Analysis of Influencing Factors of Wood Moisture Meter
At present, the two measuring instruments with the highest market share are the resistance method and the microwave method wood moisture content meter. When the moisture content of the wood is less than the fiber saturation point, there is a certain linear relationship between the resistance of the wood and the moisture content. The resistance method wood moisture content meter is designed based on this relationship. When using it, you only need to insert the probe into the wood board. In the middle, the moisture content value can be read directly. The main factors affecting the measurement results of the moisture content of the resistance method are wood material and temperature: because the ash content and crystallinity of each tree species are different, the resistance of wood varies with different species; and the resistance of wood varies with temperature. Higher and smaller, its resistance has a linear relationship with absolute temperature, so it is necessary to consider the influence of tree species and temperature during verification. The ST-85 resistive wood moisture content measuring instrument produced by Shanghai Industrial Research Institute was used to measure the poplar samples prepared according to the method stipulated in the regulations, and to adjust the correction and temperature adjustment selection of each tree species.
It can be seen that for the resistance wood moisture meter with correction gear, the correction coefficient between different tree species is about 2.2%. For the instrument with temperature correction gear, in the common temperature range, every 1 °C increase , the moisture content measurement results decreased by 0.17%~0.10%. Therefore, in the calibration process of instruments with temperature and tree species selection gears, the accuracy can be ensured by selecting the appropriate temperature and tree species gears; for instruments without temperature correction, the calibration environment must be kept at "normal temperature"; For instruments with selected gears for tree species, the measurement results should be corrected according to the instructions, or the allowable error of the indication value of such instruments should be increased.
Influencing factors of microwave method
The microwave wood moisture content meter began to appear in the 1990s. It uses the difference in the absorption of electromagnetic waves by wood moisture to measure the moisture content of wood. It has the characteristics of not damaging the wood surface, convenient and fast, and stable and reliable readings. The measured moisture content value is the average value of the moisture content of the wood covered by the instrument sensor, which is not affected by temperature, but for different species of wood, different compensation values are divided according to the density, and the correction file can be selected according to the species and density of the wood to be measured. During the verification process, since the thickness of the sample specified in the regulations is 10mm, and the penetration range of the microwave moisture content meter can reach 50mm, it is necessary to keep the wood sample suspended in the air during the verification, and at the same time, it is necessary to attach the sensing surface of the instrument to the wood surface. tight to ensure measurement accuracy.
