10.1 Introduction

Temperature is without doubt the most widely measured variable. Thermometers can be traced back to Galileo (1595). The importance of accurate temperature measurement cannot be overemphasized. In the process control of chemical reactions, temperature control is of major importance, since chemical reactions are temperature-dependent. All physical parameters are temperature-dependent, making it necessary in most cases to measure temperature along with the physical parameter, so that temperature corrections can be made to achieve accurate parameter measurements. Instrumentation also can be temperature-dependent, requiring careful design or temperature correction, which can determine the choice of measurement device. For accurate temperature control, precise measurement of temperature is required ^[1]. This chapter discusses the various temperature scales used, their relation to each other, methods of measuring temperature, and the relationship between temperature and heat.