Non-interference NDIR detection method for mixed gases based on differential elimination

A multi-gas NDIR (non-dispersive infrared spectroscopy) detection system consisting of two broadband light sources and multiple detectors is established, and an interference-free method for measuring mixed gases based on differential elimination NDIR is proposed. By developing a differential model, the sensor response SR is only dependent on the optical path L, the concentration C, and the absorption constant k of the gas to be measured, independent of other factors (the light source drift, ambient temperature, humidity, etc.). Likewise, multi-gas measurements can be achieved in this method by altering and increasing the type and number of detectors. As an example of two-gases measurement, a three-dimensional surface C−SR is constructed by calibration, with the known two gas concentrations (CO2: 0–5000 ppm, CH4: 0–3000 ppm) are used as independent variables, and the sensor responses SR1 and SR2 are used as dependent variables, respectively. The predicted correlation coefficient and root mean square error can reach 0.9985 and 0.0024. The proposed measurement system is smaller, less expensive, and more stable than conventional multi-channel detection system. A more robust method is provided for detecting various gases.