A low power magnetometer for vehicle detection

A miniature, low power two-axis Brown type ring. core magnetometer is described which can be used for motor vehicle detection. For relatively little power (<1mw), the sensor functions over a large dynamic range (
\pm.8\times10^{-4}
Tesla) with a sensitivity of 7μv/nT (both orthogonal axes) and a self noise at zero field less than 3nT
p_p
(.03 to 3 Hz). A low power digital feedback loop has been developed to null the magnetometer signal and compensate for temperature induced offset variations. The sensor is also suitable for a stationary short baseline gradiometer.