Resistance strain gauges are elements used to measure strain. It can convert changes in strain on mechanical components into changes in resistance. The resistance strain gauge is made by wrapping of copper wire or nickel chromium wire (Φ=0.02-0.05mm) into a grid (or corroding into a grid with very thin metal foil) sandwiched in two layers of insulation sheet (substrate). It is connected with the strain gauge wire with silver plated copper wire as the lead of the resistance gauge.

There are many forms of resistance strain gauge, commonly used wire type and foil type. It is made of a diameter of 0.02 ~ 0.05mm of copper-wire or nickel-chromium wire wrapped into a grid (or corroded into a grid with a very thin metal foil) and clamped in two layers of insulation sheet (substrate). The tinned copper wire is connected with the strain gauge wire grid as the strain gauge lead, which is used to connect the measuring wire.

The measuring principle of the resistance strain gauge is that the resistance value of the wire is related to the nature of the material as well as the length and cross-sectional area of the wire. When the metal wire is pasting on the component, when the component is deformed by force, the length and cross-sectional area of the metal wire also change with the component, and then the resistance changes.

DR/R = Ks * ε

Among them, Ks is the sensitivity coefficient of the material, and its physical meaning is the resistance change rate per unit strain, which marks whether the resistance strain gauge effect of this kind of wire is significant or not. ε is the strain at the measurement point, which is a dimensionless quantity, but it is still customarily given as unit micro-strain, which is commonly expressed by the symbol με.

It can be seen that when the strain effect of metal wire occurs, the strain ε has a linear relationship with the resistance change rate dR/R, which is the theoretical basis of using metal strain gauges to measure the strain of components.