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为了分析并抑制中红外甲烷检测中模数转换器(ADC)参考电压噪声对检测性能的影响,本文理论推导了待测浓度和电压波动的关系式,计算了电压波动对ADC实际分辨率的影响。一方面,为了降低噪声水平,设计了一种三级稳压电源,使参考电压的平均波动由原来的2mV降至0.6mV;另一方面,考虑到噪声无法避免,不同待测电压对应的数字量彼此交叠,致使无法精确测量各性能参数,本文提出了一种新型二次量化抑制方法,以有效消除电压噪声的不利影响。在不同的ADC参考电压噪声水平下,利用提出的二次量化抑制方法,实验测试了系统稳定性、精度、灵敏度和检测下限等性能。结果表明,当ADC参考电压的平均波动由2mV降至0.6mV时,测量精度可由12.9%降至5.0%以下,检测下限可由约26×10-6降至20×10-6。最小检测下限处的检测灵敏度可由约30×10-6降至20×10-6。这些证实,本文给出的基于二次量化思想的噪声抑制方法是可行的,并且该方法也可用于其它具有类似机理的气体检测。
In order to analyze and restrain the influence of reference voltage noise of ADC on the detection performance in mid-infrared methane detection, this paper theoretically deduces the relationship between the measured concentration and voltage fluctuation, and calculates the influence of voltage fluctuation on the actual resolution of ADC . On the one hand, in order to reduce the noise level, a three-stage regulated power supply is designed to reduce the average reference voltage from 2mV to 0.6mV. On the other hand, considering the unavoidable noise, the numbers corresponding to different voltages under test Therefore, it is impossible to accurately measure each performance parameter. In this paper, a new quadratic quantization suppression method is proposed to effectively eliminate the adverse effects of voltage noise. Under the different ADC reference voltage noise level, the proposed method was used to test the system stability, accuracy, sensitivity and lower limit of detection. The results show that when the average fluctuation of ADC reference voltage drops from 2mV to 0.6mV, the measurement accuracy can be reduced from 12.9% to 5.0%, and the detection limit can be reduced from about 26 × 10-6 to 20 × 10-6. The detection sensitivity at the minimum detection limit can be reduced from about 30 × 10 -6 to 20 × 10 -6. These prove that the method of noise suppression based on the second-order quantification given in this paper is feasible, and the method can also be applied to other gas detection with similar mechanism.