Les aspects théoriques régissant l'instrumentation d'un capteur thermique pariétal à faible inertie

The theoretical aspects of the instrumentation of a weak inertia parietal thermal sensor. From a simple semi-infinite model, we present theoretical developments allowing the optimisation of the instrumentation of parietal thermal sensors. Generally equipped with two thin thermocouples, these sensors must present a weak thermal inertia in order to characterise thermal boundary conditions in fast unsteady regime. Performances of such sensors are described by three characteristics: response time, measurement sensitivity and accuracy. For a given material, the constraint on the response time determines diameter and position of the second thermocouple. In a second time, the position of the first thermocouple results from a good compromise between measurement sensitivity and accuracy. This compromise depends itself on the sensor response time, particularly at the beginning of the studied thermal phenomena.