USRE16317E - martin - Google Patents

Description

A ril 13 192s.

T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM 5 Sheets-Sheet 1 original Filed March 21, 1908 TsZbuZ G. Marfm.

April 13 1926.

T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM F a z omww n o 9 wm w u mum kw M 1 i .3

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April 9 T. c5. MARTIN TWOJIIRE AUTOMATIC TELEPHONE SYSTEM 5 h 0 t m H H T, a P m M 5 W yd? o i i Filed March 21, 1908 April 13,1926. R 16,317

T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM Qriginal Filed March 21 1908 5 Sheets-Sheet 4 R 16,317 T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM m 9 1 3 m A original Filed March 21, 1908 v 5 Sheets-Sheet 5 Inusn 1211- Talbul 52H STA Reissued Apr. 13, 1926.

"res PATENrO FFICE.

.mmo'r c mm, or omcaeo, rumors, ASSIGNOR, BY MESNE assremn'rsso 'nm, or cmcaeo, rumors, A conrona'rxon or 1mm;-

- TWO-m AUTOMATIO'TELE PHONE-SYSTBM.

application fled mm, 1908, saw no.

en ine In. 1,249,159, dated December 4, 1m. -10. 5'

* To allnohom in may come-m:

- Bent knownthat I, TALno'r G. MARTIN, a citizen of the United States of America, and resident of Chicago, Cook County, Illinois, .have invented a (ertain new and useful Improvement in Two-Wire Automatic Tele phone Systems, of which the following is a specification. My invention relates to telephone systems in general; but more particularly to automatic or semi-automatic telephone exchange system, and especially to systems in which the. subscribers" lines are free from operatgroimds outside ofthe exchgn e or central Station, these rbeilig'ordinari y known astwo-wire systems. P' Y Objects of my invention are to provide a two-wim system-- in which automatic. partyline service can be given the subscribers thereof; to provide a two-wire automatic telephone exchange system in which subscriberson the same line signal each other by means of ush-buttons at their respective stations, whil a called subscriber on another line is signaled automatically from the exchange or central station; to provide a twowire automatie telephone exchange system in which the connectors ,willlock .on busy called lines, without closing the calling line in connection r therewith, the calling subscriber being at the same time given a bus) signal; to provide atwo-wire automatic telophone exchange system in which provision is made for enabling a party-line subscriber to call back on his own line, in order toestablish telephonic communication with another'subscriber on the same line; and a.

.provide certain novel details and-features of improvement and combinations tending to increase the general etficiency and serviceability of a-:telephone exchange system of Y this particular character.

To the foregoing and other useful endsv my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Figure 1 is a diagrammatic representation of-party- "line equipment embodying the principles of my invention. The substations A and A are allotted to a common line which terminates atthe central office in the line switch Renewed April 12, 1e17, Serial No. 161.050.

Application for reissue filed August 30,1918. Serial C. At D is represented the master switch for controlling the line switches of the group of. which the switch C is ,a member. represents diagrammatically a first-selector switch. v Fig. 2 represents diagrammatically the central office second-selector switch F and the connector switch H. At C is shown a line switch allotted to the party-line of which substations A and A are members. A central battery B having its positive terminal preferably grounded at G provides battery current for talking and operating purposes, Fig. 3 shows how a subscriber may-operate central ofiice switches to call back and signal a subscriber on his own line.

Fig. 4 represents more fully the I line switch C and the controlling master switch D. Fig. 5 is a detail View of the master switch bank 0.

rangement of the lines by means of which the different substations may be signaled selectively.

In this system each subscribers line is, of course, provided with a line switch similar to the line switch C, and usually one- .hundred of these ,form a group. Also, to each Such group there is allotted a group of first-selector switches in common. The firstselector switches may'in turn be operated to first select any one of a number'of groups of second-selectors, and then some one, of the selected group which may be idle. The second-selector switches may in turn be operated to first select any one of a number of groups of connector switches, and then some one of the connectors of the selected group which may be idle. Each group of connector-switches is also arranged to take care of one-hundred subscribersthat is, if any subscriber in the system wants to call another subscriber he must, through the ,medium of the first selector and second-selector switches, pick out a certain group of connectors, any one of the connectors of-which group is capableof establishing the final connection with the desired subscriber in a particular, hundred.

or approved type. As shown, it will be seen that substation A is somewhat different from e .usual lutomatio substation, mid subst on A being arranged and modified to operate in connection with a two-wire stas -that -With a s stem in which no gqmd is us at the subscribers substation. Substation A, for example, comprises the usual receiver 2, switch-hook 3, induction. coil 4 which consists of the griuniry'winding 5 and secondary windin ti an'smitter 7, condenser 8, ringer 9 an im ulse wheel 10 which has the usual im- 16 which, when the switch-hook is up, peroiuding the transmitter mite the springs 17 and 18 to engage, thereby bridging across the subscribers line conductors 19 and 20. the rimary circuit inin series with the 'rimary winding 5; but when the switchhook is lowered the spring 17 is carried out of engagement with the spring 18 and into engagement with the spring 18, whereby the ringer 9 in series with the condenser 8 is bridged across the line conductors 19 and 20 instead. Furthermore, the substation A is provided with a .signaling button 5 which, when pressed, disengages the springs 6 and 7, whereby the short-circuit or shunt around the resistance coil 8 is removed. The line switch C (Fig. 4) comprises a plunger 21, plunger arm 22, trip magnet 23, and switch-release magnet 24, all of which are assembled u on a suitable 'base or frame (not shown). he said switch-release ma net is rovided with an'armature 25 that 1s 'vot on a in 26 which rises from the se of the swltch. The said armature cararmature 27 that is controlled by the trip magnet 23. The pin 28 about which the armature 27'moves is carried on the end of thearmature 25. The plunger 21 is pivotally secured by'the pin 29 to the plunger arm 22, which latter is in. turn pivoted by a pin 30 that rises from the switch frame not shown). The lug 31 may be stamped m the frame and is provided as a stop for the armature 25. Upon the armature '27 is secured the member 32 which is adapted to normally engage the end 33 of the plun 1 arm 22. Furthermore, the said line switc is provided with a bank of terminals, usually ten in number, but only one of which is shown at Q (Fi 4). The said terminal Q is shown turned rom its true position with respect to the swing of the plunger 21, and

the bushing 34 is correspondingly turned,

all for the pur ose of making the illustration clearer. T e terminal Q, comprises the springs 35 and 36, 37 and38, 39 and 40, and 41 and 42. These s rin are normally disconnected from eac ot er, but are driven into contact, as shown in the drawings, when the plunger 21 engages the bank terminal Q. When the plunger 21 dise ages from the bank terminal Q, the said p unger may take one of two positions relative to the plunger shaft 43-'-that is, the plunger may return to either locked or sliding engagement with the shaft 43. When the plunger 21 is in locked engagement with the plunger shaft 43, the notch 44 is in engagement with the flange or web 45 of the shaft 43; and when in sliding engagement the fan-like tail-piece 46 rests in the position shown by the dotted lines in Fig. 4--that is, when the plunger shaft is operated the plunger 21 is not carried along with the locked plungers, but remains in the dotted position, the plunger shaft sliding upon the edge of the tail-piece 46. The general operation of the switch is as follows: The trip magnet'23 is energized when the receiver is removed from the switch-hook and the armature 27 is attracted against the magnet cores. When the armature 27 is attracted the catch 32 slides out of contact with the end 33 of the plunger arm 22, and the said plunger arm 22, owing to the tension of the spring 47, moves about the pin 30 and thrusts the plunger 21 into the bank terminal Q; and when the trip magnet again deen'ergizes, the trip armature 27 falls against the end 33 of the plunger arm 22, as shown. Furthermore, when the line switch operates, and the plunger 21 is thrust onto the bank terminal Q, the shaft 43 is advanced one step, as will be explained, to carry the locked plungers opposite the next idle trunk-line. The switch is restored by the release magnet 24, on whose energization the armature 25 is attracted, and accordingly the triparmature 27 is moved upwar-dly until the catch 32 slides overv the end 33; then whenthe release magnet 24 becomes deenergized the armature 25 returns to normal position and remains at rest against the stop 31. Furthermore, since the ill] Ion

plunger arm 22 is now in engagement with the catch 32 of the armature 27, the said plunger arm'is also moved about the pin 30, whereby the plunger 21 is moved from 'svidedfor controlling the sta isca in plunged .rnad But if after the plunger is released,

netjn engement. with the lunger shaft web'45. fter all the trunk-liiies have been successively seized, the shaft 43 then passes from its last position and moves toward point, picking up the plunger 21 when t webiofthe said shaft over which the slot :44 normally rides arrives at the position in which the plunger 21 was originally released-that is, the plunger passes into locked engagement with the shaft when the'slot 44 slips over the web of said shaft.

From thence on the plunger 21 is carried in locked engagement by the shaft 43 until it in when another call is and before theshaft 43 returns to pick up said plunger, the switch C is again operated, the plunger 21 again engages the same terminal Q. The bridge-cut-ofi relay 48 is prosprings 49, 50,

-51 and 52, and, upon energizing, operates to shift the s rings 49 and 51 out of engagement with tli thexsprings are thus operated the line switch Ci a disconnected from the substation line a springs 50 and 52. When conductors.

' Theimaster' switch D, which may be of any. suitable or approved type, is provided for operating the plunger shaft 43 and for controlling certain circuits that will be dis ,olosed hereinafter. It, comprises the following details: A motor magnet 53 for operatthe ratchet wheel 54, which latter is .designed for operating the plunger shaft 43 vthrough the medium of the cam 55, and a differential rela 56- for controlling the energizing circuit the motor ma et 53. The

., wiper,

said master switch also has a ank 0 com- .prlsing a plurality of individual contact segments a and a common metallic segment .57, as shown in Fig. 4. The wiper 58 is adalpted toremain in constant engagement wit thefiaank O, and to at all times, except when the wiper is passing from the extreme ,left t contact 59 to the extreme right contact 60, maintain some. one of thesegments a in electrical connection with, the common segment 57. As shown in Fig. the individual segments a are separated from the common segment 57 by the insulating strip61. The

spring 62 is provided so that when the wiper is carried to the contact on the extreme right, theupper part of the wiper 58 slides I on uide spring 62, thus preventing the From placing any of the individual segments a in contact with the common segment 57, whereby some interference might be caused with the master switch. The

wiper 58 is operated in a step-by-step manner by the ratchet wheel 54, through the medium of the cam member 55 rigidly secured torthe said wiper 58, and is adapted to successively engage the pins 63, 64, 65

and 66 upon the said ratchet wheel 54; The

motor magnet 53 is provided with an armature 67 upon the end of which there is suitably secured apawl 68. Each time that the, said magnet is' energized, the armature 67 is attracted against the magnet cores, and the pawl 68 engages a tooth on the ratchet wheel 54 thereby advancing the latter one step. It will be seen, therefore, that. as the ratchet wheel 54 advances, the wiper58 advances step by step from right to left; and when the pin 63, for instance, clears the cam 55, the retracting spring 69 then re-- stores the wiper 58 to its first position at the right of the bank. and in engagement with the first segment 60. The said motor' magnet is provided with 'a couple of interrupter springs 70 and 71 that are included in the energizing circuit of the said motor magnet, which energizing circuit also comprises the springs 72 and 73 controlled by the difl'erential relay 56. Therefore, whenever the difierential relay is energized the springs 72 and 73 are pressed into contact, and the motor magnet 53"operates step by step as long as the differential relay 56 remains energized. Furthermore, it is assumed that the terminal Q of the line switch .C is the first terminal ofthe line switch bank. While in normal locking engagement with the shaft 43, the plunger 21 is retained in vfront of said terminal by the plunger shaft 43, whenever the master switch wiper 58 is in engagement with the bank segment 60; but as the motor magnet 53 advances the wiper 58 onto the second segment 74, the said plunger and all idle plungers similarly engaging the shaft-43 ale carried opposite the next terminal of the line switch bank. It should be-noted that in each line switch bank all of the springs 35 are permanently connected and may be made of one common piece. 'The springs 36, however, are individualthat is, there is one separate and distinct spring for every bank set Q,,there bein ten in'the bank. The sprin 37, 39 and are a 1 common, and the sprin 38, 40 and 42, like the springs 36, are individual. For every bank terminal Q there is a trunk-line of three conductors 75, 76 and 77 leading to a selector; and there is also a normal trunkline comprising the conductors 78, 79 and 80 leadin to the connector banks. The subscribers 1ne conductors 19 and 20 terminate in the springs 35 and 37 which, as has been stated, are common springs. When thesubscriber operates the line switch-C, and the plunger 21 engages the terminal Q, the subscribers line conductors 19 and 20 are extended to the vertical and rotary trunk conductors 75 and 76, thence through the windings 21 and 22 of the relay 23,(as shown in Fig. 1) to the first-selector switch E.

The first-selector switch shown atE is of the general type described in United States Letters Patent No. 815,321, granted March 41, like the springs 35, a

vi nd abate the rotary trun-k line conductor trials the vertical ma 13, 1906,,to Keith, Erickson & Erickson, and, CI, ,is modified to adapt it to operate in connection with a two-wire system. It embodies among other details the following ieatnres: The switch shaft (not shown) car- ,ries the negative and positive line wipers 81 and 82, and the private wiper 83. The side :Ilitch is well known and comprises the side lswitch 'wiqnrs 84, '85, 86 and 87 which may He i =1: ated as the vertical, rotary and private side switch wipers, and the rotary .magnetwviper,respectively. The side switch :ia-mnder the control of the private magnet 88, and when the side switch is in normal f m position the wipers 84, 85, 86 and 87 occupy thevcontact points 89, 90, 91 and 92, nespectively. In the second position the -wipersnest on the contact points 93, 94, 95 a-l1d96, mespectively; and when in third po- 1 Edition the contact points 97, 98, 99 and 100 mortgaged by their respective wipers. The windings of the usual vertical and rotary dine relays are, in this case, combined into one double-wound relay 101 comprising the 2 winding 102 which is connected with the blttery dead 103, and also with the vertical "wank-line conductor, when the side switch wiper 84-h; in first or second position. The second winding 104 is connected to ground,

7 'Whenthe side switch wiper'85 is in first or second sition. Through the medium of this don I -wound relay, and While the side switch is in first position, the subscriber conet 105 which operates to raise the switc shaft and wipers 81, 82 and 83 vertically. This line relay 101 also controls the private magnet relay 106, which latter in turn controls the private magnet 88. As usual, the private magnet controls the side switch. While the side switch in in second position the rotary magnet 107 which operates to carrythe switch shaft and wipers "81, 82-and 83 in a rotary direction, is ener- "4 6 The release magnet 108 provides means for restoring the selector switch to normal position. Upon the switch shaft which carries the wipers 81, 82 and 83 there is mounted the arm 109 which, when the shaft is {raised one or more steps, permits the spring 110 to engage the contact point 111,

whereby the release magnet 108 is connected,

to the battery lead. Therelease relay 112 is provided for closing the energizing circuit ofthe release magnet 108 after the switch is operated. The'back-release relay 113 is provlded for opening the energizing circuit through the release magnet 24 of the line switch. The relays 106, 112 and 113 are slow-acting relaysthat is, they are so provided with a copper shieldgthat when .enerd and the energizing circuit then broken, fii e said relays remain in an operated posiftion for a moment or so. In other words,

be recognized and understood.

they do not instantly return to normal position after the energizing circuit is broken.

The second-selector F (Fig. 2) is similar to the first-selector E, and is provided with the usual double-wound line relay 114 having the windings 115 and 116 connected with. the vertical and rotary side switch wipers 117 and 118 in the same manner in which the windings of the relay 101 of the selector switch E are connected with their vertical and rotary'side switch wipers. Since like parts are similarly represented, the rotary magnet 119 and the vertical magnet 120 will The release magnet 121 is operated in the same manner in connection with the switch F that the release :magnet 108 is operated in connection with the switch E. The private magnet 1 22 is controlled by the private magnet relay'123. The release relay 124 of thesecond-selector switch F performs the same function in connection with this switch-that the release relay 112 and the back-release relay 113 perform in connection with the first-selector switch E-that is, the springs controlled by the relays 112 and 113'are so arranged in the second-selector switch F that they are controlled by the one relay 124. In the switch F the rela s 123 and 124 are so arranged that they eenergize slowly,'the same as the relays 106, 112 and 113 of the selector switch E.

The connector switch H is a modified form of the connector switch disclosed in United States Letters Patent No. 815,176 granted March 13, 1906, to Keith, Erickson Erickson. The connector switch shaft (not shown), like the switch shaft of the Belector, carries the line wipers 125 and 126 and a private wiper 127. The connector switch is also controlled by the calling subscriber though the medium of a doublewound line relay 128. The line relay "128 is provided with the windings 129 and 130. One terminal of the winding 129 is connected to the battery lead, while the other terminal is connected with the vertical trunkline conductor. The winding 130 is connect ed with ground and also with the rotary trunk-line conductor. This line relay 128 directly controls the vertical magnet 131. The purpose of the vertical magnet 131 is to give the shaft and shaft wipers a vertical motion, and the rotary magnet 132 imparts to the shaft and shaft wipers a rotary or circular motion. The connector switch is also provided with the slow-acting release relay 133 which is the same as'the release relay 124 of the second-selector switch. As usual, the private magnet relay 134 controls the private magnet 135, which latter controls the side switch wipers 136, 137, 138, 139 and 140. The back hndge relay 141, comprising the windings 142 and 143, provides the means whereby: the called subscriber. is furnished withhattery current for talking purposes. As here shown, my connector I switch. is of the automatic ringing typell thatis, a si aling of the called subscriber is nbb idepeliti ht upon the calling subscriber fissingia signaling button when he calls a not his own; for as-Soon ias. connection is'aestablished withthe desired line the interrupter 144 intermittently closes an-energizing.v circuit through the ringer relay 145,

whenehythe terminals of the ringer generator=.I-,are;intermittenly bridged across the normal conductors of. the called line. The relay 146v isso arranged that if a busy line is called the connector. side switch is locked in second :Rosition, and the-calling subscriber is 'ren t e busy-signal. The means whereby i with the winding 150 of the'induction-coil '30 151+; eThe windin 152 is connected with the 153, and w on the relay'146 energizes, fl8-:Wi%l,b6' explained, the busy-signaling apparatus is connected with the connector or side switch 136.

.tfi'heoperation of the system may be, more clearly understood from-an explanation of m bpcrationi in establishing a connection. It will wbfi assumed that the subscriber at substation A wishes to call the subscriber at substation A, to which latter is allottedthenumber 2220. To call the number 2220 (substation ,A, Fig. 2) the subscriber at substation A (Fig. 1) removes his receiver from the-switch-hook, and operates the calls, ing dewice'for-eachdigit, in the well-known manner-that-is, when the receiver is removedrfromthe switch-hook a preliminary impulse provides an energizing circuit for the. m magnet 23 of the line switch C, whereby the line switch C-is operated to an-Qidle and waiting or preselected trunk-lineleading to a first-selector switch. Tile-dill is turned for the first digit, and u n neturning to normal positionoperates.

first-selector switch'to establish connection mith an idlertrunk-line leading to a sepondvsele'ctor switch. in similar manner f the-dial, upon returning to normal position gpgsthetsecond digigoperates the second- 1w r aswitch. Into. establish connection with an idle-truhk-liile .leading: to a con- 1m ,Lswiteh..-= she-amp delivered by iorthelast'two digits are directed towardithe connector H, which latter opertgplace shaft wipers in connection with the contacts corresponding to the desired subscriber. The preliminary impulse for energizing the trip magnet 23 occurs when the receiver 2 is removed from the switch-hook 3 and the cam-arm I6 permits the spring-.17 to engage the .spring 18., thereby removing the rmger from across the line and bringing the primary circuit instead. When the primary circuit is thus' through battery Bto ground G. As soon as the .trip magnet 23 energizes, the armature 27 I is attracted and the plunger 21 is liberated and thrust into the bank terminal Qbythe spring 47, assuming that the plunger .21 is opposite theterminal Q at the time. When the plunger 21 engages the bank terminal Q, an energizing clrcuit is established through the motor magnet relay 56, which inturn operates to close an energizing circuit through the motor magnet 53 of the master=switch D. The motor magnet then operates to advance all idle plungers that are in locking engagement with the shaft 43 opposite the next idle bank terminal similar to the terminal Q. The circuit through the relay '56 extends from ground G through the winding 158 of the relay56 to the common segment 57, thence through the wiper 58, through the contact 60, conductor 159, bank terminal springs 42 and 41, through the Winding of therelease magnet 24 to the battery lead 103;, thence through battery B to ground G. Although this circuit includes the release magnet 24, the said magnet does not operatively energize, since the winding of the relay 56 is of a high resistance, while the winding of the release magnet 24 is comparatively low. The relay 56, upon energizing, operates to-place the sprlngs 72 and 73 n contact, whereby a circuit is completed throu h. the motor magnet 53, said circuit exten ingsfrom ground G through the springs 72 and 73, motor magnet springs and 71, through the winding of the motor magnet 53 tothe battery lead 103,. thence through batteryB to'ground G. The motor magnet 53, upon energizing,'attracts its armature 67, whereby the pawl 68*engages the ratchet wheel 54, advancing the latter one step. When the armature 67 is attractedagainst the magnet cores, the springs 70 and 71 disengage, thereby breaking the energizing circuit through the motor magnet 53 and permitting the armature 67 to return to normll The cam 55, bein 1n engagemcn with the pin 63 upon the ratchet wheel 54gis operated to advance the plunger shaft43 andall idle plungers that may be inmormal locked position with the shaft 43,

' opposite another terminal similar to the terminal Q, assuming the next succeeding trunk is idle.- Consequently, the wiper arm 58 1s carried from the contact point 60 (which corresponds to the terminal Q) to the contact point 74, which latter corresponds to the terminal beiore which the advanced idle plungers are now restin Suppose that nine subscribers have cal ed, and that the master switch has thus operated ninesteps, carrying the wiper 58 to. the last contact point 59. Now, when the motor magnet 53 operates for the next step, when the tenth subscriber calls, .the wipe:- 58 passes back and drops into engagement with the contact pointdO. If the first trunk is still busy thawiper58 finds a battery potential on w the contact 60, and an energizing circuit is established through the differential relay 56,

which in turn operates "to close an energiz ing circuit through the motor magnet 53. The current through the said relay 56 fiows from =the said contact 60 through the wiper mm, however,

, time 58 to the common segment '57, and through the winding 158 of the difl'erential relay: 56 to ground G. When this rela energizes it operates to close the circuit -t rough the motor magnet 53, and the motor magnet then operates, as previously explained, to

rotate the ratchet wheel 54 one step, and the master switch bank wiper 58 one step also andinto en gemont with the secondsegmerit 74. en thus advanced one step the plunger shaft 43 carries all idle" plungers that are in locking engagement with said shaft' 'op te the second bank terminal, as rcvious y explained. If there should still a 'arding' potential at the bank segment 7:, 'the differential relay 56 will re main energized, whereby the energizing circuit through the motor magnet 53 is agam completed when the motor magnet sprlngs 70 and 72 again engage, and as a result the motor magnet 53 is again operated, whereby the pin shaft 43 and the master switch wipor"5 are advanced another step. This process continues as long as the wiper 58 con ti'nuesto find segments with'guarding potentifls. As soon as an idle segment is the one "zing circuit throng; the relay 56 is bro n, at which I esaid may in turn breaks the energining circuit iorthe motor magnet 53, until the floatsubscriber makes a. call. At the that the longer 21 enters the bank termini! Q the 0 lowing sptrings are pressed into'contnctr and 36, 3 and 38, 39 and 40511111 4]. and 49. The an of the man rings 39 and 4t) closes a circuit through t e cut-oil relay 48 extending from ground G through the springs 16 and 17, springs 18 and 19 of the relay 23 (which is now energized, as will be explained), conductor 157, through the sprin s and 39, conductor 160, rel 48 to t c'battery lead 103, thence through li attery B to ground G. The said relay, upon energizing, operates to carry the springs 49 and51 out of en agement with the springs and 52. on these springs disengage, the resistance coil 154 is disconnected from the vertical line conductor 19, and the trip magnet 23 is disconnected from the rotary line conductor 20. The engagement of the bank springs 39 and 40' also establishes a guarding potential by way of the normal conductor 8.0 to the connector private bank contacts corresponding to the line that terminates in the line switch C, to revent any subscriber from calling the sai line after the calling subscriber at sub station A removes his receiver preparatory to making a call, as explained. Also, the closure of connection between the springs 41 and 42 establishes a guarding potential at the master switch bank contact 60, over the following circuit: irom battery B to the battery lead 103, thence throu h the winding of the release ma =et 24,'t rou h the springs 41 and 42, con uctor 159 to t said contact point 60. It will be understood that the bank terminal Q, being the first bank terminal of the line switch bank, corresponds to the first segment of the masster switch bank 0 and, therefore, to the trunk-line the conductors 7 5, 76" and 77 of which terminate in the first-selector switch E. This arding potential protects the seized trun conductors 75, 76 and 77 from being seized by other plungers, as already explained. The closure of connection between the springs 35 and 36 extends the calling subscribers vertical line conductor 19 to the vertical trunk conductor and the side switch wiper 84 of the first-selector switch E. The closure of contact between the springs 37 and 38 in a similar manner extends the subscribers rotary line conductor 20 to the rotary trunk conductor 76 and to the side switch wiper 85 of the selector E. The subscriber has thus established connection with the next selector switch, which is now operated by the impulses that are delivered when the dial returns to normal ositionfor the first digit. When the subscribers' line conductors 19 and 20 are thus extended to the first-selector switch E, an energizing circuit is established through the line relay 101 extending from ground G 'through the winding 104 to'the contact point 90, side switch wiper 85, wind ing 22 of the rela 23, trunk conductor 76, through the ban springs 38 and 37 to the rotary line, conductor 20, through thesprings 17fand 1*8, impulse springs and 14, rimary winding 5, transmitter 7 to the vertical line conductor 19, through the bank springs and 36, trunk conductor 7 5, windi ing 21 of the relay 23, side switch wiper 84,;con'tactpoint 89, through the winding 102 to the battery lead'103, thence through battery B to, round G. Both windings'of therelay 23 eing included in this circuit, 1 the said relay operatively energizes to place the springs 19 and 18 in contact, thereby providing the guarding potential for pro- V tecting' the line and completing an energizing circuit forthe-bridge-cut-off relay 48, as

is'established through the-releaserelay 112 i e iitending from ground Gr through the circuit is established through the private magnet 88. This circuit extends from ground G through the springs 167 and 168, private magnet 88 to the battery lead 103, thence through battery B to ground G'. The private magnet relay 106 deenergizes after the last vertical impulse, since its energizing circuit is no longer maintained after'the springs 161 and 166 disengage. Hence, the said relay I deenergizes, permitting the springs 167 and 168 to disengage, whereby the energizing circuit through the private magnet 88 is in turn broken, which private magnet now deenergizes and permits the side switch to pass from firstto second position, permitting the side switch wipers 86 and 87 to engage the contact points 95 and 96, respectively. The closure of contact between t e side switch wiper 87 and the contact i0 springs 161 and 162, relay 112 to the battery as lead 103, thence throu h battery B to ground G. The'release reiay 112, upon energii ing, operates 'to carry the spring 163 out efengagement with the spring 164 and into point 96 sets up an energizing circuit for the i rotary magnet 107 from ground G through the interrupter spring 169, through the'winding of the rotary magnet 107, contact point 96, side switch wiper 87 to the ,with th -i'nglG-i' This iS fl zcondition ofthe first-sel switch E 'wliefi the subscriber operates the dial for the iii tdigit. The first digit being 2, the im- "pulse spring 14 is twice carried out of engageme it with the impulse spring 15. As

a' result the energizing circuit throughthe v linerelay 101is broken twice, and the spring 161"comes into contact with the spring-"166 twice. .After the two impulses are thus I trimsinitted,-the-line relay 101 again enerand carries the spring 161 into contact with the spring 162. As previously expIained,- the relay 112 is slow-acting--that is,

" slow todeenergize; and when its energizing I: e'iifcuitis momentarily broken, during the vertical impulses just delivered, the said does not deenergiz'e, but remains in an opemted position with the spring 163 in contact Wlth the spring 165. Then, when his ring'lfil en'gages the spring 166, two iifip F are transmitted to the vertical In et 105*iro1h-ground Gr through the sp 161*and-166 to the springs 163' and 165, t rough the private magnet relay 106,

' through the windin of the vertical magnet- 105, contact int side switch wiper 87 v foithe battery lead 103, thence through batteryiB'to' ground G. The impulses being i r If, transmitted, the vertical magnet 105' is thereby energized twice; and -the shaft :firs are? given two vertical steps in the known manner. It'will be seen that the =priiatemagnet relay-106 is included in the a energizin circuitof thevertical magnet 105.

i re

' V my also energizes but being a slow= afifing re ay it energizes-on the first im-i pnlse -aflfllremains so until all the impulses transmitted." This relay, upon-enerratesto close the springs 167 slid in contact, whereby sun-energizing battery lead .103, thence through battery B to ground G. The said rotary magnet then operates to rotate the shaft wiper-s81, 82 and 83 of the selector E into engagement .lines, t en as soon as the private wiper 83 engages the first private bank contact, the private magnet 88 again energizes, locking the side switch in second position. The energizing circuit for said private magnet extends from the grounded terminal G of the battery B through an occupying switch (not shown), through the private wiper 83, thence through the conductor 173 to theside switch wiper 86, contact point 95, throu h the winding of theprivate magnet 88 to t e battery lead 103, thence. through battery B to ground G. The private magnet 88, upon thus becoming energized, locks the side switch wiper 87 in, engagement with the contact point 96, whereby the rotary magnet 107 will be energized step by step until the wipers are carried beyond the last busy with the first contact of the secondvlevelof trunk-line. At the instant that the private 1 wiperleaves the last busy contact point the energizing circuit through the .private magnet 88 is destroyed, and as a result the selector'side switch passes to third position If, however, thereare no busy trunk lines, the private magnet '88 releases 'the side-switch to third position as soon as the wipers are carried into engagement with the first trunk- As soon as the side switch. passes to third position, as stated, the subscribers line conductors 19'and 20 are extended to the conductors 170 and 171, which, in this case,

s n a I.

98,. respectively.

it is assumed lead to the second-selector switch F. The extending ofthe line occurs, of course, as soon as the side switch wipers 84 and 85' engage the contact points 97 and When the subscribers line conductors are thus extended to the selector switch F an energizing circuit is established through the line relay 114, in the some manner in which the energizju ing circuit was established through the line re ay 101 of the selector E when the subsoribers line conductors 19 and 20 were extendodrtl'irough the line switch bank to the trunk conductors and 76. The relay 114, ll energizing, operates to shift the spring 41mm the spring 17 5 to the spring 176. when thesprings 174 and 176 engage, an cnergizin circuit is established through the misuse re y 124. This circuit extends from as mild G through the springs 174 and 176, onfih-the relay 124 to the battery lead 103' t ence through battery B to ground G.

V The relay, upon energizing, 0 rates to shift the spring 177 from the spring 17 8 to the w 4 179, and the springs 180 and 181 are n '-i' in contact. This operation of the second-selector switch F occurs at the instant M the side switch wipers 84 and85 of the-selector switchE ass to third position wand the subscribers line conductors l9 and 20 to the second-selector switch F. when the secondselector switch, therefore, thus operates, a guarding potential is establinhedat the private wiper 83 for protect- T86 ing theseized trunk-line conductors 171 and 1:72 againm seizure b another calling firstmlector. This guar ing potential extends from ground G8 to the contact point 182, side switch wiper 183, through the springs 60 181 and 180, conductor 172 to the contact engtgedi'by the rivate wiper 83. Furthermore, when the rst-selector, switch E operates and the side switch passes to third position',a new energizing circuit is established ll through therelease relay 112. This energzingoircuit extends from ground G at so eetor switch F through the springs 181 and 180, conductor 172, shaft wiper 83, condu0t0r' i173, through the side switch wiper 86, contact oint'99, relay 112, through the blttery' le 103, thence through battery B to ground G; The relay 112 thus remains in an operated position with the spring 163 in 1' cut with the spring 165, but the line my 101 returns to normal position when the sidoswitch wipers 84 and 85 engage the contact points 97 and 98, respective y. The" circuit through the line relay 114 extends I u 'ound G through the wind- .ing 116) to "t e side switch wiper 118,

' thence through the conductor 171, wind- 29, conductor 76 and line conductor 20, through the primary circuit of the substation, throu the vertical line conductor 1; g")! the trunk conductor .75,

winding 21, conductor 170, side switch wiper 117, through the winding 115 of the relay 114 to the battery lead 103, thence through battery B to ground Gr. When the dial returns to normal position for the 1 second digit 2, this circuit through the line relay 114 is interrupted twice, when the im pulse spring 14 is carried out of engagement with the spring 15 by the impulse teeth on the wheel 10. The circuit being interrupted twice, said relay 114 momentarily deenergizes twice, thus permitting the spring 174 to engage the spring 175 a like number of times, whereby an energizingcircuit is twice completed through the vertical magnet 120 1 extending from groundGr to the springs 174 and 175, springs 177 and 179, through the winding of the private magnet relay 123, through the winding of the vertical magnet 1 20, contact point 184, side switch wiper 185 l to the battery lead 103, and through battery B to ground G. The private magnet relay 123 being included in this circuit energizes, and since it is a slow-acting relay it remains in an operated position until the last ver- .0 tical impulse is transmitted, and the relay 114 remains energized with the'spring 174 in contact with the spring 17 6, whereby the circuit through the private magnet relay and the vertical magnet 120 remains open. When the relay 123 energizes, the spnngs 186 and 187 are pressed into contact, thereby causing an energizing current to flow throu h the private magnet 122, the circuit exten ing from ground G through the springs 187 and 186, through the winding of the private magnet 122 to the battery lead 103, thence through battery B to ground G. When the relay 123 deenergizes and breaks the energizing circuit through the private magnet 122, the private magnet also deenergizes and permits the side switch to pass from first to second position. When the side switch wiper 185 pawes to second position and finto engagement with the contact point 188, an energizing circuit is established through the rotary magnet 119, which latter now operates, as explained in connection with the rotary magnet 107 of the selector switch E, to select an idle trunk-line leading to the connector switch. After the switch comes to rest, with the side switch in third position, the shaft wipers 189, 190 and 191 are in engagement with thetrunk conductors 192, 193 and 194, respectively, which lead to the connector switch H (Fig. 2). At the instant that the side switch wipers 117 and 118 pass to third position, in engagement with the contact points 195 and 196 the subscribers line conductors are extended to the connectorswit'ch H and an energizing circuit is established through the line relay 128 and the differential relay 23, in the same manner in which the energizing eir- .cuit was established through the line relay 114 of the selector switch F when the side switch wipers of the first-selector passed :to tliirdf 'osition". 'The energizing circult 6 through 't e line relay 128 extends from ground G? through the winding 130, trunk conductors 193,171 and 76 to the line conducto'r 20, thence through the substation to the vertical line conductor 19, trunk con- .lo'ductors 7 5, 170 and 192, thence through the winding 129 to the battery lead 103, and ,through battery B to ground G. The line b relay 128, upon energizing, operatesto shift the spring 196 from the spring 197 to the y 1 7 spring 198, whereby an energizing circuit is established through the release relay 133 extending from ground Gr through the .Lsprin s 196 and 198, relay 133 to the bat- ,tery lead 103, thencethrough battery B to 0, ground G. When the relay 133 energizes,

the spring 199 is shifted out of contact with the spring 200 and into contact with the spring 201,andthe spring 202 is shifted into engagement with the spring 203. This primary operation of the connector relays 128v and 133 occurs at the instant that the side switch wipers 117 and 118 of the selector F pass to third position and extend the subscribers line conductors to the connector H. Theengagement ofthe springs 203 'and 202 establishes a guarding potential for protecting the trunk-line conductors 192 193 and 194against seizure by another line and second-selector. This potential extends from ground G to the side switch wiper 139, springs 203 and 202, conductor 194 to the private-bank contact engaged by the shaft wiper 191. Furthermore, when the side switch of the second-selector F passes to third position a new energizing circuit is established throu h the release relay 124, said Circuit extenl 'ng from ground (ii at the connector switch to the conductor 194, through the shaft wiper 191, side switch 5 wiper 204, conductor-205, through the re "lease relay 124 to the battery lead 103, thence through battery B to ground GI Also, this same guarding potential established at the contact enga ed-bythe private shaft wiper 191 is exten ed-to the private bank contact the shaft wiper-83 of the firsten d b i gage y side switch of the secselector E, when the end-selector F path over whic this potential extends is as follows: from ground G 'at the connector switch H (Fig. 2) through the side switch wiper 139, springs 203 and 202, conductor 194, shaft wiper 191, side switch wiper 204,

conductor 205, contact point 206, side switch wiper 183, springs 181 and 18O, cond-uctor 172 to the bankcontact engaged by the prifvate wiper 83 of the selector switch E. The ,o ration of the dial for the last two digits a ects the connector switch, and when the can is'operated for the third digit 2 the passes to third position. The

impulse spring 14 is twice carried out of engagement with the spring 15, thereby momentarily deener izing the line relay 128 twice, whereby t e spring 196 twice en-. gages the spring 197, thus sending'two impulses to the vertical magnet 131 from ground G throu'gh the springs 196 and 197, springs 199 and 201, through the vertical magnet 131, contact point 207, side switch wiper 140, private magnet relay 134 to thebattery lead 103, thence through battery B to ground G. The private magnet relay 134 energizes when the first impulse is delivered, and since the said relay is slowacting it remains'in an operated position until all the vertical impulses are sent. The vertical magnet, upon being energized, operates one step at a time to carry the shaft wipers 125, 126 and 127 two steps to a-point opposite the second level. The relay134, upon energizing, shifts the spring 209 out o engagement with the spring 210 and into engagement with the spring 211; also, the spring 212is shifted out of engagement with the spring 211. When the springs 209 and 211 engage, an energizing circuit is established through the; private magnet 135 from ground Gr through tht's prings 211 and 209, private magnet 135 to the battery lead 103, thence through battery B to ground G. The relay 134, being a slow-acting-relay, remains in an operated position while the vertical impulses are being sent; but

after all the impulses are delivered, and the line relay 128 returns to its operated position, the circuit through the relay 134 becomes broken, thus permitting the springs 212 and 209 to return to normal position. When the springs 209 and 211 disengage,

the circuit through the private magnet 135 becomes broken, wherebythe said magnet deenergizes, permitting the side switch to pass from first to second position. The calling subscriber now operates the calling device for the last digit 0, thereby transmit-- ting ten impulses and operating the line relay 128 ten times. Each time that the line relay springs 196 and 197 engage, an energizing circuit is established through the rotary magnet 132 from ground G through the saidsprings 196 and 197 and through the springs 199 and 201, rotary magnet 132 and locking-relay springs 211 and 212 to side switch wiper 140, and through the private magnet.134 to the battery lead 103, thence through battery B to ground G. Again the private magnet relay energizes, as in the previous case,'remai ning so until all the impulses are transmitted, thereby retaining the private magnet energized also. The rotary magnet 132 then operates to rotate the shaft wipers into engagement with the desired line #2220. If this line is busyat the time, the connector side switch the contact point 213, thence through the I mar Scription of how a connection is established will'be' completed. As soon as the line relay 128' ceases to operate for the last digit, the private magnet relay 134 deenergizes, as heretofore explained, in this instance pera'mittin the side switch to trip to third position.

I e result is that the side switch wipers 136, 137, 138, 139 and 140 engage the contact points 214, 215, 216, 217 and 218,v

respectively. When the side switch wiper 138engages the contact point 216 a guarding potential is. completed at the private wiper 127 for protecting the seized line from outside interference while the connection is established. This guarding potential extends from ground G to the contact point 216, thence by way of the side switch wiper 138, locking-relay springs 219 and 220 to the private wiper 127. Not only does this arding. pOtential prevent other connectors 0m se zing the same line. over multiples of the normal conductors 221, 222 and 223, Y but it also provides means for energizing the cut-off relay 224 of the line switch C, whereby the switch C is prevented from operating when the called subscriber removes his receiver 225 from the switch-hook 226. It will also be seen that when the side switch passes to third positionthe trunkrelease conductor 194 that runs between the second-selector and the connector is provided with guarding potential from ground G through the line relay springs 196 and 198,,contact point 217, side switch wiper 139, release relay springs 203 and 202 to the trunk conductor 194. However, while the side switch is in first or second position a: guarding potential for this trunk conductor 194 is also provided from ground G but through the side switch wiper 139 direct.

- the same trunk-line.

passes to third position, however, there is no such possibility, and the potential is pro- The reason for this is that the guarding potential from ground G is interrupted while the'line relay 128 is operating, and there is some liability of some other selector similar to the second-selector F stopping on After the side switch I vided from ground G through the line relay springs, as stated, in order to expedite the release of the selectors when'the calling subscriber hangs up his receiver Of course, when the side switch wipers 136 and 137 engage their third-position contact points, .214- and 215, the-calling subscribers line is placed in connection with the called subscribers line over the heavy conductors shown, passing through the ringer relay springs 227 and 228 on one side, and 229 and 230 on the other side. As soon as connection is thus established the ringer relay 145 is energized over the circuit established when the side switch wiper 140 engages the contact point-218, the energizing current flowing from ground G through the interrupter 144, through the back-ridge relay springs 231 and 232, ringer relay 145, conductor 233, contact point 218, side switch wiper 140, private magnet relay 134 to the battery lead 103, thence through battery B to ground Gr. It will be seen that as the cuit of the ringer relay 145 will be broken periodically, so as not to ring the called subscriber continuously. It will be seen that each time that the ringer relay is energized the springs 228 and 230 are separated from the ringer relay springs 227 and 229, thereby breaking the calling line from the called line and pressing the springs 228 and 23(] onto the springs 244 and '245, which are the terminals of the ringer generator I. As a result ringing current is sent over the'called line for energizing the bell 234 while the springs 237 and 246 are in contact. It should be explained that the connector H, like all the connectors. of the two-thousand two-hundred group, may be arranged to draw its ringing current from a ringer generator I that furnishes current of such character that only the ringer 234 of the substation #2220 will be operated by said current; while the ringers of all other substations on the same line may be so tuned that they will not respond to the current from said generator. Similarly, the connectors of the two-thousand three-hundred group, which are employed when substations of this group are called, may be arranged to draw their ringing current from a rin er generator that furnishes current of character that only ringers tuned to respond to the current of this particular character will be operated. Likewise, the connectors of the four and one hundred groups of the two-thousand may in turn draw their ringing current from still other generators that supply current of such characters that only these ringers that are correspondingly tuned will operate. It is evident, then, that when generator current is projected out on the line by the connector H of the two-thousand two hundred group only the ringer 234 will be operatively affected. However, as soon as the called subscriber answers, the back-bridge relay 141 is energized by a flow of current'from ground G,

switch-hook springs. 237 and 238, impulse tssprings 339,and 240, transmitter 241, vernqnductor 221, vertical line Wiper 125, cont? tact point 214, side switch wiper 136, ringer relay springs 228 and 227, conductor 243,

5 winding 142 of the back-bridge relay 141, thence to the battery lead 103, and through battery B to ground G. \Vhen the back- .10;- =b cidge relay 141 is once energized, however, -the energizing circuit for the ringer relay sfil45iis interrupted .at a point between the gsprings 231 and 232, thus making it impos- Isiblefor theoringer relay to energize as long calfiifasthe calledsnbscriber is on the line. The

subscribers being thus connected, they may communicate over the main talking conilductorsindicated by the heavy lines and ina eluding on one side the condenser 147 at the R ponnectoi' H and on the other side the conrdenaer 148. This talking circuit also in- 'cludies the windings 21 and 22 of the douible-wohnd coil 23". For the purpose of l clearing the talking circuit of the impedance W of these 'coils, theoondensers 247 and 242$vv are provided across the said windings, as shown. 'Abfter thesnbscriberstre through talkingyii the calling subscriber hangs up "aihieirecetiver he opens the;line.circu-it at a 'wrpoint'hetween the springs17 and 18, thereby i therrelease of all of, the switches.

1.1:Thisi release is as follows:' At the instant that the circuit is broken between the said springs 17. and18,the double-wound line re- 35.235133! 128and the nelease relay 1330f the connector H deene'rgize. At the instant that theisloweacting relay 133 and. the line relay 128 deenergize, the energizin circuit for the areleasemagnet 133is close at a point be- ,1 other point between the springs 196 and 197. 4A.- fiow of current is, therefore, set up front ground G through. the springs 196 wand 197, through the springs 199 and 200 to i the release magnet 133", thence through said magnet and to the oil-normal spring 132, .fiqto the contact point131, and to the battery lead 103, thence through battery B to ground G. The release magnet instantly reswitzih, therebygbreaking the energizing cir ncuitfiirough the hack-bridge relay 141, if 1 the called subscriher ihas not-in the meantime restored his receiver, and also the energizing circuitthrough the bridgecu't-ofl relay 224 of thecalled'line switch C. As soon as the connector switch'shaft reaches ;:.its,lowest positionit' breaks the circuit for the release ma et133 by separating the ofi normal spring 132 from the contact point l3l", at which instant the release mag- V net ofr the connectonis also restored. The "-operr1tion of the linerelay 128 and of the :slow-acting relay -133 not only causes the iez feleasegof the connector, as described, but

lease magnet 108 is closed.

tweennthe springsol99 and-200. and at anthe connector switch shaft and side.

also the release of the preceding switches,

G tothe trunk-release conductor 194 is interrupted by both of these relays. Since the release re ays 124 and 112 are depend:

ent upon that ground for their energized the battery lead 103, thence through battery B to ground G. As soon as the, release magnet 121 energizes, the second-selector side switch, andswitch shaft are restored, which latter, upon reaching its lowest position, opens up the release circuit at a point be-, tween the off-normal spring 250 and the contact point 249, whereby the release magnet 121 is deenergized. \Vhen the release relay 112 of the selector E deenergizes, the springs 163 and 164 are brought into contact, and as a result the energizing circuit for the re- The energizing current for this release magnet 108 then flows from ground Gr through the springs 161' and 166, and through the said springs 163 and-164 to the release magnet 108, thence through ,said magnet to the contact point 'for therelease magnet 108 at a point between tlie offs-normal spring 111 and contact point 110. Furthermore, when the relay 112 deenergizes and closes the springs 163 and 164 in contact, a series energizing circuit through the release magnet 24 and the release relay 113 is established. This circuit extends from ground Gr through the springs 161 and Y166, springs 163 and 164, through the relay 113, springs 251 and 252, conductor 77 to the bank springs 42 and 41,

ythence through the release magnet 24 of theline switch C to the battery lead 103, ant! through battery B to ground Gr. It will be seen that the release-magnet will then energize and, as previously explained, cause the trip armature 27 to fall over the plunger arm 22, whereby the members 32 and 33 engage; (See Fig. 4). As the release relay 113 energizes and separates the springs 251 and 252, the series release circuit is broken for an instant, which permits the release magnet 24 of the line switch C to deenergize, thereby withdrawing the plunger21 because the ground-connection from ground eticalhline conductor 242, vertical normal l 1', thence to the private bank contact.

from the bank terminal Q; As a result the bank springs 41 and 42, as well as the other bank springs of the line switch 0, are separated, thus preventing any other action from 5- 'the trunk. After the switches are thus restored the calling subscriber can, of course,

a then proceed to make another call.

Returning now to that stage of the call where the calling subscriber was operating the connector switch in accordance with the *aground terminal similar to the ground terminal G in the connector switch H, as already explained; but if the line switch C is calling, a guarding potential is established from the trunk-line relay ground as in Fig. In a similar manner the line switch 0 protects the calling line A- (when the bank springs 39and'40come into contact) from ground "G, from which ground connection. is established through the said bank springs to the private normal conductor 80. Therefore, when the subscriber sends in the last impulse the private wiper 127 is carried onto gizes, instead of the side switch tripping to thirdlaausition, as in the case where the line is not sy, it is locked and the calling sub-- scriber is then given the busy-signal. The

40 method by which this side switch is locked is as follows: The slow-acting relay springs 209, 210 and 211 are so arranged that as the relay 134 deenergizes, the spring" 209 on gages the spring 210 before it leaves the spring 211, and in this way the private magnet 135 isprevented from deenergizing, because the spring 210 is connected with the I rivate wiper 127 at the time, over the fol spring 220, thence to the ring 2l9 an through the winding 143 of t e back-bridge relay 141 to the talking line conductor 235, thence through the ringer relay springs 229*and'230 to the side switch wi r 137, contact point 253 (the side switch being in second position) to the slow-acting relay spring 210. Therefore, when the spring'209'engages the spring 210 the private magnet 135 is not deenergized. since the energizing circuit is maintained from the rivate wiper 127 to the said spring 210,

as escribed, thence through the spring 209, and through the private magnet 135 to the battery lead 103, thence through battery B to ground G,- The private magnet therefore wing-:cincuit: from the private wiper 127 to the l'ockin new remains energized, retaining the side switch in second position. It will be seen that at the same time the back-bridge relay 141 energizes in series with the privatemagnet 135, over this circuit, from the private wiper 127. Therefore, the back-bridge relay 141, upon energizing, presses the springs 254' and 255 into contact, thereby energizing the lockingrelay 146 over the following circuit: from ground G through the slow-acting relay springs 211- and'212, through the private magnet springs 256 and 257, through the said relay 146, and through the backbridge relay springs 255'and 254' to the battery lead 103, thence through-battery B'to ground G It will be seen that when the relay 146' energizes, the connection between the rotary magnet 132 andthe battery lead 103 is broken at a point between the springs 211 and 212-. The object of thisarrangement is to prevent the calling subscriber from further rotating the connector switch if he should attempt to operate his dial while receiving the busy-signal-that is, while the connector switch is locked in second position. It will also be seen that when the relay 146 energizes, the circuitfor maintaining the private magnet 135 energized is shifted from theprivate wiper 127 'tothe spring 258, which latter is connected to ground G. The object of this arrangement is to prevent the side switch from unlocking and'passing to third position, if the switch that is maintaining the called line busy should be released while the calling subscriberA (Fig. 1) is receiving the busy-Sig. nal. It will be evident that if the ground G were not substituted for the ground at the private wiper 127', the private magnet- 135'would deenergiz'e if the switch that is supplying ground at the private wiper 127 should release, which would, of course, be undesirable- It will also be seen that the relay 146, upon energizing,-closes the springs 259 and 153 in contact, thereby establishing the busycircuit as follows: from the secondury windin oft'he busy coil 151 through the springs 15 and 259 to the second-position side switch contact point 260, side switch wiper 136, ringer relay springs 228 and 227, through the condenser 147, through the substation-A to the rotary side" of the line, then over said rotary side back to the connector H, through the winding 180 of the line relay- 128 to ground G to the interrupter ground G through the interrupter 149 to the primary winding'of the busy coil 151 back'to the secondary winding, \Vhen the calling subscriber receives the busy-signal he understands'that the line is'busy and'hangs up his receiver. The line circuit is opened, as alreadycxplained, with the result that the line and slow acting relays 128 and 133 of theconne'ctor. H deenergize, causing the release of the connector and all other switches,

'as heretofore explained. It will, of course,

the energizin circuit for the locking relay 146' is contro led by the back-bridge relay 141, the said locking relay is also'deenerf gized, and the connector switch is left in a...

' normal condition.

the foregoing itha's been shown how a subscriber may operate the central office switches to establish connection with another line. It will now be pointed out how a-gisubscriber may operate the central oflice apparatus to call and signal a party on the same line. This may be more clearly understood'from an explanation of Fig. 3 when it is assumed that the subscriber at substation A desires to signal the subscriber at sub station A, whose number is 5320. To call this number the substation dial is operated in theusual manner. When the line switch operates to seize a trunk-line leading to a first-xle'ctor switch, a guarding potential is established at the connector bank through the trupk-line relay springs, as previously explained. The master switch D operates as usual to carry the idle plungers opposite the next available trunk-line. The impulses for the first digit 5 are received by thefirstselector switch E, whichoperates to select idle trunk-line leading to a second-selector F. The second-selector responds for the second digit 3 to select a connector switch 1 H of the fi fty-three-hundred group. This connector is operated by the last two digit impulses to select the line number 20 of this roup.- The usual guarding potentials are established to protect the various trunk lines used in establishing the connection.

As previously-explained, the trunkline relay 23 operates when the impulses are transmitted. The operation of this relay is of no importance until this particular timethat is, when a subscriber is about to operate a connector switch to callback on his own line. Thisrelay is provided for temporarily removing the guarding potential from the connector banks, so that the connector switch H will not find the line busy. The operation of the trunk-line relay 23 is as follows: When the impulses are transmitted the relay 23 deenergize's at each impulse, permitting the spring 19' to engage the spring 20 momentarily. The engagement of these two springs provides an energizing circuit for the slow-acting relay from ground G" through the said relay, springs and 19!, bank springs 40 and 39, through'the winding of the bridge-cut-off relay 48 to the battery lead 103, thence through battery B to ground, G. The relay 15 thereupon energizes and separates the springs 16 and 17, whereb the guarding potential for the normals 0 the calling line is removed. It will be understood, of course, that while the V relay 23 energizes and deenergizes during each impulse, the slow-acting relay 15 does not, since the intermittent closing of its energizing circuit is suflicient tomaintain the said relay in an operated position. After the impulses are delivered the relay 23 remains in an energized position, maintaining bank. From the foregoing it will be seen that while impulses are being transmitted, the protecting potential of the line is te'mporarily removed. \Vhen the connector switch is operated for the last digit 0, the connector side switch does not lock in second position, but passes to third position, establishing connection with the desired line. The subscriber at substation A having operated the central ofiice switches, including a first-selector, second-selector and connector switch H, to call subscriber A on his own line, now presses the signaling button 5 in order that the ringer generator may be bridged across the line to signal the called subscriber. The connectors of the fiftythree-hundred group may be arranged to draw their ringing current from a generator of such character that only the ringer 260 on the party-line will be sounded, as previ-' ously explained. When the subscriber A called the subscriber A it was explained that the back-bridge relay 141 energized when the called subscriber answered and bridged his transmitter across the line. In this instance (the called and calling lines being identical) a provision is made where by the efl'ect of the bridgeof the calling subscribers transmitter is overcome, and the back-bridge relay 141 deenergized to permit the closing of the energizing circuit through the ringer relay 145, as follows: When the button 5 is pressed the springs 6 and 7'? disengage, introducing the high resistance coil 8 into the circuit of the back-bridge relay 141 and the front-bridge line relay 128. When the resistance coil 8 is placed in this circuit sufficient current does not flow to maintain the back-bridge relay in an energized position; Hence it falls back, closing the circuit through the ringer relay 145, as previously. However, suflicient current still flows to maintain the line relay'128 in its energized positionand thus prevent a premature release of the switches. lVhen the subscriber at substation A answers by removing the receiver from the switch-hook and bridging his transmitter across the line conductors, a new circuit is formed which shunts the resistance coil 8. The relay 141 now ener izes, breaking the circuit of the rin er re ay 145. The two substations A an A are thus placed in communication,

the guarding potential at the connector 7 vJwhich is provided with three substations (A, A and A) and connected to an individual or line switch] From the line switch groups trunks lead 'to first selector switches, from which latter switches trunks :lead to second selector switches. From the second selectors trunks lead to connector switches. In this diagram the switches and substations are represented by circles and the different have s of bank contacts are represented by straight lines. It will be assumed that the substations A A? and A are numbered 2120, 2220, and 2320, respectively. Since the last two digits of each of these numbers are 20, the line to which these substations are connected would be connected to the last or 0 contact in the second level in each of the three groups of connectors H, H and H Each group of connectors is connect ed to a dilferent generator, I, I or I, each having a different frequency. Since the group of connectors H is connected to the rst level of the second selector banks, the connection with the called line will be completed b one of these connectors if the number 21 I is called. Ringing current will then be supplied by the generator I which is of the proper frequency to actuate only the bells at substation A. It number 2220 is called the connection will be completed by one of the connectors H, and rin ing current will be furnished by generator which is of the proper frequency to signal substation A Likewise, a connection for substation #2320 will be completed by the connector H and ringing current supplied by generator I.

From the foregoing it will be seen'that I provide efficient party-line service in a twowire automatic telephone exchange system that is to say, in' a system in which the Subscribers lines are free from operating grounds outside of the exchange or central station. It will also be seen that I provide a two-wire automatic system .in which party-line subscribers can signal each other on the same line through the medium of push-buttons at their respective stations, whereas any called subscriber who is not on flmxsameline with the calling subscriber is automatically signaled from the exchange or central station. Furthermore, I provide a two-wire automatic system in which the connectors are capable of automatically locking on busy lines, without closing the connection from the calling line to the called line, the subscriber on the calling line being given a busy signal. Also, and

through the medium of the slow-acting rev lays 48 and 15 and the double-wound line relay 23 a two-wire party-line subscriber trunking system. In connection with this system it will be understood that whenever I use the word trunking I mean any operation that carries the calling line nearer the called line. For example, in the connector switch I consider for the purposes of this application the first operation of the connector switch as a trunking ope-ration.

Vhat I claim as my invention is '1. In a telephone system, subscribers lines, each substation having a calling mechani'sm operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation for the next digit, means for extending connection to a called line by using the two sides of the calling line in series aplurality of substations on the called line, means for selectively ringing the different substations on the party-line, said first means comprising a means for said trunk selector res onsive to perform the first trunking operation of the selector in response to the closure of both sides of the calling line in series to reject busy trunks and to select an idle trunk independent of any further action from the line.

2. In a telephone system, subscribers lines, each substation having a calling mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation for the next digit, means responsive to the current corresponding to a plurality of digits of the called number for extending connection to a called line by using the two sides of the calling line in series, a plurality of substati'ons on the callin line, means for releasing controlled from any calling substation on the party-line, said first means comprising a trunk selector individual to the calling line, trunk lines accessible to said selector, and means for said trunk selector responsive to perform the first trunking oeration of the selector in response to the c 'o'sure of both sides of the calling line in series to reject busy trunks and to select an idle trunk indeoffsubstationcontrol e'd means for ringing "another substation on the same line of the called lineby using the line in series,

calling subscriber, andautomatic means for rin g a substation on a line other than the callhn line. a 4. l n a. telephone system, the combination of means for extending connection to the two sides of the callsubstation-controlled means for ringing another substation on the same line of the calling subscriber, and automatic means for ringing a substation on a line othertha'n the calling line. I

5.. A two wire selective ringing party-line automatic telephone exchange system free from operating grounds outside of the exchange or central station, a plurality of lines, a substation for each line, means for connecting any two lines, sai d 'means comprising a trunk selector individual to the calling line, trunk lines accessible to said selector, and means for said trunk selector responsive to perform the first trunking operation of the selector in response to the closureof both'sides of the calling line in series to reject busy trunks and to select an idle trunk independent of any further action from the line, each substation having a calli ig mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation for the next digit;

6. A party-line automatic telephone exchange system having release mechanism,

- and a high resistance at each substation on the party-line to prevent a release when one subscriber signals another on the same line.

7. In a telephone system, a ringin key, an automatic subscribers line provi ed at the substation thereof with a high resistance coil normall short-circuited by the closed contacts of t e ringing key.

"8. In a telephone s stem, a ringing key, an automatic subscri ers line, means for automatically extending connection there- ,from by using the two sides thereof in sefries, and a resistance'coll in the line at the substation thereof normally short-circuited by the closed contacts of the ringing key.

.9. In a telephone system, trunks for connection with calling lines, subscribers lines,

means for automatically extending connection to a called line by using the two sides of the calling line in series, a slow-acting bridge=cut-off relay for each line, and a double-wound relay and a slow-acting relay for each trunk to which calling lines can be i directl connected, as set forth.

10. n a. telephone system including party lines, trunks or connection with callin lines, means for enabling a subscriber to call back on his ownline, comprising a slow-'acting' relay'individual to the party-line, and a slow-acting relay and another relay for each trunk to which the party-line can be directly connected, as set forth:

substations thereon, means for automati'-' cally extending connection therefrom by using the two sides of the line in series, each substation having a caliing mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation for the next digit, trunk-release circuits, means for initiating the release over the line circuits, said first means comprising a trunk selector individual to the calling line, trunk lines accessible to said selector and means for said trunk selector responsive to perform the first trunking operation of the selector in response to the closure of both sides of the calling line in series'to reject busy trunks and to select an idle trunk independent of any further action from the line.

12. In a'telephone system, the combination of a party-line having a plurality of substations thereon, means for automatically extending connection therefrom by uslng the two sides of the calling line in series, each substation having a calling mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation for the next digit, trunk-release circuits provided with slow-acting release relays, and means for initiating the release over the line circuits.

13. A subscribers' telephone line free from operating grounds outside of the exchange or central station and provided with a slowacting bridge-cut-ofl' relay and a bridge-normally closed through the contacts thereof.

14. A subscribers telephone line free from operating grounds outside of the exchange or central station, a slow-acting bridge-cutofi' relay, abridge on said line normally closed through the contacts of said relay, a trunk, a double-wound line relay and a slowacting relay for said trunk, and two circuits for the first slow-acting relay, one circuit through the winding of the second slowacting relay and the other through the contacts of the same relay, both circuits controlled by said line relay.

15. A two-wire automatic telephone exchange system free from operating grounds at the substations thereof provided with automatic means for lockiiig on a busy line without connecting the calling line therewith, each substation having a calling mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come

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