Common strain gauges belong to resistance strain gauges, which convert the measured non-electric quantity into the change of resistance value, and achieve the purpose of measuring non-electric quantity by measuring the change of resistance value. Strain gauges are divided into foil strain gauges, wire (wound) strain gauges and semiconductor strain gauges. The metal wire strain gauge is the earliest used, but because the creep of the metal wire strain gauge is large, the metal wire is easy to degumming, and it is gradually replaced by the foil type. However, its price is cheap, and it is mostly used for large-scale and one-time tests of strain and stress.
The foil strain gauge is a structure in which the metal foil is etched into a grid shape on a thin resin material electrical insulator, and then the leading wire is installed, as shown in Figure 4. The general foil strain gauge is a plastic film called the base (15-16μm) pasted with a sensitive grid (3-6μm) made of thin metal foil, and then covered with a layer of film to make a laminated structure. The contact area between foil strain gauge and substrate is much larger, the heat dissipation condition is better, the creep during long-term measurement is smaller, the consistency is better, and the temperature influence can be reduced to the minimum degree, which is suitable for mass production.
Attach the strain gauge to the measuring site using a special adhesive. The strain generated at the measuring site is transmitted to the sensitive grid through the adhesive and the substrate of the strain gauge. In order to accurately measure strain, the strain gauge and adhesive selected must meet the conditions of use such as the measured material and the use temperature.
