| Carbon monoxide is the main culprit of mine explosion and mine fire as well as one poisonous and harmful gases product. On the one hand, the explosion limit of carbon monoxide is about twelve percent to seventy-four percent; it is very easy to explosion in such a wide range of mixed with air. On the other hand, carbon monoxide is often seen as a main prevention indicator of mine fire. In addition, carbon monoxide is an important tracer in atmospheric chemistry analysis, environmental monitoring, industrial process control, and life sciences, etc. So, no matter for coal mine safety monitoring, or atmospheric chemistry analysis, or environmental monitoring, or industrial process control, as well as life science research, and many other areas, it has very important practical significance to build a set of high selectivity, high sensitivity, low response time, stable performance of trace carbon monoxide detection system. This topic is derived from the national science and technology support project " key technology and equipment research and development for coal mine water inrush, fire and other major accident prevention and control ", the subject name: infrared CO detector(sensor) research and development for coal mine(project number: 2013 2013BAK06B00, topic number: 2013BAK06B04).Infrared light source plays an important role in the gas detection system based on infrared spectroscopy technology, it not only decides the choice of the infrared detection technology, but also is closely related to system key parameters(e.g., the minimum detection limit, the system stability, etc.). So it is quite necessary to make the infrared light source work safely, steadily and effectively. In view of the pulse-mode and continuous wave distributed feedback quantum cascade lasers, two kinds of special board-level drive powers were developed. The pulse-mode drive power was designed based on the concept of“Multiple Isolation‖. The rise time/ drop time of drive pulse was nanosecond level; over-current protection response time was 200 ns, linearity of output current was 0.004%, long-term stability of output current was 2.5×10-5. Continuous mode drive power was for the purpose of applying in Wavelength Modulation Spectroscopy detection technology. It had both of dc and modulation double working modes, and integrated the function of temperature control. The over-current protection response time was 43 ns, linearity of output current was 0.007%, long-term stability of output current was 3×10-5, precision of temperature control could be up to + /- 0.005 ℃.According to the absorption characteristics of carbon monoxide in the mid-infrared region, by using of quantum cascade laser, a trace gas detection system is developed based on Direct Absorption Spectroscopy detection technology. The system used a high power, pulsed operation, distributed feedback quantum cascade laser operating at room temperature as the excitation source. Pulse Amplitude Modulation, Pulse Frequency Modulation, Phase Sensitive Detection as well as software filtering method were used to reduce the influence of light source fluctuation, system noise and improve measurement precision and detection sensitivity. For the P(10) CO absorption line, located at 2103.2697 cm-1, a minimum detection limit of 25 parts per million(ppm) at atmospheric pressure was achieved with a 1 sec acquisition time. At the same time, the long-term stability of the system(2h) was analyzed; the results showed that the system stability was 0.037 and 0.007 when CO concentration was 100 ppm and 1000 ppm, respectively.In order to improve the overall performance of the infrared carbon monoxide detection system, a detection platform was designed and set up based on the continuous wave quantum cascade laser. The detection system adopted a high-power, continuous operation, distributed feedback quantum cascade laser operating at room temperature as the core, combined with Wavelength Modulation Spectroscopy detection technology, Differential Absorption Spectroscopy detection technology and Phase Sensitive detection technique, etc., effectively reduced the influence of light source fluctuation and the system noise and improved the measurement precision and sensitivity of the system. For the selected P(11) absorption line of CO molecule, located at 2099.083 cm-1, a minimum detection limit of 0.42 ppm at atmospheric pressure was achieved with a 1 sec acquisition time. Allan deviation analysis was performed to investigate the long-term performance of the CO sensor, and a measurement precision of ~ 0.05 ppm was observed with an optimal integration time of approximate 100 s. The superior performance of the developed trace gas detection platform, made it not only adapt to the mine safety monitoring, and can satisfy the atmospheric chemistry, environmental monitoring, industrial process control, and in the field of life science, and many other fields which have requirements of carbon monoxide.Innovations of the thesis are as follows:i. Direct Absorption Spectroscopy experimental model of carbon monoxide detection system based on pulse-mode quantum cascade lasers and Wavelength Modulation Spectroscopy- Differential Absorption Spectroscopy hybrid experimental model of carbon monoxide detection system based on continuous wave quantum cascade lasers are well established respectively. The experimental models are mainly used to simulate and estimate the system output value under different condition including target gas concentration, absorption path length, temperature, atmospheric pressure, wavelength, etc.ii. In view of the pulse-mode distributed feedback quantum cascade laser whose centre wavelength is 2103cm-1 developed by Institute of Semiconductors, the Chinese Academy of Sciences(ISCAS), a pulse-mode drive power is designed based on the concept of“Multiple Isolation‖. The stability of the output current is improved effectively by use of deep voltage negative feedback combined with proportional-integral-differential software algorithm. In addition, it also has high stability power supply system and perfect protection system.iii. In view of the continuous wave distributed feedback quantum cascade laser whose centre wavelength is 2099cm-1 developed by Institute of Semiconductors, the Chinese Academy of Sciences(ISCAS), a modulation drive power which has both of dc and modulation double working modes, and integrates the function of temperature control(precision of temperature control can be up to +/- 0.005 ℃) is developed. In addition, drive current monitoring, system protection function can effectively ensure quantum cascade laser work security and stability. Furthermore, this is the first board-level modulation drive power for the purpose of driving continuous wave quantum cascade lasers in our country as far as knows.iv. A carbon monoxide detection system adopted a high-power, continuous operation, distributed feedback quantum cascade laser whose centre wavelength is 2099cm-1 and operate at room temperature as light source, combined with Wavelength Modulation Spectroscopy detection technology, Differential Absorption Spectroscopy detection technology and Phase Sensitive detection technique, etc. has never been reported in our country as far as knows. |
PDF Full Text Request