Importance

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Abstract

A sensor used for detecting the passage of vehicles over a roadway is formed of a force sensing variable resistor which is embedded in a resilient, rubber-like strip that is molded around the resistor within an elongated sheet metal channel. The channel is sized to fit within a narrow saw-cut groove across the roadway, so that the strip exposed surface at the open top of the channel is exposed at the road surface for contact by the tires of passing vehicles. The resistor is formed of a printed circuit having a pair of separated conductive stripes with a repetitive pattern of gap areas between them, and a sheet of variable resistance material overlying each of the gap areas to form conductive shunts between the printed conductive stripes. The material forming each of the sheets normally resists the flow of electrical current, but its resistance decreases in response to physical pressure so as to become a conductor over its respective gap area in response to the direct pressure from a vehicle tire compressing the resilient strip above the sheet. A detector is used to sense the flow of current through the printed circuit for sensing the vehicle.

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First Claim