One Minute StrainTalks: Gage Factor.

In this podcast Anton discusses about Gage factor, GF, (sometimes) K.
The ratio of (a) the relative resistance change in a strain gage to (b) the Lagrangian unit strain causing the resistance change.
Gage Factor (GF) is the measure of sensitivity, or output, produced by a resistance strain gage. Gage factor is determined through calibration of the specific gage type, and is the ratio between ΔR/Ro and ΔL/L (strain), where Ro is the initial unstrained resistance of the gage. It is affected somewhat by pattern size, geometry, S-T-C number, and temperature. Each gage package is supplied with the GF as well as its tolerance and temperature sensitivity. Nominal gage factors for various alloys are: A = 2.05; K = 2.1; D = 3.2; P = 2.00.
Ideally, a strain gage bonded to a test part would respond only to the applied strain in the part, and be unaffected by other variables in the environment. Unfortunately, the resistance strain gage, in common with all other sensors, is somewhat less than perfect. The electrical resistance of the strain gage varies not only with strain, but with temperature as well. In addition, the relationship between strain and resistance change, the gage factor, itself varies with temperature. These deviations from ideal behavior can be important under certain circumstances, and can cause significant errors if not properly accounted for. When the underlying phenomena are thoroughly understood, however, the errors can be control.

[anabravo]

El Factor de Banda(GF) es la medida de la sensibilidad, o salida, producida por una banda extensométrica resistiva, que viene determinado por la variación de la resistencia de la banda dividido entre la variación de su longitud.