System and method for determining gas optical density changes in a non-linear measurement regime

A method comprising the steps of:

• providing a gas concentration monitoring system that monitors concentration of a gas along a path irradiated by electromagnetic radiation, wherein absorption of at least some of said electromagnetic radiation at a specific wavelength by said gas is indicative of a measure of said concentration of said gas along said path, said gas concentration monitoring system including first and second sensors positioned to simultaneously detect said absorption along said path;
• calibrating each of said first and second sensors to thereby define a unique response curve associated therewith that relates a change in voltage output for each of said first and second sensors to a change in optical density, wherein each said response curve includes a unique non-linear response region thereof;
• forming a ratio-of-responses curve defined by a ratio of said response curve associated with said first sensor to said response curve associated with said second sensor;
• collecting outputs from each of said first and second sensors;
• generating a ratio of sensor output changes using said outputs from each of said first and second sensors, said ratio of sensor output changes defined as a ratio of output changes associated with said first sensor to output changes associated with said second sensor;
• and
• establishing an operating point on said ratio-of-responses curve using said ratio of sensor output changes, said operating point being indicative of an optical density wherein, when said operating point is in said non-linear response region of at least one of said first and second sensors, said operating point and said optical density corresponding thereto can be used to establish an actual response of at least one of said first and second sensors that is used in determining changes in said optical density.