基于共振型高灵敏度光声光谱技术探测痕量乙炔气体浓度

doi:10.3964/j.issn.1000-0593(2017)09-2673-06

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Abstract Acetylene is a kind of fault gases used to judge the operating state of transformer, and its concentration reflects the operation condition, so the detection of acetylene concentration has important significance in transformer maintenance. In order to detect acetylene concentration generated in the running process accurately to provide technical parameters for transformer maintenance, this paper has done a research based on the DFB laser photoacoustic spectroscopy for trace acetylene detection, which improves traditional photoacoustic spectroscopy detection system. The intensity of photoacoustic signal is proportional to the incident laser power based on photoacoustic theory, so in this paper a reflector was installed opposite the light-emitting window of the photoacoustic cell to reflect infrared light back to increase the power of incident light, which can enhance the intensity of photoacoustic signal and then further improve the detection sensitivity of the photoacoustic detection system. The photoacoustic spectroscopy detection system will have the optimal detection performance under the optimal modulation frequency and modulation depth, so in this paper the important parameters of optimal modulation frequency and modulation depth were studied. Through the intensity of photoacoustic signal of a certain concentration of acetylene gas under different modulation frequencies and modulation depths, the optimal modulation frequency and optimal modulation depth of the system were determined as 767 Hz and 0.3 mV. Before the detection of unknown concentration of acetylene gas, the photoacoustic detection system was calibrated by different concentrations of acetylene gas. The photoacoustic signal and gas concentrations were fitted by the least squares, which had a good linearity. The stability of the system was evaluated by Allan variance, which clearly showed that the system reached the minimum detection concentration using the average time of 200 s. The experiments show that the minimum detection limit of the system is 0.3 μL·L^-1 under the atmospheric pressure with a integration time of 10ms. In this paper, the wavelet denoising technique was used for low concentration acetylene gas photoacoustic signal processing, which showed that the noise was effectively eliminated and the signal-to-noise ratio was improved. The resonant photoacoustic spectroscopy detection system designed in this paper has the advantage of easy operation and conforming the lowest detection concentration to the national standard in the detection of acetylene gas for transformer maintenance, which has a broad application prospect in the field of transformer maintenance.

Key words：Photoacoustic; Wavelet denosing; Gas detection; Sensitivity

Received: 2016-08-04 Accepted: 2016-12-18

ZTFLH:

O433.5

Corresponding Authors: GAO Xiao-ming E-mail: xmgao@aiofm.ac.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2017)09-2673-06 OR https://www.gpxygpfx.com/EN/Y2017/V37/I09/2673