The Wheatstone bridge can be used in various ways to measure electrical resistance:
- For the determination of the absolute value of a resistance by comparison with a known resistance
- For the determination of relative changes in resistance
The latter method is used with regard to strain gauge techniques. It enables relative changes of resistance in the strain gauge, which are usually around the order of 10-4 to 10-2 Ω/Ω to be measured with great accuracy.
The image below shows two different illustrations of the Wheatstone bridge which are electrically identical: figure a) shows the usual rhombus representation in which the Wheatstone is used; and figure b) is a representation of the same circuit, which will be clearer for an electrically untrained person.
The four arms or branches of the bridge circuit are formed by the resistances R1 to R4. The corner points 2 and 3 of the bridge designate the connections for the bridge excitation voltage Vs; the bridge output voltage V0 , that is the measurement signal, is available on the corner points 1 and 4.
The bridge excitation is usually an applied, stabilized direct, or alternating voltage Vs.