Materials Handling
Advances in strain gauge measurement
There are a number of technical factors that determine the successful usage of strain gauges – and it pays to take some expert advice.
T
he most universal measuring device for the electrical measurement of mechanical quantities is the strain gauge. Several types of strain gauges
depend on the proportional variance of electrical resistance to strain: the piezoresistive or semi-conductor gauge; the carbon-resistive gauge; the bonded metallic wire; and foil resistance gauges.
size and low mass, and has fairly high sensitivity to strain.
In a strain gauge application, the carrier matrix and the adhesive must work together to transmit the strains from the specimen to the grid. In addition, they serve as an electrical insulator and heat dissipater.
The three primary factors influencing gauge selection are operating temperature, state of strain (gradient, magnitude, and time dependence) and stability required.
Because of its outstanding sensitivity, the Wheatstone bridge circuit is the most frequently used circuit for static strain measurements. Ideally, the strain gauge
Fig. 1. Omega offers strain gauges with temperature characteristics matched to ferritic steel and aluminium. Picture courtesy of Omega.
The bonded resistance strain gauge is by far the most widely used in experimental stress analysis. These gauges consist of a grid of very fine wire or foil bonded to the backing or carrier matrix. The electrical resistance of the grid varies linearly with strain. In use, the carrier matrix is bonded to the surface, force is applied and the strain is found by measuring the change in resistance. The bonded resistance strain gauge is low in cost, can be made with a short gauge length, is only moderately affected by temperature changes, has small physical
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Fig. 2. The strain gauge is one of the most important tools of the electrical measurement technique applied to the measurement of mechanical quantities. Picture courtesy of Omega.
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