| Carbon dioxide is generated in cell as a production of metabolism. It is transported via blood and outputted through lung. The content variation of carbon dioxide in the expired gas reflects the metabolism of organs, the circulations, the breath and the functional changes of air duct and lung system. This kind of variation is of great importance in clinic. The partial pressure or concentration of carbon dioxide in the end of expiration is one of the important life indexes and also a clinical monitor index for the anesthetized patients and those who suffer from respiratory dysfunction.Currently, the philosophy of measurement of carbon dioxide in the above mentioned area is based on non-dispersive in-frared(NDIR) technique. It mainly focuses on the corresponding relationship between the gas concentration and the in-frared decrement. Gas concentration is then calculated by the decrement. In this paper, a real time carbon dioxide monitor device is designed on the basis of in-frared absorption. A special sensor structure is designed. Main-stream gas circuit technique is utilized to make gas sampling. Data collection is controlled by ARM chip. Concentration calculation and compensation are then carried out to realize continuous in vivo detection of parameters, such as concentration of carbon dioxide and breathing rate.In this paper, the basic principle of in-frared detection is represented and special attention is paid on introducing single-channel double-wavelength compensation technique. In the foundation of analyzing the NDIR principle, a mainstream ET-CO2 detection system is designed, and is usually used to measure the ET-CO2 concentration, respiratory pattern and respiratory rate. In order to ensure the accuracy of test results, the system uses ADμC7026 to do various compensation algorithms, including limiting filtering, temperature compensation and nonlinear correction. And also it can use gas concentrations to judge the respiratory rate. |
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