ofi normal contacts 421, and release magnet 415 to battery. By the operation of the release magnet 415 the switch shaft and wipers are restored to normal position, the circuit of release magnet 415 being broken at ofi' normal springs 421. With the switch in normal position all the relays deenergize and they control circuit is lli restored to its normal path to ground through line relay 407. The line relay 332 of switch G also deenergizes vand opens the circuit of release relay 327 which deenergizes and removes ground from the release trunk conductor 253 at armature 34.6. It is easily seen that since there is nothing now to hold the line relay 476 of connector H enground through impedopens the bridge across line at one exchange,

1,eva,oss

ergized that it must fall back and release must take the equipment is now restored to common use.

In view of the foregoing it isobvious that the subscriber at', substation A'. can obtain connection with the subscriber at substation A', and it maybe stated also that they subscriber at substation A can by Dcalling the proper number obtain connection with any other subscriber whose line terminatesin the same C. A. X. without first obtaining connection with the operator, for in making such calls there is no charge. The same is true for the subscribers in the other C. A. X. The subscriber at'substation Q, however, can make no call whatsoever except through the operator at the large automatic ex change.

After a careful study of the systemit beplace in the usual manner. All

subscriber Y at substation Qto obtain connection with the subscribers in the large automatic exchange. This is taken care ofby roviding outgoing trunks extending from t e operators position to automatic switches through the medium of which the operator/can extend a. connection to l line terminates in the exchange in which she is loca-ted. There may be other `toll lines also from other exchanges, either automatic or manual, terminating in front of the same operator. It is easily seen that the operator can'extend a call from any one of these toll lines to any other by means of her cord circuits in the usual manner. call from any one of these toll lines or from the large automatic exchange, can be extended to any subscriber whose line terminaipes in either C. A. X.' or tothe subscriber at substation Q. These connections, however, involve the use of apparatus whose operation has already been fully described,

Likewise a i and consequently they need not be considered in detail.

Having described our invention, what we consider to be new and desire to secure by Letters Patent will be pointed out in the'appended claims. What we claim as our invention is: l 1. In a telephone system, twov exchanges and an interconnecting toll -line comprising only two conductors, branches of said toll extending said branches separately into conau`tomatic switches for lll nection with subscribers lines, a manual.

switch. board at the other exchange, and means wherebythe operator can control said switches to establish a -three way talking circuit including herself and two subscribers in the distant exchange.

2. In a telephone system, a trunk line extending from an operators position in one

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