Development Of Measurement And Control System In Near-Infrared Spectrometer

The Near-Infrared spectroscopy technique is the most advanced and attractivespectrum analytical technique since 1990's, praised as analytical giant. BecauseNear-Infrared technique has many advantages such as high analyze speed, low cost andno-pollution, it has been used more and more widely. Traditional spectrometers belong tolarge precise instruments. They not only have large bulk, but also request harsh environment.They are not suitable for in situ analysis. So the research on potable Near-Infraredspectrometer has become a hotspot recently. After years of hard work our lab has developedthe prototype of Near-Infrared spectrometer, which has realized the fieldworkers' dream'bring the analytic lab out to the field'. The paper analyzes the shortcomings of the prototypeand improves it. A Near-Infrared spectrometer product is designed.This paper totally includes seven chapters. The contents of the paper are asfollows:The first chapter expounds the principle, application areas, current researchstate and existed problems of Near-Infrared spectrometer, analyzes the possibilityand necessity of the development of portable Near-Infrared spectrometer.The second chapter analyzes the shortcomings of the prototype, puts forwardthe research content of this project. The hardware platform and interface is selectedby comparison , and the measurement and control system of Near-Infraredspectrometer is designed. The standard RS232 interface and USB interface are bothadopted as the communication interface. There are two sets of software, one is themeasurement and control software based on standard RS232 interface and Windows CEoperating system, which is mainly used in the field;the other one is based on USB bus andWindows 2000/XP operating system. Users can select different sets of scheme according totheir own needs.The third chapter talks about the research on Lock-in Amplifier inNear-Infrared spectrometer. Firstly it introduces the principle of Lock-in Amplifier,discusses the advantages and disadvantages of analog Lock-in Amplifier (ALIA)and digital Lock-in Amplifier (DLIA). Secondly it does some researches on digitalLock-in Amplifier, analyzes the measuring errors caused by frequency fluctuationof spectrum signal, puts forward a new integer-period sampling DPSD method, anddiscusses several noticeable points. At last the comparative signal-to-noise testresults between this method and ALIA are presented. Theoretical analysis and testresults show that this method can be used in Near-Infrared spectrometer's weaksignal detection, and the spectrum signal can be acquired from the strong noiseaccurately.The forth chapter designs the communication interface of the measurement andcontrol system. The characteristics of PDIUSBD12 are introduced, the noticeablepoints of USB interface circuit are discussed, the development methods and diagramof firmware are presented, and the development ideas of driver are explained.The fifth chapter talks about the development of measurement and controlsoftware, including system self-checking module, spectrum scanning module,parameter setting module, spectrum data pretreatment module and helpdocumentation. Aiming at the two sets of scheme, the software based on PC andPDA platform are designed. The functions and key techniques are expounded.1. Develop DLL based on VC++6.0, which packed all the communicationfunctions for USB bus, made upgrading and modifying the software much easier.2. The method of operating the instrument through CLF node using DLL isintroduced.3. Aiming at the characteristics of Near-Infrared spectrum analysis, thespectrum data pretreatment module is designed via LabVIEW's strong dataprocessing functions.4. Make some improvement on the former software based on Windows CEoperating system, improve work efficiency via multithread programming.In the sixth chapter the performance test results of Near-Infrared spectrometer productare presented. The comparison experiments among the Near-Infrared spectrometer product,Spectrumlab 400 from Shanghai and PIMA made in Australia demonstrate the instrument canreflect the spectral characteristics of samples and the measurement and control system meetsthe design requirements.The seventh chapter summarizes all this paper, and puts up some questionswhich should be researched continuously in the future.