- Temperature coefficient of grid resistance α_R [10⁻⁶/K]
- Temperature coefficient of the measuring-grid resistance: it states by how many millionths electrical resistance changes per kelvin even without mechanical load. Manufacturers tune it to a specimen material, creating a self-compensating strain gauge. Source: datasheet or thermal-output graph for the gauge batch. If the individual coefficient is not given, use the published thermal-output curve as the governing correction.
- Thermal expansion of the part α_B [10⁻⁶/K]
- Thermal expansion coefficient of the part the gauge is bonded to: by how many µm/m it expands freely per kelvin. The bonded gauge is stretched along with it. Source: material tables; ferritic steel ≈ 11–12, austenitic steel ≈ 16, aluminium ≈ 23, titanium ≈ 9, plastics 50–100 (·10⁻⁶/K).
- Thermal expansion of the grid α_M [10⁻⁶/K]
- Thermal expansion coefficient of the grid material itself. The difference from the part's expansion forces a strain on the grid that looks like a reading. Source: constantan (standard grid) ≈ 14.5·10⁻⁶/K, Karma ≈ 13; stated in the gauge datasheet.
- Gauge factor k
- The gauge factor is the sensitivity of the strain gauge: it states how much the electrical resistance changes when the gauge is stretched (ΔR/R = k·ε). Without it no strain can be computed from an electrical signal. Source: printed on every gauge package or in the manufacturer datasheet, typically 2.0 to 2.1 for constantan foil gauges; valid at room temperature. The same value must be set in the amplifier.
- Temperature change ΔT from balancing [K]
- The temperature change is the difference between the temperature at bridge balancing and the temperature during measurement. Only this difference produces temperature-related errors; if balanced at measuring temperature it is zero. Source: thermocouple or resistance thermometer at the measuring point or cable.
- Nominal resistance R₀ [Ω]
- The nominal resistance is the electrical resistance of the unloaded strain gauge. It sets how large the absolute resistance change is for a given strain and how much current flows for a given excitation. Source: printed on the gauge package; standard values 120 Ω and 350 Ω, less often 700 Ω or 1000 Ω. Higher values mean less self-heating and less cable influence.