E1C08 09/14/2010
14:54:1 Page 354
Radiative Temperature Measurements
Commercially applicable radiation thermometers vary widely in their complexity and the accuracy
of the resultant measurements. We will consider only the basic techniques that allow measurement
of temperature.
Radiometer
Perhaps the simplest form, a radiometer, measures a source temperature by measuring the voltage
output from a thermopile detector. A schematic of such a device is shown in Figure 8.28. The
increase in temperature of the thermopile is a direct indication of the temperature of the radiation
source. One application of this principle is in the measurement of total solar radiation incident upon
a surface. Figure 8.29 shows a schematic of a pyranometer, used to measure global solar irradiance.
It would have a hemispherical field of view, and measures both the direct or beam radiation, and
diffuse radiation. The diffuse and beam components of radiation can be separated by shading the
pyranometer from the direct solar radiation, thereby measuring the diffuse component.
Figure 8.30 shows infrared (IR) thermopile sensors that are manufactured using micromachining and advanced semiconductor processing methods. The hot junction of the thermopile is placed
under the IR filter and the cold junctions under the IR mask. Manufacturing methods allow hundreds
Diffuse
radiation
Radiation
from housing
Radiation
from dome
Thermopile
receiver
Direct
radiation
Dome
Figure 8.29 Pyranometer construction.
IR Filter
Mask
Hot junctions
Cold junctions
Figure 8.30 Industrial infrared (IR) thermopile sensor.
354 Chapter 8 Temperature Measurements
14:54:1 Page 354
Radiative Temperature Measurements
Commercially applicable radiation thermometers vary widely in their complexity and the accuracy
of the resultant measurements. We will consider only the basic techniques that allow measurement
of temperature.
Radiometer
Perhaps the simplest form, a radiometer, measures a source temperature by measuring the voltage
output from a thermopile detector. A schematic of such a device is shown in Figure 8.28. The
increase in temperature of the thermopile is a direct indication of the temperature of the radiation
source. One application of this principle is in the measurement of total solar radiation incident upon
a surface. Figure 8.29 shows a schematic of a pyranometer, used to measure global solar irradiance.
It would have a hemispherical field of view, and measures both the direct or beam radiation, and
diffuse radiation. The diffuse and beam components of radiation can be separated by shading the
pyranometer from the direct solar radiation, thereby measuring the diffuse component.
Figure 8.30 shows infrared (IR) thermopile sensors that are manufactured using micromachining and advanced semiconductor processing methods. The hot junction of the thermopile is placed
under the IR filter and the cold junctions under the IR mask. Manufacturing methods allow hundreds
Diffuse
radiation
Radiation
from housing
Radiation
from dome
Thermopile
receiver
Direct
radiation
Dome
Figure 8.29 Pyranometer construction.
IR Filter
Mask
Hot junctions
Cold junctions
Figure 8.30 Industrial infrared (IR) thermopile sensor.
354 Chapter 8 Temperature Measurements