Understanding Infrared Thermography Reading 3

86.Radiation rererenee source - A blackbody or other target of known temperature
and effective emi ssivity used as a reference 10 obtain optimum measurement
accuracy. ideally. traceable to NIST.
87.Radiation thermometer – See infrared radiation thermometer.
88.Radiosity – See Exitance, thermal.
89.Rankine - Absolute temperature scale related to the fahrenheit relative scale. The
Rankine unit is equal to 1ºF; 0 Rankine = - 459.72 ºF ; the degree sign and the
word degrees is not used in describing Rankine temperatures.
90.Ratio pyrometer - An infrared thermometer that uses the ratio of incoming infrared
radiant energy at two narrowly separated wavelengths to detennine a target's
temperature independent of target emittance; this assumes graybody conditions
and is normally limited to relatively hot targets (above about 149 ºC, 300 ºF).
91.Reference junction - In a thermocouple. the junction of the dissimilar metals that is
not the measurement junction. This is normally maintained at a constant reference
temperature.
92.Reflectivity, (reflectance) (ρ) - The ratio of the total energy reflected from a surface
to total incidence on that surface; ρ = 1 - Ɛ - τ; for a perfect mirror this approaches
1.0; for a blackbody the reflectivity ρ is 0. Technically, reflectivity is the ratio of the
intensity of the reflected radiation to the total radiation and reflectance is the ratio
of the reflected flux to the incident flux. In tthermography, the two terms are often
used interchangeably. (only subtraction where is the division, ratio?)
Charlie Chong/ Fion Zhang