Normalization of inductive vehicle detector outputs

• US 6,876,949 B2
• Filed: 03/07/2003
• Issued: 04/05/2005
• Est. Priority Date: 03/08/2002
• Status: Expired due to Fees

• Current Assignee: Inductive Signature Technologies Incorporated
• Original Assignee: Inductive Signature Technologies Incorporated
• Inventors: Yerem, Geoffrey C., Hilliard, Steven R.
• Primary Examiner(s): Raymond, Edward
• Application Number:
  US10/384,164
• Publication Number:
  US 20030174071A1
• Time in Patent Office: 760 Days
• Field of Search: 702/182, 702185-188, 340/933, 340/941
• US Class Current: 702/182
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

Methods and apparatus for such that a measurement made for a given vehicle by a given detector is substantially repeatable using either the same detector from one time to another, or using a different detector. In one embodiment, normalization coefficients are determined by measuring one or more common probe vehicles and standardizing the outputs of the detector(s) to give a consistent output. In another embodiment, normalization coefficients are determined by measuring one or more operating or circuit parameters of the detector circuit(s), and compensating the outputs of the detector(s) for variations in these measured parameters.

Claims

1. A method for normalizing signatures obtained from a plurality of inductive vehicle detectors, said method comprising the steps of:

a) driving a first vehicle over a first wire loop sensor connected to a first detector;

b) producing a first inductive vehicle signature from said first detector;

c) driving said first vehicle over a second wire loop sensor connected to a second detector;

d) producing a second inductive vehicle signature from said second detector;

e) comparing said first inductive vehicle signature to said second inductive vehicle signature; and

f) determining at least one normalization coefficient from a comparison of said first inductive vehicle signature to said second inductive vehicle signature.

2. The method of claim 1 wherein said at least one normalization coefficient includes a first order coefficient, and said method further including a step of applying said first order coefficient to said first detector.

3. The method of claim 2 wherein said first order coefficient is a scaling coefficient whereby said output of said detector is multiplied by said scaling coefficient.

4. The method of claim 1 wherein said at least one normalization coefficient includes a second order coefficient, and said method further including a step of applying said second order coefficient to said first detector.

5. The method of claim 1 further including a step of manipulating said first inductive vehicle signature to produce a normalized inductive vehicle signature.

6. The method of claim 5 wherein said step of manipulating is performed digitally.

7. The method of claim 1 wherein said steps a) through d) are repeated with a second vehicle.

8. A method for normalizing signatures obtained from a plurality of inductive vehicle detectors, said method comprising the steps of:

a) measuring a first parameter of a first inductive vehicle detector;

b) measuring a second parameter of a second inductive vehicle detector;

c) comparing said first parameter to said second parameter;

d) determining at least one normalization coefficient from a comparison of said first parameter to said second parameter.

9. The method of claim 8 wherein said first parameter is related to a Q-factor of said first inductive vehicle detector, and said second parameter is related to a Q-factor of said second inductive vehicle detector.

10. The method of claim 8 wherein said at least one normalization coefficient includes a first order coefficient, and said method further including a step of applying said first order coefficient to said first detector.

11. The method of claim 8 further including a step of multiplying an output of said first inductive vehicle detector by a factor equal to said at least one normalization coefficient.

12. The method of claim 8 further including a step of manipulating an output of said first inductive vehicle detector to produce a normalized inductive vehicle signature, wherein said step is performed by a differential amplifier.

13. The method of claim 8 further including a step of manipulating an output of said first inductive vehicle detector to produce a normalized inductive vehicle signature, wherein said step is performed by a differential amplifier having a programmable gain controlled by said first parameter.

14. The method of claim 8 further including a step of manipulating an output of said first inductive vehicle detector to produce a normalized inductive vehicle signature, wherein said step of manipulating is performed digitally.

15. The method of claim 8 further including steps of

a) measuring a third parameter of a first inductive vehicle detector;

b) measuring a fourth parameter of a second inductive vehicle detector;

c) comparing said third parameter to said fourth parameter;

d) determining at least one normalization coefficient from a comparison of said third parameter to said fourth parameter.

16. An apparatus for normalizing an inductive vehicle signature, said apparatus including:

a wire loop sensor;

an inductive vehicle detector connected to said wire loop sensor;

a differential amplifier connected to said inductive vehicle detector, said differential amplifier having a gain equal to a first order normalization coefficient;

whereby said differential amplifier multiplies the inductive vehicle signature by said first order normalization coefficient.

17. The apparatus of claim 16 further including a measuring circuit for determining a loop circuit impedance for said inductive vehicle detector and said wire loop sensor, said measuring circuit automatically setting said gain of said differential amplifier.

18. An apparatus for normalizing an inductive vehicle signature, said apparatus including:

a wire loop sensor;

an inductive vehicle detector connected to said wire loop sensor, said inductive vehicle detector producing the inductive vehicle signature;

an analog to digital converter connected to an output of said inductive vehicle detector; and

a processor connected to said analog to digital converter, said processor applying at least one normalization coefficient to the inductive vehicle signature.

19. The apparatus of claim 18 wherein said at least one normalization coefficient includes a first order coefficient, said processor multiplying the inductive vehicle signature by said first order coefficient.

20. The apparatus of claim 18 wherein said at least one normalization coefficient includes a first order coefficient, said processor right-shifting a raw inductance measurement sample.

21. The apparatus of claim 18 wherein said at least one normalization coefficient includes a first order coefficient and a second order coefficient, said processor applying said first order coefficient and said second order coefficient to the inductive vehicle signature.

22. The apparatus of claim 18 wherein said at least one normalization coefficient includes a second order coefficient, said processor applying said second order coefficient to the inductive vehicle signature.

23. The apparatus of claim 18 further including a differential amplifier connected between said inductive vehicle detector and said analog to digital converter, said differential amplifier having a gain equal to a first order normalization coefficient.

24. The apparatus of claim 18 wherein said processor includes a routine that measures an average differential energy of a series of raw inductive signature samples, a sensitivity threshold is adjusted by said average differential energy whereby said average differential energy corresponds to a measure of an average noise level on said series of raw inductance measurement samples.

25. The apparatus of claim 18 wherein said processor includes a routine that

measures a baseline noise level of a series of inductive vehicle signatures on said inductive vehicle detector;

avoids an other detector having a frequency that is identical to an operating frequency of said inductive vehicle detector by selecting said operating frequency having a relatively low baseline noise level;

automatically sets a detection threshold to an optimal level to minimize false detections and maximize real detections;

measures a vehicle detector signal level;

measures a quality of a recent history of vehicle detection events; and

when the quality of said recent history of vehicle detection events falls below a pre-determined threshold, re-evaluating a plurality of operating conditions of said inductive vehicle detector and re-configuring for a more favorable signal-to-noise ratio.