US2905810A - Motor car protection system for railroads - Google Patents

Description

G. o. FERM Filed oct.A 1.7, 1955 MOTOR CAR PROTECTION SYSTEM FOR RAILROADS 005km n?.

sept. 22, 1959 STEL IIT/VENTOR. G o. PERM 4HIS ATTORNEY HUI United Statsy 1 MOTOR CAR PROTECTION SYSTEM FOR RAILROADS Glenn 0. Ferm, Gates, N.Y., assignor to General Railway Signal Company, Rochester, N.Y.

Application October 17, 1955, Serial No. 540,803

6 Claims. (Cl. 246-63) This invention relates to motor car protection system for railroads and it more particularly pertains to automatic means for controlling railway signals to indicate the presence of a motor car within a given stretch of track.

Some cars, such as the motor cars used by railway maintenance men, either have their axles insulated to prevent the shunting of the track rails, or the cars are so light as to make shunting of the track rails unreliable. Therefore, these cars must generally proceed with no signal protection.

The system according to the present invention provides a means for automatically registering when a motor car or similar vehicle passes a particular point and for providing signalling protection for the vehicle to be effective for a predetermined length of time after registration has been made. The registration of the presence of the car is accomplished by the inductive coupling of a tuned coil of the vehicle with a wayside receiver coil located at the entrance to the territory 'in which protection for a motor car is to be provided. When this registration means is actuated, the last signal in the rear is put to stop, and the signal behind that is put to caution. These signals are again permitted toclear at the end of a predetermined time interval.

It is further provided for single track railroads that motor car protection can be provided for the stretches of track, or blocks, between passing sidings in a manner to automatically render protection eiective for motor cars entering the respective blocks, but to be ineiective for the passage of Vmotor cars in the opposite direction, as it is assumed that these cars will use the passing sidings. If trains are encountered on the passing sidings, they are generally proceeding slow enough to allow suthcient time for motor cars'to be removed from the track.

This distinctive control as to direction of movement of the motor cars is accomplished by the use of two track coils at each end ot-each block, direction being indicated by the sequence of the loading of detector apparatus associated with the respective track coils.

An object of the present invention is to provide means inductively initiated for providing signaling protection for amotor car fora predetermined time interval.

Another object of the present invention is to automatically initiate a timer for the control of wayside signals upon passage of a motor car in one direction but not the other. l

Another object of the present invention is to distinctively indicate when signaling protection for a motor car has been rendered eiective.

Other objects, purposes and characteristic features of the present invention will `be in part obvious from the accompanying drawings and in part obvious as the descriptionprogresses.

In describing the invention in detail, reference is made to the accompanying drawings in which:v

Fig. lis a schematic diagram of one embodiment of ice the present invention as applied to a typical stretch of trackway; and

Fig. 2 is a sequence chart illustrating the sequence of operation of the relays upon entrance of a block by a motor car.

The illustrations employed in the disclosure of the present invention have been arranged to facilitate the disclosure as to the mode of operation and the principles involved rather than for the purpose of illustrating the construction and arrangement of parts that would be employed in practice. Thus, the various parts are illustrated by conventional symbols, and some parts well known in the art have been shown by block diagram. The symbols and are employed to indicate connections to the respective positive and negative terminals of suitable batteries or other sources of direct current.

With reference to Fig. l, the embodiment of the invention illustrated is shown as being applied to the control of signals governing entrance to a stretch of single track conveniently called a block connecting passing sidings A and B. Signals 2 and 5 are provided for governing entrance to the block at the respective ends of the block, and the signals 3 and 4 are provided for governing trains leaving the block. These signals can be of any conventional type such as signals having individual color light units or searchlight signals. It is to be understood that other signals are included within the block according to the requirements of practice in the portion illustrated as being broken. The passing siding A is connected to the main track by a track switch 2W and the passing siding B is connected at its left hand end to the main track by the track switch 3W.

Located along the trackway at the ends of each block are respective pairs of receiver track coils TC, the track coils lTC and ZTC of Fig. l being respectively disposed along the trackway so as to be subject to inductive coupling successively by the passage of an eastbound motor car (traic to the right) upon entering the block' between the passing 'sidings A and B, and the track coils STC and 4TC being respectively disposed along the trackway so as to cooperate inductively and in succession with the vehicle carried coil on a westbound motor car (traflic to the left) upon entering the block between the passing sidings A and B.

Each of the track coils TC is a part of a tuned circuit of a radio frequency oscillator, and although the oscillator is shown only in block form in Fig. l, it is to be understood that this oscillator can be constructed according to the disclosure of Fig. 5 of the U.S. Patent of H. C. Kendall et al. No. 2,693,525, granted November 2, 1954. The oscillator disclosed in that patent is of the sweep frequency type, which has the advantage of increasing the sensitivity of the receiver. lt is to be understood, however, that a conventional oscillator without the sweep frequency feature can be used if desired.

Detector and ampliiier apparatus, as is illustrated in block form in Fig. l, is associated with the respective oscillators for the purpose of detection of times when the associated oscillators are loaded by inductive coupling with a tuned vehicle carried coil. This apparatus can be in the form of a reaction detector connected to the control grid of the tube of the associated oscillator. There is suicient amplication provided to furnish an output to pick up a relay, or a gas tube is triggered to operate a relay, in accordance withv the requirements of practice. The reaction detector, ampliier, and control gas 'tube organization can be provided according to the system fully disclosed in the above mentioned-Kendall et al.

.3 each of the track coils TC as a means for registering the detection of the passage of a motor car.

Each of the motor cars -istprovided with a vehicle carrled .tunedeoil VIC snh as thecoi1N'1Ct11ustrated in Fig. 1 as being associated with a motor car 1l). This coil istuned to .a.given frequency -by .a .condenser 11 connected in .multiple therewith.

The track layout is divided into track circuits tforithe control of the v.signals in -a .conventional manner, and conventional :automatic signaling means is provided `Jvith modifications as will bezhereinaftereonsidered. The track section 2T isillustrated las having-associated .therewith a conventional track relay Z'I'R, .the track section .2T .being the. Section-immediately aheadof .the-.signal Q for .governi@ .eastbound trahie.

l A .line circuit .controlled arelayJI-ID Ais illustrated .as being associated-with.the.control .ofssignzal 2,.and a line CICU 9011I01led relay 5HD...is :illustrated .aas :being associated with the'eontroLoffsgnaL-S. Signals f2 and have associated therewith slow drop away pole changing relays. 2PC and-PC-respectively.

A reset relay RS .isprovided lor resetting the Erelays 'IICP vand ZTCP .subsequent to their actuation .and for use ingcverning-.othercontrol circuits,1the relay RS having associated therewith a thermal lrelay TH which must be. actuated before thefrelay ;RS. can :be picked np. Relay RS is made:slowito-.dropnwaybyz its windingbeing shunted by a .condenserS .in series witha .resistorS-T.

A normally .energized .timingreneater stick relay TES is used in controlling a motor -..dr iven timer which governors the amount of .time for which protection is provided for a.motor .car .-snbsequentto passage-.of an associated receiver track .coil .upon entering the block between passing sidings. AThistirner is required to time a relatively longinterval, and .thus themotor timer struc- 'ture according to the U.S. patent of O. S. Field, No.. 2,378,293granted June l2, 1945,.is particularlyadapted for this, purpose.

Signals A2A ,and .5A are .provided .for .indicating .when the. motor .carprotection is effective.. These indicators Shuld .be so .disposed as to .be -.yisible to .theonerators of the `.motor `ears, and it :may .be .advisable V.that -the indiatQrs be .disposedso .as .to-beivisibleto ytheoperators of trains .as Well. .Each -pf the indicators .2A and 5A has .a slow drop :away approach tcontrol stick relay vAPS associated therewith.

A rllQWer-.Olrelay P is provided :for rendering the system inetlective when the power is o.

The relay Kcontrol .apparatus has been .illustrated par tieularly associated .wtih'the .track coils JTC and ZTC, and -it ,is to be considered .that .this apparatus -is typical of the .apparatus .that .is provided in .association with each pair Aoitracls: coils ,that may be provided -at.the entrance end of .the .respective .blocks for vboth .directions of ltr-aine.

Having thusonsidered .theapparatus in general, consideration -will .now be given .as to the `snecitic .circuit organizationwhen :considering the mode of .operation Bilder Sneeiie assumed typical ,operating conditions.

Operation Normally,` with no trains or motor cars Ypresent,...tl1e track relays are all energized inthe =usual manner-.and the signalsare clear, the signaling :organization .assumed to be .provided for the present .embodiment being aconventional three wire .absolute permissive .block signaling system.

The receiving relays TCP are all normally maintained energizedby their respective stick circuits, relay lTCP, for-example, being maintained picked upby a stick circuit- -through -its front `contact 12 in accordance with energization -`by `the 'detector and ampliiier 13.

TI-he vtiming-*stick lrelay TES is l-normally maintained picked nplby -a-stiek circuit extending `from Ci-}-) including front contact 14 of relay ITCP, 'front 'contat i5 Of relay'TES and winding-of relay TES', to

The line relays HD and the pole changing relays PC are normally energized according to usual practice. Relay SHD, for example, which is associated with the control of signal 5, is normally energized by a circuit extending from including front contact 16 of relay SPC, front Contact 17 of relay I2IR, front contact 18 of relay TES, line Wire 19,fslectons as indicated by XX,

- WindinsofreteyfSHDermnemretum'wre @eend-front contact 21 of relay 312C, mit-fp), In accordance with such energization, the signal 5 is normally clear lbecause cause of theenergizationof acirenit-.extendingirom'( vir) -including front contact 26 of relay TES, back contact 2 -'l of relay TE, front contact .2,8 of relay -2 HD, and winding ofreley 2PC-to Thepower-ot relay PO is normallyenergized because of the application-of .energy directly .to-'its-Winding-from `the same souree-.of alternating-current that l.is Iused-for the energization of the oscillators and .detector :and ampliiier .equipment at .the associated kreation.

To-eonsider .the rnode of opergation under a typical operating condition, it will :be .assumed that a motorcar .10 is equipped as-has, been .described with a vehiclecarried :coil -VTC whicheis .tuned :by 1a. lcondenser .11. When this coil NTC .becomes tinductively-.coupled with the track coil AHTC upon entrance of the smotor car -into `Ithe block between thetpa-ssing :sidings A and B, -the ose. eillator 29 becomes .loaded .and Ithus :causes fthe detector .and amplifier .-13 to interrupt-the :energization of .thedetector-relay ITC-P so-as to-eause-th-at .relay-tobe dropped away. Although the loading [ofthe-'oscillator 29 only .momentary in accordance wth-thefmotionof the motor car 10, the relay ITCP is not again irmnediatly'picked up when energy is 'restored :to the '.outpnt 30 andl of the .detector and amplifier d after :passage :of ..the car. This .delay in restoration iis established-do. insure time -for operation .of -othen relays iintaccordance. withthepresenee-,of the motorv car lhhaving-daeen detected... u Upon --the--droppingg of relay: theatiming; stick relay TES fbecomes vdropped.away :by the :opening .of its.

stick .circuit at. :front oontactlML-nfurelay yEIChe droppingaway -offrelay lilCP @also `.the heatin'giof the thermal relayV by energizationxo .a'rcircuit shunt the` contact :lingers .34 .and 35 off-.the thermal :relay TH out of the .circuit .just described, :Because-.ofthe time involved in the opera-tion of the thermal relay TH, in all probability the motor loar y10 has proeeedecl to the point of .causingthe dropping awayof therelayZTCP-and the dropping away of this v.relay #has been .elective to.v

close its back-contact 36 Ato also ,provide energy forthe relay RS.

The picking up of relay RS causes .the restoration .ofv the relay ITCP toits'piked up by the. closure of front contact 37, and this relay when jpicked'fup is maintained energized -by its stick `eirciiit includngfront contact 12 which is conneeteifin multiple with frontlcontact '37, Similarly, 'the relay ZTCP 'becomes picked up upon the closure of front contact 38 of relay RS, and the picking up of this relay establishes avstick circuit -through front contact r39 which is connected in multiple with front contact 38 of relay RS. Relay RS then becomes dropped away because of back contacts 32 and 36 of relays ITCP and 2TCP respectively being both open.

Assuming -that there are no-trains approaching the right-handyend of the passing siding A, `proceeding ini either direction, therelays 2HD and SHD are both in their picked up positions as has been-described, and in accordance therewith, the relay APS is'v picked up at this time to applygenergy to the motor car indicator kklamp- 2A. The pick-up circuitfor relay APS extends fromincluding'front contact 40 o f relay 2HD, frontcontact 41 of relay v3HD, front contact 42 loi? relay RS, and winding of relayAPS, to This relay when picked up is maintained energized through a stick circuit shunting contacts -41 and 42 of relays ASIA-ID and RS, respectively, out of :the circuit just described. This stick circuit eX-tends from including front contact 40 of relay 2HD, back contact 43 of relay'TES, front contact 44 of relay APS, sand winding of relay APS, to

The picking up of relay APS causes the energization of the motor car indicator signallamp 2A by a circuit extending from including front contact 45 of relay APS, back contact 46 of relay TES, tron-t contact 47 of relay PO, and lamp 2A, to

The dropping away of relay TES in response to detection of the presence of the motor car proceeding in the direction as 'specified is effective to put lthe signals 2 and 5 which govern entrance to the block to stop. lSignal 2 is put to stop because of the dropping -away of the relay 2PC upon the opening of its circuit at front contact 26 of relay TES. The opening of front contact 24 of relay 2PC opens the circuit for the green lamp G off signal 2, and the closure of back contact 24 establishes a circuit for the energization of the red lamp R of that signal.

Signal 5 is put to stop because of the opening of the circuit for relay SHD at front contact 18 of relay TES. This relay in dropping away opensa circuit (not shown) for a relay SPC comparable to the circuit shown in det tail for the control of relay 2PC so that such relay is dropped away. The dropping away of this relay lis effective like the dropping away of relay 2PC to extinguish the green lamp lG of the associated signal 5 and energize the red lamp R of that signal.

As soon as the relay 1TCP 'has become picked up after its actuation,l a circuit is closed 'for the energizationof the timer TE to time the'interval during which protection is to be maintained for the motor car.' The circuit for energi'zation of the timer TE includes front contact 14 of relay 1TCP and back contact v15 of relay TES. The

duration of the time interval for which the timerl TE is set to time, is such as to provide thedesiredtime of protection for the motor car in order that the motor car may have time to reach its destination which m-ay be the next siding, -or the car may be set off the track within the block. After the timer TE has completed its operation, the relay TES is picked up by the energization of a circuit extending from including front contact 14 of relay 1TCP, front contact 56 of relay ZTCP, fiont contact 48 of timer TE, and winding of relay TES, to Relay TES, when picked up, closes the circuit for relay SHD at front contact 18 and closes the circuit for relay 2PC at front contact 26 so as to permit the lsignals 2 and 5 governing entrance to the block to be restored to their normally clear indicating conditions. The picking up Aof' relay TES opens the circuit for-the energization of the tirnerLTE at back contact of relay TES,.and thusthe timer TE is restored toits normal conditionso as'to close backco'n tact 27 in fthey circuit -for .relay 2PC. Relay ATES isy maintained energized alt'this ,timeV `by the stick circuit thatv has been described as beingnormally effective for that relay, and thus the opening ofjzfront contact 48 of the entrance of a motor car into the block between the passing sidings A and B.

For the passage of traiic in the opposite direction, similar apparatus (not shown) associated with the receiving coils STC and 4TC is operated in a similar manner to the mode of operation that has been described for the passage of an eastbound car.

lf a westbound motor car leaves the block, however, the inductive coupling of the vehicle carried coil VTC with the track coils ZTC and 1TC -successively does not kput the signals 2 and 5 to stop because of the car leaving the block rather than :entering it. This lis because of the sequence in which coupling with these coils is established. The dropping away of the receiver relay ZTCP prior to the dropping away of relay lTCP maintains relay TES picked up by the energization of a stick circuit extending from including back contact 49 of relay ZTCP, front contact 50 of relay TES, and winding of relay TES, to The reset lrelay RS is picked up by a similar mode of operation to that which has been considered, and this relay when picked up establishes another stick circuit for fthe relay TES to maintain it picked up until the relay 1TCP yhas been restored to its picked up position after passage of the motor car. The stick circuit by which relay TES is maintained energized by relay RS extends from (-1-), including front contact 51 of relay RS, front contact 50 of vrelay TES and winding of relay TES, to

Because of the relay TES being maintained picked up when a motor car leaves the block, singals 2 and 5 are not put to stop as the circuit :for the signal control relay 2PC is maintained closed at back contact 26 ofy relay TES and the circuit for relay SHD is maintainedl at a time when the entering signal at the associated entrance end of the block is at stop. Such a signal indication is indicative of the presence of a train in the immediate vinicity and thus no signal should be given the motor car indicating that protection has been provided. In other words, the failure to illuminate the motor car indicator 2A is an indication that the motor car does not have protection and should be set oi of the track. Failure to illuminate the indicator 2A under these conditions is effective because the relay TES is maintained picked up whenever either of the relays 2HD or SHD which are associated with the head block signals respectively are dropped away. Thus, relay TES is maintained picked up by a stick circuit extending from including back contacts 52 and 53 of relays ZHD and 3HD respectively connected in multiple, front contact 50 of relay TES, and winding or relay TES, to With relay TES maintained picked up, the circuit for the' In case of an alternating current power failure, the de-l tector relays TCP become dropped away because theirenergization is dependent upon the electronic apparatus. .y

Such dropping away of the relays TCP should not put the signals to stop, and thus` the power-off relay PO is l accenno? provided forthe purpose of maintaining -therelay TES 4^ picked upunder these conditions,

'Dlxe-relay-l is normallyenergized-,tand isA dropped I awayuponl Ia-power failure: Uponfdropping--away relay- PGprovides energizationoffaestick cireuit'forerelayjTES` extending. from -I- 5 includingbacio contact'54L of `relay` PQ,- front-contactv15of relay TESiand--winding offrelayy In casethe power fail-ure# should occhi"` accordance-with the-passage of a'rnotor cargth'erelay extelidsfromn (+L including; back contact54 of *relay* PO; baekI contact 55 of--relay-PO; frontcontact' 48j of' relay TE, and windingfof relay TES, to A(J-)p' Infcase-ofsimultaneous entry-ofa train atone end of-'a block and a motor car atA the other; end, it is provided that' the energizationofthe motor, carV indi`` cater; such as' indicator 2A, is delayedl untiltlre signal; control ttunbledown system hasb'ecome effective to prevent thepicking-upof the'relay- AjPS; This is ,desirable, E because incase oftsimultaneous entry,v therewould be, no-warning signal* displayed for the train to, indicate thatthefbloclcwas occupiedrby a'motor car, Vthus itshould be -providedthat-noY clearance is Vgiven-a `motor car by the c energization of the indicator 2A- under these conditions of simultaneous entry.

Uponconsideration of "the'circuit fortlr'e relay APS,

itwill be noted that this relay-1 cannotbe. picked: up

until-'frontcontact 42-of th'e reset relay RSfhas. been, closed. Relay; RS, however, cannot-be pickedjup' until' the'y thermal relay TH has completed its operation,` and the-'energization of the thermal relay F['Hgis effecteduppnpassageof a motor carover one of 'the track gcoils, ItVV Willthus-b'e seenivthat there is considerableu time delayF after entrance of a motor, car into the block before the relayvAPSvcanbe'picked up to close its` front contact 45', and thus'provide venergization `for the motor car in dcator 2A; In this'length of time, .ifthere hasgbieen a simultaneousY entry of a train upon accepting signaljS,` thefusualtumble downof the signal circuits has been, elected so as`toycause the` dropping away oftl ie.`vrelay ZHD; Uponthe dropping' away of "this.relay, th'e open. ing'offront'contact dllprevents the energization ofth'e stick relay-'APS from hecomingleffectivenupon,the pickingupf of the resetirelay RS. Therefore, there is no energization-under these conditionsof'the indicatorZA', andthusthe operator` of thev motor car is warned "that, the motorcarv should be; removed fromV the track as there isatrainin' the vicinity. Y

I- Iaying-thusV described'a motor car protection system as-one'fspecic embodiment ofthe present invention, it is to beunderstood that'this form has been vdisclosed more particnlarlyfor an illustration ofthe mode ofopzeration and principles involved 'in the present invention, andthat variousmodications, adaptations, andalterations may` bejmadeto therspecific form shownwithin `the scope ofthev present invention as detined byy the appendingw claims.

WhatI claim is:

1;k A motor car` protection system for a stretchA of single track having passing. sidings andhaving railway traincontrolling signals vfor 'governing' entrance to the stretch oftrack at its respective ends comprising, av track' coil energized at a particular frequency at'eaclr endof said-stretch ontrack, a coil tunedto Ysaid frequency4 carried'byr a motor car and positioned thereon so as to pass throughY an inductive coupling relationship with said track' coilas said motor car enters .said stretch of track, detector means operativelyl connected 'to each'ofthetracl; coils and 'being distinctively operated 'from a normaljto anv abhormalposition upon passage of said tuned'CQil.

past the associated 'track' coil`for registering thepresence,y

of "the motor car in said'stretch oftrack', timing means responsive toitl1eactuatonvofi'said deteetonmeans-lto sai d-4 abnormal t condition: ftflrftf'ningL a predeternziinf'ed-lA iink terval; andfsignaicotrli'meansf fore said signals-gov` erned said tin'ringr nneawns vfor J putting' saidJ signalsto# n1ined'interval}- 2: Am'otocar protection system-accordingftovclaim 1 wherein' the@ detectormeansincludes J a detector: relayL that is-niaintainednofmallyenergizedand isfoperatedtto itsdreppedfaway'positionuponepassage of said tuned;

coil past fthe; associatedA trackl" coil.i

3*." A motorcaiproteetion#system'.accordingato\claiixL 1' Whereinthe; detector means includes #al detector relay` pling ofsaid tunedcoil with' .the assoeiateditracld coil' and`A is restored to itsnorrnally :energized "positionfat theend'ofa predterminedtir'neg after 'its operation.`

4,' A'motorcar protection`systemfora stretch ofsingle track having passing'sidings and-*havingj-motorcar traffic control signals `for goy'erningi entrance tothe; stretclr ofc track atits respective' endscomprising,r a trackj` coil energized at a" particular* freqnency` at each end" of said stretch o f"track`,1a coiltunedto saidfrequency;carried* through an inductive coupling relationshipjwith said track' coil, as said motor car. enters' sairlfstretch4 oiwtrack;` dee tectorfmeans'L olnerativelyj'connected` to each'othe track. coils and?being, distinctively;operated;fromaanormal toiI an abhormalppsition uponpass'age of"saidj` tunedcoilf past the, asspciatedftrack coilfor registeringj:the;presence` of-'the tn otjsrcaninfsailfstretctt of traclgf,` timingmeansresppnsive; to v, tlie actuation of said detector; means to said 'abnormfdll condition Yfor timing a predeterminedinr; tervalilld lgllalcontrol I neans n for said motor :car traf-I fic controllsignals gnvernedlby said`tirning ."meansV distinctivelifr conditioned only, drnasaid. nredeterrniued final-us inten/alii 5; A motor. car'prottiongsyfemf for a Sfrelh Ofi' singlenrackextenr'ing betweenrpassingfjsidings andhaving railway, trainjcontrolligvsignals for governingentrance` to, the, stretchQofj, track at. resp'ectiy/'eV ends, comprising, uro'trak'.,coilseaclrenerglzed.withalterllatl ina ,currentof a. particular .frequencxc'andlcgated a short: distance apart alongA the traclgway at,oiga-.engl,of th'e,v Stretch of: trank,= a., coil luned to said frequency; and` beine canrieclfby aL motor can andppsitioned'tlereon ,So as. to.` nasa throughw an: yindusztiye, coupling, relationshim with Said: trask coils' successively, as Said motor, car l enterssaidtretch ontrack, ,aiatandlsecondl detector respectively,andlengdistinctveli, Operated om a nor.-

maitoanabllflrml condition .1112911 passa'slaol-` said tunedf' coil, past.- thefassocated track, coil,` for, registering, the` Presencecuil the, motorI car,- iu: Said Streich. o nach.. at. normally.. energized lcletetor., relay, `Ritiri-11n' Circuit' .means for energizing; Saiddetctor relay; when SaidLSt and' I deuergizationosaidxleteetor relay. ;k

SZ-.LA autotour camprotectnni systemefer as stretch` otftraekbtneenrpassinasSdingas-havingrailwaymaimcorn trolling; sigaalsf for: aovemingi entrances tori that stretchy, tfrak @sits rrspeetive;endssomprisinsesignalecontroll mansion conlssllsslhf:illlliaiellsroesaisls Signals im accordano e, with, conditional, motorf carcarried-l Avmeans for denotingthe presence of a motor car in the system, detector means at each end of said stretch of track for detecting the passage of said motor car carried means, registering means controlled by said detector means for registering the response of said detector means, and normally inactive timing means controlled by said registering means for controlling the signal control means for a given period of time irrespective of the time period of control by said registering means.

References Cited in the tile of this patent UNITED STATES PATENTS Thompson Nov. 11, 1952 Muse Dec. 29, 1953 Groenendale Feb. 23, 1954 Coughlin Aug. 9, 1955

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