US2350620A - Coded track circuit signaling system - Google Patents

Description

June 6, 1944. T. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM Filled Aug. 24, 1942 gsheets-Sheet 1 BTE 212 l l l l l RF1-E QJ* ci@ ETE E E ontrol Office Appai'atus CTCLomrriuncaton Syste.

June' e, 1944. T, J, JUDGE 2,350,620

CQDED 'TRACK CIRCUIT SIGNALING SYSTEM 5H DI @if {IFI- BY g f3 mw June 6., 1944. T. J. JUDGE `2,350,520

" conm TRACK cmcum smNALINe sYsTEM l Filed Aug. 24, 1942 9 sheets-sheet 5 June 6, `1944. 1'. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM s sheets-sheet 4 Filed Aug` 24, 1942 ATTORNEY June 6, 1944. r. J, JUDGE 2,350,620

f CoDE'D TRACK CIRCUIT SIGNALINC sYsTEM Filed Aug'. 24, 1942 9 sheets-sheet s maze-'21:19. ...J "gym l BY MM (,/LAZTTOIQEY l T. J. .JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM June 6, 1944.

EiledAug. 24, 1942 9 sheets-sheet e FIGA.

. ATTORNEY June 6, 1944. r. J. JUDGE CODED TRACK CIVRCUVIT SIGNALING SYSTEM Filed Aug. 24, 19'42 9 sheets-sheet '7 TTORNEY June 6, 1944. T. J. JUDGE com: TRACK cmcu'r SIGNALING sYsTEM Filed Aug. 24, 1942 9 Sheets-Sheet 8 53 BEP E m021. E M vou Plum@ ATTORNEY `*lune 6, 1944. T. J. JUDGE CODED TRACK CIRCUIT SIGNALING' SYSTEM 9 sheets-Sheet 9 Filed Aug. 24, 1942 ...9N :o wuvm. xus. E 0251.5 II .muon Humm E, VIAS@ E JV 7 j wII EN r V T I f llmmpfwmw |Nv NTO ATTORNEY Patented June 6, 1944 CODED TRACK CIRCUIT SIGNALING SYS TEM

Thomas J. Judge, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application, August 24, 1942,. Serial No. 455,922

46 Claims.

This invention relates to coded track circuit signaling systems for railroads, and it more particularly pertains to a system for single track railroads used in connection with centralized traiiic control.

According to the general organization of the system provided by the present invention, the automatic control of the signals in accordance with tra-flic conditions is effected entirely through the track rails by coded track circuit control, the only line wires required' being those associated with the communication of controls from a control oilce to the respective ends of the passing sidings generally known as field stations. Although the apparatus at the eld stations can be governed by direct wire control from the control oflice, it is generally desirable for the purpose of saving line wires that a suitable code communication system be employed as is shown, for example, in the patent to Judge et al., No. 2,082,544, dated June l, 1937, or in the patent to Halles et al., No. 2,259,561, dated October 21, 1941.

One object of the present invention is to provide coded track circuits in which driven code pulses are normally transmitted in opposite directions at different intervals through each track section. Such a driven code is characterized by having its impulses transmitted in accordance with the intermittent operation of coding'contacts and also called oscillator contacts. 'I'he invention then provides that the coding contactsv normally eiective at the opposite ends of each track section (or track circuit) operate at substantially different predetermined rates. This application of code pulses of di'iierent rates at the opposite ends of a track section causes the pulses to combine in a manner to effect the intermittent operation of the track relays at both ends of the section in accordance with what has been conveniently termed a beat code. Although the code following track relay at each end of a section operates as a result of impulses transmitted from the opposite en'd of the section, such operation is not in exact conformance to the operation of the coding contacts at that other end but is in accordanceA with a modified or beat code whichv is used to detect occupancy and provide a tumble-down circuit control as required for a centralized trafc control system for single track railroads. y n

Such an organization is considerably different than thoseY known in the prior art where a driven code is transmitted inl one direction through a track section andan inverse codey is transmitted in the oppositeV direction through that track section, because the transmission of an inverse code is wholly dependent upon the reception of the driven code and is tranmitted during the 01T periods of such driven code. Thus, in such an organization the cessation of the driven code also causes the cessation of the inverse code, while in the system of the present invention, the stopping of the transmitting means at one end of a track section merely allows the driven code at the other end to be transmitted without interference and received in accordance with the exact rate of its coding contacts then effective.

Also, in such prior systems the driven code in a track section has a rate' in accordance with the coding contacts at the transmitting end, while the inverse code takes the samerate as the driven code. But, when the present invention transmits driven codes in opposite directions through a section, the result is beat codes which operate the track relays at both ends of the track section as above mentioned.

Another object of the present invention is to so control the code transmitters at the opposite ends of a track section during normal beat code transmission, that the impulses making up. the

,beat code are of substantial duration to causeV a positive operation of the track relays at both ends of that track section. `This is accomplished in accordance with the present invention by controlling each transmitter of a track section so that it cannot interrupt the reception of a pulse from the other end of that track section. Thus, once a transmitter has applied an impulse, such impulse `can be terminated only' by that transmitter, which provides that the impulses of the beat codes are. usually of suflicient length to cause the positive response of the code following track relays.

l In a centralized traffic controlling system for a stretch of single track railroad having signals governing traffic in opposite directions over the stretch, it is necessary that the manual control f a head-block signal governing the entrance of trac at one end of the stretch shall act to prevent the manual control of the head-block signal governing the entrance of traic into the` other end of the stretch. Thus, a further object of the invention is toso organizev the' presentV sys--l tem that the code transmission through each track section of the single track stretch will be dependent upon the code transmission in the preceding track section for Vthe corresponding direction of code transmission with the manual.

control of a head-block signal acting bto cause the stopping of the code transmission from its end of the stretch. This cessation of code transmission in each of the track sections for one direction in response to the manual control of a signal obviously prevents code reception at the distant end of the stretch and thus holds the opposing signal at stop, and also acts to prevent manual interruption of the code transmission from such distant end of the stretch. This latter feature is essential so that a manual control for the distant end of the stretch cannot, in any way, interrupt the cleared head-block signal or any cleared intermediate signal if the train has already en- H tered the stretch. Y

Another object of the present'inventionis to automatically control the intermediate signals in a stretch of track between passing sidings in such a manner that they canbe safely allowed to indicate proceed for the passage of a train inv either direction through a stretch of single track after such train has entered the stretch from an outlying track switch located at some intermediate `point in the stretch. y

Another object ofthe present invention is to provide indications at the control oce as to trafc direction established and as to the presence oi' trains in Various portions of track. Y

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in partpointed out as the description of the invention progresses. f v

In describing the invention in detail reference will be made to the accompanying drawings in which those parts having similar features and functions are designated throughout the several illustrations by like letter reference characters `which are generally made distinctive by reason of preceding numerals indicative of the location of the signal with which such parts are associ--` ated and in which: f

Fig. l illustratesV diagrammatically manual control means at a control ofce for the communication of switch' and signal controls to the various field stations, together with means provided at the control ofce for visually indicating on the control panel thejconditions or' track occupancy and traic direction established invariousportions of track; Y a

Figs. 2A through 2D when placedpside byside respectively illustrate the manner in which coded track circuits are applied to the' control of the signals and to the control of traic direction for this embodimentl of the present invention;

Fig. 3 illustrates in detail the manner in which approach locking relays are controlled for the signals at a particular eld station;

Fig. 4 illustrates the manner in which approach locking is applied in the power operation of a track switch to provide for its safe operation, together with the control of correspondence relays associated with that track switch; l p

Fig. 5 illustrates the manner in which .the various indications are provided in response to conditions at the respective reld stations;

Fig. 6A through Fig. 6K illustrate diagrammatically the vconditions of track circuit code transmission for thevarious track sections. under certain typicalA conditions `of train Eoperation;

Fig. 7 illustrates diagrammatically 4how beat code; impulses are formed by the combination of 75 and'120 codes inthe form.A of the invention shown in Figs. 2A-2D. Y Y

Fig. 8 shows the trackway of Figs; 2A and 2B and a portion of their circuits to illustrate a simplified form of the invention.

Fig. 9 illustrates diagrammatically how beat code impulses are formed by the combination of 75 and 120 codes in the form of the invention shown in Fig. 8.

The illustrations employed inthe disclosure of thisj embodiment of thefpresent invention have been arranged to facilitate the disclosure as to the mode of operation and the principles involved rather than for the purpose of illustrating the construction and arrangement of parts that would `Uv bei employed in practice.

1 their contacts are shown in a conventional manner, certain 'relaycontacts being shown in written Thus, the relays and circutfornl and 'identified as of particular relays by the reference characters appearing directly A abve"` such contacts.

The symbols (-1-) and are employed to indicate the positive and negative terminals respectively of suitable batteri-es or other sources offdirect-current, and the'circuits with which those symbols'are .used always have current owing in' the same direction. The symbols (B+) and (B) indicate connections to the opposite terminals of. a suitable battery or other direct current source'whichhas a central or intermediate tap designated asv (CN), and the circuits with whichl those symbols are used may have current flowing in one'direction or the other dependent upon the particular terminal-used in combination .with the intermediatetap '(CN).

'In order to simplify the description of the present invention, reference is made from time totimeA to vfunctions common to al1 .parts of a similar Acharacterby use in the description of letter reference characters without their preceding numerals'for the designation ,of such parts. It is to be 'understood 4that such a reference applies toiany parts designated in the drawings by reference characterszthat are similar except for preceding numerals Y. associated therewith.

The trackway for vwhich this embodiment of the present invention is'provided comprises a main stretch of track divided into several track sections and having associated therewith passing sidings A and B- (see Figs. 2A through 2D). The right-hand end of` the passing siding A is connected tothe main track byra track switch 2W, and the left-hand end of the passing siding B is connectedto the main track by the track switch each ofwhich has Acoded track circuits. It is to be understood,- and it will be readily apparent as the description progresses, that the number of track sections inthe stretch of track between the passingsidings A andyB can be increased or decreased in accordance withthe requirements of practice.

Associated with the righthand end of the passing siding A are manually controlled signals 2A, 2B, .3A and 3B, signals 2A andZB being headblock signals governing entrance into the stretch of track between the passing sidings, and signals 3A and 3B being entering lsignals for governing train movements into the siding section and into the passing siding respectively. In a similar manner signals 8A, 8B, 9A and 9B are associated with the left-hand end of the passing siding B. Intermediate signals 4, 5, 6 and 1 are included in the stretch of track between passing sidings, signals 4 and y being provided for governing eastbound traicito ltheright) `andlsignals 5 and 1 being provided for governing westbound traffic (to the left). w

Although the signals illustrated in this embodiment of the presentv invention are of the searchlight type such, `for example,:as disclosed in the patent to O. S. Field, No. 2,239,316, dated April 22, 1941, it isl to be understood that other types of signals such as semaphore signals, position light signals, or signals havingv individual color lamp units could be employedby slight modication of the circuits disclosed in this embodiment of the presentinvention in a manner which will readily be recognized by those familiar with the art. The distinctive indications provided by the searchlight signals in this embodimen-t oi the present invention are green indications for clear, yellow indications for caution, and red indications for danger or stop.

Each of the track sections in the stretch of track between the passing sidings Aand B; and each of the siding sections 3T and 8-l IThas a coded track circuit which includes a code following track -relay TR and a source of current at each end of the track section. For the purpose of obtaining the. best operating conditions of vthe code following track' relays" and certain broken-down insulated joint protection, it is desirable that each track relay TR have a polar structure so arranged as to cause the relay contacts to be biased to a deenergized position from which they can be moved only upon energization of the relay windings with a particular polarity so that current will flow in a direction indicated by arrows in the windings.- Eachof those track sections also hasat each end a code transmitting relay CP which is. controlled by suitably selected coding con-tacts for applyingdriven codes of different rates to the track rails. For purposes of obtaining-the high'speed operating characteristics for the relays CP, such relays may have polar structures corresponding to Athat described above for thev track relays 'IR,'but this has not been indicated in the. drawings.

Suitablecode forming devices, or coding contacts, lare provided for the respective signalv locations for forming the, different,code rates employed'. `Although it is tobe understood that l motor driven .coders or .other code forming devices could be employedl,fthe codes" are formed in this embodiment of the present invention by code oscillators, or coding; contacts, which can be of a structure such as isishown,l for example, in the application of O. S. Field, Ser. No. 369,862, dated December 12, 1940. "An oscillator of such nature is capableofiorming but one code, thus requiring'separat'e oscillatorsfor forming the 180, l`and vrT5 codesrespectively; The system is so organized' thatV each signal location requires an oscillator i800 and either an oscillator IZUC or 15C depending'upon its relation to other signal locations. In this embodiment, the' successive signal locations have oscillators 15C` and |20C provided alternately inV order that the code oscillators forthepopposite' ends oreach track section will be normally active atsubstantially different rates'for purposes tobe' hereinafter considered. 'l l Relays H and"`D controlled through the medium of decoding transformers'are provided for the ends of the coded track circuits in the usual manner, each of the H relays being maintained steadily picked upr responsive to the pulsing of the associated code Afollowing track'.I relay at either code rate, andeachof. the relays D being. picked upr responsive only to the pulsing rof the associated code following relay at a rate.

Each of the iield stations has oiiice controlled relays for use in the manual control of the track switches and signals, a relay RGZ (see Fig. 2A) being provided for governing the clearing of signals for eastbound trafc, a relay LGZ being provided for governing signals for westbound traffic, a stop relay B being provided for the manual restoration of a signal to stop, a relay WN (see Fig. 4) being provided for governing the power operation of the track switch to its normal position, and a relay WR. being provided vfor governing the power operation of the track switch to its reverse position.

Each of the intermediate track sections has included inits track circuitat each end a series relay SR. which follows a code only in response to the presence of a trai-n in that track section, and upon following the code causes the' energization of the associated slow acting series repeater relay SRP. At the ends of the stretch of track between passing sidings the relays SRP are used for indication purposes, while the relays SRP at the intermediate signal locations are employed in the control of directional stick relays S, directional stick relay S being provided for each intermediate signal for governing the transmission of codes in the rear of such signal for the control of the signal in the rear under conditions involving the passage of following trains.

Certain of the signals have associated therewith relays YGP which repeat their proceed conditions, light-out relays LO, and relaysv RGP for repeating the stop or danger conditions of the signals.

Having thus considered the control apparatus employed in this embodiment of the present invention, a consideration will now be given to the mode of operation of the system under various typical operating conditions which would beencountered in practice.

Operation y General.-Befcre considering in detail the circuit organization provided in accordance withthe present invention, brief mention will be made as to the general mode of operation of the system in order to obtain the desired mode of operation without specic reference to the circuits involved.

With reference to Fig. 6A, the normal conditions of track circuit codetransmission are illustrated, the direction of the arrows indicating the direction of track circuit lcode transmission through the respective track sections. From this diagram it will be noted that a '75 code oscillator located at the field station at the right-hand end of theY passing..siding-` A governs transmission through the track rails in both directions from that point. At theinterniediatev signal location having signals 4 and 5, however, 1a 120 oscillator governs transmission through the track rails in both directions from that point, and inthis way the code transmitters for the opposite -ends of each of the track sections are normally active as governed by oscillators of substantially different rates. As a result of the transmitters attempting to transmit atidiierent rates for the opposite ends lof each of the track sections, beat code impulses are transmitted through the track rails in both directions to energize the track relays at both ends of each track section-in thev manner later explained. y D' In accordance with the specific embodimentl of theinvention shown, although theV transmission of a beat code in 'each direction through ea'ch'vof the track sections-under normal conditions energizes a signalcontrol relay H for each of the intermediate signals, the intermediatesignals fas well as the manually controlled signals at the field stationsare at. stop. Thisis true because each Vof fthe interr'riediate signals can be` controlled to a proceed position onlyv if theH relay for governing; the'oppo'sing signal atkthatlocationis deenerg'ized.

V`According to he diagram-of Fig. 6B, conditions are illustrated in which ahead-block signal has been cleared for governing passage of an eastbound train into the stretch of track between the passing sidings A and B. Inasmuch as the signal 2B governs `passage" of a train outof the passing 'siding A, thev conditions of code transmission in thefsiding'section are vnot changed from their normal conditions, butl the manual control ofthe signal 2B to its proceed position causes the removal of the 75 code normally transmitted from left to right in thertrack section 2-'-`5T'. The removal of such code causes a tumble-down through the remaining track sections in the stretch between passing sidings to providean interlock for the `head-block signals governing entrance to that stretch of track so that the signal SAHor the signal 9B cannot be controlled to display a proceed indicationfor an opposing train movement. Such tumble-down also provides an interlock in the circuits to prevent'the Vremoval of the 120Y code transmitted from rightxto' left in the track ysectionii--9T, as the removal of such code by an operator inadvertently "attempting Vto establish'an opposing route would cause restoration of the signal 2B rtostop in advance of the train.

. With reference to Fi'g.v6C, it will be noted that a lmanualfcontrol has' been communicated from.

the-control oflice for causing the signal 8A to indicate proceed, and such control of thatsig'nal has caused the removal of the'beat code-normally transmitted from right to` left in the siding track section Il -llfl` to establish an opposing signalvinterlock forpurposes just described vwith respect to the'interlock Afor the opposing 4signals governingmovement ofA trains in thestretch of track between vthe passing sidings A land B. y

` ItY will -be noted inthe diagrams of Figs. 6C through 6F that' normal conditions of code transmission are restored for the tracksections in the rear `of an eastbound train, and the restoration of such conditions provides a means for allowing thev settingup of'a route for a following train by the manual control of the head-block signal 2A or the signal 2B, such control being effective in the same manner'as if the entire stretch of track between the passingsidings Were unoccupiedbyatrain. y

- In Fig. 6G it is illustrated how the system provides for the back-up movement of trains in a stretch of track between passingrsidings. as.v is often required, for example, as in the movement of a work train. Under the conditions illustrated it is assumed that an eastbound train has proceeded pastthe intermediate signal v(i so as to allow the track section lf-'l'l to become unoccupied in the rear ofaV train and thus allow the restoration of the directional stick relay 4S `for the next signal `in the rear as illustrated in Fig. 6E. VIf under these conditions the train desires to., reverse its direction'of movement, the desired procedure is that the train move across thev rail joints past the intermediate `signal -T which would be at s'top under such conditions and send a flagmanv in the direction of signal 5 to observe the indication of that signal.'4 If it is safe for the train to Vproceed 'with its back-up movement, the signal will be atv caution as illustrated in Fig. 6G (if the manually controlled signal 3A or 3B at theright-hand end of passing siding A is at stop). If it isunsafe for the train to proceed in' its backward movement because of the establish'ment of a. route for a following eastbound train by the controlof signal 2A or 2B, the signal5 will be maintained at stop, and the flagman will not allow the train to proceed with its backup movement.v

' With'reference vto Figs.' 6Hthrough 6K it will bey noted that the system can be readily adapted to conditions in practice in which outlying track switches areprovided at intermediate points between the passing sidings. With reference to Fig. 6H,'it has been assumed that the eastbound train has entered the outlying switch 5W to a pointV beyond `fouling position and has restored the track switch to its normal position. Subsequent to the restoration'of that switch, the normal conditions of code transmission in the stretch of track are restored, and the return of the train to the main track as illustrated in Fig. 6J causes a tumble-down of the code transmitters in both directions from the track section directly associated with the outlying switch. In accordance with such' tumble-down,v intermediate signals 5 arid 6 are controlled to indicate proceed for train movement in either direction from the Vtrack section directly associated with the outlying switch. Such signalswill indicatel clear of caution inY accordance with the conditions of the signalsfin advance. in Fig. 6K, the man'- ual control of the signali3Al`to ra proceed position allows the transmission of a, driven code from left to right in the track section 2-5'1' to provide fork the clearindication of signal 5.,' Normal conditionsl--Under normal beat code conditions, the code'l` transmitter vrelays CP for the opposite ends of each track 'section are intermittently Y energized by their 'associated codin-g l-contacts,` 'but these coding contacts operate at diierentv code rates, such'a's 75 and 120 times per minute'jso that'current pulses somewhat variablei-in duration and spacing are intermittently transmitted in oppositedirections at dierent intervalsvover the track rails of this track section, and thus intermittently energize the code following track relays TR at both ends of the track sectionat recurrent intervals to'maintain energized an associated code responsive H relay.

Referring.tother normal beat code conditions for the track section Z-ST-,inFigsfZA and 2B astypical of' the othertrack sections, and consideringzthe preferred organizationv in which a transmitter relay 1CP may be energized by closure of its coding contacts -only if the associated track relay TR.` is deenergized, Fig. '7 shows diagrammatically inthe form of a time chart the relativetimingginthe oper-ation of the coding conof the oscillators 15C and |200 at the signals 2 andv 5 which .governY rthe lenergization of the transmitter relays ZCP and SCP respectively, together with the directionv and duration of the'current pulses in the track rails for this track section and the resultant energization ofthe track relays ZTR and STR. at the opposite ends of this track section..v In this explanatory diagram yor time. chart of Fig. '7, the vertical lines on thevgraphsv for Ythe oscillator 15C and 120C indicate'opening and closing of the coding contacts during the lapse of time from left to right, and the combined vertical and inclined lines in the graphs for the transmitter relay 2CP and CP and the track relays 2TH. and STR indicate energization or deenergization of these relays, the horizontal lines indicating the time duration of an unchanged condition in the opening or ,closing of the coding contacts or energization of the relays. With this explanation of the nature of the explanatory diagram of Fig. 7, consideration may now be given to the circuits and operation in detail.

With reference to Fig. 2B, the relay v5CP is normally active to intermittently connect the track relay 5TR and the track battery across the rails of the track section 2-5T, such relay being controlled by the Contact of the oscillator lZC. Assuming :the relation of the oscillators l 20C`and '15C for the opposite ends of the track section 2-5T to be as assumed .for the 'rst impulses in the diagrams of Fig. 7, the relay SCP is ener- -gized for an on period yof the `oscillator' [26C by a circuit extending from (-H, including inormally closed contacts |04 and vH15 of signal 5, contact 52 of oscillator lZC, front .Contact 53 of relay 4H, front contact 54 of relay 5H, winding of relay 5CP, and back contact v55 of relay 5TH., to The energization of relay 5CP under such conditions is diagrammatically illustrated in Fig. 7 -by the dotted line 56. The picking up of the relay 5CP closes a track circuit for the energization of the track relay `2TH. at the opposite end of the track section extending from the positive terminal of the track battery 51 including winding of relay 5SR, front contact :58 of relay .5CP, upper rail of track section 2-5T, back contact 59 of relay 2CP (see Fig. 2A), winding of relay 2TR, and lower rail of track -section 2-5T, @to the negative terminal of track battery 51 (see Fig. 2B) With reference to the diagrams of Fig. 7, the impulse applied to the track circuit by the relay 5CP is terminated by the oscillator IZBC as indicated by the dotted -line 6B. The dropping away of the relay 5CP causes the termination lof the impulse in the track rails by the .opening of front contact 58 (see Fig. 2B), andas a result of the termination of the impulse, ,the track relay 2TR (see Fig. 2A) is dropped away. `The closure of back contactl of relay ZTR causes the energization ofthe relay 2CP for the transmission of an impulse from left to right in the track section 2-5T as indicated by the dotted line 62 in the diagrams of Fig. 7. Such circuit is closed immediately because of theffon period formed by the oscillator C. vThe circuit .by which relay 2CP (see Fig. 2A) is energized lextends from including contact 63 of oscillator 15C, front contact `611 Vof lrelay Ztl-I, front contact B5 of relay 2-3TR, front contact 4$6 of relay ZAS, Winding of relay ZCP, and back `contact El of relay ZTR, to

The picking up of lthe relay 2CP opens the circuit for relay 2TH, at back contact v59 ,and closes a circuit for the energization of ithe relay ETR extending from thepositive terminal of track battery 61, including the winding yof the relay ZSR, front contact V59 of relay yZCP, upper .rail of track section 2-5'1, back contact L58.of;relay ECP (see Fig. 2B), winding of relay and.

lower rail of track section 2-5T, to the negative terminal of track battery El (see Fig. 2A). vIt will be noted from the circuit just described :that the relay 2CP is vmaintained picked upior the duration of the on period of the oscillator 15C,

irrespective of the condition of the oscillator at the opposite end of the track section. This is true because the relay ECP for the opposite end of the track section can be picked up for the transmission of an impulse only after the track relay 5TH. has vbeen dropped away. Thus, the termination of the on period of the oscillator 15C causes the dropping away of the relay 2CP -by the opening of contact 63 of oscillator 15C as indicated by the dotted line 68 in the diagrams of Fig. 7, and the dropping away of the relay 2CP terminates the track circuit code impulse and thus causes the dropping away of the relay 5TH (see Fig. 2B). The closure of back contact -55 of relay ETR closes a circuit by which the relay 5CP can be picked up, because the oscillator IZUC is at that time providing an on period. Thus', the relay BCP gains control of the track circuit for the transmission of an impulse by the energization of circuits corresponding to those which have just been described.

Thus, as indicated in the explanatory time chart of Fig. 7, under normal beat code conditions current pulses are transmitted over the track Yrails of the track section 2-5T in both directions at different intervals, and hence .the code following track relays 2TR and 5TR at the opposite ends of this track section are both intermittently energized. -In the preferred organization under consideration, these current pulses are transmitted rst in one direction and then in the opposite direction alternately as many times per minute as the slower 75 code rate, but the duration and spacing of these current pulses ,is variable. This is because each transmitter relay 2CP or 5CP is able to apply a `current pulse to the track rails upon closure of the associated Coding contacts only after the release of the associated track relay ZTR or STR upon cessation of the current pulse from the opposite end ...of the track section. For example, if the vcoding contacts IZOC governing the energization of the transmitter relay .ECP should close during' Ythe off interval between the current pulses vfrom the opposite end of the track section, then this transmitter relay SCP is at once energized and is also maintained energized until these coding contacts again open, regardless of the closure of the coding contacts for the .opposite end of the track section, so that the resulting pulse is as long as the regular on period for the 1 20 code rate, as indicated in Fig. 7 for the first impulse of the series between the dotted lines 56 and vlill. On the other hand, if the coding contacts i200 governing the energization of the transmitter relay 5CP should close .at a time when the track relay 5TR is energized by ya current pulse coming from the opposite end of the ytrack section, this transmitter relay cannot be energized until such pulse ceases; and this results in shortening or sometimes entirely Vblanking out the current pulse for that particular elo,- sure of the coding contacts |20C, as indicated in Fig. 7 for the second and third operations of the oscillator coding contacts C in the series shown.

In other words, as can be seen by a stud-y of the time chart of Fig. 7, in the preferred organization for creating beat code conditions, as contrasted in the alternative form vin Figs. 8 and 9 later discussed, the current pulses in opposite directions in `the track rails of the track section are not the direct result of the combined operation of coding I contact-s operating at .different code rates of 75 and 1,20 times per minute; but these current pulses have their duration andifspaccalled a beat cycle.

t'site 'ends of the track section at the same time,

and each track battery isr connected to the 'opposite ends of the track section alternately at different intervalsv and with a periodicity comparable with the slowerV code rate, thereby providing aduration and spacing of current pulses suitable for operating both code following track relays'to `rmaintaina code responsive device energized in substantially the same manner as inresponse to regularly spaced code impulses at the `slower code rate.

The time chart of Fig. 7 merely indicates for purposes of explanation approximate operating times and conditions for certain selected 75 and 120 code rates; andit should'be understood that the'duration and spacing of the current pulses in opposite directions as shown in this Fig. '7 'are merely illustrative or typical of the beat code operation characterizing this invention. -In this connection, it can be seen that coding contacts operating independently at diiferent code rates, such as 75 and 120l code rates, will change progressively from a given time relationship with respect to the on periods until after a predetermined time interval, this same time relationship again exists. This time interval may be For example, as indicated in Fig. 7, if the coding contacts operating at 75 and 120 times per minute open at the'same instant,'as assumed for Fig. '7, this same relationship recurs after a beat cycle of `4 seconds corresponding with the time required for 5 complete code pulses at the 75 rate and 8 complete pulses at the 120 rate.

`Inasmuch.V as the oscillators for the opposite ends of a track section operate independently of each other, and may happen to start at different instants or perhaps change their exact code rate, there can be other relative time relationships between the on periods for 'l5 and 120 code rates not illustrated in Fig. '7. Generally speaking, Vthe precise duration and spacing of the current pulses and the length of the beat cycle under the beatcode conditions contemplated, de-

pend 'upon the code rates chosen, the relative timing relation of the coding contacts, the accuracy with which each oscillator maintains its particular code rate, and other factors'; but the parts of the system can be readily organized to give under such normal beat code conditions a duration and periodicity of current pulses in both directions at intervals suitable for the energization of code responsive means at both ends of the track section for the purpose of detecting occupancy and providing tumble-down control for a system of centralized traflic control for a single track railroad.

At the left-hand end of the track section 2-5T, the pulsing ofcontact 6l of the relay 2TR (see Fig. 2A) causes the track repeater relay 2T? to follow the beat code 'being received at that end of the track section. It will be noted that the repeater relay ZTP is employed-primarily to lighten the contact load of the track relay ZTR. l' The pulsing of contact 69 of relay Z'I'P energizes the primary winding of the transformer `'lllfn'st indone direction and then the other in an obvious lmanner toinduce `an alternating volt- 'age in the secondary windings ofV that -transformer. The relay 2H energized under 'normal conditions by current flowing through its winding in a single direction because of its connection to the center tap of the secondary winding 1| in combination with the use of the rectifying contact l2 of the 'relay 2TP. The relay 2H is sufciently slow acting. to be maintained steadily picked up when the relay 2TP is active.

At the right-hand end of the track section 2-5T the relay 5H (see Fig. 2B) is normally picked up in response to the pulsing of contact 13 of relay STP in a manner corresponding to thatwhich has been described for the energization of the relay 2H, except that energy is applied to contact 13 of relay STP for the energization of the primary Winding of the transformer only in accordance with the closure of back contact 14 of the stick relay 4S associated with the intermediate signal 4. The reason for the inclusion of such contact in the circuit will be hereinafter considered.

The inclusion of a back contact of each track relay TR in the circuit for its associated code transmitting relay CP not only causes more positive operation of the code following track relays at the opposite ends of a track circuit during the beat code transmission in that track circuit, but also provides a check against the energization of the associated home relays H by foreign currents applied to the track rails. This is because` the application of a steady foreign current (of a particular polarity if the track relays are polarized as shown) causes the track relays TR at the opposite ends of the track circuit to be steadily picked up, which, of course, causes their associated home relays H to drop away and remain deenergized, but this steady energization of the track relays could not occur if it were not for the back contacts of such track relays included in the circuits for their respective code transmitting relays CP. In other words, the absence of such back contacts would permit the respective transmitting relays CP to cause the coding of theirY own track relays by energy from the foreign source. This feature of the present inventionis to be considered an improvement over a similar check against foreign currents provided in connection with inverse codes shown in the prior application of N. D. Preston, Ser. No. 365,- 065, dated November 9, 1940, and no claim is made herein to any subject matter disclosed in such prior application.

It may be noted that the connections to the track rails vof the track relays and battery sources are staggered for adjoining track sections so as to give the usual broken-down joint protection.

Having thus considered the manner in which a beat code normally transmitted in both direc- -tions through the track section 2-5T is effective -to cause the relays 2H and 5H to be picked up,

it is to be understood that a similar condition exists under normal conditions for each of the other track sections having a coded track circuit, the energization of the H relays for the intermediate signals being eifective only in accordance with the deenergized condition of the opposing stick relays Sas described with respect to the-control of the relay 5H. d

The circuits for the code transmitter relays CP are somewhat different for the intermediate signallocations in order to provide the desired mode of operation for an interlock of the opposing signals. Thus, the code transmitter relays for cuits arranged to provide a tumble-down of code transmission in a particular direction throughout the entire stretch of track lbetween the passi-ng sidings if such tumble-down is initiated by the rendering inactive of the code transmitter at one end of the stretch of track. Generally speaking, the circuit for the code transmitter relay CP at an intermediate signal for transmitting code pulses over the track vcircuit in the rear of that signal is governed by the signal control relay H for the adjacent end ofthe adjoining track section in advance of this signal to provide this tumble-down control. More specically, the relay 4CP (see Fig. 2B) is normally active for transmission of each impulse of a beat code from left to right in the track section 4-1T because of the energization during an on"`period of the oscillator |20C of a circuit extending from including contacts 50 and 5| of the mechanism of signal 4 closed when such mechanism is in its danger position, contact 45 of oscillator |200, front contact 16 of relay 5H, front contact 11 of relay 4H, winding of relay HCP, and back contact 18 of relay ATR, to It will be noted from the circuit just described that the dropping away of the relay 5H because of the relay ZCP being rendered inactive at the left-hand end of the track section 2-5T would cause the relay 4CP to be inactive for the transmission of a code from left to right in the track section 4-1T.

In a similar manner the dropping away of the relay 1H (see Fig. 2C) at the right-hand end of the track section 4-1T upon the rendering of the relay 4CP inactive would open the circuit for the relay BCP (which corresponds to the circuit just described for relay ACP) at front contact 19 to stop the transmission of a code from left to right in the track section 6--9T.

The control of the code transmitter relays CP for the ends of a siding section diiers primarily in that it is the manual control of the associated signals governing entrance to the sections involved that renders the code transmitters inactive. The relay 8CP (see Fig. 2D), for example, is normally energized for the transmission of each impulse of a beat code by a circuit extending from including contact 80 of oscillator |2|JC, front contact 8| of relayv 8H, front contact 82 of relay 8-9TR front `contact 83 of relay 8AS, winding of relay 8C?, and back contact 84 of relay 8ATR, to It Will be hereinafter pointed out specifically how the manual control of the signal 8A to a `caution position causes the dropping away of the relay BAS. and the dropping away of such relay renders the relay BCP inactive for the transmission of a beat code because of the opening of front contact 83. The code transmitter relay CP for the vopposite end of the track section 8| IT is controlled in a similar manner (corresponding to the relay 3GP to Fig. 2A).

The manually controlled signals are all normally at stop and normally dark except for the dwarf signals 2B and 9B governing train movements out of the passing sidings A and B vrespectively. The intermediate signals are also normally at danger, and normally dark.

The signal mechanisms for the signals at the iield stations are normally at stop in accordance with the usual practice in centralized traiiic control systems because of the deenergized condi.- tion of the cnice controlled relays LGZ and RGZ associated with the control of the manually controlled signals. The manually controlled .signals that are normally dark are dark 4because of the joint energization of the H relays for the coded track circuits adjacent that iield station, such condition being indicative of a normal condition with no routes established.

The intermediate signals have their .signal mechanisms normally at danger because each signal can be cleared only if the H relay for the opposing signal at that location is deenergized. Thus, for example, the mechanism of signal 5 :is at stop because the circuit for such signal -is open at back contact of the relay 4H for governing the opposing signal 4. The lamps of the 4intermediate signals are normally dark because of the joint energization of the H relays for the adjacent coded track circuits as has been pointed out with respect to the control of the lamps for certain of the signals at the field stations.V

Clearing of a head-block signaLJ-Assum'ing the normal conditions to exist as they have lbeen described, and as they are diagrammatical'ly illustrated in Fig. 6A, a typical condition will be described in which it is assumed that an operator desires to establish a route for the passage of an eastbound train out of the passingsiding A. Such condition is illustrated in the diagram of Fig. 6B. Y

To establish such route an operator at the control oiiice actuates the signal control lever 2-3SGL (see Fig. l) to its right-hand position, and the closure of contact 86 of such lever in its right-hand position applies energy to wire v2 6 for the energization through a code communication system or by direct wire of the pick-up winding of the relay ZRGZ (see Fig. 2A). If a code 'communication system is employed, `the lower winding of the relay ZRGZ will have a stick circuit to maintain such relay4 picked up until it is desired to Icause the signal to be restored to' stop. Such stick circuit can be provided in accordance with the principles of stick signal control, for example, as shown in my prior application, Ser. No. 365,669, dated November 14, 1940. y

The picking up of the relay ZRGZ under-such conditions closes a circuit for the energizationof the mechanism of signal 2B witha polarityfto cause such signal to indicate Acaution (yellow) exftending from including front contact 81 of relay Z-STR, back contact 88 of relay 2D, front contact 89 of relay RGZ, winding of 'signal 2B, front contact 90 of relay ZRGZ, front contact 9| of relay ZRCR, back contact 92 `of relay ZNCR, front contact 93 of relay 2H, yand back contact 94 of relay 2D, to It is of course to be understood that the reverse correspondence relay ZRCR is picked up for allowing such signal to indicate proceed only after the track switch 2W has been operated to its reverse position. The track switch 2W can be operated to its reverse position in accordance with the actuation of the switch control lever ZSML (see Fig. 1) to its right-hand position. The positioning of that lever closes a circuit at contact 95'of the lever lZSML in its right-hand position to apply energy to wire 28 for causing the picking up of a relay v2WR (not shown) at eld station No. 2. The control ofthe relay ZWR is provided in a manner similar to that illustrated in Fig. 4 for the corresponding relay SWR'associated with the control of the track switch 3W. The picking up of relay 2WR causes the power operation of the track switch 2W 'to its reverse position, and when it is in its reverse locked position, the associated correspondence relay ZRCR (corresponding to relay 3 RCR) is picked up to close the signal control circuit just described.

In accordance with the operation of the mechanism of the signal 2B to a proceed indicating 91.;` 'For the purpose of simplifying thedrawings,

thejcontrol circuit for therelay 2AS is merely indicated-by dotted lines as the circuit for such relay corresponds to the circuit illustrated in detail in Fig. 3 for the corresponding relay SAS associated with the left-hand end of the passing sid- .ing B.

When the relay ZAS is dropped away in response to the operation of the mechanism of signal 21?,r the relay v2CP is rendered inactive for the transmission of a code in the track section 2--5T bythe opening of front contact 66. This initiates a tumble-down which will be effective to render the corresponding code transmitters inactive for therespective track sections included in the stretch ofi track between the passing sidings A and B. f Y.

, At theright-hand end of the track section 25T,V the relays STR (see Fig. 2B) and 5TP become inactive because of the inactivity of the code transmitter relay 2CP at the opposite end of the track section, and the relay 5H is dropped away. 'I'he dropping .away of relay 5H closes obvious circuits for the energization of the signal lamps of signals 4 and 5 at back contact 98, the circuits for the lamps including light-out relays 4LO and 5LO respectively. w The closure of back contact 99 of relay 5H establishes-a circuit for the energization of the mechanism of signal 4 with a polarity to cause such signal to indicate caution. Such circuit extends from including back contact 99 of relay 5H, backcontact |00 of relay 4D, winding of signal 4, front contact of relay 4H, and back contactI |02 of relay 4D, to The conf ditioning of the mechanism of signal 4 to indicate caution establishes a circuit to cause the picking up of the relay 4YGP extending from including contacts 50 and 5| of the mechanism of signal 4, back contact |03 of relay 5SRP, and winding of relay AYPG, to The relay 4YGP is suiiiciently slow Ain dropping away to be main-v tainedpicked up upon the shifting in the position of the mechanism of signal 4 to change from a yellow to agreen indication or vice versa.

Conditions are now established whereby the relay 5CPfbecomes active for the transmission of a 180 code from right to left in the track section 2-5T. Such circuit extends from includingcontacts |04 and I 05 of themechanism of sig;- nal 5 in its. danger position, contact |06 of oscillator |800, front contact |01 of relay 4LO, front contactv |08 of relay 4YGP, back contact 54 of relay 5H, winding of relay 5CP,'and -back contact 55 of `relay 5TR,to It will be noted that back contactr55 of relay 5TR does not alter the pattern of the 'code transmitted because the relay STR remains deenergized.

`At the left-hand end of the track section .'2'L5T,'the pulsingl of contact' 69 of relay 2`TP (see -Fig..-2A)A responsive to the 180 code causes suiiicint energy to flow in the tuned circuit for the relay 2D'to cause that relay to be steadily picked up. Upo'nthe picking up of the relay 2D the shifting of contacts 88 and 94 of such relay in the circuit forjthe control of signal 2B pole changes the winding of such signal in an obvious manner to cause that signal to shift in its position to proevo A cycle of operation withrespect to ytrack circui-t code. transmission'in the track section 4--1T is initiated very similarly to the cycle of operation which'has been describedwith respect to the transmission and reception of track circuit codes in the track section 2-5'1, such cycle of operation for the track section 4-1Tbeing initiated when the relay 4CP see Fig.. 2B) is rendered inactive for the transmission of a code upon the dropping away of the relay 5H V.to open its circuit at front contact 16. l n p When vthe relay 4CP becomes inactive for the transmission of a code in track section 4-1T, the relays 1TR (see Fig. 2C) and 1TP at the right-hand end ofthe track section become inactive, and the cessation of the pulsing of contact |09 of the relay 1'I'P causes the dropping away of the relay 1H. The dropping away of such relay closes obvious circuits at back contact 0 for the `energization of the lamps of signals 6 and`1 and for the energization of the light-out relay 6LO and 1LO. The mechanism of signal 6 isenerg'ized upon the dropping away of the relay 1H with a polarity to cause such signal to indicate caution byY a circuit extending from including back contact of relay 1H, back contact ||2 of relay 6D, winding of signal 6, from contact' ||3 of relay 6H, and back contact |14 of relay 6D, to The operation of the mechanism of such signal to a po# sition to indicate caution causes the picking up of the relayv lYGl?y by the energization of a circuit extending from including contacts ||5 and ||6 of the mechanism of signal 6 in its caution position, back contact ||1 of relay 1SRP, and windingv of relay'BYGP, to 'I'he pick ing up of relay 'EYGB establishes a circuit by which the relay '1CP .becomes active for the transmission' of a lcode from right to left through theV track'rails of trackV section 4-1T. The relay 10P' is lpicked up during the on periods of the oscillator |C by the energization of a circuit extending from including contants ||8 and ||9 of signal 1' closed withthe mechanism oi?Y signal 1 in its danger position, contact 46 of oscillator |80C, front contactV |2| of relay'BLO, front contact |22 of relay GYGP', back contact |23 of relay 1H, winding of relay 1CP, and back contact |24 of relay 1TR, to The reception at the left-hand end ,of the track section 4-1T of the 180 code causesl the pulsing of contact |25 of relay 4TP (see Fig. 2B) at a rate to elect the picking up of the relay 4D to pole vchange the circuit for the winding ofsignal 4 by the shifting of contacts |00 and |02, and thereby causev s uch signal to displa a clear (green) indication. i

The relay 6GB (see-Fig 2C) at the left-hand end of the track section 6--9T is rendered inactive by the dropping away-of the relay 1H and the opening of its circuit at front contact 19, thus causing the relays 9'IR. and STP (see Fig,l 2D) for the right-hand end of the track section 6-9T to become inactive. The cessation of the pulsing of contact |26 of'relay STP causes the droppingawayfoi the relay 9H, and the dropping away oisuch relay is effective upon the closure of back contact |21 to energize 'obvious circuits for the lamps of signals 8A and 9A, such circuits including the light-out relays 8LO and 9LO respectively@ l v' y Y Inasmuch as itjhas been assumed that no manual control has been communicated `to the field station No,l v3 for the clearing of a signal at yide for the displayv or a clear (green) indication. Y7s such v:field station, thev dropping. away of relay 9H is effective only to establish a new circuit by which the relay vQCP is active for the transmission of a 120 code as selected by the deenergized condition of the relay BYGP. Such circuit extends from including contact |28 of oscillator |20C, back contact |29 of relay BYGP, back contact |30 of relay 9H, front contact |3| of relay S-Q'IR, front contact |32 of relay SAS, winding of relay BCP, and back contant |33 of relay STR, to It Will be noted that the relay SCP is active to transmit a 120 code without interference under such conditions, the code transmitter for the left-hand end of the track section 6-0'1 being inactive. The reception of the 120 code at the left-hand end of the track section 6-9'1' serves to maintain the relay 6H picked up and the signal 6 at caution because the relay 6D is responsive only to a 180 code.

' If an operator has caused the signal 8A at field station No. 3 to indicate proceed, in a manner to be hereinafter considered, the relay 8YGP is picked up, and the energized condition of such relay causes the transmission of a 180 'driven code from right to left in the track section 6-9T as indicated in Fig. 6C. Under such `conditions the relay QCP (see Fig. 2D) is active for the transmission of a 180 code by its energization for each on period of the oscillator 180C by a circuit extending irom (-1-), including contact |34 of oscillator ISOC, front contact |29 of relay 8YGP, back contact |30 of relay 9H, front contact |3| of relay B-STR, front contact |32 of relay SAS, winding of relay SCP, and back contact |33 of relay STR, to

If a 180 driven code is transmitted from right to left in the track section 6-9T, the reception of such code at the left-hand end of the track section causes the energization of the relay 6D (see Fig. 2C),` and the picking up of that relay pole changes the circuit for the energization of signal 6 at contacts ||2 and ||4 to cause such vsignal to display a clear indication.

It will be noted that the dro-pping away of the relay 9H at the right-hand end of the track section 6-9T provides an interlock for the opposing signals at the'ends of the stretch of track between the passing sidings to prevent an operator from causing the signal 9A or the signal 0B to indicate proceed if he should inadvertently cause the transmission of a manual control from the control o-filce for the proceed indication of either of such signals. In the case of the occupancy of the route by an eastbound train. the interlock notonly prevents the proceed indication of an opposing signal, but, in that a proceed indication of such signal is essential in order to render the code transmitter relay CP inactive for the transmission of a code in the track section 6-9T, the interlock insures that the relayA SCP will be continuously active to transmit a code .in the direction of the eastbound train. independent of any act on tbe part of an o-perator'at the control office with respect to the transmission of controls to eld station No. 3.

Considering the description as it has been set forth for the clearing of the head-block signal 2B for governing train movements out of the siding A, it is believed to be readily apparent to those skilled in the art that a similar mode of operation is eiective in the control of the signal 2A associated with train movements from the siding section 3T into the stretch of track between the passing sidings A and B. Thus, if an operator were to cause the clearing of signal 2A, he would operate the switch control lever 2SML (see Fig. 1)

to its normal position, and would operate the signal control lever 2-3SGL to its right-hand position. In accordance therewith, the relay ZRGZ would be picked up in a manner which has been described, and the operation of the track switch 2W to its normal position would cause the energization of relay 2NCR, if such track switch were not already in that position. A circuit would be closed under such conditions for the energization of the mechanism of signal 2A with a polarity to cause such signal to indicate caution extending from (-f-), including front contact 81 of relay 2-3TR back contact 88 of relay 2D, front contact '8g of relay 2RGZ, winding of signal 2A, front contact |35 of relay ZRGZ, back contact |36 of relay ZRCR, front contact 92 of relay ZNCR, front contact 93 of relay 2H, and back contact 94 of relay 2D, to

The opening of contact |31 of the mechanism of signal 2A upon' the operation of that mechanism to a caution position would cause the dropping away of the relay ZRGP, and the dropping away of such relay would be eiective to render the relay 2CP inactive in a manner which has been described as being effective in response to the operation of the mechanism of signal 2B to a caution position. The rendering inactive of the relay 2CP would be eiective to cause a tumbledown of the corresponding code transmitting means for each of the other track sections in the stretch of track between the passing sidings A and B, and the application of a code at the right-hand end of the track section 2-5T would cause the picking up of the relay 2D to pole change the winding of signal 2A by the shifting of contacts 88 and 94 to cause such signal to be operated to a position to provide a clear indication.

Clearing of entering signaZ.--To consider the control oi a signal governing entrance to a siding section, Fig. 2A will be assumed as being placed to the right of Fig. 2D, the circuits of Fig. 2A which have been provided for the right-hand end of the passing siding A corresponding with the circuits which are provided but not specifically shown for the right-hand end of the passing siding B.

For consideration of a typical condition with respect to the clearing of an entering signal, it will be assumed that an operator desires to cause the signal 8A to be cleared for the passage of a train on the main track into the siding section 8-| IT, To cause such signal to indicate proceed the operator actuates the'lever B-SSGL (see Fig. 1) to a right-hand position and closes a circuit at contact |38 to apply energy to wire 34 for the communication of a control to the eld station No. 3 for energizing the relay SRGZ (see Fig. 2D). After such relay is picked up, a stick circuit is established in a manner corresponding to that which has been described when considering the control of relay ZRGZ.

The picking up of the relay BRGZ closes a circuit for the energization of the mechanism of v signal 8A with a polarity to cause such signal to assume its caution position. Such circuit extends from including front contact |39 of relay 8-9TR, back contact |40 of relay 8D, front contact IGI of relay SRGZ, winding of signal 8A, front contact |42 of relay SRGZ, back contact |43 of relay 3RCR, front contact |44 of relay 3NCR, front contact |45' of relay 8H, and back contact |46 of relay 8D,.to It will be noted that although the signal mechanism `is energized, the signal is maintained dark unless a route is established in the vrear of such signal as illustrated in Fig'. 6C, or unless thereis a train in approach of ythat signal; If there were a route established as illustrated in Fig. 6C, the relay 9H would be deenergiz'ed, and the closure of back contact |21 of such relay` would establish obvious circuits for the illumination of the lamps of signals.8A,'8B and 9A," such circuits including'the windings of lightout relays BLOand SLO respectively.

The dropping away of the relay 8RGP upon the opening rof its circuit at contact |41 of mechanism of signal 8A causes the dropping away of the 'relay -8ALS b'y opening the circuit for such relay at front contact |48 (see Fig. 3 for the complete circuit'for' relay 8AS). The dropping away f When the relay 8CP becomes inactive, the cessationzof the pulsing atthe right-hand end of the siding-section of contact |49 of relay 3TP causes the dropping away ofthe relay 3H: When the re- Ylay 3H isfdropped away, 'the relay 3GP is rendered active to transmit a '15'code (if the relay ZYGP is dropped away). The circuit by which the relay 3GP. isiactivefor the transmission of a 75 code extends from including contact |50 of oscil.. lator C,l back contact |5| of relay ZYGP, back contact |52 of relay 3H, front Contact |53 of relay 2-"3TR, front contact |54 of'relay 3AS, winding of relay 3GP, and back contact |55`of relay .'3'I'R,` to 'It will be noted that "the code transmitted is a.true '15code rather than a beat code because of the relay 3TR being steadily deenergized to maintain the back contact |55 closed. The reception at the left-hand end of the siding section of the 75 code maintains the` relay Y0I-l picked up, andV maintains the conditions vwhich have beenA describedwith respecttov the caution condition of theV signal 0A.

'If'it'is assumed that an operator proceeds to set p'aroute-foraneastbound train so as to a proceed'position by a circuit extending 'from ;including'contactsV |56 and |31 of signal 2A, front contact |51 of. relay ZLO, winding of relay ZYGR-iandbackfc'ontact |58V of relay 3H, to vIt'will benoted Vthat the inclusion of back con- Ytact`|58 ofrelay 3H in the circuit for the relay ZYGPLchecks that the beat code normally transmitted fro'nileft to right in the siding 'section has been removed before therelay 2YGP is allowed to bey picked up and to thereby cause an increase in therate' of code transmission in the rtrack 'section 3T; It willl be noted vthat this increase in rate is accomplishedby the shifting of contact |5|, of relay ZYGP inthe circuit for frelaySCP, the closure ofy front contact I 5| of suchrelay applying energy through contact |59 :o'f oscillator Y| 80CV to acirc'uit which has been described forthe energizationof the relay BCP.

. lWhen a .180 code is transmitted from right to .left in the 'track section-8-I IT as illustrated ln Fig;' 6D, the polarity applied to the signal 8A is V.reversed uponftheshifting of contacts |40 and such B by controlling -the signal' 8B to indicate caution,v the operator at the control omce would actuate the switch control lever 3SML to a reverse operating position to cause the application of venergy to 'the wire 35 for causing the power operation of the track switch 3W.

With reference to Fig. 4, theapplication of energy to wire 35 causes the picking up of the relay SWR by the energization of its upper winding and the Picking' up of such relay causes the release of relay 3WN by opening its stick circuit at back contact |60, the dropping away of relay 3WN establishes a stick circuit for relay 3WR, extending from (-1-), including back contact |6| of relay 3WN, front contact |60 of relay 3WR, and lower winding of relay 3WR, to (-)Q In accordance with the picking up of relay 3WR, a

reverse operatingcircuit for the switch machine f 3SM is closed atV front contact4 |52, such circuit including normally closed "contacts |63 and |64 of the approach locking relays 8AS and SAS respectively. When the track switch has completed its operation to a reverse position, the relay SRCR is picked up by the energization of a circuit extending from including front contact |65 of relay 3WR, back contact |66 of relay 3WN, winding of relay 3RCR, contact |61 of relay 3WP in its left-hand position, and front contact |68 of relay 3WP, to

The relay SRGZ (see Fig.v2D) would be picked up in a manner which has been described if controls were communicated to leld station No. 3 for the establishment of a route governing train movement into the passing siding B. The energized condition "of the relay SRGZ, 'with the track switch 3W operated to its reverse position, would cause the signal'B to be energized with a polarity to operate its mechanism to a caution position. Such circuit extends from (-1-), including front contact |69 of relay 8RGZ,winding of signal 8B, front contactA |10 Vof relay 8RGZ, front contact |1| of relay 3RCR, back contact |12 of relay SNCB, and front contact |13 of "relay s-9TR,t0 j j It will be noted that although the operation of the mechanism of signal 8B to a caution position would cause thedropping away of relay BRGP by the opening of its circuit at contact |14, and the dropping 'away of relay 8RGP would cause the dropping away of relay 8AS by the opening of its circuit at'front contact |48, the code transmitter relay 8CP would not be rendered inactive because of the closure of frontl contact |15 of the correspondence relay SRCR to shunt contacts 82 and 83 of relays 8-9 TR and BAS out of the circuit by which the relay 8CP is normally active. Thus,-thle control of signal 8 for the passage of Ya traininto the passing siding B has no effect upon the beat code normally transmitted in the siding section 8| I'If, therefore allowing the establishment of a route for an opposing train vthrough the siding section as is often desirable upon the meetingof trains.

Passdgeofua train-With reference to Figs. 6B through 6F, 'typical conditions will be considered with respect to the passage of an eastbound train fromr the passing siding A to the passing siding B. 1

With reference 't`o Figs. 6B and 6C, it will be assumedlthat the eastbound train accepts the head-block signal 2B which has been allowed to clear in a manner which has been described and has entered the end section 2--5T in the stretch .of track between the passing sidings A and B. Thepassage of the train into the detector trackl section 2-3T causes the dropping away of the relay 2RGZ (see Fig. 2A) by .the opening of the stick circuit for such relay in accordance with usual practice in the control of stick signals (not shown). It is to be understood, however, that non-stick signals can be used in accordance with the requirements of practice. The closure of back contact 90 of relay ZRGZ shunts the winding of signal 2B in an obvious manner to cause such signal to be put to stop. When the signal is restored to stop, the stop repeater relay 2RGP is picked up by the energization of a circuit extending from including contacts |56 and |31 of signal 2A in its stop position, co-ntacts 05 andv |16 of signal 2B. in its stop position, and winding of relay ZRGP, to The closure of front contact 91 of relay ZRGP with the OS track section 2-3T occupied by the train establishes a pick-up circuit for' the relay 2AS corresponding to a pick-up circuit provided under similar conditions for the'relay QAS as illustrated in detail in Fig. 3. It will be noted that the picking up of the relay ZASl cannot render the relay 2CP active for the transmission of a code in the track section 2-5T while the OS section is occupied because the circuit for such relay is open at front contact 55 of the relay 2-3TR.

When the detector track station 2-3T becomes unoccupied in the rear of the eastbound train, the relay 2CP becomes active for the transmission of a 75 code in the track section 2-5T in the rear of the train as indicated in Fig. 6C. The circuit by which the relay 2CP is active for the transmission of such code corresponds to that which has been described when considering the normal conditions of the system. It will be noted that the relay 2CP applies a true 15 code under such conditions because the back contact 6| of relay ZTR is maintained steadily closed.

The presence of the train in the approach of signal 4 causes sucient current to flow in the track circuit for track section 2-5T to render the series relay 5SR (see Fig. 2B) active, and in accordance with the pulsing of contact |11 of relay 5SR, the slow acting repeater relay SSRP is picked up and maintained in a picked up po` sition.

The picking up of relay SSRP closes a pick-up circuit for the directional .stick relay 4S extendlng from including contacts 50 and 5| of signal 4 in its clear position, front contact |03, of relay BSRP, front contact |18 of relay 4YGP,

and winding of relay 4S, to The picking up of that relay closes a stick circuit at front contact |19 for shunting front contact |18 of relay llYGP out of the circuit just described. The relay 4YGP is deenergized upon the picking up of relay ESRP by the opening of back Contact |03, but it is suiciently slow in dropping away to allow time to insure the picking up of the stick relay 4S. The dropping awai7 of the relay 4YGP opens the pick-up circuit for the relay 4S at iront contact |18, and closes a stick circuit to maintain the relay 4S picked up extending from (-5-), including back contact |78 of relay lYGP, iront contact |19 of relay 4S, and winding of relay 4S, to It will be noted that by this circuit organization the stick relay 4S is picked up when an eastbound train is in approach of signal 4, rather than being dependent upon a straddle joint type system of energization which is often faulty in its operation upon the passage of short trains.

With the relay S picked up and the relay 4YGP dropped away, the relay ECP becomes active `for the transmission of a 12,0 code because of the energization for each onv period of the oscillator |20C of a circuit extending from (-1-), including contacts |04 and |05 of signal 5 in its danger position, contact 52 of oscillator |200,

-front contact ofl relay 4S, back contact |08 of relay HYGP, back contact 54 of relay 5H, winding of relay 5CP, and back Contact 55 of relay 5TR, to The transmission of such 120 code in track section 2-5T conditions the system so that a signal 2A or 2B may be manually cleared for a following train when the track section 2-5T becomes unoccupied by the train under consideration. This is true because the normal conditions of beat code transmission becomes ef,- fective in the track section 25T when such section becomes unoccupied in the rear of an eastbound train as illustrated in Fig. 6D, thus conditioning the system so that the signal 2A or 2B can be controlled if desired to establish a route for a following train. The normal conditions of the code transmission become effective in the track section 2-5T when such section becomes unoccupied in the rear of a train because the code transmitters for the opposite ends of the track section are both activel at that time.

It will be noted that the relay 4YGP is dropped away in connection with the control of the stick relay 4S prior to the restoration of signal 4 to danger. Such signal is operated to its danger position when the eastbound train enters the track section 4--'|'T, and by shunting such section causes the dropping away of relay 4H. The dropping away of that relay opens the circuit for signal 4 atl front contact |0I.

When the eastbound train occupies the track `section 4-1T as illustrated in Fig. 6D, and the track section 2-5T has become unoccupied in the rear of the train, although a beat code is transmitted from left to right in the track section 2-5T, the relay 5H (see Fig. 2C) is maintained dropped away because of the inclusion in its circuit of back contact 14 of the stick relay 4S. Thus, the opposing intermediate signal 5 is maintained at danger even though the block in advance thereof is unoccupied by a train. This is in accordance with the desired mode of operation for governing the passage of trains making back-up movements. Such train movements will hereinafter be more fully described.

The presence of the eastbound train in the track section 4-1T causes the series relay 1SR to be active, and to effect the picking up of the directional stick relay 5S by the energization ci circuits corresponding to those which have been described in detail with respect to the control of the relay 4S. The picking up of the relay BS causes the relay 1VCP to be active for the transmission of a 75 code by the energization of a circuit corresponding to that which has been described by which the relay 5C? has been active for the transmission of a code in accordance with the energized condition of the relay 4S.

As the eastbound train proceeds further so as to cause the track section 4--1'1' to become unoccupied in the rear ofthe train, as illustrated in Fig. 6E, the 120 code transmitted from right toleft in the track section 4-1T causes the picking up of the relay 5HV (see Fig. 2B). The picking up of such relay with the relay 4D deenergized closes a circuit for the energization of the mechanism of signal 4 with a polarity to cause such signal to indicate caution. Such circuit extends from (-l-), including back contact 99 oi

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