US1811146A - Automatic telephone system - Google Patents

Description

R. G. RICHARDSON ET AL- June 23, 1931.

` AUTOMATIC TELEPHQNE SYSTEM Aoriginal Fired Feb. l2:4, 1922 lO Sheets-Sheet l Ennfnabr r June 23, 1931. R. G. RICHARDSON ET AL. 1,81146 AUTOMATIC TELEPHONE SYS TEM original Filed Feb. 23, 1922 1o sheets-sheet 2V 7% EIT-y:

June 23, 1931. R. G. RICHARDSON ET AL 1,811,146

AUTOMATIC TELEPHONE SYSTEM original Filed Feb. 23. 1922 l0 Sheets-Sheet 3 June 23, 1931. R. G. RlcHARDsoN ET AL 1,811,146

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 23, 1922 10 Sheets-Sheet 4 En dugg lllmhjafsnn-Heil LNaZsUn /f. ya@ Fm? l.

June 23, 1933. R. G. RICHARDSON ETAL 1,811,146

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. '25, 1922 10 Sheets-Sheet 5 `I'une 23, 1931- R. G. RlcHARDsoN ET AL 1,811,146'

AUTOMATIC TELEPHONE SYSTEM original Filed Feb. 25, 1.922 1o sheets-Sheet e I s En Url-reg E Bmhar/:SUIL HE7-fifi L NEZSUIL @l 7X 51T;

June 23, 1931. lR. G. RICHARDSON ET AL SQMG AUTOMATIC TELEPHONE SYSTEM Original Filed Feb, 23, 1922 10 Shees-Shet 7 Hail-15H EzzhgrdPSm HLZSDH June 23, 1931. R. G. RICHARDSON ET AL. 1,811,146 f AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Sheet Original Filed Feb. 25, 1922 E Bmhad'snn Harm-LNEED Bud-nay A f'g:

June 23, M931. R. G. RxcHARDsoN ET AL LLM AUTOMATIC TLPHONE SYSTEM Original Filed Feb, 23, 1922 l0 Sheets-Sheet 9 June 23, 1931., R. G. RlcHARDsON ET AL 1,811,146,

AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 23. 1922 l0 Sheets-Sheet 10 F1 :ll

En nfl-Leg E Emhr :f5 1n-METER L Nesn'n Patented June 23, 1931 UNITED STATES PATENT oF'FlcE BODNEY G. RICHARDSON, OF CHICAGO, AND MARTIN I. NELSON, OF ,PARK RIDGE, ILLINOIS, ASSIGNOBS, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., OF

CHICAGO, ILLINOIS, A CORPORATIONYOF DELAWARE AUTOMATIC TELEPHONE BYSTEII Application med February 23, 1922, Serial llo. 588,551. Renewed August 4, 1880. i

The present invention relates in general to automatic telephone systems, but more particularly to systems of the well-known Strowger or decimal type; andthe general object of the invention is the provision of new and improved circuit arrangements and apparatus which enable the Strowger system to be conveniently used in largesystems having complex multi-oiiice networks.

The Strow er system has been'used for large multi-o ce systems before this, and with considerable success, but its use under such conditions is not all that could be ,desired owing to the inflexibility of the inter-olce trunking, which must correspond to the directory numbering. The rigid association of the trunking with the numbering is also objectionable where existin manual networks are converted to automatic operation, for in such cases it is usually desirable to retain the old manual exchange names as part of the automatic numbering system and the occurrence of similar names in different areas and dissimilar names in the same area renders itA exceedingly difficult to arrange `the trunking on an economical and eiiicient basis.

In order to avoid diiiiculties of the foregoing nature, it is proposed herein to provideregistering and translating equipment in each oilice which is adapted to register the digits in called numbers as they are dialled, 'and which is adapted to translate those digits which have to do with the oiiice selection or inter-oiiice trunking into suitable oiice codes. The registering and translating devices thus make it ossible to arrange the trunking between o ces on the most eihcient basis, and entirely without reference to the directory numbering.-

The invention is illustrated in the accompanying drawings, comprising Figs. 1to12, inclusive, of which 'the first ten are circuit diagrams of the a paratus, Fig. 11 is a schematic diagram showing how the various v sheets should be joined together, while Fig. 12'is a front view of the subscribers calling device, showing the numbering of the dial.

Referring to Fig. 1, the substation A is an automatic substation of the usual type, having .the usual transmitter, receiver, and ring-` Aa forward direction only.

In common with other similar line switches the line switch C has access to a plurality of trunk lines, one of whichis shown in the drawings as extending by way of the relay equipment D to the first selector E1, Fig. 2. The relay equipment D Qis ,inserted in the trunk in order to provide for connecting and disconnecting a' registering and translating equipment at the proper time. The first selector E1 is a Strowger vertical and rotar switch lof the usual type, having its ban contacts arranged in ten horizontal rows or levels. Second, selectors E2 and E22, also shown in Fig. 2, are similar to the rst selector El. At the right of the selector E22 is shown a trunk line extending to an operators positionr and there terminating in jack J.

The lower half of Fig. 3 shows a secondary line switch C1 and a repeater R. ,The former is accessible to the second selector E2 and other similar selectors, and in construction is similar to the primary line switch C. The repeater R is adapted to repeat automatic switch operating impulses received over the two sides of the trunk in series, and is provided with a repeating coil in lieu of the condensers which have been-widely used heretofore.' The upper half of Fig. 3 shows third and fourth selectors E33 and E, which are similar to the selectors already described, and the repeater R1, which is the same as the repeater R.

Fig. 4 shows the third selector E3, and the fourth selectors E4 and E4, together with the repeater R2, all of which arethe same as the selectors and repeaters previously described.

Fig. 5 shows an' automatic connector switch H, which is ofthe usual Strowger vertical and rotary type', and which is adapted to re- 1D0 spond to two successive series of impulses in order to direct its wipers to the contacts of a particular line to which it has access, differing in this respect from the selector switches hereinbefore referred to, which respond to only one series of impulses and which have an automatic trunk hunting movement. The mechanical construction of the connector H is, however', very similar to that of the selectors. The rotary line switch C2 is individual to the line of station A1 and is similar to the line switch C, Fig 1.

A complete set of registering and translating equipment may be called a director from its function of directing or routing calls to their proper destinations. One such complete equipment, or director, is shown in Figs. 6, 7 8 and 9, and the lower half of Fig. 1. This director comprises the finder F, Fig. l; the master digit controller M1, Fig 6; the A impulse register M1, Fig. 6; nine Strowger switch mechanisms for registering the B and- C impulses, of which one is shown at H1, Fig. 7 the thousands register M1, a hundreds register M5, a tens register M8, and a units register M7, all of which are shown in Fig. 6; an impulse sending switch S1, Fig. 8; a sequence switch S2, Fig. 9; and the intermediate distributing frame I.D.F., Fig. 7

In .mechanical construction the finder switch F is similar to the rotary line switch C.

This finder switch, together with the finders` which are allotted to other directors, has access to a group of trunk lines, one of which is the trunk line shown in the drawing and extending to the first selector E1. Assuming that the finder F has twenty-five sets of contacts in its bank, which is the usual size,there would be twenty-tive trunks in thei group to which the finder has access, requiring the provision of about six or seven directors to handle the traiiic. It will be understood that any other convenientmethod of associating the directors with the trunks may be employed if desired, such for example as the scheme of providingrotary switches individual to the trunks which hunt for idle directors.

The master digit controller M1, the A impulse register M2, and the 4 digit registers M4 to M7, inclusive, are simple ten-point step by step switches, each of which is provided with an operating magnet and a release magnet, and a set of off normal springs which are operated when the switch wipers lare advanced out of their normal pos1tion.`

The Strowger switch mechanism H1 is the .same in mechanical construction as an ordi- 220 to 223, inclusive, and shown near the center of the drawing, Fig. 7 which also shows a portion ofthe first and second levels of the bank to which these wipers have access. Each of the other eight Strowger switch mechanisms in this particular director is also provided with 4 wipers, and the wipers of all the switches are connected in multiple. The banks, however, are not multipled, but each set of 4 contacts has a set of 4 individual wires which is terminated on the left hand side of the I.D.F. coming from the first set of contacts in the second level of the switch H1 and terminating in the first 4 contacts on the I.D.F., 4 wires coming from the second set ofy contacts in the second level and terminating in the next 4 contacts on the I.D.F., and 4 wires coming from the first setof contacts in the first level and terminating in the next 4 contacts on the I.D.F. The bank of each Strowger switch in the director is wired up to the left hand side of the I.D.F., the same as has been explained in the case of the switch H1; thus it will be seen that there will be 400 wires coming from each switch, or 3600 wires in all. There are also some additional wires coming from the relays shown in Fig. 9, which will be explained hereinafter.

The right hand side of the I.D.F. consists of 13 continuous strips or .bus-bars or multipled terminals, with facilities for crossconnecting any terminal on the left hand side with any one of the 13 bus-bars. The

The drawing shows 4 conductors first ten bus-bars correspond to the ten digits, y i

l. to 0, inclusive, and are so marked in the drawings. These bus-bars are connected in multiple with the banks of the register switches M4L to VM7, inclusive, and with the bank of the sending switch S1, as is shown in Figs. 6 and 8. The three lower bus-bars are provided for special purposes which will be explained fully later on. 1

The sending switch S1, Fig. 8,' and the sequence switch S2, Fig. 9, are rotary switches similar in mechanical construction to the line switch C, Fig. 1, that is, the wipers move in a forward direction only. Each of these switches, however, has a normal or home position in which it stands when at rest.

The repeater R3, Fig. 10, is not included in the main layout of the system, but is provided for a special purpose as willI be pointed out hereinafter.

The invention is illustrated as applied to what is known as a 10,000,000 line system, that is, one in which each telephone number consists of seven digits 'or other characters. This numbering scheme provides for a maximum of one thousand 10,000 line oflices, which is large enough for the Very largest exchange areas. In order to assist the subscribers in-remembering the telephone numbers, the first three letters of the exchange names are used in place of a corresponding .number of digits, and are'printed in the directory in capital letters. For example, CARI- tn 2345, or NORth 6789; The letters of the alphabet are, of course, marked on the subscribers dial as well as the ten digits, as shown in Fig. 12: The trunkingbetween oices is along wellknown lines, except that as before stated it is entirel independent of the numbering scheme. n general each oiice is provided with first, second, and third selectors for selecting oups of inter-otlice or local trunks, and wit fourth and fifth selectors and connectors for complleting local connections. Then, following t code will consist of three digits or series of impulses, which are roduced byV .a suitable Y translation from the nrst three letters of the exchange name, and which serve to actuate the first, second and third selectors at the originating oliice to select an idle trunk in the grou extending to the desired distant office, or a ocal trunk if the called vparty is in the same oirlce. In either case the trunk selected terminates in a fourth selector in the desired oliice, which together with a fifth selector and connector serves to complete the connection.

It will be understood, therefore,` that the general plan is to have direct trunks from each oilice to eve other otlice andithat these trunks are taken om the banks of the third selectors. This plan, however, need not be v rigidly adhered to and in fact-is departed from in a good many cases.l For instance, if

all the inter-oiiice trunks were taken from the banks of third selectors` 1,000 groups of trunks could be had, which is much more than is required in any known case. It is estimated that not much over 200 offices will lbe required for the very largest systems, such as 4:0 New York or London. In view of this a large number of trunk grou s can be taken from the banks of the secon erable advantage. In a. typical. oiiice, for

Y example, eight levels in each of the nine 4'5 groups of second selectors (the 0 level, is used for long distance) may be used for inter oiiice trunks, which would give seventy-two groups of trunks, selected by a two digit code.

This would leave two levels in eachgroup of second selectors for trunking to third selectors, providing for eighteen groups \of third selectors. From the banks of the third selectors would be'obtained 18,0 groups of trunks, selected by a three digit code, which v:iii with the 7 2 groups of two digit code trunks would make 252 groups in all. i A

' Another departure from the general plan introduces the feature of tandem trunking,

y which is desirable in manycases' to secure eilicient trunk groups. To illustrate, a number of oiiices in a'distant area may have four digit codes assigned, the rst three digits of.

code woulds'elect a mainlgroup o trunks to e general plan, each oiiice f A to other points; all of which will afford selectors to a consid- -step b be `assumed,the refore, that at the time the the tandem oce, a centrall located oce with respect to the others in t e area in question after which an incoming fourth selector d in the tandem olice would respond tol the fourth digit of the code to selecta grou of trunks to the particular oilice desired. his arrangement would, of course, involve the use of fth and sixth selectors in the oliices y reached by way of the tandem oice, and usually in the tandem officeitself, although of course in many cases the main group of trunks to the tandem office could be selected by a two digit code instead of by a three digit codev in order to avoid the use of sixth selectors. 80 The foregoing will give a general idea of the typeA o system to which the invention is applied, suiiicient to understand lits operation and special uses. The drawings, of course, do not show a complete trunking system, no r is this necessary in view of the extended knowledge of the subject. It has been considered suiiicientto show a typical switch train, such as may be used to establish a connection between a calling station A, Fig. 1, in the originating oiiice and a called station A1, Fig. 5in a tandem oiiice, and portions of several other switch trains,

which show the routing of calls from station ample opportunity to explain the operationof the director..

Initiation of the @azz The op ration of thefsystem will now b e describe in detail, it being assumed for this purpose thatthe subscriber at station A, Fig.1, desires to establish connection with V the subscriber at station` A1, Fig. 5. When the receiver is removed at station A, a cir# cuit is completed'over the line conductors` 12 and 13 Vfor the line relay 18 of line switch C. Upon energizing, relay 18 closes a circuit for the switching relay 19 in series with the stepping magnet 20 at armature 26, and at armature 25 connects the test wiper 32 tothis circuit at a point midway between the switching relay and the ma et. ,The operation now depends upon w ether the test contact 36 with which the test wiper 32 1s in engagement is grounded or not grounduis ed. .If the trunk line shown is busy, the test contact 36 will be'grounded, the switching relay 19 will be short-circuited, and the stepping magnet 2O will beoperated intermit- 120 tently, due to the fact that it interrupts its own circuit, to advance the switch wipers 'y l'step in search of an idle trunk line. Thisoperation is well understood, and it may 'i subscriber removes his receiver .and energizes the line relay 18, the trunkline upon Vwhich the wipers ofthe line switch `are standingis idle. Under these circumstances there will be no ground potential on test con- V130 tact 36 and no rotation of the switch will take place, but instead the switchin relay 19 is energized as soon as its circuitfis completed. On attracting its armature 23, the switching relay disconnects the test wiper 32 from armature 25 of the line relay and connects it instead to its own lower terminal, the ground potential which is thus placed upon the test contact 36 being cifective to render the trunk line busy to other calls. In addition to the foregoing, relay 19 prepares a circuit for the meter Z at armature 22, and at armatures 21 and 24 disconnects the line conductors 12 and 13 from the line relay 18 and from ground, respectively, and extends them by way of wipers and 33, bank contacts 34 and 37, conductors 40 and 42, and armatures 62 and 65 of relay 53 to the upper and lower winding of the line relay 50in the relay group D.

When the calling line i.; extended to the line relay 50 as previously explained, this relay is energized and at armature 55 closes a circuit for the slow-acting release relay 51.

l ground tothe release trunk conductor 41 at armature 56, thereby closingv a holding circuit for the line switch C, which extends by way of the said conductor 41, test contact 36, test wiper 32, armature 23 and its working contacts, winding of the switching relay 19, and the Winding of the stepping magnet 20 to battery. This holding circuit is vestablished before the slow-acting line relay 18 has had time to deenergize, and is effective to retain the line switch C in operated position `throughout the connection. It will' be observed that a ground potential is also placed on the private normal conductor 14 in order to render the calling line busy to incoming calls'according to the well-known practice. The electropolarized relay 17 at this time has its lower winding energized by the ground on conductor 41, while its upper winding is in series with the line relay 50. Relay 17 is so adjusted that it will not operate except from the cumulative eil'ect of both of its windings, and since the windings are now in opposition the relay remains inoperative.

@onf/Lecting idle'clz'rector 150 trunk Returning now to the relay group D, when relay 51 is energized as before described, it removes ground from the test contact 101 at armature 59, and at armature 57 closes a circuit for the starting relay 86 of the finder switch F as follows: from the grounded con- -ductor 41 by way of armature 57 and its Upon energizing, relay 51 connects of the starting relay 86 is completed, the said relay is energized and at armature 114 completes a circuit for the switching rela 85 in series with the stepping magnet 89, whi e at armature 113 the test wiper 91 is connected to the above circuit at a point between the winding of the switching relay and the interrupter contact of the stepping magnet. If the finder is not already in engagement with the set of bank contacts associated with the trunk in use, it will now commence to rotate, but on the assumption that the wipers are in the position shown in the drawing, the test wiper 91 will findr no ground potential on test contact 101, the normal ground connection to this particular test contact having been removed by the energization of relay 51, and no rotation of the switch will take place. The switching relay 85, however, is immediately energized and at armature 108 completes a locking circuit for itself which extends from ground by way of armature 60 of relay 51, holding conductor 77, bank contact 102, wiper 92, armature 108 and its working contact, the winding of switching relay 85, and the winding of stepping magnet 89 to battery. At the same time that the foregoing circuit is established, ground is placed on the test wiper 91 at armature 107, thereby closing a circuit which extends by way of the said test wiper 91, test contact I101, armature 59 and its working contact, and the winding of relay 52 to battery. The closure of this circuit renders the trunk line in use busy to other finder' switches by grounding test contact 101, and also energizes relay 52, which takes ground off the start wire 78 at armature 61. As a further result of the energization of relay 85, the starting wire is disconnected from the starting relay 86 of the finder switch F, and when the starting relay deenergizes is transferred by way of conductor 78 to the starting relay of the next finder switch.

As a further result of the energization of switching relay 85, a bridge is closed across the trunk conductors 82 and 83 extending'to the selector E1, Fig. 2, which may be traced from the upper trunk conductor 82 by way of contacts of relays 54 and 53, conductor 80, bank contact 104, wiper 94, armature 110 and itswork'ing contact, conductor 137, winding of polar relay 375, Fig. 8, resting contact of armature 374 and the said armature, conductor 136, resting contact of armature 120 and the said armature, working contact of armature 122 and said armature, wiper 93, bank contact 103, conductor 79, and the contacts of relays 53 and 54 to conductor 83. By the closure of the foregoing'bridge, or loop, the line relay 400 of the first selector El is energized and completes a circuit for the slow-acting release relay 401. Upon energizing, relay 401 grounds the release trunk conductor 41 at armature 410, and at arma-to the lower heavy talking conductorl 'by means of a smallcondenser, by means of ture 408 pares a circuitfor the vertical magnet 40g. The polar relay 375 is energized in series with the line relay 400 of the selector E1, and thedirection of current ilow is such. that the armature of the polar relay is operated to close a circuit for relay ,378. Upon energizing, rela 378 completes a locking circuit for itsel which extends from ground at the relay group D by way of armature 60, conductor 77, bank contact 102, wiper 92, armature 109 and its 'workingcontact armature 119 and its resting contact, conduct or 135, armature 384 and its resting contact, armature 388'and its working contact, and the winding of relay 378 to battery. Relay 378 also removes the short-circuit from resistance r' at armature 387 and at armature 390 prepares a locking circuit for, relays 376 and 360.

`A branch of the grounded conductor 135l may be traced from junction point 125 by way of the holding conductor 133 toFig. 6, where the release relay 142 of the master digit controller M1 is now energized. Relay 142 removes ground from the releasing conductor' 160 at armature 148at amature 159 separates conductors 398 and 399, and at armature 147 connects up the stepping magnet 163 of the time limit switch M1; This stepping magnet is now intermittently operated under the control of the timer cam T, which makes about one revolution every 5 seconds or more. The operation o f this time limit switch will be neglected for the time being, and itsfunction will be explained fully subsequent to the explanation of the regular circuit connection. It will be noticed also that the slow-acting relay 88 of. the finder switch F is energized from the grounded holding conductor 77, and that this relay causes the energization of relay 124. The operation of these relays, however, is lof no effect at the present time. l

Still another result of the energization of the switching relay 85 of the iinder switch F,

is the preparationof an yimpulsing circuitfor operating the registers of the director. This circuit may be traced from ground by way of armature of relay 50 and its resting contact (the circuit is now open at this point due to the energization of relay 50), working contact of armature 58 and the said 'armature, conductor 75, bank contact 100, wiper 90, armature 106 and'its working contact, Farmature 1 17 and its resting contact, conductor '134, winding of low resistance slowacting, relay 140, lwiper 157 of the master digit controller M1, `armature 151 and its v resting contact, winding of the stepping magnet 155 of the A impulse register M2, and the low resistance secondary winding of the tone transformer Q to battery. At the relay M group Dt-he above traced circuit is Connected vwhich anfal/ldible signal known as the dial tone is transmitted to the calling subscriber. .Setting the A mpwke register Bein advised by the signal thus transmitted to. im that the exchange vequipment is ready for operation, the calling subscriber will now proceed to operate the dial of his calling 'device in accordance with the three significant letters and the four digits in the number ofthe called station. We will assume that" this member is CARlton 2345.

-When the dial is operated in accordance withY the letter C, four/interruptions are producedV in the calling subscribers line circuit` in the 'well-known manner, and theline relay 50 of the relay group D is accordingly deenergized `four times. At each deenergization relay 50 transmits an impulse of current over the previously traced impulsing circuit through the stepping magnet 155 of the A impulse switch .M2 and the stepping magnet is operated to four impulses is being received. At `armature 144 relay closes a circuit for the slowcloses a circuit for the release magnet '164 of the time limit control switch M3. This acting relay l141, and at armature'145 it latter function is mentioned ink passing in order that it may be understoodthat in the ordinary operation ofthe system this switch.

is released before it canperform any of'its functions. At the end ofthe series of im- -pulses the slow-acting relay 140 d'eenergizes and breaks the circuit of slow-acting relay 141. During the interval between the deenergization of relay 140 and the deenergization of relay 141 an impulse of current is 'transmitted from ground by way of armature 144 and its resting contact, armature 1 461and its working contact, and the winding of the stepf ping magnet.153 ofthe master digit control switch M1 to battery. Stepping magnet 153 is accordingly actuated to advance the wiper 157 to its second position. A branch of the circuit of magnet 153 may be traced through the windingvof relay 143 to battery, which relay, upon energizing, establishes a lock--4k ing circuit for itself at-armature 150. At armature 151 relay 143'disconnects the impulsing circuit from the stepping magnet 155 `and transfers it by way of wiper 170 and conductor 176 to the Strowger switch H1, Fig. 7, andat armature 149 extends the grounded holding conductor 133 by way of wiper 171 and conductor 17 5 to relay 200 of switch H1. Relay 200 1s aerdingly energized and at arf `aul mature 204 opens the circuit of the release magnet 210.

Settingihe B a/nd C impulse registers When the calling subscriber dials the next letter of the number, or the letter A, two interruptions are produced inthe line circuit, and the line relay deenergizes twice, thus transmitting two impulses of current over the previously traced impulsing circuit to the vertical magnet 21,4 of the switch H1. The impulses come in over conductor 176 and follow a path which extends by way of off normal springs 211 and 213, winding of the slow-acting series relay 201, and the winding of the vertical magnet 214 to battery. By the operation of the vertical magnet wipers 220 to 223,-inclusive, are raised two steps to a position adjacent the second level of bank contacts. Series relay 201 is energized at the same time as the vertical magnet 214, and maintains its armature 205 attracted in order to preserve the continuity of the impulsing circuit notwithstanding the-shifting of the off-normal springs, which occurs on the rst vertical step. At the end of the vertical movement of the switch relay 201 retracts its armature and transfers the impulsing circuit to the rotary magnet 215.

During the transmission of the `second series of impulses the slow-acting series relay 140, Fig. 6, is energized the same as it -was during the transmission of the rst series, and by cooperation with relay 141 transmits another impulse of current to the stepping magnet 153 of the master digit control switch M1. Wiper 157 is thus advanced to its third position.

The calling subscriber may now .dial the third letter R, whereupon the line relay 50 is again caused to deenergize twice, and

transmit another series of two impulses over the impulsing circuit to the switch H1.

Now, however, these impulses traverse the winding of the rotary magnet'21'5, and the switch wipers 220 to 223, inclusive, are rotated until they come to rest in engagement Y, with the second set of contacts in the second level. The -slowacting series relay 202 is energized during the rotary movement of the switch and closes a circuit for relay 203, which upon energizing, establishes a locking circuit for itself at armature 207.

Immediately following the transmission of the third series of impulses the stepping magnet 153 of the master digit control switch M1 is operated the same as before to advance the wiper 157 to its fourth position. In passin from its third to fourth position, wiper 15 transfers the impulsing circuit to the stepping magnet 184 of the thousands register switch M4.

Sending the first oice code digit The calling subscriber will Jnow, of course,

which has been selected by the dialling of ers the first three letters in the calledl subscri number. When the relay 203 in the 'switch H1 is energized at the beginning of therotary movement of the switch, it closes a circuit over conductor 231 for the relay 379, Fig. 8. Upon energizing, relay 379 short-circuits the polar relay 375 at armature 386. At the end of the rotary movement of switch H1, when the slow-acting relay 202 falls back, it places ground on conductor 230 by way of armatures 206 and 208. Conductor 230 extends to the sequence switch S2, Fig. 9, where it is connected to the home or normal position contact of wiper 318, and to the first, second, third and fourth position contacts of wiper 317. It follows, therefore, that when conductor 230 is grounded a circuit will be completed through wiper 318 and through the stepping magnet 321 of the sequence switch S2 to battery, and magnet 321 is accordingly operated to advance all the wipers of the sequence switch to first position. The operation will be understood fully if it is recalled that a switch of this type advances the wipers when its armature is retracted. Thusl on energizing, magnet 321 attracts its armature to engage another ratchet tooth, and at the same time breaks its ownv circuit. Ondeenergizing, the retraction of the armature under the tension of its spring drives the wipers into rst position, and the initial energizing circuit of magnet 321 is broken, by -wiper 318.

The code of the distant office in which the line of stat-ion A1 terminates is 34, as will be perceived from an inspection of Figs. 2 and 3, which show that the trunk line comprising conductors 541 and 542 is accessible from the fourth level of the third group of second selectors in the originatingoice. Accordingly, the second set of contacts in the second level of the fourth Strowger switch H1, which set of contacts is selected by the dialling of the letters CARv of the called number, is so cross connected at the I.D.F. as to cause the transmission of two series of impulses, the irst series comprising three interruptions and the second serles'comprising four interruptions. More in detail, terminal 257 is cross connected to bus-bar 3, terminal 256 is cross connected to bus-bar 4, while terminals 255 and 254 are cross connected to bus-bars 271 and 270, respectively. These cross connections will cause the required series of impulses -to be transmitted by the sending switch S1, as will be understood shortly.

rives first position, it places ground on the" No. 3 bank contacty associated with the stop" e cuit Vbeing tracable as follows:

wiper 364 of the sending switch S1 the cir- Girounded wiper 319 in first ngsition, conductor 224, wiper 220 of switch 1 and bank contact engaged thereby, terminal 257 on the I.D.F.,

a jumper, bus-bar 3, and conductor 243 to the No. 3 contact in the lower bank of switch` S1. The grounding of this contact determines that there will'be three interruptions c in the first series transmitted. Wiper 317 on arriving in' first position, closes a circuit for the impulsing relay- 362 of the sending switch S1 as follows: from the grounded conductor 230, by way of wiper 317 in first position, conductor 340, resting contact of armature 368 and the said armature, winding of relay 362 and the machine interrupter I to battery. The interru ter I is continuously driven, and consists ci) any suitable cam arrangement for intermittently connecting batterrupter tery to the relays such asrelay 362, at thev rate of about ten times per second. When its circuit is closed, therefore, or shortly afterwards, depending on the position of the inrelay ,362 is energized and opens the impulsing contact' 374, this operation being of no effect, however, due to the yfact that the contact at armature 374 is short-circuited at armature 371 of relay 361. Relay 3 62 also closes a circuit for steppingmagnet 365 at amature 373, and the said magnet is .ener-'- gized. When the circuit of rela-y 362 is broken by the interrupter I an instant later the said relayalls back, again closes its interrupter contact, and breaks the circuit of the stepping magnet 365, which thereuponretracts 1ts armature and advances the wipers 363 and 364 one step. A circuit is now completed for relay 361 by means of wiper 363, and this relay, upon energizing, removes the .short-circuit from around theimpulsing contact" 374 at armature 371, and at armature 372 closes a circuit over conductor 341 for thev ste ping magnet 321 of the sequence switch 1. Magnet 321 is accordingly energized, but without aiecting the position of its wipers, which as previously explained, .are

advanced upon the ldeenergization of the stepping magnet. vThe second time that the v Acircuit of relay 362 is closed by the -interrupter I, the said relay'closes the circuit of the stepping magnet 36,5 as before, and also, since relay 361 is now energized, at armature ,374- it breaks the circuit of the line relay 400 `of the selector E1. When the circuit of relay I362 is broken by the interrupter, it deenergizes and breaks the circuit `ofthe stepping magnet 365, which retracts its armature and advances wipers 363 and 364 one more step, thus bringing the stop wiper 364 into en'- gagement with the number 1l contact in its bank. It will be seen that they sending switch S1 is caused to make an initial or f alse step before it actually begins `transmitting impulses, and this, 1t ma be stated, is done in order to 'insure that t e first impulse transmitted'will be of the standard length. `The energiz'ations and deenergizations .of the relay 362 continue in quick succession under the control of the interru ter I. After the second deenergi'zation, w ich terminate the first interruption, wi er 364 is advanced. into engagement with lts No. 1 contact, as stated, after the third'deenergization wiper 364 is advanced into engagement with its No. 2

contact, and after the fourth deenergization 'the said wiper is advanced into engagement with its No. 3 contact. The required number of interruptions have now been produced in the circuit-of the line relay 400 of the selector E1. As previously explained, the No. 3 contact inthe lower bank of send-in switch S1 is grounded, and, when the stop wiper 364 -comes into engagementfwith this'contact a circuit is completed for the stop rela 360 and relay 376'in arallel. Upon energizing,

lrelay 376 closes'a ocking'circuit foritself and relay 360 which extends from ground by way of armature 390 and'its working contact, resting contact of armature 385 and said armature; resting. contactof armature 394- and said armature, armature 382- and its workin contact, and the windingsof relays 376 an 360 in parallelto battery. 'Relay 376 also removes the short-circuit rom'the polar relay 375 at amature 381. c Relay 360, on energizing, opens the circuit of the impulsing. relay 362 at armature368, to stop the transmissionof impulses, and in addition, at armature 366, closes an auto f matic stepping circuit for magnet 365, which of switch H1 to wiperv221, which results in the grounding of the No. 4 contact in the bank of the ,stop wiper 364. The ground potential on said contact is established by way of the grounded .wiper 319 in second position, conductor 225, wiper- 221, terminal 256, a

yjumper, No. 4 bus-bar, and conductor 244 to the No. 4 bank contact associated with the stop wiper 364.

' Although the sending switch S1 has been n returned to normal, the stop relay 360 and the -rom first to second position is the transfer Aof the ground connection from the wiperv 220 ICQ) relay 376 still remain locked up, due to the previously described locking circuit. The latter relay, it should be noted, removes the short-circuit from the polar relay 375 at armature 381.

Operating the first selector The operation of the selector E1 responsive to the first series of impulses of the code may now be considered. As explained-before, the circuit of the line relay 400 is interrupted three tim'es at contact 374 of the impulsing relay 362, and the said line relay accordingly deenergizes three times and at armature 418 transmits three impulses to the vertical magnet 407. In response to these impulses the vertical magnet operates to raise the selector shaft step by step until the wipers 420, 421, and 422 reach a position opposite the third level of bank contacts. Slow-acting series relay 402 is energized in serieswitli the vertical magnet 407, maintains its armature 409 attracted throughout the vertical movement of the switch, and as soon as off normal springs 413 close on the first vertical step, completes a circuit for the stepping relay 403. Upon energizing, relay 403 closes a locking circuit for itself at armature 411 and at armature 412 prepares a circuit for the rotary magnet 405. At the end of the vertical movement of the switch relay 402 falls back and at the resting contact of its arma` ture 409 completes the rotary magnet circuit. The rotary magnet 405 is, therefore, energized and advances the wipers into engagementwith the first set of contacts in the level opposite which they were raised. At the same time the rotary magnet breaks the locking circuit of the stepping relay 403, and the stepping relay deenergizes and breaks the circuit of the rotary magnet at armature 412, whereupon the rotary magnet deenergizes also and again closes its interrupter contact. The operation now depends on whether the test contact engaged by the test wiper 421 is grounded or not.` If the first trunk line terminating in the third level is busy, the test contact associated with such trunk line will have a ground potential on it, the switching relay 404 will be short-circuited, and the stepping relay 403 will be again energized. Relay 403 accordingly again closes the rotary ma gnet circuit which operates to advance the switch wipers another step into engagement with the contacts associated with the next trunk line. These operations, involving alternate energizations of the rotary magnet andthe stepping relay, continue until the wipers reach a set of contacts in which is terminated an idle trunk line. lIt will be assumed that the first idle trunk line encountered is the one' comprising conductors 440, 441 and442, and extending to the second selector E?.

When the test'wiper 421 is brought to rest in engagement with test contact 424, it finds no ground potential and it follows, therefore, that on the retraction of the armature of the rotary magnet 405, the stepping relay 403 will not be energized. Instead, the switching relay 404, which .for the time being h as been short-circuited, is energizedA in series with relay 403, the high resistance of relay 404 preventing the latter relay from operating. Onenergizing, relay v404 connects the release trunk conductor 41 to the test wiper 421, thereby grounding test contact 424 and making the selected trunk line busy. In addition, relay 404 removes ground from the line relay armature at its armature 414, and at armatures 415 and 417 relay 404 disconnects the incoming trunk conductors 82 and 83 from the windings of the line relay 400 and extends them by way of wipers 420 and 422, bank contacts 423 and 425, trunk conductors 440 and 442, and armatures 456 and 455 to the windings of the line relay 450 of the second selector E2. Line relay 450 is accordingly energized 'and closes a circuit for the slow-acting release relay 451. At its lowerarmature relay 451 prepares the switch for its vertical operation in the usual manner, and at its upper armature connects ground to the release trunk conductor 441, thus establishing a holding circuit which extends by way of conductor 441, test contact 424, test wiper 421, and armature 416 and its working contacts to the release trunk conductor 41. The holding circuit including conductors 441 and 41, except that it is grounded further along in the connection, will be used later on to retain the switches' in rolved in the connection in operated p0- sition.

Sending the second oyjce code digit It will be observed that the trunk conductors 440 and 442 extending to the second selector E2 are reversed or transposed, and it follows, therefore, that as soon as the'connection is extended to this selector, thedirection of current flow Iin the trunk conductors 82 and 83 and in the loop impulsing circuit comprising conductors 136 and 137 will be reversed also, resultin in the operation of the polar relay 375. elay 375 now operates its armature inthe proper direction to close the circuit of relay 377, which prepares a locking circuit for itself at armature 383, and .breaks the locking circuit of relay 378 at armature 384. The latter relay accordingly falls back, whereupon the previously prepared locking circuit for relay 383 is completed at armature 389. When relay 377 energizes, at its armature 385 it removes ground from armature 382 of relay 376, and since ground is not reapplied to armature 382 until relay 378 has had time to fall back, the locking circuit for relays 376 and 360 is broken long enough to permit the former relay to retract its armature 382,

which permanently o ens the locking c1rcu1t and dpermitspboth re ays to remain deener- The foregoing is descriptive of the operation provided the sending switch S1 reaches its normal position before the polar relay 375 is operated. It may happen, however, as for example when a short series of 1mpulses is transmitted, or when no extended trunk selecting operation of the selector 1s required, that the polar relay is operated first, in which case the relays 360 and 376 w1ll Vnot be unlocked by the operation of the polar relay and relay 377, but will be held up unt-1l the sending switch returns to normal. This is taken care of by relay 395. Assuming that the sending switch S1 is still rotating when the polar relay and relay 377 are operated, the relay 361 will be in energized position, and when relay 377 opens the locking c1r cuit of relays 360 and 376 at armature 385, these relays will be held up over a new circuit extending from ground by way of armature 370 of relay 361, armature 393 and its resting contact, -winding of relay 395, armature 382 and its Working contact, and the windings of relays 360 and 376 in parallel to battery. Relay 395 is at once energized and at armature 394 opens the previous locking circuit. Then when the sending sw1tch eventually arrives at its normal position, the deenergization of relay 361 opens the circuit of relays 395, 360, and 376 at armature 370, and all these relays deenergize, the original locking circuit being broken at armature 382 before it can be reestablished at armature The second series of code impulses is now transmitted similar to the manner in which the first series was transmitted. When the stop relay 360 falls back it completes the circuit for the impulsing relay at armature 368, and this relay is accordingly operated intermittently by the interrupter I to advance the wipers of the sending switch step by step through the medium of the stepping magnet 365. At the first step of the switch, relay 361 is energized, closes the circuit of the stepping magnet 321 of the sequence switch S2 at armature 372, and at armature 371 removes lthe shunt from around the impulsing contact 374, which permits relay 362 to interrupt the circuit of the line relay 450 of the second selector E2 each time it closes the circuit of the stepping magnet 365. Thus four interruptions will be produced in the circuit of said line relay by the time the stop wiper 364 arrives at the No. 4 contact in its bank. The No. 4 contact is now grounded, as previously explained, and relays 360 and 376 are accordingly again energized, a locking circuit being established at armature 382 as before. Relay 360 also breaks the circuit of the impulsing relay 362 at its armature 368, and at armature 366 closes the automatic rotary circuit for the stepping magnet 365, by means of which the sending switch is advanced to normal. Relay 361 then falls back and at armature 372 breaks the circuit of the magnet 321 of sequence switch S2, whereupon the sequence switch wipers are advanced to third position.

Skipping the third and fourth oce code digits The operation of the second selector E2 responsive to the second series of code impulses and the subsequent operations which result in the extension of the connection to the repeater R, Fig. 3, will be deferred a while to permit the explanation of operations in the director which result from the advance .of the sequence switch to third position. It may be explained that the provision of four wipers on the Strowger switches, such as the -switch H1, and the circuit arrangement by which these wipers are grounded successively by the wiper 319 of the sequence -switch renders it possible to transmit codes comprising a maximum of four series of v impulses, which is thought to be sufficient in most cases, al-

though additional series of impulses can be provided for by adding more wipers and banks to the Strowger switches. In the present case, since the code consists of onlytwo series of impulses, the sequence switch must be advanced automatically through its third and fourth positions, in order to have the director ready for the transmission of the impulses corresponding to the thousandsdigit as soon as the second selector E2 and the secondary line switch C1 have completed their operations. This is accomplished by connecting terminals 255 and 254 to the special bus-bars 271 and 270, respectively, instead of to any of the upper bus-bars which are associated with the bank of the sending switch. With this explanation, it will be readily understood that when the sequence switch arrives in third position, a circuit will be completed for the stepping magnet 321 as follows: grounded wiper 319 is third position, conductor 226, wiper 222, terminal 255, a jumper connecting said terminal with bus-bar 271, conductor 238, wiper 318 in third position, the interrupter contact of magnet 321, and through the winding of said magnet to battery. The completion of this circuit causes a momentary energization of magnet 321 to advance the sequence switch wipers to fourth position, whereupon a similar circuit is completed by way of the grounded wiper 319 in fourth position, conductor 227, wiper 223, terminal 254, a jumper connecting said terminal with bus-bar 270, conductor 239, wiper 318 in fourth position, and thence through the interrupter contact and stepping magnet to battery. The stepping magnet is accordingly again energized momentarily to adtions of the stepping magnet 321 take place very rapidly, and thepsequence switch is advanced through its third and fourth positions in a small fraction of a second.

Operating the second selector and the outgoing secondary Zine switch The operation of the second selector E2, Fig. 2, responsive to the second series of impulses of the oflice code may now be considered. As before explained, four interruptions are produced in the circuit of the line relay 450, and this relay is accordingly deenergized momentarily four times to raise the wipers 460, 461, and 462 opposite the fourth level by means of the vertical magnet 457. In view of the` explanation of the operation of the first selector E1 which has already been given, it will be unnecessary to explain in detail how the second selector E2 operates; but it will be suflicient to say that after the wipers are raised to the fourth level they are automatically rotated by the rotary magnet 458 until an idle trunk line is reached. Assuming that the first idle trunk line encountered is the one comprising conductors 500, 501, and 502 extending to the secondary rotary line switch C1, Fig. 3, when the selector wipers arrive at bank cont-acts 463, 464, and 465 the rotation of the switch will cease and the switching relay 454 is energized. At its armature 459 the switching relay 454 connects the release trunk conductor 441 to the test wiper 461 in order to make the selected trunk line busy; and at its armatures 456 and 45-5 the switching relay 454 disconnects the trunk conductors 440 and 442 from the windings of the line relay 450, and extends them by way of wipers 460 and 462, bank contacts 463 and 465, trunk conductors 500 and 502, and armatures 508 and 511 of relay 503 of the line switch C1 to the winding of the line relay 504 and to ground, respeetively.

When the connection is extended to the line switch C1 as previously described, the line relay 504 is energized and at armature 507 connects ground to the release trunk conductor 501. This operation serves to maintain a local ground on the test contact 464 after the slow-acting relay 451 of the selector E2 has fallen back. The line relay 504 also closes a circuit for the switching relay 503 in series with the stepping magnet 512 at armature 506, while at armature 505 it connects the test wiper 521 to the circuit of the switching relay at a point between said relay and the interrupter Contact of the stepping magnet. If the wipers of the line switch are standing on a busy trunk line, the switch now operates in the well-known manner to advance its wipers through the medium of the stepping magnet 512 to an idle trunk line,

but if thel trunk line upon which the wipers are standing is idle, as will be assumed to be the case, no rotation of the switch will A'take place. Instead, the switching relay 503 is immediately energized, and at its armatures 509 and 5l() connects the incoming release trunk conductor 501 with the test wiper 521 in order to make the selected trunk line busy by grounding the test contact 524. At the same time, of course, the test wiper is disconnected from the test circuit at the resting contact of armature 510. In addition to the foregoing, at arn'iatures 508 and 511 the switching relay disconnects the incoming trunk conductors 500 and .502 from .the line relay 504 and from ground, respectively, and extends them by way of wipers 520 and 522, bank contacts 523 and 525, trunk conductors 526 and 528, left hand windings of the repeating coil in the repeater R, and contact springs of the reversing relay 534 to the lower and upper windings of the line relay 535 of the said repeater, respectively.

'hen the connection is extended to the repeater R as explained in the foregoing, the line relay 535 is energized and completes a circuit for the slow-acting release relay 536 at armature 538. On energizing, relay 536 places ground on the release trunk conductor 527 at armature 540, and thus establishes a holding circuit which includes release trunk conductors 527, 501, 441, and 41. This holdingcircuit is still grounded at armature 56 of relay 51 in the relay group D, Fig. 1,but the ground at this point is only temporary as will appear subsequently, and after the use of the director is dispensed with the ground at the repeater R will serve to maintain all of the various switches so far considered in operated position. It is noted at this time that the right hand winding of the shunt iield relay 533 is energized from the grounded release trunk conductor 527 at the repeater R. Owing to the fact, however, that the right hand core of relay 533 has a complete magnetic circuit including the left hand core and the two heel pieces, the flux is shunted away from armature 537 and this armature remains unaffected.

When the line relay 535 of the repeater R is energized, it also connects the right hand windings of the repeating coil in bridge of the trunk conductors 541 and-542 at armature The trunk line comprising conductors 541 and 542 extends to the distant office in which the wanted station A1 is located, and there terminates in the incoming third selector E, .F ig. 4. Upon the closure of the bridge across the trunk line at the repeater R in the originating ndice, the line relay 600 of the third selector E3 is energized and completes a circuit for the slow-acting release relay 601, which accordingly operates and prepares the switch for its vertical movement in the usual manner. The left hand

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