USRE16268E - Ltxgeii - Google Patents

Description

. Re. 16,268 E. A. Ml=:|.f".q:1|-calany TELEPHONE EXCHANGE AUTOIMTIC SWITCHING SYSTBI Feb. 1s 192s.

Original Filed-Seht- 4, 1908 IS Sheets-$114391:4 "5

d' E *Hsmger l Reissued Feb. 16, 1926.

UNITED STATES PATENT OFFICE.

EDWARD A. MELLINGER, OF CHICAGO. ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC., 0F CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

TELEPHONE-EXCHANGE AUTOMATIC SWITCHING SYSTEM.

Original application filed September 4, 1908, Serial No. 451,674. Renewed August 1G, 1919, Serial No.

318,040. Serial No. 567,821.

To r/ZZ whom t may concern:

Ile it known that I, EDWARD A. MEI.- LiNorn, a citizen oit the United States of America. und resident of Chicago, Cook County, Illinois, have invented acertain new and usctul Improvement in Telephone- Exchange Automatic Switching 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 systems, and especially to systems that have no operating grounds at the substations, which are commonly called two-wire systems.

Objects of my invention are the provision of an improved non-numerical trunking switch-that is to say, a switch for auto- -matically selecting idle trunks without reference to any digit of the called number; the provision of an improved master switch for controlling the operation of a plurality of said non-numerical trunking switches. whereby the latter select idle trunks ahead ot the calls; the provision of an improved selector or numerical trunking switch for a two-wire system; the provision of an improved connector switch for finding the called line;.and the provision of certain details and features of improvement and combinations tending to increase the general efficiency of a telephone system of this par ticular character.

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

In the accompanying drawings Figure l shows diagrammatically the calling subscribers substation A and the central oce switching` apparatus of a system involving the principles of my invention. To the line of substation A is allotted the line switch C controlled by the master switch D. At E is represented a first-selector switch, and at l a diagram of a second-selector switch is shown.

In Fig. 2 there is shown diagramma-tically a connector switch H, at I a central oice ringer generator is shown and at J a busysignaling device. K represents a devicefor interrupting the energizing circuit of the ringer relay-that is, by means of the ap- Original No. 1,343,462, dated June 15, 1920. Application for reissue iled June l2, 1922.

paratus K the ringer relay may be caused to energize intermittently. To the line of the substation A there is allotted the line switch C which is like the line switch C'.

Figs. 1 and 2 taken together represent diagrammatically the central oiice switching apparatus involved in establishing a connection between two substations. In Fig. 2 a central battery is shown at B having its positive terminal preferably grounded at G. The central oice switching apparatus is of the general type disclosed in English Patent No. 26,301 of 1906, but with modifications and circuit changes to adapt the same to operate in connection with a twowirc systemthat is, a system in which there is no ground connection at the subscriber-s telephone. The line switches of which C and C' are modified forms are also disclosed in The Western Electrician of January 25, 1908, and the American Telephone Journal of June 6, 1908. The master switch D is also of the form disclosed in the said Testern Electrician and the American Telephone Journal. Thc first-selector E and second-selector F are of the general type shown in United States Letters Patent No. 815,321, granted March 13, 1906, to Keith, Erickson and Erickson, while the connector switch H is of the general type shown in United States Letters Patent No. 815,176, granted March 13, 1906, to Keith, Erickson and Erickson.

Fig. 3 is a. diagrammatic view sho-wing the line switch, the line switch plunger and the line switch bank, together with the circuits and parts of the master switch.

The subscribers substation, it will be seen, is somewhat different from the usual automatic substation, substation A being arranged and modified to operate in connection with a two-wire systemthat is, a systeln in which no ground connection is used at the subscribers substation. Substation A, for example, comprises the usual receiver 2. switch-hook 3, induction coil 4 which consists of the primary winding 5 and secondary winding 6, transmitter 7, condenser 8, ringer 9 and impulse wheel 10, which latter has the usual impulse teeth 11. The impulse wheel 10 is secured to the shaft 12, to which shaft there is also secured the dial (not shown). Then the dial is turned the impulse teeth 11 are adapted to engage the cum 13 upon the end ot' the spring 14 and thereby carry the latter out ot` engagement with the spring 15. Upon the switch-hook 3 there is the cam 16 which, when the switchhook is up, permits the springs 17 and 18 to engage, thereby bridging across the subscribers line conductors 19 and 20 the primary circuit including the transmitter 7 in series with the primary winding 5; but when the switch-hook is lowered the spring 21 is carried into engagement with the spring 22, whereby the ringer S) in series with the condenser 8 is bridged across the line conductors 19 and 20 instead.

The connector switch H (Fig. 2). like the line switch C and first-selector E, is arranged to operate is a system in which there is no ground connection at the subscribers station.

A clearer understanding of my improved system may be had from an explanation of its operation when a subscriber operates the central oliice Switches to establish a connection. For example, it will be pointed out how the subscriber at substation A may operate the main ofce switches to establish connection With substation A (Fig. 2), the number of which is 2220. To call the number 2220 the subscriber at substation A, after removing the receiver from the switch-hook, operates the calling device for each digit in the well-known manner. wWhen the receiver is removed from the switch-hook, and the springs 17 and 18 engage, an energizing circuit is closed through the line relay 23 of the line switch C. Vhen this relay energizes, a circuit is closed through the trip or plunger magnet 24, which then operates to force the plunger into a bank terminal and extend the calling line conductors to a trunk-line leading to a selector switch. The dial is operated for the first digit, and upon returning to normal position operates the first-selector switch to establish connection with a trunk-line leading to a second-selector switch. The second-selector is then operated for the second digit to select a trunk-line leading to a connector switch. The impulses delivered by the dial for the last two digits are directed toward the connector, which operates to place its shaft wipers in connection with the contacts corresponding to the desired number. When the substation primary circuit is bridged across the line conductors 19 and 20 an energizing circuit is established through the line relay 23, said circuit extending from ground G through the springs 26 and 27 to the line conductor 20, through the transmitter 7 and primary winding 5, impulse springs 14 and 15, springs 17. and 18 to the line conductor 19, springs 28 and 29, winding of the line relay 23 to the battery lead. 25, thence through battery B to ground G. rlhe line relay, upon energizing, presses the springs 30 and 31 into contact. As shown, the line relay 23 is slow-acting-that is, when once energized and the energizing circuit is then broken,

the relay does not instantly' return to normal position, but remains in its energized position for a short interval. The engagement ot' the springs 30 and 31 closes an energizing circuit through the trip or plunger magnet 24, which magnet operates to attract the plunger arm and thrust the plunger into an idle bank terminal. The plunger magnetcircuit extends from ground G through the springs 30 and 31, plunger magnet 24 to the battery lead 25, thence thfyough battery B to ground G. lVhen the plunger enters the bank terminal and closes the bank springs 32 and 33 into contact an energizing circuit is closed through the motor magnet relay 34, which in turn operates to close a circuitI through the motor magnet 35 of the master switch D. The motor magnet then operates to advance all idle plungers that are in locked engagement with the plunger shaft 36 to a position opposite the next idle bank terminal similar to the one just engaged. The circuit through the motor magnet relay extends from ground G2 through the relay 34 to the common segment ot the master switch bank, wiper 37, individual segment 38, through the bank springs 32 and 33 to the battery lead 25, etc. The relay 34, upon energizing, operates to place the springs 39 and 40 in contact, whereby a circuit is closed through the motor magnet 35, said circuit extending from ground G3 through the motor magnet 35, interrupter springs 41 and 42, motor magnet relay springs 39 and 40 to the battery lead 25, etc. The motor magnet, upon energizing, attracts its armature 43, and the pawl 44 engages a tooth ot the ratchet Wheel 45 and moves the latter one step. l/Vhen this occurs the spring 46 engages the spring 47 (bearing in mind that the spring 46, prior to this operation, cngaged a notch of the toothed wheel 48), and when the ratchet wheel 45 is given one step the spring 46 slides oli from the top ot the notch and engages the spring 47. The enf gagement of these two springs provides a new energizing circuit for the motor magnet 35, said circuit extending through the springs 46 and 47 to the battery lead 25 instead ot' through the springs 39 and 40. Furthermore, the motor magnet, when energized, separates the interrupter springs 41 and 42, therebybreaking its own circuit like a buzzer. The motor magnet 35 continues to operate in this manner as long as the springs 46 and 47 remain in engagement. 'When the next succeeding tooth on the wheel 48 advances far enough the spring 47 disengages from the spring 46, thereby opening the energizing circuit for the motor magnet.

By the time the last notch disengages the springs 46 and el? the master switch Wiper 37 has passed from the first contact 38 to the second contact 49. Suppose, however, that when the wiper 23T engages the individual segment JCE) there then is a guarding poteir tial present. In that event an energizing circuit is closed through the motor magnet relay 3l, said circuit extending from the contact through the Wiper 37, common segment ofA the master switch bank, through the Winding ot the relay 3l to ground G2, as previously traced. The motor magnet relay again energizes and closes the circuit :tor the motor magnet. The motor magnet operates as before, and the Wiper 3T is carried to the next contact. and the next tooth of the wheel i8 separates the springs 4G and 17. This operation continues as long as the Wiper 37 continues to tind contacts with protecting potential. It will be understood, of course, that when the motor magnet thus operates, the plunger shaft 36 and all plungers that are in locking engagement with the said shaft are moved to a new position opposite an idle bank terminal similar to the one engaged by the line switch C, and at t-he same time the bridge-cut-ofl' springs 26 and 29 are separated from the springs 27 and 28, respectively, to disconnect the line conductors from the line switch C. At the instant that the plunger enters the bank the following springs are pressed into contact: 50 and 51, 52- and 53, 54 and 55, and 32 and 33. The engagement of the springs 50 and 51 and 54 and 55 extends the calling subscribers line conductors 19 and 20 to the trunk-line conductors 56 and 57 which terminate in the first-selector E. This extension of the line provides an energizing circuit for the line relay 58 of the tirstseleotor. The circuit extends from ground Gr* through the Winding 59, side switch Wiper 60, trunk conductor 57, bank springs 55 and 521-, line conductor E20, transmitter 7 primary Winding 5, impulse springs 14 and 15, springs 17 and 18, line conductor 19, bank springs 50 and 51, trunk conductor 56, side switch Wiper 61, through winding 62- to the battery lead 25, thence through battery B to ground G. The line relay 58 thereupon energizes and operates to' carry the spring 63 out of engagement with the spring 64 and into en* gagement with the spring 65, thereby providing an energizing circuit for the slowacting release relay G7, which latter in turn operates to provide an energizing circuit for the bridge-cut-oft relay 66 of the line switch C. This circuit extends from ground G5 through the springs 68 and G9, winding ot the supervisory relay 71"). conductor Tl, bank springs and 52, lnidge-cut-oti` relay 66, trip or plunger magnet 24 to the battery lead 25, thence through battery B to ground G. viince thonet-off springs 126.31m 2T are already in an operated position the energizetion ot' the relay (3G at this time is without particular' Function. The trip or plunger magnet l-i. being` also included in this circuit` retains the plunger arm in an attracted pcsitiou and the plunger in the baul; terminal. Thus it will he seen that tbe line switch. atte-r being operated 'from the subscribers station, is maintained in its operated position by a ground connection at tire tirstselector su'itch l. lJ`lii't'liei-iiioic. thtl supervisory relay 'T0 also energizes and places the springs T2 and T3 in Contact, thereby closing a circuit through the supervisory iamp Tl which extends from ground (tu through the side switch wiper T5, springs 72 and T. lamp Tsi lo the battery lead 25. thence through battery l to ground (l. The slow-acting release relay GT also carries the spring T53 t'roin the spring TT and into Contact with the spring T8.

The foregoing is the condition ot' the central oiiiee switches after the calling subscriber removes his receiver and betere the dial is turned. llfhcn the dial returns to normal position for the lirst digit. the first-selector switch E is operated, The first digit being 2, the impulse spring it t Yice carried out ot engagement with the impulse spring 15. As a result the energizing circuit through the line relay 5S is broken twice, and the spring G9 comes into contact with the spring 64 twice. At'ter the tvvo impulses are thus delivered the line. relay 58 again energizes and carries the spring 63 into Contact with the spring (55. As previously explained. the relay (iT is a slow-acting relay-that is, slow to deenergize; and when this energizing circuit is momentarily broken during the vertical iinpulses just delivered, the said relay does not deenergize but remains in an operated position with the springs 68 and T6 in contact with the springs 69 and 7S. Then when the spring G3 engages the spring 65 two impulses are transmitted to the vertical magnet 79, extending from ground Gr7 through the springs 63 and G1 t5 the springs 7G and 78. through the private magnet relay 80, through the Winding of the vertical magnet T9, contact point Si, side switch wiper S2 to the battery lead Q5. thence throng-h battery B to ground G. The two impulses being delivered. the vertical magnet 79 is thereby energized twice. ard tbe shaft Wipers are given two vertical steps in the well-knoivn manner. It Will be seen that the private magnet relay 80 is included in the energizing circuit of the vertical magnet T9. This relay also energizcs, but being a slen-aeting relay it cnergizes on the tirstimpulse and remains so until al1 the impulses are transmitted. This relay, upon energizing. operates t0 close the springs 83 and Si in con.- tact, whereby an energizing circuit is established through the private magnet S5, This circuit extends from ground G7 through the vsprings S3 and H4, private magnet 85 to the battery lead 25 thence through battery B to `ground G. The private magnet relay deencrgizcs after the last vertical impulse, since this energizing circuit is no longer maintained after the springs G3 and (Si disengage. llence. the said relay again drenc fizei permitting the springs S3 and Si to ngage. whereby the energizing circuit through the private magnet S5 is in turn broken, which pri vate magnet now deenergizes and permits the side switch to pass troni iirst to second position, permitting the side switch wipers 80 and 82 to engage the contact points 87 and S8, respectively. The closure ot contact between the side switch wiper S2 and the contact point S8 sets up an energizing circuit for the rotary magnet As shown at L in Fig. 1. a pair of relays provided for producing the intermittent energization of the rotary magnet S9. The energizing circuit extends from ground GS through the springs 90 and 91, relay 92, winding of the rotary magnet 89, contact point 88, side switch Wiper 82 to the battery lead 25. thence through battery B to ground G, the rotary magnet and relay 92 energizing in series. The rotary magnet moves the shaft Wipers one step, and the relay 92, upon energizing. places the springs 93 and 9st in contact, whereby a circuit closed from ground G8 through the said springs and relay 95. The relay 95 then operates to separate the springs 90 and 91, thereby breaking the circuit for the relay 92 and the rotary magnet 89, which rest-ore to normal. iVhen the relay springs 93 and 9i disengage, the circuit for the relay 95 is broken and it returns to normal, permitting the springs 90 and 91 to engage, thereby closing the circuit through the relay 92 and the rotary magnet 89 as before, as long as theside switch wiper 82 remains in second position. From the foregoing it will be seen that one relay, upon energizing, provides a circuit for a second relay, which latter, upon energizing, breaks the circuit for the first relay, which then -restores to normal, breaking the energizing'circuit for the second relay. It should be stated that the relays L may be allotted to a group of irst-selector switches and used in common to produce the intermittent energizing of the rotary magnets. At M there is shown a like pair of relays for producing the intermittent energization of a group of secondselector switches. The said rotary magnet then operates to rotate the shaft wipers 9T, 9S and 99 of the selector E into enga-gement with the first Contact of the second level of the selector banks. from which contact 1t is assumed that the trunk-line conductors 100, 101 and 102 lead to the second-selector switch F. It the firstl trunk-line is busy, however, and the wipers have to pass over` busy trunk-lines, then as soon as the private wiper 99 engages the First private bank contact the private magnet S5 again energizes, locking the side switch in second position. rl`hc energizing circuit t'or said private 1nagnet extends t'rom the grounded terminal (si ot the. battery B through an occupying switch (not shown).l through the private wiper 99. thence through the conductor 103 to the side switch wiper S0, contact point ST, through the winding of the private inagnet S5 to the battery lead Q5` thence through battery B to ground G. The private magnet upon thus becomingr energized, locks the side switch wiper 52 in engagement with the contact point. SS, whereby the rotary magnet 89 will be energized step by step until the wipers are carried beyond the last busy trunk-line. At the inst-ant that the private wiper leaves the last busy coutact point the energizing circuit through the private magnet S5 is destroyed. and as a result the selector' side switch passes to third position. It, howerer, there are no busy trunk-lines the private magnet 85 rev leases the side switch to third position as soon as the wipers are carried into engagement with the first trunk-line. As soon as the side switch passes to third position, as stated, the subscribers line conductors 19 and 20 are extended to the conductors 100 and 101 which, in this case, itis assumed lead to the second-selector switch F. The extending of the line occurs, of course, as soon as the side switch wipers 01 and 60 engage the Contact points 10-1 and 105, respectively. W'hen the subscribers line is thus extended to the selector switch F an energizing circuit is established through the line relay 106 in the same manner in which the energizing circuit was established through the line relay 5S of the selector' E when thc subscribers line conductors 19 and 20 were extended through the line switch bank to the trunk conductors 56 and 5T. The rela;7 10G, upon energizing, operates to shift the spring 107 from the spring 108 to the spring 109. Then the springs 107 and 109 engage, an energizing circuit is established through the slow-acting release relay 110. T his ein cuit extends from ground G9 through the springs 10i and 109` through the relay 110 to the battery lead 25, thence through battery B to ground G. The relay, upon energizing, operates to shift the spring 111 from the spring 112 to the spring 113, andl the springs 114 and 115 are also closed in contact. This operation of the secondselector switch 'F occurs at the instant that the side switch wipers G1 and G0 of the selecto: switch E pass to third position and extend the subscriber-S line conductors 19 and 20 to the second-selector switch F. Then the llO second-selector switch, therefore, operates, a guarding potential is established at the private wiper 99 for protecting the seized trunk-line conductors 100 and 101 against seizure by another calling irst-selector. This guarding potential extends from ground G10 to the contact point 116, side switch wiper 117, through the springs 115 and 114, conductor 102 to the contact engaged by the private wiper 99. Furthermore, when the First-selector switch E operates and the side switch passes to third position, a new energizing circuit is established through the release relay 67. This energizing circuit extends from ground G10 at the selec-tor switch F through the springs 115 and 114, conducto-r 102, shaft wiper 99, conductor 103, through the side switch wiper 86, contact point 118, relay 67, thence through battery B to ground G. The relay 67 thus remains in an operated position with the spng 68 in engagement with the spring 69, but the line relay 58 returns to normal position when the side switch wipers 60 and 61 engage the contact points 105 and 104, respectively. The energizing circuit through the line relay 106 extends from ground G11 through the winding 119 tc the side switch wiper 120, thence through the conductor 101, conductor 57 and line conductor 20, through the primary circuit of the substation, through the line conductor 19, thence through the trunk conductor 56, conductor 100, side switch wiper 121, through the winding 122 of the relay 106 to t-he battery lead 25, thence through battery B to ground G. Vhen the dial returns to normal position for the seco-nd digit 2, this circuit through the line relay 106 is interrupted twice when the impulse spring 14 is carried out of engagement with the spring 15 by the impulse teeth on the wheel 1U. The circuit being interrupted twice, the said relay 106 momentarily deenergizes, thus permitting the spring 107 to engage the sp1-in 108, whereby an energizing circuit is comp eted through the vertical magnet 122, said circuit extending from ground G12 to the springs 107 and 108, springs 111 and 113, through the winding of the private magnet relay 123, through the winding of theI vertical magnet 122, contact point 124, side switch wiper 125 to the battery lead 25, thence through battery B to ground G. The private magnet relay 123, being included in this circuit. energizes and, since 1t is a slow-acting relay, remains in an operated position until the last vertical impulse is delivered` and the relay 103 remains energized with the spring 107 in contact with the springv 109, whereby the circuit through the private magnet relay and the vertical inagnet 122 remains open. W'hen the relay 123 energizes, the s rings 126 and 127 are pressed into contact, tereby causing an energizing current to flow through the private magnet 128, the circuit extending from ground G12 through the springs 107 and 108, through the winding of the private magnet 128 to the battery lead 25. thence through battery B to ground G. When the relay 123 deenergizes and breaks the energizing circuit through the private magnet 128, the private magnet also deenergizes and permits the side switch to pass from rst to second position. Vhen the side switch wiper 125 passes to second position and into engagement with the contact point 129 an energizing circuit is established through the rotary magnet 130 which now operates, as cxplained in connection with tlie rotary magnet 89 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 131, 132 and 133 are in engagement with the trunk conductors 134, 135 and 136, respectively, which lead to the connector switch H (Fig. 2). At the instant that the side switch wipers 121 and 120 pass to third position into engagement with the contact points 137 and 138, the subscribers line conductors are extended to the connector switch H, and an energizing circuit is established through the line relay 139 in the same manner in which the energizing circuit was established through the line relay 106 of the selector switch F when the side switch wipers of the first-selector passed to third position. The energizing circuit through the line relay 139 extends from ground G13 through t-he winding 140, trunk conductors 135, 101 and 57 to the line conductor 20, thence thro-ugh the substation to the line conductor 19, trunk conductors 56, 100 and 134, thence through the winding 141 to the battery7 lead 25, and through battery B to ground G. The line relay 139` upon energizing, operates to shift the spring 142 from the spring 143 to the spring 144, whereby an energizing circuit is established through the release relay 145 extending from ground G through the springs 142 and 144. springs 146 and 147, relay 145 to the battery lead 25. thence through battery B to ground G. Then the relay 145 energizes, the spring 148 is shifted out of contact with the spring 149 and into contact with the spring 150, and the spring 152 is shifted into engagement with the spring 151. This primary operation of the connector relays 139 and 145 occurs at the instant that the side switch wipers 120 and 1 21 of the selecto-r F pass to third position and extend the subscribers line conduct-ors to the connector H. The engagementof the springs 151 and 152 establishes a guarding potential for protecting the trunk-line conductors 134, 135 and 136 against seizure by another line and second-selector. This potential extends from tial for this trunk 13G is provided from ground Grl5 directly through the low resistance winding 1553 and the side switch wiper 154. The reason 'for this is that the guarding potential troni ground G1* is interrupted while the line relay 1239 is operating, and there is a possibility ot sonic other selector similar to the selector' F stopping on the same trunk-line. After the side switch passes to third position, however, there is no such danger, and the potential is provided from ground G1* through the line relay springs, as stated. Ot course, when the side switch wipers 182 and 183 engage their third-position Contact points 184 and 185 the calling subscriber`s line is placed in connection with the called subscribcrs line over the heavy conductors shown, passing through the ringer' relay springs 186 and 187 on one side, and 188 and 189 on the other side. As soon as connec-tion is thus established the ringer relay 190 is energized over the circuit established when the side switch wiper 162 engages the contact point 191, the energizing current liowing from ground G at the ringer-interrupter, through the windin 192 of the relay 196, through the backridge relay springs 193 and 194, ringer relay 190, conductor 195, contact point 191, side switch wiper 162 to the battery lead 25, thence through battery B to ground G. The relay 196 thereupon enervizes, while the ringer relay 190, which is or lower resistance, remains in normal position. The relay 196, upon energizing, closes the springs 197 and 198 in Contact, thereby closing` a circuit through the motor magnet 199 which operates the ratchet wheel 200. As the wheel 200 rotates, the teeth a momentarily press the springs 201 and 202 into contact, thereby closing a circuit through the second winding-203 of the relay 196. This winding is of lower resistance and the ringer relay 190 now energizcs, while a tooth a maintains the springs 201 and 202 in contact. It will be seen that as the ratchet wheel 200 revolves, the energizing circuit of theringer relay 190 will be broken periodically so as not to ring the called subscriber continuously. Furthermore, it will be seen that each time that the ringer relay is energized tho springs 186 and 188 are separated from the ringer relay springs 187 and 189, thereby breaking the calling line from the called line, and pressed into engagement with .the springs 204 and 205 which are the terminals of the ringer generator I. As a result ringing current is sent over the called line for energizing the bell 206 while the springs 207 and 208 are in contact. However, as soon as the called subscriber answers, the back-bridge relay 209 is energized by a How of current from ground G, contact point 174, side switch wiper 172i, winding 210 of the laugh-bridge relay 200, ringer relayv syn-ings 18'.) ani 188, side switch wiper 181), contact point 185, line wiper 104, normal. conductor 170, conductor 211, transmitter privi-ary winding 2121, impulse springs 214. switchhook springs' 215 and 211i, line coinlncior 2li', normal conductor 17.3', line wiper 111353, Contact point 184, side switchl wiper e2. ringer relay springs 180 and 18T, winilirri' 218 ot the haelt-bridge relay 209. thence to the battery lead 25 and through batti-1"' B to ground Cr. 'hen once the ha relay 209 is energized the energizing circuit t'or the ringer relay 190 is interrupted at. a. point between the sprirgs 193 and 155-1-, thus making it impossible for the ri relay to energize as long` as the called suhscriber is on the line. Furthermore, when the relay 209 energizcs, Ithe springs and 147 also disengage, thereby interruptimg the circuit which provided a guarding potential to the conductor 136.

Vfhcn the springs 146 and 14T thus disengage, the relay 221, being included in series instead of in multiple as before, energizcs. but at this time produces no eitect. The subscribers being thus connected may communicate over the main talking conductors indicated by the heavy lines in Figs. 1 and 2 and including on one side the condenser 219 at the connector H and on the other side the condenser 220. After the subscribers are through talking. it the calling subscriber hangs up his receiver 'he opens` the line circuit at a point between the springs 17 and 18, thereby initiatingthe release of all the switches. This releise is brought about as follows: At the instant that the circuit is broken between the said springs 17 and 18 the double-wound line relay 139 and the release relay 145 of the connector H deenergize. At the instant that the slow-acting relay and the line relay 189 deenergize, the energizing circuit for the release magnet 222 is close-il at a point between the springs 14S and 149 and at an other point between the springs 142 and 143. A flow of current is, therefore, srt up from ground G1* through the syn-ings 142 and 148, through the springs 148 and 149 to the ott-normal spring 223, to the contact point 224, to the release magnet 222, thence through said magnet to the hattery lead 25. and through batteri,v B to ground G. The release magnet instantl)r releases the connector switch shaft and eide switch, thereby. breaking the energizing circuit through the back-bridge relay 200 (if the called subscriber has not in the meantime restored his receiver). and also the energizing circuit through the bridge cut-oit relay 1T 8 of the called line switch C. As soon as the connector switch shaft reaches its lowest position it breaks the crcuit for the release niagnet 222 by separating the ott-normal spring 2225 from the contact point 224:, at which instant the release magnet ot' the connector is also restored. l`lie operation ot' the line relay 139 and of the slow-acting relay not only cam-es the release of the connector, dcrf-cribefl. but also the release ot' the preceding swit;hes, because the ground connection iroin ground Gr14 to the trunk-release conductor 13; is interrupted by both ot' these relays. Since the release relays 6T and lili are dependent upon this ground for their energized condition, as already explained, it follows that they will fall back with the following results: As ,soon as the release rela) 110 ot' the second-selector F deenergizes, the springl 111 falls back into normal engagement with the spring 112, thereby closing an energizing circuit for theV release magnet 225 from `around G12 through the springs 1(77 and 10S. through the springs 1li and 112 to the release magnet 225. thence to the contact point i226, ott-normal spring "ci" to the battery lead 25, thence through batter),r B to ground (lr. As soon as the release magnet. energizes, the secondselector side switch and switch shaft are restored, which shaft, upon reaching its lowest position, opens a release circuit at a point between thel oit-normal spring 22T and the contact point 2:26, whereby the release magnet 225 is restored also. Then the release relay G7 ot' the selector E deenergizes, the springs 7G and 77 are brought into Contact. and as a result the energizing circuit for the release magnet 228 is closed. The energizing current for this release niagnet 29S then ows from ground GrT through the springs 63 and 64 and through the said springs TG and 7T to the release magnet 228, thence through said magnet to the contact point @molt-normal spring 230 to the batter)Y lead thence through battery B to ground G. The release magnet, upon enci'4 zing, then restores the first-selector side su tch and switch shaft, which shaft, upon reaching its lowest position, opens the energizing circuit for the release magnet 22S at a point between the ott-normal spring :230 and the contact point 9.29. Furthermore, when the release relay 6T deenergizes and separates the springs 68 and 69, the energizing circuit of the bridge-cut--otf relay in series with the plunger magnet 24 becomes -Jreken, and as a result the bridge-cutotf relay and plunger magnet 24 restore to normal position. Consequently the bank springs 52 and 53, as well as the other bank s; rings of the line switch C, are separated, thus preventing any further action from the trunk. After the switches are thus restored the calling subscriber can, of course, then proceed to make another call.

Returning now to that stage of the call where the railing subscriber was operating the connector switch in accordance with the last digit t), it will now be explained what takes placein the event that the desired line is busy. li'hcn the line #2220 is calling, or when it has been called by someone else, the private bank contacts iu which the normal conductor 17T terminates are connected to ground. If another connector switch has lalled the line this guarding potential would be supplied through the connector switch from a ground terminal similar to the ground terminal Gr1T in the connector switch il, 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. 1 and thence to the private bank contact. In a similar manner the line switch C protects the calling line A when the bank springs 52 and 53 come into Contact from ground G5, from which ground connection is rstalilished through the said bank springs to the private normal conductor 231. Theretore, when the subscriber sends in the. last impulse the private wiper 165 is carried onto the grounded contact, and when the slow-acting relay 159 oi the connector deenergizes, instead of the side switch tripping to third position, as in the case where the.

line is not busy, the connector is given the busy-release as follows: lVhen the private magnet relay 159 deenergizes and the springs 166 and 16T engage, an energizing circuit is completed through the release magnet 222, said circuit extending from the busy or grounded private bank contact, private 'wiper 165, side switch wiper 11'3, Contact point 232 (bearing in mind that the side switch is in second position), springs 1(3(5 and 1G?, normal spring i228, contact point 221, through the release magnet Q22 to the battery lead 25. thence through battery l to ground G. The release magnet thereupon energizes and operates to restore the side switch and shaft wipers 'to normal position. lVhen the side switch restores to first position. the calling subscriber is given the busysigual. The path ot' the busi-'signaling current extends troni ground G15 through the winding 153 ot' the induction coil 233, through the side switch wiper 154: which is now in lirst position, conductor 231i, side sn-t1h wiper 183, ringer relay springs 188 and 189, through the condenser 220 to the trunk conductor 135, thence through the subscribers station to the line conductor 19 and trunk conductor 153i, through the winding il of the line relay to the battery lead 9.5, thence through battery B to ground G. YVhen the calling subscriber receives the busy-signal he understands that the line is busy and hangs up his receiver. The liuc circuit is opened, as already explained, with the result that the line and slow-acting relays 139 and 145 of the connector H deenerlll gize, causing the release ot' the connector and all other switches, as heretofore explained.

It should also be stated that the connector H is provided with a back-release relaythat is, a release relay which so controls a circuit o'l the, release magnet that when the called subscriber restores his receiver to the switch-hook (before the calling subscriber releases the connector) the energizing circuit for the release magnet 222 is closed. rlhis back-release is initiated as follows: lVhen the called subscriber answers, the relay 209 encrgizes and separates the springs 146 and 147, which removes a shunt from the relay 221, thus permitting the latter to energize and place the springs 235 and 236 in contact, Now. when the called subscriber restores his receiver the relay 209 deenergizes and permits the springs 237 and 238 to engage, thereby closing an energizing eircuit for the release magnet 222. This circuit extends from ground Gr19 through the springs 237 and 238, springs 235 and 236, normal spring 223, contact point 224, through the release magnet 222 to the battery lead 25, thence through battery B to ground G. The connector release magnet then energizes and restores the connector side switch and shaft wipers to normal position. The release of the remaining 'switches used in establishing the connection is brought about when the calling subscriber restores his receiver to the switch-hook.

In the foregoing it has been pointed out how the subscriber at A may establish connection with the substation A. Any other subscriber of the entire system may operate the central olice switching mechanism in a similar manner to extend connection to any desired line. It will be seen that the relay 23 of the, line switch C is normally connected with the battery lead 25 through the springs 239 and 24() of the so-called open main relay 241 which energizes in multiple with the motor magnet 35. The object in thus putting the energizing circuit in the relay 23 under the control of the relay 24:1 is to prevent any subscriber from operating his line switch while the master switch is operating, to eliminate any possibility of a line switch tripping onto a trunk that is already in use. It will be seen that when the relay 241 energizes, the spring 239 is separated from the spring 240 and carried into engagement with the spring 242, through which latter a busy-signal may be transmitted to the subscribers station in case he should attempt to make a call while the master switch is rotating. It is obvious that if all of the trunks are made busy the master switch will not stop until some one of the trunks becomes idle, so that the subscriber not only gets a busy-signal if he attempts to operate his line switch while it is passing from one point to another, but also if he tries to call while all of the trunks are busy.

It will be seen that the line switch C diagrammatically shown in Fig. 1 is more fully represented in Fig. 3. In the said Fig. 3 the plunger arm is more fully shown, controlling by its lett terminal the spring 26 and carrying on the right end the plunger which operates the bank springs, such as the bank springs 50, 51, 52, 53, 54, 55, 32 and 33.

From the foregoing it will be seen that I provide an improved and highly eflicient two-wire system for automatically trunking calling lines into connection with called lines.

`What I claim as my invention is 1. In a telephone system, a line, a plurality of tr s, a plunger for traversing the trunk and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cut-ot relay, and a circuit for energizing said magnet and cut-off relay in series.

2, In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-eut-ofl relay, and a circuit for energizing said magnet and cutot'f relay in series, said magnet provided with an armature having a fin er adapted to open the springs of said cut-o relay.

3. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cut-off relay, and a circuit for energizing said magnet and cut- .ol relay in series, said circuit including a trunk conductor.

4. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cut-otf relay, and a circuit for energizing said magnet and cutolf relay in series, said circuit including a third or non-talking conductor of any one of said trunks.

5. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line rela bridged on the line and controlling sai magnet, a. bridge-cut-of relay, a

circuit for energizing said magnet and cutotl' relay in series, and a third relay, said circuit including normally open contacts ot said third relay, said relay provided with an energizing circuit closed during conversation.

6. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged ou the line and controlling said magnet, and a bridgc-cut-otr" relay, said magnet provided with an armature having a. finger adapted to open the springs of said cut-otl' relay.

7. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cut-otf relay, a circuit for energizing said magnet and cut-oli relay in series, said magnet provided with an armature having a finger adapted to open the springs of said cut-off relay, and a third relay, and said circuit including a third or non-talking conductor of any one of said trunks, depending on which one is in use, and including normally open contacts of said third relay, said relay provided with an energizing circuit closed during conversation.

8. In a telephone system, a plurality of automatic switches, trunks to be seized by said switches, and a master switch common to said automatic switches, said master switch provided with a notched wheel and a motor magnet and ratchet for operating the same, contacts operated by the notches on saidwheel, a circuit for said magnet normally open at said contacts, an interrupter for said circuit operated by the said magnet, and a relay provided with normally open contacts connected in parallel with said tiret-mentioned contacts.

9. In a telephone system, a pluralit of automatic switches, trunks to be seizedr by said switches, and a master switch common to said automatic switches, said master switch provided with a notched wheel and a motor magnet and ratchet for operating the same, contacts operated by the notches on said wheel, a circuit for said magnet normally open at said contacts, an interrupter for said circuit operated by the said magnet, a relay provided with normally open contacts connected in parallel with said firstmentioned contacts, and a wiper operated by said magnet and provided with a bank of contacts each representin a diierent trunk and controlling circuit tirough the winding of said relay.

10. In a telephone system, a pair ol' line conductors, a third conductor, a selector provided with a lamp signal, a supervisory relay controlling said lamp, and a slow-acting relay controlling said supervisory relay over said third conductor.

11. In a telephone system. a called line. a connector having two selecting motions for seizing said line and for setting up a talkingr circuit from the calling to the called line, a busy test circuit Jfor the called liuc separate from the talking circuit, means i'or applying a busy potential to the said circuit when the called line is busy, automatic means responsive to said busy potential Jfor releasing the connector it the called line is busy, a nd means for controlling said connector over two sides ot the talking circuit in series by means of a varying number ot impulses dependent upon the digit ot' the called number.

12. In a telephone system, calling and called lines, a connector responsive to the calling subscriber to seize the called line. and for setting up a talking circuit Jfrom the calling to the called line, a busy test circuit for the called line, means for applying a busy potential to said circuit when the called line is busy; automatic means operative to release the connector if the called subscriber hangs up his telephone ahead ot the calling subscribed, and means for controlling the connector, over two sides ot the talking circuit in series.

13. In a telephone system, subscribers stations including calling mechanism, a plurality of trunk lines, two switches, one switch for selecting an idle trunk line independently of any operation of said calling mechanism, and thus extend aconnection over said selected trunk to the second switch, a -magnet for maintaining said first switch in coutact with said trunk, means including a circuit extending from said second switch for controlling said magnet, and means for controlling said switches over two sides of a line circuit in series.

14. In a telephone system, a line, a plurality of trunks, an automatic switch, a plunger for traversing the trunks and connecting the line with an idle one thereof to extend connection to said automatic switch, a magnet for drawing the plunger into position to close connection, and means including a circuit extending from said switch for controlling said magnet.

15. In a telephone system, a line, a plurality of trunks, ah automatic switch, a plunger for traversing the trunks and connectingr the line with an idle one thereof to extend connection to said automatic switch, a magnet for drawing the plunger into position to close connection, means including a circuit extending from said switch for controlling Isaid muguet. and means for controlling said switch over two sides ot' the line in series.

lt. ln a telephone system, a plurality ot automatic switches` trunks to be seized by said switches, a master switch common to said automatnl switches, a pair of normally open contacts. a short-circuit adapted to be closed around said contacts` means tor initially closing said short-circuit to operate said master switch, and means t'or continuing the operation ot said master switch through the medium of said contacts.

1T. In a telephone system. a plurality of automatic switches, trunks to be seized by said switches, a master switch common to Said automatic switches, a pair ot normally open contacts. a short-circuit adapted to be closed around said contacts. means t'ol initially closing said short-circuit to operate said master switch, means tor continuing the operation of said master switch through the medium of sa'id contacts, and means for controlling said switches over two sides ot a line circuit in series.

1S. In a telephone system, a plurality ot automatic switches, trunks to be seized by said switches, a master switch common to said automatic switches, a motor magnet for operating said master switch, means comprising a pair of springs for initially operating said motor magnet, and independent means comprising a pair of springs for short circuiting said first pair for continuing said operation after the initial operation.

19. In a telephone system, a plurality of automatic switches, trunks to be seized by said switches, a master switch common to said automatic switches, a motor magnet for operating said master switch, a pair ot springs and a relay for initially operating said motor magnet, and independent means comprising` a pair of springs for short cireuiting said first pair for continuing said operation after the initial operation.

20. In a telephone system, a plurality of lines, an automatic switch to automatically extend a connection over said lines, means for seizing said switch, a` supervisory signal for said switch, means for displaying said signal when said switch is seized, and means for controlling said switch over two sides ot a line circuit in series.

2l. In a telephone system, a plurality' of lines divided into groups, an automatic switch to automatically extend a connectie., over said lines, means for seizing said switch, a'supervisory signal for said switch, means tor displaying said signal when said switch is seized, and means for controlling said switch over two sides of a line circuit in series, said switch having motion in one plane to select groups and motion in an intersecting plane to rind a line in a selected group.

22. In a telephone system, a line, a plurality of trunks, a plunger tor traversing the trunks and connecting the line with au idlev one thereo't'- a magnet t'or drawing the plunger into position to close the connection. a line relay bridged on the line and controlling said magnet. a bridgc-cut-oti` relay. a circuit for energizing said magnet and eurotf relay in series. and means for controlling said line relay over two sides ot the line iu series.

Q3. In a telephone system, a line, a plurality of trunks` a plunger tor traversing 'he trunks and connecting the liuc with an idle one thereof, a magnet for drawing the plunger into position to close the conne-tion, a line relay bridged on the liuc and controlling said magnet'. a bridge-eut-oli relay. a circuit for energizing said magnet and eutofi'l relay in series, said magnet provided with an armature haring a finger adapted to open the springs of said cut-cti' relay, and meansI for controlling said line relay over two sides ot the line in series` 24. In a telephone system, a line, a plurality ot trunks, a plunger for trarersing the. trunks and connecting the line with an idle one thereof, a. magnet t'or drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cut-ofi1 relay, a circuit tor energizing said magnet and eut-ott relay in series, said circuit. including a trunk conductor, and means for controlling said line relay over two sides of the. line in series.

25, In a telephone system, a line` a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, aline relay bridged on the line and controlling said magnet.. a bridge-cut-ott relay, a circuit for energizing said magnet and cut-off relay in series, said circuit including a third or non-talking conductor of any one ot said trunks, and means for controlling said line relay over two sides of the line in series.

26. In a telephone system, a line, a plurality of trunks, a plunger for traversing the trunks and connecting the line with an idle one thereof, a. magnet for drawing the plunger into position to close the connection, a. line relay bridged on the line and controlling said magnet, a hridge-cut-oit relay, a circuit for energizing said magnet and cutott' relay in series, a third relay, said circuit, including normally open contacts of said third relay, said relay provided with an energizing circuit closed during conversation, and means for controlling said line relay over two sides of the line in series.

27. In a telephone system, a line` a pmrality of trunks, a plunger for traversingF the trunks and. connecting the line with an idle one thereof, a magnet for drawing the plunger into position to close the connection, a line relay bridged on the line and controlling said magnet, a bridge-cutoff relay, said magnet provided with an armature haring` a finger adapted to open the springs ot' said cut-off relay. and means tor controlling said line relay over two sides ot the line in series.

28. In a telephone system, a line, a plurality ot trunks` a plunger for traversing the trunks and connecting the line with an idle one thereot` a magnet for drawing the plunger into position to elo-:e the connection, aline relay bridged on the line and controlling .said magnet. a bridge-eut-oit' relay, a circuit for energizing said magnet and cutoti' relay in series, said magnet provided with an armature having a tinger adapted to open the springs of said cut-ott relay, a third relay, said circuit including a third or nontalking conductor of any one of said trunks` depending on which one is in use, and including normally open contacts ot said third rela-y. said relay provided with an energizing circuit closed during conversation, and means for controlling said line relay over two sides ot the line in series.

29. In a telephone system, a plurality of automatic switches, trunks to be seized by said switches, and a master switch common to said automatic switches, said master switch provided with a notched wheel and a motor magnet and ratchet for operating the same, contacts operated by the notches on said wheel, a circuit for said magnet normally open at said contacts, an interrupt-er for said circuit operated by the said magnet, a relay provided with normally open contacts connected in parallel with said firstmentioned contacts, and means for controlling said automatic switches over two sides ot' a linehcircuit in series.

30. In a telephone system, a plurality ot automatic switches, trunks to be seized by said switches, and a master switch common to said automatic switches, said master switch provided with a notched wheel and a motor magnet and ratchet for operating the same, contacts operated by the notches on said wheel, a circuit for said magnet normally open at said contacts, an interrupter for said circuit operated by the said magnet, a relay provided with normally open contacts connected in parallel with said lirstmentioned contacts, a wiper operated by said magnet and provided with a bank ot contacts each representing a different trunk and controlling circuitl through the winding of said relay, and means for controlling said automatic switches over two sides of a line circuit in series.

31. In a telephone system, a line circuit, a pair of line conductors, a third conductor, a selector provided with a lamp signal, a supervisory relay controlling said lamp, a

slow-acting relay controlling said supervisory relay over said third conductor, and means tor controlling said selector over two sides ot said line circuit in series.

S2. In a telephone system, subscribersl lines, a connector switch, means controlled trom any one ot said lines for seizing said connector switch and for operating said switch to extend a talking circuit to any other one ot said lines, a line relay ltor said connector switch energized over the two sides ot' the talking circuit in series to control the operation ot said switch, a release magnet tor said comiector, and means for energizing said magnet when connection is made with a busy line to release said connector.

53:3. In a telephone system, a called line for establishing a talking circuit with the called. line, a connector for seizing said line, means for controllingr said connector over two sides of the talking circuit in series, a release magnet for said connector, an energizing circuit tor said magnet. a side switch tor said connector, a relay for controlling the operation of said side switch and likewise controlling the circuit ot said release magnet, and means for energizing said release magnet when connection is madewith a busy line in order to release said connector.

3st. In a telephone system, a called line, a connector tor seizing said line, a release magnet for said connector, a rotary magnet for controlling the operation of said switch, a slow acting relay controlling the circuit of said release magnet and adapted to remain energized while said rotary magnet is operating, and means for energizing said release magnet when connection is made with a busy line in order to release said connector.

35. In a telephone system, a called line for establishing a talking circuit with the called line, a connector for seizing said line, means for controlling said connector over two sides of the talking circuit in series, a release magnet7 a side switch having a plurality of positions, a relay for controlling said side switch, a. private wiper, and means tor closing a circuit for said release magnet through said private wiper and said side switch while in second position, whereby said connector may be released when connection is made with a busy line.

36. In a telephone system, a called line, a connector for seizing said line, a release magnet for said connector, a side switch, a slow acting relay-controlling the operation of said side switch, springs controlled by said slow acting relay for controlling the energizing circuit of said release magnet, said relay being slow acting to prevent its operation during the operation of the switch to thereby prevent a premature release, a private wiper, and means for closing a circuit for said release magnetover said privat-c wiper and through said side switch when in second position, to thereby release said connector when connection is made with a busy line,

37. In a telephone system, a called line, a connector for seizing said line, a release magnet for said connector, a relay for controlling a circuit tor said magnet, and means whereby said relay is normally short-circuiied.

38. In a telephone system, a called line, a connector for seizing said line, a release magnet for said connector. a relay for controlling a circuit for said magnet, means whereby said relay is normally sliort-circuited, and means for removing said shortcircuit when the called subscriber answers.

39. In a telephone sys-tem, a called line, a connector for seizing said line, a release magnet for said connector, an energizing circuit for said release magnet, said circuit including normally open and normally closed contacts, means Jfor closing said normally open contacts and opening said normally closed contacts when the called subscriber answers, and means for again closing said normally closed contacts when. the called subscriber replaces his receiver upon the hook to thereby release said connector.

40. In a telephone system, a called line, a connector for seizing said line, a release magnet for said connector, an energizing circuit for said magnet, said circuit including normally open and normally closed contacts, a slow acting relay controlling said normally open contacts, a second relay for controlling said normally closed contacts, means for energizing said second relay upon the response of the called subscriber to thereby open said normally closed contacts, and to energize said slow acting relay to thereby close saidnormally open contacts, and means for deenergizing said second relay when said subscriber replaces his receiver upon the hook to thereby again close said normally closed contacts, whereby the circuit for the release magnet is closed and the connector released.

41. In a telephone system, a plurality of subscribers lines, means for establishing a connection between two of said lines, means for supplying rinffino' current to the called line. said means including a'Tinging relay, an energizing circuit for said ringing relay including a second relay, means for closing said circuit to energize said second relay but not said ringing relay, and means for thereafter increasing the flow of current in said circuit to thereby energize said ringing relay to apply ringing current to the called line.

42. In a telephone system, a plurality of subscribers lines, means forv establishing a connection between two of said lines, a ringer relay, a circuit for said relay including a second relay having sufficient resistance to prevent energization otl said ringer relay, means for intermittently ope-rating said second relay to thereby increase the flow of current through said ringer relay, and means controlled by said ringer relay for supplying ringing current to the called line.

43. In a telephone system, a calling line, a called line` a progressively movable trunking connector switch for connecting the two over a talking circuit. a busy test circuit for the called line separate from the talking circuit, means for operating said connector over two sides of the talking circuit in series to find the called line, means for supplying a busy test potential to said Lest circuit whenever the called line is busy, and means responsive to said potential for releasing said connector.

44. In a telephone system, a calling line, a called line, a progressively movable trunking connector switch for connecting the two over a talking circuit, a busy test circuit /lg the called line, means or opera lng said mctor'vnwo sides of the talking circuit in series to find the called line, means for applying a busy test potential to said test circuit whenever the called line is busy, means responsive to said potential for releasing said connector, and a busy signaling circuit for indicating to the calling line that the called line is busy.

45. In a telephone system. a calling line, a called line, a progressively movable trunk- ,ing connector switch for connecting the two over a talking circuit, a busy test circuit for the called line, means for operating said connector over two sides of the talking circuit in series to find the called line, means for applying a busy test potential tb said test circuit whenever the called line is busy, means responsive to said potential for releasing said connecter, and a busy signaling circuit for indicating to the calling line that the called line is busy, said last circuit controlled by the release ot the connector.

46. In a telephone system, a calling line, a called line, a progressively movable trunking connector switch for connecting the two over a talking circuit, a busy test circuit for the called line separate from the talking circuit, means or operating said connector over two sides of the talking circuit in series to find thel called line, means for applying a busy test potential to said test circuit whenever the called line is busy, means responsive to said potential for releasing said connector, said last means comprising a release magnet, and an energizing circuit for said release magnet, said circuit comprising in turn a busy test circuit individual to the connector switch, said energizing circuit controlled by the release of the connector.

47. In a telephone system, a gro-up of sec- 130 ond selector switches, each operative in accordance with the second digit of the called number, trunks to be selected by said second selectors, a pair of relays common to said second selectors, operating to intermittently interrupt the flow of current through any selector until an idle trunk is found, each relay controlling the circuit ot' the other, a talking circuit, line relays for said selectors connected to said talking circuit, and means for controlling said relays over two sides of the talking circuit in series.

48. In a telephone system, a plurality of second selector switches, each operative in accordance with the second digit of the called number, a plurality of controlling relays common to all of said second selector switches, local circuits controlled by said relays, a talking circuit, line relays for said selectors connected to said talking circuit, and means for controlling said relays over two sides oi the talking circuit in series.

49. In a telephone system, a switch having vertical and rotary motions, an operating magnet controlling the rotary motion of said switch, an energizing circuit for said magnet, a pair of relays controlling said energizing circuit, means for energzing one of said relays in order to energize the second of said relays, and means for opening said energizing circuit for said operating magnet by the energizing of said second relay while said first relay is energized.

50. In a telephone system, a vertical and rotary motion switch, a vertical operating magnet, a rotary operating magnet, a slow acting relay connected in series with said vertical operating magnet, a second relay controlled by said slow acting relay, and means for closing the energizinor circuit for said rotary operating magnet tby first energizing said relays and then deenergizing said slow acting relay.

51. In a telephone system, a switch having vertical and rotary motions, an operating magnet controlling the rotary motion of said switch, an energizing circuit for said magnet, a pair of relays controlling said energizing circuit, means for energizing one of said relays in order to energize the second of said relays, means for opening said energizing circuit for said operating magnet by the energizing of said second relay while said first relay is energized, and means for controlling the operation of said switch ove-r two sides of the line.

52. In a telephone system, a vertical and rotary motion switch, a vertical operating magnet, a rotary operating magnet, a slow acting relay connected in series with said vertical operating magnet, a second relay controlled by said slow actin relay, means for closing the energizing circuit for said rotary operating magnet by first energizing said relays and then deenergizing said slow acting relay, and means for controlling the operation of said switch over two sides ot the line circuit in series.

53. A telephone exchange system comprising telephone lines, automatic connectors less in number than said telephone lines, selectors less in number than the telephone lines, subscribers individual switches corresponding in number to the telephone lines, subscribers devices for closing the lines to control said individual switches and selectors and connectors by a varying number of impulses, line circuits by which the said individual switches and selectors and connectors are controlled, each line circuit including the two sides of a calling telephone line in series, said devices having provisions for determining the number of impulses necessary for each digit ot' the called number, and means Jfor releasing said individual switches and selectors and connecs tors by the opening of the calling line.

54. A telephone exchange system comprising telephone lines, automatic connectors less in number than said telephone lines, selectors less in number than the telephone lines, provided with means having vertical step-by-step motion to select different operative levels, depending on the number called, and rotary step-by-step motion to connect with a line in the selected level, subscribers individual switches corresponding in number to the telephone lines, subscribers devices for closing the lines to control said individual switches and selectors and connectors, line circuits by which the said individual switches and selectors and connectors are controlled, each line circuit including the two sides of a calling telephone line in series, and means for releasing said individual switches and selectors and connectors by the opening of thc calling line.

55. A telephone exchange system comprising a calling telephone line, a called telephone line, means including a plurality ot selectors and a connector for extending connection from the calling line to the called line, calling mechanism requiring a separate manual operation thereof for each digit ot the called number, operative to transmit suitable controlling current for one digit before the said mechanism is manually' operated for the next digit, line circuits for 'controlling the selectors, and a line circuit for controlling the connector, each line circuit including said mechanism and the two sides of the calling line in series.

5G. A. telephoe exchange system comprising telephone lines, automatic connectors less in number than said telephone lines, selectors less in number than the telephone lines, subscribers individual switches corresponding in number to the telephone lines, subscribers apparatus for closing the lines to control said individual switches and selectors and connectors, comprising a calling mechanism requiring a separate manual operation thereof for each digit of the called number, operative to transmit suitable controlling current for one digit before the said mechanism manually operated for the next digit, line circuits by which the said individual switches and selectors and connectors are controlled, each line circuit including said mechanism and the two sides ot a calling telephone line in series, and means for releasing said individual switches and selectors and connectors by the opening of the calling line.

5T. A telephone exchange system comprising a calling telephone line, a called telephone line, calling mechanism re uiring a se iarate manual o )eration thereot for each thgiE'Tt-tlmled numiier, operative to transmit suitable controlling current for one digit before the said mechanism is manually operated for the next digit, means including a plurality of selectors and a connector for extending connection from the calling line to the called line, provided with means having vertical inotion to select different operative eve s, depen( ing on the number called, and rotary motion to connect with a line in `the Mmmm circuits for controlling the selectors, and a line-circuit for controlling the connector, each line circuit including said mechanism and the two sides ot' the calling line in series.

58. A telephone exchange system comprising a selector switch, another selector switch provided with a side switch, a line relay for said other switch, and means for energizing said line relay after said first switch extends connection to said other switch, adapted to maintain said line relay energized as long as the side switch ot' said other switch remains in tirst or second position, provided the line circuit to said first switch is kept closed at the same time. y

59. In a telephone system, a connector switch; a side switch, a test wiper, a release magnet, and another electromagnet therefor; an energizing circuit for said release magnet controlled by said other electromagnet while the side switch is in second position, the said other electromagnet retaining its armature attracted while said test wiper is passing over busy contacts to prevent the release of said connector switch.

GO. A telephone system comprising a series of switches each provided with a release relay, a subscribers telephone and line, the first switch of said series being allotted to the line, means whereby when a subscriber removes his receiver the release relay of the first switch energizes and remains energized until the subscriber hangs up, means whereby the rst switch may be mad to connect with the second switch of said series, and

whereby the release relay of said second switch energizes as soon as connection is made with said second switch, which second release relay remains energized until the subscriber hangs up and means whereby said second switch may be made to connect with the third switch of said series, and whereby the' release relay ot said third switch then energizes and remains energized until the subscriber hangs up his receiver.

(il. A telephone exchange system comprising a selector switch, another sclcclor switch having a side switch, said other switch provided with means having vertical motion to select dill'erent operative levels lcpcnding upon the number called, and rotary motion to connect with a line in the selected level, a line relay for said other switch, and means for energizing said line relay after the first switch extends connection to said other switch adapted to maintain said line relay energized as long as the side switch of said other selector remains in iirst or sccond position. provided the line circuit to said lirst switch is kept closed at the same time.

(32. In a telephone system, a connector switch for con'ipleting connection to a desired subscribers line; a test wiper, a release magnet and another electromagnet therefor; an energizing circuit for said release magnet controlled by said other electron'iagnet, said other electromagnet retaining its armature attracted while said test wiper is passing over busy contacts to prevent the release ot said switch.

G3. In a telephone system, a plurality of selectors, a connector, release relays in each ot said selectors, and means in said connector for maintaining all of said relays energized.

(3l. In an automatic telephone exchange trnnkng system, a calling subscribers line and a called subscribeus line, a plurality ot switches for establishing connection between .said lines` a slow-acting relay in each ot' said switches, one o't said switches adapted to supply the talking circuit with talking current, the said talking current supplying switch comprising means for maintaining all the said slow-acting relays energized In an automatic telephone exchange trunking system, a calling snbscribers line and a called subscribers line, means including a plurality of selector switches and a connector switch for connecting the two lines, a releasing mechanism for each switch and a releasing relay for controlling each releasing mechanism, parallel circuits 'for said release relays, and a line relay for the connector switch` said line relay adaptel to control the parallel circuits of all of said release relays after the two lines are connected.

G6. In an automatic telephone exchange trunking system, a calling subscribers line and a called subscribers line, means including a plurality of switches for extending connection between the two lines in a stepby-step manner, a release mechanism for cach switch, a slow-acting release relay for controlling each releasing mechanism, the slowacting releasing relay ot' the last switch brought into the connection being adapted to control the circuit of the slow-acting release relays of all the preceding switches,

the releasing relay of each switch adaptedto become energized from the instant that this switch is brought into use until it is released, and means for maintaining the release relays of the preceding switches energized from the time such switches are brought into use until the inal switch is brought into use.

67. In an automatic telephone exchange trunking system, a calling subscribers line and a called subscribers line, means including a plurality of selector switches and a connector switch for connecting the two lines, a releasing mechanism for each switch and a releasing relay for controlling each ieleasing mechanism, parallel circuits Jfor said release relays, and a line rela-t for the connector switch, said line relay adapted to control the parallel circuits of all of said release relays after the two lines are connected, the releasing relay of each switch adapted to become energized from the instant that this switch is brought into use until it is released, and means outside the connector for maintaining the selector release relays energized from the time the selectors are brought into use until the connector is brought into use.

(38. In an automatic telephone exchange trunking system, a calling line and a called line, a plurality of switches for connecting the calling line with the called line, including a switch individual to the calling line, line bank springs for the said individual line switch included in the connecting line circuit, and automatic means whereby it said springs are separated all of the switches are released.

69. In an automat-ic telephone exchange trunlring system, a calling subscribers line and a called subscribers line, a series of switches for trunking the calling line into connection with the called line, a private wiper-for one of said switches, a trunk line accessible to said last mentioned switch and included in the connection, and automatic means whereby if the private wiper is disconnected from the said trunk the said switch and all switches between said switch and the called subscribers line will be released.

70. In an automatic telephone exchange trunking system, a calling subscribers line and a called subscribers line, a series of automatic switches for trunking the calling subscribers line into connection with the called subscribers line, a private wiper for one ot' said switches, a trunk line accessible to said last mentioned-switch and included in the connection, and automatic means whereby if the private wiper is disconnected from the said trunk the said switch and a switch at each side thereof arc released.

Tl. In a telephone system, a connector provided with an element having vertical and rotary motion to find the called subscriber, release mechanism for restoring the connector to normal position, and a doublewound line relay having a battery normally connected in series between the windings thereof and operative to control the vertical and rotary motion and the release of said connector.

72. In a telephone system, a plurality ot trunks, an automatic trunking switch provided with an element having vertical and rotary step-by-step motion to find an idle trunk, and a double-wound line relay having a battery normally connected in series between the windings thereof and operative to control the vertical motion and start the rotary motion.

73. In a telephone system, a plurality of switches, each provided with a private wiper, the first switch adapted to establish connection with the second switch, the second switch adapted to establish connection with the third switch, the first switch adapted to establish a guarding potential at the private wiper thereof until the second switch is brought into use, and after being thus brought into use the second switch serving to provide a guarding potential at the private wiper of the first switch and also at its own private wiper until the third switch is brought into use, and the third switch when brought into use adapted to provide a guarding potential at its own private wiper and also at the private wipers ot' the tirst and second switch, as set forth.

7l. In a telephone system, a selector, means for producing impulses for operating said selector, a line relay therefor responsive to said impulses, a pair of relays controlled by said line relay, said pair of relays being relatively slow acting, whereby they are not operated by the impulses for operating said line relay, a release circuit controlled by one of said pair of relays, a private magnet controlled by the other of said pair of relays, and a side switch controlled by said private magnet.

7 In a telephone system, a subscribers line, a selector switch, means for producing impulses for operating said switch, a double wound line relay normally bridged across said line and responsive to said impulses. another relay controlled by said line relay, said other relay being relatively slow acting, whereby it is not operated by the impulses for operating said line relay, and a the said slow acting relay therefor and also battery bridged between the double winding of the line relay for supplying the operating current thereto.

76. In a telephone system, a selector switch` means for producing impulses for operating said switch, a line relay therefor responsive to said impulses, another relay controlled by said line relay, said other relay being relatively slow acting, whereby it is not operated by the impulses for operating said line relay, and another selector switch7 said other switch having release mechanism controlled by said other relay of said first mentioned switch while said first mentioned switch is in normal position and while the same is operating responsive to impulses as set forth.

7T. In an automatic telephone exchange trunking system, a pair of selector switches, a trunk line running from one of said switches to .the other of said switches and comprising a trunk release conductor, and means whereby the said other switch may, when the trunk is seized by the first switch and before the other switch is operated, instantly put a guarding potential on said trunk release conductor.

78. In an automatic telephone exchange trunking system, a plurality of selectors and a connector, means whereby a line circuit may be established through all of the said selectors to the said connector, said line circuit comprising a trunk release conductor, and means whereby the connector may establish a guarding potential in said trunk release conductor at the instant that the line circuit is completed.

79. In an automatic telephone exchange trunking system, a first selector, a second selector and a connector, a trunk line running between the first selector and the second connector vand comprising a trunk release conductor. a trunk line running between the second selector and the connector and comprising a trunk release conductor, and means in said connector whereby as soon as the last trunk line is seized the guarding potential is instantly established in all of the said trunk release conductors.

80. In an automatic telephone exchange trunking system, a first selector switch, a line relay and a slow acting relay therefor. a second selector switch, a line relay and a slow acting relay therefor, a connector switch, a trunk line running from said first selector switch to said secon-d selector switch and adapted to be seized by the former, a trunk line running from said second selector switch to the connector switch and adapted to be seized by the former, means in said first selector switch for maintaining said slow acting relay therefor energized until the first trunk line is seized, means in said second selector switch for then maintaining the said slow acting relay for said first selector switch energized until the second trunk line is seized. and means in said connector switch for then maintaining both of said slow acting relays energized.

Si. In an automatic telephone exchange trunlring system. a first selector switch comprising a line relay and a slow acting relay, a second selector switch comprising a line relay and a slow acting relay, a connector switch comprising a line relay and a slow acting relay, a trunk line extending from said rst selector switch to said second selector switch, the first selector switch being adapted to seize said trrnlf line to establish connection with said second selector switch, a trunk lineextending from said second selector switch to said connector switch, said second selector switch being adapted to seize the second trunk line, said first selector switch comprising means for maintaining its slow acting relay energized after an operation has begun and until the connection is established with said second selector switch, said second selector switch comprising means for maintaining its own slow acting relay and the slow acting relay of said first selector switch energized after said first selector switch establishes connection with said second selector switch, and until connection is made with said connector switch. said connector switch comprising means for maintaining all of the aforesaid slow acting relays energized after said second selector switch establishes connection with said connector switch.

82. In an automatic telephone exchange trunking system, a series of switches, two pairs of line bank springs for the first one of said switches together with automatic means. whereby if either or both of said pairs of springs are separated all the switches are released.

irl. In an automatic telephone exchange trunking system, a calling subscribers line and a called subscribers line. a series of switches for trunlring the calling subscribcrs line into connection with the called subscribers line. two trunk connecting springs or wipers allotted to the second switch of said series, together with automatic means whereby if either or both of said springs are separated from the trunk line all of the switches are released.

84:. In an automatic telephone exchange trunking system, a calling subscribers line and a called strbscribers line, a series of switches for trunking the calling line into connection lwith the called line, two trunk connecting springs or wipers allotted to the third switch of said series together with automatic means whereby if either or both of said springs are separated from the trunk line all of the switches are released.

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