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How do near infrared moisture meters work

Aug. 05, 2020

The infrared moisture meter is a non-contact moisture detector for various materials. The infrared moisture meter is suitable for many industries such as metallurgy, coal, chemical industry, chemical fiber, papermaking, tobacco, food, construction, etc. It can quickly and accurately measure the moisture value of each process in the production line to reduce manual sampling and testing. The use of infrared moisture meters is beneficial to collect and analysis real-time moisture data and guide the production. For example, soil, food, instant solid drink etc. need to maintain a certain amount of moisture to ensure good performance and quality of products. Too high water content of grain leads to mildew and deterioration. Too low water content changes the taste and the particles are easily crushed.

Water has strong absorption characteristics for infrared light in some specific wavelengths. When the material is irradiated with infrared light of these specific wavelengths, the water contained in the material absorbs part of the energy of the infrared light. The more water it absorbs, the more it is absorbed. Therefore, the decrease in reflected light can be measured to calculate the water content of the material. Since the reflectivity of materials to infrared rays varies due to their different absorption characteristics and stray characteristics, if only the absorption wavelength of water is used, the surface condition, color, structure and other factors of the material will interfere with the moisture measuremen. Therefore, the three-wavelength method is used for eliminating the interference of other factors during the moisture measurement.

The detection system of infrared moisture meters consists of an optical probe and a circuit. The optical probe consists of an infrared light source, an optical lens (B270), a beam splitter with optical filters and a plane optical mirror. There are two filters on the spectroscope, which are the measurement wavelength and the reference wavelength. The reflector material needs to have good thermal stability, high softening temperature, high mechanical strength and good surface smoothness. K9 optical mirrors with alumium coating can be used.

First, the light source in the infrared moisture meter emits infrared light through the different filters on the beamsplitter. Then the light is directed toward the material to be measured through the optical reflector. Different filters on the beamsplitter only allow a certain wavelength of infrared light (reference light and measurement light) to pass through. The beamsplitter rotates at a high speed. The infrared light is alternately directed towards the material to be measured. The reference light is firstly transmitted on the sample, and then the measurement light is transmitted on the sample. The reference light and the measurement light alternately pass through the high-precision infrared filters. The retained beam will be focused on the measured object. Part of these infrared light is absorbed by the material and partly reflected to the concave mirrors. These two energy pulses of light will be reflected back to the photoelectric sensor and converted into two electrical signals, through which the moisture can be inferred.

Over the years, CLZ Precision Optics Co., Ltd. has provided many domestic and foreign companies with high-precision optical components, including optical lenses, optical domes, optical mirrors, optical filters and optical prisms. Our company produces and processes various optical materials according to the drawings and requirements provided by customers. The optical material may be optical glass (N-BK7, K9, etc.), fused silica, sapphire, silicon, etc. According to the customer's applications, the processed optical element can be coated with dielectric coatings or metal coatings. If you need related optical products, please contact