Research On Multi-Wavelength Near-Infrared Moisture Detection Without Moving Parts

The moisture of materials is an important parameter during the production process in many fields.It is significant to detect the moisture of materials quickly and precisely.With the feature of non-contact,continuation and fast measure speed,the method of near-infrared detection has been widely applied to many fields in moisture detection.There are moving parts in traditional near-infrared moisture meter,which influence accuracy and stability of measurement by its machinery rotation,power consumption and volume of the equipment is larger as well.A new near-infrared moisture detection scheme without moving parts was proposed in this thesis,which against the disadvantages of traditional near-infrared moisture measurement instrument.Traditional high power light source was replaced by near-infrared LED,while mechanical modulation was replaced by electrical modulation.Useful signal drowning in strong noise background can be extracted by phase-lock amplifier technology.The main content in this thesis reads as follows:(1)The theory of near-infrared moisture detection has been studied,including near-infrared spectral analysis theory,diffuse quantitative analysis theory and the principle of three wavelength measurement.Phase-lock amplifier technology has been researched and applied to detect the weake signal.(2)Optical system of the near-infrared moisture meter was designed and simulated by LightTools.The optimal designing scheme of optical system was chosen after comparison and analysis.(3)Hardware circuit of moisture meter was designed and made to entity,which including power circuit,light source driving circuit,signal processing circuit and digital circuit.(4)The microcontroller procedures of near-infrared moisture meter was writed by C language,The PC software was completed in the Lab VIEW development environment.(5)The best measuring distance experiment,moisture meter calibration experiment,repetitive experiment and stability experiment was conducted by near-infrared moisture meter under laboratory conditions,which taking sinter mixture as moisture detection object.The results show that the best measuring distance was 0-150mm.Absolute variation in stability experiment was within 0.31%moisture content while measuring sinter mixture of 3%-8%water content.Relative standard deviation in repetitive experiment was 2.14%.Measuring error of this instrument was under 0.34%moisture content.