Steady State and Transient Response Characteristics of Commercial Non-Dispersive Infrared Carbon Dioxide Sensors

Abstract

Non-dispersive infrared CO2 sensors are well established and are commonly used to provide demand control ventilation for commercial buildings. The aviation industry has shown potential interest in adapting these sensors to provide air quality monitoring in airliner cabins. Two possible applications have been identified: CO2 sensors have the potential to detect bleed air contamination events and provide demand control ventilation by determining the adequacy of ventilation to dissipate contaminants emitted by the passengers and materials which are present in the cabin. To evaluate the suitability of these NDIR sensors for the two proposed applications, three commercial NDIR CO2 sensors with a variety of form factors were obtained. The sensors were exposed to near instantaneous changes in CO2 concentration to determine their transient and steady state responses. Because the levels of CO2 are not expected to reach steady state during a transitory contamination event, it is important to understand the sensors’ transient response. Therefore, this response was evaluated under two sets of conditions. In the first set of experiments, the gas was flowed through inlet and outlet ports integrated into the sensor. In the second set of experiments, the gas was allowed to diffuse into the sensor from the surrounding environment. In both cases, the sensors’ readings were allowed to reach equilibrium and their steady state performances were characterized by applying a range of CO2 concentrations.