CAPACITANCE MOISTURE METER AND WINGLIKE PROBE

• US 3,581,197 A
• Filed: 10/03/1969
• Issued: 05/25/1971
• Est. Priority Date: 10/03/1969
• Status: Expired due to Term

• Current Assignee: Dennison H. Morey Jr, Gordon D. Browning, Silva Melvin
• Original Assignee: Dennison H. Morey Jr, Gordon D. Browning, Silva Melvin
• Inventors: Morey, Dennison H. Jr., SILVA MELVIN, Browning, Gordon D.
• Application Number:
  US04/863,665
• Time in Patent Office: 599 Days
• US Class Current: 324/690
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01N 27/225 by using hygroscopic materials

Abstract

Free moisture in yieldable matter (defined to include water, alcohols, and other liquids of relatively high dielectric constants occurring on the surface of solids or as drops in another liquid) is measured by an instrument which includes a radio frequency oscillator (e.g., 2 MegHz.), preferably voltagestabilized, connected to an LC circuit that can be made substantially resonant, one of the elements being a capacitance probe, and the potential over one of these elements is measured to indicate the moisture content. The probe preferably includes an outer sheath of metal which partly covers a body of moistureimpermeable dielectric material and leaves a part of the surface of the material exposed, and an inner conductor embedded in the material and thereby completely insulated from the outside of the probe; the capacity between the sheath and conductor varies with the amount of moisture which contacts the exposed surface of the body. When testing material of variable density, such as soil, the probe is placed within the material and the latter is compacted to a predetermined degree if required.

Claims

1. An elongated capacitance probe for measuring free moisture in yieldable matter which comprises:

a. a body of dielectric material which is nonpermeable to moisture;

b. a first electrical conductor forming one element of a capacitor for making contact with said yieldable matter and covering a part of said body and leaving an external surface of said dielectric material exposed for engagement with the yieldable matter at a sensing portion;

c. said dielectric material having a cross section at said sensing portion which is exposed and which consists of a central portion with a pair of wings extending outwardly therefrom;

d. said first electrical conductor substantially covering said wings of said dielectric;

e. a second electrical conductor forming a second element of said capacitor situated within said dielectric body completely insulated from said first conductor and being located within the central portion of said dielectric at said sensing portion, and;

f. said dielectric material completely filling the space between said conductors permitting moisture to contact only the exposed surface of said dielectric along said central portion at said sensing portion.

2. A capacitance probe as defined in claim 1 wherein said exposed surfAce of said dielectric is smooth, convex, and has a length greater than its width and said first electrical conductor having a sharpened spade end for insertion into said yieldable matter and being formed with elongated grooves from the sharp end to said sensing portion.

3. A device as described in claim 1 in a capacitance moisture meter which comprises:

a. a radiofrequency oscillator having an output circuit;

b. an inductance connected in series with said capacitance probe across said output circuit; and

c. a measuring circuit connected to measure the potential across said inductance of paragraph b.

4. A capacitance moisture meter as defined in claim 3 wherein:

a. said measuring circuit includes an indicator calibrated in terms of moisture content of said yieldable matter.

5. A capacitance moisture meter as defined in claim 3 wherein:

a. said measuring circuit is connected to measure the potential across said probe.