AOE 3054 Self-Taught Unit 1

3.2 Wheatstone Bridge

The Wheatstone bridge circuit contains four resistors arranged in a diamond. Voltage v_s is supplied across the vertical diagonal of the diamond. The voltage v_out appears across the pair of terminals connected along the horizontal diagonal.
v_out = v_A - v_B = i₂ R₃ - i₁ R₄ and,
i₁ = v_s / ( R₁ + R₄ ) and i₂ = v_s / ( R₃ + R₂ ) therefore,
v_out / v_s = R₃ / ( R₃ + R₂ ) - R₄ / ( R₁ + R₄ ) A common use for this type of circuit is operation of a transducer or sensor whose resistance varies with the quantity being measured. A good example here is the strain gage - a length of wire whose resistance varies as it is stretched. Strain gages can be used to measure minute strains. In combination with a simple structure with a known stress/strain relationship they can also be used to measure stresses.