非调制型NDIR传感器及其信号处理方法的改进

Non-modulating NDIR sensor with improved signal processing

基于非色散红外(NDIR)光谱分析原理,设计了一种非调制双波长CO2传感器。采用的热电堆探测器可以响应直流或缓变光强信号,无需对光源进行调制,而用恒流电路驱动,提高了光源的稳定性。设计了斩波调零放大电路检测微弱直流信号,解决了放大直流信号和抑制漂移的矛盾。在低浓度的情况下,线性吸收规律可以近似指数吸收规律,用差动法代替了对数法进行信号处理,实验结果表明:对数方法可以抑制光源辐射功率波动的影响,但温度系数较大;差动方法具有较小的温度系数,但结果受光源辐射功率波动影响较大。

A non-dispersive infrared （NDIR） spectrum analysis was used to design a CO2 sensor which is non-modulating and double-wavelength. Since the thermocouple infrared detector responds to invariable and low-frequency variable infrared light, the lamp is driven by a stable current without modulation. A chopper-stabilized circuit is designed to detect tiny DC signals. The conflict between the DC signal amplification and drift was also resolved. At low gas concentrations, the exponential absorption law can be approximated by a linear absorption law and the logarithmic calculation is replaced by a differential calculation. Experimental results indicate that the influent of fluctuation of the lamp radiating power can be eliminated by the logarithmic analysis, but temperature fluctuations greatly influence the sensor. In contrast, with the differential analysis, the temperature coefficient is low, but the measurement is greatly influenced by lamp radiating power fluctuations.