Development Of The Near-Infrared Moisture Measurement Device Based On Laser Diode Light Source

The moisture content of foods and agricultural products is a very important parameter both in production and life.Measuring and controlling the moisture is very important because it influences the quality and shelf life of the products.The traditional moisture measurement employs methods such as drying and conductive methods cannot realize online and non-contact measurement.Therefore,a simple and convenient method for moisture measurement is in great demand.In this thesis,near infrared spectroscopy has been introduced for moisture measurement.This method provides a quick and non-contact measurement to moisture in foods and agricultural products.The measuring principle of near infrared spectrometer has been introduced firstly. This study is based on the theories that water molecule has special characteristic absorption peaks in near infrared spectrum area and the amplitude of absorption has positive correlation with moisture content.For improving measurement precision and the system’s ability of anti-jamming,suitable specific wavelengths have been selected. In this study,relative reflectance of two characteristic absorption peaks has been chosen to describe moisture content in the sample.In this study,a near-infrared moisture measurement device based on laser diode source,integrating sphere and InGaAs detector has been designed by using virtual instrument as designing platform.In order to enhance the system signal noise ratio, light source stability has been improved and spare components and spectroscopic devices which are necessary in general spectrometer have been removed.Meanwhile, steady driven circuit for source and signal-amplified circuit for weak signal were designed,and personal computer was used to deal with digital signal getting from analogue-digital conversion.The result of experiment indicated that the linearity was 0.99%within the prescribed limits,and the repeatability was more than 1‰and the stability was 1‰. Using the self-made spectrometer to test the moisture content in milk powder and tea samples,the result of the models based on MLR and multivariate regression shows that it meets up to the practical demands.Compared with the WQF-400N Fourier Transform Spectrometer,the model precision of milk is better,while that of tea is worse.