US1627844A - Automatic telephone system - Google Patents

Description

M l0 \19 ay 27 H. M. FRsENDLY AUTMATIC TELEPHONE SYSTEM origina] Filed Feb. 17. 1921v 9 SheetsSheeL 1 `Illllllll ||s|||||| f uuml May 10,1927." A LGT/,844

H. M, FRIENDLY AUTOMATC TELEPHONE SYSTEM May 1o, 1927. M2184@ H. M. FRIENDLY AUTOMATIC TELEPHONE SYSTEM origina] Filed Feb. 17, 1921 9 sheets-sheet` 3 HEPE/EFZLZ'ZlFrian/jlg May 10, 1927.

H. M. FRIENDLY V AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 17. 1921 9 Sheets-Sheet 4 a. 4 8, A7.. 2 il M E T S mw E. N w m m R E F n T Mw T H m O T U A. 7. 2 ,94 1 m l W.. nm, M. QM

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H. M. FRIENDLY AUTOMATIC TELEPHONE sYsTEM Qgriginal Filed Feb. 1v, l1921. s sheets-sheen 6 m u n im n n Q y 1* l] ll l)v Il l 192 l May o 7 H. M. FRIENDLY AUTOMATIC TELEPHONE SYSTEM origina] Filed Feb. 17. 1921, 9 sheets-Sheen May 10,1927. M2282@ H. M. FRIENDLY AUTOMATIC TELEPHONE SYSTEM original Filled Feb. 17. 192i .9 sheets 'sheet ,8

i Y w22/844 May 10 1927 H.^M. FRIENDLY AUTOMATI C TELEPHONE SYSTEM origina] Filed'Feb. 17. 19 21 9 shams-sheet4 9 @Gunn lll] [l Patented May 10,v i927.

stares lltttd HERBERT IVI. FRIENDLY, OF CHICAGO, ILLINOIS.

.AUTOMATIC TELEPHONE SYSTEM.

Application tiled February 1'?, 1921, Serial No.` 445,761.` Renewed November 8, 1926.

The present invention relates in general to an automatic telephone system, andis particularly adapted to a system that includes a `main exchange, having a plurality of branch offices tributary to it.

More specifically, the invention relates to an improved method and apparatus for permitting either'a calling party in the main exchange or a called subscriber ina branch exchange lto transfer the call lto anotherdesired subscriber in the branch exchange. thersystemshave been inventedwhich em .body certainl arrangements of this nature, rbut herein are provided many new features together with improvements in the structure of such a system.

Among the important features of the invention an arrangement is provided whereby, after a call has been transferred from one `branch exchange subscriber to another the three parties may remain on the line `for a conference,rand as soon'as this is terminated either party'at the branch exchange may release the other by dialing the digit 1; or should this feature not be desirable the first called party may be automatically released upon the second called party an-V swering.

Another important feature is the provision of means whereby if the branch rexchange subscriber upon receiving a call should desire to obtain information from another subscriber in the branch exchange without the knowledge of the calling party he may do so by dialing the calling man on t-o a holding circuit,` after which the called party may release and call normally in the branch exchange or into the rvmain exchange; yafter obtaining the information desired, the called subscriber may again connect with the original calling subscriber and subsequently pass or transfer the calls as in the ordinary operation of the system.

Means are also provided whereby cert-ain (or all)-branch exchange subscribers may have special services of an operator if they so desire.

These and other features of the invention will be fully disclosed hereinafter.

Referring now yto the drawings:

Fic. 1 shows a schematic trunkino` dia-l gram of the system disclosed in lthe remaining drawings. i

Fig. 1a shows the manner in which the different sheets of drawings are placed for a complete view ofthe system.

In F ig. 2 the apparatus at the lmain exchange is shown diagrammatically and consists of a subscribers substation A, having a preselector -or rotary lineswitch C5 individual thereto,-and which has access in common lwith a lplurality of other similar lineswitches to lfirst selectors of the standard Keith-Erickson two wire class, one of which is shown'at4 E. These selectors have access to selector repeaters off a vcertain 'level of bank contacts. The selector repeaters may be of lany well known .two wire rtype such as that shown in Fig. 1 of the 4patent to Emil Jacobsen No. 1,332,217, issued March 2, 1920. These selector repeaters have access to trunk lines going to branch exchanges one of these is shown in the drawings and vcomprising the conductors 26 and 27.

These trunk lines terminate in what is known as dual selector switches in the branch exchanges. The switches are of the 'general type shown in Figs. 9 and 10 of the British .patent to Friendly 139,000 the circuits ofwhich are modified in accordance with the features of the present invention. The trunk `line comprising conductors 26 and 27 Vis shown terminating in such adual switch, Figs. 3 and 4.

In Figs. 5, 6, 11 and'13 ordinary selector switches of the Keith Erickson two wire type are shown, the circuits of which have been vmodified to operate in this system.

Figs. 7, 8, and 9 show connector switches of the well known Strowger type which also have been modified as will appear fully hereinafter.

Fig. 10, shows an improvement that has been designed for controlling a large number of otl normal springs when the weight of the switch shaft is inadequate to shift them.

Fig. 12 shows an operator-s cord-pair.

Figs. 14 and 15 show certain details of the present invention which will be described fully hereinafter. l

Vhile in the drawings a plurality of batteries have been shownyit will be understood that there vis perferably, but one battery having its negative pole grounded for each exchange.

rlhe operation of this improved system will now `be described in general, reference being had to Fig. 1.

Let us Consider first what is shown on the left of the dotted line, where is `indicated the apparatus in the main exchange. The

. these selector switches terminate selector repeaters one ot which is shown immediately to the right ot the. first selector. Another level oi the selector switches has access to local second selectors shown diagrammatically at the bottom square on the lett; and as` shown one level of these selectors go to local connectors which have access to main exchange subscribers lines. The selector repeaters have access to trunk lines going to the branch exchanges andY termimiting there in dual selectors, one ot' which is shown terminating in the dual selector switches in the branch exchange. The switches in the branch exchange shown on the right of the dotted line consist ot two groups, those used in a local call and those used .in an incoming call. The dual incoming selectors have access to incoming second selectors off` certain levels of their bank contacts. These second selectors have access to incoming connectors which are adapted to connect with local subscribers lines. The local subscribers, shown at upper extremity of the drawing, have each an individual rotary line switch which has access to local branch exchange tiret selectors. A certain level of these selectors, the second as shown, is multipled into the second level of the incoming dual selectors, this is for a special purpose as will later appear. Other levels have access to local second selectors, while the 0 level is used for outgoing callsI to the main exchange.

The process of setting up connections will now be briefly considered. Suppose vfirst thata subscriber in. main exchange wishes to connect with al subscriber in the branch. exchange. lhen the receiver is removed at the calling station the rotary line switch in dividual thereto operates to select an idle first selector. The callingI subscriber' will thereupon dial the digit. which corresponds to the level leading to the selector repeater and which in this case is the digit 7. Then this digit is called the selector steps to the seventh level and operates to automatically select an idle selector repeater. The calling subscriber may now call the digit 6 whereupon the selector re eater will operate vertically to the sixth evel and rotate to lind an idle trunk line going to the branch exchange and terminating there in a dual selector. The calling party may now call the remaining :tour digits ot the desired branch exchange subscribers number whereupon the connection will be completed `in the usual manner. lt' 1t should be found, upon the called subscriber answering, that ari-g .may be again passed, if necessary, as many si' times as desirable.

Let us consider also the case of where the called party .desires to communicate with another subscriber in the branch exchange. He will dial the digit 2 which will cause the other dual selector element to step to the 'second level and connect with the holdingr trunk which is multipled into the second level of the local branch exchange first selectors. The called subscriber may now rclease the connection to himself and use the local branch exchange switches to call another party. After obtaining whatever information he desires he may dial the digit 2 which will cause the local first selector to step tothe second level and then rotate into connection with the holding trunk. The called party is now in communication with the original calling party again and the call may be passed as in the case first mentioned.

The local branch exchange subscribers by dialing O operate a first selector vertically to the tenth level whereu on the switch automatically rotates to fin an idle .two way trunk going to the main exchange. As soon as this is found the line switch associated therewith in the main exchange oper ates to select an idle first selector' whereafter the call is completed in the usual man ner to a main exchange subscriber.

Special service is also provided for cer` tain subscribers in the branch exchange. By .removing their receivers and dialing l the first selector under their control is stepped to the first level and automatically rotated. This action serves to light a line lamp before an operator who can now res-'pond and set up a connection `troni the calling line either manually or automatically in a well known manner. y

Having described the general objects ot' this invention and the general manner ot' obtaining these objects. the detailed operation of a system embodying those improvements will no'w be considered.

For this purpose it will be assumed that a subscriber at substation A in the main exchange desires to call the branch exchange subscriberat substation P and that the said calling subscriber has, by operating his call lili] inceneririiig dev-ice vtor a vseries ot digits seized the two way trunk .line comprising conductors 2G and .27 by .ineaiiso't' thefselector repeater C, in la iwell flinown manner.

lVhen the .call 4is 'thus extended 'to .the

vtrunk line. =a1fcircuit is completed "i'ior the `trunk conductorl@ through the winding oi relay 34L`to battery. The latter relay. on

energizingplaces vground on the multipled release trunk inthe banlrs of local selector :switches in which this inconiing trunk is accessible.

Now, -wlieii'the calling device of the calling 'subscriber' v'isfoperated to open the line fcircuit a number of times in accordance with a digit of the called number, the line relay of the selector `repeater will produce a correspondingserics :of interruptions in the c.ircuit:of the line` relay 56 of the main selector F. Upon each retraction ot' itsarinature theline relay 56 closes a circuit extending from ground G11, by -wayo'f armature 91 `and its back contact, conductor 137, armature 220 and its iresting Contact, yconductor 146, armature `104i and its back contact, ar-

mature 94: and its tront contact,'through "the 4winding o1e the slow acting relay 58, conductor 139, baclrcontactfand armature 215, conductor 1111, armature 155 and its back contact, back cont-act andarmature 89, and

thence throughthe `winding of the vertical magnet 64 to battery. Relay 58 energizes in sei-ieswitlrthe vertical magnet, and being ra slow acting relay, `maintains its armature attracted.during the operation ot the switch.

Magnet 64 operates to raise the wipers 112- 115, inclusive, step by step until they are placed opposite Soinelevelfo'fbanl; contacts, in which are terminated trunk lines leading `to I.the branch exchange second selector switches.

Ars soon as the wipers leave theirnorinal position the spring 119 is shifted into engagement with its front contact thereby coni- .pletiiig a circuit i'or magnet GT. The operation ot this 'magnet may readily be :i-'een b retei'rino` to F i9'. 10. Uaon attractino its tn t5 :1

`armature 201', magnet 67 shifts the ott' norinal springs 116,"117'and 118,-etc., into their alternate positions lwhere they lare mechanically locked by thespring 200. When the shattf-of the yswitch is released the pin 202 mounted thereon Awithdraws the spring'200 thereby allowing the off normal-springs to return to their original position.

To continue, 4whenithefod normal springs battery. Relay are operated a circuit is ycompleted extending lroin ground G3, through armature v93 Iand its liront contact, `arma-ture 9o and its vlront contact, armature 87 and its back contact, armature 159 and its resting contact, oil normal springs lltiiaiid thence through the windingot the interrupter relay 59 to .59' energizes to prepare the rotary magnet circuit at armature 100 and locks itseltl to ground at armature 99. llfhe slow acting relay 5S t'a'lls back an instant atter the impulses to the vertical Amagnet have ceased. lVhen this occurs a circuit is completed for the rotary magnet-* extending from ground G3, by way ot armature 93r and'its front contact, armature 96 .and

its` bach contact, armature 100 and vfront contact, and through the winding of the rotary magnet 65 to battery. Magnet 165 operates to rotate the wipers 112 to 11.5, inclusive, into eiiga'geiiient `with the lirst set of contacts` in the selected level and-atthe saine time opens the locking circuit ot relay 59iwhich deencrgizes, breaking the circuit-of the rotary magnet which deeiiergizes also.

"When magnet 65 deenergizes it prepares a new circuit for the interrupter relay 59 `extending from the Atest wiper 112, through Aarmature 88 and its restingcontact, baclr contact and armature 160,arinature 159 and 'its bach contact, ofi' norinal springs 116, and

thence through the winding ot' relay 59 to battery. Now, it the iirst trunk line oi this level, on the test contact of which the wiper 1121 now rests, is busy al ground potential willbe present thereon and relay 59 will energize over the above` traced circuit. On

energizing, l'relay 59 operates :as before to close the rotary Iii'iagnet circuit. lilagnet tloperates to advance the switch wipers into engagement with the ot banl'contacts associated -with the next trunk line `and to again brcalt the circuit ot the interi'upter relay, which relay on dcenergizing breaks the rotary magnet circuit. This alternate yoperation oi relay V59 and magnet 65 continues unt-il an iidle trunk line is found which, it .will befassiiiiied, is the trunk line comprising ther conductors 25() to 253, in-

clusive, and which terminates in the selector H Fig. When the switch wipers are i'otated iinto engagement with this trunk line 4no ground will be present on the test contact engaged by the wiper 112 and relay 59 will not be again energized to close the rotary magnet circuit. lt will be noticed that during the rotation of the switch in search of an idle trunl-z line the switching` relay 55 was short circuited by ground on the successive busy test contacts through lwiper 112, now, however, 'when an idle trunk line is reached, the relay is no longer short circuited and hence it will cnergize over a circuit extending trom ground G3, through armature 93aiid its front conit. Upon energizing, relay 55 opens the ver-` tical magnet circuit at armature 89, connects ground to the wiper 112 at armature i 88, prepares the circuit oit the wiper cut on relay 63 at armature 36, and completes a repeating circuit at armature 90. This repeating circuit extends from ground G1, by way of armature 02 and its front contact, armature 77 and its back contact, back contact and armature 72, conductor 127, armature 194 and its back Contact, back contact and armature '199. conductor 121., front contact and armature 90, armature '153 and its back contact, through the winding of the slow acting series relay 61, wiper 113, bank contact 258, coinluctm' 251. ari'nature 300 and its resting contact, and through the winding of the line relay 301 of the selector to battery. The line relay 301 cnergizes in series with relay 61 and said relays 301 and 61 actuate over this circuit and conipletes a circuit in the usual manner for the slow release relay 302. This relay on energizing prepares the vertical magnet circuit at rarmature 341 and its front contact. The actuation of relay 61 disables relay 63.

The calling main exchange subscriber may now operate his calling device in accordance with the next digit of the desired number. A series of interruptions is thereby produced in the circuit of the line relay 56 of the main selector F which relay operates and at each retraction of its armature 92 opens the previously traced circuit for the line relay 301 of the selector H. The latter relay at each deenergization sends a current impulse through the slow acting relay 304 and the vertical magnet 307 in series to battery. By the operation of the vertical magnet the selector shaft is raised step by step until the wipers 3104-313, inclusive, stand opposite the desired level of bank contacts. The slow acting relay 304 energized in series with the vertical magnet, retains its armature,attracted throughout the `vertical movement of the switch, and upon the closure of' the 4vertical oil normal springs 314 and 315 completes a circuit for the interruptor relay 305. Upon energizing relay 305 prepares a circuit for the rotary magnet 308 at armature 317, and at armature 318 establishes a locking circuit for itself. At the end of the vertical operation o1' the switch the slow acting relay 304 is deenergized and closes the circuit of the rotary magnet, which is thereupon energized to advance the wipers 310-313, inclusive, into engagement with the first set oli bank con tacts in the level opposite which they were raised. The rotary magnet also breaks the circuit of the interrupter relay 305, which is accordingly deenergized to break the circuit of the rotary magnet, which thereupon deenergizes also and again closes its interrupter contact. The operation now depends upon whetherl the test contact with Which the test wiper 310 is now in engagement is or is not busy. If this test contact is busy it will have a ground potential on it, and the interrupter relay 305 will be energized again over a circuit which extends from the said grounded test contact, by way of the test wiper 310, armature 320 and its back contact, the interrupter cont-act 322 of the rotary magnet, the oi normal springs 314, and the winding of the interrupter relay 305 to battery. The interrupting relay will therefore energize to again close the circuit ot' the rotary magnet 308, which will operate to advance the switch ywipers into engagement with the next set of bank contacts. This operation by which the interrupter relay and the rotary magnet are alternately' energized and deenergized will continue as long as the test wiper 310 engages busy or grounded `test contacts. In the present case it will be assumed that the truul: line shown in the drawings is the first idle trunk line and when therefore, the test wiper 310 arrives at test contact 325 and the rotary magnet is deenero'ized, the interruptor relay 305 Will not e energized, but instead, the switching relay 306, which has hitherto been short circuited will be operated by current flowing over the following path: grounded conductor 250, winding of the switching relay 306, interrupter contact 322 of the rotary magnet, olf normal springs 314, and the winding of the interruptor relay 305 to battery. Owing to the high resistance of the switching relay 306, the interrupter relay is not operated. Upon energizing, relay 006 disconnects the incoming dialing conductor 251 from the winding of the line relay 301 and extends it by Way of armature 300 and its front contact, Wiper 311, bank contact 326, conductor 328, arma ture 366 and its back Contact, back contact and arn'iature 361, and through the winding of line relay 350 to battery. The switching relay 306 on energizing, also extended thel release trunk conductor 250 by way of front contact and armature 320, wiper 310, bank contact 325, conductor 327, and through the winding of relay 351 to battery. This latter relay energizes and prepares the circuit of the vertical magnet of the connector J.

It might have happened however, that all `the trunk lines in the selected level were busy. Under these conditions the rotation of the switch H would continue until the springs 310 and 311 were closed which occurs on the eleventh rotary step of the switch, being operated by the cam on the Y switch shaft in a well known manner- These springs on operating, connect the dialing conductor 251 direct through the-winding of the line relay 301 to battery and at the same time place a busy tone on'the upper line conductor rlhis busy tone is audible to the calling subscriber over a circuit that extends over conductor 252, bank cont-act 256, wiper 11st, armature 103 and its back contact, armature 85 and its front contact and thence over the line of the calling subscriber. Upon hearing this tone, the calling subscriber will replace his receiver on the switchhook knowing that ier the present he is unable to btain his desired connection. The replacement of the receiver at the calling substation initiates the release of the operated switches in a inannerto be described hereinafter.

Returning now to the operation of the system after the trunk line comprising the conductors 323330, inclusive, has been seized; the calling subscriber may now operate his callingV device for the next digit of thel called subscribers number, thereby causing the. line relay 56 to again operate in response to the said impulses and repeat thein to the line relay 350 of the connector J'. At eachl retraction of its armature 356, the line relay 350 completes a circuit for the vertical magnet 372 in series with the slow acting private control relay 352, which relay maintains its armature attracted during these impulses. Magne-t 372 operates to raise the switch shaft step by step until the wipers 377-330, inclusive, stand opposite the desired level of bank contacts. On energizing, the slow acting relay 352 completes a circuit for the private magnet 371 at armature in multiple with relay 353. The operation of relay 353 is at this time without function. The private magnet, however, controls the sideswitch in the usual manner, and upon the deenergization of the slow actingl private control relay 352 permits the sideswitch wipers to advance to their second position.

rlhe. calling subscriber may now operate his calling device in accordance with the final digit in the called number, thereby producing a series of interruptions in the circuit of the line relay 56 which repeats them to the line relay 350 as before. Now, however,` this latter relay transmits a corresponding number ofv impulses to the rotary magnet 373. The circuit being traced from `ground Gl by way of armature 356 and its back contact, .armature and its front contact, through the winding of the private control relay armature 362vand its back Contact, and through the winding of the rotary magnet 373, and sideswitch wiperl in the second position to battery. By the operation of the rotary magnet, in response to the impulses of current which it receives,

the switch shaft is rotated step by step, until the wipers 377-380, inclusive, arebrought into engagement with the bank contacts in which the desired subscribcrs line terminates, which in this case, it will be assumed, are the bank contacts 331e38t, inclusive, .in which the line of the subscriber at substation 1 is terminated. rlhe relay 353 and the private magnet 371' are energizedas before, and in case the calle-dA line is idle when the relay 352 deenergizes, the private magnet alsovdcenergizes, and the sideswitch wipers are advanced to their third position.

ltY will first be assumed however, that the line-of the substation l), when called as above described, was busy. Under these condi-A tions there would be a ground potential on the test contacts 331and 332 which are engaged by the test wipers 377 and 378 with the result that the private magnet 371 willl not deenergize when the circuit is broken for its inner winding at armature 353 but is maintained operated over a test circuit eX- tending as follows: ground on test contact 332, test wiper 378, sideswitch wiper in the second position, and through the outer winding of the private magnet 371 to battery. Also relay a is energized over the following circuit: grounded test Contact 381, test wiper 377, springs 365, armature 359 and its bac c contact, through the winding of relay 354 and the sideswitch wiper in the second position to battery. On energizing, relay 354 closes a locking circuit for itself and the private magnet independent of the test wipers 377 and 373, this circuit extending from ground G16, oil' normal springs 375, armature 364 and its front contacts, inner winding of the private magnet to battery and in multiple with this last traced circuit by way of armature 359 and its back contact, through the winding of relay 354 and the sideswitch wiper in the second position to battery. Relay 35st opens the rotary magnet circuit at armature 362, opens the circuit of the line relay 350 at armature 361, and places the tone from the busy machine T2 on the upper heavy talking conductor 329. When the circuit of relay 350 is opened relay 61 in the main selector F, in

series with the dialing circuit, deenergizcs and completes the circuit for the wiper cut on relay 63. rlhis circuit may be traced from ground G12 by way of front Contact and armature 36, armature 103 and its back contact, and through the winding of relay 63 to battery.

The busy tone is now placed on the tone of the calling subscriber by the operation of the relay 354 over a circuit which extends from the busy machine T2 by way of armature 363, conductor 329, bank contact 323, and wiper 312, front contact and armature Sli 321, conductor 252, bank contact 256, wiper 114, armature 103 and its frontcontact, ar-

mature 105 and its back contact and thence through the lower winding of the ring cut oil' relay 62 to battery. This operation will inducea current corresponding to the busy tone in the upper winding of ring cut 0E relay 62 from whence it flows over conductor 121 through the lower winding of the back bridge rela 51, off normal springs 48, back contact an armature 69, througli the condenser and thence over the lower line conductor to the substation A and back through the upper winding ot' relay 51 to battery. This tone will inform the calling subscriber at substation A that the line of the subscriber at substation P is for the time being, inaccessible, and he will replace his receiver. The disconnection of the various switches will be described hereinafter.

Having thus described the operation of the connector J when the called line is busy, it will now be assumed that when the connection therewith was attempted the line of the substation P was idle. Under these circumstances, when the slow acting relay 352 deenergizes at the end of the final series ot impulses the private magnet 371 is deenergized also and the sideswitch passes to the third position. By the advance of the sideswitch wipers to their third position two circuits are closed in multiple. One extending from ground G17, sideswitch wiper in the third position, through the test wiper 378, test contact 382, private normal conductor 385. springs 386, conductor 387, the winding of switching relay 407 of the lineswitch C', and the winding ofthe stepping magnet to battery. In parallel with this circuit one is also closed for the busy lamp 452 thereby notifying an operator who has access to the line of the subscriber at substation P that this line is now busy. The current flow in this circuit serves to energize the switching relay 407, the stepping magnet remaining deenergized, and the line conductors 405 and 406 are thereby disconnected from their normal battery and ground connections in the lineswitch C. It should be here mentioned that when relay 407 energizes as described above it. is prevented from completely attracting its armatures by reason ot a mechanical interlocking device controlled by the armature of the line relay 408 when in normal position. Ground at G, of course, also extends to multiples of test contacts 381 and 382 in other connector switches both incoming and local which 4have access to the line of the substation P in order to render this line busy. lVhen the sideswitch steps to the third position another circuit is also completed in multiple with the above for the wiper cut on relay 355 in an obvious manner. On energizing, relay 355 prepares the ringing circuit at armatures 367 and 368, and at armature 366 opens the circuit of the line relay 350. f As before, as soon as the circuitto the line relayv 350 is broken the slow acting series relay 61 in the main selector F deenergizes. A circuit is thereby completed gizes a short interval afterwards. During` this interval a distinctive tone from the tone machine T is placed on the calling subscribers line conductor thereby notifying him that his call is proceeding satisfactorily. Relay 63 upon energizing, completes the ringing circuit for the called subscribers telephone which extends from theungrounded pole of generator V, over conductor`245, conductor 145, back contact and armature 107, armature 111 and its front contact, wiper 115, bank contact 257, conductor 253, armature 260 and its front contact, wiper 313, bank Contact 324, conductor 330, armature 368 and its front contact, wiper 380, bank contact 384, line conductors 393 and 401 of the substation P, through the ringer and condenser of the said substation, line conductors 400 and 390, bank Contact 383, wiper 379, front contact and armature 367, conductor 329, bank contact 323, wiper 312, 'front contact and armature 321, conductor 252, bank contact 256, wiper 114, armature 108 and its front contact, armature 105 and its resting contact, and thence through the lower winding of the ring cut off relay 62 to battery. This ringing current also causes an induced tone in the upper winding of the ring cut ofi' relay which is audible to the calling subscriber, thereby notifying him that his call is proceeding satisfactorily. The ringing of the called substation P will continue intermittently in the ordinary manner until the subscriber thereat removes his receiver. When this occurs a circuit for direct current is completed over the previously vtraced ringing circuit through the switchhook springs, transmitter, and receiver of the called substation for the ring cut oli' relay 62, which, while it is adjusted not to respond to alternating current,will operate over this circuit. On energizing, relay 62 disconnects the ringing current from the called line at larmature 107, at the same time. connects the talking circuit to the windings of the back bridge relay 51 at armatures 105 and 107 and their front contacts, and locks itself energized at armature, 106 and its front contact. A circuit is now completed extending from ground G13 off normal `springs 118 and its working contact, front contact and armature 106, conductor 121', through the lower winding of the back bridge relay 51, working contact of off normal spring 48 and the said spring, front contact and armature 107, and then over the previously traced lll),

ringing circuit back to wiper 114, armature 108 and its front contact, armature 105 and its front contact, working contact of oil' normal spring 4:9 and the said spring, and through the upper winding of the baclr bridge relay 51 to battery. Relay 51 will therefore energize,completing a circuit erttending trom ground G4 by way ot armature and its trent contactspring'117 of key K and its resting Contact, conduct-or 132, armature 200 and its resting contact, conductor 131, resting contact ot spring 118 and the said spring, andthrough the winding ot the slow actin(y relay 52 to battery. Relay 52 will attract its armatures and at armature 7 3 complete the circuit ot relay 53 and at armature 76 place ground on conductor 36 extending throughl the winding of relay 25 to battery. On energizing, thislatter relay .reverses the connections of the line relay 56 with regard to the trunk conductors 26 and 27 thereby reversing the battery back to the calling Vline vfor any desired purpose. The energization ot relayv 53 simply prepares the f operating circuits of the auxiliary selector G. y'llhe calling and called subscribers may now converse over the heavy conductors in theusual manner.

When the conversation is completed the connection may be released by the hanging up of the receiver at the calling' substation. Relay 56 will therefore ileenergize opening` the circuit ot' the slow acting release relay 57, which deenergizes also. This latter re` lay on decnergizing removes ground trom the release trunk 'conductor and at the same time closes circuit t'or the release magnet extending from ground G by way of armature 93 and its back contact oli' normal springs 117, and through the winding ot the release magnet 66 to battery. r1`he switch F will be immediately released by the energization ot magnet 66 and as the holdingcircuit tor the slow acting release relay 351 ot' the connector J and the switching relay 306 of the selector H has been opened. by the deenergization oit relay 57 each ot these relays will accordingly deenergize. tending from ground G2, by way of armature 399 and its back Contact. oli normal springs 374, and through the winding otl the release magnet 369 to battery, and rel.fcompletes a circuit extending from by way ot' armature 308 and its back contact, back contact and armature SL10, armature 341and its back contact, ott' normal springs 4315, and then through the windingl et the release magnet 342 to battery. lttag-v nets 869 and '312 will operate to restore their respective switches to their normal position. Thusnin the above described manner all the switches will beirestored to normal.

Let us now assumethat the calling` subscriber who has directed. the extension of the Dtelay 351 completes a circuit err;

previously described connection, desires to tall; with some other subscriber in the branch exchange. In order to do this he will merely dial the local branch exchange number ot that subscriber, thereby operating` the auxiliary selector G to select an idle branch eX- change second selector, after which the call will proceed in the ordinary manner.

This operation will now be described. lli'lhen the calling device of the substation A is operated a series ot' interruptions is produced in 'the circuit ot the line relay 56. At each retraction ot its armature 91, a circuit is con pleted extending troni ground G11, by way of armature 01 and its baci; contact, conductor 137, armature 220 and its bach contact, conductor 1&6, armature 104- and its resting Contact, armature 94 and its trent contact, armature 97 and its back contact, conductor 1110, through the winding ot' slow acting series relay 171, armature 281 and its baclr contact, armature 211 and its back Contact, and through the winding ot' the ycrtical magnet 177 to battery. will be noticed that this circuit was also operative when the main selector was operated in the original connection but under these conditions the series relay 58 is adjustH ed to'pull up lirst breaking the above traced circuit at armature 97, whereupon it was then ineti'ective. Relay 56 also completes another circuit. at each retraction ot' its armature 02 ent ,riding *from ground G by way ot armature and its back contact, front contact and arn'iature 95, conductor 138, and thence through the winding oll slow acting relay 170 to battery. This relay energiyes, and at armature 213 places fijround on conductor 136, and at armature and its trout contact places ground on conductor 151, extending by way ot armature and its trout contact, oli' normal springs 117, and through the winding of release magnet 66 to battery. lilagnet 06 operates to loci; itseli to ground on conductor 13 at armature 157, to open the operating and repasting circuits ot' the main selector F and 'to restore the said switch to its normal position. The slow acting series relay 171 cnergizes in series with the vertical magnet 177 and opens the operating circuits ot the main selector l? at armature 215. Magnet 177 operates in the usual manner to step the wipers 2351-238, inclusive, opposite some level otbanlr contacts in which trunk lines leading to selectors are terminated. Upon the wipers leaving their normal position the circuit ot the oli normal magnet 160 is completed and it operates to shift the springs 2110, 241, 2*-1r2, 2-15, and 2416 into their otln normal position in a similar manner to magnet 67. A circuit isthereby completed ex-` tending trem ground by way of armature 93 and its front Contact, conductor 36. conductor 123, armature 216 `and its trout contact, armature 234 and its back contact, olf normal springs 240, and thence through the winding of relay 172 to battery. Relay 172 energizes over this circuit locks itself to ground at armature 218 and its front contact, by Way ot the interrupter springs 181 ot' the rotary magnet 178, and at armature 219 and its front contact prepares the rotary magnet circuit. The release magnet 66 of the main selector F remains energized until the slow acting relay 17() deenergizes at the end of the vertical movement of the switch Gr, having maintained the operating circuits of the main selector F open. After the impulses to the vertical magnet 177 cease, the circuit through the winding oi relay 171 is open at back contact ot armature 91, relay 171 therefore deenergizes after an instant and completes a circuit to the rotary magnet 178. Magnet 178 operates to step the Wipers 235-238, inclusive, onto the first set of bank contacts in the selected level and also to open the locking circuit ot the interrupter relay 172 which deenergizes and opens the circuit of the rotary magnet which deenergizes also. Now if the selector switch associated with the tiret set of bank contacts is busy a ground potential will be present on the test contact engaged by the test Wiper 235. Then as soon as magnet 178 deenergizes the circuit of relay 172 will again be closed from ground by Way of the said test Wiper, armature 299 and its back contact, interrupter springs 181, and then over the previously traced circuit through the Winding of relay 172 to battery. The relay 172 will again energize therefore to close the circuit of the rotary magnet at armature 219 and its front contact. The rotary magnet operates as before to step the Wipers 235-238, inclusive, on to the next set of bank contacts and to open the locking circuit of yrelay 17 2 which deenergizes opening the rotary magnet circuit which deenergizes This alternate operation of relay 1.72 and the rotary magnet 178 continues until. an idle trunk is found which We Will assume, is the 4trunk line comprising conductors 262. 263, 264, and 265, the test contact 268 of which will be ungrounded and hence there will be no circuit for relay 172. The switching relay 169 which has hitherto been short circuited by the ground on the various test contacts will no7 be energized as there is no` ground potential on the test Contact ot' an idle trunk line. The circuit for the energization of relay 169 extends from ground on conductor 123 through the Winding ot relay 169, springs 181, thence over the previously traced circuit and through the Winding of relay 17 2 to battery. Relay 169 is of such high resistance that it alone will energize over the above traced circuit thereby opening the vertical magnet circuit at armature 211, placing ground on the reline relay 350 of the selected selector I.

This circuit extending from ground Gr11 by way of armature 92 and its front contact, ari'nature 77 and its resting contact, back contact and armature 72, conductor 127, armature 1,94-and-its back contact, back contact and armature 199, front contact and armature 210, armature 233 and its back contact, through the Winding of slow acting series relay 173, wiper 236, bank contact 269, conductor 263, armature 355 and its resting contact, and through the Windingof the line relay 350 of the selector 1.

Relays 173 and 350', Will energize over the circuit, relay 173 completing the circuit of slow acting relay 174 at armature 221, and relay 350 completing the circuit of' the slow acting rcleaserelay 351. The calling subscriber at substation A may novs7 operate .his calling device for the next digit of thedesir-ed number thereby 'producing a series of interriiptions in the circuit of the .line relay 56 oi? the main selector .F Which operates to repeat them to the line relay 350 of the selector I over the previously traced circuit. The line relay 350 responds thereto, to control the operation ot the vertical magnet 356 which operates to step the Wipers 359-362, inclusive, opposite the desired level of bank contacts. The selector then rotates to find an idle trunk line in identically the same manner as the selector H operated, which operation Was described fully hereinbefore.

Upon an idle trunk being selected which, we l will assume, is the trunk line comprising conductors 379-382, inclusive, the switching relay 354' will energize in the usual manner in series With the interlnpter relay 353. On its energization, relay 354 disconnects the incoming dialing conductor 263 from the Winding of the line relay 350 and extends it through armature 355 and its front Contact, Wiper 360, bank contact 376', conductor 380', armature 425 and its resting contact, back contact and armature 426 and then through the Winding of the line relay 400 of the connector K to bat tery. The switching relay 354 also extends therelease trunk conductor 262 by Way ofI front contact and armature 357', test wiper 359', bank contact 375', conductor 37 9', and through the Winding of the slow acting release relay 401 to battery.

The calling subscriber may now operate his calling device for the last two digit-s of his desired number thereby causing the line relay 56 of the main selector D to repeat these impulses to the line relay 400 of the connector K in the usual manner. The line relay 400 controls the operation of the connector to connect with the desired line. If this line should happen to be busy then the ductor 881 at armature 419.8 and at armature 426 opening the circuit to the line relay 400 or" the connector K. Pllhe busy tone is audible to the calling subscriber over a circuit similar to the one hereinbelore traced, and upon hearing this tone the calling subscriber will hang up thereby releasing the operated switches in a manner similar to that her-einbetore described.

Assuming no-w that the second called subscribers lin-e is idle, then as soon as relay 4.05 energizes the dialing conductor is opened as before at armature 1125, and the ringing circuit is prepared at armature 1127 and 129. As before described, as soon as the circuit to the line relay lOO is broken the slow acting series relay 17 3 deenergizes completing the circuit for the wiper cut on relay 176 and at the same time places the connector cut on tone in the calling subscribers line for a short interval noti 'ying him ot the operation. Upon relay 176 energizing, the ringing circuit tor the called subscriber is completed from the generator V and this current flows over a circuit similar to when the subscriber at substation P was signalled, through the ringer of called substation back through the low-er winding ot the ring cut oil relay 175. llfhen the subscriber answers the ring cut off relay energizes over the line circuit and operates to cut od the ring and complete the circuitoil the bach bridge relay 165 which also energizes over a circuit including the called subscribers line loop. Upon energizing., .relay 165 closes circuit tor the slow `cting relay 166 which relay operates to prepare the operating circuits of the main selector F, completes the circuit oit the slow acting relay 167 and also places ground on conductor 128 which extents througl'i the winding ot' the reversing relay to battery. rlhis latter relay operates as before, to reverse the battery over the trunk line tor any desirable purpose. Conversation may now be carried on between the two parties over the heavy line cnductors. Alfter this is terminated the connection may be released as before described by the calling subscriber replacing his receiver onthe switchhoolz.

rlhis passing ot 'the callv by the calling subscriber may be continued indefinitely as long as desirable each time releasing the called party in the connection upon the first digit of the nef-:t subscribers number if the called party remains on the line. lt however, the called subscriber hangs up irst a circuit tor the release magnet ot the selector which is then in use is effective. kAssuming the main tor l? to be in use; when the called subiber replaces his receiver on the switchbridge relay 165.

hook the circuit ot the back bridge relay 51 is opened which relay deenergizes sending` an impulse of current at armature to the slow acting yrelay 5&1 which energizes. A circuit is now effective extending trom ground G1, ottl normal spring 242 and its resting contact, conductor 148, front contact and armature 82, armature 74 and its back contact, oli normals rings 117, and through the winding ot release magnet- 66 to battery. Magnet 66 operates, opening the operating circuits ot the main selector as bei'iore, and restores the switch F to normal. Now, it' the calling subscriber should pass the call he will operate the main selector F again as in the case lirstdescribed, all the apparatus being now in its original position.

1t will now be assumed that the second called subscriber' called through element G finds that it is necessary to call another sub- -1 scriber for the calling party. Under these conditions the second called party will operate his calling device 'for the 'local subscribers number producing a number of series of interruptions in the, circuit of the back ilillien the second called subscriber operates his calling device tor the iii-st digit ot the local number the hack bridge relay 165 responds to the interruptions in its Iline circuit and at each retraction of its armature 193 completes a circuitk as follows:

`from ground G14 by way ot armature 193 no etlect. Relay 185 also energizes in parallel with the relay 168 and -being slow act-- ing relay, maintains its .armature attracted throughout each series of impulses serving to open the circuit to the line of the calling subscriber thereby preventing the dial impulses from causing him lany annoyance. The slow actingseries relay 58 also energizes in cries with the vertical magnet circuit and maintains its armature attracted thro-ugl-iout the vertical movement ot the switch. Magnet 611 operates before, to step the wipers 1124.15, inclusive, opposite some level of banlr contacts in which terminate trunk lines leading to selector switches. As beiore described, upon the wipers leaving their normal position the oli normal springs operate and a circuit is completed for the interruptor relay 59, which energizes, establishes a locking circuit 'for itself, and prepares the vrotary magnet circuit. At the end of the vertical movement of the switch, relay 58 deencrgizes completing the circuit of the rotary magnet 65 which operates to open the locking circuit of the interrupter relay 59 and to r0- tate the wipers 112-115, inclusive, into engagement with the first set of bank contacts in the selected level. The interrupter relay, of course, deenergizes, breaking the circuit of the rotary magnet which also deenergizes. The trunk selecting operation will go forward in the manner previously explained until a trunk is found terminating in an idle selector switch which it will be assumed is the trunk line compris-ing the conductors 250, 251, 252, and 253. Vhen the switching relay energizes, upon an idle trunk line being found, a repeating circuit is completed extending as follows: ground G11, armature 92 and its front contact, armature 7 7 and its back contact, back contact and armature 72, conductor 127, armature 194 and its front contact, front contact and armature 199, conductor 121, front contact and armature 90, armature 158 and its back cont-act, through the winding of the slow acting relay 61, wiper 113, bank contact 258, conductor 251, armature 800 and its back contact, and thence through the winding of the line relay 301 of the selector H. The operation of this selector and the connector operated in response to the succeeding digits of a third calle-d subscribers number will, of course, be identical with that hereinbefore described. Should the second called party discover that he made an error in calling one of his numbers before sending the lastdigit or during its transmission he may replace his receiver on the switchhook thereby breaking the. cir cuit of the back bridge relay 165 which deenergizes. A circuit is then completed extendfrom ground G13, off normal spring 118 and its working contact, armature 109 and its back contact, conductor 150, armature 203 and its front contact, back contact and armature 196, conductor 180, off normal springs 117, and through the winding of the release magnet 66 to battery. Magnet 66 voperates in the usual manner to restore the ymain selector to normal after which the succeeding switches will be restored by their respective release magnets.

However, if the second called subscriber completes the connection to the third called subscribers line and should then desire to release in case the line is busy or the party called dont answer he may do so by dialing the digit 1, thereby producing another interruption in the circuit of the back bridge relay 165 which operates to send an impulse of current to the slow acting relay 168 in the usual manner. A circuit is then effect-ive extending as follows: from ground G15 by Way of armature 192 and its front contact, armature 205 and its front contact, conductor 151, armature 110 and its front contact, (relay 63 now being energized), off normal springs 117 and through the winding of the release magnet 66 to battery. Magnet 66 will operate and the switch F will then be restored to its normal position. The operated switches will then be restored to normal in a manner hereinbefore described.

It may sometimes happen under certain conditions that an impulse of current is sent to the vertical magnet of one of the dual switches. It will be assumed that an impulse of current has been sent to the vertical magnet of the main selector F. Under these conditions magnet 611 will operate stepping the shaftup one step thereby causing the springs 1,19 to operate and upon the deenergization of the slow acting series relay 58 a circuit is completed extending from ground. G22, spring 119 and its front contact, back Contact and armature 98, off normal springs 117, and through the winding of the release magnet 66 to battery. Magnet 66 will operate and the switch F will be restored to normal. Therefore, even though the vertical magnet does operate one step the corresponding dual selectorl will be automatically restored to normal. that a subscriber who has connected over a trunk to the ldual switches may by dialing digit 1 four times restore which ever one of the dual switches next to be used to its normal condition because if the said one of the switches is normal it will step to the first level and release four times responsive to the four digits. If in an operated position the selector then seized and thereafter a connector will be operated, and finally a circuit will be completed for the release magnet of the operated dual switch in response to the next digit over` one of the release circuits herein described so the said selector' and con- It also follows nector will also be restored. Any subsequent digits 1 sent after the restoration of the switches will operate the restored dual switch and thereupon restore it. That is, if four digits 1 are not required to link the connector to the called line terminals and restore it, the extra digits 1 sent will have no linking effect as the dual switch element will operate and release idly for each extra digit 1.

lt will now be assumed that the second called subscriber after completing the setting up of the connection yto a third partys line does not wish to hold the line until that party answers. He will therefore replace his receiver on the switchhook, the circuit of\ the back bridge relay 165 is thereby broken and on its deenergization sends an impulse of current to the slow acting relay 168. A circuit is now effective fora'elease magnet 179 of the auxiliary selector G extending from ground G13, through ofi' normal Spring 118 and its working Contact, armature109 and its front Contact, conductor 1119, armature 204 and its front contact, armature 197 and its back contact, off normal springs 241,

f long as desired.

and then through the winding ot the release magnet 179 to battery. The magnet 17 9 will operate to restore the auxiliary selector G to normal after which the switches K and I that maintainedv the connection to the second calledsubscriber will be released by 'the operation of their respective release magnets. In the meantime the signalling' ot the third called subscriber will be going on and upon an answer being obtained conversation between the original calling and third called parties may take place over the same switches that were operated in the lirst case described. After the conversation is terminated the release will take place in the usual manner upon the subscribers replacing their receivers upon the switchhooks.

This third called subscriber may pass the call to a fourth subscriber in a manner similar to that above described except that the back bridge relay 51 will be operated in response to the various digits to control the operations of the auxiliary selector and the succeeding switches.

It will thus be seen that this passing of a call by either the calling or called subscriber may go on indelinitely and in each case only the two subscribers are in communication at once. It may be desirable however to arrange this system so that the three subscribers may remain on the connection for a conference, in this case the key K associated with the dual switches is operated by some person say the exchange attendant. Now when the Acall is passed by a called subscriber the three parties may remain in on the connection. The operation ot the system in this case will now be briefly described.

For the purposes of this description it will be assumed that a calling main exchange subscriber at substationrhas called abr-anch exchange subscriber at substation P by means ot' the main selector F and the succeeding switches in a mann-er similar 'to that hereinbefore explained, and that the subscriber thereat has responded and has extended the connection to the line' of another branch exchange subscriber such as the .one at substation O through the medium of the auxiliary selector G and the switch-es I and K. The subscriber at the substation O will be rung in the ordinary manner and that subscriber upon removing' ihis receiver from the switchhook will stop the ringingI ope"ation and complete the circuit ot the back bridge relay 165 as described hereinbefore. Upon energizing, relay 165 will close the circuit yot the slow acting relay 166 through the key spring 120 and its working contact and hence the release circuit through the contacts of the slow acting relay 52 is inettective. The three parties may now converse as It' atany time one of the branch exchange subscribers, the one at substation P for example, should desire to tall; to the calling subscriber alone he will simply operate his calling device for the digit 1, thereby producing one interruption in the circuit or' his back bridge relay 51. Upon the retraction of armatur 70, slow-releasing relay 54 will actuate, so when armature 71 retracts a circuit may he traced from ground G5 by way of armature 71 and its Yliront contact, armature 84 and its front contact, conductor 135, armature 229 and its front contact, oli normal .spring 241, and thence through the winding of the release magnet 179 to battery. Magnet 179 operates to restore the auxiliary selector G to normal a-tter which the selector l and connector K will be released. It will be seen that the subscriber at substation O could have released the subscriber at substation P in a similar manner by dialing 1. This circuit would extend 'trom ground G15, by way of armature 192 and its front contact, armature 205 and its front contact, conductor 151, armature 110 and its front contact, ott normal springs 11T and thence through the winding or the release magnet 66 to battery. ln this manner the system may be arranged so that the three subscribers may remain on the connection and at the same time providing means so that ir" it becomes necessary or desirable for one of the parties to converse secretly with the party calling over the trunk from the main exchange the third may be released. It will be seen that any digit might be dialed in place of 1 to release for the reason that the operated switch will release upon the first impulse as above described and then the release magnet will lock up through its armatures opening the operating circuits ot' that switch. This locking circuitot the release magnet will be cll'ective until all the `impulses ot' the digit called to release have ceased tor 'the reason that one slow acting series relay will be energized locking 'the release magnet in an obvious manner.

Under certain conditions it mightbe desir-able to arrange groups oi telephones under one number and it' one of these were busy the other would be selected automatically. The connectors J and K have also been designed to serve this class of subscribers. To arrange the connector J to serve this class oit subscribers the tie between the two testv .or .private bank contacts such as 381 and 382 is omitted in all except the private contacts o't the last telephone in the group. Now when this connector under the control of a calling subscriber attempts to connect with the first telephone in the group and this being busy, ground will only be present on the lower test contact. A circuit is now completed from the said grounded test contact by way of the test wiper 37S, sideswitch wiper in the second position and through the outer winding oli the private

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