Calibration and verification of thermometers. Calibration techniques

The demand for calibration services with the best uncertainties is constantly increasing. The most popular temperature range is from -80°C to 250°C, but there is a growing demand for calibration services in sub-zero temperatures, due in particular to the need to control the cold chain in the agri-food and healthcare sectors. Against all expectations, calibration services for liquid expansion thermometers, although decreasing from year to year, still account for 20% of calibrated instruments, as they are still widely used in the agri-food sector.

The aim of this article is to guide the experimenter in the choice of a calibration technique appropriate to his needs, and in the implementation of this technique. Temperature measurements are so commonplace that operators sometimes forget that they need to master several areas of physics in order to obtain measurement results with an uncertainty compatible with their needs.

The experimenter is often faced with the difficulty of establishing an uncertainty budget associated with his measurement. The information provided in this article will serve as a basis for reflection when establishing an uncertainty budget associated with a temperature measurement.

In this article, we shall confine ourselves to the field of contact thermometry, i.e. calibration methods in which the temperature sensor is in direct contact with the calibration medium. We will also restrict this document to calibrations carried out in the temperature range from 83.8058 K to 2041.35 K. This range covers most industrial requirements.

This article does not cover devices for measuring temperature by analyzing radiation: on this subject, the reader is referred to the article Optical Pyrometry [R 2 610] in the present treatise.

This article does not deal with cryogenic probes used below 83.8058 K.

This article does not deal with surface temperature measurements.