A security portal includes magnetic field sensors in a sensor assessment network (SAN) for tracking a magnetic dipole target. Each sensor includes a sensor transducer, a sensor coil, and a digitally controlled potentiometer. A sensor controller applies a stepped voltage, samples an output frequency at each stepped voltage value, generates a magnetic sensor response curve, and converts a non-linear response of the sensor transducer to a magnetic field value for each x, y and z channel as a function of frequency for a specific potentiometer setting based upon the sensed magnetic dipole that is tracked in the security portal. A SAN controller receives the magnetic field values from each channel and determines the magnetic field vectors of the target over each sample.