The concentration of a single gas species can be detected using a single beam NDIR gas sensor having a differential infrared source element producing radiation having a first spectrum at a first high temperature and a second spectrum at a second lower temperature, a detector and a dual pass band filter. The gas sensor further includes a driver driving the source at either the fjrst or second temperatures; a feed back loop; a differential gain amplifier creating a high cycle amplified output during a high cycle and a low cycle amplified output during a low cycle; a controller for synchronizing the driver and driving the source at the first temperature and applying high cycle amplification during the high cycle and driving the source at the second temperature and applying a low cycle amplification during the low cycle; and a signal processor for determining the concentration of he gas species.
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