A Temperature Compensation Technique for Near-Infrared Methane Gas Threshold Detection

Methane is the primary constituent of natural gas and is used in many industrial processes. Detection of the presence of methane is important, especially before it reaches explosive concentrations. Earlier sensor types are based on catalytic adsorption (which may limit the sensor lifetime) at elevated temperatures (requiring additional power and possibly compromising safety). Recently, optical sensors based on infrared (IR) absorption by hydrocarbon molecules have become an important research focus. One unsolved problem when using solid-state IR sources is that of optical flux variation due to heating. This paper introduces a novel power compensation approach for IR LEDs employed in gas detection, which accounts for variations in the optical flux of the source. The contribution of this paper is threefold. First, we propose the idea of compensating for emitted IR flux by means of pulsed junction voltage measurement and explain why this is effective. Second, we introduce a compensation algorithm which shows how to take advantage of this concept. Third, experimental results demonstrate that the discrimination algorithm is at least six times better than the uncompensated measurements. The convergence of the algorithm results in a stabilized measurement in less than 1 s.