Exploration of the metrological performance of a gas detector based on an array of unspecific infrared filters

The feasibility of a non-dispersive infrared (NDIR) gas detection system based on an array on non-specific detectors is studied in this work. The measurement system, that is intended to be low cost and of reduced dimension, is aimed to the simultaneous quantitative detection of different gases with IR absorption bands in the region of the 1000–4000 cm−1. The detector is a single module that has been already fabricated. It is composed by an array of broadband infrared filters and a matching array of thermopile detectors joint together by means of flip chip. The elements of the filter array are not tuned for the specific measurement of any gas, in opposition to traditional NDIR setups, making necessary the use of multivariate regression techniques (Partial least squares) to predict the gases concentration. A preliminary evaluation of the metrological characteristics of the complete NDIR system is carried out using a realistic model of the system. Two arrays sizes, 3 × 3 and 4 × 4 elements, are studied for the discrimination of a mixture composed by methane, carbon monoxide and carbon dioxide at different concentrations. Prediction errors about tens of ppm are found for an optical path length of 10 cm. In traditional NDIR systems infrared source aging is compensated by means of a reference channel where no absorptions bands are present. Instead, in this in this work these effects are removed using a digital component correction technique.