Temperature Compensation Methods of Nondispersive Infrared CO2 Gas Sensor with Dual Ellipsoidal Optical Waveguide

To measure CO2 gas concentration, a nondispersive infrared (NDIR) gas sensor is fabricated by implementing a thermopile detector that includes an application-specific integrated circuit (ASIC) chip for signal conditioning, a temperature sensor, and a unique dual ellipsoid optical waveguide. To characterize its temperature dependence, the sensor module is tested with varying temperature ranging from 253 to 333 K at different CO2 gas concentration levels. In the absence of CO2 gas (0 ppm), as ambient temperature increases, the output voltages of the CO2 and reference sensors show a linear dependence: the output voltage-to-temperature ratios are 13.4 and 8.4 mV/K, respectively. The temperature sensor's output also indicates good linearity as a function of temperature, and ambient temperature can be expressed as T(V) = 216.03 + 67.087 V-T. The concentration-dependent property of the sensor module is expressed using three parameters, each of which exhibits temperature dependence only. By combining the temperature and concentration dependences, a general equation is derived by which the CO2 gas concentration is estimated at different temperatures with an average error of 1.544% and a standard deviation of 4.799% from 253 to 333 K.