US2237788A - Railway traffic controlling apparatus - Google Patents

Description

4 Sheets-Sheet l i 35 WQ Filed May 28, 1938 F. H. NICHOLSON ETAL.

RAILWAY TRAFFIC CONTROLLING APPARATUS LLL April 8,1941.

[ Em c INVENTORS Fran]: H/V [200012 and BYL THEIR ATTORNEY April 1941- F. H. NICHOLSON ETAL 2.237.788

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed May 28, 1938 4.Sheets-Sheet 2 INVENTORS Frank H/Wbfzolran and BY Le z'eRAllz'ron THHR ATTORNEY April 8, 1941.

F. H. NICHOLSON ET AL 2.237.788.

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed May 28, 1938 4 Sheets-Sheet 71min [5 Code 75 Code April 1941. F. H. NICHOLSON ETAL 2.237.788

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed May 28, 1938 4 Sheets-$heet 4 Fly. 8.

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c715 A INVENTORS Fran]: HMolzalrozz and 15 THEIR ATTORNEY Patented Apr. 8, 1941 UNKTED ST 'i E. 5 l ht" i i QFFICE RAJILVVAY TRAFFIC CONTRULLIING APPARATUS Frank H. Nicholson, Penn County, and Leslie R. Allison,

Township, Allegheny Forest Hills, Pa.,

assignors to The Union Switch 8: Signal Company, Swissvalc, Pa, a corporation of Pennsyl- Vania 16 Claims.

Our invention relates to railway trafiic controlling apparatus and it has special reference to the organization of such apparatus into signalling systems of the class wherein a code-following relay at each wayside location and/or on a train receives coded operating energy from the traokway and in accordance with the character of that energy effects various control functions through the medium of associated decoding equipment.

Broadly stated, the object of our invention is to lower the cost, simplify the construction and improve the operating characteristics of decoding equipment of the referred to type.

A more specific object is to assure that this equipment will not falsely respond when rectifier or other foreign ripples are present in the decoding transformer supply circuit.

Another object is to safeguard the decoding equipment against false response in the event that the front and back contact points of the associated code following relay become accidentally interconnected.

An additional object is to permit the code following relay safely to be adjusted for closer spacings between the movable member and the front and back points of each of its contact sets.

A further object is to assure that the wayside decoding equipment will respond to each initial shunting of the associated track circuit with a quickness which is adequate for all possible train running conditions.

A still further object is to detect codes and distinguish between different pulse rates thereof without employing the usual resonant or frequency tuned circuits.

An additional object is to provide the above features of operation through the use of a restricted number of contacts on the code following relay.

A still additional object is to accomplish the above without dispensing with any of the desirable features of continuously coded track circuit control.

In practicing our invention we attain the above and other objects and advantages by associating the various decoding equipment parts with the code following relay in new and improved manners. Involved in these associations are a number of cooperating features of which introductory mention wil1 here be made of but two? (1) rectifying the secondary voltage of the decoding transformer over a contact of the code following relay and using this rectified output to energize a code detecting relay, and (2) serially including in the primary supply circuit of the decoding transformer the windings of relays which repeat the front and back contact closures of the code following relay.

We shall describe several forms of railway traffic controlling apparatus embodying our invention and shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed in the accompanying drawings, in which.

Fig. 1 is a diagrammatic representation of traffic governing apparatus embodying the feature of our invention first named above;

Fig. 2' is a similar representation of apparatus which embodies both of the features named above;

Fig. 3 is a diagrammatic view of trackway apparatus which additionally embodies still further features of our invention;

Figs. 4, 5 and 6 are diagrammatic showings of one application of the principles of our invention to a combined wayside and cab signalling system of the three indication type;

Fig. '7 is a similar representation of an application wherein the number of wayside signal indications is extended to four; and

Fig. 8 is a diagrammatic view of a still further application of the improvements of our invention to a railway signalling system.

In the several views of the drawings, like reference characters designate corresponding parts. Referring first to Fig. 1, character TR designates a track relay of the code following type, DT a decoding transformer which receives primary current under the control of a pole changing contact l of the track relay, H a code detecting relay of the direct current delayed release type which is energized from a secondary winding lilof the decoding transformer, and DIM a code distinguishing relay which is energized from a secondsecondary winding 9 of the transformer through a resonant or frequency selective circuit J I80.

Device TR typifies relays which are used in any of the various different code following applications encountered in railway signalling. In addition, therefore, to being a track relay as shown, it may, for example, also be a train carried master relay adapted to control a cab signal, or a code following relay which receives operating energy over line wires. In the illustrative application represented in. Fig. 1, this relay TR is directly connected to the rails I and 2 of a section of railway tr-acl: E-F which is separated from adjoin.- ing sections by the customary insulated joints 3 and along which it will be assumed that traffio moves in the single direction indicated by the arrow.

Installed at the opposite or exit end of the section is a source of trackway energy, shown in the form of a direct current battery 5, which is connected to the rails I and 2 over a contact 6 of a relay CR and by way of a circuit which includes the usual current limiting impedance I. Each time that contact 6 is in its uppermost position, the rail supply circuit is completed and the voltage of battery 5 then is impressed between the rails and by them transmitted to the winding of relay TR at the opposite or entrance end of the section. Each time, however, that contact 6 occupies its open position, the rail supply circuit is interrupted and the winding of the track relay TR then is deenergized.

Device CR typifies apparatus for coding the trackway energy at one or another of a plurality of distinctive rates in accordance with preselected conditions. In the system of Fig. 1, it will be assumed that under certain conditions of advance trafiic this device periodically actuates its contact (i at one rate to provide what will be termed a low speed code and that under other conditions it increases the rate of periodic opening and closing of the rail supply circuit toprovide what will be referred to as a high speed code. In receiving this coded energy, relay TR picks up its contacts upon the occasion and for the duration of each pulse thereof and releases its contacts each time that the relay winding is deenergized, thereby repeating the operation of the coding relay CR.

Aside from having two separate secondary windings, the decoding transformer which is shown at DT in Fig. 1 is of the conventional type and under the control of contact 4 of the code following relay TR its single primary winding receives energizing current from any suitable direct current source, designated by the terminals plus and minus. In territory in which the energy for operating the signalling system is supplied fro-m an alternating current transmission line (not shown) which runs along the right-of-way in the customary manner, these terminals are usually identified with the output circuit of a rectifier of the full wave type shown at Z. Typically, such a rectifier consists of four branch paths or units 8 interconnected in the manner shown, and ordinarily its input terminals receive 100 cycle or other signal frequency energy from the mentioned power supply line through a circuit which includes a transformer 2| and power source terminals B and C.

Each time that the pole changing contact 4 of relay TB is picked up, direct current flows downwardly through one portion of the transformer primary and by way of a circuit shown as extending from the positive terminal of rectifier Z, through front contact 4, conductor l8, the upper half of the transformer winding, and mid tap t9 back to the negative terminal of the supply rectifier. Likewise, each time that contact 4 is released, current flows in the opposite direction or upwardly through another portion of the winding and by way of a circuit shown as extending from the positive supply terminal through back contact 4 of device TR, conductor 22, the lower half of the transformer winding, and mid tap 19 back to the negative terminal of rectifier Z.

In thus pole changing the direct current primarycircuit for the decoding transformer D'I, contact 4 causes the transformer to induce in each of its two secondary windings 9 and [0 an alternating voltage the frequency of which is the same in cycles per minute as the code pulse rate of the trackway energy to which relay TB is responding. If this frequency is of the high speed rate, code distinguishing relay D responds as a result of its winding receiving actuating energy from the secondary winding 8 of transformer DT through the tuned circuit J18!) which is arranged to be resonant to the high speed frequency only. If, however, the referred to frequency is of the low speed rate, this tuned circuit fails to transmit sufficient current to operate relay DIM and the contacts of that relay then are released.

As a result of incorporating the improvements of our invention, the energizing circuit for the code detecting relay H functions to supply unidirectional operating current to that relay whenever the track relay TR is following either the high speed or the low speed code. In either event, the alternating voltage which is generated in the secondary winding H] of the decoding transformer U1 is rectified over a second contact H of the code following relay TR and in this rectified condition it is impressed upon the direct current winding of the relay H.

The particular circuit shown, therefore, causes unidirectional current to be supplied to relay H. To this end the transformer winding 10 is provided with a mid tap connection l2 which is joined, through a conductor l3, with one side of the H relay winding and the other side of the relay winding is connected to the heel of contact H by means of a conductor M. Finally, the end terminals of the secondary winding ID are joined to the front and back points, respectively, of contact H by means of conductors l6 and H.

In operation, each time that contact H is in its picked up position, the winding of relay H is connected with the lower half of the secondary winding 10 of the decoding transformer DI through a circuit which extends from the mid tap I2 of that winding, through conductor 13, the winding of relay H, conductor l4, front contact H, and conductor ilfi back to the lower terminal of winding 10. In consequence, what will be referred to as the positive half cycles of the induced transformer voltage become effective for circulating current through the winding of relay H.

Likewise, each time that the track relay contact H is in its released position, the winding of relay II is connected with the upper half of the transformer secondary I8 through a circuit which may be traced from the mid tap l2, through conductor t3, the winding of relay H, conductor I4, back contact H, and conductor H back to the upper terminal of winding II). In consequence, what will be termed as the negative half cycles of induced transformer voltage also become effective to provide current flow through the winding of the relay.

To clarify the foregoing explanation, the direction of current fiow during the positive half cycles of induced-transformer voltage is designated in Fig. 1 by the small full line arrows while the direction of current flow during the negative half cycles of this voltage is similarly designated by the small broken line arrows. From that explanation it will be apparent that the winding of code detecting relay H receives recurring pulses of unidirectional energizing current during the continuance of each code following operation which is effected by relay TR.

The constants of the H relay energizing circuit are so chosen that these pulses are effective to pick up the relay contacts. In order that this picked up condition may be retained continuously as long as relay TR continues to follow a trackway code, relay H is further designed to have sufi'icient release retardation to span the open circuit interval during which the contacts of relay TR move from one position to the other in response to the current pulses of the coded operating energy. For this purpose, any one of a number of familiar expedients may, of course, be

used. As shown in Fig. 1, the release delay is provided by means of a snubbing resistor 23 which is bridged across the terminals of the winding of relay H in a well-known manner..

In operation of the just-described decoding equipment of Fig. 1, when the contacts of the code following relay TR occupy one position continuously (as, for example, when the relay fails to receive coded energy from the track section E-F) decoding transformer DT passes no energy and the contacts of both of the relays H and D180 then occupy the deenergized or released position. Each time, however, that relay TR receives and responds to a trackway code, contacts 4 and II thereof simultaneously pole change the primary and secondary circuits of the decoding transformer and in consequence the contacts of relay H are then picked up, as are also those of relay D|8fl when the responded to code is of the high speed frequency. In other words, as long as relay TR fails to receive coded energy, the contacts of both of the relays H and DIBO occupy their released positions; when relay TR responds to the slow speed code, the contacts of code detecting relay H only are picked up; and when relay TR responds to trackway energy of the high speed code, the contacts of the code distinguishing relay D180 are also picked up.

Any desired use of the just-described response characteristics of relays H and D189 may, of course, be made. As shown in Fig. 1, the represented contacts 24 and 25 of these devices are arranged to control the energizing circuits for the lamps of a wayside signal Se. This signal is of a well-known color light type and comprises three lamps G, Y and R which, when lighted, respectively project into the range of vision of the engineman of an approaching train beams of light having the colors of green, yellow and red.

Assuming that the apparatus of Fig. 1 is combined into a system of automatic block signalling in the manner partially represented, the opera tion will be as follows: As long as the rails I and 2 transmit energy of the high speed code to the track relay TR, lamp G of signal Se will be lighted to display the clear indication as a result of relays H and Diilli both being energized and completing for the lamp an energizing circuit which may be traced from the positive terminal of a suitable supply source through front contact 24 of relay H, front contact 25 of relay Dlilll, conductor 26 and the lamp G back to the negative terminal of the supply source.

When the track relay TR receives energy of the "slow speed code, the contacts of relay H only will be picked up and the signal will then display the approach indication as a result of lamp Y receiving lighting current over a circuit which extends from the positive supply terminal through front contact 24 of relay H, back connow safely be adjusted tact 25 of relay DIBD, conductor 21 and the lamp Y back to the negative supply terminal.

Finally, in the event that the relay TR fails to receive coded energy, as when the track section E-F is occupied, the contacts of both relays H and DIBU will be released and the signal will then display the stop indication as a result of lamp R receiving lighting current over a circuit which extends from the positive supply terminal through back contact 24 of relay H, conductor 28 and the lamp R back to the negative supply terminal.

Among the advantages afforded by our improved arrangement of Fig. 1, mention may be made of the simplification of code detecting apparatus and also of the superior operating characteristics. Regarding the former, the single relay H performs all of the code detecting functions for which a pair of repeater relays (for the front and back contacts of the code following device) formerly have been required and thus this expedient reduces both the cost and complexity of decoding equipment of the character under consideration.

Regarding the improvement in operating characteristics, the novel feature described above effectively guards against the display of a false approach wayside indication should rectifier ripples be introduced into the decoding transformer supply circuit or should the front and back contact points of the code following relay TR accidentally become interconnected, as by fusing due tolighting. In the latter event, if the interconnection involves the points of contact H, the resulting short circuiting of the transformer secondary I 0 will permanently deenergize relay H and thereby effect completion of the circuit for the stop lamp R of the associated signal S. Likewise, if the faulty condition referred to takes place at pole changing contact 4, transformer DT will transfer no energy at all and relay H will again be deenergized continuously.

Concerning the introduction of rectifier or other foreign ripples into the decoding transformer supply circuit, this may happen as a result, for example, of failure of one of the branch units 8 of the supply rectifier Z. If the energy were supplied to relay H by means of the conventional static circuits (comparable to J it!) but untuned) these ripples might, due to alteration of the primary current of transformer DT, effect actuation of that relay under conditions of contact stalling by relay TR.

With the circuits of Fig. 1, however, such. false response by the decoding equipment is effectively guarded against, for with contact H stalled in either position, the winding of relay H is continuously connected to the decoding transformer secondary iii. Being of the direct current design, this relay H is incapable of picking up on any resulting alternating current which it may receive and in this manner false response to foreign current ripples in the transformer supply circuit is effectively prevented.

An attendant advantage of the arrangement of Fig. l is that the code following relay TR may for closer spacings between the movable member and the front and back points of each of its sets of contacts. In

previous decoding arrangements, safety requirements made it imperative that relatively wide Contact spacings be used in order to avoid any possibility of false operation. However, by means of our improved apparatus, the contact spacings I may safely be reduced to a value which is limited only by the normal operating characteristics of the code following device. By thus lowering the range of movable member travel, such a reduction has the effect of raising the efficiency of the relay TR and hence is most desirable from an operatig point of View.

Referring now to Fig. 2, the apparatus there disclosed incorporates not only the just-described feature of our invention, but it also employs front and back contact repeater relays FP and BP which cooperate in a novel manner with the code following relay TR. and the decoding transformer DT.

As in the case of Fig. 1, our improved code detecting apparatus is'shown in Fig. 2 as forming a part of an automatic block signalling'system for atrack 1-2 over which traffic moves in the direction of the arrow and only one block or section KL of which is completely represented. The particular track shown in' Fig. 2 is adapted for use in electrified territory and is provided with facilities, in the form of impedance bonds 30 of the usual character, for transmitting electric propulsion current around the insulated joints 3 which divide the rails into track circuit sections.

Moreover, use ismade of alternating current energy to operate the track circuits and this is impressed between the rails by a suitable source, designated: by the terminals'B and C, through the medi 'im of the usual track transformer TT. Similarly, the track relay TB. is shown as being of the single element alternating current type. Except for the fact that alternating instead ofdirect current energy is supplied to the relay winding through the track rails, this code following device of Fig. 2 operates in the same manner as does the track relay TR of Fig. 1.

The trackway current coding facilities of Fig. 2 are embodied in a code transmitter CT which is provided with a pair of contacts and I80. By a motor or other suitable mechanism (not shown in detail) these contacts are continuously actuated at such speeds as respectively provide slow speed and high speed codes of '15 and 180 energy pulses per minute. Under various conditions of system operation, one or the other of these contacts is included in the circuit through which the primary winding of the associated track transformer TT receives energy from the alternating current source B--C.

As in the case of the apparatus of Fig. 1, the code following relay TB is provided with a pair of contacts 4 and II, which, respectively, are included in the primary and the secondary circuits of the decoding transformer DT. Contact 4 pole changes the supply of direct current to the transformer primary, in the manner already explained, and contact ll periodically reverses the output of the transformer, also in the same manner as in Fig. 1, for supplying unidirectional current to the circuit for the winding of a code detecting relay H15. This relay corresponds to device H of Fig. 1. In the case of relay H15, the release retardation characteristic necessary to bridge the intervals between recurrent code pulses is obtained by means of a copper ferrule (not shown) or other internal design expedient which makes the use of an externally connected snubbing resistor, such as shown at 23 in Fig. 1, unnecessary.

In addition, the apparatus of Fig. 2 includes the before referred to repeater relays FF and BP, the windings of which are included in the conductors l8 and: 22 of the primary supply circuit for the decoding transformer DT. Each time that contact 4 of relay TR is picked up, the resulting current which flows through the upper half of the transformer primary (again from a source designated by the terminals plus and minus) thus is passed through the winding of relay FP. Likewise, each time that the contact 4 is in its released position, the resulting flow of current through the lower half of the decoding transformer primary similarly passes through the winding of the second repeater relay BP, relay FP of course remaining picked up at this time so that its front contact 35 remains closed.

In order that each of the relays FF and BP may maintain its contacts continuously picked up whenever the track relay TB. is responding to a trackway code, a snubbing element comparable to resistor 23 of Fig. 1 is bridged across the winding of the relay. In the case of device FP, this element takes the form of a rectifier 33 which is connected in polarity opposing relation to the direction of energizing current flow through the winding and, in the case of relay BP, use is made of a comparably arranged rectifier 3 1 which is serially connected with a resistor 55 and a contact 36 of the first repeater relay FP.

In the case of the snubbing circuit for each of the relays, the unidirectional characteristics of the rectifier forming a part thereof prevent the flow of energizing current through the relay winding from being lay-passed. At the same time, however, they allow the rectifier to establish a discharge path which becomes effective upon interruption of the energizing circuit to delay the collapse of flux in the magnetic circuit of the relay and thereby cause the contacts to release slowly. In order that the second repeater relay BF may open its contacts relatively soon after those of relay FP have released, the before referred to contact 35 is included, in the manner shown, in the snubbing circuit of relay B'P to open that circuit each time that relay FP releases.

For assuring that relay H15 will receive energizing current only when the contacts of the second repeater relay BP are picked up, the energizing circuit for the winding of relay H15 includes a front contact 31 of relay BP'. Likewise, for assuring that relay H15 will not pick up its contacts until after at least three code periods (such as on--off-on in that order) have been responded to by the track relay TR, a contact 38 of relay H15 may be serially included in the energizing circuit for this relay which includes the back point of contact H of relay TR. Contact 38 will, of course, be open when relay H15 is deenergized. Accordingly, the first 'on interval will pick up relay FP; the next off interval will. pidk up relay BP; and the succeeding on interval will complete an energizing or pick-up circuit for relay H15 from the lower portion of winding [0, over the front contact ll of relay TR. The use of contact 38, therefore, requires that the relay pick-up current always originate in the lower portion of decoding transformer winding Ill and be carried over an on contact of relay TR. By properly selecting the retardation characteristic of relay H15, it is possible to enforce the foregoing three point pickup of relay H15 without the necessity for contact 38.

As long as the track relay TR fails to receive coded energy and holds its contact continuously in either position, the contacts of all three of the relays FP, BP and H15 remain released. When, however, relay TR responds to energy of either the slow speed or the high speed codes produced by device CT, the first pick-up operation of the contacts of relay TR. picks up the front contact repeater relay FP over a circuit extending from the positive supply terminal through front contact 4, conductor I8, the winding of relay FP, conductor 40, the upper half of the primary of transformer DT, and the mid tap I9 back to the negative supply terminal; the following release action of the contacts of relay TR. similarly picks up the back contact repeater relay BP over a circuit extending from the positive supply terminal through back contact 4 of relay TR, conductor 22, front contact 35 of relay FP, conductor II, the winding of relay BP, conductor 42, the lower half of the primary of decoding transformer DT, and the mid tap I5 back to the negative supply terminal; and the second pick-up action of the part of the contacts of relay TR induces in the secondary winding II] of transformer DT a positive half cycle of voltage which picks up relay H over a circuit extending from the mid tap i2 of winding Ill, through conductor I3, the winding of relay H15, conductor 43, front contact 31 of relay BP, conductor I4, front contact II of relay TR, and conductor I6 back to the lower terminal of winding l0. Contact 38 now closes and prepares the energizing circuit for relay H15 which includes the upper portion of winding Ill and the back contact II of relay TR.

From the foregoing it will be seen that code following operation on the part of relay TR causes all three of the relays FP, BP and H15 to maintain their contacts continuously picked up. Regarding relay H15, its winding now receives recurring pulses of energizing current from transformer DT over rectifier contact I I of relay TR. As in the case of the apparatus of Fig. 1, this contact repeatedly connects the relay alternately to the lower and to the upper portion of transformer winding H1 in step with the generation therein of positive half cycles of secondary voltage in a manner which causes current flow through the relay winding always to be in the same direction.

One particular application which can be made of the apparatus embodying our invention disclosed in Fig. 2 is the provision of an added safety feature known as a lock out circuit.

Such a lock out circuit is more completely described in the copending application, Serial No. 210,743, filed by Howard A. Thompson, on May 28, 1938, for Railway traflic controlling apparatus.

The purposeof such a lock out circuit is to prevent the giving of a false proceed indication on the part of the wayside signal Sic should an insulated joint 3 at location K become defective when the track section K-L is occupied by a train or under other conditions. The particular circuit represented makes use of contacts 45, and 41 of relays FP, BP and H15, respectively, which, together with the contacts 15 and I85 of the coding device CT, are connected, in the manner shown, in the primary circuit of the track transformer TT at location K. These contacts control the supply of code to the rear section in such manner that should this code be fed falsely to relay TR over defective rail joints, this relay will be held steadily energized or locked out by steady energy supplied over back contact 45 and front contact 45 of relays BP and FF, respectively.

Because of their well-known character and g close correspondence to the signal control circuits already described in connection with Fig. 1, the circuits through which the decoding apparatus of Fig. 2 controls the lamps of the wayside signal Sic have not been completely shown. From a comparison of the two figures, however, it will be seen that by providing relay H15 of Fig. 2- with a contact corresponding to member 24 of Fig. 1 and by supplementing the equipment of Fig. 2 with another relay corresponding to device DI of Fig. 1 (which may, be energized from transformer DT through an appropriate frequency selective circuit corresponding to that shown at J I80 in Fig, l) circuits such as include conductors 26, 21 and 28 may be provided by which lamp G of wayside signal Sic of Fig. .2 will light when the track relay TR responds to trackway energy of the high speed or I80 code, lamp Y will light when the received energy is of the low speed or 15 code, and lamp R will light when device TR fails to receive coded energy.

In operation of the equipment of Fig. 2, whenever track section K-L is occupied by a train, the contacts of all four of the relays TR, FP, Bl? and H15 are released, lamp R of signal Sic is lighted to show stop, and the track circuit to the rear of location K receives energy of the 15 or slow code over a circuit which extends from supply terminal B through conductor 48, back contact 45 of relay BP, conductor 55, the coding contact 15 of device CT, conductor 5I, and the primary winding of track transformer T1 back to the supply terminal C.

When the rear of the train clears the eXit end of section K-L, the coding apparatus (not shown) at location L will transmit coded energy of 15 code through rails l and 2 to the track re lay TR at location K. The first on period of this code picks up the contacts of device TR and energizes and picks up relay FP in the manner already explained; the following off period picks up repeater relay BP; and the following on period causes relay Hi5 also to pick up. It will thus be seen that an on-ofi--on sequence of initially received trackway energy is required to pick up the code detecting relay H15. This action has already been referred to as a three point pick up.

When all three of the relays FP, BP and H15 are thus picked up, the rails of the track section to the rear of location K are supplied with energy of the IE5 or high speed code over a circuit which may be traced from the supply terminal B through coding contact Hill of device CT, conductor 52, front contact 4'1 of relay H15, front contact 45 of relay BP, front contact 45 of relay FP, conductor 53, and the primary winding of track transformer TT back to the supply terminal C.

In the eventthat one of the insulated joints 3 at location K should become broken down when the track section K-L is occupied and the lamp R of signal Sic is lighted to show stop, the following operations will take place: Energy of the 1'5 code will first feed from transformer TT across the defective joint (and impedance bonds 3t) and into the rails of section K-L. As soon as the rear of the train has advanced a substantial distance beyond the faulty joint location, this leakage energy may become effective for operating the track relay TR at location K. In responding to the first effective pulse of that leakage energy, relay TR picks up front contact repeater relay FF and thereby establishes a circuit tion K-L continues to be occupied but also after the train has cleared the exit end thereof. In consequence, front contact repeater relay FP also stays picked up, relays BP and Hi remain re- -1ease'd, and lamp R of the wayside signal Sic remains lighted, thereby continuing to display the indication of stop uninterruptedly until the defective joint has been repaired.

One important requirement of a circuit of the lock out type just described is that intermittent interruption in the supply of steady energy to the rear track section will not permanently discontinue the lock out conditions which hold the associated wayside signal at stop. An Y 1 examination of Fig. 2 will show that the improvements of our invention therein disclosed meet this test. In applying it, asume that for some reason or other the supply of steady energy over back contact 46 of relay BP and front contact 45 of relay FP should become interrupted in an intermittent manner, that is, temporarily broken and then reestablished. As the contacts of track relay TR release, repeater relay BP is picked up and the steady energy supply connection is broken at contact 46. Relay Hi5 being released, there is at this instant no supply of energy to the primary of the track transformer TT. Likewise, relay TR being released, repeater relay FP also releases at the end of its delay period and in con sequence the second repeater relay BP then also drops out.

This, however, establishes the i5 coding circuit for the rear track section, which circuit extends from terminal 13 through conductor 48, back contact 46 of relay BP, conductor 58, the coding contact 15 of device CT, conductor 5!, and the primary of track transformer TT back to the supply terminal C. Trackway current of the thus supplied 15 code now may leak over the defective joint and energize the control winding of the track relay TR. Under the influence of this energy, the track relay will reestablish the lock ou circuit in the automatic manner previously explained in detail.

From the foregoing it will be seen that the improvements of our invention which are disclosed in Fig. 2 possess advantages in addition to those previously, discussed in connection with the arrangement of Fig. 1. Thus, the represented inclusion of the windings of repeater relays F? and BP in series with the conductors of the primary energizing circuit of the decoding transformer DT eliminates the need for an extra or third contact on the code following relay IR to control these repeater relays when used. Since, in a constantly operating device of the code following type shown at TR, it is desirable to reduce to a minimum the number, size and weight of the moving parts, this is a feature of practical importance.

46 .of the repeater relays (and the use of contact 36 of relay FP in the snubbing circuit of relay BP) assures that the decoding equipment will respond to each initial shunting of the forward track circuit with a quickness which is adequate for all train running conditions. In particular, this means that the coding of the energy supplied to the rear section rails will be changed from the H30 to the 15 rate as soon as relay FP releases following the shunting of relay TR. In a system of the improved type shown in Fig. 2, the combined release periods of relays TR and FF may readily be made less than the time required by the shortest and highest speed rail vehicle to move over and clear the insulated joints 3 of a section dividing location and in this manner a temporary flashing of an undesired signal indication at the entrance of the rear track section is effectively prevented. In addition, our novel application of the three point pick up principle to the relays FP, BP and H75 enables the lock out circuit controlled by these relays to protect against defective insulated rail joints in the advantageous manner already explained.

A third application of the improvements of our invention is disclosed in Fig. 3. There the apparatus is shown as forming a part of a four indication automatic block signalling system for a stretch of track wherein the rails l-2 are divided into successive track sections of the character represented at MMa. As in the system of Fig. 2, the track circuit of this illustrative section is supplied with alternating current energy from a source B-C through a track transformer TT connected with the rails at the exit end of the section.

The code following track relay TR which is installed at the opposite or entrance end of the section is represented as being of, the direct current type and is operated by rectified pulses of alternating current trackway energy which are transmitted thereto from the track rails by a circuit which includes a rectifying unit 54 of conventional character. In the manner already explained in connection with Fig. 2, a first contact 4 of this relay jointly controls the primary energization of a decoding transformer DT3 and the supply of operating current to the windings of a pair of repeater relays FF and BP. Likewise, a second contact ll of the track relay controls the current which is supplied to the winding of a relay Dl20 from the secondary ll] of the decoding transformer also in a manner which is equivalent to that explained for relays H and H15 in connection with the disclosures of .Figs. 1 and 2.

A third contact 56 is additionally provided on the code following device TR for the purpose of aiding in the control of a code detecting relay H20. Also participating in this control are front contacts 51, 58 and 59 of devices FP, BP and H20. When the contacts of all three of the relays TR, FF and BP are picked up, the winding of relay H20 receives energizing current over a pick-up circuit which may be traced from the positive terminal of a suitable supply source through front contact 56 of relay TR, conductor BI, front contact 5'! of relay FP, conductor 62, front contact 58 of relay BP, conductor 63, and the winding of relay H20 back to the negative terminal of the supply source. Once picked up, the contact 59 of relay H20 continuously completes this energizing circuit as long as both of the repeater relays PP and BP remain picked up. The stick circuit then effective may be traced from the positive supply terminal through front contact 59 of relay H28, conductor 64, front contact of relay FP, conductor 62, front contact 58 of relay BP, conductor 63 and the winding of relay H back to the negative supply terminal.

From the foregoing it will be seen that the code detecting relay H20 remains released as long as the track relay TR fails to receive coded energy. In that case, by continuously maintaining its contacts in one position, relay TR causes the energizing circuit of relay H28 to be interrupted at either or both of the contacts M and 58 of relays FF and BP. When, however, relay TR responds to trackway energy of any of the code speeds normally used in the track circuit MMa, the first on period of this code picks up relay FP, the following off period picks up relay BP and the second on period completes for relay H29 the pick-up circuit traced in the preceding paragraph. In con sequence, relay H20 also picks up its contacts and completes its own stick circuit (also traced above). In this manner relay H20 responds to each code following operation on the part of relay TR and holds its contacts continuously picked up until such operation is interrupted.

From the above description it will further be evident that code detecting relay H28 has three point pick up" characteristics which are comparable to those of relay H of the system of Fig. 2. That is, following each vacancy of the track section MMa, three periods or one and one-half cycles of the transmitted trackway code must be received by the relay TR at the entrance end of the section before the associated code detecting relay H20 picks up its contacts. Moreover, since the Winding of code detecting relay H20, once energized, receives steady or uninterrupted current as long as both of the repeater relays FF and .BP remain picked up, this relay H20 does not require retardation characteristics of any kind and thus may be an ordinary neutral acting device.

The system of Fig. 3 makes use of a first code distinguishing relay DIM which is arranged to pick up only when the code following relay TR responds to energy which is coded at or above a medium speed rate, such as is produced by a coding contact I29 of a transmitting device of the usual type represented at GT3. This, of

course, means that the relay fails to respond to code rates of a lower order, such as produced by a second coding contact 20 of device GT3, but will respond to either the or the 180 code. To facilitate explanation, it will be assumed that the coding contact I20 operates at a rate which produces 120 energy pulses per minute, that contact til codes at the much slower rate of 20 pulses per minute, and that a third contact I80 of device GT3 codes at the much faster rate of energy pulses per minute.

The above stated selective response on the part of relay DIM is preferably produced by designing the decoding transformer DT3 in such manner that at the lower code rates it is incapable of transmitting sufficient energy to pick up the relay. One convenient way of doing this is to make the magnetic circuit of the transformer of comparatively small cross section and so coordinate the primary and secondary windings therewith that the speed of operation of contact i of relay TR must at least approach the 120 code rate before the voltage induced in Winding it] will be adequate to circulate current of pick-up strength through the winding of relay DlZfl.

The system of Fig. 3 additionally makes use of a second code distinguishing relay DDIBB. This relay is designed to respond only to code frequencies of the high speed order which are produced by the third coding contact I80 of the transmitting device GT3. To this end it is supplied with operating energy from the decoding transformer DT3 through a tuned circuit J l80 which may be a duplicate of the correspondingly identified resonant circuit of Fig. 1. Instead, however, of using a separate secondary winding 9, as does the apparatus of Fig. 1, the arrangement of Fig, 3 makes use of a direct connection across the end terminals of the decoding transformer primary.

For the purpose of controlling, in the system of Fig. 3, the lamps of the four indication wayside signal Sm shown at location M, the three relays H20, Dl20 and DDlBll are provided with contacts which are included in the lighting circuits for the signal lamps. As long as the contacts of relays H20 and DDilit are picked up, lamp G displays a clear indication by virtue of receiving lighting current over a circuit which extends from the positive terminal of a suitable supply source through front contact 66 of relay H20, conductor 61, front contact 68 of relay DDldi), conductor 69, and the lamp G back to the negative terminal of the supply source. This is the condition which obtains when the code following relay TB, is responding to trackway energy of the high speed or code.

When the contacts of relays H28 and Difil are picked up and those of relay DDlfiil are released, as in the event that energy of the medium speed or 120 coding is received from the trackway, the signal Sm displays the approach medium indication by virtue of both of its lamps Y being lighted. The circuit for the upper lamp may be traced from the positive supply terminal through front contact 65 of relay H20, conductor 61, back contact 68 of relay DDIBU, conductor Ill, and the lamp Y back to the negative supply terminal. The circuit for the lower lamp Y may be traced from the positive supply terminal through front contact 65, conductor El, front contact ll of relay DlZG, conductor 12, back contact 73 of relay DDIBil, conductor M, and the lamp Y back to the negative supply terminal.

When the code following relay TR responds to trackway energy of the 20 code, the contacts of relay H20 only are picked up and those of both relays D120 and DDl 80 are released. Under this condition only the upper lamp Y of the signal S is lighted to display the approach indication. The circuit now active is the same as that traced in the preceding paragraph.

Finally, when the code following relay TR fails to receive coded energy from. the trackway, the contacts of all three of the relays H29, DIE!) and DDlfill are released and the wayside signal then displays the indication of stop by virtue of lamp R thereof being lighted over a circuit which extends from the positive supply terminal through back contact 66 of relay H20, conductor 11, and the lamp R back to the negative supply terminal.

In the system of Fig. 3, the two relays I-IZU and DI 20 additionally serve to select which of the contacts 20, I20 and I86 of the coding device GT3 is included in the circuit through which the alternating current source B-G supplies coded energy to the rails of the track section to the immediate rear of location M. When the contacts of both of these relays are picked up, as in the event that energy of either the 120 or the 180 code is received from the forward section of trackway, the rails of the rear section receive energy of the high speed or 180 code over a circuit which extends from the supply terminal B through coding contact I86 of device GT3, conductor 18, front contact 19 of relay Dl20, front contact 8| of relay H29, conductor and the primary winding of track transformer TT back to the supply terminal C.

When the contacts of relay H20 are picked up and those of relay DlZil are released, as in the event that energy of the 20 pulse per minute code is received from ahead, the rails of the rear track section are supplied with energy of the 120 code over a circuit which extends from the supply terminal B through coding contact I20 of device GT3, conductor 82, back contact 19 of relay D120, front contact 8| of relay H28, conductor 5| and the primary of transformer TT back to the supply terminal C. Finally, when the code following relay TR fails to respond to coded energy and the contacts of both of the relays H28 and Dim are released, the rails of the rear track section receive energy of the 20 code over a circuit which extends from the supply terminal B through coding contact 26 of device CT3, conductor 83, back contact 8! of relay H26, conductor 5! and the primary of transformer TT back to supply terminal C.

For applications of the character shown in Fig. 3 wherein under certain conditions steady or uncoded energy (not shown) may be supplied to the track circuit for detection purposes of one form or another, comparable systems heretofore known may be subject to the disadvantage of producing an undesired momentary approach indication on the part of the wayside signal in the event that a following train enters the track section and shunts the track relay during the time that this steady energy is being received. This is for the reason that immediately preceding such a shunting, the contacts both of the track relay TR and of the repeater relay F? are picked up under the control of the steady trackway energy. When, now, the mentioned shunting does occur, the release of the track relay contacts completes, at back contact 4, the energizing circuit for the second repeater relay BP and thereby picks up this relay.

When, as in prior art systems, this relay BP directly controls the energizing circuit of the code detecting relay H, a pulse of energizing current is circulated through the winding thereof, and the stop indication on the part of the wayside signal (which should be displayed continuously) may then be interrupted and an approach indication given for a period equal to the release time of the repeater relays PP and BP. The improved arrangement disclosed in Fig. 3 effectively prevents this undesired approach indication since, under the conditions stated, only two of the three steps required for the energization of the signal controlling relay H20 have been performed. The necessary cycle and onehalf of code not being simulated, the relay H20 maintains its contacts continuously released and in consequence the stop indication is not interrupted.

As an illustrative arrangement for supplying the just discussed steady energy to the track circuit under predetermined conditions, the diagram of Fig. 3 shows at the exit end of the track section M-Ma a relay CR3 which directly controls the energy which source B-C supplies to the track transformer TT at location Ma. During normal operation of the automatic block signalling system, this relay operates its contact 35 in synchronism with one or another of the three coding contacts 28, I28 and I30 of a de vice GT3 (not shown) associated with location Ma. Under other conditions, such as might be occasioned by the control of a cut section which is associated with highway crossing protective devices (also not shown), contact is maintained continuously picked up and the referred to steady energy then is supplied.

Use may also be made of an auxiliary contact 86 of the front contact repeating relay FP for the purpose of controlling a relay XR which governs the operation of the previously referred to highway crossing protective signals. As long as the contacts of relay FP are picked up, as under conditions of vacancy of the complete track block which the wayside signal Sm guards, the winding of relay XR receives energizing current over contact 86, and that relay, in turn, maintains its contact 81 picked up to interrupt the operating circuit (partially represented as including a conductor 88) for suitable highway crossing signals.

When, however, a train enters the section of which location M marks the entrance, the resulting shunting of the track relay TR allows repeater relay FP to release its contacts. This interrupts the circuit for relay XR, which re leases its contact 81 and thereby completes the crossing signal operating circuit. As the rear portion of the train moves past the location Ma of the highway intersection, relay CR3 is so controlled as to supply steady energy to the rails with which relay TR at location M is directly connected. This steady energy picks up relay TR, energizes repeater relay FF, and it, in turn, picks up its contacts to discontinue operation on the part of the highway crossing signals.

Among the further advantages which are afforded by our improved arrangement of Fig. 3, mention may be made of the provided assurance that the decoding equipment will respond to each initial shunting of the associated track circuit with a quickness which is adequate for all train running conditions. Involved in this is contact Bl of relay H20 which transfers the coding of the rear section energy to the lowest or 20 pulse per minute rate when a train first enters section MMa. By carrying the energizing circuit of that relay H20 over contact 51 of relay FP (as well as contact 58 of relay BP) a release of relay FP in response to the mentioned train entry immediately causes relay H20 to effect the coding transfer described above. As all of this can readily be arranged to take place before the shortest and highest speed train vehicle has time to clear the insulated joints at the exit end of the rear section, the signal at the entrance end of that section is prevented from temporarily displaying an indication higher than the desired approach.

The Fig. 3 arrangement of the pick-up and stick circuits for code detecting relay H20 thus represents a desirable and practical improvement over circuits previously used. While retaining the three point pick-up characteristics, the need for delayed release characteristics in the relay H20 is eliminated and the quick shunting response above discussed is provided in a very simple and eifective manner.

Referring now to Figs. 4 and 5, these show a still further application of improvements of our invention to an automatic block signalling system of the three indication type. Fig. 4 represents: a stretch of protected track which includes four section dividing locations U, V, W and X; the distribution of the coded train control energy which is present in the four track sections immediately behind a train A; and the aspects of the associated wayside signals S.

From Fig. 4 it will be seen that three codes designated as i5, 15, and I 30 are employed. These are respectively produced by correspondingly designated contacts of a code transmitter GT forming a part of the apparatus of Fig. 5 which is installed at each of the section dividing locations. As in the case of the systems of Figs. 2 and 3, the trackway energy is derived from an alternating current source, designated by the terminals B and C, and is transmitted to the trackway through the medium of the usual track transformer TT. Use is made of alternating current track relays TR of the code following type, described in connection with Fig. 2, and of three aspect color light wayside signals 5 of the character shown in Figs. 1 and 2.

In the apparatus of Fig. 5, the repeater relays FP and BP are energized alternately over contact t of the track relay through circuits which include the primary winding of the decoding transformer DT5 and which are arranged in the same manner as in the systems of Figs. 2 and 3. Through an employment of means not represented, each of these relays is provided with a retardation suiiicient to maintain the contacts thereof continuously picked upwhen the track relay responds to a code frequency of cycles per minute or higher.

The code detecting relay shown at H15 is comparable to the similarly designated device of Fig. 2. It receives energizing current from the secondary winding ill of the decoding transformer DT5 over circuits which include contact l l of the code following relay TR, which contact controls the relay currentin the same manher as has been explained in connection with each of Figs. 1, 2, and 3. This relay, however, does not pick up on the lowest or l5 code and responds only when the code frequency is of the medium or 75 pulse per minute order or higher.

This selective characteristic is preferably obtained by designing the decoding transformer DT5 to have saturating characteristics equivalent to those explained in connection with device DT3 of Fig. 3 and as a result of which the amount of energy transferred at the low or 15 code frequency is insuificient to pick up the relay contacts. When thus arranged, relay H15 maintains its contacts in the released position as long as the relay TR responds to a code as low as 15 cycles per minute. However, on a code frequency of 75 cycles per minute or higher, the relay picks up its contacts and holds them continuously at full stroke.

For the purpose of controlling the lamps of the wayside signal Su, relays BP and H15 are provided with contacts 9!] and 9i which control the lamp lighting circuits in the usual manner. Likewise, for the purpose of selecting which of the three contacts 55, 15, and mi] of the device 0T5 is included in the primary winding circuit for the track transformer T1 connected to the rails of the rear track section, these two relays BP and H15 are further provided with contacts 92 and 93. Further included in the rear section rail supply circuit is a contact M of the repeater re-- lay FP, which contact functions to quicken changes in signal aspect in a manner later to be described.

In operation of these signal control and code selecting circuits, when the track relay TR fails to receive coded energy, as in the event that a train occupies the associated tracksection (as shown ahead of location X in Fig. 4), the resulting deenergization of all three of the relays FP, BP and H15 causes their contacts to be released. In consequence, the wayside signal 811. shows stop by virtue of lamp R thereof being lighted over a circuit which extends from the positive supply terminal through back contact 95 of relay BP, conductor 28, and the lamp R back to the negative supply terminal. At the same time, the rails of the track section to the rear receive energy of the 15 code over a circuit which extends from the supply terminal B through coding contact l5 of device (3T5, conductor back contact 92 of relay BP, conductor 5| and the primary winding of transformer TT back to the supply terminal C.

At the entrance of the first vacant block behind the train, or at location W in Fig. 4, the response by the track relay TR. to this 15 code causes the contacts of relays FP and BP only to be picked up. Under this condition, the controlled wayside signal Sw shows the indication of approach by virtue of lamp Y thereof receiving lighting current over a circuit which extends from the positive supply terminal through front contact 95 of relay BP, back contact 9| of relay H15, conductor 21 and the lamp Y back to the negative supply terminal. At the same time, the rails of the track section to the rear of the location receive energy of the code over a circuit which extends from the supply terminal B through coding contact 15 of device GT5, con-.

ductor back contact 93 of relay H15, conductor 99, front contact 9 3 of relay FP, conductor Hill, front contact 52 of relay BP, conductor 5| and the primary of track transformer TT back to supply terminal C.

At the entrance of the second vacant section behind the train, or at location V in Fig. l, the response by the track relay TR to this 75 code causes the contacts of all three of the relays FP, BP, and H15 to be picked up. Under this condition, the wayside signal Sv displays the indication of clear by virtue of lamp G thereof receiving lighting current over a circuit which extends from the positive supply terminal through front contact 90 of relay BP, front contact 91 of relay H15, conductor 25 and the lamp G back to the negative supply terminal. At the same time, the rails of the rear track section receive energy of the code over a circuit which may be traced from the supply terminal 13 through coding contact I80 of device GT5, conductor 153, front contact 93 of relay H15, conductor 99, front contact 94 of relay FP, conductor lflll, front contact 92 of relay BP, conductor 5| and the primary of transformer TT back to the supply termi nal C.

At the entrance of the third vacant block behind the train, or at location U in Fig. i, the response by the track relay TR to the 180' code again causes all three of the relays FP, BP and H1 5 to be picked up and produce the clear indication on the part of the controlled signal Su and an inclusion of the coding contact in the rail supply circuit for the rear section. These conditions, moreover, are also duplicated at each of the locations further to the rear which are associated with unoccupied track sections.

Regarding the action of the contact 94 of relay F? in the rail supply circuit, it has been indicated that this contact functions to quicken the change of signal aspect. This quickening occurs as a result of the fact that upon a stalling of the track relay TR in response to an entry ofa train into the associated track section, relay FP must release its contacts before the winding of relay BP can be deenergized by a breaking of its supply circuit at contact 36. Accordingly relay BP does not release its contacts until after its full period of drop out delay has expired following the opening of the contacts of relay FF, and the contact 92 thereof thus does not transfer the coding device connection from the 15 contact to the 15 contact until some time following the release of relay FP.

It will thus be seen that by including contact 94 of the latter relay in the rail supply circuit in the manner shown, the supply of all energy to the rails of the rear track section is temporarily cut off by the release of the contacts of relay FF and resumed at the lowest or 15 code upon the subsequent release of the contacts of relay BP. In a system of the character shown in Fig. 5, this action is a desirable one in that it substantially accelerates response of the cooperating apparatus at the entrance end of the rear section.

The selection of codes just described in connection with Figs. 4 and 5 affords special advantages when the trains which pass through the protected stretch of track are equipped with cab signalling apparatus of the conventional type which does not respond to code frequencies as low as the pulse per minute value. As has been seen, energy of that low frequency code is supplied to the rails of the track section immediately behind the one occupied by an advance train. One very practical benefit is that a one block overlap for the control of a stop cab signal is obtained without enforcing a corresponding stop indication at the wayside signal.

Typically, the referred to train carried cab signalling apparatus may be of the construction shown and described in United States Patent No. 1.773.472 granted to Paul N. Bossart on August 19, 1930, for Railway trafiic controlling apparatus. Such apparatus makes use of devic s for inductively receiving energy from the track rails. an amplifier which strengthens the received energy. a code following master relay which is ener ized from the amplifier output, a decodin transformer which is supplied under the control of the master relay with code following pulses of primary current. decoding relays which a e connected with the decoding transformer through freouency selective circuits. and a cab signal having a plurality of ind cating units which are selectively energized under the control of the decoding relays.

In the event that a train provided with equipment of the character just described passes over the protected stretch of the track which is represented in Figs. 4 and 5, a three unit cab signal thereof of the type shown at CS in Fig. 4 will respond in the manner there represented as the train progresses through the successive sections behind the advance train A. Of this signal, the top unit is assumed todesignate full authorized speed, the center lamp approach speed, and the lower lamp the most restrictive or stop indication.

When the signal carrying train is receiving the 180 code, the top lamp of the signal CS is lighted; when the '75 code is received the middle lamp is lighted; and when energy of a code as low as the 15 pulse per minute variety is received, the equipment fails to respond and the lower lamp of the signal then lights to display the indication of stop. This failure of response under conditions stated is due to the fact that the ener y pulses of the 15 code are too widely separated to effect the picking up of the contacts of any of the frequency selective decoding relays which are carried on the train.

Referring now to Fig. 6, certain of the improvements of our invention which are shown in Fig. 5 are there represented as being applied to a cab signalling system which is arranged to cooperate with the trackway apparatus of Figs. 4 and 5 in a manner which causes a cab signal CS6 to repeat on board the train the indications which the wayside signals S of Figs. 4 and 5 display along the wayside. In this modification, it will be understood that the cab signalling apparatus is so designed that it responds to 15 code as well as to 75 code.

This signal CS6 takes the form of three lamps which are selectively supplied with energizing current over circuits which are controlled by the contacts and 9! of relays BP and H15. These relays together with a companion device F? are duplicates of those shown and described in connection with the apparatus of Fig. 5. They, together with a decoding transformer DT5, are controlled by a train carried master or code following relay MR which corresponds to the track relfiay 'I5'R of the cooperating wayside apparatus of This master relay is of the direct current polarized type and is provided with a pair of contacts I06 and Hi! which are respectively included in the circuits of the repeater relays FP and BP and of the code distinguishing relay H15. The relay MR receives operating current from an amplifier of any suitable well-known character, which, in turn, is controlled by the output voltage of a pair of windings I08 of the usual receiver I (lit-I09 which is mounted ahead of the advance truck of the equipment carrying vehicle just above and spanning the two rails l and 2. When alternating current of the character supplied from source B-C flows in the rails, voltages are induced in and additively combined by these windings.

Like relay TR in the system of Fig. 5, the train carried master relay MR shown in Fig. 6 follows the coding of the energy transmitted thereto from the track rails l and 2 through the receiver windings I08, the amplifier, and the relay transformer RT. Both of its contacts I06 and Hi! shift from one position to the other when the polarity of the relay energization changes and when the relay is deenergized these contacts stay in the position to which they were biased by the last energization of the relay. Thus, at the beginning of each pulse of trackway energy (when build-up of current in the primary of transformer RT induces in the transformer secondary a surge of given polarity voltage), the contacts are moved to the right-hand position (shown heavy) and at the end of each energy pulse (when decrease of current in the primary of transformer RT induces in the transformer secondary a surge of opposite polarity voltage) they are returned to the left-hand position (shown dotted) where they remain untilanother pulse of energy appears in the trackway.

The operation of the cab signalling apparatus of Fig. 6 is similar to that of the wayside signalling equipment previously explained in connection with Fig. 5. When the receiver I08 picks up no energy at all or uncoded steady energy, the contacts of master relayMR are at'rest andrelays BP and H15 then are both deenergized. Under this condition the cab signal CS6 displays the indication of stop by virtue of the bottom unit thereof receiving lighting current over a circuit which extends from the positive supply terminal through back contact 90 of relay BP, conductor III, and the unit itself back to the negative supply terminal.

When the received energy is of the 15 pulse per minute code, the resulting response thereto by the master relay MR. causes the contacts of repeater relays FF and B1? to be picked up and still allows those of H15 to remain released. Under this condition, the cab signal CS6 displays the approach indication by virtue of the middle unit thereof receiving lighting current over a circuit which extends from the positive supply terminal through front contact 90 of relay BP, back contact 9| of relay H15, conductor H2, and the unit itself back to the negative supply terminal.

Finally, when the received energy has a code rate of '15 pulses per minute or higher, the con tacts of all three of the relays BP and H15 are picked up and the cab signal CS then displays the clear indication by virtue of the top unit thereof receiving energizing current over a circuit which extends from the positive supply terminal through front contact 99 of relay BP, front contact 9| of relay H15, conductor H3, and the unit itself back to the negative supply terminal. It will be seen, moreover, that energyof the 180 code has the same effect as does that of the '15 code just described in acting to produce the clear indication of cab signal CS6.

With the exception of the fact that the contacts H35 and Ill! of the master relay MR are substituted for contacts t and H, respectively; of the track relay TR, the relay and the decoding transformer circuits shown in Fig. 6 are duplicates of those previously explained in connection with Fig. 5. Hence, the train carried relay MR controls these circuits in precisely the same manner as does the wayside track relay TR. The arrangement of Fig. 6 thus provides a three indication cab signal system without the use of the usual resonant or frequency tuned decoding circuits. In it, as has been seen, the approach indication is obtained with 15 code (instead of '15 code as at present) and thelSO code has no different effect on the aparatus than does the '15 code which produces the clear indication.

Likewise, the wayside apparatus of Fig. also offers the same advantage of detecting codes and distinguishing between different pulse rates thereof without employing frequency tuned circuits. As these involve comparatively bulky and expensive apparatus the stated advantage is a practical one. Moreover, through the represented inclusion of contact 94 of relay FP in the rail supply circuit for the rear track section, the equipment of Fig. 5 provides quick shunting response of the character discussed in connection with Figs. 2 and 3.

Referring to Fig. '7, we have there shown a further application of the improvements of. our invention to a system of automatic block signailing wherein the number of wayside indications is extended to four. In this application, there is installed at the entrance end of each block section the equipment which is shown at the single location U of the drawing figure.

This equipment includes a code following track relay TR of the alternating current type already described, a decoding transformer DT'l controlled by contact 4 of that relay in the same manner as in the system of Fig. 1, a pair of relays FF and BP arranged to repeat the front and back positions of a second contact Hi4 of relay TR, a first code distinguishing relay H15 which is energized from secondary 39 of transformer DTl and a second code distinguishing relay DlSFJ which is energized through frequency selective circuits J Hill in the manner explained for relay DDldil in the system of Fig. 3.

The facilities for coding the trackway energy are the same as those described in connection with the system of Fig. 5. They include a code transmitter 0T5 having three contacts [5, 15 and it!) which, under the control of contacts 82 and 93 of relays Bl? and H15, are selectively connected in the rail supply circuit to interrupt the supply of primary current to transformer TT at the rate of 15, '75 or 130 times per minute. To quicken the shunting response of this apparatus use also is made of a contact 94 of relay FP, again arranged as in Fig. 5.

Regarding the wayside signal Su, it consists of five lamps controlled by contacts I21, I23 and :25: of relays BP, H15 and DlBO to give the four different indications which will be described presently.

In operation of the relays of Fig. '7, devices FF and BP respond in the same manner as in each of the systems of Figs. 2, 3 and 5. That is, both respond to the presence of coded energy in the associated track section. Consequently, trackway energy of any one of the three 15, and codes is effective to pick up both of devices PP and BP. The relay control circuits shown differ from those of the earlier figures only in that a separate contact HM of the track relay TR is used to control the repeater devices.

The first code distinguishing relay H15 picks up only in response to codes of the 75 pulse per minute rate or higher. It is of the same direct current type as that used in the system of Fig. 5 and rectification of its energizing current is effected by a full wave rectifier lit. As in the case of the decoding transformer of each of the systems-of Figs. 3 and 5, transformer DIT is so designed that at code frequencies substantially below the '75 rate it fails to transmit sufficient energy through its secondary winding 89 to pick up the contacts of relay H15.

To safeguard that relay against false response when rectifier or other foreign ripples are present in the decoding transformer supply circuit. a contact 31 of relay BP is interposed between winding 89 of the decoding transformer and the winding of relay H15 supplied therefrom. If.

now. relay TR is not following code, this contact opens the circuit under consideration and thus provides the protection just stated. Obviously, the same result may be obtained by interposing the contact 31 between relay H15 and rectifier H6 (as in Fig. 8) instead of between the rectifier and transformer winding 89 as shown.

The second code distinguishing relay Didi! picks up only in response to codes of the 180 pulse per minute rate or higher. It, therefore,

is the full equivalent of relay D080 of Fig. 1 and of relay DDI80 of Fig. 3.

In operation of the complete signal location equipment of Fig. '7, whenever the track relay TR fails to receive coded energy, as in the event that the track section ahead of location U is occupied, the contacts of all three of the relays BP, H15 and DI80 are released. Under this condition, the rails of the rear track section receive energy coded by contact I of device GT5 and the wayside signal Su displays the indication of stop as a result of lamp R thereof receiving lighting current over a circuit which extends from the positive supply terminal through back contact I21 of relay BP, conductor I3I and the lamp R back to the negative supply terminal.

When energy of the code is received by relay TR, the contacts of relays FF and BP only are picked up. Under this condition the rails of the rear track section receive energy coded by contact 15 of device GT5 and the signal 811. displays the indication of approach as a result of its lower lamp Y receiving lighting current over a circuit which extends from the positive supply terminal through front contact I21 of relay BP, back contact I28 of relay H15, conductor I32, and the lamp Y back to the negative supply terminal.

When energy of the 75 code is responded to by relay TR, the contacts of relay H15 also are picked up. Under this condition the rear track section is supplied with energy coded by contact I80 of device CT5 and the wayside signal Su shows the approach medium indication as aresult of its upper lamp Y and its lower lamp G being simultaneously energized over a circuit which extends from the positive supply terminal through front contact I21 of relay BP, front contact I28 of relay H15, back contact I29 of relay DI 80, conductor I33 and both of the named lamps back to the negative supply terminal.

Finally, when energy of the 180 code is responded to by relay TR, the contacts of all four of the relays FP, BP, H15 and DI80 are picked up. Under this condition the track section to the rear of location U is again supplied with energy coded by contact I80 of device CT5 and the wayside signal Su displays the clear indication as a result of its upper lamp G receiving lighting current over a circuit which extends from the positive supply terminal through front contacts I 21, I 28 and I29 in series, conductor I 34 and the lamp G back to the negative supply terminal.

Regarding the advantages of the arrangement of Fig. 7, the represented inclusion of contact 31 of relay BP in the energizing circuit for relay H15 assures that the latter relay will not falsely respond when rectifier or other foreign ripples are present in the supply circuit of th decoding transformer DT1. Moreover, the use of contact 9 of relay FP in the rail supply circuit assures the same quick shunting response as was discussed in connection with Fig. 5.

Referring to Fig. 8, we have there represented a modified form of circuits for obtaining the same wayside and cab signal operation as the circuits of Figs. 4 and 5. In this modified arrangement, however, the function of relays FF and BP of Fig. 5 is performed by a single relay BPI5 which is energized through a capacitor H5 in a manner more completely described in a copending application, Serial No. 198,935, filed by Frank H. Nicholson on March 30, 1938, for Railway tramc controlling apparatus. Also, the energizing circuit for the code distinguishing relay H15 is modified to use, as does the apparatus of Fig. '7, a full wave rectifier IIB of the copper oxide or other equivalent type, which is connected with the single section secondary winding 89 of the decoding transformer DT8.

The primary winding of this transformer is controlled by contact 4 of relay TR in the same manner as that explained in connection with the representation of Fig. 1. As in the case of device DT5 of Fig. 5, the decoding transformer DT8 of Fig. 8 is designed to transmit to relay H15 sufficient energy to cause it to pick up its contacts only when the frequency of the coded energy to which the track relay TR responds has a value of 75 cycles per minute or higher.

Repeater relay BPI5, however, is arranged to pick up its contacts upon code frequencies of 15 cycles per minute or higher. Moreover, it is provided with a contact 31 which is included in the supply circuit of relay H15 and arranged, as in the system of Fig. '1, to eliminate the possibility of falsely energizing that relay when ripples of rectifier or other foreign origin are present in the decoding transformer supply circuit.

Considering first the energizing facilities for the relay BPI5, these are controlled by a contact I02 of the code following track relay TR, which in its front or picked up position completes for th capacitor II5 a charging circuit and which in its back or released position disconnects the capacitor from its charging source and connects it across the terminals of the relay winding. The mentioned charging circuit may be traced from the positive terminal of a suitable supply source through front contact I02, conductor II8, the capacitor II 5, and conductor II9, back to the negative terminal of the supply source. The referred to discharging or relay energizing circuit may be traced from the left or positive terminal of the capacitor II5 through conductor I I8, back contact I02 of relay TR, conductor I2I, the winding of relay BPI5, and conductor I22 back to the negative terminal of the capacitor In operation of the circuits just described, as long as the contacts of relay TR are at rest the winding of relay BPI5 remains deenergized and the contacts of the relay then, of course, are released. In the event, however, of code following response on the part of th relay TR, the capacitor II5 becomes charged each time that the relay contacts are picked up and then is discharged through the winding of BPI5 each' time that the code following contacts are released. By providing relay BPI5 with a release retardation sufficient to bridge the intervals between pulses of the lowest or 15 code, relay BPI5 is in this manner enabled to hold its contacts continuously picked up as long as a trackway code is being received.

Accordingly, the device operates in the same manner as the corresponding relay B? of Fig. 5 and in cooperation with relay H15 it controls, in the manner already explained, the lamps of the Wayside signal S at location Q and aids in selecting the coding of the energy which is supplied to the rails of the track section to the rear of that location.

In situations where it is desired to control highway crossing signals of the character described in connection with the relay XR of Fig. 3, a second repeater relay FPI5 may be added to the apparatus of Fig. 7 by bridging the Winding thereof across the terminals of the capacitor H in the manner represented. Should, now, the track relay TR at location Q receive steady energy and continuously hold its contacts picked up, the winding of relay FPI 5 will receive operating current over a circuit which may be traced from the positive supply terminal, through front contact I02 of relay TR, conductor H8, the winding of relay FPl5, and conductors I24 and H9 back to .the negative supply terminal. Under this condition, contact 86 of the relay becomes effective in the manner previously explained to discontinue operation on the part of the referred to highway crossing signals (not shown) Regarding the advantages of the arrangement of Fig. 8, detection of code is effected through the use of but a single relay BPIE; the-function of distinguishing between different code frequencies is performed by a second relay H and conventional circuits; and immunity to false response to rectifier ripples in the supply circuit for decoding transformer DT3 is obtained by including contact 37 in the energizing circuit of relay H15.

From the foregoing description of Figs. 1 to 8, inclusive, it will be seen that all of the herein disclosed embodiments of our invention are effective to lower the cost, simplify the construction and improve the operating characteristics of decoding equipment which is suitable for control by a code following relay in railway signalling systems of the continuously coded track circuit class. In applying our inventive improvements, moreover, none of the desirable features of this advantageous form of signalling system control is dispensed with and in all of the represented applications (except Fig. 3 which uses three) only two sets of cont-acts are required on the code following relay to effect the desired code detecting and code distinguishing functions.

Althoughwe have herein shown and described only a few forms of railway traffic controlling apparatus embodying our 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 our invention.

Having thus described our invention, what we claim is:

1. In a railway signalling system, the combination of a forward and a rear section of track, a code following relay operated by energy received from the rails of said forward section, a first repeater relay energized over a circuit which includes a front contact of said code following relay, a second repeater relay energized over a circuit which includes a back contact of the code following relay and a front contact of said first repeater relay, a snubbing circuit for said second repeater relay which includes the said first repeater relay contact and which imparts slow release characteristics to the second repeater relay only when the first repeater relay is picked up, means for supplying the rails of said rear track section with coded energy, and a contact carried by said second repeater relay for selecting the rate of coding for said energy.

2. In a railway signalling system, the combination of: a forward and a rear section of track; a code following relay operated by energy received from the rails of said forward section; a first delayed release repeater relay energized over a front contact of said code following relay; a second delayed release repeater relay energized over a back contact of the code following relay and a front contact of said first repeater relay;

a code detecting relay having quick releasing characteristics; a pick-up circuit for said code detecting relay which includes a series connection of a front contact of the code following relay, a front contact of said first repeater relay, and a front contact of said second repeater relay and which supplies the code detecting relay with pick-up current upon the second successive pickup of said code following relay; a stick circuit for said code detecting relay which includes a front contact of that relay connected in series with the aforementioned front contacts of said two repeater relays and which holds the code detecting relay continuously picked up during operation of said code following relay and allows it to release immediately upon each stalling of the code following relay and the drop-out of said firs-trepeater relay which accompanies that stalling; means for supplying the rails of said rear track section with coded energy; and a contact carried by said code detecting relay which selects the rate of coding for said energy and which quickly changes that coding rate upon passage of a train vehicle from said rear section into said forward section 3. In combination, a code following relay operated by energy received from the trackway, a decoding transformer having an input winding, a first repeater relay energized over a front contact of said code following relay through a portion of said input winding, a second repeater relay energized over a back contact of said code following relay through another portion of said input winding and a front contact of said first repeater relay, and a snubbing circuit for said second repeater relay which includes said front contact of the first repeater relay and which imparts slow release characteristics to the second repeater relay only when the first repeater relay is picked up.

4. In combination with a section of railway track: means for supplying coded energy to said track; a code following relay operated by said coded energy; first and second repeater relays respectively energized over front and back contacts of said code following relay; a decoding transformer having portions of its input winding which are respectively included in the energizing circuits of said relays; a code detecting relay having a pick-up circuit which includes a series connection of a front contact of the code following relay, a front contact of said first repeater relay and a front contact of said second repeater relay; a stick circuit for said code detecting relay which includes the aforementioned front contacts of said repeater relays connected in series with a front contact of the code detecting relay; a code disinguishing relay energized from said decoding transformer; and means for causing said code distinguishing relay to respond only when the bode frequency of the energy supplied to said track exceeds a given rate.

5. In combination with a section of railway track, means for supplying said track with energy coded at a low speed rate under certain traffic conditions, at a medium speed rate under other conditions and at a high speed rate under still further conditions, a code following relay operated by said energy, a code detecting relay controlled by said code following relay and arranged to pick up when that relay responds to trackway energy of any one of said three coding rates, a decoding transformer energized over a circuit which is controlled by said code following relay, a first code distinguishing relay energized by the output of said transformer over a contact of said code following relay and an untuned circuit and requiring a relatively high degree of energization for pick up, said transformer having a core and windings which are so coordinated that the operation of said code following relay must be of said medium speed rate before the decoding transformer will transmit energy of said relatively high degree, a second code distinguishing relay also energized from said decoding trans former but arranged to respond only when the coded energy is supplied at said high speed rate, and traffic governing apparatus jointly controlled by said code detecting and code distinguishing relays.

-6. In combination with a section of railway track, means for supplying coded energy to said track, a code following relay operated by energy received from said track, front and back contact repeater relays associated with said code following relay, a decoding transformer having portions of its input win-ding respectively included in the energizing circuits of said repeater relays, a code distinguishing relay energized from said transformer over a circuit which includes a rectifying contact of said code following relay, said transformer having a core and an output winding which are so coordinated that the transformer supplies said code distinguishing relay with energy of pick-up value only when the code rate of said received trackway energy exceeds a given value, a code detecting relay controlled over circuits which include contacts of said code following relay as well as of the two repeater relays and 'of itself, and trafiic governing apparatus jointly controlled by said code detecting and code distinguishing relays.

'7. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with first and second contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer, a source of direct current exciting energy for said transformer, a connection of the transformer primary with said exciting source which includes said first contact of the code following relay and which respectively is established and interrupted by that contact upon movement thereof to and away from one of its positions whereby when said contact is recurrently picking up and releasing said transformer generates a secondary voltage pulse of one relative polarity upon each of said pick-ups and a secondary voltage pulse of the op posite relative polarity upon each of said releases, a decoding relay having an operating winding together with a contact that becomes picked up when and only when said operating winding receives current that has a single predominant direction of flow, and a connection of the transformer secondary with said decoding relay winding which includes said second contact of said code following relay and which respectively is established and interrupted by that contact upon movement thereof to and away from one of its positions whereby during response of the code following relay to said coded energy the current circulated through said decoding relay winding by the then generated pulses of said transformer;-

secondary voltage is given the said single predominant direction of flow that is effective to pick up said decoding relay contact and whereby during failure of said code following relay to respond to coded energy such current as results from pulses of transformer secondary voltage that may then be generated by fluctuations in the transformer exciting current is passed through the decoding relay winding in a periodically changing direction that is ineffective for picking up the decoding relay contact.

8. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with first and second contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer, a source of direct current exciting energy for said transformer, a connection of the transformer primary with said exciting source which includes said first contact of the code following relay and which is so controlled thereby that said transformer generates a secondary voltage wave of one relative polarity upon each pick-up of that contact and a secondary voltage wave of the opposite relative polarity upon each release of that contact, a decoding relay having an operating winding together with a contact that becomes picked up only when said operating winding receives current of unchanging direction of flow but not when current of periodically changing direction of flow is received, and a connection of the transformer secondary with said decoding relay winding which includes said second contact of said code following relay and which is established in one relative polarity relation when that contact is released and in the reversed polarity relation when that contact is picked up whereby during response of the code following relay to said coded energy the impulses of current which the then generated waves of said transformer secondary voltage circulate through said decoding relay winding are caused to have the said unchanging direction of flow that is effective to pick up said decoding relay contact and. whereby during failure of said code following relay to respond to coded energy such impulses of current as result from waves of transformer secondary voltage that fluctuations in the transformer exciting current may then generate are passed through the decoding relay winding in the said periodically changing direction of flow that is itnegfective for picking up the decoding relay con- 9. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with pole changing and rectifying contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer, a direct current exciting circuit for said transformer which includessaid pole changing contact and which when that contact is recurrently picking up and releasing causes the transformer e sence to geheratea secondary'voltage wave of one relative polarity upon each of said pick-ups and a secondary voltage wave of the opposite relative polarity upon each of said releases, a decoding relay having an operating winding together with a contact that becomes picked-up only when said operating winding receives current of unchanging direction of flow but not when current of periodically changing direction of flow is received, and a connection of the transformer secondary with said decoding relay winding which includes said rectifying contact of said code following relay and which is established in one relative polarity relation when that contact is released and in the opposite relative polarity relation when that contact is picked up whereby during response of the code following relay to said coded energy the impulses of current which the then generated waves of said transformer secondary voltage circulate through said decoding relay winding are given the said unchanging direction of flow that is effective to pick up said decoding relay contact and whereby during failure of said code following relay to respond to coded energy such impulses of current as result from waves of transformer secondary voltage that fluctuations in the transformer exciting current may then generate are passed through the decoding relay winding in the said periodically changing direction of flow that is ineffective for picking up the decodin relay contact. 7

10. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer which generates an alternating current secondary voltage upon application thereto of unidirectional exciting current in either periodically interrupted or fluctuating form, a direct current exciting circuit for said transformer which includes a first contact of the code following relay and which is periodically interrupted-by that contact'when and only when said control circuit transmits said recurring pulses of coded energy to said relay, a decoding relay having an operating winding connected to be energized by the secondary voltage of said transformer and being provided with a l contact which picks up only when unidirectional current is received by said operating winding, and a second contact of said code following rclay included in the said decoding relay energizing connection and effective when and only when the code following relay is responding to said coded energy to rectify the current which flows in said connection and thereby cause the decoding relay contact to be picked up by transformer secondary voltages which result from said code following relay response but not to transformer secondary voltages which result from fluctuations in the transformer exciting current that may occur when said control circuit fails to transmit said coded energy pulses to said code following relay.

11. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which dis- ,continues that transmission at other times,.a:

code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with pole changing and rectifying contacts which occupy a released position when said windin is deenergized but-which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer having a primary winding and also a secondary winding that is provided with a mid tap, a direct current exciting circuit for the primary winding of said transformer which includes said code following relay pole changing contact and which causes the transformer to induce in its said secondary winding a voltage wave of one relative polarity upon each pick-up of said contact and a voltage wave of the opposite relative polarity upon each release of that contact, a decoding relay having an operating winding together with a contact which picks up only when said operating winding receives unidirectional current, means connecting one terminal of said decoding relay winding to the heel of said code following relay rectifying contact and the other terminal of the decoding relay winding to the mid tap of said transformer secondary Winding, and other means connecting the end terminals of said transformer secondary winding respectively to the front and back points of said rectifying contact whereby to establish circuits by way of which the said waves of voltage that are induced in said transformer secondary windin when said code following relay is responding to coded energy circulate unidirectional current through said decoding relay winding and thereby pick up said decoding relay contact and by way of which other secondary voltage waves that said transformer may generate when said code following relay is not responding to coded energy supply said decoding relay winding with unrectified current which is ineffective for picking up said decoding relay contact.

12. In a railway signaling system, in combination, a control circuit which transmit recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with pole changing and rectifying contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of the said energy pulses that said winding receives, a decoding transformer which generates an alternating current secondary voltage upon application thereto of unidirectional exciting current in either pole changed or fluctuating form, a direct current exciting circuit for said transformer which includes said code following relay pole changing contact and which causes the transformer to generate a secondary voltage wave of one relative polarity upon each pick-up of said contact and a secondary voltage wave of the opposite relative polarity upon each release of that contact, and a decoding relay having a winding which is connected to receive all secondary volt ages of said transformer over a circuit that includes said code following relay rectifying contact and being provided with a contact which picks up only when the flow of transformer secondary current through said winding circuit is rendered unidirectional by code following opera- :tion of said rectifying contact but never when said rectifying contact isat'rest as a result of said control circuit having discontinued transmission of said coded energy pulses to said code following relay.

13. In a railway signaling system, in combination, a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times, a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with first and second contacts which occupy areleased position when said winding is deenergized but which are moved to a pickedup position during each of the said energy pulses that said winding receives, a decoding transformer, a source of direct current exciting energy for said transformer, a connection of the transformer primary with said exciting source which includes said first contact of the code following relay and which is so controlled thereby that said transformer generates a secondary voltage wave of one relative polarity upon each pick-up of that contact and a secondary voltage wave of the opposite relative polarity upon each release of that contact, a decoding relay having an operating winding together with a contact that becomes picked-up only when said operat ing winding receives current, of unchanging direction of flow but not when current of periodically changing direction of flow is received, a connection of the transformer secondary with said decoding relay winding which includes said second contact of said code following relay and which is established in one relative polarity relation when that contact is released and in the opposite relative polarity relation when that contact is picked up whereby during response of the code following relay to said coded energy the impulses of current which the then generated waves of said transformer secondary voltage circulate through said decoding relay winding are given the said unchanging direction of fiow that is effective to pick up said decoding relay contact and whereby during failure of said code following relay to respond to coded energy other secondary voltage waves that said transformer may generate supply said decoding relay winding with periodically reversing current that is ineffective for picking up the decoding relay contact, and an impedance bridged across said decoding relay winding to impart to said decoding relay contact slow release characteristics which cause that contact to stay continuously picked-up whenever said code following relay is responding to said coded energy.

14. In combination: a control circuit which transmits recurring pulses of coded energy at times and which discontinues that transmission at other times; a code following relay having a winding connected with said control circuit to receive said transmitted energy pulses therefrom and provided with contacts which occupy a back position when said winding is deenergized and which are picked up to a front position during each of the said energy pulses that said winding receives; a first delayed release repeater relay energize-d over a'front contact of said code following relay; a second delayed release repeater relay energized over a back contact of the code following relay and a front contact of said first repeater relay; a code detecting relay having quick releasing characteristics; a pick-up circuit for said code detecting relay which includes a series connection of a front contact of the code following relay, a front contact of said first repeater relay and a front contact of said second repeater relay and which supplies the code detecting relay with pick-up current upon the second successive pick-up of said code following relay; and a stick circuit for said code detecting relay which includes a front contact of that relay connected in series with the aforementioned front contacts of said two repeater relays, said stick circuit holding the code detecting relay continuously picked up during response of said code following relay to said coded energy and allowing the code detecting relay to release immediately upon each discontinuance of coded energy transmission to the code following relay and drop-out of said first repeater relay which accompanies that transmission discontinuance.

15. In combination, a section of railway track, means at the exit end of said section for supplying the rails thereof with recurring pulses of coded energy, a code following track relay at the entrance end of said section having a winding connected with said rails to receive said coded energy pulses therefrom and provided with contacts which occupy a released position when said winding is deenergized but which are moved to a picked-up position during each of said energy pulses that said winding receives, a decoding transformer, a source of direct current exciting energy for said transformer, a connection of the transformer primary with said exciting source which includes a first contact of said track relay and which is so controlled thereby that said transformer generates a secondary voltage wave of one relative polarity upon each pick-up of that contact and a secondary voltage wave of the opposite relative polarity upon each release of that contact, a slow release code detecting relay having an operating winding together with a contact that becomes picked up when and only when said operating winding receives unidirectional current, a signal for governing the passage of trafiic into said section positioned at the entrance end thereof and controlled by said detecting relay contact in such manner as to show proceed when that contact is picked up and stop when that contact is released, and a connection of the secondary of said decoding transformer with the winding of said detecting relay which includes a second contact of said track relay and which is established in one relative polarity relation when that contact is released and in the opposite relative polarity relation when that contact is picked up whereby during code following operation of said track relay the impulses of current which the then generated waves of said transformer secondary voltage circulate through said detecting relay winding are given the said unidirectional character that is effective to pick up said detecting relay contact and whereby during failure of said track re lay to respond to coded energy other secondary voltage waves that said transformer may then generate supply said detecting relay winding with periodically reversing current that is ineffective for picking up the detecting relay contact and that hence cannot falsely put said controlled signal at proceed while said track section is occupied.

16. In combination, a section of railway track, means at the exit end of said section for supplying the rails thereof with time-spaced pulses of coded energy which recur at a high speed rate at times and at a low speed rate at other times, 'a code following track relay at the entrance

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