Design on Detection Circuit to Faint Signal for Difference Absorption Gas Sensor

摘要

Since the gas infrared absorption spectrum line breadth is only several nm occupying intensity of source several in a thousand, it is even less than the noise of optical source. The signal of gas absorption is submerged in the noise, so it is impossible to measure the concentration of gas with spectrum absorption directly. In this paper, according to the principle and parameters of difference absorption system of CH_4 gas, a detective circuit is designed centering lock-in amplifier. Experiment results indicated that the detective circuit can satisfy the demand of the whole system, the limit concentrate is 150 X 10~(-6).