USRE14462E - martin - Google Patents

Description

T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED JULY 13. I91]- 3 SHEEIS-SHEET I Reissued Apr. 23, 1918.

/ I gfnganlqr iIli-i Reissued Apr. 23, 1918.

T. e. MARTIN. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 13 I911.

3 SHEETSSHEET 2;

T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 13. I917- Relssued Apr. 23, 1918.

' STATES oEFioE.

manor a. tantrum, or omoneo', nimois, assmnon, BY 'nnsma assrommn'rs, mo

AUTOMATIC ELECTRIC ILLINOIS.

ori inal 110. 1,176,715, dated To all whom it may concern:

, citizen of the United States of America, and

resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Telephone-Exchange Systems, of which the following is a specification.

My invention relates to automatic or semiautomatic telephone systems in which the system is divided into districtsthat is to say, in which the subscribers telephone lines are divided into groups, and in which the lines of each: group-terminatefat sub-central or outlying'stations connected by trunk lines with a main on central trunking station. My invention also relates more especially to district telephonesystems of this character in which the automatic selection ofv an idle trunk line running from the sub-central station to the main or central station is accom-[ plished by momentarily grounding the callm telephone line.

fiienerally stated the object of myinvention is the provision of an improved and hi hly efiicient telephone exchange system. pecial objects of my invention are the provision of means by which the-attendant at the main or central station of a district system of this character mayhave supervision and control over the automatic trunking apparatus at the'sub-central or outlying trunkln stations; the pro 'sion of means by whic an attendant at t e main or central trunking station may release or restore to normal condition any portion of the automatic trunking machinery at any sub-central or outlying trunking station; the rovision of means for enablin the atten ant at the main or central trun ing station to know when a ground is accidentally established on any subscribers line running to any one of the sub-central or outlying trunking stations, and to then restore the automatic switch or switching machinery which was operated at, the sub-central station by the accidental grounding of the subscribers line; the provision of means for enabling the attendant at the main or central trunking I station to disconnect any subscribers line from a ,trunk line, whenever such connection is brou ht about by the accidental grounding of t e subscribers line, and for thus preventing the accidental grounding of telephone lines from putting a corresponding groundlng I specification or named Lett -ravine Rei sned Apr. 23, 191d;

larch 21, 1910, Serial 1%. 881922, filed August 17, 1900. reinue flledluly 13, 1917. Serial No. 180,448.

number of trunk lines tem orarily 'out of service, which latter Wool, of course, be the case were it not the sfact that the attendant at-the main or central trunking sta-" t1on can lmmediately, and whenever he discovers such an abnormal'condition, promptly release the off-normal switchor switches at the sub-central station or stations; the proil ppflcation for comm, or CHICAGO, ninmo s, a oonrona'rron org.

vision of a releasing trunk between eachsubi A central station and the main or central 5 Y trunking station, to ether with releasing switches located at tfi and selectively controlled from the central station of'the said releasing trunks, whereby it is possible for an attendant at the main or central station to release or restoreany e sub-central stations 1 trunking connection which may have been"-;

established by the accidental and temporary of a subscribers telephone line, thus ma ing it unnecessary to send a trouble man to the sub=central stations to restore the ofl-normal switches; and the provi'sionof certain details and features of improvement andcombina-tions .tending to in? crease the general efiiciency and improve the trict system and the subscriber #220 of a second sub-central oflice in the same district system, said system involving the principles of my invention. The line of the subscriber #500 (Fig. 1) terminates in the line switch A ofthe five-hundred sub-central, which line switch, like all the switching apparatus in the system, is controlled by means of current from the battery B, located at the main trunking ,station and from which battery leads run to the various sub-central stations. The said line switch A is adapted to select any one of a number of local trunk lines and is shown tem orarily connected with the t at leads to the repeater.

trunk line C, from which repeater a sub-central or incoming trunk line leads .to' ,the main trunking ofiice and there terminates in the first-selector D. The said first-selector D is adapted ,to select anyone of a number of' local trunk lines'an is shown as having solected one'leading to there eater C (Fig. I

2). From the sai epeater 1 amain trun ing station or outgolng trunk line leads to the two-hundred sub-central and terminates in the connector E. The said connector E is also adapted to connect with any one of a I number of subscribers lines and is shown in connection with the lineleading to'the substation #220. Bridged across the called line is the line switch A allotted to the said line. Each sub-central station has a roup of line switches which is controlled y a master switch. One of said master switches is shown at F (Fig.1)- and as represented is allotted to the five-hundred sub-central. As-

previously stated, the current is supplied to the various central offices by battery leads from a central battery B; but provision is made for using the ground as a return, and preferably, therefore, the positive terminal of the battery B is grounded at G.

Fig. 3 shows more in detail the mechanical connection between the master switch and the line switch, and also shows more clearly the bank arrangement of the line switch.

j v Fig. 4 shows in detail the construction of the master switch bank J.

In Fig. 1 is shown the apparatus 'H by means 0 which the attendant at the main 'trunkinfiloiiice may release the line switch A if he ould desire. Said apparatus is known as an auxiliary releaseswitch.

The substation ma I approved type. Sai substation is equipped T switch-hook is arm. 12 through the medium springs 13 and 14, and the ringer circuit is with means whereby moving has receiver 2 from the switch-hook 3 rrliay disconnect his ringer 4 from its norma ground connection to certain points from which the necessary switching, signaling and releasmg apparatus of the system may be controlled. More particularly the substation is of the common battery type in which trolled by the cam arm "11,- so that when the said springs are down the serparated and the primary circuit opened. T e ground circuit is controlled by the camof the ground controlled by the cam arm 15, which latter controls thev springs 16 and 17 that are included in series with the ringer 4 and condenser 18. The subscribers calling device may also be of any suitable design, but as shown in Fig. 1, it. comprises the switching impulse transmitting device comprising the I said be of any suitable or the subscriber by re-- connection across the line, may close the primary circuit, and close the substation" oral as follows:

restores his vreceiver, then attracts its armature 50, and raises the of the signaling button 26 which is adapted,

, After t e connection is, established the signaling is dofie by means when ressed,to shift the spring 27 away from t e contact point 28 and into engagement with the contact point 29. After a call has been made the switching apparatus may be restored by means of the release springs 30, 31 and 32 which are adapted to the pressed into contact at the sametime by the cam arm 33. The preliminary impulse attachment comprises still another cam arm 34 and the ground spring 35, which latter the cam arm is adapted to engage and through which a circuit is established with the rotary side of the subscribers line.

The line switch A may be of any suitable or approved type, such, for example, as the general type of line switch shown in British atent No. 26,301 of 1906. Said line switch comprises, as shown in Fig. 3, the cutoff relay '35, trip magnet 36, release magnet 37 furthermore, is shown passing centrally through the set. The set,

as shown, comprises the springs 38 and 39, 40 and 41, 42 and 43, and 44 and 45. For operating the bank springs the line switch is equipped with a plunger 46 pivotally mounted upon the plunger arm 47, which latter is subject to the rotative tension of an operating sprin 48 about a pivot 49. The armature 50 o the release magnet 37 is normally controlled by a retracting spring 51. Sa d armature in turn carries on its end pivotally mounted the armature 52 of the trip magnet 36. Said armature 52 is normally controlled'by the retracting spring 53. The end of'said armature is provided with an angled section 54 adapted to so engage the plunger arm 47 that normally the plunger 46 is retained within the channel 55 of the plunger shaft 56, which latter is controlled by the master switch F. The individual switches a whole operates in gen- When thesubscriber removes his receiverfrom the switch-hook the trip magnet 36 is energized for a moment and the armature 52 is attracted in order that the catch 54 may disengage from the plunger arm 47; then the spring 48 rotates the plunger arm 47 about the pivot 49, thrusting the plunger 46 into the bank I. The plunger thus brought into use may be restored by a momentary energization .of the release magnet.37, when thesubscriber which release magnet only one set being illus-,

from its true position ger 46 lS Cflll'lGd into engagement wit 'ank I, as described, a guarding potential is armature 52 of the trip magnet 36, so that the retracting spring 53 causes the end 54' to latch the plunger arm 47. When the re- ,lcasevmagnet 37 deiinergizes, the retracting spring 51 then restores the plunger 46 to normal position within the slotted section 55 of the plunger shaft 56. When the lull:- t 0 established at a proper contact of the bank J of the master switch F for operating the said masterswitch.

The master switch F comprises a motor magnet 57, an auxiliary relay '5&.and a differential relay 59. The latter is adapted to control the energizing circuit of the motor magnet 57, while the said motor magnet in turn controls the ratchet wheel 60. As shown in Fig. 4, the master switch bank J comprises the individual contact points a separated from the common plate 149 by the insulating strip 61'. The insulated spring 62" is so arranged that when the wiper 61 engages the last contact point-63", and their on the next step is carried to the contact point 141 on the right, the upper part of the wiper 61 slides on the spring 62. This provision is made in order that the wiper 61, in passing from the extreme left contact point 63 to the extreme right contact point 141, may not place the segments a in connection with the common ger shaft 56 to carry all idle inc switch plungers opposite the next idle trunk line in readiness to be seized by the next calling subscriber.

The repeater C comprises the vertical line relay 62, arotary line relay 63, a differential..relay 64, a pole changing relay 65 and an auxiliary relay 66. The main circuit that passes through said repeater is divided into two sections by] the condensers 67 and 68.

Normally the vertical line relay 62, in series.

with the winding 69 of the dill'erential relay 64. and the rotary line relay 63, 1n ser1es with the winding 70 of the differential relay 64, are bridged across the line in front of the said condensers 67 and 68.

The

auxiliary relay 66 is adapted to energize as soon as the line switch connects with the repeater C, so that a circuit is established through the first-selector D, whereby a lamp signal is set an at the said selector to indicate that the trunk leading thereto has been shaft 71.

- rotating the shaft.

seized. Furthermore, said relay 66 bridges the pole changin role. 65 across the trunk line leading to t 1e sai selector D for purposes to be hereinafter described. The 'line relays 62 and 63 of the repeater are adapted to receive impulses from the substation over the circuit in front of the condensers 67 and 68, and to repeat the said impulses to thetrunk line leading to the first-selector D over circuits behind the condensers 67 and 68. The differential ,rela 64 controls the trunk release circuit for t 1e line switch A, and controls the energizing circuit of the pole changing rela 65.

The auxiliary re ease-switch H. is a similar mechanical device mounted upon any suitable base and comprises a, rotatable switch shaft 71 provided with a number of longitudinal teeth 72 and a wiper 73. Said wiper is adapted to engage a set of bank contacts 74. The switch is provided with a rotary magnet 75, the armature of which is provided with a pawl 76 for rotating the Said pawl is retained normally out of engagement with the longitudinal teeth ,72; but when the magnet is energized said pawl then engages said teeth for In addition the switch has a release magnet 77 for controlling the pawl 78, which pawl retains the shaft. in each advanced step. The shaft is given a normal tendency to rotate in a clockwise direction by a suitable spring 79, and, therefore, whenever the release magnet 77 isenergized the said spring 79 returns the shaft to normal position, Said release magnet is )1'0- vided with a couple of springs 80 am 8[ which, when the release magnet is energized, are adapted to engage for connecting the wiper 73 with ground and, therefore, for grounding either of the bank contacts with which the said wiper may be in engagement.

The first Selector D is of the general type described in Patent No. 815,321, granted March 13th, 1906, to Keith, Erickson and Erickson, and is provided with'the usual shaft (not shown) that carries the line wipers 88 and 89 and the private wiper 90.

The said shaft is adapted to lnovein a vertical and in a rotary direction, the vertical movement being effected by the so-called vertical magnet 91, and the rotary movement by the rotary magnet 92. 'llhe'vertical magnet 91 is-controlled by the vertical line relay 93, and the rotary ,magnet 92 by the private magnet 94, which latter is in turn controlled by the rotary line relay 95. The

' said line relays 93and 95 are normally connected with the side switch wipers 96 and 97. respectively. The selector side switch comprises, in addition to theselector side switch wipers 96 and 97, the side switch wipers 98 and 99. Said wipers are adapted to be placed, as is well known, in. any one of threepositions known as the first, second and third positions of the side switch. As

shown in Pig. 1, the vertical trunk line conductor 1- terminates in the side switch wiper 96 and the rotary trunk conductor 101 terminates, instead, 111 the switch shaft spring 102, which latter,- whenthe switch is in normal position, is in conn'ectidn with the supervisory relay 103, but when the switch shaft is raised it engages the contact point 104, which latter is connected to the rotary 'line relay 95. The said supervisory relay 103 when energized presses the springs 105 V and 106 into contact, whereby the signal lamp 107 flashes up and indicates that the trunk leading to the switch D is infuse. As soon as a line switch seizes upon the repeater 0, therefore, the supervisory lamp 107 at the switch D lights; but as soon as the switch-shaft is raised the said light goes out,

and when the side switch wiper 99 passes to third position another supervisory lamp 108 lights instead to indicate that a connection has been completed by the switch D.

The repeater C is very much like the re eater C. .There are certain difl'erences, owever, which will be pointed out. It is provided with. vertical'and rotary line rebe of any suitable or approvedtype. The mechamcal details are very much the same as'those of the selector D, butthe circuits are quite difl'erent. The connector-switch shaft (not shown) carries the usual wipers 116, 117 and 118. Said switch is controlled by the calling subscriber through the medium of the vertical and rotary line relays 119 and 1 20. The vertical line relay 119 controls, directly, thev vertical magnet 121 and 'a'lsothe rotary magnet 122. The function of the-said vertical magnet is to give the shaft and shaft wipers a vertical movement, and the rotary magnet 122 imparts to said shaft and wipers a rotary or circular motion. The rotary line. relay 120 controls the private magnet 123, which latter controls theside switch. The sideswitch com-- prises, as is well "known, the side switch Wipers 124, 125, 126 and 127, which wipers are all rigidly connected and adapted to assume any one of three positions in-the accomplishment of certain switching operations that are well known. The line relays 11 9. and 120 conjointly .control the release magnet 128. Under. certain conditions the said release magnet 128 controlled by the private magnet 123. Like the repeater, the

K connector divides the circuit that passes through it into two sections by thecondcnsers 129 and 130. The connector has, in addition, a ringer relay131 by means of which the called subscribers line is disconnected from .the ehlling subscribefis line and bridged across the ringer generator 132 when the calling subscriber desires to signal the called subscriber. The system is, also provided with a busy signaling machine K which may be of any suitable or approved design and may be located at any desired point (preferably at, the main trunking station) and from which suitable leads may be extended to the various sub-central staso tions or other offices at which the connectors are located.

The line switch A is the same as the line switch A and needs no further description, since throughout the drawings like parts are likewise represented.

The substation #220 is, of course, the same as the substation #500 which has been described.

The general operation of the system may be described as follows: If the subscriber #500 wishes to call the substation #220 he removes his receiver from the switch-hook, thereby sending a preliminary impulse to the line switch A, which latter operates to release the plunger, as already described, seizing an idle trunk line to the repeater C, assuming, of course, that the plunger is cpposite the set of line bank springs that constitute the terminal of the repeater C, At that instant the master switch F is caused to operate to carry the plungers of all other idle line switches opposite the first idle trunk line. The seizure of the trunk line of the repeater C not only operates the master switch F, but the auxiliary relay 06 of the repeater G is also operated at the instant of seizure, establishing an energizing circuit through the supervisory relay 103 of the selector D, which relay-in turn causes the lamp 110 107 to be lighted, as already described. The

subscriber then operates the calling device for the digit 2, operating the vertical button 19 twice and the rotar button 20 once. The repeater C receives t e said impulses and transmits similar impulses over the vertical and rotary trunk conductors 100 and 101 for operating the selector D. The impulses to the vertical trunk conductor 100 raise the shaft of the selector D to the second level,

assumed, leads to the repeater C The subscriber then presses his vertical button 19 twice and the rotary button 20 once for the second digit. The impulses are then taken 130 .up by the repeater C, repeated to the trunk conductors 100 and 101, which repeated impulsesare taken up by the repeater (1 and repeated to the trunk conductors 133 and 134 for operating the connector E. The 1mpulses to the vertical trunk conductor, 133 operate to raise the connector-shaft to the second level and the impulse to the rotary trunk conductor 134 operates to send the connector side switch to second POSltiOIl, The subscriber then, for the digit 0 (which is the last), operate the vertical button 19' ten times and the rotary button 20 once. These impulses are taken up by the repeater C, repeated to the repeater C and again re-' peated to the connector E, whereby the shaft of said connector is rotated ten steps into enagement with the terminals of the substation #220 by the impulses delivered to the vertical trunk conductor 133. The impulse delivered to the rotary trunk conductor 134,

after the above has been accomplished, op-

erates to .do either of two things, namely to shift the side switch to third position and complete the connection, or to release the connector-switch E if the called line'isbusy; The subscriber resses his signallng button 26, which acts t e same as pressin the vertical button 19. The said vertica impulse is transmitted to the repeater C, then to the I repeaterC, then to the connector E, which latter then 0 crates to raise the connectorshaft, thus 0 oslng-a circuit from the busy signaling machine K to the' callin substation. In the former case-that is, i the con-' nection is madethe impulse passes from the repeater C to the reepater C and then to the connector E, whereby the rin relay 131 is energized for disconnecting t e calling subscribers line from-the called subscribers line, and for bridging the ringer generator 132 across the called subscribers line. But in either case the calling subscriber eventually must restore his receiver to the switch-hook to restore the switching appastated, to call the number 220 the calling subscriber removes his receiver and sends a preliminary impulse for operating the line switch A. The preliminary. impulse is transmitted when, as" the switch-hook rises,

the cam'arm 34 en ages the ground spring 35 after the groun springs 13 and '14 en- As a result the trip magnet 36 is energized over a circuit t a through said trip ma at 7 extends from ground G at the substation, through the springs 14 and 13 to the preliminary 1mpulse ground spring, 35, thence to the cam arm 34, contact oint 24, spring 22, rotary line conductor 1 5, cut-ofi relaysprings 136 and 137 to the trip magnet 36, thence et and through the springs 138 and 139 of the auxiliary rela 58 to the battery lead 140, thence t roug batte B to ground G. It is assumed that the p unger '46 is at this time opposite the first set of bank springs ofthe bank I, and, therefore, that the master switch wiper 61 is resting on the first bankcontact 141. This being the case, when the trip magnet 36 is ener ized-the armature 52 is attracted and .the plunger 46 driven-into engagement with the first set of bank springs, as shown in Fig, 3; and as a result the springs 38 and 39 are brought into contact, also the springs 40 and 41, the springs 42 and 43, and the springs 44 and 45. The closure of connection between the springs 44 and 45 estab- P through the coil 66 to the s rings 44 and 45,

release magnet 37 to the attery lead 140, thence through battery B to ground G.

Although the circuit passes 'throu h the re-.

lease magnet 37 the resistance of t e coil 66 at the repeater C is sufiicient to prevent the release magnet 37 from becoming opera tively energized. As soon as'the auxiliary relay 66 is operated the springs 143 and 144,

under its control, .are carried into engagement, and as a result an energizing circuit is established for the supervisor relay 103 of the selector D. The current or. energiz: ing said relay 103 flows from ground G at the selector D, through the supervisory relay 103 to the contact point 145, switch shaft spring 102, rotary trunk conductor 101,'conductor 146 of the repeater C, springs 143 and 144 of the auxiliary relay 66-, springs 147 and 1480f the differential relay 64 and I through the pole changing relay 65'to the vertical trunk conductor 100, thence throu h the vertical line relay 93. of the selectorto the batter lead 140, and through battery B to oun Gr Theenergization of the supervisory relay 103 causes the closure of connection between the springs 105 and 106, whereby a flow of current is sent through the lamp 107 from ground G through the said springs 105 and 106, the said lamp 107 andto the battery lead 140, thence through battery B to ground G. The main trunking office is, therefore notified as soon as the selector D is. seized b a switch at the #500 sub-central station. he current that enerrelay 65 and line relay 93, but the said supervisory relay is of suflicient resistance to cut down the current. to such an extent that the pole changing relay 65 and line rela 93 do not become operatively energ zed. he closure of connection between said springs 44 and 45 not only accomplishes the energization of the auxiliary relay 66, but also establishes a guarding potential at the master switch bank contact 141 for driving the master switch into the next position. It has been assumed that the master switch wiper 61 is in engagement with the contactpoint I mon plate 149. The auxiliary relay 58 and 141, the said wiper being sufliciently long to always maintain connectlon with the comthe difierential relay 59 of the master switch F are energized at the instant that the said guarding potential is established at the con- .tact point 141. The circuit over which the said guarding potential is established is as" ferential relay follows: from the battery lead 140 to the release magnet 37 of the line switch A,

thence through the springs 45 and 44 to the bank contact 141. Current then flows from the said contact through the wiper 61 to the common plate 149, thence through the auxiliary relay 58 and windin 152 ofithe dif- 59 to the ground terminal G. Therefore, both the auxiliary relay 58 and the difierential rela 5 9 become energized, the latter forcing t esprings 153 and v 154 into contact, setting u a circuit through he current flows the motor magnet 57.

ground G through the springs 154 and from p to the battery lead 140 1 1t1 ence through battery B to ground G.

said ratchet wheel controls the plunger shaft motor ma et'57 then attracts its armature 157, driving the ratchet wheel 60 to the next position; The

i a 56 and the master switch wi er 61. Therefore, the advance of the sai ratchet wheel one step carries the master switch wiper 61 to the next position and into enga ement with the bank oontact158, and also a vances the plunger shaft 56, so that all the idle plungers are carried 0 posite the second set of bank springs, whic, it is assumed, are

I connected to the next idle'trunk line. If the said trunk line is not idle, however, there will also be a guarding potential at'the master switch contact point 158, so that the energizing circuit through the differential relay 59 is still maintained, and the motor magnet 57 a ain operated to rotate the ratchet wheel 0 anothe step. As soon as the master switch wiper. 1 finds a bank contact without a guardlng otential the difierential relay 59 becomes dgner ized, the differential relay springs 153 an 154 separate,

and the energizmg circuit through the motor magnet 57 is permanently, broken. It will be understood that the trip magnets 86 rough thesaid motor magnet 57, and .through the interrupter s rings 155 and-156 of all the line switches of the samegroup are connected to the spring 138 of the auxiliary relay 58, and therefore that when said relay becomes energized the connection is broken between all trip magnets 36 and the battery lead 140 to prevent another line switch from, operating while the master switch E is in operation to carry all idle plungers to their proper positions-that is, opposite an idle trunk lme. The engagement of the line switch'bank springs 40 and 41 at the same time causes the energization ofthe cut-oil magnet 35 of the line switch A, which latter then operates to separate the springs 136 and 137 to revent the trip magnet 36 from being uselessly energized when the subscriber proceeds to send further impulses from his substation. The en-V ergizing circuit for the said cut-01f magnet 35 extends from ground G: throu h the said springs 40 and 41 and through t e cutofi ma et 35 to the battery lead 140, thence throug battery B to ground G. It will" be noticed that the so-called private normal conductor 159 terminates in the sprin 41 of thelineswitch A. Said conductor 1%ads to the connector switch banks and terminates in contact points that correspond to the substation #500. When the springs 40 and 41 engage, a guardin potential 1s established from ground through the springs 40} and 41. and over the said private normal conductor 159 to the said connector banks, to prevent a calling subscriber from calling'in on the subscriber #500 while the latter is calling. Along with the said private normal conductor 159 run the line normalconductors 160 and 161, over which the connection is made between the callin subscriber and the substation #500. Whei i the springs '38 and 39 come into contact the subscrrbers Vertical line conductor 162 is extended 'to the repeater C, "and when the springs 42 and 43 engage, the subscribers rotary line conductor 135 is extended to the repeater C, so that the succeeding impulses rected, first, to the re eater C. a

The first digit being 2 the subscriber presses his vertical button 19 twice, grounds the vertical line conductor 162 and operates sent from the substation #500 are all dithe vertical line relay 62 of the re eater C.

The ground to the said Vertical ine conductor 162 is made when the vertical button 19. presses the spring onto the ground post 25, and the established circuit permits a current to flow from the ground Gr at the substation to the ground post 25, thence to the spring 21 and through the vertical line conductor 162 throu h the line switch springs '39 and 38 to t e vertical line relay 62, thence through the winding 69 0f the difierential relay 64 to the battery lead 140, thence through the battery B to ground G.

Each time that the vertical line relay 62 is "are pressed into contact and the vertical conductor .100 is grounded. from the repeater ground G'. The circuit'over which this current is established extends from ound G through the said s rings 164 and 68, conductor 165 pole c angi rela springs 166 and 167 to the verticagtr conductor 100. Grounding the said vertical trunk conductor. establishes an energizin circuit through the vertical line' relay 93 o I the selector D. The energizing current flows from the vertical trunk conductor 100 through theside switch wiper 96, contact point 168 to the vertical line relay 93, thence through the said relay to the battery lead 140 and through battery B to ground G. The said vertical line relay upon energizing presses the line relay. sprin together, sending a flow 0 current from" ground. G through the said springs 169' and 170 and through the private magnet springs 171 and 172 to the vertical magnet 91, thence to the battery lead 140 and the repeater G passes through'the winding 69 of the differential relay 64, energizing fcs through battery B to ground G. The said vertical magnet, as is well known, operates to raise the shaft and, therefore, the wipers 88, 89 and 90 one step at a time. Since the vertical button 19 is pressed twice the said shaft is raised two steps. that energizes the vertical line relay 62 of said differential relay and causing thelat'ter to separate the spring 147 from the spring 148. The object in separating the said springs is to destroy the circuit established between the vertical and rotary trunk conductors 100 and 101 when the auxiliary re-v lay 66 energizes to prevent the impulses delivered to the vertical trunk conductor 100 from passing to the'rotary trunk conductor The passage of ,Sald impulses, were 101. the said springs 147 and 148 to remain in contact, would take place through the ole chan ing relay 65, through the said di erentia relay springs 148 and 147, auxiliary relay springs 144 and 143 to the rotary trunk conductor 101. When the' switch shaft of the first selector D is raised by the first operation of the vertical magnet 91, the normal post arm 173 of the said selector permits'the switch shaft spring 102 to leave the contact point 145 and break the ener 'zingcircuit through the supervisory re ay 103. mits the springs 105 and 106 to separate and destroys the line signal at the lamp 107."

point 104 and thus connects the rotary trunk conductorlOl with the side switch wiper 97, which wiper is normally in engagemencwith the rotary line relay 95. When the subscriber presses the rotary but:

the differential relay 169 and 170 springs lmpll se The same current Said supervisory relay in turnper ton-20 he presses the spring 22 onto 'the und st 25 and thus grounds the rotary 1n'e con uctor 135. As a result the rotary line relay 63 of the re eater C, as well as become energized. The energizing current flows from ground G to the ground post 25, thence to the sprin 22 and to the rotary line conductor 135, ank springs 43 and 42 of the line switch A to the rotary line relay 63 of the repeater C, thence through the winding 70 of the d fferential. relay 64, through the pole changm relay springs 174 and 175 to the battery ead'140,thence through batter B to ground G. The energizing of the di er-' ential relay 64 separates the springs 147 and 148 forthe purpose (already described) of separating the established'connection between the trunk conductors 100 and 101.

"The rotary line relay 63 upon energizin presses the spring 176 onto the groun 164, thereby delivering a ground to the rotary trunk conductor 101. The said impulse in turn operates the rotary line relay 95 of the first selector D. The current flows from the round G: at the repeater C through the a ove traced circuit to. the 'rotary trunk conductor 101, thence through the switch shaft springs 102 and 104 to the side i switch wiper 97, thence through the rotary line rela to the battery lead '140, and through battery B to ground G. The-rotary line relay 95 .in turn' presses the spring 177 onto the spring 169, as a result energizing the private magnot 94. The current through the said magnet flows from ground G at the said selector through the springs 169 and 177 to the private magnet 94, thence through the said magnet to the battery lead and through battery B to ground G The private magnet then operates to trip the side switch to second position, at which time the side switch wiper '99 engages the grounded contact point 178. A clrcuit is thus established from ground G to the contact point 178,

side switch wiper 99 to the rotary magnet 92, thence from said magnet and interrupter spring 179 to the battery lead 140, and I through battery B to ground G. The said rotary magnet then rotates the shaft the first step, and after the private wiper 90 is driven into engagement with the grounded contact point the rivate'magnet 94 is again energized by a ow of current from the said grounded contact point to the private wiper 90 through the back-release relay 180, side switch wiper 98, contact point 181, private magnet 94 to the battery lead 140, and thence through battery B to round Gr.

The said private magnet then loo s the side switch in second position until the rotary magnet 92 carries the wipers beyond all busy trunk lines. The private magnet 94 then, of course, denerglzes, releasing the private magnet 94 and thus releases the side switch from second to third position. As soon as the side switch reaches the third position the side switch wipers96 and 97 engage the contact points 182 and 183, so

. tended to the repeater C when the side switch wiper 98 engages the passage of the side is the lighting of the supervisory lamp 108.

that the'calling subscribers extended line conductorslOO and 101 are still further ex- Furthermore,

grounded contact point 184 a guarding potential is established at'the private wiper 90 from ground G for protecting the seized trunk line against interference. This circuit from said ground .G" extends to the contact point 184, thence through the side switch wiper 98, back-release relay 180 to the private wiper 90. Another 'efiect ofthe switch to third position The circuit over which the said lamp is energized, as shown, extends from .the;

ground terminal G of battery ,B through the said lamp and through the side switch wiper 99 (when the latter is inthird position) to the rotary magnet 92, thence through the said magnet to the battery lead 140, and through battery B to round G. The resistance of the said lamp 08 is sufficient to prevent the flow of current from becoming strong enough to operatively energize the rotary magnet 92. 1

The second digit of the desired number being 2 the vertical button 19 is again pressed twice and the rotary button 20 once. When the vertical button 19 is ressed twice the vertical line conductor 162 is again grounded twice and the vertical line relay 62 of the repeater C correspondingly operated. Said re ay in turn repeats the impulses to the 1 vertical trunk conductor 100, which im pulses are directed to the repeater O for operating the vertical line rela 109 of said i through the said relgy. 60' 6 repeater and also the differential relay 111. The energizing circuit for operating said relays at the repeater C flows from und G at the re eater G, as already descrl d, to the vertical through the side switch wiper 96 of the first selector D, contact point 182,-vertical line wiper 88, vertical trunk conductor 185 to the vertical line relay 109 '(Fig. 2), thence and through the winding 112 of the di rential relay 111 to the battery lead 140, thence through battery B to ground G. The vertical line relay 109 upon operating p the springs 186 and 187 into contact, whereby ceived by. the vertical, line relay 109 are retical trunk fe'rential re trunk conductor 100, thence the impulses re-,

peated to the vertical trunk conductor 133. I 7 he circuit over which the impulses aredelivered extends from ground G through con uctor 190 to the spring 186, andthence to the spring 187, conductor 191 and vertical the pol g gy springs 188 and 189,

trunk conductor 133. 'The said ground im pulses are directed to the connector E for operating the verticalline relay 119 of said connector. The 'im ulses continue from the vertical trunk con uctor 133 through the vertical line relay 119 of the connector, winding 192 of the differential relay 193 to the battery lead 140, thence through batter B to ground G. The said vertical line re ay,

each time it is energized, presses the springs 194 and 195 into contact and energizes the vertical magnet 121 for operating ,the connector switch shaft one step. at a time. The energizin circuit extends from ground G through t 1e said springs 194 and 195, private springs 196 and 197, side switch wiper 127, contact point 198, vertical magnet 121 to the battery lead 140, thence through battery B to ground G. The dififerential relay 111 of the repeater-Q", like the differential relay 64 of therepeater (l, energizes in series with the vertical line relay 109 and separates the springs 199 and 200 for destroymg the nor-; mal circuit (through the pole changing relay 114) that exists between the rotary and verconductors 133 and 134, as shown,

thus preventing the transfer of impulses from one of said trunk conductors to the other. When the subscriber presses his rotary button 20 he energizes the rotary line relay of'the repeater C, which latter then presses the springs 176 and 1,64 together, sending.v

animpulse to the rotary trunk conductor 101 over circuits already described. The

said impulse is then directed to the repeater" C (Fig. 2) for energizing the rotary line relay 110. The energizing circuit for said rotary line relay isestablished from ground Gatthe repeater C to the rotary trunk conductor 101, thence throu h the switch shaft springs 102 and 104 of t e first l selector D, side switch wiper 97, contact point 183, rotary line wiper 89, rotary trunk conductor 201, rotary line relay 110 ofthe repeater C (Fig. 2), winding 113 of the difay 111 pole changing relaysprings 202 and 203 of the pole changing relay 114 to the battery lead 140 thence through battery B to ground G. It will be noticed that the energlzing circuit includes the differential relay 111, which-relay is enseparating the springs 200 and 199 to prevent the transfer of impulses from the rota trunk conductor 134 to the vertical trun conductor 133. The rotary line relay 110 when operated as above explained, resses the spring 204 onto'the springs186 an sends ergized by the impulses to the vertical or rotary trunk conductors 100 and 101 for rhanging relay sprin 'a ground impulse to 'the rotary trunk con- 4 ductor 134 for operat ng the rotary line rela 1200f the conductor E. The circuit throng said rotary line relay 120 is established from ground (1" at the. repeater 0 through the pole changing relaysprings 188 and 189, line relay springs 186 and 204, conductor 205, pole 207 and 206. to the rotary conductor trun 134, rotary line rela 120, winding 208 of the difierentialrelay 1932 through the back-bridge relay springs 209 and 210 "to the battery lead 140, thence through battery B to ground G. The rotary line relay 120 on becoming energized presses the line relay spring 211 onto the ground sprin 194, energizing the private magnet he energizing current flows through .123. the springs 194 and 211, through the private magnet 123, thence through the back-bridge relay springs 209 and 210 tothe battery lead 140, thence through battery B to ground G.

v The private magnet 123 when operated releases the side switch of the connector from first to second position. The side switch wiper. 127, therefore, enga es the contact point 212, and the side switc m er 126 engages the contact point 213. T e shifting presses the vertical button of the side switch wiper 127 onto the contact oint 212 substitutes the rotary magnet 122 or the vertical magnet 121, bringing the former under the control of the vertical line relay differential relay 193 is energized each time I that the vertical or rotary line relays are energized, being in the same 'ener 'zing circuit; but the cnerglzation of said di erential relay is of no consequence at this stage. 7

The third digit being 0 the subscriber 19 ten times, then the rotary button 20 once. Pressing the vertical button 19 ten times grounds the vertical line conductor 162 ten times. The impulses are received by the vertical line relay 62 of the repeater C and repeated to the vertical trunk conductor 100 and in turn received by the vertical line relay 109 of the repeater C Saidvertical line relay repeats them again to the vertical trunk conductor 133 for operating the vertical line relay 119 of the connector E. Said vertical line relay becomes energized at each impulse, as already described, as a result causing the spring195 to be pressed against the spring 194. Each timethat the engagementof said springs occurs the rotary magnet 122 is energized by a flow of current from ground G" at the connector E through the said sprin 194 and 195, private springs 196 and 197 tothe side switch-wiper 127, thence through the rotary magnet 122 to the battery lead 140, and through battery B to ground G. The rotary magnet 122 is thus energized ten times and the connector-shaft and wipers rotated ten stepsalong the second level and into engagement with the terminals of the that are already known.

119. It will be understood that the;

. fi rst-selector scriber presses his rotary button 20 he groundsthe rotary conductor 135 and oper- 101, operatin the rotary line relay 110 of the repeater said rotary line relay in turn operating to energize the rotary line relay 120 of the connector E. The encrgization' of said rotary line relay 120-of the connector E produces the energization of lhe private magnet 128 of the connector over circuits net upon being operated causes either of two operations, namel hector-switch E i the called line is busy, or

substation #220. When the calling sub-- Said private mag' the release of the conthe release of the connector side switch to third position if the line is not busy whereby the calling subscribers line is connected with the called subscribers line over circuits indicated'by the heavy conductors (Figs. 1 and 2). It will be assumed, first, that the operation of the private "magnet produces the latter result -that is, releases the connector side switch to third position. When the side switch passes to third position the side switch wipers 124 and 125 pass into engagement with the contact points 214 and 215, thus completing the connection between thetwo subscribers lines, as already stated. The connection may be traced as follows: Beginning with the subscribers transmitter 8 at the substation #500 it extends through the primary winding 7 of the induction-coil 6 to the 'rotary line conductor 135,- thence 42 to the condenser 68 of the repeater C to v the vertical trunk conductor 100, side switch wiper 96 of the selector D, contact point 182, Kertical line wiper 88, vertical trunk con-' ductor 185, condenser 115 of the repeater C (Fi 2), rotary line conductor 134 to the con enser 130 of the'conncctor E, ringer re lay springs 216 and 217, side switch wiper 125, contact point 215, rotary line wiper 117, rotary normal conductor 218, rotary line conductor 219, ringer springs 220 and 221, ringer 222, condenser 223, vertical line conductor 224, vertical normal conductor 225, vertical line wiper 116, contact point 214, side switch wiper 124, condenser 129, verticaltrunk conductor 133, condenser 116 of the repeater C,rotary trunk conductor 201, rotary linewiper 89, contact point 183 of the D, side switch wiper 97, switch shaft springs 104 and 102, rotary trunk con= ductor 101, condenser 67 of the repeater C, springs 38 and 39 of the line switch A, vertical line conductor 162, spring 21, contact point 23, springs 10 and 9 to the transmitnaling button 26 and grounds the vertical line c'nductor 162 over a circuit thatextends rom ground G through the, ground springs, 14 and 13"to the contact point 29 of the .si aling device, thence through the spring 2? and springs 9 and 10 to the vertlcal line conductor 162. As a result the vertical linerclay .62 of the repeater C reside switch wiper 126, contact point 213 I ceives theimpulse and operates to ground operationof the ringer relay 131. The

the vertical trunk conductor 100 and to, therefore, operate the vertical'line relay 109 of the repeater C (Fig. 2). The vertical line relay 109 in turn grounds the vertical trunk conductor 133 and operates the vertical-line relay 119 of the connector E. The operation of said relay, since theside switch wiper 127 is in third position, causes the 0 crating current flows from ground G through the line relay springs 194 and 195 to the side switch wiper 127, contact point 226 to the rib er relay 131, thence through the springs 22 and 228 of the differential relay 193 to the battery lead 140, and

through battery B to ground G. When the ringer relay spring 217 is pressed onto the spring 229 and the spring 230 onto the spring 231, thereby bridging the ringer generator 132 across the called subscribers line, the ringer 222 of the substation #220 is rung over a line circuit that has already been pointed out. It will be noticed that when the side switch nector E engages the grounded contact point 232, whereby a guarding potential is established at the prlvate' wiper 118 to protect thecalled line against interference after switch wiper 126 tothe private wiper 118.

The said guarding potential, furthermore, forces a current through the cut-off relay 233 of the line switch A springs 234 and 235- are separated to disconnect thetrip magnet 236 from the'line,

thus making'it impossible for the ringing current to operate the line switch A and cause an interference.

As explained, busy lines are protected by guarding potential, whether they are calling or whether they are called. In either case a guarding potential a pears at the connector private banks. X when the subscriber operates the rotary line relay 120 of, the connector E for the last digit the desired line is busy, the connector side switch will be restored to normal positioii, and the connector switch shaft as well.

vIn other words the connector-switch is released. I

The busy release results as soon as the private magnet presses the springs 237 and 238 into contact. As a result a circuit is passes to third posi-- 'tion the side switch wiper 126 of the conwhereby the ssuming now that in engagement with a ground established through the release magnet 128,

mitgnet 128, t ence through the springs 227 an 228 of the differential relay 193 to the battery lead 140, and'through battery B to ground G. It will be clear of course, that the differential relay springs 227 and 228 arein enga ement at the time, since the differential re ay 193 energizes in series with the rotary line relay 120.- When the release magnet 128 energizes, the connector-switch is, of course, restored to normal position and the switch-shaft also returns to normal position; and then when the subscriber presses his signaling button and operates the vertical line relay 119 of the connector E, since the connector is now in normal position, he operates the vertical magnet 121,

engage and close a circuit over-which a busy signal is sent to the calling subscribers station. The circuit for the said busy signaling current extends from the coil 241 of the busy machine K to the connector switch shaft springs 239 and 240, thence to the contact omt 242, side switch wiper 125, ringer re ay s rings 217 and 216 to the condenser 130 ,0 the connector E, trunk conductor 134, condenser 115 .of the repeater C vertical trunk conductor 185, vertical line wiper 88 'of the selector D (Figfil), contact point 182, side switch wiper 96, vertical trunk conductor 100 to the condenser 68 of therepcater C, thence through the springs 42 and 43 of the-line switch A to the rotary line conductor 135, through the primary winding 7 of the substation #500 to thevertical line conductor 162, thence through the springs 39 and 38 of the line switch A to the vertical line relay 62 of the repeater 0, through the winding 69 of the difl'erential relay 64 to the battery lead 140, then back to the coil 241 of the busy machine K. The calling subscriber upon hearing the busy signal restores his receiver to the switchhook, and as a result the switching apparatus that he has brought into use is re leased.

' The release occurs when the release springs 30, 31 and 32 are brought into contact. The. vertical and rotary line conductors 162 and 135 are thus grounded simultaneously atthe substation ground G The vertical and rotary line relays 62 and 63 of the repeater C are thus energized simulta- .neously. The energizing circuit for the .formeris established from ground Gto the release spring 30, thence through the ential re through battery B to release springs 31- and 32 to the vertical line conductor 162 and through the vertical line rela 62 and winding 69 of the difiery 64 to the battery lead 140, thence ground G. The-energazing circuit'for the latter extends from groimdG to the, release-spring 30, thence f ts the release spring 31 andtolthe rotary 62 ,.and 68 energize, but thedifle'rential relay. 64 energizes also, since the windin 69 and 70 receive current inmultip e. Therefore the difierential'relay springs 243 1' g and 244 are in contact at the same time that the line relays 62 and 63 press the trunk release springs 245 and-246 into engagement.

' A release circuit is thus established for the release magnet 37 of the line switch A that extends from ground G through the differential relay springs 244-and 243, trunk releases'prings 246 and 245 and springs 44 and'45 of the line switch A to the release ma et 37, thence to the battery lead 140, amf through battery B to ground G. 'The release in st 37 thenattracts its armature 50 (Fig. 3 thrusting the'armature 52 of Q the trip magnet 36 over the end of the plunof the repeater C through the r-arm 47. ishment of the said release circuit produces a denergization of the' auxiliary relay66 round between und terminals G'- an 'G (Fig. 1). It will be noticed that since the spring 44 of the line'switch A is connected to ground during the establishment of this release cirsuit the contact 141 of the master switch bani: is also connected to ground. If it should happen that while the said contact is grounded the master switch wiper 61 passes onto the said grounded contact 141, the differential relay 59 will be energized the same as if the said contact'point were connected to main batte the only difference being that the energizing circuit for said difierential relay instead of extending through the winding 152 to ground G", as

previously described, extends through the winding 247 as follows: From ground G at the repeater C and through the trunk release springs 246 and 245 to the spring 44, thence to the contact point 141, master switch wiper 61 to the common member 149 of the master switch bank J, thence through the auxiliary relay 58. and winding 247 o the difierential relayv59 to the battery lead 140, and through battery B to ground G. The energizing of the difierential relay 59 ofcourse, causes the energization of-the motor magnet 57 for operating the Inn rshaft 56, as already explained.

ur er- At the same time the estabam, the simultaneous swim... a the relays, 62' and 63 grounds the vertical and rotary trunk conductorsIOO. and '101 simultaneously whereb vertical and rotary line relays 109 and 110 and the difierentia'l relay 111 are energized at. the same time.

Therefore, the trunk release springs 249 and 250 are brought into The release circuit is thus esta through the back release relay 180 of the first-selector D over the trunk release conductor 253. The circuit is as follows: Fromground G at the first-selector D to the contact pomt 181, thence to the side switch wiper 98, back release relay 180, private wiper 90, trunk release conductor 253, trunk release rings 249 and 250, resistance coil 254, difierential rela springs 252 subscribers release springs separate. Not

only does'the repeater C thus energize the release magnet of the selector D, but causes a simultaneous groundingof the trunk conductors 133 and 134 in a wel known man ner whereby the vertical and rotary line .relays 119 and 120 of the connector E are energized at the same time and with the differential relay 193. As a result the trunk ment at the same time that the difierential relay 251 and 252 are brought into engafiglza release springs 258 and 259 are brou ht into contact while the differential re ay sprin 228 and 227 are in contact. The result 18 that the release magnet 128 is energized by a flow of current from ground- G through the trunk release springs 258 and 259 to the said release magnet 128, thence through said magnet and through the springs 227 and 228 to the battery lead 140, and through batte B to ground G. The release magnet of t e' connector upon energizing releases the switch-shaft of the connector. The foregoing all occurs while the release springs 31 and 32 are in engagement, but as soon as the said'springs separate the -line relays 62 and 63 of the repeater C as well as the differential relay 64 of said repeater deenergize, whereby the energizing circuit for the release ma et 37 of the line switch A is destro e at whichinstant the said line switch is restored. to normal condition. Also, the

denergization of said relays produce the deiinergization of the back release relay 180' 1B 8 of the selector D and of the release st 257, ereby the first selectoris resto to normal condition and furthermore the ground connection to. the trunk conductors 133 and 134 is broken. As a result "the line relays 119 and 120 and the difierential relay 193 of the connector E deiinergize, permitting the release ma st 128 ofv said connector to define a so. All: the switching apparatusis us restored to normal condition. In casethe subscriber at the substation #220 does not answer after connection is made, "as described, therelease of the switching apparatus occurs in the same mannection is made with his line, when the cona to close ringing 611121116,

.263 of the back the subscribers switc -hook goes rela 264 energizes and the transmitter 265 of t e substation nector side switch as already descri by removin his receiver 259' from the switch-hook, us causing the primary circuit springs 260 and .261 the primary circuit and break the by permitting the'ringer spr ngs 220 and '221 to separate. The primary circuit com rises the windings 262 .and rid relay 264, and when up the said 220 is provided with battery for talking. e circuit over whi'ch the said talking current flows extends, from ground G at the connector to the contact point 232, thence to the side switch wi er 126, winding 263 of the back bridgere ay 264, ringer relay springs 216 and 217, sideswitch wiper 125, contact point 215 rotary line wiper 117 to the rotary line conductor 219, thence through the primary winding 266 of the induction-coil 267, transmitter 265, prima circuit springs 260 and 261 t9 the vertical ine conductor 224, thence to the vertical line wiper 116', contact oint 214, side switch wiper 124, winding" 62- of the back-bridge re ay 264, difierential frela sprin 268 and 228 to the battery lead 14 and t rough bat soon as the back-bridge relay 264 energizes the springs 269 and 209 are pressed into .contact, and as a result the pole chaenigin relay 114 of the repeater C. is energiz ergizing current flows from ground G to the side switch wiper 126, thence to the back-- bridge relay sprin 269 and 209 to the winding 208 of the di erential relay 1'93, thence through the rotaryiline relay 120, rotary trunk conductor 134 to the pole changing relay 114 of the re eater -0 thence through V, the. difierential re ay' springs 200 and 199 to the vertical trunk conductor 133, througlrwv the vertical line relay 119, winding 192 of the line relay springs to third position,

cal trunk con BtogroundG. As.

een-.

theidiflerential relay193 to the battery lead 140, thence through battery B to ground G. Of course,-the pole changing relay'114 of the repeater Cand the hne relays 119 and 120 of the connector E energize'in series, and

pressed into contact ut with no result, since the energizingbcircuit for the ringer relay 131 1s broken 'etween the diflerential :relay springs 228 and 227, and the private magnet 123 is short-circuited throu h ground'between the grounds G and due to the engagement of the back-bridge relay springs 195, 194 and 211 are 269 and 209. The pole changmg'relay 11401 the repeater C energizes to separate the sprin 202 from the sprin 203 and, therefore, rom the non-grounds terminal'of bat- Y tery B, and n s ring 188. Also, the spring 189 is separated rom the ground spring 188 to break the engages instead the grounded connection between vground and the line relay s ring 186, and the spring 206 is separated om the spring 207 to prevent the 'establishment of a short-circuit between the rotary and vertical trunk conductors 133 and 134 the spring 202 into engagement .with the ound spring 188 at the repeater C estab-- ished an .energizing circuit for the pole changing rela'y 65 of the repeater C in series with the line relays 109 and 110 of the repeater C The energizing circuit receives current from ground 188 and 202, winding 113 of t e differential relay .111, rotary line relay 110 to the rotary trunk conductor 201, rotary line wiper 89, side switch wiper 97, switch shaft springs 104 and 102, rotary trunk conductor 101, conductor 146,'aux1liar relay springs 143 and 144, differential re ay springs 147 and 148 pole changin relay 65, vertical trunk conductor 100, si e swltch wiper 96, contact point 182 vertical line wiper 88, vertiductor 1'85, vertical line relay 109 of the re eater C winding 112 of the through the springs differential re ay 111 to the battery lead 140,

thence through battery B to ground G. The

energizing of the line rela s 109 and 110,

since the pole changing re ay 114 is ener- 'zed, produces no eflect; but the energizaftion of the pole changin relay 65 at the repeater G supplies the ca ing subscriber with talkin battery-current when the pole changing r ay spring 174 leaves thejsprinfi 175 and engages the ground spring270. circuit is therefore established through the line relays 62 and 63 of the repeater C and the transmitter 8 of the substation- 500. The

current flows from the ground I through the springs 270 and 174, winding 70 of-the difierential relay 64, rotary line relay 63, springs 42 and 43 of the line switch A, rotary line conductor 135, primary winding 7 of the induction-coil 6, transmitter 8,

callin provi ed with talking battery current they and 167 are separated, and as 9 and 10 to the vercal line conductor 1 2, thence through-the rings. 39' and 38, vertical line relay 62 of e re the di erential relay- 140, and thro to the battery lead centactg'since the line relays are ener zed, ut the release circuits are not estabfi shed because the difierential rela s64 and 111 are not magnetized and, there ore, their respective release circuit springs 243 and and 251 and 252 are separated.- The and called subscribers being thus communicate with each other over circuits alread described and in a well known manner.

fter the two subscribers are through talking the calling subscriber may release the switching apparatus by hanging up his receiver and thus grounding as already explained) the vertical and rotary line conductors 162 and 135. As a result the vertical.

line relay 62 of the repeater O is maintained gether with the winding 70 of the difierential relay 64 are short-circuited through ground for a moment between the ground points G" at the repeater C andG at the substation. The short-circuitin path extends from ground G throu the pole changing relay sgrings 270 an 174, thence through the win ing 70 of the differential relay 64, and rotary line relay 63 to the rotary line conductor 135, thence through the release sprin 31 and 30 to the ground G. As a result t e differential relay 64 becomes unbalanced and ener 'zes, separating the springs 147 and 148 t at control the energizing circuit through the pole chan 'ng tween the line relay'spring's 163 and 176 relay 65, and brings into contact the re ease circuit springs 243 and 244. There results, therefore, first, the deenergization of the pole .changinlg relay 65 of the repeater C. As soon as t e energizes the springv174 returns to engagement with the spring 175, and the springs 166 and 167 and the springs 272 and 271 reengage, thus restoring the connections be- Y and the vertical androtary trunk conductors 100 and 101. When the pole changing relay spring 174 reen ages with the sprin 175 the rotary line re y 63 is reenergiz ter 0, throu h the winding 69 of h battery .13 to ground G. The-line relays 2 and 63 are energizeddurpole changing relay 65 de-' .by a'flow-of current in the reverse direction,

which current'also flows through the 'windmg 70 of the pole changing relay 64, further strengthening .the magnetizing force of said relay. The result-is that the vertical and rotary line relays "62 and 63 energ'ize simultaneously, grounding the vertical and rotary trunk conductors 100 and 101, and closing the trunk release circuit through the release ma et 37 of the line switch Aat the instantt at the trunk release springs 245 and 246 of the'repeater C come into' contact. Previous to this, however and as soon as the pole changing relay is deenergized, the line relays 109 and 110 of the repeater C. also deenergize, since the are in the same circuit with the said ole c angin relay. Therefore, groundingt evertical an ' rotary trunk conductors 100 and 101 causes, as in the repeater C, the energization of the vertical line relay 1 09 and the short-circuiting of the rotary 11ne relay 110 in series with the winding 113 of the differential relay 111, as

the pole changing relay 114 is still energized. The short-circuit exists between the ground point G at the repeater C and the ground point G at the repeater C. The path of said short-circuit reaches from through the springs 188 and 202, through the w ndm 113 of the ole changing relay 111 an the rotary l ine relay 110 to the rotary trunk conductor 201, thence to the rotary trunk conductor 101 and through the pole changing relay springs 271 and 272, and through the line relay'sprin s 176 energized, but the rotary lme relay 63 tot.

and 164 to ground G. Therefore, the ifier- --en tial relay 111 at the repeater C becomes energized for the same reason described in connectlon with the difierential rela of the re eater C, and as a result the pole c anging he deenergization of the pole changing reound G" I la restores thepole changing relay springs H w ereby the ground connectlonis restored to the line relay ground spring 186, and the circuit is closed between the line relay spring 204 and the rotary trunk conductor 134. Furthermore, at the instant that the pole changing relay sprin '202 and 203 reengage, the rotary line re ay 110 is re'ner 'zed, and since the current passes .throug the winding 113 of the differential relay 111 in a direction to augment the flow of current in .the winding 112, said lifierential relay remains ener ized for the time being. There fore, since y the simultaneous energization of the line relays 109 and 110 the trunk release springs 249 and 250 are brought into contact, the trunk-release circuit is established through the back-release relay 180 of the first-selector D, and the said line relays cause the simultaneous grounding of the vertical and rotary trunk conductors '133 and 134. ,Previous to the grounding of said trunk conductors, however, the .11116 relays 119 and 120 of the connector E are deenergized together with the pole changin relay lay winding 208 are short-circuited throu h ground between the ground points G at t e connector E and G at the re eater C The path of the short-circuit is as ollows: ground G at the connector E to the side switch wiper 126, thence through the backbridge rela springs 269' and 209 to the differential re ay winding 208, rotary line relay 120 to the 'rotar trunk conductor 134, thence through the po echanging relay springs 206 and 207,- line relay springs 204 and 186, pole changin rela T springs 189 and 188 to ground a he result of the energization of the differential relay 193 of the connector- E is that the differential relay springs 268 and 228 are separated, whereby the backbridge rela 264is deenergized and the differential re ay s ring 2281s carried into engagement with t e spring 227, closing a connection between the release magnet 128 and the said spring 228. The deenergization of the back-bridge relay 264 restores the spring 209 into engagement with the sprin 210 and, therefore, with the battery lea 140, whereby the rotary line relay 120 is energized. The result is that the trunk release springs 258 and 259 are broughtinto engagement and the energizing circuit for the re lease magnet '128- completed from ground G" through the said trunk release springs and throughthe differential relay springs 227 and 228 to the battery lead 140, and through battery B to ground G. Therefore, the connector-switch and switch-shaft are restored, thelatter causing the wipers 116, 117 and 118 to return 'to normal position, breaking the .energizing circuit for the cut-off relay 233 between the ground terminal G,

rivate wiper118 and the said cut-off relay z33. The line switch A, therefore, of the called line is thus restored to the control of the substation #220. As soon as the subscribers release springs 30, 31 and 32 disen gage, the ground connection to the subscribers line conductors 162 and 135 is broken,

and as a result the switching apparatus returns to normal position in the same man'- ner described in the case of the release after the subscribergets a busy signal or before the called subscriber answers. Sometimes it may happen that b accident the line switch A is operated so 1: t the plunger 46' (Fig.

From.

,64 and 111 to two hundred and fift 3) is tripped onto the bank. In such case the auxi iary relay '66 of, the repeater C is energized and as a result the springs 143 and 144, as already explained, come into contact and energize the supervisory relay 103 ofthe selector D supervisory lamp 107 to light and remain so. The attendant at, the main trunking station on noticing the trouble-light at once knows which trunkis the one that has thus become occu ied, since each trunk line has a separate se ector D. Assuming, for example, that the-trunk line terminating in the selector D is the eighth trunk leading from the line switch bank I, contrary to what has been assumed in the prec'edin the attendant will operate the auxiliary re ease switchH by pressing the rotary button 84 eight times, energizing each time the rotary magnet 75 over a circuit from ground Gr through the springs 87 and 86, trunk con-y ductor 273 to the said rotary magnet 75, thence over the conductor 274 to the battery 'lead 140, thence through battery B. to ground G. The said rotary magnet then at tracts its armature and causes the awl 76 to engage the longitudinal teeth 72 o the shaft 1 71 each time 1t energizes and rotates the wiper 73 onto the eighth contact. He then presses the release button 83 and operates the release-magnet 77.

springs 87 and 85 tothe trunk conductor 275, thence through the release magnet 77, conductor 274 to the battery lead 140, and through battery B to ground GT The release magnet 77 then presses the sprin 80 and 81 into contact, sending a groun im-. pulse through the release magnet 37 of the 4 line switch A from ground G through the switch A is restored. At the same time that the release ma et 77 operates the said springs 80 and 81 the dog 78 is withdrawn 1 from .the longitudinal teeth 72, whereby the retracting spring 79 may restore the shaft 71 and W1 er 73 to normal osition.

' The resistance of the various coils may be of any suitable character, but good results are obtained in the repeaters C and 0 when the line relays 62 and 63 and 109 and 110 are the latter causing the The energiz n clrcult extends from ground G" throng the wound to a resistance of one hundred ohms each; the windings of the difierential relays ohms each; the pole changin relays 65 an 114 to five hundred ohms eac the auxiliary relay 66 of the repeater C to fifty five hundred ohms; and in the release switch H the rotary and the release magnets 75 and 77 to one hundred ohms each.

From the foregoing it will be seen that it s or central 1:

races -is thus temporarily tied up and put out of service, and maythen cause the ofi-normal individual switch to disconnect from the said trunk line, restoring the latter to its normally idle condition. In each case the automatic restoration is accomplished from the main or central station, and b simply puttin a ground on the trunk re ease circuit o the off-normal switch, the release, of

course, being always initiated over the re-. -lease trunk running from the central station to the sub-central station at .which the offnormal switch is located. I'do not, however, limit myself to this exact construction and arrangement, as broadl considered my invention is of course, app icable to difl'erent methods of releasing automatic switches.

Preferably, however, employ my central station superviso releasing or restoring apparatus in com lnation. with trunk release circuits extending between automatic release trunk runnin switches, or between automatic switches and re eaters.

hat I claim as my invention is 1. In a telephone exchan e system, the combination of subscribers linesterminatin at a sub-central station, individual switc es for the subscribers lines at the subcentral station, one or more of which are oflnormal, trunk lines leading from the subcentral station to a main orcentral trunking station, means for temporarily grounding any calling subscribers line to cause the corresponding individual switch to automatically select a non-busy trunk line,- a special from the main or central station to the su -central station, means for transmitting electrical impulses over said release trunk, means at the sub-central .station for receiving said electrical impulses and thereby selecting any busy trunk line,

and means by which the selection of such trunk line automatically efiects the restoration of the off-normal switch.

a 2. In a telephone exchange system, the combination of a main or central trunking station, sub-central or outlying trunking stations, trunk lines connecting the main or central station with the sub-central stations,

subscribers telephone lines terminating at said sub-central stations, automatic SWltOlb. ing machinery at the sub-central stations, a

special foreach sub-central station, said release trunks extending from the main or central station to the sub-central stations, means at the main-or central station by which an attendant may transmit electrical impulses over said release trunks,

means at the sub-central stations for receiving said electrical impulses and thereby sewhich such selection of a busy trunk line efiects the automatic release of the same from the subscribers line by which it is ma'debusy.

3. ,In a telephone-exchange s stem, the combination of a main or central trunking station, sub-central or outlying trunking stalecting any busy trunk line, and means .by

tions, trunk lines-connecting the mam or central station, with the said sub-central stations, subscribers telephone lines terminating at the sub-central stations, automatic trunkm machinery located at the sub-central stations and by which calling telephone lines are automaticall placed in connection with non-busy trunk ines, a special releasin switch for each sub-central station, said re easin trunk line, release trun s extending from the main or central station to the said releasing switches at the sub-central stations,

- means by which an attendant at the central station may transmit electrical impulses over said releasing trunks to control the operations of said releasing switches, and means by which the selection of a busy trunk line b a releasing switch automatically efi'ects a disconnection of the same from the subscribers line by which it is made busy.

4. In a tele lione exchange system the combination 0 subscribers telephone lines, individual switches for said telephone lines trunk lines to be selected by said individua switches, a s ecial. releasing. switch common to all of sai individual switches, means by which an attendant may cause said releasing switch to select any particular trunk-line which is busy, and means by which such solection of a trunk line automatically efi'ects a switches ada ted to select any restoration of the corresponding ofi-normal' individual switch.

5. In a telephone exchange system the combination of subscribers telep one lines, individual trunkin switches for said telephone lines, trunk ines to be connected by the switches, with the telephone lines, a trunk release circuit for each individual switch, a selective switch provided withmeans for putting a ground on any one of said trunk release circuits to release or re-.

store the corres ending off-normal individual switch, a re ease trunk running to said selective switch, and means for transmittin electrical impulses over said release trunfi to control the selective and releasing opera- I tions of said selective switch.

6. In a telephone exchange system, the

combination of a main or central trunking station, sub-central ,or outlying trunking stations, trunk lines connecting the main or central station with the sub-central stations, subscribers" telephone lmes terminat- 'in at the sub-central stations, subscribers" in ividual trunking switches at the sub-central stations, repeaters at the sub-central stations, connectorsat the sub-central stations, repeaters at the main or central station, selective trunkin switches at the main or central station, impulse transmitters at the sub scribers stations, the re eaters at the subcentral stations being a apted to repeat to the main or centralstation any electrical impulses received from a calling subscribers station, and the repeaters at'the main or central station, being adapted to repeat to a called sub-central station an electrical impulses received from, the cal in sub-central station, a special releasing switc at each subcentral station, said releasing switches pro vided with means for selecting any busy trunk lines, and thereby releasing the corresponding off-normal individual switches, release trunks extending from the main or central station to the said releasin switches, and

means at the main or centra station for env abling an attendant to'control the selective and releasing operations of said releasing switches.

7. In a telefphone exchange system, the

combination 0 subscribers telep one lines, an individual switch for each telephone line, trunk lines to beselectedby said individual switches, said trunk lines less in number thansaidtelephone lines, an associated selective switch provided with means for selecting an one of said trunk lines, having a bank 0? contacts corresponding in number to the saidtrunk lines, a wiper adapted to travel over said contacts to select the one corresponding to a busy trunk line, a suitable connection between said trunk llnes and their respective contacts in said bank means for first grounding the said wiper and then instantlyreleasing it from engagement with any selected contact, and means by which 1 the grounding of sand wiper automatically effects a release of the ofi-normal individual switch by which the trunk line corresponding to the selected contact is made busy.

, 8. In a tele hone exchange system, the combination 0 individual switches, an associated releasing switch'provided with means for selecting and caus' the release of any oil-normal individual sw1tch, and means for the selecting and releasing opera-' efiecti tions-o said associated switch.

9. In a tale hone exchan combination 0 a plurality o repeaters, automatic. switching machineryfor selecting non-busy re eaters, an associated releasing switch provided with means for selecting combination of a system, the

peater rovide and causing the release of any oif-normal or busy repeater, and means for controlling the selective and releasing operations of said associated switch.

10. In a telephone exchange system, the

means for establishing'connections with the said trunk 111168, an associated auxiliary switch prov ded with means for selecting and causing the release or disconnection of any busy trunk llne, and means for controlllng the selective and releasing operations of any automatic auxiliary switch. 11. In a telephone exchange system, the

including a said trunk line, an energizing circuit includ-' ing a portion of the ta king circuit for said first-mentioned relay controlled ,by said lastmentioned relay, and an autoniatic switch for selecting said trunk. V

12. In atelephone exchange system, the combination of a trunk line, 1 repeating relays at one end of said trunlgline, a selector at the other end of said trunk line a supervisory or off-normal lamp for sai selector a supervisory or off-normal rela for said selector, a local circuit forsaid amp, controlled byl-s'a'id off-normal or supervisory relay, anot associated withsaid repeating relays, and an energizing circuit for said first-mentioned supervisory relay controlled by said lastmentioned supervisory relay.

13. In a telephone exchange system, the combination of a trunk line, repeating relays at one end of said trunk line, a selector at the other end of said trunk line, a supervisory orofl-normal lamp for said selector,

.a supervisory or ofi-normal relay for said lay, another supervisory or off-normal relay associated with said repeating relays and an energizing circuit for said first-mentioned supervisory relay controlled by said lastmentioned su ervisory relay, said energizing circuit including bothsides of the trunk line. 14. In a telephone exchange system, a talking circuit, an automatic selector provided with a supervisory or off-normal lamp, a local circuit for said lamp, an ofl-normal or supervisory relay for said selector said relay controlling the circuit of said and an energizing circuit including a portion of the talking circuit for said relay.

15. In a telephone exchange system, a rewith repeating relays, a line over. w ich electricallim ulses are repeated by said relays, a supervisory signal evice plurality of trunk lines er supervisory or off-normal relay lamp,

at the other end of said line, a supervisory relay associated with said repeating relays,

1& In a telephone exchange system, the combination of a subscribers telephone line, automatic switches having vertical and rotary motion by which the subscriber conera said one po e grounded and the other pole nornects his tele hone line with some other line, operating re ays therefor, a battery for op-- switches, said battery having mally connected with one side of said telehone line, the other side of said telephone ine bein normally insulated or disconnected from bot tlzeaground and said battery, and

means opera upon the vertical movement of said switch for connecting said other side of the line with the non-grounded pole of the battery through one of said relays in the operation of one of said switches.

17. In a tele hone exchange system, the combination 0 a plurality of automatic switches, a trunk release circuit for each automatic switch, subscriber-controlled means for putting a ground on the trunk release circuit of any busy switch to restore the latter, an auxiliary switch provided with means for selecting and putting a ground on the trunk release circuit of any busy switch, and

means for controlling theselective and grounding operations of said auxiliary switch. y

18. In a telephone exchange system, an automatic selector-switch provided with first and second supervisory or off-normal lamps, a circuit for lighting the first lamp during the-initial operation of the selectorswiteh, and a circuit for lighting the second lamp after the selector-switch is through operating.

19. In a telephone exchange system, a line, a repeater on said line, said repeater provided with line and pole-changing relays, a battery having one pole normall connected with the line relays, adapted to e switched into series with and between the line relays by the energizing of the pole-changing relay, a ground connection, and connections by which the energizing of the line relays connects the line with said ground connection, said pole-changing relay provided w1th normally closed contacts controlling the electrical connection between the line and the said ground connection.

20. In a telephone exchange system, the

combination of a subscribers telephone, a subscribers telephone line, means for furnishing talking current over thetclephone line to the subscribers telephone, a repeater, a trunk line leading from said repeater, a switching machine at tho and of said trunk line, and means by which the subscriber uses the repeater for controlling the said switchpeater having vertical and rotary line conductors, a battery normally connected with both line conductors, and a pole changing relay for said repeater, said ole-changing relay adapted when energized to shift the rotary line conductor from the non-grounded to the grounded pole of said battery.

22. In a telephone exchange system, a repeater, vertical and rotary line conductors therefor, n. pole-changing relay, a battery having one pole grounded and the other pole normally connected with both line conductors, said pole-changing relay adapted when energized to shift the rotary line conductor from the grounded to the non-groundedpole of the battery, a trunk release circuit, and a differential relay, said trunk release circuit being controlled by both the diiferen tial relay and the pole-changing relay.

, 23. In a telephone exchange system, a can tral station, a sub-central station, two-wire trunks connecting the two stations, subscrlbers lndivldual switches at the sub-eentral station for automatically selecting said trunks, one or more of whlch are oil-normal,

and means for enabling a central station,

' trunks connecting the two stations, trunkselecting switches controlled by the subscribers at the sub-central station a special releasing switch at the sub-central station,

and means by which an attendant at the central station controls said releasing switch to release and restore any oil-normal trunk-selecting switch.

26. In a telephone system, a central station, a sub-central station, two-wire trunks connecting the two stations, subscribers automatic trunk selecting switches. at the subcentral station, a special trunk selector at the sub-central station, a special release trunk connecting said special switch with the central station, and means by which an I attendant at the central stationicontrols said special release trunk for the purpose of finding and releasing any ofi-normal trunking switch.

27. In a telephone exchange system, the

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