Strain gauges and Wheatstone bridges — Basic instrumentation and new applications for electrical measurement of non-electrical quantities

Strain gauges and Wheatstone bridges constitute the basic instrumentation for electrical measurement of non-electrical quantities. After presenting the fundamental properties of the resistive strain gauge and the (un)balanced Wheatstone bridge, a significant diversity of measurement techniques and means are described, typical for the present-day worldwide instrumentation. Among them: classical (metallic) strain gauges, piezoresistive semiconductors, magneto-resistive sensing elements; Wheatstone bridge circuits together with analog-to-digital converter, low noise amplifier and FFT analyzer, sine wave generator and lock-in amplifier, carrier frequency amplifiers or cantilever arrays combined with a multiplexed amplifier and connected to PC; several sensors/transducers and load cells covering the entire field of force ranges, from pico- to meganewtons. The principal aim of the paper is to outline the progress in this field, by illustrating it with suggestive examples and achievements.