Strain Gauge - Gauge Factor

Gauge Factor

The gauge factor is defined as:

where

is the change in resistance caused by strain,

is the resistance of the undeformed gauge, and

is strain.

For metallic foil gauges, the gauge factor is usually a little over 2. For a single active gauge and three dummy resistors, the output from the bridge is:

where

is the bridge excitation voltage.

Foil gauges typically have active areas of about 2–10 mm2 in size. With careful installation, the correct gauge, and the correct adhesive, strains up to at least 10% can be measured.