VEHICLE DETECTOR WITH AUTOMATIC SENSITIVITY ADJUSTMENT

摘要

VEHICLE DETECTOR WITH AUTOMATIC SENSITIVITY ADJUSTMENT A vehicle detector in which the sensitivity is adjusted by first measuring the period Tnv of an oscillator signal produced by an oscillator whose frequency varies as the inductance of an inductive sensor changes. That inductance is in turn changed by a vehicle entering a detection area. A number Nmeas of cycles of the oscillator signal, representing a measurement period, is then determined based upon the measured oscillator period Tnv and upon a desired minimum change in inductance .DELTA.L (sensitivity) which will result in an object being detected. The length of subsequent measurement periods, defined by Nmeas oscillator cycles, is therefor periodically determined, compared to a reference value, and an output is provided if the compared difference exceeds a threshold value. The desired minimum change in inductance .DELTA.L (sensitivity) may be automatically adjusted by determining an average magnitude change in inductance .DELTA.Lave caused by a plurality of vehicles and by then recalculating the number Nmeas of oscillator cycles based upon the average magnitude change in inductance. O://DRF//PATFILE//M51B-12.9//APP