Research On Moisture Content Detector Of Sapwood Based On Electrical Resistance Method

Forest contains abundant forestry resources.As the source of forest products processing,the growth status and development of living wood affect the quality of wood.Water content is one of the important indicators to reflect the growth of living wood.The traditional water content detector using resistance can only detect the water content below the fiber saturation point(30%)of wood material,and the detection of high water content has been a difficult problem in domestic and foreign research.To solve this problem,based on the theory of moisture content detection using resistance method,the overall scheme of sapwood of living wood trunk moisture content detector is proposed.Studied the detection probe,RC oscillation circuit,analog switch circuit,signal amplification circuit,temperature collection circuit,power circuit,the hardware system,single-chip microcomputer and single chip microcomputer hardware circuit,the main program of single chip microcomputer,data acquisition program,filtering,data processing program,interrupt program and other software system,detection instrument suitable for standing timber moisture content is developed.In laboratory tests,using four species of tree:fir,linden,birch and larch,test calibration and reliability test of RMC-1 type living wood sapwood moisture content detector is carried out,got the relationship between living wood sapwood moisture content and resistance at room temperature,and through the method of temperature compensation to optimize the resistance of living wood.The optimal calibration equation of water content detector and the insertion depth and width of probe are given.The research results of this paper are as follows:(1)During the development of water content detector,a new resistance detection method-RC oscillation circuit is proposed,two detection channels are designed,and anti-pulse interference filtering method is innovatively used for program design to improve the accuracy of data.(2)The hardware system of moisture content detector can detect the moisture content of sapwood,and has a good ability to detect the high moisture content of living wood;The software system realizes the accurate processing of moisture content data and the stable display of detection results.(3)The best insertion method of water content detector was determined in the laboratory test.The detection effect of birch,linden tree and larch was the best when the insertion depth was 50mm and the insertion width was 20mm.The R~2 of the fitting equation were 0.912,0.98and 0.86,respectively.The detection results of abies were best when the insertion depth was30mm and the insertion width was 20mm,and the R~2 of the fitting equation was 0.79.The mathematical relationship between water content and electrical resistance of sapwood is power function at room temperature.(4)RMC-1 live wood sapwood moisture content detector can be used to test the sapwood moisture content of fir,linden,birch,larch and other tree species.The detector has certain feasibility for the live wood moisture content detection,the average error is 2.7%,the measurement range is 0-95%.