US2332963A - Remote control system - Google Patents

Description

(5. W. BAUGHMAN REMOTE CONTROL SYSTEM Oct. 26, 1 943.

iN V EN TOR Geo/ya! y/zmazz.

HIS ATTORNEY Filed June 23, 1941 Patented Oct. 26, 1943 V asasss p .U REMOTE CONTROL SYSTEM George WQBaugIiman, Swissvale, Pa., assignor to .t i The Union Switch & SignalCompany, vSwissvale, Pa., a corporation of Pennsylvania j 1 Application June 28, 1941, Serial No. 400,287? (o1. z t-41 My invention relates to remote control-systerns, and more particularly to centralized traffic control systems for-railroads for the control of railway signals, track switches or the like, from a central "point of control, such as a. train dispatchers office, and for the indication ofsuch devices at thecontrol oflice.

One object ofmy invention is the provision of an improved system of "this character in whicha visual indicator at the oflice is continuously and directlycontrollable according to the condition of the corresponding device in the field, and in which such device may be controlled according "to the positionof a manually operable leverat the office, by means of continuously transmitted codes of impulses of a distinctive frequency, over the same line wires.

A further object of my invention is the provisionof an improved system of this character which is adapted to employ existing communication circuits in order'to efiect the transmission of such controls and indications reliably over "relatively long distances in an economical mannerjand which possesses a high degree of other; communication facilities, or from any foreign current interference likely to occur in long distance line circuits i A specific object of my invention is the provision of an improved system for controlling a manual block signal forgoverning traflic movements" into a stretcher tracknot equipped with track circuits and for continuously indicating the condition of such a signal at a distant control officea Afurther object of my invention is the provision 'of improved means for insuring that a manually controlled signal which has been put to stop 'by a passing train cannot be cleared againexcept at the will of the operator at the point of control.

I shall describe one form of apparatus embodying my invention, and shallthen point out the novel features thereof in claims.

'Referringto the accompanying drawing, the lineardiagram at the top represents a stretch of railway track of which itis to be understood- WI 'inits normal position, asshown, is included within territory provided with continuous track l Claims.

circuits in which thetrack switches and signals examplepas that'disclosed in Letters Patent of the, United::S-tates ,No. "2,229,249, granted January 21, 1941,to L. V. Lewis; the controlofiice of the centralized trafiic control system beinglo cated in the cabin or tower Al shown at the left in the: drawing." The track switch WI, in its reversed position, connects this portion with a stretch of single track extending to a second tower A2, constituting'a manual block having a short detector section with a track relay ZTS directly in advancepof signal R2, but otherwise not "provided with track circuits over whichttrain movements are governed by the manual block signals R2 and L4. SignalR2 is controlled by the apparatus of my invention as'hereinafter operator at tower A2.

'The reference characters Yand' Z designate" reporting the passage of a complete train or reporting the position of signal Lito the operator at tower Al. l 1

The line wires Y and Z' also provide a line circuit for the impulse code system by which the track switch WI and other-apparatusincluded within the centralized trafliccontrol territory" butnot shown hereingisgoverned from tower Al. This line circuit isnormally closed an'd energized'from a central ofiicebattery and 'cor'n prises a metallic circuit including linewire's Y and :Z in seriesywith suitable low pass ffilters' interposed between the centralizedtrafiic con trol apparatus as in Fig) 1 of myLetters Patent of the United States No.2,'208,l46,granted July 16, 1940, for Remote control apparatus, hut for simplicity only the centralized traflic" control ofiice unit and one station unit are shown herein,

and these only in diagrammatic form since the mentioned patents The apparatus of my 'invention is controlled over a grounded linecircuit extending from towor Al to the location of signal R2, which includes frequencydiscriminating apparatus at each end to provide separate non-interfering'control and indication line cliannels, each of which include the linewir'es Y and Z in multiple, withearth return. The control line channel is employed for the transmission of alternating current of asu itable frequency such as 60 or =cyclesfrom a source at the control office, of which only the ter- The energization of winding l3 induces code minals are shown, these being designated BX and frequency alternating current in a secondary CX, respectively. This alternating current is winding M, which current is mechanically rectimodulated or interruptedat suitable rates such, fied by the operation of contact I of relay CD2 as 75 or 120 times per minute by a code transmit 5 to energize a second signal control relay ZI-IR.

ter 150T or IZOCT at the o-ffice, and i th d The circuits for relay ZHR correspond to those livered to the control line channel in accordance for relay H in Letters Patent of the United States with theposition, Oi, a signal control lever 2L. No. 2,237,788, granted to Nicholson, et al., and is The d transmitt r CT may b of any: u tam similarlyv responsive to either '75 or.;l code but type, suchfor example, as the one shown in Letin non-responsive'toforeign alternating current in ters Patent of the United States No. 1,858,876,, w ding M, such as might be supplied thereto, granted May 1'7, 1932, to P. N. Bossart, for Coding 'for" example, through Winding I3 from an rapparatus. With lever 2L in its normali'positiofiw Jna insc rrent battery char er connected across as shown, the supply of current from terminal terminals B n C of 2 6 0 Source.

BX is normally cut off, under which cnfiditi n' I Signal-5R2; as shown; if of the usual color light signal R2 is caused to indicate stop 335th fiype; nd aSsumin'gthat the track relay S is ing of its red lamp R. Under proper conditions licked D y ZNP eas d, it Will be lamp Y f signal R2 may b li htfltt gaig f t' ,seen that when lever 2L is reversed and button permissive indication by moving lever 2L to its 3 s, e e y ZHR and DR are both right-hand or reverse position, and then lamp G" 5 picked up to l ght lamp d t at with lever may be lighted inplaceofilamp Yiltocause-isignal. hr erseda d 1 2 1 2P3 0 1 9 v ay 2BR or illQ -e g e emcee-V R2itokindicatexclear;by'tthe operatiohlofe-aupusht. is ener ized tt-r a 2 R-is ,released tolight b tt 2P v a H lamp Y, while underother conditionslampfi is;-

.W-hen:IeVerUZLJiS- reversed,z:alicircuit is closed" h e from terminal ,3 1 fea suitablealocaltsource. of; cur-1..

mu h as: t .s ene l ielii eii c n lle rentfoven the. uppertsett ofi contacts :of '.;lever; 2L fi tl b n ts f h 5 3 q r and; ush. button; zpnthreugh'the. interrupted beck Contacts of t e e sje e e y ate.

contact andwwinding. of th6L,COd8l transmitter Control 2 kl q hmi i fi z f ebm lay 150T orl'lflCT, ,dependingtupon theqposition of; N Wh Q I-WD re edee s s the r smi e .v

push button ZPB, to;thehtheh.tehhinei .c oft-the sion e tinuo ed i 7 indi in e stop source and ats the; same: time,ali-local-, circuit v.is nd ien thesi nelett tr l fi V closed from the;terminal BX of; the :alternatingv Re il'N ifi l lm ly .Q t z Q $39K; currentsource throughtheilower'. set,:.of .contacts t fl'zif -eraa e m n lfie e Q QQ WQ Pf; of -1ever;.2Lv and pushbuttOnyZPB:and-:thejntere 6 'YS,: D ;a "z g-z it w ire t ta t mittently closed contacts: of code transmitter- 5 ndlwilld ll t0 termlne t nd a O 233 150T; or 12001. through the; primary. of, trans-s o r ay. 2 completes c c t m, e m na former 3 to the other terminal cxaofbhegalt'er B over the u t t on a t n W n ehatin currentl -source... ,Theiltransmitter: 1501' a cod tr 'nime e YH B CT-C to r jmi or 1720GT thenoperates:continuouslyjatthe. rate h -cla te is mi a ype ht T t -1 of {75 or? 180;:timesiper minute; respectively,v so 0 6.9 3 6 te e e si QQ IWQl S 39 times P thatgcodedialternatingtcurrentis delivered by the; lrlinlltein. ons the e ere ze e i secondaryuof transformer :37. to the controlline. ilb relay. N5.- i he lq ll ffi nt of channeL'j This channel exte dsermmateonnee v I880?! i c nne th o h-a nden e '6 tion to ground attheoffice .throughitheseconde 1 un ndw h middle Contact th r ary; ,of transformer 13,-,condenser: Land coil 5;. 51 1 01" i t tl filzei t d-P in Connection tuned to series resonance at the frequencyeofstheg: gt n r 1 s i 1 9 i on a ts are a o O -H l er a in cu nts ureeito themid-pointcom st to, na s. 32 e d of the o a ter nection tt simplex resistors a-theneethrough. mating ur en s reez s e s. as .r e N v is 0 s ,8and.thelinez stY;and inrmultipletoenergized, and serve as s nel ..:he eer ti thev centralized ,trafiiepontroly station wh it; 39 liver. impulses ofalternately opposite polarity to xli d fih gh .QQiL e idicondensersltothe the indication line channelextending over line idpo t on cti n. fzcs ensersa ,tandethence r s a n o. t ean de ints nee i V of roun hr ue l o dens refl and t nsformer; esi t rseht e c t h h coil lit-Cor, c nden er: I 0, wh ch re a1 tu q to;resona Ceat the free; ire isto O e y PR oe undl v q eues 0 the lfi rn tinel ur ntsource,., -.A;code.; v Relay 'P 'i a se sit v la of I L'S k po ar following relay CD2- is energized ;v fromstranse type and its contact is operated to the right or former l0 through a rectifier l l ,,and:therefore left according to ,the- -po larityof, each impulse repeats the operationpfi the code-transmitter e ve nr ISG FI and i he d m e te s cally by a definite biasing: force-in its last-op;

The operation of contacts, IZofrelay CDZ comeratedj posi ion i the 2e b tween pletes circuits extendingirom one; terminal B'of impulses being rendered thereby non-respon the localsource alternately ingpppositendirections. sive to strap currents of less than,;a predet er through the primary 13 off-. azdecoding transmined value! ,Relay PR;controls acode ifollowformer to the other terminal v(lof-thissource, so 8 r pe t 1 3" C v-Wh hiSfi. neu r i that current impulses of alternatelyitopposite lay of the usual railway Signal ing-type t polarity are gen rated in windin 13. d d 1i contacts repeat. the code operation ot the I conered to a resonantdecoding 'lgqDllbymeans, tacts of relaylBllCT and therefore operate lfio of which the signal; control, relay flDR-"is, selec-.- ti 1 u e. t j v i :1 j tively energized. ,This deccding icircuit is sub .Relay CD! controls decoding apparatus simistantially similar tothatqforrelayKZ. iniLetters. ,1ar to that controlledby relay cl32 andfdelivers Patent of the'l fInite :l;States-Ncx.137'73,;lt'l2,.granted 7 impulses ofwalternatelyg opposite-;polarity to a- August 1 9, 1930, to"P;,N.,Bossart,and1provid ;.a decoding transformer :21 w and; th, etc a resoe high; degree of selectivity ion the reasons exe nantdecodingunit 1801211 103 plained in thispatepttso,thatrelay 2DRsresponds; the.- normal indication re1ay 2N ans f which is,- selectivel lz fiQdeon ytp. 1 4 v energizedsg This ,decoding ;circuit is substan- Lamp 2RE therefore is normally, maintained lighted! only as long, as the communication line extendingatothe .location'of signal R2 is energized, and intactwandthe back contacts of relays 21-11% and 2BR remain closed to hold relay 2NP pickedup. M H v i Assume now that the apparatus is in its normal condition as shown, and that the operator attower Al, knowingthatthe manual block is unoccupied, reverses switch Wl by means of the centralized traific control, system and then reverses lever 2L and presses button 2P, with the object of effecting the movement of a train from left to right through the manual block, The code transmitter |20CT becomes energized, delivering alternating current interrupted 120 times per minute to the control line channel to operate relay CD2, thereby energizing relays 2BR and ilDRand consequently releasing relay 2NP. Lamp G of signal R2 therefore becomes lighted, and lamp R is extinguished, but only as long as the communication line is intact and lever 2L and button ZPB remain their operated positions. i i

The release of relay 2NP by the signal control relaysstops the delivery of 180 code indication impulses to theindication line channel and consequently relay 2NK releases and lamp ZRE be comes dark. l M

The indicationapparatus may be arranged in a mannerwhich will be readily apparent to one;

skilled in this art, so that a different continuous code, say, of, ,75 impulses, is now transmitted over the indication channel to light a, lamp ZYE or. ZGE at the ofi'ice, to indicate whether signal 23, is displayingits permissive or.clear indication. However, such indications, andlikewise an dndication of when a train passes signal,

it is to be understood the wires 89, 90, 9|:

and 92 leading to the C. T. C. station unit are the same as the corresponding numbered wires shown in Fig. 7 of Patent No. 2,229,249, hereinbefci-re mentioned, which govern the transmission ofcertain indication codes. As far as the present invention is concerned, itwill sufiice to point out that when relay 2H3 or ZDR picks up, an impulse code" is transmitted to pick up the corresponding centralized traffic controlindication relay ZHK or 2DK at the ofllce, which relay is then heldenergized locally until another indication'code is'transmitted in response to the release-of relay ZHR or 2DR. Similarly, an impulse code is transmitted whenever relay 2TS releases, to pick up thecentralized traflic control indication relay Z'IK to light the OS lamp ZTE, and-another code is transmitted when relay -2TS picks up to release relay ZTK to extinguish lamp Z'IE. w 7

' Under the condition 'being described, that is, withsig'nalRz cleared for an approaching train, lamp ZGE is lighted-and the remaining ofl'ice indication. lamps shown are dark.

Assume .now that the train enters the .detector indicate stop, even though relays ZHR, and 2BR remain energized. The dropping of contacts 23 and 24 of relay 2T8 initiates an impulse, code;

releasing relays 2I-1K and 2DK and picking up relay Z'I'K- so that lamp 2TEbecomes lighted and lamp 2GE is extinguished; r

.The track relay ZTS is a stick relay-which remains released after 'the train vacates the detector track section until the operator has re' stored his control lever to normal. 7

Assuming'that the operator restores. lever-2L to normal and. releases button 2PB as soon ashe is apprised that the train hasi'enteredthe. manual block by the light of lamp ZTE, relay IZIJCT becomes deenergized and the control code transmission isstopped, and a circ'uitis completed from terminal BX over the lower normal contact of lever 2L and a back contact 25 of relay.

2NK through transformer 3 to terminal OK, to

apply alternating current steadily to the control line channel. 'At the station, re1ayCD2 picks up and remains steadily energized and relays 2I-IR and 2DR release, completing a circuit for relay 2NP over contact 26' of relay CD2.- Relay2NP is a slow pick-up relay of a type requiring steady:

energization for about 1.2"sec0nds to pick up,

and releasing inabout 0.1 second after its circuit is opened. Consequently it is non-responsive to the. code operation of relay CD2 which occurs when lever 2L is reversed, even though relays ZHR and 2BR fail to pick up in response to the code,'and picks up only in response to the uncoded current supplied when lever 2L is normal.

whereupon relay2TS initiates a centralized traffic control code by the deenergization of wire 9|, releasing relay 2TK and extinguishing lamp 2TE,

thereby restoring the apparatus to the normal condition as shown.

his to be noted thatrelay ZNP might be an ordinary relay controlled only by back contacts of relays ZHR and 2DR, its control by relay CD2 being omitted, without loss of function in normal operation. In that case relay 2NP wouldpicku p' due to the deenergization of the signal control relays, in response to the restoration of lever 2L to normal. However, suchdeenergization might occur as a result of a circuit failure, and the operator happened to leave the signal lever reversed after the detector section has been vacated, and the line wires were then temporarily grounded, for example, it might happen that the signalcontrol relay ZHR would be released long enough to pick up relay ZNPand thereby reenergize relay 2TS. Then when the ground connectionfdisappeared relay ZHR would become reenergized and the signal would clearv again automatically, and thus defeat the purpose of the stick control of relay 2T5. With the arrangement shown, however, this cannot occur, because relay. ZNBresponds selectivelyto a signal of dis-i track sect ion,releasing relay 2TS.. The dropping of contact 22 of relay 2TS causes signal 22R to tinctive' character. transmitted only when signal level: is normal.

,It gisalsoi to be noted that lrelay ZTS functions; as an; ordinarynon-stick track relaylwhen axltrain' moving fromright to; left passes through the detector lsection, since in this .case the signal R2 has. not. (been; cleared :and consequently. relay ZNP remains picked up. l

pendance tothe controlcode current. 1 The selec-' tiizity of the .circuit. .for relay-PR is fur-therein;

creasedv :by the provision v of: .a resonant 2 shunt comprising condenser. 28 and coil 2% similar to condenser .4 andcoil 15. 5 l

At. the field. station; :the condensers?! .-,providei.a connection to v.the ,line wires forlthe control. and. indication line channelswithout affording a path for-.rcurrent frombattery 89 tointerfere with the operation of .,the centralizedtrafiic control line relays. such as, relay. 1 R; Condensers .1 9 and .l 6 isolatethe local battery from ground so.that the same battery .may be usedtoenergize other. circuits .which are .to be .maintained'r free .from grounds. .in accordance with the. usual practice inzrespect to-railwaysignaling circuits. The impulses. delivered by. relay IBQCFI torthejline are also impressed upon condenser!) and transformer: lll,. -.but. the .frequency and consequently. the L ener y-of theseimpulsesds.far too lowto operate relay .CDZ, furthermore, ..the ..circuits are .interlockedback contacts of the relays. controlled by relay. CD2 being included in-zthe, circuit for relay IRUCI, rendering relay 3180GT wholly incapable of..maintaining relays 2HR. and'rZDR pickediup Attheoniceiassuming a iailure .of the resonant circuit-elements. to occunpduegto. short circuits. or. otherwise, so that. relay P3; is renderectresponsive tq, the ,coded alternating current delivered v;by 159317 or IZBQT, it Wil be seen thatin thiscase thev n a t o .ar. R; w brate d rinet e. i

U ndprr ehfia d pos een i ne th f f, er d. det rm netely for the reason the code transin-itt ers are nonw et ner ...wiiht re st t a l: tin a erei t a e- R la D i n we en i etqt e man nt de ve d du in the ift. r l'thecode, d1ie vto gits relativel'y hi gl react et t er r p k l n yiw th Ic n: ea r ia ermane l ta dp isi i during an off period. Consequently, the; result ingop ration of relay CD isnot in accordance withan'y definite. code pattern suchlas is required for' the 1 op e ratior v of relayJZNKQA cross or groundon one of the line wires would cause current from battery 80 to pas through reI'ayl R. but this beingof jone polarityonly cannot cause its response to fa centralized traffic control ,code; Such a failuredioweven is immediatelytbrought to *the attention of *the operator attower '1 Al by there'sulting nois'e produced by the code'in his loud speaker normally connected-to line wires 'Y" and-Z; due to circuit unbalance. Theuse of difijerent code-frequenciesfor control and. indication as illustratedprovides in itself a definite. check against false operation oh relay 2NK, lhulit'his is=not-.essential; as it will be clean Deriodsotthe alternat g current code and will a sae s from-thelforeg'oing that the system may besafely eXpanded'to -pro'vide.additional controls andindications by the use of thesamecode frequencies for transmission in two directionslif desired.-

"Although I have herein shown and described only one-form ot remotecontrolsystems embodyinginy invention, it is understood that various changesand modifications may be made thereinwithin the scope of the=appended claims' without departing from-the'spirit and scope of :myinven- Having thus described my invention,.-what I claimis:

' -1.-- Ina remote control system, two stations connectedby-line wires, a-movalole-deviceat one station, means effective onlywhensaid device-is in a given -position fordelivering spaced impulses of alternately opposite polarity and of a fixed freque'ncy to-said line wires, a polar relay of the at -the irequencypfsaid impulses for selectivelyenergizing said indication relay '2. In a-remotecontrol system two tations connected by a line circuit, means at one station including a sourceofdirectcurrent of reversible polarity in SGIieSf-Wltha, condenser for delivering spaced impulses-of alternatel opposite polarity and of a fixed frequency to 'saidline circuitwithout ailording a metallic' connection betweensaid line circuit and said source, a polar relayof the magnetic stick-type at the other stationoperable alternately between two positions in-response to the impulses delivered-to said line wires and held magnetically inits last operated position during the intervalsbetween-impulse a circuit tuned to electrical 're'sonance at the frequency of said I impulses, means controlled by said polar relay for energizing's aid tuned circuit by impulses the relative poiarity of which is dependent upon the position of saidpolarrelay, an indication relay, andmeans i-ncluding'said tuned circuit; for selectively energizing said indication relay.

' 3. 'In' a remote'control system, two stations connectedby line wires, means --at one station for deliveringspa'ced impulses of alternately opposite polarityandof a fixed "frequency to said line Wires, a polar r'elay operable alternately between twdposiitions in responseto said impulses and held magnetically in its '.'last operated position during. the inte'rvals -petwe'en impulses, a" circuit tuned to electrical resonance at the frequency of saidirnpulseslmeans responsive to each energizae tion of said-polar relay by an impulse of given polarity to deliver an impulse of corresponding polaritytosaid tuned circuit, an indication relay, and means controlled by. saidtuned circuit and clependentupon ,thecontinued operation of i said polar relay for selectively; energizing said indicaenr la l 4, J The; combination with a stretch of railway ack ha inaa d t tor t ac .s onand si f r. eovem ne t afi c m e t to 5 4M5 tion with line wires connectingthe location of. said, signal with l a ,distant control oflice and, affording a plurality of communic ion. h nnelsforthe control. from. said .office oftrafiic g0Vern-.-.

ing devices along the tracklincludingsaidsignal;

ands-for indicating. trackway conditions at said ofiice, of an additional channel comprising said line wires, 2. connection from said line wires to ground atsaid office including a polar relay of the magnetic stick type, and from ground through condensers to said line wires at the location of said signal, together with a pole changer, a local undergrounded source of direct current for controlling said signal connected to contacts of said ofiic e dependent upon the continued operation of said polar relay at said fixed rate for visually indicating such condition.

5. In a remote control system, an ofllce and a station, line wires connectingsaid onice and station, a line relay at said station, a communication channel for energizing said line relay when alternating current is supplied to said channel at said ofiice, comprising said line wires and selective circuit elements electrically resonant to the frequency of said current at said oilice and also at said station, manually controllable means at said oflice for at times supplying alternating current to said channel and for modulating said current to periodically operate said line relay at different low frequency rates, a railway signal at said station, a plurality of signal control relays, circuits 6. In a remote control system, an oifice and a station, line wires connecting said oflice and station, a line relay at said station, a communication channel for controlling said line relay comprising a source of alternating current at said ofiice, said line wires, and selective circuit elements electrically resonant to the frequency of said current at said oflice and also at said station, means at the oiiice for modulating said current to cause periodic operation of said line relay at a fixed low frequency, manually operable lever contacts for controlling said means, a circuit tuned to electrical resonance at said low frequency, a railway signal at said station, and a signal control relay for clearing said signal controlled by said line relay over said tuned circuit.

'7. In a remote control system, an oflice and a station, line wires connecting said ofiice and station, a line relay at said station, a communication channel for controlling said line relay comprising a source of alternating current at said office, said line wires, and selective circuit elements electrically resonant to the frequency of said current at said office and alsoat said station, means at the office for modulating said current to cause periodic operation of said line relay at one or another low frequency, manually operable lever contacts for selectively controlling said means, a circuit tuned to electrical resonance at the higher of said low frequencies, a three-position railway signal at said station, a first signal control relay responsive to the low frequency operation of said line relay, a second signal control relay controlled by said line relay over said tuned circuit, and circuits controlled by said signal control relays for causing said signal to indicate clear when both relays are energized and to display a more restrictive indication when only said first signal control relay is energized, said signal indicating stop when both said signal con trol relays are deenergized.

8. In a remote control system, an cfiice and a station connected by line wires, a railway signal at said station, a source of current at said ofiice, a line relay at said stationadapted to be controlled by said current over said line wires, means at said oflice for modulating said current to periodically operate said line relay, a manually operable signal lever having a reverse contact for supplying current modulated by said means and a normal contact for supplying unmodulated current from said source to said line wires, a signal control relay controlled by said line relay and selectively responsive to said modulated current for clearing said signal, an indication relay controlled by a front contact of said line relay and by a back contact of said signal control relay, and a visual indication at the ofiice controlled by said indication relay.

9. In combination with a detector section of railway track, a track circuit for said section, a

signal for governing trafiic movements into said section, a line circuit extending from the location of said signal to a distant control oifice, a signal control lever at said ofiice, a normally deenergized signal control relay at the location of said signal, a normally energized indication relay controlled over a back contact of said signal control relay, a stick track relay controlled over the rails of said detector section having a pick-up circuit controlled by a front contact of said indication relay, a circuit including a reverse contact of said lever and said line circuit for effecting the energization of said signal control relay, a circuit for clearing said signal effective only when said signal control relay and said track relay are both energized and a circuit requiring the energization of said line circuit over a contact of said lever in its normal position for effecting the re energization of said indication relay.

10. In combination with a detector section of railway track, a track circuit for said section, a signal for governing traffic movements into said section, a line circuit extending from the location of said signal to a distant control office, a signal control lever at said ofiice, a signal control relay at the location of said signal, a stick relay which releases when said track circuitis occupied, means requiring said signal control relay to be released and also requiring the energization of said line circuit by current of distinctive character with said signal control lever in its normal position to pick up said stick relay, means requiring the energization of said line circuit by current of a different character with said signal lever in its reversed position to pick up said signal control relay, and a circuit for clearing said signal including front contacts of said signal control relay and of said stick relay.

GEORGE W. BAUGHMAN.

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