US2512343A - Coded track circuit system involving highway crossing signal control - Google Patents

Description

R. M. LAURENSON CODED TRACK CIRCUIT SYSTEM INVOLVING HIGHWAY CROSSING SIGNAL CONTROL Flled March 19 1946 June 20, 1950 INVENTOR Haber/Mlaapmmzz.

Patented June 20, 1950 CODED TRACK CIRCUIT SYSTEM IN- VOLVING HIGHWAY CROSSING SIG- NAL CONTROL Robert M. Laurenson, Verona, Pa", assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application March 19, 1946, Serial No. 655,635

7 Claims. (Cl. 246-130) My invention relates to railway signaling apparatus, and has particular relation to coded track circuit systems of railway signaling of the type in which approach functions are controlled through the medium of current transmitted through the traffic rails. More particularly, my invention relates to coded track circuit systems of the type described incorporating means for providing a clearing out control of such approach functions.

An object of my invention is to provide novel and improved railway signaling systems incorporating means for controlling approach functions. 7

Another object of my invention is to provide novel. and improved railway signaling systems incorporating improved means for obtaining clearing out controls of approach functions.

Another object of my invention is to provide novel and improved means for supplying both feed-back and clearing out code in a track circuit for controlling approach functions.

Another object of my invention is to provide in a coded track circuit system of railway signaling, means for supplying the track rails of a section with code having similar characteristics both when such code is generated by the feedback principle in response to the receipt of master code, and when the code is locally generated as a supplemental clearing out code.

The above-mentioned and other important objects and characteristic features of my invention are obtained by energizing the impulse relay at the entrance end of a section through a transformer both when operated on feed-back code and when operated on special supplemental code 10- cally generated, by providing means at the exit end for reversibly operating the polarized track relay at that end when clearing out code only is applied to the track rails, and by providing other novel and improved apparatus described in detail in the accompanying specification.

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

The accompanying drawing illustrates a preferred embodiment of my invention represented in connection. with the control of an approach function constituting a highway crossing protective device.

Referring to the drawing. the reference characters L and fa designate the traffic rails of a stretch of railway track over which traflic normally operates in a given direction as indicated in. the drawing by an arrow, or from leit to right as viewed in the drawing. The track rails l and la are divided by insulated joints 2 into a plurality of successive adjoining track sections, of which only one section, D-F, is shown in the drawing. Section D-F is further divided by insulated joints 2 located at E into adjoining subsections DE and E-F, and as indicated in the drawing, subsection D-,E is intersected at grade by a highway H at the exit end of that subsection. Located at the intersection of highway H and the stretch is a highway crossing protective device XS which may take any one of a number of suitable forms, but which is illustrated for the sake ofsimplicity as a highway crossing bell. The bell XS is normally deenergized but is supplied with energy over an obvious circuit whenever back contaot 41 of a relay EVM is closed.

The stretch of track is provided with a coded track circuit system for controlling signals, such as signal DS located at D, located along the stretch at the entrance of each section for governing the movement ,of trafiic in the associated section, and also for controlling approach functions. The coded track circuit system of signaling provided for section DF comprises master code transmitting means and approach function control means located at section end F, master code repeating or cascading means and approach function control means provided at location E, and master decoding means and approach control code transmitting means located at entrance end D of the section.

The apparatus at section end F comprises a transmitting relay FCTM, a two-winding stick polar relay FVR, and an oscillation detecting relay FVM controlled by relay FVR. through the medium of a transformer It. One portion of primary winding II .of transformer i0 is supplied with unidirectional current from a suitable source indicated conventionally in the drawing by the reference characters B and .C, when contact [3 of relay FVR. is in its left-hand position as illustrated in the drawing, and the other portion of winding ll of transformer It is supplied with unidirectional current when contact E3 of relay FVR. is operated to its opposite or right-hand position. The mid terminal tap. ,of secondary winding l2 of transformer I0 is connected to one terminal of relay FVM and the opposite end terminals of winding 12 are alternately connected to the other terminal of relay F-VM according as contact M of relay FVR is in its left-hand or right-hand position, the arrangement being such that alternating current of relatively low frequency is induced in secondary winding ii of tween its left-hand and right-hand positions, but. when relay FVR maintains its polar contact con-"" stantly in either of its positions, the 'supplyof'v energy to relay FVM is then discontinued and-= that relay releases.

The transmitting relay FCTM is controlled over a circuit which may, for example, be similar to the circuit hereinafter traced for the corresponding transmitter relay DCTM, and is energized periodically at one or another of a plurality of code rates, preferably '75 or 180 cycles per min-g ute, to operate its contacts and. 2| at the corresponding rate alternately between front and back positions. Contact Id of relay FCTM in its front position connects a battery FB to the track rails in series with winding I6 of a transformer l1 and resistor I9, thereby applying to the track rails an impulse of energy. while contact [5 of relay FCTM in its back position disconnects battery FB from the track rails and connects one winding of the two-winding stick polar relay FVR to the rails. Contact 2| of relay FCTM in its front position connects a battery 22 in circuit with the other winding 23 of relay FVR and this battery is poled to energize'the relay in adirection to cause it to operate its polar armature to its left-hand position. The relay FVR is of the stick polar or stay-where-put type arranged to hold its polar armature in its last operated position.

The track circuit current intermittently applied to the rails of section EF each time front contact l5 of relay FCTM is closed, is transmitted through the track rails to the intermediate location E to effect energization of track relay ETR located at that point. This track circuit current I shall term the ,master code. Track relay ETR has associated therewith a decoding transformer EDT, a. code detecting relay EH, and an impulse relay EIR. Front contact 25, of relay ETR supplies one portion of primary winding 26 of transformer EDT with unidirectional current, and

back contact of relay ETR supplies unidirectional current to the other portion of winding 25 of the transformer. One secondary winding 2! of transformer EDT is connected with code detecting relay EH through the medium of contact 28 of relay ETR with the circuit connections being arranged so that relay EH is supplied with unidirectional current when the armature of relay ETR operates alternately between its released and picked-up positions, but relay EH becomes deenergized when the armature of relay ETR remains continuously picked up or released, respectively. Another winding 29 of decoding relay EDT is connected to primary winding 30 of a transformer 3| which has its secondary winding 32 connected to the terminals of impulse relay EIR. Relay EIR is of the polar biased type responsive only to current of a preselected polarity and the parts are so arranged that transformer winding 29 cooperates with transformer 3! to supply an impulse of current of the preselected polarity to relay EIR, each time back contact 25 of relay ETR closes. Relay EIR controls a contact 33 which when closed in its back position connects relay ETR to the track rails, and which contact 33 when picked up disconnects relay ETR 4 from the track rails and connects a battery EBF' in series with the resistor 34 across the track rails. This connection of relay EBF to the track rails when front contact 33 of relay EIR is closed, is effective to transmit energy, which I shall term a feed-back code, through the track rails to the other end F of the section for supplying winding 20 of the two-winding stick polar relay FVR at that location with current having a polarity 'efi'ective to cause the relay to operate its polar armature from its left-hand position to its righthand position, as Will be pointed out in more detail hereinafter.

' When relay ,ETR is following impulses of master code energy received from track rails l and la of subsection E-F, impulse relay EIR will be supplied with an energy impulse of the proper polarity to pick up that relay, only upon the release of relay ETR so that relay EIR picks up to disconnect relay ETR from the track rails only during the interval that relay ETR is released due to the off period of the master code energy in the track rails, and it follows that the supply of feed-back code energy to the track rails from battery EBF is in step with the supply of energy to relay E'IR andis provided during the off period of the master code in the section. The arrangement of transformer winding 29 and transformer 3i operates to supply relay EIR with a relatively short pulse of energy of the predetermined polarity so that relay EIR has a very short on time, that is, it will maintain its front contact 33 closed for a relatively short time which insures that the relay will release to close its back contact 33 and connect relay ETR to the track rails prior to the start of the next on time of the master code supplied at the opposite end of the section.

The apparatus at location E also includes a, two-winding polar stick relay EVR, an oscillation detecting relay EVM controlled by relay EVR in a manner corresponding to that pointed out in detail whereby relay FVM is controlled by relay F'VR at location F, and another relay EVRA energized whenever contact 35 of relay EVR is in its left-hand position as indicated in the drawing. The circuit for relay EVRA extends from terminal B through contact 35 of relay EVR in its left-hand position, asymmetrical unit 36 in its low resistance direction, and the winding of relay EVRA to terminal C, with resistor 31 and condenser 38 connected in multiple with the winding of relayEBRA to provide slow release characteristics to this relay. Relay EVRA controls a circuit for winding 46 of relay EVR, passing from terminal B through back contact 39 of relay EH, the winding 46 of relay EVR, and back contact 49 of relay EVRA to terminal C, with the polarity of current selected to cause relay EVR to operate its polar armature to its left-hand posi- 'master code energy as long as front contact 40 of relay ETR remains picked up, and energizing winding 45 of relay EVR with energy of a polarity such that the relay operates its polar armature to its left-hand position. Contact 40 of relay ETR when released disconnects battery EBD from the track rails to terminate the on pe.

rlod of the master code impulse while maintaining the connection of winding 45 of relay EVR to those rails, thereby preparing a circuit whereby winding 45 may be energized by energy transmitted through the track rails from the entrance end D of the section.

The impulse of master code energy applied from battery EBD- to the track rails of section D-E-each time contact 40 of relay ETR is closed in its front position is transmitted through the track rails when subsection D-E is vacant to the entrance end D for operating a track relay DTR located at that point. Relay DTR has associated therewith a decoding transformer DDT, a code detecting relay DH energized through the medium of transformer DDT in a corresponding similar manner to that explained in detail whereby relay EH is controlled by relay ETR through transformer EDT, a code discriminating relay DD energized through transformer DDT and a tuned circuit involving a condenser 56 with the circuit proportioned to effectively energize relay DD when and only when relay DTR operates in response to 180 code in the track rails, and an impulse relay DIR biased to respond only to current of a preselected polarity. Relay DIR has its terminals connected to the secondary winding of a transformer 52 which in turn has its primary winding 53 connected to secondary winding 54 of transformer DDT over front contacts 55 and 5B of relay DH, but when relay DH is deenergized and contacts 55 and 53 close to their back points, Winding 53 of transiformer 52 is then supplied with unidirectional energy over contact 51 of a coding device 150T. The arrangement is such that when relay DH is picked up relay DIR is supplied with one pulse of current, having a polarity selected to cause operation of the relay, each time that relay D'IR releases to close its back contact 58, and when relay DH is released to close its back contacts 55 and 5B, relay DIR is likewise supplied with an impulse of current of the proper polarity each time contact 5'! operates from its front to its back position. It will be noted that the energization of relay DIR is effected through the medium of transformer 52 both when the impulse originates in secondary winding 54 of transformer DDT and when the impulse originates through the closing of contact. 51 of the code originating means CT. In each [0358, therefore, the impulse of energy that is induced in secondary winding 5| of transformer 52 will be substantially identical because it is the result of the supply of energy to winding 53.

Relay DIR operates a contact 50, which when closed in its back position connects the track relay DTR across the track rails to receive master code energy over the track rails from exit end E of the subsection. Contact 60 when picked up disconnects relay DTR from the track rails and connects a battery DB in series with resistor 6! across the track rails, with the battery poled in such a manner as to supply feed-backcode energy having a polarity such as to energize winding 45 of relay EVR-and operate the polar armature of that relay to its right-hand position. When relay DTR is following impulses of master code energy received from the track rails i and la, of subsection D-E, impulse relay DIR operates in the manner described with reference to relay EIR to apply impulses of feed-back code to the rails of the subsection during each off period of the master code in the subsection.

6, The-decoding relays DH and DD associated with relay DTR cooperate in the usual manner to control signal DS located at the entrance end of section DF. This signalDSmay take any desired form but is represented as a color light signal. Control of. signal DS as shown is established when both relays DH and DD are picked up, through a circuit passingfrom terminal B through front contact 62 of relay DH, front con! tact [i3 of relay DD, and the filament of lamp G of signal DS to terminal B; when relay DD is released'butrelay DH is picked up, the circuit passes from-terminal B through front contact 62 of relay DH, back contact 63 of relay DD and the filament of lamp Y of signal D8 to terminal B; and when both relays DH and DD are re leased, lamp R of signal DS is energized over an obvious circuit including back contact 62 of re lay DH.- a Y Relay DH also controls the energization of code transmittingrelay DCTM provided for the section in the rear of section DF. This control of the transmitter relay is established through a circuit for the winding of relay DCTM passing either through contact 64 of coding device 1323GT (which operates its contacts alternately between front and back positions at the rate of I 180 times per minute) and front contact 65 of relay DH, or through contact 65 of coding device 750T (which operates its contacts alternately between front and back positions at the rate oi times per minute) and back contact 55 of relay DH. It isreadily apparent that when section D-F is unoccupied so that the relay DH is-picked up, the transmitter relay is'then energized periodicallyat the rate of code pulses per minute, but that when section D'r' is occupied so that relay DH is released, relay DCTM is then ener gized periodically at a rate of i5 code cycles per minute. The devices IHBCT and lBCT are arranged so that front contact t t of lfltCT is closed for an intervalequalto the interval that contact 64 is in its back position, and likewise contact [56 (and 51) of 'EBCT is closed in its front position for an interval equal to the m terval that contact 66 (and El) occupies its back position. This results in the generation of a master code in which the on intervals of the 180 code are equal in duration the off intervals'of that code,- and the on intervals of the 75 code are equal in duration to the off intervals or that code.

Inorder to describe the operation of the apparatus set forth above, I shall assume that the section in advance of section D-F is unoccupied so that transmitter relay FC'IM at location F is energized periodically at the rate of 180 code pulses per minute, and shall also assume that section D-F is unoccupied. Under these conditions, the apparatus of my invention will be in the condition illustrated in the drawing. In this condition, relay. FCTM alternately opens and closes its contacts I5 and H at the rate of 180 times per minute to intermittently energize winding 23 of relay FVR and provide 180 master code energy in the rails of subsection E-F. This current in the track rails operates relay ETR at a corresponding rate and as a result relay EH is picked up. Also, the operation of relay ETR results in the operation of relay EIR at a similar rate with the result that during the ofi period of each pulse of master code in subsection E-F, feedback code supplied at E is transmitted through the track rails to end F where it energizes winding .20 of relay EVR, The alternate energization oi winding 23 of relay FVR by current from battery 22 having polarity such as to operate the relay armature to its left-hand position, and of winding 20 of relay FVR. with'current from battery EBF having a polarity suchas to cause the relay to operate its armature to its right-hand position, results in relay F'VM being picked up.

At location E of section D-'-F, the operation of relay ETR. at the 180 code rate results in the operation of its contact 40 between its front and back positions at a rate of 180 code pulses per minute, with the result that 180 master code is repeated from section E-'F into the rails of section D-E. This 180 code pulse current is transmitted through the track rails to the entrance end D of the section where it operates relay DTR at the corresponding code rate, and relays DD and DH are picked up. Also, relay DIR at location D is energized at the 180 code rate to apply energy impulses of feed-back code from battery DB to the track rails of subsection D-E each time an off interval occurs in the master code applied to subsection D-E and this feed-back code applied from battery DB is transmitted through the track rails to exit end E where it energizes winding 45 of relay EVR. The energization of winding 45 of relay EVR alternately by current from battery DB having a polarity to operate the polar armature of the relay to its right-hand position, and by current from battery EBD having a polarity to operate the polar armature of the relay to its left-hand position, results in the energization of repeating relay EVM. Also, relay EVRA is picked up because of this reversible operation of relay EVR, the slow releasing features of the relay serving to maintain the relay picked up during the intervals that contact 35 occupies its right-hand position.

At entrance end D of the section, the energization of relays DH and DD results in illumination of lamp G of signal DS to indicate clear trafiic conditions in the section, while transmitter relay DCTM is energized at the 180 code rate and will function in the ordinary manner to apply 180 ,code rate pulses to the rails of the section in the rear of section D-F.

If a train operating in the stretch in the normal direction of trainc enters section DF, the energy impulses supplied to the rails of subsection D--E at E are then shunted by the train wheels and axles away from relay DTR, whereupon that relay releases and maintains its contacts in their back positionsso that relays DH and DD also release. This causes signal DS to display its red aspect R, and also shifts the energization of transformer 52 from winding 54 of transformer DDT to contact 51 of coding device lCT. Relay DIR thereupon operates at the '75 code rate, and battery DB is alternately connected to and disconnected from the rails of section D-E at the rate of 75 times per minute, but the energy applied at this time from battery DB to the track rails is shunted away from relay EVR by the train wheels and axles. This coded energy differs from the feed back code previously mentioned because it is not generated in response to operation of relay DTR by master code energy, but is locally generated by coding device 15CT. This locally generated code I shall term a clearing out code.

At location E of section D-F, relay ETR continues to operate its contact 40 at a rate corresponding to the code rate of the current in the rails of subsection D,F, with the result that code pulses. oi energy are continuously-applied to thexrails of. subsection DE, but as pointed out hereinbeforeqthis energy is 1 shunted away from relay DTR; The connection of battery EBD to the track rails energizes winding 45 of relay EVR with current "having a polarity effective to operate the relay armature to its left-hand position, and since no energy from battery DB is transmitted through the track rails to winding 45 of relay EVR, the polar armature of that relay remains in its left-hand position.

The polarized relay ENE at location E now ceases to operate its contact alternately between its left and right-hand positions and as a result relay EVM releases to close its back contact 41 and complete an obvious energizing circuit for crossing signal XS which now becomes active to indicate to highway users that a train is approaching the intersection. Contact 48 of relay EVM may also close to complete an obvious circuit for primary winding 43 of transformer 42, this winding being energized from a suitable source of alternating current conventionally indicated in the drawing by the reference characters BX and OK. The energization of winding 43 causes the induction of alternating current in winding 4| and the intermittent connection of this winding to the track rails through front contact 40 of relay ETR. supplies coded alternating current to the track rails which may be utilized for controlling train carried brake control or cab signal apparatus on the train.

When the train enters subsection D-F, relay ETR becomes shunted and operates its contacts to their back positions, so that relay EH releases to close its back contact 39 and prepare the energizing circuit for winding 46 of relay EVR. Winding 45 of relay EVR is now constantly connected to, and battery EBD is disconnected from, the rails of subsection D-E. At the opposite end F of the subsection, the two-winding relay FVR ceases to operate its contacts alternately between the left-hand and right-hand positions, due to the fact that relay EIR remains released to out 01f battery EBF from the rails of section EF, and as a result approach control relay FVM releases to close its back contact 24 to connect a source of alternating current to winding [8 of transformer I1. This results in the induction of alternating current in winding I6 and the alternate connection of this transformer winding to the track rails supplies alternating current at the code rate to the rails which may be used to control train carried apparatus.

When the train clears highway H and vacates subsection D--E, the clearing out code intermittently applied to the track rails from battery DB each time relay DlRcloses its front contact 50 is transmitted through the track rails to location E where it energizes winding 45 of relay EVR with current having a polarity effective to operate the polar armature of that relay to its righthand position. This operation deenergizes relay EVRA which thereupon releases to close its back contact 49 and thereby complete for winding 46 the previously traced circuit effective to energize that winding with current having a polarity such as to operate the polar armature of relay EVR to its left-hand position. Operation of contact 35 of relay EVR to its left-hand position energizes relay EVRA whereupon that relay picks up and opens its back contact 49 to deenergize winding 46 of relay EVR, so that the next succeeding impulse of clearing out code energy supplied over the track rails to winding 45 is effective to operate the polar armature of relay EVR to its right! hand position. This cycle of operation is maintained as long as relay EH is released, and results in relay EVR operating its contacts alternately between their left-hand and right-hand positions so that relay EVM becomes energized and opens its back contact 4'! to deenerg-ize the crossing signal XS and thereby terminate operation; of that signal. Also, back contact 48 of relay EVM opens to deenergize winding 43 of transformer 42.

After the train vacates section D'F, '75 master code current is then applied at end P to the rails of subsection and. is repeated by relay ETR into subsection D--E to cause relay DTR to operate at the 75 code rate and pick up relay DH to shift the energiz ation of relay DIR to transformer DDT and thereby restore the feed-back code. .Intermeshing of the independently generated 75 master code, supplied at E to rails l and la of subsection D-E, and '75 clearing out code supplied to the rails atD, is rendered impossible because of the different characteristics of the two codes. The master code is characterized by alternate on. and off intervals of substantially equivalent durations, while the clearing out code consists of on intervals of very short duration separated byrelatively long duration off intervals. Should the first impulse of 75- master code occur at the same time as an on interval of the clearing out code, both contacts 40 of ETR and 6B of DIR might be closed in their front positions, and both relay DTR and winding 29 of FVR might be disconnected from'the track rails, but the short on time of relay DIR will result in the release of that relay while front contact of ETR remains closed, so that relay DTR will be supplied with a portion of the on impulse of the 75 master code and will pick up to energize relay DH. and shift the energization of transformer 52 to winding 54 of transformer DDT. Although both the clearing out w and, master codes appliedto the rails of subsection D- -E are independently generated by contacts of 75 code generators which have equal on and off contact times, theclearing out code is provided with the distinctive short on time characteristics through the use of transformer 52in the circuit over which contact 51 of coder TECT supplies energy to relay DIR). The use of thistransformer results in reducing the interval that energy of the preselectedpolarity is supplied to relay DIR,

from the relatively long on period that contact 5! of device 150T is closed, to the relatively short period requiredior-the flux in the transformer toreach a steady state condition (thus terminating induction of energy in secondary winding 51) following operation of contact 51.

The picking up of relay DH inresponse'to operation of relay DTR by master code results in closing the 180 code energizing circuit for the code transmittingrelay in closing the circuit for lamp Y of signal DS,- and in shifting the energization of winding 53 of transformer 52, from back contact 51 of coding device HGT, to winding 54 oftransformer DDT so that impulse relay DIR operates in synchronism with the oporation of relay to apply feed-back code impulses at the i5=code rate to the track rails of section DE duringeach off period of the master code energy applied to those rails for operation ofthe track relay DTR. The operation ofrelay ETR, at location E also results in the energization of relay EH so that the circuit for winding 46 of relay .EVR is opened at back contact 38 of relay EH, but relay EVR is now caused to operate itscontacts alternately between their left-handandright-hand positions due to the energization of winding .45 of that relay alternately by energy from battery EB D and battery DE. The reversible operation of the contacts of relay EVR maintains relay EVM picked up to deenergize the approach control functions such as the highway crossing signal KS and transformer 42. In addition, the two-winding stick polar relay FVRat location F is similarly reversibly operated by the energy supplied alternately from batteries 22 and EBF so thatrelay FVR operates its polar contacts alternately between their left and right-hand positions to cause relay FVM to pick up and open itsback contact 24 to deenergize winding [8 oftransformer 11.

'When the train clears the section in advance of the exit end F of section D-F, code transmitting relay FCTM is then caused to operate at the code rate to cause operation of relays ETR and DTR at the same rate, whereuponrelay DD at location D becomes energized; the green lamp of signal DS becomes illuminated; and the apparatus is restored to the normal condition as illustrated in the drawing.

It is to be noted that my invention is applied to the control of a stick polar relay used as an approach code detecting relay in coded track circuit signaling systems provided with reverse or feed-back codes to obtain control of approach functions. The invention provides a novel and improvedmeans in such systems, for obtaining a clearing out controliof the approach functions to terminateoperation of a highway crossing Sig-.- nal after atrain vac'ates a highway intersection.

The principle .of using a transformer in the circuit .forthe impulse relay energized by the locally operated generator, thereby to provide distinctive characteristics for the clearing out code which functions to .prevent the intermeshing of the clearing-out and master codes despite the use of the same rates for the two codes, may of course be used-infeed-back coded trackcircuits incorporating feed-back operated track relays of a-type different from the two-winding polar stick type illustrated. For example, this principle may be used where the feed-back code operated relay is of the single winding type and the circuit ar: rangement for connecting this relay .to the track rails is-similar to that shown in Letters Patent of the United States No. 2,213,186, granted to Herman G. Blosser on September 3, 1940, orin other arrangements such as those making use of a polar biased relay such asis shown for example inv an application for Letters Patent of the United States SerialNo. 452,983, filed by Howard A. Thompson on July 31,,1942,.now U. S.

Patent 2,401,201. r

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

Having thus described my invention, what I claim is: 1 I I 7 1,111 combination with a stretch of railway track over which traific operates in onedirection and having an insulated track section, a source of direct current,-a two-winding stick polar re-' la, and a coding contact continuously operated between a first and a second position when the stretch in advance of said section is vacant, a circuit including said contact in its first position connecting said source and one winding of said tw -w ndi r lay in s r s with th ails at which traflic operates in one direction and having end of said section for applying energy to said rails and for operating the polar armature of" said two-winding relay to one of its two extreme positions, a, circuit including said contact in its said second position for disconnecting said source from said rails while maintaining the connection of said one winding of said two-winding relay to the rails at said one section end, means at the opposite end of said section effective when said section is vacant and following operation of said coding contact from said first to said second position for supplying an impulse of energy to the rails at that section end, said impulse of energy having a polarity selected to cause operation of said polar armature of said two-winding relay to its other of said two positions, other means effective when said coding contact remains continuously in said second position for periodically supplying current of said selected polarity to the rails at said opposite end, means effective when said polar armature of said two-winding relay i in its said other position and said coding contact remains continuously in said second position for energizing the other winding of said two-winding relay with energy having a polarity such as to cause the polar armature of said two-winding relay to operate to its said one position, and control means governed by the arma ure of said two-winding relay.

2. Highway crossing signal control apparatus for a coded track circuit system of railway signalin provided for a stretch of railway track over which traffic normally operates in a given direction and including an insulated section of railway track intersected at its exit end by a highway, said system having at said exit end a source of direct current, a two-winding polarized stick relay, and a coding contact continuously o erated between a first and a second position when the stretch in advance of said section is vacant, a circuit including said contact in its said first position for connecting said source and the one winding of said two-winding relay in series with the rails of said section for applying energy to said rails and for operating the polar armature of said two-winding relay to one of its two extreme positions, a circuit including said contact in its said second position for disconnecting said source from said rails while maintaining the connection of said one winding of said two-winding relay to the rails, said system having at the entrance end of said section means effective when said section is vacant and following each operation of said coding contact from said firstto said second position for supplying an impulse of energy to the rails at that section end, said impulse of energy having a polarity selected to cause operation of said polar armature of said twowinding relay to its other of said two positions. other means effective when said coding contact remains continuously in said second position for periodically supplying current of said selected polarity to the rails at said entrance end, means effective when said two-winding relay operates its polar armature to said other position and when said coding contact remains continuously in its said second position for supplying the other winding of said two-winding relay with energy having a polrality effective to cause operation of the armature of said two-winding relay to its said one position, and highway crossing control means governed by the operation of said armature of said two-winding relay.

3. In combination with a railway track over an insulated track section, a source of direct current, a two-winding polarized stick relay, and a coding contact at the exit end of said section, said coding contact continuously operating between a first and a second position when the stretch in advance of said section is vacant and efiective in said first position for connecting said source and one winding of said two-winding relay in series with the rails of said section for applying energy to said rails and for operating the polar armature of said two-winding relay to one of its two extreme positions and effective in the second position of said contact for disconnecting said source from the rails while maintaining the connection of said one winding of said two-winding relay to the rails, a track relay and an impulse relay responsive only to current of a selected polarity at the entrance end of said section, a transformer having its secondary connected to said impulse relay, a circuit for inducing in the secondary winding of said transformer current of said selected polarity to cause operation of said impulse relay each time said track relay releases and controlled by said track relay, another circuit controlled by said track relay for inducing in the transformer secondary periodically interrupted current of said selected polarity when said track relay ceases to follow code in said track section, means controlled by said impulse relay for alternately connecting said track relay and a source of current to the track rails at said entrance end of said section with said track source poled to supply current having a polarity to cause operation of the polar armature of said twowinding relay at said exit end to its other position, means eflective when current is applied at the entrance end of said section while said coding contact remains in its said second position for energizing the second winding of said two-winding relay with current having a polarity to cause operation of said armature of said twowinding relay to its said one position, and control means operated by the armature of said twowinding relay.

4. Highway crossing signal control apparatus for a coded track circuit system of railway signaling provided for a stretch of railway track over which traflic normally operates in a given direction and including an insulated section of track intersected at grade by a highway, said insulated section subdivided by insulated joints at said intersection into adjoining front and rear subsections, said system including means at the exit end of said front subsection for applying to, the track rails thereof coded track circuit current comprising alternate on and on intervals during which respectively current is and is not supplied .to the track rails and a track relay at the entrance end of said front subsection receiving energy from the rails thereof and alternately picked up and released in step with the on and off intervals of said coded track circuit energy; said system also including a source of direct current and a two-winding polarized stick relay at the exit end of said rear subsection, and circuits connecting one winding of said two-winding polarized relay to the track rails of said rear subsection alternately in series with said source of current when said track relay for said one subsection is picked up and directly to the rails when said track relay of said one subsection is released, said series connection of said source and one winding of said two-winding polarized relay applying energy to the rails of said rear subsection and operating 13 said polarized armature of said two-winding polarized relay to one of its two extreme positions; said system also including: a track relay and a source of direct current at the entrance end of said rear subsection, an impulse relay picked up only on current of a selected polarity for alternately connecting said track relay and the current source to the track rails at said entrance end of said rear subsection according as said impulse relay is picked up or released, said current source poled to supply energy having a polarity effective to operate said polarized armature of said two-winding polarized relay to the other of its said two positions, a transformer having one winding connected in circuit with said impulse relay and having another winding, means controlled by each release of the track relay at said entrance end of said rear subsection for .supplying energy to said other winding of said transformer whereby an impulse of current of said selected polarity is induced in said one winding and supplied to said impulse relay, means controlled by said track relay at said entrance end of said rear subsection effective when that relay ceases to operate alternately between its pickedup and released positions for periodically supplying energy to said other winding of said transformer; said highway crossing signal control apparatus comprising a control relay energized only when the armature of said two-winding polarized relay operates alternately between its said one and second positions, a second relay energized over a circuit including a contact closed when said armature of said two-winding relay operates to its said one position, a circuit for the other winding of said two-winding polarized relay including the back contact of said second relay and a contact closed only when the track relay of the front subsection ceases to operate alternately between its picked-up and released positions and a source of current poled to cause energization of said second winding of said twowinding relay in such a manner as to operate said polarized armature to its said one position; and a highway crossing signal at said intersection controlled by said control relay.

5. Coded feed-back apparatus for a coded track circuit system for a section of railway track in which coded energy is applied to the track rails at one end of the section, said apparatus comprising in combination, an impulse relay, a code responsive track relay connected to receive energy from the track rails at the other end of said section when said impulse relay is released, a source of current connected to the track rails at said other end of said section when said impulse relay is picked up, a decoding transformer having a primary winding supplied with a pulse of direct current energy of one relative polarity each time said track relay picks up and of the other relative polarity each time said track relay releases, an impulse transformer having its secondary winding connected to said impulse relay, a circuit connecting a secondary winding of said decoding transformer to the primary winding of said impulse transformer, said impulse relay and the secondary of said impulse transformer being arranged so that the impulse relay picks up only in response to the induction of energy of a preselected polarity in said secondary winding, a coding contact operating between first and second positions, and a circuit including said coding contact effective when said track relay ceases to respond to the coded energy supplied to the track rails for energizing the primary winding of said impulse transformer.

6. In a coded track circuit system for a section of railway track in which coded energy is applied to the rails at one end of the section, said system including an impulse relay and having a code responsive track relay and a source of current connected respectively to the track rails at the other end of the track section according as said impulse relay is released or picked up respectively, said system also including a decoding transformer having a primary winding supplied with direct current of one relative polarity or the other according as said track relay is picked up or released respectively, the combination with said impulse relay and decoding transformer of an impulse transformer having its secondary winding connected to said impulse relay, a circuit connecting a secondary winding of said decoding transformer to the primary winding of said impulse transformer, said impulse relay and secondary of said impulse transformer being arranged so that the impulse relay picks up only on the inducthe track relay ceases to pick up and release alternately in response to the coded energy supplied to the track rails.

7. In a coded track circuit system for a section of railway track in which coded energy is supplied to the track rails at one end of the section, said system including an impulse relay and having a track relay and a source of current connected respectively to the track rails at the other end of the track section according as said impulse relay is released or picked up respectively, said system also including a decoding transformer having a primary winding supplied with direct current of one relative polarity or the other according as said track relay is picked up or released respectively, and also including a detecting relay connected to receive energy from said decoding transformer and picked up only when the primary winding of that transformer is alternately supplied with current of one relative polarity and the other as a result of the response of the track relay to coded energy received from the track rails, the combination with said impulse relay and decoding transformer of an impulse transformer having its secondary winding connected to said impulse relay, a circuit connecting a secondary winding of said decoding transformer to the primary winding of said impulse transformer, said impulse relay and secondary of said impulse transformer being arranged so that the impulse The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,213,186 Blosser Sept. 3, 1940 2,332,874 Staples et a1 Oct. 26, 1943 2,335,765 Judge Nov. 30, 1943 2,405,860 Thompson Aug. 13, 1946

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