| 摘要 |
A vehicle detector includes an inductive sensor (12) which is driven by an oscillator (16) to produce an oscillator signal having a frequency which is a function of inductance of the inductive sensor. The presence of a vehicle is detected when the measured frequency of the oscillator signal changes by more than a threshold value. The effects of magnetic flux produced by adjacent power lines are compensated for by means (20, 34, 36, and 38) for measuring the frequency of the oscillator signal during a plurality of sample periods and for characterizing fluctuations of the measured frequency as a function of phase of a power main signal. During a normal measurement period, the frequency of the oscillator signal is measured, and the phase of the power main signal during the measurement period is determined. An output signal is produced by means (20, 22, and 32) based upon the measured frequency, the phase, and the known fluctuation of measured frequency as a function of phase of the power main signal. <IMAGE> |
