Portable Ndir Gas Sensor Key Technology Research

Non-dispersive infrared (NDIR) gas sensors have many characters, such as excellent selectivity, high sensitivity, Anti-interference ability and low price. Lots of NDIR gas sensor products have a wide application in industry, agriculture, medical, smart building, analysis equipments and so on. In order to improve NDIR gas sensors characters, new structure NDIR portable gas sensor system is designed in this paper. Key technologies such as MEMS infrared light source, gas absorption chamber and MEMS micro-pre-concentration have deeply researched.The content and innovation of this paper are listed as follow:1. NDIR portable gas sensor system was designed and fabricated. Hanging film by power tuning MEMS infrared light source and mid-infrared hollow optical fiber absorption chamber are used in the system. The system can monitor many kinds of gases real time. The low range of detecting CO2 gas is 5ppm, which is lower than that in the similar system which absorption chamber is stainless. Also the sensitivity of the new system increase three times.2. Hanging film structure MEMS infrared light source was designed and fabricated. Results show that these kinds of MEMS infrared light sources have short temperature increasing time, which is stable in 28ms. The light sources are power tuning, uniform temperature distribution in radiation area, long life time and excellent stability.3. The absorption chambers of NDIR gas sensor are researched. Mid-infrared hollow optical fiber, stainless chamber and copper chamber and different length of the chamber were made to test the influent on the sensitivity and the low detecting range. The responses of gas sensor system with the diameter of the chambers are 5mm and the length of 79mm,97mm,118mm,141mm and 161mm are researched. The results indicate that the sensitivity and the response rate are largest at the chamber length of 97mm. Different quantities of fibers bundles testing results show that the diameter of the chamber is bigger, the response of the gas sensor is larger, while the diameter chamber is smaller than the radiation of MEMS infrared light source and the infrared detecting monitor. Research results in this paper show that the relationship of the length of the absorption chamber and the response of the gas sensor is not fit the Lambert-beer law because of dispersive of the light source and the absorption of the chamber wall. The hollow optical fiber improve the sensitivity of the sensor for the reflect rate of the chamber wall improved.4. MEMS micro-pre-concentration is researched. The low detecting range of the NDIR gas sensor decrease by MEMS micro-pre-concentration. It was designed, fabricated and passed the reliability test. The design and the fabricated process are available. The pre-concentration characters of Silicate-1 type zeolite material are researched by QCM, which the absorption rate is more than 90% at 250℃.