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

乙炔气体作为判断变压器运行状态的一种故障气体，其浓度的高低反映了变压器的运行状况，因此对其浓度的探测在变压器的维护中具有重要意义。为了准确探测变压器运行过程中产生的乙炔气体浓度，为变压器的维护提供技术参数，针对基于DFB激光器的共振型光声光谱技术痕量乙炔气体检测技术开展研究，对传统的光声光谱探测系统进行改进。根据光声光谱技术的理论可知，光声信号的强度与入射激光的功率成正比，所以在光声池的出射窗口采用一个平面反射镜将红外光再次反射到光声池中以增加入射光功率，增强光声信号强度，进一步提高了光声系统的探测灵敏度。通过一定浓度的乙炔气体在不同调制频率和不同调制深度下光声信号强度的变化，确定光声探测系统的最佳调制频率和最佳调制深度为767 Hz和0.3 mV。利用不同浓度乙炔气体对系统进行标定，然后采用最小二乘法对光声信号与气体浓度进行拟合，二者具有很好的线性度。通过Allan方差计算可知，系统在平均时间达到200 s时，能够达到最低探测极限浓度。实验表明，在一个大气压下，积分时间为10 ms时，改进后的共振型光声光谱探测系统对乙炔气体的最低探测极限浓度达到了0.3 μL·L-1。还将小波去噪技术引入到低浓度下乙炔气体的光声信号处理中，有效消除了低浓度气体光声信号中的噪声，提高了信噪比。设计的共振型光声光谱探测系统操作简单，最低探测浓度符合国标中对变压器维护过程中对乙炔气体的探测需求，在变压器维护领域具有广阔的应用前景。

Acetylene Detection Based on Resonant High Sensitive Photoacoustic Spectroscopy

Acetylene is a kind of fault gases used to j udge 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 ma-intenance,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 in-cident 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 pho-toacoustic 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 modula-tion 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 0.3μL·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.