Influencing factors and methods for measuring small strains
Gage-Factor
In the first approximation, all metal foil strain gauges have the same "sensitivity" (the same "gage-factor"), namely 2
Strain gauges based on metal foil technology with higher gage factor typically do not have self-compensation. The disadvantage of the higher drift predominates the advantage of the higher signal amplitude
Strain gauges with higher gage factor based on other physical effects than the "Thomson effect" typically have a higher noise amplitude and due to the lack of self-compensation a higher temperature-related drift.
Bridge circuit
The "bridge circuit" as "full" or "half-bridge" and through the bridge feed tension one can influence the signal level.
Excitation Voltage
Due to the self-heating or power loss of the strain gauge, the supply voltage can not be increased arbitrarily.
Summary
With a metal foil strain gauge with K-factor 2 is a resolution of approx. 0.01μm/m possible. For comparison: The thermal expansion of steel is about 12μm/m per ° C.
The use of a semiconductor strain gauges or an optical strain gauge can still be useful for certain applications.