Understanding Infrared Thermography Reading 7 Part 2 of 2.pdf

Spectrally selective instruments employ interference filters to allow only a
very specific broad or narrow band of wavelengths to reach the detector. (A
combination of a spectrally selective detector and a filter can also be used.)
This can make the instrument highly selective to a specific material whose
temperature is to be measured in the presence of an intervening medium or
an interfering background. For example, for measuring the temperature of
objects from 200°C to 1000°C inside a heating chamber with a glass port, or
inside a glass bell jar, an instrument operating in the 1.5 to 2.5 µm band will
see through the glass and make the measurement easily. A very important
generic example of the need for spectral selectivity is in the measurement of
plastics in the process of being formed into films and other configurations.
Keywords:
interference filters
Charlie Chong/ Fion Zhang