Testingand Analysis System For Trace Ethylene Based On TDLAS Technology

In recent years, rapid development has made China's air pollution seriously, and the state also paid much more attention to the developing of gas pollutant detecting, especially for the trace gases. And there is also an urgent demand to test all kinds of dangerous, flammable, explosive trace gases for industrial production safety. Such as chemical measurement, accuracy and speed of traditional methods are hard to meet the detection of trace gases. But now the non-contact optical techniques for trace gases detection are developing very rapidly because of making up for these shortcomings in recent years. And gas detection technology based on tunable diode laser absorption spectroscopy (TDLAS) is the one of these techniques. TDLAS is high accuracy, fast response, simultaneous detection of multiple parameters without manual calibration and pre-sampling. And there is a broad development prospect in the harmful trace gas detection. The systems is to detect trace gas underground mine ethylene. And changing the light source the system can be applied to the detection of other trace gases. It is universal reference value to the trace gas detection.The system makes combining of wavelength modulation spectroscopy technology and long-path gas absorption cell in the TDLAS. So the system can achieve high accuracy, especially for weak signal detection of trace gas, using second harmonic detection and long-path prism reflecting pool method of detection. And the best parameters of the experiment, such as the number of harmonic detection, modulation depth, gas chamber pressure, etc. is chosen by theoretical derivation of infrared absorption spectroscopy; and it is also demonstrated through experiments. Furthermore the best working conditions of tunable diode laser is done. These are all very meaningful to other similar systems. At the same time there are some differences to other similar instruments. The system applies modular circuit design in the harmonic detection, including lock-in amplifier, signal generator, frequency multiplication circuit. It makes the system reducing the size, cost and improving the accuracy, providing a reference for the development of the portable system. It is also improved to design the air chamber and the laser collimator. Finally, experimental data makes noise reduction pretreatment, and it is a very effective way to reduce background noise and other noise, so further improve accuracy and sensitivity of the system. The calculation of the concentration uses the method of linear fitting. Software editor uses LabVIEW for graphical software design.