US2376352A - Telephone or like system - Google Patents

Description

y 2, 1945. c. GILLINGS ETAL 2,37 ,352

TELEPHONE OR LIKE SYSTEM FiledMay 51, 1943 8 Sheets-Sheet l Facy 1 .INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE' ATTORNEY TELEPHONE OR LIKE SYSTEM Filed May 31, 1945 8 Sheets-Sheet 2 IN VE N TO R5 CHARLES GILLINGS CHARLES EDMUND BEALE ATTORNEY y 4 c. GlLLlNGS ET AL 2,376,352

TELEPHONE OR LIKE SYSTEM Filed May 31, 1943 8 Sheets-Sheet 3 I I C1 c'na l anb1 cncl c'nd1 CNB CNc CND I 2' lfus CNC r cnbz :r-cna cnbs C1103 I g Fif 3' INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE wag ATTORNEY May 22, 1945.

c. GILLINGS ET AL 2,376,352 TELEPHONE OR LIKE SYSTEM Filed Ma 31, 1943 8 Sheets-Sheet 4 INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE %Zai4.

AT TORN EY May 22, 1945. c. GILLINGS ET L 6,

TELEPHONE OR LIKE SYSTEM Filed .May 31, 1943 8 Sheets-Sheet 5 YE Fyz Y INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE ATTORNEY May 22, 1945.

C. GILLINGS ET AL TELEPHONE OR LIKE SYSTEM Filed May 31, 1945 8 Sheets-Sheet 6 f NI;

,INVENTORS CHARLES GILLINGS C HARLES EDMUND BEALE ATTORNEY y z, 1945. c. GILLINGS ET AL 2,376,352

TELEPHONE OR LIKE SYSTEM Filed May 31, 1943 8 Sheets-Sheet 7 INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE ATTOR NEY y 1945- c. GILLINGS ET AL 2,37 ,3

TELEPHONE OR LIKE SYSTEM Filed May 51, 1 9415 8 Sheets-Sheet 8 /L $52 "a ccz cbs Q 2 HI.

1 560cm 12 4 sec of? i t2 cca 9Y I40 ms 01'] seems off i 13 INVENTORS CHARLES GILLI NGS CHARLES EDMUND BEALE ATTO Patented May 22, 1945 UNITED STATES PATENT OFFICE TELEPHONE on LIKE SYSTEM Gharles Gillings and Charles Edmund Beale,

Liverpool, England, assignors, by mesne assignments, to Automatic Electric Laboratories, Inc., a corporation of Delaware Application May 31, 1943, Serial No; 489,136

In Great Britain July 28, 1942 a 11 Claims. '(01. 179-48) The present invention relates to telephone or like signalling systems and is more particularly applicable to the setting and control of automatic telephone switching apparatus over long lines, which may include speech transmission ther mionic repeaters, by means of voice frequency the chief object of the invention to provide a.

system in which this problem, at least as far as the voice frequency signalling line is concerned,

is avoided. p

According to one feature of the invention, in

a telephone system suitable for long distance i automatic working and employing signals of a plurality of voice frequencies for effecting the selective setting of automatic switches over a trunk line, a variable length train of impulses received from a calling party by equipment at the outgoing end of the trunk line istransmitted over the trunk line in the formof a single pulse of substantially constant length comprising one or more voice frequencies the nature of which varies in accordance with the number of impulses in the train.

According to another feature of the invention, in a telephone system suitable for long distance automatic working and employing signals of a plurality of voice. frequencies for effecting the selective setting of automatic switches .over a trunk line, a pulse comprising a plurality of frequencies is transmitted prior to the selective pulses to prepare the equipment for response thereto.

A further feature of the invention is that in a telephone system suitable for long distance automatic working and employing signals of a plurality of voice frequencies for effecting the selective setting of automatic switches over a trunk line, each train of impulses received from a calling party by equipment at the outgoing end of the trunk line is transmitted over the trunk.

line in the form of a code of substantially constant length regardless of the number of impulses in the train and arrangementsare provided for varying the interval between codes representing successive impulse trains dependent on the number of impulses in the preceding train.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings, comprising Figs. 1-8.

Figs. 1-4 when arranged in the manner indicated in Fig. 3a. show the circuits of an outgoingmanual-to-automatic relay set which connects over a V. F. signalling line with a distant incoming relay set, the circuits of which are shown in Figs. 5-8 which should be arranged in the manner shown in Fig. 7a. The local outgoing anddistantincoming relay sets together provide for V. F."signalling and coded impulsing from an outgoing trunk line operators position of the sleeve controlled type as already employed for on demand trunk service.

Before the detailed circuit operations are dealt a with, the method of working will be described generally. When the operator plugs into the jack of a free outgoing line equipment, her call ing supervisory lamp flickers and a 100 millisecondim. s.) X voice frequency pulse is sent forward to the distant incoming end to seize the associated selector. The operator-now operates the dialling key whereupon the lamp is extinguished and she then dials the required subscribers number which is received and stored on uni-selectors at the outgoing end. Each train of impulses received is re-transmitted over the line.

in coded digit form involving up to three of four voice frequencies, hereafter referred to as W, X, Y, and Z,-and each coded digittransmitted is preceded by a preparatory signal comprising all four frequencies W-Z, which is effective at the distant exchange to prepare the voice frequency receiver thereat to receive the coded digit which follows. i

At thedistant end each received coded digit 3 has to be converted back to a train of direct ourrent loop impulses to actuate the switching apparatus thereat, and the receiving equipment is so arranged that after a preparatory signal comprising all fourfrequencies together has been received, the digit code following and consisting of not more than three frequencies W-Z will operate a W, X, Y, Z relay contact pyramid by means of which the code information can be decoded and converted into a marking on a uniselector for controlling the sending out of a corresponding train of loop impulses.

The second coded digitis transmitted after an interval sufficient to meet the numerical setting and hunting requirements of the selector and at the terminating end of the line it is decoded as before. Similar remarks apply to the succeeding digits, and when all have been received at the distant end, and when the switching equipment thereat has been set to connect with the required subscriber, the calling operator will'receive ringing tone, busy tone, or number unassigned tone to denote the state of the called line. In the mean time, on completing the dialling of the required digits, the operator will have restored the dialling key, and will thus have caused her supervisory lamp to glow. When the called subscriber answers, a Y tone of 200 In. s. length will be sent back to the originating end to extinguish the supervisory lamp and to establish conversational conditions thereat. i

Conversation now takes place, and when'the calling subscriber clears, 140 m. s. length pulses of Y tone at spacings of 360 m.- s. are returned from the incoming 'end to the. originating .end 1 and cause the operators supervisory lamp to glow. When the operator clears by removing the plug from the outgoing jack, a X tone of 1%2-2 seconds length is sent forward to the incoming end, followed by a Y tone of 300m. s. length and the distant equipment is thereupon restored to normal.

Among special arrangements provided according to the present invention to secure efficient operation is the adjustment of the length of the pause between coded digits transmitted over the line. in accordance with the. setting up and hunting time required by the distant. selector switches. Inthe illustrated embodiment, itis arranged that for thedigits 1-5 a predetermined pause is providedwhich will cover the setting up and hunting requirements of digit 5 where the maximum time is involved, and that for the digits 64} this Paus is, increased to cover the requirements of the greatestv digit 0. By providing pauses between transmitted coded digits which will cover the setting up and hunting requirements of the distant switches in turn, it is possible to avoid providing storage facilities for more than one digit H at the incoming end of the line as the same storage relays can be repeatedly used for each digit in. turn, while the adjustable pause arrangement ensures, that this form of digit transmission shall not be unduly extravagant in time.

Considering the operation in detail, when the outgoing operator plugs her cord circuit calling plug into thejack OGJ associated with the outgoing relay set shown in Figs. 1-4, if the cord circuit speaking key is thrown, battery via the cord circuitcalling supervisory lamp controlling relay in the operators position circuit will be extended over the sleeve of theplug and jack to operate relay M by way of its left-hand low resistance winding, whereupon at contacts ml it brings up relay MM and at contacts 1122, Fig. 4, it steps switch TS from its home position to position 1. Relay MM in operating, at its contacts mmZ, connects a flicker earth source via lead ill to the left-hand low resistance winding of relay 2 lar function at this time but relay FXY at contacts fryl, Fig. 1, connects X frequency to one winding of transformer TI, the return path being completed over lead RTN. The Xfrequency is thereupon applied to the outgoing trunk line conductors l4 and i5, whereupon at the voice frequency receiver VFR2, Fig. 5, associated with the distant incoming relay set, an X frequency responding relay or its equivalent is operated and at contacts 83:! brings up its relief relay XR. Rela XR in operating, at contacts m3, Fig. '7, brings up relay K, which thereupon at contacts lcl locks independently of relay XR, at contacts k2 prepares a circuit for relay AR in readiness for the termination of the X frequency and at contacts 706, Fig. 8, brings up relay PY which how- I ever has no function at this stage.

At the outgoing end relay FXY at contacts fry 3, Fig. 4, completes a self-driving circuit for switch TS to advance its wipers to position 3, whereupon the circuit of relay FXY is opened at wiper and bank TSi, Fig. 2, an d this relaycommences to release slo-wly. Relay on re.- leas ing, at contacts Jmyi, Fig. 1, terminates the sending out of the X frequency, the period of application of which will have been of the order of 100 m. s. as determined by two steps of the switch TS at 20 m. s. per step plus the m. s. release lag of relay FXY. Relay FXY also at contacts fan/l reconnects a suitable V. F. line termination via resistance YD and at contacts fxyZ, Fig. 2, brings up relay FC. which thereupon looks over its contacts fcl to earth via bank and wiper T82. Rela F0 also at contacts'fc2, Fig. 4, advancesthe TS switch to position 4 from which it is t pped. to position 6 over bank and 'wiperfIfSS from an interrupted earth source connected to lead II and delivering 140. m.s.'on, 366 m. s. off, the stepping time therefore being one second.

At the distant incoming end where relay XR has been held operated in response to the X fre-. quency and where relays K'and PY areal-so op erated, the cessation of the X frequency results in the release of relay XR, whereupon at contacts M3, Fig. '7, earth is extended forward over operated contacts k2 to bring up relay AR. Relay AR in operating, at contacts arl, Fig. 6. extends a seizing earth via the winding of relay IR and one winding of the repeating coil RPCZ over'. the

negative wire to the A relay of the selector switch associated with the incoming relay set. The selector A relay and relay IR operate in series and the former prepares the selector for receiving direct current loop impulses from the incoming relay set, while the latter at contacts irl, Fig. '7, [brings up relayv NN and at contacts irZ, Fig. 8, holds relay PY independently of relay K. Relay N has mainly a preparatory function at this stagebut contacts not, Fig. 6, provide a shunt path round contacts art of rela AR. f

No further circuit operations occur at either end of the, trunk line until the operator'throws her position dialling key, whereupon battery is extended forward from the position over the cord tip and ring conductors and a high resistance is introduced into the sleeve circuit to extinguish the calling supervisory lamp. The battery over the tip conductor brings up relay RR. Fig. l. and this relay in operating, at contacts m l brings up relay AM, whereupon at contacts aml, Fig. 4, earthis extended to operaterelay B, Fig. 2. Relay B in, operating, at contacts, b2 and b3,

' 1, connects relay AM to thetip and ring conductors so, that this relay now holds over its upper winding independently of relayjRR,

the circuit of whichis disconnected at contacts b4 so that it releases after a short interval. At contacts b the flicker earth circuit isfopened cuit but owing to the high resistance whichhas been includedin this circuit in response to the operation of the dialling key, relay'KRwill not operate though relay M remains held.

and relay KR is introduced into the sleeve cir- The operator now dials the first digitof the required number; and when the dial is moved off-normal, the battery connection to the tip and ring conductors at the operators position is removedand these conductors are now; looped together. over the dial impulsing springs so that 3 relay AM is nowheld energised over both its windings in series. On the first interruptionof the impulsing circuit, relay AM in releasing-at contacts aml, Fig.4, extends earth over contacts .bl and low resistance winding of relay C, wiper and bank DDZ of the digit distributor switch DD to the magnet DSAM of digit switch DSA, while on the subsequent re-operationof relay A the magnet is de-energised to advance its wipers to position 1. If the digit 5 is dialled, the DSA switch wipers will be advanced to position.5. RelaysB andC hold operated during the train and contactsicz en'ergise the magnet DDM out, the leads representing these frequencieswill of.1th.e .digitdistributor switch DD during this time. On the release of relay C at the end of the train, magnet DDM is dc-energised and advances the DD switch wipers to position 1, while at contacts cl Fig. 3, earth iseXtended via'corltacts anal and wiper DSA2 in position 5 to operate relays .CNA and CNR in series. Relay CNA in operating,-at .lts contacts cna l locks itself over wiper and bankDSAZ independently of the contacts cl, at contacts cnaZ prepares a"fur DSB, DSC (not shown) and to digit switch s1),

reception of digits onthese switches bringing up the associated relays CNB, CNC and CND, Fig. 3. Immediately the first dialled impulse train has been completely received as indicated by the operation'of relay CNR, sending out ofthe corresponding V. F. coded digit over trunk line l4, l5 isinitiated. Onthe operation of relayCNR,

contacts cnrl step. switch SC oif-normal, where-.

upon it operates relay ST by way of both its windings in series with magnet SCM which cannot. operate in this circuit. Relay ST thereupon at contacts stl short-circuits its left-hand high resistance winding, whereupon magnet SC-M is operated and switch SC self-drives to position 4 where the holding: circuit for relay ST is opened and this relay commences to release. 'During the operated. time of relay ST, contacts st2-st5,

1, apply all four. frequencies W-Z to the trunlr line by way of transformer TI to provide the preparatory signal which precedes the transmission of each: codeddigit, while contacts st6, Fig. 2, disable the V. F. receiver VFRI associated with the outgoing relay set. on the release of relay ST, contacts .stl, Fig. 3, operate relay. S'oyer both its windings and bank and a 3 wiper SC'lin series'with'magnetSCM'and when relay S operates and at its contacts sl] shortcircuits its left-hand high resistance winding,

SWitCh SC will commence'to self-drive to position 9', Relay ST in releasing disconnects the four-frequency signalling circuit and relay S in operating, at contactss4, Fig. 1, connects up to line a frequency combination in accordance with the digit dialled as controlled by the DSA switch banks DSA3-DSA6 which connect up with contacts 34 over operated contacts cna4 and resting contacts 273. i

The proposedlV. F. digit code is as. follows:

Code Digit one 1 -Inresponse to the dialling-ofdigit 5.17118 DSA switch wipers will have been set to position 5, andinorder that in this instance a coded digit comprising frequencies W and Z may be sent be wired up to contacts ,5 on banks .DSA3 and DSA6,the contacts 5 on banks BSA-4 and DSA5 beinglleft unwired. On the operation of relay S following the release of ,relay ST, the four prepare frequencies W-Z will therefore be replaced by the two frequencies W and Z.

Thesending out of thetwo frequencies W and Z continues until the switch SC reaches position 9 where the circuit of relay S is opened. In this position during the slow release of relay S, relay ZR operates over its lower high resistance wind ing in series with magnet SCM whichis inopera tive owing to the high resistance of relay ZR.

Relay ZR thereupon at contacts zrl completes a homing circuit for the digit switch DSA y ia its upper low resistance winding, contacts cnal5 and wiper and bank DSAl, at contacts 272 completes a locking circuit for relays CNA and CNR in series and relay CNR will also. release if no further digits have yet been dialled. I

If bythis time the operator has completed the dialling of the second digit, which willbe assumed to be 8, relay CNB will have been operated inseries with relay CNR and consequently with relay CNR still held, switch SC on reaching its home position will commence another cycle of opera tion. Relay ST is again operated and functions in the same manner as before to send the prepare pulse and is followed by relay S to sendout the code corresponding to digit 8 which is The SC switch on advancingto contact 9 ter- "minates the sending out of the W, X and Y frequencies corresponding to digit 8 by. operating relay ZR which proceeds to home the DSB switch, the homing circuit extending in this case via the upper low resistance winding of relay ZR,.resting contacts cnafi and operated contacts cnb5 and bank and wiper DSBI. This is followed by the homing of switch SC, whereupon the equipment position 9.

will be ready to send out the next received impulse train-in coded vform.

The interdigital pause is "partly determinedby the bathing time of the digit switch controlling the coded digit which has just been sent out, the time concerned being the homing time from the position to which this switch has been set by diallingplus the homing time of switch S from This arrangement provides a suitable interdigital pause for-digits up to 5. In the case of digits 6-0 this time would be slightly less and in fact a longer time is required to cover the correct functioning of the switches at the distant end. This is taken care of by arranging to operate a relay EP, Fig. 3, when relay S operates to initiate the sending out of a coded digit of a value from 6-0. For instance when relay S operates to initiate the sending out of the frequencies W, X and Y corresponding to the second dialled digit 8, on the operation of relay S, (3011-. tacts s3 complete a circuit to operate relay EP from earthed operated contacts cnb'l, wiper D832 of the first digit 5, or the reduction 'tO-f'PEQIZEHe cies W, X and Y in the case of the second digit 8, the short-circuit will be removedfifrom relay CB which now operates. Relay CE in operating, at

- its contacts 0124 and cbl, .Fig. 5, completes holdon contact 8, operated contacts cnb3, normal I contacts cnall, operated contacts s3 to battery via the winding of relay EP. In this instance relay CNB will have'been operated byway of its right handwinding, the .left hand winding only being used for digits up to 5. Relay EP in operating, at its contacts epl locks itself independently of relay S and at its contacts e123 ,(not shown, but assumed to be located in Fig. 4 and connecting the home contact of bank DSBI with the other contacts) preparesfor the provision of an extra pause after the second digit 8 concerned, the other contacts ep2, ep' l and ep5 serving simifllarly'ior providing an extra pause if required,

after the first, third and fourth digits respectivelypy y When switch DSB restores to its home position after the sending out of the coded digit 8, since relay EP is operatedat this time the switch Wipers are again advanced to position 1 from which the switch continues to rotate through another full cycle. 'During this time'relay ZR will be maintained operated and will maintain relays CNB and CNR from earth over contacts 2T2, cnaZ, cn-b-Zleft-hand winding of relay CNB to battery via relay'CNR. .While switch D83 is stepping to position 6, the holding circuit for relay EP will be opened. at bank and wiper D832 and this relay will release during this time so that when switch DSB'reaches position 6 relay EP will be unable to re-operatej Hence when the switch DSB reaches the home position on the additional cycle, since relay EP will now be nor mal, there will be no circuit to step it on from its homeposition and relay ZR will therefore release. 7 Relay ZR in releasing homes the SC 'switchand releases relay CNB. ,The SC switch on reaching its home position waits until the next digit has been received, or, as before described, continues another cycle if this .has already been received,

- Considering now the reception of the coded V. F. digitsat the incoming end, the WXYZ .prepare signal which precedes each digit operates all four relays Wit-ZR, Fig. 5, contacts of which bring up relay CA, Fig. 6. It. will be remembered that at this incoming end relays K, PY, AR, IR andNN are operated as a result of the seizure of the trunk line. On the operation of relay XR, relay AR, Fig. V7, is released but without eflect, while on the operation of relay CA, contacts cal,

prepare an operating circuit for relay CB ing circuits for relays WR. and ZR which are-op erated in response to thecoded digit frequencies W and Z where digit 5 is involved, so that on the cessation of these frequencies, relays WR' an'd ZR will remain held. Other contacts of these re-' lays which are, not shown are arranged "in' a known pyramid formation so as to setup aIsuitable marking over the fifth otthe ten leads 14), Fig. 8, to contact 6 of the bank SS2 0f the sender switch SSso as to control the sending out ofa number of direct current loop impulses correspondingto the V. F. coded digit 5 concerned.

Relay CB also at contacts 0225, Fig. 7, brings up relays Pand C. Relay C in operating, at contacts cl bringsup relays CC and GY and at contacts c2 and 03, Fig. 6,-releases relay IR and loops the outgoing negative and positive leads via the impulse sending circuit which involves the motor a driven loop impulsing contact springs IMPI;

to! connects these springs to magnet SSM. 0h

at present short-circuited by Wiper SS! in its home position. Relay P in operating looks over its contacts pl and at .its contacts p5, Fig. 8, operates relay CK, contacts old and 0703, Fig. '5,

of which serve to'terminate the trunk line 'via resistance YE whi1e loop impulses are subse-' quently' transmitted from the incoming relay set. Relay GY has no direct function at this stage but relay CO in operating; 'at'its conta'cts'cc'l, Fig. 8, connects earth to the motor driven mag net impulse springs IM'PZ.

The impulse springs IMPI and IMP2a're' operated ten times per second,"the former being closedfor 33 of. the period of each impulse and the latter being closed for the remaining 66% of the period. If on the operation of relay CO the impulse springs IMPZ are open, or if not, when they next open',,relay IG operates and at contacts the next closure of the springs IIMPZ, magnet SSM is energised and on the next opening, magnet SSM is de-energised and advances the SS wipers to position 1. At this point the loop impulse springs IMPI are closed, so that when springs IMPZ again close to re-energise 'magnet SSM, springs IMPI in'opening produce tion of the first output impulse. On the next opening of springs IMPZ, the SS switch wipers are advanced to position 2 while springs-IMPI nowclose to terminate the break portion of the first output impulse. During the stepping fromposition 2 to position 3 the second impulse is sent out and so on until five impulses have been sent out corresponding to, the received V. F.'coded digit. Wiper SS2 on reaching position 6 at this time will encounter an earth marking which will be con-- nected thereto over} contacts'of relays WR and ZR. within the known pyramid arrangement. Re

lay SZ thereupon operates and looks over its contacts sel, while at contacts s22 it short-circuits the loop impulse springs IMPI to prevent furvther impulses being sent out'to the first selector, and at contacts s23 it releases relays CB and CA. In response to the train of five loop impulses, the first selector is stepped up to level fi and then-proceeds to perform an automatic rotary the break porhuntingioperation to find a succeeding selector infltheselected group. Relay GB in releasing, at contacts c114 and cbl releases relays WR and ZR, atcontacts cbBre-operates relayAR over contacts ca.2 and yr3 and opens the circuit of relayC, andat contacts cbfi it releases relay 1G whereupon-the SS switch self-drives to its home position relay SZ remaining locked to bank and wiper SS3 during this time. When switch SS3 reachesiitshome position, relay SZ releases and re-preparestacircuit for relay CB. .011 the re. lease of relay after its slow period, relay CC, is released and relay GY commences to release slowly an d the repeating coil RPC2 is re con nected to the outgoing negative and positive leacls so that relay IR re-operates. Relay CK, Fig. 8, is connected upfoverlead 12 to an interrupted earthsourcewhich gives one second pulses at four second intervals and therefore slowly, pulses but without e'fiect" at this stage except under specialtonditions when busy tone is returned from "the selector as described later. With relays PY, NN, P, AR and IR held and with relay CK pulsing, the incoming end is now ready ta receive a further set of frequencies corresponding to the next dialled digit 8, which will be transmitted from the outgoing end after the pulseformtb set up the selector trainto the required subscriber.

I At the outgoing end, where relays M, CO',

FC, AM and Bar held operated, the operator after, dialling the required digits will restore her diallingkey, whereupon a comparatively low resistance battery potential is momentarily applied whereitis further slowly interruptedby contacts cm and 0763 though withoutany particular purpose in thisinstance. The tone then extends back tothe outgoing relay set where it finds a circuit to the outgoing operator'via transformer Tl, the singleway orso-called stopper valve SV and repeating coil RPCL Theprimary function of valve. SV, is l to prevent transmission from a the cord circuit to the trunkfl line so as to prevent noise or'the like at the outgoing end switching the linefecho. suppressors against the passage of tonesand signals from the distant incoming end. At the incoming end, during the transmission of ringing tone, relays K, AR, PY, NN, IR and P continue to be held operated, while relay CK continues'to beslowly pulsedL j 1 When the called subscriber answers, the line battery feed to the calling side of the final se:

lector circuit is reversed and the battery applied to the positive lineoperatesrelay I, while'relay IR releases. Relay Lin operating, at contacts il,

Iiigflf, releasesrelay K and this relay' atcontacts k3 bringswup' relayGX,lwhile at contacts k6, Fig. 8, th'ejcircuit of relay PY is opened. During the release time of relay PY relay FY is broughtji ip over' contacts 272 kt and p213 and, at contacts {31] steadilyYenergises relay CK which up to now has been pulsing. Relay PY'in releasing opens the circuits or relays FY and 0 and during thereleas'e time of these two relays a200 m. s. Y frequency subscriber answerf signal is sentfback to theoutgoing end to dim the op'erators calling supervisory lamp and tocomplete the conversa at the operator's position circuit to the sleeve of the calling plug and this battery extendsover jackOGJ to bring up relay KR. Relay KR thereupon at contacts l crz prepares for called party supervision, at contacts krl removes the battery feed for relay AM which remains held on its upper winding to battery applied to the tip and ring conductors in the position circuit and at contacts Fort provides a local locking circuit for relay KR After the momentary application ofresistance battery to the sleeve circuit, the high resistance originally introduced into this circuit on operation of the dialling key is short-circuited, while ashortinterval later the battery applied to the tip and ring'condu'ctors in the position circuit is removed and, relay AM releases. On the reticnalconditions thereat.

,'At the outgoing end relays M, MM, KR, CO and PC are held operated at this time and "the TS switch isin positiont. On receipt of the Y frequency, this extendsover transformer T2 into theV.1F. receiver VFRI and brings up a Y relay or its equivalentcontacts'yl of which bring up relay RS. Relay BS in operating, at contacts rsl prepares a circuit for relay R D, and at can. tacts r82 operates relaySA which thereupon at contacts sal brings up relay, CT and at contacts sa2locks via bank and wiperjTS2. Relay CT in operating, at contacts ctZ, Fig. 1, applies battery via resistance, YC to the ring, conductor for through supervision purposes in cases wherethe outgoing operators position. is serving in an in:

terme'diate capacity between a calling and ,a

. called exchange, at contacts ct3 disconnects the sultant release of relay B after its slow period,

contacts I connect earth over contacts ctZi, Icri, b5 and mmZ, and the left-hand low resistan ce winding of relay M to the sleeve circuit so asfag'ainto bring about the lighting r the calling supervisory lamp. This condition persists until the called; subscriber answers.

Meanwhile, the 'selector train at the distant exchange will have connected with the required subscriber and if he is free, the final selector will return the interrupted ringing tone back over the speaking conductors to the incoming relay 'set,

earth appliedtothe sleeve circuitso asto enmguish the calling supervisory lamp, and at con? tacts cit and 0155 establishes through conversational conditions at the outgoing end. At the conclusion of the Y frequency pulse, relay RS commences to release slowly and during this time relay RD operates and maintains relay CIHover contacts 1111' and ctl. when relay "Rs releas s, relay RD slowly releases in' turn, relay CT now remaining held to earth via contactssal and bank andWipe'rTSLQ f H Conversation nowproceeds between the calling and' called parties, relays AR, NN, I, P, and GK being held operated-at the incoming end. At its conclusion'the called party. on hanging up brings about restoration tolunormal of the line feeding battery potentialat the final selector, whereupon relay IR again operates and relayI releases, results in the transmission of a clearing signal comprising llO m. s. pulses of Y frequency at spacings of 360 in. s. back to the outgoing endto eifect the lighting of the outgoing operatorslsu pervisory 8 ml Relay I in releasing, atlcontacts iZ liig; 8, brings-up relay OK and this relay at contacts clcl connects up a 14.0 m. s. on, 360' m. s. ofl' earth source over lead B to relay FY, whereupon at contacts i1 2, Fig. 5, 140 m. s. pulses of Y frequency are returned over the trunk line con- At the outgoing end where relaysM, MM, CO, FC, KR, SA and CT are held operated, the first Y pulse brings up relay RS and the first off period brings up relay RD during the slow release period of relay RS and relayDR maintains relay CT. When'the next Y pulse arrives, relay RD will not yetihave released due to the combined release times of this relay and relay RS being longer than the 360m. s. off period so that the holding circuit for relay CT which has been previously maintained overcontacts rd l,'ct|,' 3 1, $156 andsS to earth is nowopened at contacts y! and relay CT now releases; Relay RS operates on this and" subsequent Y frequency pulses and relay RD remain steadily operated since it is energisedduring the release time of relay Rs duringeach interval and remains hel'd due to itsslug during each impulse. n the release of relay" CT, the conversational condition atthe outgoingend is broken down at contacts @154 and ct5 and at contacts ct3 earth is extended forward over the sleeve circuit to give the clearing'signal to the operator by lighting the-calling supervisory lamp.

Thereason for arranging the'circuit to require two pulses to give the required control is to prevent simulation of the clearing signal by speech.

On receipt of the clearing signal, the operator will withdraw her calling plug from jack OGJ' and relay M thereupon releases, whereupon relay MM commences to release slowly; The otherrelays SA, CO, F'C' remain held to bank and wiper TSZ, relay CO, on the release of relay MM; main taining an engaged test battery via resistance YB on the sleeve ofj'ack OGJ. Relay MM also releases relay KR. Relay M at contacts mZFi'g. 4; causes the TS switch to advance'to position 7 from which earth over contacts sa4 "causes'it to self-drive to position where its'driving circuit is opened at bank TS4. During thistime relay B, Fig; 2, is operated over bank. and, wiper TSI. when switch TS reaches contact I5, it proceeds to advance onward" to position 19 under control of a 140' ms. on, 360' m; s, olfinterrupted' earth supply connected to lead I'l whichextends to magnet TSM viabank and' wiper TS3. When position I9 is reached; relay B has its circuit opened and commences to release slowly, while relay FXY is now operatedlj' This operation of relays B- and in turn serves to send forward a clear down? signal comprising, a 1% second pulse of X frequencyfoll'owed bya 300 m. 's."pul'se of Y frequency, 'It will be seen from Fig. 1 that relay B in operating, at contacts b6 extends X frequency over contacts mm l; st2', fxyl and resistance YD to the winding] of transformer Tl from whence-it extends to line. This, circuit is maintained until relay FXY operates and opens the)! frequency circuit at contacts ,frtyl, the time being determined by the stepping of switch TS from position I to position 19. On' the operation of relay FXY, contacts ,fwy'l connect Y- frequency toline. On the release of relay B after its, 'slow period, a self-interrupted driving circuit is completed for switch TS at'contacts b8 and the switch thereupon advances itswipers to position '20., The circuit for relay FXY is now broken .atba'nk. and wiper TS-l andafterthe slow" release period of I this relay; the transmission of the Y frequency to-line-'is terminatedi Itmay be mentioned-here that the X frequency pulse will have-forced the line echo suppressors to change round infavour of forward sen'dingfrom the'out'going end, so that during this time relays Rs and-RD will have re-;

' position 24, it will remain there until both relays- RS and RD restore when contacts rs4 and rd! will allow the switch to step on to its home-position. In this position-relays- SA, FC and CO which have been held operated from wiper and bank T82 are released and the outgoing relay set is ready to deal with further calls.

At the incoming end, theposition is thatrelays AR, NN', P; IR, or: and (so; are held operated while relay FY is pulsing; .On receipt of the X frequency which will occur during the silent period of the Y' clearing signal being sent fromthe' incoming end, relay XR- operates and at its contacts m3, Fig. '7, operates-relay GY which disconnects the pulsing circuit of relay FY and so terminates the sendingoftheY pulses, while at the same contacts the circuit of relay GX is opened so that it commences to release slowly. On the release of relayGXrel'ay CC is operated and the equipment now awaits the Y frequency from the outgoing end; On'receipt of this frequency, relay YR in operating, at contacts 3 1'3 brings uprelay CR. This relay atcontacts er: operates relay 0 and at contacts crl locks itself and disconnects relay NN which commences to release slowly. Relay C -in operating releases relays IR and AR; so that when relay NN releases, the forward holding loop to the selector train is opened and this train. now restores to normal. Relay NN- inrel'easing alsoreleases relays P, CC, GY and C and on therelease of relays P and CC, relay CR releases. frequency,v relay YR releases and the incoming equipment is ready-for further use.

c The primary function of'rela-ys GK and" GY at the incoming end is to prevent false operation due to components of speech simulating the X and Y signalling frequencies and the arrangements are such that afalse X frequency followed by a false Y frequency will be ineffective unless the false X frequency is of at least 300* milli' seconds duration. It will be appreciated that the possibility of a false X frequency of at least 300 milli seconds immediatelyfollowed by a false Y frequency is extremely remote. During conversa tion the operation of the supervisory relay I'will have restored relay K tonormal so that if a component of speech during this time simulates the X frequency, relay GX will start to release slowly owing to the operation of relayXR). Only if the component is sufiiciently long, i. e., above 300 milli-seconds duration, will relay GX be released and relay CC operated, andthe connection will only be releasedif a; false'Y signal follows immediately so asto operate relay CR.

Assuming now that the outgoing operator clears in face of number unassigned tone or if the called subscriber fails to :answer, in "order to be sure of clearing, down the distant incoming equipment particularlyin face of number unassigned tone which may be, applied continuously for 4 seconds, it is arranged that the X frequency of the clear down signal is lengthened to a p'eriod of, the order of 6 seconds, thisfrequencyfbeing followed by the usual300 m. s. .Yffrequency,'v

Onthe withdrawal of the plug, relays On the terminationof the relay GX releases, relay CC operates.

and KRrelease as before. Relay M in releasing causes the TS switch to advance to position 7, but in this instancesince relay SA has not been operated owing to non-receipt of a subscriber answer signal, the switch TS will not new selfdrive to position .15 as before, but insteadwill advance step by step from the. interrupted earth supply on lead H to this position from which it will again advance under control of the same earth supply to position 19 as before. i From position 19 theswitch moveson .to its home position as already described. During the stepping from position '7 to position 19rel'ay B is operated to send out X frequency as before, but. in this instance the increased stepping time of switch TS gives approximately a fi-second period of transmission of X frequency. The 3007111. s. Y frequency then follows in themanner already described.

At the incoming end relays K, AR, NN, PY,

P and IR will be in operated condition and relay CK will be being slowly pulsed. The reception of the X frequency results in the operation of relays XR, C, CC and CY in turn. Relay C in operating causes the steady operation of relay CK, releases relay; IR and transfers the selector holding loop to wiper and bank SSI. The receipt of the Y frequency brings up relays YR and CR, whereupon relays K, NN, CK, C,,CC, PY, P and CR are released and the loop to theselector train is broken. At the. termination of the Y frequency, relay YR releases and the incoming equipment isrestored to normal.

In case busy tone is returned from the final selector, or a preceding selector, the circuit operations at the outgoing end are the same as described for the number unassigned or ringing tone, but at the incoming end beforereception of the clearing signal, relay I will beimpulsed from the busy flash battery applied atthe selector in addition to the relays held as already mentioned. The first full operation of relay I re leases relay K which cannot re-operate and relay K in releasing operates relay GK and opens the slow pulsing circuit for relay CK so that this relay now remains normal. The busy tone now extends through without further interruption from the final selector to the operator, the interruption at the incoming relay set being unnecessary with busy tone as the echo suppressors can readily restore during the silent periods.

When the operator subsequently withdraws her plug, the G-second X, 300 m. s. Y frequency clear down signal is now sent forward asdescribed.

At the incoming end relay XR responds to the X frequency and brings in relay GY, while when In response to the Y frequency relay YR brings up relayCR which operates relay C and also releases relay NN which disconnects the circuits of relays C, CC, CR, P and GY. The operation of relay C releases relays IR and AR and relays AR and ,NN initiate the release of the selector train so that on the release of relay YR at the end of the Y frequency, the equipment will be 7 quired to select an outgoing V. F. trunk to a further exchange, when the tandem selector Cil change.

five battery applied tolthe test lead P will be returned to the tandem incoming relay set to provide a through .path from the incoming relay setto the selected tandem outgoing relayset in 1 order to allow the subsequent coded digits to extend. straight throughto the terminating ex- Referring now to Fig. 6,if after the transmission ofthe appropriate number of trains of loop impulsesa positive battery is applied to the testylead P at the tandem outgoing relay set taken into use, relay DCO operates. and. at its contacts dcol cuts off any further circuit for relay CB and at the, same contacts completes a locking circuit for itself. At this time relays K, PY, AR, NN, IR, and P will be operatedand relay CK will be pulsing, whilerelays CA, 2GB and C will be normal. ates, at contactsdcoa it opens the circuitof :relay K, and on release v ofthis relay contacts k3 connectup relay GK and ,contactslc5 release relay CK. Thereupon atcontactsckZ and'ck3 the incoming trunk conductors. and 15 are extended" through via repeating coil RPCZ and the tandem selector train to the tandem outgoing relay set taken in use. Hence received codedV. F. signalsv corresponding'tothe subsequent digits dialled will extend straight through to the-tandemoutgoing equipment without having been operative at the incoming equipment since as relay .03. cannot be operated, the digits are not stored and no eircuit is completed for stepping, the switch SS. The coded V. F. signals accordingly extend through the tandem outgoing equipment and, out

incoming V. F. trunk as described. above, however, no conversion will be necessary asthe digitalinformation will already be in V. F. coded form, To enable the tandemoutgoingrelay set to meet these two requirements a suitable discriminative method ofseizureis utilised, seizure in the former case where conversion is required being. characterised by a direct current loop train has been set up, an outgoing DC/VFrelay across both legs of the incoming line, while seiz ure in. the latter case where conversion is not required will be characterised by a balanced earth connection on to both legs of, the line via the relays I and IR in thentandem incoming relay set concerned.

In the system just desc ranged to precede each coded V. F; digit by a preparatory signal comprising all the signalling A frequencies ,in combination. One function of this is to ensure that the line echo suppressor is switched inthe, right direction in readiness for the following coded digit and so to prevent clipping thereof, andanother function is'to exercise the incoming voice frequency signal receiven. An advantage of this arrangement is that unless all the frequency responsive relays in the incoming voice frequency receiver function correctly, it will be impossible to send out trains of impulses and hence the sending out of incorrect digits due to partially stored frequency codes is prevented. Further-more if on seizure of a selector by the When relay ,DCQ oper 9 "bed it has been ar incoming equipment; transients of the order of the dialing frequencies. are encountered, these might. be stored by the incoming voice frequency receiver and sent outin corresponding impulse forms With the illustrated arrangements however, this trouble is avoided since the incoming equipment is not properly responsive unttlsafter a prepare signal has been received. Though it ispossible to avoid trouble due .to signal clipping by the echo suppressor by making each coded d'igit or su-fficien't duration as to be substantially.

unaffected thereby, the other troubles which arise when the prepare signal is not utilised would still'obtain and the arrangement described therefore adds appreciably to the reliability of the system;

What we claim as new and desire to secure by Letters Patent is l 1. Ina telephone system, a trunk line, aresponsive device, means in the trunk line responsive to different length series of impulses received from-a calling party for transmitting over the frequencies in said single impulse varying in accordance with the number of impulses in said re? ceived series.

3. In atelephone system, a trunk line, a plu- 1 tion of the switches. v

rality of "automatic switches accessible thereto,

means associated with the trunk line for transmitting' an impulse of currentthereover compris ing a plurality of voice frequencies before each switch is. operated and means for thentransmitting another impulse comprising a lesser number of said voice frequencies'to the switches to operate the same, the number of voice frequenciesi in theseco'ndf impulse varying in accordance with the, operations required in each of said automatic switches.

4. In. a telephone system, automatic switches, "a register, means for transmitting series of impulses" to said register to variably operate the the time interval between transmitted impulses representing received seriesof impulses, depend: ent on the number of impulses in thepreced ing series. v

'Z. In a telephone system, a trunk line, auto matic switches, means for simultaneously transmitting a plurality of voice frequencies to said automatic switches to. extend a connection over said trunk line and means for transmitting a supervisory signal back over thev trunk line after the connection is extended comprising a single one of the voice frequencies used in the opera- 8'. In a telephone system, a trunk line, an automatic switch, a plurality of sources of-"alter nating current of difierent frequencies, means of connecting one of said sources to said trunk line to seize said switch, means for simultaneously connecting all of said sources to the trunk line to prepare the switch for operation, and means for simultaneously connecting particular combinations of said sources to the trunk line" to selectively operate the switch to extend a connection. 9. In a signal system, two control offices having an interconnecting line, a plurality of sources of signalling current each source having different electrical characteristics than the other sources, devices in one of saidoflicessaid devices respon sive to a plurality of received signals for transmi tting said signals over the line by meansof' a signal of substantially constant length'including a'code impulse of current from all ofsaid sources, a receiving device at the other office responsive to said code, and means controlled by said receiving device to translate the code to signals corresponding tosaid receivedsignals;

1-0'. In a telephone system, a trunk line connecting two exchanges, a plurality of frequencies of alternating current, aplurality of automatic switches successively controlled by received'impulses to select a plurality of particular combinations of said frequencies, means for successively controllingeach of the switches connected tosaid particular frequencies to individually apply to said line a signal including a code pulse of the selected frequencies, the interval between the same, means in the register, for simultaneously transmitting a, plurality of voice frequencies to operatethe switches, each plurality of'voice frequencies simultaneously transmitted varying in composition in accordance with the number of impulses in the series registered.

'5. In a telephone system as set forth'in claim 4 in which there is means in the registerior delaying, the time of transmission of" the voice frequencies corresponding to a series of impulses for a time period. varying in accordance :with the number of impulses in the series registered.

6. In a telephone. system, a register, means in the register responsive to a plurality of received series of impulses for transmitting an impulse of substantially constant length foreach series received', regardless of the number of impulses in the series, and means in. the register for varying connection of each of the successive signals con trolled by the switch that applied the'precedi-ng code, a device responsive to said code signals; other automatic switches, and means controlled by said-responsive device to operate said other switches by pulses corresponding to the received impulses used to operate each of said first automatic switches to select the connected frequen cies.

11. In a telephone system, a toll line terminating on a device responsive to particular voice frequencies for controlling switches from received digital information, means for transmitting over said line particular digital information as a voice frequency signal of constant length comprising a preliminary portion of said voice frequencies to prepare the device on said: line for the. digital portion comprising a lesser number of said frequencies for operating the switches.

CHARLES GILLINGS. I I CHARLES EDMUND BEALE,

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