High sensitivity inductive sensing system for position measurement

In this study, high sensitivity inductive sensing system for position measurement is presented. The proposed sensing system has higher sensitivity than a conventional Linear Variable Differential Transformer (LVDT) system. By rearranging the conventional LVDT components and improving the structure, high sensitivity for sub-micron measurement is obtained. The proposed sensing system is asymmetric and is a closed loop type. The high ferromagnetic material in the secondary coil is used to draw the flux, the air-gap along the flux paths is reduced, and a closed loop type is accepted to decrease the flux loss. The elements that affect the system characteristics and sensitivity are turn ratio, the air-gap between the fixed and moving part, capacitance effect and excitation frequency. By experimental investigation, the influences of these elements are examined and parameters of elements are selected to obtain high sensitivity. The proposed system's sensitivity is about 2400 [mV/(V/spl middot/mm)] without amplification.