US2350652A - Electrical signaling system - Google Patents

Description

June 6 1944, R. TAYLOR ETAL 2,350,652.

ELECTRICAL 6 IGNALING' SYSTEM Fil ed June 13, 21.942 3v Shasta-Shawn 1 INVENTORS .VREGINALD TAYLOR GEORGE THOMASBAKER ATTORNEY 'June 6, 1944. I R. TAYLOR ETAL 2,350,652

ELECTRICAL S IGNALITNG SYSTEM Filed June 15, 1942 3 Sheets-Sheet 2 a, PP m H I TM www

'- I 5 INVEIATORSL REGINALD TAYLOR GEORGETHOMAS BAKER ATTORNEY June 6, 1944.

R. TAYLOR ETAL ELECTRICAL SIGNALING SYSTEM Filed June 1:, 1942 3 Sheets-Sheet 3 INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER ATTORNEY Patented June 6, 1944 UNITED STATE s PATENT OFFICE ELECTRICAL SIGNAIJNG 'sYsrEM Reginald Taylor and George Thomas Baker, Liverpool, England, assignors, by mesne :assignments, to Automatic Electric Laboratories, Inc.,. Chicago, 111., a corporationof Delaware Application June 13, 1942, Serial No. 446,900 f In Great Britain August 9; 1941 1 26 Claims. (01. 179-16).

Such a method of impulsing The present invention relates to electrical signaling systems such as automatic telephone systems in which impulses are utilised to effect the positioningof selective apparatus an like operations, and it is more particularly concerned with arrangements for responding to control impulses whereby greater reliability may be obtained when signaling over lines of poor characteristics.

When impulses are transmitted over long nonrepeatered lines as are'sometimes'encountered in.

telephone systems, the received signals tend to be both highly attenuated and distorted so that impulses which when generated have make and break ratios within predetermined limits du to distortion cannot when received ensure reliable operation of the selectors in the'distant exchange. Distortion may be due tothe capacity eflect of a long line, to low insulation resistance, to impedances connected across the line or to combina- V tions of these, the general effect being to cause the impulses to depart considerably from a rectangularform. A further distortion is introduced due to the sluggishness of response of receiving equipment. 1

One of the objects of the present invention is.v

dial switches which is considered permissible, it will be clear that there is a serious restriction on the length of lines which can be used for direct dialling if the ratio of make to break periods of the contacts of the impulse responding relay are to be maintained within the prescribed limits for. i

successful operation of the selectors.

An arrangement has been proposed in our application Serial No. 434,762 filed March 14, 1942, whereby the operation of selector switches need no longer be dependent upon the usual make to break ratios but rather upon th period which elapses between the corresponding parts of successive pulses so that the only limit is the actual speed of impulsing which must not be so slow that the period between similar parts of successive pulses exceeds a predetermined amount. such period is exceeded, aswitchin'g operation is arranged to take place characteristic of the end "of a series or of a release of a connection accord- When ing to thefinal condition of the control circuit.

is sometimes referred to asspeed timing. a 1- It is a further object of the invention to guard against false operation by parasitic currents.

Such parasitic currents which it is desirable to "guard'against are either low voltage currents which may persist or higher voltage currents which have a very short duration or frequency character.

The invention is characterized in that'the reare of a high -ceiving equipment for responding to the signals -or impulses is not operative in accordance with the actual value of the signaling or impulsing currents but in accordance with the change or changes which take place when a signal or impulse is transmitted, e. g. when one condition of 'current flow changes or when one condition of current flow changes and restores. When the invention is applied to alternating currents which maybe of the power frequency or voice frequency type or even of the carrier type it is necessary to providemeans to respond to the actual rise and fall of the envelope of the signal currents as distinct from the actual values of the current. In

direct current signaling arrangements it is the rise and fall of the actual value of the currents which controls the impulse responding equipment.

[The 'rise and fall of the envelope of alternating.

currents can be readily determined byrectificasoI ' According to one feature of tion as is welleknown.

the .invention an impulsing circuit in which the impulses consist of 5 3 respond to either the fall or rise of the current 1 during impulsing so that when the interval after breaks in a direct current circuit is characterised by the provision of impulse responsive means, in-

cluding a timing device, which are adapted to a decrease or rise of the"current in the direct current circuit without a further decrease or rise taking place exceeds a predetermined time 'a con- 'trol operation is eflected." Preferably a transformer is employed which causes unidirectional I impulses to be derived on the fall and'rise of the current, unidirectional impulses of one direction s only being arranged'to start the timing device and restart it with each succeeding-impulse.

.According to a further -feature of the invention direct-current impulse-responsiv equipment is .provided includinga gas discharge tube in which no which is subsequently completed independently of the remainder of the impulse.

the change at the beginning of each impulse as received is arranged to initiate a control opera- A ccording to a further featureof the invention impulse responsive equipment is provided in which the" change at the end of each impulse as received is arranged to initiate a control operation which is subsequently completed independently of the beginning of a succeeding impulse.

According to a further feature of the invention which is particularly useful in connection with supervision over lines of poor transmission characteristics twojgas discharge tubes are provided, one responsive to a change of signaling current to prepare the second tube for operation, which second tube can only operate when the sig-' naling. current changes in the oppositedirection.

According to a further feature oi the invention unidirectional impulses in opposite directions are derived due to the rise andfall in 'the value of the signaling currents respectively' which 'impulses are applied to the grid of a gas discharge tube arranged so that impulses in .one'selected direction only can afiect a signal-responsive device in the anode circuit.

At the present time telephone exchanges are usually provided with equipment which'willonly respond to impulses having amake to break ratio within predetermined limits which can hardly be obtained over lines having poor transmission characteristics and another of the'objects of the invention is to enable impulses to be transmitted over a line having poor characteristics and arranging that such impulses should operate the selectors reliably.

According therefore to another feature of the invention trains of impulses are transmitted over a line or cablefor the purpose of controlling impulse responding equipment in response to changes in one sense only of currents flowing over said lines, translating equipment being providedto cause impulses tobe transmitted numerioally equal to those received, but modified so as to be of a character suitable for the operation 'of the impulse responding equipment. This can conveniently be effected by an impulse regenerator of the electro-mechanical type. r

A further object of the'invention concerns the prevention of false operation by parasitic currents. Where a line is subject to parasitic currents it is obvious that if the parasiticcurrents are of the same nature or more powerful than the signals to be transmittedlover the line, the line will not be capable of being used reliably. However parasitic currents are usually of .a different nature and therefore it is possible to make good use ofaline even although the parasiti currents maybe quiteconsiderable,

According-therefore to -a further feature-of the invention the change in the value of the signaling currents is adapted to cause the generation of a. uni-directional impulse. the signal-responsive means being adapted to respond only to such a unidirectional impulse if in'a'. certain direction and having a strength: combined with duration nloying a biassin'g battery for a grid-controlled as discharge tube and bi'jemploying fora transsuitable for use in the provision of on demand pulses persist sufficiently long to charge the condenser to the desired voltage.

The invention will be better understood from the following description of a portion of a telephone system showing the invention applied both to impulsing and supervisory circuits, reference being bad to the accompanying drawings, comprising Figs.'1-3. Of these, Fig. l'shows the circuits of an outgoing direct current loop dialling relay set at a sleeve-controlled operators position trunk: telephone service and assumed to be located at an exchange X. Fig. 2 shows the circuits of an incoming direct current dialling relay set at an automatic exchange Y which relay set is assumed to terminate a long junction line ex- Jtendin'g between the two exchanges X and Y.

Fig. 3 shows an improved circuitfor preventing falsesignaling by parasitic currents.

exchan'geY. It is assumed however that the length of junction line between the two exchanges X and Y greatly exceeds the hitherto accepted maximum limit for direct current junction working and this form of working is rendered possible by the improved arrangement according to' the invention.

It willbe seen that the supervisory signal and impulse signal receiving arrangements at the respective"exchanges X and Y incorporate hotcathode' three -e'lectrode gas discharge tubes which are transformer-coupled to line in such manner that they are triggered into operation by a voltage surge characteristic of the incremental or decremental wave form of the particular signal they are to receive. They thereupon efiect the operation of v the relevant responding relay in a local circuit which i's'independent-of the length ofthe signaling line and moreover by virtue of the lock-in characteristic of the gas discharge tubes, the relays can be -maintained operated independently of the received signal until the required operation has i been effected.

Inorder to permit the use of only a single gas 1; discharge tube per impulse responding device, the

incoming relay set in the arrangement illustrated is provided with what may be termed a speedi timing impulsing circuit which operates in asso- I ciation with an electro mechanical impulse storage-and regenerative device.

The regenerator,

; which is assumed to be of the type disclosed in former-an ordinary telephone relay which is not responsive efficientlytofthe high frequency currents orto impulses of .veryj short duration or referably in addition or alternatively to the ineificient transformer a condenser-charging areither by impulses of high voltage if the duration is short, or by lower voltage impulses if theimfunctions of the slow-to-release B and C relays 1 usually provided in association with an impulse specification No. 2,188,461, McClew and Woodland, is adapted to receive signals from the gas discharge tube anode relay characteristic of the [impulse trains received over the junction line, and in response thereto is adapted to re-transmit,

to automatic selector switches of normal stepby-step type, loop impulses correct 'as regards make and break ratio and speed. The speed timing circuitis'of the type disclosed in our previously mentioned application No. 434,762 and it does away with the separate time measuring receiving relay A. It comprises a single time measuring circuit including a condenser,- a repare the total length of the :make plus break period of each impulse .of'a received-'train with a predetermined period substantially equal to the total length of each impulse at'the slowest impulsing speed tolerated in practice. 'This circuit is set into operation at the beginning-of the first impulse of a train and is restored tonornia-l by each successive impulse of a train until'the last pulse is received, after which it-functions either to initiate release of the connection or to mark mechanically on the regenerator the value of the particular digit which has been received, according to the conditions obtaining at the time. These arrangements will be better appreciated from the following description of the circuit operations which occur when an operator at exchange X sets up a connection to'a subscriber connected to the automatic exchange'Y;

To do this she will insert the calling plug of the cord circuit in use into jack J whereupon, assuming that the appropriate cord circuit speaking key has been thrown, battery will be extended from the position circuit over the sleevesof the plug and jack to operate relay SR by 'way of its lower winding. This relay on operating at contacts srl brings up relay SS which at-contacts ssl extends a resistance battery potential back over lead K and the IDF strapping connection to operate the supervisory lamp relay SLR and hence to light a busy lamp associated with the outgoing relay set taken into use. 1 Relay SS also at contacts ss extends a loop over common leads I I and I2 to start up the flicker earth generation equipment and at ss2 connects flicker earth over common lead l0 back to the operator's cord circuit via the low resistance lower winding of relay SR so as to flash a lamp at the operators position to indicate that the relay set is ready to'receive dialled impulses. At cs4 relay SS completes a circuit for the series connected filaments of three-electrode gas discharge tubes GDTI and GUI! in readiness for their subsequent use when supervisory signals are transmitted back from'the distant incoming relay set.

The operator now throwsher position dial key This relay at contacts WI" it by the earthed winding of relay MR which to the fact that the operation of-the dial-key in the position circuit has introduced a-high resistance into the sleeve circuitz relay SR however remains operated under these conditions. Relay DT also at contacts (H3 and di l disconnects the operating circuit for relay RR and provides a through connection from the jack tin and ring conductors to the outgoingside of the circuit. whereupon the loop in the osition circuit is extended forward to operate the sensitive linecurrent feeding relay A in the incoming relay set at exchange Y. This relay on operatin brings up relay B which completes a circuit f r the filament of the tube GDT3. completes a looking circuit for itself, prepares a loop impulsin circuit at contacts 173 to the incoming selector switch associated with the incoming relay set in question, and at M applies a guarding and holding earth to the P conductor of this selectorl j The first digit of the'required number at exchange Y'is now dialled and when the operators dial is moved off normal, the impulsesprings' of the dialare looped across the tip and ring con-' ductors' and the original seizing impedance is short-circuited; hence on the release ofmedial,

ercise the function of a relay in enabling the tube filamentcircuit to be under the control of the calling party so as to avoid the necessity for continuous operation thereof. It does not necessarily release during impulsing although as shown it will operate and release over the line circuit, that is to say the break period of an impulse may not be sufiicient to enable it to release.

In'response to the first break impulse delivered by the operator's dial, the line current falls and as a result a voltage surge is induced in the middle winding of relay A in such a direction as to reduce the normal negative bias on the grid of tube GD'I'3 with respect to the filament. The tube is thereupon triggered into operation and brings up the anode relay P. The characteristic of the tube is such that when once it ionises, the

"grid loses control and the tube is subsequently 'extingu ish'able only by opening the anode or charging circuit via resistance YP' for the condenser QF of the so-called speed timing arrangement. Relay C at contacts 0 completes a local locking circuit for itself, at 03 energises the regenerator marking magnet MM, the function of which will be described later,'and at .04 prepares a charging circuit for the speed timing condenser QF viaresistance YQ to positive battery, which circuit becomes effective on the release of relay P after the satisfactory operation of magnet RM. Owing to the inherent lock in feature of the tube GDT3, relay P will remain operated until magnet RM has fully energised. no matter how short is the duration of the voltage surge produced by the break'impulse, and when magnet RM has fully operated, its interrupter contacts rm open to 'e'xtingui'sh the tube and release relay P. g

The regenerator may be described as comprising essentially a receiving arm and a sending arm which are arranged on opposite sides of "a plate carrying a circular row of pins. The re"- end of each train of received impulses and which thereupon pushes 'a pin corresponding to the digit dialled through the pin plate into the path of the sending arm. For each digit received a corresponding pin is pushed through the plate and these pins serve to determine the movement of the sending arm which controls the generation of outgoing pulses by means of the regenerator imnulsing springs IMP.

Returning again to the operation of the magnet -R-M, relay P on releasin de-ener ises this ma net, whereupon the receiving arm is advanced to its normal value and in response thereto. a

further voltage surge is induced in the middle winding of relay A. In this instance however since the current is rising, the induced voltage will be such as to bias the grid of the tube GDT3 more negatively and so it will not strike at this time. Relay P therefore remains inoperative until the commencement of the second break impulse when the tube GDT3 again strikes and re-operates relay P to advance the receiving disc a further step. 1 i

Considering the speed timing arrangements, the values or the condenser QF and resistance YQ are such that if the charging circuit is undisturbed for a period of the order of 120 milliseconds, condenser QF will be charged to the striking voltage of the neon tube NT and this tube will flash and energise relay H which initiates the sending out of the digit stored in the regenerator in a manner to be described. This period of 120 milli-seconds added to the RM magnet operating time and the P relay release time, gives a total period of the order of 143 milli-seconds which is representative of .a complete impulse from a dial of standard ratio which is running at the slowest allowable speed of seven impulses per second.

' Assuming that the digit dialled is 2 or more. the second negative'bias surge will occur before condenser QF' is able to charge up to the striking voltage of neon tube NT and hence when relay P re-operates on this surge, a rapid discharge circuit will again be completed for condenser QF via contacts p2 and resistance YP so as to restore this condenser to normal. Magnet RM is energised a second time and condenser QF' commences to charge again when theoperation of this magnet releases relayP and the cycle of operations described is repeated until the last impulse of the trainis received.

Approximately 140 milli-seconds after the com- .mencement of the break period of the last'impulse of the train, the voltage on condenser QF rises to the striking value of neon tube NT, whereupon the tube flashes and brings up relay H. Ihis relay thereupon at contacts'hl releases relay C and at 712 renders the operation of relay B dependenton the continued operation of relay -A from the calling operators position. Relay C on releasing; at contacts cl completes an operating circuit for relay BY'which locks and at- 03 opens the circuit for. the marking magnet MM,

while at 04 it disconnects any further charging circuit for condenser QF; The marking magnet MM in'restoring causes the lever carried by the receiver arm to push a pin corresponding to the digit dialled into the path of the sending arm. Relay BY at contacts by! and M2 connects the regeneratorimpulsing springs IMP across the negative and positive conductors outgoing to the selector switch,whereupon the impulsing relay therein is operated and prepares the switch -for receiving the train of impulses corresponding to the stored digit. A circuit is also completed at contacts by4 for relay -IP which is slow to operate and release and at b 5 for relay IS which is quick to operate and slow to release.

Relay IS operates first but without eiiect and when relay IP operates, it opens the circuit of relay IS at contacts ipl so that when the latter releases, an energising circuit is completed for the regenerator transmitting magnet TM.

It will be understood that by the operation of magnet TM the pin in the regenerator which was displaced to mark the termination of the last train of impulses involved in the previous call is pushed out of the path of the sending arm and back to its normal position by a resetting pin designated RP connected in circuit .with relay IP, but, owing to the stepped head on the reset pin as indicated diagrammatically in the drawings, the sending arm is not immediately released but remains held until magnet TM is de-energised. Magnet TM at its contacts tm disconnects relay IP which on releasing after its slow period opens the magnet energising circuit and as fully described specification No. 2,188,461 previously mentioned, the sending arm is released and rotates until the reset pin comes up against the stop pin which has been set to indicate the termination of the first train of pulses received thereon. During this rotation of the sending arm the springs IMP are intermittently operated to generate standard impulses at the rate of one for each pin passed over by the sending arm.

It will be noticed that since the-reset pin RF is not connecting with any stop pin such'as SP during the movement of the sending arm, relay IP cannot be re-operated, and the impulses generated by the impulsing springs IMP are delivered to the group selector over the outgoing negative and positive conductors. Relay IS is re-operated during this time and serves subsequently for the purpose of timing the interdigital pause.

Previous to, and during this time, further trains of dialled impulses may be received and effect setting of the receiving arm and it will be appreciated that the two operations of reception and transmission may go on simultaneously but independently of each other.

When the sending arm comes up against the stop pin indicating the termination of the firstv received digit, relay IPis again operated and relay IS is disconnected. After the release time of relay IS which determines the interdigital pause, and assuming that at least one further digit has by this time been stored on the regenerator, the sending magnet TM againreceives a momentary energisation in order to release the sending arm once more to generate a second train of impulses in the manner described.

When all the digits received have been retransmitted, the sending arm will catch up with the receiving arm whereupon the off-normal contacts NL open and release relay BY. Relay BY thereupon at contacts byl and M12 re-completes the through connection by way of condensers QD and QF from the incoming to the outgoing. sides of the relay set. Relay IS will have been held operated during the sending out of the last digit of the transmitted trainin the usual manner and during its. slow-to-release period it maintains a holding path via contacts is2, impulse springs IMP and resistance YK .acrossthe outgoing leads to minimise the effect on the distant final selector impulse receiving relay of the introduction of the supervisory relay 2D, polarised by virtue of the dry plate rectifiers MBA and MRB, and retard 21 across the outgoing lines in place of the initial short-circuit path via the springs IMP.

The operator on concluding the dialling of the required number will restore her position dial key to the normal position, whereupon the resistanoe introduced into the sleeve circuit by the operation of this key will be short-circuited and the resultant increased current flow over this circuit will enable relay MR in the outgoing relay set to operate. This relayopens the holding circuit for relay DT at conta-cts mrl and at mrZ completes a local locking circuit for itself, and relay DT on releasing at contacts dt3 and 11254 're-inserts the transmission condensers QA and QB'.in the speech transmission line and ex tends a 'full'earth back via contacts d3, mr3', dtZ and ss2 the low resistance Winding of relay SR and thesleeve circuit to light the cord circuit calling supervisory lamp to indicate to the operator that a reply is being awaited from the distant called subscriber. Relay MR also at mrB connects the tubes GUI! and GDTZ across the line by way of the transformer TR and at mrli connects the supervisory relay D to the anode circuit of tube GDTZ.

If the called subscriber is busy, the operator will receive busy tone from the distant final selector and will act accordingly. If he is'free, however, and answers the call, when he replies relay 2D in the incoming relay set is operated in the usual manner by battery reversal from the final selector, whereupon the battery feed over the incoming junction is reversed jat contacts 2d! and'ZdZ. As a result a voltage surge is induced in thesecondary winding of thetransformer-TR at the outgoing relay set and this will be of such polarity that the normal-=negative bias on the grid of tube GDT2 will be reduced-an'd this tube thereupon triggers into operation and brings up relay D. The tube continues to conduct after the termination of thesurge until such time as the anode or cathode circuit is broken and relay D is therefore maintained operated during this time. Thi relay on operating, at contacts dl connects-relay RR to the anode circuit of the other tube in readiness for a subsequent supervisory. signal, and at d2 ex .tends a battery line feed to the jack side ofthe circuit via the windings of retard I, whileat d3 the full earth-connection is removedfrom thesleeve circuit so as torextinguish the lamp on the calling side of the operator's cord cir- .cuit to indicate that the called party has answeredr V The operator now releases her cord circuit speaking key to dissociate this circuit from her position and to cause a through'connection to .b provided therein between the two sides 'of the circuit. The calling and called parties are now connected to one another and conversation" may take place. At the end of the conversation, when the sub scribers 'replace their receivers, the hanging'up of the calling subscriber will be communicated tothe operators cord circuit in the usual manner, while When the called subscriber hangs up, the battery feed to line at exchange Y is-restored to normal by the restoration ofrelay 2D.- The 'resultantvoltage surge produced in transformer TRby battery reversal over the-line causes tube GDTI to trigger and bring :up relay RR which atrri releases relayD. RelayD there, upon by replacing the-earth onthe sleeve circuitv at.d3 re-lights the operators cord circuit calling supervisory lamp and thegoperator on seeing both the answering and calling lamps glowing onfthe cord circuit concerned will withdraw theplugs 'l I The withdrawal of. the calling plug from the jack-'J releases relay, SRfwhich'in turn releases relays SS and 'lVLR whereupon the loop extended forward to exchange 2 via transformer TR is opened; and the filament'circuits of tubes GDTI and GDilarejopened to release the'locked-in relay RR, The opening off'the loop t'o exchange Yreleases relay Afin the' di tant incoming relay serene] thej'release of th s. relay renders the continued holding of relay B-dependent 'on the equal sed normal' conditionfof relay The ial'lfin the, current flowin the windings of relay A however, simulates thecommencemnt of a break impulse andt'ube GDT3 therefore comes into operation" and brings'up relay P. Relay P on operating functions as for a singlebreak impulse and the speed timing circuitis brought into operation. After the lapse of l40 milli-seconds, relay His operated to release relay B and also relay C which will have been operated on the operation. of relay P and the regenerator will send'out the equivalent or astored digit I into an open circuit after which the incoming relay set will be ready for further use. Relay B, on releasing opens the 1001) forward to the incoming selector switch and, so brings about release of the automatic equipment taken into use.

Substantial immunity from false operation by transient signals ofl'a parasitic nature will be effected by virtue of the standing'negative bias on the gas discharge, tube control grid, which bias will be made such that the maximu'm expected value of parasitic surge voltage will not be sufiicient to cause the tube to strike',as well as by the in'etli'ciency of the relay as a translorm'er at high'l'requencies, This voltage discrimination arrangement presupposes that the voltage kick resultingfrom the beginning or end of a signal wave, accordingto which'is being utilised, shall'always be suflicient to reduce the standing negative'potential to a value such that the tube Will strike, that is to say ,;that the kick shall" be greater, tharila transient surge voltage. Inniany cases the line conditions will be such that the front and! termination [of a received signal wave will not be. steep, so that the induced kick in the transformer secondary winding will not be great. Whereas -an"'idea'l rectangular wave-form pulse 'may give a momentary induced kick of say 10 volts,'the]actualwave-form due to distortion maygive a .kick the'secondary winding vof theorderjjoi' say 12 yolts which while being much less infvalu'e lwill", persist during the comparatively slow 'Tiseor fall'in the signaling current, that is tosayforjexample' for a period of lomilli-seconds instead of one milli-seoond orless with. the rectangular wave-form. The voltage due .ftoa tran'sierit parasiticsignal of rectangular wave-form must .be less than the voltage represented by a signal also .oirectangular wave-form, bu't'it may 'be' greater "than the voltage derived froman actual distorted wave as it is likely tobe either .of a'momentary nature or fluctuatingoralterna'ting in value. False operation under these conditions can be avoided by employing the -time-volta'gi'ei "discrimination arrangement for instance as shown inFig. 3;

Referring to this figure, it Willbe seen that a condenser QG is vintroduced,intothe gridbiassing circuit in such'mannerthat any change in the, grid voltageisdependent on the build-up of a charge .onth'e' condenser. It will be under-.

stoodthatthe standing" negative voltage on the grid of tube GDT3andthe values of resistance YJ and condenser QG are such that-the striking voltage will not be built up on condenser QG unless the induced voltage is sufiiciently large to build'upthe voltage in the condenser before it falls' away; 'This' can be effected by amomentary pulse if'the voltageis sufliciently great orfby a prolongedjpulse of "less voltage provided thatthe voltage isgreater than the voltage required to strike the tube andpersists long enough to enablethevoltage' across the condenser to reach the strikingvolt'aga'" Surges generally if momentary will givea"vol tage less than that required to strike-the tube and if they persist will either fluctuate or alternate in value so that the voltage across the-condenser" cannot build up to the striking voltage. V

he voltage from'a distorted signal, which may have a maximum value less than the surge voltage 'willhowever' be able to cause-"the tube to strike, since its persistence for up tosay 10 milli-seconds will allow the condenser QG t'ocharge up to the requisite striking value; Inth'e ideal case where a rectangular pulse is received, then although the kick'will be momentary its value will be'greater and it will persist longer than the usual'surge voltages. i

The arrangements'proposed according to the invention will it is believed be'found to give more reliable'impulsing over lines in poor condition than is possible with the usual impulsing methods and allowing for the greater sensitivity will be as'immune if not more immune to outside disturbances.

Alternatively to the arrangements described above two gas discharge tubes might be used, one responding'to decremental wave fronts'and the other to incremental wave fronts, and since both parts of an impulse will now be detected as against-one part only with the speed timingarrangements described, 'the more well-known types of impulse receiving circuits such as those using B and'C relays can be employed. As a fur ther alternative it is possible that use might be made of a single gas discharge tube which would respond to either "an": incremental or decremental wave front, and which might be combined with any of the well-known impulse correction dee vices. Inthis-case the'lock-in nature of the gas discharge tube would play an important part in theimpulse correcting device along the lines already outlinedin the foregoing description.

It is not essentialthat a regenerator be'provided at the incoming relay set, asshown, if the automatic; s'elector'train is equipped with speed timing impuls'ing arrangements, since the sig-' nals could inthi's" instance be delivered direct from the relay P to the various selectors involved. It may also be desirable for the triggering of the gas discharge tube in "theincomihg'rel'ay set to take place on the incremental surge at the termination of each impulse break period instead of on thedecremental surge as described.

The grid con'trolled gas discharge tubes as proposed to be used in this invention may be of such types as themercury vapour; argon and neon tubes; The preferable type as so far tested is the mercury'vapo'ur;

What we claim as new and desire'to secure by Letters Patent is: j

'1; Ina signaling system, a transformer having two windings, a source 'of current connected to one of said windings 'to cause current to flow over said winding in 'a certain direction, means for at times reversing the direction of said flow of cur rent and at other times restoring said flow of current to said certain direction, said reversal effective to induce a, transitory potential of one polarity in'the other winding of said transformer and said restoration effective to induce a transitory potential of the opposite polarity in said other winding, a pair of grid-controlled gas discharge tubes, at least one of said tubes having its grid connected to-said other winding whereby said one tube is efiective to strike responsive to a transitory potential of one of said two polarities being induced in said other winding, means operated responsive to said one tube striking for conditioning the other of said tubes to strike responsive to a transitory potential of the other of said two polarities being induced in said other winding, and a plate circuit for said other tube thereafter energized responsive to a transitory potential of said other polarity being induced in said other winding.

2. In a signaling system, a transformer having two windings, a source of current connected to one of said windings to cause current to flow over said winding in a certain direction, means for at times reversing the direction of said flow of current and at other times restoring said flow of current to said certain direction, said reversal effective to induce a transitory potential of one polarity in the other winding of said transformer and said restoration effective to induce a transitory potential of the opposite polarity in said other winding, a pair of grid-controlled gas dischargetubes, at least one of said tubes having its grid connected to said other winding whereby said one tube is effective to strike responsive to a transitory potential of one of said two polarities being induced in said other winding, means operated responsive to said one tube striking for conditioning the other of said tubes to strike responsive to a transitory potential of the other of said two polarities being induced in said other winding, a plate circuit for said other tube thereafter energized responsive to a transitory potentiallof said other polarity being induced in said other winding, and means controlled by the energization of said plate circuit for extinguishin said one tube.

3. In a signaling system, a transformer having two windings, a source of current connected to one of said windings to cause current to flow over said winding in a certain direction, means for at times reversing the direction of said flow of current and at other times restoring said flow of current to said certain direction, said reversal effective to induce a transitory potential of one polarity in the other winding of said transformer and said restoration effective to induce a transitory potential of the opposite polarity in said other winding, a pair of grid-controlled gas discharge tubes, at least one of said tubes having its grid connected to said other winding whereby said one tube is eiiec'tive to discharge responsive to a transitory potential of one of said two polarities being induced in said other winding, means controlled by said discharge for conditioning the other of said tubes to discharge-responsive to atransitory potential of the other 01 said two-polarities being induced in said other winding, a discharge circuit for said other tube thereafter energized responsive to a transitory potential of said other polarity being induced in said other winding, and means controlled by the energization of said. discharge. circuit for terminating the discharge of. bothsaid tubes.

4. In a signaling system,v a transformerhaving two windings, a source of currentconnected to one of said windings to cause current to flow over said winding. in. a certain direction, means for at times reversing the direction of said flow of cur-. rentand at other times restoringsaid flow of current tosaid certain direction, said reversal e,ffective. tQinduce ,a transitory potential of .one polarity in the other .windingof said transformer and said; restoration effectivetoinduce atransiw tory potential of the opposite polarity in said other winding, a pair of grid-contrplled gas discharge tubes each having its grid connected to said otherwindinaone of said tubes .havinga normally disabled discharge circuit, the other of said, tubes effective .to discharge responsive to a transitory potential of one of said two polarities being inducedinsaid other winding, means controlled by the discharge of said other tube for enabling said discharge circuit of said on tube, whereby, responsive to a transitory potentialfot the other of said twopolaritiesbeing induced in saidother winding, said one tube discharges and hence causes said dischargecircuit to be ener gized, means controlled by said energization of said discharge circuit for terminating the dis: charge of said other tube, said second means efiective responsive to sthe termination of thedis charge oi said other tubeto disable said "discharge circuit of said one tube, thereby to terminate the .dischargeoi said one tube." I 5. In a signalingsystem, a circuit upon which impulses of different polarity are impressed alternately, a pair oi gas discharge tubes eachihaving a grid, means for connecting'said grids to said circuitso that oneoi said tubes is brought'to its critical grid potentialwhenever an'impulse of one of said polarities is impressed upon said circuit and the other of said tubes is brought to its critical grid P tential whenever an'imbulse of the other of said polarities is impressed'upon said cir cuit, each oi said tubes effective" to fire'when brought toits critical grid'potential, means an: trolled by said one tube, uponfir'in fbr 'ei'rtin guishing said other tube, and means controlledby said other tube, upon beingextinguishd, for extinguishing said one tube.

. 6. In a signaling system, a circuit 'up'onwlii'ch impulses of different polarity are impfessfedjaltr f nately, a pair of. gas discharge tubeseach having a grid, means for connecting said grids to said circuit so that one of said tubes is brought t6 its critical grid potential whenever an impulse .of one of saidpoiarities is impressed uponsaid circuit and the otherof saidtubes isbrought to its crltical grid potential whenever'an impulse of the other of said polarities impressed iipon said circuit, each of said tubes fiective-totire; when, broughtto its critical grid potential, and means nt o d by co o aid t be o x n i h n the. other tube. V ,4 W

- na signaling s st m a circuit e Wm h current is flowing in a particular direction, means operated at will first to reverse thedirectidnof said current fiow and then, aftera variable interval of time, torestore said current flow to its original direction, a pair of gas discharge tubes, means coupling one ofsaid tubes to said circuit so, that it y, will strike responsiveonly to the transient current condition existing in said circult. during the. time that said current flow is be: ing. changed from said particular direction to the reverse .direction, and .meanscontrolled .by said tube will strike responsive only to the transient current condition subsequently existing in said. circuit during the time .thatsaid'current flowis being restored .to said particular. directionfrom said reverse direction. 8. In a signaling system, acircuit .overwhich current. is flowing in a particular direction, means operated at will first. to. reverse. the direction. of. said current flow and then, after. a variable in.- terval of. time, tov restore said; current vflow. to. its, originaldirection, a gas discharge tubehaving a grid, .andmeans. for coupling said grid to: said circuit so, that said tube will strike responsive only to the transient current conditionexistingin said circuit during the time. that said current flow isbeing changed from said particular direction to the-reverse direction.

,9. Ina signaling system, a circuit overwhich currentis flowing in a particular direction, means operated at will first to reverse .thedirection of. said current flow and then, after ,avariable in terval of time, to restore said current fl'owto its original direction. a, as discharge tube having a grid and means for ccupling said grid tosaid whereby the other of said tubes is effective todis chargelresponsive only to areversal oi' said current flow from one particular direction t the opposite direction, said first means controlled by the discharge of said other tube for enablingsaid, one tube, said one tube thereafter efiective to disoh r o r on ve. o a s b e rvor lo sai cmrent fiow fron' said opposite direction to Said ne o roo n- 1-. In a el pho st m. wh re n ed roor. tion o t e. .flow re t ov th woo c rcu t is reversedattimes, a pair of gasdischarge tubes, ea swh reb n o d. tu s. i ofieo voto. e o si y t a e e o s urront wfmm ne. a t o ordi o n to t op osite direction, and means whereby the other- 1f said tubes is effective to fire responsive only to a reversal of said .current flow from said opposite di t to Sa dono o ro i oh, L 1

12. In a signaling system whe rein signalin is effected by reversals in the direction of I the flow of current over a signaling circuit, atransformer having one windingin said circuit, a grid-cop: troll d a schar e t havin its rid 0011-. nected to another winding of said transformer, sa d be. ef ect ve to'fi o responsive tater-tam. o said reversals but. not responsiveto others .de.. pending upon the polarity of the potential in duced in saidoth r. winding b h r versa and a rouit f rsa u ee rei dwhcne rsaidut b e .13. In a signaling system, atransformer having. two. win in s, mean o impr s n are-w ve. upon one of saidwindings, a grid-controlled gas discharge tubehaving its grid connected to.. .the other of said windings whereby said tubeis effective to strike whenever the voltageinducedin said other winding by said square wave is of acertain polarity, a second gas discharge. tube,and means controlled .by. said. first tube, whenever it strikes;

for conditioning said second tube for'operation, whereby said second tube'is eifectiveutorstrike whenever the voltage induced in said other'winding by said square wave is of the opposite polarity.

14. Inasignaling system, a transformerhaving aprimary winding and a secondary winding, means for impressing impulses upon said primary winding, the beginning of each impulse effective to induce a transitory potentialof a certain polarity in saidsecondarywinding,land the end of each impulse effective to induce a transitory po= tential of a different polarity in said secondary winding,-a gas discharge tube having an anode circuit and a grid for controlling said circuit, a connection from said grid to said secondary winding whereby said tube is effective-t strike responsive to a transitory potential ofone of said two polarities being induced in said'secondary Winding but is not efiective to strike responsive to a transitory potential of the otherv of said p0- larities being induced in said secondary winding, and means in said anode circuit operatedrespon sive to said tube striking; a A i g 15. In a signaling system, a transformer having two windings, means for impressing electricalim: pulses upon ,one of said windings; the beginning of each impulse effective to induce a transitory potential of a certain polarity in the other of said windings and the end of each impulseeifective to induce a transitory potential of a different po larity in the other of said windings, agrid-controlled gas discharg tube having its grid connected to said other winding whereby said tube is effective to discharge responsive to said induced potential whenever said induced potential is of one of said two polarities, said tube being-non responsive --toan induced potential of: the-"other of *said two polarities, and means 'controlled'by each discharge of said tube for terminating that discharge. i1

16. In a signaling system, a transformer having two windings, means for impressing electrical im-' pulses-upon one of said windings, acondenser connected to the other of said windings and charged by the-potential induced in said other winding responsiveto each said impulse, a' gridcontrolled'gas discharge tube having its-grid con-- nectedto said condenser whereby said-tube iseffective to discharge whenever the charge o'n said condenser reaches a certain value, and means controlled by each discharge or said tube for terminating that discharge.-

17. In a signaling system, a transformer having two windings, means for impressing electrical impulses upon one of said windings, a grid-controlled gas discharge tube *havingitsgridconnected to the other of said windings whereby said tube is effective to discharge'once responsive toeach impulse impressed upon said winding; and meansefiective to terminate each said discharge substantially immediately regardless of the length of the impulse to which that-discharge is -re'-' ponsive I. V. 18. Inc. signaling system, a transformer having two windings, means for impressing electrical impulses upon one of said windingsa grid-controlled gas discharge tube having its grid connected to the other of said windings whereby-said tubeis effective to discharge once responsive to each impulse impressed upon said winding, and means for terminating the discharge occasioned by each impulse before the beginning of the hex impulse.

cal impulses upon one of said windings, a gridcontrolled gasdischarge tube having its grid connected to the other of said windings whereby said tube is effective to discharge once responsive to each impulse impressed upon one said winding, means eifectiveto terminate each said discharge substantially immediately regardless of the length of the impulse to which that discharge is responsive,--a device, time delay means conditioned by each discharge of said tube to operate said de- Viceaftera' predetermined interval of time, and means "responsive only toanother discharge of said tubeiwithin said interval of time for preventingthe-operation of said device by said time delay means. 1

20. In a signaling system, a circuit over which train of impulses are transmitted at times, a gas discharge tube; means for associating said tube with said circuit whereby said tube is effective to fire at a particular point in each impulse, said point being the same forall said impulses, timing equipment, means operated under control of said tube whenever said tube fires for causing said equipment to start a timing operation, and a device operated under control of said timing equipment only if said tube fails to fire again within a predetermined interval of time after the beginning of any such timing operation.

21. In a signaling system, atransformer having'two' windings, means for impressing a train of impulses'upon one'of'said windings thereby byeach suchdischarge of said one tube to dischargethe other 'of said tubes after a'predetermined'intervalof time,'and means responsive only to another discharge of said one tube within said interval of time for preventing the discharge ofsaidothertube by said time delay means at the end of such interval. a

2.3. In a signaling'system, a gas discharge tube having a grid, means for impressing upon said grid at different times transitory electrical impulses of'different polarity, said tube eiiective to discharge responsive only to impulses of a particular polarity impressed upon its grid, timing equipment, means operated responsive to each discharge of said tube-for causing said equipment'to start a timing operation, and a device operated under control of said timing equipment only if said tube fails to discharge again within a predetermined interval of time after any discharge.=-"" I '24; In asigIiaIing system wherein electrical impulsesof different polarity are transmitted a1- ternately, a gas discharge tube having a grid, means for impressing said impulses upon said grid,-- said tube efi-ective' to discharge responsive only to alternate'ones of said impulses, a device; time delay means conditioned by each discharge of said tube to operate said device after a predetermined interval of time, andmeans responsive only to another discharge of said tube within said interval of time for preve ti t Operation of said device by said time delay means.

25. In a signaling system, a circuit upon which electrical impulses of different polarity are impressed alternately, means responsive to the impulses of one polarity impressed upon said circuit but non-responsive to the impulses of the other polarity, a device, time delay means conditioned by each response of said first means to an impulse of said one polarity to operate said device after a predetermined interval of time, and means elfective only upon the response of said first means to another impulse of said one polarity within said interval of time for preventing the operation of said device by said time delay means.

26. In a signaling system, a transformer having two windings, means for impressing a square wave upon one of said windings, a grid-controlled ga discharge tube having its grid connected to the other of said windings whereby a discharge of said tube is initiated whenever the voltage induced in said other winding by said square wave is of a certain polarity, and means controlled by each discharge for terminating that discharge a predetermined interval after its initiation.

REGINALD TAYLOR. GEORGE THOMAS BAKER.

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