US1997322A - Railway traffic controlling system - Google Patents

Description

\ April 9, 1935.

C. F. STOLTZ El" AL RAILWAY TRAFFIC CONTROLLING SYSTEM Filed F eb. 26, 1931 a". zw'zrswwm,

zut; More specifically stated; this invention provides for the transmission over two polarized line circuits of the control's'requi're'd for:a'pov ler-operated switch machine, and distinctive continuing Patented Apr. 9, 1935 UNITED AT c I 99 :1. I RAILWAY TRAFFIC CONTROLLING SYSTEM i still der. wei h, Cincinnati;

'. Ohio, assignors to 'Genera-l' Railway Signal CQmP n R s "N- t a Application February 26, 1931, serial No; 518,308:

. 12 Claims.

This invention relates to traflic controlling sys-r tems for1 railroads, and more pa'rticulafly to 1 a system for the remote switch machines. s

In a system of remote control ofpower-operated switch machines for use in connection with terminals; interlocking plants, and centralized traflic control systems, it is desirable to obtain the various controls and indications 'required"for=eificient operation of a switchmachine overamini mum number of line wiresbetween the tower or.

central o'flice for each switch; :and Y therefore; one object of the present inventioniis to provide a simple and reliable arrangement'of'line circuits and-relays by means of which several distinctive controlling and indication conditions 'may be transmitted or communicated instantaneously in de-e'nergization response tothe energization or of. the line circuits; Y

indications'of the presenceof a train'fon the usual detector track circuit at the switch, the position of the switch points if over and locked, the-"op crating or mid-stroke condition of {the-switch,

and the presence of a train approaching the switch within certain approach'lockingi-limits.

' Anotherobject of the invention is to provide'; in connection with the approach and detector locking usually employed with-- power-operated I switch machines-an improved form of means for ,requiring movement of the control lever at th'e time the .approach'and detector locking i's niit er festive, in order to operate the switch machine,

' so that the switch machine will not operate after erator shifts-the control level.-

Various other characteristic features vantages of the invention willbe mpart apparent and in part pointed out, as the description progresses. l

In theaccompanying 'drawinglthe principles 2. train movement over the switch until the 'op-" ,and functions of theinvention are exemplified'b'y .one specific embodiment applied to a single switch, the various devices andcircuits' being illustrated f in a simplified and diagrammatic manner; more with the object of making it'easy to understand the nature and mode of operation of the'invent-ion, than with thepurpose of showing in detail how theparts and circuits would be constructed and arranged in'practice.

The stretch of tra'ckjwith the single switch .SW, a'ndthe signals 1 and IA'governing trafficf in the facing direction overthis switch, 'as shown in the drawing, are merely typical or'representa tiveof a simple facing-point switch layout; and it should be understood'that the invention is applicablei to the vvariousflswitch and signal-:ar-

control of po-wer' oprated" and 'adrangements, including crossovers, i uloubleslip switches," movable =point "frogs, .with signals gov-ia erning. trafic'in one 1 or both.-.directions;. and the like encountered injp'ractice: The explanation Y Y of the inventionyas: applied to the simple single switch and signal arrangement illustrated in the accompanying drawing;gwillimakeiclear-to those skilledin theq'art' how the principles; functions; and: mode of operation ofrthe'invention' may be; applied to meetall other conditions:erico'un'tered: inrpracticei; 2

' The switc SW isintended be operated ny a suitable powerkswitchmachine, designatedSM? v and while this sw'itchtrmachinesmay zbe'iaiiy tone: of: the-'well-knownttypes,:.it is assumedto' be of the electricallyop'e'rated type; suchiu'as {dis-1 closed, for example, iri the patent to'lWzKi Howe, No; 1,466,903; dated -September 4,fll923; Inaccordance: with this invention; i theg'switch Ema-' chine is supplied with operating current from'a local battery-lpor otheif'suitable sourcefof direct or' alternating current; i in V accordance with well-'- current to ther switchs machine SM-Qoirerridrin'fl and reversezoperating wires-5 and 6', is controlled by aisuitable: polarized'lremote control relay WZ. v

If direct current sis employed for 'the control of this switch machine, as in" the particular embodiment illustrated; this control relay WZ may be of the V well-known neutralpolaratypefi andif a1 ternating Icurrenttis employed for the control of the; switch machine, thisrelay' WZ may be any one ofgthe well-knownitwo-eleme'nt alternating current relays'.- The 'spe cific construction of this control "relay :"WZ is not material to the inv'ention, its function' being to shift the contact-finger 1', or eq'uivalent circuit controlling-imeans, in response to reversals ofthe polarity of'energization of a switch machine controlcircuit so to select the normal and reverse operating wires 5 and 6.

Associated with the switch" SW are suitable point detector contacts;designated-PD; which'are operated, either as apart of the switch machine SM, Ior lby separate' connections" to the switch I points, in accordance with the po'si'tio'n and locked condition cl the switch points. 4 Onetype of point detector, suitable for 'thispur'pose is shown and 'described'ain the patentJtO- C. S. Bushnell, N0;

1,517;236,dated November 25-19241 As Shown diagrammatically in "the accompanying drawing, this point detector} PD comprises four pairsof contact fingers 8-! I', two. movable contact blocks I 2 and l3, and shunting contacts I! and 15'.

When the' switch points arebverand locked in 5 the normal position as -shown,'the pairs of contact fingers "I 0 and H are bridge ski by the contact 1- blocks I2and' I3, the shunting contact 15 is closed, and the other shunting contacttlfi is opened Whenthe switch points; are unlocked or in midstroke, thecon'tact blocks "IT and 13 are signal selecting neutral-polar relay KR, with one automatically shifted to an intermediate position, out of engagement with all of the pairs of contactfingers 8-H, and both of the shunting contacts [4 and-l5 are closed. When the switch points are over and locked in the opposite or reverse position, the other pairs of contact fingers ,8 and 9 are bridged by the contact blocks I2 and I3, and the shunting contact I4 is closed, while the shunting contact I5 is open. A suitable source of current, such as the battery 16, and the pair of control wires I1 and IB' in combination with the contacts of the point detector PD, provide for the energization of a local switch repeating or polarity of current or the other, in accordance with-.th'e locked position of the switch points,

' and the deenergization and shunting of the relay KR, when'zthe' switch pointsare unlockediorin midstroke, "as will be readily apparent to those skilled in the art, 'without tracing the circuits in detail. h it The track rails ofthe stretch of track and the turn-cut track, up" to the fouling point for the switch SW, are provided with insulated'joints and cross-bonding, in accordance with well-known practice, to provide the usual detector-track cir-"- I cuit T-l, having aidetector track relay IT.

current. v i

To simplifyitheillustration; many of the circuits on the accompanying drawing'are' illustrated in a similar conventional manner as terminating at indicating a connection to one terminal of a suitable source of direct or alternating current,-and at indicating a connection to the opposite terminalof said source,

In accordance withythe invention, it'is con-- templated that the track adjacent to the switch SW will be in practice provided with track circuits, wayside signals, line: circuits, and the like constituting suitable approach locking, for the switch. The specific details: of such approach locking circuits are not material to the present invention; and as merely representative of such approach locking, the stretch "of track at the left of the switchSW is shown conventionally asprovided with two track circuits-T2 and T-3. having track relays 2T and 3T, the track circuit T--3 being inithe rearof a distant or approaching signal 2, governing east-bound traflic toward the switch SW, and located braking distance in the rear of the signals land IA. "A stick relay L,-;representative of .an approach lockingrelay, is energized over" a stick circuit through the front contacts 2| and, 22 of the track relays 3T- and- ZT and its owrifront contact 23; This relay L has-apick-up circuit. through the same front contacts of the track relays-3T and 2T and a back contact ;of the detector track relay IT.

In this simplified arrangement, an east-bound train approaching the signal deenergizes the relay L and this relayrL remains deenergized until this train. has passedv on ;to the detector track circuit-Tl. In the practical application of the invention, the approach locking will'have other features of control bythe indications of the signalsgdirectional ,control, time release, and the like but this simplified arrangement of the relay ;L 'willbe suifi ient tomake. clear to those chine is operating or in transit.

skilled in the art the nature of the present invention, and how the various types of circuits for complete approach locking protection, such as shown for examplein the application of S. N. Wight, Ser. No. 120,423, filed July 3, 1926, may be employed in accordance with this invention.

" The equipment in the tower or central control office, which is located, at any.desired distance from the switch SW, is diagrammatically illustrated in the left-hand part of the drawing, and

' comprises a suitable manually operable control lever LV for governing the switch machine SM; a portion of the usual track diagram which in cludes the switch SW, with an automatically operated miniature switch point to indicate the positions of the switch points if over and locked; relays KRP,,LS and WLy-andindicating lamps OS, TL, and HO. Y

The control lever LV is shown conventionally as comprising an operating handle 25, movable up and down to two extreme positions, corresponding to normaland' reverse positions of the switch.. .This handle 25 is mechanically connect ed to movable contact fingers 26 and 21, co-operating'with stationarycontacts, indicated conventionally as arrows, in the normal and reverse extreme positions of the lever handle 25. r The indicator of the switch position, in the specific form shown, comprises a pivoted miniature switch 1 point 28; positioned adjacent two wide lines .29 and 30 on the track diagram which represent. the main track and turn-out track; and this miniature switch point 28 is, connected to the armature 3| of two electro-magnets 32 and 33. When the electro-mag'net 32 is energized, the armature 3Iisattracted to the position shown, and shifts the miniature switch point 28 to the normal position shown; and if the other electro-magnet 33 is energized, the miniature switch point 28 is automatically shifted to the other reverse position.

The indicator for the detector track circuit T| is preferably a small indicator lamp OS, of the type commonlyv used on telephone switch boards, which is preferably'located adjacent to the miniature switch point 28. A similar electric lamp indicator TL, preferably located adjacent tothe control leverLV, when lighted in the manner hereafter explained, indicates to the operator that the switch machine is not over and locked. This-indicating lamp TL, conveniently termed a 'transit light, is lighted while the switch ma- A similar electric indicating lamp HO, also preferably located adjacent to the lever LV, is lighted in the manner hereinafter explained when there is a train on the ,detector track circuit, or a train approaching the switch under signal indications which make it unsafe to operate the switch. Since any movementonthe part of the operator to control the switch machine underthese conditions will be ineffective, the indication given by this lamp H0 is conveniently termed a hands-off indication.

These different indicating lamps OS, TL, and H0 are causedto give distinctiveindications either by reason of their color, or location, or both. 1If desired, other forms of electrically responsive indicators may be used instead of lamps.

vThe relay KRP, which is a repeater of the relay KR, isof the neutral-polar, or equivalent three- .position type, of which-the polar contacts 44 are of the magnetic stick type. This relay KRP is connected in an indication circuit, including line wires-35 and 36, which extends from the tower or control ofiice'to the point where the switch SW is located :This indication circuit iincludcswa fronticontact 31 of the detector track relay repeater ITP, a front neutral,contact38 and a polar contact-s9 of the relay KR, andaone of the; ,batteries and 40. When the switch SW. v ris over and locked in thenormal position shown,

and no train. is on;-the detector track icircuitiso that the relay 'lTP is-"energizedjthen the relay KRP; is energized with current of one polarity:

fromthe battery 40 over a circuit readily traced upon the drawing through the, polaricontactgiifl 40 current, of the normal polarity'opensiits neutral back contacts and 43, and positions itsgpolar contact 44 tothe right. Theerelay KRli' might-i' be controlleddirectlyv by the point detector.;con-' i beenergizedrandfits frontic'ontact- 6 4 .clcsed, the, switchmachine operates infthe usual wayto 1-in-- tacts PD, without the relay KR. r Y 1" The relay LS is a stick relay of the' usualfn eur tral type, andis included in series in the switch control circuit which includes line-wires 45v and 46, and extends from thecontrol'.oflicef-to'the switch. ,TherelayWLis a'slowi-release relay ene' ergizedby local circuits at the c'ontroloflicai The various electrical iCOIlnECtiOIiS between these various devices need 'notbe. specifically ilescribed; the .various; circuits involved in the op eration': being pointed zout .:in the following explanation of;the operation :of the system Operation.The parts andcircuitsare shown on the drawing inflwhat may be termed the nor-:1

mal condition, corresponding with thesw'itch'SW over and locked: in thenormalposition; and no trains adjacent. to or approaching the switch.

Underthese normal; conditions, the; relay KRP" is energized with. positive polarity over the indication circuit 35-36, positioning its polar contact 44 to the right and establishing. acircuit for energizing the operation electric magnet 32 from polari contact "M of a the relay KRP} wires 15 and 16, magnet 32,.to (-'')-.l With the contact 21 and the control lever LVi'nithe-same corresponding normal positidnairelay iWL is ener gized bythe circuitv from polar-contact of relay KRP to the right, wires'15 and lLlever contact 27 in the normal position, wire (8, relay VVL to The switch machine controlcirtauit; including wires"4546; forenergizing the relay WZ 'with normal polarityirom the battery in the central office, may be tracedlfrom the lower terminal ofthe battery 50, wire 5|, lever'contact -Zii normal, wires 52and 53, front contact 54 of relay LS, wires 55 and 56, relay LS, line wire-l6,relay- WZ, wire 51, ifrontlcontact 58 ofthe detector trackirelay'lT, wire 59,- front "contact -60 of-ap' p'roach locking relay L, linewire45, to the other terminal of the battery. 50.. Thefront contact 6| of the relay WL, together with the wires"62'-55 and 6353, forms a shunt :for the frontcontact 54 of the relay LS.

In this normalcondition'of the system all of the indicating lamps OS, TL, and H0 are extinguished. I Y

Assume nowthat the operator desires to have the switch SW o'peratedhto itsreverse' position,

and further that' no trains are presentto 'render it unsafe to operate the switch; The operator shifts the lever LV to the reversepositiongmov ing the lever contact 26 to thedotted-lineposi tion and including-thebattery 50 in theswitch control circuit to energize the relayIWZ with opposite polarity; :Duringf-the'movement of the lever .:contactl.:Z 6;;fromaitsnorma1i to its reverse position,= the supply Of-CIJIIGIItJtO the-switch cont- 'trol circuit 45-46 is momentarily-interrupted,

deenergizingthe relay L S; Also, upon'rnovementj of --the levcrzcontact 21 to-the- '=.dotted-line position,-out oiicorrespondencewith thepolarcon tact 4 ,4 pf ithej: switch ,r epeater relay; the relay-WL (is deenergized; but this ,relay'WL' is made sufliciently slow releasing j as to remain closed during them'omentary deenergization" of, the switch; control-fcircuit when; 1 the ;lever LV- is shiftedifromone positionito the other in an or'-.

dina'ryway: F'; Consequently; the relay LS at once picks" up a'eesoon as the switch control circuit is energized with the reverseqoolarity.- "Ilheenergization' of, the relay wZ :with current of the reverse; polarity establishes the reverse operating circuit for the switch machine SM; and;

sin'aei the ia'pproach lockingrelay z L-;i s assumed; to.-

lockrthe;switchj:SW,- shiit its points to the re-- I verse :position,--and'-again' lock thev points; 5 1 'PDuringwthis --operation of the switch machine,

when Fit isfirst-unlocked relamIgRiydeenergize-d;

openin'gfliatits neutrabcontact fit the {indicationcirc'uit 6; and? deenergizing'; the relay-,- KRP, Under these'iconditions; ther;transit -"lightislighted'j over: aicircuit ffrom-r (3 back-=-contact operator'- thatrtlierdes'ired control has (been (transmittedto the' aswitchfinachine and'that ithas commenced "its regular; operating cycle When 7 the 'switch' machine*SMrcompletesiits operation,-

and the *switchxpointsfafei locked in; the reverseposition, the re1ay*KR"isrenergizedfromthe bat-'1 tery fli through thelpbirit detector contacts PD- with' -"current Y of: reversepolarityfclosing its -neu- 1 tral contact"38',iand shifting; its" polar contact 39 w the -dotted-line position; Thisenergizes the relayKRP with reverse polarity;opening its back2- cOIit act 13 to extinguish the transitlight 1 and Shifting "its p'OIar' 'co'nta'ct 44 t6 the-dotted-line position," in correspdndenc'e withthe position of thelever Contact 21 that the reIayrWIfisagaim energized. At-*the same' time? the selectro-magnet 33isenergizedto 'shiftthe'miniature switch point 2s terth'e fevise positionii' If, due to afi obstriiction in thepoints or ior' any?other reason, tneswitchmachine should-fail tocofi1plete"its -operation', the relays KR an'd KRP remain deenergized and the transit light TL point 28f butf when; this transit light TL is ex tinguished," the position 'of theminiatureswitch point 28 represents the 'existin glposit'ion' or the;

The same explanation is true for an operation of the switch from the reverseposition'to the normalp0Sition{Y fnssumenow that the switch is overa'nd locked inon'e position; that the signals l or IA and the a-p'1 roach signal; I operator" by controllingfmeans' not material "to the present'inver'ition 'andnot illustrated, and which may-be of the type disclo'sed 'in'theWight application, T Sen 'Ndi i20,423* =above' mentioned Caz 'be enl cleared by switch. When thisapproachingf train arrives within the approach locking limits, therelay-L is deenergized, This opens the switch control circuit at the front contact (ill of the relay L and drops the relaylLS, thereby lighting the lamp HO over a circuit-from lampHO, wires and II, back contact 68 of relay Lsto In this way the operator isadvised of an approaching train. I r As the train in question'advance's and enters the detector track circuit T ''l the track relay IT and the repeater relay ITP are de-"energized'. The opening of-thefront contact 58 of the track relay IT maintains theiswitch control circuit P013811 and the relay LS is de-energized. The opening of the front contact 31 of" the repeater relay lTP breaks the indication circuit and de-energizesi the relay KRP. In this way, the lamp OSis lighted over a circuit from back contact 42 of the relay KRP, wire 12, lamp OS,.wires I3 and 1|, back'contact 68 of relay LS, to' )'L- 'When -the train leaves the detector track circuit,'the' switch control circuit and indication circuit are'again established, and'assuming that the lever LVhas been left in a position corresponding with the position of the switch, so thajttherelay W'L'is energized, then both of the -relays LS and KR]? are energized and the lamps -HO and OS are extinguished; r 3 Assume now that, while an approaching train;

a is within the approach-locking limits; and the relay LS is deenergized to light the lamp HO, the operator should for some reason move the control 'lever LV to its other extreme position;-'I'l1is has passed and the approach lockingiis restored to normal, closingfthecswitchl control circuit at the switch, this circuit r is maintained broken at the front contact 54 oftherelay LS, since this relay LS cannot be energized with the relay WL de'energized. LWhen this condition occurs, before.-

the switch can be operated from its existing condition,'the;operator is obliged to restore the lever LVto its former position, in correspondence with the polar contact 44 of the'relay KRP, so as to pick up the relay WL, and in turn permit the relay LS to pickup, whereupon the lever LV can, be shifted to operate the switch to its other position. l o

The provision of the stick relay LS, having its pick-upcircuitcontrolled by the relay WL, which is deenergized when the lever is notin a positionin correspondence with the switch, assures that the control levermust be shifted by the operator after a train approaching the switch haspassed. In other words, the manipulation of the lever LVrequired of the-operator is substantially'the same as if this leverwere equipped with anelectric lock restraining its movement; when, the detector andapproach-locking is effective. With this arrangement, no control tend ing to operatethe switch tot a diiferent position can betransmitted from the control omce to the switch location, when the presence; of a train,

makes it unsafe to operate the s witch, so. that conditions cannot be setup by the operator for the switch tooperate, and reliance placed entire- 1y upon the control of the switch machine bythe detector and approach looking to prevent an: improper switch machine operation. This is considered to add to the protection against improper switch machine operation by requiring co-operation of the-operator with the automatic detector and-approach locking. Also, if the operator should accidentally or carelessly shift the contrcl lever LV with altrain approaching, the switch cannot'operate 'upon departure of the train 'to'a position which the operator perhaps would not :want. Moreover, with this arrangement, the'operator is penalized for any attempt to shift the control lever LV, when it is improper to'doso, because he is then required toshift the lever over and back to regain control of the switch machine. 5

From the foregoing, it can be seen that this "invention-provides for the direct line circuit control of a power-operated switch machine over one-polarized line circuit, and for repeating by the reiayKae directly over a polarized line circuit the'over and locked position of the switch points. It is evident that this switch repeater relay KRP, being directly and reliably controlled, may be utilizedtoselect signal circuits, by means of electricconnectionsin the tower or control oflice; in: accordance with recognized practice in interlocking systems, in addition to operating the pointrindicator 28. This invention provides for the transmission, over these same line circuits, of indications of the. occupancy of the detector track circuit, the presence of an approaching train rendering efiective the approach locking, and the operatingor mid-stroke condition of the switch machine, so that the operator has the necessary information of conditions at the distant switch location tocontrol the switch and associated signals to'the best advantage. tures of the inventionrender it safe and practicable to govern fromone tower or central control ofiice the operation of any desired number of switches, located at any'distance from such control point, with a minimum number of line wires, and through the agency of simple-control levers, which dojnot require electric locks, indication devices, or mechanical locking.

Various, additions, modifications, and adaptations may be made in the particular construction and arrangement ofparts and circuits shown and described without departing from the principles end mode ofoperation characterizing the inven- 1on. lWhatwe claim is:.-

'1. Ina traflic controlling system of the character described, a power-operated switch, a polarized control circuit for governing the opera tion of said switch, a-polarized indication circuit having its continuity and polarity governed inaccordance with the locked condition and ex tremepositions of said switch,ca'dete'ctor track circuit;interrupting both of said circuits, a relay at a distant control point included in each of said circuits, and means controlled by said relays for giving distinctive continuing indications of the presence of a train on the detector track circuit, the locked or unlocked. condition of the switch, and the position of the switch if over and locked.

'2. A system of control and indication for power-operated switches comprising, a polarized control circuit and a polarized indication circuit extending from a central control oflice to each;;switch,fmeans responsive to a train approachingtheswitch and breaking the control circuit, means, for, breaking the indication circuit-when the switch is unlocked, a detector track circuit, means controlled by said track circuit foriinterruptingbothsaid control circuit and said These various feasaidcircuit, and means for shunting said stick indication circuit, and indicating means in said control oilice selectively responsive to the interruption of either or both of said circuits for giving distinctive continued indications of the presence of a train on the detector track circuit, an approaching train and the unlocked condition of said switch.

3. A system for controlling power-operated switches comprising, a polarized control circuit for controlling a switch machine for operating a track switch, a stick relay having its winding in said circuit and also governing its continuity, circuit controlling means responsive to the position of the switch, a control lever for controlling said circuit, and means for restoring said stick relay only if said control lever is in a position corresponding with the position of said circuit controlling means. c

4. In a system of the type described, the combination with a power-operated track switch, a polarized control circuit for governing the operation of said switch, a control lever for controlling the energization of said circuit, means means for maintaining said control circuit open upon movement .of the lever to a. .position out of correspondence with the existing position of the switch at atime when said circuit is opened by said track circuitcontrolled means, said last mentioned means also main-, taining said control circuit closed if it is closed at the time of such movement of the lever.

5. In a trafiic controlling system'of the'type described, the combination with ,a control lever and a polarized control circuit for governing the operation of a distant power-operated switch machine, indicating means responsive to the position of said switch, track circuit controlled means at the switch for interrupting said circuit, a stick relay included in said control circuit, a pick-up circuit for said stick relay, and a slowreleasing relay for governing said pick-up circuit and having its energization dependent upon the correspondence between the position of said lever and the position of said switch indicating means.

6. A system for protecting the operation of power switch machines comprising, the combination with a control lever and a polarized control circuit for governing the operation of the switch machine, track circuit controlled means at the switch for interrupting said circuit, and

means for maintaining said circuit open if the.

control lever is moved to a position out of correspondence with the position of, the switch when said circuit is interrupted including a'stick relay and its stick contact in series in said circuit and a contact closed for a definite short time'following movement of said lever for shunting said stick contact, saiddefinite short time being independent of the rate of movement of said lever.

7. A system for protecting the operation of power switch machines comprising, the combi nation with a control lever and a polarized control circuit for governing the operationof the switch machine, track circuit controlled means at the switch for interrupting said circuit, a stick relay and its stick contact included in series in contact responsive to a circuit portion closed only when said lever and said'switch machine assume corresponding positions.

8.'A system for protectingthe operation of power switch machines'comprising, the combination with a control lever having a normal and a reverse position and a polarized control circuit 'for governing the operation of the switch machine, track circuit controlled means at the switch for interrupting said circuit, a stick relay and its stick contact included in series in said movement of said lever.

9.,A system for protecting the operation of power switch machines comprising, the combination with a control lever and a polarized control circuit for governing the operationof the,

switch machine, track circuit'controlled means at the switch for interrupting said circuit, and a slow acting relay energized only when'said lever .and said switch machine assume corresponding positions for controlling the continuity of said circuit. I

10. A system for protecting the operation of power switch machines comprising, the combination with a control lever and a polarized control circuit for governing the operation of the switch machine, track circuit controlled means at the switch for interrupting said circuit, and a slow acting relay for controlling the continuity" .of said circuit and actually energized only when said lever and said switch machine, assume corresponding positions but maintaining the con tinuityof said circuit for a predetermined time after such correspondence has been discontinned.

11. A system for protecting the operation of power switch machinescomprising, the combination with a control lever and a polarized control circuit for governing the operation of the switch machine, track circuit'controlled means at the switch for interrupting said circuit, and a slow acting relay energized only when said lever and said switch machine assume corresponding positions, and assumingits deenergizedposition a short period of time after such correspondence I has been discontinued for controlling the continuity of said circuit.

12. In a centralized traific control system forpreach locking means associated with said track switch for opening and closing said polarized control circuit in accordance with traflic conditions, an approach lock repeating relay having windings included in'said polarized control 'cir-- cuit and associated with said control lever for indicating the condition of said approach looking means, and means including said lock repeating relay for requiring said control lever'to be in correspondence with said trackswitch subsequent to theopening of said polarized control circuit by said approach locking meansbefore said control lever can again govern said switch control relay. r

CARL F; STOLTZ. WlILMER WELSH.

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