Differential inductive sensor-to-microcontroller interface circuit

Abstract

This paper proposes a low-cost interface circuit for differential inductive sensors where the sensor is directly connected to a microcontroller unit (MCU) without any active intermediate electronics in between. The timer embedded into the MCU is employed to measure the discharging or charging time interval of two passive RL networks formed by each sensor coil and an external resistor. Two topologies of the circuit are presented, evaluating their advantages and drawbacks. One of the topologies is implemented using a low-cost 8-bit MCU (Atmel ATmega328P) and its transfer characteristics is evaluated when measuring a commercial displacement inductive sensor. Experimental results show that, in a range of ±25 mm, the non-linearity error is smaller than 1%, and the resolution is 9 bits for an overall measuring time of a few milliseconds.