Strain Gauge
A resistive strain gauge changes resistance when it deforms with the surface it is bonded to. Gauge factor relates fractional resistance change to strain: ΔR/R = GF × ε. Common metallic-foil gauges have a gauge factor a little above 2, but use the selected gauge's specified value.
A bonded resistive pattern deforms with its substrate. A bridge or other suitable measurement circuit detects the small resistance change. Gauge orientation, bridge arrangement, excitation, lead resistance and temperature compensation all influence the reading; a full bridge does not automatically cancel every thermal error.
In plain terms
Like a stretched rubber band with conductive ink painted along it — pull the band, the ink stretches, the resistance climbs, and you've measured how far you pulled.
Why designers use it
- The sensing element in nearly all precision load cells, torque transducers, and pressure transducers.
- Stress analysis — bond gauges directly to a structure (bridge, aircraft wing, tower) to measure live stress under load.
- Wide range — same architecture covers pico-Newton to mega-Newton, from MEMS pressure sensors to dam-monitoring rosettes.
- Decades-stable — properly installed gauges hold calibration for 20+ years.
Best for
- Load cells
- Torque sensors
- Stress testing
Key specifications
- Gauge factor: Use the selected gauge's calibration data
- Resistance and geometry: Match the bridge and measurement direction
- Installation: Substrate, adhesive, preparation and curing requirements
- Measurement errors: Temperature, lead resistance, self-heating and bond quality
When not to use it
- Where dynamic frequency >5 kHz is needed — bonded foil gauges have inertia limits; pull piezoelectric.
- On rough or curved surfaces where bonding is unreliable — pull a strain-rosette or interferometric strain measurement.
Common mistakes
- Choosing an adhesive without checking the installation life, temperature, surface preparation and curing instructions.
- Leaving air gaps or a poorly bonded layer that introduces creep or hysteresis.
- Ignoring lead resistance or applying a three-wire/four-wire correction without matching the actual measurement circuit.
- Treating temperature compensation as perfect under every thermal gradient.
Where you will find it
- An HBM K-XY3-3-350 rosette strain gauge on the wing-spar of a Boeing 787 during DT&E flight tests: the gauge measures combined longitudinal and bending strain at the critical wing-fuselage junction during a 2.5 g pull-up, validating the structure's fatigue-life model.
- A Vishay Micro-Measurements EA-06-125AD-120 strain gauge bonded to a Caterpillar 797F mining truck's hauler frame during a stress survey: the gauge's 120 Ω resistance and 0.05 % linearity supplies the data behind Caterpillar's frame-life prediction software.
- A Tekscan FlexiForce A201 (uses a strain-gauge-style polymer-resistor element) embedded in a hospital bed's pressure-redistribution mattress: the strain mat reads each patient's body-pressure distribution to alert nursing staff when a patient hasn't moved in two hours.
A short history
A resistive strain gauge changes resistance as it deforms with the object to which it is attached. For a typical metal gauge, stretching increases resistance and compression decreases it. A bridge circuit measures the small change, and the specified gauge factor relates that change to strain.