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IR Moisture Technology





Near Infra-Red Reflectance Moisture Analyzer Technology

Measuring Principle

Water offers four absorption bands in the near infra-red region at 1.2, 1.43, 1.94, and 2.95 micrometer wavelenghts. When a material is subjected to the light having any of these wavelengths, the light is absorbed in proportion to the moisture content of the material (the absorbance varies with the content).

The water content can then be determined based on the attenuation. However, with only the light having a water absorption wavelength, the measurement is influenced by many factors including the surface conditions, grain size, color, and other absorbing components which will result in unstable moisture measurement. Therefore, near infra-red radiation which is not absorbed by water is used as the reference comparison wavelength light. The ratio of the energy of the reflected indicating absorption wavelength light to that of the reflected reference wavelength light is measured and converted into the moisture content.

It is very important to choose the appropriate indicating absorption wavelength as well as the reference wavelength(s) very carefully. Our moisture analyzers incorporate a multiwave measuring technique which allows for increased sensitivity and the ability to measure sample types such as black bodies. The 2 and 3 wavelength based equipment may have difficulty in measuring many types of samples due to a limited reference signal which is overcome by the multiwave approach. The lamp intensity also plays an important role in obtaining good results with this type of equipment.

Dedoussis Engineering offers The OMM-3000 NIR process unit for on-line measurent and production quality control as well as for bench analysis.

This type of measuring technique is best suited for moisture between 0 to 80%. Since it is a sample absorbance/light reflectance measuring technique, it is most applicable for homogenious solids or powders. The accuracy is generally related directly to the surface characteristics of the sample and typically is less that 0.1% water. The low range measuring limit is around 0.1% water.

This technique is excellent for quality control or quality assurance measurement. The unit is generally calibrated using a loss on drying technique or Karl Fisher titration method. After sample calibration, (required only one time), the measurement is instantaneous and requires no chemicals or sample preparation. The equipment is easy to use and anyone can be trained to operate either instrument in a very short period of time.



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Last modified: April 26, 2000