Pyrometry
Optical pyrometry identifies the temperature of a surface by its color, or more precisely the color of
the radiation it emits. A schematic of an optical pyrometer is shown in Figure 8.31. A standard lamp
is calibrated so that the current flow through its filament is controlled and calibrated in terms of the
filament temperature. Comparison is made optically between the color of this filament and the
surface of the object whose temperature is being measured. The comparator can be the human eye.
Uncertainties in the measurement may be reduced by appropriately filtering the incoming light.
Corrections must be applied for surface emissivity associated with the measured radiation;
uncertainties vary with the skill of the user, and generally are on the order of 5C. Replacing
the human eye with a different detector extends the range of useful temperature measurement and
reduces the random uncertainty.