Research Of High-precision Optical Density Detector

Optical density detector is an instrument that used to detect the transmittance ofobjects，which is widely used in biology, medicine, industrial coating etc.. In thefields of biology, medicine and industrial inspection, the optical density value ofoptical chip reflects the internal structure of the be measured objects; In the coatingproducing fields, the workers quality inspection of products through the real-timedetection of optical density. The accuracy of optical density detector directly restrictsthe development of these areas, so as to improve the accuracy of optical densitydetector has very great significance.This paper analyzed the basic principle of optical density detector, found the keyquestion that limits optical density detector’s accuracy is unable to accurately detectthe weak signal. Thus the author presented a detecting method of optical density thatbased on digital signal processor TMS320VC5509, to improve the accuracy of theoptical density detector.This paper introduced three modules of high precision optical density detectorsystem: light emitting module, optical sensing module and signal processing module.Then the author analyzed the fundamentals of this three modules and the selection ofthe key devices, completed hardware circuit design and software design of the system.The working process of high precision optical density detector is: the light emittingdiode (LED) issued a sine wave changing light, whose amplitude and frequency iscontrolled by TMS320VC5509A, and then used the photo sensor to detect theemergent light. According to the incident light and the transmitted light, you cancalculate the optical destiny value of the object to be measured. Because when theoptical density value is large, the emergent light is very weak, external noise makesit very difficult to detect. General electronic device will bring in error to this system,so this paper used digital signal processing method to analysis spectrum of emergentlight signal. Because the frequency characteristic of the useful signal and the interfering signal are different, we can detect useful signal accurately by this method,so as to improve the accuracy of optical density detector.Finally, the Proteus and MATLAB were used to simulate this system. And theDSP experimental box was connected with external circuit to test the standard opticaldensity slices.