The Research On Gas Detection Demodulation System Based On Tdlas

In today’s increasingly serious environmental pollution, air pollution is closely related to each person’s health. That is why existing monitoring methods need to be improved, the sensitivity of the instruments needs to be enhanced, and the real-time and accuracy of test results need to be strengthened. Therefore, designing a reliable real-time instrument to detect density of the pollutant gas has important social and economic significance to protect people’s lives and national security.Firstly, tunable diode laser absorption spectroscopy technique is proposed to detect gas density based on the principles and methods of existing monitoring. After comparing several spectral absorption type optical fiber gas sensor monitoring technology, the wavelength modulation is chosen to modulate the light intensity, which effectively eliminates the background noise of the system and improves the work quality of the system. In order to measure the gas accurately in real time, an open chamber gas sensor is designed and it employs double filtration of integrated design. In this gas sensor, collimator is composed by a self-focusing lens aligned by free space path, and two optical antipollution devices------the coarse filter and fine filter------are designed outside the open air chamber, which strengthen the anti-jamming capability of whole optical system and make the monitoring results more precise. Meanwhile, in order to monitor the remote gas proceeds in a relatively safe environment, a lens optical gas sensing telemetry module is designed, which consists of luminescence and condenser system. Application of this lens can achieve real-time, continuous and non-contact measurement, and a large scale of distribution monitoring. It is easy to measure gas components accurately, and it makes the measurement of gas more secure, more stable, and more sensitive.Secondly, photoelectric conversion is made to the optical signal by photoelectric detector, and the circuit is optimized through pre-amplification and band-pass filter. In order to obtain signal related to the gas density, harmonic detection is employed to obtain the second harmonic amplitude of the signal. Harmonic detection can make the frequency of the monitoring system high, suppress the low frequency noise and external interference, and thus improve the detection sensitivity of the system.Finally, Jinan SanKe DMP609 data acquisition card is used. Therefore, designing PC software has the function as follows: data acquisition, data icon display, concentration information display, channel selection, and the preservation and display of historical data.