WO2020225811A1

WO2020225811A1 - Water filled tensiometer for determining soil moisture levels for irrigation

Info

Publication number: WO2020225811A1
Application number: PCT/IL2020/050492
Authority: WO
Inventors: Oleg KOROL
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-05-04
Filing date: 2020-05-03
Publication date: 2020-11-12
Anticipated expiration: 2021-11-04

Abstract

A water-filled tensiometer designed to produce more accurate readings of soil moisture levels by means of preventing the underground part of the tensiometer adjacent to its porous tip from heating up above the temperature of the surrounding soil, which is generally constant during the crop growing season. This is accomplished by using a material with low heat conductivity for the tensiometer body and adding thermal insulation of various types, as described in the four embodiments, to the part of tensiometer body located in the soil levels subjected to diurnal temperature fluctuation.

Description

WATER FILLED TENSIOMETER FOR DETERMINING SOIL MOISTURE LEVELS FOR

IRRIGATION

Relationship to other applications:

The present patent application is related pursuant to the concept of the unity

of an invention to US provisional patent application 62843366 and claims benefit of the filing date of said provisional application.

Background of the Invention

1. Field of the Invention

This invention relates to devices for measuring the water tension in the soil for

the determination of irrigation watering requirements and their timing.

2. Description of the Prior Art

There are a number of prior art water-filled tensiometer designs which typically include at least one internal chamber filled with water and comprising either a porous tip or a porous membrane. The US patent 3910300 is a good example of such prior art comprising a water- permeable tip and a diaphragm; which the vacuum produced in the internal chamber will flex thereby moving a linkage connecting said diaphragm with a switch or a valve. The US patent 6772621 features the heat conducting stainless steel casing with the porous stainless steel membrane built into it. It also comprises a pressure sensor for sensing the degree of vacuum produced, which is in fluid hydraulic connection with the internal chamber. Neither of these two cited and fairly typical prior art patents has any features to block the conductivity heat transfer from the upper part of the tensiometer, which is exposed to the outside heat. Thus the lower, underground part of the tensiometer will operate at a temperature noticeably higher than that of the surrounding soil. That will cause the thermal expansion of water inside the tensiometer and will also affect the surface tension of the water thus influencing the tensiometer readings and will also cause increased evaporation from the surface of the water inside the tensiometer, as well as release from it the air dissolved in the water - thereby making the tensiometer readings significantly inaccurate. One way to limit the heating up of the tensiometer long known in the art is the use of shading means. Another way to limit the heating up of the underground part of tensiometer, as described in application PCT/IL2015/051013 is to incorporate a low thermal conductivity/insulating ring into the main body of the tensiometer and to limit evaporation from water inside by placing a floating barrier on its surface. There are also patents which feature corrective action to reduce the influence of temperature variations. For example patent CN103884830A features automatic temperature compensation by the processor to reduce the magnitude of erroneous tensiometer readings due to changes in temperature. Patent US4068525A attempts a different approach; minimal volume of water used minimizes errors due to change in temperature to which the instrument is subjected. Patent US3103117 proposes to reduce tensiometer readings changes due to diurnal variation of temperature by means of making tensiometer body of material with about the same temperature expansion coefficient as the water to compensate for water’s thermal expansion. All of the above described approaches mitigate or reduce the effect of temperature fluctuations affecting the tensiometers, however not one of these proposals eliminates the problem itself; heating of tensiometer above the temperature of soil at the depth where tensiometers porous tip is located.

In light of the above we conclude that the prior art is inadequate and new solutions are required. It is well known that at a certain depth, soil temperature stays at about the same constant level during the crop growing season, however at depths closer to the surface said temperature varies during each 24 hour day and rises significantly in daytime even if shading means are used. The proposed solution to this problem is to use materials with very low heat conductivity for the tensiometer body and to encase tensiometer body into a thermal insulating sleeve, jacket or enclosure at least down to the depth where soil temperature is generally constant during the crop growing season.

3. Objects and Advantages

One object is to provide a tensiometer with the largely eliminated heating of its underground part above temperature of the surrounding soil at the depth of its porous tip.

4. Brief Description of the Drawings.

1. Fig. 1 shows a tensiometer with a part of its body enclosed into a hollow jacket.

2. Fig. 2 shows a tensiometer with parts of its body having thickened walls. 3. Fig. 3 shows a tensiometer with thickened wall insert.

4. Fig. 4 shows a tensiometer with solid sleeve enclosing a part of its body.

5. Fig. 5 shows a tensiometer partly enclosed into an inflatable insulating sleeve.

5. Description.

The first embodiment is as follows; (Fig 1) it will comprise a water-filled tensiometer (1 ) with a porous tip at its end (2) wherein the body (3) of tensiometer is made of low conductivity material such as for example; polystyrol ®, polyester or expanded polystyrene. Said body is enclosed over a part of its length, corresponding to the expected area of contact with soil layer where diurnal temperature variability is present, by a hollow sleeve or jacket or enclosure (4) which can be made of the same material as the body of the tensiometer or from a different material with low thermal conductivity. To prevent the penetration of water, any foreign matter or biological contaminants said jacket on two of its ends is resting on suitable gaskets also made of material with low heat conductivity such as for example rubber gaskets (5). To securely affix said jacket (4) to the body of tensiometer (3) threaded connection in the socket (6) is used. To further reduce or eliminate any possibility of water, soil or other foreign matter such as biological contaminants penetrating the inside of said sleeve sealants (7) and/or glue can be used on gaskets (5). However to reduce cost sealants (7) can be used alone without the gasket (5). Said jacket (4) can be filled with air which has fairly good insulating properties or it can be filled with other gazes. Many gazes widely used in industry have lower thermal conductivity than air, however some gazes such as for example krypton, bromine and xenon have thermal conductivity which is only a fraction of air’s thermal conductivity. Alternatively vacuum of the kind used in light bulbs can be used to achieve even better thermal insulation. There is also the possibility of using foam, powdered, granulated, particle, fluff or fiber filler (8) with good thermal insulating properties inside the jacket (4).

Second embodiment of this invention will comprise a water-filled tensiometer with a porous tip at its end wherein the body of tensiometer is made of low conductivity material of the kind mentioned above for the first embodiment. Said body (Fig 2) has walls as thin as possible (9) to assure minimal area of heat conductivity from the top down, but comprises significantly thickened to a predetermined size walls (8) which may be an integral part of tensiometer body made of the same material as the body of the tensiometer or in second version of this embodiment (Fig 3) said walls can be implemented as an insert (10) made from the same or a different material with low thermal conductivity. To prevent the penetration of water, any foreign matter or biological contaminants, said insert (10) on two of its ends is resting on suitable gaskets also made of material with low heat conductivity such as for example rubber gaskets (5). To securely affix said insert (10) to the body of tensiometer (3) threaded connection in the socket (6) is used. To further reduce or eliminate any possibility of water, soil or other foreign matter such as biological contaminants penetrating the inside of said insert (10) sealants (7) and/or glue can be used on gaskets (5). However to reduce cost sealants (7) can be used alone without the gaskets (5).

Third embodiment of this invention (Fig 4) will comprise a water-filled tensiometer with a porous tip at its end wherein the body (3) of tensiometer is made of low heat conductivity material such as for example; polystyrol, polyester or expanded polystyrene. Said body is enclosed over a part of its length, corresponding to the expected area of contact with soil layer where diurnal temperature variability is present, by a solid sleeve or jacket or enclosure (4) which can be made of the same material as the body of the tensiometer or from a different material with low thermal conductivity. To prevent the penetration of water, any foreign matter or biological contaminants said jacket’s ends are sealed with sealant (7) and said enclosure (4) may optionally have coating or surface sealing cover (not shown). Fourth embodiment of this invention (Fig 5) will comprise a water-filled tensiometer with a porous tip at its end wherein the body (3) of tensiometer is made of low conductivity material such as for example; polystyrol, polyester or expanded polystyrene. Said body is enclosed over a part of its length corresponding to the expected area of contact with soil layer where diurnal temperature variability is present, by a permanently inflated or an inflatable sleeve or jacket or enclosure (11). From above it is protected from pressure of soil which may include sharp rocks or roots by a disk cover (12), and from below by a sliding disk (13). On the sides between said disks the sleeve (1 1) can optionally be protected by flexurally openable cylindrical with lengthwise cut enclosure with a letter“C” like cross- section (not shown). To prevent the penetration of water, any foreign matter or biological contaminants between said jacket (1 1 ) and the body of tensiometer (3) and to securely affix said sleeve (1 1 ) to the body of tensiometer (3) sealants (7) and/or glue can be used. Said sleeve (1 1) is to be filled with air, but can optionally be filled with other gazes having lower thermal conductivity. Said inflatable sleeve (1 1 ) needs to be made of a suitable strong material such as for example rubber or rubberized strong fabric which would minimize or eliminate the possibility of its puncture by sharp stones or roots.

6. Sketches and Diagrams.

Provided Separately

7. Operation.

For the embodiments 1 , 3, 4 and 5 described above, in operation when the tensiometer is set into the ground to a predetermined depth its jacket or sleeve will insulate the

tensiometer body (3) from diurnal soil temperature fluctuations and thereby prevent the introduction of inaccuracies into its reading due to said temperature fluctuations. Meanwhile the material with low thermal conductivity of which the tensiometer body is made and/or due to the heat conductivity minimizing design of tensiometer body, the heat transfer from the upper part of tensiometer to its lower underground part is also minimized.

For the second embodiment the thickened part of its body, made of material with low thermal conductivity, will minimize inward heat transfer into the tensiometer body from the surrounding soil, whereas the low conductivity of the tensiometer body’s material, possibly in combination with its design feature(s) to limit heat transfer downward from the

tensiometer top; such as by reducing its wall thickness, to as much as minimally acceptable to assure its structural integrity.

Claims

Claims. What claimed is:

1. A water filled tensiometer comprising a thermal insulating enclosure of its body extending downward at least to the end of soil layer wherein diurnal temperature fluctuations are occurring during the crop growing season.

2. The tensiometer of Claim 1 wherein said insulating enclosure is hollow.

3. The tensiometer of Claim 2 wherein said hollow insulating enclosure is filled with air.

4. The tensiometer of Claim 2 wherein said hollow insulating enclosure contains vacuum.

5. The tensiometer of Claim 2 wherein said hollow insulating enclosure is filled with with a gas other than air.

6. The tensiometer of Claim 2 wherein said hollow insulating enclosure contains a thermal insulating filling.

7. The tensiometer of Claim 1 wherein said insulating enclosure is comprised of solid thermal insulating material of at least one kind.

8. The tensiometer of Claim 1 wherein said insulating enclosure is inflated.

9. The tensiometer of Claim 8 wherein said inflatable insulating enclosure is filled with air.

10. The tensiometer of Claim 8 wherein said inflatable insulating enclosure is filled with a gas other than air.

1 1. The tensiometer of Claim 6 where said filling is at least partly powdery.

12. The tensiometer of Claim 6 where said filling is at least partly granular.

13. The tensiometer of Claim 6 where said filling is at least partly fibrous.

14. The tensiometer of Claim 6 where said filling is at least partly comprised of a material that has properties of a foam.

15. The tensiometer of Claim 6 where said filling is at least partly comprised of particulate matter.

16. The tensiometer of Claim 6 where said filling is at least partly comprised of fluffy matter.

17. The tensiometer of Claim 6 where said filling is at least partly comprised of feather-type matter.

18. A water filled tensiometer made of low thermal conductivity material whose body comprises a part with significantly thicker walls extending downward at least to the end of soil layer wherein diurnal temperature fluctuations are occurring during the crop growing season.

19. The tensiometer of Claim 18 where its body part with significantly thicker walls is a component part assembled together with the rest of tensiometer body.

20. The tensiometer of Claim 1 whose body is of low thermal conductivity from the top to the lower parts of tensiometer body.