WO2000012997A1

WO2000012997A1 - Fluid sensing device and method for use in particular in milking machines

Info

Publication number: WO2000012997A1
Application number: PCT/SE1999/001452
Authority: WO
Inventors: Jan Eriksson
Original assignee: Alfa Laval Agri Ab
Priority date: 1998-08-26
Filing date: 1999-08-25
Publication date: 2000-03-09
Also published as: SE9802855D0; SE9802855L; AU5891199A

Abstract

The present invention relates to a device and a method for determining the composition of a fluid (37) in which a sample of the fluid (37) being tested is drawn by capillary action between two sides (27', 27'') of a hollow cavity (25) which are joined with a small angle α between them. Electromagnetic radiation such as visible or infrared light is supplied to one of said sides (27') and collected at the other said side (27''). The amount of light that is detected is dependent on the capillary attraction between the fluid and the material that the container (24) is made from. The detected light is measured and can be compared to measurements made on samples of known composition to determine the composition of the tested fluid.

Description

FLUID SENSING DEVICE AND METHOD FOR USE IN PARTICULAR IN MILKING MACHINES

The present invention relates to a fluid sensing device and method for use in particular in milking machines of the type mentioned in the preambles of claims 1 and 8.

In milking machines it is necessary to regularly clean the pipe system leading from the milked animals udder to the milk storage container. This is done by flushing the system with cleaning fluids and it is important to be able to distinguish between water, milk, milk diluted with water, cleaning fluid, air, etc. in the hoses or pipes so that milk is not inadvertently sent to a container intended for waste products and so that waste products, cleaning fluid or contaminated milk are not sent to containers intended for pure milk. It is often also important to detect when a teat or udder has finished supplying milk to prevent excessively prolonged stimulation of the empty teat or udder.

US-A 4 756 274 describes an end of milking detector for use in a pipe in which a horizontally directed infra-red light source sends a beam of infra-red light to a detector on the opposite side of the pipe. If the fluid in the pipe reaches or passes above the level of the infra-red light source the beam is prevented from reaching the detector and it is assumed that the pipe is full of milk. This device can only determine that there is an absence or presence of milk (or other right blocking substance) above the level of the detector in a pipe. It cannot measure the composition of the substance blocking the light beam.

The device and method of the present invention has the object of solving the problems of the prior art.

The object is achieved according to the present invention by means of devices and methods having the features mentioned in the characterising parts of the independent claims. Further developments and improvements of the present invention are mentioned in the dependent claims.

In particular the object is achieved by providing a fluid sampling container with means for producing an output signal which depends on the surface tension of the fluid being sampled. As the surface tension of the fluid depends on its composition then this device can detect changes in the composition of fluids being sampled.

Preferably the device has a hollow container with straight sides as this is easy and inexpensive to manufacture. One or more curved sides could however be used to vary the spacing between the sides in a non-linear manner in order to achieve an increased capillary effect at certain positions of special interest.

If the cross-section is triangular then the device is easy to manufacture and does not take up as much space as a trapezoidal shape would.

The device may have sides which intercept at a small angle. This means that the distance between the sides increases as one moves away from their line of intersection and that the height that capillary attraction of the fluid will pull the fluid up the sides will decease in that direction. This will lead to different wetted areas of the sides depending on the composition of the fluid being sampled. The angle between the sides can be varied to achieve a compromise between a small angle which gives a high degree of accuracy but requires a long device and a large angle which gives less accuracy but which enables the device to be made shorter.

The device can be provided with means for ejecting the fluid from the container so that after each sample has been measured the container can be positively emptied to ensure it is ready to receive a new sample.

The invention will be described more closely with the help of examples of embodiments and the appended figures in which: Figure la) is a view from above of an embodiment of a sensing device according to the invention;

Figure lb) is a view from the side of the device shown in figure la);

Figures lc) and Id) are views from the side of the device shown in figure lb) showing the effects of different capillary actions.

Figure 2a)-2d) shown schematically further possible embodiments of devices according to the invention

Figures 3a) and 3b) show another embodiment of a sensing device in accordance with the invention.

An embodiment of a sensing device in accordance with the present invention is shown in figures la) to Id). The sensing device comprises a source of electromagnetic radiation, such as a visible light emitting diode 23, on one side 27' of a fluid containing transparent container 24 having a hollow cavity 25 with a triangular cross-section with a shallow angle α between the two long sides 27', 27". The choice of angle is dependent on a compromise between a large sensitivity to different capillary actions which requires a low angle α and a small size which is achieved with a large angle α. Angle α can be from 0° to about 30° and is preferably between 2° and 15° (note that if the angle is 0° then the cross-section will be rectangular and the sides 27, 27' will be parallel. In this case sides should be placed a small distance apart e.g. in the order of a millimetre so that capillary forces can cause a fluid to rise between the sides. The height that the fluid rises being a measure of its composition). At least the bottom end 29' of the container 24 is open. A light detecting means 31 which generates a voltage proportional to the light it receives, is on the side 27" of the cont.ainer opposite to the light source 23. The light from the light source 23 is transmitted through .an light distributing optical element such as lens 33 so that it enters the cavity 25 through long sides 27' and is preferably substantially evenly distributed over the surface of the long side 27'. Any light passing through the cavity 25 is collected by an light collecting optical element such as lens 35 on the opposite long side 17 which leads the collected light to light detecting means 31. In use the cavity 25 is placed in contact with the surface of the fluid 37 being tested so that capillary action pulls the fluid 37 up into the interior space 39 of the cavity 25. The closer the sides are the higher the fluid is lifted by capillary action - see figure 3a). Thus fluid which is nearest the join between the two long sides 27', 27" is lifted higher than fluid which is nearer the opposing short side 41 of the cavity 25. The strength of the signal 43, e.g. a voltage, generated by the light detecting means 31 depends on how much of the surface area of the long sides 27', 27" of the cavity 25 is made opaque by the fluid drawn into the internal space 39 by capillary action. This depends on the surface tension of the fluid being tested and this is dependent on the composition of the fluid being tested - see figures lc) and Id) in which the fluid in figure lc) has a greater capillary action than the fluid in figure Id) and hence fills space 39 more completely. By comparing the generated signal to signals generated by samples of known composition it is possible to identify the composition of the sample currently being tested. This comparison can take placing in automated means such as a computer 45.

In another embodiment of this device the light collecting lens 35 is replace by a photo-electric cell (a so-called " solar cell") the light collecting surface of which is at least the same size as the surface of long side 27" and which is positioned to receive the light passing though the long side. The voltage generated by the photoelectric cell is then dependent on the composition of the sample being tested. Figures 2a)-2d) show further conceivable cavity cross-sections which could be used in sensing devices in accordance with the invention. The same reference numerals have been used for parts having equivalent functions. Figures 2a) and 2b) show trapezoid and parallelogram shaped cavities which can conceivably be used instead of triangular cavities. It is conceivable that one or both of the sides 27', 27 " could be concave or convex as shown in figures 2c) and 2d). It is furthermore conceivable that the sides can taper vertically so that the distances between the top and bottom edges of the long sides can be made different. In other words the long sides do not have to be parallel in the vertical direction but may converge or diverge with an angle β between them which could be in the range of 0° to 30°. This can be used to adjust the sensitivity of the sensing to the composition of the fluid being tested. Several cavities of different shape and hence having sensitivities to different ranges of fluid composition could be arranged in groups to enable improved sensitivity over a number of ranges of fluid composition.

The amount of Hght received by light detecting means 31 is dependent on a number of variables, such as, for example, the strength of the light source 23 and the distance between the light source 23 and light detecting means 31, the opacity of the fluid 37 in the container 24, the capillary action of the fluid 37, etc. If all the other variables are kept constant then any variation in the amount of light detected by light detecting means 31 is dependent on the composition of fluid 37 which affects its opacity and capillary attraction. The signal or voltage generated by this light can be analysed, for example by comparison to the signals received from calibration mixtures of known composition, in order to determine the composition of the fluid in the pipe. This comparison can be performed manually by an operator, for example by comparing an indicated voltage against calibration charts showing indicated voltages obtained for different fluids of known composition. However in a preferred embodiment of the invention the comparison is performed by automated means such as comϋuter 45. In another embodiment of the invention shown in figures 3a) and 3b) the light collecting lens 35 is replaced by a photo-detector array 51. This images the surface of the long side 27" as a plurality of picture elements (pixels) and enables the shape of the wetted surface of long side 27" to be recorded. This shape depends on the surface tension and hence the composition of the fluid being tested. As the shape of the wetted area can vary depending on the composition of the fluid being tested this device gives more information concerning the fluid being tested. It allows discrimination between two fluid which wet equally large areas of the surface of the long side 27" but with different shapes.

The presence of blood or other coloured contamination can be detected by using a suitable, preferably removable, colour filter or a providing more sensing devices according to the invention, each having a filter adapted to detect different contaminants.

The device in accordance with the invention can be used by supporting it on the surface of the fluid being tested. In order to ensure similar conditions apply during all measurements the device is preferably provided with flotation means in order to hold it at approximately the s.ame height in relationship to fluid being tested.

The device in accordance with the invention can be used by attaching it to the upper part of a pipe full of the fluid being tested and allowing the fluid to climb up into the device by capillary attraction. Preferably ejecting means such as compressed air nozzle are provided so that the fluid can be ejected from the interior space of the measuring device once the measurement have been made.

Accurate measurement of the velocity of the fluid can be obtained by using two or more sets of light sources and detector spaced a known distance apart in the direction of flow of the fluid being examined. By comparing the signals generated by the spaced apart detectors in order to identify similar irregularities in the signals the speed of the flow can be calculated from the time it takes for irregularities in the waveform of the first generated signal to appear in the second generated signal.

As the source of electromagnetic radiation and sensing means are on the outside of the pipe there are no problems in keeping them clean and no special sealing arrangements are required.

In order to provide more sensitive sensing it is possible to provide a plurality of light detecting means which receive light from different sections of the light collecting lens or the light receiving surface. It is also conceivable to have a plurality of detectors which are sensitive to different wavelengths of light and corresponding hght sources in order to analyse the composition of the fluid being tested. This can also be achieved by providing filters in the path of the beam of light.

In order to more accurately determine the composition of the fluid being tested it is advantageous to have a calibration light source and detector which measure the opacity of the fluid. Once the opacity of the fluid has been determined then it is possible to compensate for the effects of the opacity of the fluid on the strength of the signal received by the light detecting means. This means that the signal will only depend on the capillary attraction and thus the surface tension between the fluid and the material of the container. This simplifies the comparison of the tested fluid against fluids of known composition.

While the invention has been illustrated by the use of visible light it is of course possible to use other forms of electromagnetic radiation such as infra-red, ultraviolet or other suitable wavelengths. In addition to using any electromagnetic radiation to detect the extent the fluid has risen in the cavity it is also possible to measure the electrical properties of the fluid by applying a voltage across the container preferably after it has been suitably insulated from the bulk of the fluid and measuring the resistance or capacitance of the container and fluid. This measuring can be combined with a measurement of the wetted surface of the container to give a value for the conductance or capacitance per unit surface area or unit volume of fluid. This value can help to identify the composition of the fluid.

Claims

1. Device for use in milking machines for determining the composition of a fluid (37) in a container (24) wherein said container (24) is in the path of a beam of electromagnetic radiation emitted by at least one source (23) and detected by at least one detecting means (31), said at least one detecting means (31) producing an output signal (43) which is dependent on the surface tension of said fluid (37), characterised in that said fluid (37) is retained in said container (24) by capillary action.

2. Device according to claim 1 characterised in that said hollow container (24) has straight sides (27', 27").

3. Device according to claim 1 characterised in that said hollow container (24) has at least one curved sides (27', 27' ').

4. Device according to any of the previous claims characterised in that said container (24) has two sides (27', 27") which intercept at an angle ╬▒ which is in the range of from 0┬░ to 30┬░.

5. Device according to any of the previous claims characterised in that said container (24) has two sides (27', 27") which intercept at an angle ╬▒ which is in the range of from 2┬░ to 15┬░.

6. Device according to any of the previous claims characterised in that said container (24) has a hollow triangular cross-section.

7. Device according to any of the previous claims characterised in that it comprises means for ejecting said fluid from said container (24).

8. Method of deterrmning the composition of a fluid characterised in that it comprises the steps of: allowing the fluid to enter by capillary action a hollow container (24) having two sides (27', 27") which intercept at an angle ╬▒ where ╬▒ is in the range of from 0┬░ to 30┬░; supplying a beam of electromagnetic radiation to one of said sides (27'); measuring the amount of said beam transmitted through said fluid and container (25) to the other said side (27"); comparing the measured amount of said beam transmitted against measurements from samples of known composition.

9. Method according to claim 8, characterised in that said comparing the measured amount of said beam transmitted against measurements from samples of known composition is performed by computer.