<p>The concentration of a gas species is detected by using a single beam NDIR gas sensor in which an infrared source element is driven at two different temperatures, a feed back loop senses an operation voltage of the source, a differential gain amplifier creates a high cycle amplified output during a high cycle and a low cycle amplified output during a low cycle while a controller synchronizes the source driver so that a signal processor can determine the gas concentration through use of the high cycle amplified output and the low cycle amplified output. The infrared source can be a non-genuine blackbody source such as an incandescent miniature light bulb when the sample chamber is a thermally insulated aluminum tube that is maintained at a preselected temperature greater than ambient so that the glass envelope of the bulb is maintained at an equilibrium temperature (such as approximately 30 degrees Celsius plus or minus two degrees Celsius) during its low cycle operation state.</p>
