| With the rapid development of science and technology, there is a growing demanding for fast, accurate and on-line measurement of gas concentration in more and more areas. Conventional measuring methods for gas concentration, such as gas sensors and gas chromatography, have been unable to meet this need. This paper researched a new measuring system for gas concentration, which was based on the infrared absorption spectroscopy. The new system with the advantages of gas selectivity, good stability, high sensitivity and fast response can implement on-line, non-contact measurement.In this paper, CO2 was selected as the target gas. Its infrared absorption model was established and the concentration was calculated based on the analysis of the infrared absorption principle and the Lamber-Beer law. So the overall plan of NDIR (Non-Dispersive Infrared) measuring system has been designed, which can be divided into three parts.1. Optical parts. The design and installation of optical system were completed by comparing and selecting the light source, infrared detector, gas chamber and other optical components.2. Hardware parts. According to the character of the source and detector, the functional modules were designed, including source driver, signal processing, A/D conversion, control, display and temperature control. The anti-jamming design of the system was carried out based on the analysis to the cause of interference.3. Software parts. In accordance with the identity of hardware and the requirements of the system, the single-chip software was developed based on PICC language, including the main program, data collection subroutine, data processing subroutine and display subroutine.After designing and debugging for the function modules of the system, the theoretical calibration and preliminary experiments were proposed. Finally, the theoretical error analysis was carried out. The results of the experiments showed that the expected performance specifications of the system were achieved. |
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