US2594652A - Coded track circuit signaling system with improved feed-back code circuits - Google Patents

Description

A ril 29, 1952 A. LfJEROME CODED TRACK CIRCUIT SIGNALING SYSTEM WITH IMPROVED FEED-BACK CODE CIRCUITS 2 SHEETS-SHEET 1 Filed March 6, 1947 Approaoli Compolled C'zireaz'c allllll-llll l'llu a M0 IR V 0 W n M m m P A 2 L C B F A S B Y c J c m m F H Um m .1 m a 5/ THE Zo April 29, i952 I l A. L. JEROME CODED TRACK CIRCUIT SIGNALING SYSTEM WITH IMFROVED FEED-BACK CODE CIRCUITS FiIed March 6, 1947 2 SHEETS-SHEET 2 ww mE N INVENTOR. Amlzul' .Jerome.

HISAZZWIZNEK Patented Apr. 29, 1952 CODED TRACK CIRCUIT SIGNALING SYS- TEM WITH IMIPROVED FEED-BACK CODE CIRCUITS Arthur L. Jerome, Edgewood, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application March 6, 1947, Serial No. 732,866

My invention relates to railway signaling systems, and particularly to an improved rail-way signaling system of the coded track circuit type.

In coded track circuit systems, in addition to the use of a master code of various frequencies, which is transmitted from one end of the section to a track relay at the other end of the section, there is sometimes provided a feed back code which energizes a code following or track relay at the feed end of the section by impulses of feed back energy transmitted during the off periods of the principal or master code.

As usually arranged, the code following or track relay at the feed or exit end of the section which responds to the impulses of feed back energy is intermittently connected across the'rails of the section bythe code transmitting relay. Should extraneous or foreign energy be supplied to the track rails, of the proper polarity and value to operate this feed back track relay, the feed back track relay will respond to such energy if it is alternately connected to and disconnected from the section rails by the code transmitting relay.

It will be seen, therefore, that if in the presence of foreign current the transmitting relay for the master code operates to cause a false coding action of the feed back track relay intended 'to respond only to impulses of feed back energy transmitted from the other end of the track circuit, it might create an unsafe condition if the feed back code is relied upon for safety.

This condition is protected against by requiring that the feed back track relay be released before a pulse of master code energy ma be transmitted. It follows that if the feed back track relay is improperly energized, it will remain energized with the result that the supply of master code impulses interrupted, and the coding in both directions is stopped, putting to stop the signal controlled by the master code and thus showing that an abnormal condition exists.

' Where the equipment is arranged so that an impulse of master code cannot be supplied to the track rails until the feed back track relay releases a delay in supplying the impulses of feed back energy to the ction rails during the off periods of the master code may delay the start of the on eriods of the master code with the result that the impulses of master code are objectionably reduced length. this delay in the supply of impulses of master code .to the track rails the equipment may be arranged'to apply the impulseof feedback energy tothe' section immediately upon the release oi the. track relay which responds "to the master In order to eliminate 10 Claims. (Cl. 24638) code. However, if these impulses of feed back energy are short enough to avoid distortion of the on time of master code of the highest frequency, the periods between impulses of feed back energy are substantially longer than the on periods of the feed back energy when the master code is of low frequency. This results in an unequal operating cycle of the track relay which is operated by the feed back energy and interferes with the operation of the decoding means governed by this track relay.

It is an object of my invention to provide an improved type of coded track circuit signaling system in which the contacts of the track relay which respond to feed back energy are maintained in one position substantially as long as they are maintained in their other position.

Another object of my invention is to provide an improved type of coded track circuit in which the apparatus for supplying impulses of feed back energy incorporates various safety and self-protecting features.

An additional object of my invention is to provide an improved means for highway crossing warning signal control which may be used with coded track circuit signaling systems.

A further object of my invention is to provide for the track relay which responds to feed back energy an improved stick circuit which holds the relay contacts picked up throughout the off periods in the master code and is arranged so that it does not interfere with the control by this track relay of the transmitter relay.

Another object of my invention is to provide in a track circuit of the type described a feed back track relay having pick up and holding windings the circuits of which are independently controlled the track relay.

In practicing my invention, I arrange the equipment at the entrance end of the track section so that the impulses of feed back energy are supplied to the track rails immediately upon release of the track relay. The feed back control means comprises a slow release relay which is energized by current supplied over a front contact of the track relay and when picked up establishes a circuit including a back contact of the track relay for supplying energy to the track rails. The track relay when picked up establishes a stick 'circuit for itself while the means for detecting code following operation of the track relay is governed by a contact of the track relay and also by contacts of the slow release relay so as to prevent improper energization of the decoding means in the event the contacts of the track relay or the stick circuit for the track relay are defective. At the exit end of the track section a transmitting relay is provided and has contacts which control connection of the track battery and of the winding of a feed back track relay with the track rails. The circuit of the transmitting relay is governed by a back contact of the feed back track relay so that the contacts of the transmitting relay can be operated to interrupt the circuit of the feed back track relay only when the contacts of this relay are released. The feed back track relay when picked up establishes for itself a stick circuit governed by the code transmitter which governs the transmitting relay to thereby keep the feed back track relay contacts picked up until the end of the off period in the master code and thereupon leaving it connected across the track rails so that it will release only if foreign current is not present.

In a track section approaching a highway intersection I provide means for operating the slow release repeater relay for the track relay to thereby supply energy to the track rails to discontinue operation of the crossing signals when the approach section is vacated.

I shall describe four forms of coded track circuit signaling systems embodying my invention, and shall then point out the novel features thereof in claims.

In the drawings,

Fig. 1 is a diagrammatic view of a section of railway track equipped with a coded track circuit signaling system embodying my invention,

Fig. 2 is a fragmentary view of a modification of a portion of the equipment shown in Fig. 1,

Fig. 3 is a diagrammatic view of a section of railway track equipped with a coded track circuit signaling system embodying my invention for controlling a highway crossing warning signal, and

Fig. 4 is a fragmentary view of a modification of a portion of the equipment shown in Fig. 3.

In the drawings similar reference characters refer to similar parts in each of the several views.

Referring to Fig. 1, there is shown therein a section of railway track T having track rails l and 2 which are isolated from the rails of the adjacent section by the usual insulated joints 3. Trafiic normally moves through this section in the direction indicated by the arrow, that is, from left to right. A signal S, which as shown is of the color-light type having a green lamp G, a yellow lamp Y, and a red lamp R, is located at the left-hand or entrance end of the section T and governs movements of traffic into the section T.

The signal S is controlled by master code energy fed from the exit end of section T, and it is assumed that at the exit end of section T it is desired to provide a relay which is responsive to the occupancy of the section T.

The equipment at the entrance end of section T comprises a code following track relay TR, which is of a type the contacts of which are biased to their lower released position and pick up when and only when energy flows through the windingi 4 in the direction indicated by the arrow, that is, from right to left; an auxiliary code following relay TP, which is of a type the contacts of which are slightly slow in releasing; slow acting relay FSA and slow release relay BSA which detect code operation of the track relay TR and repeater relay TP; a decoding relay DR which is supplied with energy from a decoding unit IDU; a decoding transformer DT; and a feed back battery At the exit end of section T, the equipment comprises a feed back code following relay K which is of a type similar to the track relay TR; a code transmitting relay CTM; code transmitters [800T and I5CT; slow release relays KA and KB which detect code operation of relay K; a control relay CR; and a track battery TB.

At each end of section T, in addition to the apparatus listed above, there is provided a source of direct current, not shown, whose positive and negative terminals are denoted as B and C, respectively.

The equipment is shown in the drawings in its normal condition, with track section T unoccupied. Code transmitters IBUCT and TSCT operate continuously, the contacts of code transmitter I80CT being operated at a frequency of complete cycles per minute, while the contacts of code transmitter 'ISCT are operated at a frequency of '75 complete cycles per minute. As shown, the control relay CR, which may be controlled in any suitable manner by traflic conditions in advance of section T, is picked up and when the contacts of code transmitter I80CT pick up, a circuit is established to supply energy to the relay CTM. This circuit is traced from terminal B, over back contact In of relay K, which at this time is released, over front contact l2 of relay CR, over front contact M of code transmitter I8DCT, and through the winding of relay CTM to terminal C.

As a result contact [6 of relay CTM picks up and establishes a circuit for supplying energy to track relay TR over the section rails l and 2. This circuit is traced from the positive terminal of battery TB, over front contact l6 of relay CTM, through the winding l8 of relay K from right to left, over section rail I, through the winding of relay TR from right to left, over back contact 20 of relay TR, over back contact 22 of relay TP, and over section rail 2 to the negative terminal of battery TB.

Accordingly, the track relay TR picks up and its back contact 20 interrupts the circuit traced above for supplying energy to the relay winding. However, the characteristics of this relay are such that when it is energized by energy of sufiicient value to cause the relay to open its back contacts, the contacts will continue to move to their other position. When contact 2i) of relay TR picks up, it by-passes contact 22 of relay TP and establishes a direct connection to track rail 2 for supplying energy to the winding of relay TR.

When contact 24 of relay TR picks up, it establishes a circuit for supplying energy to the winding of relay TP. This circuit is traced from terminal B, over front contact 24 of relay TR, and through the blocking rectifier RI and the winding of relay TP to terminal C. When the contacts of relay TP pick up, contact 22 picks up and thereby connects the negative terminal of battery FB to section rail 2. However, the positive terminal of the battery FB remains disconnected at this time since contact 20 of relay TR is picked up.

After a time interval, contact M of code transmitter IBIICT releases, interrupting the circuit for supplying energy to relay CTM, which thereafter releases. When contact I5 of relay CTM releases it interrupts the supply of energy from battery TB to the section rails I and 2 and efiectively connects the winding I8 of relay K across the section. rails l and 2.

When the supply of energy from the battery TB. is interrupted, relay TR. releases and its contact. 2'4 interrupts the supply of energy to relay 'IP, Relay TP is slightly slow in releasing its contacts, and when contact of relay TR closes in its released position a circuit is established for supplying a short impulse of feed back energy from battery FE to the relay K over section rails I and 2. This circuit is traced from the positive. terminal of battery FB, over back contact 20 of relay TB, through the winding of relay TR from left to right over section rail 1, through the track or pick up winding 18 of relay K from left to right, over back contact [6 of relay CTM, over section rail 2, and over front contact 22 of relay TP to the negative terminal of battery FB. When relay TP eleases, the circuit traced above for supplying the feed back. energy to relay K is interrupted by contact 22 of relay The relay TP is selected so that its release time is shorter than the intervals between the impulses of master code energy.

Accordingly, the relay K receives a short impulse of energy flowing in such a direction that its contacts will pick up. When contact H] of relay K. closes in its picked-up position, it establishes a stick circuit for maintaining the relay K energized until the code transmitter lilliCT again picks up its contacts. This circuit is traced from terminal B, over front contact it] of relay K, over front contact 28 of relay CR, over back contact 3!! of code transmitter IBEECT and through the holding winding 32 of relay K to terminal C. As a result, whenthe relay K picks up its contacts in response to an impulse of feed back energy, the relay contacts will remain picked up until such time as code transmitter ISOCT again picks up its contacts.

After a time interval, code transmitter lBOCT again picks up its contacts, thereby interrupting the circuit previously traced for maintaining the holding winding 32 of relay K energized, whereupon relay K releases. Upon the release of relay K, its back contact [0 reestablishes the circuit originally traced for supplying energy to the relay C'TM, and the cycle of operation described above is repeated.

It will be seen, therefore, that with the track section T unoccupied and the control relay CR energized, impulses of master code energy are supplied to relay TR; 180 times per minute and the contacts of relay TR pick up and release 180 times per minute. Relay TP also operates its contacts atthe same rate, but its contacts are slightly slow in releasing and each time that relay TR releases its contacts, an impulse of feed back energy is immediately supplied to relay K for a period determined by the release time of relay TP. When relay K is picked up by an impulse of feed back energy, its contacts are maintained in their picked-up position until the end of the impulse supplied over the track rails and also are maintained in their picked-up position by the relay holding winding until the next impulse of master code energy, is to'be transmitted, at which time it is necessary that can pick up to supply an impulse of master code energy to the rails of section T.

Since the impulses of feed back energy are supplied to the track rails immediately upon release of the track relay these impulses may be long enough to insure that relay K will pick up, and at the same time will terminate soon enough to permit relay K to release immediately upon. interruption of the circuit of the relay holding winding. .This eliminates distortion of the impulses of master code which might occur if after release of the track relay there is any delay in the supply of feed back energy to the track rails.

The relay FSA is energized each time contact 24 of relay TR and contact 34 of relay TP are picked up. Energy is supplied to relay FSA over the circuit which is traced from terminal B, over front contact 24 of relay TR, over front contact 34 of relay TP, and through blocking rectifier R2 and the winding of relay FSA to terminal C.

Blocking rectifiers RI and R2 serve to isolate the relays TP and FSAinsofar as counter electromotive force generated by the relays upon interruption of their energizing circuits is concerned.

When contact 24 of relay TR. releases, energy is supplied to relay BSA over the circuit which is traced from terminal B, over back contact 24 of relay TR, over back contact 36 of relay TP, overfront contact 38 of relay FSA, and through the winding of relay BSA to terminal C.

Accordingly, it will be. seen that while the contacts of relays TR and TP are following code, the relays FSA and BSA are alternately energized and their contacts will pick up and remain picked up at this time, since the relays are slow enough in releasing to bridge the intervals in the supply of energy thereto. Thus the relays FSA and BSA are energized and their contacts are picked up when and only when the track relay TR. and its repeater relay TP are respond ing to coded energy. If the track relay TR or its repeater relay TP ceases to operate and its contacts remain continuously released or continuously picked up, the supply of energy to relay BSA will be interrupted, and its contacts will release after its release time has expired.

Similarly, since relay K is at this time following the impulses of feed back energy, relay KA is energized each time that contact 43 of relay K is picked up, and when contact 40 of relay K releases energy is supplied over a front contact 52. of relay KA to the winding of relay KB, which picks up its contact 44 to establish the supply of energy to the approach controlled circuit governed thereby. Accordingly, the relays KA and KB detect the code following operation of relay K in a manner similar to that in which relays FSA and BSA detect the code following operation of relay TR.

As pointed out above, after the contacts of relay K are picked up by an impulse of feed back energy supplied over the track rails during an picked-41p periods of relay K to pick up-the contacts of relay KA and keep them picked up in the released periods of the relay K.

When relay CR is energized, the frequency of the master code is 180 cycles per minute, and accordingly the contacts of the relay TP are picked up and released at that rate. When contact 46 of relay TP picks up and releases, energy is alternately supplied to the upper and lower halves of the primary winding 48 of decoding transformer DT. As a result, an alternating current having a frequency of 3 cycles per second is induced in the secondary winding 50 of transformer DT, and is supplied therefrom through the decording unit IBODU to the relay DR. This decoding unit, well known in the art, is constructed and arranged so that energy of a value sufiicient to pick up the contact of relay DR is passed by the unit when and only when the frequency of the energy supplied thereto is that for which the unit is designed to respond.

Accordingly, at this time relay DR is energized and its contacts are picked up. Contact 52 of relay DR and contact 54 of relay BSA cooperate to supply energy to the green lamp G of signal S. This energy is supplied over a circuit which is traced from terminal B, over front contact 54 of relay BSA, front contact 52 of relay DR, and through the lamp G to terminal C. Thus, when control relay CR is picked up to denote favorable conditions in advance of section T, the supply of master code energy having a frequency of 180 cycles per minute causes signal S to display a green aspect indicating proceed.

With the equipment operating normally as described above, it is assumed that a train moving from left to right passes signal S and enters section T. The wheels and axles of the train offer a low resistance path to the impulses of master code energy, and the relay TR no longer receives suificient energy to pick up its contacts. As a result, the contacts of relay TR release and remain released as long as the train occupies section T. Since contact 24 of relay TR remains released, the supply of energy to relays TP and FSA is cut off. After a short time interval relay FSA releases, interrupting the supply of energy to relay BSA. When contact 54 of relay BSA releases, it interrupts the circuit previously traced for supplying energy to the green lamp G of Signal S and establishes the circuit for supplying energy to the red lamp R of the signal. Contact 46 of relay TP now remains released, and as a result, energy is no longer supplied from the secondary winding 50 of transformer DT to the winding of relay DR through decoding unit I BODU and the contacts of relay DR release.

At this time, as relay TP remains released, impulses of feed back energy are no longer supplied to the section rails I and 2. Accordingly, relay K remains deenergized, and subsequently, relays KA and KB release. When relay KB releases, its contact 44 interrupts the supply of energy to the approach controlled circuit governed thereby.

When the train under consideration passes out of section T, relay CR will release and relay CTM will be supplied with energy by a circuit which is traced from terminal B, over back contact H] of relay K, back contact 12 of relay CR, front contact 56 of code transmitter CT, and through the winding of relay CTM to terminal C.

. As stated above, code transmitter 150T operates its contacts at a frequency of 75 complete cycles minute, and coded energy is supplied to the section rails l and 2 at this rate.

Relay TR will again respond to the master code energy, and relay TP will similarly operate. Energy will now be supplied to relays FSA and BSA and their contacts will be picked up.

However, since contact 46 of relay TP picks up and releases times per minute, the energy supplied to relay DR from transformer DT through the iSfiDU decoding unit is insuflicient to pick up the contacts of relay DR. As a result, the yellow lamp Y of signal S is supplied with energy over front contact 55 of relay BSA and back contact 52 of relay DR.

Each time that relay TR releases, an impulse of feed back energy is supplied to the section rails l and 2 from battery FB during the interval between the time that contact 20 of relay TR releases and contact 22 of relay TP releases. The impulses of feed back energy pick up the contacts of relay K, and when contact Iil picks up, a stick circuit for relay K is established and may be traced from terminal B, over front contact ill of relay K, over back contact 28 of relay CR, back contact 58 of code transmitter T, and through the winding 32 of relay K to terminal C. When the contacts of code transmitter 150T pick up, the stick circuit traced above is interrupted, and relay K releases, whereupon the contact [0 reestablishes the circuit for supplying energy to relay CTM.

The recurrent operation of the contact 40 of relay K causes relays KA and KB to be energized, and energy is again supplied to the circuit controlled by front contact 44 of relay KB.

It will be seen from the foregoing that the apparatus responds in the same manner with respect to the 75 code as it does with respect to the code, with the exception, as explained above, that the relay DR is not picked up during the time in which relays TR and TP are responding to 75 code, and thus causes a yellow or caution signal to be displayed at the entrance end of section T.

In addition, it will be seen that the stick circuit for the feed back track relay K is governed in such manner that the relay contacts remain picked up for the entire length of the "off periods in the master code irrespective of the frequency of the master code.

After the train proceeds a suiricient distance beyond section T, relay CR picks up, and its front contacts I2 and 28 again connect the code trans- -mitter itlllCT into the circuits previously traced for supplying energy to relay CTM and to winding 32 of relay K.

As a result, relays TR and TP at the entrance end of the section are operated at the rate of 180 cycles per minute. Relays FSA and BSA remain energized and additionally, the relay DR will now receive sufiicient energy from the decoding unit IBBDU to enable it to pick up its contacts. When contact 52 of relay DR picks up, it interrupts the supply of energy to the yellow lamp Y of signal S and establishes the circuit for supplying energy to the green lamp G.

The relay K at the exit end of the section will now respond to feed back energy at the rate of 180 impulses per minute, and the relays KA and KB will remain energized.

At this time, therefore, the equipment will have been restored to its normal condition, as previously described.

If foreign potential should become present across thesection rails l and 2 and should have such polarity'and be of such value'as tocause therelay K topick up, contact Ill of relay K will interrupt the circuit which supplies energy to relay" Consequently relay will. remainreleased and. track relay will no longer re:-' ceive-impulses of coded energy. As: a. result, the relay BSA. will be: released and the; signal Swill display a. red aspect, indicating: that. an unsafe; condition. exists in the section T.

Additionally, when. contact 40 of relay becomes. picked up, the. supply or energy to relay KB-is. interrupted. and relay KB releases,,thereby interrupting the: circuit controlled by contact; 44.

At this time. as relay K ispicked up-its contact. H1- establishes the. circuit for; supplying: energy tov to; the relay holding winding 32* during, the. re.-- leased periods; of: the code transmitter 'I-BCT, if relay CR. is. released, or of code transmitter LBUCT', if the relay CRis picked. up. During the. picked-upperiods; of; the contacts. or. the efiectiye. code transmitter thecircuit of the. holding wind-- ing. 32 of relay K is interrupted but. contact. of relay K does notrelease since itismaintained picked. up by energy supplied; from. the track rails. to the pick up or track winding 1.8 of the. relay. During the. picked-upperiods.- of-v the contacts of the eirective code transmitter energy is not. supplied tothe circuit of. the relay CTM. since con-- tact to. of. relay Kis. picked up. so the relay CTM remains released and maintains. the. circuit of. the winding [8 of relay K.

The operation of the equipment. therefore, is such that. when foreign current is. present. and picks up the contacts; of. the. relay K. the. circuit of; the relay CTM is interrupted. and the contact. of relay CTME, is certain to remain released and maintain. the circuit of. the. winding [8. of the relay K. so that foreign current keeps. the. contacts: of. relay K picked. up... As. long. as the contacts or relay K. are. picked up. by foreign current the. circuit of the. relay holding winding 32 is recurrently established and. interrupted by a. contact of. one of the code transmitters. but interruption of the circuit of. the winding. 32' cannot. interiere. with: the. circuit. of. the winding. I Bot relay Kand cannot. cause release of. the. contenets of. relay K. when foreign current. is present.

The. control of. the circuit. of; the. holding. wind-- ing 32- of relay K". is such,. therefore, that. under normal conditions the relay contacts, when picked up remain. picked up for the durati'fon of the. off periods in the. master code,- and release promptly atthe startof each on period. This insuresthat con-tact lll of relay K will establish the: circuitof. relay KA ti r p i d l ng. enough: torv maintain relay picked; up; and also; insures that contact: or of. relay K. will complete thecircuit of relay promptly upon movement of the contacts of the code transmitter so that.

theimpulses of master code energy supplied tothe' track rails will not be objectionably' reduced in length.

The control of the circuit of the holding wind ing 32 of relay K is also such that this: circuit interrupted" each time the contacts, of the effectiye. code transmitter pick up. However, picking. up of. the code transmitter contacts does not disturb the. circuit. for connecting. track winding l-E of relay Kacross. the. trackrails. and if. foreign current is present the contacts of relay K will be maintained. picked upby energy supplied. from the track railsto the. winding is. relay K is maintained picked up by energy supplied to winding" I18, the circuit ofv the relay QTM will not be established; and its; contact It 10 Willg remain released" and maintain the circuit of the winding l8 of relay K.

It will be; seen, therefore, that the circuit of the-winding 3.2- of relay K isarranged to permalt the: relay to release when the code trans-- mitter picks: up if conditions are proper, but not to-causeit to release if conditions are not proper.v

This equipment is also-arrangedso that if foreignpotenti-a-l should be present across the section rails I and 2 and is of such polarity and value as tocause the relay TRto pick up and if in. addition, the. stick circuit governed by front con-tact 20 of relay TR. should be ine-fiectivethe' signal Swill display its red aspect.v

It Willbe assumed. thatwhen relay TR. picks. up,, movable contact 29 does. not engage; its stationary front. contact, or that. the wire connectionto thev stationary contact is broken. Under these circumstances, the relay TR. will pick up,v but-when contact 21!, interrupts. the pick-up circui-t. which was previously traced, the supply of energy to the winding ofrelay TB is interruptedandthe contact 26 again closes in its released position in. which it reestablishes the. circuit for supplying energy totherelay winding. Thisre-- sultsina door-bell action of relay TR,. that. is, when relay TR attempts topick up, itsv contact. 211 interrupts; the, supply of energy tothe relay winding, and the. relay releases and again at.- tempts. to. pick up., Such repeated. cycles cause the. relay to operate. in. a manner similar to. a conventional electric vibrating bell, hence thename. door-bell action. On. each. pick-up of contact 24 of. relay TR,, energy is. supplied. to. re-

lay TB, but. relay TP' requires a. short time to pick up its contacts, and since relay. TR immediately releasesinsufiicient energy is supplied to the winding of relay T1? to. pick up. the relay contacts. and as a result the relay TP' may r e-- main released. When. relay TP is released its. contact 34 interrupts the. supply of energy to relay FSA, and consequently, relaysv FSA and BSA. are. released andisignal. will display ared' aspect.

As. pointed. out. above a short time. interval isrequired for the contacts of relay TP to pick upv after the circuit forv supplying energy to the winding. of. relay TP is established by front con;- tact. 24? of. relay TR. When. the door-bell action-of relay TR. occurs the contacts of relay TR I lay TR,, the: contacts. of relay 'TP probably will not-move totheirpicked-up position until after the contacts of relay TR. have released. Accordingly', energy will notbe supplied torelay- FSA. since relays TR andTP must both be picked up to establish the circuit of relay FSA.

When the: relay TP picks up its contact.- 22 interrupts the pick up circuit. for relay TR and establishes the circuit for supplying energy from battery FB through the winding, of relay TB; to the track rails on release of relay TR. The energy supplied from battery F3 to the trackrailsthrough: the winding of relay TR holds the relay contacts released and, creates; in the relay core flux: which must be overcome before the: re:- lay contacts. can be picked? up again. Accord:- ingly, if relay TP becomes: picked up as a re;- sult of door-bell operation of relay TR, contact. 22 of. relay TP interrupts the pick up circuit of: relay TR to' prevent relayTR; from picking up to establish. the circuit of relay FSA..

Furthermore, because of the supply of energy from the battery FB through the winding of relay TR the contacts of the relay TR will not pick up for a short time subsequent to release of relay TP. As aresult, if relay TP becomes picked up in response to door-bell operation of relay TR, the operation of relay TR is interrupted for a period so the relay TP will release and will not thereafter pick up for an interval.

If the relay TP should pick up before relay TR releases, the period during which the contacts of both of these relays are picked up is extremely short. The relay FSA is of a type the contacts of which are slow to pick up and the energy which can be supplied thereto in the intervals in which relays TR and TP are both picked up at times when the stick circuit for relay TR is defective is insufficient to pick up the contacts of relay FSA. As relay FSA remains released the relay BSA also remains released, and maintains the display of a stop indication by the signal S.

It will also be seen that if the connection to front contact of relay TR is deranged, during the normal operation of the system, the relay TR will be released immediately after picking up on the supply of an impulse of master code energy with results similar to those described above in connection with the foreign current.

The equipment also operates to prevent improper energization of the relay BSA in the event the contact 24 of relay TR is defective or out of adjustment so that it simultaneously engages both of the associated stationary contacts. As long as movable contact 24 engages its upper or front stationary contact, energy is supplied to relay TP and its contacts are picked up so that energy is supplied over its front contact 34 to relay FSA. However, as relay TP is picked up its contact 36 interrupts the circuit of the relay BSA and it is certain to remain released and maintain the circuit of the red lamp R of signal S.

Referring to Fig. 2, there is shown therein a modification of the equipment located at the entrance and of section T. This modification makes it unnecessary for the track relay TR to pick up over its back contact 26, and has different operating characteristics from the arrangement shown in Fig. 1, in the event a derangement of the circuits including front contact 26 of relay TR arises.

In operation, impulses of master code energy are supplied to the track relay TR by a circuit which is traced from rail I, through the winding of track relay TR from right to left, over back contact 22 of relay TP, and back to rail 2. When track relay TR picks up, its front contact 20 establishes a stick circuit to maintain the relay picked up. This circuit is traced from rail I. through the winding of track relay TR, and over front contact 20 of relay TR to rail 2. When contact 24 of relay TR picks up, it establishes a circuit for supplying energyto relay TP which is traced from terminal B, over front contact 24 of relay TR, and through the blocking rectifier RI and the winding of relay TP to terminal C. When relay TP picks up, its back contact 22 interrupts the circuit previously traced for connecting the winding of relay TR to the track rails but relay TR is now connected to the rails I and 2 over itsown front contact 20, and will remain picked up.

Additionally, when relay TP picks up, energy is supplied to relay FSA over front contact 24 of relay TR and front contact 34 of relay TP.

At the end of the impulse of master code energy, relay TR releases and its front contact 24 interrupts the supply of energy to relays TP and FSA. Since relay TP is slow in releasing, its front contact 22 will remain closed for a short time interval and at this time feed back energy is supplied to the section rails I and 2 over the circuit which is traced from the positive terminal of battery FB, over back contact 20 of relay TR, through the winding of relay TR from left to right to section rail l, and from section rail 2 over front contact 2 2 of relay TP to the negative terminal of battery FB. The fiow of energy through the winding of relay TR is in such a direction that the contacts of this relay remain released. When relay TP releases, its contact 22 interrupts the circuit for supplying feed back energy to the section rails and reestablishes the circuit for connecting the winding of relay TR to the section rails. Additionally, when contact 24 of relay TR releases, energy is supplied to relay BSA by the circuit which is traced from terminal B, over back contact 24 of relay TR, back contact 36 of relay TP, front contact 38 of relay FSA, and through the winding of relay BSA to terminal C.

The functions controlled by contact 54 of relay BSA and contact 46 of relay TP are identical with those previously described in connection with Fig. 1 and further description of them is unnecessary.

As previously explained, whenrelay TR picks up, its contact 20 should connect the relay winding across the section rails independently of contact 22 of relay TP. In addition, when relay TR picks up its contact 24 establishes the circuit for supplying energy to relay TP and its contact 22 interrupts the circuit which it controls for connecting the relay TR across the track rails. If the circuit established by front contact '20 of relay TR should be defective for any reason, such as a broken wire, the supply of energy from the track rails to the winding of relay TR will be interrupted when relay TP picks up, and the contacts of relay TR will thereuponrelease. In the period in which the contacts of relays TR and TP are both picked up energy is supplied to relay FSA, but this period is extremely short since relay TR releases very soon after relay TP picks up.

During the time interval in which the contacts of relay TP remain picked up after relay TR releases, feed back energy is supplied to the section rails l and 2 by the circuit previously traced. As the source of feed back energy is the battery FB which is adjacent the track relay, the impulses of feed back energy supplied through the track relay winding are of substantially greater value than the impulses of master code energy supplied to the track relay. Since the feed back energy is of opposite polarity to the master code energy supplied to the relay winding, the effect of the feed back energy on the relay TR is to cause its contacts to remain released. When relay TP releases, if the impulse of master code energy is still in effect, the relay TR will again I pick up and the cycle of operations just described will be repeated. The operation of relays TR and T1? is such that the periods during which both of these relays are picked up are relatively short compared to the intervening periods during which one or both of these relays are released. Since relay FSA is of a type which is slow in picking up its contacts as well as being slow in releasing, the momentary energization'of its winding during the periods in which relays TR and TP are both picked up is insufficient to cause the contacts of relay FSA to pick up. Accordingly, relay FSA remains released and relay BSA is not supplied with energy at this time and its contact 54 remains released, and since the remainder of the equipment is arranged identically with that shown in Fig. 1, it will cause the signal S to display a stop aspect.

The modification shown in Fig. 3, like that shown in Fig. 1 operates to maintain relay BSA released in the event contact 24 of relay TR is defective.

Referring to Fig. 3 of the drawings, there is shown therein a stretch of railway track having track rails l and 2 over which it is assumed that traffic normally moves in the direction of the arrow, that is, from left to right. This track is divided into sections by the usual insulated rail joints 3. The reference characters I and II respectively designate the entrance and exit ends of the full signal block length of the track stretch, and character III designates the location of the cut which subdivides this block into a rear or approach track section ET, and an adjoining forward track section QAT. This cut is occasioned by a highway II which intersects the track and with which a crossing signal XS, here shown as a bell, is associated to warn the users of that highway when railway traflic approaches the intersection over the approach section 2T.

Positioned at the entrance of each of the signal block lengths of the illustrated track is the usual wayside signal S together with the control apparatus therefor. 'The apparatus and circuits, not shown, for the control of the signals SA and SB, which are here shown as being of the colori light type, are identical with those shown in Fig. 1 and further explanation of them is unnecessary.

In this arrangement, impulses of master code energy supplied from the exit end II of the block are repeated by the apparatus at the cut location III to control the signal at the entrance end I of the block. During the off periods of the master code, impulses of feed back energy are transmitted from the entrance end I of the section to the cut location III to maintain the highway crossing signals or similar apparatus inactive under all vacant conditions of the rear or approach section IIII, including times when the section IIIII ahead of the cut may be occupied. When a train occupies the rear section I-III, the supply of feed back energy is cut off, and the cut section apparatus is brought into operation. When the train clears the exit end of the rear section IIII, coded energy --is again supplied over the track rails to location III from location I and the equipment is thereby restored to its inactive state.

At the exit end II of the main signal block I--II, there is shown a track battery 2ATB which supplies energy to the section rails I and 2 of 5'.

section EAT, when contact 16 of relay 'CTM is picked up. The relay CTM maybe controlled in a manner similar to that shown in Fig. 1, but, in any instance, it will be continuously operated at one or another of the usual plurality of distinctive code rates.

The equipment at the cut location III comprises a code following relay 2ATR, which 'is responsive to the impulses of coded energy supplied over the track rails I and 2 from the exit end II; a track battery 2TB, from which energy is supplied to the rails l and 2 of section 2T; a detector relay K, which responds to impulses of feed back energy supplied from the entrance end I during the off periods of the master code; slow release code detecting relays KA and KB; and the crossing signal XS.

The equipment at the entrance end location I, comprises a code following relay TR; a code following repeater relay TP having two windings; a feed back battery ZFB; slow release code detecting relays FSA and BSA; and a coding device CT, having continuously operating contacts.

In operation, with the block I--II unoccupied, the equipment assumes its normal condition as shown in the drawings. At this time the relay CTM picks up and releases its contact H5 at a code frequency determined in the customary manner by the condition of the section in advance of signal SB. When relay CTM picks up, energy is supplied to relay ZATR at location III. by a circuit which is traced from the positive terminal of battery ZATB, over front contact 66 of relay CTMT, over rail i of section EAT, through the winding of relay ZATR, over back contact 60 of relay K, and over rail 2 of section ZA'I' to the negative terminal of battery ZATB. When relay ZATR picks up, a circuit is established for supplying energy to relay ZTR. This circuit is traced from the positive terminal of battery 2TB, over front contact 62 of relay ZATR, through the winding of detector relay K from right to left, over rail i of section 2T, through the winding of relay 2TB, from right to left, over back contact 22 of relay ZTP, and over rail 2 of section 2T to the negative terminal of battery 2TB.

Relays K and ET?- are of a type the contacts of which pick up when and only when energy flows through the relay windings in the direction shown by the arrows. Accordingly, at this time the contacts of relay K remain released, while the contacts of relay 2TB, pick up. When relay 2TB, picks up, it establishes a stick circuit for itself over its front contact 20. Additionally, front contact 24 of relay ZTR establishes a circuit for supplying energy to the winding of relay 2'I'P. This circuit is traced from terminal 3, over front contact 24 of relay 2TB, and through the blocking rectifier Bi and the winding 64 of relay 2TP to terminal C. When relay vZTP picks up, its back contact 22 interrupts the circuit previously traced for supplying energy from the track rails to relay ZTR. However, relay ZTR, will now be supplied with energy over the stick circuit established by its front contact 29 and will remain picked up for the duration of the impulse of master code energy. Additionally, when the front contact 35; of relay TP closes, energy is supplied to the winding of relay FSA by a circuit which is traced from terminal B, over front contact 25 of relay TR, over front contact 3c of relay TP, and through the blocking rectifier R2 and the winding .of relay FSA to terminal 0.

When relay CTM releases its contact it, the supply of energy to relay ZATR is interrupted, and when relay 'ZATR releases, its contact 62 interrupts the supply of energy to relay 2TR, which then releases. Upon the release of contact 2&3 of relay 2TB, a circuit is established for supplying an impulse of feed back energy to detector relay K over the rails of section ET. This circuit is traced from the positive terminal of battery ZFB, over back contact 29 of relay 2TR, through the winding of relay 2TB from left to right, over rail l of section 2T, through the winding of relay K from "left to right, over back contact -62 of relay ZATR, rail 2 of section 2T,

15 and over front contact 22 of relay ZTP to the negative terminal of battery 2FB.

The direction of flow of feed back energy is such that relay 2TB, remains released, while the contacts of relay K are picked up.

The supply of energy to relay ZTP being interrupted by the release of contact 24 of relay 2TB, relay 2TP will release after a short time interval and interrupt the supply of feed back energy to relay K which thereupon releases. After a time interval, contact [6 of relay CTM picks up to supply energy from battery ZATB to relay 2ATR, and the cycle described above is repeated.

As stated before, each time that contact 24 of relay 2TR. and contact 34 of relay 2TP are picked up, energy is supplied to the winding of relay FSA. Relay FSA is slow in releasing and its contacts will remain picked up during the normal intervals during which contact 24 of relay ZTR and contact 34 of relay 2TP are released. Additionally, when contact 24 of relay 2TR and contact 38 of relay 2TP are released, relay BSA is supplied with energy by a circuit which is traced from terminal B, over back contact 24 of relay 2TR, back contact 35 of relay 2TP, front contact 38 of relay FSA, and through the winding of relay BSA to terminal C. Accordingly, while impulses of master code energy are being received, contact 54 of relay BSA is picked up, and a circuit similar to that shown and described in connection with Fig. 1 may be established over contact 54 of relay BSA to supply energy to the green lamp of signal SA.

At location III, relay K picks up and. releases its contacts in response to the supply of feed back energy, and when contact 68 of relay K is picked up, energy is supplied to the winding of slow release relay KA and its contact Ill picks up. When relay K releases, energy is supplied to the winding of relay KB by a circuit which is traced from terminal B, over back contact 68 of relay K, over front contact 10 of relay KA, and through the winding of relay KB to terminal C. Relays KA and KB are sufficiently slow in releasing to bridge the intervals in which contact 68 of relay K interrupts the supply of energy to their windings, and accordingly, while relay K is responding to the impulses of feed back energy, relays KA and KB will remain picked up. At this time, contact 12 of relay KB interrupts the supply of energy to the warning signal bell XS and the bell is inactive.

It will now be assumed that a train moving from left to right passes signal SA and enters section 2T. The wheels and axles of the train shunt the master code energy to such an extent that relay ZTR does not receive sufficient energy to pick up and accordingly its contacts remain released. As contact 24 of relay 2TR remains in its released position, the supply of energy to relays ZTP and FSA is interrupted and these relays release. When contact 38 of relay FSA opens it interrupts the supply of energy to relay BSA, and when relay BSA releases, its contact 54 interrupts the supply of energy to the green lamp of signal SA and establishes the circuit for supplying energy to the red lamp of this signal.

As previously pointed out, the supply of energy to the winding 64 of relay 2TP is cut off by the release of contact 24 of relay ZTR, and as long as relay 2TR remains released, winding 64 of relay 2TP receives no energy. However, when relay FSA releases, a circuit is established for supplying impulses of energy to a second winding 14 of relay ZTP. This circuit is traced from terminal B, over back contact 24 of relay 2TB, over back contact 16 of relay FSA, over front contact 18 of coding device CT, and through the winding 14 of relay 2TP to terminal C. The coding device CT is continuously connected to the local source of energy, and accordingly its contact 18 is recurrently opened and closed at a selected rate. As a result, at this time the winding M of relay 2TP is periodically energized, and each time winding 14 of relay 2TP is energized contact 22 picks up so that an impulse of feed back energy is supplied to rails l and 2 of section 2T over the circuit previously traced. However, the wheels and axles of the train assumed to be present in section 2T keep relay K from picking up.

When relay K releases and remains released, its contact 68 no longer establishes the circuit for supplying impulses of energy to relay KA, and relay KA releases, thereby interrupting the circuit governed by its front contact 10 for supplying energy to relay KB. When relay KB releases, its contact 12 establishes the circuit for supplying energy to the bell XS. Accordingly, the bell XS becomes active, warning the users of the highway H of the approach of a train.

When the train advances into section 2AT, the impulses of master code energy transmitted from location II are shunted by the wheels and axles of the train, and as a consequence relay 2ATR releases and remains released. Accordingly, contact 62 remains released and the supply of impulses of master code energy from battery 2TB to rails l and 2 of section 2T is cut off, while relay K is continuously connected across the rails of section 2T.

When the train vacates section 2T, the impulses of feed back energy which are at this time supplied to the rails l and 2 of section 2T by operation of relay TP by the circuit previously traced, are effective to operate relay K, and as a result the relays KA and KB are again energized. When contact 12 of relay KB picks up, it interrupts the supply of energy to the bell XS, which then becomes inactive.

As long as any part of the train remains in the section 2AT, the winding of relay K remains continuously connected across the rails of the section 2T, since contact 62 of relay 2ATR then continuously occupies its released position. When the rear of the departing train clears the exit end of the forward section 2AT, the rails of that section once more transmit master code energy from the battery ZATB to the code following relay 2ATR at location III.

At this time relay K is responding to feed back coded energy supplied from location I and governed by the circuits including contact 18 of coding device CT. However, during the periods that relay K is released between impulses of feed back energy, its back contact 6!! establishes the connection of relay 2ATR to the rails l and 2 of section 2AT, and relay 2ATR will pick up when supplied with an impulse of master code energy from location II. Contact 62 of relay 2ATR will then establish the circuit for supplying energy from the battery 2TB to the rails I and 2 of section 2T, and relay 2TR at location I will respond to the energy by picking up its contacts. When contact 24 of relay 2TR picks up, energy is supplied to winding 64 of relay ZTP, and when relay 2TP picks up, its contact 34 completes the circuit for supplying energy to relay FSA and its contacts pick up so that contact 16 interrupts the circuit governed by code transmitter CT for supplying energy to winding 74 of relay ZTP. The relay 2TP now operates in the manner originally described. when the block III was vacant, and impulses of feed back energy are supplied to relay K during the ofi periods of the master code energy, thus retaining the relays KA and KB picked up and rendering the bell XS ineffective.

Additionally, continuous operation of relays 2TB and 2TP will cause relay BSA to become energized. The equipment is now restored to its normal condition as originally described.

The arrangement of equipment shown in Fig, 3 embodying my invention is particularly advantageous in that the effects of foreign energy which might exist in the section rails are prevented from creating a dangerous condition. It will be assumed that a train is present in the approach section 2T, proceeding towards the highway crossing at location III. If a foreign potential of the proper polarity and magnitude exists across the rails I and 2, the relay K will pick up. However, when contact Si) of relay K picks up, it interrupts the connection of relay ZATR to the rails of section ZAT, and relay ZATR. remains released and its contact 62 will connect the winding of relay K across the rails of section 2T continuously. Accordingly, the foreign energy will retain relay K picked up and its contact $33 will interrupt the supply of energy to relay KB, which will release and thereby cause the bell 218 to operate, as is proper at this time.

If foreign energy should pick up the relay K,- with the result described above, at a time when the block III is vacant, rela'y 2ATR will remain continuously released because its circuit is interrupted by contact 6?! of relay K. Accordingly, the supply of impulses of master code energy from battery 2TB to relay ZTR. will be cut oil, and the relays FSA and BSA will release, with the result that the signal SA will display a red aspect, denoting a dangerous condition existing in the block I II. Although after release of relay BSA the relay 2T1? is operated by the circuit including contact 18 of coding device CT, the impulses of feed back energy supplied as a result of operation of relay TP only serve to maintain the relay K picked up.

Referring to Fig. 4, I have there represented a somewhat modified form of entrance end facilities which are suitable for use with the arrangement shown in Fig. 3 and may be substituted for the apparatus represented at location I in that figure. These modified facilities of Fig. 4: are generally the equivalent to the corresponding entrance end facilities of Fig. 3, except that it will be assumed that the block III is a part of a block signaling system, and that section IT is another block extending rearwardly from location I. Also it will be assumed that the master code may have one or the other of two frequencies, 75 cycles per minute if the immediate block in advance is occupied, and 180 cycles per minute if the next block in advance is additionally vacant.

Contact ate of relay ZTP and contact 54a of relay BSA govern circuits (not shown) to provide control of signal SA which is similar to that shown in Fig. 1.

During normal operation of the equipment, with the track section 2T vacant, the apparatus functions substantially the same manner as previously described in connection with Figs. 1

and 2 and a detailed explanation and tracing of the various circuits is unnecessary.

Section IT is provided with a coded track circuit for controlling a signal (not shown) in the rear, and as long as block III is occupied master code energy will be supplied to section IT 75 times per minute, and when block III is unoccupied master code energy will be supplied to section IT 180 times per minute. Code transmitting relay ICTM, therefore, is operated 75 times per minute or 180 times per minute, ac-

. cording as block III is occupied or unoccupied.

When the block III is unoccupied, relay BSA is picked up and relay ICTM is supplied with energy by a circuit which is traced from terminal B. over contact 82 of coding device I8llCT, over front contact 84 of relay BSA, and through the winding of relay CTM to terminal C.

. When the block III is occupied, relay BSA is released and its contact 84 interrupts the circuit governed by contact 82 of coding device IBECT for supplying energy to relay ICTM. However, at this time relay 2TB. is released, and a circuit is thereby established to supply energy to relay ECTM. This circuit is traced from terminal B, over back contact 24 of relay 2TB, over contact 83 of coding device TECT, over back contact 8d of relay BSA, and through the Winding of relay lCTM to terminal C.

Additionally, during occupancy of block III impulses of feed back energy are supplied to rails l and 2 of section 2T to discontinue op eration of the crossing signal when the rear of the train clears that section 2T, as explained in connection with Fig. 3. At this time relay ZTP is supplied with energy by the circuit'which is traced from terminal B, over back contact 24 of relay 2TR, over contact 88 of coding device 150T, over back contact 90 of relay lCTM, over back contact '36 of relay FSA, and through the winding M of relay ZTP to terminal C.

Accordingly, each time contact 88 of coding device T closes, relay 2TP is picked up, but in a very short time interval relay ICTM will pick up, interrupting the supply of energy to winding '84 of relay 2TP. It will be seen, therefore, that the relay ZTP is operated to provide impulses of feed back energy having a very short duration. These impulses, though short, are adequate to operate the relay K at the exit end of section IT to energize the relays KA and KB and discontinue operation of the crossing signal. The use of short impulses of feed back energy during the time that block III is occupied is advantageous in that it allows a longer off period during which when the master code energy is again supplied from the exit end of the block, the track relay 2ATR may pick up to regain its control of section 2T.

Although I have herein shown and described only four forms of signaling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In means for indicating at both ends of a section of railway track the condition of occupancy of said section, in combination, a first code following track relay at the first end of said track section and a second code following track relay at the second end of said track section, each of said track relays having front and back contacts closed respectively according as the relay is energized by energy supplied to the relay Winding over the section rails or is deenergized, a transmitter relay having a contact movable between a first position in which it effectively connects the winding of said first track relay across the rails of said section and a second position in which it connects a source of energy across said section rails, a code transmitter having contacts movable between a first and a second position at a selected rate and occupying each of their two positions for substantially equal time intervals, an operating circuit including a first position contact of said code transmitter and a back contact of said first track relay for moving the contact of said transmitter relay from its first to its second position, code detecting means responsiv to alternate establishment of circuits governed over front and back contacts of said first track relay, means for prolonging the picked-up periods of said first track relay to thereby facilitate operation of said code detecting means without interfering with the control by said track relay of the circuit of said transmitter relay, said means comprising a circuit including a front contact of said first track relay and a second position contact of said cod transmitter, a repeater relay to which energy is supplied over a front contact of said second track relay, a circuit including a back contact of said repeater relay for connecting the winding of said second track relay across said section rails, a circuit including a front contact of said second track relay for also connecting the winding of said second track relay across said section rails, a circuit including a front contact of said repeater relay and a back contact of said second track relay for connecting a source of energy across said track rails, and means for detecting'operation of said second track relay, said means comprising a slow acting relay energized I by a circuit including front contacts of said second track relay and said repeater relay in series, and a slow release relay energized by a circuit including back contacts of said second track relay and said repeater relay and a front contact of said slow acting relay in series.

2. In combination, a section of track, a first code following track relay located at the first end of said section and having front and back contacts closed respectively according as the relay is energized or deenergized, a transmitting relay having a contact movable between a first position in which it effectively connects said first code following relay across the rails of said track section and a second position in which it connects a first source of current across said track rails for supplying master code energy, a coding device having a contact operated between a first and a second position, an operating circuit including a back contact of said first code following relay and a first position contact of said coding device for moving the contact of said transmitting relay from its first to its second position, said coding device operating in such manner that the transmitting relay contact normally occupies its first position for predetermined time intervals, a second code following track relay located at the second end of said section and having front and back contacts closed respectively according as the relay is energized by master code energy sup plied over the track rails from said first source of current or is deenergized, a code following repeater relay to which energy is supplied over a circuit including a front contact of said second code following track relay, said repeater relay 20 having a release delay shorter than the period between the impulses of said master code energy, a pick-up circuit including a back contact of said repeater relay for connecting said second track relay across the rails of said track section, a stick circuit including a front contact of said second track relay for also connecting said second track relay across the rails of said track section, a circuit including a back contact of said second track relay and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said track section, means for detecting operation of said second track relay by master code energy supplied over the rails of said section, said mean comprising a slow acting relay to which energy is supplied over a circuit including front contacts of said second track relay and said repeater relay in series, and a slow release relay to which energy is supplied over a circuit including back contacts of said second track relay and said repeater relay and a front contact of said slow acting relay in series, and a circuit governed by a contact of said slow release relay, a circuit including a front contact of said first code following track relay and a second position contact of said coding device for supplying energy to a winding of said first code following track relay to thereby prolong the picked-up periods of the contacts of said first code following track relay without interfering with the control by said first code following track relay of the operating circuit for said transmitting relay, a second detecting means for detecting the code following operation of said first code following track relay, and a circuit governed by said second detecting means.

3. In a coded track circuit of the feed back type, in combination, a section of track, means for supplying to the rails of said section at the first end thereof impulses of master code energy, a code following track relay located at the second end of said section, a code following repeater relay to which energy is supplied over a circuit including a front contact of said track relay, said repeater relay having a release delay shorter than the period between the impulses of said master code energy, a pick-up circuit including a back contact of said repeater relay for connecting said track relay across the rails of said track section, a stick circuit including a front contact of said track relay for also connecting said track relay across the rails of said track section, a circuit including a back contact of said track relay and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said track section, and means for detecting operation of said track relay by master code energy supplied over the rails of said track section, said means comprising a slow acting relay to which energy is supplied over a circuit including front contacts of said track relay and of said repeater relay in series, and a slow release relay to which energy is supplied over a circuit including back contacts of said track relay and of said repeater relay and a front contact of said slow acting relay in series, and a circuit governed by a contact of said slow release relay.

4. In a coded track circuit of the feed back type, in combination, a section of track, means for supplying to the rails of said section at the first end thereof impulses of master code energy, a code following track relay located at the second end of said section, a code following repeater relay to which energy is supplied over a circuit including a front contact of said track relay, said repeater relay having a release delay shorter than the period between the impulses of said master code energy, a pick-up circuit includin a back contact of said repeater relay for connecting said track relay across the rails of said track section, a stick circuit including a front contact of said track relay for also connecting said track relay across the rails of said track section, a circuit including a back contact of said track relay and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said track section, and means for detecting operation of said track relay by master code energy supplied over the rails of said track section, said means comprising a first auxiliary relay to which energy is supplied over a circuit includfront contacts of said track and repeater relays in series, and a second auxiliary relay to which energy is supplied over a circuit including back contacts of track and repeater relays and a front contact of said first auxiliary relay in series, said first auxiliary relay being of a type the contacts of which are slow enough in picking up to become picked up only when the circuit for supplying energy thereto is established for time intervals substantially longer than the time required for s id track relay to release in the event that its stick circuit fails to close, said auxiliary relays being slow enough in releasing to remain picked up during normal code following operation of said track relay, and a circuit governed by a contact of said second auxiliary relay.

5. In combination, a section of track, a first code following track relay located at the first end of said section and having front and back contacts closed respectively according as the relay is energized or deenergized, a transmitting relay having a contact movable between a first position which effectively connects said first code following relay across the rails of said track section a second position in which it connects a first source of current across said track, rails, a coding device having a contact operated between a first and a second position, an operating circuit including a back contact of said first code following relay and a first position contact of said coding device for moving the contact of said transmitting relay from its first to its second position, said coding device operating in such manner that the transmitting relay contact normally occupies its first position for predetermined intervals, a second code following track relay located at the second end of said section and having a contact biased to a, released position from which it is moved to a picked-up position by master code energy supplied over the track rails from first source of current, means governed by said second code following track relay and operative upon each movement of the contacts of said relay to their released position to connect a second source of energy across said track rails for a period substantially shorter than said predetermined time intervals, a circuit including a front contact of said first code following track relay and a second position contact of said coding device for supplying energy to a winding of said first code following track relay to thereby prolong the picked-up periods of the contacts of said first code following track relay without interfering with the control by said first code following track relay of the operating circuit for said transmitting relay, detectin means for detecting the code following operation of said first code following track relay, and a circuit governed by said detecting means.

6. In combination, a section of track, a first code following relay located at the first end of said section and having a contact biased to a released position from which it is moved to a picked-up position on the supply of energy to a winding of the relay, a transmitting relay having a contact movable between a first position in which it efiectively connects said first code following. relay across said track rails and a second position in which it connects a first source of current across said track rails, a first coding device having a contact operated between a, first and a second position at a selected rate, a second coding device having a contact operated between a first and a second position at a different rate, a control relay having contacts movable between a first and a second position and governed by traffic conditions afiecting said section, a first operating circuit including a contact of said first code following relay closed in its released position, a first position contact of said control relay and a first position contact of said first coding device for moving the contact of said transmitting relayfrom its first to its second position, a second operating circuit including a contact of said first code following relay closed in its released position, a second position contact of said control relay, and a first position contact of said second coding device for also moving the contact of said transmitting relay from its first to its second position, said COdlllg devices operating their contacts so that the contacts remain in their first and their second positions for a predetermined time interval so that the transmitting relay contact normally occupies its first position for predetermined time intervals, a second code following relay located at the second end of said section and having a contact biased to a released position from which it is moved to a picked-up position by energy supplied over the track rails from said first source of current, means governed by said second code following relay and operative upon each movement of the contacts of said relay to their released position to connect a second. source of energy across said track rails for a period substantially shorter than said predetermined time intervals, a first stick circuit including a contact of said first code following relay closed in its picked-up position, a first position contact of said control relay and a second position contact 01"; said first coding device, a second stick circuit including a contact of said first code following relay closed in its picked-up position, a second position contact of said control relay and a second position contact of said second coding device, said stick circuits supplying energy to a winding of said first code following relay Without interfering with the control of the operating circuits for said transmitting relay by said first code following relay, detecting means for detecting the code following operation of said first code following relay, and a circuit governed by said detecting means.

'7. In combination, a stretch of railway track having adjacent rearward and forward sections through which traffic normally moves in the order named, means for supplying impulses of master code energy to the track rails at the exit end of said forward section, a first code following track relay at the entrance end of said forward section, a second code following track relay of the polar biased type and a first source of energy located at the exit end of said rearward section, the winding of said first track relay being connected across the rails of said forward section by a circuit including a back contact of said second track relay, means including a front contact of said first track relay for supplying impulses of master code energy from said first source to the rails of said rearward section according as said first track relay is operated by impulses of master code energy received over the rails of said forward section, means including a back contact of said first track relay for connecting the winding of said second track relay across the rails of said rearward section during the intervals between impulses of master code energy, means for detecting the operation of said second track relay, a circuit controlled by said detecting means, a third code following track relay located at the entrance end of said rearward section, a code following repeater relay having a first and a second winding, a circuit including a front contact of said third track relay for supplying energy to the first winding of said repeater relay, said repeater relay having a release delay shorter than said intervals between impulses of master code energy, a pick-up circuit including a back contact of said repeater relay for connecting said third track relay across the rails of said rearward section, a stick circuit including a front contact of said third track relay for also connecting said third track relay across the rails of said track section, a circuit including a back contact of said third track relay 1 and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said rearward track section, means for detecting operation of said third track relay by master code energy supplied over the rails of said rearward track section, said means comprising a slow acting relay to which energy is supplied over a circuit including front contacts of said third track relay and of said repeater relay in series, and a slow release relay to which energy is supplied over a circuit including back contacts of said third track relay and of said repeater relay and a front contact of said slow acting relay in series and a circuit governed by a contact of said slow release relay, and means for causing operation of said repeater relay when said third track relay is released to thereby cause impulses of energy to be delivered to the rails of said rearward section when master code energy is not supplied over the section rails, said means comprising a coding device having recurrently operated contacts and and a circuit including back -contacts of said third track relay and of said slow acting relay and a contact of said coding device in series for supplying energy to the second winding of said repeater relay.

8. In combination, a stretch of railway track including adjacent rearward and forward sections through which traflic normally moves in the order named, means for supplying impulses of master code energy to the track rails at the exit end of said forward section, a first code following track relay at the entrance end of said forward section, a second code following track relay of the polar biased type and a first source of energy located at the exit end of said rearward section, the winding of said first track relay being connected across the rails of said forward section by a circuit including a back contact of said second track relay, circuit means including a front contact of said first track relay for supplying impulses of master code energy from said first source to the rails of said rearward section according as said first track relay is operated by impulses of master code energy received over the rails of said forward section, means including a back contact of said first track relay for connecting the winding of said second track relay across the rails of said rearward sec tion during the intervals between impulses of master code energy, means for detecting the operation of said second track relay, a circuit controlled by said detecting means, a third code following track relay located at the entrance end of said rearward section, a code following repeater relay having a first and a second winding, a circuit including a front contact of said third track relay for supplying energy to the first winding of said repeater relay, said repeater relay having a release delay shorter than said intervals between impulses of master code energy, a pick-up circuit including a back contact of said repeater relay for connecting said third track relay across the rails of said rearward section, a stick circuit including a front contact of said third track relay for also connecting said third track relay across the rails of said track section, a circuit including a back contact of said third track relay and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said rearward track section, means for detecting operation of said third track relay by master code energy supplied over the rails of said rearward track section, said means comprising a slow acting relay to which energy is supplied over a circuit including front contacts of said third track relay and of said repeater relay in series, and a slow release relay to which energy is supplied over a circuit including back contacts of said third track relay and of said repeater relay and a front contact of said slow acting relay in series and a circuit governed by a contact of said slow release relay, and means for causing operation of said repeater relay when said third track relay is released, to thereby cause impulses of energy to be delivered to the rails of said rearward section when master code energy is not supplied over the section rails, said means comprising a coding device having recurrently operated contacts, a coding relay supplied with energy by a circuit including a contact of said coding device and back contacts of said slow release relay and of said third track relay in series, and a circuit including back contacts of said third track relay and of said slow acting relay in series, and also including a contact of said coding device and a back contact of said coding relay for supplying to the second winding of said repeater relay impulses of energy having a substantially shorter duration than said intervals between the impulses of master code energy.

9. In a coded track circuit of the feed back type, in combination, a section of track, means for supplying to the rails of said section at the first end thereof impulses of master code energy of a given polarity, a code following track relay located at the second end of said section, said code following track relay being of the type which is responsive when and only when energy of one polarity is supplied to the winding of the relay, a code following repeater relay to which energy is supplied over a circuit including a front contact of said track relay, said repeater relay having a release delay shorter than the period between the impulses of said master code energy, a pick-up circuit including a back contact of said repeater relay for connecting said track relay across the rails of said track section, a stick circuit including a front contact of said track relay for also connecting said track relay across the rails of said track section, and means for detecting operation of said track relay by master code energy supplied over the rails of said track section, said means comprising a slow acting relay to which energy is supplied over a circuit including front contacts of said track relay and of said repeater relay in series, and a slow release relay to which energy is supplied over a circuit includv ing back contacts of said track relay and of said: repeater relay and a front contact of said slow acting relay in series, and a circuit governed by a contact of said slow release relay.

10. In a coded track circuit of the feed back type, in combination, a section of track, means for supplying to the rails of said section at the first end thereof impulses of master code energy of a given polarity, a code following track relay located at the second end of said section, said code following track relay being of the type which is responsive when and only when energy of one polarity is supplied to th winding of the relay, a code following repeater relay to which energy is supplied over a circuit including a front contact of said track relay, said repeater relay having a release delay shorter than the period be tween the impulses of said master code energy,

a pick-up circuit including a back contact of said.

repeater relay for connecting said track relay} across the rails of said track section, a stick cijr-j cuit including a front contact of said track relay. for also connecting said track relay across the rails of said track section, said pick-up and stick 1 circuits being arranged so that the impulses of said master code energy supplied over the circuits to said track relay are of the polarity required to n v m) cause operation of the track relay, a circuit including a back contact of said track relay and a front contact of said repeater relay for connecting a source of feed back energy across the rails of said track section, and means for detecting operation of said track relay by master code energy supplied over the rails of said track section, said means comprising a first auxiliary relay to which energy is supplied over a circuit including front contacts of said track and repeater 'relays in series, and a second auxiliary relay to which energy is supplied over a circuit including back contacts of said track and repeater relays and a front contact of said first auxiliary relay in series, said first auxiliary relay being of a type the contacts of which are slow enough in picking up to become picked up only when the circuit for supplying energy thereto is established for time intervals substantially longer than the time required for said track relay to release in the event that its stick circuit fails to close, said auxiliary relays being slow enough in releasing to remain picked up during normal code following operation of said track relay, and a circuit governed by a contact of said second auxiliary relay.

ARTHUR L. JEROME.

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

UNITED STATES PATENTS Number Name Date 1,214,375 Rudd Jan. 30, 1917 2,177,090 Blosser Oct. 24, 1939 2,184,543 Blosser Dec. 26, 1939 2,269,292 Staples Jan. 6, 1942 2,282,083 Nicholson May 5, 1942 2,362,419 Thompson Nov. 7, 1944 2,401,201 Thompson May 28, 1946 2,403,744 Nicholson July 9, 1946 2,458,746 Shields Jan. 11, 1949 2,465,794 Fereday Mar. 29, 1949

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