The equipment works off the principle of infrared absorption spectroscopy. As the spectral signature of certain constituents is known, by measuring the absorption at certain wave-lengths, it is possible to determine the content of the constituent in the material.
An infrared source irradiates the sample on “useful” wavelengths. The backscattered light flow is then collected towards a detector. The moisture content being sought can be deduced by an analysis of the measured values correlated with a calibration.