Broken rail detector

[57] ABSTRACT

Herein described is apparatus for detecting a broken rail in a pair of railroad rails. The apparatus includes a transmitter which provides pulses of a predetermined code to a relay which intermittently, according to the code, applies electrical energy to each track at different polarities. A receiver receives the coded energy at a position remote from the transmitter and change m the received code indicates to the transmitter that a change in the track characteristics has occurred.

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PATENTED0CT3 1972

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3,696,243

BROKEN RAIL DETECTOR

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to railroad signalling devices and more particularly to a novel and improved system which detects a break in either one of the rails in a railroad track.

2. Discussion of the Prior Art

Heretofore many systems have been devised to detect a broken rail in a pair of railroad tracks. Included among these are the type which senses disturbances in a magnetic field formed around the railroad track under test. The magnetic field is generated by a high D.C. current which is passed through the rails. Systems of this type are set forth in the prior art.

The use of railroad tracks as a transmission media for coded signal from transmitting to receiving stations has been used in the prior art in the past. Track transmitting and receiving systems presently are used to detect the presence or absence of a vehicle on a track section. In this type of system, the wheels of a train shunt the track to cause a loss of signal at the receiver and thereby indicate the presence of a train in the track area between the transmitter and receiver. In the continuity testing art, pulse signals are transmitted down a suspect transmission line and the magnitude and time relationship between the transmitted and reflected pulses if any, indicates the magnitude and location of the fault, respectively.

The fact that the railroad tracks are now used for an electrical transmission media, the tracks virtually become crowded with electrical signals. This creates a problem that the signals thereon become inseparable and therefore errors can be made in detecting broken rails, detecting presence of vehicles and the like.

In the general field of track circuits used in railway signal systems, a common weakness exists in the lack of ability thereof to reliably detect a broken rail. This weakness is partly because railroad tracks, when used as an electrical circuit, experience a gross change in their electrical characteristics with changes in atmospheric conditions. These changes in electrical properties result in a number of undesirable conditions. For instance, the electrical currents flowing through a track signal circuit between a battery feedpoint and a relay connection to the rails will suffer losses, or attenuation, resulting in an undetermined current flowing through the track relay at any given time. Too, the losses of electrical energy are dissipated into ground, through variable leakage paths, resulting in an uncharted signal circuit current in the ground. As a result of the losses and attenuations first set forth, it is impossible to maintain an exact operating current through the relay without making adjustments to overcome high and low current levels which occur during weather changes. The latter condition results in a possible source of signal current through the ground, which can feed energy back into a rail which has become broken, the level of which depends upon the track ballast conditions. It can be shown that a sufficient current will exist to sustain the operation of the track relay under certain conditions which are commonly encountered in track circuit applications. Thus, a need has arisen for a new electrical system which effectively detects a broken rail.

SUMMARY OF THE INVENTION

Briefly described, the present invention set forth in the described embodiment includes a transmitting means which is coupled to a pair of rails at one end of a track circuit. The transmitter is adapted to apply direct current electrical signals, for example, to each rail in a manner which is coded, either by polarity, time division multiplexing, or both, or the like. The resultant electrical signals impressed on each rail may, for example, have a distinct electrical polarity in relation to each other as well as to a ground reference. Two individual voltage sensing receiving means are included which are designed to accept a particular polarity and code whereby one pair of input terminals is coupled between one rail and earth ground, and the second pair of input terminals is independently connected between the other rail and earth ground. This unique technique of sensing of the track circuit signals is one of the features of this invention. Electronic utilization circuitry is included which will operate a relay continuously until a broken rail or a train is detected.

Using this system, a very positive indication of a broken rail is obtained in the receiver. This indication occurs because the electrical potential on the receiver side of the break in the rail will be the same as ground. Consequently, there will be no input signal to the receiver which is sensing between the broken rail and ground. Further, when a train, or any electrical short circuit, is located between the transmitter and receiver the receiver will detect this condition since both rails will become the same potential with respect to ground. Unbalance in the losses between each rail and ground do not disturb this detection property since this will only result in a change in electrical polarity occurring at one receiver input terminal, which is treated the same as a loss of signal in the receiver sensing circuitry.

The present invention provides a technique of detecting broken rails which is far more effective than devices heretofore set forth. The present invention using the aforesaid techniques is effective in longer lengths of tracks than prior art devices and yet still maintain the precise accuracy needed for current safety standards employed by the railroad industry today. ^J

A further feature of this invention is that when the pulse technique is used, an improved signal-to-noise ratio is possible over the longer length track circuits.

DESCRIPTION OF THE DRAWINGS

These and other features and advantages will become more apparent to those skilled in the art when taken into consideration with the following detailed descriptions wherein like references correspond to like and corresponding parts throughout the several views and wherein:

FIG. 1 is a block diagram of the basic system of one embodiment of this invention;

FIGS. 2a and 2b are block diagrams and partial electrical schematic drawings of the transmitters used in the embodiments set forth;

FIG. 3 is a block diagram of the receiver used in the embodiment set forth in FIG. 1; and

FIGS. 4 and 5 are electrical schematic diagrams of the phase detectors used in the receiver set forth in FIG. 3.

3,696,243

DESCRIPTION OF ONE PREFERRED EMBODIMENT

Turning now to a more detailed description of one embodiment of this invention, there is shown in FIG. 1 a railroad track including a pair of rails, each of which is given the reference numerals 10 and 12. Positioned at one end of the track is a transmitter 14 and at the other end, remote from the transmitter 14, is a receiver 16. Electrical energy is induced into the rails 10 and 12 by the transmitter 14 and received at the receiver 16.

One embodiment of a transmitter used in the embodiment set forth in FIG. 1 is shown in FIG. 2. An oscillator or pulse transmitter 18 is provided and provides pulses of electrical energy to a relay coil 20. The pulses may be of a predetermined time duration so that coded pulses are provided. The relay coil 30 actuates a pair of switches 22 and 24 which applies electrical energy from a battery 26 to the rails 10 and 12 each time they are closed. The battery 26 is arranged to provide electrical energy to each rail 10 and 12 at different polarities. In this embodiment a negative polarity is applied to rail 10 when switch 22 is closed and positive polarity is applied to rail 12 when switch 24 is closed.

The opposite polarity coded pulses are applied to the receiver 16 through the rails 10 and 12. The receiver 16 includes means for determining whether or not both signals are received by the receiver 16. Should one signal be missing, that is, not received by receiver 16, then it is an indication that a broken rail is present between the transmitter 14 and the receiver 16.

An example of a receiver 16 which operates in accordance with one of the principles of this invention is shown in FIG. 3. A pair of input terminals 28 and 29 is coupled directly to the rails 10 and 12 respectively to receive the coded pulses of the transmitter 14. The terminals 28 and 29 are coupled into a pair of frequency selection circuits 30 and 32 respectively which may be band pass filters which are tuned to the frequency of the coded pulse from the transmitter 14. This eliminates any signals from reaching the receiver circuitry and the ultimate utilization circuitry except the pulse coded signals from the transmitter 14. The other inputs of the frequency selection circuits 30 and 32 are connected to the ground reference.

It may be desirous to provide either A.C. signals or a modulated A.C. signal to the rails 10 and 12. To do this, FIG. 2b shows that the battery 26 is replaced with an oscillator 27. For continuous operation, bypass switches 23 and 25 are closed. For modulated signals, bypass switches 23 and 25 are opened and pulser or oscillator 18 is enabled.

Suitable amplifiers 34 and 36 are coupled to the outputs of the frequency selection circuits 30 and 32 respectively to amplify the coded pulses to an acceptable amplitude to be used in the receiver 16 when detecting signal errors.

The signals from the transmitter 14 to the input terminals 28 and 29 may be sinusoidal crossing through the zero crossing point as shown in the graphs 40 and 42. This, then, being a further example of useful transmitted signals, can operate in place of the pulses heretofore mentioned.

Means are then included to set forth whether or not a loss has occurred as to one of the signals. This loss is due to the fact that a rail is broken and continuity of the track circuit is discontinued. This can be accomplished in the remainder of the circuitry set forth in FIG. 3. The circuitry shown therein is operating on the assumption that the signals received are A.C. as shown in graphs 40 and 42 and the transmitter 14 is generating A.C. signals into the tracks 10 and 12.

The signals from amplifiers 34 and 36 appear as shown in graphs 44 and 46 wherein +e_a is the positive going signal and —e_a is the negative going signal from track 10 and +e₆ is the positive going signal and —e_b is the negative going signal from track 12. Both signals e_aand e_b are applied to the primary winding of a transformer 48 and the signals are combined therein to produce the signal shown in graph 50. The primary winding and the secondary winding of transformer 48 are shown in the given relation by the phase dots indicated thereon.

The secondary winding of transformer 48 is applied to a gate generator 52 which generates gate signals as shown in graphs 54 and 56. These gate signals are produced on output leads 58 and 60 and are substantially square wave gating signals of opposing polarities. Such gate generators are well known to those skilled in the art and no attempt will be made at this time to discuss the operation thereof.

The output of amplifiers 34 and 36 are also simultaneously applied to respective phase sensitive detectors 62 and 64 respectively. The phase sensitive detectors 62 and 64 are also responsive to the signals generated by the gate generator 52. Thus, means are herein provided for generating a signal (E, and E₂) which is D.C. for an A.C. continuous wave signal generated by the transmitter 14 or would follow a modulation for a modulated A.C. signal.

The output signals from phase detectors 62 and 64 would be similar to those shown in graphs 66 and 68. It should be noted that these signals are now in phase and have positive polarities. The details of how these signals are generated will be discussed in detail in connection with FIGS. 4 and 5 hereafter.

The outputs of detectors 62 and 64 are applied to voltage level detectors 70 and 72 respectively where only signals of a predetermined threshold level are applied to detector logic circuit 74. The exact structure and operation of such voltage level detectors are well known to those skilled in the art and no attempt will be made to describe this structure and the operation thereof. These voltage level detectors are provided to reduce spurious signals from triggering the detector logic 74.

The detector logic 74 is of the type which gives an output only if both input signals are above threshold levels and of opposite polarities. Such a detector logic is well known to those skilled in the art and can be designed by using “AND/OR” logic. For example, assuming the output of level detector 70 is A and the output of level detector 72 is B, then detect a change in the output 75 from logic circuit 74 (stated in Boolean notation) is:

Output 75 = A B + A · B

The output 75 from detector logic 75 is applied to a demodulator 76. Thus, if a modulated C.W. signal is used, the carrier signal is all that is used to operate a relay drive circuit 78. The relay drive circuit is the type

3,696,243 which is operated when a signal is applied thereto. A Joss of signal from demodulator 76 (or from detector 74 if _a C.W. signal is used) will cause the relay drive circuit to cause relay 80 to drop out and indicate that there is a break in one of the rails or the track is occupied with a train shorting the rails together.

Referring now to FIG. 4, there is shown a circuit of the phase sensitive detector 62 which is responsive to the gate signals from the gate generator 52. Detector 62, in effect, provides semi-continuous wave signals (or modulations to the level detector 70) as long as gate signals are generated in the manner heretofore discussed. The purpose of phase detector 62 is to detect where a change occurs in the phase relationship of the signals applied to terminals 28 and 29 to receiver 16. Specifically, the phase detector detects a loss in signal to either input terminal.

The circuit described in FIG. 4 includes a transformer 100 which has an input winding 102 having one end 103 coupled to the output of amplifier 34. The other end of winding 102 is coupled to the ground reference. The signal applied to transformer 103 across terminal 103 and ground is the sine wave depicted in graph 104. The output winding 106 includes a center tapped output 108 which is coupled to the input of level detector 70.

A pair of insulated gate field effect transistors 110 and 112 have the drain electrodes 114 and 116 thereof coupled to ends 118 and 120, respectively, of output winding 106 of transformer 100.

Field effect transistors 110 and 112 are turned on by the gate signals on leads 58 and 60 generated by gate generator 52. The coupled configuration of field effect transistors 110 and 112 is effective to cause them to be non-conductive from drain to source with zero or negative signal on the gate electrodes 122 and 124 thereof, respectively. The gates 122 and 124 render the field effect transistors 122 and 124 conductive drain to source by positive signals being applied to terminals 58 and 60.

Thus, when a continuous A.C. signal or intermittent modulated A.C. signal is applied to receiver 16, transistors 110 and 112 are alternately enabled in phase therewith. Simultaneous therewith the secondary winding 106 induces a D.C. level (or pulsating D.C.) into level detector 70 through lead 108 as depicted bv graph 126.

The circuit 64 set forth in FIG. 5 operates in a manner similar to that shown in FIG. 4 with the exception that field effect transistor 110' is enabled by positive signal applied thereto from terminal 60 (rather than terminal 58 as set forth in FIG. 4) and field effect transistor 112 is enabled by positive signals applied thereto from terminal 58 (rather than terminal 60). The center tapped output from transformer 100' is ap. plied to lead 108' to level detector 72.

Thus, there is shown in FIGS. 4 and 5 phase detectors 62 and 64 which are capable of providing signals to ultimate logic circuits as long as the opposing relationship thereto is present.

The herein described embodiment of this invention provides one mode of carrying out the invention hereinafter defined in the claims.