Abstract: A protective device for a humidity sensor protects the sensor from aggressive substances in a fluid to be analyzed. The protective device for the humidity sensor comprises a protective cap having openings that are covered with a membrane in such a manner that mass transfer between a measuring medium present in the environment and the interior of the protective cap can only take place through the membrane, said membrane including a plastic material which is highly permeable to water vapor, has high thermal stability and high corrosive resistance.

Abstract: The invention relates to a process and a device for measuring a gas medium with a chemical sensor that has a nominal measuring range. The chemical sensor is exposed to a gas mixture consisting of sample gas stream and dilution gas stream. In order to ensure that the chemical sensor always works within its nominal measuring range, the dilution ratio is readjusted. According to the invention, the dilution ratio is determined by substance concentration measurement of a defined substance component.