Study On Dual-Loop Gas Concentration Measurement System Based On Cavity Ring-Down Method

The poisonous, harmful, combustible and explosive gases produced by the industrial production have seriously polluted the environment and threatened human health and industrial process safety. Therefore, the real-time concentration detection of these gases is very important. Fiber loop ring-down Spectroscopy (FLRDS) is a very high sensitive absorption spectroscopy technology, combining cavity ring-down spectroscopy (CRDS) with optical fiber sensing technology, which is especially suitable for trace gas detection. However, in practical application, there still exist deficiencies which affect the measurement precision. In the paper, a dual-loop concentration measurement system based on the FLRDS technology is proposed and studied. The primary content includes:First, the concentration measurement principle of FLRDS technology is analyzed, and the corresponding mathematical model is built. The advantages of FLRDS technology is introduced, the main factors that affect the gas concentration measurement precision are also researched.Secondly, a dual-loop concentration system based on FLRDS is designed, and the performance and working principle of main devices are analyzed. A light feedback loop is proposed to improve the stability of the erbium-doped fiber amplifier (EDFA). In order to reduce inaccuracy caused by the amplified spontaneous emission noise of EDFA, an adaptive filter is used to process experimental data, and the filtering effectiveness is theoretically emulated.Finally, the gain characteristics of the designed gain control EDFA are analyzed, and the overall design of the measurement system is experimentally verified. Through the contrast experiment, it is proved that the measurement accuracy has been improved by using the adaptive filtering method. Then, the absorption characteristics in CO gas with different concentrations and the relationship between ring-down time and concentration are also analyzed.