SPVD: A magnetic vehicle detection system using a low power magnetometer

The Self Powered Vehicle Detector (SPVD) is a motor vehicle detection system, presently under development, that detects a vehicle's presence by measuring its magnetic signature in the roadway. An optimized two axis Brown fluxgate magnetometer is used as the transducer with a digital nulling loop to perform sensor offset nulling and logic functions. An FM telemetry link containing three encoded tones conveys the roadway emplanted SPVD vehicle presence and device status information to a roadside control unit which may interface with other traffic control systems. A minimum one year operational lifetime is anticipated in a roadway with a 20,000 vehicles/day traffic flux.