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Single inductive sensor vehicle detection and speed measurement

  • US 5,278,555 A
  • Filed: 06/17/1991
  • Issued: 01/11/1994
  • Est. Priority Date: 06/17/1991
  • Status: Expired due to Term
First Claim
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1. A vehicle monitoring method using an inductive sensor consisting of a single inductive element having an inductance which changes upon the presence of a said vehicle and which is driven by an oscillator to produce an oscillator signal having a period which is a function of inductance of said inductive element and having certain predetermined waveform parameters unique to various particular types of vehicles, the method comprising:

  • (a) setting an initial predetermined threshold beyond which a further change in said period is indicative of the presence of a said vehicle;

    (b) detecting entry of a vehicle into a detection area associated with said inductive element based upon a change in the inductance thereof exceeding said threshold;

    (c) monitoring the period and waveform of said oscillator signal to determine a magnitude of change in said period when the time rate of change significantly decreases and a proportionality value associated with a type vehicle entering the detection area;

    (d) measuring a representative time rate of change of the period during an analysis period which is that time between the time at which the change in the oscillator signal exceeds said predetermined threshold and the time at which the magnitude change is determined;

    (e) calculating an entry distance for a particular type of vehicle by multiplying a predetermined, average entry distance by said proportionality value;

    (f) calculating an entry time by dividing the determined magnitude change in the period by the representative time rate of change of period; and

    (g) providing an output based on said magnitude change, representative time rate of change, entry distance, and entry time.

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