US2369053A - Railway signaling system - Google Patents

Description

Patented Feb. 6, 1945 RAILWAY SIGNALING SYSTEM Arthur L. Jerome, Edgewood, 'Pa., assignor to The Union Switch & Signal Company,,- Swissvale, Pa., -a corporation of. Pennsylvania Application October 29, 1943, Serial'No. 502x113 7- Claims.

My invention relates to. railway. trafiiccontrolling apparatus andaparticularly to a system. employing coded energy in the track circuits thereof.

. In application for Letters Patentofthe United States, Serial No. 436,327 of Howard A. Thompson, .there isv shown a signaling system arranged so that in the event that the insulated joints separating two .track sections are defective, the equipment for the track section in advance'of the defective joints operates 'to causethe signal for that section to displayits mostrestrictive indication, while coded energy is suppliedtozthe adjacenttrack sectioniin the rear to cause the signal for that sectiontodisplay its most restrictive permissive indication.

equipped with signaling apparatusembodying my invention.

In practicing my invention, Iprovide a code detecting relay which is picked up when'and only when the associated track relay is respond ing to coded energy, while I provide a circuit including a back contact of this relay for'supplying energy of '75 code frequency to the rails of the adjacent section in the rea g'and I provide another circuit. including. a back contact of this detector relay and a front contact of the associated trackrelay and over which steady energy may be supplied to the rails of the section in the rear. I also-provide a .slow releasing relay for controlling the detector relay and the supply of steady energy tothe section in the rear. .A circuit isprovidedfor this relay when the detector relay is picked up while when the detector relay is released, this relay is energized over a stick circuit including its own frontcontact and a back contact of the-track relay so that if steady energy feeds across a defective joint and keeps the track relay picked up, the slow release relay will release to out oh the supply of steady energy and prevent the supply of energyto its own winding vor to the detector relay.

Referring. tothe: drawing, there. is shown therein a stretch.oftrail-waytrack-havingtrack rails l and 2 over which trafiic normally moves in the direction indicated by an arrow; that is from left to right. The rails of the track stretch are divided by insulated joints '3 into the customary successive track sections for signaling purposes.

Electric current is employed'for propulsion purposes in the track stretch shown inthe' drawing and, for this reason, alternating current energy is employed inlthe track circuits, while impedance bonds 4 of the'customary form are provided to conductpropulsion current around each pair of insulated rail joints. As the descriptioh proceeds, 'howevengit will be apparent that the apparatus of this invention'is equally well suited for use on a steam road, in which case either direct or alternating current may be employed in'thetrack circuits While the impedance bonds maybelomitted.

.In the drawing, one complete section, whichflis identified as section'l'2T,and parts of two other sections, identified as sections HT and HT, are

shown. Each of these sections has at the entrance end thereof a wayside signal S for governing traflic in the track stretch. The signals illus trated are of the familiar color light type having a green or, proceed lamp G, a yellow or caution lamp Y,an'd a redIamp'R. which may be considered a stop or slow-speed indication. It should be understood, however, that this invention 'isnot limited to the use of signals of this type and that any appropriate form of signal maybe used,

Likewise, the invention is not limited to a system employing wayside signals but is equally applicable to track stretches without wayside signals and over which are operated locomotives equipped with cab signal apparatus of well-known con- .struction, such as thatlshown in 'LettersPatent suitable source and. may be distributed. throughout the track stretch by a transmissionline not shown, while the terminals of .the'alternating current source are designated BX andCX. It will be assumed that'the energy supplied from this source is alternating current of afrequency 'of cycles per second.

Each signal location is also provided with a suitable source of direct'current such asiaprimar-y orstorage battery, not shown, the terminals of which are designated B and C.

provide '75 and 180 energy pulses per minute,

which are separated by periods of equal duration in which no energy is supplied.

Each track circuit includes a code following track. relay TR connected across the section rails at the entrance end of the section. As shown, the track relay l 2TB is of the direct current type and is connected across the section rails through a resonant rectifier unit I2RU, This unit includes a transformer, a. capacitor and a reactor so arranged and proportioned as to freely pass 100 cycle signal control energy, but so as not to pass propulsion current of a different frequency.

This unit includes, in addition, a rectifier which converts into direct current the alternating current supplied through the unit.

The track relay, IZTR has associated therewith auxiliary relays I2H, I2J, and I2LOS, and

a decoding transformer IZDT, while each of the other signals in the track stretch has associated therewith equipment corresponding to that associated with signal I2S.

The equipment is shown in the condition which it assumes when the track stretch is vacant. At

such times, energy of 180 code frequency is supplied to the track transformer. I2TT by the equipment associated with section I3T. The equipment for section I3T operates'in the same manner as that for section I2T.

The coded energy supplied to the track transformer IZTT feeds to the track relay IZTR and produces, code following operation of this relay with the resultthat its contact l5 alternately establishes the circuits of the two portions of the primary winding of decoding transformer |2DT and energy is induced in the secondary windings of this transformer. On release of the track relay IZTR, its contact 16 establishes a circuit including front contact I! of the second auxiliary relay I ZLOS for supplying energy from the secondary winding l8 of transformer I2DT to the first auxiliary relay I2H. The energy impulses supplied from the transformer to relay I 2H pick up the relay contacts, While this relay is of a type the Qcontacts of which are slow to release so that they remain picked up in the intervals between energy impulses. As relay [2H is picked up, its contact 20 establishes the circuit of relay |2LOS and its;

the resonant rectifier unit IBUDU and picks up the relay iZJ. The unit IBDDU is similar in con struction to the unit IZRU, but its elements are winding 24 of transformer I2DT feeds through arranged to pass sufiicient energy to pickup relay 7 I2J when and only when the energy supplied thereto is of the frequency present when the track relay is responding to energy of 180 code Operation of equipment on passage of a train through the track: stretch When a train moving in the normal direction of traflic enters section IZT, the track relay IZTR is shunted and energy is no longer supplied through the transformer IZDT to relays I2H and I 2J and their contacts release with the result that contact 25 of relay l 2H interrupts the circuit of the green lamp G and establishes the circuit of the red lamp R of signal 12S. I

In addition, on release of relay IZH, its contact 20 interrupts one circuit for relay I'2LOS and establishes a'stick circuit for this relay which includes front" contact 21 of relay IZLOS, back contact 28 of track relay IZTR, and back contact 20 of relay IZH so relay IZLOS remains picked up. The relay IZLOS is of a type the contacts of which are slow to release so its contacts remain picked up during movement of the contacts of relay I 2H between the picked-up and released positions.

On release of relay 12H, its contact 22 interrupts the circuit for supplying energy of 180 code frequency to the transformer I ITT and establishes the circuit controlled by contact 15 of code transmitter IZCT for supplying energy to transformer IITT, and energy of code frequency is supplied to the rails of section II T. As hereinafter explained in connection with section I2T,

energy of 75 code frequency supplied to the rails I of a track section Will cause the signal for that section to display its yellow or caution indication.

At this time, as relay IZLOS is picked up, its contact 3!] establishes a circuit controlled by track relay contact 3| and over which steady energy may be supplied to the track transformer I ITT. However, as long as section HT is occupied and track relay IZTRIis released, this circuit is interrupted by track relay contact ill and energy is not supplied over this circuitto the track transformer, so energy of 75 code frequency is supplied through this transformer to the rails of section II T. 1

When the train enters section I3T, the equipment for that section operates in the same manner as that for, section IZT, and the signal I38 is caused to display its red indication, while the energy supplied to the rails of section I2T is changed from to 75 code frequency. When the train vacates section I2T, this energy feeds to track relay IZTR and produces code following operation of the relay.

ing energy to relay IZLOS. As track relay contact 23 is picked up, the circuit for supplying energy to relay IZLOS is interrupted but, because of the slow releasing characteristic of this :rclay; its contactsrremain picked up -forzazperiod.

When the track .relay contacts pick up :at 'a time when relay IZH is released and rfelayr IZLOS .is picked up, energy. is :supplied :to the trans iormer IITT xover vthe circuit whichvincludes front contact of relay I2LOS,Jfront contactiiill of relay I2TR, and. back (contact zi'ofrelay I2H.

If the insulated joints 3-separating sections HT and IZT are intact so that energysupplied to the rails of section I IT does'notlteedrto track tact I'5 causes a changein energization oithe primary winding of transformer: I2DT's0' impulses I of energyare induced in the transformer-secondary windings wh'ile contact I6 of the trackrelay establishes the circuit for supplying-energy, from the transformer-secondarywinding I 8i' 'to relay IZH. The various parts -01" the apparatus. I 'are proportioned'so that-one impulse or energy supplied from Winding I8-to relay I2-H will pick up the relay contacts. Accordingly;onrelease -of the track relay contacts, therelay l I2H picks up and its contact 20 establishes. a circuit to maintain the relay IZLOS energized, whileeontact'f-.2 2 of relay IZI-I interrupts the circuits'for'supplying energy of 75 code frequency andior supply ing steady energy to transformer II TI, and establishes the circuit for supplying energy of 1180 code frequency to the transformer I ITT.

In addition, on picking up of relay IZI-Ipits contact .25 interrupts :the circuit ofathe red lamp R and establishes the circuit including: backcontact 26 of relay I2J for supplying energy to the yellow lamp Y of signal I25. 7 I

When the train advancesfar enough intthe track stretch to vacate section I3T, the energy supplied to transformer IZTT'is changed from 75 to 7180 code frequency, and on th resultin change in the rate of operationsof relay 12TH, the

relay I2J picks up and its contact 26 interrupts the circuit of the yellow lampY' and establishes the circuitof the green lampG-oisignal I28, while relay IZHremainspicked up so that energy of 180 code frequencyis supplied to the'rails of section HT.

Operation of the equipment if an insulated joint breaks down as a result ioj passcge 015a: train.

On release of relayIZH, its-contact 20interrupts one circuit for relay IZLEOS and establishes forthe relay IZLOS the stick circuit which includes front contactZ'I of relay I2LOS',ba ck contact 28 of relay IZTR, and back contact-.23 of relay IZH, so relay l2LOS remains picked-up and its front contact3fl is closed to permit energy to be suppliedover the circuit controlled by this contact.

For purposes oi-illustratiomit will he'assumed that .thetrain: entering section RT broke down accents c oneaaefilthe .insulated joint a3; separating-sections HT and MT. i;'B.eca-use-.-ot;thelwelleknown autotransi'ormer zaction gof tthe qtimpedance bonds, -breaking-down clone .iinsulated joint permits .energysupplied to therails bisection? I-|.T:-toi feed tto theitrackrrelay' IiZTRs and pick upzitscontacts.

:Accordingly, when the train -ladvances Jar enough: for the reartofs'the irain .to be? located some distance in advvancetofptherentrance endzoi section I2T so :that :the :train .is .inefiective'to shuntthe track re1ay= tZTRwii-h respectgto energy feeding acrossthe defective joint; the track relay I Z'IRwill: respondptoenergysupplied-:iromtransformer I IJI T; I I i i 0n pickingup. of the :track relay I 2TB, itscontact 18 interrupts the stick -;-circuit for relay I2LQS,-;:whileits vcontact 3I- establishes the ciracuit over.whichsteady'energy.issupplied totransformer I I'ITI as long was relay- IZLQS remains picked up. ;'I'her circuit for supplying steadyc-energy-to transformers I ITITTI" includes; front: -contact 3010i relay IZLQSLfmntcontactJSl-pf relay IITR,

and back: contact 22 of :relay: I2H,-while energy supplied over I this circuit {$0 :transformer 5 I ITT ieedszacross the defective joint torclay zI2TR and-keeps its contacts pickedup so thatacontact 28 interrupts the stick circuit ior relay I2LOS.

- 0n 7 picking upof relay IZTB, its contact i I5 causes a change incenergization ,oftthe primary winding of transformer. I2DT and an impulse" of v energy is: induced in secondary Winding lflavbut, at this time) track -relay:contact-li interrupts the circuitof-relay?12H sorenergy is not supplied to the relay I2H-and itStOOIXtECtS remainreleased so that contact 22-maintains theccircuitz-traced above forzsupplying steadykenergy; to transformer I ITT, while contact zu-causes relay l2LOS-;to :be controlled by itsstick circuit. Y

At this time, therefore, the-track relay-is held picked .up ,by isteady energy feeding across! the defective; joint and; as: the track relay is. notsrespending to -coded energy, relay IZH remains released, while as the track relay is picked am) and relay 1 Mil is released, the acircuit --of :relay IZLOS is interrupted. =tOn expiration of I the. release time of relayJZLOS, its contacts release and contact :21 interrupts the relay stick circuit to preventsupply' of energy to (the relay on:- subsequent release of; the-track 'relaycontaots, while I contact I1 interrupts' the circuit-airelay IZH to prevent picking up of thcscontacts of. rela HH on subsequent, code following operation of track relay I 2'I'R. In addition, on ;re1ease::oi:reiay I2LOS, its contact 30- interrupts the-circuit for supplying steady energyto vthe transformer I'I'TT. Afterreleaseof relay I2LOS,;ene fgy. of '15.:code frequency continues: to .be' supplied, to the trans former IITT over contact 1.5 of the-codextransmitter I2-CT and .back .contacirfl. of relay IZH. This :energy will operate :the equipment, not shown, eat the: entrance end :of section a I tT- to cause the: sisnal for c section; I I-T- display? its yellow or caution: indication -while this zecnergy will cause the cab-signal apparatus: on:a locomotive in section I IT to provide its caution :in'dication.

The energy of, .75 codejfrequency supplied :to section I LT after release otrrelay IZLOS, will also feed, over the defective insulated joint." and cause code following operation of track relay- IZTR,

but. this. operation of:re1ay' IZTR iswithout: eflect as the circuitrof relay I2H is interruptedgby contactdl of; relay I2LOS. Accordingly, relay-"I23 remains releasedato prevent; supply-oi: energy to tains the circuit of the red lamp R of signal l 25. t Will be seen, therefore, that if an insulated joint is defective, coded energy supplied to the section in the rear of the joint will feed across the joint and pick up the track relay for the section in advance of the joint, while on picking, up of this track relay, a circuit is established to supply steady energy to the section in the rear.

This energy feeds across the insulated joint and holds the track relay picked up until the relay LOS releases to cut off further supply of steady energy to the section in the rear and to prevent picking upof the relay H. After the relay LOS releases, the associated signal is caused to display its most restrictive indication, and subsequent code following operation of the track relay will not alter the'signal indication. This insures that once a defective insulated joint has been detected, the signal at that location will be caused to provide'its most restrictive indication, while there is no possibilit that changes in track circuit conditions occurring thereafter will cause the signal to display a less restrictive indication. This system includes means for restoring the escapes "relay IZLOS, while contact25 of relay 121-! 'mainthe associated relay LOS releases to 'cut off apparatus'to normal operation after a defective joint has been repaired. This is done by depressing the normally open push button I2PB to thereby establish a pick-up circuit for relay IZLOS. When relay I2LOS picks up, its contact I! establishes the circuit of relay l2I-I, while contact 21 of relay IZLOS establishes the circuit for supplying energy torelay I2LOS duringthe re leased periods of the track relay contact 28 long as the relay IZH is released.

This system operates sojthat the signal for the section in the rear of the insulated joint will be caused to display its yellow or caution indication.

For purposes of illustration, it will be assumed that an insulated joint 3 separating sections I2T and |3T breaks down as a result of passage of a train, and that the equipment for section [3T When the train vacates section IZT, the energy of '75 code frequency supplied to transformer IZTT feeds to the track relay IZTR and the first impulse of coded energy picks up the track relay contacts, while on the'first off period in the code, the contacts of relay I2TR. release and an impulse of energy is supplied from winding I8 of transformer |2DT to relay IZH and its contacts pick up 'so' that contact 20establishes the circuit for steadily energizing relay IZLOS.

When the train advances far enough for the rear of the train to be located some distance in advance of the entrance end ofsection l3T, the train is no longer effective toshunt the track relay for section I3T with respect to energy feeding fro-m transformer I2TT across the defective joint. On the'first movement of the track relay for section i3T to its picked-up position, the circuit for supplying steady energy to section NET is established, and this energy feeding across the defective joint keeps the track relay picked up until further supply'of steady energyto the rails of :section IZT. The steady energy supplied to section I 2T feeds :to the track relay l 2TB and picks up its contacts and holds them picked up so that energy is no longer supplied .to relay 12H. As long as relay 12H remains picked up,,energy is supplied over its front contact 20 to relay i2LOS, but after a time interval, relay IZH releases and interrupts the circuit of relay IZLOS so that the'release period of relay, |2LOS begins.

to pick up its contacts and reestablish the circuit for steadily energizing relay IZLOS. Accordingly, relay iZI-I picks up to reestablish th circuit of relay ZLOS before relay 1 ZLOS releases to interrupt the circuit of relay IZH. I

On continued supply of coded energy to track relay IZ'IR, the relay IZI-lis maintained picked up and causes signal IZS to display its yellow or caution indication, while energy of 180 code frequency is supplied to the rails of section HT.

Operation of equipment if an insulated joint breads downwhen the track stretch is vacant For purposes of illustra'tion,.it will be assumed that an insulated joint separating sections HT and IZT breaks down at a time when the stretch is vacant. As the stretch is assumed to be vacant, energy of 180 code frequency is sup-plied to transformer IZTT, while relays NH and I ZLOS are both picked up and energy of 180 code frequency is supplied to the rails of section HT. If, at the time the insulated joint separating sections HT and [2T breaks down, the impulses of energy supplied to section HT are out of step with those supplied to section lZT, the impulses of energy supplied to section HT and feeding over the defective insulated joint to track relay IZTR will fill in the off periods in the code supplied to section IZT so that the track relay l2TR' will be maintaine-d picked up all, or substantially all, of

I they'will soon become out of step. This will be true because the code transmitters ar driven by electric motors of the squirrel cage induction type, and these motors will not operate at exactly the same speed for any substantial period of time. Accordingly, if track relay IZTR is not held picked up an abnormally large proportion of the time immediately upon breaking. down of the joint, thetrack relay'will soon be held up an abnormally large proportionof the time because of the increase in the time during which energy is supplied to the track relay when the tWo codes et out of step. v

L1 consequence of the lengthened picked-up periods of track relay IZTR, contact IE will not engage its back contact, or will engage it for such short time intervals that energization of relay [2B is reduced below the value effectiv to maintain the relay picked up. On release of relay l2H, its

assume onrel'ease 'ofirela'y 1 2H; .itscontactifl interrupts the circuit. for steadilyenergizin'g' relayv |2LOS and establishes the stickycircuit. for this-relay.

The. steady energy supplied :to trans-former .l lTT after releaseof relay I2H..feeds across the'cdes fective joint and. keeps :.the contactsaof :the track relay IZ'I'R picked up so thatrcontazcttrQBv:inter rupts the circuit 'ofrel'ay i2L'GS,.while'contact only one formuofrailway signaling system ern'-.

bodying myyinventioncit is. understood that various changes andlmodifications; 'may be made thereinwithin the scope of the appended claims without departing.v from the. spirit and scope of my. invention.

Having thus describedimy invention, what I claimis:

1; In a coded railway signalingsystem, income bination, a stretch of. railway. trackhaving a pair of track-rails divided by insulated joints into a pluralityof successive track'sections: including a forward'andza rearward. section, .acode following' track relay having a: winding receiving energy over. the 'rails of said forward section,.a

first and a second auxiliaryrelay associatediiwith said track relay, aacircuitincluding a front contact of said. second.auxiliary -relay for supplying energy to. saidfir'st auxiliaryv relay when and only when said track relay is. responding: to coded energy, a circuitincludinga back contact of said first auxiliary relay'for supplying codedenergy to the rails of said. rearward section, a .circuitin eluding a back contact of said first auxiliary re= lay and front contacts ofsaid track relay and of said second auxiliary relay and over which steady energymay be supplied to the rails ofsaid rearward section, a circuit including a front contact of the first auxiliary relay for supplying energy to the second auxiliary relay, and a circuit including a front contact of said second auxiliary relay and back contacts of said firstauxiliary relay and of said track relay for also supplying energy to said second auxiliary relay.

' 2. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of successive track sections including a forward and a rearward section, a code following track relay having a Winding receiving energy over the rails of said forward section, a first and a second auxiliary relay associated with energy; a circuit for. supplying; coded 1 energy to therailsiof: said; rearward section, a circuitin cludingjfrontcontacts of saidtsecond auxiliary .relay and of said track relay and over: which steady. energy. may be: supplied to-the-rails of said rearward section a :circuitincluding a front oonta'ct of the first auxiliary relay for supplying energy to; the secondauxiliarygrelay, anda cir"- cuit including. a front contact. of said second auxiliaryrelay-andback contacts of the track relay; and of saidsfirst auxiliary relay for also supplying energy to saidsecond auxiliary relay.

3; In a codedtrailway signaling system, in combination, a stretch of irailway, track having, a pair ofltrack railssdividedllay-insulated joints into a plurality 'of: successivertrack sections including a forward anda. rearward section,- a-code follow ing track relay having ;.a winding receivingenerg-y over the-railsof saidforward section, a first and a second auxiliary, relay associated with said track relay, a; circuit including, a front contact of said. second auxiliary'relay, for supplying energy to, said-.first-auxi-liary relay whenand only when said track'rela-y is responding to coded energy; a 'circuityincluding'.afront. contact of said first auxiliary-relay forsupplying energy; of a first code frequency to.-the rails .of saidrrearward: section, acircuit including; abackcontact of said first auxiliary, relay for. supplyingyenergy of a secondcode' frequencyte the :rails ofsaid rearward sectionga circuit. including aback contact of said first auxiliary relay and front contacts of said secondauxiliary relay and ot'saidtraclcre lay and over which steady energy may be. sup plied to therailsof said rearward section, a circuit' includingaifront contact of said first auxiliary'relay; forsupplying energy. to the second auxiliary relay, .and a circuit including a front contact of. said second auxiliary relay and back' first and-a second auxiliary relay, and a decod ingtransformer associated'with said :track relay, means governed bya contact of saidtrack relay for varying-.energization voibtheprimary; winding said track relay, a circuit includingja front conof said decoding transformer, acircuit including a front contact of? said secondauxiliary relay for supplying. energy from a secondary winding. of said decoding transformer-rte said first auxiliary relay, a circuit including a front contact of said first auxiliary relay for supplying energy of a first code frequency to the rails of said rearward section, a circuit includinga back contact of said first auxiliary relay for supplying energy of a second code frequency to the rails of said rearward section, a circuitincluding aback con tact of said first auxiliary relay and front contacts of said second auxiliary relay and of said track relay and over which steady energy may be supplied to the rails of said rearward section, a circuit including a front contact of said first auxiliary relay for supplying energy to said second auxiliary relay, and a circuit including a front contact of said second auxiliary relay and back contacts of said track relay and of said first auxiliary relay for also supplying energy tosaid second auxiliary relay.

5.- In a coded railway signaling system, in cornbination, a stretch of railway track having a pair of track rails divided by insulated joints into a Y plurality of successive track sections including lay, a-circuit including a front contact of said first auxiliary relay for supplying energy of a first code'frequency to the rails of said rearward section, a circuit including a back contact of said first auxiliary relay for supplyingenergy of a second code frequency to the rails of said rearward section, a circuit including a back contact of said first auxiliary relay and front contacts" of said'second auxiliary relay and of said track relay andlover which steady energy may be supplied to the rails of said rearward section, a circuit including a front contact of said first auxiliary relay for supplying energy to said second auxiliary relay, and a circuit including a front contact of said second aux-iliary relay-and back contacts of said track relay and of said first auxiliary relay for also supplying energy to said second auxiliary relay.

6; In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of successive track sections including a forward and a rearward section, a code following trackrelay having a winding receiving energy over the rails of said forward section, a first and a second auxiliary relay anda decoding transformer associated with saidtrack relay, means governed by a contact of said track rela for varying" energization of the primary winding of said decoding transformer, a circuit including a back contact of the track relay and a front contact of the second auxiliary relay for supplying energy from'a secondary winding of said decoding transformer to said first auxiliary relay, a circuit including a front contactof said first auxiliary relay for supplying energy of a first code frequency to the rails of said rearward section, a circuit including a back'contact of said first auxiliary relay for supplying energy of a second code frequency to the rails of said rearward section, a circuit including a back contact of said first auxiliary relay and front contacts of said second auxiliary relay and of said track relay and over which steady energy may be supplied to the rails of said rearward section, a circuit including a front contact ofsaid first auxiliary relay for supplying energyto said-second auxiliary relay, a circuit including'a front contact of saidsecond auxiliary relay and back con-' tacts of said track relay and of saidfirst auxiliary relay for also supplying energy to said second auxiliary relay, and a wayside signal for said forward section controlled so 'as to display its most restrictive indication when said first auxiliary relay is released. V

7. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails dividedby insulated joints into a plurality of successive tracksections including a forward and a rearward section, a code following track relay having a winding receiving energy over the rails of said forward section, a first and a second auxiliary relay associated with said track relay, a circuit including a front contact of said second auxiliary relay for supplying energy to said first auxiliary relay when and only when said track relay is responding to coded'energy,

said second auxiliary relay being slow acting and having contacts which normally occupy a first position and which are movable to a second posi-' .tion, means effective when the contacts of the first auxiliary relay are picked up to maintain the contacts of the second auxiliary relay in their first position, means effective when the contacts of the first auxiliary relay are released and the contacts of the, track relay are picked'up for causing the contacts of the second auxiliary re-- lay to move to their second position, means effective on movement of the contacts of said second auxiliary relay to their second position to maintain the relay contacts in their second position, means responsive to code following operation of said track relay for supplying energy to said first auxiliary relay provided the contacts of said second auxiliary relay are in their first position, a circuit including a front contact of said first auxiliaryrelay for supplying energy of a first code frequency to the rails of said rearward section,

a circuit including a back contact of said first auxiliary relay for supplying energy of a second code frequency to the rails of said rearward section, and a circuit including a front contact of said track relay and a back contact of said

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