The strain gauge is attached to the material to be measured, so that it expands and expands with the strain of the material, so that the metal foil inside grows or shrinks with the strain. The resistance of many metals changes when they are mechanically extended or shortened. The strain gauge applies this principle to measure the strain by measuring the change of resistance. Generally, the sensitive grid of the strain gauge uses copper-chromium alloy, and its resistance change rate is constant, and it should become directly proportional.
Such as:
R: strain gauge original resistance value Ω(ohms)
R: Resistance change due to elongation or compression Ω(ohms)
K: Sensitivity factor of strain gauge (constant, provided by strain gauge manufacturer)
ε: Strain
Different metal materials have different proportionality constants K. Copper-chromium alloys have a K value of about 2. In this way, the measurement of strain is converted by the strain gauge into a measurement of the change in resistance. But because the strain is a fairly small change, the resulting change in resistance is also extremely small.
It is very difficult to accurately measure such a small resistance change, and ordinary resistance meters cannot meet the requirements. To measure this small resistance change, we use a special strain gauge with a Wheatstone bridge.
