Vehicle presence detection system

• US 6,292,112 B1
• Filed: 12/14/1999
• Issued: 09/18/2001
• Est. Priority Date: 06/25/1992
• Status: Expired due to Fees

• Current Assignee: Primetech Electronics, Inc. (Celestica Incorporated), John Mcallister Holdings Inc.
• Original Assignee: 3461513 Canada Inc.
• Inventors: Bader, Clifford, De Renzi, Charles
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): Nguyen, Tai T.
• Application Number:
  US09/460,793
• Time in Patent Office: 644 Days
• Field of Search: 340/941, 340/341, 340/901, 340/933, 246/202, 246/249, 246/247, 324/178, 324/179
• US Class Current: 340/941
• CPC Class Codes: B61L 29/284 using rail-contacts, rail microphones, or the like, controlled by the vehicle
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

A passive magnetic detector is 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 reversals are detected in the passive detector signal. The reversal signal is analyzed and a train presence output signal is generated for controlling a level crossing gate system or other such crossing warning system. For parallel tracks, pairs of passive magnetic field detectors detect objects over each track and the reversals are analyzed to check that an inbound train does not sneak by undetected as an outbound train is leaving and passing over the same detector pair. At the level crossing, static magnetic field detectors are used to ensure that no equipment remains on the island after detecting that the moving train has left the crossing, so that the crossing gates can be safely lifted as soon as possible.

Claims

1. A train presence detection apparatus for use with a level crossing warning system, the apparatus comprising:

at least one passive magnetic detector provided at ground level or buried below ground level near rails of a railroad track at a distance from said level crossing for detecting a plurality of magnetic field disturbances caused by ferromagnetic objects passing overhead on said track;

magnetic field reversal detector connected to said passive detector for detecting reversals in a magnetic field detected by said passive detector and outputting a reversal signal; and

train presence analyzer analyzing said reversal signal and outputting a train presence output signal.

2. The apparatus as claimed in claim 1, wherein said reversal detector is powered by a DC power line connected to said analyzer, said reversal signal being an AC signal sent over said power line.

3. The apparatus as claimed in claim 2, wherein said AC signal comprises one tone for a positive magnetic field change and another tone for a negative magnetic field change.

4. The apparatus as claimed in claim 2, wherein said reversal detector has a threshold of about 15 milligauss for generating said reversal signal.

5. The apparatus as claimed in claim 2, wherein said train presence analyzer outputs said presence signal when 2 reversals are detected within a period of about 5 seconds.

6. The apparatus as claimed in claim 2, wherein said passive magnetic detector comprises a linear array of search coils, said linear array including a first outermost coil at approximately 1.25 miles from said level crossing, a second of said coils at approximately 1 mile from said crossing, said train presence analyzer means including means for determining a speed of an oncoming train for adjusting a timing of activation of said level crossing warning system.

7. The apparatus as claimed in claim 1, wherein said reversal detector has a threshold of about 15 milligauss for generating said reversal signal.

8. The apparatus as claimed in claim 1, wherein said train presence analyzer outputs said presence signal when 2 reversals are detected within a period of about 5 seconds.

9. The apparatus as claimed in claim 1, wherein a pair of passive magnetic detectors are provided for a pair of rails, said train presence analyzer 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.

10. The apparatus of claim 1 in which the passive magnetic detector is provided in between the rails.

11. The apparatus as claimed in claim 1, wherein said passive magnetic detector is a coil.

12. The apparatus as claimed in claim 1, further comprising communication and power control interface circuitry which can control and power at least two passive magnetic detectors and magnetic field detection circuits.

13. The apparatus as claimed in claim 1, wherein said train presence analyzer means outputs said presence signal when at least three reversals are detected in a five second period.

14. The apparatus as claimed in claim 1, wherein said train presence analyzer means outputs a no train present signal when at least three reversals are detected in a five second period.

15. The apparatus as claimed in claim 1, wherein said passive magnetic detectors are multiple axis magnetometers.

16. The apparatus of claim 15 in which the passive magnetic detector is provided in between the rails.

17. A vehicle motion detector circuit for analyzing at least one passive magnetic field detector output signal to generate a signal indicating on which one of a plurality of lanes or tracks a vehicle is travelling and causing a disturbance in a magnetic field detected by said detector, the detector circuit comprising:

an analyzer analyzing said detector output signal to determine a sharpness thereof and for outputting said lane or track discriminating indicating signal, said sharpness being dependent on a proximity of said vehicle to said magnetic field detector while moving past, whereby the lane or track on which said vehicle is traveling is detected.

18. The circuit as claimed in claim 17, wherein said sharpness of said detector output signal includes signal characteristics selected from the group of frequency of polarity change, intensity and waveform shape.

19. The circuit as claimed in claim 17, further comprising an alarm signal generator 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 on a track or lane adjacent the detector.

20. The circuit as claimed in claim 17, wherein said analyzer includes a magnetic field reversal detector and a comparator comparing a number of reversals within a predetermined time period for determining said lane or track on which said vehicle is traveling.

21. 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 near rails of said railroad track for detecting static magnetic field levels caused by ferromagnetic objects located overhead on said track at said crossing;

a recording device recording, as recorded values, magnetic field level signal values from said detectors when no object is present on said track at said crossing; and

a train presence analyzer comparing signal values from said detectors to said recorded values and outputting a train presence output signal.

22. The apparatus as claimed in claim 21, further comprising:

logic control circuitry which includes the train presence analyzer circuitry;

magnetometer interface circuitry operatively connected to the array of magnetometers and which interface circuitry includes the recording device; and

wherein the logic control circuitry commands the magnetometer interface circuitry to continuously sample and store the magnetic field levels of the array of magnetometers.

23. The apparatus of claim 22, wherein the crossing is located in an island section and which apparatus further comprises a first activity sensor set at a first end of the island and a second activity sensor set at a second end of the island, said first and second activity sensors are operatively connected to activity sensor interface circuitry;

and wherein the magnetometer interface circuitry continues to sample and store the magnetic field levels of the array of magnetometers until activity is detected at the first or second activity sensor, whereupon the sampling is halted and a sample set is created as a base line for train presence analysis.

24. The apparatus of claim 23, wherein the sample set is at least one of the sets of readings taken between the time the crossing is cleared as a result of the generation of an approaching train signal and the sensing of activity at the first or second activity sensor.

25. The apparatus of claim 24, wherein the sample set is an average of several sample sets taken.

26. The apparatus of claim 23, wherein after the train presence analyzer determines the train has exited the island and the activity sensor on the end of the island from which the train will exit signals the train has passed an all clear signal is immediately sent which raises crossing gates and allows use of the crossing by traffic and thereby minimizing any delays in allowing traffic to use the crossing after it is safe for traffic to use the crossing.

27. The apparatus of claim 21 wherein the magnetometer detectors are fluxgate sensors.

28. A method for moving or stationary train presence detection at a railroad crossing comprising the steps of:

sampling magnetic field level signal values from an array of detectors in an island of a grade crossing when no train is present;

recording sets of magnetic field level signal values obtained from the sampling;

comparing the recorded field level signal values with readings taken from the array of detectors; and

generating a train presence detection signal when train presence analysis means detects the presence of a train on comparison of the recorded sets with readings being taken by the array of detectors.

29. The method of claim 28 further comprising the steps of:

continuously sampling the detectors of the array and recording sets of magnetic field level signal values when no train is present in the island;

monitoring the approach to the island from both directions;

generating a train approach signal upon the detection of the approach of a train.

30. The method of claim 29 further comprising the steps of:

clearing the crossing and lowering gates at the crossing after receiving the train approach signal when it is determined the crossing will be unsafe with adequate time for traffic to clear the crossing;

halting sampling by the array upon the receipt of a signal that the train is about to enter the crossing;

generating a sample set of magnetic field level signal values for use as the recorded set, the sample set comprising at least one of the sets recorded between the time the crossing was cleared and the signal halting sampling is received; and

continuously monitoring the array of detectors and comparing these readings with the recorded set to determine at the earliest possible moment when the train has exited the crossing so that gates can be raised and traffic can use the crossing without undue delay after the crossing becomes safe for traffic to use it.

31. The method of claim 30 wherein the step of generating a sample set comprises taking the average of the last several sets of magnetic field level signal values recorded between the time the crossing is cleared and the signal halting sampling is received.

32. A method for the safe control and operation of a railroad grade crossing comprising the steps of:

monitoring the approaches to a crossing for reversal activity which would indicate a train is approaching;

determining that observed reversal activity is the signature of a train and thus indicates the presence of a train;

determining the speed of the train as it approaches the crossing by looking for its signature at successive sensors that the train will pass as it approaches the crossing and thereby specify when to declare the crossing unsafe, with adequate warning time for traffic and pedestrians to clear the crossing;

determining the direction of the approaching train based on the sequence in which the sensors detect the signature of the train; and

declaring the crossing safe when no signature activity exists at any sensor and the sequence of reversal activity in the sensor array indicates that it is not possible for a train of short length to be in transition between outer and inner sensors.

33. The method of claim 32 comprising the further step of:

determining, in a multi-track crossing, the track which an approaching train occupies.

34. The method of claim 33 comprising the further step of:

monitoring for the approach for at least a second train on an adjacent track during passage of the first train through the crossing.