Resistance Metrology
Thermal measurement procedures establish precise mathematical relationships between platinum resistor electrical resistance and international temperature scales. Rigorous PRT calibration minimizes measurement uncertainty by determining sensor-specific ice point resistance and temperature coefficients. Metrology laboratories perform these evaluations in fixed-point cells or highly stable thermostatic liquid baths against primary reference standards.
Measurement boundaries depend on sensor purity, mechanical strain relief and operational temperature limits ranging from cryogenic levels up to high thermal bounds.
Reference Comparison
Fixed-point cells provide absolute reference temperatures defined by the phase transitions of pure substances. Triple point of water cells and metal freezing point cells supply invariant thermal reference nodes with millikelvin precision. Comparison measurements in liquid baths supplement fixed points across intermediate operating temperature ranges.
Interpolation Equation
Mathematical equations transform measured resistance values into temperature readings using standardized interpolation models. Polynomial coefficients derived during PRT calibration correct for non-linear resistance changes across the sensor operating band. Fitting residual errors determine the achieved measurement accuracy reported on calibration certificates.
Hysteresis Boundary
Mechanical shock and thermal cycling induce physical strain in platinum wire elements during field operation. Internal strain shifts baseline resistance at zero degrees Celsius, causing measurement drift over time. Periodic recalibration verifies resistance stability and restores traceability to national metrological standards.
