US1636648A - System - Google Patents

Description

1,636,648 July 19, 1927. A. J RAY A MULTIOFFCE AUTOMATIC TELEPHONE SYSTEM Original Filed Fb. -2, 1923 4 Sheets-Shut 1 A. J. RAY

MULTIOFFICE AUTOMATIC TELEPHONE SYSTEM July 19 1927.

' Inval-Zar ihur J. Bag

July 19, 1927.

A. J.' mwr MULTIOFFICE AUTOMATIC ,TIELEPHO'NE' SYSTEM vJuly 19, 1927.

A. J. RAY

MuLTxoFFIcE AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 2. 192s rams-sheet 4 Patented July 19, 1927.

UNITED STATES 1,63G,liati PATENT OFFICE.

ARTHUR RAY, OF CHICAGO, ILLINOIS, ASSIGNGR T AUTOMATIC ELECTRIC, INC., OF

i CHICAGO, ILLINOIS, A CORGRATION OF DELAWARE.

MULTIOFFICE AUTOMATIC TELEPHONE SYSTEM.

Application led February 2, 1923, Serial N-o. 616,476. Renewed December 13, 1926.

The pros-ent invention relates in general to automatic telephone systems oit the mult1- oiiice type, hut is more particularly concernedwwith systems of this character in which the main ofces oi" the system have smaller evcluuujes subsidiary to them, the latter hen g commonly knowii as sub or satellite exchanges; and the object of the iuvcntion to provide a new andimproved method ot completing` connections between adjacent sub `exchanges as well as local sub excluu` re connections, the sub-exchange to mainexchangc and the main-exchange to sul'rcxchangetrunk lines not being used for such connections, the whole to he accomplished wit-hout departing from orv any way modifying the standard numbering arrangement.

lil Patent No. 1,542,958, i=sued June 23, i925. lo A J. Ray, a switching selector' repeater is illustrated and described which 1s capal'fle of completing local sub-exchange connections without utilizing sub to inaniexchange or main-exchange to sub-exchange trunk lines. A switching selector repeater, as described in the above nicntihned application, ordinarily operates in a sub oiiice in which at least the vfirst two digits ot all numbers are Vthe same` but when it is required to suf'ii'ch trom the hanls oi the switching selector rei'ieater to another sub ottico, the snf'itchiiug|` selector repeater may be required to switch on two entirely diiierent combina,- tions ot digi Vifhen this is the case it is necessary te inovide means to prevent coinbinations ot digits out ot the switching coinbin, ns from causing the switching selector repeater to cut olf the main exchange trunk. For cxaniiple, it the local switching 'nation is Sile, while the switching` comn lor an adjacent `sub exchange is i the switching selector repeater must not switch on 913 and 761i, as these combina tions represent trunk connections through the main o'liice.

More speciiically.,V one oi' the principal ob- `iecls el the present invention is to provide the means above referred to.y the said means preventing the `swit hing ot the switching selector repeater on any combination of tig ures except those designating the local sub exchange or an adjacent sub exchange.

r'lherc are other objects of the invention not non' specifically mentioned which, to-

gether with those referred to above, will he described more `fully hereinafter.

Although the invention is applicable to systems of different sizes, it will be assumed -tor convenience that we are dealing with a system that .has an ultimate capacity. of 100,000 lines. It will be assumed further that there arc ar number of main oflices, 0i' 10,000 lines each, and that certain ot these oliices each have an associated sub exchange ot 100 lines. It will also be assumed that the geographical location of certain ci'l these sub exchanges is such that it is desirable to complete calls trom one to the other directly, rather than by the customary routing Afrom first sub to first exchange, to second exchange to second sub. In a 100,000 line system the lirft digit dialed determines to which'group oi 10,000 lines the call is The second digit determines to which group ot 1,000, while the third digit determines the particular group of 100 lines for which the call is intended. New since each sub exchange has only 100 lines in it and the third digit dialed picks out the hundreds group, we must have in the sub o'llices switching selector repeaters capable of switching on the third digit.

The general trunking arrangement is not novel and consequently is not shown, the. drawings showing only such ot the equipment as will be used to explain the novel features ol the invention. Figs. l, 2, 3, and el show by means of the usual circuit diagram the apparatus required to enable the subscriber at substation A l) in a sub exchange to extend local calls, to extend acall to station A in the lmain exchange, or to extend .calls to other sub exchanges. Fig. 1l, more speciiically, shows the arrangement of the wiring in the banks ot' the switchingl selector repeater' in the sub exchange.

Fig. 5 is a layout showing how sheets l. to 4l, inclusive, should be joined together.

The substation A shown in Fig. 1 and the substation A', Fig. 3, are ordinary automatic substations. Suhstation A is one of a. hundred similar substations that terminate in a sub exchange. Each substation line may terminate at the sub exchange in a rotary line` switch of the usual type, the line switch in which the line of substation A terminates being indicated by the reference character C. The line switch in which substation A lilo terminates is also a rotary line switch and is indicated by the reference character C', Fig. 3. The line switches in the sub eX- change have common access to a group of switching selectorrepeaters, one ot which is shown in Fig. 2 and is indicated bythe reference character D.

The switchingy selector repeater D is a vertical and rotary switch o't' the usual l" Strowger type so tar as mechanical construction is concerned, having special relays and circuits added, however, that enable it to Jfunction as a repeater. In this case the selector functions of the switch D are those lf of a third selector for it operates on the third digit to pick out an idle connector, or

a repeater, depending upon whe-ther the call is for the local or adjacent sub exchange'.

rilhere is a secondary line switch suoli as '3Q the line switch indicated by the PGGI'GHCC character C3, Fig. 1, associated with each switching selector repeater, whose functionis to pick out an idle trunk line leading to the mam exchange tor the purpose of completing the call to main'in case the call is to go there or to any other `main otlice, or in tact anywhere except to the local sub exchange or the adjacent sub exchange. One ot the trunk lines to the main exchange to which 3 the secondary line switch G3 has access is 4o sinned to be iilar to the selector E.

The connector switch denoted by the reterence character H is assumed to be ot the well known vertical and rotary type and for that reason the circuit is shown only in pa rt.

rlie bank contacts shown. in Fig. /1 yare accessible to the switching selector repeater shown in Fig. The upper and lowcrcontarts ot the lower bank, as well as the lower contacts et the upper bank, are innltipled 5U between switches in the usualv manner. 'The upper contacts ot the upper bank are not multipled, and they, together with the ren lays shown at the right, are associated only wit-h the switching selector repeater having access to this particular bank.

'lfo complete the general description of the system it may be said that calls from a main exchange to a sub exchange may be co1n pletcd by way of agroiip ot trunks that ter- GU min'ate in'inconiing connectors lat the sub exchange.

The .foregoing paragraphs will serve to give-a general understanding, of the char# acter of the apparatus andthe system of l5 trunking which is employed. The system having been described in general, a detailed description will now be given of its operation, and for this purpose it will be assumed that the subscriber at substation A desires connection with a subscriber in the same sub exchange, whose telephone number is 91,4167.

Vilhcn the receiver is removed at the calling substation A a circuit is complet-ed over the conductors 11 and 12 for the line relay ot the line switch C. Upon energizing, relay 15 closes a circuit at its armature 2O which includes the winding of the switching relay 1/1 and the stepping magnet 16 in series, and at its armature 21 connects test wiper 26 to the above circuit at a point midway between the said switching relay and the stepping magnet. The operation now depends upon whether the trunk line with which the line switch wipers are associated is busy or idle. It the trunk line is busy there is a ground potential upon the test contact with which the test wiper 26 is in engagement, the switching relay 14 is short circuitcd and the stepping magnet 16, which interrupts its own circuit, is operated in the manner of a buzzer to advance the switch wipers in search of an idle trunk line. We may assume, however, in the present case that when the call/is initiated the trunk line upon which the wipers oit theline switch are standing is idle. `Under these circlnnstances when the line relay 15 is energized the switching relay 14 is not short circuitcd and the stepping magnet 16 is not operated because of the high resistance of said switching relay. The latter relay, however, is energized, grounds the test wiper 26 at armature 13, and at armatures 17 and 19 disconnects the. vline conductors 11 and 12 from the winding of relay 15 and ground, respectively, andV extends Vthem by way oi wlpers and 2, and bank contact-s 2S and 30, conductors 31 and 33, armatures 54 and 58 and their resting contacts, normally closed contacts ot the clectrtrpolarized reversing relay i4- to the upper and lower windings Vot the line relay 35 ol the switching selector repeater D. The line relay 35 immediately energizes and closes the circuit ot release relay 36 at armature 57. Release relay 36, upon energizing, closes at armature 61 a holding' circuitextending from. groundV at armature 61, conductor 32, test contactr29, test wiper 26, armature 18 and its working Contact, switching relay 14 and stepping magnet 16`to battery. It is understood that this circuit is established before the slow acting line relay 15 has had time todeenergize. By means of a ground potential on test contact v29 and its multiples, this holding circuit serves to render the switching selector repeater D busy to other line switches, and the busy potential also extends by way of private normal 13 to multiple test conf tacts in the banks ofthe connectors, thereby lia) lessees 411 to battery. This nfinding` is of high re sistance and few turns, and, therefore, can-V not operate the relay until it is assisted by current in the lower winding.

l.'"Vluen the line relay is energized a bridge is closed across the trunk line conductors which is effective in operating the line relay 119 et the secondary line switch The circuit `for relay 119 is as follows: troni `round through relay 110, resting; contact and armature 125, conductor 105, armature 93 and its workingcontact, eleventh ro tary step cam spring 53, operated by cam 0% and resting contact ot said spring, lower vinding of electro-polarized relay dll, impedance 38, resting contact andai-mature 66, conductor 101, armature 122 and its resting contaet, resistance common conductor 14:6, armature 145 and its resting); contact to battery. The line relay 110 will energize over this circuit, but the current that flows in the lower winding et relay ell opposes that in its upper winding and consequently it does not energize. Upon the energization oil? release relay 36 a. circuit wastraceable 'troni ground at armature (32, eleventh rotary step cam springv 49, operated bycam 94, and its resting; contact, conductor 102, relay 18, and stepping;` .magnet 117 to battery. `llVith relay 110 energized, it is seen that test wiper 132 is connected to the above circuit at a peint between the switching relay and the stepping magnet. These. circuit conditions are substantially the same as those that were descril'ied in connection with the operation et line switch (l, and it necessarily follows that the line switch C operates to select an idle trunk line to the main exchange. Aisshiningthat the trunk line comprising conductors 133 and 139 is the first one 'found idle, when the test 4wi per 132 arrives at test contact 13G the rotary movement ceases, no ground liieinfr found by test wiper 132, and the Switchingl relay 113 is energized. a result the conductors 101 and 105 are disconnected from common battery conductor 146 and thel winding; ot the line relay 110, respectively, and are extended by way of armatures 122 and 125 and their working contacts, armatures 129 and 126 and their worlrino; contacts, wipers 130 and 133, contacts 1311v and 137, trunlr conductors 138 and 139,

armatures 168 and 171 and their resting contacts to the upper and lower windings. re spectirely, et the line relay 151 ot the lirst select-or E in the main exchange. 'There being' a bridge across conduct- ors 101 and 105, asah'eady explained, the line relay 151 of the selector E energizes and operates the release .relay 152 in the usual manner therei by making the selector E ready for the usual vertical impulses.

`lleturnirngto a consideration ot the line fnritch C3 it may be said that when rel 113 enerfrized it brolre the original energin- 1 v' circuit oit line relay 119, but when armatuin 124 operated it opened the test circuit and closed a locking circuit tor the line rey 110 betere the said relay had time to .ene rnizo. The aforo-mentioned circuit e2;- tcnds rein the working contact and arma ture 1241, through armature 12T and its i Torlaing1 contact, and stepping' magnet 11?w to battery. Stepping magnet 11T, being; wound with itew turns and haring;v a stitl a: ment does not energize at this time. turther result et the energization ot swtch- 'irrorelay 113, armature 121 closes a. circuit that entends from grounded conductor 102 through relay 120 to battery. Relay 120 en.- ciggizes and places ground ou the test con-- tact 130 and its multiples in the banks ot other secondary switches, in order to malte the selected trunk busy, and at armature 1/10 it clr es a point in the circuit el relay letal- The Ariuiction et relay 1441 will be fully exlaiued at a later time.

i 'the calli line has been extended to the -switcln selector repeater D and a branch troni the said switch has been extended by way ot the secondary line switch G3 to the hrst selector lll in the main exchange. rlhe dial lone produced by the dial tone machine T. Fig'. 3, is now audible to the calling` subiber, it being placed on the trunlr by yirtue ot the lower windingo't the line relay 151 of selector E. 1We may now assume that the calling subscriber dials the first digit Sl oli the called number, as a result ot which nine interruptions are produced in the cir-- cuit ol` line relay 35 et switch l). .At cach interruption, the line relay 3.3 reeuerig'izcs and sends an impulse ot current through the rertical magnet 47 over the following circuit: from ground through armature o0 and its resting' Contact, armature 57 and its restinn; cmitactv1 armature 03 and its working* Contact, normally closed contacts controlled by arniature 09, slow-acting relay 410, and vertical magnet t7 to itery. 'lhe slow-- acting relay is energized in series with the vertical magnet and vretains its armature attracted during; the Vertical movement. The slow-acting` relay 3T is energized in parallel with the slow-acting relay 4-0. and the Vertical magnet, and it also retains its arma ture attracted during); the vertical movement. U pon the first upward step of the s ialft, the vertical eti'7 normal springs 51 and .52 come into Contact with their working; contacts. The operation ot the otl normal spring closes the circuit ot the vertical. oil3 normal relay 30 which energizes and at armature r1.9 .transfers the impulsing circuit so that it passes through the working contact ol arma-- l ture 69 and said armature, armature 74 and its working contact, and over the previously traced circuit to the vertical magnet 47. The' The deenergization of line relay not only brings about the operation of the verticalv magnet 47, but also produces interruptions in the bridge across conductors 101 and 105, at armature 93. As a result, the line relay 151 of the dist-ant .selector E is deenergized nine times and the wipers 172, 173, and 174 are raised opposite the ninth level of bank contacts. In brief, the line relay 35 functions in the same manner as the line relay of the well-known automatic ref peater to repeat the impulses to the line relay of the selector E. As a result, the switch D and the selector E are operated practically simultaneously. It will be noted that while the impulses are being repeated, the relay 37'is energized, and at its armature 66 closes the bridge acrossconductors 101 and 105 by way of a more direct path that ercludes relay 44 and impedance 38. This is the usual expedient made use `of to obtain tirst-class switch control.

The selector E, after raising its wipers to the ninthlerel, proceeds in theusual manner t-o select an idle trunk, and it may be assumed that the trunk line leading to second ,elector E is the one first found to be idle.

Returning to a consideration of the switching selector repeater D, it will be found that slow-acting relays 37 and 40 deenergize following the last vertical impulse. Relay 37, at armature 66, replaces the original bridge across conduct- ors 101 and 105, while relay transfers the impulsing circuit from its working cont-act to its resting contact. Springs 97 and 98 are .so placed on the switch that they are now in an operated position, on. account of the shaft having been raised. opposite the critical level 9. It may be stated here that a critical level is a level corresponding to the first digit of a switching combination. y

It is assumed that the calling subscriberv now dials thc second digit 1 of the desired number. In response to the interruption in the line thus produced, the lino relay 35 is deenergized once and, as before, repeats this impulse to the trunk line comprising conductors 138 and 139 leading to the main exchange. In response to this repeated impulse, selector E raises its wipers one step to a position opposite t-he first level of bank contacts and rotates them in search of an idle trunk line. It may be assumed that the trunk line leading to the selector E2 is the first to be found idle.

At the same time that relay 35 of switch D repeats the impulse to the main exchange,

it operates the rotary magnet 46 over the following circuit: from ground over the previously described impulsing c-ircuit to I `tary magnet receives one impulse over this circuit in multiple with slow relay 37 and, accordingly, steps the wipers 251-254, inclusive, into engagement with the first set of contacts in the ninth level. Relay 37 now Y deenergizes and completes a circuit for relay 43 as follows: from ground through the upper winding of relay 255, Fig. 4, bank contact 266, wiper 251, conductor 95, resting contact and armature 65, relay 43 to battery. Relay 43 will not energize at this time due to the high resistance of relay 255. The

latter relay, upon energizing, closes a locking circuit for its lower winding by way of grounded release trunk conductor 32 and armature 267. A further result of the energization of' relay 355 is the operation of armature 268, which removes ground from bank contact 269 and places direct'ground upon bank contact 266, whereupon relay `43 will become energized. Relay 43, when energized over the above circuit, closes a circuit traceable as follows: from ground over the previously traced circuit for relay 43, to working contact and armature 86, working contact and armature 70, armature 79 and its resting contact, release magnet 4.8 to battery. Release magnet 48 accordingly energizes and restores the switch shaft and wipers to normal. In order that the circuit of release magnet 48 and relay 43 may be maintained after the wiper 251 leaves bank contact 266, therrelease magnet, upon encrgizmg, locking circuit for itself and relay 43 as follows: from ground at the armature'of release magnet 48, working contact and armature 70, and over previously traced circuit to the release magnet 48, a branch circuit extends by way of armature 86 and its working contact to relay 43. When the shaft reaches its normal position, it forces off normal spring 52 away from its working Contact which opens the circuit of the off normal relay 39. Relay 39 deenergizes and at its armature 70 removes direct ground from the circuit of the release magnet 48 and, in so doing, it leaves the release magnet 48 and the lower winding of relay 42 connected in series over the following circuit: from ground at armature 84, lower winding of relay 42, armature 79 and its resting contact, and release magnet-'48 to battery. Owing to the relatively high resistance of the lower winding ofv relay 42, the release magnet 48 deenergizes while the relay 42 energizes and at armature 82 locks attracts its armature and closes a itself to grounded release trunk conductor 32 by nieans ot its upper winding. This is accomplished by so adjusting the relay ft2- ever, does not deenergize, because a locking` circuit has been closed through its upper winding.

Vlhe effect o1 the calling of the second digit has been to raise the wipers of the second selector E in the inain exchange to the first level, whereupon the connection was extended to the third selector E2. In the sub exchange the switch D rotated its wipers one step, and, upon its wiper 251 iinding a grounded Contact in the associated bank, operated the release inagnet 118, thereby causing the shaft and wipers to be returned to normal.

It may now be assumed that the calling subscriber dials the third digit a ot the called number' and, as a result, four iinpulses are repeated to the third selector in the inain exchange, which raises its wipers opposite the fourth level of bank contacts and rotates in search et an idle trunl: line. It will be assumed that the trunk line terniinating in bank contacts 197, 198, and 199 is the first to be found idle. Since this trunk line is reached by calling 914e, it. must necessarily7 give access to the sub exchange, accordingly, itleads to a repeater and trol-n there to an incoming connector located in the sub exchange.

lit the saine tin'ie tl at the switch D repeats the tour impulses to the selector E2, it inierates its vertical nia-guet 47 in the saine nianncr as it did when the lirst digit u' .i called. ln this case, the 'vertical niagnet causes the wipers to be raised opposite the 'fourth level ot banlr contacts. The vertical oli' normal springs close and coinplete the circuit ot oil' norinal .'elay 39 which energiaes as be'iiore. Upon energizing, itcoinpletes at arnfiature 72 the ifollowing circuit: troni ground at arn'iature 62, arniature Gil and its working contact, resting contact of eleventh rotary step cani spring` 50, arinature i' and its working Contact, resting contactand ai nature working contact and arinature lll, stepping rela7 Ll1 to battery. Relay fil energizes over this circuit and at armature Z' establishes the `following locking circuit tor itsell: l'roin ground at ari'nature G0, ariuature TG and working contact, armature and :restingy contact of rotary magnet all, and thence over previously traced circuit to relay ell. ill-it the end or' the vertical movement, the slow-acting relay o7 deenergizes and at armature Gil closes a circuit for rotary inagtraced circ net 1G as follows: 'troni ground at arn'iature (32, armature (i4. and its resting Contact, arniature if and its working contact, and rotary niagnet li-G to battery. Rotary magnet Lili, upon energizing, steps the wipers 251 to 'W/ i" e, into engagement with the first 1 ot contacts in the ourth level ot their i; fociated banlrs, and at the saine tii'ne operates to breal: the locking circuit oi steppingl relay all. ltelay l1 accordingly deener* giaes and at armature 75 brealis the circuit ot' rotary magnet Alti, which, in turn, dcener- The operation now depends upon whether the i'irst trunk is busy or idle. li the lirst trunk is busy, there is a ground on the private conductor tern'iinating in the tes contact 265, con'ipleting a circuit extending 'troni contact 265 through test wiper conductor 9G, armature 88 and its resting contact, armature 59 and its resting contac", arn'iature 81 and its working contact, resting contact and armature ot rotary magnet etti, and over the previously traced circuit to relay Lil. ftelay l`l-l. accordii'igly energizes and at armature 'i5 closes 'the previously ut tor rotary niagnct al1 which operates to step the wipers over to the next set ol" contacts. 'lhis cycle ot operation is Vrepeated until an idle trunk is reached.

illheu an idle trunl; is found, relay l5 energizes in series with the stepping relay Ll1 over the i'ollowing circuit: trom grounded conductor '32, switching relay 45, armature and resting contact ,oli rotary magnet etti, and over the previously traced circuit through relay /11 to battery. 4ltelay 451, however, due to its relatively Isinall number of turns, does not energize in series with relay e5. lt will be assumed that the trunl; line terminating in the l'irst eet ol" contacts idle, and when the wipers reach the first set et contacts, the test .viper linds no ground, and the switching relay elo is accordingly energized.

Upon energizing, relays?) connects test wiper to conductor 32 by way ot' arinature 239 and its worlring contact, and at armatures :i4- and :38 disconnects the incoming line couductors troni the upper aud lower windings ot line relay and extends thorn by way ot' conductors 9i and 92, wipers 252-3 and Q54-, bank contacts E256 and 257 to trunli line conductors 259 and Q60, understood to extend to and terminate in the line relay oi a local connector suf'itch. rlhe line and release relays oi the connector are accordingly energized and the latter grotuids the release trunk conductor rllhis ground extends back to conductor 32 and its multiples and by means ot it relay 14. ot the line switch C and relay ot switch l) are maintained energized and thus hold the switches C and l) in an operated position. It is understood that this liolding circuit is established belfore the sloweacting release relay 236 has had time to deenergize. The connection through Sli itu;

the main otiice isreleased by the deenergizaslow-acting, do not release immediately and the stepping magnet 117 is energized and steps the wiper' of switch C3 into engagement with the next set ot' bank contacts. The object ot' steppinol the wipers ahead one step upon releasing, is not only to secure a better distribution of the calls, but also to prevent the tying up of a call by a defective trunk line. Suppose the trunk line comprising conductors 13S and 139 is defective, in such a case a party might try repeatedly to get a main exchange number without success for on each attempt he might get the same detective trunk line. Vith the arrangement shown, however, the iirst attempt would'be unsuccessful, if the connection was attempted by way of the 'detective trunk line, but when the calling party disconnected to try the number over again, he would get a new trunk line, and ultimate success would be assured, even it it should be necessary to try all of the available trunks.

The connection under consideration has now been extended to a local connector in the sub exchange, and the trunk line to the main exchange has been released and restored to common use.V The calling subscriber may now dial the remaining digits 6 and 7 of the desired number, with the result that the local connector to which the call has been .extended is operated to complete the connection to the desired called line. This part of the operation is old and need not be further considered. K

A description will now be given of the operation oit' establishing` a connection between substation A and a substation in the adjacent. sub exchange, whose number will be assumed to be 76,367. lhen the subscriber at substation A` removes his receiver, it may be assumed that the connection is extended i to the switch D, and by way of the secondary line switch C to the first. selector E, inthe manner previously explained'. Uien the dial is operated for the first digit 7 ot the called number, the selector E operates to raise its wipers opposite the seventh level ot' bank contacts and to select an idle trunk line therein. It may be assumed that conductors 161, 162, and163 represent the first vidle trunk, and thatthey extend to a repeater (not shown) associated with a trunk line terminating in an incoming second selector in the 70,000 oliice. The dialling ot the digit 7 also causes the switch' D to raise vture 65, relay 43 to battery.

Vinsalate dialling of the digit 6 also'causes the switch D to rotate the wipers 251 to 254, inclusive,

yinto engagement with the ysixth contacts inv their respective banks. Vhen relay 37 deenergizes, following the last rotary impulse, a Vcircuit is closed for relay 43 as follows: from ground through the upper winding of relay 270, Fig. 4, bank contact 27,1, wiper 251, conductor 95, resting'contact and arma- Relay 43will not energize at this time due to the high resistance of relay 270. The latter relay, upon energizing, closes a lockingv circuit for its lower winding by way of grounded release trunk conductor 32 at armature 272. A further result of the energization of relay 270 the operation or' armature 273, which removes ground from bank vcontact .274 and places direct ground upon bank contact 271, whereupon relay 43 will becomee'ncrgized. A still further result of the energization ot relay 270 is the placing or' direct ground upon bank contact 266. Relay 43, upon energizing, brings about the releaseV orn ,the switch D in the manner previously explained.

lVhen the calling subscriber dials the third 'digit 3 of the called number, the third selector in the 7 0,00() oiiice raises its wiper opposite the third level of bank contacts, and r0- tates in search of an idle trunk line. Since the idle trunk line is reached by calling 763, it must necessarily give access to the adjacent sub exchange. Accordingly it leads to a repeater and from there to an incoming connector located in the adjacent sub exchange. The diallingl off the digit 3 also causes the switch D to raiser the wipers 251 to 254, inclusive, opposite the ythird level of bank contacts, whereupon it rotates in search of an idle trunk line, as before explained. It will be assumed that the trunk line terminating in the first set or" contacts is idle, and that trunk conductors 275, 276, and 277 extend to a repeat-er associated with an incoming connector in the adjacent sub exchange. The releasing of the main oiiice trunk and the completion of the connection is brought about in the manner previously explained, and need not be described again.

A description will now be given ot the operation of establishing a connection between station A and a substation in the main exchan 0e, whose number will be assumed to be 91,361. As previously explained, the switching selector repeater under discussion lil.)

. saine as the second digit of the nuinbersof lines terminating in either sub exchange, the second digit called will determine that the ca-ll cannot be intended for either sub eX- change and, consequently, the switch D will not need to move its wipers after the second digit is called. It will be assumed that the subscriber at substation A has removed his receiver and has called the digit 9 and he has obtained connection with the saine switches, or in other words, conditions are exactly the saine in this case as they were at the end of the digit 9, when the call to station 91,467 was described. It will be remembered that the shaft of switch D has caused the operation of spring 97, and that the switch is ready to rotate under the control of the calling device. The selector E in the main exchange in response to the calling of the first digit 9, raised its wipers opposite the ninth level of bank contacts and rotated to pick out an idle trunk leading to the second selector E. With the call thus extended, the subscriber at substation A op crates his calling device for the second digit 5 of the desired number. The result in the main exchange is that the selector lrraiscs its wipers opposite the fifth level of banlc contacts and rotates topiclr out'an idle trunk line leadingto a third selector (not shown),

At the sub' exchange the switch D rotates its wipers five steps into engagement with the fifth set of contacts in the ninth level.

As soon. a'sthe slow-acting relay 87 deener-` gizes, Ythe following circuit is completed: from ground through resistance R, Fig. 4, banl; contact 268, wiper 251, conductor 95, resting contact and armature 65, and relay 43th battery. Relay 43 energizes and locks itselfat armature 87,' thus becoming independent of armature 65, and atarmature 86 closes a circuit for release magnet 48 as follows: from ground over the previously traced circuit for relay 43, working contact and armature 86, working contact and armature 70, armature 79 and its resting Contact, and release magnet 48 to battery. `Release magnet 48, having a winding of few turns and having also a stiff adjustment, does not energize at this time. A further result of the energization of rela-y 43 is the closing of a circuit through relay 42 which may be traced as follows: from ground at armature 84, lower winding of relay 42, armature 79 i and its resting contact, and release magnet 48 to battery. At this time release magnet 48 is feeding battery through the lower winding of relay 42 in parallel with resistance R; due to its structure release magnet 48 does not energize at this time. Relay 42 energizes and just beforearniature 7 9 breaks away from its resting contact, armature 82 makes onv its working contact, thereby lock- The calling of the remaining digits 5, 6,

and 7 produce no movement of the wipers of the switch D, the switch acting merely as a repeater to repeat the impulses to the main exchange where, by means of the switches not shown, the call is completed. After vthe terniination of the conversation, the sub scribers hang up their receivers and the release takes place in the usual manner. Si)

A description will now be given of the operation of establishinga connection between substation A and any substation which is in an office other than the main ofiice, or the local or adjacent sub exchange, for ini nce station 84,567. Since the first digit of j s number is not the same as the first digit e t the numbers of lines tern'iinating in either sub exchange., 'the first digit called will determine that the call cannot be intended for either sub exchange and, consequently, the switch D will not need to move its wipers after the first digit is called. It will be assumed that the subscriber at substation A has removedA his receiver and obtained connection with switch D. i

lli/'hen the calling subscriber operates'his calling` device for the first digit 8 of the desired number, the switch D operates in the usual manner to raise its wipers opposite the eighth level of bank contacts7 while the selector E in the main exchange raises its wipers opposite the eighth level and rotates to pick out an idle trunk liiieleading to repeater (not-shown) and thence to an incoming second selector in the 80,000 office. Since, the eighth level in the bank of switch D is not a critical level, the shaft spring 9T is not operated at this time, and, consequent` ly, the circuit of the rotary magnet isV Vpeii -at that point. This being the case.y the switch D can function onlv a, repeater. When the subscriber at substation operates his calling device for the remainingI digits 4, 5, 6, and 7 of the called number, the sw ii'ch D, acting' as a repeater, repeats the impulses to the repeater in the main exchange which again repeats them to the switches in the 80,000 office. This part of the operation is old and need not be further considered.

The rather complex operations hereinbefore described may be summarized as tol` lows: If the first digit dialed is a` critical digit, that is, a digit corresponding to the local or adjacent sub-exchange, the switch D raises its wipers in response to the. digit dialled, operates shaft springs 97 and 98, thus preparing for a dial controlled rotary movement.

If the first digit dialled is not a critical in j ` digit, switch D raises its wipers in response to the digit dialled. The springs 97 and 98 are not operated, however, and, therefore, no dial controlled rotary movement can take place. The s yitch remains in the operated position and functions only as a repeater. If the iirst digit dialled is a critical digit, followed by asecond critical digit, that is, the second digit appearing in the switching combination of the sub exchange determined by the iirst digit called, .switch D rotates in response to the second digit and releases. In doing so a relay is operated which re moves ground from the guarding Contact corresponding to the last digit of the switching combination of the sub exchange determined by the lirst digit called.

lf the first digit dialled is a critical digit, followed by a second digit which is not critical, switch D rotates in response to the second digit, but the switch does not release. The switch remains in the operated position and functions only as a repeater.

If the first two digits dialled are critical digits, followed by a third critical digit, that is, a third digit. appearing in the switching combination'of the sub exchange determined by the first digit called, switch D raises its wipers in response to the third digit` cuts in on the selected level and seeks an idle trunk to a local connector or toa repeater as the casemay be. At the same time the trunk to the main exchange is released. y

If the first two digits dialled are critical digits, followed by a third digit which is not a. critical digit, the switch D raises its wipers in response to the third digit and cuts in one step on the selected level, remaining in that position and functioning only as a repeater. i

A special case is presented when the first digit of the switching combination is the same as the third digit, the additional equipment required is shown in connection with the second level of the banks shown in Fig. 4. In order that this feature may be made clear, Vit will be assumed that a third sub exchange may be reached. from the banks of the switch D. should the. combination 232 be called. The switch D, in response to the dialling of the digits 2 and 8, will cause the wiper 251 to engage bank contact 278, whereupon a circuit closed for relay 43 over the following circuit: from ground at armature 279. upper winding of relay 280, bank contact 278, wiper 251 and over the previously traced circuit through relay 43 to battery. Relay 43 will not energize at this time owing to the high resistance of the upper winding of relay 280; the latter relay will energize, however, and close the circuit of relay 281 at armature 282. A further result of the energization of relay 280 is the operation of armature' 283 which places ground through the low resistance low-er winding of relay 280 upon bank contact 278, whereupon relay 43 will energize and close the usual circuit-through release magnet 48 and the lower winding of relay 42. The resistance of the lower winding of relay 280 is so low that it effectually shunts the lower winding of relay 42, therefore, the latter relay does not energize at this time. The release magnet 48, however, en-

closes a circuit through relay 281 at arma ture 282. `Relay 281, upon energizing, forms a locking circuit for its-elf from grounded release. trunk conductor l32 by wayn of armature 284, thus rendering it independent of the further operation of relay 280. A furthier result of the energization of relay 281 is the removal of ground from the resistance R2 at armature 279, and the. placing of ground upon bank contact 266 by way of armature 285. Relay 280 will remain operated until such time as release magnet 48 places direct ground upon the circuit at which time relay 280 deenergizes and clears bank contact 278.

It will be assumed that the switch D now responds to the dialling of the digit 2 by raising its wipers opposite. the second level of bank contacts and, since relay 43 is now .deenergized as previously explained and since there is no ground upon any of the bank contacts yaccessible to wiper 251, the switch D will automatically rotate in search of an idle trunk line leading to a repeater, the said repeater being associated with a trunk line terminating in an incoming connector' located in the third sub exchange. The main othce connection is released in the usual manner.

The introduction of the third sub exchange has still further complicated the operation, and for that reason reference is ,again made to Fig. 4. It will be remembered that the fourth level contains trunk lines, such as the trunk line represented by reference characters 258. 259vl and 260, which lead to connectors inthe local sub exchange. The ythird level contains trunk lines. such as the trunk line represent-ed by reference characters 275, 276, and 277, which lead to repeaters, the said repeaters being associated with incoming connectors at the second sub lil switch -D'willv raise its wipersjopposite 'the exchange; The second level; contains trunk lin-esy suoli` as the trunlc line represented. by reference Vcharacters 286, 287, and. 28S'. win-cli leadto repeaters, the said repeaters being .associated with incoming 'connectors at the third sub exchange- The switching combi* nation' of the. local? sub exchange is 9l-l, while the switching combination ofy the sec-- Vond Asub exchange is. 763, and that of the `third exchange is 232.

Then considering` the second operation of the calling; device, the critical: digit thc second digit occurring/iny the switching-coin bination determined' bythe first. digit'. That is, the digit l is a critical dig-it' only when it follows the digity 9, the digit 6 is a critical digit only when `it follows the digit 7, while 3 is a critical di O'it only when-it fol'- lowsv the digit 2. .If-agY first criticah digitv is.`

dialled, followed byl a. second digit Awhich is not critical, for .instance 92,711, or 2t), theswitch D will 'rotatetlie wiper 251' intoeirgagenient with a banl'r contact grounded through al resistance, such 4as R or R2, and

Athe switch VD will vremain in the operated position and' function onlyas a repeater. a first critical digit is dialled, followed by second critical digit, for'instance 91,76, or'

23, tlievswitch D will'rotatethe wiper 251 into engagement with "a bank contact" which becomeslgrounded, either directly orthrou gli a very low resista-nce, whereupon the switch D releases and' in sov doing, causes :i relay, such as the relays 255, 270,01* 280 to operate and remove ground from the first guarding bank contact Vinthe level corresponding to the third digit inthesWitching combina tion determined by the first digit. I

When considering the third operation of i the calling device,the critical dijit the 'thirdfdigit occurring in the switching cour bination determined by the first digit. That is, the digita-is critical only when itfoliows the number' 91; dialled, 1followed by a 'digit which not critical, for "instance 917, 762", oi' Z3-l1, ther desired level and automatically cuts in on Vthe lirst setv of cont-acts. flVhereupon the wiper 251' engages a contact grounded direct ly or' tlirouglifa resistance-such.' asili' T? l .min

ii im) Critical" Clisi@ MG' either case, relay 43 of switch D will energize to prevent the operation of switching relay 45. v The switch D will remain in the operated position and will function only as a sistance upper winding of relay 255, means;

must be provided whereby this contact :nay be grounded to meet the requirement above referred to. Therefore the relay associ-ated with the guarding contact corresponding to v e s. ont ciOi o i eaci s'wi cninvcon iinath ec l lgt i l t1 g il lf the tion is provided with a pai-r of springs which are multipled in such a-.way that contact 260 l Will be grounded when any one of the above mentioned relays yare energized. It may be stated that-the first guardi-ng contact, in any level which may be reached by a critical digit followed by a non-critical digit, grounded through a resistance suoli as the resistance R or R", `rather than by direct ground. This prevents the release of the switch. D, should the Contact in question be reached at the end of the second digit, yet.

provides a circuit for relay 4.3 should the saidv contact be reached at the endvofftlie third digit. Y

Iftwo critical digits are dialiled followcifl Y by a; digit that is critical, yfor instance Ell 763, or .232, the switchv D will raise its wipr ers opposite the desired level and a-utoniati4 cally cut in on the first set of contacts. and,

since there isnogioundrupon the guarding contact,.the switch D' rotates. in search of an idle trunk leading to a local connector, or to :i repeater, :is the case may be. At the saine time, released. 1

- It will be seen that the switching combinations are not limited to any particular coinbiiiation of digits, and it will also be understoodthat addition al levels may be wired for local.` or adjacent switching if so desired.

rllie foregoing part 'of the explanation will now beV supplemented `by adetailed consideration of some of the circuit refinements that have been incorporated in the circuit of switch D.

The switchingselector repeater disclosed in the before mentioned patent .was de-Y signedi'to supply dial tone to the vcalling subscriber asv soonv as a connection was extended thereto. ,The calling subscriber,

Since contact 2661 the trunk to the malin exchange is therefore, received notification' tof proceedr with the-` dialling before the associated secoiiclarylin'e itch had selected anidlemain excliange tifunllz.4 This obiectionable feature has been eliminated' in the present disclosure nosas/is by arranging the circuits in such a way that the dial tone will be received from the incoming first selector at the main exchange. It' all the trunks to the main exchange are busy7 it is evident that dial tone cannot be received from a first selector therein; yet it is necessary at this time to provide a dial tone, since there is a possibility that the contemplated call will be for a number located in the local, or one ot the adjacent, sub eX- changes. An explanation will now be given of the operation of providing dial tone should all ot the main exchange trunks be busy when a call is originated in the sub eX- change. j

Upon referring to Fig. 1, it becomes evident that when all trunks to main, such as the trunk lino comprising conductors 138 and 139 are busy, all relays, such as relays 120, 142, and 143, are energized and 'thus complete a circuit extending from ground by way ot the working contact oit armature 140 and said armature, and the corresponding contacts and armatures on relays 142 and 143 to battery through relay 144. Relay 144, upon energizing, removes battery -from common conductor 146. In case all ot the trunks to main are busy when the subscriber at substation A makes a call by way ol switch D the energization of line relay 35 closes bridge across conductors 101 and 105, but, since battery is removed from common conductor 146, the relay 119 of switch E cannot energize. Switching relay 118, however, energizes as before, duc to t-he closure ot its circuit by relay 36 at armature 62. At this time it is to be noted that the circuit extending to wipers 180 and 133 is open at armatures 129 and 126, respectively, ot relay 119; and that local dial tone is now audible at substation A, it being delivered over the following circuit: from ground through the secondary winding ot dial tone machine T, resting contact and armature 77, resting contact and armature 71, resting contact and slia'l't sliriifig 96, conductor 164, armature 12S and resting contact, working contact aud armature 122, conductor 101, armature 66 and resting contact, upper talking condenser', resting contact and armature 54 to line conductor 31; the return circuit being completed through the lower winding of line relay 35. The calling subscriber now operates his calling device for the first digit of the desired number. The dial tone is cut ott at armature 71 when relay 39 energizes in response to the operation et nii" normal spring` 52. It the number called is such that switch D releases at the end of the second digit, the dial tone is not again placed on the line for, under the condition just stated, its circuit will be open` at armature TT ot relay 42.

il' hile not a part of the present invention,

the method ot giving the busy tone to the calling subscriber when all main oiiice trunks are busy will now be described. Returning to the circuit arrangement outlined in the. preceding paragraph, it may be assumed that the calling subscriber has heard the dial tone and now operates the dial for the first digit ot the desired number. At the first vertical step, relay 89 will energize and operate to place the busy tone from machine B upon .line conductor 31 over the `following circuit: lrom battery through secondary winding and condenser' ot busy machine B, working contact and armature 71, resting contact and shaft spring 9S and over the 1, nevicusly traced circuit to line conductor 81. It tie lirst digit dialled be other than a critical digit, the shaft spring 98 will remain in au unoperated position, and the calling subscriber will receive the busy tone as soon as his dial returns to normal. It the tiret digit dialled is a critical digit, there is a possibility that the call is for anumber .in the local, or one ot the adjacent, sub 3tchanges-and, under the condition just stated, the busy tone will not be audible because shaft spring 98 is in an operated position.

It the lirst digit dialled is a critical digit, followed by a second digit which is not critical, relays 43 and 42 will energize. The open contact at shaft spring 96 will be shunted by the closed contact of armature 76 ot relay 42 and the calling subscriber will receive the busy tone as soon as his dial. returns to normal. It the tiret digit dialled is a critical digit, followed by a second critical digit, there is a possibility that the call is for a number in the local, or one ot the adjacent, sub exchanges and, under the condition just stated, the busy tone will not be audible owing to the open circuit at armature T1 oit relay 39, it being remembered that switch D released to normal because of the dialing of two critical digits. i

It the two tirst digits dialled are critical digits, followed by a third digit which is not critical, relay 39 will again energize and, under the condition just stated, the calling subscriber will receive the busy tone soon as his calling device returns lo normal. li the two first digits dialled are critical, Vtol-- lowed by a third critical digit, the switch D will select a trunk to an idle connector or repeater, the switching relay 4.5 operating to cut oil the main exchange trunk and.. uuder the condition just stated. the busy tone will not be audible owing to the open circuit at armature 54 of relay 45.

ln the drawing the springs 49., 50, and are shown divided for convenience only,

tually they are grouped together and controlled by a single cam. The purpose of these springs is to give the calling subscriber a busy signal when he calls a number in the local, or in an adjacent, sub exchange and iinds all the trunks busy. Under the condiil l) loo f tion above set `forth the trunk to the main fill' exchange is also released. fldlhen the switchV .trunk line is not foundv the Wipers are ro'- tated until they pass'oti the last set of contacts in that level and when they do so, the shaft cam llloperates the springs a9, 50, and 53. At spring 50, the circuit oit switching relay is broken to prevent the said relay from energizing and opening the circuit ot line relay 35. Spring 53 opens the bridge across conductors lOl and 105,' thereby releasing the connection to main, While spring i9 opens the holding circuit ot switch C, thus freeing the main exchangeV trunk. Spring 53 in addition to opening the bridge across conductors lOl and 104,- also closes a circuit from busy machine B to theloiver talking condenser and thence bacl to the calling subscriber to interni `him that he cannot obtain the desired connection.

The 'features ot the invention having been described and ascertained, what is considered to be new and' desired to have protected by Letters Patent ivill be pointed out in the appended claims.

I claim l. In a telephone system, tivo main exchanges each having a branch exchange subM sidiary thereto, automatic switches in said exchanges, a snv'itcliing selector repeater in one ot said bra ch exchanges accessible to a calling subscriber, means Vin said selector repeater responsn-'e to the hrst three digits in the called number tor repeating impulses over a trunk line to the associated main exchange to operate a series ot said switches, local connectors accessible to said selector repeater, trunk lines extending to the other branch exchange also accessible to said sclector repeater, means tor operating said'selector repeater in its prin'iary movement fesponsivc to the `lirst digit in the called nienber, incansior operating said selector vrepeater in its s-econdary movement responsive to the second digit in the called number.V means iter then automatically releasing' said selector repeater, means 'for reoperating said and pea-'ter in, one of. said branch exchanges,

local trunk lines accessible to said switching selector repeater, trunk lines extending to another branch accessibley to said selector' repeater, trunk lines to a main exchange, a line switch individual to said selector` repeater having access to said mainexchange trunk lines, means tor operating said line switch to select a main exchange trunk line when said selector repeater is taken for use, means in said selector repeater for repeat'- ing the lirst, three digits in the number called over the selected main exchange trunk line, .said selector repeater having Wipers operated responsive to such meansy effective in case threedigits are called which identity the called line as being in the local branch orin said other branch for causing said Wipers to select and connect with an idle local or branchl trunk, ,as the `case maybe, and means torreleasing the partially established connection in the main exchange. V A

3. ln a telephone system, a main exchange and a branch exchange, main exchange trunk lines connecting Ysaid exchanges, a second` exchange accessible to vsubscribers in said branch exchange via said trunk lines, a switching selecto).- repeatery in said branch exchange having means for seizing a `maincxchange trunk line and toi'V repeating the digits in called numbers over such trunk line, local trnnl: lines and direct trunk lines to -said second exchzmge accessible to the wipers oit said` selector repeater,` and means for operating the said selector repeater 'Wipers to selectone of said local trunk lines or on@ of said second exchange trunklines, as the case may bean`d release, the .selected main exchange trunkline, Whenever such digits are called as determine that the called line iscither a. local line or a line in .said sccond exchange. Y

1l. In a telephone system, a main exchange and a plurality ot branch' exchanges, ai

switching selector repeater' in one/oit said branch exchanges for extending localV or outgoing calls, means m said selector repeater peater for switching local calls or calls to another branch exchange over routes by- P digits also,

.or preliminarily routing all calls viaV the* Vmain exchange, means in said selector re ing the main exchange when `digit comi binations are called which exclude the mainl exchange, and means tor preventing false'V lll() main exchange, means in said selector repeatcr for switching local calls or calls to another branch exchange over routes bypassing the main exchange when digit conibinations are called which exclude the main exchange, and meansl iter preventing a 'talle switching operation in case all but one olf the digits in a certain switching combina tion are called followed by the iinal digit in another switching combination.

6. In a telephone system, a main exchange and a plurality ot branch exchanges, a switching selector repeater in one or said branch exchanges for extending local or outA going calls, means in. said selector repeater -lfor preliminar-ily routing all calls via the main exchange, means in said selector repeater for switching local calls or calls to another branch exchange over routes bypassing the main exchange when digit conibinations are called which exclude the main exchange, and means for preventing false switching operations diie to the calling ot digit combinations made up ot one or more digits in each or two switching digit conibinations, said means comprising relays individual to said selector repeater, there being a rela-y for each switching combination, and circuit connections from said relays to the bank contacts in said selector' repeater'.

7. In a telephone system, a main exchange and a branch exchange, a switching selector repeater in the branch exchange tor handling all originating calls, means in said selector repeater lor preliminarily routing all calls via the main exchange, means in said selector repeater for switching a call from the main exchange to the branch exchange as soon as suilicient digits are called to determine the destination of the call, means for transmitting a dial tone to a calling branch subscriber from the main exchange provided a main exchange trunk line is available, said tone informing the subscriber that he can proceed to call the desired number, and means igor giving the calling subscriber a dial tone from the branch exchange in case all the main exchange trunk lines are busy.

S. In a telephone system, a iirst ol'lice and a second ol'lice, trunk lines between said oilices, other trunk lines, means for extending a connection trom said iirst otlice to said second oliice over one of said inter-office trunk lines, a register, means responsive to the calling of a portion of the desired number for operating said register to record such portion and for transmitting corresponding impulses over the trunk line to the second oilice, a pluralityof relays, means operative in accordance with the setting of said reg ister for operating any one oi said relays to record such setting and for releasing said new position of said register l'or severing the connection to the second oliice and Ator ex tending the connection to one ol said other trunk lines.

9. In a telephone system, a iii-st ottice and a second otlice, trunk lines between said oi- 'iices, two otherl groups oit trunk lines, means for extending a connection from said tirst oiiice to said second cnice over one or said inter-ofiice trunk lines, a register individual to said connection, said register having two critical positions, two relays assigned to said critical positions, respectively, means respon-sive to the calling or a portion of a desired number corresponding to either critical position for setting said register into the critical position corresponding to such called portion and for transmitting corresponding impulses over the trunk line to the second oliice, means responsive to the setting ot the register for operating the relay associated with the selected critical position and for releasing said register, two switching positions or said register normally ineffective correspending, respectively, to said other groups of trunk lines, and associated with said critical positions, respectively, means controlled by the operated relay for rendering the associated switching position eilective, said operating means being again effective to operate said register to record another digit, and means effective only in case such other digit corresponds to the last named switching position for severing the connection to the second olice and tor extending the connection to an idle trunk line in the one oi said other groups of trunk lines which corresponds to the last named switching position.

l0. In a telephone system, two main exchanges, each characterized by a separate and distinct block oi" telephone numbers, two branch exchanges associated with said main exchanges, respectively, each branch having assigned to it a portion oit' the numbers allotted to its associated main exchange, a switching selector repeater in one of said branch exchanges for extending local or outgoing calls, means in said selector repeater for preliminarily routing all calls via the associated main exchange, and means in said selector-'repeater tor switching local calls or calls to the other branch over routes by* passing the main exchanges.

ln 'witness whereof, l hereunto subscribe my naine this 30th day of January, A. D., 1923.

ARTHUR J. RAY.

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