Use of a Dynamic Enclosure Approach to Test the Accuracy of the NDIR Sensor: Evaluation Based on the CO2 Equilibration Pattern

As part of a quality assurance (QA) study for sensor systems, an enclosure approach is applied to assess the accuracy of non-dispersive infrared (NDIR)-based CO2 sensors. To examine the performance of the sensor system, an enclosure chamber containing six sensor units of the two model types (B-530 and H-500) was equilibrated with calibrated CO2 standards at varying concentration levels. Initially, the equilibration pattern was analyzed by CO2-free gas (0 ppm) at varying flow rates (i.e., 100, 200, 500, and 1000 mL min-1). Results of the test yielded a highly predictable and quantifiable empirical relationship as a function of such parameters as CO2 concentration, flow rate, and equilibration time for the enclosure system. Hence, when the performance of the NDIR-method was evaluated at other concentrations (i.e., 500 and 1000 ppm), all the sensor units showed an excellent compatibility, at least in terms of the correlation coefficients (r > 0.999, p = 0.01). According to our analysis, the NDIR sensor system seems to attain an overall accuracy near the 5% level. The relative performance of the NDIR sensor for CO2 analysis is hence comparable with (or superior to) other methods previously investigated. The overall results of this study indicate that NDIR sensors can be used to provide highly accurate and precise analyses of CO2 both in absolute and relative terms.