一种基于双气室切换分时扫描的新型气体吸收光谱补偿方法

A Novel Compensation Method of Gas Absorption Spectrum Based on Time-Sharing Scanning Spectra and Double Gas Cell Switching

针对变压器油中溶解气体傅里叶红外光谱在线分析应用中,气室与光谱仪之间气隙中气体的带来的干扰,以及基线漂移与畸变问题,提出一种基于双气室切换分时扫描的新型气体吸收光谱补偿方法。在传统单气室测量的基础上,增加一个与测量气室的结构、尺寸等参数基本相同的背景气室,背景气室充满氮气,而测量气室通入待测样气,通过工控机实现双气室的切换控制。但是,采用常规的吸光度计算公式处理的光谱在波数1 100~1 200 cm-1范围存在不明吸收峰,且存在严重的基线漂移现象,说明该计算方法已不适用于双气室切换。因此,为了消除双气室间参数无法一致的不利影响,特别是窗片的滤光特性的差异,提出了一种适用于双气室的新型气体吸收吸光度光谱计算方法;实验发现漂移量由近0.3降为0.005左右,证明其可以消除不明吸收峰和基线漂移。最后,于陕西某变电站的变压器中,取得油样,经脱气处理后,获得相应的气体样本,分别采用常规单气室扫描方法(组别1),提出的双气室补偿方法(组别2),以及气相色谱法(组别3)进行实验。结果表明,组别1的甲烷的浓度分析结果总是大于组别2。同时,组别1的二氧化碳浓度总是大于组别2的二氧化碳浓度,而造成这样分析结果的明显差异极可能是由于光谱仪与气室间气隙中空气的影响;且从总体上看,相比于组别1,组别2的分析结果更接近于气相色谱法的分析结果。综上所述,所提出的基于双气室切换分时扫描的新型气体吸收光谱补偿方法可以有效的解决光谱基线漂移与畸变问题,获得较为理想的光谱,在气体分析上可以消除气室与光谱仪的间隙干扰气的影响,获得更为准确地分析结果。

Aiming at the interference caused by the gas in the air gap between the gas cell and the spectrometer, as well as the baseline drift and distortion in the application of Fourier infrared spectroscopy on-line analysis of dissolved gas in transformer oil, a new method of gas absorption spectrum compensation based on time-sharing scanning with two gas cell, was proposed. Based on the traditional single-gas cell measurement, a background gas cell is added that is the same as the structure, size, and other parameters of the measurement gas cell. The background gas cell is filled with nitrogen, and the measurement gas cell is filled with the sample gas to be measured. Besides, the controller is used to realize the switching control of the background gas cell and the measurement gas cell. However, the spectrum processed by the conventional absorbance calculation formula has unknown absorption peaks in the wavenumber range of 1 100 to 1 200 cm-1. There is a severe baseline drift phenomenon, which indicates that the calculation method is no longer suitable for double gas cells. Therefore, in order to eliminate the adverse effect of the inconsistency of the parameters between the two gas cells, especially the difference in the filter characteristics of the window, a new method for calculating the gas absorption absorbance spectrum based on the double gas cell time-division scanning is further proposed, which was proved to eliminate unknown absorption peak and baseline drift, and the drift value decrease from 0.3 to 0.005. Finally, a transformer oil sample was obtained at a substation in Shaanxi, and the corresponding gas samples were obtained after degassing treatment. Conventional single-cell scanning method(group 1), two-gas cell compensation method(group 2), and gas chromatography(group 3) were used for experiments. The results show that methane concentration in group 1 is always more significant than that in group 2. At the same time, the carbon dioxide concentration in group 1 is always greater than the carbon dioxide concentration in group 2. The obvious difference in such analysis results is most likely due to the influence of the air gap between the spectrometer and the gas cell. On the whole, compared with group 1, the analysis results of group 2 are closer to those of gas chromatography. In summary, the new gas absorption spectrum compensation method based on double gas cell switching time-sharing scanning proposed in this paper can effectively solve the problem of spectral baseline drift and distortion. In gas analysis, this method can eliminate the influence of interfereing gas between the gas cell and the spectrometer, and obtain more accurate analysis results.