Thermal Verification
A metrological procedure validates the accuracy of a sensor across its intended operating range above ambient conditions. Performing high temperature calibration involves comparing the device under test against a traceable reference standard inside a controlled furnace or bath. The process ends when the sensor reaches thermal equilibrium and its output stabilizes.
Reference Standard
Specialized thermometers such as platinum resistance detectors or type S thermocouples provide the baseline for these measurements. These standards must possess a calibration history that links them back to the International System of Units. Using a standard with low drift ensures that the uncertainty of the calibration remains within the required limits.
Error Correction
Technicians record the difference between the sensor reading and the reference at multiple setpoints. This data allows for the creation of a correction curve or a set of coefficients for the sensor electronics. Without this step, thermal expansion or changes in material conductivity would cause the sensor to report values far from the truth.
The procedure also identifies hysteresis, where the sensor output differs depending on whether the temperature was rising or falling. Minimizing these errors is a requirement for high-precision aerospace or industrial furnace controls.
Environmental Control
Maintaining a uniform thermal zone prevents gradients from introducing bias into the measurement. Insulation and active cooling of the sensor head are often necessary to protect non-sensing parts of the instrument.
