Dual-Slope Inductance-to-Digital Converter for differential reluctance sensors

A new, simple and high accuracy Dual Slope Inductance-to-Digital Converter (DSIDC) suitable for differential reluctance sensors is presented in this paper. Differential reluctance sensors have two inductors that vary in a push-pull manner with-respect-to measurand. Also, the relationship between inductance of such sensors and measurand is non-linear. It is known that a small linear range can be obtained by taking the difference between the values of the sensor inductances. The proposed DSIDC accepts the sensor inductances having nonlinear characteristics, and provides a linear digital output directly proportional to the measurand. The output is linear for the full range of the sensor. As the output is in digital form, it can be easily stored and processed in a digital system. The DSIDC is based on dual-slope analog-to-digital converter principle and possesses many advantages. A prototype DSIDC has been built and tested with a typical differential inductive sensor arrangement with a nominal value of 30mH. Output from the DSIDC was linear for the full range of input and the worst-case error was less than 0.07%.