E1C08 09/14/2010
14:53:55 Page 309
Chapter 8
Temperature Measurements
8.1 INTRODUCTION
Temperature is one of the most commonly used and measured engineering variables. Much of our
lives is affected by the diurnal and seasonal variations in ambient temperature, but the fundamental
scientific definition of temperature and a scale for the measurement of temperature are not
commonly understood. This chapter explores the establishment of a practical temperature scale
and common methods of temperature measurement. In addition, errors associated with the design
and installation of a temperature sensor are discussed.
Upon completion of this chapter, the reader will be able to
describe the primary standards for temperature,
state the role of fixed point calibration and the necessity for an interpolation method in
establishing a temperature standard,
describe and analyze thermal expansion thermometry,
state the physical principle underlying electrical resistance thermometry,
employ standard relationships to determine temperature from resistance devices,
analyze thermoelectric circuits designed to measure temperature,
describe experiments to determine thermoelectric potential for material pairs,
state the principles employed in radiation temperature measurements, and
estimate the impact of loading errors in temperature measurement.
Historical Background
Guillaume Amontons (1663–1705), a French scientist, was one of the first to explore the
thermodynamic nature of temperature. His efforts examined the behavior of a constant volume
of air that was subject to temperature changes. The modern liquid-in-glass bulb thermometer
traces its origin to Galileo (1565–1642), who attempted to use the volumetric expansion of
liquids in tubes as a relative measure of temperature. Unfortunately, this open tube device was
actually sensitive to both barometric pressure and temperature changes. A major advance in
temperature measurement occurred in 1630 as a result of a seemingly unrelated event: the
309
14:53:55 Page 309
Chapter 8
Temperature Measurements
8.1 INTRODUCTION
Temperature is one of the most commonly used and measured engineering variables. Much of our
lives is affected by the diurnal and seasonal variations in ambient temperature, but the fundamental
scientific definition of temperature and a scale for the measurement of temperature are not
commonly understood. This chapter explores the establishment of a practical temperature scale
and common methods of temperature measurement. In addition, errors associated with the design
and installation of a temperature sensor are discussed.
Upon completion of this chapter, the reader will be able to
describe the primary standards for temperature,
state the role of fixed point calibration and the necessity for an interpolation method in
establishing a temperature standard,
describe and analyze thermal expansion thermometry,
state the physical principle underlying electrical resistance thermometry,
employ standard relationships to determine temperature from resistance devices,
analyze thermoelectric circuits designed to measure temperature,
describe experiments to determine thermoelectric potential for material pairs,
state the principles employed in radiation temperature measurements, and
estimate the impact of loading errors in temperature measurement.
Historical Background
Guillaume Amontons (1663–1705), a French scientist, was one of the first to explore the
thermodynamic nature of temperature. His efforts examined the behavior of a constant volume
of air that was subject to temperature changes. The modern liquid-in-glass bulb thermometer
traces its origin to Galileo (1565–1642), who attempted to use the volumetric expansion of
liquids in tubes as a relative measure of temperature. Unfortunately, this open tube device was
actually sensitive to both barometric pressure and temperature changes. A major advance in
temperature measurement occurred in 1630 as a result of a seemingly unrelated event: the
309