The Study On Key Techniques For Near-Infrared Spectroscopy Analysis Of The Grating Monochromator In Gasohol

Fuel ethanol can improve the octane rating of gasoline and can also increase the concentration of oxygen in the gasohol. It can accelerate the combustion, and also reduce the exhaust emission of CO and HC effectively. In view that the energy crisis is more and more severe, and with the pressure from the environmental protection agencies,many countries begin to use gasohol in order to solve the problem.In order to decrease the use of petroleum, reduce the air pollution and have a good agriculture cycle, our country has begun to use gasohol in many provinces. When the concentration of ethanol in gasohol is not normal, it will reduce the power output of engines and harm the parts of the autocar. In order to ensure the quality of the gasohol and guarantee the benefit to the owner of the autocar, it is necessary to measure the content of the ethanol in the gasohol.Near-Infrared Spectroscopy (NIRS) analysis technique analyses the characteristic of sample by using the property that the near infrared active sample can absorb the energy of special bands. The instrument is portable and is convenient to use. The analysis technique is quick and will not cause pollution to the environment. The application of the technique is based upon chemic metrology,instrument science and computeracy.The laboratory have developed some instruments about near infrared analysis and got the sponsorship from Jilin Provincial Science & Technology Department (20050529): application research that is based upon light-fine photoelectricity analysis instrument and measuring the content of ethanol in the gasohol. Based on previous study, this thesis researches the feasibility that the near infrared technique can be used in gasohol analysis and design portable near-infrared spectroscopy analysis instrument system. The instrument is the grating monochromator, and can be used in transmission analysis of the ethanol gasohol and in diffuse reflection analysis of mineral. The key techniques in instrument design, creation of analysis model, and abnormal value extraction in near-infrared spectroscopy analysis of the ethanol gasohol are solved.The main study work and productions:1 . Design structure of the instrument, according to the different characteristics of diffuse reflection analysis to solid sample and transmission analysis to liquid sample, different loading sample system and sample pool is adopted. The optics and machine systems that can be used in transmission analysis and diffuse reflection analysis are devised. According to differences from samples'form (liquid and solid), different sample pool and different testing flow are adopted in order to realize the spectrum measure of sample.2. The technique of Lock-in Amplifier. It does some researches on digital Lock-in Amplifier (DLIA).The measuring errors caused by frequency fluctuation of spectrum signal and the disadvantages of analog Lock-in Amplifier (ALIA) in near-infrared spectroscopy instrument of the grating monochromator scan type are analyzed. A Digital Phase Sensitive Detector (DPSD) design principle and method of synchronization integer-period sampling are put forward. Finally, the comparative signal-to-noise test results that contrast this method with analog lock-in magnifier are presented.3. The design of power supply system. The high quality power is required by lamp,optical chopper,amplifier,step motor and digital control circuit in the system. This thesis analyzes the characteristic of portable instrument and different demand of the power supply system. According to the characteristic and demand, the suitable power supply system is designed. This system can work by battery or by the city electricity system. The battery can also be charged by the system. There is no difference when the instrument work through the designed power supply system and the big combined power supply system that can be bought from the market. The result can satisfy precision demand.4. The study on methods to create the application model of near-infrared spectroscopy analysis in gasohol. With Principal Component Regression (PCA) and Artificial Neural Net (ANN), the application model to get the content of ethanol in gasohol is created. The principal component number choice is selected by PRESS value. The actual result indicates that the quality of models can be improved through reasonable principal component number and effective pretreatment method of the data.5. Dynamic local model creating. In order to improve the quality of the model, the dynamic local model method is designed. Through model forecast error and predictive value of the sample to be predicted, the possible range of sample attribute is set, which reduce the range of the ethanol content in the sample. Through settled rule in advance, the standard samples are dynamic adjusted and the prediction veracity is improved6. The study for the extraction method of abnormal samples. The extraction method of abnormal samples include the extraction of abnormal value of the spectrum in special wavelength, abnormal spectrum and abnormal value of the attribute to be predicted. In order to eliminate the unrelated wavelength and get the effective wavelength, the correlation coefficient method is used. The abnormal samples are firstly selected through Mahalanobis distances. The abnormal samples that come from all kinds of resean and can not be selected by Mahalanobis distances are selected by the repeated prediction method.The main innovation work.1. The portable near infrared spectrometer of grating monochromator is designed. The spectrometer can be used to analyze the liquid samples in transmission analysis and to analyze solid sample in diffuse reflection analysis. 2. The digital Lock-in Amplifier for the grating monochromator is designed.3. The mathematics model for content analysis of the ethanol in gasohol is designed. The model is used in the field analysis of gasohol.4. The repeated prediction method is designed in order to select the abnormal samples according to the characteristics of the abnormal samples in near infrared analysis of the gasohol.The work of this thesis will have following function:1. Supply a new method for the field fast analysis and new instrument which should have independent knowledge right.2. The process of the field near infrared spectrometer with our right to the market will be speeded up. It will supply a reference for the multi-function design of the near infrared spectrometer.3. Advance the application of the near infrared analysis and speed up the development of the near infrared analysis software.In the mean while,the study of the key techniques will advance the application of near infrared analysis in gasohol analysis. The process of analysis will be simplified, so that the quality of the gasohol and the energy stratagem will be guaranteed.