Description

Field of the invention

This invention generally relates to the fields of agriculture, horticulture and landscaping, and in particular to that of soil management. More specific, this invention relates to a sensing probe for sensing a parameter of the ground at a certain depth therein, and, although not limited thereto, in an embodiment thereof a probe which can further determine a measured value of a property of the ground, such as humidity, temperature or salinity, from the sensed parameter.

The invention further relates to methods of placing such probes and using such probes to sense a parameter of the ground.

Background of the invention

In the field of agriculture, and more generally in the field of management of a piece of land for the purpose of growth of at least certain plant species, it is often advantageous and helpful to know certain parameters of the soil. This knowledge can for instance be used to manage nutrients in the substrate in which e.g. plant species are cultivated, or predict growth thereof.

Although other parameters can be measured as well, the critical property decisive for survival of plants or other non-animal living species cultivated in the ground, such as mushrooms, is moisture in the ground and control the humidity thereof is of major significance to agriculture, horticulture and landscaping. For example, irrigation of land is often carried out in areas where water is a scarce resource. Because of the scarcity of this resource in such areas, ideally, water is only supplied to land in controlled quantities, when and where there is a need for the supply of the water. Even in areas where water is not scarce, control of the quantities of water such that the humidity corresponds to the specific requirements of the species to be grown allows to ameliorate growth conditions and yield. To determine the degree of irrigation required, the availability of data which reveals the present amount of moisture in the ground at a meaningful level from the surface is a pre-requisite.

To measure properties like moisture, it is known to bring a sensing probe into the ground, which senses a parameter of the ground and which is used by a measurement system to generate a measured value of the property of interest, e.g. moisture. Although reference is here made to measuring moisture, other properties such as salinity, temperature etc can be measured as well or alternatively.

To place a probe, various techniques are possible. However, for the known probes these all present some disadvantages.

One could for instance form a hole first, place the probe in the formed hole, and fill the hole up again. Such a method is for example disclosed in United States patent 4929885, in which first a hole is drilled with an auger. However, this is time consuming, disturbs the soil and requires special equipment that needs to be operated by relatively skilled users and that needs to be well maintained.

Alternatively, one could first insert with significant force a base without the sensitive parts of the probe, such as the electronics and then separately mount those parts after the base has been installed. From United States patent US 7788970 it is for example known to first hammer a pole or probe body without sensors into the ground and subsequently mount a separate sensor mast onto the pole. This allows exerting a significant impact force onto the pole without risking damage to the sensitive electronics but has the disadvantage that placing the pole is complex and requires assembling in-situ the probe from the separate parts and accordingly a highly skilled technician.

Also, one could add water to the soil to soften the ground and then install the probe in the softened ground. This requires the local supply of water at the very spot where the probe will be installed, is time consuming, and requires much coordination.

One could alternatively, insert the complete probe immediately into the ground without preforming a hole, e.g. by hammering or screwing the complete probe into the ground. However, the known probes are not capable of withstanding a significant amount of force. The known probes of the type than can be integrally inserted without preforming a hole are thus only suitable for relatively soft types of substrates, e.g. wet soil, and limited depths and limited depths, such as less than 20 cm.

For example, from United States patent 3968428 a portable soil moisture tester for horticultural applications and home gardening is known. The device has a soil inserting rod in a casing. The inserting rod may be graduated or marked to indicate the appropriate depth to which the soil moisture is to be tested for a specific plant, or in alternative embodiment provided with a collar that limits the insertion to ensure repeated equal insertion. However, the mechanical construction of the tester will not resist the forces required to insert the tester deep into the ground and/or in hard layers such as rock or dry clay. The depth at which the moisture can be measure is therefore limited to about 20 cm and the tester is only suitable for soft gardening soil.

In a similar manner, German utility model DE 20 2005 020951 U1 discloses a device for measuring and displaying the humidity of earth of a pot plant, which comprises a battery and a LED. When the moisture content of earth between the electrodes of the device is high enough, the voltage over the LED will exceed the threshold voltage thereof and the LED lights up. If the moisture content in the soil drops below a threshold value, the light-emitting diode goes out because the voltage over the LED will drop below the threshold voltage. The device can be stuck into the earth in the pot, to a depth where the electrodes are in the area of the roots of the plant.

However, such a device is only suitable for soft earth in a plant pot and is not suitable for agricultural applications, and in particular cannot be placed deep into the ground or hard layers because the mechanical construction of the tester will not resist the forces required to insert the tester deep into the ground and/or in hard layers such as rock or dry clay. In addition, the LED measures only a binary electrical parameter: whether or not the voltage exceeds the threshold voltage or not. Accordingly, it does not allow to obtain the information required for agricultural applications. The known probes thus all suffer from several drawbacks which render installing them cumbersome and limits the conditions in which they can be used. Most importantly, they are for various reasons not capable to withstand large forces. Without limiting to other reasons, it has been found that one of the root causes of this vulnerability lays in the complex and sensitive electronics used in the known probes. These electronics are vulnerable to breakdown under the mechanical forces of the type required to insert the tester into hard ground or deeper depths.

of the invention

The present invention provides probes, measuring systems and methods for installing and using such probes as described in the accompanying claims.

Specific embodiments of the invention are set forth in the dependent claims.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

Fig. 1 shows a sectional view of an example of a sensing probe positioned into the ground.

Fig. 2 shows a perspective view the example of FIG. 1 during installation thereof.

Fig. 3a and 3b shows a sectional views of a part of an elongate body suitable for the example of FIG. 1 , taken along the lines a-a and b-b therein respectively.

Fig. 4 shows a circuit diagram of an example of an electronic circuit suitable for the example of FIG.1.

Fig. 5 shows a block diagram of an example of a measurement system which can use the circuit of FIG. 4 and/or the probe of FIG. 1.

Fig. 6 shows a flow chart illustrating a method of sensing a parameter of the ground at a certain depth.

Detailed description of the preferred embodiments

In the following, the terms“ground” and“soil” are used interchangeably. However, these terms are meant to embrace more than ground established as fit for agriculture. For instance, also very dry ground, or even sandy ground with large particles (stones) in a somewhat rocky area is meant to be covered by the term“ground” as used in this disclosure. The ground may be a naturally occurring substrate, such as the ground of the earth, but may also comprise other, artificial substrates. The substrate can be any suitable substrate, such as rock, stones, gravel, sand, silt, clay, soil, mud, concrete, just to name a few and/or be porous or non-porous. The substrate may have a homogeneous composition or have a composition which varies as a function of depth (over the depth to which the probe is inserted). The substrate may e.g. include one or more layers of different composition, such as a top layer of soil and one or more different underlying layers such as sand or clay, just to name a few examples. The substrate may be one on which a non-animalistic living organism, (such as a plant or a fungus) is grown, although the probes may also be used to as sensors for other substrates e.g. to measure conditions in non-agricultural areas.

Referring to FIG. 1 , the example of a sensing probe 1 shown therein is placed in the ground G. The probe 1 has an elongate body B with a tip 2 as the leading end and a head 3 as the trailing end. The term“leading end” refers to the use wherein the tip 2 will be placed onto the ground and leading the way" into the ground. As the tip 2 advances into the ground, the head 3 is basically trailing behind, i.e., following the probe 1 as a part of the elongate body B that advances into the ground. The head 3 is shaped such that a force can be exerted on the body B in an inserting direction from the head 3 towards the tip 2, to insert the body B into the ground to a desired installation depth. As shown, the probe has a subterranean part which extends from the surface of the ground downwards to the installation depth, and an exposed part which extends upwards from the surface.

The probe can be used to sense a parameter of a portion of the ground G at a certain depth, between the surface and the installation depth. A large variety of parameters can in principle be sensed, and in this example electrical parameters of the portion, such as resistivity or permittivity are sensed. To that end, the elongate body B comprises at least one electrode 7 which is electrically connectable (and in FIG. 1 shown connected to), at a predetermined position of the body, to a portion of ground G which, when the probe is entered into the ground, is adjacent to the body B at the predetermined position. In FIG. 1 for example, along the length of the elongate body B several electrodes at a distance from each other are provided. The shown example thus allows the sensed parameter to be sensed at different positions, e.g. different depths. However, more or less electrodes, e.g. a single electrode, may be present, depending on the specific implementation.

In this example, the body B, and more specifically the shaft 1 1 which extends from the head 3, forms a casing 10 inside which the electronic circuit 20 is integrated in the probe. The electronic circuit is provided on a board 8 which extends inside the casing, parallel to longitudinal direction of the body in FIG. 1 and more specific in this example from the head 3 towards the tip 2 up to a lowest electrode. Alternatively, the probe 1 may comprise a separate casing e.g. by attaching and fixating a separate element to the body.

As explained below in more detail, the electronic circuit allows a current path through the portion of the ground to be established (as represented by resistances R _so n in FIG. 1). Through the current path, a DC current flows during sensing. Because of the DC current, the circuit 20 does not require high frequency components, or frequency converters. Accordingly, the circuit can be implemented as a simple circuit with relatively few and robust components capable of withstanding the forces required to install the probe 1 in hard ground or relatively large depths. This in turn allows a simple installation of the probe 1 , where the entire probe can be installed in a single operation, e.g. by hammering or otherwise exerting a large force, without requiring mounting additional parts of the probe after installation of e.g. a base and with limited risk of damage to the probe. A circuit diagram of an example of a suitable electronic circuit is for instance shown in FIG. 4.

In this example, the probe is suitable to receive an impact force, such as of a hammer. As explained below in more detail the probe has a construction capable of withstanding the impact force while the risk of damage to especially the electronics is significantly reduced compared to the known probes. The probe 1 can thus e.g. be hammered into the ground without the need to separately install the electronics or other parts. This allows to install the entire probe 1 at the desired location in a simple manner into the ground, e.g. by in a single operation where the body B is inserted to a desired depth into the ground. Such an operation can be performed without requiring a highly-trained expert. During tests, it has been shown that the single operation can be be performed in less than 2 minutes, for example less than 1 minute, although this is, of course, not required.

Additionally, the electronic circuit 1 can have relatively small power consumption because the losses stemming from the generation and/or conversion of a high frequency signal can be avoided. In this respect, it has been found that even with very small DC currents through the current path, e.g. in the range of the range of 0.1 -10 mA, parameters can be sensed with a precision sufficient to obtain practically usable measurement values.

Referring to FIG. 2, in this drawing a suitable manner of installing the example of FIG. 1 at a desired location is illustrated. As shown, in this example, the head has a flattened impact surface 31 and an impact force is exerted in a longitudinal direction of the body B. The force is exerted with a tool 4 striking on the impact surface, such as in this example a hammer. The body B is in this example (as more clearly seen in FIG. 1 ) comprises a shaft 1 1 which is attached with an upper end to the head 3 and extends downwards towards the tip 2. In this example, the tip is formed by the lower end of the shaft 1 1 but instead a separate tip may be mounted on the lower end.

In this example, the shaft is a straight shaft 1 1 which extends (between head 3 and tip 2) perpendicular to the impact surface. Thus, the body B transfers the impact force from the impact surface 31 to the tip 2 to drive the body B into the ground to the desired depth. Advantageously, when the impact force is exerted on the impact surface, the probe 1 (with its tip 2 put on the surface of the ground and the elongate body B aligned with the direction of gravity) remains straight, and does not permanently deform or noticeably bend elastically. This facilitates installing the probe with simple and widely available means such as a hammer into relatively hard layers and/or deep into the ground, and by any labourer who is fit enough to use that hammer. The probe 1 can thus be installed in a simple manner to sense at a significant depth.

As shown, after installation, the head 3 may remain exposed at the surface, and either be flush therewith or project from the ground. This allows a wireless data communication connection between a transmitter in the head of the probe and e.g. a remote data station, via which data collected by the probe can be transmitted. ln the shown example, the electronic circuit 2 is provided on a board 8 in the body B and more specifically embedded in the material thereof, with direct contact between the board and the material of the body. Thus, the electronic circuit in this example lies between the head and the tip and is fixated relative to the body and unmovable with respect to the body. As a result, the electronic circuit 2 is not shielded from the impact forces and e.g. vibrations or shocks induced thereby in the body will transfer to the board. However, given the mechanical robustness and due to the embedding of the board in the material of the body, the board 8 cannot move relative to the body B and accordingly mechanical wear due to repetitive flexing thereof can be prevented.

Inside the head 3, circuitry sensitive to mechanical forces, such as communication circuitry like e.g. transmitter, a receiver or a transceiver can be provided, with an antenna for wireless transmission of data and/or receiving GPS data to determine a location of the probe 1 may be provided, and/or a battery. As illustrated, the communication circuitry may be embedded in a shock absorbing material 12, such as a silicon gel based material. This material absorbs the vibrations generated by the impact force and thus shields the (typically high frequency and thus relatively sensitive) electronics from impact forces exerted on the head 3 when inserting the probe into the ground. Advantageously, this allows separately shielding the sensitive circuitry from the impact force, while enabling to mount the robust circuitry without additional protection for the robust circuitry.

Between the electronic circuit 2 in the body and the shock-shielded, sensitive circuitry (in this example in the head) a suitable connection may be present, such as an l ^z C bus connection.

The body B may have any shape and dimensions suitable for the specific implementation. It has been found that due to the robustness of the electronic circuit, even probes with an elongate body with a length of at least 0.9 meter, such as at least 1 meter can still be inserted with a limited risk of damage to the electronics. It is further found that a length of less than 1 .7 meter, such as less than 1.5 meter can be sufficient for accurate measurements of parameters of interest deep into the ground. The length can for example be in the range of 1 to 1.5 meter. In particular a length in the range of 1.1 to 1.3 meter has found to be suitable to sense the parameters of interest while still being capable of being inserted into the ground in a single operation, e.g. by hammering or otherwise with a relatively large force. Preferably, the probe protrudes from the ground after installing, and for examples senses to a depth of between 70% and 90% of its length, such as about 75%. Particularly good results have been obtained with a probe having a body of 1.2 m, senses to a depth of 0.9 m.

It has further been found that even a relatively thin elongate body can be construed with sufficient strength, without requiring e.g. reinforcing ribs or other reinforcing elements at the outside thereof. For example, this can be an elongate body without reinforcing elements over at least the lower half of the body, between the tip and the middle of the body and preferably without such elements over the entire length of the body, from the tip up to the bottom of the head.

The body can for example have a needle like shape or other slender cylindrical pointed or tapered shape. For instance, a body (for example with the above specified lengths) with a maximum diameter of less than 5 cm, such at less than 3 cm, for example 1 inch (about 2.54 cm), less than 2 inch, or even smaller such as 0.5 inch or less and even not more than 1 cm can be inserted without breaking. It has further been found that an elongate body with a diameter of at least 0.7, such as 1 cm, for example 2 cm already is sufficiently strong to withstand the forces.

The elongate body B can e.g. have a needle or stick-like shape, like a cylindrical pointed or (slightly) tapered shape. The elongate body B is preferably long and thin. This allows the friction to be reduced when the probe is advanced into the ground, and allows relatively deep levels in the ground with a limited amount of force being required. For example, the body may have a lengtlrdiameter (I/d) ratio of at least 30, such as for example at least 40, and even at least 80 for instance. Tests with a ratio between 50 and 70 and in particular about 55 to 65 have yielded satisfactory results. Such ratios can advantageously be applied in elongate bodies with a length and/or diameter within the ranges specified in the preceding paragraphs.

In the shown example, the probe has a mechanical construction which strengthens the elongate body while retaining a smooth outer shape thereof and without requiring e.g. reinforcing ribs or other elements at the outside of the elongate body. Thereby, a probe can be obtained which exhibits relatively little friction between the probe and ground when inserting, and the amount of force required to insert the probe be reduced accordingly. More specific, the elongate body is formed in FIG. 1 as a straight shaft, which reduces the friction between body and ground when inserting. In particular, the straight shaft has a diameter or thickness which, from the head towards the tip does not increase, but is either constant or reduces. Said differently, at any given location along the length of the straight shaft, the diameter or thickness is not larger than the diameter or thickness at all the other locations between the head and the given location.

Furthermore, the body B comprises a rod 5 and a tube 6 extending along the length of the rod 7 from the head up to the tip. The tube 6 encloses the rod 5 and is of a different material. Thereby, a body B is formed that, when exerting on the head a force with the tip on or into the ground will resist resilient or plastic bending of the parts above the ground. More specific, the impact force will be efficiently transferred from the head to the tip without generating noticeable force components transverse to the longitudinal direction.

The tube 6 and rod 5 are preferably made of different materials. This allows electing a material for one of them that compensates for weaknesses of the other, and vice versa. For example, the compressive deformability in the longitudinal direction and the bending stiffness of the rod can be higher than of the tube. In such a case, the tube enhances the longitudinal transfer of the impact force because the tube shields the rod from the impact, whereas the rod prevents bending of the tube upon impact. Alternatively, the compressive deformability in the longitudinal direction and the bending stiffness of the tube can be higher than of the rod. This allows forming the tube as a containment sleeve or kind of“straight jacket” for the rod, which constrains a freedom of movement of the rod and/or the impact force induced expansion of the rod transverse to the longitudinal direction. Thereby, for example, a body with good “hammerable” properties can be obtained, such as resistance to plastic deformation upon impact forces. This because the tube completely or partially inhibits bending of the rod induced by the impact force and hence dispersion of this force in other directions than the longitudinal direction of the body B. This allows to a particularly slender (i.e. high length/diameter ratio) body which can be inserted with relatively little effort. A suitable material for a constraining sleeve can for example be a fibre-reinforced composite material, like glass or carbon fibre-reinforced, whereas a suitable material for the rod can e.g. be a hard material like an epoxy based resin. The probe can then e.g. be manufactured by placing the board 8 in a tube 6 and filling the void(s) between the tube and board with a liquid precursor of the rod material which is subsequently hardened. This allows to obtain a strong body B in a very simple manner.

In the shown example, the electronic circuit 20 is implemented on a board, such as a printed circuit board (PCB)). The components of the circuit 20 are mounted on the board and in this example connected via tracks in the board, as generally known in the field of PCBs. The components of the electronic circuit 20 may alternatively be placed on another carrier e.g. a part of the rod and/or be connected in a different manner such as through a suitable wiring. The board 8 is located inside the rod 5, more specifically embedded in the material of the rod 5. The rod 5 may for instance form a potting of the board 8.

In the shown example, the rod 5 fills the complete inside of the tube 6 and accordingly there is no empty space between the board 8 and the tube 6. This allows to seal off the electronic circuit from e.g. moisture penetrating the body while, due to the robustness of the circuit, it will withstand the mechanical forces transferred via the rod. In this respect, the inside of the tube 6 may be filled after the electronic circuit 20 and electrodes 7 are placed in the tube 6. This allows seal-off any openings between the electrodes 7 and the tube 6 and thus hermetically sealing the inside of the tube, for example against moisture or soiling.

The electrode 7 may be implemented in any manner suitable for the specific implementation, for example such as to make resistive and conductive contact with the portion of the ground. In addition, the contact may e.g. have a capacitive component. In addition, the current path through the portion of the ground may be connected to the DC current source or sink in any suitable manner. In this respect, the electrode 7 may be used to provide the current path to any suitable type of electronic circuit, and may be connected to other types of electronic circuits, e.g. more complex and less robust instead of one sensing with a DC current through the ground. Referring to FIG. 3, as shown, for example, the body may comprise electrical connections 9 which connect the electrodes 7 to the electronic circuit 20. In this example, both the electrodes and the electronic circuit 20 are mounted on the board 8 and electrical connections 9 are provided as tracks on the board 8. The board 8 is embedded in the rod, without gaps between the board 8 and rod 6. The board can thus not move relative to the rod 6 and probe 1 has a very robust elongate body B. Moreover, in this robust body this risk of loosening of the connection between electrodes 7 and circuit 20 when the probe is inserted into the ground is very low.

As shown in FIG. 3, the electrode 7 can be provided on the outside of the elongate body B. The electrodes are preferably flush with the outer surface of the elongate body B, so that the electrodes do not provide additional friction when the measuring probe is advanced into the ground. In this example, the electrode 7 extends, in radial direction of the body B, from the board up to the outer wall of the tube 6. The electrode 7 lays exposed to touch and may physical contact with the portion of the ground, and thus make conductive contact therewith. In this example, the body B (and in this specific example the tube 6 thereof) is provided with a window at the location of the electrode, which is closed off by the exposed surface of the electrode, and preferably sealed in a liquid tight manner. The windows present a local weakening of the tube, but it has been found that this still allows good‘hammerability’. In particular, it has been found that a window with a width w, as illustrated in FIG. 3b of less than 20% of the circumference, for example less than 16% does not noticeably affect the strength of the body B. Preferably, but not necessarily, in such a case the window has a height h which is less than 1 .5 times the width, such as a square window. In addition, it has been found that by, as in FIG. 3a, alternating the position of the window on the body B to be either at one side or the other side of a plane through its longitudinal axis, the hammerability can be further improved

The probe 1 may have one or more than one electrode 7. As more clearly seen in FIG. 1 , the probe 1 can for instance comprise at least one pair of two electrodes which are spaced apart in the longitudinal direction of the body, for establishing a resistive current path (as illustrated with the impedances Rsoil in FIG. 1) between the electrodes of the pair through the portion of the ground. This not only allows to sense the parameter at different depths into the ground but also allows to avoid cross-over currents and ensures that the currents through the different portions remains separated from each other. Accordingly, the accuracy can be improved.

As seen most clearly in FIG. 3a, the electrodes are arranged in pairs, with the side of the tube at which the electrodes are exposed, and thus make contact with the ground, alternating. Thus, in the direction from head 3 to tip 2, the side of the ground that is sensed by a pair alternates and for example a first pair can sense at a first side of the tube 6 whereas the next, lower pair can sense at the opposite side of the tube 6. This allows for example to reduce the risk that at one side, for example, the contact between electrode 7 and ground is insufficient, such as due to an airgap between those for example. Such gaps can e.g. occur when the ground dried after placing the probe.

The electrodes 7 can, as in the example, be separated in the longitudinal direction of the elongate body B. For example the electrodes 7 can be distributed over several positions over a certain length of the elongate body B, in order to sense at different depths and e.g. determine a variation of a property of the ground as a function of depth, e.g. nutrient concentration or humidity. For example, the predetermined positions may all be equally distributed along the elongate body of the sensing probe 1 . Preferably, at least one electrode 7 is located closer to the tip 2 than to the head 3 and for example an electrode 7 is provided at or close by the tip 2. In such a case, for example the tip 2 can be electrically conductive. The distance, in the longitudinal direction of the body, between successive electrodes or between successive pairs thereof may vary, and for example increase with towards the tip. This allows to obtain a more accurate sensing in the portions where high precision is required with a relatively small number of electrodes. Fig. 4 shows a schematic diagram illustrating an electronic circuit 20 which can be used in the example of a sensing probe 1 of FIG. 1 . Because the illustrated example may for the most part be implemented using electronic components and circuitry known to those skilled in the art, details thereof will not be explained in any greater extent than that considered necessary for the understanding and appreciation of the underlying concepts.

The electronic circuit 20 may be provided inside the sensing probe 1 . The shown example of an electronic circuit 20 is connected to a power source 21 which is internal to the probe 1 and part of the circuit prior to the probe being placed, but it will be apparent that the electronic circuit 20 may alternatively or additionally be connected to an internal power source which e.g. is placed inside the probe only after installing the probe in the ground, or be connected to an external power source. In this example, the power source 21 is a DC power source, such as a commercially available battery having a voltage of, for example, 3.6 V. However, also other kinds of (rechargeable) batteries with other voltages may be used.

The circuit 20 comprises a DC current source 23, in this exampled implemented as a capacitor, which is connected to the electrode 7, for establishing a current path through the portion of the ground (as represented in the FIG. by the resistive component Rsoil oi the impedance of this portion), through which a DC current flows which monotonically changes the charge in the DC current source. The current path can e.g. provide a conductive connection between two electrodes 7 or between an electrode and an external mass, external to the probe, which forms an electrical ground. The DC current flowing can for example monotonically charge the source 23 or, alternatively, monotonically discharge the source 23. In this example, a DC current source is present and charge stored therein can be discharged through the current path, but it will be apparent that alternatively a DC current sink may be present in which charge is stored through the current path. The DC current may for example be a constant current or a monotonically changing current, such as one exhibiting an exponential decay.

As a further advantage, a DC current can travel unaided over a relatively long distance without loss of information about the monotonic change. Consequently, the location of the electrodes can be relatively remote from the electronic circuit 20, and for example the electronic circuit 20 be located at a head-side end of the board. Therefore, the need to have in the body itself already bulky processing circuitry or complex and sensitive elements like transmission lines is obviated. This enables allows a long and thin probe, which in turn allows for measuring at a deep level in the ground, and a robust design of the probe. The robust design in turn allows for an installation process of the probes, in which the probes may be hammered into the ground using a hammer or the like.

The circuit 20 further comprises a signal generator which generates a signal representing the sensed parameter. The signal generator determines the sensed parameter from an aspect of the monotonic change. Since in the shown electronic circuit 20, when in operation, the DC current flows through the portion of the ground, and the sensed parameter is determined from an aspect of the monotonic change, the circuit does not require high frequency components, or frequency converters.

The signal generator may use any aspect of the monotonic change suitable for the specific implementation and the sensed parameter may likewise be any suitable parameter which can be derived therefrom. The parameter can for example be the impedance of the portion(s) of the ground, or components of the impedance.

In this example, for instance, the signal generator comprises a timer 28 which can measure a period of time it takes to monotonically change the charge from a predetermined initial level L1 to a predetermined second level L2. At an output (out) a signal representing the measured period of time t can be outputted. Such a circuitry can be implemented in a simple manner by timing circuitry which consumes little power and is mechanically robust. For example, the timing circuitry may comprise a clock generator and a clock counter which is triggered by the voltage over the capacitor to start counting the clock pulses of the clock generator.

The timing circuitry may e.g. measure the time, and additionally be arranged to generate an error signal when the period of time exceeds a predetermined maximum, such as for example less than 0.1 second for example less than 0.05 seconds, such as 0.02 seconds or less. The timer can, additionally or alternatively, be arranged to generate a value of zero when the period of time is below a predetermined minimum, such as not more than 1 millisecond, such as 0.5 milliseconds or less, for example 400 ps.

Additionally, measuring the time allows to obtain a digital value without requiring e.g. analog to digital converters or other complex circuitry to convert an analog sensor signal. Thus, the circuit 20 directly generates a signal which can be processed by a suitable digital processor.

In the shown example, for instance, the capacitance C of the DC current source is known and constant, and accordingly the variation in impedance of the ground determines the differences in time required to monotonically discharge the capacitor, e.g. the voltage changing from a predetermined initial level L1 to a predetermined second level L2. This impedance can thus be sensed by measuring the time.

Alternatively or additionally, the signal generator may use another aspect of the monotonic change, such as the voltage over opposite sides of the portion of ground or the amount of current through the path to determine the sensed parameter. For example, the electronic circuit may e.g. comprise a current multiplier circuit, like a current mirror with non-unity mirroring which measures the amount of current flowing through the current path, e.g. over a predetermined period of time and generate a signal which represents the sensed parameter, e.g. determined therefrom.

As another example, the sensed parameter may be the dielectric constant of the portion of ground. In such a case, the signal generator may e.g. use the capacitance of the electrodes 7 to determine the sensed parameter. For example, the monotonic change may be for a predetermined period, and the signal generator determine both at the start and end of the period e.g. the voltage over the electrodes 7 at opposite sides of the portion prior and determine the dielectric constant therefrom. Assuming for instance the portion being highly resistive, the electrodes 7 will act as a capacitor and accordingly the voltage there over be a function of the capacitance, which in turn is linearly proportional to the dielectric constant. Thus if the other parameters of the circuit do not change, the variations in voltages can be related to the changes in the dielectric constant. It will be apparent that this may e.g. be combined with measuring the resistance and given that the voltage over a capacitor is a function both resistivity and dielectric constant be determined from several measurements.

The example of FIG. 4 may be operated as follows. Initially, a loop between the power source 21 and the DC current source 23 may be enabled, e.g. with switch 27 closing the loop. This allows the DC current source to be charged to a predetermined initial level L1 , with current flowing from the source 21 through charging resistor 24. For example, the DC current source 23 may be charged for a predetermined period of time, e.g. 10 milliseconds. Assuming that the resistance 24 is known, this results in a predetermined charge to the initial level L1. Worded mathematically, when charging the capacitor:

V _bmten = I (t) R ₀ + q (t) C ₀

Where:

no represents the current, ^q ^ represents the charge on the capacitor ( ⁺ ^ on one plate r> z

and ^C 1 on the other), ⁰ represents the resistance of the resistor 24 and ^{L 0} represents the capacitance of the capacitor. This can be rewritten as:

Assuming that when starting the charge is zero, this has solution:

In this respect, in case of a sufficiently long duration, the second term in this equation can be neglected and the charge q(t) becomes simply V _battery C ₀ . It has been found, that for practical purposes, the duration of setting the charge to the predetermined level can be relatively short and for example a charging of less than 50 milliseconds, such as less than 20 milliseconds, e.g. 10 milliseconds be sufficient to apply this approximation. It has been found that even if a sufficiently small capacitance is used that renders the time constant R ₀ C ₀ a fraction of this period of time, still such a capacitance can provide sufficient current to accurately determine the sensed parameter.

The loop may then be interrupted and another loop be closed of which the current path through the portion of ground is part and accordingly the capacitor be discharged. When using the probe 1 , the anode or cathode of the DC current source or sink 23, the portion of ground and the electrodes 7 at the beginning and end of the current path through the portion are connected in series. Accordingly, when discharging a DC current will pass through the portion of the ground. The impedance thereof determines the current flow, and thus the manner in and rate at which the charge of the DC current source or sink is changed. In this respect, in the shown example the anode and cathode are connected to each other (through a serial loop), but it will be apparent that instead e.g. only one thereof, such as the cathode, can be connected in series with the electrodes via the current path, e.g. to an electrical ground connected to a negative electrode. Also, in this example, the serial connection is without parallel branches and accordingly all current will pass through the portion. In an alternative, the circuit may contain branches parallel to the serial connection, like for example a current mirror which copies the current flowing through the portion to allow to measure this current, for example.

In this example, the current path connects two electrodes 7 at opposite sides of the portion and the cathode of the capacitor is connected through the, resistive, current path with the anode thereof. Assuming that the resistive component R _so n of the impedance of the ground is much higher than the other components and these can therefore be ignored, the resistive component determines the rate at which the charge changes, i.e. the capacitor discharges and accordingly the time required to discharge the capacitor 23 from the initial predetermined level L1 to another second predetermined level L2 is a measure for the impedance of the portion of the ground.

Continuing the example above, when discharging the capacitor, the power source is no longer present and so:

Assuming that the impedance is mainly resistive, for discharging the capacitor from fully charged through the current path, the solution is:

Where Rsoii represents the resistive component of the impedance of the ground, as represented in the circuit diagram of FIG. 2 with resistor R _s0 n . As a consequence, by measuring the time required to discharge the capacitor from the initial level to the predetermined level the only unknown in this equation is the resistance. This resistance can thus be determined from the measured time, the known charging time and the known battery voltage.

As illustrated explained below in more detail with reference to FIG. 6, for example, to sense the parameter of the ground, the following method may be performed. Initially, the capacitor or other DC current source may be charged to the predetermined initial level L1 . The DC current source may then be discharged and upon starting to discharge, a timer 28 may be started. As shown, the change in charge can for example be measured by measuring the voltage over the capacitor and to that end the circuit 20 comprises a voltage meter 25 which provides input to a comparator 26. The comparator receives as a reference a voltage corresponding to the second predetermined level L2 and outputs a signal when the measured voltage drops below the second level L2. This signal is transmitted to stop a timer (elk) 28 which when stops outputs a signal representing the value of the time when stopped. In this respect, it will be apparent that the voltage meter and comparator may be implemented with relatively simple and robust circuitry.

Referring to FIG. 5, the circuit 20 can be part of a measurement system which comprises in addition thereto a calculator 29 which can calculate the measured value from the sensed parameter, for example based on a predetermined model P(t) = f(t ), in which P(t) represents the measured value of the parameter and f(t) a mathematical function of the measured time t.

As illustrated, the circuit 20 may e.g. be provided on a board, like a printed circuit board with connections to the respective electrodes. The circuit may be connected to transmission circuitry 30, such as a transmitter with an antenna. The transmission circuitry 30 may for example be off— board. Such off-board circuitry can e.g. be present in a shielded space where the circuitry is shielded from the impact forces and vibrations, whereas the circuit 20 is unshielded, such as embedded in the body B. The signal from the signal generator can for example be output to a remote calculator 29 outside the probe, such as a remote data centre, which calculates therefrom a measured value of a measured property of the ground. In the example, for instance, a signal representing the measured period of time t can be output by the transmission circuitry 30 via a wireless connection, and from the period of time a measured value of the measured property be determined, such as a humidity percentage. However, alternatively, the probe may be connected via a wired connection to a data collecting node, for example a collecting node placed in a field where several probes are present, all connected via wires to the node. The collecting node may then be connected, e.g. via a wired or wireless data communication network, to a remote data centre or other data processing node.

Alternatively, the calculator 29 can be integrated in the probe and connect the circuit 20 to the transmission circuitry 30. The calculator may then, for example, calculate measured values from the signal received from the circuit 20 and send those via the transmission circuitry to a receiver outside the probe via a wired or wireless connection.

For instance in the example of FIG. 4, as explained the measured time correlates to the impedance and can be used by the calculator 29 to calculate a measured property of the ground, such as humidity. Likewise, if the sensed parameter is the dielectric constant of the ground, the humidity thereof can be calculated based on the known dielectric constants of water and dry ground. The model may for example be a known model and accordingly this is not described in further detail. It should be apparent that in this respect the resistive and/or capacitive components of the impedance can be determined in absolute terms or in relative terms (e.g. changes therein).

The probe can be arranged to obtain a sensing result, or measurement derived therefrom, on the basis of a single charge and/or single discharge of the capacitor through a portion of ground. Accordingly, obtaining data will cost very little energy. The probe can for example be arranged to sense by performing a single monotonic change, e.g. just of a single charge or of a single discharge. Accordingly, only a small amount of energy is required to obtain relatively accurate measurement data.

Alternatively, the probe may e.g. comprise a memory connected to the calculating circuitry for storing multiple sensing results or measurements. As illustrated in FIG. 5, the probe may be provided with a transmitter 30, via which a wired or wireless connection can be established to a receiving node, and the measurement system transmit via the connection in a single batch of data, data representing the stored results. This allows to reduce the energy required to transmit the data and hence the overall power consumption of the probe. Referring to FIG. 6 this flow chart illustrates a method of sensing with a probe a parameter of ground at a depth in a portion of ground adjacent to the probe. The method can e.g. be performed in a probe with a circuit as shown in FIG. 4 or another suitable electronic circuit. Such a method may comprise the use, with the probe inserted into ground to a desired depth, of the portion as a current path for a DC current which monotonically changes the charge of a DC current source or current sink from a predetermined initial level to a predetermined second level. A period of time elapsing between changing the charge from the predetermined initial level to the predetermined second level or from another aspect of the monotonic change the sensed parameter may be determined. A signal representing the elapsed period of time may be outputted.

In the specific example of FIG. 6, as illustrated with block S1 , a capacitor 23 is charged by the power source 21 to level L2. As illustrated with block S2, the charged capacitor 23 may be discharged through the current path to the level L1.

As illustrated with block S3, the probe 1 the time needed to discharge the capacitor 23 to the level L1 is measured. For instance, the probe 1 may be provided with a stopwatch or a timer, or the like, which is able to measure the time. Preferably, the probe 1 is configured to measure the time with accuracy in the order of micro-seconds.

The sensed parameter, such as the resistivity, may be determined from the measured period of time, as explained above and illustrated with block S3. This may e.g. be outputted to outside the probe, e.g. to a remote data processing station, or to other circuitry inside the probe. Subsequently, as illustrated with block S4, from the determined period of time a measured value of a measured property, such as salinity, temperature or humidity may be calculated, as illustrated with block S5. Data may then be outputted which represents the measured value, as illustrated with block S6. This data may for example be outputted in a for human perceptible form, in order to e.g. allow a farmer to manage the growing of crop, or for instance to a soil management system which controls the condition of the soil and compares the measured value with a present criterion to e.g. add or reduced the concentration of nutrients, water or otherwise in the ground.

The probe 1 may be arranged to carry out a single measurement. Accordingly, it may not be necessary to perform the charging and or discharging more than once to obtain a measurement result. This may allow for qualitative results of the properties of the portion of ground. However, if desired, the changing of the charge may be performed several times and for example an average value be determined therefrom or data representing a batch of measurement values be sent.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader scope of the invention as set forth in the appended claims and that the claims are not limited to the specific examples described and shown. In this respect the term“preferred” or“ preferably” is use to express a preferred and advantageous element but, unless explicitly stated otherwise, such an element is optional and not a mandatory or required one. For instance, although in the examples resistors and capacitors are shown, it will be apparent that the physical implementation may differ from a discrete resistor or capacitor and that e.g. a transistor may be connected such to form a resistor or a capacitor.

Likewise, for example, the DC current source may be a battery, and the electronic circuit comprise circuit that measures or calculates e.g. the charge or current delivered by the battery during a certain period of time and which outputs the measured or calculated value to the signal generator. Such a circuit can be e.g. a commercially available integrated circuit battery management system or BMS, such as sold by NXP Semiconductors of Eindhoven, the Netherlands under serial number MC33771 B. In such a case, the DC current source and the power source may be the same.

For example, the terms“front,”“back,"“top,”“bottom,”“over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

Furthermore, the connections between electronic components as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals.

Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. For example, the calculator 29, sensing circuit 20 and/or transmission circuitry 30 may be implemented on a single printed circuit board, or as physically separate elements.

Also, although reference is here made to measuring moisture, the probe can, alternatively, or additionally, be dedicated to measuring other parameters of the ground, such as salinity, temperature etc. which can be determined from the sensed parameter.

In addition, although the examples have been described with reference to sensing for agriculture, horticulture and landscaping purposes and soil management, the probe may also be used in other applications, such as for example surveillance like monitoring the risk of desertification or forest fires, for example.

Furthermore, in the examples the probe has a single elongate body with a single tip. However, it is likewise possible to have multiple of said elongate bodies. For example, the bodies may extend in parallel with their respective tips at the same side and the probe further comprise a transversal connection between the bodies which fixates the transversal distance, transversal to the longitudinal direction of the elongate bodies, for maintaining the bodies into position relative to each other when simultaneously inserting the elongate bodies into the ground.

However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms“a" or“an," as used herein, are defined as at least one or more than one. Also, the use of introductory phrases such as“at least one” and“one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one” and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as“first” and“second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.