Design Of A Mini Fast Scanning Near Infrared Spectrophotometer

Near Infrared Spectroscopy has been widely used in agriculture, pharmaceutical industry, food safety testing, chemical and other fields, due to its simple fast operation, reliable analysis, non-destructive, non-invasive sampling characteristics. The smaller and intelligent instrument has also been more and more attention.This article surveyed the near-infrared spectrum instrument's development and introduced the basic structural framing, also have studied the present small near-infrared spectrum instrument's principle of work and the application domain. In view of the serious stray light in this kind of instrument and the problem of scanning velocity, a small rapid scanning type near-infrared spectrometer (NIR) based on improved Czerny-Turner optical structure with its simulation and test results is presented. To reduce the stray light caused by multiple diffractions and multiple reflections, the optical structure is arranged and optimized by the Cary principle, the simulation and analyze result using optical software Tracepro are also presented in this paper. On the order hand, in order to increase the scanning speed, a harmonic motor is used to drive the grating directly instead of the traditional structure with a screw driver between the motor and the grating. Finally some basic test results of the near infrared spectrometer are presented.This paper innovatively presents Cary theory used in the design of rays path and optics software Tracepro that can be used to simulate and analysis the light-splitting optical system. The experiments result shows that the improvement structure has obviously suppressed the system stray light by reducing the second diffraction and excrescent stray light which reflects many times.This paper also improves the structure by changing traditional sinusoidal motor driving screw between motor and the scanning grating with using a harmonic motor directly to drive diffraction grating. The volume of the structure is reduced and the spectrum scanning speed is raised. The relationship between rotation of diffraction grating and the scanning wavelength is determined, and a signal detector is enough to detect the signal and process the data.In order to guarantee the stability of the instrument's performance, the circuit design has adopted the analogy and the digital closed loops in the design, which had guaranteed the photo and power source's stability. It is very important for the instrument wavelength accuracy and repeatability, as well as the instrument's absorbance accuracy and repeatability.Finally, the prototype's performance has carried on the test in near infrared light wavelength band. According to the principle of near-infrared technique as well as the near-infrared absorption theory, the transparent glucose solution is selected to take the sample experiments, it has carried on the simple qualitative analysis as well as the different density solutions opposite experiment.