Microcontroller-based Interface Circuit for Inductive Sensors☆

This work proposes a fully-digital interface circuit for the measurement of inductive sensors using a low-cost microcontroller (μC) and without any intermediate active circuit. Apart from the μC and the sensor, the circuit just requires an external resistor and a reference inductance so that two RL circuits with a high-pass filter (HPF) topology are formed. The μC appropriately excites such RL circuits in order to measure the discharging time of the voltage across each inductance (i.e. sensing and reference) and then it uses such discharging times to estimate the sensor inductance. Experimental tests using a commercial μC show a non-linearity error (NLE) lower than 0.5 %FSS (Full-Scale Span) when measuring inductances from 1 mH to 10 mH, and from 10 mH to 100 mH.