Communications: electrical – Vehicle detectors – Inductive
Reexamination Certificate
1999-12-14
2001-09-18
Wu, Daniel J. (Department: 2632)
Communications: electrical
Vehicle detectors
Inductive
C340S901000, C340S933000, C340S398100, C246S202000, C246S249000, C246S247000, C324S178000, C324S179000
Reexamination Certificate
active
06292112
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicle presence detection system for detecting the presence of trains or the like. In particular, the invention relates to a train presence detection apparatus for use with a level crossing gate system or other such warning system equipment, a vehicle motion detector circuit for analyzing a passive magnetic field detector output signal to generate a lane or track indicating signal, and a stationary or slow moving train presence detection apparatus for detecting an object on a railroad track at a level crossing.
BACKGROUND OF THE INVENTION
Conventional systems for detecting the presence of an oncoming train moving towards a level crossing for controlling the level crossing gate system have been relatively unsophisticated. Typically, a voltage between rails in an electrically isolated section is provided, and the conductive wheels of the train passing over the section allow for current to pass which is used to generate a signal for the level crossing gate system. While the reliability of such unsophisticated train presence detection systems is very high, the potential danger to human life by the failure of conventional systems makes it of paramount importance to provide detection apparatus which is as reliable as possible, if not 100% reliable.
In U.S. Pat. No. 4,179,744 to Lowe, a system for analyzing performance of electric traction motor powered railway locomotives is described in which the magnetic fields of electrical operating components of the electric traction motor powered vehicles are sensed. The results of the sensing are used for performance and maintenance evaluation purposes. While the speed of the train is obtained from the measurements, the system described measures the movement and operation of electrical operating components without providing useful information on the movement of vehicles containing no electrical operating components. While most trains in the United States have electric traction motors, it is possible for certain types of long freight trains to have locomotives in the middle or at the rear of the moving train. It is also possible for a train to have its traction motors turned off while still in motion. In the case that the locomotive at the front of the train is absent or turned off, detection of electrical operating components cannot be used as a reliable means for detecting the presence of a train moving towards a level crossing.
In U.S. Pat. No. 4,283,031 to Finch, a magnetic sensor for detecting the movement of a wheel of a rail car is described in which the speed and the direction of the rolling wheel can be determined. The wheel movement measurements from various sensors on each side of the level crossing are used to control the level crossing gate system. The wheel movement sensor disclosed in Finch is an active device mounted in close proximity to the moving wheel and is mounted above ground. By providing the sensor above ground and in a predetermined position adjacent the moving wheels of the train, the sensor is both exposed to the elements and exposed to risk of damage either by the train itself or by vandalism. The wheel sensor disclosed by Finch is not suitable for mounting at or below ground level.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a train presence detection apparatus which is able to detect the presence of ferromagnetic objects moving above ground with accuracy and reliability while safely housing the detection apparatus at ground level or buried below ground level so as to be protected and concealed from the elements, normal maintenance operations and vandals.
It is a further object of the present invention to provide a passive magnetic vehicle motion detector system able to distinguish between vehicle motion on adjacent tracks or lanes.
It is yet another object of the present invention to provide a train presence magnetic detection apparatus which is able to detect an object on a railroad track at a level crossing even if the object is stationary or slow moving.
According to the invention, there is provided a train presence detection apparatus for use with a level crossing gate system or other such warning system, the apparatus comprising: a passive magnetic detector provided at ground level or buried below ground level in between rails of a railroad track at a distance from the level crossing for detecting magnetic field disturbances caused by ferromagnetic objects passing overhead on the track; magnetic field reversal detection means connected to the passive detector for detecting reversals in a magnetic field detected by the passive detector and outputting a reversal signal; and train presence analyzer means for analyzing the reversal signal and outputting a train presence output signal. A magnetic reversal is a change in state or the change in sense in which a magnetic signal is changing by either increasing and then decreasing, or by decreasing and then increasing. It is not necessarily a change in net reversal of the signal through zero.
Preferably, the magnetic field reversal detection means are powered by a DC power line connected to the analyzer means and the reversal signal is an AC signal sent over the same power line. Preferably, the reversal detection means has a threshold of about 15 milligauss for generating the reversal signal.
In another aspect of this invention the AC signal uses one tone for a positive magnetic field change and another tone for a negative magnetic field change.
In yet a further aspect of this invention the train presence analyzer means outputs said presence signal when 2 reversals are detected within a period of about 5 seconds.
In an additional aspect of this invention a pair of passive magnetic detectors are provided for a pair of rails, said train presence analyzer means including means for comparing reversals from said magnetic field reversal detection means for each of said pair of passive magnetic detectors, and said train presence output signal indicates a track on which train presence is detected.
The invention also provides a vehicle motion detector circuit for analyzing at least one passive magnetic field detector output signal to generate a signal indicating a lane or track on which a vehicle is travelling and causing a disturbance in a magnetic field detected by the detector, the detector circuit comprising: analyzer means for analyzing the detector output signal to determine a sharpness thereof and for outputting the lane or track indicating signal, the sharpness being dependent on a proximity of the vehicle to the magnetic field detector while moving past, whereby the lane or track on which the vehicle is travelling is detected.
Preferably, the sharpness of the detector output signal includes a signal characteristic such as the frequency of polarity change in the signal, the intensity of the signal and the waveform shape. Also preferably, an alarm signal generator means is included for generating an alarm signal when a moving vehicle is detected which is on a track or lane closest to the detector but not when a moving vehicle is detected which is on a track or lane adjacent to the detector.
The invention further provides a stationary or slow moving train presence detection apparatus for detecting an object on a railroad track at a level crossing, the apparatus comprising: an array of magnetometer detectors provided at ground level or buried below ground level in between rails of the railroad track for detecting static magnetic field levels caused by ferromagnetic objects located overhead on the track at said crossing; recording means for recording, as recorded values, magnetic field level signal values from the detectors when no object is present on the track at the crossing; and train presence analyzer means for comparing signal values from the detectors to the recorded values and outputting a train presence output signal.
REFERENCES:
patent: 1797302 (1931-03-01), Vantassel
patent: 2224395 (1940-12-01), Kemmerer
patent: 3210539 (1965-10-01), Malaquin
patent: 3271821 (1966-09
Bader Clifford
De Renzi Charles
3461513 Canada Inc.
Anglehart James
Nguyen Tai T.
Swabey Ogilvy Renault
Wu Daniel J.
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