Chapter 2 Temperature Fundamentals

Abstract

Publisher Summary The chapter presents the basic principles, definition and measurement of temperature. The chapter begins with a brief outline of the fundamental principles, and then introduces the concept of thermodynamic temperature and some primary means of its determination. The requirement for a defined scale is explained and a brief historical outline of temperature scales is presented, including a description of the current temperature scale, the International Temperature Scale of 1990 (ITS-90). In the context of radiation thermometry the chapter then discusses the issues of calibration, traceability and accreditation. This is followed by a discussion on determining uncertainties in temperature measurement with the emphasis firmly on non-contact thermometry. The chapter concludes by discussing possible approaches that could lead to better non-contact thermometry scale realization and dissemination in the future. The zeroth law of thermodynamics describes the existence of thermal equilibrium between two or more macroscopic systems. Temperature is the parameter of state that has the same value for any systems which are in thermal equilibrium. Johnson noise thermometry is based on the temperature dependence of the mean-square noise voltage. Total radiometry utilizes the Stefan-Boltzmann law for the total radiant exitance M ( T ) of a blackbody, which is essentially the integration of Planck's law over all wavelengths. The basic principle of the ITS-90 is to generate a temperature scale that is precise and simple to realize by National Metrology Institutes (NMIs) and properly equipped commercial calibration laboratories and to disseminate to the users of the scale through the process of calibration. The chapter also discusses calibration, traceability, basic principles of uncertainty analysis, and uncertainty in scale realization above the silver point.