Induction loop vehicle detector

Details Induction loop vehicle detector Induction loop vehicle detector

1983-06-02

1986-02-04

Groody, James J.

Communications: electrical

Vehicle detectors

Environmental or drift compensation

324236, 340941, G08G 101, G01R 3312

Patent

active

045689377

ABSTRACT:
An induction loop vehicle detector comprises an oscillator circuit having a plurality of capacitors switchable in circuit with a road loop under the control of a microcomputer to determine the oscillator frequency. The microcomputer monitors the oscillator frequency and controls the switching of the capacitors to periodically return the frequency to a predetermined value. A counter counts a predetermined number of oscillator cycles and gates of h.f. clock into a second counter whereby the count of the counter represents the oscillator period. A "vehicle detected" output is given when the monitored frequency alters by more than a predetermined amount, representing a decrease in the inductance of the loop. On detecting an increase in the inductance above a predetermined threshold the detector is inhibited for a predetermined time, e.g. about 1 second, to avoid errors caused by magnetic effects.

REFERENCES:
patent: 3820100 (1974-06-01), Ballinger
patent: 3838270 (1974-09-01), Ballinger
patent: 3863206 (1975-01-01), Rabie
patent: 3863555 (1975-04-01), Potter
patent: 3943339 (1976-03-01), Koerner et al.
patent: 3989932 (1976-11-01), Koerner

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