Method and apparatus for analyzing traffic and a sensor therefor
First Claim
1. An apparatus for detecting vehicles passing a fixed position, the apparatus comprising:
- a first magnetic field detector for generating a first analog signal indicative of changes in magnetic field strength adjacent the first detector in response to a vehicle passing thereby;
a differentiating circuit for differentiating the first analog signal and for producing a first output that changes binary states in response to detecting a predetermined change in the differentiated first analog signal;
a counter which accumulates values at a predetermined rate; and
a processor for storing a counter value for each change in the binary state of the first output of the differentiating circuit, for converting into a first time series profile the stored counter values corresponding to the changes in the first output of the differentiating circuit and for accumulating and storing a count of passing vehicles.
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Abstract
A detector for detecting a characteristic and a speed of a vehicle includes a first magnetic field sensor for generating a first analog signal indicative of changes in magnetic field strength adjacent the first sensor in response to the vehicle passing. A differentiating circuit differentiates the first analog signal and produces a first output that changes binary state in response to detecting a predetermined change in the differentiated first analog signal. A counter accumulates values at a predetermined rate and a microprocessor stores values of the counter corresponding to each change in the binary state of the first output of the differentiating circuit. The microprocessor converts the stored counter values into a first time series profile corresponding to changes in the first output of the differentiating circuit and accumulates and stores a count of a characteristic of the passing vehicle based on the first time series profile. A second time series profile is produced from counter values accumulated in response to the differentiating circuit producing a second output. The second output of the differentiating circuit changes binary state in response to detecting a second analog signal output from a second magnetic field sensor spaced apart from the first magnetic field sensor. The microprocessor detects spaced equivalent positions between the first time series profile and the second time series profile and calculates a speed of the vehicle from the elapsed time between the equivalent positions. The microprocessor accumulates and stores a count of the calculated speed.
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Citations
20 Claims
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1. An apparatus for detecting vehicles passing a fixed position, the apparatus comprising:
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a first magnetic field detector for generating a first analog signal indicative of changes in magnetic field strength adjacent the first detector in response to a vehicle passing thereby; a differentiating circuit for differentiating the first analog signal and for producing a first output that changes binary states in response to detecting a predetermined change in the differentiated first analog signal; a counter which accumulates values at a predetermined rate; and a processor for storing a counter value for each change in the binary state of the first output of the differentiating circuit, for converting into a first time series profile the stored counter values corresponding to the changes in the first output of the differentiating circuit and for accumulating and storing a count of passing vehicles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A sensor for detecting a moving magnetically permeable mass by disturbance of the earth'"'"'s magnetic field adjacent the sensor, the sensor comprising:
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a ferromagnetic strip having a conductive winding wrapped thereabout; a permanent magnet positioned to bias the ferromagnetic strip in a substantially linear part of its BH curve, wherein the magnetization of the ferromagnetic strip remains in the substantially linear part of the BH curve regardless of the orientation of the ferromagnetic strip in the earth'"'"'s magnetic field and regardless of a disturbance in the earth'"'"'s magnetic field; a sensing circuit for sensing a changing inductance of the conductive winding in response to a moving magnetically permeable mass disturbing the earth'"'"'s magnetic field adjacent the ferromagnetic strip and for producing an analog signal output indicative of the changing inductance; a differentiating circuit for differentiating the analog signal output of the sensing circuit and for producing an output that changes binary states in response to detecting a predetermined change in the analog signal output of the sensing circuit; a counter for accumulating values at a predetermined frequency; a capture circuit for storing the current value of the counter in response to a change in binary state of the output of the differentiating circuit; and a processor for processing the stored count to characterize the permeable mass. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method of determining a characteristic of a magnetically permeable mass passing a fixed position, the method comprising the steps of:
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detecting a change in the earth'"'"'s magnetic field at a fixed position in response to a magnetically permeable mass passing thereby; generating an analog signal corresponding to the change in the earth'"'"'s magnetic field; differentiating the analog signal; generating a binary changing signal that changes binary state in response to each occurrence of the slope of the differentiated analog signal changing to zero; recording times when the binary changing signal changes the binary state; producing a time series profile from the recorded times; and determining from the time series profile if a mass has passed the fixed position. - View Dependent Claims (18, 19)
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20. A method of determining a speed of a magnetically permeable mass, the method comprising the steps of:
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detecting a first change and a second change in the earth'"'"'s magnetic field at respective first and second locations in response to a magnetically permeable mass passing thereby, the first and second locations spaced a fixed distance apart along the direction of travel of the magnetically permeable mass; generating first and second analog signals corresponding to the respective first change and second change in the earth'"'"'s magnetic field; differentiating the first analog signal and second analog signal; generating a first binary changing signal and a second binary changing signal that change binary state in response to each occurrence of the slope of the respective differentiated first analog signal and second analog signal changing to zero; recording times when the first binary changing signal and second binary changing signal change the binary state; producing a first time series profile and a second time series profile from the recorded times; comparing the first time series profile and second time series profile; determining equivalent positions in the first time series profile and second time series profile; measuring an elapsed time between the equivalent positions; and calculating the speed of the mass as a function of the elapsed time.
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Specification