Development Of Sampling Integrator In Fluorescence Spectrum Detection System

Sampling integrator is also known as the Boxcar average. It is a measurement device that utilizes the sampling and averaging technology to detect a cyclical signal buried in the noise. As Fluorescence detection system to detect the fluorescence signal is a single molecular collision, the luminescence is extremely weak, quantity is from several photons to tens of thousand of photons per sec, which is not competent for a conventional optical measurement, and the fluorescence signal pulse waveform of the rising or falling contains a wealth of high frequency waves. If a lock-in amplifier was used, low-pass filter in the output place would remove the high frequency, and waveform distortion appeared. For these signals in the detection, the integral sampling method is a very good choice.The issue is the steady-state measurement sampling integral. namely, integral sentinel sampling, the signal for a fixed period will be sampled in every periods, which is cumulated in a long time and averaged, and to get the accurate amplitude information of this point. It basically is affected by noise. Integral to sentinel sampling methods is used in detecting fluorescence spectroscopy measurement system fluorescence signal intensity, which is ingenious combination between weak signal detection technique and fluorescence spectroscopy technique. At the same time getting real signal, it isn't also to improve signal-to-noise ratio and improve system performance, but also greatly reduce the speed analog-to-digital conversion requirements.This Paper is divided into six chapters, whose structure and content are as follow:The first chapter describes the development trend and the areas of application about the fluorescence spectrum technology, and analyzes the feasibility and necessity of using sampling integral technical in the fluorescence spectrum detection system.The second chapter introduces the principle and the detection method of the fluorescence spectrum, and presents the whole Fluorescence detection system with focusing on the optical part of fluorescence spectra detection system.The third chapter discusses the applications of the integral sampling technology in the detection of fluorescence spectroscopy, analyzing the applications of sampling integrator and frequency response characteristics, and determining the sampling method and the parameter selection of the Sampling integrator in the detection system of fluorescence spectra, which supplies the theoretical basis for the sampling integrator.Chapter four based on the previous chapters shows the designed blueprint of the Sampling integrator in the fluorescence spectroscopy system. The blueprint is as follows: photomultiplier module——To improve the detection-sensitivity of the optical signal. Detecting fluorescence signal adopts CR114 - photomultiplier tube, studying the photomultiplier characteristics and designing the power circuit to meet the requirements of photomultiplier; Low-noise preamplifier module——MAX410 chip is used to amplify the weak telecommunication from the photoelectric detector output, reference trigger signal of sampling integrator is from driving frequency of the LED drive circuit; Sampling pulse circuit——MCU and CPLD is used to generate an adjustable door-pulse Tg, using 89C51 microcontroller, using of external 4X4 keyboard is to set microcontroller, electronic switch in sampling integrator adopts Fairchild's MOSFET IRF630B, using the circuit-level conversion circuit as driver; The firing circuit——emitter follower adopts OP₀7 in order to reduce the interaction between fore-and-aft poles that plays a buffer role; Filter circuit——using MAX275 special chip of MAXIM company in the United States to design active low-pass filter, designing the data sampling circuit and serial communication circuit.Chapter five is to test transmission characteristics of sampling integrator, and apply sampling integrator to the detection of fluorescence spectroscopy system. Characteristics of the system are tested, and compare the result of testing to UC920 fluorescence spectrophotometer, the result of which achieve the task expected.Chapter six summarizes the research work and results of the text, with analyzing some design yet to be further improved, and make some advices for future improvement.