A gas sensor system with dielectric and mass sensors

Commonly chemical sensors use only a single physical property of their sensitive material, e.g. interdigital capacitors (IDC) the permittivity. For this gas sensor-system we exploit the physical properties of the sensitive material. The sensitive material of adsorptive dielectric gas sensors changes other properties under the influence of gases too: An alteration of the mass and the optical properties (IR- absorption) under the influence of gases was observed at the sensitive material (heteropolysiloxane, HPS) of dielectric S02-sensors with conventional analytical methods. A direct comparison of the dielectric and mass adsorption isotherm of S02 was practiced with a dielectric sensor (IDC) and a mass sensor (10 MHz bulk-waveoscillator) . The two adsorption isotherms show significant differences. The dielectric adsorption isotherm reaches its saturation point at a lower S02 concentration than the mass adsorption isotherm. In a sensor system this effect could be used for an exact determi nation of the saturation point. Further characteristics of this sensors and a proposal for an physical sensor system will be discussed.