The Research Of Locking Wavelength Of The LD Of The Gas Detection System Based On TDLAS

Hydrogen sulfide is a highly toxic gas. H2S leak not only influences the productionequipments of the oil wells, especially threatens to the security of human life. Therefore, thehigh precision, fast, real-time monitoring for hydrogen sulfide gas is of great significance.Tunable diode laser absorption spectroscopy (TDLAS) has no need to pre-sampling, highsensitivity, good selectivity, fast response characteristics, and be one of the ideal gas detectionmethods.In the gas detection system, based on tunable diode laser absorption spectroscopy(TDLAS), the performance of LD which is considered as the core components of the systemmakes a direct impact on the accuracy the reliability of the system. In order to match thewavelength of LD with the absorption line of the detected gas, the wavelength of thedistributed feed-back (DFB) LD which is chosen should be locked. With the feature that theDFB LD is easily influenced by afflux current and inside temperature, the wavelength islocked by controlling the temperature and the afflux current.The main work of the paper is as follows: by taking Beer-Lambert law as the theoreticalfoundation and combining the theory of gas absorption spectrum and the line-type theories,the paper introduces the principle of gas concentration measuring based on tunable diode laserabsorption spectroscopy (TDLAS), deduces the principle of harmonic detection based onwavelength modulation and designs the system scheme. To the core components of the system——LD，the paper analyzes the effects of the injection current and temperature, and make thescheme to lock the wavelength of LD. At the same time, in order to ensure the wavelength ofLD stability, the temperature is controlled. Combining the PID and TEC, the temperaturecontrol circuit in which the main components are TEC and inner thermoelectric refrigerator ofLD is designed and completed. The experiment result shows the control accuracy has beenachieved to be±1pm. Then a scheme is designed to test the system performance including thecurrent stability, the temperature stability and so on.The experiment result shows that the system works well in locking wavelength, and thework can improve the performance of the gas detection system.