Design Of Dual-gas Detection System Based On The NDIR Technology

With the rapid development of the national economy,China has a high demand for energy,and coal plays an unshakable role in China's energy structure.Gas is the general term for various harmful gases in coal mining,whose main components are CH₄ and CO₂.Excessive concentration of those gas causes explosion or suffocation easily.For guarantee the safety of coal miners,it is necessary to test the gas concentrations.This paper develops a two-component gas sensing system with the advantage of high-precision,low-cost,miniaturized based on non-dispersive infrared?NDIR?.The specific research is as follows:For the design of the optical air chamber,Solid Works was used to complete the 3D modeling of three air chamber structures including direct-injection,reflection,and double-ellipsoid type.Then,the light propagation direction of the cavity was analyzed by the optical simulation software Light Tools,and the parameters were determined.Finally,the air chamber was printed by the 3D printing technology based on the previously designed model.The power supply circuit,voltage conditioning circuit and light source driver circuit are the important part of the hardware circuit and need to be designed.The modulation of the light source is achieved the square wave pulse which is output by external voltage and timer of single chip microcomputer;the voltage signal output by the infrared detector is amplified and filtered to a threshold that can be recognized by the single chip microprocessor;The voltage data is converted into concentration information and transmitted to the upper computer system.In order to realize the information interaction between the computer and the microprocessor,the Qt platform is used to develop the upper computer system.Through the built-in RS232 serial port module of the single chip microcomputer realizes the information transmission.After reading of the serial data,the functions of data display and concentration-time curve drawing are realized on the data acquisition interface.A two-component gas sensor test platform was set up and the precision tests,repeatability experiments,and stability tests were carried out.The experimental results show the sensor can accurately measure the methane and carbon dioxide gas concentration in a range of 0-2000ppm,with the full range accuracy up to 4.5%,which can meet the practical application of two-component gas detection demand.