Analog Circuit Design

23

Delta sigma ADC bridge measurement techniques

Mark Thoren

Introduction

Sensors for pressure, load, temperature, acceleration and many other physical quantities often take the form of a Wheatstone bridge. These sensors can be extremely linear and stable over time and temperature. However, most things in nature are only linear if you don’t bend them too much. In the case of a load cell, Hooke’s law states that the strain in a material is proportional to the applied stress—as long as the stress is nowhere near the material’s yield point (the “point of no return” where the material is permanently deformed). The consequence is that a load cell based on a resistance strain gauge will have a very small electrical output—often only a few millivolts. In ...