Robert Frodl

A High-Precision NDIR

A new high-precision spectroscopic gas sensor measuring carbon dioxide (CO2) for harsh environmental conditions of automotive applications is presented. The carbon dioxide concentration is the primary parameter for sensing in cabin air quality, as well as an important safety parameter when R744 (carbon dioxide) is used as the refrigerant in the air conditioning system. The automotive environment challenges the potential sensor principles because of the wide temperature range from -40degC to +85degC, the atmospheric pressure from 700 to 1050 mbar, and relative humidity from 0% to 95%. The presented sensor system is based on the nondispersive infrared principle with new features for reaching high precision criteria and for enhancing long-term stability. A second IR source is used for internal recalibration of the primary IR source, redundancy purposes, and software plausibility checks. The CO2 sensor system achieves an accuracy of better than plusmn5.5% over the whole temperature, pressure, and humidity ranges, with a resolution below 15 ppm and a response time shorter than 5 s. The operating time of the sensor system is more than 6000 h over a corresponding lifetime of more than 15 years. Experimental results show outstanding results for the intended automotive applications