Breakthrough in CO2 Measurement With a Chamberless NDIR Optical Gas Sensor

CO2 measurement using the nondispersive infrared (NDIR) gas sensing method is conventionally performed using a gas chamber as the main part of the sensor. In this paper, we report on a novel approach using a light source with an embedded parabolic reflector to measure CO2 concentrations above 400 ppm without the need for a chamber. Four alternative structures for CO2 detection were fabricated that combine gold-coated reflective surfaces and a parabolic reflector with a light source and detector. These simple and cost-effective structures were exposed to CO2 at 400-2200 ppm. The results show linear, accurate, and repeatable calibration curves at different CO2 concentrations. The proposed chamberless structure simplifies the industrial use of the NDIR technique. Complete analysis of variance was carried out to evaluate and compare the operational advantages of the proposed sensory structures. The experiments demonstrated the effect of the gold-coated walls in structured light source compartments with and without a parabolic reflector. Mixtures containing N2O, CH4, and CO2 were examined to determine the effect of interfering gases having absorption peaks similar to CO2 on the robustness of the proposed sensor. It was concluded that, although the use of a parabolic reflector concentrates rays on the detector area and increases its temperature, enhanced natural convection in the proposed sensor structure lowered the rate of temperature increase and the resulting thermal drift.