Device for activating inductive loop sensor of a traffic light control system
First Claim
Patent Images
1. A system for activating a traffic presence sensor of the type based on an inductive loop, the system comprising:
- an oscillator coupled to a coil;
a mixer coupled to said oscillator and to said coil;
a filter coupled to said mixer;
a detector coupled to said filter which detects an output of said filter;
anda controller which controls the frequency of said oscillator based on measurements taken from an output of said detector.
0 Assignments
0 Petitions
Accused Products
Abstract
A system and method for activating vehicle sensors which are based on inductive loops. A voltage controlled oscillator is scanned throughout the required frequency range while a balanced mixer, low-pass filter, and detector are arranged to show the presence of a signal from an inductive loop by the amplitude of the resultant signal at a difference frequency. The voltage controlled oscillator is then made to dwell at or near the frequency of the sensor loop by adjusting so as to keep the amplitude of that low-frequency difference as high as possible.
4 Citations
16 Claims
-
1. A system for activating a traffic presence sensor of the type based on an inductive loop, the system comprising:
-
an oscillator coupled to a coil; a mixer coupled to said oscillator and to said coil; a filter coupled to said mixer; a detector coupled to said filter which detects an output of said filter; and a controller which controls the frequency of said oscillator based on measurements taken from an output of said detector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A method for activating a traffic presence sensor of the type based on an inductive loop comprising:
-
generating a first signal with adjustable frequency; impressing said first signal onto a coil; bringing said coil near to the inductive loop of a presence sensor; combining said first signal with output of said coil in such a manner as to generate a second signal substantially containing the difference in frequency between said first signal with adjustable frequency and the frequency of the current driving said inductive loop; measuring the amplitude of said second signal; and adjusting said frequency of said first signal such that said difference in frequency is small enough to cause activation of said traffic presence sensor. - View Dependent Claims (12, 13, 14, 15, 16)
-
Specification