Grain refers to raw and finished grains such as cereals, beans and potatoes for consumption. Moisture is one of the important chemical components in grains. It not only affects the physiological changes of grains, but also affects the processing and storage of grains and foods. The production. In order to accurately measure the quality of grain and ensure the quality and safety of grain in all links of grain procurement, processing, storage, and transportation, it is necessary to accurately measure grain moisture. So how is grain moisture detected? The following is a compilation of grain moisture detection methods for your reference.
1. The direct method is to directly remove the moisture in the grain through drying or chemical methods to detect the absolute moisture content of the sample. This type of method has high detection accuracy, but it is time-consuming and not suitable for online detection.
(1) Oven method: The direct drying method refers to placing the sample in an oven and testing in accordance with the GB 5009.3-2016 National Food Safety Standard for the determination of moisture in food.
(2) Halogen fast moisture meter detection method: The grain halogen fast moisture detector adopts the national standard method for moisture detection, and the result is basically the same as that of the oven, and the operation is simple, no special training is required, and the test time for outstanding characteristics is greatly shortened. Food samples can be done, a sample in a few minutes.
2. The indirect method is to measure the water content of the material through the detection of physical quantities related to water (such as the electrical conductivity and dielectric constant of the material). Such methods are generally fast, easy to realize online detection, and have good development and utilization prospects.
(1) Conductivity method: It is designed using the principle that the conductance or DC resistance of an object changes with its water content, and the water content of the object is detected according to the change in conductance. Its advantages are simple structure, fast response speed, low cost, etc.; the disadvantage is that grains generally need to be ground and pressed into a resistor of fixed size and shape. It is not suitable to detect the moisture of trace and high water content substances. In addition, the electrode is in contact with the sample The state of time will also affect the accuracy of detection.
(2) Capacitance method: It is designed by using the difference in dielectric constant of different materials. At room temperature, the dielectric constant of water is larger than that of other substances (water is 81, and food is about 2-5). As the water content of a substance increases, the dielectric constant also increases. Therefore, if the dielectric constant of the substance is detected, the water content in the substance can be calculated. The electrode structure of the capacitor is also different according to the measured substance. There are mainly flat plate and cylindrical electrode structures. The capacitance method uses non-contact detection, which is highly reliable, simple and economical, and easy to maintain. It can be used for online guillotine detection and is suitable for detecting high water content. The disadvantage is that there are many influencing factors and complex data. Among the grain moisture meters in the former Soviet Union, 43% of them use the capacitance method. At present, the detection accuracy can reach 0.5%, and the detection time is less than 5 minutes.
(3) Infrared absorption method: The theoretical basis is Beer's law. The infrared radiation with moisture at 1.649m or 1.94/zm has a strong absorption band. Because the water content of the substance is different, the absorption energy of specific wavelength radiation is also different. As long as the absorbance is measured, the water content can be determined. Specific methods include reflection method, projection method, and reflection and projection combined. The reflection type is mainly used for grain moisture detection. It has the advantages of non-contact, fast speed, continuous detection, large detection range, high accuracy, and good stability. It can also measure the moisture of conductive materials with the highest accuracy of 0.1%; the disadvantage is that it is affected by the shape and density of the sample. It is difficult to detect the internal moisture of the substance due to the influence of, thickness, etc., and the equipment price is relatively high.
(4) The microwave method is to use ultra-high frequency energy to calculate the moisture value through the change of energy loss generated by the sample. The dielectric constant of water is particularly high compared to that of grain, and there is a maximum dielectric loss in the ultra-high frequency range. Its advantage is non-contact measurement, can detect the absolute value of moisture content, and can be continuously detected online. The disadvantage is that the structure of the instrument is complicated and the price is high due to the influence of shape, density, thickness, etc.
(5) Neutron method: It works according to the principle of molecular scattering. Using a neutron source capable of emitting fast neutrons, the emitted fast neutrons meet with the substance containing hydrogen nuclei and collide with each other and slow down to slow neutrons. According to the measured density of slow neutrons, it is possible to know The total amount of hydrogen, calculate the water content of the substance. It is a more advanced online moisture meter, which can accurately detect without destroying the structure of the material and without affecting the normal operation of the material. The neutron moisture meter has disadvantages such as manual calibration and unstable hydrogen scattering.
Because traditional methods have complicated operations, low efficiency, and relatively high requirements for inspectors, in the rapid inspection of grain moisture, people mainly use professional instruments- grain moisture meters to complete the inspection work. The instrument operation is simple and efficient, and the operation is simple Easy to use, it is very suitable for all aspects of grain acquisition, processing, storage, transportation and other applications, and it is very practical.
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