US3083573A - Electrical hygrometers - Google Patents

Electrical hygrometers Download PDF

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Publication number
US3083573A
US3083573A US37800A US3780060A US3083573A US 3083573 A US3083573 A US 3083573A US 37800 A US37800 A US 37800A US 3780060 A US3780060 A US 3780060A US 3083573 A US3083573 A US 3083573A
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layer
water
pores
humidity
permeable
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US37800A
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John L Shaw
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • G01N27/225—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity by using hygroscopic materials

Definitions

  • the invention provides a humidity-sensitive element for a hygrometer, which element comprises a metal base (preferably of aluminium) provided with a surface layer (preferably an electrically anodized layer) having pores or capillaries, or the like, which extend partly through it from its outer face and are partly filled with an aqueous solution of a hygroscopic substance, which layer is covered by a water-vapour-permeable layer of electrically conductive material (e.g. graphite or vacuum evaporated metal), whereby the electrical capacitance between the base and the water-permeable electrically conductive layer varies with the humidity to which the water-permeable layer is exposed.
  • the said aqueous solution of said hygroscopic substance is preferably applied as a saturated solution.
  • the aqueous solution which partly fills the pores gains or loses water by passage of water vapour through the water-vapour-permeable layer until the vapour pressure at the mouths of the pores approaches equilibrium with that outside of the water-vapour-permeable layer, so that the amount of solution in the pores, when such equilibrium has been substantially reached, is a measure of the humidity.
  • the electrical capacitance between the watervapour-permeable layer and the metal base varies with the amount of solution in the pores and consequently that capacitance varies with the humidity.
  • the variation of the electrical capacitance in accordance with the humidity can be measured or indicated by any suitable means, which may be calibrated in absolute or relative humidity.
  • the aforementioned pores or capillaries are formed automatically during the anodizing process, but it may be necessary to try variations of the anodizing conditions to obtain best results.
  • the aqueous solution may be introduced into the pores in the necessary quantity by applying a very thin layer of the saturated solution to the outside of the watervapour-permeable layer if that layer is also water-permeable, in which case the solution permeates that layer, but preferably it is done by applying a very thin layer of the saturated solution to the outer face of the anodized layer before the water-vapour-permeable layer is applied.
  • the necessary thickness of the layer of saturated solution to achieve partial filling of the pores is of the order of a few microns.
  • the invention includes a method of manufacturing a humidity-sensitive element for a hygrometer, which method includes the steps of anodizing a metal base to form an anodized layer thereon, covering the anodized layer with a water-vapour-permeable electrically conducting layer, and applying a very thin layer of an aqueous solution of a hygroscopic substance either to the outer face of the water-vapour-permeable layer, if that layer is also Water-permeable, or to the outer face of the anodized layer before it is covered by the water-vapour-permeable layer.
  • the particular hygroscopic substance employed is preferably chosen in accordance with the humidity conditions which are to be measured or indicated.
  • Lithium chloride is particularly useful for the purpose and enables elements to be made which can be used with humidity conditions at 20 C. having dew points between l120 C. and -20 C.
  • Use of calcium chloride enables elements to be made which can be used with humidity conditions at 20 C. having dew points between -70 C. and 0 C.
  • Chromium oxide is suitable for use in elements which are intended for use in relative humidities in the range 2-40%.
  • the hygroscopic substance used must of course be one which in fact goes into solution in the water, so that some of the water can escape from the solution when the humidity falls, and not one which combines chemically with the water and prevents such escape.
  • FIGURE 1 illustrates, by a magnified partial cross section, one example of construction of an element according to the invention.
  • FIGURE 2 illustrates one example of an electrical circuit for use with the invention.
  • the element consists in an aluminium wire a which is anodized in a 3% solution of oxalic acid at a potential of volts for a period of 30 minutes to produce an anodized layer 12 containing a multiplicity of pores or capillaries 0.
  • the wire is washed to remove traces of the acid.
  • a very thin layer d of an aqueous solution of lithium chloride is painted over the anodized surface so as to partly fill the pores, this can be done by dipping a dry camel hair brush into the solution, squeezing out the surplus liquid, and lightly brushing over the anodized surface.
  • the outer electrically conducting layer 2 is then applied in a high vacuum and consists of 24 carat gold evaporated onto the anodized layer.
  • An element 5 cms. long and of 20 s.w.g. Wire constructed as above. described has a capacitance of the order of 0.02 microfarad.
  • FIGURE 2 shows one example of an electrical circuit with which an element constructed as above described can be used to indicate low dew points.
  • This consists of a capacitance bridge 1 operating at 50 c./s. or 60 c./s. and having its terminals connected respectively to the aluminium wire a and its outer conducting layer 2. The change in capacitance observed on the bridge is then proportional to the humidity surrounding the element.
  • a humidity-sensitive element for a hygrometer comprising an aluminium base provided with an oxidized porous surface layer of aluminium oxide, said surface layer having pores which extend partly through it from its outer face, said pores being partly filled with an aqueous substantially saturated solution of a hygroscopic substance, and immediately over said liquid-treated layer a continuous covering consisting of a water-vapour-permeable layer of electrically conductive material whereby the electrical capacitance between the base and the waterpermeable electrically conductive layer varies with the humidity to which the Water-permeable layer is exposed, said partially filled pores permitting the release and picking up water vapor to the liquid in the pores by-the vapor transmitted through said covering layer.
  • a humidity-sensitive element according to claim wherein said hygroscopic substance is calcium chloride.
  • a humidity-sensitive element according to claim wherein said hygroscopic substance is chromium oxide.
  • a method of manufacturing a humidity-sensitive element for a hygrometer which method includes the steps of anodizing an aluminium metal base to form a thin porous aluminium oxide layer thereon, applying to the surface of saidanodizedlayer a very layer of the order of microns of an aqueous substantially saturated splutiqn of a; hygroseq ic sulbstance to partly fill the pores of tihe enodiz ed ayer and thereafter hovering the 1i1uidi tqd nam ngweewramy fill d; t aq e u y r x e' uq i l e h, r a ex-v n a-nermca e tr e ll' w sllletin r e ea whea bx the e e r ee l apae ai qb twea e

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
US37800A 1959-06-23 1960-06-21 Electrical hygrometers Expired - Lifetime US3083573A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB21423/59A GB947857A (en) 1959-06-23 1959-06-23 Improvements relating to electrical hygrometers

Publications (1)

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US3083573A true US3083573A (en) 1963-04-02

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US37800A Expired - Lifetime US3083573A (en) 1959-06-23 1960-06-21 Electrical hygrometers

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US (1) US3083573A (ja)
CH (1) CH383034A (ja)
GB (1) GB947857A (ja)
NL (2) NL130518C (ja)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3243674A (en) * 1963-02-01 1966-03-29 Ebert Gotthold Capacitor type sensing device
US3350941A (en) * 1965-05-20 1967-11-07 Johnson Service Co Humidity sensing element
US3416356A (en) * 1965-12-17 1968-12-17 Vapor Corp Dew point hygrometer
US3440396A (en) * 1965-11-22 1969-04-22 Ugc Ind Inc Moisture and snow detector
JPS4859882A (ja) * 1971-11-24 1973-08-22
US3765100A (en) * 1971-09-22 1973-10-16 Gen Electric Capacitive sensing dryer control
US3895271A (en) * 1971-05-24 1975-07-15 Molecular Controls Limited Moisture sensors
US4217623A (en) * 1977-06-06 1980-08-12 Matsushita Electric Industrial Co., Ltd. Humidity sensor of capacitance change type
US4532016A (en) * 1980-07-09 1985-07-30 Commissariat A L'energie Atomique Capacitive hygrometer and its production process
WO2011050381A1 (de) * 2009-10-30 2011-05-05 Peter Hagl Feuchtigkeitssensor
US20130139587A1 (en) * 2011-12-02 2013-06-06 Stmicroelectronics Pte Ltd. Tunable humidity sensor with integrated heater
US20140070827A1 (en) * 2012-09-13 2014-03-13 Alliance For Sustainable Energy, Llc Systems and methods for compensated barrier permeability testing
US9019688B2 (en) 2011-12-02 2015-04-28 Stmicroelectronics Pte Ltd. Capacitance trimming with an integrated heater
US9140683B2 (en) 2010-12-30 2015-09-22 Stmicroelectronics Pte Ltd. Single chip having the chemical sensor and electronics on the same die

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2554440A (en) * 1946-02-21 1951-05-22 Serdex Inc Meteorological instrument
US2701832A (en) * 1951-11-09 1955-02-08 Phillips Petroleum Co Moisture-sensitive element
US2710324A (en) * 1953-02-04 1955-06-07 Harmantas Christos Sensing element for the electric hygrometer
US2884593A (en) * 1953-05-06 1959-04-28 Miyata Akira Device for determining moisture content of various materials and substances

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2554440A (en) * 1946-02-21 1951-05-22 Serdex Inc Meteorological instrument
US2701832A (en) * 1951-11-09 1955-02-08 Phillips Petroleum Co Moisture-sensitive element
US2710324A (en) * 1953-02-04 1955-06-07 Harmantas Christos Sensing element for the electric hygrometer
US2884593A (en) * 1953-05-06 1959-04-28 Miyata Akira Device for determining moisture content of various materials and substances

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3243674A (en) * 1963-02-01 1966-03-29 Ebert Gotthold Capacitor type sensing device
US3350941A (en) * 1965-05-20 1967-11-07 Johnson Service Co Humidity sensing element
US3440396A (en) * 1965-11-22 1969-04-22 Ugc Ind Inc Moisture and snow detector
US3416356A (en) * 1965-12-17 1968-12-17 Vapor Corp Dew point hygrometer
US3895271A (en) * 1971-05-24 1975-07-15 Molecular Controls Limited Moisture sensors
US3765100A (en) * 1971-09-22 1973-10-16 Gen Electric Capacitive sensing dryer control
JPS4859882A (ja) * 1971-11-24 1973-08-22
JPS5125356B2 (ja) * 1971-11-24 1976-07-30
US4217623A (en) * 1977-06-06 1980-08-12 Matsushita Electric Industrial Co., Ltd. Humidity sensor of capacitance change type
US4532016A (en) * 1980-07-09 1985-07-30 Commissariat A L'energie Atomique Capacitive hygrometer and its production process
WO2011050381A1 (de) * 2009-10-30 2011-05-05 Peter Hagl Feuchtigkeitssensor
US9140683B2 (en) 2010-12-30 2015-09-22 Stmicroelectronics Pte Ltd. Single chip having the chemical sensor and electronics on the same die
US20130139587A1 (en) * 2011-12-02 2013-06-06 Stmicroelectronics Pte Ltd. Tunable humidity sensor with integrated heater
US9019688B2 (en) 2011-12-02 2015-04-28 Stmicroelectronics Pte Ltd. Capacitance trimming with an integrated heater
US9027400B2 (en) * 2011-12-02 2015-05-12 Stmicroelectronics Pte Ltd. Tunable humidity sensor with integrated heater
US20140070827A1 (en) * 2012-09-13 2014-03-13 Alliance For Sustainable Energy, Llc Systems and methods for compensated barrier permeability testing

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Publication number Publication date
CH383034A (it) 1964-10-15
NL130518C (ja)
GB947857A (en) 1964-01-29
NL252982A (ja)

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