US2237006A - Electric hygrometer - Google Patents

Description

April 1, 1941. KQLLER 2237300 ELECTRIC HYGROMETER Filed April 21, 1958 ALUMINUM Imvefitor. Lewis R.Koller;

t-hs Attorney.

'such as a metallic oxide I2.

Patented Apr. 1, 1941 ELECTRIC HYGROMETER Lewis R. Keller, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 21, 1938, Serial No. 203,297

Claims.

My invention relates to humidity or moisture indicators and regulators and concerns particularly humidity responsive elements which vary in electrical conductivity with variations in humidity,

It is an object of my invention to provide a humidity responsive element having a high conductivity and which will carry sufficient current to operate contact-making and indicating devices and instruments directly.

It is a further object of my invention to provide a humidity responsive element which responds quickly to variations in humidity and quickly reaches equilibrium after a change in humidity. Other and further objects and advantages will become apparent as the description proceeds.

In carrying out. my invention in its preferred form I provide a base of electrically conducting material on the surface of which is coated a very thin film of hygroscopic material such as a metallic oxide, which is covered with a foil of material which can be beaten very thin, such as gold foil. A voltage is applied between the two surfaces of the oxide film by means of terminals connected to the metallic base and to the foil covering, and variations in current are observed to determine variations in humidity- The invention may be understood more readily from the following detailed description when considered in connection with the accompanying drawing and those features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto.. In the drawing Figure 1 is a perspective view diagrammatically representing one embodiment of my invention. Figure 2 is a fragmentary enlarged cross sectional view of the arrangement of Figure 1. Figure 3 is a circuit diagram of a humidity indicatorutilizing a humidity responsive element of the type illustrated in Figures 1 and 2; and Figure 4 is a circuit diagram of a humidity controller corresponding to the arrangement of Figure 3.

Like reference characters are utilized to designate like parts throughout the drawing.

The humidity responsive element illustrated in Figure 1 comprises a plate ll of conducting material serving as a base, the surface of which is coated with a suitable hygrometric material surface I 2 of the base II a cover of very thin conducting material such as metallic foil I3 is laid and electrical connections are provided for the base H and the foil cover l3. If desired. the foil l3 may be electrically and mechanically rein- Upon the coated forced for the electrical connection by providing a sheet I of thin electrical conducting material 'in contact with a portion of the surface of the numeral I! in Figures 3 and 4 and the element I1 is connected to a source of alternating current IS in series with a current responsive device such as an indicating instrument ill or contact-making circuit controlling device or a relay 20. In Figure 4 the contact-making device 20 is shown with a movable contact 2! and a pair of stationary contacts 22 included in an electrical circuit 23 which may be an operating circuit for any suit able type of humidity varying device 24 such as, for example, a blower for introducing humidifled air into a chamber or a steam valve for controlling the heating of a chamber to dry the atmosphere, or the like.

Although my invention is not limited to the use oi. particular chemical substances for constructing the humidity responsive element H, I have found that satisfactory results may be obtained by utilizing as the base i I a plate of aluminum and forming a film of aluminum oxide l2.

thereon electrolytically'in a sulphuric acid electrolyte. Although not limited to the specific thinness of film I have found a thickness of approximately of a mil to be satisfactory. I have obtained satisfactory results by using gold leaf as the cover I3 for the aluminum oxide and I believe that golf leaf has the advantage of permitting moisture to pass through it quickly to the aluminum oxide or to the atmosphere. In view of this property of the foil and the extreme thinness with which aluminum oxide can be prepared I find that the humidity responsive element reaches equilibrium very quickly after a change in the humidity of the surrounding atmosphere, so that my humidity responsive element is useful in cases where quick response to variations in humidity is desired.

I have found that the conductivity of the aluminum oxide film l2 varies approximately linearly with the aqueous vapor tension of the surrounding atmosphere for the humidities in the range usually experienced in ordinary rooms.

With a -volt alternating current source I have found the relationship between aqueous vapor tension of the atmosphere and current in microamperes for every square centimeter of surface of oxide film to be approximately as represented in the following table:

Microamperes per sq. cm. at

Aqueous vapor tension (in mm. of Hg.)

100 volts It will be obvious that the current-carrying capacity of the device may be varied by varying the surface area of the film.

The electrical supply source l8 may be either alternating current or direct current but where the apparatus is to be in operation for extended periods of time I prefer to utilize an alternating current source since I find that there is no fatigue effect with alternating current.

Although I have obtained satisfactory results by the use of an aluminum base Ii it will be understood that my invention is not limited thereto. For example, I may employ a base of chromium metal with the surface oxidized. Likewise, I have found that satisfactory results are obtained from a steel base on which chromium oxide has been painted to form the hygroscopic film. The hygroscopic film may also be formed by dipping a steel plate into a mixture of chrome oxide, acetone, and a small amount of alkyd resin or varnish such as that sold under the trade name Glyptal." It will be observed that both aluminum oxide and chromium oxide are refractory oxides.

The foil cover of the arrangement illustrated in Figure 2 consists of a sheet of commercial gold leaf, which has a thickness of approximately 10- centimeters, and is applied to the oxide film I2 by merely laying the foil on the coated base i I, connecting the terminals [5 and it to a voltage source and allowing the electrostatic attraction to hold the foil against the coated plate. After a short time, I find that the foil l3 adheres firmly even without the electrostatic attraction. Although I have found such a golf leaf cover satisfactory, my invention is not limited to the use of this precise form of cover. For example, the thickness, the

material, or the method of producing may be leai upon the oxide film l2, the cover l3 may, for

example, be applied by the evaporating process or by cathode sputtering in a manner somewhat similar to these well known processes of producing thin metallic coatings for use as mirror surfaces. In the specification and claims, I use the word foil to specify any very thin sheet regardless of the method by which it is produced.

Aluminum oxide has a volume specific resistivity of approximately megohmn cm. I am enabled to use such a high resistance hygroscopic material effectively by utilizing a very thin film of large area and passing the current through it transversely. I believe that the aluminum oxide formed in a film as described acts as a-spongy holder for atmospheric water which is hydrolized by the electric field and carries current varying with the humidity.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A humidity responsive element which varies in electrical conductivity with variations in humidity, said element comprising an aluminum base having an electrolytic refractory oxide film thereon and a gold foil lying against and substantially covering the oxide film, with electric terminals connected to the aluminum base and to the gold foil, said film comprising a moisture sensitive oxide of the group consisting of aluminum oxide and chromium oxide, and said gold foil being sufficiently thin to permit atmospheric moisture to reach and affect the oxide film.

2. A humidity responsive element which varies in electrical conductivity .with variations in humidity, said element comprising a base of conducting material having a film of aluminum oxide thereon of a thickness less than one mil and a gold foil lying against the oxide film, with electric terminals connected to the base and to the gold foil.

3. A humidity responsive element which varies in electrical conductivity with variations in humidity, said element comprising an aluminum base with an oxidized surface and a thin metallic foil lying against the oxidized surface, with electric terminals connected to the aluminum base and to the metallic foil. 7

4. A humidity responsive element which varies in electrical conductivity with variations in humidity, said element comprising a base of an electrical conducting material, a film composed of a refractory metallic oxide coated on the surface of the base and a thin metallic foil lying against and substantially covering the oxide film with electric terminals connected to the base and to the foil, said film comprising a moisture sensitive oxide of the group consisting of aluminum oxide and chromium oxide, and said metallic foil being sufiiciently thin to permit atmospheric moisture to reach and effect the oxide film.

5. A humidity responsive element which varies in electrical conductivity with variations in humidity, said element comprising a film of hygro- CERTIFICATE OF CORRECTION. Patent No. 2,257,006. April 1, 191a.

LEWIS R. KOLLERV It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, second column, line 56, for the word "golf" read --gold; page 2, second col umn, line 55, claim 1;, for "effect" read --affect--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of May, A. D. 19141.

- Henry Van Arsdale, (Seal) Acting Commissioner 0% Patents.

v CERTIFICATE OF CORRECTION. Patent No. 2,257,006. April 1, 19m.

' LEWIS R. KOLLER.-

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Pagel, second column, line 56, for the word "golf" read --gold-; page 2, second column, line 55, claiml for "effect" read --affect-; and that the said'Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of May, A. D. wi l.

I Henry Van Arsdale, (Seal) Acting Commissioner 0% Patents.

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