US2304448A

US2304448A - Condenser for soil moisture meter

Info

Publication number: US2304448A
Application number: US346373A
Authority: US
Inventors: Joel E Fletcher
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-07-19
Filing date: 1940-07-19
Publication date: 1942-12-08
Anticipated expiration: 1959-12-08

Description

Dec. 8, 1942. J. E. FLETCHER CONDENSER FOR SOIL MOISTURE METER Fil ed July 19, 1940 2 Sheets-Sheet l ,I JVR NW TKIHCQM FIG.

INVENTOR Joe/ E. Fla/char ATTORNEYS Dee. 8 3.9420

J. E. FLETCHER Filed July 19. 1940 FIG. 4

PER

2 Sheets-Sheet 2 INVENTOR Joe/ E, F/eic/zer ATTORNEYS latented Dec. 8, 1942 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 7 Claims.

This application is made under the act of March 3. 1883, as amended by the act of April 30, 1928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a device for electrically measuring the moisture content of soil and is more particularly concerned with the condenser unit thereof which is adapted to be sunk or imbedded in the ground where the moisture determination is to be made.

In the accompanying drawings .there are illustrated two general embodiments of my invention The first embodiment, referred to generally as the plate type, is illustrated in Figures 1, 2, and 3; Figure 1 being a front elevational view, Figure 2 a section along the line 2-2 of Figure 1, and Figure 3 a section along the line 3-3 of Figure 1.

The second embodiment, referred to generally as the cylindrical type, is illustrated in Figures 4, 5, and 6.; Figure 4 being a longitudinal section, Figure 5 being a cross section along the line 55 of Figure 4, and Figure 6 being a fragmentary elevational view, portions of the dielectric material being broken away to show the helical arrangement of the apertures in the outer cylindrical plate.

Referring with more particularity to Figures 1, 2, and 3, the embodiment illustrated comprises a pair of copper plates H), which may be of heavy foil, disposed in fixed spaced relation and covered with a coat I l of lead glass, Lucite, or other suitable material. Between the coated plates 10, a water-absorbent dielectric material I2, such as plaster of Paris, or other suitable material, is disposed. This dielectric material l2 also serves to hold the plates I 0 in position. A long hollow pipe I3 is bifurcated at one end to form two forks I4, between which the coated plates I0, together with the dielectrical material [2, as a unit, is disposed and secured in place by means of bolt and nut assemblies l5, substantially as shown. Wire leads 16, of shielded microphone cable are connected to the plates 18 at one end; the shield being fastened to one plate and the center lead to the other plate. The other ends of the leads I6 are threaded through the hollow core of the pipe l3 and connected to suitable tip jacks (not shown).

The embodiment illustrated in Figures 4, 5, and 6, comprises a metal base I! to the bottom 0! which is removably secured a spear tip l8. Adjacent the tip 18, the base I! is recessed to provide a cylindrical core l9 about which there is first disposed a coated cylindrical collar 20 of copper or other suitable material, the coat 2| thereof being preferably of Lucite or lead glass. Another copper cylinder 22 is disposed concentric with the cylinder 20 and likewise covered with a coat 23 of Lucite, lead glass, or other suitable material. The cylinder 22 is larger than the cylinder 20 and the space between their two coatings is filledwith plaster of Paris 24, or other suitable water-absorbent dielectric material. The outer cylinder 22 is provided with apertures 25 in helical relation. These apertures are also filled with the dielectric material used between the two cylinders 20 and 22, and on the outside of the cylinder 22 a coating 26 of the same dielectric material is provided, The member I1 is provided with a longitudinal bore 21 through which electrical shielded wire leads 28 are disposed and connected to the cylindrical plates 20 and 22 in the same manner as above described with reference to the first embodiment illustrated in Figures 1, 2, and 3. The upper end 29 of the member 1! is threaded for a removable connection to a suitable pole or rod 30 so that the device can be inserted in the ground at desired depths, as hereinafter explained.

To use either of the two embodiments abovedescribed, a hole is drilled diagonally into the soil to the desired depth with an auger, or other suitable tool, having the same diameter as the condenser unit. The condenser unit is then forced firmly against the bottom and sides of the hole. It is necessary for the exposed portions of the plaster of Paris to press firmly against the soil on the sides of the hole to make a good contact for the passage of the moisture. The sides or the hole should be packed firmly all around and the remainder of the hole filled with soil and packed tight to prevent water from following the pole or rod to the plates. The wire leads from the condenser plates are then connected to a meter for measuring capacity. The capacity of the buried condenser varies with the dielectric constant, which in turn varies with the moisture content in the dielectric material. This moisture content is afiected by the moisture of the surrounding soil. The lower the moisture content of the dielectric material the smaller is the value of the dielectric constant and, consequently, the capacity of the condenser is lowered. Thus, the capacity of the condenser becomes a function of the percentage of moisture in the soil.

Having thus described my invention, I claim:

1. A condenser for a soil moisture meter comprising a pair of metal plates disposed in fixed spaced relation, a coating of lead glass about each of the said plates, a plaster of Paris dielectric permanently fixed between said plates; said dielectric being communicable with the soil to be tested.

2. An article of manufacture comprising a rod, a condenser secured at one end of said rod; said condenser comprising a plurality of spaced metal plates, a coating of insulation about each of said plates, a water-absorbent dielectric permanently fixed between said plates, and electrical wire leads attached to said plates for connection to a capacity meter.

3. An article of manufacture comprising a rod having a spear point at one end and a cylindrical recessed portion adjacent said spear point, an insulated metal cylinder disposed about said recessed portion, a layer of water-absorbent dielectric material about said cylinder, an insulated foraminous metal cylinder about said dielectric material, and another layer of water-absorbent material about the exterior of said foraminous cylinder contacting the dielectric material between said cylinder through the perforations of said foraminous cylinder.

4. An article of manufacture as defined by claim 3 in which the perforations of the forminous metal cylinder are disposed in helical relation.

5. An article of manufacture comprising a rod having a spear point at one end and a cylindrical recessed portion adjacent said spear point, an insulated metal cylinder disposed about said recessed portion, a layer of plaster of Paris about said cylinder, a perforated and insulated metal cylinder about said layer of plaster of Paris, another layer of plaster of Paris about said peri'orated cylinder; said layers of plaster of Paris being in contact with each other through the perforations of said perforated cylinder.

6. A condenser for a soil moisture meter comprising a pair of metal plates disposed in fixed spaced relation, a coating of insulation about each of said plates, a dielectric material permanently fixed between said plates, said dielectric being communicable with soil to be tested and capable of absorbing moisture from said soil.

'1. A device of the character described comprising a condenser having electrode plates, a moisture shield surrounding each of said plates,

- and a permanent dielectric material between said plates capable of absorbing moisture from adiacent soil, the dielectric constant of said material varying with the quantity of moisture absorbed.

JOEL E. FLETCHER.