Powerdensity Measurement System Of Laser Surgery Instrument

The purpose of this experiment is to research and design a kind of power/power density measurement system which is especially profit for Low-Power laser therapy and PDT therapy. Considering that the spectrum of Low-Power laser therapy and PDT therapy is between 1 millwatt to several watts, this experiment need to design a kind of amplification circuit that can both amplify the weak DC signal and change the range of measurement. The circuit must also fulfill the need of low distortion and noise. As the reason that the main factor of which can effect the curative of Low-Power laser therapy and PDT therapy is the power density of laser instrument, the measurement of powerdensity should also be designed in the experiment.During the research, the first task was reading a large mount of materals which contain the content of the main measurements of power and powerdensity and the development of this area in the world. By the information of these materials, thermopile was chosen to be the sensor of the measurement system. Then a series of experiments were done to discovery the truth of thermopile and make sure the signal type of the thermopile's output. By the use of frequency-domain analysis, the frequency response of thermopile had been made sure, and the noise sources were also found.This paper introduced the En-In amplifier noise model and the deduce of its formula. By the use of En-In amplifier noise model and frequency response of thermopile signal, the chip of advance amplification which was especially fit for thermopile was chosen after comparing the capability of several kinds of chips. After that, the system function of this amplification circuit was deduced and the frequency domain model was established. Then the sigal and noise of the thermopile output was analyzed by frequency domain analysisi means. The signal dispose circuit was designed based on all mentioned above. The design of range-changing circuit(using OP07 as the core), AD conversion circuit(using ADS7805 as the core), digital disposition and display circuit(using Atmega16 as the core)were introduced too.By the means of structure design, the program of power/power density measurement system was designed. In this article, the entire program flow chart and the principle of subprogram were expounded. The oversampling technology which was used in eliminating error and the mean value approximation technology which was used in initiating clear were the main innovation of the article.After associated testing of the soft/hardware, the parameters of power and powerdensity were obtained. By the means of data processing and analyzing, we can ensure that the function of realtime power and powerdensity measurements was realized, and it proved the precision of the obtained average laserpower satisfies it's design requirement (error<2%, standarded by Gentic SOLO PE powermeter). it obtained that the precision of laser power and laser power density satisfies its design requirement(error<2%).At the end of this paper, the system error was analyzed. The advise of soluting these error was gaven. This article also displayed the model machine which based on this research.