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Title: Humidity indicator
Claims: What is claimed is: 1. A humidity indicator comprising: (a) a housing formed with a cavity; (b) sensing element means constrained within said cavity for movement relative to said housing, said sensing element means composed of a material that changes dimensionally in response to humidity variations, said sensing element having a head that is formed with a through hole; (c) a flexible diaphragm captively held within said cavity in contact with said head; (d) an adjusting member received within said hole, said adjusting member configured to move said flexible diaphragm; (e) first plate means received within said cavity, said first plate means formed with an opening on one face thereof, said flexible diaphragm disposed between said head and said first plate means, a reservoir formed between said first plate means and said flexible diaphragm; (f) second plate means formed with a capillary groove, said first plate means and said second plate means formed with a port interconnecting said reservoir and said capillary groove; and (g) a transduction fluid within said reservoir constrained to flow within said capillary groove when the volume of said reservoir changes as a result of movement of said flexible diaphragm in response to dimensional changes in said sensing element due to variations in humidity. 2. The humidity indicator as claimed in claim 1 wherein said second plate means includes a cover plate and a dial plate, said cover plate formed with at least one groove to comprise said capillary groove, said dial plate having indicia in the form of a scale representing percent of relative humidity, said cover plate superposed on said dial plate for forming said capillary groove. 3. The humidity as claimed in claim 2 wherein said capillary groove is in the form of at least first and second interconnected grooves that lie in a substantially spiral path. 4. The humidity indicator as claimed in claim 3 wherein a free end of said first groove extends radially inward and a free end of said groove extends radially outward, said free end of said first groove aligned with said interconnecting port. 5. The humidity indicator as claimed in claim 1 wherein the composition of said housing, said sensing element and said tranduction fluid is such that the volume change of transduction fluid due to thermal expansion plus the displaced volume of said reservoir due to thermal expansion of said sensing element equals the displaced volume in said reservoir due to thermal expansion of said housing. 6. A humidity indicator comprising: (a) a housing formed with a cavity; (b) a sensing element received within said cavity, said sensing element composed of a material that changes dimensionally in response to humidity variations, said sensing element having a head that is formed with a through hole; (c) a flexible diaphragm received within said cavity in contact with said head; (d) retainer means for captively holding said flexible diaphragm against said sensing element and for providing contiguity of the abutting faces of said flexible diaphragm and said sensing element; (e) an adjusting member received within said hole, said adjusting member configured to move said flexible diaphragm; (f) an intermediate plate received within said cavity, said intermedite plate formed with an opening on one face thereof, said flexible diaphragm disposed between said head and said intermediate plate, a reservoir formed between said intermediate plate and said flexible diaphragm; (g) a cover plate formed with a groove on one face thereof; (h) a dial plate superimposed onto and affixed to said one said of said cover plate said dial plate sealing said groove and forming an open ended capillary tube, said intermediate plate and said dial plate formed with apertures defining an interconnecting port between said reservoir and one end of said capillary tube; and (i) a transduction fluid within said reservoir constrained to flow within said capillary tube when the volume of said reservoir changes as a result of movement of said flexible diaphragm in response to dimensional changes in said sensing element due to variations in humidity. 7. The humidity indicator as claimed in claim 6 wherein said groove formed in said cover plate is in the form of a pair of interconnected grooves that lie in a substantially spiral path. 8. The humidity indicator as claimed in claim 7 including a barrier fluid within said capillary tube in contact with said transduction fluid. 9. The humidity indicator as claimed in claim 8 wherein said dial plate includes indicia representing percent of relative humidity, said indicia disposed along one of said grooves, percent of relative humidity being indicated on said indicia at the interface of said transduction fluid and said barrier fluid. 10. The humidity indicator as claimed in claim 9 wherein said transduction fluid is composed of a mineral oil containing a dye and said barrier fluid is glycerine. Other info: Inventors: Captain, Khushroo M. (Cambridge, MA, US) Application Number: 786006 Filing Date: 1977-04-08 Publication_date: 1978-07-04 Assignee: Foster-Miller Associates, Inc. (Waltham, MA) Primary Class(es): 73/335.11 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Queisser, R. C. Assistant Examiner: Appleman, John S. Attorney: Morse, Altman, Oates & Bello |
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