A low power magnetometer for vehicle detection

Abstract

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 ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm.8\times10^{-4}</tex> Tesla) with a sensitivity of 7μv/nT (both orthogonal axes) and a self noise at zero field less than 3nT <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p_p</inf> (.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.