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Title: Capacitive humidity transducer
Claims: What is claimed is: 1. In a capacitive humidity transducer, electrically non-conductive base means having an outer supporting surface, at least a pair of electrically conductive coatings carried by said base means at said outer supporting surface thereof, said electrically conductive coatings being spaced from each other and being passive with respect to water absorption, dielectric film means also carried by said surface of said base means, said dielectric film means covering at least a portion of said electrically conductive coatings and being composed at least in part of a film which is active with respect to water absorption and which has a dielectric constant which changes as a function of the amount of water absorbed thereby, and an outer, thin, electrically conductive, water-permeable layer carried on the outer surface of said dielectric film means, said layer because of its water permeability permitting moisture in the atmosphere to reach said dielectric film means which is situated at least in part between said electrically conductive coatings and said electrically conductive water permeable layer, said dielectric film means maintaining said electrically conductive water permeable layer out of contact with at least a portion of one of said electrically conductive coatings to form a capacitor therebetween, another portion of said electrically conductive coatings and a portion of said electrically conductive water permeable layer being in contact with each other to form an electrical connection so that said capacitor can be connected to measuring means for indicating atmospheric humidity, said capacitor being supported in its entirety by said base means which provides a stable support for said capacitor enabling said dielectric film means to provide a rapid response to changes in humidity under a wide variety of atmospheric conditions. 2. The combination of claim 1 and wherein said base means also is passive with respect to water absorption. 3. The combination of claim 1 and wherein said electrically conductive water permeable layer is in electrically-conductive contact with the other of said coatings to form said electrical connection therewith. 4. The combination of claim 1 and wherein said dielectric film means maintains said electrically conductive water permeable layer out of contact with both of said electrically conductive coatings with a portion of said dielectric film means being situated between and in contact with said other electrically conductive coating and a portion of said electrically conductive water permeable layer to form therewith a second capacitor and means for connecting said second capacitor, in series with said first-mentioned capacitor, and both of said capacitors being supported in their entirety by said surface of said base means. 5. The combination of claim 1 and wherein said dielectric film means is formed in its entirety of said active film. 6. The combinatin of claim 1 and wherein said dielectric film means has in addition to said active film an electrically non-conductive film which is passive with respect to water absorption and which carries said active film, and both of said films being situated at least in part between said electrically conductive coatings and electrically conductive water permeable layer to form therewith a pair of capacitors, and means for connecting said pair of capacitors in series, said pair of capacitors being supported in their entirety by said surface of said base means. 7. The combination of claim 6 and wherein said active film is situated between said passive film and said layer. 8. The combination of claim 7 and wherein said active film is discontinuous, having an area less than that of said passive film. 9. The combination of claim 1 and wherein said active film is a polymer film. 10. The combination of claim 1 and wherein said base means is made of glass. 11. The combination of claim 1 and wherein said conductive coatings are made of gold. 12. The combination of claim 1 and wherein a pair of conductors are respectively connected electrically with said coatings so that a capacitance can be measured between said conductors. 13. The combination of claim 1 and wherein said dielectric film means is composed in its entirety of said active film, and the latter film having a thickness on the order of 1 micron. 14. The combination of claim 13 and wherein said film is a polymer film. Other info: Inventors: Suntola, Tuomo S. (Espoo, FI) Application Number: 598034 Filing Date: 1975-07-22 Publication_date: 1979-08-21 Assignee: Vaisala Oy (FI) Primary Class(es): 73/335.04 361/286 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Yasich, Daniel M. Assistant Examiner: Attorney: Steinberg & Blake |
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