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Strain gauge is a bonded, electrical-resistance transducer that converts surface strain in a substrate into a proportional change in resistance. The sensing element is a thin metallic grid (foil or sputtered thin film) laid out in a meander to maximize axial sensitivity and bonded to the test surface with a calibrated adhesive; as the substrate elongates or contracts, the grid’s length and cross-section change, producing a resistance change characterized by the gauge factor (≈2 for metal gauges). Nominal resistances are typically 120–350 Ω (also 1 kΩ and others), with gauge lengths from a few millimeters to tens of millimeters, and usable strain ranges on the order of ±5,000–10,000 µε with kHz-class bandwidth when properly installed. Alloys such as constantan (Cu-Ni) and Karma (Ni-Cr-Al-Si) provide stable, low-creep performance; high-temperature variants (e.g., Pt-W) and self-temperature-compensated patterns minimize thermal output. Single-axis, biaxial, and rosette configurations resolve principal strains and shear, while quarter-, half-, and full-bridge circuits with lead-wire compensation and shielding improve sensitivity and reject temperature and noise. Key error sources include transverse sensitivity, adhesive creep, hysteresis, and moisture ingress, addressed by correct surface preparation, alignment, encapsulation, and calibration. Strain gauges are the primary sensing element in load cells, torque meters, pressure transducers, and structural health monitoring.
