Research And Development Of The Near Infrared Moisture Measurement Device

In the fields of medicines, food processing, papermaking, tobacco and chemical industry, measuring and controlling of the moisture is very important in manufacturing because it directly influences the quality and storage life of the products. The traditional moisture measurement methods by the use of drying or conductance measuring cannot realize online and non-contact measurement, and therefore have not been widely used. In this thesis, near infrared spectroscopy has been introduced for moisture measurement. This method is suitable for online moisture measurement in the industrial procedure. By using this method moisture can be measured on large area without touch in succession quickly. The important analysis fundamental of near infrared moisture measurement is Lamber-Beer law. Measurement principles and data processing methods of near infrared spectroscopy have been presented at first. And then the research of methodology about the near infrared moisture measurement has been done. The spectral experiments on the moisture measurement have been carried out with Bruker high-accuracy spectrophotometer. The results presented confirmed that the absorption peaks of H2O are around 5200cm^-1 and 6900cm^-1 within the band of near infrared. By modelling around two absorption peaks, the precision of the moisture measurement can be up to 0.2% and 0.3%, respectively. Based on the research of methodlogy, the device for moisture measurement with NIR was designed with grating as the optical component. It is three-layer structure, including light source layer, grating layer and circuit system layer. Lamp-chamber includes the three layers structure to increase the light energy and the system SNR. Quartz optic fibre was used to transmit light energy. The InGaAs detector was selected as the receiving device, which can be replaced according to the quantity of the necessary wavelength in order to lower costs. Signal collection circuit and data processing and control circuit were designed to collect and process the signal detected. The experimental results from home-made device showed that the wavelength range of the instrument is 1000-1700nm and the wavelength of measuring moisture is accurate. The repetitive precision of the instrument is 0.5‰ and its stability is about 1‰. Meanwhile, the results of moisture measurement showed that the precision of measurement with the model from 32 wavelengths is about 0.35% and the precision of measurement with 5 wavelengths is about 0.5%. Therefore, the home-made device can meet the requirement for the moisture measurment.