US3172627A

US3172627A - hughson

Info

Publication number: US3172627A
Authority: US
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 J. D. HUGHSON 3,172,627

CAB SIGNAL RECEIVING SYSTEM FOR RAILROADS Filed Dec. 2, 1960 3 Sheets-Sheet 1 TRAFFIC DIRECTION H I2 5:} i TRACK RAIL\S I '2: f'r

l4 II TRACK CURRENT l5 l6 l7 CODING APPARATUS FILTER AND SATURABLE (TRANSMITTER) AMPLIFIER REACTOR RECT'F'ER fiCR l8 W l9 DECODING LOCOMOTIVE APPARATUS CONTROL AND DISPLAY FIG. 2. n I +5 W 48 EJ525122 w I I6 36 40 42 1 46 E/ I E I 5O 2O v I? I 2 2 J CR .iLJ L DECODING o 3 29 APPARATU I i. H 4 L I CONTROL AND DISPLAY a APPARATUS 9 INVENTOR. g J.D.HUGHSON l4 'I/l/I; Jill/I SECTION 2-2 FROM FIG. I.

HIS ATTORNEY March 9, 1965 o. HUGHSON CAB SIGNAL RECEIVING SYSTEM FOR RAILROADS BY HIS ATTORNEY March 9, 1965 J. D. HUGHSON 3,172,627

. CAB sxcmu. RECEIVING SYSTEM FOR RAILROADS Filed Dec. 2, 1960 3 Sheets-Sheet 3 FIG. 4.

A INPUT VOLTAGE TO AMP.

r' 1'? r' B OUTPUT V V \7 VOLTAGE OF AMP. 22

c ,i ,1 OUTPUT V V V VOLTAGE OF AMP 23 II 1 D A COMBINED VOLTAGE OUTPUT FROM AMPS. 22 AND 23 FLUX CHANGE IN CORE :6

IN V EN TOR.

J.D.HUGHSON HIS ATTORNEY United States Patent ce 3l7zfiz7 Patented Mau'. 9, 1965 Heretofore, each receiving coil was connected to a sep- 3,172,627 .arate amplifier so that a distinct channel was made avail- CAB SIGNAL SYSTEMFOR able on the output side for each induced track current in J. Donald Hughson, Rochester, N.Y., assignor to General Signal Corporation Filed Dec. 2, 1964), Ser. No. 73,434 9 Claims. (Cl. 246-63) This invention relates to railway signaling systems, and more particularly pertains to the vehicle-carried receiving apparatus for what is commonly known as a continuous inductive coded type system.

In such continuous inductive type systems it is common practice to classify these with respect to the method of transferring the signal to the moving vehicle and the kind of signal being transmitted through the track rails. This invention is limited to a continuous inductive coded A.C. type system in which the transmitted signals are continuously available through an inductive coupling on the moving locomotive and these same transmitted signals in the rails are time spaced coded groups of constant a. plitude A.C. voltages. The transmitted groups of these AC. voltages may be said to be coded since their frequency is usually indicative of the signal indication at the forward end of the block toward which the train is moving.

The cab receiving apparatus makes it possible to provide a continuous control and display in a locomotive cab concerning the tralfic conditions on the track ahead. Essentially, this is accomplished by applying pulses of electrical energy at distinctive coding rates to the track rails at the exit end of each block which may involve one or more track sections. These pulses travel along the track rails toward the train and induce voltages in receiving coils mounted on the locomotive and positioned over each track rail ahead of the leading wheels. The traincarried equipment amplifies the induced voltage pulses and detects their rate of occurrence. Since the particular coding rate in effect at any time corresponds to the trafiic conditions ahead, it becomes possible to provide one of a number of different cab signal aspects to the train operator which reflect existing trafiic conditions.

As in all signaling systems for railroads, it is imperative that high standards of reliability and fail-safe operation are designed into the system. The receiving apparatus, since it is carried on the moving vehicle, is highly subject to mechanical shock, and therefore, should be designed to withstand considerable abuse in this respect. Also, this apparatus must be extremely sensitive to rail currents, since the magnetic coupling is relatively loose because of rail clearance requirements which allow only minute voltages to be induced into the pick-up or receiving coils. These receiving coils are generally mounted forward of the most forward wheels and axle of the locomotive and disposed over each rail so that they will inductively couple with the rail currents, and thereby be effective to act as the secondary of a transformer; the rails themselves, with the rail currents flowing therein, act as the primary of this transformer. Substantially, shockproof amplifiers have previously been designed to overcome these obstacles; however, other considerations are of some consequence. Only rail currents, one in each rail, which are in phase, and no others, must be capable of signaling a particular train. Under certain-conditions wherein one-track circuit may have a high resistance due to a high resistance bond or an open bond, stray track currents from an adjacent track may have a substantial infiuence on the amplifiers, and consequently their output will most likely produce a false indication. Failings within the receiving apparatus itself may also produce false cab indications, if these are not in some way prevented.

each receiving coil. This output, in one instance, was directed to a two-phase relay to insure proper phasing of the induced track currents and to prevent operation if only one of the two channels of induced track currents were available after amplification, possibly due .to .an open circuit in the other channel. The amplified induced track currents were arbitrarily displaced in phase so that both, when recombined in the proper phase relationship, would operate a relay, but neither alone would operate this electromagnetic device. The major disadvantage of the two-phase relay is that it will not respond to the frequency of the usual track code pulses because its armature is too sluggish. Other disadvantages of the two phase relay are that it is large, heavy, and expensive. Another scheme to insure that the track currents are in proper phase relationship used a coincidence gas discharge tube to gate both in-phase track currents to the output circuits. The disadvantage of the coincidence tube and the other required associated electron tubes is that it is no more shock-proof than any other electron tube configuration.

t is with the aim of preventing any false indication or control to the locomotive that my invention is particularly directed. The saturable reactor in the embodiment of this invention is a more desirable substitute for either the two phase relay or a coincidence vgating electron tube for it is fast in response, small, light in Weight, inexpensive, and rugged in structure for operability under extreme shock conditions.

The feed for this saturable reactor is obtained from two separately channeled amplifiers, each of which clips one-half of the oppositely polarized portions of the cur rent waveform and later combines each half in successive phase relationship to reform a complete in-phase Waveform. The application of each half of the waveform to separate halves of the primary of the saturable reactor saturates the core first in one direction, then the other, under normal operating conditions. If one rail current becomes nullified by another stray leakage rail current from an adjacent track, or if one of the amplifiers should become open circuited, this loss of one-half of the output waveform would be eflective to saturate the core of the reactor in one direction only where it would remain, thereby providing no output. Under another situation if a short circuit appeared in one channel of the amplifier and thereby produced a large DC. current through .onehalf of the primary of the reactor this would hold the magnetization of the core at the saturation level and thereby again act as a gating device to produce no .output. Likewise, under ditferent circumstances, whenonechaunel is producing a weak signal output, then no saturation will result on its polarity direction of magnetization, but the other channel will act normally and saturate the core to it's polarity direction thereby sticking it, for the weak signal will be insuificient to reverse the magnetization to the other direction.

In view of the above, one object of this invention is to provide a reliable and fail-safe signal receivingsystem for railroad locomotives. 7

Another more specific objectis toprovide a method for through gating the amplified track currents when each is normally operating.

Another object is to provide a cut off gate for the track currents when either one or .the other channel is lacking.

Another object is to provide a cut off gate for Vt-he' V amplified track currents when either one or the other channel is short circuited. k 1

Another object is to provide a cut off gate for the amplified track currents when either track current functions in out of phase relationship with the other.

Other objects, purposes and characteristic features of this invention are in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing this invention in detail reference will be made to the accompanying drawings illustrating one specific embodiment of this invention and in which:

FIG. 1 represents a block diagram of the overall code communication system;

FIG. 2 shows a typical circuit arrangement for the receiving coils, filter, amplifiers, saturable reactor, and a block diagram of the decoding apparatus and control and display equipment;

FIG. 3 illustrates a group of waveforms representing normal operation of the system for a period of time and later shows the efiect of an open circuit on this normal operation; and

FIG. 4 shows waveforms that illustrate how the saturable reactor will function as a cut off gate when the track currents are out of phase.

To simplify the illustration and facilitate the explanation of this invention various parts and circuits have been shown diagrammatically. Certain conventional illustrations have been used and the drawings have been made to make it easier to understand the principles and manner of operation rather than to illustrate the specific construction and arrangements of parts that might be used in practice. The symbols and indicate the opposite terminals of a suitable source of direct current power or may also be used to indicate instantaneous polarities appearing on certain conductors. The symbols +B and ground are used to indicate the positive and negative terminals of the energy source respectively for electron tube potentials.

Apparatus It will be noted by referring to FIG. 1 that the track current coding apparatus along the wayside for applying coded train control energy to the track rails has not been shown in detail since it may be of the type shown, for example, in the patent to T. J. Judge No. 2,141,535 granted on December 27, 1938. This wayside apparatus 10 provides means, as in Judge above, for placing alternating current of a frequency different from the usual commercial frequencies, such as 100 cycles per second, on the track rails in coded form constituted by interrupting the current periodically at various rates. The particular codes involved in the usual system are those having a rate of 180, 120 and 75 interruptions per minute. The system is so arranged that a train in a block immediately to the rear of an occupied block will receive a constant uninterrupted alternating current having no coding rate, which, in turn, will display the most restrictive indication in the locomotive cab; one in the second block to the rear of the occupied block will receive the 75 code rate or a less restrictive indication; in the third block to the rear of the occupied block the 120 code rate or a still less restrictive indication, and in the fourth block to the rear and all the blocks to the rear thereof the 180 code rate or a clear indication. In different systems and/ or under different conditions within the same system there may be various assignments of code rates to the blocks other than the above, for example, two successive blocks may receive the 120 code rate.

The transmission line in this communication system consists of one track rail 12, the most forward wheels and axle of the locomotive 13, and the other track rail 14.

The usual receiving apparatus may be thought of as comprising the filter and amplifier 15, the rectifier 17, the code responsive relay CR (or a master relay MR), decoding apparatus 18, and control and display apparatus 19. In former systems either a two phase relay or a coincidence gate comprising gas discharge tubes was used between the filter and amplifier 15 and rectifier 17 to insure that only properly phased currents would operate the rectifier 17. In this system a saturable reactor 16 is used for this purpose.

It is common practice to use pick-up or receiving coils 11 and 11, which are also an essential part of the receiving equipment, one over each rail to separately drive an amplifier, which, in turn, feeds one phase of a two phase relay. Thus each receiving coil must be receiving a signal of the proper phase and each amplifier must be working at the proper level in order to obtain proper operation of this two phase relay. The main disadvantage of this type relay is its failing to respond to the codes in a coded track system because of its inherent sluggish response. This last restriction limits the number of available indications to the very minimum, whereas the saturable reactor possesses a rapid response characteristic and therefore can readily respond to the track code pulses.

In the filter and amplifier 15 tuning circuits are arranged in the advance portion to pass the cycle per second energy and exclude the usual commercial power frequencies such as 25, 50 and 60 cycles. In the embodiment of this invention two such filters are arranged, one for each receiving coil. The output of the filter feeds a class A amplifier which inverts the signal but maintains the same waveform as the input. The

electron tubes

20 and 21 shown in FIG. 2 represent this class A amplifier. The output of this amplifier feeds a class B push-pull amplifier embodied in

electron tubes

22 and 23 which eliminates the positive-going half of the waveform and at the same time again inverts the input waveform. The output of this class B amplifier then has the same wave form except for the half which is eliminated as was provided from the output of the filter. When each of these half waves are added back-to-back or in phase relationship in the respective primary windings 24 and 25, they will combine to form a complete sine wave, therefore each channel makes up each half of this continuous sine wave which now appears as an in-phase voltage.

The saturable reactor 16 is designed in such a manner so that its core will readily saturate by each of the peak voltages which are applied to each half of the primary windings 24 and 25. The secondary winding 26 connects to a detecting device, such as the rectifying bridge 27 so that the rectified output from this bridge may be used to operate the code response relay CR. Inasmuch as this unit is a saturable reactor, the only time a voltage will be induced into the secondary winding is during the time of a change of flux in the core. Such flux changes will be considered later when the operation under various conditions is discussed in detail. The core of this saturable reactor possesses a magnetic material such that its characteristic is what is commonly known in the art as a rectangular hysteresis loop.

To simplify the explanation of this receiving system hereinafter, the signals will be terminated at the code responsive relay CR, for it is here at this relay, when it ceases to function at any of the transmitted coding rates, that the cab indication will go to a stop display, and in some systems may further apply the brakes to the locomotive, this latter, usually after some time delay.

The decoding apparatus 18 is required to accept the coded message and transform it into a control and/ or display signal which can be accepted by the locomotive control and display apparatus 19. It should be understood that the decoding apparatus 18 per se is not a part of this invention but is required to complete the system. For this reason this apparatus is not shown in detail for it is similar to that shown in Patent No. 2,731,553 by F. P. Zaifarano et al. on a Coded Cab Signalling System for Railroads dated January 17, 1956.

The locomotive control and display apparatus 19 may take on many different forms. One possible combination is as shown in detail by W. H. Reichard et al., in

' around the circuit shown in FIG. 2.

Patent No. 2,223,131 dated November 26, 1940, for example.

Operation The operation of this system evolves more specifically In the lower portion of this figure a mechanical section 2-2 is taken from FIG. 1 of the cross section of the

rails

12 and 14. Let us start this discussion with the assumption that the instantaneous rail current in any one of the pulse groups is flowing toward the reader in rail 12, which is designated by a dot, and the current in rail 14 is flowing away from the reader, indicated by a sign. This is a normal condition of these track currents, for at some instant the current (see FIG. 1) will be flowing from the transmitter 159, through track rail 12, through the most forward wheels and axle 13 of the locomotive, and return to the transmitter it via rail 14.

On each side of the locomotive, receiving coils 11 and 11' are disposed above

rails

12 and 14 respectively, so that the magnetic material within these coils forms a portion of a magnetic circuit with respect to each of the track currents flowing in the rails. Each of these receiving coils may be thought of as the secondary of a transformer which has multiple turns on the secondary, whereas the primary is simply a partial single turn formed by each of the two rails. If the current is flowing as indicated in rail 12 and is increasing in magnitude a voltage will be developed across coil 11 having a positive polarity on wire 34? and a negative polarity on wire 31. Similarly, the current flowing in rail 14 in the direction indicated when increasing will produce a positive polarity on wire 32. and a negative polarity on wire 33. Connected across each of these coils is a

momentary shorting switch

28 and 29 which may be used to momentarily short-circuit each input to determine whether the remaining circuitry is working properly. More will be discussed about this feature later during the discussion of various modes of operation.

The next apparatus involved in this circuitry is the filter 34 which is a portion of the filter and amplifier shown .in FIG. 1. Each of the voltages generated across a .receiving coil are applied to each input of this filter 3 through a

series capacitor

36 and 37 respectively. The voltage from receiving coil 11 will cause a current to how through the primary winding .38 in an upward direction or away from ground potential, whereas the voltage induced in coil 11' will cause the current to flow through primary winding 39 also in an upward direction but to ward ground potential. The combination of capacitor 36 and winding 38, and capacitor 37 and winding 39 are respectively tuned to a frequency of 100 cycles per secend, which is the same frequency being transmitted through the track rails; consequently, this filter is designated to accept maximum energy at this frequency. The transformers 4i and 41 within the filter transfer the energy to the grid circuits of the class A amplifier tubes and 21. The secondaries of these

transformers

42 and 43 are each tuned by a parallel capacitance 44 and 45 respectively. If we now assume that the transformers are connected in phase (note dot polarity indications) rather than 180 out of phase, then the secondary side of the transformer at the potential progressing farther above ground will be connected so that a positive-going pulse will appear at this instant on the coupling capacitor 45. Similarly, at this same instant, a ne ative-going pulse will appear at the coupling capacitor 47 in the opposing circuit. The sine voltage waveforms are shown in FIG. 2 which are applied to the grids of

tubes

26 and 21. Note that these are 180 out of phase.

The

electron tube

20 and 21 are typical class A amplifiers biased above cut-off by resistors 59 and 51 respectively, and therefore, as well-known in the art, the output voltage waveforms appearing at the plates of these tubes 6 will be complete waveforms of the input but one of phase by 180. These voltages are, in turn, applied through

coupling capacitors

48 and 49 to the grids of the class B amplifier tubes 22 and 2.3 respectively.

It is also well-known in the art that since aclaSs B amplifier is biased at cut-off, in this instance by the

batteries

52 and 53, it will clip the positive-going portion of the output voltage waveform. Therefore, since the phase relationship is again inverted by 180 through this amplifier a negative-going waveform will appear at the output of tube 23. After a half cycle the remainder of this waveform will be clipped; however, at this time tube 22 is about to produce a negative-going waveform because of the phase relationship of the voltage applied to its grid, whereas during the first half of the cycle its output voltage waveform had been clipped.

The output of each class B amplifienboth of Whichare arranged in push-pull fashion, is connected to each half of the primary winding of the saturable reactor 16. Assuming that a positive-going pulse produces a current from plate to cathode within the class B amplifier a current will flow in winding 25 from the battery to the plate of tube 23. This current flow may be represented by the direction of the arrow adjacent to this winding 25. Similarly, during the next cycle the current will flow in winding 24 in the direction of the arrow shown adjacent to this winding. Let us assume that the arrow in an upward direction saturates the core to a positive condition or flux density, whereas an arrow in the downward direction produces a saturation in the core in a negative direction or negative flux density. When each of these class B amplifying tubes are operated first one, then the other, in proper time relationship, then the core will be saturated first to a negative state, and alternately to a positive state within the course of each cycle.

In any transformer a change in flux density within the core produces an output voltage on the secondary side such as within winding 26. This induced voltage in the secondary may be rectified by a typical bridge rectifier such as 17, which, in turn, may be used .to operate the code responsive relay CR. In some systems this same relay is designated as a master relay MR, but the function of this MR relay substantially the same as that of the CR relay. At a frequency of cycles per second the inductive reactance of either the CR or MR relay is sufiicient to maintain this relay energized from one-half cycle to the next by the current supplied to it from the bridge rectifier 1.7. The coding rates of 75, and 180 cycles per minute are considerably slower however; consequently when the 100 per cycle per second energy is interrupted at these rates, the code responsive relay will then drop out during each interrupted period. When the cycle per second energy is reinitiated the CR relay will again pick-up, consequently this relay will follow the code which is transmitted through the track rails and induced into the receiving coils 11 and 1-1.

It is not deemed necesary to show or explain any details re arding the decoding apparatus 18 and the control and display apparatus 19 since this invention is concerned primarily with fail-safe operation of the .CR relay. Any one familiar with the former art may examine the considerable quantity of former patents regarding the details of these two major sections of the apparatus. Furthermore, a designer for some particular control and display system may design other apparatus than that shown in former patents for some specific purpose, and accordingly design the decoding apparatus 18 to conform with all of the necessary coding rates involved. It is to be understood that the above mentioned interruption rates are given by way of example only, and furthermore even higher coding rates than those mentioned may readily be accommodated by the saturable reactor 16.

The waveform of FIG. 3 illustrate normal operation of the system at the start with a fault developing later during the illustrated period; whereas FIG. 4 illustrates .and thereafter a faulty condition is represented.

an abnormal condition which may possibly occur and in each instance will provide a fail-safe result.

More specifically the waveforms A through G of FIG. 3 involve normal operation of the system for some rate of interruption of the transmitted signal up to time T3 In waveform A of FIG. 3 a sine wave is shown which is induced into the receiving coils 11 and 11 from the track rails and applied to the input of the filter 34. The frequency of this waveform, as stated before, is of the order of 100 cycles per second. The actual waveform is represented at a lower frequency than this merely for simplification. For some period from 20 to t1 this frequency is turned on, whereas from the time period between 11 and t2 this frequency is turned off. This cycle of application and interruption of the voltage is repeated at the various coding rates such as 75, 120 and 180 cycles per minute so that at time t2 the waveform is again shown turned on until time t4.

The waveform B of FIG. 3 illustrates the output from amplifier 22 and as heretofore explained only the negative half portions of this waveform appear in the output at this point. Similarly waveform C of FIG. 3 shows the negative half portions of the output from amplifier 23. Note that these two half cycles appear in time sequence, first the latter then the former. In waveform D of FIG. 3 is represented the combined A.C. outputs from

amplifiers

22 and 23 applied to the primary of the saturable reactor 16 with respect to ground potential. Due to the push-pull arrangement of the

amplifiers

22 and 23 in connecting to the primaries 24 and 25, the output from amplifier 22 will remain unaltered but the output from amplifier 23 will be reversed to a positive-going pulse, with respect to ground. Consequently, the portion 60 of waveform C in FIG. 3 becomes the inverse portion 61 of waveform D in FIG. 3 and the portion 63 of the waveform D remains of the same polarity as portion 62 of waveform B. The combination of

portions

61 and 63 of waveform D therefore constitute a complete in-phase cycle for operation of the saturable reactor 16.

At some time t3 between times t2 and t4 let us assume a fault occurs in amplifier 22 such that no output or very little output results. In the waveform B of FIG. 3 at time 23 a very small output is shown as represented by the voltage wave 64. In the Waveform D at time t3 the original sine wave will be merely half sine Wave pulses from this point henceforth in the case amplifier 22 is completely open, or will be some low amplitude sine wave such as denoted at 65, if only a small output results from amplifier 22. The final result of this fault will be dis cussed later.

The waveform E of FIG. 3 shows the change in flux in the core of the saturable transformer 16. If we assume that the core resides in a negative state of saturation such as shown by point 66 the positive-going pulse in waveform D will saturate the core to the positive direction and after some time period ending at t5, for example, a certain number of volt-seconds or webers, such. as W1, will be added to the core material. Inasmuch as the core material in this transformer has a rectangularly shaped characteristic of hysteresis, the flux cannot change any further at this point for the duration of this half cycle. This constant flux condition is shown by the straight horizontal line 67 in the waveform E of FIG. 3. After the input waveform crosses the axis and proceeds in the negative direction, it accumulates a certain number of negative webers as time progresses and at time t6, for example, the core is completely saturated in the negative direction and from this point forward within this half cycle no additional flux can be added to the core. When the 100 cycle per second energy is cut off at time t1 the core will reside in the negative saturated condition where it started.

Let us now consider the result of the change in output from amplifier 22 which happened at time t3 of waveform B. Just prior to this time t3, the core has saturated in the positive direction as indicated by the straight line segment 67 in waveform E. The portion 65'of waveform D is not sufficiently negative to produce a quantity of webers within the next complete half cycle to saturate the core in a negative direction, consequently for the duration of this period, and even beyond time 14, the core will remain in a positively saturated state.

In waveform F of FIG. 3 an induced current waveform flowing in the secondary winding 26 is represented which is the result of the flux changes in the core 16 as shown in waveform E of FIG. 3. Whenever the core is in the process of saturating to a positive direction a positive-going current results, and similarly whenever the flux changes in the negative direction a negative-going current results. Whenever there is no negative state, the current will exponentially drop to O. The portion 68 of the waveform F represents the positive-going current caused by a change in the flux level from the negative to a positive state. The curve 69 represents the voltage exponentially dropping toward 0 during the time after t5 when the flux saturation is at a substantially constant level. As soon as the flux changes in the negative direction a negative-going current is started which is represented by curve 70. This negative-going current will continue until the flux reaches the negative-state of saturation, and at that time another current curve 69 will be generated, for during this period the current will be attempting to reach 0. Near the end of the on period the flux of waveform E becomes constant on the negative polarity side, and at this time curve 71 is generated in waveform F signifying that the current after some time period drops to 0. If we do examine the point at time t3 in this same waveform F it will be noted that when the saturation level of the flux is in the positive direction, such as indicated by curve 67 of waveform E, the current of waveform F will drop toward 0 exponentially from a positive direction as indicated by curve 72.

The waveform G of FIG. 3 represents the current through the CR relay due to the application of the current such as developed in accordance with waveform F. After a short period of time the initial current will rise sufficiently to energize the CR relay which is shown picked-up at point 73 in this waveform. The inductance of the CR relay is sufiicient to cause some time delay in this circuit, consequently the inductive reactance of the relay will tend to maintain the current flow. A slight reduction in current is shown by curve 74 in this waveform F when the current is tending toward 0. Even a very rapid change in current, such as represented by curve 70 in Waveform F, will not produce a radical change in the curve of waveform G as shown by the curve section '76. When the current again becomes positive-going due to rectifier action of bridge circuit 17, curve 77 will result in the current waveform, and as a result, sufficient current will be continued through the relay to maintain it in an energized condition. It is only after the current drops to 0 as represented by curve 71, that the current, as represented by curve 79, will even more slowly drop to 0. At some level lower than point 73 on this curve such as at 80 the CR relay will drop out. This point is shown at a lower current level than that required to pick up the CR relay, since a relay usually requires more energy for attracting its armature above that required to drop it out. In waveform G at point 81 the CR relay will become deenergized due to the fault occurring in amplifier 22 at time t3, and remain henceforth deenergized until such fault is corrected. This is one condition then under which fail-safe operation is achieved, inasmuch as the decoding apparatus may readily be arranged so that a maintained drop out of the CR relay, rather than a drop out during a coding period, will cause the control serve to check each channel of the amplifiers.

and display apparatus 19 to place the locomotive in a stop condition.

The operation of the push button switches 28 and 29 across the respective receiving coils 11 and 11 in FIG. 2 Since this input alone from each receiving coil should be producing the input to each half of the primary winding of the saturable reactor 16, the elimination of each separately should cause the CR relay to stop pulsating at the intervals of transmission of the pulses. More specifically, when the operator depresses push button 28 it will shortcircuit the induced energy into the receiving coil 11 and thereby provide no output for the upper amplifier channel in FIG. 2. This output is normally fed between ground potential and the input capacitor 36 within the filter 34. When this input signal is eliminated, and providing the lower amplifier channel is Working properly, the saturable reactor 16 will be receiving energy of half-cycle pulses only in the primary winding 25. From FIG. 3 in our former discussion we have ascertained that this condition would result in a positive flux saturation of core 16, and consequently the CR relay would not operate in response to a track code. If normal operation persists when this button 28 is depressed the operator realizes that such operation is caused by some malfunction such as stray voltages which are causing this channel to apparently operate in a normal manner. The operator also has at his disposal push button 29 by which he may similarly short out the induced energy in receiving coil 11' and thereby check whether the lower amplifier channel is really producing any input energy to saturate the reactor 1 Another malfunction which may occur is a short circuit in one amplifier. Let us assume that a shortcircuit having some resistance has occurred in amplifier 22 which is sufiiciently high so that the primary winding 24 will not become open circuited from excessive heat. Rather than provide another illustration, this situation may readily be followed by referring to FIG. 3. A cathode to plate short (not a direct short, for this'is quite uncommon) would cause a large negative current to flow through winding 24 in FIG. 2 thereby producing a. large negative voltage which could be represented as a negative horizontal line in the curve B of FIG. 3 and having a high amplitude fore-shortened negative sine wave pulses as indicated by curve 64. The effect of this high negative voltage may be thought of as a shift in the central axis of the waveform to a rather high negative position. The positive half wave pulses acting with reference to this shifted axis would have no effect in changing the core saturation to the positive side, consequently the core of the saturable reactor 16 would be maintained in a negatively polarized saturated condition. This again would result in no response from the CR relay, consequently the system may be said to be failsafe with respect to a short-circuit occurring in one amplifier.

In FIG. 4 waveforms A through E represent another type of malfunction which produces no input to the CR relay. In waveform A of FIG. 4 the induced track voltages are shown out of phase by 180. This energy will produce the same output from amplifier 22 as before, consequently waveform B of FIG. 4 represents the sarne voltage output as that shown in waveform B of FIG. 3. Since the voltage into the other channel is reversed by 180 the output of amplifier 23, on the other hand, as shown in waveform C of FIG. 4, will be 180 out of phase with respect to that shown in Waveform C of FIG. 3. As before the output from each of these amplifiers is added together, consequently when the waveform B of FIG. 4 is added to that of waveform C of FIG. 4 one will cancel the other resulting in no output as represented by the dotted cancelled waveform D of FIG. 4. It must be remembered that the waveform C of FIG. 4 is inverted due to the push-pull connection into the primary of the saturable reactor 16. Since current input to the saturable reactor 16 is equal and opposing at all times, it will remain in its last saturated condition which as we assumed is usually the negative saturated condition. Because of this, a straight line is represented by E FIG. 4 below the central axis to indicate this negative saturated condition of the core. This again will realize another fail-safe functioning of the system.

It should be noted that either polarized saturated condition causes no energization of the CR relay, the system will remain inactivated, and consequently the control and display apparatus 19 on the locomotive will be placed to a stop condition.

It should be understood that although the embodiment of this invention illustrates electron tubes for amplifiers, transistors may be used as well. Furthermore, it should be understood that a diode clipper or other detection means could also be used as a substitute for the

class B amplifiers

22 and 23.

Having described a continuous inductive cab signal receiving system comprising a saturable reactor as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which the invention may assume, and it is further to be understood that various adaptations, alterations, and modifications may be applied to the specific form shown to meet the requirements of practice without in any manner departing from the spirit or scope of the present invention.

What I claim is:

l. A system for receiving inductively an A.C. voltage that is applied to a conducting means having a loop circuit configuration comprising;

(a) receiving means positioned in inductive relation to said conducting means at opposite sides of said loop circuit, each receiving means being inductively influenced independently by the AC. voltage in its respective opposite side of said loop circuit;

,(b) an amplifying means electrically connected to each said receiving means effective to produce a pair of output signals in predetermined phase relation when the AC. voltage in said conducting means is uniform in both sides of said loop circuit;

(c) means responsive to said pair of output signals effective to produce an output corresponding to the first half cycle portion of one of said pair of signals during the first half of each cycle of said A.C. voltage and an output corresponding to the second half cycle portion of the other one of said pair of signals during the second half of each cycle of said A.C. voltage;

(d) a transformer having a saturable core, a primary winding and a secondary winding, said primary winding effective to saturate said core from one predetermined state to another predetermined state in response to a signal of predetermined amplitude during the first half of each cycle and to saturate said core from said other state to the one state in response to a signal of predetermined amplitude during the secend half of each cycle, said secondary winding opera tive to produce an effective output only while said core is changing from said one saturated state to the other and vice versa;

(e) means operatively connecting electrically the outputs of said last named .means to said primary winding to cause said primary winding to saturate said core from said one state to saidother state in response to one of said pair of signals during the first half of each cycle and to saturate said core from said other state to said one state in response to said other signal during the second half or" each cycle only when said pair of signals are of predetermined amplitude during it V 7 their respective half cycle periods; and

(f) means electrically connected to said secondary winding effective to be operated only while said secondary winding is producing an effective output.

2. A system according to claim 1 wherein said predetermined phase relation between said output signals is 180.

3. A system for receiving inductively an A.C. voltage that is applied to a conducting means having a loop circuit configuration comprising;

(a) receiving means positioned in inductive relation to said conducting means at opposite sides of said loop circuit, each receiving means being effective to be inductively influenced independently by the A.C. voltage in its respective opposite side of said loop circuit;

(b) an amplifying means electrically connected to each said receiving means etfective to produce a pair of output signals of the equal amplitude and 180 out of phase relative to each other when the A.C. Voltage is uniform and of predetermined phase relation in both sides of said loop circuit;

() means responsive to said pair of output signals effective to clip one-half cycle from both said output signals to produce a varying DC. voltage output;

(d) transformer means having a saturable core; a primary winding and a secondary winding, said secondary winding being operative to produce an effective output only while said core is changing from one pre determined saturated state to the other and vice versa;

(e) means electrically connecting the output of said rectifying means to said primary winding effective to cause said primary winding to saturate said core from one state to the other in response to said varying DC. output during each first half of each cycle and to saturate said core from said other state to said one state in response to said varying DC. output during the second half of each cycle when the signals are of predetermined amplitude during both said half cycles; and

4. A system for operating a code responsive device at a rate corresponding to the on and off times of an A.C. voltage that is applied across a pair of track rails only when the A.C. voltage during the on times is of predetermined phase relation in both said track rails, comprising;

(a) a first receiving coil positioned to receive inductively the A.C. voltage in one of said track rails;

(b) a second receiving coil positioned to receive inductively the A.C. voltage in the other of said track rails;

(c) means operatively connected electrically to said first and second receiving coils effective to provide during each cycle of said A.C. voltage a first output corresponding to the A.C. voltage in one of said track rails during an odd half cycle and a second output corresponding to the A.C. voltage in the other track rail during the even half cycle;

(d) a saturable transformer having a primary and a secondary winding and a saturable core, said secondary winding being operative to produce an effective output only when said core is changing from one predetermined state to another predetermined state and vice versa;

(e) circuit means electrically connecting operatively the first and second outputs from said last named means to the primary winding to cause said core to saturate from said one state to said other state in response to the first output of predetermined amplitude in the odd half of each cycle when said core is in said one state at the beginning of said odd half cycle and to cause said core to saturate from said other state to said one state in response to the second output of predetermined amplitude in the even half of each cycle when said core is in said other state at the beginning of said even half cycle;

(f) and code responsive means electrically connected to said secondary winding and responsive to an effective output therefrom.

5. A train control system of the continuous inductive type for railroads wherein an A.C. voltage is applied across the track rails to have distinctive on and off periods at different selected rates in accordance with traffic conditions, comprising:

(a) a first train carried receiving coil positioned in inductive relation with one track rail to receive inductively the A.C. voltage in said one rail;

(b) a second train carried receiving coil positioned in inductive relation with the other track rail to receive inductively the A.C. voltage in said other rail;

(0) a saturable reactor on the train including a primary winding and a secondary winding and a saturable core, said secondary winding being operative to produce an effective output only when said saturable core is being operated from one predetermined saturated state to another predetermined saturated state and from said other state to said one state by an A.C. voltage applied to said primary winding of a predetermined phase and amplitude;

(d) means electrically connecting operatively both said receiving coils to said primary winding effective to induce an A.C. voltage in said core characteristic of the A.C. voltage in said one rail during the first half of each cycle and characteristic of the A.C. voltage in the other rail during the second half of each cycle, whereby said secondary winding provides an effective output only when the A.C. voltage in both said track rails are of a predetermined amplitude and in predetermined phase relation; and

(e) train governing apparatus operatively connected to said secondary winding effective to be operated in response to an effective output from said secondary winding.

6. A train control system of the continuous inductive type for railroads wherein an A.C. voltage is applied across the track rails to have distinctive on and off" periods at different selected rates in accordance with trafiic conditions, comprising:

(a) a first train carried receiving coil positioned in inductive relation with one track rail to receive inductively the A.C. voltage in one of said rails;

(b) a second train carried receiving coil positioned in inductive relation with the other track rail to receive inductively the A.C. voltage in the other of said rails;

(c) amplifying and clipping means electrically connected operatively to each of said receiving coils effective to amplify said inducted A.C. voltage in each of said coils independently and to clip one polarity of each of said A.C. voltages;

(d) a saturable reactor having a primary and secondary winding and a saturable core;

(e) means including said primary winding electrically connected to the output of said amplification and clipping means effective to invert the clipped signal from said first receiving coil and combining said inverted signal with the amplified and clipped signal from said second receiving coil to produce a continuous waveform in said primary winding characteristic of the A.C. voltage flowing in both said track rails;

(f) said core being operative to saturate from one predetermined state to the other predetermined state and from said other state to said one state in response to the waveform applied to said primary winding only when the waveform of each half cycle is in predetermined phase relationship and of a predetermined amplitude;

(g) said secondary winding being operative to produce an effective output only when said core is changing from one saturated state to the other and vice versa;

(h) and means connected to said secondary Winding operative in response to an eifective output from said secondary winding only.

7. A train control system of the continuous inductive type for railroads wherein an A.C. voltage is applied across the track rails to have distinctive on and off periods at different selected rates in accordance with ,"trafiic conditions, comprising:

([7) a second train carried receiving coil positioned in inductive relation with the other track rail to receive inductively the A.C. voltage in said other rail;

() an amplifying means electrically connected operatively to each of said receiving coils eifective to produce a pair of amplified output signals of equal amplitude and 180 out of phase relative to each other when the A.C. voltage in both said track rails is uniform and of predetermined phase relation;

(d) means responsive to said pair of output signals efiective to clip one-half cycle from both said output signals to produce a varying DC. voltage output;

(2) transformer means having a primary winding and a secondary Winding and a saturable core, said secondary winding being operative to produce an effective output only while said core is changing from one predetermined saturated state to the other and vice versa,

(f) means electrically connecting the output of said rectifying means to said primary winding effective to cause said primary winding to saturate said core from said one state to the other in response to the 14 varying DC. voltage during the first half of each cycle and to saturate said core from said other state to said one state in response to the varying DC.

voltage during the second half of each cycle when both said half cycles are uniform; and

(g) means electrically connected to said secondary winding effective to be operated only While said secondary winding is producing an effective output, whereby said last mentioned means is operated in response to the A.C. voltage across said track rails only when said A.C. voltage in one track rail is in proper phase relation with the A.C. voltage in the other track rail and the amplitude of the voltage in both said track rails is uniform.

8. A system according to claim 7 wherein said first and second receiving coils are connected in series and said amplifying means includes a class A amplifier having an output for each of said receiving coils.

9. A system according to claim 8 wherein said clipping means includes a class B amplifier effective to clip one polarity of each output from said class A amplifier during adjacent half cycles.

References Cited in the file of this patent UNITED STATES PATENTS 1,704,110 Snavely Mar. 5, 1929 2,054,676 La Pierre Sept. 15, 1936 2,197,414 Place Apr. 16, 1940 2,649,557 Ransom Aug. 18, 1953 2,676,253 Ayres Apr. 20, 1954 2,731,550 Stafford Jan. 17, 1956 2,731,553 Zaifarano et al Jan. 17, 1956 2,781,479 Rice Feb. 12, 1957 2,959,670 Kendall et a1. Nov. 8, 1960 2,982,851 Maenpaa May 2, 1961 3,030,521 Lucke Apr. 17, 1962

Claims

1. A SYSTEM FOR RECEIVING INDUCTIVELY AN A.C. VOLTAGE THAT IS APPLIED TO A CONDUCTING MEANS HAVING A LOOP CIRUCIT CONFIGURATION COMPRISING; (A) RECEIVING MEANS POSITIONED IN INDUCTIVE RELATION TO SAID CONDUCTING MEANS AT OPPOSITE SIDES OF SAID LOOP CIRCUIT, EACH RECEIVING MEANS BEING INDUCTIVELY INFLUENCED INDEPENDENTLY BY THE A.C. VOLTAGE IN ITS RESPECTIVE OPPOSITE SIDE OF SAID LOOP CIRCUIT; (B) AN AMPLIFYING MEANS ELECTRICALLY CONNECTED TO EACH SAID RECEIVING MEANS EFFECTIVE TO PRODUCE A PAIR OF OUTPUT SIGNALS IN PREDETERMINED PHASE RELATION WHEN THE A.C. VOLTAGE IN SAID CONDUCTING MEANS IS UNIFORM IN BOTH SIDES OF SAID LOOP CIRCUIT; (C) MEANS RESPONSIVE TO SAID PAIR OF OUTPUT SIGNALS EFFECTIVE TO PRODUCE AN OUTPUT CORRESPONDING TO THE FIRST HALF CYCLE PORTRION OF ONE OF SAID PAIR OF SIGNALS DURING THE FIRST HALF OF EACH CYCLE OF SAID A.C. VOLTAGE AND AN OUTPUT CORRESPONDING TO THE SECOND HALF CYCLE PORTION OF THE OTHER ONE OF SAID PAIR OF SIGNALS DURING SECOND HALF OF EACH CYCLE OF SAID A.C. THE VOLTAGE (D) A TRANSFORMER HAVING A SATURABLE CORE, A PRIMARY WINDING AND A SECONDARY WINDING, SAID PRIMARY WINDING EFFECTIVE TO SATURATE SAID CORE FROM ONE PREDETERMINED STATE TO ANOTHER PREDETERMINED STATE IN RESPONSE TO A SIGNAL OF PREDETERMINED AMPLITUDE DURING THE FIRST HALF OF EACH CYCLE AND TO SATURATE SAID CORE FROM SAID OTHER STATE TO THE ONE STATE IN RESPONSE TO A SIGNAL OF PREDETERMINED AMPLITUDE DURING THE SECOND HALF OF EACH CYCLE, SAID SECONDARY WINDING OPERATIVE TO PRODUCE AN EFFECTIVE OUTPUT ONLY WHILE SAID CORE IS CHANGING FROM SAID ONE SATURATED STATE TO THE OTHER AND VICE VERSA;