Method Of On-line Measurement Of Paper Moisture Base On Microwave Resonance Cavity Perturbation

The measurement and control of paper moisture is directly related to the paper quality and production efficiency in paper production. In order to ensure the stability of production quality and production process, it is necessary to maintain the stability of the paper production process.On-line measurement of paper moisture can fully reflect the real-time distribution of paper moisture,it is the basis of quality control of paper.This thesis based on embedded system technology,combined with microwave cavity sensor technology to complete scheme design of paper moisture measurement system.Thus the change of paper moisture content in the microwave cavity will lead to the change of dielectric constant of the medium within the resonator, and it ultimately will reflect to the resonance frequency and power change. This system is to achieve on-line measurement of paper moisture by the detection of the resonance frequency and-3db bandwidth of the resonant cavity. In this paper,the hardware design and software programming are achieved,the real-time collection,calibration and storage of paper moisture are realized.The detection method has the advantages of fast, high accuracy, non contact, continuous and non impact on paper quality and density.This design mainly includes:1.Discuss the basic principle of measuring the water content rate of paper microwave resonant cavity method.establish the mathematical model between moisture content of paper and-3db power offset and bandwidth of the resonance frequency of the resonant cavity.2.Hardware design of detection system: related technologies to realize the function of each module are studied, the circuit of DDS+PLL frequency source module, the detector module, the main control circuit module are designed.3.System software design : the program design of each module of the system.Including the construction of software platform, the transplantation of em Win graphics library, the main program flow design, the sweep frequency source software design,the upper computer software design, etc..4.Experiment verification: using data of paper moisture collected by this system in the laboratory. using the least square method, according to the moisture content of paper and the corresponding microwave parameter fitting relation curves of moisture content, and the experimental data of the error are analyzed.