US2721933A - Railway signaling systems - Google Patents

Description

Oc 1955 L. D. DICKINSON RAILWAY SIGNALING SYSTEMS Filed Aug. 8, 1950 INVENTOR. La 1h ckz'nson HIS ATTORNEY United States Patent RAILWAY SIGNALING SYSTEMS Leon D. Dickinson, Omaha, Nebr., assignor to Westinghouse Air Brake Company, a corporation of Pennsyi- Vania Application August 8, 1950, Serial No. 178,321

2 Claims. (Cl. 246-34) My invention relates to railway signaling systems, and particularly to a railway signaling system including a pair of line wires for supplying coded alternating current to the track rails of a stretch of track and also for governing a signal control relay at the entrance end of the stretch.

It has previously been proposed to provide railway signaling systems in which the track is divided into a plurality of block sections, each of which is provided with a wayside signal to govern the movement of traffic into the block section. Additionally, the block sections are each subdivided into a plurality of track sections, to each of which alternating current is supplied at times at the exit end thereof to govern train-carried cab signals on trains moving through the section. A pair of line wires extends the length of each block section and is arranged to have alternating current energy supplied thereto at the exit end of the block section in accordance with trafiic conditions in advance of the block section. The alternating current energy is supplied to the rails at the exit end of the various track sections in the block sections by connections or taps to the line wires. Additionally, the wayside signal at the entrance end of the block section is governed by the energy supplied to the line wires at the exit end of the block section.

In previous systems of the type described, the apparatus is arranged in such manner that the failure of the alternating current energy supply would result in the interruption of the supply of energy for governing the train-carried cab signals and would also result in the interruption of the supply of energy for the control of the wayside signals. As a result, neither cab signals nor wayside signals would be operative, and train movements could not be made with the benefit of signal protection. Under certain conditions, it is desirable to permit the operation of trains in accordance with wayside signal indication, despite a failure in the supply of alternating current energy normally utilized for controlling the cab signals.

Accordingly, it is an object of my invention to provide a railway signaling system in which both wayside and train-carried signals are normally controlled by alternating current energy supplied over a wayside line circuit, and which system is arranged to provide control of the wayside signals alone from a standby source of direct current energy in the event of an interruption of the alternating current energy.

Another object of my invention is to provide a system of the type described, in which coded pulses of alternating current energy are normally supplied to a line circuit extending through a block section, and are supplied from the line circuit to the track rails of each track section in the block for the control of train-carried cab signals, and are additionally supplied to a signal control relay at one end of the block section to thereby reflect trafiic conditions ahead, which system is arranged to supply direct current energy over the line wires to govern the signal control relay in the event of the failure of the alternating current energy supply.

Patented Oct. 25, 1955 Other objects of my invention and features of novelty will be apparent from the following description, taken in connection with the accompanying drawing.

In practicing my invention, I provide a pair of line wires extending the length of each block section in the stretch of railway equipped with a signaling system embodying my invention. At the exit end of the block section, coded alternating current energy is normally supplied to the line wires, in accordance with conditions ahead of the block section. At the exit end of each track section in the block section, the primary winding of a transformer is tapped to the line wires, and the secondary winding of the transformer is arranged to supply the coded alternating current energy of proper value to the rails of the track section to operate cab signal equipment on trains occupying the track section. At the entrance end of the block section, a transformer is connected to the line wires and supplies pulses of energy through a rectifier to energize the winding of a direct current signal control relay. Contacts of the signal control relay govern an associated Wayside signal to thereby reflect conditions in advance of the block section. Additionally, there is provided at the exit end of the block section means responsive to a failure of the alternating current energy supply, for connecting the line wires to a standby source of direct current, governed by conditions ahead of the block section. At the entrance end of the block section, there is provided means for connecting the winding of the signal control relay directly to the line wires upon the failure of the A. C. energy, so that the signal control relay is then governed by the direct current energy supplied over the line wires in accordance with trafiic conditions in advance of the block section. Moreover, the circuits may be arranged so that the line circuit, when operated on direct current, includes in series therewith, at the exit end of the block section, the winding of an approach lighting relay, so that the wayside signal is energized only when a train is approaching the signal to thereby conserve energy during the interruption of the alternating current energy supply.

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

The single accompanying drawing is a diagrammatic view showing a stretch of railway track and associated wayside circuits for a signaling system embodying'my invention.

Referring to the drawing, there is shown a stretch of railway track having track rails 1 and 2, over which trailic moves in the direction shown by the arrow, that is, from left to right. The stretch is divided into block sections, such as the section XO, and a wayside signal, such as 18 and 28, is provided at the entrance end of each of the block sections to govern tralfic entering the block section. Each of the block sections is divided into at least two track sections, such as the sections IT and lAT, by the insulated joints 3, and each of these sections is provided with a direct current track circuit comprising a track relay connected across the rails at the entrance end of the track section, such as relays ITR and lATR, and a track battery connected across the rails at the exit end of the section such as batteries 1TB and lATB. The secondary winding of a track transformer, such as transformers 1TT and lATT, is connected in series with the track battery in a manner well known in the art, in order to superimpose coded alternating current upon the direct current track circuit energy, to operate train-can ried cab signals. The primary windings of the track transformer are supplied with alternating current energy in a manner to be subsequently described.

It will be seen that front contact a of track relay lATR governs the supply of energy to traclc section IT, in the arrangement known in the art as a relayed cut section so that if either section IT or section lAT is occupied, the track relay lTR will be released. The wayside signals, such as 18 and 28 may be of any type, and are shown as being of the well-known color-light type having a red lamp R, a yellow lamp Y and a green lamp G. The circuits for supplying energy to the signal lamps are arranged so that the red lamp R is lighted when the block section immediately in advance of the signal is occupied, the yellow lamp is lighted when the first block section in advance of the signal is unoccupied, but the second block section in advance is occupied, and the green lamp is lighted when the first two or more block sections in advance of the signal are unoccupied. The apparatus at the entrance end X of the block section XO also includes a first signal control relay lHR, a line power off relay ILPOR, a rectifier ILPRX, a line transformer lLPT, and a condenser lPQ, all of which provide for governing a second signal control relay 1DR by energy supplied over the line wires L1 and L2 extending from the entrance end X of the block section to the exit end of the block section. The primary windings of the track transformers lTT and 1ATT are connected to the line wires L1 and L2 through condensers 1TQ and 1AT Q, respectively.

At the exit end 0 of the block section, the apparatus includes two control relays ZHR and 2DR, governed by conditions in advance of signal 28, an approach lighting relay 2AER, for governing the supply of energy to the lamps of signal 28 as will be subsequently described, a power olf relay ZPOR supplied with energy from a transformer 2PT through a rectifier ZPRX, and a coding device 180CT having contacts which are recurrently opened and closed at some specified rate, such as, for example, 180 times per minute. At each location, there is provided a source of direct current energy, such as the batteries 1LB and 2LB, the positive and negative terminals of which are designated by the reference characters B and N, respectively.

The apparatus is shown in its normal condition, with no trains occupying the block section XO, and traffic conditions in advance of signal 28 such that relays 2HR and 2DR are picked up. Additionally, it is assumed that alternating current energy is being supplied at this time from the terminals BX and NX of a suitable source, not shown, to the primary winding 7 of transformer 2PT. The alternating current energy induced in the secondary winding 9 of transformer 2PT is rectified by the full wave rectifier ZPRX and the resultant direct current energy is supplied to the winding of relay ZPOR so that the contacts of relay ZPOR are picked up as long as alternating current is supplied to the primary winding 7.

Under the normal condition, energy is supplied to the green lamp G of signal 25, by a circuit which may be traced from terminal B of the source, over front contact 0 of relay 2POR, front contact d of relay ZHR, front contact a of relay 2DR, and through the green lamp G to terminal N. Accordingly, the signal 28 displays a proceed aspect at this time.

With the power off relay ZPOR picked up, the line wires L1 and L2 are connected to the secondary winding 9 of transformer 2PT over front contacts b and c of relay 2HR, front contacts a and b of relay 2POR, and the recurrently operated contact a of coding device 180CT. It will be apparent that, at this time, impulses of alternating current energy are supplied to the line wires L1 and L2 at the rate of 180 per minute.

Track relay 1ATR is energized by energy supplied over the track rails 1 and 2 of section lAT from the battery lATB. Also, impulses of alternating current energy coded at the 180 rate are supplied from the line wires L1 and L2 to the primary winding 13 of transformer lATT through the condenser lATQ. The alternating current impulses induced in the secondary winding 15 of transformer lATT are superimposed on the direct current energy supplied to the track section lAT. Such a superposition of alternating current energy impulses upon direct current track circuit energy for the operation of train-carried cab signal or train control apparatus is well known in the art.

Since relay 1ATR is energized at this time, the track battery 1TB and the secondary winding 21 of transformer ITT are connected in series across the track rails 1 and 2 of section IT at the exit end of the section, over front contact a of relay 1ATR. The primary winding 19 of transformer 1TT is connected to the line wires L1 and L2 through the condenser 1TQ. Accordingly, impulses of alternating current energy supplied from the line wires as well as direct current from the battery 1TB are supplied to the rails of section 1T.

At the entrance end of the block section XO, track relay 1TR is energized by the direct current energy supplied over the track rails from battery 1TB, and relay lHR is energized by energy supplied over a circuit including front contact a of relay ITR. Alternating current impulses are supplied from the line wires L1 and L2 to the primary winding 23 of transformer lLPT through the condenser 1PQ. Impulses of alternating current energy induced in the secondary winding 25 of transformer 1LPT are rectified by the full wave rectifier lLPRX and the resultant impulses of direct current are supplied to the winding of relay lLPOR and to the winding of signal control relay 1DR by a circuit including front contact a of relay ILPOR and front contact a of relay IHR. The relays 1DR and lLPOR are of the type which are slow in releasing their contacts, so that when the windings of these relays are supplied with direct current impulses from rectifier ILPRX, the contacts of the relays will remain picked up during the short time intervals between the direct current impulses. At this time energy is supplied to the green lamp G of signal 13 by a circuit which may be traced from terminal B, over front contact b of relay lHR, front contact a of relay 1DR, and through the green lamp G to terminal N.

From the foregoing, it will be seen that with the block section X-O unoccupied, and relays ZHR and 2DR picked up, the signals 28 and 13 display a green aspect and coded alternating energy is supplied to the rails of sections 1AT and IT.

It will now be assumed that a train moving from left to right passes signal 15 and enters the track section 1T of the block section XO. Accordingly, the track relay lTR is shunted and its contacts release causing the relay lHR to be released. When contact b of relay IHR releases, it interrupts the circuit for supplying energy to the green lamp G of signal 18 and establishes an obvious circuit for supplying energy to the red lamp R of the signal. Additionally, when front contact a of relay lHR releases, it interrupts the circuit for supplying energy to the signal control relay lDR, so that relay 1DR releases. If the train is equipped with cab signal or train control apparatus responsive to alternating current impulses in the rails, it will be seen that the impulses of alternating current energy induced in the secondary winding 21 of transformer 1'IT are supplied to the rails to influence the equipment, and in the usual manner with such apparatus, the supply of alternating current impulses at a rate of times per minute will cause the signal apparatus to display a clear indication on the cab indicator.

When the train advances into track section lAT, relay 1ATR is shunted and its contact a releases, interrupting the circuit for supplying energy from the battery 1TB and the secondary winding 21 of transformer lTT to the rails of section 1T. At this time the cab signal or train control equipment is governed by the alternating current supplied to the rails of section 1AT from the secondary winding 15 of transformer lATT located at the exit end of section 1AT.

When the rear of the train vacates section 1T, no energy will be supplied to the track rails 1 and 2 of the section since front contact a of relay IATR interrupts the circuit for connecting the track battery 1TB and the secondary winding 21 of transformer ITT across the section rails.

When the train passes signal 28, relay 2HR will release, the relay 2HR being controlled in a manner similar to relay IHR. The front contact a of relay 2HR will interrupt the circuit for controlling relay 2DR, so that relay ZDR will also release. When contact d of relay 2HR releases, it interrupts the circuit previously traced for supplying energy to the green lamp G of signal 28 and establishes a circuit for supplying energy to the red lamp R of the signal, which circuit may be traced from terminal B over front contact 0 of relay 2POR, back contact d of relay 2HR, and through the red lamp R of the signal 28 to terminal N. When contacts b and c of relay 2HR release, the supply of alternating current impulses to the line wires L1 and L2 is interrupted and the back contacts of relay 2HR shunt the line wires. Accordingly, the supply of alternating current impulses from the secondary windings of the track transformers 1TT and 1ATT is discontinued, and similarly the supply of energy through the transformer lLPT and the rectifier ILPRX at the location of signal 18 is interrupted, so that relay ILPOR releases its contacts. Relay IDR is still released at this time, since relay lTR is released, as a result of the train still occupying section 1AT of the block section X-O. When the rear of the train vacates section lAT, energy from battery IATB flows over the section rails to the winding of relay lATR, and relay lATR picks up. When front contact a of relay lATR closes, the battery 1TB is connected across the rails of section IT, to thereby supply energy over the section rails totrack relay lTR. When track relay lTR picks up, the relay I'HR is energized and its front contact b establishes a circuit for supplying energy to the yellow lamp Y of signal 18, which circuit includes a front contact b of relay IHR and back contact a of relay lDR.

At this time, with the train in advance of signal 28, sothat relays 2HR and 213K are released, signal 28 will display a red aspect and the signal 18 will display a yellow aspect indicating approach next signal prepared to stop. At this time, there are no alternating current impulses being supplied to the line wires L1 and L2, and as a result there is no alternating current energy supplied to the rails of track section IT and lAT, so that should a train pass the yellow signal 18, the cab signal equipment on the train would not be influenced, and the cab indicator would display a restrictive indication, as is proper under these conditions.

If it is assumed that the signal 28 is governed by traflic conditions in the block in advance of the signals similar to the block X-O, then when the train in question clears the block in advance of signal 28, the relay 2HR will pick up. When relay 2HR picks up, a circuit is established for supplying energy to the yellow lamp Y of signal 28, which circuit may be traced from terminal B, over front contact c of relay 2POR, over front contact d of relay 2HR, and over back contact a of relay 2DR, and through the yellow lamp Y of the signal to terminal N. Additionally, when contacts b and c of relay 2HR pick up they reconnect the line wires L1 and L2 to the secondary winding of transformer 2PT through the recurrently operated contact a of the coding device 180CT and the front contacts a and b of relay ZPOR. Accordingly, impulses of alternating current energy are again supplied to the line wires L1 and L2 at the rate of 180 impulses per minute.

The reestablishment of the supply of impulses of alternating current energy to line wires L1 and L2 causes the transformers 1TT and 1ATT to be recurrently energized, so that impulses of alternating current energy are supplied from the secondary windings of these transformers to their respective track sections, as was previously described.

The reestablishment of the supply of alternating current impulses to the line wires L1 and L2 also causes" energy to be again supplied to the transformer lLPT at the entrance end X of the block section, and the energy from the secondary winding 25 of the transformer is rectified and supplied to the winding of relay ILPOR, so that relay ILPOR picks up its contacts a and b, and establishes the circuit for supplying impulses of direct current energy to the winding of relay lDR. When relay IDR picks up, its contact a establishes the previously traced circuit for supplying energy to the green lamp G of signal 18. It will be seen therefore that at this time, the signal 28 is displaying a yellow aspect, the signal 18 is displaying a green or clear aspect, and coded alternating current energy is being supplied to the rails of track sections IT and lAT. Accordingly, a second train passing signal 18 at this time would receive a clear indication on cab signaling equipment carried by the train, in accordance with the traffic conditions.

When the train in question advances sufl'iciently far beyond signal 28, the circuit for energizing relay 2DR will be completed in the conventional manner, over front contact a of relay 2HR and the line circuit for the block section in advance of section XO, and when contact a of relay 2DR picks up it reestablishes the previously traced circuit for supplying energy to the green lamp G of signal 28. At this time, therefore, the apparatus is restored to its initial condition as previously described.

It will now be assumed that, with the apparatus in its normal condition as shown, the source of alternating current energy supplied to the primary winding 7 of transformer 2PT is interrupted. As a result, rectified energy is no longer supplied through the rectifier 2PRX to the power-off relay 2POR, and this relay will release. When contacts a and b of relay ZPOR release, they interrupt the circuit for connecting the line wires L1 and L2 to the secondary winding of transformer 2PT and establish a connection between the line wires L1 and L2 and the terminals of the battery ZLB, with the winding of a series approach relay 2AER interposed in the lead to the positive terminal B of the battery. The interruption of the supply of alternating current impulses over the line Wires L1 and L2 cuts off the supply of rectified energy from the rectifier lLPRX to the power off relay ILPOR located at the entrance end of the section, and relay ILPOR releases. When contacts a and b of relay ILPOR are released, they establish a circuit for connecting the winding of signal control relay 1DR directly to the line Wires L1 and L2 over front contact a of relay IHR. At this time, therefore, energy is supplied to the windings of relay 2AER and signal control relay lDR by a circuit which may be traced from terminal B of battery 2LB' at the exit end of the block section, through the winding of series approach relay 2AER, over back contact a of relay ZPOR, front contact b of relay 2HR, line wire L1, back contact a of relay ILPOR, front contact a of relay lHR, through the winding of relay lDR, back contact b of relay ILPOR, line wire L2, front contact c of relay 2HR, and back contact b of relay 2POR to terminal N of battery 2LB.

Accordingly, it will be seen that with the supply of alternating current energy at the exit end 0 of the block section interrupted, the line circuit comprising line wires L1 and L2 is energized by direct current energy, so that relay lDR is now governed by the direct current energy supplied over the line wires. With relays 2HR and 2DR picked up, and track sections IT and lAT unoccupied, relay lHR and relay 1DR establish the circuit for supplying energy to the green lamp G of signal 15.

At the exit end of the block section, the lighting circuit for signal 28 now includes a back contact a of relay 2AER, and the back contact 0 of relay 2POR. With no train occupying the block section X-O, relay 2AER will be picked up, and accordingly the supply of energy to the lamps of the signal will be interrupted. Thus signal 23 is normally dark, so that the supply of energy from the battery 2LB is conserved by keeping the signal lamps dark as long as no train is approaching the signal. Since in a conventional signaling installation, the battery 2LB would be a storage battery trickle charged by a rectifier normally supplied with alternating current from the source having terminals BX and NX, it is important to conserve the battery energy during interruption of the alternating current supply, by approach lighting the signals.

It will now be assumed that a train moving from left to right passes signal 18 and enters the track section 1T. As a result, relay ITR is shunted to release the relay 1HR and its contacts a and 11 release. When contact b of relay lHR releases it establishes a circuit for supplying energy to the red lamp R of signal 18, and when contact a of relay lHR releases it interrupts the circuit previously traced for energizing the signal control relay 1DR and the series approach relay ZAER at the exit end of the section. When relay ZAER releases, its back contact a establishes the lighting circuit for signal 2S, and since relays ZHR and ZDR are considered to be picked up at this time, the circuit is established for supplying energy to the green lamp G of signal 28, which circuit may be traced from terminal B, over back contact a of relay ZAER, back contact of relay 2POR, front contact d of relay ZHR, front contact a of relay 2DR and through the green lamp G of signal 28 to terminal N. Accordingly, the signal 28 is lighted in advance of the approaching train to provide the proper aspect.

It will be noted that during the time that the line wires L1 and L2 are energized with direct current energy due to the release of the power of relay 2POR, the direct current flowing in the line wires L1 and L2 is prevented from flowing through the primary windings of the track transformers lTT and lATT, and the control transformer lLPT, by the condensers associated with the transformers, so that there is no loss of direct current energy through the primary windings of the transformers.

It will be seen that at this time there is no supply of alternating current impulses to the track sections IT and lAT for the control of the cab signal of the train occupying these sections, but the direct current track circuit comprising the batteries and track relays operate in the same manner as previously described so that relay lTR is released during the time that the train occupies the section XO. When the train moves by signal 28, relay 2HR will release, and its back contact d establishes a circuit for lighting the red lamp R of signal 28, and its contacts b and c interrupt the supply of direct current energy to the line wires L1 and L2 and establishing a shunt across the line wires by means of the back contacts b and c. When the rear of a train vacates the block section XO, track relay lTR and in turn relay IHR will pick up at the entrance end of the section, and front contact b of relay IHR will establish a circuit in conjunction with back contact a of relay IDR to supply energy to the yellow lamp Y of signal 18. Although front contact a of relay lHR is now closed in the control circuit for relay 1DR, relay 1DR remains released, since relay ZHR is released at the exit end of section XO.

When the train advances sufficiently far to permit the relay ZHR to pick up, energy is again supplied to the circuit previously traced including the winding of relay ZAER, the back contacts of relay 2POR, the front contacts of relay ZHR and the front contact a of relay lHR, so that relays ZAER and 1DR are again energized. When relay lDR picks up, the circuit for supplying energy to the green lamp G of signal 18 is again established, and when relay ZAER picks up, its back contact a interrupts the supply of energy to the lighting circuits of signal 25, so that the signal lamps are extinguished.

Should a following train pass signal 18 displaying a green aspect at this time, the relay ZAER will be released as previously described, and if it is assumed that the train in advance has not proceeded sufiiciently far to permit the relay 2DR to pick up, when the back contact a of relay ZAER releases, a circuit is established for lighting the yellow lamp Y of signal 25 over back contact a of relay 2DR.

When the supply of alternating current energy to the primary winding 7 of transformer 2PT is again established, the relay 2POR will pick up, and its contacts a and b will reconnect the line circuit to the secondary winding 9 of transformer ZPT over the recurrently operated contact a of coding device CT. Additionally, contact 0 again connects the lighting circuits for signal 28 directly to the direct current source so that the signal 25 is again continuously lighted. The supply of alternating current impulses to the track sections IT and lAT is reestablished, and the supply of alternating current impulses to the control transformer lLPT at the entrance end of the section results in relay ILPOR picking up to disconnect the circuit for relay 1DR from the line wires and connect it to the rectifier lLPRX. The relay 1DR is therefore energized by the direct current impulses supplied from the rectifier lLPRX, as previously explained. The apparatus is now restored to its normal condition, as shown in the drawing.

From the foregoing, it will be seen that my invention provides for the supply of direct current energy over the line wires which are normally used for the supply of alternating current energy to the track sections in the block section, the direct current energy being supplied to the line wires during the time which the supply of alternating current energy is interrupted, and the apparatus at the entrance end of the block section being arranged so that the signal control relay is normally governed by the presence of alternating current impulses in the line circuit, and is arranged to be connected directly to the line wires to be governed by steady direct current energy in the event of interruption of the alternating current impulses.

Although I have herein shown and described only one form of railway signaling system embodying my invention, it will be apparent to those skilled in the art 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.

Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track divided into a plurality of track sections, a wayside signal for governing traffic entering said stretch, a track circuit for each of said track sections including a track relay and adapted to influence train-carried train control apparatus when supplied with coded alternating current energy, a line circuit governed by traflic conditions in advance of said stretch, a source of coded alternating current, a first and a second power off relay each having front contacts which are closed when coded alternating current energy is supplied to a Winding of the relay and back contacts which are closed when the winding is deenergized, means including said front contacts of said first power off relay for connecting said line circuit to said source of coded alternating current energy, a source of direct current energy, means including said back contacts of said first power off relay for connecting said line circuit to said source of direct current energy, means for supplying energy from said source of alternating current energy to a winding of said first power off relay, a transformer for each of said track circuits having a secondary winding connected to the track rails and having a primary winding connected across said line circuit, a condenser for each of said transformers and connected in series with said primary Winding to prevent the fiow of direct current through said primary winding, a control transformer having a primary and a secondary winding, a condenser associated with said transformer, a rectifier, a signal control relay, said primary winding of said second transformer being connected to said line circuit through said associated condenser, means for supplying energy from said secondary winding of said control transformer to a winding of said second power off relay, circuit means including front contacts of said second power off relay for connecting the winding of said signal control relay to said secondary winding of said control transformer through said rectifier, circuit means including back contacts of said second power off relay for connecting the winding of said signal control relay directly to said line circuit, and means governed jointly by said track relays and said signal control relay for controlling said wayside signal.

2. In combination, a stretch of railway track divided into a plurality of track sections, a wayside signal for governing trafiic entering said stretch, a track circuit for each of said track sections including a track relay and adapted to influence train-carried train control apparatus when supplied with coded alternating current energy, a line circuit governed by traffic conditions in advance of said stretch, a source of coded alternating current, a first and a second power 01f relay each having front contacts which are closed when coded alternating current energy is supplied to a winding of the relay and back contacts which are closed when the winding is deenergized, means including said front contacts of said first power oif relay for connecting said line circuit to said source of coded alternating current energy, a source of direct current energy, means including said back contacts of said first power off relay for connecting said line circuit to said source of direct current energy, means for supplying energy from said source of alternating current energy to a winding of said first power off relay, a transformer for each of said track circuits having a secondary winding connected to the track rails and having a primary Winding connected across said line circuit, a condenser for each of said transformers and connected in series with said primary winding to prevent the flow of direct current through said primary winding, a control transformer having a primary and a secondary winding, a condenser associated with said control transformer, a rectifier, a signal control relay, said primary winding of said control transformer being connected to said line circuit through said condenser associated with said control transformer, means for supplying energy from said secondary winding of said control transformer to a winding of said second power off relay, circuit means governed by said track relays and including from contacts of said second power off relay for connecting the winding of said signal control relay to the secondary winding of said control transformer through said rectifier, circuit means governed by said track relays and including back contacts of said second power off relay for connecting the winding of said signal control relay directly to said line circuit, a series approach relay having a winding connected in series with said line circuit and said source of direct current energy when the back contacts of said first power off relay are closed, means governed by said series approach relay, and means governed jointly by said track relays and said signal control relay for controlling said wayside signal.

References Cited in the file of this patent UNITED STATES PATENTS 1,991,086 Failor Feb. 12, 1935 2,045,992 Nicholson June 30, 1936 2,049,399 Reichard July 28, 1936 2,150,292 Pfiasterer Mar. 14, 1939 2,194,371 Wallace Mar. 19, 1940 2,280,464 Witrner Apr. 21, 1942 2,281,957 Shields May 5, 1942

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