COMPARISON OF IR LED GAS SENSORS WITH THERMAL SOURCE PRODUCTS

Physical principles for infrared gas sensing using LEDs as sources are examined, A number of LEDs from different sources are compared for po wer output, polar diagram and temperature dependence of output. Some o f these have been incorporated in a practical gas sensor based on the Edinburgh Sensors' Gascard, Thus a direct comparison of signal levels between thermal sources and LEDs has been made using thermal detectors . Gas sensing is demonstrated for CO2. The paper describes the ranges, accuracies and stability with time and temperature presently exhibite d by thermal source sensors and suggests criteria for the widespread u se of LED sensors. Some advanced concepts are mentioned with respect t o future sensing requirements.