Data Acquisition And Processing System Of UV Spectrophotometer Based On USB Bus

Spectrophotometer is a kind of optic instruments for analyzing various kinds of substances chemical components and their content based the principle that the substance can radiate or absorb to light in some wavelength. Now it has been used extensively in many fields such as food detection, Medical, Eduction &Research, Quality control departments, etc.There are some disadvantages for the traditional spectrometer, such as low efficiency, poor portability, and so on. In this thesis, a novel real time data acquisition and processing system of spectrometer based on USB bus and CCD is proposed. It is smaller, lighter, cheaper and faster than traditional spectrometer, has satisfied the request of stability, portability and cost control.This paper is composed of by such followings:1) It has been analyzed and compared that the current situation of domestic and foreign research and application of micro spectrometer. A new design of data acquisision and processing system is then proposed.2) The hardware of acquisition card for spectrum analysis based on USB bus and CCD is designed, which includes lamp circuit, CCD diver circuit, amplying circuit, A/D converter, communication circuit and clock generator. In this design, A 2048-Pixel CCD is selected as photo-electronic array dectector, which would satisfy the need of spectrum wavelength range between 190-780nm. A CPLD(Complex Programmable Logic Device ) is used to generate a synchronous clock,which drives the CCD to expose. Then the Analog signal is shifted. After analog and digital conversion, the result is writed into FIFOs(Fist In First Out)buffer by the asynchronous clock. At last,data is readed by host computer. Checking Mechanism in hardware is established to avoid the lost and mistake of data transmission. There are 4 digital output to control the external port,whose purpose is to control baffle for testing dark current.3) The software driver for acquisition card is designed, which includes the firmware of USB chip, Dynamic Link Library(DLL) and firmware of CPLD. Checking mechanism in software is established to avoid the lost and mistake of data transmission. In the standard development, driver has been tested and evaluated.4) Based on the interface of hardware and software, main framework of application software has been built.5) On the base of completed programme and tool MATLAB, the performance of acquisition card is tested and evaluated. Some experiments are completed in which Mercury lamp is used, then the data can be saved and exported.6) The properties of the signal obtained by data acquisition system is analyzed, then Some methods are applied to reduce the noise. Wavelet and average methods are applied in the spectrum signal processing of UV Spectrometer. The result are showed in the aiticle.