US2509331A

US2509331A - Railway train interval detection system

Info

Publication number: US2509331A
Application number: US775588A
Authority: US
Inventors: Paul M Brannen
Original assignee: Union Switch and Signal Inc
Current assignee: Hitachi Rail STS USA Inc
Priority date: 1947-09-23
Filing date: 1947-09-23
Publication date: 1950-05-30
Anticipated expiration: 1967-05-30
Also published as: IT454470A

Description

May 30', 1950 Filed- Sept. 23, 1947 P. M. BRANNEN 2,509,331

RAILWAY TRAIN INTERVAL DETECTION SYSTEM 2 Sheets-Sheet 1 71min 5 Train A.

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l Z2 59- Z B 1 INVENTOR. "f fimlznezz May 30, 1950 P. M. BRANNEN RAILWAY TRAIN INTERVAL DETECTION SYSTEM Filed Sept. 23, 1947 2 Sheets-Sheet 2 INVENTOR.

,HTIORNEY MN Q r w S R Patented May 30, 1950 RAILWAY TRAIN INTERVAL DETECTION SYSTEM Paul M. Brannen, Duquesne, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 23, 1947, Serial No. 775,588

4 Claims. 1

My invention relates to distance measurin apparatus, and particularly to improved means for measuring the distance between two railway trains.

The usual method of railway operation which provides safety for trains proceeding in the same direction on the same track involves establishment of a space interval between the train in advance and the following train. Among the means for establishing this space interval are the well-known block signaling systems, both manual and automatic, cab signaling systems, etc.

In these systems, a railway is divided into a number of sections or blocks, which may vary in length from a few hundred feet to several miles. Information is supplied to the engineman of the train by wayside or cab signals as to whether the adjacent section in advance is or is not occupied, or if a section some distance in advance is occupied. However, these systems do not provide a continuous measurement of the actual distance between trains, and the train in advance may have just entered a section, or may be leaving at the far end of a section, or may be stopped anywhere within the section.

It is an object of my invention to provide improved means for measuring the distance between two trains on a stretch of railway track.

Another object of my invention is to provideimproved means for continuously and reliably determining and indicating the distance between two trains proceeding in the same direction on a stretch of railway track.

A further object of my invention is to provide improved means for determining and indicating the distance between two trains proceeding in the same direction on a stretch of railway track,

which means will promptly indicate improper operation.

Another object of my invention is to provide improved means for determining and indicating the distance between two trains proceeding in the same direction on a stretch of railway track, which means comprises checking means which normally operates to check the integrity of the apparatus, and which becomes inoperative during the time that the apparatus is measuring and indicating the distance between two trains.

Another object of my invention is to provide improved means of the type described including means for continuously checking the proper operation of the apparatus which checking means is rendered inactive when two trains come within the maximum range of the equipment. so that the checking of the equipment does not inter- 2 fere with the measurement of the distance between the two trains.

In practicing my invention, I provide on the head or front end of each train a first high frequency radio transmitter which is arranged to transmit radio energy at a first carrier frequency, hereinafter referred to as the interrogator frequency, from a first transmitting antenna which is constructed and arranged to radiate substantially all of the energy in a forward direction, 1. e., directive in a forward direction. Also on the head end of each train I provide a first high frequency radio receiver which is arranged to receive radio energy of a second carrier frequency which is different from the first carrier frequency, and is hereinafter called the responder frequency. This receiver receives energy from a first receiving antenna, which is forwardly directive. The transmitter is controlled by a keyer which causes the transmitter to continuously supply short pulses of radio energy of the interrogator frequency to the associated transmitting antenna. An indicator, which may be of the cathode-raytube type, is jointly controlled by the keyer and the first receiver in a manner to be subsequently explained.

.:.-On the rear end of each train, there is provided a second high frequency radio receiver which receives energy from a second receiving antenna, directive to the rear. This second receiver is arranged to respond to radio energy at the interrogator frequency, and controls a sec- 0nd radio transmitter which is arranged to transmit radio energy of the responder frequency from an antenna directive to the rear.

In operation, at the start of a measuring cycle the keyer causes the first transmitter to transmit a short pulse which is radiated in a forward direction from the head end of the train. When this pulse is received by the second receiver located on the rear end of the proceeding train, it is detected and amplified and is then applied to the second transmitter to cause it to transmit a similar pulse at the responder frequency which is radiated rearwardly from the preceeding train.

When this pulse is received by the first receiver,

is is amplified and demodulated, and thereafter supplied to the indicator.

At the time the keyer causes the first transmitter to supply an impulse of radio ener y. an impulse of energy is also supplied to the indicator. By any of several well-known means, the time interval between the sending of an impulse by the first transmitter and the reception of an impulse by the first receiver may be measured, and the information may then be displayed by the indicator. It is apparent that. since the velocity of propagation of radio waves is constant, the travel time of an impulse is proportional to the distance covered, and consequently is proportional to the distance between the trains.

Accordingly, it will be seen that my invention provides for continuous measurement of the distance between the head end of one train and the rear end of the preceding train.

The checking equipment comprises means for recurrently causing each transmitter to supply radio energy of the proper frequency to the receiver associated with the transmitter, and means for detecting the recurrent operation of the receiver by this energy.

Other objects of my invention and features of novelty will be apparent from the following description taken in connection with the attached drawings.

1. shall describe two forms of distance measuring apparatus embodying my invention, and shall then point out the novel features in claims.

In the drawings,

' Fig. 1 is a diagrammatic view of distance measuring apparatus embodying my invention.

Figs. 2 and 3 are illustrations of the face or screen of the indicator under different conditions, and Fig. 4 is a diagrammatic view of a modification of the equipment shown in Fig. 1 to provide checking of the equipment.

In the drawings similar reference characters refer to similar parts in each of the two views.

Referring to Fig. 1, there is shown therein a stretch of railway track i, over which two trains A and B are proceeding from right to left.

The head end of train A is equipped with. the

apparatus shown in a dotted rectangle and comprising a keyer It, a transmitter i2 with its associated antenna M, a receiver is with its associated antenna I8, a sawtooth generator 20, and a cathode ray tube 22. The rear end of train B is equipped with the apparatus shown in a dotted rectangle and comprising a receiver 24 with its associated antenna 26, and a transmitter 28 with its associated antenna 30. The antennas [4, I8, 26, and 30 may be of any conventional type having highly directive characteristics, such as, for example, an array of elements with reflectors and directors. The antennas I4 and I8 are arranged to have a radiation pattern extending forwardly from the head end of train A, and the antennas 26 and 30 are arranged to have a radiation pattern extending rearwardly from the rear end of train B.

In operation, the transmitter l2, which is located on the head end of train A, is continuously pulse modulated by pulses supplied from the keyer l0. As a result, short pulses of radio energy 3| of the interrogator frequency Fl are radiated forwardly from the antenna I4.

Simultaneously with the delivery of a pulse to transmitter l2, the keyer l delivers a pulse to the sawtooth generator 20. The sawtooth gen-- erator provides a deflection voltage for the horizontal deflecting plates 32 of the cathode-ray-' tube 22 and is arranged and constructed so that each time the keyer l0 supplies a pulse of energy to the sawtooth generator 20, the electron beam of the cathode-ray-tube 22 is deflected horizontally across the face 38 of the tube from left to right at a substantially constant rate and then returns to its original position in an extremely short time interval.

Accordingly, each time a pulse of radio energy is radiated from the antenna H, the electron beam of the cathode-ray-tube 22. starts from its initial position at the aft side of the tube, where it is positioned by centering means,- not shown, and sweeps across the face of the tube from left to right at a predetermined speed. The sawtooth wave voltage then drops suddenly to zero and the electron beam is returned to its original position in an extremely short interval of time.

The vertical deflecting plates 34 of the oathode-ray-tube 22 are supplied with energy from the receiver l6. At this time, it is assumed that no signals are being picked up by the receiver I8 and, accordingly, there is no deflecting voltage applied to the vertical deflecting plates 34. As a result, the electron beam is not deflected vertically as it travels across the tube, and, as shown in Fig. 3, the trace 38 displayed on the face 38 of the cathode-ray-tube is a straight line.

The equipment on the rear end of train B is constructed and a ranged so that energy pulses 3! of interrogator frequency picked up by the antenna 26 are supplied to the receiver 24 where the energy is demodulated and amplified, and is then supplied to the transmitter 28. The transmitter 28 is constructed and arranged to supply radio energy of responder frequency to the antenna 30 only upon the supply of energy from the receiver 24. Accordingly, when no pulses of energy of interrogator frequency are picked up by the antenna 26, or when such pulses, if picked up by the antenna 26, are too weak to operate the receiver 24, it will be seen that transmitter 28 remains inactive. When pulses of energy of ihterrogator frequency having sufficient signal strength are picked up by antenna 26, the receiver 24 will cause the transmitter 28 to retransmit pulses of energy of responder frequency F2 I in accordance with the pulses of energy of interrogator frequency which are received.

It will be apparent that the operating range of the equipment may be adjusted by varying the power output of the transmitters l2 and 28, and also by adjusting the sensitivity of the receivers i6 and 24, so that signals of sufficient strength to operate the receivers l6 and 24 will be received only when the trains are within a predetermined distance from each other, and so that the equipment will be inoperative when the distance between the trains exceeds the predetermined distance.

It is now assumed that train A approaches within a predetermined distance of train B, such as for example, 3000 yards. At this time the pulses 3| of energy of interrogator frequency F i are picked up by antenna 26 on the rear end equipment of train B and are of sufiicient strength to operate receiver 24. These pulses are detected and amplified by the receiver 24 and are thereafter supplied to the transmitter 28. As previously explained, the transmitter 28 is arranged and constructed so that it transmits a pulse of energy of the responder frequency F2 in response to each impulse supplied to it from the receiver 24. The pulses of energy of responder frequency F2 are radiated rearwardly from the antenna 30, and are picked up by the receiving antenna l8 on the head end of train A. After being demodulated and amplified by the receiver IS, the pulses are applied to the vertical deflecting plates 34 of the cathode-ray-tube 22, producing a vertical deflection or pip 40 on the trace of the electron beam, as shown in Fig. 3.

Since the electron beam moves across the face of the tube at a substantially constant velocity,

groomer and is started at the time a ulse of energy of interrogator frequency is transmitted, it will be seen that the thne at which the beam is deflected vertically by a pulse of energy of responder frequency is proportional to the time required for the pulse of energy of interrogator frequency to travel from train A to train B, plus the time for a pulse of energy of responder frequency to travel from train B to train A, neglecting the time re 'quired for the receiver 24 and the transmitter 20. to respond to the signal and re-transmit the signal.

The velocity of radio waves in space is approximately 186,000 miles per second, and is substantially constant, so that if the time required for the signals to span a distance is known, that distance can be accurately determined.

As shown in Figs. 2 and 3, a scale on which suitable distances are marked is affixed to the face 38 of the cathode-ray-tube 22, and is'calibrated so that the point at which the vertical pip so appears indicates thee between -train A and train B. This scale is corrected to allow for the delay between the reception of a pulse by the receiver 24 and the re-transmission of the pulse by transmitter 28. The .pip" d9 shown in Fig. 3 stands at the first large division on the scale, which may indicate, for example, a distance of 1000 yards.

. It will be apparent that, as the distance between the train A and train B changes, the "pip" 65 will move in accordance with the change. If the distance between the trains increases, the pip dd will move to the right a proportional distance shown, is provided for the head end and for the rear end equipment, the positive and negative terminals of these sources are designated as x and 0, respectively. There is also provided the usual source of plate, bias and filament voltage necessary for the operation of the electron tubes.

The coding devices CTA and-0TB are continuously connected to the low voltage source of energy and are equipped with contacts which are recurrently operated at a selected rate, for exampie, 180 times per minute, and may be of the type shown and described in Letters Patent of the United States No. 1,913,826, issued to Herman G. Blosser on June 13, 1933.

In operation, pulses from the keyer l0 modulate the transmitter i2 to thereby cause the along the trace 36, and if the distance between the trains decreases, the pip" 60 will move to the left a proportional distance long the trace 38 toward the zero mark of the scale.

When train B approaches within a very short distance of train A, say, for example, 100 yards, the time required for the pulses of radio energy to travel between train A and train B becomes too short for the equipment to measure accurately,

but the reflected pulses still show as a pip" on or near the zero mark of the scale, thereby indi cating that train A is extremely near train B.

From the foregoing it will be seen that my invention provides means for detecting the presence of a train ahead of another train, and provides a continuous indication of the distance between the trains between certain predetermined mammum and minimum distances.

In Fig. 4, there is shown a modification of the equipment shown in Fig. l and described above. The arrangement as shown in Fig. 4 provides means for continuously checking the operation of the equipment and provides a warning if the equipment is functioning improperly or is not functioning.

The equipment on train A and train B is similar to that shown in Fig. 1, but in addition there is provided on train A an auxiliary receiver at and its associated antenna 45, an auxiliary transmitter 48 with its associated antenna 50, a code foilowing relay DRA, a decoding transformer D'lA, a code detecting relay CRA, an indicator lamp KA, a warning bell XA, and a coding device CPA. The equipment on train B is supplemented with an auxiliary transmitter 52 with its associated antenna 54, an auxiliary receiver 56 with its associ ated antenna 58, a code following relay DRE, a decoding transformer DTC, a code detecting re.- lay CRB, an indicator lamp KB, a warning KB and coding device CTB. Y

.; Additionally, a low voltage source of energy, not.

transmitter J2 to continuously transmit short pulses 3| of radio energy of interrogator frequency Fl which are radiated in a forward direction from train A by the antenna I4. A ortion of the energy radiatedin these pulses is picked up by the antenna 66, and is demodulated and amplified by the auxiliary receiver 44. During the closed periods of contact 60 of code transnutter CTA the amplified pulses are supplied to the auxiliary transmitter 58 over the circuit including front contact 84 of relay CRA and back contact 08 of relay DRA and cause the transinitter 68 to transmit pulses of energy of responder frequency from its associated antenna 88. The energy radiated from antenna 50 is "picked up by the receiving antenna is and is demodulated and amplified by the receiver it and is then supplied to relay DRA. Accordingly, it is apparent that during the time that contact E8 of coding device CTA is closed, a pulse of energy of responder frequency is supplied through auxiliary transmitter 68 to the receiver I6 each time that a pulse of interrogator frequency is radiated from the antenna M.

The code following relay DRA is supplied with energy from the output of the receiver i6 and is constructed and arranged so that its contacts will not be picked up by the usual noise" present in the receiver, but will be picked up when and only when a signal of responder frequency of a predet'ermined energy level is supplied to the receiver 1 6. when the contact of coding device CTA is picked up, the recurring supply of pulses from auxiliary transmitter 68 through the receiver it will cause the code following relay DRA to pick up its contacts. Although the duration of the dividual pulses is very short, the repetition fre- A army is such that as long as contact 60 of code transmitter GPA is closed substantially continuoils energy is supplied to the relay DRA with the result that the contacts'of relay DRA pick x31) and remain picked up throughout each closed period of the contact of code transmitter CTA.

a, time interval, the coding device CTA o'pens its contact 60 thereby interrupting the supply of pulses to the auxiliary transmitter 50. As a result, the relay DRA is no longer supplied with energy from the receiver i6 and the contacts of relay DRA release.

After a time interval, the contacts of coding device CTA again close, and pulses of energy of responder frequency are again supplied by the auxiliary transmitter to the receiver I6 in the of responder frequency are being returned from the rear end of a preceeding train, and recurrent groups of pulses of energy of responder frequency are supplied locally to the receiver II from the auxiliary transmitter 48, and the relay DRA picks up and releases its contacts in accordance with the groups of pulses received by receiver IS.

The relay DRA has associated therewith a code detector relay CRA which is energized by current supplied through the decoding transformer DTA when and only when the code following relay DRA follows coded energy, as explained in Letters Patent the United States No. 2,237,788 to Frank H. Nicholson et a1.

At this time, therefore, the recurrent operation of thecontacts of relay DRA causes the contacts of relay CRA to pick up and remainpicked up. Front-contact e: of relay CRA establishes the circuit for supplying energy to the indies tion lamp KA, leach contact 6'2 interrupts the circuit for supplying energy to the warning hell Xe, and front contact to in the circuit traced for. the auxiliary transmitter d8 remains closed.

The control grid $58 of cathode -ray tuhe 22 is supplied with a negative bias voltage from a source designated B(-) by a circuit including contact to of code transmitter CIA and a front contact Bil oi relay CRA in multiple with a hack contact of relay DEA, so that the trace #38 of the electron beam or the cathode-rey tuhe shown in Fig. 2 is recurrently flashed during the time that the coding device (ETA is operating and this flashing of the trace on the face of the cathode-ray-tuhe indicates the operation of the coding device CTA. Intensity modulation of a cathode-ray-tube in this manner is welidrnown in the art.

From the foregoing it will be seen that during the time in which there is no train having rear end equipment within range, the equipment located on the head end or a train operates to continuously transmit pulses of energy of the interrogator frequency. At recurrent intervals, pulses of responder frequency are transmitted to the receiver on the head end of the train from an auxiliary transmitter in response to the reception of pulses of interrogator frequency detected by an auxiliary receiver. The recurrent response of a code following relay to the received pulses of energy of responder frequency causes a detector relay to be picked up, which relay controls ap propriate indication circuits to indicate the proper functioning of the equipment.

The equipment provided for the rear end of each train, and shown in Fig. 4, comprises a receiver 24 with its associated antenna 26, a transmitter 28 with its associated antenna 30, an auxiliary transmitter 52 and antenna 54, an auxiliary receiver 56 and antenna 58, a code following relay DRE, :3, code detecting relay ORB with its associated decoding transformer DTB, an indication light KB, a warning bell XB, and a coding device CI'B similar to the coding device CTA previously described.

It is assumed at this time that the equipment is operating normally and that the rear end equipment shown in Fig. 4, is not within operating range of a train carrying the head end equipment previously described. The coding device CTB is continuously connected to the source of energy, and its contact I0 is recurrently opened and closed at a predetermined rate. When contact of coding device CTB is closed, a circuit for supplying energy to the auxiliary transmitter 52 is established. This circuit is traced from the positive terminal of the high voltage source desig nated B,(+), over contact I0 of coding device CTB, and over-front contact 12 of relay CR3 to the auxiliary transmitter 52. when relay D83 is released its contact 14 also provides a circuit for supplying energy to transmitter 52 when the contact 10 of coding device CTB is closed. Accordingly at this time, the transmitter 52 transmits radio energy of interrogator frequency from its associated antenna 54 during the periods in which contact 10 of coding device CTB is closed.

This energy is picked up by antenna. 26 and is detected and amplified by the receiver 24, and is then supplied to the transmitter 28, which thereupon transmits energy of responder frequency which is radiated from antenna 30. This energy is picked up by the antenna 68 and sup- .plied to the receiver 56 where it is demodulated,

amplified and supplied to the code following relay 333.. The code following relay DRB is constructed and arranged so that it will pick up when and only when a signal of predetermined energy ievel is picked up by the antenna 58 and will not pick up its contacts as a result of the I usual "noise in the output of the auxiliary receiver 55.

Accordingly, the contacts of relay DRE will pick up at this time.

When contact Ill of coding-device CTB moves to its open position, the supply of energy to the auxiliary transmitter 52 is interrupted, and as a result radio energy of interrogator frequency is no longer supplied to the receiver 24. Accordingly, the transmitter 28 ceases to supply energy of responder frequency to its antenna 30. With the interruption of the supply of energy of responder frequency, the auxiliary" receiver 56 no longer supplies to the relay DRB sufilcient energy to keep the relay contacts picked up, and its contacts release.

After a short time interval, contact 70 of coding device C'I'B again closes, and, as previously explained, the various components of the equipment operate with the result that the contacts of relayDRB again pick up.

From the foregoing it will be seen that the recurrentoperatlon of contact In of coding device CT'causes recurrent operation of the com tacts of 'relay DRB. By means of the decoding transformer DTB and the relay CRB, the recurrent operation of the contacts of relay DRB is detected, as previously explained in connection with the equipment provided on the head end of the trains.

As long as the equipment is functioning properly, 'the recurrent operation of the contacts of relay DRB supplies energy through the decoding transformer DTB to the relay CRB andthe contacts of code detecting relay CRIB are picked up.

Front contact 16 of relay CRB establishes the circuit. for supplying energy to the indication lamp KB, and back contact 16 of relay CRB interrupts-the circuit for supplying energy to the warning bell XB.

It will be apparent from the foregoing description that if any part of the equipment becomes defective, the relay DRB will remain continuously energized or deenergized. For example, if the receiver 24 should become inoperative, the transmitter 28 would not transmit pulses of responder frequency and the auxiliary receiver 5' would not supply sufficient energy to relay DRB to pick up its contacts, and its contacts would remain released. Likewise, if the transmitter 28 should become'deraneed so that it "continuously transmits energy regardless of whether or not energy was supplied thereto from the receiver 24, the auxiliary receiver 58 would continuously supply energy to the relay BBB, and its contacts would remain continuously picked up.

The cessation of operation of the contacts of relay DRB interrupts the supply of energy to the relay CR3 and its contacts release. When contact 1B of relay CRB releases, it interrupts the supply of energy to the indication lamp KB, and establishes the supply of energy to the warning bell XB, which indicates to the trainmen either that the equipment hasfailed, or as hereinafter explained, that a following train is within operating range of the equipment so that the proper precautions may be taken to protect the train from'being overaken by a following train.

Additionally, it will be seen from the above description that the equipment on train A will function in a similar manner to indicate a failure of the equipment. For example, if the receiver it should become inoperative, the relay DRA would not receive sufilcient energy to pick up its contacts, and its contacts would remain continuously released, or, should the auxiliary transmitter 48 become defective, so that it continuously sup plies energy to its antenna 50, th receiver it would continuously supply energy to relay DRA, and the contacts of relay DRA would be continuously picked up. As a result, the supply of energy to relay CRA through the decoding transformer DTA would be cut ofl, and the contacts of relay CRA would release. When contact 62 of relay CRA releases, it interrupts the supply of energy to the indication lamp KA and establishes the supply of energy to the warning bell XA, which indicates to the trainmen either that the equipment has failed, or as hereinafter explained, that a preceding train is within operating range of the equipment and that the equipment will now operate to measure the distance between the trains.

It is to be understood that the auxiliary transmitters t8 and 52 may be constructed and arranged to have a power output which is weaker than the weakest signal which the receivers l6 and 2t will receive when the trains are separated by the maximum distance through which it is desired to detect and measure the interval between the trains. Additionally, the auxiliary receivers M and 56 may be constructed and arranged so that they will not respond unless the transmitters l2 and 28 are operating at* their maximum power output, to thus insure that a drop in the efficiency of the equipment will be promptly detected.

I will now assume that the train A approaches within the operating range of the head end and rear end equipment which range may be, for example, 3000 yards.

When this occurs the antenna 28 on the rear of train B picks up the pulses of energy of interrogator frequency transmitted by the head end equipment of train A in addition to the energy recurrently supplied by auxiliary transmitter 52. As pointed out above, the transmitter l2 on the head end of train A transmits energy of the interrogator frequency substantially continuously. Accordingly, when this energy is received on train B, the substantially continuous supply of energy to the receiver 24 causes the transmitter 28 to transmit energy of responder frequency substantially continuously. The auxiliary receiver 56, in

response to the substantially continuous supply of energy picked up by its antenna 58, supplies energy to relay DRB to keep the relay contacts continuously picked up. The supply of energy I is to the relay CRB is interrupted on the cessation of operation of the contacts of relay BBB, and relay CRB releases its contacts with the result that the indication lamp m is extinguished and the warning bell X8 is sounded.

Additionally, when contact I2 of relay CRB releases it interrupts the circuit previously traced for supplying energy to the auxiliary transmitter 52 and as a result, the recurring transmission of energy of the interrogator frequency from the auxiliary transmitter is cut oil. Thereafter, the transmitter 28 transmits a pulse of energyof responder frequency each time a pulse of interrogator frequency transmitted by the equipment on train A is received by the receiver 24. The repetition rate of these pulses is sumciently fast to provide a substantially continuous output from the auxiliary receiver 56 to relay DRB, with the result that the contacts of relay DRB remain picked up, and relay CRB remains released as long as the equipments of trains A and B are within operating range of each other.

It will be seen from the foregoing that when the equipments on trains A and B are within operating range of each other, the recurrent operation of the relay DRB ceases, and the relay CRB releases to interrupt the recurrent operation of the auxiliary transmitter 52. Thereafter, the equipment operates in such manner that a, pulse of responder frequency is transmitted each time a pulse of interrogator frequency is received.

As previously explained, at the time train A advances close enough to train B to be within the operating range of the equipment, the equipment on the head end of train A is continuously transmitting pulses of interrogator frequency, a portion of which are received by the auxiliary receiver M and are supplied to the auxiliary transmitter 48 by the circuit including contact 50 of coding device CTA. The response of the receiver it to these pulses causes the contacts of relay DRA to operate recurrently and the relay CRA therefore is energized.

When the pulses of responder frequency radiated from the rear end of train B are picked up by antenna it of train A, they cause energy to be substantially continuously supplied from receiver it to relay DRA with the result that the contacts of relay DRA pick up and remain picked up. Relay CRA thereupon releases, since energy is no longer supplied to the relay through the de coding transformer DTA. When contact 62 of relay CRA releases, it interrupts the circuit for the indication lamp KA and sounds the warning bell XA, to thereby call the attention of the trainmen on train A.

When relay CRA releases, its front contact 66 interrupts the circuit for supplying pulses from the auxiliary receiver 44 to the auxiliary transmitter 48. However, the repetition rate of the pulses of. energy of responder frequency which are received from train B is such that the relay DRA is maintained picked up.

Also, when relay CRA releases, its front contact interrupts the biasing circuit for the control grid 68 of the cathode-ray-tube 22 so that the trace on the face of the cathode-ray-tube is not recurrently flashed at this time.

At this time, when the keyer 10 supplies a pulse to operate the transmitter H, a pulse is also supplied to the sawtooth wave generator 20 to provide a deflection voltage for the deflecting plates 32 of the cathode-ray-tube. When a pulse of responder frequency is supplied to the receiver it, it supplies a momentar demaybe provided a scale on the face 38 of the cathode-ray-tube, graduated in convenient distances, and the distance from the beginning of the trace to the pip is proportional to the distance between the trains. Therefore, by means of the aforementioned scale, the direct distance from the head end of train A to the rear end-of train B may be read directly from the scale.

Let it now be assumed that the train A decreases its speed, or train B increases its speed, so that the trains become separated by a distance greater than the operating range of the equipments.

At this time the pulses of energy of interrogator frequency picked up by the antenna 28 of the rear end equipment located on train B become too weak to operate the receiver 24, and as a result, the supply of impulses from the receiver 24 to the transmitter 28 is cut oil, and the transmitter 28 ceases to transmit. Accordingly, pulses of responder frequency are no longer picked u by the antenna 58, and the auxiliary receiver 56 ceases to supply energy to relay DRB.. When the relay DRB releases its back contact H establishes the circuit includingcontact Ill of code transmitter OTB for recurrentlv supplying energy to the auxiliarytransmitter 52. I

When the coding device C'IB closes its contact 10, energy of interrogator frequency is supplied from the auxiliary transmitter 52 to the receiver 24, which'then causes transmitter 28, to transmit energy of responder freouency to the auxiliary receiver 56. The response of auxiliary receiver 58 to the supply of energy of responder frequency causes the relay DRB to pick up and its contact H interrupts the supply of energy to the auxiliary transmitter with the result that the transmission of energy outlined above is interrupted and the contacts of relay DRB release. When relay DRB releases, its contact '14 again establishes the sunply of energy to auxiliary transmitter 52 andthe cycle described above isrepeated. The rate of operation of the coding device CT is such that the relay DRB will complete several cycles ofthe "door bell action described above during one closed period of' the contact of coding device CT.

The door bell" action of the contacts of relay DRB causes energy to be supplied through the decoding transformer D'IB to relay CRIB, which thereupon picks up its contacts. when contact 12 of relay ORB picks up, it establishes the circuit previously traced for supplying energy to the auxiliary transmitter 62. and when contact 1 of relay'CRB picks up it establishes the circuit for supplying energy to the indication lamp KB and interrupts the supply of energy to the Waming bell 'XB.

The rear end equipment of train 13 is now restored to its normal condition as previously described. The apparatus on the head endof train A also shows when the trains A and B become separated by a distance greater than the operating range of the equipments. When the trains become separated by this distance, the value of the energy of the impulses of responder frequency supplied to the receiver It falls below the amount required to cause the receiver It to supply suflicient energy to maintain the contacts of relay DRA picked up, and as a result the conta ts 0! this relay release. When releases, it establishes the circuit including the contact of code transmitter CTA for supplying pulses of energy from, the auxiliary re-,

When contact 66 of relay DRA picks up, it' interrupts the circuit for connecting the receiver H to the transmitter 48, and the consequent interruption in the supply of pulses of responder frequency to the receiver It causes the relay DRA to be deenergized and when contact 66 of relay DRA releases, the cycle described above 1 is repeated.

'I'he recurrent pickup and release of the contents of relay DRA again causes energy to be supplied to the relay CRA through decoding transformer MA, and when contact 04 of relay CRA picks up it establishes the circuit previously traced for connecting the auxiliary receiver 44 to the auxiliary transmitter 48.

When contact 62 of relay CRA picks up, it interrupts the supply of energy to the warning bell XA and establishes the circuit for supplying energy to the indication lamp RA.

The equipment on the'head end of train A is now restored to its normal condition as previous.- ly described. v Y

From the foregoing it will be seen that my invention provides means for measuring and indi-- cating the distance between two trains proceeding in the same direction on a stretch of railway track, and additionally provides means for continuously checking the apparatus and promptly indicating a failure which might result in the non-detection of a train. Additionally. my invention provides means for measuring and indi eating the distance between two trains proceeding in the same direction on a stretch of railway claims without departing from the spirit scope of my invention. Having thus described my invention, what I claim is: a

1. In a system for the measurement ofthe tance between a first and a second vehicle, in combination, means located on said first vehicle for generating and radiating pulses of energy of a first frequency, means located on said second vehicle for receiving said pulses of energy of said first frequency and retransmitting pulses of energy of a second frequency, means located on said first vehicle for receiving said pulses of energy of said second frequency, indicating means located on said first vehicle and governed by said receivingmeans for visually indicating the time contact 66 of relay DRA can vehicle, auxiliary transmitting means for transmitting energy to the receiving means or -the same vehicle, means for recurrently causing the operation of said auxiliary transmitting means,

means for detecting the response of said receiving means to energy received from said auxiliary transmitting means, and indicating means controlled by said detecting means.

2. In a system for measuring the distance between a first and a second vehicle comprising a first principal radio transmitter located on said first vehicle for transmitting pulses of radio energy of a first frequency to said second vehicle at a certain pulse rate, a first principal radio receiver located onsaid second vehicle for receiving pulses of radio energy of said first frequency, a second principal radio transmitter located on said second vehicle for transmitting pulses of radio energy of a second frequency to said first vehicle, a second principal radio receiver located on said first vehicle for receiving pulses of radio energy of said second frequency, and means located on said first vehicle for measuring the time interval between the transmission of a pulse by said first principal transmitter and the reception of a pulse by said second principal receiver,-to thereby indicate the distance between said first and said second vehicle, the combination with the foregoing apparatus of checking means located on each vehicle for continuously and reliably checking the proper operation of the apparatus, said checking means comprising, a first auxiliary radio transmitter and a first auxiliary radio receiver located on said first vehicle, a second auxiliary radio transmitter and a second auxiliary radio receiver located on said second vehicle, a coding device located on each vehicle, said coding devices having contacts which are recurrently operated at a rate substantially less than said pulse rate, a first code following relay responsive to energy supplied from said econd principal receiver, a second code following relay responsive to energy supplied from said second auxiliary receiver, a first code detecting relay energized when and only when said first code following relay is following code, a second code detecting relay energized when and only when said second code following relay is following code, a warning device on said first vehicle governed by said first code detecting relay, a warning device on said second vehicle governed by said second code detecting relay, circuit means on said second vehicle for causing said second auxiliary transmitter to operate each time said coding device associated therewith closes its contacts provided said second code detecting relay is picked up or said second code following relay is released, and means for causing said first auxiliarytransmitter to operate in response to pulses of radio energy received by said first auxiliary receiver when and only when the contacts of the associated coding device are closed provided said first code detecting relay is picked up or said first code following relay is released.

3. In a system for measuring the distance between a first and a second vehicle comprising a first principal radio transmitter located on said l ergy-ofafirst frequency to said second vehicle at: a certain pulse rate, a first principal radio receiver located on said second vehicle for receiving-pulses of radio energy of said first frequency, a second principal radio transmitter located on said second vehicle for transmitting pulses of radio energy of a second frequency to said first vehicle, a second'principal radio receiver located on said first vehicle for receiving pulses of radio energy of said second frequency, and means includinga cathode-ray-tube having a control electrode located on said first vehicle for measuring the time interval between the transmission of a pulse by said first principal transmitter and the reception of a pulse by said second principal receiver, to thereby indicate the distance between said first and said second vehicle, the combinatlon with the foregoing apparatus of checking means located on each vehicle for continuously and reliably checking the proper operation of the apparatus, said checking means comprising, a first auxiliary radio transmitter and a first auxiliary radio receiver located on said first vehicle, a second auxiliary radio transmitter and a second auxiliary radio receiver located on said seccond vehicle, a coding device located on each vehicle, said coding devices having contacts which are recurrently operated at a rate substantially less than said pulse rate, a first code following relay responsive to energy supplied from said second principal receivena second code following relay responsive to energy supplied from said second auxiliary receiver, a first code detecting relay energized when and only when said first code following relay is following code, a second code detecting relay energized when and only when said second code following relay is following code,

a warning device on said first vehicle governed I by said first code detecting relay, a warning device on said second vehicle governed by said second code detecting relay, circuit means on said second vehicle for causing said second auxiliary transmitter to operate each time said coding device associated therewith closes its contacts provided said second code detecting relay is picked up or said second code following relay is released, means for causing said first auxiliary transmitter to operate in response to pulses of radio energy received by said first auxiliary receiver when and only when the contacts of the associated coding device are closed provided said first code detecting relay is picked up or said first code following relay is released, and a circuit including a contact of the associated coding device for applying a bias voltage to the control electrode of said cathode-ray-tube.

4. In a system for the measurement of the distance between a first and a second vehicle, in combination, means located on said first vehicle for generating and radiating pulses of energy of v ceiving means for visually indicating the time between the radiation of a pulse from said first vehicle and the reception of a pulse from said second vehicle, and means located on said first vehicle for checking the operation of said system, said checking means comprising auxiliary receiving means responsive to energy transmitted first vehicle for transmitting pulses of radio n 7 from said vehicle, auxiliary transmitting means can:

' 15 for transmitting energy to the receiving means 01' the same vehicle, means for recurrently causmeans controlled by said detecting means.

PAUL M. REFERENCES crrEn The following references are of record in the file of this patent:

1B UNITED STATES PATENTS N ber N ing the operation of said auxiliary transmitting 3 fii ig ,g means, means for detecting the response of said 3398.333 Tu'ot 1937 receiving means to energy received from said 5 3,134,718 Gum 1938 auxiliary transmitting means, and. indicating 3. 5

OTHER REFERENCES Pr 0! the IRE. vol. 30. No. 3, pp. 129 I, to 131 March