Optimization of a Portable Pulse-Modulated Gas Sensing System and a Calibration Platform toward Electronic Nose
Date Issued
2009
Date
2009
Author(s)
Lin, Yu-Chun
Abstract
An electronic nose is a gas sensing system which mimics the mammalian sense to distinguish and quantify some components of odors. In this thesis, a portable gas sensing system based on the cyclic heating method modulated by voltage was implemented to do environmental monitoring and a calibration platform was set up to evaluate the response of the gas sensing system to some odors. This portable gas sensing system was based on the microcontroller MSP430FG439 which advantages were low power consumption, small size as well as real-time processing. The gas sensor of this system was tin oxide (SnO2) gas sensor. Furthermore, there were a liquid crystal display (LCD) to show some information about odors in real-time and a wireless communication module, ZigBee to transmit data to a terminal computer to store or analyze. Because the SnO2 gas sensor would be activated by heating the sensing material, the cyclic heating method was used to heat the SnO2 gas sensor so as to achieve better reproducibility. Moreover, the cyclic heating method could avoid increasing the operation temperature due to the accumulation of heat. Otherwise, it could also extend the lifecycle of the SnO2 gas sensor and lower the power consumption of the gas sensing system (67% off) to do long-term monitoring. The parameters of the cyclic heating method such as the duration of heating or operation temperature controlled by the voltage were modulated to optimize the performance of the gas sensing system. The calibration platform was constructed by an alumina stage covered with a glass cylinder chamber and it was put inside a fume exhaust hood. The static and dynamic calibration curve of the gas sensing system was evaluated by this calibration platform. Three samples, acetone, ethanol and methanol with the concentration of 5, 10, 20, 30 and 40 ppm were introduced to the gas sensing system and the gas sensing system was the most sensitive to ethanol but less sensitive to acetone. Otherwise, the gas sensing system could quantify the concentration of these three samples and it had good linear relationship between the reactive intensity and these three samples with the concentration from 10 to 40 ppm.
Subjects
electronic nose
gas sensing system
calibration platform
SnO2 gas sensor
cyclic heating method
Type
thesis
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