Resistance strain gages
In resistance strain gages, the elongation caused by the deformation of the element on which they are mounted produces a change in electrical resistance. The relative change in resistance is a multiple (gage factor) of deformation, ranging from two to five in the wire strain gages (see Section 1.4.2). The deformation measured can be related to the force or the bending moment acting on the element. The wire is usually bent zig-zag or spiral to increase the effective length and is embedded in a thin Bakelite support that is glued onto the rod. The typical lengths of strain gages are 0.5 to 1 cm, much larger than those used in structural analysis. Semiconductors have a gage factor of order 100 but are
much more common in pressure transducers than in aerodynamic balances.