DE102012106841A1 - Soil moisture measuring device - Google Patents

Abstract

A soil moisture measuring device with at least one soil probe is provided, which has a carrier, a capacitive measuring device with at least one capacitor with a first capacitor element and a second capacitor element, between which an electric field can be generated, the capacitive measuring device being arranged on the carrier, and at least one access element, which covers the capacitive measuring device to a measuring outer space, which is open-pored and which is impregnated with a hydrophilic material.

Description

The invention relates to a soil moisture measuring device with at least one bottom probe.

Soil moisture meters are used to determine the moisture content in the soil. For example, irrigation of the corresponding soil is controlled as a function of the determined moisture content.

The soil whose moisture content is measured is, for example, a garden soil, an agricultural soil or a soil in a flower pot.

From the DE 167 30 46 a device for measuring the soil moisture is known in which the moisture content of the measuring base can be determined from a capacitance measurement, wherein a dielectric of known porosity and pore size is arranged in the electric field between electrodes of a measuring capacitor and brought into contact with the measuring bottom.

From the WO 2010/097689 A1 For example, a system for determining the state and / or changes in the state and / or condition of a potted plant and for displaying the determined state and / or the change to an owner or user by means of wireless communication is known. Sensors for measuring the temperature and / or humidity of the earth are provided in or on a planter.

From the US 2008/0202220 A1 For example, a method for determining the moisture content of soil is known in which a temperature change is generated by heating a measurement sample which is arranged in the measurement medium. A temporal temperature change is dependent on the moisture content of the soil and the corresponding change is used to determine the moisture content.

From the US 2011/0043230 A1 For example, a device for measuring the moisture content in a material is known.

From the US 2010/0251807 A1 Another device for determining the moisture content is known.

The invention has for its object to provide a soil moisture measuring device of the type mentioned, by which can be determined in a simple and safe way, the moisture content.

This object is achieved with the above-mentioned soil moisture measuring device according to the invention that the bottom probe comprises a carrier, a capacitive measuring device with at least one capacitor with a first capacitor element and a second capacitor element, between which an electric field can be generated, wherein the capacitive measuring device the support is arranged comprises, and at least one access element, which covers the capacitive measuring device to a measuring outer space, which is formed open-porous and which is impregnated with a hydrophilic material comprises.

In the solution according to the invention, the open-porous access element ensures the coupling of the capacitive measuring device to the ground to be monitored. It will get a good ground contact. Corresponding measurement signals can be achieved independently of the soil type.

By capillary effects in the at least one open porous access element, water contained in the measuring bottom is guided into a field loading region of the at least one capacitor. Even with relatively poor ground contact, a transverse distribution of water in the porous access element is possible and stable measurements are achieved.

The proportion of water in the access element is a measure of the soil moisture of the soil which is present at the access element. The water content in turn influences the capacity. The capacity of the at least one capacitor is a measure of the soil moisture. By determining the capacity, the soil moisture can be detected.

In the solution according to the invention, a defined access path for water is provided to the capacitive measuring device via the at least one open porous access element. No calibration is necessary since the capacitive measurement is directly dependent on the soil moisture of the soil, which is present at the open porous access element.

By impregnating the access element with a hydrophilic material while maintaining the open porosity, a defined access path for water is provided to measure the moisture content of the soil. Soil water is conducted to the field loading area by capillary effects. The impregnation forms an inner coating in the pores of the access element.

The access element represents a porous medium medium between the measuring bottom and the capacitive measuring device. The hydrophilic impregnation (inner coating) does not limit the water transport through the open-porous access element.

It is advantageous if the first capacitor element and the second capacitor element (the electrodes of the capacitor) are formed as conductor tracks, which are arranged on the carrier, wherein the conductor tracks are particularly flat. This makes it possible, in particular, to achieve direct, gap-free contact between the at least one access element and the at least one capacitor.

For the same reason, it is favorable if the carrier is designed to be flat at least on one side, on which the capacitive measuring device is arranged.

Furthermore, it is favorable to obtain a gap-free direct contact between the at least one access element and the at least one capacitor, if the at least one access element facing at least the capacitive measuring device has a flat side.

Preferably, the at least one access element is arranged in a stray field region of the at least one capacitor. The at least approximately homogeneous field region of the at least one capacitor lies directly between the first capacitor element and the second capacitor element. The at least one access element covers the capacitor above this. It is thus permeated by the stray field. Due to the moisture content in the access element of this stray field is influenced accordingly, that is, the dielectric constant changes.

It is particularly advantageous if the at least one access element contacts electrical insulation for the first capacitor element and the second capacitor element directly and in particular without gaps, and in particular if the electrical insulation contacts the first capacitor element and the second capacitor element directly and without gaps. The access element thereby forms a porous medium medium between the soil and the capacitive measuring device (the sensor surface). Due to the direct contact, the medium affects the measurement only minimally or not at all. The electrical insulation is applied for example as a coating on the at least one capacitor. In principle, it can also be arranged on the access element, for example as a coating.

In a manufacturing technology favorable embodiment, the carrier and the at least one access element are separate components. The carrier and the at least one access element can thereby be produced separately.

As a result, in particular the access element with its open porosity and impregnation can be produced in a simple manner.

It is advantageous if a clamping device is provided, through which the at least one access element is clamped to the carrier and pressed against it. This makes it possible to achieve a direct and in particular gap-free contact between the capacitive measuring device and the access element in a simple manner.

In one embodiment, the at least one bottom probe has a housing on which the carrier is arranged, wherein the housing comprises at least a first housing part and a second housing part, wherein the second housing part is connected to the first housing part and the at least one via the second housing part Access element is pressed against the carrier. Through the housing, a clamping device is realized, which braces the at least one access element to the housing and thereby presses against the capacitive measuring device.

Conveniently, the second housing part has at least one window recess for the at least one access element, wherein the at least one access element has a particular circumferential contact surface for abutment with the second housing part in the region of the at least one window recess. The at least one access element is at least partially submerged through the window recess to allow contact with soil. By means of the contact surface, the at least one access element can be pressed against the carrier with the capacitive measuring device via the second housing part.

It is advantageous if the at least one access element is fixed interchangeably on the at least one bottom probe. This makes it easy to use different access elements for different types of soil and the like.

In one embodiment, the at least one access element is applied to the carrier. In this case, the at least one access element and the carrier are directly connected to each other.

In an alternative embodiment, the at least one access element forms the carrier for the capacitive measuring device, that is, the capacitive measuring device is arranged directly on the at least one access element.

It has proved favorable if the at least one access element has a thickness as the distance between the capacitive measuring device and a measuring object (the soil) in the range between 0.5 mm and 10 mm and in particular in the range between 1 mm and 5 mm. As a result, a soil moisture content can be reliably determined by determining the capacity of the at least one capacitor.

It has also proved favorable if a porosity (volume fraction of the pores) of the at least one access element is greater than or equal to 15% and in particular greater than or equal to 30%. As a result, the ability of the water transport in at least one access element as a medium medium adapted to the surrounding soil and the at least one access element limits the water transport. This, in turn, can be determined in a safe way, the soil moisture. For example, sandy soil has an effective porosity of 10% to 15%. If the porosity is then greater than or equal to 15%, then the at least one access element does not interfere with water transport as compared to the surrounding soil. The porosity is limited upwards by the mechanical stability of the access element. For example, it is less than 60%.

It is particularly advantageous if the at least one access element has a set pore distribution which has at least one maximum at a pore size which is adapted in particular to a type of soil whose moisture content is to be measured. The adaptation can be exact or the adaptation can be such that, for example, several types of soil can be detected. It is thereby ensured that the at least one access element does not limit the water transport. The water absorption and release of water is essentially the same as in the surrounding soil.

It is basically possible that the pore distribution is monomodal or multimodal. In a monomodal pore distribution, pores of average pore size have the highest frequency. There are no other major maxima in pore distribution. (For reasons of production technology, it may be one or more secondary maxima with pore sizes which are not relevant for the measurement.) The corresponding monomodal pore distribution can be designed to be sharp or broad by the maximum with the average pore size. With a "sharp" pore distribution the frequency decreases strongly from the maximum. With a broad pore distribution, pore sizes which are more distant from the mean pore size still have a relevant frequency. In a multimodal pore distribution, the pore distribution has several maxima. The maxima are preferably at pore sizes that are adapted to appropriate soil types. A multimodal pore distribution can be considered as a superposition of monomodal pore distributions. A monomodal pore distribution, especially when this is relatively sharp, often allows a higher accuracy of measurement, especially for a particular type of soil. This advantage also results in a multimodal pore distribution for several soil types, if the maxima are adapted accordingly. With a broad monomodal pore distribution, the moisture content of different types of soil can be determined.

It is favorable if a set of access elements with different average pore size is provided for different soil types and / or the at least one access element has several access element regions of different average pore size and / or the at least one access element has such a pore distribution that moisture determinations in different soil types can be carried out , Thereby, with the soil moisture measuring apparatus, a moisture content measurement on different soil types can be performed with high accuracy.

The soil moisture measuring device according to the invention can be used in a universal manner if a plurality of access elements or multiple access element regions of different average pore size are arranged on the at least one bottom probe and / or a plurality of bottom probes are provided with access elements different in average pore size and / or with respect to the middle one Pore size different access elements are provided for replacement at the at least one bottom probe. As a result, the soil moisture can be determined on the one hand even with different soil types in an accurate way and on the other hand results in a wide range of applications.

It can also be provided that the at least one access element has an adapted to sandy soil average pore size and / or in a pore distribution has a maximum at a pore size, which is adapted to a sandy soil. This average pore size or pore size with maximum is especially in the order of 22 microns. Sandy soils have an average pore size (determined by weighted averaging) of about 22.3 μm. The weighted averaging of the pore sizes in sandy soils is characterized by calculated a weighting of the values of the pore diameter for fine pores, center pores and coarse pores and formation of the arithmetic mean. Compared to common soil types, sandy soils have the largest pores and dry out quickly. If the at least one access element is set to a sandy bottom, which dries relatively quickly, and which has the largest pores in comparison to other conventional soil types, it is ensured that the average pore size or maximum pore size in the at least one access element is greater than or equal to / as in the surrounding soil. As a result, at least not too high soil moisture is displayed. For example, if the soil moisture meter is integrated with an irrigation system, then irrigation can be prevented from occurring too late.

It is particularly favorable if the average pore size or a pore size with maximum in the at least one access element is in the range between 10 μm and 25 μm and in particular in the range between 15 μm and 25 μm and in particular in the range between 18 μm and 25 μm. The weighted averaging of pore sizes of sandy soils gives a pore size of 22.3 microns. It is achieved by a good adaptation.

It can be provided that a pore distribution of the at least one access element is such that, if a pore size deviates from the average pore size by more than 25%, a corresponding frequency is smaller by at least 75% compared to the frequency with the average pore size. This results in a relatively sharp distribution of the pore size around the average pore size.

In one embodiment, the pore distribution is such that at a pore size of 10 microns and / or 25 microns, a frequency is at least 25% of a maximum frequency. This results in a relative pore distribution, in which even pore sizes of 10 microns or 25 microns have a relevant frequency. At least one frequency maximum is in particular a pore size which is between 10 .mu.m and 25 .mu.m and, for example, about 20 .mu.m or 22 .mu.m. It can thus be determined with a monomodal or multimodal pore distribution of moisture content in a variety of soil types. Such a pore distribution can cover all typical pore sizes in conventional soils.

In one embodiment, the at least one access element is a sintered part. Such a sintered part can be produced with its open porosity in a relatively simple manner. For example, the access element is sintered from polyethylene.

In particular, the at least one access element is made of a plastic material or ceramic material. Possible plastic materials are, for example, polyethylene or polyurethane. Possible open-porous ceramic materials are, for example, cordierite-based or aluminum oxide-based.

It is particularly advantageous if the at least one bottom probe is designed as a spit. This makes it easy to bring in the soil.

It is advantageous if an evaluation device is provided which is in signal-effective connection with the capacitive measuring device, by which in particular a pulsed electric field can be generated at the at least one capacitor. As a result, the capacity can be measured in a simple manner and this in turn makes it possible to easily determine the soil moisture.

The following description of preferred embodiments is used in conjunction with the drawings for further explanation of the invention. Show it:

1 an exploded perspective view of an embodiment of a soil moisture measuring device according to the invention;

2 a schematic enlarged view of the area A according to 1 ;

3 a schematic representation of a soil moisture measuring device, in which a bottom probe is arranged in a measuring space and schematically the conditions at the bottom probe;

4 a pore distribution in one embodiment of an access element; and

5 a further pore distribution in a further embodiment of an access element.

An embodiment of a soil moisture measuring device according to the invention, which in 1 shown in an exploded view and there with 10 is designated comprises a bottom probe 12 , This soil probe 12 is designed as a ground spike; it can be plugged into the ground, for example, in a flower pot or in a garden.

In one embodiment, the ground probe includes 12 a housing 14 with a first housing part 16 and a second housing part 18 , The second housing part 18 is on the first housing part 16 for example, about screws 20 fixed.

The housing 14 extends in one direction 22 , The housing 14 is in an area along the direction 22 at least approximately cuboid shaped. At one end 24 the housing has a cross-sectional constriction 26 transverse to the direction 22 on. This cross-sectional constriction 26 is for example formed by the housing 14 at the end 24 is formed pyramidally, tetrahedral or conical.

In the case 14 is a carrier 28 arranged. The carrier 28 is designed in particular as a circuit board. On the carrier 28 sits a capacitive measuring device 30 which (at least) one capacitor 32 (see 2 ) with a first capacitor element 34a (first electrode) and a second capacitor element 34b (second electrode).

The carrier 28 is plate-shaped. He has a first level side 36a and a second level side 36b on. The first page 36a and the second page 36b are parallel to each other.

The capacitor (s) 32 are on the first page 36a arranged. The first capacitor element 34a and the second capacitor element 34b are in this case by respective planar capacitor plates, in particular in the form of conductor tracks on the carrier 28 educated. The corresponding metallic material of the first capacitor element 34a and the second capacitor element 34b is in particular directly on the carrier 28 applied. The capacitor 32 is a plate capacitor.

On the carrier 28 are also leads to the capacitor 32 arranged in the form of traces (not shown in the drawings). A conductor track, which forms a feed line, and a conductor track, which is a capacitor element 34a . 34b (ie an electrode), differ in their transverse dimensions: An electrode has larger transverse dimensions than a lead.

In one embodiment, the carrier comprises 28 an area 38 which is outside the ground probe 12 lies. In this area 38 is an evaluation device 40 on the carrier 28 arranged.

The first capacitor element 34a and the second capacitor element 34b are spaced from each other with a non-conductive (dielectric) intermediate region.

The capacitor 32 is via the evaluation device 40 driven. He is driven in particular pulsed. A pulse frequency is for example in the kHz range.

On the condenser 32 forms between the first capacitor element 34a and the second capacitor element 34b an electric field 42 ( 2 ) out. The electric field 42 has a homogeneous area 44 and a stray field area 46 , In the homogeneous area 44 the field lines of the electric field run 42 unbraked between the first capacitor element 34a and the second capacitor element 34b , In the stray field 46 The field lines run outside the gap between the first capacitor element 34a and the second capacitor element 34b curved.

The capacitor 32 and preferably also the supply lines is associated with an electrical insulation. The electrical insulation is in 2 with the reference number 47 indicated. In one embodiment, on the carrier 28 an insulating layer 47 arranged, which the or the Kodensatoren 32 and the supply lines covered.

The first housing part 16 has an investment area 48 on which in its shape to the wearer 28 is adjusted. At this investment area 48 is the carrier 28 at. The carrier 28 is with through holes 50 provided by which respective screws 20 have gone through.

The second housing part 18 encloses the housing 14 , It is achieved by fixing the second housing part 18 with the first housing part 16 also the carrier 28 in the case 14 held.

In the field of capacitive measuring equipment 30 has the second housing part 18 a continuous window recess 52 on. In the window recess 52 sits an entrance element 54 , The access element 54 covers the capacitive measuring device 30 to a measuring outdoor space 56 at the window recess 52 from. The access element 54 represents the actual measuring interface of the capacitive measuring device 30 to the outside space (if the ground probe 12 in a soil, towards the ground).

The access element 54 indicates the capacitive measuring device 30 facing a first flat side 58a on. Further, in one embodiment, it has opposite a second planar side 58b on.

With the first level page 58a lies the access element 54 directly on the capacitor (s) 32 without gaps.

With the second level side 58b is the access element 54 through the window recess 52 pervaded so that the access element 54 for example, flush with an outside of the second housing part 18 is or extends beyond this. The second level side 58b of the access element 54 can also be against the outside of the second housing part 18 be reset.

In one embodiment, the access element is 54 formed as a plate, which is a first area 60 and a second area 62 includes. The first area 60 and the second area 62 are integrally connected. The first area 60 has larger transverse dimensions than the second area 62 , This is a circumferential investment area 64 at the first area 60 educated. The area 62 is in the window recess 52 arranged. The investment area 64 lies on an inside 66 of the second housing part 18 at.

If the second housing part 18 with the first housing part 16 is connected, then presses the second housing part 18 over its inside on the investment area 64 and thus presses the access element 54 against the capacitive measuring device. It is characterized a tensioning device 68 formed, which is the access element 54 in the case 14 with the carrier 28 and the capacitive measuring device 30 braced.

The access element 54 is made of an open porous material. In particular, it is made of a plastic material. The plastic material is in particular a sintered material. An example of the material used is polyethylene.

It is also possible in principle that the access element 54 is made of a foam material such as a polyurethane foam material or of a porous ceramic.

In one embodiment, the access material is made of cordierite. It is also possible that, for example, alumina-based ceramics may be used.

The access element 54 is impregnated with a hydrophilic material. Water in the measuring exterior 56 can pass through the pores of the access element 54 the capacitive measuring device 30 reach. The capacity of the capacitor 32 the capacitive measuring device 30 varies depending on the dielectric constant of the medium between the first capacitor element 34a and the second capacitor element 34b , The dielectric constant of this material depends on the water content. The water content in the access element 54 In turn, it depends on the water content of the surrounding soil medium, that is, on the water content in the measuring exterior.

Due to capillary effects due to the open porosity in the access element 54 gets water from the measuring exterior 56 to the capacitive measuring device 30 guided.

A thickness D (compare 3 ) of the access element 54 lies in the range between 0.5 mm and 10 mm and in particular in the range between 1 mm and 5 mm. The thickness D is also the distance between the measuring outer space 56 and the capacitive measuring device 30 ,

The housing 14 the ground probe 12 is on a housing 70 arranged. When the soil moisture measuring device 10 is positioned by the soil probe 12 into the earth to be examined, then lies the housing 70 above the ground. In the case 70 is the evaluation device 40 arranged. The housing is closed fluid-tight.

On the case 70 is for example a battery recording 72 for a battery 74 arranged. The battery 74 provides the necessary electrical energy for the evaluation device 40 ready. Furthermore, the necessary electrical energy is provided to the electric field 42 at the capacitive measuring device 30 to create.

The soil moisture measuring device 10 works as follows: For a measuring process is the soil probe 12 immersed in the measurement environment. The access element 54 is at the earth with the second side 58b.

The access element 54 is the intermediate element that provides the ground contact.

At the capacitive measuring device 30 is on the capacitor (s) 32 a pulsed electric field 42 generated. The dielectric constant is influenced by the medium which is in the stray field region 46 lies. This medium in the stray field area 46 is the access element 54 with corresponding water content.

As in 3 indicated, forms the access element 54 a porous cover of the capacitive measuring device 30 , The access element 54 Contactlessly contacts the respective capacitor 32 ,

Through the access element 54 in the window recess 52 Soil contact between the sensory part of the soil probe 12 and the soil improved. By capillary effect, soil water is transmitted through the access element 54 into the measuring area, namely the stray field area 46 guided. Basically, even in bad ground contact a transverse distribution of water in the porous access element 54 possible.

The dielectric constant is dependent on the water content in the medium (access element 54 with water). This water content in turn is a measure of the soil moisture. By appropriate evaluation at the capacitive measuring device 30 via the evaluation device 40 can be determined by the soil moisture.

Due to the porous access element 54 you get reproducible, stable readings. Calibration is not necessary.

The access element 54 is in particular made of a plastic material. Such a plastic material is usually hydrophobic. By a hydrophilic impregnation of the access element 54 , in which the open porosity is maintained, a water transport through the pores of the access element 54 to the stray field area 46 and the water transport through the pores is adapted to the water transport in a natural soil matrix.

The hydrophilic impregnation takes place in particular under defined process conditions. For example, in the production of a vacuum impregnation with curing, excessive temperatures are carried out.

In one embodiment, a solvent-based dispersion of nanoscale particles is used as the impregnation material. The active ingredient base are hydrophilic surface-modified SiO ₂ nanoparticles. The solvent evaporates in a drying process during the production of the impregnation and the hydrophilic inner coating of nanoparticles remains. The impregnating material (with solvent) was previously introduced under reduced pressure into the pores of the starting material of the access element.

Basically, the access element 54 adapted in its pore structure and pore distribution to the soil structure. For example, a sandy soil has a grain size in the range of 0.063 mm to 2 mm. A typical pore size (weighted average) for sandy soil is 22.3 μm. An effective porosity for a typical sandy soil ranges between 10% and 15%.

For a silty / loamy soil, a typical grain size ranges from 0.002 mm to 0.063 mm. A typical pore size in the soil is approx. 11.8 μm. An effective porosity for such a soil is between 3% and 6%.

For comparison, the grain size of a typical clay soil is below 0.002 mm. A typical pore size is 0.062 μm and the effective porosity is between 0% and 3%. Such clay soil is hardly permeable to water.

For the reasons mentioned, it is advantageous if the porosity in the access element 54 (that is, the pore content in the total volume) is greater than 15%. It is advantageous if the pore size is between 10 μm and 25 μm. A sandy soil is usually the most permeable soil, that is also the soil that loses water the fastest. When the soil moisture meter is used for irrigation control, it is advantageous to use the corresponding parameters for sandy soils.

It makes sense if a mean pore size in the access element 54 in the said range between 10 microns and 25 microns and, for example, is about 20 microns.

The porosity of the access element 54 is greater than or equal to 15%. In one embodiment, it is greater than or equal to 35%. It is preferably less than 60%, so that a mechanically stable access element 54 is realized.

In an embodiment which is in 4 is shown, there is an average pore size s in the access element 54 at 19.24 microns. (A minimum pore size is 12.28 microns and a maximum pore size is 41.74 microns.)

Pores of average pore size s have the highest frequency N in the pore distribution. The pore distribution is monomodal. The mean pore size has a maximum of frequency. Secondary maxima, which are at smaller pore sizes, are production-related and have no influence on the mode of operation. In particular, the frequency of pore sizes is around the average pore size s such that pores whose pore size differs from the average pore size by more than 25% have a frequency in comparison to the frequency at the average pore size s which is at least 75% smaller. This results in a relatively sharp frequency distribution around the average pore size.

In principle, it can be provided, in particular in order to achieve a high measuring accuracy, that the access element 54 adapted to a soil type. This is done, for example, in that the mean pore diameter is adjusted accordingly with a sharp distribution around the mean pore diameter (cf. 4 ).

It may be provided that a plurality of different access elements 54 (with different mean pore diameter s ) are present, these being interchangeable with the housing 14 can be fixed.

It is alternatively or additionally possible that the soil moisture measuring device 10 a plurality of soil probes 12 comprises, wherein at different soil probes different (with respect to the mean pore diameter s ) Access elements 54 are arranged.

It is in principle also possible that at a soil probe 12 different access elements 54 are arranged, in principle, a plurality of different access elements may be provided or an access element 54 having different areas with different mean pore diameter.

It is also possible that an adaptation to different soil types via a set pore distribution at the access element 54 he follows.

In one embodiment of a pore distribution 76 ( 5 ) is included starting from a maximum s the pore distribution relatively wide, so that in particular even pore sizes of 10 microns and 25 microns have a relevant frequency, which in particular at least 25% of the frequency at the maximum (in the pore size s ) is. By such a wide pore distribution an adaptation to different soil types with a single access element is possible.

The pore distribution 76 is monomodal.

It is also possible that a multimodal pore distribution 78 is provided with a plurality of maxima 80a . 80b . 80c , The maxima for corresponding pore sizes are adapted to different soil types. With such a set pore distribution, the moisture content of different soil types can be performed with high accuracy.

By the inventive solution, in which an open porous access element 54 is provided, which is impregnated with a hydrophilic material, a measurement can be carried out, which is largely independent of grain size and ground contact of the soil probe 12 , It is measured in the stray field. The access element 54 also provides an electrical insulation layer. Through the porous access element 54 a targeted capillary water exchange can be achieved according to the natural soil matrix if the mean pore size s is suitably chosen. If the pore size is adapted to the pore size of a sand grain, then no limitation of the water exchange is effected for all other types of soil. As a result, the resulting readings are a reliable measure of soil moisture; the determined capacity at the capacitive measuring device 30 is a direct and accurate measure of soil moisture.

In the described embodiment, the access element 54 and the carrier 28 separate elements which are braced together.

In an alternative embodiment, the access element is 54 directly on the capacitive measuring device 30 on the carrier 28 applied.

In a further alternative embodiment, the capacitive measuring device 30 directly on the access element 54 produced. The access element 54 is then the carrier for the capacitive measuring device 30 ,

The soil moisture measuring device 10 can pass on its measurement results to a higher-level control unit or this higher-level control unit can enter the evaluation unit 40 be integrated. The higher-level control unit controls, for example, an irrigation system as a function of the measured values of the soil moisture measuring device 10 ; if it turns out that the soil is too dry, an irrigation process is initiated. In particular, a control process may be arranged in which irrigation takes place until the soil moisture measuring device 10 provides a measurement signal according to which a desired moisture content is reached.

LIST OF REFERENCE NUMBERS

10

 Soil moisture measuring device

12

 floor probe

14

 casing

16

 First housing part

18

 Second housing part

20

 screw

22

 direction

24

 The End

26

 Cross-sectional narrowing

28

 carrier

30

 Capacitive measuring device

32

 capacitor

34a

 First capacitor element

34b

 Second capacitor element

36a

 First page

36b

 Second page

38

 Area

40

 evaluation

42

 Electric field

44

 Homogeneous area

46

 Stray field area

47

 electrical insulation

48

 plant area

50

 Through Hole

52

 window opening

54

 access member

56

 Measuring outer space

58a

 First level page

58b

 Second level side

60

 First area

62

 Second area

64

 plant area

66

 inside

68

 tensioning device

70

 casing

72

 battery tray

74

 battery

76

 pore distribution

78

 pore distribution

80a, b, c

 maxima

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 1673046 [0004]
• WO 2010097689 A1 [0005]
• US 20080202220 A1 [0006]
• US 20110043230 Al [0007]
• US 20100251807 A1 [0008]

Claims (27)

Soil moisture measuring device with at least one soil probe ( 12 ), which comprises: - a carrier ( 28 ), - a capacitive measuring device ( 30 ) with at least one capacitor ( 32 ) with a first capacitor element ( 34a ) and a second capacitor element ( 34b ), between which an electric field ( 42 ), wherein the capacitive measuring device ( 30 ) on the carrier ( 28 ), and - at least one access element ( 54 ), which the capacitive measuring device ( 30 ) to a measuring outside space ( 56 ), which is open-porous and which is impregnated with a hydrophilic material. Soil moisture measuring device according to claim 1, characterized in that the first capacitor element ( 34a ) and the second capacitor element ( 34b ) are formed as conductor tracks, which on the carrier ( 28 ) are arranged, wherein the conductor tracks are particularly flat. Soil moisture measuring device according to claim 1 or 2, characterized in that the carrier ( 28 ) at least on one side ( 36a ), on which the capacitive measuring device ( 30 ) is arranged, is formed flat. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) at least the capacitive measuring device ( 30 ) facing a flat side ( 58a ) having. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) in a stray field area ( 46 ) of the at least one capacitor ( 32 ) is arranged. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) an electrical insulation ( 47 ) for the first capacitor element ( 34a ) and the second capacitor element ( 34b ) touched directly and in particular without gaps, and in particular that the electrical insulation ( 47 ) the first capacitor element ( 34a ) and the second capacitor element ( 34b ) touched directly and without gaps. Soil moisture measuring device according to one of the preceding claims, characterized in that the carrier ( 28 ) and the at least one access element ( 54 ) are separate components. Soil moisture measuring device according to claim 7, characterized by a tensioning device ( 68 ), by which the at least one access element ( 54 ) with the carrier ( 28 ) and is pressed against this. Soil moisture measuring device according to claim 7 or 8, characterized in that the at least one soil probe ( 12 ) a housing ( 14 ) on which the carrier ( 28 ), wherein the housing ( 14 ) at least one first housing part ( 16 ) and a second housing part ( 18 ), wherein the second housing part ( 18 ) with the first housing part ( 16 ) and via the second housing part ( 18 ) the at least one access element ( 54 ) against the carrier ( 28 ) is pressed. Soil moisture measuring device according to claim 9, characterized in that the second housing part ( 18 ) at least one window recess ( 52 ) for the at least one access element ( 54 ), wherein the at least one access element ( 54 ) a particular circumferential contact surface ( 64 ) for engagement with the second housing part ( 18 ) in the region of the at least one window recess ( 52 ) having. Soil moisture measuring device according to one of claims 7 to 10, characterized in that the at least one access element ( 54 ) exchangeable at the at least one ground probe ( 12 ) is fixed. Soil moisture measuring device according to one of claims 1 to 6, characterized in that the at least one access element ( 54 ) is applied to the carrier. Soil moisture measuring device according to one of claims 1 to 6, characterized in that the at least one access element forms the support for the capacitive measuring device. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) a thickness (D) as a distance between the capacitive measuring device ( 30 ) and a measurement object in the range between 0.5 mm and 10 mm and in particular in the range between 1 mm and 5 mm. Soil moisture measuring device according to one of the preceding claims, characterized in that a porosity of at least an access element ( 54 ) is greater than or equal to 15% and in particular greater than or equal to 30%. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) has a set pore distribution which has at least one maximum at a pore size which is particularly adapted to a soil type whose moisture is to be measured. Soil moisture measuring device according to claim 16, characterized in that the pore distribution is monomodal or multimodal. Soil moisture measuring device according to one of the preceding claims, characterized in that a set of access elements ( 54 ) with different average pore size ( s ) is provided for different soil types and / or that the at least one access element ( 54 ) multiple access element regions of different average pore size ( s ) and / or that the at least one access element ( 54 ) has such a pore distribution that moisture determinations on different types of soil are feasible. Soil moisture measuring device according to one of the preceding claims, characterized in that a plurality of access elements ( 54 ) or multiple access element regions of different average pore size ( s ) at the at least one ground probe ( 12 ) are arranged and / or a plurality of soil probes ( 12 ) with respect to the average pore size ( s ) different access elements ( 54 ) are provided and / or with respect to the average pore size ( s ) different access elements ( 54 ) for replacement at the at least one bottom probe ( 12 ) are provided. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) adapted to sandy soil average pore size ( s ) and / or has a maximum in a pore distribution at a pore size which is adapted to a sandy soil. Soil moisture measuring device according to one of the preceding claims, characterized in that the average pore size ( s ) and / or a maximum of the pore distribution at a pore size in the range between 10 .mu.m and 25 .mu.m and is in particular in the range between 15 .mu.m and 25 .mu.m and in particular in the range between 18 .mu.m and 25 .mu.m. Soil moisture measuring device according to one of the preceding claims, characterized in that a pore distribution in the at least one access element ( 54 ) is such that when a pore size of the average pore size ( s ) by more than 25%, the corresponding frequency compared to the frequency at the average pore size ( s ) is at least 75% smaller. Soil moisture measuring device according to one of claims 1 to 22, characterized in that a pore distribution is such that at a pore size of 10 microns and / or 25 microns, a frequency is at least 25% of a maximum frequency. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) is a sintered part. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one access element ( 54 ) is made of a plastic material or ceramic material. Soil moisture measuring device according to one of the preceding claims, characterized in that the at least one soil probe ( 12 ) is designed as a spit. Soil moisture measuring device according to one of the preceding claims, characterized by an evaluation device ( 40 ), by which in particular a pulsed electric field ( 42 ) on the at least one capacitor ( 30 ) is producible.

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