Design And Application Of High Precision Near Infrared Moisture Analyzer

The sections for producing the materials, such as tobacco, chemicalengineering, spinning, paper and food...etc., the moisture capacity is directly orindirectly one of the index signs for many products quality examination. Thetraditional method of measuring moisture is replaced by the infrared principle fordetermining moisture capacity, then the techniques and the instrument which areused to measure the moisture capacity are gradually in unify and perfect.Meanwhile development of chip stimulated the appearance of the high performance,low cost MCU. Hereafter, design for the small-sized, standardized, intellectualized,high accuracy, high stability of the instrument for measuring the moisture capacitybecomes the very realistic demand.The high precision infrared moisture instrument carries on the quantitativeanalysis for the moisture capacity. So it involves more extensive and basicknowledge and technologies concerning three aspects of the infrared optics study,the geometrical optics study and the photoelectron study.Experiments prove that different matters have different characteristic absorbapices in infrared spectrum area, then taking use of this character can design theinfrared moisture analyzer to measure the moisture capacity. In many characteristicabsorb apices in infrared spectrum area, characteristic absorb apices are adequatelyselected to be measured and computed. For improving measure precision and thesystem ability of anti-jamming, in addition two other wavelengths next to thiswavelength are selected, and with the absorbency expressions about threewavelength, the absorbency of samples measured can be got, and by computing themoisture capacity of samples are finally confirmed.Infrared photoelectron system has many sorts based on characters and requestof system. Infrared moisture analyzer adopts the type of aptitude photoelectronsystem, which is made by initiative and reflecting optic system. Halogen lamp isused for infrared lamp-house, the modulator modulate beam of emergent light.through the reflecting optic system, the light reaches the photo-electric detector.Finally the chip microprocessor handles, displays and controls. For improvingprecision, phase sensitive circuit is used for extracting feeble signal frombackground noise.Halogen lamp works within the scope of certain voltage. It is abundant ofinfrared emission spectrum, which can be used to measure moisture capacity aslight source. There is a chopper with three wave plates, which modulates the beamof light into three wavelengths needed.The system includes two parts: optical system and circuit system.i) Optical system is composed of infrared light source, two paths of ray, reflectingmirror, optical lens, chopper, electrical motor, sample table… The halogen lamp,half reflection lens, reflecting mirror, and collecting mirror make up of reflectiontype optical system. Light from the halogen lamp is divided into two beams by halfreflection lens, and becomes parallel light though reflecting mirror and lens. Theparallel light is modulated by the chopper and becomes three wavelengths. Threewavelengths light expose the sample on the sample table in turn, and then reach thephoto-electric detector by reflecting, so the photo-electric detector can take thesignal, which is the water absorption spectrum. Blacking inwall of the wholeoptical system can avoid the interference light from the background radiation.ii) Circuit system is composed of infrared photo-electric detector, preamplifiercircuit, synchronized device, phase sensitive circuit, MCU, displaying circuit…Theweak electric voltage signal from infrared photo-electric detector is magnified bypreamplifier circuit, phase sensitive circuit detects the modulated signal and getssignal needed and filter out the noise. The signal gets into PIC single chip throughthe A/D channel, the single chip carry on the data processing, manifestation andresult will be printed by printer connected with system.After the system is designed, a sample machine is made and some kinds ofpaper are chosen to carry on the test. The result indicated: The system works stably,accurately. It meets needs on the whole;The system functions well: Measuremoisture capacity. The system comes to the request for intelligence, it can completesignal receiving, data processing, result manifestation, print and communicatingwith exterior calculator automatically. However, this is the sample machine for testonly, and it is still not perfect somewhere, so produced the certain error. The reasonis various: Power supplies inaccurately, unsteadily, which leads to poor quality ofthe light source;Incomplete machine structure affects the test result bymiscellaneous light outside;Certain linearity the infrared photo-electric detectorexists and single multiple of the electric voltage in the circuit make measurementand signal processing not accurate enough;the background light interferes with thedetector because of the system poor enclosed. If taking into the improvement fromthis several aspects, the instrument can completely attain the function practicably.