Electronic Interface Circuits for Resistance-Based Sensors

This tutorial explores the many different ways that electrical resistance can be used to sense changes in the environment. Resistance-based sensors span a wide spectrum of transfer characteristics from the linear to the non-linear and from small, sub-Ohm changes to changes in resistance that span many orders of magnitude. Electronic interface circuits suitable for measuring these resistances range from those that convert sensor resistance to an analog voltage to those that generate a square wave whose frequency, duty cycle, or phase indicates resistance. In this tutorial, voltage dividers, Wheatstone bridges, current sources, and current pumps are discussed to represent the broad choices for converting resistance to an analog voltage. Oscillators, resistance-to-phase converters, direct interface circuits, and analog to digital converter circuits that convert signals directly from resistance to digital signals are also discussed. This tutorial seeks to provide the novice circuit or sensor designer with a place to start in selecting the right interface circuit for processing signals from resistance-based sensors. It also offers some additional interface circuit alternatives to the more experienced engineer.