US1732186A - wicks - Google Patents

Description

J. WICKS TELEPHONE SYSTEM Filed Jan. '7, 1927 '7 Sheets-Sheet Imranlnrfm www.

.Jahn Lllicks J. wlcKs TELEPHONE SYSTEM Oct. 15, 1929.

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Im- Jahn Midis /Zd/mm Oct. 15, 1929. J. wlcKs TELEPHONE SYSTEM Filed Jan. '7, 1927 '7 Sheets-Sheet 4 aww Jahn .Minka Oct. 15, 1929. J. wlcKs TELEPHONE SYSTEM Filed Jan. '7, 1927 7 Sheets-Sheet 5 Der. 1s, 1929. J. wicks TELEPHONE sY s'rEm v Sheets-sheet e Filed Jan. '7, 1927 Jahn .Wicks www;

Oct. l5, 1929. J. wlcKs TELEPHONE SYSTEM 7 Sheets-Sheet 7 Filed Jan. 7, 1927 Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE JOHN WICKS, OF OAK PARK, ILLNOIS, ASSGNR TO RESERVE HOLDING COMIANY, OF CHCAGG, ILLTNOIS, A CORPORATON 0F DELAWARE TELEPHONE SYSTEM Application filed January 7, 1927.

This invention relates in general to automatic telephone systems; and the object ot the invention, broadly stated, is the provision of new and improved automatic switching mechanism and controlling apparatus rtor use in an automatic telephone exchange.

Two well known types of automatic switches are at present extensively used in automatic telephone exchange system; one type being the well known Strowger vertical and rotary type of switch, and the other the well known rotary type of switch having a vswitches have been proven to vbe most economical and reliable from every point of consideration. v

However, the uni-directional rotary switch mechanism, having a single motor magnet, is recognized as being a very rugged and comparatively inexpensive mechanism, much less expensive than the two-motion switch mechanism of the Strowger typeA having two motor magnets and a release magnet. The rotary switch mechanism may also be operated safely at much higher speeds than the Strowger two-motion type of switch. The main object of this invention, specically stated, is the production of an automatic telephone system in which all the switches are of the uni-directional rotary type, the directive switches, that is the selectors and connectors, as well as the hunting or p reselecting switches. c

The principal advantages ot' a system of this kind are; first, the reduced cost of the exchange apparatus, since vuni-directional rotary switches are less expensive than twomotion Strowger switches; secondly, the maintenance of the exchange apparatus is simpliiied and as a result the cost thereot is reduced by the employment of just one kind of switch throughout the exchange. Another Serial No. 159,525.

advantage is that a call may be extended from calling to called subscribers more quickly, thereby reducing the amount of equipment required in any given case.

Another object of this invention is the production of a new and improved register sender for controlling the operation of the new and improved uni-directional automatic switches, the particular method of control being such as to permit the control circuits of the new automatic switches to be very simple and reliable. y

The invention, its features and operation will be described in detail in the following specii'ication with the aid of the accompanying drawings comprising Figs. 1 8, inclusive. Figs. 1-5, inclusive, when arranged as shown in Fig. 8 with the corresponding lines in alignment, show by means ot the usual schematic circuit diagrams the new and improved selector, connector, reverting call switch, and register sender, and suiiicient of the associated apparatus for rendering possible a thorough understanding of the invention. In Fig. 6, a modilication of the selector and of the connector are shown. In Fig. 7, the grouping of the banks of the new switches is diagrammatically shown.

In Fig. l of the drawings, the subscribers line comprising conductors 2 and 3 serves the sub-stations ALAN), inclusive, and terminates at the main automatic exchange in the rotary lineswitch LS. The substations 15V-A10 are of the usual automatic type with ringers connected from either one or the other side ot the line to ground, and the lineswitch LS is of the well known rotary type oit non-numerical selecting switch having no normal position and having a forward motion in only one direction. The lineswitch LS together with other similar lineswitches have access in their banks to a group of trunk lines, one of which is shown comprising conductors 22-25, inclusive, with its associated trunk relay group TRG and its individual register sender selector RSS, terminating in the lirst selector switch S.

Mechanically and in principal of operation, the register sender selector RSS is of the well known rotary type oi non-numerical selecting switch having no normal position and having a forward motion in only one direction. In the banks of the register sender selector RSS, as well as in the banks of other similar register sender selectors multiply connected with the banks of the register sender selector RSS, access is had to a group of register senders, one of which is shown in Figs. 2

and 3 combined, designated RS.

The register sender shown in Figs. 2 and 3 comprises essentially four digit registers upon which the line designating digits of a called number are registered, sequence switch S for controlling the operation of the digit registers, sequence switchSS for successively associating the registers with the circuits for vcontrolling .the operation of the directive switchesa frequency selecting switch'FS for selectingtheproper frequency of ringing current to be applied to a. called line (as determined by the last digit of a called number),

a group of two-step counting relays for controlling the application of ground potential to the ten marking conductors of the digit registers,.and the various controlling relays. The conductors 576-580, inclusive, connected to the lower bankcontacts of the frequency selecting switch FS, are connected to the correspondingly marked conductors shown in Fig. 5 connected to the live ringing generators (SV-G5. A common interrupter I which periodically grounds conductor 200 momentarily isalso-shown in Fig. 2. The function thereof will be described hereinafter.

The various sequence switches and registers of theregister sender are of the well'known .single Lmotion type of switch having a motor magnet lfor stepping thel switch wipers in a forward direction and a release ,magnet for returning the switch wipers to normal.

Mechanically, the switch mechanism of the selector .S 4is similar to the switch mechanism of the common rotary lineswitch, ex-

cept that it has been provided with two `sets of single-ended multiply connected wipers `.mounted on the same shaft, wipers 131, 133,

and 135 being one set and wipers 132, 134, and 136 being the other set, and a separate set of banks for each set of wipers, the two sets of banks being placed side-by-side. The two sets of wipers are positioned on the shaft 180 degrees apart, so that when oneset of wipers is moved olf the last set of contacts of its associated set of banks, the other set o f wipers is moved onto the first set of contacts vin .its associated set of banks.

The bank contactgrouping of a selector i S is shown more in detail diagrammatically in Fig. 7, to which reference is new made. In each set of banks of the selectoraccess `is had Atoifive groups of trunks of ten trunks each,

groups O, 1, 2, 3, and 4 being Vaccessible in the set of banks associated with wipers 131, 133,

and 135,'and groups 5, 6, 7, 8, and 9 being accessible in the set of banks associated with wipers 132, 134, and 136, in the order named. (Only wiper 131 of one set, and wiper 132 of the other set and the bank Contact of each set associated with these two wipers, are shown in Fig. 7 Each group of contacts comprises 11 sets. The ten trunks of a group are respectively accessible in the irst ten sets of contacts of the corresponding group. The

eleventh set of each group is the over-flow position, to which the wipers are moved when all the trunks of the corresponding group test busy, as is described in detail hereinafter.

The shaft upon lwhich the switches are mounted, also carries two cams, namely cams 121 and 120. Gam 121 controls the ycam springs 124, and has recesses on its circumference so spaced that the springs 124-a-re closed whenever either set of wipers is in engagement with the lastfive sets of contacts of any group, these springs opening as ythe wipers are moved onto the first set of contacts of the succeeding group. Cam controls the cam springs 122 and 123, and has one recess, maintaining springs 122 and 123 closed in all.

@ne of the trunks, accessible in the third` group of bank contacts of selector S', and in the third group of bank contacts ofthe other similar selectors multiply connected therewith, is shown, comprising conductors 142, 143, and 144 terminating in the second selector S2, Fig. 4. lThe second selector S2 is identical in circuit operation and also in mechanical construction to the first selector VS shown in Fig. 1. In Athe banks of the `selector S2, as well as in the banks of other similar second selectors multiply connected with the banks of the second selector S2, access is `had to anumber of groups of connector switches. The connector C shown is accessible in the seventh group of ybank contacts vby A way of the trunk comprising conductors 452-454, inclusive. In thel banks of the second selectors, access is also hadto a group of trunks extending to an operators position, and to a group of trunks extending to revertingr call switches. 'The trunks to the operators position are accessible in the second group of contacts, one of which is shown comprising conductors 437-439, inclusive and terminating in jack J. 'Ihe trunk .to the reverting call switches are accessible .in the first group of contacts, one of which is shown comprising conductors 442-444, inclusive, and terminating in vthe reverting call switch RV Fig. 5.

ice Y the selector S', and has the same wiper and bank construction. In the banks of the connectors, the lirst set of contacts in each group is unequipped and the ten subscribers lines of a group terminate, respectively, in the next ten sets et contacts of .a group, differing in this respect from the bank connections of the selectors in which the first ten sets of contacts of each group terminate trunks and the eleventh setl is unequipped. Thecontrol circuits of the connector` C form a particular Vpart ot this invention and will be described in detail hereinafter.

The subscribers lines accessible in the banks 01": the connectors may be either individual lines or party lines, the party line comprising conductors 492 and 494 and serving the substations Bl-Blo, inclusive, and provided with the individual lineswitch LS, being shown. The lineswitch LS is similar to the lineswitch shown in Fig. 1 except that the Wiper for controlling the operation of a completed-call meter has been omitted. The substations Bl-Blo are identical to the substations A-A10, inclusive, shown in Fig. 1.

Mechanically, the reverting call switch RV `shown in Fig. is also similar to the connector C. The control circuits oi the reverting call switch form a part of this-invention and will be described hereinafter. The bank contacts of the reverting call switch are grouped like those of t-he connector C, and together with the bank' vcontacts ot the other reverting call` connector multiple connected therewith are connected in various combinations to the ringing generators (irl-G5, inclusive, and the interrupter l5.

In the drawing, connections for signalling two subscribers whose ringers are connected to one side of the line, two subscribers whose ringers are connected to the other side of the line, two subscribers whose ringers are connected to opposite sides of the line and respond to the same frequency of ringing current, and two subscribers whose ringers are connected to opposite sides ot the line and respond to different frequencies of ringing current. are shown for illustration. lt is understood that the iive ringing generators til-G5 are all ot different frequencies and that the ringers at the party-line substations respond to only one frequency of ringing current. For explanatory purposes, it has been assumed that the ringers at the respective party-line substations A to A5A" to A10, B1 to B5, and B toBlO respond to ringing current from the respective generators @rb-G5.

lVith this general description ot' the objects of the invention., its features, and the apparatus used, in mind, a further understanding and appreciation ot the invention may be gained Jfrom a detailed description ot the operations performed in the establishment of various connections. For this purpose it will first be assumed that the subscriber at substation A5 wishes to establish a connect1on with the subscriber at substation B5.

@all from substation, A5 to substation B5 scriber at substation E5, the subscriber at substation A5 lirst removes his receiver. Removing the receiver at substation A5 places a bridge across the line conductors 2 and 3, thereby closing a circuit tor line relay 6 of' the lineswitch LS. Line relay 6 operates and places ground potential on the private normal conductor 3 at armature 12 to mark the line to substations iV-A10 busy and at the same time to prepare an energizing circuit for switching relay 5. At armature 13, line relay 6 closes the stepping circuit for magnet 7, providing the trunk upon which the switch wipers are positioned at this time is busy, in which case ground potential will be present on the contact engaged by test wiper 15. lf such is the case, stepping magnet 7 operates in a buzzer-like manner to advance the switch wipers 14-17 inclusive, in search ot an idle trunk. During this operation switching relay 5 is prevented from operating by reason ot the ground potential on both ends of its winding.

W'hen an idle trunk is reached, indicated by the absence of ground potential on the contact engaged by test wiper 15, stepping magnet 7 ceases to operate, and relay 5, being no longer short circuited, energizes in series with magnet 7. 1n operating, relay 5 prepares a circuit for the subscribers meter M at armature 10, prepares a holding circuit for itself at armature 9, and at armatures 8 and 11 disconnects the line conductors from the line relay 6 and ground, and extends the talking connection by way ot these armatures and their working contacts, wipers 14 and 17, conductors 22 and 25, normally closed contacts 59 and 62 controlled by armatures 59 and 62, through the upper and lower windings ot line relay 31 to battery and ground, respectively. Line relay 31 operates and closes a circuit for release relay 32 at armature 41. Release relay 32 energizes and grounds the release conductor 23 at armature 42 thereby maintaining relay 5 operated, closes a circuit for the switching relay 72 ot the register sender selector RSS in series with the lower winding ot relay 34 and magnet 71 at armature 44, and at armature 41 closes the stepping circuit for magnet 71, at the same time short circuiting switching relay 72, providing the wipers ot the register sender selector RSS are in engagement with the bank contacts associated with a busy rggister sender, in which case ground potential is present on the bank contact engaged by test wipers 85. It such is the case, magnet 71 operates in a buzzer-like manner to advance the wipers 84-87, inclusive, until an idle register sender is reached, which may be assumed to be the one accessible by wayoii the conductors 94-97, inclusive. When this register sender is connected with, its idle condition being indicated by the absence of ground potential on conductor 915 connected to bank contact now engaged by wiper S5, magnet 71 ceases to operate and the short cir-V cuit is removed trom switching relay 72. The switching relay 72 then operates to perform the following circuit Changes: At armature 74; the impulsing circuit over which the digits of the called number are to be sent to the register sender is liircpared. itt armature 75 ground potential through the lower winding of relay 34 of the trunk relay group TRG is placed on the test contact to which conductor 95 is connected and on the test contacts of the other register sender selectors multiply connected therewith to mark the register sender in question busy, at the same time closing a circuit for release relay 200 of the register' sender in series with relay 3/1. Release relay 206 operates and opens a point in the circuit of release magnets 331-387, inclusive, at armature 222, at the same time grounding locking conductor 263 and 201 by way of armature V226 and its resting contact, and prepares a circuit at armature 220 tor the time impulse relay 240 to be described more in detail later. nsutlicient current Hows in this circuit at this time to cause the operation of relay 34, yrelay 206 having a comparatively high resistance winding. As a further result or" the operation of relay 72, the bridge to be placed across the outgoing conductors 102 and 1041- is prepared at armatures 76 and 77.

The foregoing operations all take place in a comparatively short time responsive to the removal of the receiver at the calling substation. After removing the receiver, the calling subscriber at substation A dials the directory number oit the called subscriber, which for the sake of example, will be assumed to be 27035. Responsive to the dialling of the first digit 2, line relay 31 oi' the trunk relay group TRG operates in the usual manner and closes the impulsing circuit a corresponding number of times, this circuit extendingfrom ground at armature 411 and "the resting contact, armature 43, armature 74, wiper 84, conductor 94, armature 212 and the resting contact, conductor 252, armature 308 and the resting contact, wipers 311 of the sequence switch S in engagement with its first bank contact, winding of stepping magnet 320 of the first digit register to battery. Stepping magnet 320 respondsv a correspondin@ number of times and steps the switch wipers 324e and 325 into engagement with the second contacts of their respective banks. By the movement of wipers 324iA and 325 oil their normal position, oil-normal springs 391 and 391 are closed. The circuits including these circuit oiE relay 302. Relay 302, being slow-V acting, maintains its armatures operated for a moment after its circuit is opened, and as a result a circuit is momentarily established for stepping magnet 310 of the sequence switch S, this circuit including armature'30ev and the working contact, and armatures 30a and the resting contact. Magnet 310 operates and steps the wiper 311 int-o engagement with its second bank contact. vSlow acting relay 312 also falls back at the termination of this first series of impulses and closes a start circuit for causing the operation of the iirst selector switch terminating the seized trunk line. For convenience, however, the descriptionof this operation will be deferred until later. Wiper 311 on moving into its second position,shifts the incoming impulsing circuit from the stepping magnet 320 of the first digit register to the stepping magnet 321 of the second digit register, thereby preparing the second register -to receive the neXt series of impulses. Y 1

Responsive to the .dialing of the next digit 7, line relay 31 again operates and this time closes the impulsing circuit now including stepping magnet 321 of the second digit register a corresponding number of times. Stepping magnet 321 operates responsive thereto and steps the wipers 326 and 327 into engagement with the corresponding contacts of their respective banks. Slow-acting relay 313 operates in multiple with magnet 321, the function of which is similar to the function of relay 312 and will also be described later. Relay 301 again operates during the impulsing period, this time in multiple with magnet 321 and again closes a circuit for energizing relay 302, these two relays again functioning to momentarily close the circuit of stepping magnet 310 at the termination of this second series of impulses. Wiper 311 is then stepped into engagement with its third bank contact, thereby shitting the im! pulsing circuit so as vto include the stepping magnet 322 of the third Idigit register, and disconnect magnet 321 of the second digit register.

The third digit 0 as dialed by the calling subscriber is then energized on the third digit register, wiper 328 being stepped to the corresponding contact in its bank by the operation of stepping magnet 322, after which wiper 311 is stepped -into engagement with its fourth bank contact to shift the impulsing The slow-acting relay 312 also' 'the operation of magnet 323, after which wiper 311 is stepped into engagement with its fifth bank contact. Wiper 311, in being stepped to its fifth position, shifts the impulsing circuit from the stepping magnet 323 to the stepping magnet 341 of the frequency selecting switch F S, thereby preparing for the registration of the final digit, which determines the frequency of ringing current and the side of the line to which itl is to be 'applied to signal the desired party. Responsive to the dialing of the final digit 5, magnet 331 operates to step the switch wipers 342 and 344 into engagement with the fifth contact in their respective banks. By the engagement of wiper 343 with the fifth contact in its bank, to which the conductor 80 associated with ringing generator G5, Fig. 5, is connected, the frequency of ringing current to be used is determined. Furthermore, since ground potential is connected to the first live contacts in the bank of wiper 342, a circuit is now closed for reversing relay 202. This relay, in operating, determines that the selected ringing current is to be applied to that side of the called line that will be connected to upper talking conductor extending through the automatic switches.

This completes the description of the registration of the digits of the called number on the registers of the register sender. During the time that this is vtaking place, however, the call is being extended by the operation of automatic switches controlled by the setting of the registers, and a description of the operation thereof will now be given. It will be remembered that at the termination of the dialing of the first digit, slow acting relay 312 deenergizes. As a result, a circuit is closed which may be traced from ground by way of the resting contact and armature 316, off-normal springs 391 closed upon the first step of wipers 324 and 325, wiper 346 of sequence switch S in engagement with its first bank contact, conductor 256, through the winding of start relay 209 to battery. The relay 209 operates and closes a bridge across the trunk conductors 102 and 104, thereby closing the control circuit for controlling the operation of selector S which may be traced from ground by way of the resting contact and armature 109 of selector S', conductor 22', armature 57 and the resting contact, armature 51 and the resting contact, armature 77, wiper 87, conductor 97, armature 230 and the resting Contact, armature 224, through the winding of impulsing relay 207, armature 229, resting contact and armature 231, conductor 96, wiper 86, armature 76, resting contact and armature 58, resting Contact and armature 62, conductor 25', armature ll'land the resting contact, resting contact and armature 118, through the winding of line relay 106 of selector S to battery. impulsing relay reason of its lower winding being short cir-t cuited. In the selector S, the line relay106 also operates when the control circuit is closed by the operation of start relay 209. Relay 106, in operating, closes a circuit for release relay 107 at armature 112, there being ground potential on release conductor 23, and shunts armature 118 at armature 113 and the working contact. closes a locking circuit for itself to release conductor 23 at armature 117, and opens a` point in the initial energizing circuit of line relay 106 at armature 118, this. armature how ever having been shunted by the operation of armature 113 of relay 106. At armature 119 a circuit is prepared which will be described presently. As a further result of the operation of line relay 106, a selfeinterrupting circuit for Stepping magnet 108 is closed at armature 114 and the workingeontact, Vand at armature 115 a circuit for sending impulses to (short circuiting) the impulsing relay 207 in the register sender is prepared. Stepping magnet 108 now operates and continues to operate in a buzzer-like manner and rotates the switch wipers step-bystep over the bank con* tacts as long as the control circuit is closed. As the switch wipers 131, 133, and 135 come into engagement with the sixth set of contacts of the 0 group (see Fig. 7), the cam 121 secured to, and rotating with, the shaft carrying the wipers closes contacts 124, thus short circuiting the impulsing relay 207 0f the register sender and at the same time closing a local holding circuit for line relay 106. The impulsing relay 207 in the register sender thereupon deenergizes and by releasing yits armature 223 removes the short circuit from the lower winding of the two-step relay 351. This relay thereupon operates to its second step, operating all its armatures their full stroke. Relay 351, in operating to itssecond step, connects conductor 260 to the second marking relay 352 at armature 356, and at armature 361 connects ground potential to marking conductor 331 connected to the iirst contacts in the lower banks of the digit registers by way of armatures 365, 364, 363, and 362 andtheir respective resting contacts.

Rotary magnet 108 continues to "operate, and when the switch wipers 131, 133, and 135 come into engagement with the first set of Release relay 107 operates andv contacts ofV group 1, the cam springs 124 areagain opened. As a result, the short circuit aroundl the impulsing relay 207 of the I register sender is removed, and this relay again operates 1n series with line relay 106 of l la ,207 ofthe register sender is short circuited w en the switch wipers are rotated over the lastfive contacts in group 1 by the closure ofsprings 124 under the control of cam 121. As s oon` as this relay is short circuited, it again deenergizes and permits the second marking relay 352 to operate in its secondstep,f.wliich in so doing connects conductor 260 to the upper winding of thethird marking conductor relay 353l at armature 357, causes the restoration of the first marking relay 3551 by opening its circuit to the grounded conductor 261 at armature 377 and at armatiure1 362 disconnects ground from the first markingconductor 331 and connects it to the second marking conductor 332 connected to the second contacts in the lower banks of the digit registers. wiperV 325- is in engagement with the second Contact; itsbank connectedto marking conn ductor 332. Therefore, as soon as groundl potentialy is connectedto this marking conductor, a circuit is closed which may be traced fromvgroundonl conductor 332, wiper 325 in engagement with its second bank contact, wiper 347 in engagement with its first bank contact, conductor 257, through the windingoff'stop relay 208 to battery.y Relay 2081opcratesl and opens the control circuit at armature; 224closes a circuit for relay 204 at armature 225, the function of which willbe described later, and at armature 226 disconnects ground from conductor 261 thereby opening the circuit of the marking relay 352, which thereuponfrestores to normal. Furthermore, byftheoperation of relay 208 a circuit is closed for` stepping magnet 345 at armature 227. This magnet energizes and in so doing moves the. switch wipers 346 and 347 into engage ment with the second contacts and their respective banks. By the movement of wiper 347 into engagement with its second bank contact,l the circuit for stop relay 208 is opened, and by the movement of wiper 346 into engagement with its second bank contact, the rst circuit for energizing start relay 209V is opened. If the second digit is registered onthe second digit register by the timethese operations following the registration ofthe first digit take place, the start rclay 209`is again immediately energized from It will be remembered thatI groundby way of the resting contact and' ar` mature 317, oH-normal springs 392', Wiper 346`in engagement with the second bank contact. Relay 208, however, is slow to fall back, and retails its armatures attracted' for an interval after its circuit is opened.

Returning now to the operation of the seilector S, during the time in which relays' 208 and 207 operate and stepping magnet 345 steps the wipers of the sequence switch S" into engagement with the second set of bank,- contacts, relay 106 of the selector S is held operated over its local circuit includingarmature 115 and cam springs 124 and magnet 108 continues to step'the switchwipers until the wipers 131, 133, and 135 are stepped into engagement with the first setj ofl contacts of group 2. As soon as this. position is reached,

ysprings 124 again open, thereby opening the local holding circuit of line relay 106. Since the stepping of the wipers over the last five contacts of group 1 takes place ina comparatively short time, relayl 208 of the register sender has not had time to release its armatures. For this reason, the circuit of line relay 106 of the selector S is now openwhereupon relayf106 deenergizes and releases its armatures. Sometime after the release of thev armatures of relay 106, stop relay 208 of the register sender releases its armatures, and again closes the control circuit, assuming that start relay 209 is again energized, but since release relay 107 is. operated, no circuit is closed` thereby, and impulsing relay 207 ofthe register sender remains dee-n` ergized. y, p

The selectorS has now operated to posi` tion its wipers into lengagement with the first set ofcontacts ofthe group corresponding to the first digit" dialed, and is now about to select an idle trunk in that group. Line relay 106, in releasing armature 114, closes a circuit for switching relay 105 in series with stepping magnet 108 and closes the regular hunting circuit for stepping magnet 108, providing the trunk accessible at the first set of bank contacts in group 2 is busy at this time, which condition willbe indicated by the presence of ground potential on the bank contact enga-ged by test wiper 133. Assuming this tov bethecase, the stepping magnet 108 again operates, this time over the circuit from ground on the contact engaged by test wiper 133,.armature`110 and the resting contact, working contact and ar` mature 119, resting contact and armature 114, interrupting' springs1`25, through the winding of tstepping magnet 108 to' battery, and continues to rotate the switch wipers until the wipers 131, 133, and135 are rotated intofengagement with the cont-acts terminating an idle trunk line,whichwillbe assumed to be the trunk line` comprising' conductors 142, 145, and 144, the idle" condition thereof being indicated# by the' absence of ground potential on the release conductor 143 terminating in the contact now engaged by wipers 133. While the selector S is hunting for an idle trunk, switching relay 105 is short circuited by reason of ground potential on both ends of its winding. As soon as this idle trunk is reached, however, the short circuit around switching relay 105 is removed and this relay operates over the circuit from ground potential on release conductor 23, through the winding` of relay 105, working contact and armature 119, resting contact and, armature 114, through the winding of magnet 108 to battery. Due to the high resistance of relay 105, current 'flow in t-his circuit is insufficient to cause the operation of stepping magnet 108, so the switch wipers are arrested in this position. Switching relay 105 operates, however, and applies ground potential t-o release conductor 143 by way of armature 110 and the working cont-act and wiper 133, and extends the connection by way of armatures 109 and 111 and their working contacts, wipers 131 and 135, trunk conductors 142 and 144 to the second selector S2, wherein the connectionl extends to ground by way of armature 409 and the resting contact, and to battery by way of armature 411 and its resting contact, armature 418, through the winding of line relay 406.

As soon as the connection is so extended to second selector S2, the circuit is completed tor the line relay 406 in series with the impulsing relay 207 in the register sender providing the second digit of the called number has been registered on the second digit register and the start relay 209 has again operated. If the second digit has not yet been registered, the line relay 406 remains deenergized until it is registered and the start relay 209 of the register sender again energizes and closes the control circuit at its armature 229. Line relay 406 of the second selector S2, in operating, performs circuit changes in the selector S2 similar to those performed by the operation of the line relay 106 in the selector S', previously described. Selector S2 then operates in a manner identical to the way in which selector S operated, rotating its wipers over the bank contacts, short circuiting the impulsing relay 207 ot' the register sender by the closure ot cam springs 424 each time the wipers are moved over the last five steps of contacts ot a group. Each time the impulsing relay 207 is energized and deenergized, conductor 260 is grounded causing one of the two-step marking relays 351-355, inclusive, to operate and connect ground potential to the next marking conductor numbered higher in order; i. e., the first impulse to the marking` relays (the first application ot and removal of ground potential on conductor 260) operates relay 351; the second impulse operates relay 352 and releases relay 351; the third impulse operates relay 353 and releases relay 352; the fourth impulse operates relay 354 and releases relay 353; the fifth impulse operates relay 355 and releases relay 354; the sixth impulse reoperates relay 351, relay 355 remaining up; the seventh impulse reoperates relay 352, relay 351 and relay 355 remaining up. l/Vith relays 355 and 352 operated, ground potential is applied to marking conductor 337 by way of armature 365 and its working contact, armature 369 and its resting contact, armature 368 and its resting contact, and armature 367 and its working contact. As soon as conductor 337 is grounded, which results after the impulsing relay 407 has been energized and deenergized seven times, being deenergized for the seventh time as the wipers 432, 434 and 436 move over the last five contacts of group 6 (remembering that when wipers 131, 133, and 135 move oil the last set of contacts of group 4, the wipers 132, 134, and 136 move on to the first set of contacts of group 5), a circuit is again closed for the stop relay 208, this time from ground by way of conductor 337, wiper 327 in engagement with its seventh bank contact, and wiper 347 in engagement with its second bank Contact, through the winding of relay 208 to battery. Again relay 208 operates and opens the control circuit at armature 224, disconnects ground from the holding conductor 261 at armature 226 thereby allowing the operated marking relays to restore to normal, and closes a circuit for a stepping magnet 345 at armature 227. Stepping magnet 345, in operating, moves the wipers 347 and 346 into engagement with the third contacts in their respective bank, which opens the circuit ot stop relay 208 and the present circuit of start relay 209.

When wipers 432, 434, and 436 move into engagement with the first set of bank contacts in group 7, the local circuit of line relay 406 including cam springs 424 is opened, and since the control circuit is now open also, stop relay 209 in the register sender having operated, line relay 406 falls back and closes the hunting circuit for magnet 408. The switch wipers are then further rotated until they are brought into engagement with the contacts terminating an idle trunk in group 7 which will be assumed to be the trunk comprising conductors 452, 453, and 454 terminating in connector C. When this trunk is reached, its idle condition being indicated by the absence of ground potential on the contact engaged by wiper 434, switching relay 405 operates and extends the control circuit by way of armature 409 and 411 and the working contact, wipers 432 and 436, conductors 452 and 454 to connector C, wherein the connection extends to ground by way ot armature 461 and the resting contact and to battery by way oi armature 464 and the resting contact, resting contact and armature 467, through the winding ot line relay 457.

A. short time after its circuit is opened, during Which time the switch Wipers moved to 'the iirst set ot contacts in group 7 and line relay 406 fell bach, relay 208 again releases its ari'natures and prepares the imp ulsing circuit at armature 224, and start relay 209 erating, performs circuit changes similar tol those performed by the operation ot the line relays of the selectors S1 and S2; namely, the circuit of release relay 456 is clesed at armature 470, armature 476 included in the initial energizing circuit of line relay 457 is shunted at armature 471, the circuit ilor sending impulses to (shortl circuiting) the inipulsing relay in the register sender is arepared at armature 472, and the self-interrupting stepping circuit for magnet 460 is closed at armature 472. {el-ay 456 operates, closes a locking circuit ior itselt' at armature 466 to the grounded conductor 453, and performs other circuit changes to be described later. Magnet 460 operata' in a buzzer-like manner to rotate the Vswitch Wipers in this case one complete revolution until wipers 482, 484 and 486 are again rotated into engagement With the i'irst, in th case dead, contact in group 0. By the rotl tion ot' the shaft carrying the Wipers to this position, the cam springs 424 are closed ten times by thevaction of the cam 42l, thereby causing the impulsing relay 207 in the register sender to deenergize and reenergize ten times and ground the control conductor 260 ten successive times. The mark-ing relays 351-355 are operated thereby, the lirst seven impulses are resulting in relay 355, relay 351 and relay 352 being operated as previously described, the eighth impulse reoperating relay 353 and releasing relay352, the ninth impulse reoperating relay 354 and releasing re# lay 353, and the tenth impulse again reoper ating relay 352. With relays 351, 352, 354, and 355 operated, ground potential applied to marking conductor 340 from ground b 'f Wa of armature 365 andthe workin!r contact, armature 369 and the Werking contact, and armature 370 and the Working contact. As soon as this conductor connected to contacts number 10 of the lower banks et the digit registers is grounded, stop relayf208 is again energized, its energizing circuit this time including 'the now grounded conductor 340, Wiper 328 in engagement with its tenth bank Contact, and Wiper 347 in engagement With its tliirdbanlz contact. Stop relay 208 iysaise again operates, opens the control circuit atv the release of the operated marking relaysand closes the circuit of stepping magnety 345 at armature 227. Magnet 345 operatesv to step the Wipers 346 and 347 into engagement'.

with the fourth contacts in their'respective banks, thereby opening the circuit of stop relay 208 and opening the presentcircuitof start relay 209. After the switch Wipers yhave been rotated one completey revolution backto the lirst set of contacts in group 0, the local circuit of line relay 457 including springs 424 is opened, and'since stop relay 208 h as been. operated to open the control circuit, line relay 457 is deenergized. By the release of armature 471, line relay 457 islisconnected from the control circuit, andl by the engagement of armature 47 2fwith its resting contact the control circuit" is ext-ended to include the Windingof thecontr'ol rela-y' 459, Working Contact and ar1nature468, restine' Contact and armature `472,- interrupting contacts 479, andthe Winding of stepping magnet 460 connectedto battery.Y j

A short time aiter its circuit isfopened'stop relay 208 in the register sender releasesv its armatures and again preparesthe control circuit armature 224. After the fourth digit is registered, start relay 209v of the register sender again operates, this time fromgroun'd by Way of resting contact and armature 319; closed oil-normal springs 3941, Wipei'346 in engagement Withits fourth bank Contact, con*- ductor 256, through'the Winding of relay 209 to battery, and again closes the'controlcircuit at armature 229. Obviously,inlthisiinstance, as in previous instances, il the next digit is registered andrelay 209 has already operated when stop relay releases its'armaturethe con trol circuit will be closedinnnediately at that time. N hen the' control circuit-is again closed, impulsin g relay 207 again energizes, this time in series with relay 459'and steppingmagnet 460 oli connector' C. The current lowin this circuit is insuliicient to operate stepping mag# net 460. Relay 459, however, isI energized through it is'some'what slow tofpull up as Well as slow to releasefdueto a slug-on the armature end of its core (indicated in the drawing by the solid black portion onv the upper end of' its core). Relay 459,in operL ating, closes a circuit for sloW-toire'lease relay 459, which op erat'e's and maintains its armai tures attracted continuously even' though' its circuit is momentarily opened during operai ti on of relay 459 asivil-l be `described presently. Relay 459, in operating, also closes ay local circuit 'for stepping mag-net 460 at armature 478, and at the Sametimev shortcirc'uitsitself and impulsing relay 207 in -theregister sender.V The impuls'in'g relay 207 in the register sender thereupon' deenergizes and removes ground from the control conductor'260' with the'result previously described. By reason oi its sloW acting characteristic, relay 459 does not deenergise immediately, therefore maintains the circuit ot magnet 460 closed for a short time. rlliis magnet therefore operates near the end ot its stroke opens the control circuit at interrupting springs 479. After the elapse oit the interval for which it is adjusted, relay 459 deenergises and opens the circuit of stepping magnet 460 by releasing armature 473. Magnet decnergizes and in so doing moves the switch Wipers into engagement with 'the second set of bank contacts in group 0 in Which access is had to the first line in the group 0, and also closes the control circuit by closing interrupting springs 479. Again impulsing relay 207 energizes to ground. conductor 260, and aiftcr an interval relay 459 also energizes again. 'lhe above described operations concerning relay 459 and stepping magnet 460 again take place, resulting in the movement ot the switch Wipers into engagement with the next set ot contacts terminating the second line in group 0. In a similar manner these operations are repeated until the impulsing relay 207 in the register sender has operated to ground conductor 260 eight successive nimes. lis previously described, when eight impulses are w all sent to the marking relays 35l-355, inclusive,

relays 351, 353, and 355 are operated with the result that ground potential is applied to marking conductor 333. `When conductor 333 is grounded, a circuit is closed 'from ground on this conductor, Wiper 329 in engagement With its eighth bank contact (the fourth digit dialed having been eight) resting contact and armature 349, Wiper 347 in engagement With its fourth contact, through the Winding ot stop relay 203 to battery. Relay 208 then operates with the usual results, including the closure of the circuit tor magnet 345 for stepping the Wipers 346 and 347 into engagement with the lilith contacts in their respective banks and the opening of the control circuit thereby preventing turther operation ot the impulsing relay 207 of the register sender and the control relay 459 of the connector C. As a result Wipers 481, 433 and 435 are brought to rest on the contacts terminating line 8 et group 0 which is assumed to be the line comprising conductors 492 and 494 serving substation BLE, inclusive.

The line serving substations lll-B1", inclusive, may be either busy or idle at this time, ll the line is idle, the proper signalling current is sent over the proper line conductor to signal the desired subscriber; but ii'4 the line i` busy, the called subscriber at substation A? notilied accordingly. rl'lo describe these operations, it will tiret be assumed that the line servir@ substations ELEM), inclusive, is busy at t is time, Which will be indicated by the pres of ground potential on the bank contact ngaged by Wiper 433. Since relay 459 is energized at the time when the Wipers are rotated into engagement with the contacts terminating the desired line, a circuit is closed for busy relay 453 troni ground by Way of Wiper 433, armature 477 and the Working contact, through the Winding of relay 458 to battery. Relay 453 operates and connects conductor 430, connected to the busy tone machine BT' (Fig. l), to the upper talking conductor 452 at armature 474 at the same time disconnecting Wiper 481 therefrom, prepares a holding circuit for itself at armature 475, and connects battery potential through the Winding ot magnet 460 to the lower talking conductor 454 at armatures 476, at the same time disconnecting Wiper 435 therefrom. clay 459, in releasing its armatures following the opening of the control circuit by the stop relay 208 in the register sender, maintains the circuit for the slow acting relay 459 open. fitter an interval this relay deenergir/,es and completes the holding circuit for busy r1 453 in series with the lower Winding of switching relay 455, this circuit eX- tending from ground on release conductor 453, through the lower Winding of relay 455, armature 470, armature 475 and the Working contact, spring 477 closed by the release of armature 477, through the Winding ot busy relay 453 battery. Busy relay 458 theretore ren'iains energized, and switching relay 455 encrgizes, completing a holding circuit itself to release conductor 453 at armature 463, connecting talking conductor 452 to talking conductor 452 noW connected to the busy tone machine at armature 461, and connecting talking conductor 454 to talking conductor 454 now connected to battery through the Winding of rotary magnet 460 at armature 462.

Certain operations now take place in the register sender and in the trunk relay group Titti; as a result of the above described operations, which will nonT be considered. lt will be remembered that When stop relay 208 of register sender RS was operated the last time, a circuit Was closed 'for the motor magnet o't sequence switch S which stepped the Wipers 346 and 347 into engagement With the litth contacts in their respective banks. By this operation, a circuit is immediately closed for control relay 210 in series With start relay 209, this circuit including conductor 259, Wiper 346 in engagement with its fifth banl; contact, and conductor 256. The operation et relay 209 at this time is Without function. Relay 2l0 operates and disconnects relay 207 'from the control circuit and connects conductor 96 to conductor 96 and conductor 97 to conductor 97. t Will also be recalled that the auxiliary test relay 204 is operated over a circuit completed at armature 225 each time stop relay 203 is operated. This relay, in operating, disconnects conductor 97 and 96 from the ringing circuit and at the saine time connects conductor 96 to test relay 203. rihis operation having had no function up to this time, new performs two functions, the first being to connect up the testrelay 203 to test whether the connectors has engaged a busy or idle line, and the second being to delay the connection of the ringing current to the talking conductors until the switching relay 453 has had time to energize, providing the engaged line is idle.

In the present case, in which it has been assumed that the engaged line is busy, it will be remembered that both the busy relay 458 and switching relay 453 in the connector are operated, and that battery potential is connected to the lower talking conductor extending through the operated switches now connected by way ot conductors 96 and 96 to the test relay 203. Relay 203 therefore o aerates, its circuit being completed through the winding ot' relay 204 to ground, and in turn completes a circuit which causes the disassociation of the register sender RS from the connection and the completion ot a connection from the calling subscriber line to the talkinfr conductors of the connector C, one ot whic i is connected to busy tone machine. These operationstake place as follows: The circuit closed by the energization ot test relay 203 extends `from ground through the resistance R, working contact and armature 216, conductor 94, wiper 84, armature 74, resting contact and armature 54, armature 40, armature 53, through the winding of switching relay 35, through the upper winding of switchingthrough relay 36 to battery. Due to the resistance R, the current flow of this circuit is nsufcient to cause the operation of switching-through relay 36. Relay 35 operates, however, and performs the following circuit changes: At armature 55 a locking circuit is established 'for relay 35, and at armatures 53 and 54 the initial energizing circuit for this relay is'opcned. At armatures 51 and 58 the connection from the subscriber at substation A5 is switched through and extended to the talking conductors of the connector C, one ot' which is now connected to the busy tone machine, at the same time disconnecting conductors 96 and 97 of the register sende-r 'from the connection. At armature 56, the circuit of the switching relay 72 of the register sender selector RSS, and the circuit of the release relay 206 ot theregister sender is opened. Switching relay 72 releases its armatures, rcstoring the register sender selector RSS to normal condition, the wipers remaining in position on the previously selected contacts. IRelease relay 206 of the register sender also restores its armatures, disconnecting the. interrupter I from the time impulse relay (to be later described) at armature 220, and closing the circuit for the release magnets 381-387 inclusive, at armature 222 and the resting contact. The magnets 381-387, inclusive,operate and restores their respective associated switch wipers to normal. By the return of wipers 346 to normal, the circuit of relays 210 and 209 is opened whereupon these relays restore to normal. The circuit of stop relay 208 was opened as soon as sequence switch S moved its wipers into cngagement with the fifth contacts following the final movement of the connector C. An interval thereafter, this relay restored its armatures to normal, opening the energizing circuit of auxiliary test relay 204 at armatule 225. It this takes place before the register sender is disconnected' from the connection by the operation of switching relay 35 of the trunk relay group TRG, relay 204 is held up in series with test relay 203 which is energizcd in series with the stepping magnet ot the connector C, until it is disconnected therefrom by the operation of relay 35, after which relays 203 and 204 deenergize and restore to normal. The register sender is then in its normal con-dition and is again selectable to other register sender selectors.

The calling subscriber hears the busy tone 'from the busy tene machine BT and is thereby informed that the line served by the desired subscriber is busy at this time, where-upon he will replace his receiver with the intention of calling again at some later time. Replacing the receiver at the calling substation causes the release ofthe automatic switches and their restoration to normal in a manner to be described later. Y

In the above case, it was assumed that the line serving substations B-Blo, inclusive, was busy when the Wipers of the connector C were rotated into engagement with the bank contacts terminating this line. It will now be assumed that the called line is idle when the wipers oi connectorV C are rotated into engagement with the contacts terminating the line. In this case, no ground potential is encountered by test wiper 484, and consequently test relay 458 is not operated. IIowever, when relay 459 releases its armature 477, switching relay 455 is operate-d, this time over the circuit traceable from ground on release conductor 453, through its lower winding, armature 470, armature 475 and the resting contact, resting contact and armature 477, wiper 483, private normal conductor 493, through the winding of switching relay 495 ofthe lineswitch LS', through the winding of the stepping magnet 497 of this lineswitch to battery. Switching relay 495 opcrates in the well known manner to disconnect ground and battery through line relay 496 from the line conductors. Likewise switch-- ing relay 453 operates as in the previous case, closing a locking circuit for itself to release conductor 453 at armature 463, `placing ground potential on the bank contact ter-4 minating the private normal conductor 493, and on the corresponding bank contacts of other connectors multiply connected therewith, to mark the line to substations Bl-B10 busy, by connecting the release conducto-r 453 to wiper 483 at armature 462 and the working contact, and by the actuation of armatures 461 and 464 the connection is entended to the called line by way ot armatures 474 and 476 and their resting contacts, and wipers 481 and 485.

T-n the register sender RS, relay 204 again operates to disconnect the conductors 97 and 96 from the ringing circuit and connect conductor 96 to the test relay 203 as previously -described when stop relay 208 operates to arrest the final movement of the switch wipers ot' the connector C. Start relay 209 and ring control relay 210 are again operated in series when the sequence switch wiper 346 is moved into engagement with its sixth banlr contact, relay 210 operating to Connect conductor 96 toiconductor 96 and conductor 97 to conductor 97, all as described in the previous case. In this case, however, test relay 203 is not operated since the lower talking conductor extending forward and connected to conductor 96 is free from battery potential. Therefore the circuit :tor switching relay is not closed at this time. New when auxiliary test relay 204 releases its armatures which it does a short time after its circuit is opened by the release of stop relay 208, a circuit for signalling the desired subscriber is prepared. This circuit is closed as soon as the linal digit is registered-the registration of this digit, it will be recalled, consists in the setting ot the wipers 342 and 343 in engagement with the contact set corresponding to the linal digit dialed which was assumed to be the digit 5-or if the final digit be already registered when relay 204 falls back, the circuit is closed at that time, and may be traced from conductor 80 to which the battery superimposed generator G5 and direct battery is alternately connected by the action 01"' the interrupter T5 (see Fig. 5), wiper 343 in engagement with its fifth bank. contact, armature 307, conductor 251, through the upper winding of ring cut-oil1 relay 201,

armature 211, armature 214 and the working Contact (remembering that relay 202 is operated), armature 217, working contact and armature 230, conductor 97, wiper 87, armature 77, resting contact and armature 51, resting contact and armature 59, over the upi'ier talking conductor extending through selec-- tor S, selector S2, and connector C to line conductor 492, and thence through the ringers at substations B1-B5, inclusive, to ground. Only the ringer at substation B5 is tuned to respond to signalling 'current ot the frequency of generator G5. This ringer therefore operates and continues to operate until the subscriber at substation B5 answers the call, or

until the call is abandoned by the calling subscriber. A small amount ot ringing current also extends back to the receiver at the calling station through the condenser 52 to give the calling subscriber the usual ring back tone. (Condenser 57 serves the same purp se when ringing current is sent over the lower talking conductor.)

l/Vhen the subscriber at substation B5 removes his receiver to answer the call, a direct current bridge is placed across the line conductors 494 and 492 thereby closing a direct current circuit For the ujper winding ot ring cut-ofi relay 201 in the register sender RS. This circuit entends from conductor 8 to which the direct battery and battery superimposed generator is alternately connected by the action ot the interrupter l5, through the upper winding ot the ring cnt-oil' relay 201 ot the register sender RS, over the upper talking' conductor lirough the operated switches to the line conductor 492 as previously traced, and thence over the bridge at substation B5 to line conductor back over the lower talking conductor t irough the operated switches to conductor 2&1., and then by way of armature 62 and the rcstin g contact, armature 58 and the resting Contact., armature 276, wiper 86, conductor armature 231 and the working contact, armature 218 and the rest-ing contact, worlri 0 contact and armature 215 to ground. cut-oli relay 201 operates over this cirand closes a locking circuit for itself cui at arn'iature 213 to the grounded conductor 263, disconnects the rinoing circuit at armature 211, and at armat rre 212 and the worlcontact completes a circuit for energizing the switching relay 35 by connect-i ground through resistance R, to conductor 94, just as did test relay 203 in the previously described case, The switching relay 35 then operates and performs the circuit changes previously described which results in the restoration of the register sender and the register sender selector normal, and the extension ot the connection treni the substation through to the substation ln this case, back bridge relay also operates as soon as switching relay 33 connects it in bridge of the called line by ojeration of the armature 54 and armatures 51 and 58, and in so doing completes a circuit or the completed-calls meter 18 by connecting direct ground to the meter conductor 24 at arn'iature 47. Meter 18 now operates to register the call. may be nicntioned at this time that the magnet 18 was partially energized in series with resistance 45 when release relay 32 operated in its armature 44 at the initiation of the call. This current iiow is insniiicient to operate niagnet 18, but is sni'iicient to maincain magnet 18 operated after it has been operated, thereby preventing the meter iii from recperatand restore to normal. rthe replacement el the receiver et the colline; substation opens the circuit oit line relay Relay 33 deenergiz/.es and restores its armatures to normel, opening the circuit ot the release relay 32 et armature 11. Shortly otter its circuit is opened, releese relay deenerglzes, dis-- connectingl ground potentiel 'trom the rele s l conductor 23 and the serially related release conductors extending through the tiret selec tor S, second selector S2, sind connector C, end also from the private normal conductor 193 ot' the celled line, et armature 42 By the release ci armature 114;, the locking circuit for switching` relay end the circuit tor mdinteining` the magnet 18 et the met i M operated are opened. lillsirgnet 18 deenergizes and restores to normal switching reley 85 deenergizes and restores its ermeturee to normal. rlhe removal ot ground from releese conductor 23 opens the circuit of switch relay 5. Relay 5 deenergizes and restores the lineswitch LS to normal, the .vipere 14e-17, inclusive remaining` on the contacts last use l.

The removal ot `ground potential from the release conductor 23 opens the holding` circuit for switching relay 105 and releese relay 107 of the first selector S. Switching relay 105 thereupon deenergg'izes :ind restores its :irmetures to normel. Release relsty 107 likewise deenerrfizes end restores its armatures to normal. lly the engagement armature 119 with its restingl contact, the self-interriipting; circuit for magnet 108 tor returning the switch wipers 131413, inclusive, to normal is cloned., this circuit extending` from ground by wey ot com springs 123 closed by com 12() whenever the switch is in :in oit-norm el position., resting' contact end armatore 119, resting) contact sind armature 1141, interrupting springs 125, through the winding` el stepping` magnet 108 to battery. Magnet 108 then opes in e buzzer-like manner until the switch wipers 131436, inclusive, :ire restored to normal, in which position the stepping circuit is openec by the separation of cem springs 123. By the engr/.gement of erinature 116 end its restingl cont-ect, ground potentiel is reopplied to release conductor 23 by wey oft com springs 122 also closed whenever the switch is in en oli-nornnil position, resting Contact and orinar tore 116 sind contects 110 closed by the relee ot armature 11() ond is meintztined thereon while the switch wipere ere being rotated to normal, thereby protecting the trunk line,

comnfising conductors 227-25, inclusive, ege-inst seizure during this time. Cem

springs 122 open :is soon es the switch wipers are in their norme-l position, end the protecting ground potentiel is again removed 'from release conductor 23.'

ln a similar manner, second selector S2 is restored to normal, releye 105 end t0? deenergizing w ien ground potentiel is removed from the release conductor 143. Likewise, the trunk line terminating in selector S2 is guarded against seizure during` the time the switch wipers are being rotated beck to normal by the reepplicotion of ground potentiel to conductor 13 et springs 429. Similarly, in the connector C, switchin relay -155 ind release relay 1156 ere restored to normal by the removal oi ground potentiel trom the release conductor 4153, and the wipers oit the conneetor e rotated to normal by the operetion magnet 160, the eelt-interrupting circoit :tor this magnet being closed by the engagement it armature L168 and the restingv contact, springs 123 now being closed. Also, the trunk terminotingin connector C is guarded seizure while the switch wipers :ire bei ng rotated beck to normel by the reepplieetion of ground potentiel to releeee conductor 153 from rground by wey of cem springs 4122 closed whenever the cennector switch wipers ere oil-normal, armature 1165 sind its resting Contact, and ernniture 162 and its restino contact.

The removal of ground from the private normal conductor 193 also deenerg'izes switching reley 195 ot lineswitch LS vcansino; this relay to restore its armatures to noi-mel, thereby placing lineswitch LS in its normal position. All the switches and apparatus used in the establishment ot the above connectionV h eve new heen restored to normal :ind ere in position ready to be taken for use in the eX- tension of other cells. f

llt is evident `from the'foregoing` description that e connection to o. y other subscriber on the seme line is established in the sinne the operations ere likewise the seine es in the Y previously described connection, except tiet the final digit dialled in this case is either 6, 7, 8, 9, or O in which case the wiper corresponding to wiper 342 of the frequency selection switch of the regular sender used is moved )ast its tirst live contacts so that the circuit for the reversing relay corresponding to relay 202 of the register sender used is open. is a result, the generator used is connected to tb e li ne conductor 494,- andthe subscriber whose ringer is tuned to respond to ringing current from the selected generator and is connected to that side of the line, is signalled.

Renewing callngabstation AG t0 substation A2 In any telephone system giving service to party lines, provisions are made for making it possible for one subscriber to signal another subscriber on the same line, and this preferably without apprising the other subscribers on that line. ln this system described, the method in which reverting call switches (such as the reverting call switch RV shown in Fig. 5) are used is employed for this purpose. According to this method, in order for a subscriber at one substation to be called to his telephone and for the calling subscriber to be suitably informed when a subscriber at the called substation removes his receiver, the subscriber at the calling substation removes his receiver and dials a special reverting call number, which results in the connection through one or more selectors to a reverting call switch, and then dials another number which causes the reverting call switch to connect to certain of the generators iV-ti, and the interrupter I5 so as to cause the ringing of the bells of the two substations alternately after the subscriber at the calling substation has replaced his receiver. The ringing of the bells at the calling substation ceases as soon as the subscriber at the called substation removes his receiver. The subscriber at the calling substation then also removes his receiver and commences conversation with the called subscriber.

The reverting call switch RV is of a new type in so far as its method of control is concerned, being in accordance with the general object of its invention. Since the reverting call switch is connected to the calling line by way of one or more selector switches, and signalling current is projected back onto the calling line from the reverting call switch, the connection must be extended from the calling line straight through to the reverting call switch independent of the ordinary bridges. ln this system this is accomplished by a special switching through operation performed in the trunk relay group and controlled by means in the register sender used. The operation of the new reverting call switch and also the operation of the trunk relay group and the register sender when a connection is made with a reverting call switch in so far as these operations differ from the operations performed in extending a call to a subscriber not on the same line with a calling subscriber will now be described. For this purpose it will be assumed that the subscriber at substation A6 wishes to have conversation with the subscriber at substation A2. In this particular case with connections in the upper banks of the first and second digit registers of the register senders as shown in Fig. 3, the special reverting call number is 2l. To operate the ringer at substation A2 and also the ringer at substation A6, generator G2 must be connected to line conductor 3 and generator G1 must be connected to line conductor 2, and reverting call switch, to which the connection will be extended, must be operated so as to perform this operation.

Vilith the connections of the ringing gener ators Gil-G5, inclusive, and the interrupter I5, to the bank contacts of the reverting call switches as shown in Fig. 5, the particular number in accordance with which the reverting call switch must be operated to alternately ring the bells ofsubstation AG and A2 is 38. Therefore', to call the subscriber at substation A2, the subscriber at substation A6 removes the receiver and dials the number 2138.

Responsive to the removal of the receiver at substation AG, the lineswitch LS operates to select and connect with a trunk extending to an idle first selector', which may be assumed to be the trunk comprising conductors 22-25, inclusive, terminating in the selector S. Responsive to the seizure of this trunk, register sender selector RSS operates to select and associate an idle register sender with this trunk, which again is assumed to be the register sender RS shown in Figs. and 3. Responsive to the dialing of the digit 2 by the calling subscriber, line relay 31 of the trunk relay group FRG operates to cause the registration of this digit on the first digit register, that is, the wipers 324i and 325 are positioned in engagement with the second contacts in their respective banks. Likewise, the second digit 1 dialled by the calling subscriber is registered on the second digit register, that is, wipers 326 and 327 are positioned in engagement with the rst contacts in their respective banks; and the second and third digits 3 and 8 are respectively registered on the third and fourth digit registers, wiper 328 being positioned on its third bank contact, and wiper 329 being positioned on its eighth bank contact. As shown in the drawing, wipers 32st and 326 are connected, ground potential is connected to the second Contact of the banks of wiper 324k and relay 3&8 is connected to the first and second contacts of the bank of wiper 326. ylherefore as soon as the first digit 2 and second digit l have been registered, a circuit is closed for shunt relay 323. This relay operates and removes the

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