基于数字锁相放大器的甲烷气体检测仪设计

针对甲烷气体浓度实时检测的要求，设计了一型基于谐波检测原理的检测仪器。该仪器由DFB激光器、准直器、角反射器构成高信噪比光路系统，由数字锁相放大器提取甲烷气体吸收后的一次和二次谐波，并采用标准仪器校准、最小二乘拟合等方法，得到了甲烷气体浓度计算公式，最大测量误差不超过1.1%。测试表明：该仪器通过高性能光路系统和数字电路提取微弱信号，提高了仪器工作稳定性和检测信噪比，测量误差满足使用要求。

Design of Methane Gas Detector Based on Digital Lock-in Amplifier

According to the the requirement of real-time detection of methane gas concentration, a detection instrument based on the principle of harmonic detection was designed. The instrument was composed of DFB, laser collimator, corner reflector composed of optical system with high signal-to-noise-ratio, the methane absorption of weak one and two harmonics extracted by digital lock-in amplifier, and through the calibration, and the standard instrument of the least squares fitting method, the calculation formula of the methane concentration, the maximum measurement error was less than 1.1%. The test showed that this instrument can improve the working stability and the signal-to-noise ratio of the instrument through the design of the high performance light path system and the use of digital circuits. The measurement error meeted the requirements of the instrument.