Study On Multi-Gas Sensing System Based On Photoacoustic Spectroscopy

The improvement of gas sensing technology is significant in domains of atmospheric environment pollution monitoring, daily life, spaceflight technology, industry improvement, physiological processes research of biological tissues, and human medical diagnostic. Recently, with the modernization of industry, the environment changes complicatedly. Meanwhile, human's sense of protecting our environment becomes much stronger. In this course, the traditional gas sensing system turns out to be unable to content our request. So we need develop a novel in-stu gas detecting system with sensitive property and high resolution.This paper presents the theory of gas molecule infrared spectroscopy and gas detecting technology based on photoacoustic spectroscopy. It introduces the generating process of the PA signal. And the relationship of the PA signal and the gas concentration is given.It emphasizes on designing the structure of the PA gas detecting in this paper. It presents in details the design of the PA cell which is the core device of the system. The structure design and the significant parameters of the PA cell are deeply discussed. To realize the synchronous measurement of different gases, we choose the IR source with a wide spectrum(EMIRS200) as the light source of the system. It modulated by pulse in order to get rid of the noise caused by mechanical chopper. We choose the digital signal processor(DSP, TMS320F2812) as the core of the signal processing system to complete its interface circuit designation. PA signal from microphone is processed by the lock-in amplifier to discard its noise. Then, it is sampled and processed by TMS320F2812. With the strong calculating ability and the efficient executive ability of DSP, it is able to realize the in-stu and reliable on-line detection.This paper presents a new PAS, that is the Differential Mode Excitation Photoacoustic Spectroscopy (DME-PAS). With this method, the influence of the fluctuation of the light intensity and the microphone drift is avioded.In the end, the device is tested by the experiment of the frequency response of the PA cell, the repeatability and the stability of the system. It implies that it is feasible to utilize the DME-PAS to detect gases.