Gauge factor (GF) or strain factor of a strain gauge is the ratio of relative change in electrical resistance to the mechanical strain ε, which is the relative change in length.
In practice, the resistance is also dependent on temperature. The total effect is
Where
- ε = strain =
- = absolute change in length
- = original length
- ν = Poisson's ratio
- ρ = Resistivity
- ΔR = change in strain gauge resistance
- R = unstrained resistance of strain gauge
- α = temperature coefficient
- θ = temperature change
For many materials there is no change in resistivity, for these materials the gauge factor is simply
General examples of Gauge Factor values:
| Material | Gauge Factor |
|---|---|
| Metal foil strain gauge | 2-5 |
| Thin-film metal | 2 |
| Single crystal silicon | -125 to + 200 |
| Polysilicon | ±30 |
| Thick-film resistors | 100 |
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