Wheatstone Bridge Nonlinearity

As described in Vishay Measurements Group Tech Note TN-507, Wheatstone Bridge Nonlinearity , the common practice with modern strain gage instruments is to operate the Wheatstone bridge circuit in a resistively unbalanced mode during strain measurement. In some instruments, the resulting bridge output voltage is read directly as a measure of the strain-induced resistance change(s) in one or more of the bridge arms. In others, the bridge output signal is "balanced" (nulled) by injecting an equal and opposite voltage from a separate circuit which is powered by an equal supply voltage.

Basic Wheatstone bridge circuit.

The cause of the nonlinear behavior (when it occurs) can be demonstrated by reexamining Eq. ( 514.1a ), with reference to the basic Wheastone bridge circuit. The bridge output voltage under any initial condition can be expressed as:

  (514.10)

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