Study On Method For Fruit Sugar Measurement Based On NIR Technique

As an important agricultural products, fruit is the main food in people's daily living, and its quality is closely related to people's life. So quality check is very important to people's health. The quality check includes two aspects, i.e. shape detection and internal quality testing. External testing contains some parameters such as color, size and shape defects. Internal quality testing mainly includes sugar degree, acidity, and so on. In order to improve the quality of fruit, we need track its quality and take reasonable measures at any time on its growth progress.At present, China has not developed uniform standards on quality for all types of fruit. Each year China produces and exports many fruit, but fruit quality has a large gap to international standards and its price is low. So, we urgently need to raise our level of detection and improve quality of fruit. In many detecting aspect, sugar degree is an important indicator to classify fruit maturity.The detection of sugar degree relies on destructive sampling nowadays. It is difficult to achieve rapid, accurate and continuous measurement. In order to achieve NDT(non-destructive test), researchers have applied near-infrared spectroscopy to the detection of fruits from the beginning of the 20th century, which used the spectrometer for full spectrum scanning and regression analysis. But this method cannot provide a dedicated NDT equipment, and has much disadvantage. In recent years, as the rapid development of fiber-optic communication technology, new devices such as small semiconductor LD and LED light source are constantly emerging. This provide technical support for developing small dedicated detection equipment. The thesis research on the absorption curve of glucose, sucrose, fructose, and the water in near-infrared spectral area in apple. Monochromatic light signal, which is specific wavelength, is produced by using broadband light source and filter. The light signal is modulated first and then transmitted through optical fiber. Some method such as lock-in amplifier is used to deal with the sensor signal for extracting weak sugar absorption signal.This paper totally includes six chapters. The contents of the paper are as follows:The first chapter introduces the development of the fruit sugar degree measurement and, then talks about the research actuality in home and abroad. The second chapter explains the basic operation principle of the fruit sugar degree measurement system. Based on the analyzing of near infrared spectrum principle and the curve of absorb, the chapter chooses the working wavelength of the system, and designs the overall scheme of the fruit sugar degree measurement system finally.The third chapter designs the optical part of the system in detail. This part provides the detailed design plan of the light source modulating and the light road; in the light source part, introduces the bases of the light source choosing and the concrete implementation method of the light source modulating; in the design of the light road, explains the overall design plan of the light road system, then introduces the reason that choose the strain slide to divide light, the basic principle of optic fiber and coupling. The last, this chapter provides the reason that chooses PIN photodiode as the receiving device, and gives the characteristic parameter of PIN.The fourth chapter designs the electric controlling part of detection system. The overall project is advanced at first. Then the chapter expounds the design of photoelectric signal detection circuit, lock-in amplifier circuit, data acquisition and communication interface. In the photoelectric signal detection part, signal input circuit and preamplifier circuit is designed for the primary conditioning. As photoelectric signal is very weak, preamplifier only is not enough to extract the signal which buried in the noise and lock-in amplifier circuit is designed. Then the circuit of A/D conversion and RS232 that based on SCM is designed. The raw data is sent to PC for processing.The fifth chapter is system testing and error analysis. The standard signal is achieved after debugging the optical part and circuit. After experiments on sugar degree, the data curve is mapped.The sixth chapter sum up the work and proposes the further work to improve.