Research On The Intelligent Wood Moisture Content Measuring Instrument

The detection of wood moisture content is an important process before wood processing. Presently, the testing instruments of wood moisture content are in the situation of low-level automation, low test accuracy and large artificial errors. The aim of this paper is to design an intelligent wood moisture testing instrument which can overcome the disadvantages mentioned above.A variety of wood moisture content testing methods were described and the advantages and disadvantages of these methods were analyzed respectively, the electrical conductivity method is chosen finally as the test method for wood moisture content. The design task was determined, the structure of the hardware circuit and the software programming were designed, and the co-ordination between the software and hardware was carried out, the development of the whole system was completed, according to the functional requirements of intelligent wood moisture testing instrument.The control system of the intelligent wood moisture testing instrument is a microcontroller which is considered AT89C55 as the core. According to the control requirements, the moisture content measurement circuit, temperature compensation circuit, and the control circuit of microcontroller were designed. In the wood moisture content measuring circuit, the pre-circuit to measure the resistance of wood was designed, the ordinary bridge circuit was improved, an experiment to test the improved circuit was carried out, and then the measurement results obtained were analyzed. The electronic switching circuit was designed and manufactured, the common field effect tube (FET) switch was improved, and the transfer function model of the improved FET switch was established and simulated through MATLAB-Simulink software. The simulation results between the improved FET switch and the ordinary FET switch was compared and analyzed. Finally, the circuit of the entire hardware designed was debugged, the PCB was made. The software of the control system was designed, the main program of the system, data collection program, data processing subroutines, module programs such as temperature subroutine were programmed by using C language within KEIL software, the program flow chart was given as well. The experimental system of the intelligent wood moisture measuring instrument was produced.In order to verify the detection accuracy of the intelligent wood moisture instrument, a large amount of experiments, based on the circuit board designed and the instruments and equipments involved in the weighing method, to different types of woods were carried out. The comparative analysis of two different testing results was completed, the error analysis diagram was drawn and it shows that the measurement error of the instrument can meet the requirement of the measurement accuracy.