Non-dispersive infrared (NDIR) gas detection systems have been extensively used for gas monitoring because it is considered the simplest approach with moderate sensitivity and fast response. Concentration calculation models for calibration are particularly important in the NDIR gas detection systems because of nonlinear relationship between the output voltage ratio and the concentration.
In this paper, we propose a concentration calculation model two fitting parameters for non-dispersive infrared gas detection system, accounting for the fact that not all the IR radiation that impinges upon the detector is absorbed by the gas and for saturation effects in absorption peaks leading to the nonlinear relationship. In spite of the small number of fitting parameters of the proposed concentration calculation model, it represents high quality curve fitting to experimental data.
Most gas molecules exhibit characteristic transition bands associated with their fundamental vibrations in the mid-infrared (mid-IR) region.[1] Non-dispersive infrared (NDIR) spectroscopy is based on the characteristic absorption bands in the mid-IR, sometimes referred to as the "molecular fingerprint" as it is different for every type of gas. It is the property that makes NDIR spectroscopy a common method that uniquely identifies and quantifies the presence of target gases with high sensitivity and selectivity.
NDIR gas sensors employ broad-band IR source such as thermal emitters or light emitting diodes (LEDs) emitting entire absorption bands simultaneously, which then passes through the sample chamber that contains the gas to be detected. To analyze the concentration of a target gas, a bandpass optical filter is typically added before the detectors to eliminate cross interference caused by overlapping the characteristic absorption, passes only the wavelengths that the target gas can absorb and enables the NDIR sensor's selectivity. The detector then measures the intensity of the incoming light and produces a corresponding electrical signal, which is processed and interpreted as the gas concentration using a concentration calculation model. The sensor also uses a reference channel, at which the gas does not absorb IR light. The comparison between these two channels allows the sensor to accurately measure the gas concentration from the output voltage ratio.
For a NDIR gas detection system the concentration calculation model for calibration is particularly important because of nonlinear relationship between the output voltage ratio and the concentration. The concentration calculation model has a number of fitting parameters that are adjusted to match the fitting curves to the measured data as close as possible.
In this paper, we propose a concentration calculation model with three appropriate parameters for non-dispersive infrared gas detection system. Gas detection systems using the proposed concentration calculation model can be calibrated with measurements at the zero concentration and at two other different gas concentrations.
As can be shown in figure, the proposed concentration calculation model successfully fits the experimental data. Gas detection systems using the proposed concentration calculation model can be calibrated with measurements at the zero concentration and at two other different gas concentrations.
Our research results have been published in the "AIP Advances" with a title of "Concentration calculation model for calibration of non-dispersive infrared gas detection system"(https://doi.org/10.1063/5.0232201).
