US2230860A - Code responsive control apparatus - Google Patents

Description

Feb. 4, 1941.

c. c. BUCHANAN copE RESPONSIVE CONTROL APPARATUS Filed May 3l, 1940 2 Sheets-Sheet 1 Feb. 4, 1941.. Q Q BUCHANAN 2,230,860

CODE RESPONSIVE CONTROL AFPARATUS /\f\Y M M m rm UU vv i uv uv N vv INVENTOR @www HIS TTORNEY Patented Feb. 4, 1941 E UNITED STATES nasce PATENT OFFICE CODE RESPONSIVE CONTROL APPARATUS Applicaticn May 31, 1940, Serial No.-337,977

13 Claims.y

My-invention relates to code responsive control apparatus; and it has particular `reference to code `responsive control apparatusY of the class employed in railway ftraflic controlling systems utilizing coded energy of the irequency'code type lor controlling either or both waysidesignals and train-carried cab signals.

Railway traic controlling systems of the above described Vclass are -characterizedby the Vfact that suchsystems utilize codeiresponsive control apparatus operated by energy received from a pair of conductors, forselectively; controlling traffic governingdevices inV accordance with the ratefatwhich en-ergy received from the conductors is` coded; and the code rateat which such energy is supplied to `the conductors-is controlled by traflic conditions in` advance.A Generally speaking, the supply of energy to `the conductors, which may be the rails of lthertrackway,is periodically` interrupted 'or coded at oneor. another, of a pluralityi of code rates through :the fmedium. of aA code` transmitter or vcoding device; and the code responsive control apparatus establishes selectivecontrol over its associated trail-lc governingdevice i through :the-:medium of decoding apparatus -in cluding circuits arranged and tuned to be resonantat one or another of the code `rates-at which energy-is supplied from thecode responsiveapparatus toI such circuits. beenfound desirable'onthe one :hand to icode or interruptV thesupply of energy-tothe two'con-` ductors at` relatively low code rates,- thereby avoidingpitting and undue-wear of the contact structures incorporated in the code transmitters which other hand it has been found desirable to. supply energy `to thecode responsive apparatus coded at relativelyfhigh coderatesin order to utilize relatively small and inexpensive tuningfandl decoding t units for detecting-thevarious rates at which such of the control contacts, andtis subject to failures.

, due tothe breaking vor sticking ofthe mechani- Inf such` systems. it has i code the supplyof control energy, while on theY cally moving parts. In view of the above-mentionedwand -other important considerations, it is an object of myinvention to provide novel and improvedcode responsive control apparatus operated by energy ccdedat low code rates and incorporating means utilizing no moving mechanical parts4 for multiplying or increasing thecode rates at whichsuch apparatus suppliesenergy to its associateddecoding apparatus. A

An additional object ofmy invention isfthe provision of novel and improved railwayv-trailic` controlling apparatus-ofthe class-operated by coded energy-ofthe frequency code type.l

A' further objectof my inventionis the provision of novelfand improved code responsive control-apparatus of the class adapted'for usein control .systems selectively operated by coded energy` The above-mentioned and other important objects .andcharacteristic fea-tures of my invention 20-` which, will become readily apparent from the following idescription, are-attained in accordance with my invention by providing a controlsystem i employing code responsive apparatus of the saturation type in Whichthesupply` of energy 2&5.

from' a source-ofalternating current-toan out- A put i winding disposed `on-a'magr1etizable core is controlled inaccordance with the state of magnetic flux in such core, and 'the magnetic conditionV of-suchv-core is controlled `ty4 a, biasing 3Q winding constantly suppliedwith unidirectionalV current `for setting up a given conditionof flux of i one polarity inthe core, and by-a -control winding'supplied with-coded control `energy from apair of'conductors and effective upon such -sup- 35T;

plyfor lcreating magnetic ux in the core ofthe oppositerelative polarity andof-such magnitude thatl a resultantiiux of the opposite relativepolarity is setup finthe core. Inwother words,

I -provide a saturation type code responsive'con- 40 ,i

trol device-wherein the state of flux-in the magnetizablecore-is carried from a given ux condition through a zero or no flux condition to -a substant-iallyn equivalent flux condition of oppositerelative polarity both on the supply-of energy to 45..,

the control. winding and when such supply is interrupted, whereby the supply of current from the output winding ofthe device is caused to be coded at sa.` rate twice the` coderatev at whichV energy is supplied to the control winding.

I shall describe one form of apparatus embodying myinvention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is i a diagrammatic View illustrating a. preferred form 55 of apparatus embodying my invention. Fig. 2 is a .graphical representation illustrating a typical form of control energy which may be used in conjunction with the apparatus of Fig. 1. Fig. 3 is a graphical representation which illustrates such control energy rectified into unidirectional energy, and which also represents the ux created in the core of device SR, shown in Fig. 1, due to the supply of such rectified energy to control winding I8 of the device. Fig. 4 is a graphical representation illustrating the biasing ux normally present in the core of device SR. Fig. 5 is a curve representing the varying resultant flux conditions in the core of device SR caused by the inter-V mittent supply of control energy and the constant supply of biasing energy to such device. Fig. 6 is a curve representingthe effective currentsupplied from output winding i6 of device SR in response to the intermittent supply to such device of control energy of the type representedin Fig. 2.

Referring to Fig. 1, the reference character X designates a stretch of railway track over which tra'ic normally moves in the single direction indicated by an arrow in the drawings, and over which traffic movements are controlled by means of control apparatus embodying my invention and presently to be described in detail. The protected stretch of track X is provided with a pair of conductors to which coded energy of the frequency code type is supplied for controlling traffic governing apparatus in accordance with the rate at which such energy is coded. As shown, the two conductors comprise the two track rails I and I a of the stretch of track, which rails are divided by means of the usual insulated rail joints 2, as is the usual practice, into a plurality of successive adjoining track sections, only one section of which, D--E, is showny complete vin the drawings.

I Coded control energy is supplied to the rails I and la of section D-E adjacent exit end E of the section, for selectively controlling suitable apparatus, later to be described, in accordance with the rate at which Vsuch energy is Coded. As shown, the rails I and la are supplied with alternating energy from a suitable source of alternating current such, for example, as a generator not shown but having its opposite terminals designated in the drawings by the reference characters BX and CX. This energy is periodically interrupted or coded at one or another of the customary plurality of low code rates utilized in railway signal systems, by means of a coding device or code'transmitter CT, The device CT may take any one of many well-known forms but is illustrated as comprising a plurality of rotatable cams each 4designated by the reference character K with a distinguishing suflix. The cams K are driven at `a constant speed of. say, 15 revolutions per minute by a motor M which is constantly supplied with alternating current so that the coder is continuously active. Each of the cams K is provided with a different number of teeth or projections spaced about its periphery, which teeth successively operate an associated contact member to close periodically a circuit controlling contact as the cam is rotated. For example, cam Kl is shown provided with twelve; teeth or projections, each of which successively engages a contact member I to close periodicallya circuit controlling contact '1 -8. Similarly, cam K2 is shown ,provided with eight teeth, eachengaging an associated contact memberi9 toclose periodically contact 9-I0; and cam K3 is shown provided with five teeth each engaging an associated contact member Il to close periodically a circuit controlling Contact r lI-l2.

In accordance with certain predetermined conditions, one or another of the above-mentioned contact members operated by coder CT is conditioned to interrupt periodically or code the supply of trackway energy to the rails of section D-E. As indicated in the drawings, the control of such trackway energy may be established by suitable apparatus responsive to traflic conditions on the stretch in advance of vsection D--E. The details of the traffic controlled apparatus controlling the supply of trackway energy are not shown in the drawings since they form no part of my present invention, but such apparatus may comprise the usual decoding relays, such as relays H, BJ and AJ hereinafter referred to, controlled by traic conditions in advance of section D-E through the medium of Vcode responsive apparatus such as will be hereinafter described, and which relays set up or establish one or another of a plurality of circuits over which energy is supplied to the primary winding of a track transformer TT, which transformer has its secondary winding connected, in series with the usual current limiting impedance 5, across the track rails l and la adjacent exit end E of section D-E. As is readily apparent from an inspection of Fig. 1, one of the plurality of circuits above mentioned includes contact 1 8 of coder CT and since this contact is operated by each of the twelve teeth of cam Ki of coder CT, energy flowing in such circuit is periodically interrupted or coded at a rate of 180 interruptions per minute. The second of the plurality of circuits includes contact 9Ill of' coder CT, which contact is operated by each of the eight teeth of cam K2 and hence energy ilowing in this circuit is periodically interrupted at a rate of 120 times per minute. A third of the plurality of circuits lshown includes contact H-IZ of coder CT, which contact is operated by each of the five teeth of cam K3 and as a result energy flowing in this circuit is periodically interrupted some '75 times per minute.

I have represented graphically in Fig. 2 the form of control energy of the frequency code type that is supplied to the rails l and la over a typical one of the abovementioned plurality of circuits. For example, Fig. 2 represents the current flow of the 120 code, in which the on periods during which energy flows when contact S-Ill of coder CT is closed are represented by illustrating several successive cycles of alternating current, while the 01T periods during which no energy flows when Contact 9-I0 of coder CT is open are represented by indicating an absence of such alternating current. It is to be noted that the flow of energy in the circuit in which Contact 9-l0 of coder CT is interposed, causes control code of the frequency code type to be supplied to the rails of section D-E, which control code is characterized by the fact that the on and off intervals are substantially equal in duration.

Referring to Fig. 1 once more, I have represented the code responsive control apparatus embodying my invention incorporated into a wayside signaling system for selectively controlling a wayside signal S in accordance with the rate at which energy supplied to the track rails is coded. The wayside signal S preferably is located in the trackway adjacent the entrance end D of section D-E, and may take any one of many well-known forms, but as shown comprises a four-indication color light type signal having a green signal unit G, a yellow over green signal unit Y/G, a yellow signal unit Y and a red signal unit R, which units when illuminated indicate clean approach medium, approach and stop, respectively.

Selective control of the aspects displayed by signal S is effected in accordance with the rate at which energy supplied to the rails I and I a is coded, by means of code responsive apparatus embodying my invention and operated by energy derived from the two track rails of section D-E. As shown, such apparatus comprises a novel form of code responsive control device of the saturation type, designated as a whole by the reference character SR; a decoding transformer DT supplied with energy from device SR; and the usual code detecting and code selecting relays I-II, BJ I and AJ I controlled by energy supplied frorn decoding transformer DT.

The code responsive device SR comprises a magnetizable core I5 upon which are disposed an output winding I5, a biasing winding l1 and a control winding I8. The biasing winding I'I is constantly supplied with unidirectional current from a suitable source, such for example as a rectifier RI which has its output terminals connected to winding I1 and has its input terminals connected across the secondary winding of a transformer TI. The primary winding of transformer TI is connected across a source of alternating current designated by the reference characters BX and CX, and it follows that winding I1 is constantly energized to create unidirectional :IiuX of a given polarity in core I5 to set up a iven flux condition in such core. I have represented graphically in Fig. 4 the flux condition established in core I5 by the flux due to current in winding I'I, and I shall refer to this biasing flux as being ux of normal polarity and the magnetic condition set up in core I5 by such flux as being the normal flux condition of device SR.

The control winding I8 of device SR is supplied with energy derived from the track rails I and Ia for varying the magnetic condition of core I5 in step with the supply of such energy. As shown, energy from the rails I and Ia is supplied to winding I8 through the medium of a receiving transformer RT, which has its primary winding connected across the track rails of section D-E adjacent the entrance end D and has its secondary winding connected to the input terminals of a rectifier R2, the output terminals of this rectifier being connected to winding I8. It is readily apparent that the alternating energy supplied to the track rails I and Ia is rectied by rectier R2 into and is supplied to Winding I8 as unidirectional current. The curve shown in Fig. 3 represents the rectied current supplied from rectifier R2 to Winding I8 in response to the supply of 120 code energy to the rails of section D-E, and since such energy sets up a unidirectional flux in core I8 proportional to the ampere turns of winding I8, such curve also represents the ux created in core I5 due to the supply of such energy to winding I8.

The connection of winding I8 to rectier R2 is selected in such manner that the flux created in core I5 due to current in winding I8 opposes the flux due to current in winding Il. Preferably, the parts of winding Ill are selected and designed so that when unidirectional energy of a predetermined magnitude is supplied to winding I8, the normal iiux created by winding I'I is entirely neutralized and a resultant ux condition is established in the core of substantially equal density and opposite relative polarity to that `of the normal flux condition. The curve shown in Fig. 5 represents a typical variation of the magnetic condition of core I5 caused b-y the supplyof biasing flux and of control flux to such core. In Fig. 5, it is assumed that control flux is supplied to core I5 in responseto the supply to winding I8 of the 120 code control energy, such as is represented in Fig. 2.

In Fig. 1, the biasing winding Il and control winding I8 are illustrated controlling the magnetic condition of a saturable reactor type code responsive device, hence the magnetizable core I5 of device SR is illustrated as comprising, as is the usual practice, a three-legged structure having biasing winding II and control winding i8 disposed on the middle leg of the core and an output winding comprising two coils Iii, I6 disposed one on each of the two outer legs of the core. The two coils I6, I5 of the output winding are connected together in series to a source of alternating current, and it follows that the impedances of the tWo coils comprising the output winding of device SR are varied in step with the variations of the magnetic condition of core I5. Preferably, the connection of the two coils of winding I6 is such that both coils cooperate in circulating a flux in agreement in the two outer legs of core I 5, and as a result substantially no alternating ilux traverses the middle leg of core I5 so that no alternating current components are induced in windings I'I and I8. It is readily apparent that by properly proporticning and designing the parts of reactor SR, the magnetizable core I5 may be normally held at a given uX condition (preferably being held at a saturated condition), in response to the'biasing flux created by winding I1 so that as a result the impedance of winding It is relatively low and current of relatively high magnitude flows through winding I 5. When, however', control energy is supplied to winding I3, the flux due to current ini winding I8 flrst carries the core through an unmagnetized or no-ilux condition, wherein the impedance of winding itis greatly increased and the current flow in such winding is decreased to a relatively low Value, to a resultant flux condition of substantially equivalent or saturated density of iluX of opposite relative polarity, wherein the current ilow in winding I5 again reaches its normally high value. On the interruption of current to winding I8, a similar variation in ilux condition of the core is established with a` corresponding variation in magnitude of current traversing winding IS. The curve illustrated in Fig. 6 represents the effective current flo-w in winding I5 of device SR under the conditions wherein code is supplied to control winding I5 of the device. It is to be noted from Fig. 6 that the number of code impulses supplied from output winding I6 of device SR per unit of time is double the number of code impulses supplied to winding I8 in the same interval of time (see Fig. 3), hence it follows that device SR functions to increase the code rate or frequency at which energy is supplied to' its associated decoding apparatus in response to the supply of coded control energy to device SR.

It should be pointed out that by means of biasing winding Il, energy supplied through winding I under the'influence of coded current in winding I8 is caused to be coded at a'rate double the code rate of energy supplied to Winding I8, whereas if biasing Winding I1 is not employed, the coding of current in Winding I6 caused by the supply of coded current to winding I8 results merely in reproducing in winding l5 the coding of the current in winding I8. Ihis follows from the fact that if only winding I8 were employed, the reluctance of core I5 then would vary from a relatively high value to a relatively low value in step with the supply of current to winding i8 and current in winding I6 accordingly would vary in step with the supply of the coded impulses of current in winding I8. The effective current in winding I6 under such assumed conditions would, therefore, be represented by a curve substantially similar to that shown in Fig. 2. When, however, biasing winding I'I is employed to set up an initial or normal ux in core I5, the supply of current to winding I8 then causes the reluctance of core I5 to vary from a relatively high value to a relatively low value twice for each impulse of code supplied to winding I8, and as a result currentl in winding I6 is caused to be coded at a rate double the rate at which current supplied to winding I8 is coded.

As shown in Fig. l, output winding I6 of device SR supplies energy to a portion of the primary winding of a decoding transformer DT through the medium of a transformer T2 and a rectifier R3, which rectifier is connected to cause energy supplied from winding I6 to create in its associated portion of the decoding transformer a ux which opposes the ux normally created in the remainder of the primary winding by energy supplied from a rectier R4 constantly connected through a transformer T3 to a source of alternating current. Preferably, the parts of decoding transformer DT are so designed and proportioned that a predetermined density of magnetic flux of one polarity is set up in the core of transformer DT by the constant supply of energy from rectifier R4, and such magnetic flux is entirely neutralized and a resultant magnetic ux of substantially equal density but of opposite relative polarity is created in the core of transformer DT on the supply of energy from device SR. It can be seen, therefore, that the magnetic condition of transformer DT is carried from a given flux condition through its vzero or no flux condition to a substantially equivalent ux condition of opposite relative polarity both on the supply and on the interruption of energy from device SR so that an electromotive force is induced in the secondary winding of transformer DT due to the variations in flux in the transformer core.

The secondary Winding of transformer DT is connected to supply energy to suitable decoding apparatus, whichapparatus includes the usual decoding relays one for each of the plurality of code rates supplied to the rails of the trackway, whereby selective control of trafc governing signal S is established in accordance with the rate at which control energy is supplied to device SR. As shown, signal S is controlled to one or another of a plurality of distinctive signal aspects through the medium of three decoding relays AJ I, BJI and HI one foreach of the three assumed rates of coding, and which relays are coupled with the secondary winding of transformer DT through the medium of suitable decoding or code distinguishing units DUI, DU2 and DUS, respectively.

The details of construction of the decoding units DUI, DU2 and DU3 are not shown in the drawings, but such units usually comprise a rectifier and a reactor condenser tuning unit tuned to resonance respectively at a frequency correspending to a predetermined multiple of the 180, 120 and 75 code rates supplied to the track rails, whereby relays AJ I, BJI and III are effectively energized and picked up when and only when the predetermined multiple of its associated control code, at least, is supplied from decoding transformer DT to such relay. That is to say, the construction and design of the decoding units DU preferably are such that relay HI is energized by current supplied through decoding unit DU3 when transformer DT supplies the predetermined multiple of the r15 code; relay BJ I is energized by current supplied through decoding unit DU2 when transformer DT supplies the predetermined multiple of the 120 code; and relay AJ I is energized by current supplied through decoding unit DUI when and only when transformer DT supplies the predetermined multiple of the 180 code to such relay.

The operation of the apparatus of Fig. l is as follows: the rails of section D-E are supplied With control energy of 180, 120 or '75 code in accordance With traflic conditions in advance of the section, and when section D-E is unoccupied, this control energy is supplied from the rails of section D--E to device SR. The parts of the apparatus which supply control energy to and which receive control energy from the track rails are designed and proportioned so that under the most unfavorable ballast conditions expected to be met in practice, energy of a predetermined magnitude is supplied to device SR sufcient, at least, to create in core I5 of device SR a resultant flux condition substantially equivalent in magnitude and opposite in relative polarity to the given normal flux condition established in the core of device SR due to current constantly supplied to biasing winding I1.

If the rails of section D-E are supplied with 180 code and the section is unoccupied, then device SR functions in response to energy received by winding I 8 from section D-E to supply energy of double the rate or 360 code to transformer DT. This supply of energy of double rate or 360 code to transformer DT causes induced electromotive forces to be supplied from the secondary winding of the transformer and as a result relay AJ I is energized and signal S is caused to display its clear aspect over a circuit extending from one terminal B of a suitable source of current, such as a battery not shown, through front contact 2| of relay AJ I and the filament of signal unit G of signal S to the other terminal C of the source of current. Under the assumed conditions of code in the trackway, it is immaterial Whether or not relays BJ I and HI are also picked up since at this time these latter relays do not exert a control over signal S, but if the decoding unitsY DU are high-pass filters, relays BJ I and HI also will be picked up, as shown in Fig. 1, in response to the current that is supplied from transformer DT.

If, now, 120 code is supplied to the rails I and la. and it is received by the code responsive device SR, such device functions to supply energy of double code rate or 240 code to transformer DT, which transformer in turn supplies the current caused to be induced in its secondary wind- 1 ing to the relaysAJ I ,LBJ I ,andfI-II. ;By virtue oi r winding is controlled'by varying the relative rethe construction and .arrangement ofpthe .decoding unitsDU, relay .AJ I is releasedbut relay BJI vis Apicked up in.. response to the, current vcaused. to be supplied fromrtransformenDTunder the assumed conditionsof..120 codelirithe track rails, so that as-a result signal. S controlled to display its vapproach medium! aspect over a circuit extending from terminal B through back contact 22 of relay AJ I, front contact 230i relay BJI and the laments of `signal unit Y/G of signal S to terminal uC`.

l In the event that-75 codeeissupplied to the 1 rails of sectionv D---Iilv and is received `by device SR, then suchdevice functions to *supply` energy of-a double rate or 150 code to transformer DT,

*f and such transformer supplies; relays-HI, AJ land BJI with the-currentcaused to beY induced in transformer DTdueto vthersupply of` 150 code. vAs` pointed out heretofore, the' decoding units DU function in such` manner that only relay I-II is picked up in response to the supply of the predetermined multiple of 75 code; and as a result signal S is controlled to its approachaspect over a circuit `which passes* from" terminal B through back contact 22 of relay AJ I, back contact 24 of relay BJ I,"` front contact" 25 'of relay HI and the filament of unit Y of signal S to i terminal C.

` If, however, section D`E is occupiedso that the control energy supplied .to its rails is shuntd away from device'SR, then the impedance of winding I6 of such device is constantly held at a low value by the biasing flux present in core I5,

. circuit extending from terminal B through back contact 22 of relay AJ I, back Contact 24 of relay BJI, back contact 26 of relay HI and the lament of unit R. of signal S to terminal C.

From the foregoing description of the operation of the apparatus of Fig. 1, it is readily apparent that I have provided novel and improved control apparatus of the statictype involving no moving parts and responsive to control code for proportionately increasing or multiplying Athe `code rate at which energy is supplied to control .Y apparatusfrom the device in response to. the Vsupply of coded energy to such` device.

It is to be understood, of course, thatthe -particular construction of the code responsive saturation device SR shown in Fig. 1 is merely illustrative, and that such device may takerother `65V suitable forms wherein the supply of energy from an output winding is vcontrolled by amagnetizable core in which the flux in a'portion, at least, of such core varies between a given iiux condition and a substantiallyequivalent resultant flux condition of opposite relative polarity both on `the supply and on the interruption of `control energy to such device. For example, the code responsive device may take the form of a saturable transformer wherein the inductive coulffplingbetween a primary winding constantlysupplied -with alternating current andan output luctances or flux conditions of different portions ofa magnetizable core whichcarries such primary. and output windings.

In addition, it is to be understood that although the apparatus embodying my invention zhas been illustrated anddescribed as applied to the cori-trol of a wayside signal, such apparatus may if desired be carried on a train to control a train-carried control device in response to controlenergy inductively received from the rails of .a `trackway.

Although I have hereinshown andA described 1 only one form of code responsive control ap-V another of a plurality of code ratesin` accordance'.

with Vcertainpredetermined conditions, a magnetizable core having means for establishing in said core a normal liux condition of given density and relative polarity, a control winding disposed on said core, means for supplying from said con-- ductors` to said controllwinding energyof a predetermined magnitude and polarity for establishing insaidcore a resultant iiux condition substantially equivalent in density and. oppositen relative polarity-to said .given flux condition, an;v

output winding disposed onisaid core, and a source of alternatingrcurrent coupled through` said output windingtodecoding apparatus selectively responsive to the rate at which energy is Asupplied thereto.

2. In combination with a source of. current having means for periodically interrupting or coding such current at one or another of a plurality of code rates, Atwo magnetizable cores each having means for establishing in its respective core a normal flux condition of given density and relative polarity, twocontrol windings one: disposed on eachecore, means for supplying from said source to anrst of said `control windings current `of` a; magnitude l and polarity selected toA establish in'its associated first core a .resultant flux condition substantially equivalent in density `and. opposite in relative polaritytosaid normal iiuxcondition, an output winding disposed on said rst core and connected to the other of saidi two control windings for supplying to said other control winding current of a predetermined magnitude and polarity effective to establish in the `other ofsaid two cores a resultant flux substantially equivalent in density and opposite in rel-"' ative polarity to-said normalxiiux condition, another output windingdisposed on said other core, and control means receiving energy from. said Aother output winding and selectively -responsive to the form of lenergy supplied thereto.

3. In combination with a sourceof current having means for 4periodically interrupting or coding such-current at one -or anotherl of a` plurality of code rates, two magnetizablecores each having means -for f establishing l in its respective' core anormal-linx condition of given density and relativepolarity,` two contro-1 windings one disposed on each core, means for supplying from said source to a rst of said control windingsunidirectional current of a magnitudeand `polarity 'v selected to establish in its associated Yfirst core a l resultant flux condition substantially equivalent "winding for establishing in its associated other core aresultant iiux substantially equivalent in density and opposite in relative polarity to said normal flux condition, another output winding disposed onsaid other core, and control appara- -Y tus connected to receive current induced in said other output winding and selectively responsive l to the rate at which such current is varied.

. 4. In .combination with a pair of conducto-rs supplied at times with energy coded at one or another of a plurality of code rates in accordance with certain predetermined conditions, a magnetizable core, means for supplying magnetic ux of `a given polarity to said core for normally estab'- trol winding disposed on said core and proporlishing a given flux condition in said core, a contioned in such manner that when supplied with unidirectional energy of a predetermined magnitude and polarity said winding supplies flux of the .opposite relative polarity to said core for establishing in said core a resultant flux condition opposite in relative polarity but substantially equivalent in density to said given flux condition, means for supplying said control winding with energy of said predetermined magnitude and polarity derived from said pair of conductors for energizing said control winding in step with thesupply of energy to said conductors, an output winding disposed on said core and receiving energy from a source of alternating current under the influence of the magnetic flux in said core,

and control apparatus controlled by energy supplied from said output winding and selectively responsive to the rate at which such energy is coded.

5. In combination with a stretch of railway track having two conductors governed by traffic conditions on said stretch and having means for supplying to said conductors energy which is coded at one or another of a plurality of code 'rates in accordance with trafiic conditions in advance, a magnetizable core, means for supplying to said core magnetic flux of a given polarity for normally establishing a given flux condition in said core, a control winding disposed on said core and proportioned in such manner that when supplied with unidirectional current of a predetermined magnitude and polarity said winding Supplies flux of the opposite relative polarity to said core for creating in said core a resultant flux condition opposite in relative polarity but substantially equivalent in density to said given flux condition, means for supplying said control winding with unidirectional current of said predetermined magnitude derived from said two conductors for energizing said control winding in step with the supply of energy to said conductors, an output winding disposed on said core and receiving energy from a source of alternating current under the influence of the magnetic flux in said core, and railway traiiic controlling apparatus selectively controlled by energy supplied from said output winding in accordance with the rate at which such energy is coded for governing traffic on said stretch.

'6.4 In combination with ai stretch of railway track having means for supplying coded trackway energy to the rails of said stretch, a magnetizable core normally, held at an initially saturated condition by'flux of a given polarity, a control winding disposed on said core, means for supplying unidirectional energy of a predetertrack having means for supplying coded trackway energy to the rails of said stretch, a magnetizable core normally held at an initially saturated'condition by flux of a given polarity, a control winding disposed on said core, means for supplying unidirectional energy of a predetermined magnitude and polarity from the rails of said stretch to said control winding for saturating said 'core withresultant flux of the opposite relative polarity, a source of alternating' current, railway traic controlling apparatus for controlling traffic on said stretch and selectively responsive to the code rate at which current is supplied thereto, and an output winding disposed on said core for coupling said source to said control apparatus whereby such apparatus is supplied with coded current from said source in response to the iiux conditions in said core.

8. In combination with a stretch of railway track having means for supplying to the track rails of said stretch trackway energy which is coded at one or another of a plurality of different rates of coding, a magnetizable core provided with means for supplying ux oi a given polarity to said coreV for establishing a flux condition of given density in said core, a control winding disposed on said core and proportioned in such 'manner that when supplied with unidirectional energy of a predetermined polarity and magnitude said winding sup-plies to said core ux of the opposite relative polarity and of such magnitude that a resultant flux condition substantially equal in density and opposite in relative polarity to said given flux condition is created in said core, means responsive to said trackway energy for supplying to said control winding unidirectional;

energy of said predetermined polarity andmagnitude, an output winding also disposed on said core, and railway traffic controlling apparatus controlled by energy supplied from said output winding and selectively responsive to the codingof such energy as effected by the varying ux conditions in said core.'

9'. In combination with a stretch of railway track having means for supplying to the track rails of said stretch trackway energy which is coded at one or another of a plurality of different rates of coding, a magnetizable core provided with means for supplying flux of a given polarity to said core for establishing a given flux condition in said core, a control winding disposed'on said core, means responsive to said trackwayenergy for supplying to said control winding unidirec- .tional energy of a predetermined polarity and magnitude for creating in said core a resultant flux condition substantially equivalent in density and opposite in relative polarity to said given flux condition, an output winding also disposed on said core, a source of alternating current, decoding means supplied with energy from said source through said output winding andselectively responsive to variations in such energy as effected in response to varying impedance conditions of said output winding caused by varying flux conditions in said core, and railway traic controlling apparatus selectively controlled by said decoding means for controlling traffic in said stretch.

l0. In a code control system of th-e class wherein coded' current supplied from a control circuit selectively controls code responsive control apparatus in accordance with the rate at which such current is coded, the combination with said circuit and said control apparatus of a code repeating device receiving from said circuit current coded at one or another of a plurality of code rates and supplying current to said control apparatus at an increased rate of coding proportional to the rate at which the received current is coded, said device comprising a source of alternating current and a magnetizable core carrying an output winding coupled With said source and supplying current to said control-apparatus, said core also having means for varying the flux in said core between ilux conditions of substantially equivalent densities and of opposite relative polarities both on the supply and on the interruption of current to the device from said circuit, whereby the supply of current from said source to said control apparatus through said output Winding is caused to be coded at a rate double the rate at which current is received by the device from said source.

11. In combination with decoding apparatus adapted to be selectively controlled in accordance with the rate of coding at which current is supplied from a control circuit, a magnetizable core,

a source of alternating current coupled with an output winding disposed on said cor-e for supplying current to said decoding apparatus, and means on said core responsive to current supplied frorn said control circuit for varying the magnetic flux in said core between flux conditions of substantially equivalent densities and of opposite relative polarities both on the supply and on the interruption of current from said control circuit.

12. In combination with decoding apparatus adapted to be selectively controlled in accordance with the rate of coding at which current is supplied from a control circuit, a magnetizable core, means on said core responsive to current supplied from said control circuit for varying the magnetic iiux in said core between flux conditions of substantially equivalent densities and of opposite relative polarities both on the Supply and on the interruption of current from said control circuit, and a source of periodically varying current connected through an impedance winding disposed on said core to said decoding apparatus.

13. In combination With decoding apparatus f adapted to be selectively controlled in accordance with the rate of coding at which current is supplied from a control circuit, a magnetizable core, means on said core responsive to current supplied from said control circuit for varying the magnetic ux in said core between ilux conditions of substantially equivalent densities and of op posite relative polarities both on the supply and on the interruption of current from said control circuit, and a source of alternating current coupled through a winding disposed on said core to said decoding apparatus for supplying such apparatusy with current caused to be coded in response to variations of flux in said core.

CHARLES C. BUCHANAN.

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