The Wheatstone Bridge Circuit Explained

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 V_s. The bridge output voltage V₀ , that is the measurement signal, is available on the corner points 1 and 4.

Note: There is no generally accepted rule for the designation of the bridge components and connections. In existing literature, there are all kinds of designations and this is reflected in the bridge equations. Therefore, it is essential that the designations and indices used in the equations are considered along with their positions in the bridge networks in order to avoid misinterpretation.

Depending on the measurement task one or more strain gauges are used at the measuring point. Although designations such as full bridge, half bridge, or quarter bridge are used to indicate such arrangements, actually they are not correct. In fact, the circuit used for the measurement is always complete and is either fully or partially formed by the strain gauges and the specimen. It is then completed by fixed resistors, which are incorporated within the instruments.  

Transducers generally have to comply with more stringent accuracy requirements than measurements pertaining to experimental tests. Therefore, transducers should always have a full bridge circuit with active strain gauges in all four arms.

Full bridge or half bridge circuits should also be used for stress analysis if different kinds of interferences need to be eliminated. An important condition is that cases of different stresses are clearly distinguished, such as compressive or tensile stress, as well as bending, shear, or torsional forces.