VERSTEGE, Albertino Bernardo Maria (Smitskamp 27, HM Aalten, NL-7121, NL)
ZENTS, Otto Theodorus Jozef (Wentholtstraat 11, ES Lichtenvoorde, NL-7131, NL)
KLOOSTRA, Sietze (Pelmolenerf 22, VK Lochem, NL-7241, NL)
VAN DIJK, Jeroen (Ahuislanden 269, AJ Enschede, NL-7542, NL)
VERSTEGE, Albertino Bernardo Maria (Smitskamp 27, HM Aalten, NL-7121, NL)
ZENTS, Otto Theodorus Jozef (Wentholtstraat 11, ES Lichtenvoorde, NL-7131, NL)
KLOOSTRA, Sietze (Pelmolenerf 22, VK Lochem, NL-7241, NL)
| Claims
1. A milk meter for measuring the volume of milk provided by a milking machine for milking animals, characterized in that the milk meter comprises at least one tubular measuring section through which, in operation, milk to be measured flows, and that the tubular measuring section is provided with at least two measuring electrodes, spaced apart in the flow direction of the milk, for use of an ECT (Electrical Capacitance Tomography)-technique, and with signal processing means which are designed for determining data with respect to the volume of the milk flowing through the at least one measuring section from measuring signals provided by the measuring electrode assemblies.
2. A milk meter according to claim 1, characterized in that the milk meter is designed for determining, with the aid of ECT- technique, per measuring electrode assembly, a cross sectional image of the measuring section at the respective measuring electrode assembly. 3. A milk meter according to claim 2, characterized in that the signal processing means are designed for determining, from at least one cross sectional image, a degree of filling of the measuring section.
4. A milk meter according to claim 2, characterized in that the signal processing means are designed for determining, from at least one cross sectional image, a degree of filling of the measuring section at the location of one of the measuring electrode assemblies.
5. A milk meter according to claim 2, 3, or 4, characterized in that the signal processing means are designed for determining a correlation time τ between cross sectional images and/ or degrees of filling which are determined with the aid of the measuring electrode assemblies, and cross sectional images and/or degrees of filling which are determined with the aid of another one of the measuring electrode assemblies, with the correlation time τ being a measure for the time the milk requires for travelling the distance between the electrode assemblies.
6. A milk meter according to claim 5, characterized in that the signal processing means are designed for determining information, from at least the correlation time τ and a distance between the measuring electrode assemblies, about a flow velocity of the milk through the measuring section.
7. A milk meter according to claim 5, characterized in that the signal processing means are designed for determining information, from at least the correlation time τ, a distance between the measuring electrode assemblies and at least one cross sectional image or degree of filling, about a flow rate of the milk through the measuring section.
8. A milk meter according to claim 5, characterized in that the signal processing means are designed for determining information, from at least one course of the correlation time τ over time and a distance between the measuring electrode assemblies, about a course over time of a flow velocity of the milk through the measuring section.
9. A milk meter according to claim 5, characterized in that the signal processing means are designed for determining information, from at least one course of the correlation time τ over time, a distance between the measuring electrode assemblies and at least one cross sectional image or degree of filling associated with the correlation time τ, about a course over time of a flow rate of the milk through the measuring section.
10. A milk meter according to claim 8 or 9, characterized in that the signal processing means are designed for determining a total amount of milk flowing through or having flowed through the measuring section during one time period, on the basis of the information about the course of time of the flow velocity and/or the flow rate.
11. A milk meter according to any one of claims 1 - 10, characterized in that the tubular measuring section is a tube with a circular cross section which has substantially the same diameter as the milk line of a milking machine.
12. A milk meter according to any one of claims 1 - 11, characterized in that the measuring electrodes of a measuring electrode assembly are elongated electrodes with a longitudinal axis that extends substantially parallel to the central axis of the tubular measuring section, which electrodes are provided in a spaced apart, evenly distributed manner around the tubular measuring section.
13. A milk meter according to claim 12, characterized in that the elongated electrodes have a substantially rectangular shape.
14. A milk meter according to claim 12, characterized in that the elongated electrodes have a substantially oval shape.
15. A milk meter according to any one of claims 1 — 11, characterized in that the measuring electrodes of the measuring electrode assembly have a substantially circular shape and are provided in a spaced apart, evenly distributed manner around the tubular measuring section. 16. A milk meter according to any one of claims 1 — 15, characterized in that the electrodes of the electrode assemblies are provided on the outside surface of the tubular measuring section.
17. A milk meter according to any one of claims 1 — 16, characterized in that each electrode is provided adjacent the axial extremities thereof with a shielding electrode placed at the same potential as the electrode proper.
18. A milk meter according to any one of claims 1 — 17, characterized in that each electrode assembly is provided at least adjacent the axial extremities thereof with a grounded shielding electrode located around the measuring section. 19. A milk meter according to any one of the preceding claims, characterized in that the signal processing means are designed for forming, from measuring signals provided by the electrode assemblies, a numerical value which represents a degree of filling of the interior of the tubular measuring section at the location of the electrode assemblies.
20. A milk meter according to claim 19, characterized in that the signal processing means are designed for determining, from the measuring signals coming from the at least two electrode assemblies, with the aid of cross correlation techniques, the time τ that the milk requires for travelling the distance between the electrode assemblies.
21. A milk meter according to claim 20, characterized in that the signal processing means are designed for determining, starting from the degree of filling and the time τ, the current volume flow of the milk flowing through the measuring section, and, through integration thereof over time, the total volume flow of the milk.
22. A milk meter according to any one of claims 20 - 21, characterized in that the signal processing means are designed for determining a standardized degree of filling on the basis of the difference between the measuring section completely filled with milk, at least at the location of the electrode assemblies, and an empty measuring section.
23. A milk meter according to claim 22, characterized in that the standardized degree of filling is calculated as a number between 0 and 1.
24. A milk meter according to any one of the preceding claims, characterized by calibration means comprising a calibration chamber filled, in operation, at least temporarily completely with milk, and at least one calibration electrode assembly cooperating with the calibration chamber, designed for use of an ECT-technique, wherein the signal processing means are designed for receiving and processing further the calibration signals received by the calibration electrode assembly. 25. A milk meter according to any one of claims 1 - 23, characterized by calibration means comprising a calibration chamber which is designed, for instance formed or connected in a manner so as, in operation, to be, at least temporarily, completely filled with milk and at least one calibration electrode assembly cooperating with the calibration chamber, designed for use of an ECT-technique, wherein the signal processing means are designed for receiving and processing further the calibration .signals provided by the calibration electrode assembly.
26. A method for measuring the volume of milk provided by a milking machine for milking animals, characterized in that the milk is guided through at least one tubular measuring section; with the aid of an ECT-technique at at least two locations located at a known mutual distance along the at least one tubular measuring section, electric signals are generated and, from said electric signals, the current degree of filling and flow velocity of the milk in the tubular measuring section is determined, as well as the volume of the milk flowing through the measuring section.
27. A method according to claim 26, characterized in that the at least two locations situated at the known mutual distance are formed by at least two measuring electrode assemblies, spaced apart in the flow direction of the milk, for use of the ECT-technique. 28. A method according to claim 27, further comprising determining, per measuring electrode assembly, with the aid of ECT-technique, a cross sectional image of the measuring section at the respective measuring electrode assembly.
29. A method according to claim 28, further comprising determining, from at least one cross sectional image, a degree of filling of the measuring section.
30. A method according to claim 28, further comprising determining, from at least one cross sectional image, a degree of filling of the measuring section at the location of one of the measuring electrode assemblies. 31. A method according to claim 28, 29 or 30, further comprising determining a correlation time τ between cross sectional images and/or degrees of filling which are determined with the aid of the measuring electrode assemblies, and cross sectional images and/or degrees of filling which are determined with the aid of another one of the measuring electrode assemblies, with the correlation time τ being a measure for the time the milk requires for travelling the distance between the electrode assemblies.
32. A method according to claim 31, further comprising determining information about a flow velocity of the milk through the measuring section from at least the correction time τ and a distance between the measuring electrode assemblies.
33. A method according to claim 31, further comprising determining information about a flow rate of the milk through the measuring section from at least the correlation time τ, a distance between the measuring electrode assemblies and at least one cross sectional image or degree of filling.
34. A method according to claim 31, further comprising determining information about a course over time of a flow velocity of the milk through the measuring section from at least one course of the correlation time τ over time and a distance between the measuring electrode assemblies. 35. A method according to claim 31, further comprising determining information about a course over time of a flow rate of the milk through the measuring section from at least one course of the correlation time τ over time, a distance between the measuring electrode assemblies and at least one cross sectional image or degree of filling associated with the correlation time τ. 36. A method according to claim 34 or 35, further comprising determining a total amount of milk, flowing or having flowed during a period of time through the measuring section, on the basis of the information about the course over time of the flow velocity and/or the flow rate. 37. A method for calibrating a milk meter according to any one of claims 1 — 25, comprising filling a cross section of the measuring section at the location of at least one of the electrode assemblies completely with milk during a first time interval, and, with the aid of this electrode assembly, determining measuring signals which correspond to a degree of filling of 100%, and comprising determining, during a second time interval in which a cross section of the measuring section at the location of at least one of the electrode assembly is not filled with milk, measuring signals with the aid of this electrode assembly, which correspond to a degree of filling of 0% so as to be able to normalize a degree of filling represented by current measuring signals.
38. A method for calibrating a milk meter according to claim 24 or 25, comprising filling, during a first time interval, the calibrating chamber completely with milk and, with the aid of the calibration electrode assembly, determining measuring signals which correspond to a degree of filling of 100%, and comprising determining, during a second time interval in which the calibration chamber is not filled with milk, with the aid of the calibration electrode assembly, measuring signals which correspond to a degree of filling of 0%, so as to be able to normalize a degree of filling represented by the current measuring signals.
39. A method according to claim 37 or 38, comprising normalizing a degree of filling represented by current measuring signals according to the normalization formula (Cmeasured — Cempty) / (Cfull — Cempty).
40. A tubular measuring section provided with at least two electrode assemblies for use in a milk meter according to any one of claims 1 — 25 or in a method according to any one of claims 26 — 39. |
Title: Milk meter
The invention relates to a milk meter. In the framework of the following description, a milk meter is understood to mean an apparatus which, during milking, can measure the volume of the milk provided by a milking machine for milking animals. Such milk meters are known in various types. Many known milk meters are mechanical fill-and-dump meters, which have moving parts. A drawback of such mechanical milk meters is that the moving parts are subject to wear and need maintenance and are moreover susceptible to contamination. Further, the moving parts can become stuck. As a result of such occurrences, a milk meter can inadvertently provide incorrect measuring results, which is, of course, undesired.
From EP 0536080, a milk meter operating in a contactless manner is known, which comprises a measuring section, contains a number of channels with known dimensions, and to which the milk coming from the milking machine is fed. The number and the dimensions of the channels are selected such that during measuring, the channels are not completely filled with milk. Along each channel are arranged, fixedly spaced apart, a first and a second light source that can provide, for instance, infrared light. At the side of the channel opposite each light source a detector is placed, which can capture the light of the corresponding light source after the light has passed the channel and the milk present therein. With the aid of the detector, the attenuation of the light occurring in the channel can be determined. This attenuation is a measure for the current filling of the channel at the location of the light source. In general, the output signal of the detector is a signal varying over time, representing the course of the level of the milk over time in the respective channel. The detector cooperating with the second light source placed at a distance from the first light source provides a similar signal but shifted over time. The time difference between the two signals is measured whereupon,
through a combination with the known distance between the first and second light source, the flow velocity of the milk is obtained.
Then, from the flow velocity and the current filling of the respective channel, with the aid of a microprocessor, the flow rate is determined of the milk flowing through each channel, or through all channels together, respectively.
A drawback of the known apparatus is that the light sources and detectors are sensitive to contamination and have characteristics that change through ageing. Further, the measuring section of the known milk meter is rather voluminous as it comprises a large number of side-by-side channels.
Such a measuring section may be difficult to place in the milk line system of a milking machine.
The object of the invention is to provide an alternative type milk meter, which, like the known milk meter, has no moving parts and which further does not comprise light sources and light detectors.
More in general, the invention aims to provide a reliable and fast- acting, simple-to-install milk meter with stable properties.
To that end, according to the invention, a milk meter for measuring the volume of milk provided by a milking machine for milking animals is characterized in that the milk meter comprises at least one tubular measuring section through which, in operation, the milk to be measured flows, and that the tubular measuring section is provided, in the flow direction of the milk, with at least two spaced apart measuring electrode assemblies, for use of an ECT (Electrical Capacitance Tomography)-technique, and with signal processing means which are designed for determining data with respect to the milk flowing through the at least one measuring section from the measuring signals provided by the measuring electrode assemblies.
According to the invention, a method for measuring the volume of milk provided by a milking machine for milking animals is characterized in that milk is guided through at least one tubular measuring section;
with the aid of an ECT-technique, at at least two places located at-a known, mutual distance along the at least one tubular measuring section, electrical measuring signals are generated; from these electrical measuring signals, the current degree of filling and flow velocity of the milk in the tubular measuring section is determined, as well as the volume of the milk flowing through the measuring section.
It is preferred that in use, per measuring electrode assembly, with the aid of ECT-technique, a cross sectional image of the measuring section at the respective measuring electrode assembly is determined. Here, the preferably current cross sectional image preferably represents a distribution of milk and air in the measuring section at the location of the measuring electrode assembly. Preferably, in use, from at least one cross sectional image, a degree of filling of the measuring section is determined. With it, the degree of filling of the measuring section, for instance the distribution of milk and air, can be determined. In this way, it is also possible to determine a current degree of filling.
Preferably, in use, a correlation time τ is determined between (current) cross sectional images and/or degrees of filling which are determined with the aid of the measuring electrode assemblies, and (current) cross sectional images and/or degrees of filling which are determined with the aid of another one of the measuring electrode assemblies, the correlation time t being a measure for the time the milk requires for travelling the distance between the electrode assemblies.
Thus, from, for instance, at least the correlation time τ, a distance can be determined between the measuring electrode assemblies and information about a (for instance current) flow velocity of the milk through the measuring section. It is also possible that from at least the correlation time τ, a distance between the measuring electrode assemblies and at least one cross sectional image or degree of filling, for instance at the location of one of the
measuring- electrode assemblies, information about a (for instance current) flow rate of the milk through the measuring section is determined.
Also, from at least one course of the correlation time τ over time and a distance between the measuring sections, information about a course over time of a flow velocity of the milk through the measuring section can be determined. It is also possible that from at least one course of the correlation time τ over time, a distance between the electrode measuring assemblies and at least one (current) density profile or (current) degree of filling associated with the correlation time τ, information about a course over time of a flow rate of the milk through the measuring section is determined.
Preferably, an amount of milk flowing, or a total amount of milk having flowed during a period of time through the measuring section is determined on the basis of the information about the course over time of the flow velocity and/or the flow rate. It is possible, for instance, to determine the total amount of milk having flowed through the measuring section through integration of the current flow rate over time, or through integration of the product of the current flow velocity and the current degree of filling.
In the following, the invention will be described in more detail with reference to the appended drawing. Pig. 1 schematically shows an example of a tubular measuring section provided with sensor electrodes for use of an ECT-technique for a milk meter;
Fig. 2 shows a cross section of a tubular measuring section with eight sensor electrodes according to the invention; Fig. 3 schematically shows a detail of an example of an electrode configuration for use of an ECT-technique;
Fig. 4 shows an overall electric block diagram of an example of a milk meter according to the invention; and
Fig. 5 schematically shows an example of a tubular measuring " section of a milk meter according to the invention provided with calibration means.
Fig. 1 schematically shows an example of a tubular measuring section 1 provided with a first electrode assembly El and a second electrode assembly E2 located at a distance therefrom. A set of measuring or sensor electrodes 2 — 5 of the first electrode assembly El are visible and a set of measuring or sensor electrodes 12 - 15 of the second electrode assembly are visible. At the rear side of the tube, not visible in Fig. 1, additional sensor electrodes of the assemblies El and E2 are present. Preferably, the electrodes have an elongated rectangular shape but other shapes such as, for instance, circulair or oval are possible too. In this example, the longitudinal axis of the electrodes is substantially parallel to the central axis of the measuring section 1. The electrodes of an electrode assembly are evenly distributed at a mutual distance in a circular setup around the measuring section. With each electrode assembly a cross sectional plane or measuring surface of the measuring section is associated. Therefore, the cross sectional plane extends transversely relative to the flow direction of the milk in the measuring section. In Fig. 1, these cross sectional planes are indicated with Cl and C2. Though the electrodes have a particular length transversely to the associated cross sectional plane, the cross sectional plane is still indicated as the electrode plane.
The measuring section consists of a straight tube with a substantially constant internal cross section which is circular in this example. In principle, other cross section shapes, for instance square, rectangular, multiangular or oval are possible but require special coupling pieces for including the measuring section in a milk line.
Fig. 2 shows, by way of example, the cross sectional plane Cl of Fig. 1. In Fig. 2 it can be seen that the electrode assembly El further
comprises sensor electrodes 6 - 9, so that, in this example, the electrode assembly El comprises, in total, eight sensor electrodes, provided in an evenly distributed way around the measuring section 1. In a similar manner, the electrode assembly E2 comprises four further sensor electrodes not visible here. Other numbers of sensor electrodes are possible, for instance six or twelve.
In the example shown, the sensor electrodes are at the outside of the measuring section. As a result, the electrodes are well accessible and connecting wires can be provided relatively easily. Also, the electrodes are not in direct contact with the liquid to be measured and the interior of the measuring section remains free from electric components. Here, the milk meter is non-invasive. The electrodes can be provided directly on the tube surface when the tube is manufactured from non-electrically conductive material. In a practical situation, the measuring section 1 can form part of the milk line of a milking machine and can thereto be provided with coupling pieces (not shown) such as, for instance, connecting flanges or connecting sockets or the like. The milk flowing through the milk line also flows through the measuring section 1 of the milk meter.
The measuring section is to meet all requirements set, also those set for the conventional milk line. Therefore, the measuring section should not chemically react with the milk and should be able to withstand the usual cleaning processes used for the milk line.
With the aid of a configuration of sensor electrodes placed around a measuring section, it is possible, with the known per se technique of ECT (Electrical Capacitance Tomography), to construct cross sectional images of the interior of the measuring section and the materials present therein. To this end, according to a predetermined protocol, the electric capacitance between different pairs and/or sets of pair of electrodes is measured. The capacitance between two electrodes depends on the material present between the two electrodes. The material has a certain permittivity, which is a measure for the
difference between the measured capacitance and the capacitance if the material is air. From literature, two methods for capacitance measurement are known. The capacitance between two electrodes can be measured via the AG method and the charge -discharge method. According to the AC method, an alternating current is applied on one of the sensor electrodes (which then functions as control electrode) and then, the voltage prevailing on the other electrodes (the detector electrodes) and the phase thereof are measured. From this, the impedance between the two electrodes can be derived. The impedance consists of a resistance and capacitance parallel to each other. According to the charge/discharge method, in a first phase, the control electrode is charged and, in a following phase, the control electrode discharges again. As a result, on the detector electrodes, a return signal is produced, that can be measured and is a measure for the intermediate capacitance. The AC method offers a better signal/interference ratio and is therefore preferred in use. The function of a control electrode and detector electrode changes during a complete measuring cycle. With electrode 1 as control electrode, the electrodes 2 - N function as detector electrodes. Then, electrode number 2 becomes the control electrode and electrodes 3 — N function as detector electrodes. When the electrode pair 1, 2 (control electrode, detector electrode) has been measured, electrode pair 2, 1 needs not be measured any more. The total amount of measurements in a measuring cycle is therefore N* (N-l)/2, with N being the total number of electrodes.
When eight electrodes are involved, a set of 28 measuring results is obtained. When capacitances between groups of sensor electrodes are measured, other numbers of measuring results are obtained.
The capacitance measurements are repeated with a predetermined frequency.
On the basis of the thus obtained set of capacitance measurements, with the aid of algorithms known per se for this purpose, such as, for instance the LBP-technique (linear back projection technique), a current cross sectional
image of the measuring section at the location of the electrode assembly can-be constructed. This cross sectional image represents the current distribution of dielectric material in the cross sectional plane. In a milk meter, the cross sectional image represents the distribution of milk and air in the measuring section at the location of the cross section. Thus, the cross sectional image gives a density distribution of the material in the measuring section at the location of the cross section. Hence, the cross sectional image also indicates the current degree of filling with milk of the measuring section at the location of the cross section at the time of measuring. For use in a milk meter, it is not necessary to determine a cross sectional image as it is not the three-dimensional distribution of the milk in the measuring section that is of interest, but only the amount of milk at a particular time in the measuring section. Therefore, it is preferred that the obtained collection of measuring values is first normalized with respect to the values measured with a full measuring section and an empty measuring section according to the normalization formula: (Cmeasured — Cempty) / Cfull - Cempty), wherein C is the capacitance. This set of data too can be translated with existing techniques such as linear back projection (LBP) to a (normalized) cross sectional picture of, for instance, 32 x 32 pixels. In each pixel, a measure of the amount of material is present at that location. However, it is preferred that all measuring values are added up and divided by the number of measuring values. As a result, an end value between 0 and 1 is formed which is a measure for the filling of the sensor. Starting from the dimensions of the measuring section and the obtained end value, the degree of filling at any measuring moment can be calculated.
With the aid of two (Fig. 1) electrode assemblies located at a distance A from each other, two cross sectional images can be constructed, or, in the above described manner, a first and a second degree of filling can be determined. In the milk meter, the cross sectional image leading in the flow direction of the milk, or the first calculated degree of filling, respectively,
represents the distribution of milk and air at the location of the first electrode assembly. In Fig. 1, the flow direction of the milk through the measuring section 1 is indicated with an arrow P and the first electrode assembly is therefore electrode assembly El. After a time τ, which depends on the flow velocity of the milk, a corresponding cross sectional image or corresponding degree of filling, respectively, at the location of the second electrode assembly E2 can be determined.
The time τ determines, together with the known distance A between the two electrode assemblies and the cross sectional planes Cl and C2 defined by these electrode assemblies, the flow velocity of the milk through the measuring section.
The flow velocity of the milk provides, in combination with the current degree of filling of the measuring section, the current flow rate of the milk flow. Through integration of the varying current flow rate over time, the total volume is obtained.
It is noted that the milk flow provided by a milking machine has a pulsating nature. This leads to a degree of filling of the milk line and, hence, also of the measuring section of the milk meter, that varies over time. A cross sectional image or degree of filling, respectively, at a particular location of the measuring section at time ti therefore differs, in general, from a cross sectional image or degree of filling, respectively, at the same location at time ti±δt. In this manner, it is also possible to determine whether a cross sectional image or degree of filling, respectively, at a first location Cl at the time ti corresponds to a cross sectional image or degree of filling, respectively, at a second, downstream location C2 at a time ti + τ.
In order to compare to each other the cross sectional images or degrees of filling, respectively, at the location Cl and C2, use can be made of correlation techniques known per se. Here, in mathematical sense, for instance a mathematical function (cross correlation function) of the cross sectional
images or degrees of filling, respectively, varying over time can be calculated at both locations. This function contains the time difference τ between both cross sectional images or degrees of filling, respectively, as variable. The cross correlation function further has a maximum when the two cross sectional images or degrees of filling, respectively, correspond. The value of τ, τ ma χ, with the cross correlation function exhibiting a maximum, is precisely the time that lapses between the occurrence of a particular cross sectional image or a particular degree of filing in plane Cl and the occurrence of the substantially similar cross sectional image or the similar degree of filling, respectively, in the downstream located plane C2. Therefore, the time difference τ m ax corresponds to the displacement time of the milk between Cl and C2.
Therefore, the flow velocity of the milk can be calculated as A/τ. As already noted, the technique of making tomography (= cross sectional) images with the aid of ECT-techniques is known per se. In this context, reference may be made to a lecture of Malcolm Byars entitled
"Developments in Electrical Capacitance Tomography" held during the Second World Congress on Industrial Process Tomography in Hannover, Germany in August 2001.
The lecture was published by Process Tomography LTD, Cheshire, UK and can be found on www.tomography.com. Further information on
Electrical Capacitance Tomography can be found in, for instance, Reinecke N. and Mewes D., (1994) Resolution enhancement for multi-electrode capacitance sensors in Proc. Process Tomography, A Strategy for Industrial Exploitation, Bergen, Norway, pages 50-61, and in Yang W.Q. and Byars M. (1999), An improved normalisation approach for electrical capacitance tomography, in Proc. 1 st World Congress on Industrial Process Tomography, Brixton, UK, pages 215-218. The electrode configurations can be made in different manners, for instance by forming electrodes with the aid of photolithographic techniques on a flexible copper laminated insulated material that is wound around a tube (the measuring section) of insulating material. Preferably, the electrode
assemblies are provided with grounded shielding strips arranged at both extremities, as schematically shown in Fig. 3.
Fig. 3 shows two sensor electrodes 3 and 4 corresponding to the electrodes indicated with the same reference numerals in Figs. 1 and 2. In this example, on both sides of the sensor electrodes 3 and 4, axial shielding electrodes 3a, 3b or 4a, 4b, respectively, are provided. The shielding electrodes 3a, 3b, 4a, 4b are placed at the same potential as the sensor electrodes and promote that, between the sensor electrodes, as homogeneous an electric field as possible prevails. At the ends of the shielding electrodes remote from the sensor electrodes, there are grounded shielding strips 20, 21. Between the successive electrodes of an electrode assembly too, grounded axial traces can be provided, as indicated at 22 in Fig. 3.
Fig. 4 shows an electric block diagram of an example of a milk meter according to the invention. In this example, each electrode assembly El or E2, respectively, comprises six sensor electrodes 30 — 35 or 36 — 41, respectively. For the sake of simplicity, shielding electrodes are not shown. The milk meter shown operates according to the earlier mentioned AC-method. The separate sensor electrodes of a configuration El, E2 are connected to an interface connection 42 or 43, respectively, which actuates the successive control electrodes and receives the capacitance measurement signals obtained by the detector electrodes and converts these into voltage signals. The voltage signals are supplied, via amplifiers 44 and 45 respectively, to a single A(analogue) D(digital) converter 46, whose output is connected to a microprocessor 47. The microprocessor may be designed for calculating, from the received signals, the pixel values of cross sectional images. The cross sectional images need not be represented, but if desired, it is possible to do so. In that case, use can for instance be made of a method known from literature, wherein three colours are used, for instance blue for pixels representing the substance with the small dielectric constant, red for pixels representing the substance with the greatest
dielectric constant and green for pixels representing both substances. To such pixels, normalized numerical values can be attributed, which can be, for instance, 0.1 and a number between 0 and 1, respectively.
In the case of a milk meter, the number 0 represents air and the number 1 milk. In a similar manner, an entire cross sectional image can be numerically represented through adding all pixel values. Here, optionally, normalisation can be applied by dividing the obtained sum value by the number of pixels so that, again, a number between 0 and 1 (limits included) is obtained. This number then represents the degree of filling of the measuring section at the location of a measuring plane.
As already mentioned hereinabove, for determining the degree of filling of the measuring section, it is not necessary to determine the three- dimensional distribution of the milk across the cross section of the measuring section. Then, the values of the individual pixels need not be determined either.
Therefore, the microprocessor may also be designed for determining the degree of filling directly from the capacitance measuring values provided by the AJD converter. To this end, the microprocessor normalizes each measuring value to a number between 0 and 1 according to the earlier mentioned normalisation formula. Then, the microprocessor adds all normalized measuring values and divides the obtained sum value by the number of added up measuring values. The result is, again, a number between 0 and 1, which number represents the sought degree of filling.
The microprocessor is further designed for determining the flow velocity of the milk by means of the above-described cross correlation technique. From the data known with respect to the cross sectional shape and cross sectional dimensions of the measuring section, and the distance between the cross sectional planes Cl and C2, together with the measured/calculated degree of filling and the measured/calculated flow velocity, the microprocessor calculates the current volume flow of the milk and the total milk volume
having passed through the milk meter. The total milk volume of the inilk provided by the animal may, if desired, be represented on a reproducing device 48. It is also possible to show other data on the reproducing device.
In practice, it may be desired to calibrate the milk meter. To this end, an additional electrode assembly can be utilized, which is located in an area of the measuring section that is sometimes completely filled and sometimes completely empty.
A schematically sketched example of a milk meter provided with calibration means is shown in Fig. 5. Fig. 5 shows a horizontal measuring section 51 which is provided, in a manner simϋar to the measuring section 1 of Fig. 1, with measuring electrode assemblies El and E2, designed for generating measuring signals in the above-described manner, with the aid of which signal processing means can determine data with respect to the volume and to milk flowing through the measuring section. The measuring section 1 is provided with a feed section 52 and a discharge section 53. The flow direction of the milk is indicated with arrows Pl, P2, P3. In this example, the sections 52 and 53 extend, for instance, transversely to the measuring section.
Fig. 5 further shows a calibration chamber 54 provided with a calibration electrode assembly Ec.
The calibration chamber 54 is formed by a continuation of the measuring section 51 extending beyond the discharge section 53.
As an alternative to the calibration chamber 54 or, if desired, in combination therewith, a calibration chamber adjacent the entrance side of the measuring section can be utilized. Such a calibration chamber is indicated in broken lines 54' and is provided with a calibration electrode assembly Ec'.
In operation, the calibration chamber is continuously or at least during particular time intervals completely filled with milk by the milk flowing through the milk meter. In those time intervals, via the calibration electrode assembly Ec, measuring signals are obtained which correspond to a
degree of filling of 100%. Prior to the feed of milk, signals corresponding to a degree of filling of 0% can be obtained. With the aid of the signal processing means, the degree of filling represented by the current measuring signals can be determined with the aid of the above-indicated normalisation formula as a number between 0 and 1.
The properties of the milk flow to be measured can vary from milk yield to milk yield and even during one single milk yield.
However, such variations have no influence on the eventual measuring result if during each measuring cycle the calibration measuring signals are generated a sufficient number of times and are used for calibration.
A calibration chamber can also be formed/and or connected in another manner than the manner shown. It is also conceivable to use the measuring section itself as calibration chamber by temporarily closing it off completely or for the larger part at the exit side with a valve or the like. It is noted that after the foregoing, various modifications are readily apparent to the skilled person. For instance, other numbers of electrodes and/or electrode assemblies and/or differently formed and/or differently manufactured electrodes and/or electrode assemblies can be used than in the described exemplary embodiments. Also, if desired, the ECT images of the measuring planes can actually be represented on a monitor or the like.
Further, it is not strictly necessary for the sensor electrodes to be located at the outside of the tubular measuring section. Use of internal electrodes which are located in the interior of the measuring section and which are in contact with the liquid is also possible. These and similar modifications and variants are readily apparent to the skilled person and are understood to fall within the framework of the invention.
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