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Method and apparatus for analyzing traffic and a sensor therefor

  • US 5,877,705 A
  • Filed: 04/22/1997
  • Issued: 03/02/1999
  • Est. Priority Date: 04/22/1997
  • Status: Expired due to Term
First Claim
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1. A sensor for detecting a magnetically permeable mass by disturbance of the earth'"'"'s magnetic field adjacent the sensor, the sensor comprising:

  • a magnetic field detector formed from one or more magnetically variable resistors;

    a flux concentrator for concentrating magnetic flux towards the one or more magnetically variable resistors;

    a biasing means for supplying an electrical bias to the one or more magnetically variable resistors;

    an amplifier for sensing changes in the resistance of the one or more magnetically variable resistors and for producing an output indicative thereof;

    a differentiator for differentiating the output of the amplifier;

    a zero slope detector for detecting the output of the differentiator and for generating a binary changing signal when the output of the differentiator is zero;

    a counter that accumulates values at a predetermined rate; and

    a processor for storing a value of the counter when the zero slope detector generates the binary changing signal, for converting into a first time series profile the stored counter values and for accumulating and storing a count of masses passing the sensor.

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