US3479502A - Rail vehicle detection system - Google Patents

Description

Nov. l8 i969 J. R. wHlT'rEN RAIL VEHICLE DETECTION SYSTEM Filed June 30, 1967 r A J n In INVENTOR. XAFIES R WHHTEN HIS AWTORNEY United States Patent O ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to rail vehicle location detection and more specifically, to a novel means of establishing the border between adjacent detection zones (i.e., defining the limits of the zones) j In conventional zone occupancy detection arrangements, a source of signal energy, which may be A-C or D-C, is located at one end of a signalling zone, such as a section of railway track, to provide va suitable signal therein. A receiver, which may include a-track relay for example, is located at the other end of Athe signalling zone for receiving the signal energy from the source and is so arranged that the relay is normally energized to indicate the absence of a vehicle within the signalling zone and deenergized to indicate that a vehicle is present therein.

For example, When a track circuit is provided for a section of railway track, the track rails serve as the electrical conductors, and the signal energy applied thereto produces an inter-rail potential. When a train enters the section, its wheels provide a shunt across the track rails decreasing the inter-rail potential at the receiver to such an extent that the receiver becomes de-energized thereby indicating the presence of a train within the section.

One particular prior art arrangement for use with continuous conductive track rails utilizes low impedance connections across the track rails to define the limits of each signalling zone.

For certain applications, difficulty was experienced with this prior arrangement in that unless a sufficiently high frequency signal was employed, the receiver was required to be mounted an undesirably long distance away from the connection defining the zone limit.` Because of the distributed inductance of the track rails, .such a high frequency signal tended to be greatly attentuated so that reliable detection could be achieved only with relatively short signalling zones. Obviouslygthe distance between the receiver and the end of the zone constitutes a blind spot in which a train cannot be detected so that this distance must ordinarily be made as short as possible. Also, unless different frequency signals were employed in adjacent zones or some other suitable means -such as insulated track joints were used, sufficient cross coupling might take place between adjacent zones to give a false indication of non-occupancy of a zone which `for a system requiring fail-safe operation would not be acceptable.

In order for the system to be Afail safe, it is essential that each zone be adequately electrically insulated from the adjacent zone to prevent the cross-coupling of signals between the zones from interfering with the proper detection of zone occupancy. One prior art method of accomplishing this was to generate signals of different fre- 3,479,502 Patented Nov. 18, 1969 ice quencies in different zones. This solution is undesirable due to cost and complexity. In another method low irnpedance paths were provided at the ends of the zone, such as by the use of series resonant circuits or actual shorting bars. Still another method involved the use of insulated joints with the known disadvantages of impedance bonding and the fact that it was not usable with the continuously conductive track rail which is being more widely utilized.

SUMMARY OF THE INVENTION The invention generally contemplates establishing the border between adjacent zones by connecting a pair of capacitors across the rails at points spaced a predetermined distance from one another and associating a detector with each capacitor; A transmitter is loacted in each zone. The foregoing arrangement permits detection of the signal from the transmitter by those detectors which are associated with the zone, and prevents detection of the signal by detectors associated with adjacent zones even though identifically tuned detectors are used in each zone. The aforesaid arrangement provides an improved, efficient system which eliminates the need for short circutis, insulated joints or the like to define the zone limits; which minimizes cross-coupling between adjacent zones so as to prevent false indications of non-occupancy of the zones; which provides a definite termination of detection and/or control zones without the requriement of short circuits; which requires no intricate and complex circuitry; which may readily employ conventional type transmission equipment, such as transmitters, detectors, and the like for efficient operation, which permits the use of the same frequencies in each zone and which permits uniformity of transmitters and detectors in all zones.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, partially broken away view, of the novel zone border applied to a section of rail; and

FIG. 2 is an enlarged view of one of the inter-zone borders.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a pair of rails 3 and 5 are disposed along the right of way an-d divided into a plurality of rail vehicle detection zones, such as zones A, B and C. Each zone has a transmitting means, T, disposed at its center and a detecting means, D, adjacent each end, such as transmitter 40, and detectors 46 and 48 in zone B. Detectors 46 and 48 are coupled to the track rails in any suitable manner so as to detect the signal energy from transmitter T. For example, the transmitter 40 transmits a signal 40 along the zone rail portions 18 and 20 towards `both detectors 46 and 48 which are tuned to the frequency of signal 40. When no train is present in the zone, the detectors 46 and 48 receive the signal 40 and produce an output indicating the zone is unoccupied by a train. When a train 4 is in the zone, it will be located between the transmitter 40 and one of the detectors, thereby shunting the signal 40 and causing it to drop 'below the threshold level of the detector. As a result, the detector will produce zero output thus indicating zone occupancy. For example, when train 4 (dotted) is between the transmitter 40' and the detector 48, the signal 40 is shunted, as shown in dotted lines, and the output of detector 43 is zero. Similarly when the train 4 is located between transmitter 40 and detector 46, the output of detector 46 will drop to zero thereby ycontinuing to indicate zone occupancy. Suitable means (not shown) but known in the art may then relay the zone occupancy information to a previous zone. As is well known, this zone occupancy information may be employed to modify the speed command signal in such previous zones thereby governing vthe passage of the train therein in accordance with the condition of traflic in advance.

In accordance with a preferred embodiment of the invention, the transmitters of adjacent zones, such as transmitters 38 and 42, transmit signals 38 and 42 which, if desired, may be at the same frequency or frequency range as transmitter 40, and each detector, such as respective detector 44 of zone A and detector 50 of zone C, may be tuned to the `same frequency as are detectors 46 and 48 of zone B. In order to permit the same frequency or frequency range to be transmitted and detected in each zone in a fail-safe manner and without interference, novel zone lborders are provided which permit signals of the same frequency to be detected only in the zone in which they are transmitted, and which accomplish this objective without the use of short circuits or insulated joints.

Such novel zone borders, in accordance with the present invention, are illustrated in FIG. 1 by the zone border 7 between zones A and B, and identical zone border 9 between zones B and C. Each novel zone border includes a pair of capacitors spaced from each other by predetermined lengths of rail. For example, border 7 includes a rst capacitor 28, a second capacitor 30, and intervening rail sections 25 and 26 of rails 3 and 5, respectively. The c-apacitor 28 (FIG. 2) may be connected to the rails as by conductors F60 and 61 at points 65 and 66, and capacitor 30 as by conductors 63 and 64 at points I67 and '68. Similarly, border -9 includes a rst capacitor 34, a second capacitor 36, and intervening rail sections 31 and 32. Each border has one of the zone detectors associated with each side of the border, such as the first detector 44 and the second detector 46 of zone border 7 between zones A and B, and the comparable detectors 48 and 50 of zone border 9 between zones B and C.

It has been found that by proper selection of the capacitance of the zone border capacitors, the spacing between' the connections of the capacitors (and thus the length of rail in each of the zone border sections), the amplitude and frequency of the signal transmitted by the transmitters, the threshold level of the detectors and the distance between the transmitter Iand the nearest detectors, a system may be provided, whereby the signal transmitted by the transmitters is detected only by the nearest detector of each zone border, but not 4by the far detector. Thus, the detection of the signal is effectively confined to the Zone in which itis transmitted.

For example, in zone B, by proper selection of the values of frequency and amplitude of signal 40", the capacitance of capacitors 28 and 30, the distance between the transmitter 40 and the beginning of the zone border 7, the length of rail sections 25 and 26 and the threshold level of detectors 44 and 46, signal 40' will be detected only by detector 46 but not by detector 44 at the border 7 between zones A and B. As a result, an elfective zone border is established to prevent the detection in zone A of signals originating in zone B, and vice versa. By a similar arrangement, the cross-coupling of signals between zones B and C is also prevented.

It is to Ibe understood that some signal will appear beyond the zone border; however, where the threshold level of the detectors is properly established, this signal crossing the zone border is too small to be detected by the detector and, therefore, is ineffective.

The values for the length of the zone border rail sections, the zone border capacitors, and the frequency range of the transmitted signal will have certain inter-related practical limitations. First, the maximum frequency which can be used is limited by the desired zone length. The higher the frequency, the shorter the zone length will be, due to the greater attenuation at the higher frequencies. Similarly, there is a limitation on the lowest frequency that can be used since as the frequencies become lower, the zone border rail sections, such as sections 25 and 26, must be lengthened. If the zone border rail sections are lengthened too much, so as to Ibe greater than the length of a train to be detected, then an unacceptable blind spot lwill exist where a train cannot be detected. Thevlength of the zone border rail sections is dened by the points of connectionof the capacitors to the rails, such as between points 65 and 67 on rail 3, and points 66 and 68 on rail 5 as shown in FIG. 2.

One convenient method of arriving at the values of the various components is to rst determine the minimum length of the rail vehicle to be detected, measured from the axles at the front and rear of the vehicle. Next, the maximum zone length can be determined by the known attenuation at the Signal frequency. Then, the capacitance (which is the total capacitance of both members of the capacitance pair) can be determined by the following formula:

where L is the inductance for the zone rail sections between the pair of capacitors. lf such computation should produce a capacitance which is too high for practical purposes, then the proposed zone length can be adjusted in accordance with the foregoing formula, whereby an optimum value for capacitance and zone length is achieved.

The detectors may b e any suitable threshold level detector which provide for one output when the signal present at the detector is above the threshold level and zero output when the signal is below such level. The detectors are preferably connected across the associated capacitor. Thus, as shown in FIG. 2, detector 44 is connected across capacitor 28 by conductors 70 and 71 and detector 46 is connected across capacitor 30 by conductors 72 and 73. The threshold level should be greater than the inter-rail potential at the detector when shunted by the impedance of the wheels and axle of the train to be detected, and greater than the'level of signal cross-coupled from an adjacent zone.

The impedance at each detector must be greater than the maximum shunting impedance of the wheel and axle of a train, and substantially greater than the impedance of the associated capacitor. Since a train generally has a shunting impedance of between zero to 2 ohms, it has been found that a detector having an impedance of at least 4 ohms is preferred.

The impedance at the detector is determined by the capacitance, C, at each end of the rail section 7 (FIG. 2),

by the inductance of the rail section 7, and by the impedance of the other detector. At the radian frequency 1 Wo= VLC the impedance presented to the detector 44 terminals is given by L 1 Zt (n) where ZD is the internal impedance of the detector 46. Similarly, the impedance at the terminals of detector 46 is e ea The threshold level of each detector must be selected to be greater than the level of the maximum signal passing through the capacitor pairs so that the signal cannot be detected by the detector on the far side of such pair from a transmitter. This minimum threshold level may be determined by setting the detector threshold to be slightly below the maximum signal level for the zone transmitter. The attenuation for signals passing through the capacitor pairs would be set at a value of l0 or greater. Therefore, the signal passing through the capacitor pairs would be below the detector threshold.

One particular arrangement constructed in accordance with this invention employed signal energy at a frequency of 80,000 c.p.s. in all the detection zones each of which had a length of about 2,000 feet. Other parameters selected for this particular arrangement were as follows:

Capacitance of each capacitor in pair at each zone border micro-farms" .156 Rail length 7 (FIG. 2) ft-- 50 By the foregoing arrangement, a system of detection is provided which eliminates short circuits and insulated joints in the establishment of a Zone border while enabling the transmission and detection of signals of the same frequency in adjacent zones.

It will be understood that the foregoing description was exemplary only and was not intended to illustrate all related embodiments of the invention, and that `many changes and modifications will occur to those skilled in the art.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A rail vehicle Zone occupancy detection sytem comacross said rails spaced from said rst capacitance means and adjacent said second zone so that sections of said rails are disposed between the points of connection of said rst and second capacitance means to said rails; transmitter means applying signal energy to the track rails of said detection zones; a rst detecting means associated with said rst zone to detect the signal energy from the transmitter means of said rst zone; and a second detecting means associated with said second zone to detect the signal energy from the transmitter means in said second zone; said first detecting means being connected across said rst capacitance means and said second detecting means being connected across said second capacitance means.

References Cited UNITED STATES PATENTS 2,941,069 6/1960 Duteil 246-34 3,069,542 12/1962 Failor 246-34 FOREIGN PATENTS 855,549 12/1960 Great Britain.

73,845 9/1960 France.

ARTHUR L. LA POINT, Primary Examiner G. H. LIBMAN, Assistant Examiner

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