US1678304A - Automatic telephone system - Google Patents

Description

July 24,1928.

1%. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Original Filed ow 25 1920 4 Sheets- Sheet l k Q0 l Q0 Inu en U1" EUCZL'LEH EE'ichardsuu July 24, 1928.

1,678,304 R. G. RICHARDSON AUTOMATI C TELEPHONE SYSTEM Original Filed Oct. 23, 1920 4 sheets sheet 2 :6 5 0 as! $3 gla s i a 1m??- Fatima EFicZ-Lardsmn Jul 24. 192B.

R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM 4 Sheets-Sheei 3 Original Filed 0ct'. 23, 1920 Imreniur E. Eichauwiszm Rodne- July 24, 1928.

R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Original Filed Oct. 23. 1920 4 s t -s t 4 Patented July 24, 1928.

UNITED STATES PA-TE NT OFFICE.

RODNEY e. RICHARDSON, or .CnIcAeo, ILLINOIS, ASSIGNOR, BY mnsnn ASSIGN- or CHICAGO, rumors, A CORPORATION MENTS, TO AUTOMATIC ELECTRIC INC.

OF DELAWARE.

AUTOMATIC rnnnrnoim SYSTEM.

Original application filed October 23, 1920, Serial No. 418,894. Divided and this applicatlon flled October 21, 1926. Serial No. 143,057.

The present invention relates in general to automatic telephone systems in which connections are set up through the medium of subscriber controlled 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 1nserting secondary rotary line switches in the trunking system immediately following each class of selector switches, these secondary line switches having a group of selecting function, as well as the usual trunk selecting function; and by providing a calling device having twosets of finger holds and corresponding characters on the dial, instead of only one set. When characters in corresponding positions in the two sets are called on the dial the same effect is produced on the selector switches, but diflerent effects are produced at the secondary line switches, the group of 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 described 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 on. the return movement of the dial. This method of operating is objectionable because of the extremely short interval of time between the forward and the return movement of the ordinary calling device dial. Unless some kind of retarding device is used the return movement starts at once when the dial is released, and as a result the series of impulses 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 undtply complicates the calling device, and 0t ier means has been provided therefor to meet this difiiculty.

In the improved system herein described the group selecting operations of the secondary line switches are determined or con trolled on the forward movement of the calling dial, but none of these switches actually operate until later. The change in the line circuit conditions caused by the calling of a character in a particular row is registered on the selector switch 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 the secondary line switch taken for use is then operated in accordance with the registration at the preceding selector switch. By thus deferring the actual operation of the secondary line switches these operations are made to take place in the normal time interval between the calling of successive digits, and a system is produced which is much more satisfactory in practice than prior systems. I

Since this case is a divisional application of my Patent 1,608,960, issued Nov. 30, 1926, only certain features set forth in the specification are claimed herein, the other features being claimed in the parent case.

The trunking and circuit arrangements at the exchange and the construction of the calling device will be described fully hereinafter, reference being had to the accompanymg drawings, in which Figs. 1, 2, and 3 show by means of the usual circuit dia rams the various switches required, while Figs. 4 and 5 are two views of the calling device.

The calling as an understanding of its operation 18 essential to an understanding of the operation of the central oflice equipment. As shown herein, the calling device is much the same as the calling device described in the Patent 1,444,777, issued to Blessing, Feb. 13, 1923, there being certain changes however, which:

device will be described first,

fications consist in the substitution of a dial having two rows of finger holds for the ordinary dial shown in the Blessing application, the addition of a fixed finger stop and a slight change in the movable finger stop or lever, and in the addition of a pair of contact springs adapted to be controlled by the movable finger lever. The construction of the double hold 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 irow 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 has two positions which are displaced an amount equal to the anguler 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 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 holtl. This finger lever has an additional function, however, in the present case. The semi-circular bridge piece 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 contact springs 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 4 is pulled down with 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. lVhen the finger is removed from the finger hold the moveable figure is released and immediately returns to its normal position under the influence of the spring 10. The calling devicem'echanism 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-0f 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\ invdividual line switch C and the first selector automatic type.

D, Fig. 1; the secondary line switch E, and the second selector F, Fig. 2; and the secondary line switch E and connector H, Fig. 3.

The telephone substations are of the usual ample, comprises the usual transmitter and receiver, and the calling device S for controlling the ai tomatie switches. This cal l ing device is, of course, the one which s shown in detail in Figs. 4 and 5. The circuit at the substat an is changed somewhat from standard practice by the inclusion of the resistance 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 short-circuit 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 of the well known rotary type, in which the wipers have no normal position and move in a forward direction only. These line switches are described in the United States Patent to Lamb #1,193,160, granted August 1, 1916.

The first and second selectors D and F, Figs. 1 and 2, are of the usual Strowger vertical and rotary type and are operated according to the well known two-wire system of control. The mechanical construction of these switches is shown in the United States patent to Keith, Erickson and Erickson, No. 815321, 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 construction 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 relaymay be omitted, however, since the switching relay never operates as a cut-off 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 diflerent group of trunk lines. The operation of these secontllary line switches will be described in detai The connector H, Fig. 3, is also of the well known Strowger vertical and rotary type of mechanical construction, being similar to that shown in U. S. patent to Keith, Erickson, and Erickson No. 815,176, granted March 13, 1906'. The circuit is a simple two wire circuit which is in common use.

Having briefly described the apparatus in- The substation A. for exwipers oft-he line switch C associated is idle, and under these circumtacts 33 and 35,"c'0nductors 36 t'ures 61 and 64 and their resting contacts,

volved, I will now explain its operation more in detail with a VleW to pointing out the novel features' For this purpose it will be assumed that the subscriber at substation desires to obtain a connection with the subscriber at substation A, the telephone number of the latter substation being #B221. When 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 for the switching relay '14 in series with the stepping magnet 16 by means of its arma ture 20, and at its armature 21 connects the test wiper 31 to the above circuit at a point midway between the said relay and magnet. The latter operation is to provide for 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. We may assume, however, in the present case, that the trunk line shown in the drawing and with which the are temporarily stances when the line relay 15 is operated no rotary movement of the line switch will take place, butQthe' switching relay '14 will be energized immediately,a s soon as its circuit .is closed; Upon attracting its armature 18,

relay14 connects ground to the test wiper 31 iirorder 'to render the trunk line busy,

and by attracting its armatures 17 and 19 the switching relay extends the line conductors'll and12 by way of the said armatures 1.7 and 19, wipers 30 and 32, bank-conand 38, armaand the windings of relays 51 and 50 of the selector I) to battery and ground, respectively.

VVheiigthe 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 acting release rela 53. Upon energizing, relay 53 prepares a circuit "for the vertical magnet at its lowe'r arma- "ture and at its upper armature connects groundto release trunk conductor 37, thereby establishing a holding circuit whichj ex- I tends by way of the conductor 37 test contact 34, test wiper 31, armature 318 and-ijts wgrking contact, winding of switchingirelay 14, and the winding of the 'steppinginagnet 16 to battery. This circuit serves-to maintain relay 14 energized throughoutithe duration of the connection, and isYcomplet'ed be'afore the slowacting line relay 15 has-had tofall' back. Groundis also placed on 't'hegprivate normal conductor 24,which"ex,-

1 tends to multipleitest 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. The calling subscriber may now operate his calling device in accordance with the first character in the desired number, which is the let ter B. When 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 finger of the subscriber engages the moveable finger lever in the calling device and this lever is pulled down with the dial, thus separating the contact springs 5 and 6, and insertingthe 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 adjusted, 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 contact, armature 65 and its working contact, armature 66 and its resting contact, and the winding of the slow acting relay 52 to battery. Upon energizing, relay 52 establishes a locking circuit for itself 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 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 interruptions, in the line circuit. .Relays 50 and 51 respond to these. interruptions in the usual manner by retracting their armatures momentarily at each interruption. The operation of relay 51 at this time is of no eifect. Relay 50, however, each time it retracts its armature 65 transmits a current impulse to the vertical magnet 57 in series with the slow acting relay 54. In response to these impulses the vertical magnet is operated to raise the switch shaft step by step until the wipers 8082, inclusive, stand opposite the second level of bank contacts. Relay 54 is energized in series with the vertical magnet and being gi'zedlpos'ition a circuit is completed for the. stepping relay 55. Uponenergizing, relayi55 locks itself atits upper armature 7 0,1 and its lower armature 71 prepares a circuit for the rotary magnet'58. An infstantf'after the vertical movement of the "switchdias ceased, the slow acting relay 54 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 levelopposite 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, oridle. If this trunk line is busy, test wiper ,81 will find a ground potential upon the test contact with which it is in engagement and a 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 relay 55 to battery. The stepping relay is thereforeagain energized and again completes. the 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 level, at the same time breaking the circuit of the stepping relay 55. These operations continue as long as the test wiper 81 continues to engage busy or grounded test contacts. As soon as an idle trunk 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 84, and the stepping relay 55 will not again be energized. Instead, the switching relay 56, which up to this time has been short-circuited, is energized over a circuit which extends from the grounded release trunk conductor 37, byway of the winding of the said relay 56, interrupter contact of the rotary magnet 58, off normal a springs 60, and the winding of the stepping relay 55 to battery. The resistance of the switching relay 56 is so high that relay 55 does not operate at this time. Upon energizing, relay 56 connects the grounded release trunk conductor 37 to-the test wiper 81- at armature 62, thereby making the trunk line busy, and at its armatures 61.

and 64 extends the incoming trunk conductors' 36 and 38, by way-of the said armatures and their working contacts, wipers 80 and 82, bank contacts 83 and 85, conductors 86 and 88, armatures 104 and 107 and their resting contacts, and the windings of relays 100 and 101 of the secondary line switch E to battery and ground, re-

spect-ively.

The calling line .having been extended to the secondary line switch E in the manner explained above, it will be apprehended that relays 100 and101 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 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 timethat 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 energizing connects ground to the lower side of the line at its armature 111, thus 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 84, test wiper 81, and armature 62 and its working contact, to release trunk conductor 37, where it joins previously described holding circuit extend ing back to the switching relay 14: of the line switch C. This holding circuit, including conductor 87 is completed before the slow acting release relay 53 has had time to deenergize, and serves to maintain relays 14; and 56 in operated position throughout the duration of the connection. It is noted that the locking circuit 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 accordingly deenergized and disconnects ground from the lower side of the line by retracting its armature 68.

Returnin now to the line switch E, it will be evi ent that since 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 for the switching relay 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 cir-' cuit 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 truck 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. When an idle trunk line is reached, which we will assume to be the trunk line shown in the drawing as extendingto the second selector F, the test wiper 121 will find no ground potential upon the test 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 means of armatures 104 and 107, the incoming trunk conductors 86 and 88 are extended by way of the said armatur-es and their working contacts, armatures 112 and 115 and their resting contacts, wipers 120 and 122, bank contacts 123 and 125, conductors 126 and 128, armatures 161 and 164*and their resting contacts, and the windings of relays 151 and 1500f the second selector F to battery and ground, respectively.

When the calling line is extended to the selector F, 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 153. Upon energizing, relay 153 prepares a circuit for the vertical magnet 156 at its lower armature, and at its upper armature connects ground to the release trunk conductor 127, thereby establishing a holding circuit which extends by way of conductor 127, test contact 124, test wiper 121, resting contact of armature 114 and the said armature armature 106 and its working contact, and armature 105 and its working contact to the release trunk conductor 87, where itjoins the previously described holding circuit extending back to the selector D and the line switch CJ The switching relay 102 is connected to the holding circuit justdescribed at the working contact of armature 106, and is thus held up throughout the duration of the connection.

The calling subscriber ma now operate his calling device in accor ance with the second character in the number, which is the digit 2. Since the finger hold corresponding to the digit 2 is on the inside row, when the calling device is operated the fin- .ger of 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 up F will not fall back when the dial is pulled down. When 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 retracting their armatures.

tion of relay 151is of no eflect. Relay 150,

By the operation of the vertical magnet the shaft is raised step by step until the wipers 180182, inclusive, stand opposite the second level of the bank contacts. The slow acting relay 154 is energized in series with the vertical magnet and when the oil 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 locking 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 of 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 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 164 and their Working contacts, wipers 180 and 182, bank contacts 183 and 185, con ductors 186 and 188, armatures 204 and 207 and their resting contacts, and windings of relays 200 and 201 to battery and ground, respectively. I

When the calling line is extended 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 conduct-or 187, it will be 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 donein the case of the line switch E, but this operation has no effect on relay 201, for this relay is now held b its locking winding. It will be understoo of course, that the contact at armature 213 of relay 201 must close before the.

contact at armature 211 of relay 200. This result maybe insured by properly adjusting the contact springs, but no special ad'ustment is usually necessary on account 0 the fact that the line relay 200 is slightly slow to pull up. As in the case of the line switch E,

the line relay 200 of the line switch E grounds the incoming release trunk conductor, this operation being performed at armature 209. The holding circuit thus established stands by way of conductor 187, test contact 184, test wiper 181, and armature 162 and its working contact to the release trunk conductor 127, where it joins the previously described holding circuit extending back to switches E, D, and C. The switching relay 156, at the selector F, is held up over this holding circuit throughout the connection.

The further operation of the line switch E in selectingan idle trunk line may now be gone over briefly. When the line relay 200 energizes, it closes the usual circuit through the switching relay 202 and the stepping magnet 203 in series, at its armature 210 and at its armature 208 connects the test wiper 231 to the above circuit at a point midway between the said relay and magnet. The operation of selecting an idle trunk now takes place in the customary manner, and both sets of Wipers are advanced step by step by the operation of magnet 203, it being noted, however, that since relay 201 has been 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 trunk line, 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 204 and' 207 and their working contacts, armatures 212 and 215 and their working contacts, wipers 230 and 232, bank contacts 233 and 235, conductors 236 and 238, 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, respectively;

When the calling line is extended to the connector H, line relay 251 is energized over the line circuit and closes a circuit for the slow acting release relay 252. Upon energizing, the latter relay prepares a circuit for the vertical magnet 258 at its armature 266, and at its armature 267 closes a holding circuit which extends by way of conductor 237, test wiper 231, working contact of armature 21 1 and said armature, armature 206' and its working contact, and armature 205 and its working contact to release trunk conductor 187, where it joins the previously described holding circuit extending back to switches F, E, D, and C. Switching relay 202 is connected to this holding circuit at the working contact of armature 206, and is thus maintained energized through the connection. The locking winding of relay 201 is also connected to the holding circuit and this relay is, of course, held up also.

Before proceeding with the explanation, it may be pointed out that the initial energiza tion of relay 201, when the calling line was extended to the secondary line switch E, was due to the fact that the lower side of the line was not grounded 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 accordance with the second character in the called number. If the second character had been the letter B, instead of the digit 2, relay 152 would have been energized when the dial was pulled down by the falling back of relay 151, said relay 152 would have been locked up in parallel with the slow acting relay 153, and when the switching relay 156 energized to extend the connection through, ground would have been placed upon the lower side of the line at armature 163 of the said switching relay, with the result that relay 201 would have been shortcircuited and would have failed to pull up. The wiper set comprising wipers 220, 221, and 222 would then have been left in service and a trunk line in a different group would have been selected.

Returnin 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. \Vhen the third character is called, which is the digit 2, two interruptions are produced in the line circuit and the line relay 251 deenergizes twice momentarily and sends two impulses to the vertical magnet over the following circuit: Ground at G, armature 265 and its resting contact, armature 266 and its working contact, off normal springs 262 and 264. Winding of the slow acting relay 253, and the winding of the vertical magnet 258 to battery. By the operation of the vertical 111".gnet the connector shaft is raised step by step until the wipers, 290, 291, and 292 stand opposite the second level of bank contacts. The

slow acting relay 253 is energized in series with the vertical magnet, and by means of its armature 268 maintains the vertical magnet circuit intact after the off normal springs have been shifted, which occurs on the first vertical step: At the end of the vertical movement of the switch, relay 253 is deenergized and transfers the operating circuit to the rotary magnet 259. i

The last character in the number may now be called, this being digit 1. When the calling device is operated for the digit 1 a single interruption is produced in the line circuit and the line relay 251 sends a single impulse of current to the rotary magnet 259 net, and by means of its armature 27 5 con wipers of 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 drawing by reference characters 293, 294 and 295. The slow acting relay 256 is energized in parallel with the rotary magnects the test wiper 291 to the winding of the test relay 255. 'Relay 256' also places a shunt around the break-contact at armature 273 of the test relay by means of armature 276. This is to guard against the possibility of therotary 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 of the switch, but, of course, in the present case where the switch is rotated only one step, this provision is of no importance.

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. When the I test relay pulls up it establishes a locking circuit for itself at armature 272 (this circuit is completed as soon asthe relay 256 falls back), opens the rotary magnet circuit at its armature 273, and connects a lead from the busy si nalling machine to the lower side of the line at armature 274. By I the latter operation an audible busy signal is transmitted to the calling subscriber to advise 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 assumedthat the line is idle when called. In this case when the test wiper 291 comes to rest in engagement with test contact 294 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 237, 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 294, private normal conductor 298, winding of switching relay 14 of line switch C, and windin of the stepping magnet 16' to battery. pon the closure of the above circuit relays 257 and 14 are energized in series, and the latter relay operates to clear the line of substation A of its normal battery. and ground connection in the line switch. It is noted that due to a mechanical interlocking device, controlled by the line relay 15, the relay 14 is operated only about half way,

and the wipers of the line switch are not' connected up.

At the connector H, when the switching relay 257 is energized it establishes a locking circuit for itself at its armature 279, connects ground to the test wiper 291 at armature 27 8, breaks the rotary magnet circuit at armature 280, and at armatures 277 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 operate the ring er 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-off relay 254, and when the called subscriber removes his receiver the said ring-cut-oif 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-ofl' relay opens the ringing circuit and the working contacts of these same armatures finally completes the talking circuit. The transmitter at the calling station is supplied with talkin battery through the winding of the doub e 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-01f relay 254, and reverses the trunk conductors 236 and 238 as regards their connection to the windings 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 is a standard operation used for controlling measured service equipment, in case any such equipment 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 of the receiver at substation A the "circuit of the line relay 251 is broken and this relay is accordingly deenergized, followed by the deenerglzation of slow acting relay 2 52. The latter relay removes ground from the release trunk conductor 237, and'the line and release relays jointly close a circuit for the release magnet 260. The connector I l is thus restoredto normal in the well known manner. \Vhen ground is disconnected from the holding circuit, including conductor 237, all the relays in switches E, F, E, D, and C, which have been maintained energized over the holding circuit, are dcenergized and the associated switches are restored to normal position also. In the case of the switches C. E, and E, the relays are simply dcenergized and the wipers are left standing in their advanced position. In the case of selectors D and F, when the switching relays 56 and 156 deenergize, circuits are completed for release magnets 59 and 159, respectively, and the selectors are restored to normal in the usual manner.

Having finished with the explanation, the

' results secured may now be briefly reviewed.

v rangement 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 in creased four times and the total capacity will be 40,000 lines instead of 10,000 lines, which is the capacity of the ordinary four digit decimal system. In a five digit system the capacity is increased eight times, for the secondary line switches may be inserted at three points instead of two. and the total capacity of a five digit system, using secondary line switches according to the plans herein described. will be 800,000 lines.

It will be understood, of course, that the capacity may be further increased by the substitution of large capacity connectors for the ordinary 1000 line connectors hereindescribed. 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 be controlled by the resistances at the different telephones, according to the general plan shown in the pending applications of IV. IV. Owen, Serial Nos. 235,452 and 239,504, filed May 20, 1918, and June 12, 1918, respectively.

The system may be modified if desired by omitting the secondary line switches at some point, or by using 100 line connectors in some of the groupsfwhile 200 or 400 line connectors are used in the other groups. The telepone numbers will, of course, be assigned in accordance with the particular trunking archosen. These modifications, however, will be readily understood and will not be explained in detail.

An incidental advantage, 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 traffic and increases the size a of the. trunk groups. The latter feature is particularly valuable in case the large capacity connectors are used, as otherwise special arrangements would be required to make all the connectors in a group available in common to all incoming calls.

Having described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What is claimed is:

1. In a calling device for automatic tele: phone systems, a dial having two rows of finger holds, the finger holds in one row being displaced angularly relative to the corresponding finger holds in the other row, and

a finger stop having two positions, one for each row of finger holds, one of said positions being displaced relative to the other an angular distance equal to the displacement between corresponding finger holds in the two rows.

2. In a calling device for automatic telephone systems, a rotatable dial having two rows of fingers holds, the finger holds in one row being displaced or staggered relative to the finger holds in the other row, a two position finger stop in which one position is displaced from the other an angular distance equal to the angular displacement between corresponding finger holds in the two rows, and impulse-sending mechanism controlled by said dial so as to produce the same number of impulses regardless of the row in which the particular hold in use is located.

3. In a calling device for aiitomatic telephone systems, a calling dial, a movable finger lever operated on the forward movement of the dial, impulse sending mechanism operated on the return, a resistance in the line circuit, contact springs short circuiting said resistance, and means controlled by said finger lever when out of normal position, for

locking said impulse mechanism and for separating said contact springs.

4. In a calling device for automatic tele phone systems, a dial having two rows of finger holds, the finger holds in one row being displaced angularly relative to the corresponding finger holds in the other row, a finger stop having two positions displaced from each other by an amount equal to the angular displacement between corresponding finger hold; in the two rows, a movable finger lever operated on the forward movement of the dial when a finger hold in one row is in use and not operated when a finger hold in the other row is in use, said lever and finger stop cooperating to govern the movement of said dial.

In witness whereof, I hereunto subscribe my name this 15th day of October, A. D.

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