US2431321A

US2431321A - Multioffice telephone system

Info

Publication number: US2431321A
Application number: US507469A
Authority: US
Inventors: Fernand P Gohorel
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1939-02-24
Filing date: 1943-10-23
Publication date: 1947-11-25
Anticipated expiration: 1964-11-25
Also published as: FR50906E; FR854039A; FR50457E; US2468057A

Description

Nov. 25, 1947. F. P'. Gol-10H51, 2,431,321

MULT IOFFI CE TELEPHONE SYSTEM Filed Oct. 25, 1943 6 SheebS-Sheet. l

0E CA 21 2l 5 V2A 32 72g CALL/N6.

/VEY

OPERA Top5 P05/WON IN VEN TOR.

25, M4?. F. P. GOHQREL MULTIOFFICE' TELEPHONE SYSTEM Naw,

Filed oct. v25, 1945 6 Sheets-Sheet 2 F. P. GOHOREL MULTIOFFICE TELEPHONE SYSTEM Nov. 25, 1947.

Filed Oct. 25, 1943 6 Sheets-.Sheet 5 Q vsb IN VEN TOR. Pimm/y0. f. afm/Pn.

Nov. 25, 1947. F. P. GOHOREL Zz MULTIOFFICE TLPHONE SYSTEM 4 Filed Oct. l 23, 1943 I 6 Sheets-Sheet 4 IN VEN TOR. FFR/mwa. e 60A/0R54 Nov. 25, 194,7.

F. P. GOHOREL.

` MULTIOFFICE TELEPHONE SYSTEM Filed Oct. 23, 1943 6 Sheets-Sheet 5 INVENTOR.

-BY v Nov. 25,r 1947. F. P. GOHOREL 2,431,321

` MULTIOFFICE TELEPHONE SYSTEM Filed oct., 2s, 1921s Vs sheets-sheet e FER/VEND R 50i/017152 Patented Nov. 25, 1947 MULTIOFF'ICETELEPHONE SYSTEM f' Fernand P. Gohorel, Antony, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application October 23, 194@ SerialNo. 593,11@

In France Deceniber 5, 17938 The present invention relates to various improvements in telephone systems, and particularly in systems comprising several exchanges connected by cables, and in which communication between subscribers of diierent exchanges may be established Wholly by the operator of thev outgoing exchange without the intervention of the'incoming operator, or of the operators of the intermediate exchange or exchanges.

One of the characteristics of the invention consists in that the dialling impulses, which are transmitted in the form of interruptions of a dialling current, become effective at the incoming exchange where theyare recorded during the interruption of the current, only when the dialling current is re-established.

Another characteristic of the invention consists in thatwhen a dialling impulse Whichgis transmitted in the form of an interruption of a dialling current has been recorded, the recording device can record the/next impulse only when the previous impulse has become effective and has thus caused a particular operation or signalling function. Y

Another characteristic of the invention consists in that the device rendering the impulses'efective, operates only if the duration of the interruption of the dialling current does not exceed a predetermined maximum value.

Another characteristic of the invention is that a series relay in the device which renders the impulseseiective can operate only if operating-im` pulses are received.

' Another characteristic of the invention consists in that the devices on which the impulses must be received can participate in the hunting for the calling line only after a preliminary local test under normal conditions of operation of their detection device and of the impulse relay which is associated with said detection device.

Another characteristic of the invention consists in that the signal indicating that the impulse transmission is at an end is constituted by the stoppage of the transmission of the dialling current from the transmitting station.

` Another characteristic of the invention consists in the use at the transmitting station, and atvthe receiving station, of a single control switch in order to produce the diierent transmissions of low frequency signalling or supervisory currents.

Another characteristic of the invention consists in that each operator has at her disposal two means of access to the trunks leading to the incoming exchange: The establishment of the connection through a first channel causes lthe trans- 6 Claims. (Cl. 179%27) e fromlthef outgoing exchange o f a pre-determined signal which veffects, the necessary s vvitc'loing operations` to" connect at the incoming exchange, the circuit toga predetermined operai tor; or'subscriber. Theestablishmentof the connection -th'roughja secondV channel does not produce any predeterminedoperation; this operation canbe-'eiiectedonly when theoperator works her Antner characteristic-ofithe-invention consists that when f theV operatorgjisl'connectedwith a junction circuit over the first chfannelya momentary Aemission of the dialling current without interruptionsl `ill send a predetermined signal from the outgoing exchange; H

-jVarious other charact risticsjwillv appear `from the following'description-,given byway of-anonlimiting example.A A the attached drawings:

Y Fig.' 1 represents'fa -portionof agcord pair of an perators positionnecessary 'fior understanding the operation of the device; f Y t Fig'. Z'isthe outgoingequipment vof va circuit between exchanges; l v I Figfv is the incoming equipment'vof a circuit between exchanges; 1

Fig. l is an impulse recordiigdevice associated With the incomingH equipment; Figi 5"i's'a detector Vor'receiving device for transforming the alternating current impulses received into directcurrent impulses;

Fig'. 6 isthe equipment of 'an inter-'cnice trunk leading toA the operatorls position I at the incoming exch'ang;' d l f Fig. 7 showsa 'device-for'establishinga connection between'the incoming'equipment of an interoiiice-trunk and the automatic equipment of the incoming exchange; and'y i? Fig. 8 shows the mannerin which Figs. 1 to 7 should be connected. *jj f v *Y Y f In the following `descriptionthe relay contacts which are closed when the relayis energized, that is to say in operative position, are indicated by placing" ahead-of the number 'ofthespring the letterv TQ and th'econtactsY which are closed when the relay is not energized, that isto say in normal position the letter R. The contacts of the control switches v'arerepresented bythe shaded squaresl inserted'in the circuits. At each square thepositions'of the wipers in which the'control switcnclosesthe Contact are designated, as is the wiper of the control switchwhich closes the contact. v

The operation of the system will be explained in detail in the case in which the operator of the outgoing exchange calls a subscriber connected to high resistance of the upper winding of 6.

, Ylittle later. winding of relay 22 is` completed: earth, TI93, TZQI, R2I I, lower winding of 22 and-battery.

3 the automatic switchboard of the incoming eX- change.

The operator of the outgoing exchange plugs the cord pair of Fig. l into the jack J of the equipment of Fig. 2.

Relay is energized through its lower winding in the circuit: earth, lower winding of 4,R5 I, jack J, sleeve of plug C, windings in series of relay I and battery. On account of the high resistance of relay 4, relay I cannot attract its armature. Relay ll closes at T42 the starting circuit of cams C1 and C2. At TM, it closes the circuit of relay f which opens at RM' the circuit of the dis- Vcuit of the windings in series of relay 5 through the windings of relay I. Relay 5 pulls up, but relay I cannot be energized on account of the At T62, relay 6 completes the circuit of relay 9 which pulls up. At T52, relay 5 completes the following circuit of relay l: earth, RGI, T52, winding of l, and battery. At T73, relay .'I completes its hold# ing circuit to earth of R84. At T'II, it completes the following stepping circuit of the control switch: earth, cam C2, T'II, RIUI, T61, contact of wiper e of the control switch in position O, stepping magnet Cm of the control switch.

The control switch advances one step and passes to position I. From that time said con- IlO trol switch makes a complete rotation, the circuit of the magnet CM being closed over cam C2 by wiper e in the positions I to I0, and by wiper f in the positions I I to 2|.

When the control switch leaves its normal position O, it opens the line wires L1 and L2 of the equipment of Fig. 2 and connects them through wipers a and b, and in positions I to I0 to the low frequency current generator GeI.

A calling impulse is thus sent over conductors LI-LZ which, at the incoming exchange is received by the relay I8.

Through TIBI, relay I8 completes the circuit of the lower winding of relay I9 which pulls up, and of the winding of relay 20 which pulls up a The following circuit ofthe lower When the relay 22 pulls up, the starting circuit of the registers is completed through T222, and R232 and wire 52. It will be assumed that the first free register in engagement with the equipment of Fig. 3 is that of Fig. 4.

When earth has been applied to wire `52', it passes in the normal pocitions of the switches C01 and Co2, over R325', to energize the lower winding of relay 23 which pulls up. Moreover,

this earth passes through wire 22', R4'II,-R594,

to energize the lower winding of relay 5I Vof the equipment-of the detector of Fig. 5. Y Y Relay 5I connects at Tl andTEIS thevoice frequency current generator G63 to the input The Ydevice Dr thus `detects Ycurrent from 4 the generator Ge3 causing the energization of relay 53. Through T53I, relay 53 completes the circuit of the upper winding of relay 52 through T5I I. Relay 52 pulls up and at T5II completes its holding circuit on its lower winding; at R524 and R522, it disconnects the generator G63 from the .detector Dr whereupon relay :53 fa-lls off.

When relay 53 returns Ato normal, the following holding circuit for relay 59 is completed: battery, resistance R3, R53I, T5I3, T523, upper winding of 59 and earth. Relay 50 pulls up and at 'T591 closes lits holding circuit to earth Valo-- plied to wire 24', at T282 by relay 28; at T14, it opens the holding circuit of relay 26 which falls back. At'T502, it applies earth to wire 23 thus completing the circuit of the lower winding of vrelay 30 which pulls up.

The 'following automatic stepping circuit of the Ilnder switch C03 associated with the register is completed: earth, R323, R29I, T392, contact of magnet Cm3, magnet Cm3 land battery.

The wipers of C03 .advance in search of the incoming `equipment (Fig. `3) on which a vcall has been received.

When the wipers of C03 arrive on the bank contacts .to which theequiprnent of Fig. 3 is "connected, the following circuit is completed: bat- Y tery, windings of relay 25, wire T, `bank contact,

wiper T. windings inseriesof the relay 29, T393,

The following circuit of the upper winding -of relay 30 is completed: batteryfwindings of relay T5, wire T, bank contact, wiper T, .upper winding ofrelay 29. upper winding of relay 35, R33I, 339| and earth. Y

The direction of the upperwinding of Yrelay 39 is such that its uX is opposed to that of .the

Under these conditions the armature cf relay 33 will'fall back. The follow- Y lower winding.

ing circuit o?? relay 32 is completed: battery, winding cf 32A R391, T292 and earth. When relay 32 pulls up, Ithe register and the detection equipment are connected'to the incoming equipment.

At the end of the reception 4the can impulse,

relay I8 (Fig. 3) falls back. The lower winding of relay 2.! no longershortcircuited and this-re lay pulls up in series with the ylower winding of relay 22. `I'he following circuitY of relay 2li is completed: earth, T253, winding of .relay 24,

T2I5, contact of wiper C of the control switch in position O, resistance and battery. Through TMI., relay 22 completesV the .following circuit of the stepping Vmagnet'of the control switchof:

theY equipment of Fig. 3: earth, cam C3, TMI,

magnet Cm3 and battery.

The control switch will thus advance under the action of the impulses of the cam C3. Y

During the .passage of .thewipers of the con-V Y trol switch over positions I.to l, the following.' circuit of relay 'I is completed: battery, windingV of Il, 4contact of wiperV a of the control switchin positions I to l', 'T2-l2 and earthi The relay .I=I

connects throughTIl-Z and 'I'.lll the generator When the control switchV leaves Y'position O, the l circuit of relay 2Q is opened in wiper-c of the `control, switch and-'the relay falls back.'V Tl-le-cirfY Relay 25 also 5 cuit of the control switch is then completed at T2I3 and wiper c of the control switch.

When the control switch arrives in position II, the circuit of its magnet Cm3 is opened and the wipers remain in this position.

When the relay 25 pulls up, it completes at T251 and R232 the circuit of magnet Cm4 of the switch C04.

When the wipers of C04 arrive on a free equipment for connection with the automatic. exchange, such as that of Fig. 3, relay 28 is energized in the circuit: earth, T212 (relay 21 has pulled up on its lower winding through R265 and T251) windings in series of 28, wiper T, wire 53', R635, R682 and battery through the automatic equipment.

The relay 23 in pulling up, opens at R282 the circuit of magnet Cm4. The wipers of C04 stop on the contacts to which the equipment of Fig. 7 is connected. The circuit of relay 26 is completed through: earth, T251, T282, winding of 26 and battery. Relay I1 releases when wiper a of the control switch passes position 1. Relay I9 releases a moment after the end of the reception of the calling impulse. Relay I2 connects the line conductors L1 and L2 over T25I and T259, and the wires a and b towards the register and the detector device.

The following circuit of relay 64 of Fig. 7 is completed: battery, winding of 64, R632, wire 5I', T218, T26I, T252, upper winding of I8 and earth. Reay 64through T644 completes the circuit of relay 63 in series with relay 28 which pulls up.

The loop to the automatic switchboard is completed through: conductor 6I', T633, T643, R55I, resistance, conductor 62.

The following circuit of relays 65 (Fig. 7) and 4G (Fig. 4) is completed: earth, winding of 65, T645, T631, wire 52', T214, T261, TI50, wire I of C03, T322, R4I I, winding of relay 48 and battery. On account of the high resistance of the winding of relay 48, relay 65 cannot be energized, but relay 48 pulls up.

The return impulse sent on the line conductors Li-Lz from the incoming exchange is receivedA at the outgoing exchange on relay I2 during the displacement of wipers b and d of the control switch from positions I8 to 2|.

Relay I2 completes through TI2I the circuit of the lower winding of relay I4 which pulls up and connects the line conductor-s Lr-Lg to relay I5 which receives the end of the impulse, and through TI5I maintains relay I4 attracted on its middle winding.

When relay I4 pulls up, the circuit of relay I3 is completed through TI42, TI5I and earth. Relav I3 pulls up after a moment. The following circuit of relay I8 is completed: battery, lower winding of the relay I8, RIII, TI3I, TI42, TI5I and earth. Relay I pulls up and opens at RIOI the outgoing circuit of position O of the control switch.

At the end of the reception of the impulse, relay I releases and opens the circuit of relay 8 which fall-s back, as does relay I3. Relay I I is energized in the following circuit in which the relay I IJ is maintained: battery, lower winding of Il, Tlil, T53 and earth. The following circuit of relay I6 is completed: earth, winding of I6, TlI4, T69, tip of the plug of the cord pair, spring of key CA and its rest contact, spring I of key CE and its work contact, spring 2 of key CD and its work contact, spring Cn of the operators dial, signal lamp LI, resistance and battery, Relay I 6 is energized and lamp L1 lights up, indieating ,to the operator that she can begin todial the desired subscribers number. z. i Relay I6, whichhas pulled up,.connects theline conductors L1 and L2 to the terminals of thevoice frequencyv current generator Grez. This voice frequency current is received on the equipment of Fig. 3, and transmitted to the equipments of Figs. 4 and 5 over the circuits previously traced, andis finally received in the detector device Dr causing the holding of relay 53. The following circuit of relay 36 (Fig. 4) is completed: earth, winding of 36, wire 25', R5I I, T53I, resistance and battery. It will be seen that at the outgoing exchange owing to the fact that the dial contact-s Cn are inserted in the circuit of relay I6, said relay I6 will release for each interruption of contact C11., that is to say, for each dialling impulse. The result is that the line conductors Lr-Lz will be disconnected from the generator Gez and the transmission of the voice frequency current' to the incoming exchange will be interrupted. Thus, the dialling of the called number will take place in the form of breaks in the voice frequency currents of the generator Gez.

When, during the sending of impulses, the voice frequency current is no longer received at the incoming exchange, relay 53 (Fig. 5) releases and completes the following circuit of relay 34: battery, resistance R53I, R5I3, wire 26', winding 34, T363 (the slow-acting relay 36 does not release during the reception of one train of irnpulses), RSSI and earth. Relay 34 is energized and atT34I completes its holding circuit; At T342, it completes the circuit of relay 38 which pulls up.

At the end of the interruption of the Voice fre` quency current corresponding to one impulse, relay 53 (Fig. 5) is energized and opens the circuit of relay 34 which falls back. Relay 38 is maintained attracted in the circuit: battery, winding of 6, T382, T322', contact for the magnet Cmi and earth. After the release of 34, the following circuit of the upper winding of relay 31 is completed: battery, upper winding of 31, R312, T36I, T383, R342 and earth. Relay 31 pullsrup. Through T31I, it completes its holding circuit on its lower winding. Through T312, it completes the following circuit for the energization of magnet Cmr: battery, electromagnet Cml, T312, T36I, T383, R342.

The magnet Cmi attracts its armature andV opens its contact which causes the release of 38 and, consequently, the opening at T383 of the circuit of magnet cm1 which releases its armature, thus causing the advance of the wipers of Coi by one step.

At R38 I, relay 38 short-circuits the lower winding of relay 31 which is thus rendered sufliciently slow not to release during the period of the reception of one train of impulses.

It will be noted that if a fresh interruption of current had caused the retraction of relayv 53 before the switch C01 has ended the advance by one step following the previous interruption, relay 34 would have been unable to energize before the release of 38, its holding circuit being opened at R38I. Under these conditions the wipers of C01 will advance one step for each impulse received at the incoming exchange. The wiper b causes the looping of the condenser preceding that eX- plored by the wiper D for the purpose of causing, should occasion arise, the discharge of the condensers which remain prematurely charged.

When the reception of the train of impulses is finished, relay 3l releases after a moment, and

7. relay 36 is shortcircuited by T53l,:relay'53 being held attracted bythe voice .frequency :current emitted by the outgoing exchange; f

The condenser connected to the bank contact on which the.` wiped d. of 1G01 vhas stopped, will be charged in Athe circuit: battery, resistance, rst armatureof the condenser Ce, for example, wiper d, T353, T32I, T315, windings in parallel f -39 and earth.

. During the reception of the'se'cond train of impulses, the same operations which have just been described are repeated, and the wipers of C01 are stopped 'on the second condenserwhich is charged, and also for the various impulse trains. Y We will now explainthe re-transmissionof the impulses to the equipment-of Fig. 7.

When relay 35 pulls up, `it completes the Yfollowing circuit Vof relay 42: battery, winding of 42, R4H, R392, T352, T321" Aand earth. After a moment, relay 42 completes -through 'TllZl the circuit of relay 4l whichpulls up after-a-moment. When the impulse contact Cei is opened by laV cam driven by motor M1 -the lower winding oi relay 43 removes the short-circuitand said relay is energized in the circuit: batterywindingsjin and earth.

Through R43! it-opens the short-circuit around its lower winding, and through TMI connects through 4carri Cel magnet Cms of switch 'C02 to the earth through: T4l2, Rll-L-Rllll, T352, T32 l and earth. Through T332, relay43 completes the following impulse circuit: battery,.resistance, 'cam Co2, RMZ, T432, T4! l, T322, wiper I' of C03, wire I, T250, T267, T213, wipervB-oiiCoebank contact, wire 52', T531, T635, windingfof 135 and earth.

It will be seen that Yevery time the impulse springs Cez are closed, relay is energized and at RSSI opens the loop Vto the automatic switch,- thus causing the routing-of -theautomatic switch in the well-known manner.

The cam which operates contact Cez is driven bythe same driving motor M1 as cam Ce1.`

WhenY relay 133 pulls up upon the closing o springs C'ei, magnet Cmgenergizes in the circuit previously traced. When vthe, contacts Cel are again opened the magnet Cmz-is cle-energized and the wipers of switch Co2 advance one-step.

By a suitable arrangement on the shaft of M1 of the cams operating springs Cei and Ceg, 'it is possible to -advance by one step the wipersjof Coz for each interruption .of Ces, that is to say, ior each pullingupof relayf-e, which thus lcauses an interruption in the circuit of the automatic switch. This constitutes the retransmission of an impulse. v 1

The wiperA ci Co2 willthus advance over the bank contacts to whichthe condensers Ci, C2 are connected. When the wiper arrives onV the previously charged condenser (C'e, for example), then Ythrough the wiper d, the condenser Ce, dis,- charged in relay 5, pulls up.

AtRlll, relay i5 opens -thecircuit lof magnet Cmz. .The switch Co2 is stopped in the corre,- sponding position. Moreover, at Rfii, relay 35 8 relay 4l, whichfalls back. VRelay `dl completes at R4H the circuit of relay 3!) inseries vwith relay 63. Relay 'dopenslat Ral the circuit of relays 43, '44 and 45, which fallback. As soon as -relay 44 falls back, the 4circuit of relay t2 `is again completed, whereby afresh series of impulses is re-transmitted by relay 35. y

It will be noted that when the re-transrnission of one Y'impulse train is finished, the beginning ofthe fre-transmission of the next train is con'- trolledJrby the holding of relay sil. In the examplev given, this relay holds I.until vrelay il ffalls back, earthbeing applied to theend of the winding of '65. However, the end of the winding of 65 might be grounded under the control ofthe automatic switch at any moment, so as to 'cause the re-transmission of-animpuls'e' train only when the operations following the 'previous one 'have actually beenl carried out in vsaid automatic switch. 'Should the wipers of the 'switch Co2 -for any reasonwhatevercome against the wipers of C01 (endfofdialling, for --eXample), that is vto say, if

they'should arrive at the same Vmoment on 'the bank contacts connected to the same condenser, then'the relay wie will be energized and remain energized in the circuit: battery, winding of 45, wiper a ofCo2, bank Ycontact of Coa'corresponding bank contact of C01, wiper d, T353, `T32l, R315, winding yof relay 39 and earth. The holding of relay drecauses the stopping of the transmissie of the impulses toirelay 65. Y

When the operator at the outgoing exchange iinishes dialling'the deslredsubscribers number, she disconnects her dial key CD (Fig. 1);, The

circuit of relay 'le (Fig. '2) is opened, and this relay falls back. The transmission vof the voice irequencycurrent over the Alinelwire's ends.

At the incoming Vexchange the elimination of the voice frequency current has the effect of causingthe -iinal release of relay 53 which opens the 'circuit of -relay 33. The relay 33 in falling back Adisconnects at T353 earth from theV test wire, the relay 39 having pulled up in series with 45. Relay 29"falls back, opening 'the circuit of 28 Vand 32, which -falls back. When relay 32 falls backfthe following circuit for the restoration of switchfCoi to normal, is completed: battery, magnet Cmi, sectors associated'with'wip-er'f and 4wiper removes-the short-circuit from V.therelaydll which pulls up in the circuit: battery, windings @i12-3,

pulse circuit of the relay 35. The re-transmission of theimpulse series to the automatic switch ends.

.At R341, relay @Il opens the circuit of vrelay ,-32

which vfalls back, opening atTZl thecircuitfof f, R322', contact'of magnet-cm1 and earth.

The switchfCOi returns `to 'its normal posi` tio-n O. A When 32 is released, the following return-to-A normal circuit oi theswitch Co2 is completed: battery, winding of Cm2, Contact .of CM2, sectors associated with wiper l), and wiper '1), R32I"and earth.

The register and the detection device associated therewith vare released.

When, 'at the outgoing exchange the operatorV has released the Vvdial keyCD, `the circuit of relay ii (Fig.V 2) is rel-eased. The ltalking circuit of the' relay l yto'be energized in'the circuit previously Y traced. Thelcircuit `o i the 'supervisory lamp ci Lais closed at T11 to a rotary switch-which causes',YYY

the .lamp to flicker.

Y' VAt the Vincoming;exchange, when the register is released, the Y circuit of relay 25 (FigfS) isopened. Thisrelay falls back Sand at T252 're'- moves earthl from wire-5l"A of the equipment of Fig '7.

.The talking-circuit'is completed over the wires q Lifand Laand the equipment of Fig. 3; and the conductors I and 52' ofthe equipment of'Fig. 7.

In the equipment of Fig. 7, when earthis removed from the wire 5I,'rel'ay 64 falls back.

If the line of the desired subscriber is free, relay 66 is energized through: earth, T634, lower winding of 61, winding of At6, and battery through the automatic switch.V The ringing tone is transmitted through TBGI and T662 on wires 5I and 52' and, consequently, to the operator of the outgoing exchange.

If the subscribers lineis busy, relay 66 is not energized, anda'busy tone is sent tothe operator of the outgoing exchange through R66I and R562.

When the desired subscriber removes his receiver, relay 61 is energized and at T61I, closes the circuit of relay 68 which is energized after a moment.

The talking circuit is completed in the equipment of Fig. 1 through: conductor 5|', R64I, T63I, condenser T68i, conductor 6I' of the automatic switch on the one hand, and on the other hand conductor 52', T631, R545, condenser, T684 and conductor 62 of the automatic switch.

Through T633. relay 68 applies battery to wire 54 through T636 and the following circuit of relay 24 is completed: earth. RI 8|, wiper d of the control in position II,T2I5,.winding of 24, R53, T262, T21I, wiper S, bank contact and battery on wire 54'.

At T24I, relay 24 completes the stepping circuit of the control switch through cam C3. When the cfntrol switch passes to position I2, and in positions I2 to 2l. the circuit of magnet Cm3 is completed through T2I3, wiper d. The control switch thus returns to normal position O.

During the passage of wiper d of the control switch from position I2 to I8, relay I1 is energized by T2l2. At TI12 and TI1I. it connects the generator Gei to the line conductors Li-Lz. A low frequency alternating current impulse is sent to the outgoing ex^hange. This impulse is received in the equipment of the outgoing exchange (Fig. 2) by relay I2,'which pulls up and at TI2I, completes the circuit of the lower winding of relay I4 which is energized. Relay I4 connects the line conductors at TI43 and TI4I to relay I5 which receives the end of the impulse. Relay I5, through TI5I and TI42, completes the circuit of relay I3 which pulls up after a moment.

The following circuit of the upper winding of relay IG is completed: battery, upper winding of I9, TIII, TI3I, TIM; TI5I and earth. The two windings of I6 are so arranged that their fluxes are opposed. When its upper winding is energized its lower winding already being energized, the relay I6 releases its armature. Relay II is maintained attracted on its upper winding through earth at TI I I and the circuit previously indicated.

At the end of the reception of the impulse, relay I5 falls'back causing the release of relay II. Relay IIJ, of which the flux should be reversed, falls back and remains down. At TI I2, relay II opens the circuit of relay 9 whichfalls back, opening at T92 the short-circuit of the upper winding of relay '5, which causes the release of relay I of the'cord. The lamp L2 stops flickering and the operator is thus advised that the desired subscribed has replied;v She can get in touch with the subscriber, warn him that a communication is about to be established and complete the connection to the calling .subscriber by the second plug of her cord in the usual way.

We will now explain how the release is elected l0' at `the^end `of` the conversation. We will rst assume that the operator of the outgoing eX- change is the rst to withdraw her plug.

When the control switch arrives in position O, the following circuit of relay 8 is completed: battery, winding of 8, T12, wiper g of control switch in position O,R52, RI5I and earth. Relay 8 in pulling up, opens at R84 the circuit of relay 1 which falls back. The starting circuit of thecontrol switch is completed through cam C1 through: R1I, T83, Wiper e in positionO, magnet Cm.

The control switch advances one 'step and passes to position I; the circuit of its magnetis then completed through cam C1 and RTI by wiper e ofthe control switch in positions I to I6, and wiper f in positions II to 2I.

The control switch will thus perform one complete rotation. During the passage of the wipers a, and e, in positions I to I0, the line conductors L1 and L2 are connectedito the low frequency generator Gel anda release impulse is sent to the incoming exchange. The profile ofthe cam C1 is such that the control switch will be much slower than when it is actuated by cam C2. The result is that the period `of the release impulse will be far greater than that of a supervisory'. impulse so as to insure the release, even if a supervisory impulse were being sentirom the incoming exchange to the outside exchange.

When the control switch leaves position O, relay 8 falls back. The control switch returns to normal position O, after having made one complete rotation.

At the incoming exchange, the release impulse is received on the'relay I8 (Fig. 3) which at TIBI, completes the circuit of the lower winding of I9 which pulls up. Relay I9 applies earth at TI93 to the upper winding of relay 22. The ux of this winding being opposed to theY uX of the lower winding, the armature of relay 22 falls back. At the end, of the reception of the release impulse, relays I9 and 2I fall back. Relay 2| opens at T2I2 the holding circuit of relay 2G which falls back causing the release of the equipment of Fig. 7, or of the callequipment (Fig'. 6) of the operator.

Should the desired subscriber be the first to hang up, or should the incoming operator withdraw her plug rst,.the battery on wiper S or on wire S', is replaced by earth. Relay 24 is energized in the circuit: battery, wiper c of the control switch in position O, T2I5, winding of 9, R253, T262 and either T21I and earth on wiper S,- or R21I and earth on wire S', Through TMI, relay 24 completes the circuit of magnet Cm3 of the control switch. The control switch advances to position I I, and during the passage of the wiper a. in the positions I to 1, the circuit of relay I1 is closed and the generator G'e1 is connected to the line conductors. A low frequency transmitting current impulse is sent to the outgoing exchange.

When the control switch leaves position O, the circuit of relay 26 is opened. This relay falls back and causes the release of the equipment of Fig. 7, or of Fig. 6,

In the outgoing exchange, the impulse is received by relay I2 (Fig. 2) and causes the pulling up of relays I2, I4, I5 and I3. Relay I2' is energized on its lower winding through RIII, TI3I, TI42, TI5I and earth.

A nal low frequency impulse is sent by the inal equipment of the cord pair through: generator Gei, RI I5, TIUZ, R58,A tip of the plug, spring of CA and its rest contact, spring d of CE and its rest contact, relay 2, spring I of CE and its 111 rest contact, spring of CA and its restv Contact, sleeve of the plug, R65, TEM, RI'IB and generator The relay 2 is energized and' through T21. completes the circuit of 3, which is energized'. The following. circuit of the end lamp L is completed: earth, T3I, RII, lamp L2 and battery. 'The lamp L2 is'lighted indicating to the operator that the communication is finished.

At the end of the reception of the impulse, relay II sticks and at R|I5v cuts oi thel current transmission from Gel to the final equipment of l the cord pair.

When the operator of the incoming exchange withdraws her plug, a low frequency current is sent to the incoming exchange and causes the release of relays 1 and 8. The control switch returns toA normal, as has previously been indicated.

We will now explain how the. operator at the outgoing exchange can call the operator at the incoming exchange.

The operator atv thev outgoing exchange-inserts the` plug of her cord pair (Fig. 1', in the equipment of' Fig. 2) The same operations which were previously indicated follow in order to eiect the transmission of a call impulse and the seizure at the incoming exchangeof a freevregister detector equipment, and the transmission ofthe various supervisory signals.

In this case, however, the operatordoes-not dial but merely lifts her dial key CD as` soon as the lamp LI is lighted. The transmission ofthe voice frequency current ends.

Thevoice frequency impulse isvreceived, as has been. explained, on relay 53k causing the holdingl of relay 36. At the end of the reception of the impulse, relay 53 fallsA back and' completes the above travel holdingv circuit of relay 34. which is energized. At T342, relay'34 completes the circuit of relay 38 whichpulls up, and at T382fcloses its holdingcircuit through T322', contact of magnet Cmi and earth..

Shortly after relay 341 has pulledl up, relay 36 being short-circuited atI T343, falls back. Earth is applied to wiper V of switch Cos through: earth, R342, T383, R361, RI', wiper V.

In the equipment of Fig. 3, earth on Wire V; through T254I short-circuits the upper winding of the relay 21', which falls back. Relays 25, 26, 21 andl 28v pull up in the samemanner as in the previous case.

When the relay 21 falls back, theline conductors Li-Lz' are disconnected fromA the switch Galand are connected through R210 and R214to the equipment of Fig. 6 ofthe operators incoming position.

Relay 26 remains attracted, but relay. 23, of which the circuit. is opened at T212, falls back, opening at T283 the circuit of. relay 25, which falls back and causes the release of the register.

The following4 circuit of relay 58 (Fig; 6) is completed: battery, winding ofl 58; R5'II, Wire C', T263, R212 andearth. Relay 58'is energizedandcompletes the circuit of the call lamp L2. Through T582 and T58l, relay 58 connects the inter-urban ringing tone generator to the line conductors and thus to the outgoing operator.

When the incoming operator plugs in, the cir-A cuit of relay 59 is completed; through the equip.- ment of the cord pair. Relay 5,8, at T5`92com pletes the circuit oiY relay 51l toearth onwire. C' and at R51I opens the circuitL of relay 58, whichv falls back.4 Battery is applied through` Tt: to

wire Sf causing the transmission through the equipment ofFg. 1 of a supervisory answerA back impulse. in the same manner as hasY been explained in the previous casefwhen batteryy had been applied to wiper 'S of C04.

The outgoing operator can now,y communicate with the incoming operator.

In the case in which, after the outgoing opera.- tors equipment has been put in connection with the incoming operator, the incoming operator by keying causes the transmission of a calling current on the conductors A and B. This current causes the pulling up of relay 54 which, at TMI, applies earth to wire D', energizing the middle winding of the relay I9 and causing it.y to pull up. The line conductors L1 and L2 are cut off at RI92 andRI 94, and the calling current is not sent to the equipment ofthe outgoing ex. change so as to prevent false operations.

At'the,y end of the conversation the release is eifected`as has previously been indicated. Ob. Viously, the aboveV operations have only been given by way of non-limiting examples. Any current'frequency may be employed for-the signalling or dialling to transform the alternating currents into direct current.l at any stage of the operations, withoutdeparting from the spirit of the present invention dened'in the claims.

What is claimed is:

1. In a telephone system, a plurality of .ex- Y changes, subscribers lines terminating at' said exchanges, operatorsv at the exchanges, trunks interconnecting said exchanges, automatic switches at some of said exchanges numerically operable to establish connections with lines, an impulse device at the calling exchange operators position, a source of voice frequency current at the calling exchange,` means controlled `by the impulse device for producingl interruptions in said voice frequency current in accordance with numericall designation of the called line, means responsive to said interruptions for controlling the automaticswitches at the called exchange to select the called'line, and means at the called exchange for measuring the length of said interruptions, and means for permitting an impulsev to become eiTective only if the length of the interruption produced by the impulse device does changes, operators positions at each exchange, automatic switches at some of said exchanges.

adapted to be numerically operated to select a line, means at the calling exchange for estab-l lishinga rst connection from an operator over one of, said trunks towards an operator at the called exchange, and means for establishing aA second connection from an operator at the calling exchange over one of said trunks towards the automatic'switchesat the called exchange.

4..Ihe telephone system according to claim 3, switching means at the called exchange for connecting a predetermined operator with the first connection, andmeansoperable upon the establishmenty of the first connection for sending a predetermined signal; from the calling exchange for operating said switching means.

5. The telephone system according to claim 3,; andan impulse device at the operators position voice frequency current at the calling exchange,

means controlled by the impulse device for producing interruptions in said voice frequency current in accordance with the numerical designation of the called line to control over the second connection the operation of said automatic switches at the called exchange, and means for 15 2,141,372

producing a momentary emission of current from said source upon the establishment of the rst connection for operating said switching means. FERNAND P. GOHOREL.

REFERENCES CITED The following references are of record in the file of Ithis patent:

UNITED STATES PATENTS Number Name Date 2,155,176 Wicks Apr. 18, 1939 1,820,682 Stevens Aug. 25, 1931 1,613,246 ONeill Jan. 4, 1927 Baumfalk Dec. 27, 1938