MethodWhat is calculated?
A gauge also responds to strain transverse to its measuring direction; the ratio of sensitivities is the transverse sensitivity q (Keil eq. 2.16). Because the manufacturer calibrates k on a beam with ν₀ = 0.285, the gauge only reads without error in exactly that uniaxial field. For two perpendicular gauges, eq. 2.25 can be solved for both true strains.
Equations
ε′ = (εₗ + q·εq)/(1 − ν₀·q) (Keil Gl. 2.25)
εₐ = (1 − ν₀q)(ε′ₐ − q·ε′ᵦ)/(1 − q²)
εᵦ = (1 − ν₀q)(ε′ᵦ − q·ε′ₐ)/(1 − q²)
f = q(ν₀ + εq/εₗ)/(1 − qν₀) (Keil Gl. 2.26)
LimitsAssumptions and typical mistake
Valid for two exactly perpendicular gauges with equal q. For three-element rosettes apply the equations pairwise; q itself varies with temperature and production lot.
Using the percentage value of q as an absolute number, or ignoring the sign of q (can be negative for long grids).
InputsWhat you enter – and where the values come from
- Indicated strain gauge a (ε′ₐ) [µm/m]
- Uncorrected reading of the strain gauge in direction a. A strain gauge also responds slightly to strain across its grid; this unwanted part is what the calculator removes. Source: the amplifier strain reading for channel a after entering the manufacturer's gauge factor and zeroing the unloaded point.
- Indicated strain gauge b (ε′ᵦ), perpendicular to a [µm/m]
- Uncorrected reading of the second strain gauge oriented exactly perpendicular to a. In a T rosette this is the second grid. Source: the second amplifier channel; grid labels a and b are shown on the rosette drawing or datasheet.
- Transverse sensitivity q [%]
- Transverse sensitivity q states, in percent, how strongly the strain gauge responds to strain across its intended measuring direction. Source: gauge datasheet, usually called transverse sensitivity. Enter the number as a percentage, for example 0.8 for 0.8%.
- Calibration Poisson ratio ν₀
- Poisson's ratio of the calibration beam on which the manufacturer determined the gauge factor. Needed because a transverse component is already ‘hidden’ in the stated gauge factor. Calibration is done internationally at 0.285 (steel beam); change only if the datasheet states otherwise.
ContextWhat this calculator is for
Stress analysis with T rosettes or two single gauges, especially when one gauge lies transverse to the principal strain: Keil's example with q = 1 % and εq/εₗ = −3.33 gives an error of −3.1 %.
What comes next
- Record both indicated strains with the same gauge factor set on the amplifier.
- Take q and ν₀ from the gauge manufacturer's datasheet.
- Use the corrected strains for stress calculation and the error values to judge whether the correction matters.
SourceTechnical basis
Keil, Dehnungsmessstreifen, 2nd ed. 2017, sec. 2.3 transverse sensitivity, eqs. (2.16), (2.20)–(2.27).
The source supports the equation structure and worked examples; this calculator does not replace calibration of the measuring chain.
FAQFrequently asked questions
When can I skip the correction?
In uniaxial loading along the gauge with ν ≈ 0.285 the error is zero; Keil's rule of thumb 2.27 gives f ≈ q·εq/εₗ.
Why does ν₀ = 0.285 appear?
Because the transverse component present during calibration is already contained in the stated gauge factor (eq. 2.23).
Does it apply to 45° rosette grids?
For the 45° grid the transverse strain must be derived from the other two grids; the correction is then done iteratively or with the manufacturer's rosette formulas.
In the same cluster
All strain-gauge calculators