 Another technology employed by Kistler for its measurement projects is strain gage sensing. The principle of operation of the strain gage is based on the physical effect of the electrical resistance of a wire changing in proportion to any change in length caused by stretching or compression. It allows measurement of tension and compression without any measuring element preload. When the measuring wire undergoes a strain ε its length L, cross-sectional area A and specific resistance ρ of its material change. To obtain practical resistance values, the wire must be very thin (diameter ≈ 0,02 mm) and as long as possible. In the case of a strain gage this wire is attached to an insulating substrate in a repeated pattern and provided with solderable terminals. The wire is commonly replaced with thin (≈ 0,005 mm), metallic foil from which a meander is etched to form a measuring grid. This produces very small (for example with 1 x 1 mm grids) strain gages capable of measuring virtually at a point. The proportionality factor k between the strain and change in resistance to be measured is called the "k factor". It is a constant within the elastic range of the conductor material. In the case of selected materials such as constantan this factor remains constant even when the conductor is undergoing plastic deformation. Special strain gages like those developed in-house by Kistler for applications such as measuring wheels can be used for strains of up to 10 %. Back to Technology
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