The measurement of strain with single strain gages is an important part of experimental stress analysis. The type of circuitry employed influences the linearity and sensitivity of the measurements. Wheatstone bridge circuits and constant current circuits are the two types of circuits mainly used in the field of strain gage measuring technique. Constant current circuits measure resistance with almost no nonlinearity whereas Wheatstone bridge circuits show a nonlinear behaviour between resistance change and output voltage.

If the resistance change was really proportional to the strain (ΔR / R0 = k ∗ ε ; k = constant) the Wheatstone bridges would be nonlinear. But the upper formula is an approximation, valid only for small strain values.

An analysis shows that the relationship between resistance change and strain is also rather nonlinear. Luckily the nonlinearity of the Wheatstone bridge compensates the nonlinearity of ΔR/R0 = f(ε) almost completely. And as a result, what is even more important than linearity, the sensitivity of Wheatstone bridge circuits remains almost constant even in the case of a very high bridge unbalance.

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