Study on A Novel Fast Non-Dispersive Infrared Gas Detection

• Main Authors: Hsin-Han Huang, 黃星翰
• Other Authors: Chih-Hsiung Shen
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/63881911761680208197

碩士 === 國立彰化師範大學 === 機電工程學系 === 100 === For the detection of CO2 gas concentration, non-dispersive infrared (NDIR) play the major role of gas sensing technique in science and technology. The working principle of NDIR is based on the spectral absorbance on some specific wavelengths corresponding to the detection gas and the reduction of absorption is monotonic proportional to the gas concentration. Usually, NDIR technique includes a broad band infrared light source and an infrared sensor with a specific bandpass filter in front. Most of all, the response time of NDIR measurement will be dominated by the warm-up time of the light source which will achieve a stable spectral radiation for a long time up to 10~30 minutes. Therefore, this long warm-up time will limit the applications of gas concentration measurement and even worse, some mistakes will happen if the measurement operation does not fit the requirement of enough time to wait the thermal radiation stability. We propose a novel fast warm-up time technique with an over-drive procedure which pumps up more power to the light source in the beginning and then comes back the normal operation condition with high SNR detection. This research is realized also with the Correlated Double Sampling (CDS) circuit and different modulation experiments are analyzed to find the optimal operation conditions. The research focuses on the CO2 concentration measurement and we choose the Heimann Sensor J22 CO2 with a 4.2μm filter. The CDS operation is performed with two phases: the first phase is to turn on the light source with full power and the second phase with lower power or even turn off. Reduce the warm-up time from the conventional design with 865s to the best result of 30s. It shows almost 30 times less than before. Under the same lighting power, for different period of two phase, the best results reduces the warm-up time to 103s. Combining these two results, we propose an optimal solution to improve the measuring efficiency and a possibility of performance enhancement.