Real-Time Correction of Gas Concentration in Nondispersive Infrared Sensor

Abstract

Non-dispersive infrared (NDIR) sensors have been widely used in measuring gas concentration in process industry. However, the inhomogeneous gas diffusion in the gas chamber of NDIR sensor increases the response time and causes measurement error. In this case, the fast-and-accurate measurement of gas concentration is of great importance in avoiding accidents. This article focuses on constructing a novel gas diffusion model among normalization concentration (N-concentration), inlet flow velocity, and diffusion time. Firstly, the structure model of gas chamber is constructed based on Fluent 15.0 and the turbulence intensity is calculated based on dynamic viscosity, inlet flow velocity, concentration, temperature and pressure. The simulation model is constructed based on the assumption of simultaneous reaction and mass transfer. The initial result shows that the N-concentration along the optical path is mainly influenced by inlet flow velocity and diffusion time, while the temperature, pressure and inlet concentration have less influence on gas diffusion. According to the velocity distribution map, the critical zone of inlet flow velocity is defined to divide the gas diffusion state into different zones. Then, a novel Multi-interval exponential diffusion model is proposed to calculate the N-concentration and the real-time measurement of gas concentration can be achieved based on inlet flow velocity, diffusion time and the pre-defined critical zone of inlet flow velocity. The proposed model is suitable for the gas concentration correction of different gases. Finally, the validation indexes include the coefficient of determination (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), Mean Squared Error (MSE) and standard uncertainty shows the accuracy of the proposed model can be obviously increased.