The Development Of Multi-gas Detector Based On Infrared Light Source

Safe production is the first factor to consider under mine.Once safty accidents happened,it would not only threaten the workers’ lives but also do harm to the national economy. In the circumstance under mine, methane is the major factor that causes the mine exploring, carbon monoxide can cause fire and be poisoned to human,it will generate a lot of carbon dioxide afer exploring,and people under mine will suffocate without enogh oxygen.Above all, we have a strong need of developing a detector which can monitor the concentration of the three kinds of gases under mine which can ensure the safe production.The detecting system in this article is based on the direct absorbing method of the infrared technology.First,we use a 40 centimeter light path with a sphere reflecting mirror and an infrared light source to make a gas chamber.As to the heat drifting of the light source,the system not only uses a heat sink fixed onto the light source to reduce the heat noise,but also uses the double-channel detector which has two channels,one is measuring channel,the other is reference channel which can elimimate the interference of the light source furthermore. We makes a rotating device with a stepmotor and an encoder.Then we use the software UG(NX6.0) to simulate the real size of the detecting system in 3D,then design the plate and the foundation,fix three detectors on the plate,then make the mould with the 3D printing technology.The next work is designing the circuit,the data processing circuit includes pre-amplifier circuit, main-amplifier circuit,low-pass circuit,peak detection circuit,the driving circuit includes constant current source circuit,rotating reset circuit,stepmotor driving circuit.We use the analog switch to change among the detectors and use the peak detection circuit to change the peak value of the signal into the direct value, then take advantage of the high speed A/D inside the DSP to sample the direct value and process the data with the algorithm and calculate the concentration according to the fitting formula,display the concentration of gas with LCD.Finally the system can detect carbon monoxide,carbon dioxide and methane with the method of time-sharing technology.The detecting limit of carbon monoxide is 150 ppm,the sensitivity is 150 ppm and the detecting range is 150-20000 ppm,the detecting limit of carbon dioxide is 130 ppm,the sensitivity is 130 ppm and the detecting range is 130-20000 ppm,the detecting limit of methane is 200 ppm,the sensitivity is 200 ppm and the detecting range is 200-20000 ppm.