Apparatus for minimizing angular rotor position errors in an air core gauge

Abstract

An apparatus for minimizing angular rotor position errors in an air core gauge includes an air core gauge ( ) having a magnetic rotor ( ) and at least three coils ( and ) wound around the rotor ( ). A probe signal is applied to the first coil ( ), and output signals are developed and detected across the second and the third coils ( ) in response to the probe signal and low-frequency signals applied to one or more of the coils ( and ). The output signals are processed by a demodulation circuit ( ) and a number of DC voltage signals are produced therefrom. A control circuit ( ) is responsive to the number of DC voltage signals to determine an actual angular position of the rotor ( ), and to suitably adjust the low-frequency signals to thereby correct for errors between the actual angular position of the rotor ( ) and the desired angular position thereof. Preferably, the three coils ( and ) are disposed non-orthogonal relative to each other, and the rotor ( ) defines a non-circular cross-section along a plane normal an axis of rotor rotation ( ). The rotor ( ) is further preferably formed of a combination of low and high permeability magnetic materials to thereby optimize a tradeoff between torque production and signal feedback capability.