| In the process of industrial and agricultural production,the moisture content of some substances will have a very important impact on the performance,quality and storage of their products.Especially in the tobacco industry,the moisture content of cigarette packets affects directly the cigarettes in storage and packing in later stage,thus it is a mandatory assessment index.In view of the low real-time performance of manual sampling oven testing and the high cost of foreign water testers,combined with microwave technology,real-time online non-destructive measurement is realized on the basis of simplified design,with good reliability and high precision.First of all,after introducing the advantages and disadvantages of several commonly used moisture content measuring methods,according to the actual situation of cigarette packets and foreign related mature product detection methods,the polarization phenomenon of water under microwave is utilized,and the dielectric constant of water is higher than that of other substances.The energy attenuation after microwave transmission is mainly caused by moisture.The accurate measurement of moisture content of cigarette packets is designed based on microwave transmission technology.On this basis,its mathematical model is built,and the moisture content of cigarette packets is indirectly measured by measuring the amount of energy attenuation.According to this principle,the overall scheme of the water meter is designed and its main working principle is analyzed.Secondly,software and hardware are designed according to the overall scheme of the water meter.As for the hardware,it is difficult to analyze the microwave directly due to its high frequency.A 1 KHz square wave signal is used to modulate and measure the amplitude change of the signal.The function and main parameters of each microwave device in the microwave RF transceiver module are introduced and designed.For the signal processing circuit module,a double second-order loop filter is designed to realize frequency selection and amplification,and STM32 processor is used for data acquisition.Add peripheral circuits such as measuring objects' height,ambient temperature and humidity to improve measurement accuracy.For software,according to the needs of actual measurement tasks,transplant UCOSII operating system and write related tasks.For acquisition tasks,DMA+ double buffer + interrupt mode is used to ensure real-time performance.On the PC side,Qt-based user software is designed.Its cross-platform features are convenient for later transplantation.According to functional requirements and module division,it is mainly divided into six modules: system overview,log overview,data viewing,basic settings,about and help.After detailed design of each module,reliable communication between software and hardware is realized.Finally,through the design of a simulated application environment for experimental debugging and functional verification,the results are analyzed.Debugging results show that the water measuring instrument designed in this master thesis can measure 0 ~ 30% moisture content in the acceptable error range,with the highest measurement accuracy reaching 0.18%,and the single measurement conversion time less than 500 ms,which meets the performance requirements on the premise of realizing the main functions of the instrument. |
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