| Near infrared spectroscopy is highly efficient analytical instrument with rapid development,which is an organic combination of spectroscopic technology,measurement test technology,computer technology and stoichiometry.Compared with the traditional technology,the Near infrared spectroscopy has the advantages of nondestructive detection,no reagent,no pollution,high detection efficiency,fast analysis speed,analysis of low cost,being suitable for in situ detection and online analysis,which has been widely applied in the medical pharmaceutical,agriculture,forestry and petrochemical,and many other fields.Because of the complexity,the development of domestic near infrared is late,and most of the spectrometer has higher cost,some has many deficiencies in the instrument stability,resolution and scanning speed.Therefore,it is of great practical significance to develop the grating type highspeed scanning near infrared spectrometer.This paper combined the advantages and disadvantages of the current raster scanning near-infrared spectrometer.It adopts the gear transmission structure,the grating was driven to rotate through the stepper motor drive gear.The combination of electric subdivision and mechanical subdivision effectively improved the speed and accuracy of the spectral scanning.A spectroscopic system,a hardware system for designing a near-infrared spectrometer,and software control system were set up,and software and hardware debugging were performed.The relevant experimental verification of the practicality of the near-infrared spectrometer was carried out.The main research content was as follows:1.The basic principles of near-infrared spectroscopy and the theoretical basis for quantitative analysis using near-infrared diffuse reflectance spectroscopy was Introduced.The dispersive theory was introduced to provide a theoretical basis for the design of near-infrared spectroscopy.The overall system scheme of the near-infrared spectrometer was designed,which consists of four parts: the spectroscopic system,the signal processing system,the STM32 control system and the host computer system.2.The optical path structure of the instrument was designed,and the specific parameters of each component was introduced.The theoretical calculation of the relationship between the scanning wavelength of the grating transmission mechanism and the rotation angle of the stepping motor is mainly performed.The stepping motor was used to drive the sector gears to drive the rotation of the grating,thereby realizing the fast and high-precision scanning of the wavelength and completing the spectroscopy process of the near-infrared composite light.The detailed design of the hardware system of the near-infrared spectrometer includes the design of STM32 control system,signal acquisition module,cooling control module,motor drive module and communication module.3.The software system of the near-infrared spectrometer was designed,which included the software design of the lower computer(STM32 control system),the software design of the PC,and the software design of the Android terminal.The lower computer receives the control information from the upper computer,which realizes the drive control of the stepping motor and the collection of the spectral signals,the communication module was designed,including realization of the USB and WIFI communication in two modes respectively.From the practical application point of view,two sets of near-infrared spectrometer application software were designed and developed: The PC side application software was developed based on C# language and the functions of parameter setting,instrument control,sample data saving and spectrum display were realized,and smoothness,the data preprocessing methods such as processing,baseline correction and peak seeking were achieved.and the application of the spectrometer application program on the Android platform have enabled the control of near-infrared spectroscopy,spectrum acquisition,real-time display of maps,data storage,and WIFI communication.4.The performance test of the prototype of the near-infrared spectrometer was carried out,and the wavelength range,resolution,baseline stability,wavelength accuracy,system stability,repeatability of the absorbance,and scanning speed of the instrument were comprehensively analyzed.The sinusoidal fitting method was used to calibrate the wavelength of the instrument.The results showed that the fit of the fitting function with the calibration data was better.A high-pressure mercury lamp was used as a standard light source,the resolution of the instrument was tested,and the results showed that the resolution of the developed near-infrared spectrometer was less than 10 nm.Repeated measurements of the absorbance of the instrument were tested and the results showed that the repeatability of the absorbance was within 1 nm.100% T measurements were made on standard whiteboards,standard deviation were less than 0.0005,the instrument's baseline stability was better.The wavelength accuracy of the instrument is ±0.4.The wavelength fluctuation of the instrument during the working process is less than ±0.8%,and the system stability was high.The instrument performed a full spectrum scanning in less than 8 seconds.Near-infrared spectrometer prototype was used to quantitatively test the protein content in flour.The results showed that the model was stable and reliable. |
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