Chapter 6 - Non-contact Measurement of Temperature

Abstract

Thermal radiation is a collection of electromagnetic waves emitted by a substance, and it results from the random motion of microparticles (atoms, molecules, ions, and electrons) constituting the radiating body. Thermal radiation is governed primarily by the temperature of a radiating substance. Measuring thermal radiation allows the estimation of the temperature of a thermal source, once the relation between the temperature and radiation power is known and well established. Optical instruments for temperature measurement (often called pyrometers) are based on the universal laws of thermal radiation. Three kinds of temperature are usually defined and correspondingly three different approaches are commonly used—namely, radiation temperature, color temperature, and brightness temperature. Optical methods for the measurement of gradients inside a test object are evidently concerned with materials transparent to radiation. The measurement of gradients is a much more complicated task than the measurement of temperature in some predetermined locations. Gradients are revealed as a result of interferogram interpretation, which takes into consideration that the shape of the interference fringes depends on the temperature and variation of the refractive index along the optical path.