Evaluation of uncertainty in tunable diode laser absorption spectroscopy system used for continuous CO monitoring

Tunable diode laser absorption spectroscopy (TDLAS) is a method to detect trace-gas qualitatively or quantitatively based on the tunable characteristic of the diode laser to obtain the absorption spectroscopy in the characteristic absorption region. The concentration of CO is measured by tunable diode laser absorption spectroscopy (TDLAS) technology in this paper. The experimental results of measurement signals are inversely processed by applying the overall second harmonic least squares data processing algorithm. The experimental results indicate that the signal strength of the second harmonic spectrum changes with CO concentration. But the widths of the 2f lineshapes have not changed. The components that influence the uncertainty of measurement results during measuring CO concentration by TDLAS are analyzed and the mathematic model is built. The standard uncertainty of components and evaluation of uncertainty of measurement results are given with the direct evaluation method in detail. The evaluation results indicate that the major factors affecting measurement uncertainty are the indicating value uncertainty of the apparatus, concentration definite value uncertainty of calibrating gas.