Effect of Physical Parameters on SO2 NDIR Analyzer Using a LiTaO3 Pyroelectric Detector

Tele monitoring system (TMS) has been widely used to monitor air pollutants emitted from stationary sources in Korea. Sulfur dioxide (SO2) emitted from an industrial stack can be analyzed using the NDIR technique. The amount of energy absorbed in the infrared wavelength band varies with the concentration of gas molecules. In this study, physical influencing factors were investigated including: the effect of signal detection according to the temperature of the detector, the flow rate of the gas cell, and the change of the optical path inside the gas cell. A LiTaO3-based pyroelectric detector was applied to the NDIR analyzer. The physical parameters consisted of temperatures (35, 40, 45, 50 degrees C), flow rates (100, 500, 1000, 2000, 5000, 10000 ml/min), and optical path lengths (5.6, 7.2, 10.4 m). As a result, when the temperature increased, the magnitude of the basic signal tended to decrease. In contrast, variations of flow rates did not show a significant effect on the detector signal. In addition, the longer optical path shown the lower signal. It was found that the signal resolution of pyroelectric detector was improved with respect to low concentrations of SO2 (<50 ppm).