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为了能够在复杂的环境下实现甲烷气体浓度的高精度和高稳定性检测,在基于光谱吸收原理的光纤甲烷检测系统的基础上,提出了利用锯齿波调制的半波扫描技术,较大程度改进了系统的性能指标。采用锯齿波调制光源的方式,同时对光信号进行波长调制和强度调制,实现对甲烷气体的洛伦兹吸收线型扫描。锯齿波调制的方式能够解决信号链路噪声、环境噪声等随机信号对光强造成的干扰,消除光源波长漂移对检测带来的影响,且实现了积分处理,进一步提高检测精度;但由于甲烷吸收光谱的对称性,采用通用的全波扫描方式,气体吸收光强后进行微分处理会出现正弦型曲线,无法准确确定吸收的光强所对应的数字量;而采用半波扫描方式,气体吸收光强后进行微分处理只出现凹型曲线,可以准确确定吸收的光强所对应的数字量。实验结果表明:采用锯齿波调制的半波扫描方式,可以准确测得甲烷气体浓度;测量范围为0%~10%,精度由100 ppm提升到10 ppm(1 ppm=10-6),稳定性由0.3%提升到0.01%。该系统经过改进后在复杂环境下受温度影响小,精度高,稳定性好,抗干扰能力强。
In order to realize the high precision and high stability detection of methane gas concentration in complex environment, based on the optical fiber methane detection system based on the principle of spectral absorption, a half-wave scanning technology based on sawtooth modulation is proposed to improve greatly The system performance indicators. The method of sawtooth modulation light source, while the optical signal wavelength modulation and intensity modulation, the realization of methane gas Lorentz absorption linear scanning. The sawtooth modulation method can solve the interference caused by the random signal such as signal link noise and environmental noise on the light intensity and eliminate the influence of the wavelength shift of the light source on the detection, and realize the integral processing to further improve the detection precision. However, due to the methane absorption The symmetry of the spectrum, the use of universal full-wave scanning method, the gas absorption intensity after the differential processing will appear sinusoidal curve, can not accurately determine the amount of light absorbed by the corresponding digital; and half-wave scanning, gas absorption of light After the differential processing is only strong concave curve appears, you can accurately determine the amount of light absorbed by the corresponding digital. The experimental results show that the methane gas concentration can be accurately measured by half-wave scanning with sawtooth modulation. The measurement range is 0% -10%, the accuracy is raised from 100 ppm to 10 ppm (1 ppm = 10-6), and the stability From 0.3% to 0.01%. The system has been improved in a complex environment by the temperature of small, high precision, good stability, anti-interference ability.