Spider DSA User’s Manual
224
Bridge Type:
Refers to the strain gage bridge configuration, which can be Full, Half or Quarter
Bridge with Type 1, 2 or 3. Note that a Type 1 bridge does not require entry of
Poisson’s ratio; Types 2 and 3 require entry of this parameter.
Gage Factor:
The most fundamental property of a strain gauge is its sensitivity to strain,
expressed quantitatively as the gauge factor (GF). The gage factor is defined as the
ratio of fractional change in electrical resistance to the fractional change in gage
length (strain). Specifically:
When used in half or full bridge configurations, all of the gages must have the
same gage factor.
Nominal Gage Resistance:
Nominal gage resistance is the resistance of a strain gage in the unstrained
condition. Spider-80SG can function with any gage that has a nominal resistance
of 120 or 350 ohms. When used in half or full bridge configurations, all of the
gages must have the same nominal resistance.
Min/Max Strain:
Specifies the minimum strain detectable by the gage and the maximum strain it
can tolerate without damage. Typical strain gages have Max strain limits in the
range of a few thousand microstrain and resolution to tens of microstrain.
Poisson Ratio:
When a bar is stressed with a uniaxial tension, it stretches (strains) in that
direction. A phenomenon known as Poisson Strain also causes the girth of the
bar to contract in the transverse, or perpendicular, direction. The magnitude of
this transverse contraction, ε
t
is determined by the material’s Poisson's Ratio.
The Poisson's Ratio, γ, of a material is defined as the negative ratio of the
transverse strain (perpendicular to the force) to the strain in the force direction,
ε; that is γ = ε
t
/ε. Poisson's Ratio for steel, for example, ranges from 0.25 to 0.3.
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