Background of the invention It is known to use a measuring cell with two electricity conducting plates for weighing an animal. A voltage is connected to the two electricity conducting plates, and the mat- ter between the electricity conducting plates provides a dielectric.

When an animal is placed in the dielectric, it is possible to determine the water content of the animal, because the dielectric coefficient changes due to fact that the dielectric coefficient for air is 1 and 80 for water. The water content can then be correlated into the weight of the animal.

The disadvantage of such a measuring cell is its inaccuracy when other animals or humans pass outside the measuring cell, because the animal/human outside the meas- uring cell influences the dielectric by disturbing the electrical field inside the measur- ing cell.

It is then either necessary to isolate the measuring cell in a separated area without other animal or human activity nearby or to manufacture the plates with a thick non- electricity conducting outer plate in order to reduce the effect of nearby animal/human activity on the measuring cell. Both solutions have disadvantages.

It is not practically possible to isolate the measuring cell in a separated area because it would constitute a waste of space in a modern stable, where every square meter is used to the optimum, and it is not practical to lead each animal from the sty to the isolated measuring cell every time it has to be weighed.

The measuring cell would be a large and heavy construction, taking up to much space in the stable and not practical to transport or move around internally in the stable, if it is manufactured with a thick non-electricity conducting outer plate.

In GB2131176 a capacitance distance measuring the probe is disclosed. The probe consists of a sensing electrode, which is partially surrounded by a second area, which is connected to a copper coating to define a guard electrode. The sensing electrode is positioned opposite a conducting surface. This way the distance between the sensing electrode and the conducting surface can be measured. The invention concerns a probe for measuring distance. The probe is not adapted for measuring the weight of an ani- mal in a stable as no precautions have been taken to protect the electrodes from being in physical contact with the animal or from being disturbed by objects located outside the probe.

Object of the invention It is therefore the object of the present invention to provide an easily manufactured and simple plate for a measuring cell, which increases the accuracy of the measuring cell by reducing the effect of the electrical field of the dielectric inside the measuring cell caused by nearby animal/human activity.

This can be achieved with a plate according to the preamble of claim 1 and wherein the plate comprises at least one conducting ground layer that shields at least two sides of the electrical conducting layers.

It is a further object of the present invention to provide a measuring cell for weighing preferably animals using the aforementioned plates.

This can be achieved with a measuring cell according to the preamble of claim 8 and wherein the plates are positioned preferably parallel to each other and at a distance with the second conductive layers facing each other.

Description of the invention In the following, the plate and measuring cell are described when used for weighing an animal, preferable a pig, but both plate and measuring cell can be used for weighing or determine the water content of other animals or humans.

Furthermore, the first electricity conducting area is the same as the first guard part and the first electricity conducting layer the same as the second guard part and the second electricity conducting area the same as the sensor.

In order to protect the electrical field in the dielectric between the plates from electri- cal disturbance from the surrounding environment, e. g. animal or human nearby activ- ity, the measuring cell must be formed with plates formed with a guard that prevents any electrical disturbance, whereby it is possibly to obtain a very accurate measure- ment of the water content by the sensor.

The plate is then formed comprising a number of layers arranged in composite struc- ture wherein at least two of the layers are electricity conducting layers, where a second electricity conducting layer of the at least two electricity conducting layers is provided with a first electricity conducting area (first guard part), which preferably encloses a second electricity conducting area (sensor), and the electricity conducting areas are electrically separated, and the first electricity conducting area is electrically connected to a first electricity conducting layer (second guard part) of the at least two electricity conducting layers. Furthermore, the plate comprises at least one conducting ground layer that shields at least two sides of the electrical conducting layers. This way the conducting ground layer can eliminate the electrical disturbances caused by dirt and waste products such as pig urine etc. , which products lie on the bottom of the measur- ing cell. The waste build up at the bottom of the measuring cell generates a dielectric disturbing the weighing of the pig. However, by incorporating a ground plate arranged underneath and at the lower part of the electricity conducting area (sensor) the un- wanted disturbances can be eliminated as the ground layer generates a shielding of the electrodes.

In order to form a measuring cell two plates are positioned preferably parallel to each other and at a distance with the second conducting layers facing each other, whereby it is possible for an animal to enter in between the two plates. According to a preferred embodiment of the invention the facing plates comprise of a ground layer, which gen- erates a shielding of the plate at the lower part of the second conducting layer (sensor) and underneath the plate. This way the bottom of a measuring cell is shielded, which prevent waste, such as urine and dirt, located at the bottom of the measuring cell from disturbing the weighing of a pig. Furthermore, the backside of the measuring cell is shielded to prevent it from being disturbed by nearby objects such as people, animals or electric machinery located outside the measuring cell.

Due to the fact that the there is an electrical connection between the first electricity conducting area (first guard part) and the first electricity conducting layer (second guard part), the guard comprises both.

Optionally, the plate can furthermore comprise a third electricity conductive layer for electrical ground connection.

The guard and the third electricity conducting layer annul the sensor capacity to extend to the surrounding environment. When the sensor and the guard have the same voltage potential, the guard and the third electricity conducting layer will protect the dielectric from any electrical disturbance from the surrounding environment, e. g. from any ani- mal or human activity nearby and outside the measuring cell.

In a preferred embodiment of the present invention the plate comprises a first protec- tive layer, the third electricity conducting layer adapted for ground connection, a first non-electricity conducting layer, the first electricity conducting layer (second guard part), which is electrically connected to the first electricity conducting area (first guard part), a second non-electricity conducting layer, the second electricity conducting layer provided with the first (first guard part) and the second electricity conducting areas (sensor), where the first electricity conducting area (first guard part) is connected to the first electricity conducting layer (second guard part), and a second protective layer.

According to an advantageous embodiment of the invention the first protective layer and the second protective layer are electrical insulation layers which layers are pref- erably parallel, and the (sensor) electricity conducting area is arranged between the protective layers. The protective layers prevent the pig located inside a measuring cell from getting in electrical contact with the (sensor) electricity conducting area. The thickness of the protective area is important in order to obtain satisfactory weighing of the animal.

The protective layers could be made of a hard plastic coating, which is sprayed on the plate surface. Alternatively, the protective layers can be made of non-electricity con- ducting plates with a hard and smooth surface.

The two protective layers are provided in order to protect the plate against any physi- cal action from the surrounding environment, e. g. from animals pushing, biting and/or kicking the plates.

The first non-electricity conducting layer is preferably the carrying element of the plate and can be a wood plate, a plastic plate, a concrete slab/plate or a combination of the aforementioned.

The composite structure of the plate is formed such that the electricity conducting lay- ers are separated with non-electricity conducting layers, whereby there is no unwanted electrical connection between the electricity conducting layers.

The conductive layers are formed of a conductive foil, film, paint and/or textile. Typi- cally, the conductive foil, film, paint and/or textile is positioned on a backing plate or directly on the underlying non-electricity conducting layer, and the separation of the first (first guard part) and the second (sensor) electricity conducting areas is provided by cauterizing, cutting or covering a band between the areas.

According to a preferred embodiment of the invention the plate comprises at least one guard electrode and at least one sensor electrode, which interact with each other to get a substantially equal voltage potential. This way the sensor electrode is shielded from

the nearby surroundings, and capacitive coupling with e. g. the ground layer is avoided.

The guard electrodes prevent the capacity changes caused by one or more capacitive couplings between the sensor electrodes and the surroundings of the measuring cell from being measured. This assures that the measured capacity is due to the capacity of the dielectric present inside the measuring cell (e. g. a pig or the like) and not the sur- roundings.

According to another preferred embodiment of the invention at least one sensor elec- trode is electrically coupled to an amplifier, which amplifier has an output that is elec- trically coupled to at least one guard electrode. According to an advantageous imple- mentation of the invention the amplifier is coupled in order to function as a buffer assuring that the voltage potential of the guard electrode is the same as the voltage potential of the sensor electrode with respect to the ground. This way no voltage dif- ference between the sensor electrode and the guard electrode exists. The buffer also assures that no current is drawn from the sensor electrode.

In one embodiment of the present invention the separation of the first (first guard part) and the second (sensor) electricity conducting areas is a circumferential band posi- tioned preferably 1 to 10 centimetres from the edge of the second electricity conduct- ing layer. The separation could preferably have a band width of between 1 millimetre and 10 centimetres.

Alternatively, the separation of the first (first guard part) and the second (sensor) elec- tricity conducting areas is only along parts of the edges of the second electricity con- ducting layer.

A further alternative is that the second (sensor) electricity conducting area is divided into a number of smaller areas by through-going bands.

In one preferred embodiment of the present invention the first electricity conducting layer, the second non-electricity conducting layer and second electricity conducting layer are formed of a double sided circuit board.

By using a double sided circuit board it is very easy to provide the electrical separation of the first electricity conducting area (first guard part) and the second electricity con- ducting area (second guard part) and the electrical connection between the first elec- tricity conducting area (first guard part) and the first electricity conducting layer (sen- sor). The electrical separation can be provided on a circuit board by cauterizing a circumferential band close to the edge of the circuit board.

The size of the plate depends on the animal being weighed, but preferably the plates have a dimension which makes it possible to build the measuring cell into the interior of the stable without any visible disadvantages. Hence the plates have a dimension (length and height) adjusted to the other modules the interior of the stable.

In order to form a measuring cell the plates are positioned preferably parallel to each other and at a distance with the second conductive layers facing each other, whereby it is possible for an animal to enter in-between the two plates.

In order to be able to determine the water content of an animal, a voltage is connected to the plates, whereby the distance between the plates provides a dielectric. It is then possible to register the change of the dielectric coefficient when an animal is posi- tioned between the two plates of the measuring cell, due to fact that the dielectric coef- ficient for air is 1 and 80 for water.

In order to prevent phase displacement between the first (first guard part) and the sec- ond (sensor) electricity conducting areas of the first electricity conducting layer the measuring cell comprises an electrical circuit with an adjustable coil and/or an ampli- fier connecting the first (first guard part) and the second (sensor) electricity conducting areas of the first electricity conducting layer.

With smaller plates only an amplifier can be used, but when the plates are bigger and the capacity higher, it is necessary to use an adjustable coil and/or an amplifier, where the coil is adjusted to the resonance between the first (first guard part) and the second (sensor) electricity conducting areas

Test with a measuring cell and plates according to the present invention have shown a slightly different measurement of the dielectric coefficient when an animal is posi- tioned closer to one of the plates, which up to now has been unexplainable.

In order to eliminate this inaccuracy the electrical circuit is furthermore provided with a control unit which can switch the polarisation of the voltage connected to the plates.

By switching the polarisation of the voltage of the plates up to 1000 times per second, it is possible to calculate the average of the two different measurements, thereby de- termining a very accurate value for the dielectric coefficient.

In an embodiment of the present invention one of the plates can be formed with two electricity conducting layers with the first (first guard part) and the second (sensor) electricity conducting area and a common third electricity conducting layer for the ground connection in-between. It is then possible to place conventional plates on ei- ther sides and then create two juxtaposed measuring cells which can be positioned in the same sty or in two juxtaposed sties.

According to a preferred embodiment of the invention the measuring cell comprises a detector means which detector means is arranged to detect the presence of an object located entirely inside the measuring cell or detect if another object is on its way into the measuring cell.

A further advantage of a measuring cell with guards on the plates is the fact that it is possible to use the guards to determine if there is more than one animal inside the measuring cell. The sensor part of the measuring cell registers if any animal is posi- tioned inside the measuring cell, and the guard part of the measuring cell registers if any animal is positioned with part of its body inside the measuring cell. It is then pos- sible to discard any measurement when the guard part of the measuring cell registers a change in its dielectric coefficient and only allow measurement when only the sensor part of the measuring cell registers a change in its dielectric coefficient.

When an AC voltage is applied between the opposite plates a very small alternating current runs through the measuring cell. When a pig enters the scale, the capacity be- tween the plates is changing and the current flowing through the measuring cell in-

creases. The increase of capacity (simplified) is proportional to the material in ques- tion (a pig). The voltage field between the plates also comprises the space outside the plates meaning that nearby pigs affect the reading. This problem has been solved by using two voltage fields; the metering section and a voltage field surrounding the me- tering section-the guard field. The guard field is affected from outside, whereas the metering section stays unaffected.

According to a preferred embodiment of the invention a single sided printed circuit board is used as gauge plate, and a double-sided printed circuit board is used as guard, electrical isolation and ground. The size of the gauge plate is 700x1300 mm. A 100 mm wide copper sheet encircles the gauge plate. The strip of metal and the opposite guard are applied with an independent alternating voltage. This way the metering sec- tion is encased by a voltage field-the guard assuring that nearby objects do not affect the capacity of the measuring cell.

According to an embodiment of the present invention it is possible to determine the fat content of the animal inside the measuring cell. As the electricity conductivity in fat is lower than the electricity conductivity in meat, and the high frequencies have less in- fluence on the electricity conductivity, thus it is possible that measuring twice with different frequencies will provide a measurement of the fat content. Hence a first measurement is performed with a first high frequency, and then a second measurement is performed with a second frequency, which is approximately 1/2-1/3 of the first high frequency. The two measurements are compared making it possible to calculate the fat content.

Description of the drawings The invention is described below with reference to the accompanying drawings in which: fig. 1 shows a measuring cell with two plates according to the invention, fig. 2 shows a cross-section of a plate according to the invention, fig. 2 shows a plate according to the invention, fig. 3 shows a cross-section of a plate according to the invention,

fig. shows a electrical circuit for the measuring cell according to the invention, and fig. 5 shows the electrical field lines in a measuring cell according to the invention.

Detailed description of the invention Fig. 1 shows a measuring cell 20 comprising two plates 1 positioned parallel opposite each other, whereby a distance 21 between the plates 1 allows an animal to enter the measuring cell 20.

Fig. 2 shows a cross-section of plate 1 comprising a conducting ground layer 2, which shields the guard electrode 4 and the sensor electrode at the bottom of plate 1 and at the backside 26 of plate 1. The ground layer has a part 27 placed at the bottom of the front side 28 to shield the bottom of the electrodes 6b, 4 from the unwanted capacitive couplings due to waste products located at the bottom of the measuring cell. The guard electrode 4 and the sensor electrode are protected by a first protective layer 8 and a second protective layer. An insulation layer 25 is placed between the ground layer and the guard electrode.

Fig. 3 shows a plate 1 comprising a number of layers 2,3, 4,5, 6 arranged in composite structure with a first protective layer (not shown), a third electricity conducting layer 2 adapted for ground connection, a first non-electricity conducting layer 3, a first elec- tricity conducting layer 4 (second guard part), which is electrically connected (not shown) to a first electricity conducting area 6a (first guard part), a second non- electricity conducting layer 5, a second electricity conducting layer 6 provided with the first 6a (first guard part) and a second 6b (sensor) electricity conducting areas, where the first electricity conducting area 6a (first guard part) is electrically connected (not shown) to the first electricity conducting layer 4 (second guard part) and where the first 6a (first guard part) and the second 6b (sensor) electricity conducting areas are separated by a non-electricity conducting band 7, and a second protective layer (not shown).

Fig. 4 shows a cross-section of a plate 1 with the a first protective layer 8, the third electricity conducting layer 2, the first non-electricity conducting layer 3, the first elec- tricity conducting layer 4 (second guard part), the second non-electricity conducting

layer 5, the second electricity conducting layer 6 with the first 6a (first guard part) and the second 6b (sensor) electricity conducting areas, and the second protective layer 9 in a composite structure, where the guard is provided by the first 6a (first guard part) and first electricity conducting layer 4 (second guard part), which is electrically con- nected 10.

Fig. 5 shows an electrical circuit 30 for the measuring cell 20. A voltage is connected to the plates 1. Between the sensor 34 and the guard 31 an amplifier 32 is positioned.

Optionally an adjustable coil 33 can be positioned between the guard 31 and sensor 34.

Fig. 6 shows the electrical field lines 40,41 in a measuring cell 20 with two plates 1 provided with guards 42 and sensors 43. The electrical field lines 40 between the sen- sors 43 are straight lines and are not influenced by outside disturbance, meanwhile the electrical field lines 41 between the guards 42 are curved and reach outside the meas- uring cell 20. The band 7 is positioned close to the edges 44 of the plates, but at a dis- tance which ensures that all the electrical field lines 40 are straight lines.