Strain gauge vs linear variable displacement transducer For measuring deformation experiments, it seems that strain gauges and linear variable displacement transducers (LVDT) are commonly used. If the material exhibits geometric linearity, then couldn't we simply compute the displacement from a strain gauge measurement, or vice versa (compute strain from the LVDT displacement measurement) through the linear strain-displacement relation? If so, then what is the purpose of using both measurement tools in cases of small deformation? 
 A: Ideally, the difference in the measurements of two displacement sensors would be no different than the measurement of a strain gauge. However there are a few situations that I can think of where the difference matters:


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*There may be imperfections in the material, so that different parts of it stretch different amounts. In this case, the displacement difference will be the sum of all stretches between the two mounting points while the strain gauge would measure strain at the location where it is attached. Having both a strain gauge and two displacement sensors could be a good way to test for those material imperfections, because the two are guaranteed to agree if the material is homogeneous.

*As with any experimental situation, you may find that it is easier to attach one device or another to your sample. Perhaps you would like to measure strain in many places, and in some places it's easier to mount a strain gauge while in others it's easier to measure displacement.

*The noise in the strain gauge may be independent from the noise in the displacement sensors, because they operate on different principles. By using both you can improve the statistical power and resolution of your result.

