Strain gauge basics

https://www.youtube.com/watch?v=qHi8FPnWP6E

Summary

TL;DR — A strain gauge is a device that measures strain (deformation) by bonding to a surface and changing its electrical resistance proportionally to the applied strain. This change in resistance is influenced by the material's length, cross-sectional area, and resistivity, and is quantified by a gauge factor, which is specific to the material and geometry.

Key points

• Strain gauges work by adhering to a material and deforming with it, causing a measurable change in electrical resistance.

• For metallic strain gauges, resistance change is primarily due to changes in length and cross-sectional area, and to a lesser extent, resistivity.

• The gauge factor (GF) is a key parameter that relates the change in resistance to the applied strain, combining material properties and geometry.

• Metallic strain gauges typically have a GF of 2-2.22, while semiconductor strain gauges offer much higher GFs (around 100) but are more sensitive to temperature.

• Measuring the small resistance changes from strain gauges directly using simple circuits (like voltage dividers) results in small voltage variations and a significant DC offset, making them difficult to work with.

• Wheatstone bridge circuits, discussed in a future video, are the preferred method for measuring strain gauge output as they effectively cancel out offsets and amplify the small strain-induced signals.

Takeaway — Strain gauges convert mechanical deformation into measurable electrical resistance changes, but their small output signals necessitate specialized circuits like Wheatstone bridges for practical application.