1. Direct drying method
Direct drying method: according to ASAE standard, put the sample in the baking oven, keep it in the oven for 19 hours at 130℃; measure the weight loss, i.e., moisture content.
2. Capacitance method
Capacitance method: moisture’s electrical constant is far bigger than the electrical constants of other components in grain, the change of moisture content will inevitably cause the change of capacitance. By testing the capacitance change corresponding to moisture change of sample, the moisture content of the grain can be tested.
3. Infra-red heating drying method
Infra-red heating drying method uses infra-red light to heat the sample and remove the moisture, so as to test the moisture content. The main influencing factors are temperature and heating time. Online testing is not applicable for this method.
4. Microwave heating method
Microwave heating method uses the 2450MHz or 915MHz ultrahigh frequency microwave produced by microwave oven’s magnetron to oscillate the water molecules rapidly in order to make the molecules impact and rub each other and then remove the moisture in grain.
5. Ray method
Near infrared reflectance spectroscopy (NIRS) was first used in grain moisture testing in 1964. As different molecules have different features of absorption for near infra red lights of different wave lengths, when near infra red light (wave length 1940nm) is exposed to sample, light intensity of diffuse reflection is related to sample’s component content, in conformation with Lambert-Bill Law.
6. Micro wave absorption method
Micro wave absorption method started from 1840s. Moisture is tested indirectly by inspecting the absorption of micro wave energy by moisture or the change of parameters along with moisture like micro wave cavity resonant frequency and phase position.