Transverse Sensitivity

Transverse sensitivity in a strain gage refers to the behavior of the gage in responding to strains which are perpendicular to the primary sensing axis of the gage. Ideally, it would be preferable if strain gages were completely insensitive to transverse strains. In practice, most gages exhibit some degree of transverse sensitivity; but the effect is ordinarily quite small, and of the order of several percent of the axial sensitivity.

In plane wire strain gages, transmission of strain into the wire from a direction perpendicular to the wire axis is nearly negligible. As a result, the transverse sensitivity of these gages is due almost entirely to the fact that a portion of the wire in the end loop lies in the transverse direction. Because of this, the sign of the transverse sensitivity for a plane wire gage will always be positive, and the magnitude of the effect can be calculated quite closely from the geometry of the grid. This statement does not apply to the small "wrap-around" gages having the wire wound on a flattened core. Such gages often exhibit negative transverse sensitivities.

In foil strain gages, on the other hand, the transverse sensitivity arises from much more complex phenomena, and it is affected by almost every aspect of grid design and gage construction. In addition to end-loop effects, the foil grid lines, having a large ratio of width to thickness, are strained significantly by transverse strains. The magnitude of transverse strain transmission into the grid lines is determined by the relative thicknesses and elastic moduli of the backing and foil, by the width-to-thickness ratio of the foil grid lines, and, to a lesser degree, by several other parameters, including the presence or lack of an encapsulating layer over the grid.

Depending upon the foil material and its metallurgical condition, the contribution to transverse sensitivity from the transmission of transverse strain into the grid lines can be either positive or negative. Because of this, the overall transverse sensitivity of a foil strain gage can also be either positive or negative. While the transverse sensitivity of a foil gage is thus subject to a greater degree of control in the design of the gage, the compromises necessary to optimize all aspects of gage performance generally limit the attainable reduction in transverse sensitivity.

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