3. Errors related to the measurement chain environment

The temperature of a body is not directly accessible; it is obtained by graduating the variation of a physical quantity, sensitive above all to variations in thermal agitation energy. However, the magnitudes selected undergo non-negligible changes under the effect of influencing magnitudes other than temperature: for example, variation in resistance due to mechanical tension at constant temperature, variation in the electromotive force of a thermoelectric couple in a magnetic field at constant temperature, variation in the emissivity of a surface due to oxidation at constant temperature, electromagnetic field, high humidity.

An electric, magnetic or electromagnetic field can generate parasitic emf. A thermal field is more pernicious. Batteries, standard resistors and measurement bridges are sensitive to ambient temperature and its variations. The solution is to...