Spider DSA User’s Manual
215
Poisson Strain Gage as it experiences the Poisson strain associated with the
tension or bending strain sensed by the primary gage.
Figure x10: Poisson Strain is perpendicular to causal stress and of opposite sense
In most gage installations, the “sensitive direction” is well understood. For
example, to measure the strain of a bending beam, the sensitive “strain direction”
of the gage is oriented along the beam’s length. A second gage laid across the
beam will experience the Poisson’s strain, normally 25 to 40% of the
tension/compression experienced by the primary gage (and out of phase with it).
Special dual gage packages call biaxial strain gages are available to simplify such
installations. Biaxial gages are available in both planer and stacked formats.
When used in this manner, the channel sensitivity greater than that of a quarter
bridge installation. The output of the circuit is:
That is, the type 1 Half Bridge has a nominal sensitivity GF (1+γ) V
in
/4μV per
microstrain and it exhibits minor nonlinearities.
Figure x11: Biaxial Strain Gages
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