TABLE OF CONTENTS Thermal measurands are the temperature and the variables related to accumulation or transfers of heat (specific heat, conductivity, thermal diffusion, heat flux, among others). In this book we have limited our discussion to certain sensors. With thermal sensors, the choice is simple, since in fact all these sensors are to some extent dependent on the temperature measurement. So, we are going to discuss temperature sensors in the following sections, beginning with the definition of temperature, modes of heat transfer [CAR 69] and, lastly, the principle of thermometry by contact. We will discuss the principle of thermoelectric sensors in some detail [GOL 60].
Our bodies can qualitatively evaluate the concept of hot and cold objects, but in this sense, though this concept is assimilated to the concept of touch in the normal five senses, it is both non-linear and residual: it depends on prior experience. Like the other human senses, hot and cold cannot be measured we do not even know what it is we are trying to measure. The basic thermal sensor is, as we said above, a temperature sensor. The first question to be answered is how to define this odd measurand, which is not well understood in the physiological sense.
Temperature is a macroscopic concept which, even though it makes sense only in terms of a number of sufficiently large atoms, is dependent on a microscopic variable. This variable is the kinetic energy of each particle of...
