Laser Methane Sensor with the Function of Self-Diagnose

Using the technology of tunable diode laser absorption spectroscopy and the technology of micro-electronics, a fiber laser methane sensor based on the microprocessor C8051F410 is given. In this paper, we use the DFB Laser as the light source of the sensor. By tuning temperature and driver current of the DFB laser, we can scan the laser over the methane absorption line, Based on the Beer-Lambert law, through detect the variation of the light power before and after the absorption we realize the methane detection. It makes the real-time and online detection of methane concentration to be true, and it has the advantages just as high accuracy, immunity to other gases, long calibration cycle and so on. The sensor has the function of adaptive gain and self-diagnose. By introducing digital potentiometers, the gain of the photo-electric conversion operational amplifier can be controlled by the microprocessor according to the light power. When the gain and the conversion voltage achieve the set value, then we can consider the sensor in a fault status, and then the software will alarm us to check the status of the probe. In addition, we introduce the feedback of the temperature to compensate the environment effects, So we improved the dependence and the stability of the measured results. At last we give some analysis on the sensor according the field application and according the present working, we have a look of our next work in the distance.