Sensor wiring diagram
Strain gage transducers

Consider a circuit consisting of four equal resistors R ₁, R ₂, R ₃, R ₄ connected in a bridge configuration (figure 2). If we supply it with a current source P along a diagonal, we have at equilibrium a zero voltage between B and D. The variation of any one of the resistors causes a voltage V_s to appear between B and D, which can be measured by an instrument G. For very small variations in resistance (of the order of a few microohms in the case of gauges), the output voltage V_s is practically proportional to the relative variations in resistance ΔR /R of each of the gauges. Neglecting higher-order terms, it is :