Inductive vehicle detector

Details Inductive vehicle detector Inductive vehicle detector

1978-01-10

1981-10-20

Groody, James J.

Communications: electrical

Selective

Having indication or alarm

324236, G08G 101

Patent

active

042964016

ABSTRACT:
An electronic vehicle detection installation of the type using a detector loop laid in the roadway senses changes in the inductive time constant of the loop. The changes are sensed by determining the phase difference between a voltage impressed on the loop and the loop current or by making the time constant the predominant frequency determining parameter of an astable oscillator. A digital processing circuit is provided to sense vehicle-indicative changes in the oscillator frequency. Clock pulses are counted over a selected number of oscillator cycles, the scan cycle, and the number counted over one scan cycle is compared with that stored from the preceding cycle. Provision is made to adjust the stored value for ambient changes and for the continued presence of a vehicle after a selected presence period.

REFERENCES:
patent: 3571789 (1971-03-01), Midlock
patent: 3911389 (1975-10-01), Mills
patent: 3989932 (1976-11-01), Koerner
patent: 4075563 (1978-02-01), Battle
patent: 4131848 (1978-12-01), Battle

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