US1608960A - Automatic telephone system - Google Patents

Description

Nov. 30 1926.

R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Filed 00 2 1920 4 Sheets-Sheet 1 WE r- Hmcfne Efiuzhards an Nov. 30 1926.

1,608,960 R. G. RlCHARDSON r AUTOMATIC- TELEPHONE SYSTEM n U 2 E w a H m I \w @v 3 m a Q 1 m EQ W5 4 m% Q MS E Q Q W W i i m Q B Filed Oct Nov. 30 1926.

1,608,960 R. G. RICHARDSON AUTOMATI C TELEPHONE SYSTEM Filed Oct. 25, 920 4 Sheet s-Sheet 5 Inu IT Nov. 30 1926. 1,608,960

R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Filed Oct. 23, 1920 4 Sheets-Sheet 4 1m? Eng/hay Elfimhard'sun a; M fin:

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Patented Nov 30, 1926.

UNITED STATES PATENT OFFICE.

RODNEY Gr. RICHARDSON, OF CHICAGO, ILLINOIS, ASSIGNOIL, BY MEENE ASSIGN- MENTS, TO AUTOMATIC ELECTRIC INC, OF GHICAGG, l'fiLINDIS, A COBEORATION 0F DELANARE.

AUTOMATZC TELEPHUZ IE SYSTEM.

Application filed Qctobcr 23, 1920. Serial No. 413,894.

The present invention relates in general to automatic telephone systems in which connections are set up through the medium of subscriber controller selector and connector switches; and the object of the invention is to increase the capacity of a system of this kind without increasing the number of digits in the subscribers telephone numbers, and without changing the mechanical construction of the switches.

The desired result is accomplished by in sorting secondary rotary line switches in the trunlrinnsystem immediately following each cl '5 or selector switches, these secondary line switches having a group selecting function, as well as the usual trunlr selecting function; and by providing a calling device having two sets of finger holds and corre: sponding characters on the dial, lnstead 0t only one set. Vifhen characters in corresponding positions in the two sets are called on the dial the same effect is produced on the selector switches, but diiiierent eitects are produced at the secondary line switches, the group selecting operation in these switches being determined by the particular set, or row, in which the character used is located.

it is true that systems have been designed before in which the calling devices have been provided with two rows of characters, and in which auxiliary mechanism at the exchange is selectively controlled in accordance with the row in which the character used is located, but in these systems the auxiliary switching mechanism responds at once on the forward movement of the dial, while the usual selector switch mechanism responds 0nthe return movement of the dial. This method of operating is objectionable because of: the est-remcly short interval of time between the forward and the return movement of the ordinary calling device dial. Unless ind of retarding device is used the renoveinent starts at once when the dial released, and as a result the series of impulr produced on the return movement may be started before the auxiliary selecting mechanism has completed its operation, causing loss of impulses and resulting wrong numbers. The use of a retarding device to prevent the immediate return of the dial unduly complicates the calling device, and other means has been devised therefore li meet this diliiculty.

in the improved system herein described the group selecting operations of the seci'mdary line switches are determined or con trolled on the forward movement of the calling dial, but none oi these switches actually operate until later. The change in the line circuit conditions caused by the calling of a character in a articular row is registered on the selector s 'itch with which the line is connected, when the dial is pulled down; when the dial returns to normal the selector operates in its group selecting movement and then in its automatic trunk selecting-movement, connecting with a trunk line leading to an idle secondary line switch; and in the secndary line switch taken for use is then operated in accordance with the registration at the preceding selector switch. iy thus dc ferring the actual operation of the secondary line switches these operations are made to take place in the normal time interval be tween the caliing of successive digits, and a cm is produced which is much more sati factory in practice than prior systems. Certain features described in this application that are not claimed herein, are claimed in my copending divisional application Serial No. 143,057, tiled October 21, 1926.-

The trunking and circuit arrangements at the exchange and the construction of the calling device willbe described fully hereinafter, reference being had to the accompany ing dravi' 'ings, in which Figs. 1, 2, and 3 show by means of the usual circuit diagrams the various switches required, while Figures 4 and dare two views of the calling device.

The calling device will be described first, as an understanding of its operation is essential to an understanding oi the operation of the central oflice equipment. As shown herein, the calling device is much the same as the calling device described in the copending application of Blessing, Serial No. 354,201, filed Jan. 26, 1920, there being certain changes, however, which will be pointed out. These changes or modifications consist in the substitution of a dial having two rows of finger holds for the ordinary dial shown in the Blessing application, the addition ot a fixed huge stop and a slight change in the movable finger stop or lever, and in the addition of a pair of contact springsadapted to be controlled by the movable linger lever. The construction ot the double til) hole dial 2 is clearly shown. The finger holds in the inner and outer'rows are. designated by digits and letters, respectively, and the finger holds in the outer row are staggered or displaced relative to the finger holds in the inner row, thus reducing the size of the dial to a minimum. In order to secure the same angular movement of the dial when corresponding finger holds in the two rows are used, the fixed finger stop 3 hastwo positions which are displaced an amount equal to the angular displacement between corresponding finger holds. Thus, if the letter A, for example, is pulled on the dial, the dial will be rotated exactly the same angular distance as when the corresponding digit 1 is pulled.

The movable finger stop or lever 4.- is substantially the same as shown in the Blessing application referred to and has the same function, that is, to serve as a locking device and prevent the dial from returning to normal position until after the calling subscriber has removed hisfinger from the finger hold. This finger lever has an additional function, however, in the present case. Thefsemi-circular bridgepiece or guide 7 carries a pair of contact springs 5 and 6 which are mounted on the upper surface of the guide, as shown in the drawing. These contactsprings are included in the line circuit as will be explained presently. The upper spring 6 is provided with a tongue or leaf 8 which is bent down inside the guide 7 and'lies close to the surface of the calling device frame. When the dial is operated from any finger hold in the outer row, the movable finger lever A is pulled down wit-h the dial until it strikes the fixed'finger stop 3. In this position the bushing 9 on the finger lever 4 lies under the tongue 8 and the springs 5 and 6 are separated. When the finger is removed from the finger hold the movable finger lever is released and immediately returns to its normal position under the influence of the spring 10. The calling device mechanism is then permitted to operate and the dial returns to normal.

Attention is now directed to the circuit diagrams, Figs. 1, 2, and 3, in which I have shown sufficient of the exchange equipment to establish a complete telephone connection between a calling subscriber at substation A, Fig. 1, and a called subscriber at substation A, Fig. 2. This equipment includes the individual line switch C and the first selector D, Fig. 1; the secondary line switch E, andthe second selector F, Fig. 2; and the secondary line switch E and connector H, Fig.

The telephone substations are of the usual automatic type. The substation A, for example, comprises the usual transmitter and receiver, and the callingdevice S for controlling the automatic switches. This calling device is, of course, the one which is shown in detail in Figs. 1 and 5. The circuit at the substation is changed somewhat from standard practice by the inclusion ofthe resistancev 26 in one side of the line circuit. This resistance is normally short-circuited'by the contact springs 5 and 6, but when the calling device is operated from any finger hold in the outside row the shortcircuit will be removed for an instant, when the dial is pulled down.

The individual line switches, such as the line switches C and C, which are associated with the lines. of substations A and A, respectively, are ot the well known rotary type, in which the wipers have no normal position and move in a forward direction only. These line switches are describedin the United States Patent to Lamb #:1193160, granted August 1, 1916.

The first and second selectors ED and F1, Figs. 1 and 2, are of the usual Strowger vertical and rotary type and are operated according to the well known two wire sys tem of control. The mechanical construction of these switches is shown in the United States patent to Keith, Erickson and Erickson, No. 815,321, granted March 13, 1906. The circuits are shown complete in the drawings and will be described.

The secondary .line switches E and E, Figs. 2 and 3, are similar in mechanical con struction to the individual line switches C and ,C, that is, their wipers have no normal position and move in a forward direction only. The well known arrangement for locking the switching relay armature controlled by the armature of the line relay may be omitted, however, since the switch-- ing relay never operates as a cut-oil relay in a secondary line switch. As stated before, these secondary line switches have a group selecting function in addition to the usual trunk selecting function and each switch is provided with two sets of wipers. each set having access to a different group of trunk lines. I V A The operation of these secondary line switches will be described in detail.

The connector H, Fig. 3, is also of the well known Strowger vertical and rotary typeof mechanical construction,being similar to that shown in U. S. patent to Keith. Euckson and Erickson No. 815176, granted March 13, 1906. The circuit shown is a simple two wire circuit which is in common use.

Having briefly described the apparatus involved, I will now explain its operation more in detail with a view topointing out the novel features. For this purpose itwill be assumed that the subscriber at substation A desires to obtain a connection with the subscriber at substation A, the telephone Ins number of the latter substation being l l hen the receiver is removed at the calling station a circuit is completed over the line conductors 11 and 12 for the line relay 15 of the individual line switch C. Upon energizing, relay 15 closes a circuit tor the switching relay 1 1 in series with the stepping magnet 16 by means otits armature 20, and at its armature 21 connects the test wiper 31 to the above circuit at a pointmidway between the said relay and magnet. The latter operation is to provide tor advancing the switch wipers in search of an idle trunk line in case the trunk line with which they are associated, when the call is initiated, is busy. lVe may assume, however, in the present case, that the trunk line shown in the drawing and with which the wipers of the line switch C are temporarily associated is idle, and under these circumstances when the line relay 15 is o erated no rotary movement of the line switch will talre place, but the switching relay 14: will be energized immediately, as soon as its circuit is closed. Upon attracting its armature 18, relay lat connect-s ground to the test wiper 31 in order to render the trunk line busy, and by attracting its arn'iatures 1'? and 19 the switching relay extends the line conductors 11 and 12 by way of the said armatures 17 and 19, wipers and 32, banlr contacts 33 and 35, conductors and 38, armatures 61 and ti l and their "ing contacts, and the windings 0t relays 51 and of the selector D to bat tery and ground, respectively.

When the calling line is extended to the selector D, as above explained, the relays 50 and 51 are energized in series over the line circuit, and the former relay closes a circuit for the slow cting release relay 53. Upon energizing, relay prepares a circuit for the vertical magnet its lower armature and at its upper armature connects ground to release trunk conductor 3?, thereby establishing a holding circuit which extends by way of the conductor 3'7, test contact 3 1-, test wiper 31, armature 18 and its working contact, winding of switching relay 1%, and the winding of the stepping magnet 15 to batteiy. This circuit serves to maintain relay l l ener ized throughout the duration of the connection, and is completed before the slow acting line relay 10 has had time to fall back. Ground is also placed on the private normal. conductor 24:, which extends multiple test contacts in the banks of the connector switches which have access to the line of substation A. The calling line is thus made busy to incoming calls.

'lhe calling subscriber may now operate his calling device in accordance with the iii-st character in the desired number, which is the letter B. W hen this letter is called the dial is rotated the same angular distance as though the digit 2 had been called and also as the dial is pulled down the linger of the subscriber engages the movable linger lever in the calling device and this lever is pulled down with the dial, thus separating the contact springs 5 and 6, and inserting the resistance 26 in the line circuit. The resistance :26 may be about 1500 ohms and its inclusion in the line circuit causes relay 51, at selector D, which is marginally adjuster to retract its armature. Relay 50, however, is adjusted so that it will not fall back at this time, and a circuit is therefore completed which extends from ground G by way of armature 63 and its resting cont-ash iv armature 65 and its working contact, armature 66 and its resting contact, and the winding 01'' the slow acting relay 52 to battery. Upon energizing, relay 52 establishes a loci:- ing circuit for itseli at its armature 67, and its armature 68 prepares a circuit having to do with the control of the secondary line switch which is later selected for use, as will be explained presently.

lhe calling subscriber having withdrawn his finger from the dial, th moi-able linger lever immediately restores, contact springs 5 and 6 are closed, and the calling device dial returns to normal position, driving the impulse sending mechanism in the usual manner to produce two impulses, or interrupt-ions, in the line circuit. Relays 50 and 51 respond to these interruptions in the usual manner by retracting their armatures iomentarily at each interruption. The operation of relay 51 at this time is of no ctliect. Relay 50, however, each time it re tracts its armature 65 transmits a current impulse to the vertical magnet 5'? in series with the slow acting relay 5%. In response to these impulses the vertical magnet is operated to raise the switch shaft step by step until the wipers 8(l-82, inclusive, stand opposite the second level of bank contacts. Relay 5% is energized in series with the vertical magnet and being slow acting it retains its armature in operated position throughout the movement of the switch. At the first upward movement of the switch shaft, the oil normal springs 60 are closed and since relay 54 is in energized position a. circuit is completed for the stepping relay 55. Upon energizing, relay 55 locks itself at its upper armature 70, and its lower armature 71 prepares a circuit tor the rotary magnet 58. An instant after the vertical movement of the switch has ceased, the slow acting relay 5% falls back and closes the circuit of the rotary magnet 58. The rotary magnet is accordingly energized and advances the wipers into engagement with the first set of bank contacts in the lever opposite which they have been raised. In operating, the rotary magnet breaks the locking circuit of the stepping relay 55 which accordingly deenergizes and breaks the circuit of the rotary magnet, which then deenergizes also. The operation now depends upon whether the first trunk line terminating in the second level is busy, or idle. If this trunk line is busy, test wiper 81 will iinda ground potential upon the test contact, with which it is in engagement anda circuit will be completed by way of the test wiper, armature 62 and its resting contact, interrupter contact of the rotary magnet 58, off normal springs 60 and the winding of the stepping relay55 to battery. The stepping relay is therefore again energized and again completesthe circuit of the rotary magnet, 58, which is operated to advance the switch wipers into engagement, with the second set of bank contacts in the second levehatthe same time breaking the circuit or" the stepping'relay 55. These operations continue as long as the test wiper 81 continues to engagebusy or grounded test contacts. As soon as an idletrunk line is reached, which we will assume to be the trunk line shown in the drawing, the test wiper 81 will find no ground potential on the test contact 8, 1, and the stepping relay will not again be energized. Instead, the switching relay 58, which'up to this time has been short-cin cuited, is energized over a circuit which e};- tends from the grounded release trunk conductor 3?, by way of the winding of the said relay 56, interrupter contact of, the rotary magi'iet 58, on normal springs60,and the winding of the stepping relay 55 to battery. l he resistance of the switching relay 5 6 is so high that relay 55 does not operate at this time. Upon energizing, relay 5 6 con- 'nectsthe grounded release trunk conductor 3'? to the test wiper 81 at armature 62, thereby making the trunk line busy, and at, its armatures 61 and 641 extends the incoming trunk conductors 36 and 3.8, by way of the said armatures and their working contacts, wipers 80 and 82, bank contacts 83 and 85, conductors 86 and 88, armatures 10a: and 10. and their resting contacts, and the wind ings of relays 100 and 101 of the secondary line switch E to battery and ground, respectively.

The calling line having been extended to the secondary line switch E in the manner explained above. it will be apprehended that clays 100 and 101 of the switch E will be energized in series over the line circuit. This is true as regards the line relay 100, but relay 101 is prevented from energizing at this. t' -e by certain operations which have taken place at the selector D. It will be rememhered that the slow acting relay 52. in the relector energized and locked up when the calling device dial was pulled down, and it follows, therefore, that when the switclr ing relay 56 is energized, ground G will be extended by way of armature 63 and its working contact, and the working contact of relay 68 and the said armature to the lower line wiper 82, this line wiper being grounded at the same time that the calling line is extended to the secondary line switch E. As a result the lower winding of relay 101 is short-circuited and this relay is not energized. The line relay 100 upon energizingconnects ground to the lower side of the line at its armature lll, thu insuring that the lower winding of relay 101 will remain short-circuited until after the switch E has operated, and at its armature 109 connects ground to the release trunk conductor 87. thereby establishing a holding circuit which extends by way of the said conductor 87, test contact 8%, test wiper .81, and armature 62 and its working contact, to release trunk conductor 37, whereit joins previously described holding circuit extending back to the switching relay lei or the line switch C. This holding, circuit, including conductor 87, is completed before the slow acting re lease relay 53 has had time to deenergize, and serves to maintain relays l4 and 56 in operated position throughout the duration ot. the connection. It is noted that the lockcircuit of, relay 52 is broken by the line relay 50 when it falls back after the line has been switched through, and relay 52 is ecbordingly deenergized and disconnects ground from the lower s de of the line by retracting its armature 68.

Returning now to the line switch E; it will be evident that slnee the relay 101 has not energized, the lower set of wipers, comprising wipers 120,121, and 122, are the wipers which will be used. When line relay 100ig energized,.in addition to the operztions already described, it closes a circuit for the switchingrelay 102 in series with the stepping magnet 103 by means of its armature 110, and at its armature 108 connects the test wiper 121 to the above circuit at a point midway between the said relay and magnet. From now on the secondary line switch operates the same as a primary line switch. If the trunk line with which the wipers are associated is busy, the test'contact engaged by the test wiper 121 will be grounded, the switching relay 102 will be short-circuited, and the stepping magnet 103, being supplied with direct ground via the test wiper will operate as a buzzer to advance the switch wipers step by step in search of an idle trunk line. It is noted that both sets of wipers are moved simultaneously, but since the upper set of wipers is disconnected their movement is of no effect. V-Jhen an idle trunk line is reached, which we will assumeto be the trunk line shown in the drawing as ertending to the second selector F, the test wiper 121 will. find no ground potential upontest contact 124 and the rotary movement of the switch will cease. The switching relay 102, being no longer short-circuited, will now energize and at its armature 106 ground is connected to the test wiper 121 in order to make the selected trunk line busy. At the same time, by ieans o1 armatures 10 1 and 107, the incoming trunk conductors 86 and 88 are extended by way of the said armatures and their working contacts, armatures 112 and 115 and their resting contacts, wipers and 122, bank contacts 123 and. 125, conductors 126 and 128, armatures 161 and 16 1, and their resting contacts, and the windings of relays 151 and of the second selector F, to battery and ground, respectively.

F-fhen the calling line is extended to the selector 1*, as above explained, relays 150 and 151 are energized over the line circuit in the usual manner, and the former relay completes a circuit for the slow acting release relay 158. Upon energizing, relay 158 prepares a circuit for the vertical magnet 15'? at its lower armature, and at its upper armature connects ground to the release trunk conductor 127, thereby establishing a landing circuit which extends by way or conductor 127, test contact 124, test wiper 121, resting contact 01": armature 11 1 and the said arn'iature, armature 106 and its working con tact, and ari'nature 105 and its working con tact, to the release trunk conductor 87,where it joins the previously described holding circuit extending back to the selector D and line switch C. The switching relay 102 is connected to the holding circuit, just described, at the working contact or armature 106, and is thus held up throughout the duration oi? the connection.

The calling subscriber may now operate his calling device in accordance with the second character in the number, which is the digit 2. Since the linger hold corresponding to the digit 2 is on the inside row, when the calling device is operated the finger ot the subscriber will not engage the finger lever and the resistance 26 will not be inserted in the line circuit. Consequently the marginal relay 151 in the second selector 1 will not tall ba t-T1 when the dial is pulled down. l -fhen the dial is released and returns to normal two interruptions are produced in the line circuit in the usual manner, to which relays 150 and 151 respond by meinentarily retracting their armatures. Both relays operate together and the operation of relay 151 is of no ei'l'ect. Relay 150, however. at each deenergization sends an impulse of current to the vertical magnet 157 in series with the slow acting relay 154:. the operation of the vertical magnet the shattis raised step by step until the wipers inclusive, stand opposite. the sec of the bank contacts. The slow 1119; re av 15 1 is energized in series with 1 the vertical magnet and when the ofi normal springs 160 close at the first upward movement of the shaft this relay closes a circuit for the stepping relay 155. The latter relay, upon energizing, establishes a lock-' ing circuit for itself at its upper armature and at its lower armature prepares a circuit for the rotary magnet 158. At the end of the vertical movement of the switch, relay 154 is deenergized and completes the circuit 01" the rotary magnet, which operates to advance the switch wipers into engagement with the first set of bank contacts in the level opposite which they were raised. This initiates the automatic trunk selecting movement, which takes place precisely as was described in the case of the first selector 1). Assuming that the trunk line shown in the drawing, and comprising conductors 186, 187 and 188, is the first idle trunk line, when the test wiper 181 arrives at testcontact 1841 it will find no ground vpotential and the rotary movement of the switch will cease. The switching relay 156 is now energized and connects the grounded release trunk conductor to the test wiper 181 in order to make the selected trunk busy. The switching relay also extends the incoming trunk conductors 126 and 128 by way of its armatures 161 and 16 iand their working contacts, wipers and 182, bank contacts 188 and 185, conductors 186 and 188, armatures 204; and 207 and their resting contacts, and windings otrelays 200 and 201 to battery and ground, respectively.

When the calling line is GKtGlltiGCl to the secondary line switch E, in the manner above explained, relays 200 and 201 are energized in series over the line circuit and the latter relay immediately locks itself at its armature 213. The release trunk conductor 187, it will he recollected, has already been grounded by the test wiper 181 of the selector F. When the line relay 200 energizes it grounds the lower side of the line at armature 211, as was done in the case i of the line switch E, but this operation has no effect on relay 201, for this relay is now held up by its locking winding. It will be understood, of course, that the contact at armature 213 of relay 201 must close before the contact at armature 211 of relay 200. This result may be insured by properly adjusting the contact springs, but no special adjustment is usually necessary on account of the fact that the line relay 200 is slightly slow to pull up.v As in the case oi? the line switch E, the line relay 200 of the line switch E grounds the incoming release trunl: conductor, this operation being performed at armature 209. The holding circuit thus established stands by way of conductor 187, test contact 18 1, test wiper 181, and armature 162 and its working contact to the release trunk conductor 127, where it- "oins the reviousl described hOldlD ciri a:

' cuit extending 'back to switches E, D, and C.

Theswithing relay 156, at-the selector' F, Qis'heldup over this holding circuit throughout the connection.

The further operation of the hue switch "E in selecting an idletrunk line may now be gone over briefly. lVhen the line relay "200 energizes, it closes the usual circuit through the switching relay 202 and the stepping'magnet 203 in series, at itsarmature 210, and at its armature 208 connects the test wiper 231 to the ahove'circuit at a point midway between the said relay and magnet. The operation of selecting an idle trunk now takes placein the customary manner, and both sets of wipers are advanced step by step by the operation of magnet 203, it being noted, however, that sincerelay 201 hasbeen'energized the testing operation will be under control of test wiper 231. Assuming that the trunk line comprising conductors 236,237, and 238,'is the first'idle trunkline, when test wiper 231 arrives at test contact 234 it will find no ground potential and the rotation of the switch will cease. Switching relay 202 is now energized and at its armature 206 connects ground to the test wiper 231, thereby making the selected trunk busy. In addition relay 202 "disconnects the incoming trunk conductors 186 and 188 from the'windings of relays 200 and 201, and extends them by way of armatures 20% and 203 and their working contacts, armatures 212and 215 and their working contacts, wipers 230 and 232, hank contacts 233 and 235, conductors 236 and 38, normally closed contacts of the reversing relay 250, and the upper and lower'windings of the double wound relay 251 of the connector H to battery and ground, respecis extended to the connector'H, line relay 251 is energized over the line circuit and closes a circuit for the slow acting release relay Upon enen n'izingnthe latter relay prepares a circuit for the vertical magnet 258 atits armature 266, and at its armature 267 closes a holding circuit which extends by way of conductor 237, test contact231 'test wiper 23hworking contact oi" armature 21 1 and said armature, armature 2061and its worlrin contact, and armature 205 and its worl contact'to release trunlr conductor 187, where it joins the previously described holding cir'cuit extendb'ack to switches F, E, D, and C. Switching relay 202 is connected to this VVheu the callinp' line holding circuit atthe working contact of "it 'niay hepointed out-thitthe initial eneiu :giZa-ticn of '1"elay'jr201, .when the calling lline was extended to "the secondary line switch w as due to the fact that the lower side oi the line was notgrounded at the selector F, which in turn was due to the fact that the slow acting relay 152 of said selector was not energized when the calling device was operated in accordancewith the second character in the called number. 0nd character had been the'letter B, instead of the digit 2, relay 152 would have been en- "ergizen when the dial was pulled down by the fallinghack of relay lol, said relay 152 would have been locked up in parallel with the slow acting relay 153, and when the switching relay 156 energized to extendthe connection through, ground would have been placed upon the l'ower side of the line at arn'iature 163 cf .the said switching relay, with the result that relay 201 would have been short-circuited and would have failed topuil up. The'wiper set comprising wipere-220,221., and 222 would then have'heen 'le'ttin service and a trunk line in adiit'erent group would have been selected.

Returning now'to the process of setting up the connection, the'connector H is operated responsive to the calling of the last two characters in the desired number. "When the third character is called, which is the digit 2, two interruptions are produced in thclme circuit and the line: relay deenergnzes twice momentarilyand sends two iniand 26 i, winding of the slow acting relay 253, and the winding ofthe vertical magnet 258 to battery. viythe operation of the vertical magnet the connector shaft is raised step by step until the wipers, 290, 291, and 292, stand O QiiYOSitG the second le '01 of bank contacts. Thcslow acting relay 253 is energized in series with thefverticul ms st. and by means of its armature 268 maintains the vertical magnet circuit intact after the 06' .i'icrmal s rings have been shifted, which occurs on the first vertical step. At the end of the vertical movement oi the switch, rclay 253 is deenergized and transfers the operating circuit to the rotary magnet 259.

' The last character in the number may now he called, this being the digit'i. ii hen the c device is operated for the dig t 1 a It the secill) of the rotary magnet 259 to battery. By the operation of the rotary magnet thewipers ot the connector are rotated into engagement with the particular set of bank contacts in which the line of substation A is terminated, these contacts being indicated in the drav-iing by reference charaurters 293, 29%, and The slow acting relay 256 is energized in parallel with the rotary magnet, and by means of its armature 275 connects the test wiper 291 to the winding of the test relay 255. Relay 256 also places a shunt around the break contact at armature of the test relay by means of armature 276. This is to guard against the possibility of the rotary magnet circuit being broken. by the energization of the test relay, in case the test wiper 291. should pass over one or more grounded test contacts during the rotary movement or" the switch, but, of course, in. the present case where the switch is rotated only one step this provision is of nonnportance.

it will be assumed first that the called line is busy when connected with, as above explained. Under these circumstances when the test wiper 291 comes to rest in engagement with test contact 294, it will find a ground potential on said test contact and test relay 255 will be energized. hen the test relay pulls up it establishes a locking circuit for itself at armature 272 (this circuit is completed as soon as the relay 256 falls back), opens the rotary magnetcircuit its armatures 273, and connects a lead from the busy signalling machine to the lower side of the line at armature 274. By the latter operation an audible busy signal is transmitted to the calling subscriber to ad vise him that the desired line is for the time being inaccessible and he will replace his receiver.

Having explained the operation which takes place when the called line is busy, it will now be assumed that the line is idle when called. In this case when the test wiper 291 comes to rest in engagement with test contact see it will find no ground potential, and the test relay 255 will not be energized. Then, when the slow acting relay 256 falls back an instant later, a circuit is completed for the switching relay 257 as follows: from the grounded release trunk conductor 23?, by way of armature 272 and its resting contact, upper winding of the switching relay 257, resting contact of armature 275, and the said armature, test wiper 291, test contact 29%, private normal. eonductor 298, winding of switching relay 14' of line switch C, and winding of the step ping magnet 16 to battery. Upon the closure of the above circuit relays 257 and 14: are energized in series, and the latter relay operates to clear the line of sub-station A of its normal battery and ground connection in the line switch. It is noted that due to a mechanical interlocking; devi e, controlled by the line relay 15, the relay ii is operated only about half way, and the wipers ot the line switch are not connected up.

At the connector H, when the switching" relay 257 is energized it estal'ilishes a ing circuit for itself at its armature 2..., connects ground to the test wiper 2% at armature 278, breaks the rotary magnet circu t at armature 280, and at armatures 2?? and 281 connects up the upper and lower line wipers 290 and 292. Ringing; current from the generator GEN is now projected out over the called line in the usual manner to open ate the ringer at substation A, to signal the called subscriber. It will be noticed that the return path for the ringing current includes the upper winding of the cut-oil relay 254, and when the called subscriber removes his receiver the said ring cut-oil relay will be operated and will establish a locking circuit for itself at its armature 270. At its armature 269 and 271 the ring cut-oft relay opens the ri ing circuit and at the working contacts of these same armatures finally completes the talking, circuit. lhe transmitter at the calling station is supplied with tall-ring battery through the winding ot the double wound line relay 251 of the connector H, while the transmitter at the called station is supplied with talking current through the windings of the. double wound back bridge relay 250. The latter relay is energized as soon as the talking connection is completed by the ring cut-oft relay 254, and reverses the trunk conductors 236 and 238 as regards their connection to the wind ings of the line relay 251, thus reversing the direction of current flow in the calling; line. This reversing operation is of no particular utility in the system described herein, but is included because it a standard opera tion used for controlling measured service equipment, in case any such e'quipi'ucnt is in use.

The desired connection has now been completed, and the subscribers can converse as desired. When the conversation is finished, both subscribers will replace their receivers. By the replacement oi the receiver at substation A the circuit of the line relay 251 is broken and this relay is accordl energized, followed by the deeper slow acting relay 252. The latter relay removes ground from the release trunlr con-- ductor 237, and the line and release relays jointly close a circuit for the release magnet 260. The connector tl" catered to normal in the well known menu i i hen ground is disconnected from the ho line circuit, including conductor 23?, all the rela in switches E, F, E, D, and C. w ich l been maintained energized over the holding: circuit, are deenergized and. the associated switches are restored to normal position also. In the case of switches C," E, and E, the relays are simply deenergized and'th'e wipers are left standing in their advanced position. In the case of selectors D and F, when the switching relays 56 and 156 deenergize, cir cuits are completed for release magnets 59 and 159, respectively, and the selectors are restored to normal in the usual manner.

Iaving finished with the explanation, the results securedmay now be briefly rcviewec. It will be clear that the capacity of the system is doubled at every point where the secondary line switches are introduced, and since these switches are inserted at two points, the capacity of the system is increased four times and the total capacity will be 40,000 lines instead of 10,000 lines, which is the capacity of the ordinary four :0 di it decimal s stem. In a live di it stem the capacity is increased eight times, for the secon .ry line switches may be inserted at three points instead of two, and the total capa ity of a five digit system, using sec ondary line switches, according to the plans herein described, will be 800,000 lines.

It will'be understood, of course, that the -apacity may be further increased by the substitution of large capacity connectors for C0 the ordinary 100 line connectors herein described. These large capacity connectors may handle either 200 or 400 lines, there being two sets of wipers in one case, and four sets in the other. If these large size connectors are used the wiper selection will e controlled by the resistances at the clifferent telephones, according to the general plan shown in the pending applications of W. W. Owen, Eierial Nos. 235,452 and 239,504, filed May 20, 1918, and June 12, 1918, respectively.

Thesystem may he modified if desired by omitting the secondary line'switches at some point, or by using 100 line connectors in some of the groups, while 200 or 400 line connectors are used in the other groups. The telephone numberswill, of course, be assigned in accordance with the particular trunking arrangement chosen. These modi fications, however, will he readily understood and will not be explained in detail.

An incidentala'dvantage, one not referred to, before, but one which will be readily appreciated, is secured by the use of secondary line switches simply as trunk selectors, and without reference to their group selecting function. The introduction of these switches in the trunking system gives a better distribution of the traiiic and increases the size L) of the trunk groups. The latter feature is particularly valuable in case the large capacity connectors are used, as otherwise special arangements would be required to make all the connectors in a group available in as common to all incoming calls.

Having described my invent-ion, what I consider to be new and desire to haveprotected by Letters Patent will be pointed out in the appended claims.

lVhat I claim as my invention is:

'1'; In a telephone system, a callin device, comprising two controllin devices 101' altering the line circuit, means for operating said devices to successively alter the line circuit, two automatic switches responsive to said devices respectively, and circuit connections whereby said switches are caused to respond in inverse order in establishing a connection.

2. In a telephone system, a calling device comprising two controlling devices for altering the line circuit, means for operating said devices to successively alter the line circuit, a directively controlled switch operable responsive to the controlling device which is operated last, and a second directively controlled switch controllable thereafter and responsive to the controlling device which is operated first.

3. In -a telephone system, a substation calling device having a reciprocating dial, means for causing changes in the line circuit when the dial is moved forward and also on the return, automatic switches controlled on the forward and return movements, respectively, and means whereby the switch which is controlled on the return movement of the dial is operated before the other switch.

at. In a telephone system, two serially related switches for use in establishing'a talking connection, a substation calling device having a reciprocating dial, means for causing changes in the line circuit when thedial is moved forward and on the return, means for registering the change produced in the forward movement of the dial at the first of said switches, means for operating said first switch responsive to the changes produced on the return movement, and means for then operating the second of said switches in accordance with the registration at said firstv switch.

5. In a telephonesystem, a calling device having a reciprocating dial, means for pro ducing changes in the line circuit on the forward movement of the dial and on the return, means for registering the changes producedon successive forward movements, automatic switches directly respon iveto the changes produced on successive return movements, and other automatic switches operated alternately with the said first switches in accordance with the registered changes,

6. In a telephone system, an automatic selector switch, a plurality of auxiliary switches accessible to said first switch, means at a calling telephone for operating said selector switchto select one of said auxiliaryswitches, means for then operating the selected auxiliary switch, and means at the calling telephone for predetermining the character of the operation of the selected auxiliary switch before it is selected.

7. In a telephone system, two serially related switches, both of which have primary and secondary selecting functions, said switches operated successively under control of a calling telephone to establish a telephone connection, and two serially connected controlling means for said switches, respectivel operated in the inverse order to that in W ich the corresponding switches are 01)- erated.

8. In a telephone system, two classes of switches each having directively controlled group selection and automatic trunk selection, the switches of one class having wipers which restore to normal when not in use, while the switches of the other class have wipers which always remain in advanced position, and a trunking system in which the switches in one class are arranged alternately with the switches of the other class.

9. In a telephone system, two classes of switches each having directively controlled group selection and automatic trunk selection, the switches of one class having each a single set of directively movable wipers, while the switches of the other class have multiple wiper sets and directively con trolled wiper selecting mechanism, and a trunking system in which the switches of one class are arranged alternately with the switches of the other class.

10. In a telephone system, a line, a pair of automatic switches, a calling device on said line, aid switches operated successively in extending a connection from the line, an auxiliary controlling device on the line operated to alter the line before the calling device transmits impulses, said device controlling the switch which is operated last to extend the connection.

11. In a telephone system, a line, a pair of automatic switches, a variable impulse sender on said line, said switches operated successively to extend a connection, an auxiliary controlling device on the line operated be'tore impulses are transmitted by said sender, said device controlling relays in each of said switches during the extension of a connection.

12. In a telephone system, a line, an impulse sender on the line, a pair of automatic switches each having group and line selec tion and operated successively to extend a connection from the line, an auxiliary controlling device on the line in series with said,

impulse sender for controlling the group selection of the switch operated last, said device operated before the transmission of impulses by said sender.

13. In a telephone system, a line, a calling device on said line, a series of automatic switches operated successively to extend a connection from said line, each switch having directive group selection and automatic trunk selection, one operation of the device controlling first the group selection of one switch and then the group selection of the succeeding switch in the series, and a second operation controlling the group selection of two succeeding switches.

14. In a telephone system, a line, an impulse sender thereon, a selector switch accessible thereto having directive group se lecting movement and an automatic trunk selecting movement, non-numerical switches accessible to said selectors each having access to more than one group of trunk lines, means for operating said impulse sender to con trol the selector to seize an idle non'numerical switch, and means in the selector operated atwill by the subscriber for preselecting the group of trunk lines in which the non numerical switch will seize an idle trunk.

15. In a telephone system, a calling device comprising two serially connected controlling devices for altering the line circuit, means for operating said devices successively, two automatic switches responsive to said devices respectively, and circuit connections whereby said switches are caused to respond in inverse order in establishing a connection.

16. In a telephone system, two serially connected switches for use in establishing a talking connection, said switches each having a directive controlled group selecting function and an automatic line hunting function, a calling telephone means thereat for registering in said first switch the group selection to be made by said second switch, means for subsequently operating said first switch through its group selecting function. to select said second switch and means for controlling the group selection by said second switch in accordance with the registration in said first switch.

17. In a telephone system, two serially related automatic switches for use in establishing a talking connection, a calling telephone, successively operated devices thereat for controlling said switches, means responsive to the first of said devices for controlling said second switch and means responsive to the second of said devices for controlling said first switch.

Signed by me at Chicago, Cook County, Illinois, this 19th day of October, 1920.

RODNEY G. RICHARDSON.

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