TABLE OF CONTENTS Temperature is the most important physical parameter, because all other physical parameters are temperature-dependent. Temperature can be measured using Celsius or Kelvin, in the SI system of units, and Fahrenheit or Rankine in the English system of units. This chapter described the relations between the units and introduced the basic concept that temperature is a measure of the heat energy contained in a body or the amplitude of molecular vibration. The vibration amplitude and molecular attraction determines the phase of the material. Heat energy can be measured in British thermal units or joules, and can be transferred between bodies either by conduction, convection, or radiation. The mechanics of heat transfer was described.
A large number of instruments is available for temperature measurement. The choice of instrument is determined by the requirements of the application. New innovations, such as the semiconductor digital thermometer, have brought about the demise of the mercury thermometer. Inexpensive On/Off applications used bimetallic devices, but these are also being replaced by semiconductor devices. Wide temperature range applications typically use thermocouples, and high accuracy devices are RTDs. Some devices have long settling times due to their thermal time constant, which can be compensated for electronically [15].
[15]Stokes J., and G. Palmer, "A Fiber Optic Temperature Sensor," Sensors Magazine, Vol. 19, No. 8, August 2002.
