Carbon monoxide(CO)and methane(CH4)are the main polluting gases in the atmosphere,and both are flammable and explosive gases.The measurement of CO and CH4 concentration plays an important role in each domain of people’s production and life.In the domain of gas detection,tunable semiconductor laser absorption spectroscopy(TDLAS)technology allows real-time monitoring and fast data processing with high accuracy and selectivity.Compared with the distributed feedback laser(DFB)laser,the vertical cavity surface emitting laser(VCSEL)has series of advantages,such as small size and low power consumption.As the core light source of TDLAS system,VCSEL can effectively improve system integration and reduce system power dissipation.Therefore,this paper conducts a research of VCSEL-based CO and CH4 two-component TDLAS gas measuring system.The main innovations of this paper include:for two-component gas detection,this paper proposes a dual-wavelength time-division scanning autonomous correction detection technology,which eliminates the cross-talk of optical signals and realizes the high-precision detection of two-component gases by a single signal loop;this paper proposes a digital quadrature lock-in amplifier design method with adjustable sampling rate and gain numerical control,which realizes the second harmonic signal amplitude extraction of two-component gases and can be applied to multi-component gas detection.It can be applied to the scenario of multi-component gas detection.Relying on the National Major Research Instrument Development Project(Project No.61727822),this paper has carried out in-depth research on the basic theory and detection method of TDALS technology,and simulated the laser drive signal and detection waveform,providing a basis for subsequent system design.On the basis of theoretical analysis and simulation results,this paper put forward a hardware and software design scheme for a composite VCSEL-type CO and CH4 laser gas detection system using DSP,combining the advantages of digital signal processing(DSP)master controllers in data computing.Combined with the HITRAN database and the current status of the VCSEL laser process,1568 nm and 1654 nm are selected as the target absorption spectra of CO and CH4,and a dual-wavelength time-division scanning autonomous calibration optical structure is built.In view of the high temperature stability and low threshold current of VCSEL lasers,a high-precision temperature control circuit and a weak current drive circuit are designed to achieve a temperature control accuracy of 0.01℃and a current control accuracy of 2μA.In view of the different signal amplitudes of two-component gas photodetectors,a bias and gain CNC adjustable optical signal acquisition and processing circuit was designed to achieve a signal amplitude of 54.2d B~69.8d B.In addition,the independent sampling gas circuit and temperature and pressure measurement circuit are built to realize the automation of ambient gas sampling and internal pressure regulation of the gas chamber.Based on the hardware design,the corresponding drivers were designed,mainly including the autonomous sampling program,autonomous calibration program,laser temperature control program,laser driver and digital quadrature lock-in amplifier program.After completing the system design,the overall performance of this system was tested.The lower detection limits of CO and CH4 gases were 90ppm and 30ppm respectively,and the system detection settling time was within 3.7s with good stability. |