US1256817A - Automatic telephone system. - Google Patents

Automatic telephone system. Download PDF

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Publication number
US1256817A
US1256817A US86229214A US1914862292A US1256817A US 1256817 A US1256817 A US 1256817A US 86229214 A US86229214 A US 86229214A US 1914862292 A US1914862292 A US 1914862292A US 1256817 A US1256817 A US 1256817A
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Prior art keywords
line
relay
switch
circuit
springs
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US86229214A
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English (en)
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Frank Newforth Jr
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Automatic Electric Co
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Automatic Electric Co
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Publication date
Priority to US442086D priority Critical patent/USB442086I5/en
Application filed by Automatic Electric Co filed Critical Automatic Electric Co
Priority to US86229214A priority patent/US1256817A/en
Priority to FR481821A priority patent/FR481821A/fr
Priority to US21523918 priority patent/US1442086A/en
Application granted granted Critical
Publication of US1256817A publication Critical patent/US1256817A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q3/00—Selecting arrangements

Definitions

  • My invention relates to automatic telephone systems in general. More )articularly it relates to s vstems in whici trunk selecting apparatus lis 4employed and in which traffic trunks are used in connection therewith.
  • a tratlic line terminating in an operators position, which operator upon responding automatically cuts off the ringing current in the calling connector without operating the meter' associated w-ith the calling circuit; to provide an improved type of trunking switch; and to provide certain details and features of improvement tending to increase the eiciency and servicealoility of a system ofI the above character.
  • Fig. 1 there is shownfthe automatic substation A, line switch C, aneter X as'- sociated with the line and a. first selector switch E.
  • Fig. 2 there is shown a connector switch H, and line switch C of substation A-
  • a group of relays which may be located in a manual board andare for the purpose of allowing an operatorl toi-answer an information call or ⁇ the like withoutI operating the meter of tltefcallin line as will be hereinafter more fully 'expined-
  • Figs'. 3- and 4 represent in detail a portion of a so-called self alining line switch plunger, that is a line switch plunger which .201'l there are two arms,
  • Fig. 5 represents in detail a portion of a master switch showing the association of the line switch plungers therewith.
  • the automatic substation A (Fig. l) comprises the usual receiver 2, transmit-ter ringer 4 and condenser 5. Being an. automatic substation, it is also provided with. a suitable impulse sending mechanism for controlling the automatic switches, which mechanism is represented diagrammatically by a pair of impulse springs 6 and 7 and an impulse wheel 8, which may be' controlled A in a well known manner through the me.- dium of a .dial (not shown) provided with finger. holes in such a way that the impulse springs may bemomentarily' separated a number of times corresponding to the. respective digits of the number of the called subscriber.
  • the subscribers individual switch C is of the general type of subscribers switch sho-wn in British patent to R. W. James, #26,301 of 1906, more closel resembling, however, the particular type s own in British patent to T. G. Martin, #1419 of 1910.
  • This line switch comprises, among other details, a
  • plunger 200 shown in Figs. 4 and 5 pivotallv attached to the end of .a so-calledplunger v arm 9.
  • the back portion of this plunger 200 is fan shaped. Pivotallyvmounted on points 2,01 and 20,2 and 202, These arms 202 and 202"l are limited in their rotation by two pins 203 and 203, at their outer ends they are provided with rollnir this fan shape portion at the on the usual shaft 207, en the plunger-,2 0
  • the plunger ar'm 9 is controlled by a magnet 10, which comprises an operating winding 11 and a holding winding 12. This magnet also controls the cut-off armature 13.
  • the winding 11 operates both the plunger arm 9 and armature 13, While the winding 1-2 is strong enough only to operate the armature 13 and to hold the plunger armi) in its operated position.
  • each set forming the terminal of a' trunk line leading to a first selector switch E.
  • Eachitrunk line is connected in multiple to the corresponding springs of all the line switches of the group which is controlled by the master switch D.
  • the switch C is controlled -by the subscriber throughv the menecting relay 9 in this manner will be here- #26,301-of 1906, and #1419 of 1910.
  • the I function of themaster switch as is; well known, 1s to maintain the plungers of-all the ldle l1ne switchesinpos'ition to engage'the terminals of an idle trunk line.
  • the master switch Dv consists eS- sentia y of a motor magnet 354 which operatesthe ratchet wheel 355, a bank of contacts comprising -a number'of individual segments 4a and one common segment ⁇ 356, a Vbusy trunk .relay 357 ,and a-locking relay keep some oneof the individual segments in an electrical connection with the common segment 356.
  • a suitable mechanlcal connection theA rotary motion ofthe ,gr shaftfto give said shafts. reciprocatmotion to moyethe idle plungers back jan -frth infront of the bank contacts.
  • a call register 28 which is controlled by a The'first selector switch E of the general type of selectorswitches-disclosed inv U. S. Letters Patentto Keith, Erickson and Erickson, #815,321 granted March 13, 1906.
  • the selector E com prises a bank of contacts arranged in hori-4 lzontal rows 0r levels, which are adapted to be engaged by a set of wipers 30, 31 and 32 carried upon a shaft (not shown), which has a vertical movement controlled by the vertical ma et 33 and a rotarymotion conlgigrotary-l magnet 34.
  • the operathemedium of the double woundA line relay 35 Means orpermitting the Aswitch to be restored to normal position ,areprovided in the release magnet 36, which, upon energizing, withdraws the retaining pawls from the' shaftl
  • the spring contacts 37 and 38 are permitted to close 'only when the switch shaft has been raised one or more steps from its lowest position.
  • the vconnector shown at H (Fig. 2) is of the general Vtype of connector switch disclosed Jin U.A S. Letters Patent "to Keith', ⁇
  • the clir cuits are modiiedto adapt the switch to operate in a systennin which' the central ofiice apparatus is 'ciitnolled byirnpulses delivered over the two'j sides of the line Y 1n series.V
  • the connector is 358.
  • the wiper359 is adapted to alwaysI provided with a shaft (not shown), carry- 'ing the wi ers 41, 42 and 43, and which is controlled y the vertical magnet 4A and rotary magnet 45.-
  • the usual side switch comprising the wipers 46, 47,48 and 19 is controlled by the private.l magnet 50 in the usual and well knownnianner.
  • Magnet 53 is the usual releasem'agnet.
  • the line relay -51 is connected with the line through the re; versin springs of a socalled back bridge re1ay2, throughthe windings of which lat means through which the application otringing current vto the called line is controlled.
  • a Abusy signaling machine which is connected to sprin ot relay 55, the function of which is to send a busy tone under certain conditions back over the line. The complete operation lot' this relay will be described later.
  • the busy signaling machine as represented herein, coinprisesan induction coil or tra'usiormer, the
  • The. line switch C is similar to the, line switch C the circuits, being modified, howrIhe substation lA is similar in all respects to -the substation
  • a battery B having one terminal ⁇ groundedat *In the event of a subscriber having-,his
  • the relay 22 upon energizing, closes the circuit ofthe operating Winding 11, which operates to disconnect thel relay 22 from the line through the medium of the armature 13 and springs 60 and l(51, and to thrust the plunger of the switchvinto the terminal of the trunkbefore Which it is being held by themaster switch, whereby7 the line circuit is extended through the springs 1+ and 1S, and 15 and 19 to an idle first selector switch E.
  • the line relay of the selector switch E is thereupon energized over a circuit extending from ground G through-vl the lower Winding of said relay', springs S2 and 182j", thence over the'hea'vy conductors to and through the substation A and back over .the other side of the liii'e through the left 'hand winding of the meter magnet' 29, springs 83 and 83 and upper winding of line relay 35 to the battery lead 80.
  • the relay 35 upon energizing, closes the circuit of the relay 39;, which, in .-tuin, p
  • gization of the relay 39 at the selector E also completes, a circuit extending from .ground G* through springs 85, springs v20 and 16, through/the4 rightl hand Jiivinding of the meter magnet 29 and the springs *61,n and 6l to.- the battery lead 80.
  • the current in this Winding is in opposition't''tlie current nowing through the line winding, and the inagnet is, therefore, not operated at thiswtime.
  • the ⁇ springs 60 and 6,1 disengage atelyfup'on' the operating of the lunger arin 9 which prevents the circuit of t e line rehiy 22 from aga in being closed until the plunger arm 9 is again restored to normal position in front of an idle terminal.
  • the master switch D Upon the closure of thesprings 17 and 21 by the operation of the switch C, the master switch D operates in a well known manner to advance the plungers of the idle line switches to ⁇ a position opposite an idle trunk line.
  • the calling subscriber now operates his calling device'for the first digit 2 of the called number, whereby the substation impulse springs 6 and 7 are separated twice momentarily, eafh time breaking 'the circuit of the selector line relay 35.
  • the relay 39 of the selector being slow acting, does .not denergize during the momentary interruptions -of its circuit by the relay 35, and
  • Thefslow acting relay40 is ,maintained in its energized posltion con# tinuously while impulses arebeing transf mitted hto the vertical magnet through it, and in its energized position closes a circuit from grpund Gr through the springs 94 and 93 and private magnet 95 to thebattery' lead 80.
  • the relay 40 upon denergizing, o ens the circuit of the private magnet 95, w ich.
  • the private magnet extends from oundG1 through springs 99 and 100, and t e private magnet 95 to battery B. If the first trunk line leading from the second level of bank ⁇ contacts of the 'selector E is in use, the pri- ⁇ vate wiper 32 will find the rprivate bank contacts supplied with a gua ing ground :..V-jpotential. a circuit will than .be closed wffthrough theprivate magnet 95 after vthe rota f [magnet d'ener 'zes, extending from 'ground at'the pnvatewiper through the yswitch wiper 63 in 'second position), 4then"through, maiettto battery.
  • vs i'd'eswitch 1s' thus eld in second posi?V tion and the rotary magnet upon denergizing again closes its own circuit at springs 97 and 98 and operates to step the shaft wipers to the next bank contacts. If the next contacts are also busy the Voperation will be re#l peated, the rotary magnet operating in a manner similar to that of a buzzer to rotate the shaft wipers onto bank contacts connected to an idle trunk line, at which time the private magnet denergizes and allows the side switch to pass from second to third position.
  • the wi er 62, 'upon passing to third position shi s the battery connection from the rotary magnet 34 to the line switching relay 102, thus closing a circuit through the relay 102.
  • This circuit extends from ground- G* through springs 85, relay 102 and wiper 62 to battery B.
  • a circuit also extends from springs through wiper Y 63 (in third position) to the private wiper 32.
  • the relay 102 upon energizing, operates to disconnect the line relay 35 from the line and to connect the calling line through to the line relay 51 ⁇ of the connector H, and also operates to open the circuit of the release magnet 36. at springs 103 and 104.
  • the line relay upon being disconnected from the line denergizes and allows the relay 39 lto denergize'.
  • the -relay 39 being slow acting til a ground has been supplied to the release trunk conductor 140 bythe relay 160 of the connector switch H as will be later more fully explained.
  • the line relay 51 of the connector thereupon becomes energized and closes the circuit of the relay 160.
  • the relay 160 upon energizing, provides a holding circuit for the line switching relay 102 of the selector switch E, and for the hold in winding 12 of the line switch C.
  • the circuit for the line switching relay 102 extends from ound G -through the springs 123, conuctor 140, wiper 32, side switch wiper 63,
  • the circuitfor the hol inwinding 12 extends .over the above traced circuit to side switch wiper 63, thence 'throu bank contacts20 and 16 and the said hold 1n windingtov battery B.
  • the relay 164 opens the circuit of the private magnet 50, whichupon denergizing, permits the side switchvto advance from first to second position.' vThe movement of the side switch wiper 49 from first to second position transfers the battery connection from the vertical magnet 44 to ther tary magnet 45.
  • the relay 164 operates in response to this digit in thesame manner as for the previous digit, to cause the private magnet toadvance the side switch one more position, that is, from second to third position after the last'impulse for the digitis transmitted.
  • the side switch wipers 46 and 47 By the engagement of the side switch wipers 46 and 47 with their third position contact points the line connection is finally completed to the calledgnumber.
  • the ringing relay is energized only intermittently through the medium of the interrupter 171.
  • the vcalled subscriber his line is provided with. talking current through the windings of the back circuit for itself through its own springs 176 independent of the" springs of the back bridge relay 52.
  • a further result of the energization of the relay 52 upon the response of the called subscriber, is the transposition of the connection between the windings of the line relay 51 and trunk conductors 138 .a 1d 139, whereby the direction of current in t-U e calling line is reversed.
  • This reversal of the current in the'left hand winding of the subscribers meter relay 29 causes the two windings to assist one another to op erate the meter to register the call.
  • the connection is released by the hanging up of the receiver at the calling substation in the following manner:
  • the separation of the hook switch springs 73 and '74 destroys the energizing circuit of the line relays 51 (F ig. 2).
  • the rela-y 51 de nergizes, and opens the circuit of the relay. 160.
  • the relay 160 upon energizing, opens the holding circuits of the relay 102, of the switch E and! of the hold in Winding 12 of line switch C and at'the sametime closes the circuit of the release magnet 53 of the connector H.
  • the latter circuit extends from ground G11 through the springs 162 and 16231, springs 163 and.
  • the magnet 53 upon energizing, restores the connector switch shaft and side switch to normal position, and its own circuit is interrupted at the springs 178 when the shaft reaches its lowest position.
  • the denergization of the relay 102 of the switch E serves to close the circuits of the release magnet 36.
  • the circuit for the said magnet exten s from ground G5 through the springs 88 nd 89,
  • the relay 190a energizes over this circuit, but is oi sufiicient resistance to prevent the relay 52 from 40 operatively energizing.
  • the relay 1902 upon energizing, closes a circuit through the lamp 193.
  • the operator, Aupon noting the lowing of the lamp 193l operates the key thereby placing the talking s et across the conductors 165 and 166 and also, due to the make before break arrangement of the, springs 194, 195 and 196, sends one ini lpulse from ground Gslthrough the primary of the induction coil l197 to battery.
  • This impulse inducesv an impulse in the secondary of the coil'197, which is in series with the coil-198. ⁇
  • the relay 198 is energized by this v,impulseyand operates to momentarily short circuit t e conductors 165 and 166.
  • the line switch shown at C 2) operates over a circuit slightly different from that explained for line switch C.
  • a circuit is closed extending from ground Gr through springs 211 and 212, conductor 213, thence through substation A', conductor 214, springs" 215 and 216, windings 217 and218 in series to the battery B.
  • the current through these windings is not of sufficient strength to at-v tract vthe plungerarm 222 but however, does attract the armature 219 and is 'sufficient tfo hold the plunger in its attracted position. when once operated.
  • the operation of thev armature 219 closes a circuit for the coil 218 extending from ground G2 through springs 223 and 224, which are controlled bythe' master switch, thenc ⁇ e through v springs 225 and 226, springs 220 and 221, and the wind-v ing 218 to battery B.4
  • the arm 222 is now attractedand operates to force the plunger into the bank of contacts as described for switch (l, separates the springs 225 and 226 and causes the engagement of springs 227 and 228, The separating of contact springs 225 and 226 disconnects the ground from winding 218.
  • a discontinued subscriber at :the central oflice can be connected with'a trafiic trunk associated with an operator and the operator can answer and thereby cut off the ringing current at' the connector without permitting the current of the calling side of the line to be reversed for a suliicient length of time to operate the meter.
  • I' provide an improved form of self aliningplunger type switch in which the plunger is always in engagement with the plunger sha'Et'i-egardless of Whether the plunger is holdinglthe line in engagement with a trunk or not and which is more positire and efficient in its action.
  • Vliilc l 4hai'e illustrated my invention in connection with a special or particular type oi' apparatus and circuits, I do not wish to be limited to the exact structure shown and described.
  • What I claiin as my invention is z- 1.
  • a telephone system an automaticr ringing current, means for automatically connecting said ringing current With said contacts when said connector establishes connection therewith, a relay in said connector, means for causing a continuous fiow of current through4 said relay to energize the saine when connection is made with a subscr-ibers line andsaid subscriber responds,
  • an automatic connector switch a line with which said switcli'is adapted to make connection, a relay in said switth, a 1second. relay bridged across. said line and adapted to be connected in series with said'first relay..when said connector .establishes connection with said line,
  • switch is adapted toV make connection, a rc lay in said switch, a second relay bridged across said line and adapted to be connected in series with said first relay when said con-- nector establishes connection with said line, .said second relay being of high resistance to prevent encrgization of said Vfirst relay,
  • said second relay boing of high resistance to prcvent energization olf said first relay, a talking set adapted to be connected with said line, and means operated automatically when said talking set is connected with said line for short-circuiting said second relay to thereby cause the operation o't'said first relay, means forapplying ringing current to said line when connection is established therewith, and means controlled by the energization of said first relay for disconnecting said ringing current from the line.
  • a telephone system an auloiiiatic connector switch, a line with ⁇ which said switch is adapted to make connection.
  • a rclay in said switch a second relay bridged across said line and adapted to be connected in series with-said first relay when said-connector establishes connection ,with said line, said second relay being of high resistance to prevent energization of said first relay, a talking set adapted to be connected with said line, and means operated automatically when said talking set is connected with said line for momentarily short-circuiting said second relay to thereby cause the operation of said first relay, means for automatically connectncetion is established therewith, a trnnkline extending to said switch, and means coning ringing curi-ent. to said line when icon? trolledv by the energization -of said'first relay for disconnecting said ringing current from the line.
  • a trunk line terminating in an automatic connector switch provided with bank contacts, a plurality' of subscribers lines connected with certain of said contacta a tra flicv ltrunk connected with other of said contacts, an operators set adaptedto be connected with said traiiic trunk, a. source of ringing current, means 02 automaticall connecting said yringing cur- 4, -,rent with said contacts when said connector establishes connection therewith, a relay in' said connector, means for causing a continuous VHowl of current through said relay to energize the same when-'connection is made with a subscribers line and said subscriber responds, means for energizing said relay onlyrmomentarily upon the response of the operator. when connection is established with the tralic trunk, and means controlled by the energization of said'relay for disconnecting 'fao the ringingv current from said contacts.
  • connector switclnfa line with which said switch is adapted to make connection a relay in said switchrafsecond relay bridged across 7.1m. a telephone system, an automatic seid linependadaptedgto be connected in seriesw-ith 'said 'relay when'saidconnector establishes connection with y said line, said second relay :being ofl ⁇ high resistancel to prevent'energizationof said first relay when the two connected in series, a third relay connection of said talking'circuit withsaid controllin a short-circuit about said second relay, a ta ⁇ ing set adapted to be connected withV said line, and means controlled by.
  • an automatic connector switch a line; with which said switch is adapted to make connection, aV relay in saidfswitch, 4a second 'relay bridged l* across said line and adapted to be connected lnector establish 1n series with sa ⁇ d first relay when saidconconnectionwithfsaid line, said second relay bein of hi hresistai'me to prevent energization o said rst relay when the two are connected in series, a third relay i .controllin a shortci'rcuit about s aidsecond w'ithsaid line, andlmeanscontrolled by theV relay, a ta kingset adapted to bepconnecd connection of said talking circuit with said line ',for transmitting an inducedimpulsef through said third relay ⁇ to
  • a trunk selecting device for said lines comprising switching means common to all the lines and switching means individual to each line including two magnets for one ofsaid lines, a circuit for each magnet, a controlling point for each circuit, saidcommon means controlling one 0f said points and said individual means controlling the other of said points, said common and individual means having different time constants, and a telephone for each line provided with a switch hook.
  • a line a telephone for'isaid line provided with a switch hook, a pluralit 'of trunks accessible there to at the centra oiiice, a-non'numerical automatic trunking switch for said line, means for operating the switch for connecting the linewith an idle trunk,said .means compris ⁇ ing two magnets, a circuit for eachmagnet,
  • a telel'ione for said line provided with a switch ook, a switch for said line, a second line, means in saidswitch and line for operating the said switch to connect the two lines, saidf' means comprisin a line relay in the first line and-an auxi lary magnet, a circuit for each magnet, a controlling point I1n each circuit2 and means for controlling each point having different time constants.
  • a' telephone for each line provided with a the common controller while the connection 1s maintained, means for breaking the oo nn'ection and restorin the' individuali controller to the contro .of the common controller and then enablin -theindividuel conineans including -inagnet for said ;line, a circuit for said means for controlling said different time constants.
  • A13.- In a telephone system, a series of lines, a telephone for eachilme provided with a circuit having a' line with guet and a pluiiity of switch hook, s series o! trunks accessible, tp
  • troller l to locate an 1 e trunk, said first said lines at the central otiice, a trunk selecting equipment for said lines t'or selecting an idle trunk and forrconnecting the .line with said trunk, comprising a circuit controller common to said lines and a circuit controller individual to each line, said individual controller to locate an idle trunk,
  • said first means including a relay in said line comprising two controllingr points and controlling means at each point. having ditferent time constants.
  • a series of lines a telephone tor each line provided with a switch hook, a series of trunks accessible to said lines at the central otlicc a trunk se-Y lecting equipment for said lilies for selecting an idle trunk and for connecting the line with said trunk, comprising a circuit controller common to said lines and a circuit controller individual to'each line, said individual controller responsive while idle to said common controller to select an idle trunk, means for operating an individual controller to connect a line with a trunk and for rendering the individual controller non responsive to the common controller while the connection is maintained, means for breaking the connection and restoring the individual controller to the control of the.
  • said iii-st means including a relay in said line comprising two controlling points and controlling means at each point having diff ferent time constants for closing one point before the other.
  • a series ioflines,l a telephone for each line providedwith a switch hook, a series of trunks accessible to said lilies at the central ottico, a trunk selecting equipment for said lines for selecting an idle trunk and for connecting the line with said trunk, comprising a circuit controller common to said lilies and a circuit controller individual to each line, said indi vidual controller responsive while idle-to said common controller to select an idle trunk, means for operating an individual controller to connect a line with a trunk and for rendering.
  • the individual controller nonrespnsive to the common Controller while the connecfion is maintained, means for breaking; theconiiection and restoring the individual controller to the control of thecominon controller and then enabling the in;l dividual controllante locate an idle trunk, said first means including a relay in said 'line comprising two controlling points, one'- in the line and one -in the central otlice, and controlling means at' each point' having different time constants.
  • a series of lines a series of trunks and switches for said lines for connecting the lines with the trunks through the medium of plungers, one for cach switch, a shaft common to saidplungers for controlling the same, means "for making said plungers responsive to'said shaft., means for makin a plunger non-responsive to the shaft wien its line is connected with a trunk, and means foralways maintaining thel pliigers in connection with the shaft and for restorin the plungers to the control of the shaft w en the circuit is broken, and -means for breakin the circuit.
  • a rality of trunks each terminating in a' bankA terminal, a termin-al for said line common to 'said trunks, a circuit closer forpressing the line terminal into engagement with any one of said trunk terminals .
  • the line may be connected with one trunk at a'time, a' driving element for -said' circuit closer, means for operating the circu1t'.”c1oser, ⁇ and means whereby the circuitcloser'is made yto follow the driving element Whenever the said clement moves provided the circuit closer is'not operated, said last means comprising an elastic element whereby the circi'iitcloser may be operated and' still remain in engagement with'theilri ving element.' I. 19.
  • a'callingline In a telephone system, a'callingline; a called line, means for connecting the two, a lsignal for the called line, a source of ringing current controlled through the medium of said means for operating said signal, a source of current for supplying. the calling line 'with currentfor talking, a relay controlled over the called line yfor reversing the currentin the calling line and for again restoring it ivhcn the called subscriber' answers to produce a .signal in the receiver' of the calling line, said relayr also for cutting oit' the ringing current from the'called i line when the called subscriber answers;
  • a calling line, a called line, an operators position means im, a piu-- forvv extending connections from the calling line to either the called line or to the opera tors osition, a signal for the called l1ne, a signall for the operator, e source of ringing current controlled through the medium of said means for operatin said signals, e source of current for supp ying talking current to the calling line, a signal for the calling line, a relay controlled over the called line upon the response of the.
  • said relay also controlled by the responseA of the operator when a call 1s extended to the operators position for disconnecting said ringin current and for reversing the current 1n the calling line only momentarily for operating the signl on the calling line in another manner.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Interface Circuits In Exchanges (AREA)
US86229214A 1914-09-18 1914-09-18 Automatic telephone system. Expired - Lifetime US1256817A (en)

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US442086D USB442086I5 (cg-RX-API-DMAC10.html) 1914-09-18
US86229214A US1256817A (en) 1914-09-18 1914-09-18 Automatic telephone system.
FR481821A FR481821A (fr) 1914-09-18 1915-08-28 Perfectionnement dans le choix des lignes de jonction en téléphonie automatique
US21523918 US1442086A (en) 1914-09-18 1918-02-04 newforth

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US21523918 Expired - Lifetime US1442086A (en) 1914-09-18 1918-02-04 newforth

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FR481821A (fr) 1917-01-23
US1442086A (en) 1923-01-16

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