Limitations of gas filter correlation: A case study on carbon monoxide non-dispersive infrared analyzer

Two commercial Non-Dispersive Infrared (NDIR) analyzers for carbon monoxide (CO) coupled with a gas filter correlation (GFC) were used to investigate the interference effects by other gases except for CO. A stack level of particular gases including CO2, NO, NO2, SO2, and H2O (g) were mixed with CO to introduce into the analyzers. It was found that the measurement error of two analyzers were the lowest at 50 ppm and 70 ppm of CO, respectively. Moreover, the increase of concentrations of the interfering gases (CO2, NO, NO2, and SO2) induced an interfering effect on the performance of two analyzers. This indicated that the GFC could not cover the entire range of interfering gases. In a special case, the accuracy of the analyzers with humid mixed gases was better than that with dry mixed gases due to the absorption of water-soluble gases by condensate. However, this accuracy was only apparent with respect to low solubility of analytical target gas such as CO. The solubility of the target gas might dramatically reduce the accuracy of the analyzer.