COMPENSATION OF THE INFLUENCE OF HUMIDITY ON THE MEASUREMENT OF AN SO2 SENSOR BY SIGNAL-PROCESSING

SO2 concentrations in the ambient air can be measured using a layer that adsorbs SO2 selectively. An interdigital capacitor is coated with this organically modified ceramic. The layer changes its dielectric properties when it adsorbs SO2. Due to the adsorption mechanism the layer is insensitive to many gases; unfortunately not to humidity. To compensate the influence of humidity, a large number of sensor signals are measured within assumed relevant SO2 concentrations (0-5 vol.-ppm) and humidities (0-2 vol.%). The influence of humidity can be eliminated by a pure mathematical model. Deviations of the determined SO2 concentration from the true value are caused by long response times and hysteresis type characteristics of the sensor. Another limiting factor is the finite precision of humidity measurement. An uncertainty of a mere +/-1% relative humidity in ambient air brings about an error of 1 to 2.5 vol.-ppm of the reading.