Glossary term
Strain Gauge
A resistive sensor that converts mechanical strain into a small electrical resistance change for force, load, and deformation measurement.
Definition
deviceA strain gauge is a sensor that converts mechanical strain into a small change in electrical resistance.
Strain gauges are bonded to structures or built into transducers to measure deformation, load, pressure, torque, vibration, or thermal strain. Their accuracy depends on gauge factor, bonding quality, material surface preparation, bridge circuit, temperature compensation, wiring, calibration, and the assumption that local strain at the gauge represents the quantity of interest.
For a resistive strain gauge, the basic relation is:
where \Delta R/R is relative resistance change, GF is gauge factor, and \epsilon is strain. The resistance change is small, so gauges are usually read through Wheatstone bridge circuits with stable excitation, amplification, filtering, and temperature compensation.
Engineering use
Strain gauges are used on beams, shafts, pressure diaphragms, load cells, aircraft structures, bridges, rotating machinery, and test fixtures. Single gauges measure strain in one direction. Rosettes combine several gauges to infer principal strains and stress direction. Full-bridge configurations improve sensitivity and can reject temperature or bending effects when arranged correctly.
Installation often dominates accuracy. Surface preparation, adhesive thickness, alignment, lead-wire strain relief, moisture protection, curing, and protective coating affect the result. The gauge measures local surface strain, not average component stress. Converting strain to stress requires material properties and a valid stress model.
Measurement chain
A strain-gauge measurement is only as reliable as the complete chain from surface strain to recorded data. Bridge completion, excitation stability, amplifier input impedance, common-mode rejection, cable routing, filtering, sampling rate, and shunt calibration can all change the result. Dynamic strain work also requires attention to gauge length, adhesive stiffness, natural frequencies, and phase delay in the conditioning electronics.
Common mistakes
A common mistake is bonding a gauge near a stress concentration or support and interpreting the reading as nominal stress. Another is ignoring thermal output, lead-wire resistance, bridge nonlinearity, adhesive creep, and calibration drift. A strong strain-gauge review states gauge type, resistance, gauge factor, orientation, bridge configuration, excitation, temperature compensation, surface preparation, calibration method, uncertainty, and whether the measurement is static, dynamic, or fatigue-related.