Design Of Nondispersive Infrared Gas Sensor’s Optical And Software System

With the improvement of people’s living standards and the development of industry, theemissions of carbon dioxide and other pollution gases has been increased, and then theworld’s temperature gradually increased. When the carbon dioxide and other gas’sconcentration increased, these gases are harmful to human’s health at the same time, we needmonitor the carbon dioxide polluted gas’s concentrations strictly to protect the normal life ofhuman. Therefore, to research and design a kind of detection system to detect carbondioxide’s concentrations has great significance.According to the Beer-Lambert law and the infrared absorption spectrum of carbondioxide, a kind of Infrared light source and pyroelectric infrared detectors are chose to use inthe design of the whole system. In practical application, the infrared absorption spectrumwidth is only a little nanometers while the emission spectrum of the infrared light sourceused in the gas sensor are not narrow-band, so the absorption spectral width is only a smallpart of the infrared radiation source and the gas absorption signal will be drowned in thenoise. The entire sensor system is designed to be based on two wavelength differentialdetection principle which have two narrow band filters and one optical path to reduce eveneliminate the affect caused by instability of infrared radiation source, the interference tooptical chamber from environment, the temperature-drift of optoelectronic devices andpyroelectric infrared detectors noise. We also made a simulation comparison for severalcommonly optical chamber by using the LightTools software to arrive at a relatively goodperformance for optical systems. We work out two structures and then one structure is chosefor our test analysis.Another aspect of this study is to design the software system for the sensor detection.The C8051F350micro control unit is taken as the core processor of the whole system. Wecomplete the conversion from analog signals to digital signals, the pulse-modulated to theinfrared light source, data collection concentration calculation, liquid crystal display andalarm with light and sound. While the detected gas concentrations are over the warning limit that set before, light and sound alarm signal is generated. There is a temperature sensor in themicro control unit, AD converter also collect temperature data to achieve detection of thesystem’s temperature.