Instrument Scaling for Large Strains

It was demonstrated in the preceding section that Wheatstone bridge nonlinearity must generally be considered when shunt calibration is used for instrument scaling at high strain levels. Under such conditions, errors in gage simulation arise whenever the nonlinearity which is inherent in shunt calibration differs from that during actual strain measurement. The relationships given in this section for quarter-, half-, and full-bridge circuits provide for precisely simulating the strain gage output at any level of strain, low or high.

The subject relationships are "precise" or "exact" with respect to the specified parameters such as , , and . The effects of tolerances on these quantities are discussed in the " Accuracy Considerations " section.

Thus, the instrument scaling will also be precise when the gain or gage factor control is adjusted to register the simulated strain. It must be kept in mind, however, that if the strain-measuring circuit arrangement is nonlinear, precise scaling is achieved only at the simulated strain level. At any other level of strain, some degree of error will be present due to the nonlinearity.

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