Research On Infrared Detecting System Of Automobile Exhaust

With the increasing of the number of automobile possession in big cities, automobile brings great convenient to people's life, but it also brings serious environment problem. The gas of automobile has become social effects of pollution which makes environment pollution more seriously. So every country and region has set the limited value to restrict the exhaust. In this paper, I design a new infrared gas analytical system based on infrared spectrum and gas absorbing to measure the gas concentration.Based on analyzing the research progress of automobile gas detecting and gas detecting methods, choose non-dispersive infrared (NDIR) techniques as the detecting scheme. Using the scheme could measure the concentration of carbon dioxide, carbon monoxide in the gas at the same time.Then this paper discusses the design of detecting system structure. The NDIR system includes infrared light source and its driving ciucuit, measuring gas room, infrared detector, signal managing circuit and DAQ card. According to the infrared light character, design voltage-stabilized and modulating circuits. Comparing sorts of detectors, choose the infrared detector of thermocouple and design the signal circuits according to the character of detector signals. This project designs a equipment to assess the linearity of gas concentration, and it is simple to operate. With the help of the equipment, we can low down the calibration cost and improve the calibration efficiency.The software design of detecting system is based on LabVIEW platform. The main function of software are including: with the help of DAQ card to acquire data; analyzing data; conserving and enquiring data based on database techniques; calibration of system and the output of square signal to modulate the infrared light source. The software interface is simple and easy to operate and the stability of function implementation is also very well.During the test, debug the hardware and software and they all fulfill the desired function. Then calibrate the system with the help of designed equipment and analyze the dependent linearity of fitting line. Then Use calibrated system to detect gas and the results prove that fitting line has good dependent linearity and satisfies the calibration requirement. The detecting results prove that the NDIR infrared system satisfies the desired requirements and the system is stable and accurate.