The working principle of the online near-infrared moisture analyzer is based on the absorption characteristics of water molecules towards specific wavelengths of near-infrared light. The core process involves the absorption and reflection of light, as follows:

The absorption mechanism of light

When near-infrared light (usually with a wavelength of 900-1700nm) is irradiated onto aqueous substances, the oxygen hydrogen bonds (O-H) in water molecules strongly absorb light energy of specific wavelengths. This absorption follows the principles of quantum mechanics: when the photon energy matches the molecular vibrational energy level, the photon energy is absorbed, causing the molecule to transition from a low energy level to a high energy level. The absorption intensity is directly proportional to the moisture content, that is, the more moisture there is, the stronger the absorbed light energy, and the weaker the transmitted or reflected light energy.

Reflection of Light and Signal Collection

Unabsorbed near-infrared light will reflect, including:

Mirror reflection: Light reflects smoothly from the surface of a material, without carrying any compositional information, and is usually considered as stray light interference.

Diffuse reflection: After entering the interior of a substance, light undergoes multiple reflections, refractions, and absorptions, ultimately carrying information about the composition of the substance and scattering out from the surface. The online near-infrared moisture analyzer collects diffuse reflected light through a concave focusing mirror and converts it into an electrical signal by a photoelectric sensor.

Signal processing and moisture calculation

The instrument adopts dual wavelength or multi wavelength technology to eliminate interference:

Measurement wavelength: Choose a wavelength that strongly absorbs water molecules (such as 1450nm).

Reference wavelength: Select a wavelength with extremely weak water absorption (such as 1900nm) to compensate for the influence of physical factors such as material color and particle size on reflected light.

By calculating the ratio of the reflected light intensity of two wavelengths and combining it with a pre established calibration model, the moisture content of a substance can be accurately calculated. This process is completed by a built-in circuit, achieving real-time, non-contact measurement.