Improved Method for Linear Position Sensing Through Conductive Wall

An improvement in data processing utilizing gradient information rather than only homogenous field values and calibration of the response of each individual sensor in the AMR sensor array yields significant improvement in positioning accuracy (from about +/−3 to +/−0.6 mm) of a piston-like apparatus with ferromagnetic piston rod. The approach uses low-frequency ac excitation from an external coil allowing sensing through a 2 mm thick aluminum wall.