Evaluation of systematic errors in methane concentration determination using diode laser detector.
The errors in methane concentration determination in ambient air attributed to the difference of temperature and pressure inside the measure cells; the addition of water vapor; carbon dioxide and ethylene in the gas probe; and the random noise are evaluated numerically. It is shown that the presence of the foreign gas spectral line in the spectrum registered near the reference methane absorption line may lead to the increase or decrease of determined the methane concentration relative to true one. The total error in methane concentration detecting under atmospheric conditions due to water vapor, carbon dioxide agents in the air probe, and the random noise in measurements is less than 1%. Variations of ?the temperature and pressure of gas probe inside the measure cells less than 1 and 1 Torr, respectively, result in the error in concentration value not more than 1.5%. Under equivalent concentrations of methane and ethylene in the air probe the error of methane the concentration detection can reach 15%.