DRYING OUT

Field of the invention

Generally speaking, the present invention relates to a sensor system for the detection of the water content in moisture-carrying layers.

Background

Over the past century, the demand for water has increased at twice the rate of population growth. Water has become a scarce resource. Only three per cent of the water present on earth is fresh water. More than two thirds of this fresh water is stored in glaciers. In contrast to this, rivers and lakes only account for 0.3 per cent of our freshwater reserves. Today already, 1.6 billion people live in countries or regions that suffer from water scarcity. 80% of the freshwater reserves are used in agriculture in the production of food. Today already, 50% of food production depends on artificial irrigation. In order to be able to feed the earth's growing population in 2025, global production of food needs to be increased by up to 35%, which means that water consumption in agriculture will further increase unless countermeasures are taken.

Unsatisfactory water supply and unsuitable irrigation management or control, which lead to water shortages, result in a significant drop in the quality and productivity of agricultural crops and their products, because there is a close link between availability of water to the plant and plant biomass formation as well as fruit formation. There is an additional problem in that the increasing water consumption in agriculture results in increased soil salinity of arable land caused by inappropriate irrigation management. Degradation of good arable land as a result of soil salinity has become a worldwide problem, all the more so since in many countries (e.g. Israel, Tunisia or Jordan) water scarcity has already made it necessary to resort to the use of effluent, in other words to treated water. However, effluent in turn is saline, is to be considered as being questionable in terms of health (e.g. concentration of coliform bacteria) and results in biological contamination of spring water. Generally speaking, soil salinity considerably impairs the quality of fruit and the crop yield and in the long term causes socio-economic and environmental problems.

By introducing drip irrigation, it was possible to significantly improve irrigation efficiency when compared to normal plant irrigation, but water consumption is still far too high. The reason for this is that farmers cannot rely on measurable standardised parameters that can provide precise information relating to the water supply to plants. To be on the safe side, farmers therefore use more water than necessary in the propagation of plants. Consequently, a large part of the water is lost through evaporation.

Placing irrigation hoses underground reduces evaporation but causes other problems (e.g. no access when leaks occur; changes in the hydraulic resistance in the line system as a result of soil materials; damage from chewing animals; positional displacement of hoses as a result of roots).

Underground textile irrigation mats, to which water is usually supplied by way of hoses comprising integrated woven materials, or other water-carrying layers are confronted with the same problems but provide an advantage in that the water delivery surface is very large when compared to that of hoses. For this reason they are primarily suitable for irrigating lawns.

As a rule, tensiometers or electrically-based soil-moisture measuring devices are used to measure soil moisture. In the case of tensiometers, the soil moisture is measured by way of the water tension that arises as the soil dries out. Measuring takes place by way of a water-filled, hermetically sealed, porous ceramic cell that is inserted into the ground and is filled with degasified water. As the soil dries out, just enough water is "sucked" from the ceramic cell that an equilibrium with the surrounding water in the soil is reached. The negative pressure arising is electronically processed by means of a manometer or by means of a pressure sensor. In the case of electrically-based soil moisture sensors the water content in the soil is measured capacitively or by means of the time/frequency domain method (i.e. measuring the changes in the dielectric constant).

Tensiometers and electrically-based soil-moisture measuring devices are not suitable for moisture-carrying layers, because these devices are too large and cannot be integrated in moisture-carrying layers, or cannot be placed therein so as to be stable over extended periods of time.

The electrical connection of a substantial number of sensors located in the soil, particularly sensors (probes) installed over a large area, is subject to various influences that can result in defects in the installed lines (chewing by animals, root growth, vehicles driving over the soil surface, soil cultivation measures ...). Typically, the electrical connection of sensors located in the soil takes place with the use of individual lines for each sensor, or in some cases also with the use of the series connection of several sensors. In either case any defect in a cable (either cable interruption or cable short circuit) results in failure of all the sensors, or at least the sensors arranged downstream of the defect.

Brief description of the invention

It is thus the object of the present invention to provide a device, a measuring mat and a method for the continuous detection of the water content in moisture-carrying layers that are subject to drying out. Furthermore, it is the object of the present invention to provide a system for the continuous detection of the water content, which system is redundant in the face of the greatest possible number of line failures.

This object is met by means of the characteristics of the independent claims. The dependent claims comprise further aspects of the present invention.

According to a first aspect the invention provides a device (for example a detector) suitable for the, in particular continuous, detection of the water content in a moisture- carrying layer. The device comprises a housing with at least one water-permeable in- feed and a hygroscopic material that is arranged in the interior of the housing and by way of the water-permeable infeed can be made to be associated with the moisture- carrying layer. Furthermore, the device comprises a sensor that cooperates with the hygroscopic material, which sensor is suitable for measuring any change in the hygroscopic material on the basis of a change in the water content of the moisture-carrying layer.

In a preferred embodiment the housing can comprise a water-permeable membrane as a water-permeable infeed.

The water-permeable infeed can allow direct contact between the hygroscopic material and the moisture-carrying layer.

The housing can furthermore comprise a capsule form.

Preferably, the device furthermore comprises an attachment element in order to attach the device to the moisture-carrying layer.

The attachment element can be a clamping element, wherein the clamping element can comprise at least one first clamping element and at least one second clamping element, and the first clamping element and the second clamping element are suitable for clamping the moisture-carrying layer between the two clamping elements.

Preferably, the first and the second clamping elements comprise a magnetic material.

It is also possible to construct the first or the second clamping element from a nonmagnetic material.

One of the two clamping elements can be firmly connected to the housing or can receive the housing in a lose connection.

The clamping element can also be a spring clip. Preferably, the hygroscopic material comprises a mixture of different hygroscopic substances with different water binding kinetics and water release kinetics.

Furthermore, the hygroscopic material can comprise a mixture of hygroscopic substances and the material from the moisture-carrying layer.

The device can, furthermore, comprise a measuring transducer.

Preferably, the hygroscopic material is suitable, in a reversible process, for changing its volume due to a change in the water content of the moisture-carrying layer.

Furthermore, the sensor can be a pressure sensor or a force sensor.

According to a further aspect the invention provides a system suitable for the, in particular continuous, detection of the water content in a moisture-carrying layer. The system comprises several of the devices described above. In this arrangement, by means of signal-carrying lines, the several devices are connected to at least one measurement signal processing device, wherein the measurement signal processing device is suitable for processing the measured signals.

In a preferred embodiment the several devices are connected, by way of the signal- carrying lines, in star topology to the measurement signal processing device.

The signal-carrying lines can be connected e.g. by way of a branching flat-ribbon cable.

Furthermore, the measurement signal processing device can comprise a measuring transducer.

According to a further preferred embodiment the several devices are serially connected to the measurement signal processing device by way of the signal-carrying lines.

The signal-carrying lines can, furthermore, be connected by way of a digital bus system. Preferably, an additional signal-carrying line is provided that establishes a cross- connection between two of the several devices.

In addition the system can comprise at least one fuse on at least one sensor, which fuse is suitable for disconnecting the affected line in the case of a fault.

According to a further aspect of the present invention, a measuring mat with at least one device described above according to the first aspect, or with at least one system described above is provided. In this arrangement the measuring mat can be used as a moisture-carrying layer.

Preferably, the measuring mat in addition comprises at least one magnet that is firmly connected to the measuring mat and is suitable for attaching at least one device according to the first aspect or a system according to the invention to the measuring mat.

In this arrangement the at least one device or the system can be firmly integrated in the measuring mat.

Preferably, the measuring mat comprises a non-woven material. As an alternative, the measuring mat is made from a non-woven material.

According to a further aspect of the present invention, a method for the, in particular continuous, detection of the water content in a moisture-carrying layer with the use of at least one of the previously described devices or with the use of at least one of the previously described systems or at least one of the previously described measuring mats is provided.

Preferably, the method allows real-time detection.

According to a further aspect of the present invention, the device, the system or the measuring mat can be used in hygiene articles. According to a further aspect of the present invention, the device, the system or the measuring mat can be used for the detection of mould or mildew in buildings.

According to a further aspect of the present invention, the device, the system or the measuring mat can be used in agriculture.

According to a further aspect of the present invention, the device, the system or the measuring mat can be used in underground water lines.

The invention thus provides a monitoring system for optimal irrigation, which system determines the water content of the mats in real time and over an extended period of time (years) so that the correct quantity of water can effectively be supplied to the mats at the correct point in time.

Brief description of the drawings

Fig. 1 shows a diagrammatic view of an embodiment of the detector of the present invention;

Fig. 2 shows a diagrammatic view of a further embodiment of the detector of the present invention;

Fig. 3 shows a diagrammatic view of an alternative embodiment of the detector of the present invention;

Fig. 4 shows an exemplary measurement curve of the swelling pressure as a function of time;

Fig. 5 shows a diagrammatic view of an embodiment of the system with several detectors of the present invention; and

Fig. 6 shows a diagrammatic view of a further embodiment of the system with several detectors of the present invention. Exemplary embodiments of the invention

Below, the present invention is explained in more detail with reference to exemplary embodiments and the figures.

1. Sensor system

Figure 1 shows a preferred embodiment 10 of the present invention. The diagram shows a water-carrying layer 16 (e.g. irrigation mat, soil or moist substrate) to which a device, e.g. a detector, according to the present invention has been affixed. The device comprises a housing 15, a chamber with a hygroscopic material 12, a sensor 13, a cable 14 and a water-permeable membrane 11.

The housing 5 (capsule or miniature chamber) comprises a pressure sensor, force sensor, moisture sensor, strain gauge, or some similar sensor 13 that can absorb forces and that is enveloped or covered by hygroscopic material 12, wherein the material of the walls or delimitations of the capsules or miniature chambers 15 needs to be water-permeable, i.e. is of such a nature that the hygroscopic material 12 can hydrauli- cally communicate with the surroundings in the moisture-carrying layer 16. The capsule or the miniature chamber 15 is of such a nature that either positive pressure builds up when the hygroscopic material 12 swells as a result of contact with water, or tensile stress (negative pressure) builds up when the hygroscopic material 12 shrinks as a result of contact with water.

The capsules or miniature chambers 15 can be closed. The water exchange with the surroundings takes place by way of a water-permeable membrane 11 that is preferably integrated in the delimitation of the capsule. As an alternative, the water-permeable membrane 11 can be used as a sheath of the capsule.

The capsules 15 can be integrated in the fabric of the moisture-carrying layer 16. In this case the moisture-carrying layer 16 is, for example, a measuring mat. Figure 2 shows an alternative embodiment of the present invention. In addition to the already described components of Figure 1 , the diagram shows a first magnet 27 and a second magnet (ring magnet) 28.

The capsule or miniature chamber 25 can thus also hydraulically communicate with the material of the moisture-carrying layers 26, directly by way of the hygroscopic material 22 when the sensor 23 and the hygroscopic material 22 is held together by way of two magnets 27, 28 between which the moisture-carrying layer 26 is located, or by way of a spring. This variant is associated with an advantage in that the hygroscopic material with the sensor is in direct contact with the moisture-carrying layer and remains in the same position even in case of displacement in the soil. The moisture-carrying layer 26 is, for example, a measuring mat.

Figure 3 shows a further embodiment of the present invention. In this embodiment the diagram in addition shows a box with an integrated measuring transducer and a sensor 39, wherein the box on one side comprises a first clamping element 38 (in the diagram a magnet or a metal plate). Furthermore, a second clamping element 37 (in the diagram a magnet or a metal plate) is integrated in the moisture-carrying layer 36 (for example a measuring mat), and the sensor element 33 with a box with an integrated measuring transducer 39 is connected to an electrical data transmission system (e.g. a cable 34) so that after installation of the moisture-carrying layer 36 it is then only necessary to place the measuring transducer with the sensor element 39 and the data transmission system onto the magnet/metal plate. Optionally the arrangement can also be the other way round. If in this arrangement the first clamping element is a magnet, the second clamping element can be a metal plate or vice versa.

Generally speaking, any inorganic or organic materials, including bio materials, can be used as hygroscopic materials 12, 22, 32, provided that the aforesaid either swell or shrink as a result of contact with water, and that these processes are reversible (e.g. chitosans, alginic acid, alginates that are cross-linked to multivalent cations, cross- linked organic or synthetic polymers, soil additives, swelling sealing agents e.g. Swell- seal Mastic or Rockmax Swelling 101). Also very suitable are mixtures of these materials with the material or fibres of the moisture-carrying layers 16, 26, 36, the material or the fibres of the moisture-carrying layer 16, 26, 36 itself/themselves, or the material and the fibres of the moisture-carrying layer 16, 26, 36 comprising non-hygroscopic materials.

Furthermore, setting the different water exchange times between the housing or the capsule or the miniature chamber 15, 25, 35 and the contacting moisture-carrying layer 16, 26, 36 can take place by way of mixtures comprising hygroscopic substances with different water binding kinetics and water release kinetics (e.g. mixtures of alginates that have been extracted from Laminaria or Lessonia nigrescens and that feature fast binding kinetics, with alginates that have been extracted from Lessonia trabecularia and that absorb or release water only slowly).

It can be advantageous to determine threshold values for the irrigation of the moisture- carrying layers 16, 26, 36 with reference to changes in the release kinetics of water from the hygroscopic substance 12, 22, 32 (see arrow in Fig. 4).

2. Data transmission

Below, a system for data transmission 40 and 50 is described with reference to Figs 5 and 6.

Inter alia there are the following variants for acquiring and transmitting the measured values from the sensors (in this context among others moisture sensor for irrigation mats, soil moisture sensor, soil temperature sensor, sensor for soil permeability...) 43 or 53, which will then, for example by way of telemetry or mobile telephony, be transmitted to an internet server from where said values can be downloaded in real time:

a) Serial connection of the sensors 43, for example by way of a digital bus system (Fig. 5) comprising:

• electrical collection stations 41 (special transmitters/measurement boxes or similar) at the edge of a field

^• by way of measuring transducers 44, typically one measuring transducer for each sensor, electrical acquisition of the measured values

• measuring transducers are interconnected by way of cables; in order to improve failsafe performance additional cross-connections can be inserted if required • the system 40 can accommodate a quasi-unlimited number of sensors 43; cable lengths between measuring transducers 44 can vary.

This variant features in particular very long cable lengths (large fields) and high flexibility.

Accordingly, a mesh-like network comprising the above-mentioned elements is used. In addition, an element can be provided which in the case of a fault (as a rule in the case of overcurrent) disconnects the affected line. Typically, in such a network the fuses and sensors are grouped in a network node element. Furthermore, at least one end point is provided that is designed as an electrical module for controlling and evaluating the sensors, or for supplying energy to the sensors and if applicable to the network node elements.

The sensors form part of a shared data bus. When compared to conventional sensor circuits comprising sensors, if applicable fuses, lines and end points, in the intermeshed line-bound network the network node element (or its individual elements) assume a central role. The network node element, which in the simplest case, apart from implementing the electrical connection of several line paths, only comprises fuses in each feed line and data line, prevents influencing the remaining parts of the network as a result of the defective line. As a result of the corresponding cross-connections there are an adequate number of redundant transmission paths.

As a result of the multitude of possible paths (redundancy) the line-bound mesh-like sensor network created in this way is capable of withstanding various cable defects (either cable interruption or cable short circuit). The maximum extent of the network is limited only by voltage drop at the network elements, by adequate supply of energy for all the active network elements, and by time-related considerations in terms of the data regime. With the use of several end points it is possible, if required, to increase the maximum extent of the network and to improve its redundancy. The system can accommodate a quasi-unlimited number of sensors; cable lengths between the network elements can vary. The degree of redundancy provided can be influenced by the num- ber of cross sections.

The design of the shared data bus does not form part of this patent application; depending on the extent and number of the network elements and on the time-related and electrical requirements, several multiplex methods according to the state of the art are possible. Typically, digital addressing of the sensors is in time-multiplex operation from one end point; if required, in the case of failure of the first end point, further end points will correspondingly take its place. The data bus needs to be designed in such a manner that any unwanted cable connections (cable defect with cable short circuit) results in overcurrent and thus in the tripping of the fuses. b) Parallel connection of the sensors 53 (Fig. 6) comprising:

• electrical collection stations with measuring transducers 51 (special transmitter/measuring boxes or similar) at the edge of the field

. branching flat-ribbon cable 54

Generally speaking, this variant tends to be suitable for short cable lengths (small fields) because cable lengths are fixed and inflexible.

Although the invention has been illustrated and described in detail with reference to the figures and the associated description, this presentation and this detailed description are to be interpreted as being illustrative and showing examples, rather than limiting the invention. It is understood that the average person skilled in the art can make changes and modifications without leaving the scope of the following claims. In particular, the invention also includes embodiments with any combination of characteristics which have been mentioned or shown above in relation to various aspects and/or embodiments.

The invention also covers individual characteristics in the figures, even if there they have been shown in the context of other characteristics and/or if they have not been mentioned above.

Furthermore, the term "comprising" and derivations thereof do not exclude other ele- merits or steps. Likewise, the indefinite article "a" or "one" and derivations thereof do not exclude a plural number. The functions of several characteristics stated in the claims can be fulfilled by one unit. The terms "essentially", "about", "approximately" and the like in conjunction with a characteristic or a value in particular also precisely define the characteristic or value. Reference characters in the claims are not to be interpreted as limiting the scope of the claims.