Errors Due to Wheatstone Bridge Nonlinearity

Com mercial stat ic strain indicators and signal conditioners vary considerably in their circuit details; and, although most of them are based upon some form of the Wheatstone bridge circuit, the bridge circuit is employed in differing ways in different instruments. Because of the many variations in instrument design, a completely general treatment of instrument nonlinearities is not practicable within the scope of this publication. There is, however, a large class of static strain indicators and signal conditioners with a more-or-less characteristic circuit arrangement (employing the “unbalanced” Wheatstone bridge), and displaying a characteristic nonlinearity. This Tech Note has been prepared to provide a simple means for determining the magnitudes of the nonlinearity errors and for making corrections when necessary. Note that the error and correction relationships given here apply only to instruments having the characteristics defined in Section 2.0. For other instruments, the nonlinearity errors, if they exist, will have to be determined by direct calibration or from manufacturers’ specifications.