How do you distinguish thermal expansion of mechanically conditioned strain?

Possibilities for compensating thermal expansion and compensation of strain through transverse forces and moments

The magnitudes for thermal expansion and strain due to a force make it clear that the thermal expansion is a large source of error for a force sensor.

First, one can not distinguish heat expansion from any other type of strain.

Compensation of thermal strains or strains through transverse forces or moments

However, most materials extend uniformly in all directions of the space, while mechanical deformation occurs mainly in the direction of the mechanical load. In the other directions there is usually even a deformation with an opposite sign instead of the effect of "transverse contraction".
In the case of a bending load, zones with tensile and compressive loading occur.
These (and other) effects are used to compensate for temperature-related errors.

"Self Compensation" of strain gauges

Another method for compensating thermally conditional strains provide strain gauges over the so-called "self-compensation".

The special alloys for strain gauge strips have a negative temperature coefficient for the resistance. This negative temperature coefficient is chosen so that it indicates a "apparent" negative stretching. This "apparent" negative elongation corresponds in the amount of positive stretching by temperature increase, so that a compensation of the temperature-related elongation occurs.

This behavior "negative temperature coefficient of resistance" is technically not to maintain an arbitrarily large temperature range. As a rule, self-compensation is effective in the range of about -10 ° C to about + 60 ° C.

The curves for the course of "apparent stretching" are either mapped on the package or / and was shown as formula.

Incidentally, the so-called "self-compensation" complicates the measurement of the thermal expansion coefficient.