US2172598A - Approach lighting apparatus for - Google Patents

Description

- p 2 1939- H. A. THOMPSON 2,172,598

APPROACH LIGHTING APPARATUS'FOR RAILWAY SIGNALING SYSTEMS Filed Aug. 2, 1958 INVENTOR Hougz rdA Thom 3011.

HIS ATTORNEY Patented Sept. 12, 1939 UNITED STATES PATENT FFIE APPROACH LIGHTING APPARATUS FOR RAILWAY SIGNALING SYSTEMS Howard A, Thompson,

Edgewood, Pa., assignor Application August 2, 1938, Serial No. 222,616

Claims.

My invention relates to approach lighting apparatus for use in railway signaling systems of the coded track circuit class and it has special reference to the employment of such apparatus 6 for approach lighting wayside signals without the use of line wires.

Generally stated the object of my invention is to provide new and improved facilities of the stated non-line wire class which require approach lighting apparatus at the exit end only of each of the signal blocks.

A more specific object is to make the benefits of approach lighting available without sacrificing features of signaling system safety.

Another object is to lower the cost and reduce the quantity of the apparatus which the approach lighting facilities require and to simplify its application to coded track circuits of standard type.

In practicing my invention I attain the above and other objects and advantages by providing the exit end of each track section with a slow release approach relay which governs the clear indication lighting circuit only of the wayside signal which guards the track section in advance. This approach relay receives a measure of the coded signal control current which is supplied to the rear section rails and it is arranged to pick up and complete the named signal lighting circuit when and only when the coded current in the rear section rails has the relatively high value which accompanies a by-passing of those rails by the wheels and axles of a train.

I shall describe a few forms of approach control apparatus embodying my invention and shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed in the accompanying drawing in which:

Fig. 1 is a diagrammatic representation of a section of railway track which is equipped with one preferred form of my improved non-line wire approach lighting equipment and Figs. 2 and 3 are showings of approach relay energizing circuits modified to include hold-up aiding resistors.

In the several views of the drawing, like reference characters designate corresponding parts. Referring first to Fig. 1, the improved approach lighting apparatus of my invention is there disclosed in association with a coded track circuit system of automatic block signaling for a railway track l2 over which it will be assumed that trafiic moves in the single direction indicated by the arrow, or from left to right in the diagram.

5.5 The protected stretch of this track is divided into the customary successive sections by insulated rail joints 3 and the rails of each section form a part of a track circuit to which coded signal control energy is supplied in customary manner.

In this view of Fig. 1, reference characters D and E respectively designate the entrance and the exit ends of one of these track sections which is illustratively shown as being a full signal block in length; character TR designates a code following track relay which is installed at the entrance end of the section and operated by energy received from the rails thereof; character TB a track battery or other direct current source provided at the section exit for the purpose of supplying these rails with the relay operating energy just referred to; character CR a coding device having a contact 5 which codes this energy by periodically interrupting the rail supply circuit; and character S the usual wayside signal which guards the entrance of each of the track blocks and which is controlled by the associated track relay TR through the medium of decoding apparatus (represented generally at I!) at location D and shown more completely at location E).

An automatic block signaling system of the referred to coded track circuit type operates without the aid of line wires and in representative form it includes all of the elements above named. Such a system further comprises the customary facilities (shown at location E only and to be described presently) for continuously operating each of the exit end relays OR at one or another of the usual plurality of distinctive code rates. Selection among these rates (which in a typical three indication system may consist of and energy pulses per minute) is made in accordance with advance trafiic conditions by the referred to decoding apparatus functioning in customary manner.

This decoding apparatus (details shown only at location E and to be described presently) is controlled in the usual fashion by the associated track relay TR and it performs the further function of selectively setting up a light circuit for one or another of the lamps of the wayside signal S at the same location. In the arrangement represented, these signal lamps are designated by the characters G, Y and R and when lighted they respectively cause the signal to display the colors of green, yellow and red. The 50 necessary current for effecting this lighting is derived from a power source which is designated by the terminals plus and minus.

In order that the green or clearindication lamp of each of the signals S may be rendered active only upon the approach of a train, the apparatus installed at each of the signal locations D, E, etc. is supplemented by an approach relay AR which is arranged to maintain the lighting circuit of this green lamp interrupted at all times except when the section of track to the rear of the signal becomes occupied. In the illustrative arrangement of Fig. 1, this approach lighting function is governed by a contact 9 of the relay AR.

For rendering this approach relay AR at each signal location responsive to the approach of a train, I impress upon the operating winding of the relay a measure of the coded signal control current which is supplied to the rear section rails from the battery TB and I arrange the relay AR to pick up and complete the lamp lighting circuit above referred to when and only when the coded rail current has the relatively high value which accompanies a by-passing of the named railsby the wheels and axles of a train. In the form shown at location E in Fig. 1, the circuit which supplies the named measure of the coded current to the approach relay includes a transformer AT and a rectifier l2.

The primary winding of this transformer AT is serially included in the circuit over which the rails l and 2 of the rear track section receive coded signal control energy from the direct current source TB and at proper times the secondary winding of the transformer is connected in energy supplying relation with the operating winding of relay AR by way of the interposed rectifier I2. Preferably, though not necessarily, this rectifier is a full wave device. In addition to rectifying the alternating current output voltage of transformer AT, it acts as a snubbing element for the relay AR and thus makes that relay sufficiently slow releasing to bridge the intervals between recurrent pulses of energy from the transformer;

From the nature of its exciting circuit, it will be seen that this transformer output energy takes the form of an alternating current voltage having a low frequency corresponding to that or cycles per minute) of the code signal control code which batteryTB feeds over contact 5 of device CR to the rails of the rear track section. Thus, each time that this coding contact 5 completes the rail supply circuit the transformer is energized and it then generates what will be termed the positive half cycle of this voltage; similarly each time: that the contact interrupts the rail circuit the transformer is deenergized and the negative half cycle of the output voltage wave then is produced.

The approach relay AR is designed to be unresponsive to the relatively low intensity output of transformer AT which results when the rails of the track section D-E are vacant and to pick up when and only when the wheels and axles of a train by-pass these rails and thereby increase the intensity of current which is drawn from battery TB through the primary of transformer AT. Under the former condition, contact 9 of relay AR thus remains released. Under the latter, the relay is not only picked up on the occasion of each trackway energy pulse but because of its beforementioned delayed release characteristics the relay stays picked up conample, internal design expedients (not shown) incorporated in the relay.

The particular coded track circuit system of automatic block signaling which is illustratively represented in Fig. 1 provides three indication control of its Wayside signals S and it makes use of coding and decoding facilities of the character which are shown at the signal location E. Two different signal control codes are employed by this signaling system and these are produced by a continuously operating code transmitter CT. It will be assumed that these codes consist of 80 and 180 energy pulses per minute and that they respectively originate in contacts BE! and I80 of the named transmitter.

Included in the decoding apparatus at each of the signal locations are a pair of decoding relays DR80 and DRIBD which are respectively controlled over contacts l3 and M of the code following track relay TR at the same location. The first relay DR80 is arranged to respond when the track relay TR follows code of either the 80 or 180 energy pulse per minute rate while the second relay DR! 80 is arranged to respond to the 180 code only.

This second decoding relay DRI8!) is connected to receive energy from a transformer DT by way of a resonant or frequency selective unit DUI80. This transformer is excited from any suitable direct current source over a pole changing contact M of the track relay TR and by way of a circuit which includes a conductor l6 and a front contact I! of the first decoding relay DR80. That contact I! disconnects the transformer DT from its supply source whenever the track relay TR fails to respond to a trackway code, as when the track section ahead of location E is occupied by a train.

The first decoding relay DR80 receives its control from contact 13 of the track relay TR over a front contact l8 of a repeater relay FP. Both of the devices DR80 and FP are slow releasing, snubbing rectifiers l9 and 20 being used to impart this characteristic. As long as the track relay TR follows a code of the 80 pulse per minute or higher rate, recurring pulses of energizing current from a local direct current source are supplied to both of the named relays. In the case of repeater relay FP, this supply is directly over front contact 13 of relay TR and in the case of decoding relay DR86 the supply is over back contact I 3 andfront contact l8 of relay FP.

The beforementioned inclusion of contact l8 of relay FP in this latter circuit insures that a continuously maintained condition of the track relay TR in either the released or the picked-up position can never cause decoding relay DR8ll to pick up. When, however, the track relay follows code, the slow release repeater relay FP holds contact l8 picked up and thereby enables each release of contact I3 to complete the energizing circuit for the relay DRBB, In this manner that relay picks up when and only when the track relay responds to coded energy of the 80 pulse per minute or higher rate.

These two decodingrelays DRBO and DRISfi at each signal location control the associated wayside signal S through the medium of contacts 22 and 23. When relay TR responds to energy of the 180 code received from the forward track section, both of the decoding relays DRBU and DRIBE! pick up and set up for the clear lamp G of signal Se a lighting circuit of which conductor 24 forms a part. When relay TR responds to energy of the 80 pulse per minute code, relay DR80 only picks up and contact 22 thereof then completes for the approach lamp Y a lighting circuit of which conductors 25 and 26 form a part. Finally, when relay TR is continuously deenergized, as when a train is in the track section ahead of location E, both of the decoding relays release and contact 22 then completes for the stop lamp R a lighting circuit of which conductor 21 forms a part.

At all times one or the other of the two coding contacts and I80 of the continuously operating code transmitter CT at each signal location is included in the operating circuit of the coding relay CR for the exit end of the track section to the rear of that location. Selection between these two coding contacts is made in accordance with advance trafiic conditions by a contact 28 of the decoding relay DR80.

When energy of either the 80 or the energy pulse per minute code is received from the forward section by relay TR, this contact 28 is picked up and the coding device CR for the rear section then is energized over a circuit which includes coding contact I80 of device CT and which may be traced from the positive terminal of a suitable supply source through coding contact I80, front contact 28, conductor 29 and the winding of relay CR back to the negative terminal of the supply source. When no energy is received by the track relay from the forward section, contact 28 of relay DR80 is released and the coding relay CR for the rear section then is controlled by coding contact 80 over a circuit which includes back contact 28 and conductor 29.

Each time that the winding of coding device CR is thus energized, contact 5 is moved to its uppermost or on period position and completes a circuit over which the rear section rails are supplied with direct current energy from track battery TB. Similarly, each time that the winding of device CR is deenergized, the named contact 5 returns to its lowermost or off period position and interrupts the rail energizing circuit in the manner already explained.

As previously indicated, the improved approach lighting facilities of my invention are arranged to govern the energizing circuit for the green or clear lamp only of the wayside signals S. For this reason contact 9 of the approach relay AR is included only in the lighting circuit for the signal lamp G and not in the lighting circuits for the other two lamps Y and R. These latter two lighting circuits are controlled in conventional manner directly over contacts 22 and 23 of the decoding relays DR80 and DRIBI).

Since the approach relay AR need be actively connected with the rail supply circuit for the rear track section only when both of the decoding relays DRSB and DRI80 are picked up to set up the lighting circuit for clear lamp G, my improved facilities include further provision for short circuiting the secondary winding of the relay supply transformer AT whenever the decoding relay DRI80 is released. This provision takes the form of a contact 3| of relay DRIBB which when released completes the named short circuit and which when picked up connects the input terminals of the relay rectifier I2 with the secondary of transformer AT,

In operation of the equipment shown in Fig. 1, the signaling system portions thereof function in conventional manner, while the approach control portions thereof operate in a way which will be explained at greater length presently. Regarding these signaling system portions, itwill suffice to point out that as long as the protected stretch of track I2 remains vacant the exit end facilities for each section of that track supply the rails thereof with energy of the 180 coding, the entrance end track relay TR for each section responds to this energy, the associated decoding relays DR80 and DRI80 at each signal location are both picked up, the clear lamp G of the control wayside signal S has its lighting circuit set up and contact I80 of device CT is included in the energizing circuit. for the rear section coding relay CR.

Contact 5 of that device CR thus is continuously operated at the rate of 180 times per minute. Each time that it. is in the uppermost or on code period position, it connects the track rails I and 2 with the direct current track batter TB over a circuit which extends from the positive terminal of that battery through a transmitting impedance 33, front contact 5 of device CR, conductor 34, the track rails I and 2, conductor 35 and the primary of transformer AT back to the negative terminal of the track battery.

As long as the track section DT remains vacant, the magnitude of each code pulse of current which is thus supplied to the rails is below the minimum required to pick up the approach relay AR through its inductive connection, by way of transformer AT, with the rail supply circuit. In consequence, contact 9 of that relay releases continuously and thereby maintains the clear lamp G of the wayside signal Se in its normally inactive or dark condition.

In the event now that a train enters the referred to track section DE, the shunting action of its wheels and axles establishes a low resistance path between the track rails I and 2 and causes the current drawn by these rails from track battery TB to rise to a substantially elevated value. The magnitude of this rise is, of course, quite large even when the train first comes into the entrance end D of the track section and it further increases as the train advances closer to the exit end. At some point within this range of approach the output of transformer AT rises to the point required to pick up the approach relay AR. This point may be the extreme entrans of the section or as will usually be the case the apparatus may be designed so' that the approach relay AR will pick up only when the train has advanced partway through the section and is within say one or two thousand feet of the exit end E thereof.

In any case, the relay AR receives this pick-up intensity of energization from transformer AT over a circuit which may be traced from the left terminal of the secondary of that transformer through conductor 31, one branch of the full wave rectifier I2, the operating winding of relay AR, conductor 38, another branch of the rectifier I2, conductor 39, front contact 3I of decoding relay DRI80 and conductor 40 back to the right terminal of the secondary of transformer AT. As long as the code rate pulses of current from transformer AT continue to have the elevated magnitude which accompanies a presence of a train within section DE, relay AR not only picks up contact 9 upon the occasion of each pulse but also holds that contact picked up be-. tween successive pulses. This latter action is made possible because of the before explained slow release characteristics of the approach relay.

As a result of this picked-up condition of contact 9, the clear lamp G of the. wayside signal Se, receives lighting current overa circuit which may be traced from the positive supply terminal through front contact 22 of relay DRBO, conductor 25, front contact 23 of relay DRIBU, conductor 42, front contact 9'of relay AR, conductor 24 and the lamp G back to the negative supply terminal. In this manner the presence of a train in the track section to the rear of location E causes the wayside signal Se todisplay its clear indication.

The just described lighted condition of the signal continues until the head end of the train passes beyond location E at which time the code following track relay TR at that location ceases to operate and releases both of the decoding relays. Contact 22 of relay DRIBil now transfers the signal lighting circuit fromlamp G to lamp R. As the rear of the departing train clears location E the rail supply current for the rear section drops to a value below the pick-up intensity for the approach relay AR and when that happens, the relay AR releases contact 9 and there,- by restores the clear aspect of the signal Sc to its normally inactive or dark condition.

While the train is within the section of which location E marks the entrance, the wayside signal Se displays the stop indication as a result of the continuously deenergized condition (referred to above) of the track relay TR which accompanies the by-passing of the rails of that section by the train wheels and axles. Under that condition, both of the decoding relays DRBQ and DRlBi! are released, the lamp R of the signal receives lighting current over a circuit which includes back contact 22 of relay DB8!) and conductor 2'5 and the operating circuit of the coding relay CR for the rear track section is connected over back contact 28 of relay DRSI! with the coding contact 88 of the continuously operating device CT.

This latter action causes the coding contact 5 of relay CR to operate at the slow rate of times per minute. The output of transformer AT now, however, is diverted'frorn the approach relay AR over the secondary icy-passing circuit which under the conditions stated is completed by back contact 3! of decoding relay DRE88 andwhich may be traced from the-left terminal of the transformer secondary through conductors 3'? and 43, the back contact 3| of relay DRl8ll and conductor 48 back to the right terminal of the transformer secondary.

Under all traific conditions of the track section DE which is immediately to the rear of the now occupied one, therefore, relay AR at location E remains continuously deenergized and hence does not respond even though a following train may enter that rear section DE-. Moreover, since contact 9 of that relay is not included in thenow active lamp energizing circuit for the wayside signal Se, lamp R thereof remains continuously lighted regardless of the position of the approach relay AR.

When the rear of the forward train clears the exit end (not shown in Fig. l) of the track section of which location E marks the entrance, the rails of that section transmit signal control energy of the 80 pulse per minute code to theentrance end track relay TR. In responding that relay picks up decoding relay DRSfi only and thereby lights the approach lamp Y of signal Se over front contact 2?. and causes the coding relay OR for the rear section to be controlled by contact I80 of coding device CT over a. circuit which includes front contact 28'. The lamp light ing circuitnow active may be traced from the positive supply terminal through front contact 22 of relay DR8I), conductor 25, back contact 23 of relay DRI80, conductor 26 and the lamp Y back to the negative supply terminal.

As in the just described case involving a lighting of the stop lamp R of the signal, this lamp Y thereof remains continuously lighted as long as the second section in advance of location E continues to be occupied. Back contact 3| of relay DRI80 by-passes the transformer AT and thus causes the approach relay AR to be continuously energized even though a following train may come into the rear track section. Moreover, since contact 9 of the approach relay is excluded from the lamp lighting circuit now active, the position of this contact in no way affects the continuity of that circuit.

When the rear of the forward train clears the exit end (again not shown in Fig. 1) of the second section in advance of location E, the rails of the first section in advance of that location receive energy of the clear or pulse per minute code. In responding the entrance end track relay TR causes both of the decoding relays DRQU and DRIBU to pick up thereby setting up at contacts 22 and 23 the lighting circuit for the clear lamp G of the wayside signal Se and maintaining at contact 28 the control of the coding relay CR for the rear track section with the H30 contact of the device CT.

As long as the track section D-E remains vacant, this lamp G does not light for the reason that its energizing circuit is interrupted at contact 9 of the normally released approach relay AR. When, however, a train comes into this section, the relay AR picks up in the manner already explained in detail previously and contact 9 then completes the circuit just mentioned and thereby effects the lighting of the clear lamp G of signel Se.

Referring to Fig. 2, I have there shown an alternative or extended form of circuit for aiding the approach relay in holding its contact 9 picked up between the recurrent code step pulses of energizing current which its operating winding receives from the transformer AT in the rail supply circuit.

Interposed between the rectifier l2 and the relay winding is a resistor or other impedance 46 through which the current for picking up the relay must pass. Once the relay is picked up, however, an added contact 47 of the relay short circuits this impedance and thereby elevates the intensity of the relay energization. This enables the relay more readily to hold its front contact closed during the off periods of the signal control code from battery TB which contact 5 of device CR produces. As in the arrangement of Fig. l, rectifier l2 continues to act as a snubbing element which imparts the necessary slow release characteristics to the relay.

Referring to Fig. 3, I have there shown a modified form of connection of the impedance 46 in the winding circuit of relay AR. In Fig. 3, this impedance is built into the structure of the relay itself and serves to interconnect two 00- operating halves of the relay winding. As in Fig. 2, this impedance 46 is short circuited by a contact 4! whenever the relay picks up.

Considering further the manner of operation of the basic system of Fig. l, the feature of approach lighting the clear-indication only of each. controlled wayside signal S makes the major benefits of approach lighting available without sacrificing features of safety of the signaling system. Thus, at any time that the signal should show a restrictive indication or should be changed to show such an indication the signal will be lighted even before the approach relay AR has been picked up. Hence should a switch be thrown in the block in advance or in a second block in advance, the wayside signal will immediately display a stop or an approach indication regardless of whether a train is or is not approaching from the rear.

Since my new and improved facilities require apparatus at the exit end only of each of the signal blocks to effect the approach lighting without the use of line wires, both cost and the quantity of this apparatus is lowered and the application thereof to coded track circuits of standard type is greatly simplified.

While I have explained my invention in an application wherein the signaling system apparatus employs only two trackway codes and controls the signals to three indications only, it will be understood that my improved approach control facilities may readily be used with signaling systems wherein the number of indications is greater or less than the stated three.

Although I have herein shown and described only a limited number of forms of approach control 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.

Having thus described my invention, what I claim is:

1. In combination with adjoining forward and rear sections of railway track, means for supplying each of said sections with track circuit current selectively modulated in accordance with one or another of a plurality of different codes as determined by conditions of traffic in advance of the section, a multiple indication signal for said forward section, a code following track relay operated by energy received from the rails of that forward section, means for selectively controlling said signal according as said track relay is following one or another of said plurality of codes, an approach lighting relay for said rear track section energized inductively from the said modulated track circuit current which is supplied to that rear section and having a pick-up value determined by the value of this track circuit current which exists when the forward vehicle of a train occupies the rear section at a point which is within a predetermined distance of the exit end of that rear section, and means governed by said approach relay for controlling the display of at least one indication of said forward section signal.

2. In combination with adjoining forward and rear sections of railway track, means for supplying the rails of each of said sections with signal control current which is modulated in accordance with one or another of a plurality of different codes, a multiple indication signal for said forward section, a code following track relay operated by energy received from the rails of that forward section, means for selectively controlling said signal according as said track relay is following one or another of said plurality of codes, an approach lighting relay inductively energized from the said modulated current which is supplied to the rear section rails and adapted to pick up when and only when that current has the relatively high value which accompanies a train shunted condition of those rails, and means governed by said approach relay for controlling the display of the clear indication only of said forward section signal.

3. In combination with adjoining forward and rear sections of railway track, means for supplying the rails of each of said sections with direct current which is modulated in accordance with one or another of a plurality of different codes, a signal guarding the entrance of said forward section and adapted to display clear and restrictive indications selectively, a code following track relay operated by energy received from the rails of that forward section, means for controlling said signal according as said track relay is following one or another of said different codes, a transformer excited by the said modulated current which is supplied to the rails of said rear track section, a slow release approach relay energized by the output voltage of said transformer and being adapted to pick up when and only when that voltage has the relatively high value which accompanies the presence of rolling stock in said rear track section, and means governed by said approach relay for controlling the display of the clear indication only of said forward section signal.

4. In combination with adjoining forward and rear sections of railway track, means for supplying the rails of each of said sections with direct current which is modulated in accordance with a clear code or in accordance with a restrictive code, a code following track relay operated by energy received from the rails of said forward section, a decoding relay controlled by said track relay and adapted to pick up only when that relay is following said clear code, a signal for said forward section controlled by said decoding relay and arranged to show clear only when that relay is picked up, a transformer excited by the said modulated current which is supplied to the rails of said rear track section, a slow release approach relay energized by the output voltage of said transformer and adapted to pick up only when that voltage has the relatively high value which accompanies the presence of rolling stock within said rear section, means governed by said approach relay for making the display of said clear signal indication possible only when that relay is picked up, and means for by-passing the output winding of said transformer whenever said decoding relay is released.

5. In combination with adjoining forward and rear sections of track, means for supplying the rails of each of said sections with direct current which is modulated in accordance with a clear code or in accordance with a restrictive code, a decoding relay controlled by energy received from the rails of said forward section and adapted to pick up only when that energy is of said clear code, a transformer excited by the said modulated current which is supplied to the rails of said rear track section, a slow release approach relay connected in energy receiving relation with said transformer and being adapted to pick up only when the transformer output voltage has the relatively high value which accompanies the presence of rolling stock within said rear section, traffic controlling apparatus governed by said approach relay, and means controlled by said decoding relay for disconnecting said approach relay from the output winding of said transformer and for by-passing that output winding Whenever the decoding relay is released.

.6. In a signaling system which includes a section of railway track and a'circuit through which periodically interrupted direct current is continuously supplied to the, rails of said section, the combination of a transformer which obtains exciting current from a serial connection of its primary winding with said rail supply circuit, a slow release approach relay connected in energy receiving relation with the output winding of said transformer and being arranged to pick up and there continuously stay when said periodically interrupted. rail'current has the relatively high value which accompanies a presence of rolling stock Within said section and to remain released at all other times; and traffic controlling apparatus governed by said approach relay and rendered active when that relay is picked up.

7. In combination with a section of railway track, a source of unidirectional trackway current, a continuously operating coding contact, a circuit through which said contact recurrently connects said source to the rails of said section, a transformer having an exciting winding which is serially included in said circuit and thereby energized by the recurring pulses of direct current which are supplied to said rails, a full wave rectifier receiving the output voltage of said transformer, an approach relay energized by the output voltage of said rectifier and being arranged to pick up and there continuously stay when the magnitude of that voltage is of the relatively high value which accompanies the presence of rolling stock within said track section and to remain released at all other times, and trafiic controlling apparatus governed by said approach relay and rendered active when that relay is picked up.

8. In combination with a section of railway track, a source of unidirectional trackway current therefor, a circuit connecting said source in energy supplying relation with the rails of said'section, continuously operating coding means which periodically interrupt said rail supply circuit, a transformer having an exciting winding which is serially included in that circuit, a normally released approach relay connected in energy'receiving relation with said transformer and arranged to pick up and there continuously stay when and only when the output voltage of said transformer has the relatively high value that results when said section rails become shunted by rolling stock, and traffic controlling apparatusgoverned by said approach relay and rendered active when that relay is picked up.

9. In combination with a section of railway track, means for supplying the rails of said section with direct current which is periodically interrupted a transformer excited by said periodically interrupted current, a slow release approach relay connected in energy receiving relation with said transformer and arranged to remain released as long as the output voltage of the transformer has the relatively low value which accompanies a vacant condition of the track section and to pick up when said output voltage has the relatively high value that results when said section rails become shunted by rolling stock, an impedance included in said connection, means responsive to a picked up condition of said approach relay for by-passing said impedance whereby then to increase the relay current and assure that said picked up condition Will continue uninterruptedly as long as said rails remain shunted, and traific controlling apparatus governed by said approach relay and rendered active when that relay is picked up.

10. In combination with a section of railway track, means for supplying'the rails of said section with direct current which is periodically interrupted, a transformer excited by said periodically interrupted current, an approach relay connected in energy receiving relation with said transformer and arranged to remain released as long as the output voltage of the transformer has the relatively low value which accompanies a vacant condition of the track section and to pick up when said output voltage has the relatively high value that results when said section rails become shunted by rolling stock, a full wave rectifier included in said connection and acting as a snubbing element for said relay whereby to impart slow release characteristics thereto, an impedance'interposed between said rectifier and said relay, means responsive to a picked up condition of said relay for by-passing said impedance whereby to increase the effectiveness of said rectifier as a snubbing element and assure that said picked up condition will continue uninterrupted- 1y as long as said rails remain shunted, and traffic controlling apparatus governed by said approach relay and rendered active when that relay is picked up.

- HOWARD A. THOMPSON.

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