NL2010042C2 - A pressure sensor. - Google Patents

Abstract

The present invention relates to a pressure sensor for use in a milking system for milking a dairy animal. In one embodiment the pressure sensor includes a body, an elastic diaphragm in the body –having a measuring side and a reference side, wherein deflection of the diaphragm is indicative of pressure on the measuring side. The sensor includes a protrusion extending from a surface of the diaphragm, where the protrusion is configured as an optical barrier for a light source arranged to emit light, and a light detector arranged to detect emitted light and generate an output, wherein the light source and the light detector are arranged relative to the protrusion such that the output of the light detector is indicative of the deflection of the diaphragm. The protrusion, and at least a portion of the body surrounding the diaphragm, are made of the same material as the diaphragm.

Description

A pressure sensor TECHNICAL FIELD

The present invention relates to a pressure sensor. More 5 particularly the present invention relates to a pressure sensor for use in a milking system for milking a dairy animal.

BACKGROUND ART

In any milking system, it is important to ensure that teat cups are 10 properly connected to the teats of animals being milked. Improper connection may result in inefficient milking - if any milk at all may be extracted - and cause damage to the udder. If a teat cup becomes completely disconnected, there is also a risk that extraneous material within the milking environment will be sucked into the milk delivery system, which is highly undesirable.

15 The ability to detect these problems is especially important in an automated milking system, such as those controlled by a robot, where operators are not always present to observe an improper connection and readjust the teat cup.

One commonly used method for doing so measures sound within the 20 milking line and compares these measurements with predetermined reference values to determine whether present conditions within the line indicate that the teat cup is correctly connected to the teat. Document EP-0953829A provides an example of one such method based on this principle. Such methods suffer limitations due to the nature of the environment within the milking line. In 25 particular, the passage of liquid within the line creates significant levels of interference which makes obtaining consistent and accurate measurements difficult. Connection of the milking line to other elements within the milking plant also introduces other sources of noise.

Furthermore, such methods require placement of the sensor for 30 measuring sound within the milking line between the teat cups and milk receiver. The environment surrounding the teat cups is harsh, for example due to exposure to liquid (including cleaning chemicals), impact, and variation in temperature. Positioning of the sensor at this point is also not conducive to the generally desirable objective of minimising bulk and weight to the milking implement.

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An alternative method of determining cup connection quality is to measure the vacuum level near the teat cup. Vacuum levels in general are of interest in their own right with regard to assessing the efficiency of the milking process. However, the complexity and costs of existing sensors are not ideal for a 5 milking system - and improvements are still required.

Optical diaphragm based pressure sensing is a generally known technique. For example, PCT Publication No. WO 2006/042012 describes a pressure sensor in which the deflection of a diaphragm is determined from the amount of light reaching optical receivers from a light source. A barrier connected 10 to the diaphragm modifies the amount of light reaching the receivers according to the degree of deflection. However, while such a sensor may be technically capable of measuring pressure in a milking system, the complexity and precision required in manufacturing and assembling this sensor - particularly connecting the rigid barrier to the flexible diaphragm - would make it cost prohibitive to adopt 15 in a milking system.

US Patent No. 4,141,252 describes a pressure transducer in which a diaphragm is formed as an integral part with the supporting body, and movement of the diaphragm causes changes in capacitance. The integral nature of the diaphragm and surrounding structure may be beneficial with regard to eliminating 20 the need for an additional step to attach these parts to each other. However, for various reasons it may be desirable to use an optical based sensor in a milking environment, and it is not apparent as to how the capacitive displacement detection mechanism could be replaced with an optical system which does not retain the same problems as WO 2006/042012.

25 It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications, cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the reference states 30 what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms parts of the common general knowledge in the art, in New Zealand or in any other country.

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Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of 5 elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

10 DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a pressure sensor, including: - a hollow body defining an internal volume and an external volume; - an elastic diaphragm provided between the internal and external volume, 15 wherein deflection of the diaphragm is indicative of pressure within the internal volume of the body; - a protrusion extending from a surface of the diaphragm, wherein the protrusion is configured as an optical barrier; - a light source, and 20 - a light detector, wherein the light source is arranged to emit light, the light detector is arranged to detect emitted light and generate an output, and wherein the light source and the light detector are arranged relative to the protrusion such that the output of the light detector is indicative of the deflection of the 25 diaphragm, wherein the protrusion, and at least a portion of the hollow body surrounding the diaphragm, are made of the same material as the diaphragm.

According to another aspect of the present invention there is provided a milking system for milking a dairy animal including: 30 - at least one milk line connected to at least one teat cup for extraction of milk from the animal; - at least one pulsation airline configured to deliver varying levels of pressure to the teat cup; and - a pressure sensor as described above.

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By making the protrusion, the portion of the body surrounding the diaphragm, and the diaphragm of the same material, it is envisaged that a number of advantages may be provided - particularly with regard to manufacture. Where two different materials are to be adhered to each other, it may be difficult to find 5 an adhesive which bonds sufficiently with both materials. Similarly, if the parts are to be chemically welded together the solvent used must sufficiently dissolve both materials to allow for them to bond (if they are indeed compatible for such a process), or if thermally welded the materials must have similar melting points. By making the parts of the same material, these issues may be eliminated.

10 In the present application, "deflection of the diaphragm is indicative of pressure within the body" means that when the diaphragm deflects, the position thereof, but in particular of the protrusion thereon, with respect to the light source and light detector will change, thus screening off a different amount of light. This will in turn lead to a different reading from the light detector, from which changed 15 reading the pressure may be inferred.

In particular, the protrusion extends from the surface of the diaphragm away from the body. For example, in cases where dirt and other contaminants, and above all any interfering light are prevented from reaching the protrusion and the optical components (light source and light detector) by a 20 housing or the like around the pressure sensor, the protrusion and the optical components may be positioned on the outside of the hollow body. The hollow body could in such cases be a tube, such as a milk line, an airline, or the like. In alternative embodiments, the pressure sensor's hollow body could be a substantially closed-off body, which itself can be positioned in another hollow 25 body in which a pressure is to be measured. For example, the pressure sensor is then a closed-off housing with, as part of its outer wall, the diaphragm. The pressure sensor can then be inserted, as a kind of plug, into a wall of another hollow body such as a milk line or airline. An advantage of this embodiment is that the optical parts as well as at least one side of the diaphragm can be optimally 30 protected against contamination and indirect light. Furthermore, the amount of gas inside the hollow body of the pressure sensor is in principle fixed, thus making pressure measurements and calibrating easier. Flowever, manufacture and servicing is less straightforward.

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Note in general that the diaphragm will form a (part of a) barrier between a body of fluid on one side of the diaphragm and a body of fluid on the other side of the diaphragm. At least one of these bodies of fluid, which may each comprise gas and/or liquid, is closed off with respect to the other, as otherwise no 5 pressure difference between the two can arise that causes the diaphragm to deflect in an attempt to equalise the pressure. In an example mentioned above, the hollow body is a completely sealed body, with a known amount of gas, as a kind of stand-alone unit that can be inserted into the wall of a body in which the pressure is to be determined, such as the already mentioned milk line. If an 10 external pressure changes, the diaphragm will deflect, changing the volume of the sealed body of gas, to thereby change its pressure and making it substantially equal to the (new) outside pressure. Measuring a pressure is now an indirect measurement, based on the equality of the actual pressure to be determined and the internal pressure after equalisation of these pressures. In other examples, the 15 protrusion moves with the deflecting diaphragm in ambient pressure. This deflection is brought about by a pressure change in the body into whose wall the diaphragm has been inserted. The body itself can now be a milk line or the like, or at least a part thereof such as a length of the line. For many practical purposes, this ambient pressure is assumed to be substantially constant, or it is the pressure 20 difference between ambient and the sealed-off body which is relevant anyway. It is contemplated that both situations fall within the concept of "hollow body".

In a preferred embodiment the portion of the body surrounding the diaphragm, the diaphragm, and the protrusion are moulded as a unitary part.

In doing so it is envisaged that the problems discussed above may 25 be further alleviated. Additionally, manufacturing variations between sensors may be greatly reduced in a number of ways. While all manufacturing processes require a degree of tolerance, reducing such variation can greatly improve the ease of calibrating sensors. For example, moulding the parts eliminates the risk of the protrusion being placed in an incorrect position or at an incorrect angle 30 relative to the diaphragm. As well as affecting the flexing properties of the diaphragm, misalignment could also create difficulties with regard to the accuracy of the optical detection system.

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Further, any adhesive, welds, or other form of connection may variably affect the flexibility of the diaphragm, creating inconsistencies between sensors and making calibration more problematic.

Additional benefits may also be gained with regard to efficiencies in 5 supply chain and inventory management, with only a single material (and later part) requiring ordering, handling and storage.

The material for the diaphragm (and thus portion of the body and protrusion) should preferably be food safe for use in a milking environment, retain stable flexibility over a temperature range in the order of 0-100°C, have 10 repeatable flexibility between batches, have good resistance (particularly with regard to flexibility) to chemicals - both acid and alkali, and be opaque to reduce ambient light the light detector is exposed to.

Further, the material should preferably be capable of forming a diaphragm having the following characteristics: 15 - less than 10 mm (preferably 7 mm) in diameter in order to be used within a typical 14 mm inner diameter milk line without substantially disrupting the flow of fluid past the sensor; - substantially 1 mm thick to assist in ease of tooling and manufacture, and 20 - capable of deflecting by approximately 0.5 mm (to provide sufficient dynamic range) when exposed to a pressure differential of substantially 50 kPa (typical maximum milking vacuum).

It should be appreciated that the values provided above are illustrative of a preferred embodiment, and not intended to be limiting to the 25 invention as a whole.

Preferably the diaphragm is made from a silicone rubber. Silicone rubbers are commonly used in parts within milking systems. They have better aging characteristics than natural rubber, and flexibility is relatively stable with respect to temperature.

30 Preferably the silicone rubber has a cured hardness of substantially 48 Shore A, particularly within a temperature range of substantially 0-100°C. An example of such a silicone rubber is the silicone compound sold by Silclear Limited (UK) at the time of filing as “Silclear Black Η-Flex 48-m-C”.

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It should be appreciated that reference to the material being silicone rubber is not intended to be limiting, and that other materials -particularly elastomers- may be used in the present invention.

Preferably the protrusion extends from the geometric centre of the 5 diaphragm, and the cross-section of the protrusion at its junction with the diaphragm may be the same shape as the surface of the diaphragm from which it extends.

In doing so, it is envisaged that the behaviour of the diaphragm may be made more predictable, as the effect of the protrusion on flexibility of the 10 diaphragm is constant in all directions. The inventors have also identified that irregular shaped protrusions may also reduce the degree to which the diaphragm deflects under pressure, which affects the dynamic range of the sensor.

As a result, in a preferred embodiment the diaphragm is circular, and the protrusion is cylindrical. This may provide an easily moulded geometrical 15 shape having the desired symmetry described above.

In a preferred embodiment the body includes an aperture between an outer surface of the body and the inner surface, and the portion of the body surrounding the diaphragm forms a support structure configured to fit within the aperture. This relates to the diaphragm being mounted in a support structure for 20 handling, the support structure being fitted into the aperture, and the combination of the support structure and the diaphragm sealing the aperture.

Preferably the support structure is configured to form a seal against the aperture. There are points in milking systems which open into a milk line or airline and require plugging to seal them. It would be useful if a pressure sensor 25 might be used in place of such plugs in order to take advantage of such openings, and provide additional functionality to the plug which would be required anyway. For example the milking system may include sensors utilising lengths of tube including a well, such as that illustrated in US Patent Application Publication No. 2010/0273273. One method by which such tubes are manufactured results in an 30 aperture being formed above the well which requires sealing.

It is envisaged that an embodiment of the present invention in which the support structure and diaphragm form a distinct part to the remainder of the body may be used as a plug in such an aperture.

8

It is envisaged that the example of a tube having a well for use in other sensing applications may be particularly applicable, as proximity to the higher level processing, communication, and power supply electronics of the associated sensor(s) may allow the electronics of the pressure sensor itself to be 5 simplified.

It should be appreciated that this is not intended to be limiting, and that the entire body may be made from the same material as the diaphragm. In doing so it is envisaged that standard milk line or airline connectors may be inserted into the ends of the body itself, and being made of a resilient material to 10 achieve the desired flexibility may seal against those connectors.

Preferably the portion of the body surrounding the diaphragm, i.e. the support structure, is of sufficient thickness to resist deformation of the support structure due to pressure within the hollow body below substantially 60 kPa where the deformation which would negatively affect linearity of the output of the light 15 detector.

It is envisaged that the portion of the body surrounding the diaphragm, i.e. the support structure, may at least substantially three times the thickness of the diaphragm in order to provide this resistance to deformation. It should be appreciated that this is not intended to be limiting, and may vary with 20 the material choice and maximum pressure the sensor is to be exposed to.

It is envisaged that the surface of the support structure exposed to the interior of the hollow body may be shaped to be substantially continuous with the inner surface of the body. In particular, it is envisaged that the support structure may be curved to substantially align with the curvature of the line in which it is 25 inserted. This may reduce the invasiveness of the structure and the associated risk of turbulence being produced in milk flowing through the line. This is generally desirable in a milk line in order to reduce damage to the milk or avoid creating a point where milk residue builds up and contaminates the line. Further, turbulence may be particularly undesirable in sections of the milk line where other 30 types of sensing are to be performed.

According to another aspect of the present invention there is provided a pressure sensor for use with a hollow body including an inner surface, an outer surface, and an aperture therebetween, the pressure sensor including: 9 - an elastic diaphragm contiguous with the inner surface of the body, wherein deflection of the diaphragm is indicative of pressure within the body; - a light source and a light detector arranged relative to the diaphragm 5 such that the output of the light detector is indicative of the deflection of the diaphragm, and - a support structure surrounding the diaphragm, wherein the support structure is made of the same material as the diaphragm and configured to fit within the aperture.

10 Herein, the pressure sensor may comprise, as described above, a protrusion extending from a surface of the diaphragm away from the body or inside the body, i.e. towards the inside of the body.

According to another aspect of the present invention there is provided milking system for milking a dairy animal including: 15 - at least one milk line connected to at least one teat cup for extraction of milk from the animal; - at least one pulsation airline configured to deliver varying levels of pressure to the teat cup; and - a pressure sensor according to claim substantially as described 20 above, wherein the hollow body is positioned in either the milk line or the airline.

In the aspect of the invention described directly above, it should be appreciated that features such as the protrusion being made of the same material as the diaphragm, or being made as a unitary part may be preferred but not 25 essential to working of the invention. It should also be appreciated that the various features discussed herein, in particular all those mentioned below, may be applied to the different mentioned aspects of the present invention. Reference to features of the body may be applied to the support structure, and vice versa.

Preferably the support structure includes a recess surrounding the 30 protrusion configured to receive the light source and the light detector. In doing so, the effects of ambient light on the output of the light detector may be reduced. In exemplary embodiments the light source and light detector may be mounted on a PCB to be seated across the top of the recess, further physically isolating the light source and light detector from external sources of light.

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This may also assist in reducing the physical dimensions of the sensor, which is generally desirable in a milking system where numerous components may be required to be positioned within a limited space.

In embodiments, the pressure sensor comprises an opaque 5 covering, arranged to shield ambient light from the optical detector. As a useful example, the covering is contiguous with the support structure.

In a preferred embodiment the recess is configured to receive the light source on one side of the protrusion, and the light detector on the other side of the protrusion. In such a configuration, deflection of the diaphragm will be 10 proportional to the transmitted light received by the light detector. It should be appreciated that other arrangements are envisaged. For example the recess may be configured to allow the detector and source to be positioned side by side, with reflected light from the protrusion used to gauge deflection of the diaphragm.

In order to assist in ease of manufacture, it is envisaged that the 15 light source and the light emitter may respectively be positioned at substantially the same distance from the protrusion. This may allow the PCB on which the components are mounted to be installed in either orientation without affecting operation.

In a preferred embodiment the light source emits light having a 20 wavelength substantially between 450nm to 495nm. Preferably the light source is a light emitting diode (LED), and the inventors have identified that blue LEDs are less affected by temperature than infrared equivalents, while also being readily available in a desirable package and having greater luminous intensity than green equivalents.

25 It should be appreciated that this is not intended to be limiting, and that other types of light source operating in different sections of the spectrum may be used with the present invention.

It should be appreciated that the output of the light detector may be processed further at the sensor itself, or transmitted using any suitable means 30 known to a person skilled in the art for further processing.

Further, the pressure sensor may be arranged or positioned to output a signal indicative of the pressure in one of the milk line or the air line.

BRIEF DESCRIPTION OF THE DRAWINGS

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Fig. 1 is a diagrammatic view of a milking system according to one aspect of the present invention;

Fig. 2A is a side cross section view of an exemplary pressure sensor according to one aspect of the present invention; 5 Fig. 2B is a perspective view of the exemplary pressure sensor;

Fig. 2C is a end cross section view of the exemplary pressure sensor;

Fig. 3 is a side cross section view of an exemplary pressure sensor according to an aspect of the present invention; 10 Fig. 4 is a graph plotting diaphragm deflection against thickness;

Fig. 5 is a graph plotting coefficient of determination against diaphragm thickness;

Fig. 6 is a graph plotting relative sensor output against position;

Fig. 7 is a graph plotting sensor output voltage against vacuum; 15 Fig. 8A is a side cross section view of an exemplary pressure sensor according to a further aspect of the present invention;

Fig. 8B is a perspective view of the exemplary pressure sensor; and

Fig. 9 is a perspective view of a pressure sensor unit 20 according to a further aspect of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates a milking system (generally indicated by arrow 1) for milking a dairy animal (not illustrated). The device 1 includes four teat cups 2, 25 3, 4, 5, each connected to a pulsator system 6 by way of individual airlines, exemplified by airline 7 which is associated with teat cup 2. The vacuum line 8 for the pulsator system 6 is connected in a usual manner to a vacuum pump with balance tank (not illustrated).

Each teat cup 2, 3, 4, 5 may be automatically connected and 30 disconnected from a teat of a cow by means of a milking robot (not illustrated), although it should be appreciated that the teat cups may be applied manually.

The milk extracted by each teat cup 2, 3, 4, 5 is supplied via separate milk lines, exemplified by milk line 9 which is associated with teat cup 2, to a milk jar 10 and ultimately a milk tank (not illustrated).

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Each teat cup 2, 3, 4, 5 is provided with a pressure sensor, exemplified by pressure sensors 11 and 12, within their respective airlines and milk lines - for example airline 7 and milk line 9.

The output of sensors 11 and 12 are sent to a processor 13. The 5 processor 13 is also in communication with the pulsator system 6. It should be appreciated that the signals communicated from the sensors 11 and 12 and pulsator system 6 may include data identifying the respective sensor 11 or 12, pulsator within the pulsator system 6, and/or teat cup 2, 3, 4, 5. Data transmitted to the processor 13 may be stored in memory 14, together with other data used in 10 calculations performed by the processor 13, as known in the art.

Fig. 2A illustrates a pressure sensor 200 for use in a milking system such as that illustrated by Fig. 1. The sensor 200 includes a body 201 made of silicone rubber, and including a recess 202 therein. The recess 202 is moulded to create a circular diaphragm 203 at the base of the body 201. A cylindrical 15 protrusion 204 extends from the geometric centre of the diaphragm 203 into the recess 202.

Under pressure (as will be described further below), the diaphragm 203 deflects, causing the protrusion 204 to move up and down within the recess 202. The portion of the body 201 surrounding the diaphragm 203 - such as 20 portion 205 - is at least three times thicker than the diaphragm 203 in order to resist deformation of the support structure due to pressure within the hollow body below substantially 60 kPa where that deformation which would negatively affect linearity of the output of the light detector.

Referring to Fig. 2B, the body 201 includes a depression 206 surrounding the 25 recess 202. Returning to Fig. 2A, a PCB board is positioned within the depression 206 such that the recess 202 is physically isolated from external light sources. A light source in the form of a blue LED 208, and a light detector in the form of a photodiode 209, are mounted to the PCB facing each other with the protrusion 204 positioned between them. Arrow 210 illustrates the path of light 30 transmitted from LED 208 to the photodiode 209.

The length of the protrusion 204 and positioning of the optical components is such that substantially half of light output by the LED 208 is blocked when the diaphragm 203 is deflected substantially halfway from a maximum deflection in order to maximise the dynamic range of the sensor. The 13 position of the protrusion 204 at maximum deflection is illustrated by the dashed box 211. It should be appreciated that the relative degree of deflection is exaggerated in order to more clearly illustrate the interaction of the various components.

5 Fig. 3 illustrates a section of a milk line 300 in which the pressure sensor 200 may be used. The section 300 is moulded to form a well 301 for the collection of milk which may be sampled or have various analytical techniques applied to it. As part of the moulding process, an aperture 302 between outer surface 303 and inner surface 304 is formed above the well.

10 The pressure sensor 200 may be inserted into the aperture 302 as a convenient location for exposure to the milk line (for example milk line 9 of Fig. 1) to determine vacuum pressure in same, as well as sealing the aperture 302.

Referring to Fig. 2C, the body 201 surrounding the diaphragm 203 and exposed to the interior of the section 300 is shaped to be substantially 15 continuous with the inner surface 304. In particular, it may be seen that exposed surface 212 is curved to substantially align with the curvature of the section 300.

Fig. 4 and Fig. 5 illustrate the range and linearity of deflection of a pressure sensor configured substantially as illustrated in Fig. 2A, Fig. 2B, Fig. 2C, and Fig. 3, testing the effects of hardness of the material used to mould the body. 20 The diaphragm 203 used to produce these results was 7.4±0.1 mm in diameter. This was desirable in order to allow use of the sensor 200 within a tube having an inner diameter of 14 mm. The protrusion 204 was 2.5 mm in diameter, being the smallest size which blocked the active surface of the photodiode 209.

25 It should be appreciated that the values provided above are illustrative of an experimental embodiment, and not intended to be limiting to the invention as a whole.

Two silicone rubbers were tested across three diaphragm thicknesses which were anticipated as being across the minimum desirable 30 thickness range for ease of manufacture and robustness. The rubbers had an advertised cured hardness of approximately 48 Shore A and 68 Shore A respectively.

Referring to Fig. 4, it may be seen that the 48 Shore A sensor achieved a greater degree of deflection that the 68 Shore A version. Further, 14 from Fig. 5 it may be seen that the linearity of deflection was greater for the softer material - particularly across the desired diaphragm thickness range.

As such, further experiments were conducted using a diaphragm having a thickness of 0.8 mm thickness and being moulded from the silicone 5 compound sold by Silclear Limited (UK) at the time of filing as “Silclear Black IH-Flex 48-m-C”.

Fig. 6 illustrates the relative output of the photodiode 209 against deflection of the protrusion 204. It may be seen that the linear range of the optical components was slightly less than 2 mm. Given that the desired operating range in terms of 10 deflection is 0.5 mm (~25% of the linear range) over 50 kPa, this leaves some 1.5 mm for variation in assembly. Across the linear range the voltage output was between 0.5 V to 4.0 V, which corresponds to 0.875 V output across the desired operating range. Using a 12-bit analogue to digital converter (ADC), a 0.07 kPa resolution may be achieved, which was determined to be well within the resolution 15 required for measurements within the context of a milking system.

Referring to Fig. 7, it may be seen that vacuum level is linearly correlated with the voltage output of the pressure sensor 200. Estimated vacuum (Vac) may be estimated from the ADC value using the formula:

Fgc = Fac.p2(Kp~g'Pl) 20 where VaCv2 is the reference vacuum level (non-atmosphere) at which is determined (provided by a vacuum sensor at milk jar 10); Uv is the sensor 200 ADC value; Kvi is the low vacuum calibration value (the ADC value at atmospheric pressure); and Kv2 is the High vacuum calibration value (the ADC value at VaCv2 minus Kvi).

25 Fig. 8A and 8B illustrates an alternative structure for a pressure sensor 800 according to another aspect of the present invention. The sensor 800 includes a body 801 made of silicone rubber. A recess forming a diaphragm and protrusion substantially as illustrated with regard to Fig. 2A is moulded into the body 801 at region 802. While not illustrated, an LED and photodiode may 30 positioned within the recess and operated substantially as discussed above.

Standard milk line or airline connectors may be inserted into the ends 803 and 804 of the body 801, which being made of a resilient material seals against those connectors.

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Fig. 9 illustrates a pressure sensor unit 900 having a housing 901 configured to receive four pressure sensor bodies 800 - for example one for each milk line associated with teat cups 1, 2, 3, 4 of Fig. 1. The housing 901 may contain power supply, higher level processing, and/or communications electronics 5 which service all of the respective pressure sensors.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims (16)

A pressure sensor, comprising: a hollow body that defines an internal volume and an external volume; an elastic dividing wall (English: diaphragm) provided between the external and internal volume, wherein deflection of the intermediate wall is an indication of the pressure within the internal volume of the body; a protrusion protruding from a surface of the partition wall, the protrusion being arranged as an optical barrier; a light source, and a light detector, wherein the light source is adapted to emit light, the light detector is adapted to detect emitted light and to generate an output, and wherein the light source and the light detector are arranged relative to the protrusion that the output of the light detector is an indication of the bending of the partition wall, wherein the protrusion, and at least a portion of the hollow body surrounding the partition wall, are made of the same material as the partition wall. 2. Pressure sensor according to claim 1, wherein the part of the body surrounding the partition wall, the partition wall and the protrusion are formed as a unitary part. Pressure sensor according to claim 1 or 2, wherein the partition is made of a silicone rubber. 4. Pressure sensor as claimed in any of claims 1 to 3, wherein the protrusion 25 protrudes from the geometric center of the intermediate wall, and the cross-section of the protrusion on its connection to the intermediate wall has the same shape as the surface of the intermediate wall from which it protrudes . 5. Pressure sensor as claimed in any of the claims 1-4, wherein the part of the body surrounding the partition is of sufficient thickness to withstand deformation of the part of the body due to pressure within the hollow body below substantially 60 kPa , where the distortion will adversely affect the linearity of the light detector output. Pressure sensor according to claim 5, wherein the part of the body surrounding the partition has at least substantially 3 times the thickness of the partition. The pressure sensor of any one of claims 1 to 6, wherein the aperture 5 is present between an outer surface of the body and an inner surface of the body, and the part of the body surrounding the partition forms a support structure adapted to be disposed within the opening to fit. The pressure sensor of claim 7, wherein the support structure is arranged to form a seal against the opening. The pressure sensor of any one of claims 1 to 8, wherein the body comprises a recess that surrounds the protrusion and is adapted to accommodate the light source and the light detector. 10. Pressure sensor according to claim 9, wherein the recess is adapted to accommodate the light source on one side of the protrusion, and the light detector on the other side of the protrusion. The pressure sensor of any one of claims 1-10, wherein the light source and the light meter (read: light detector) are also positioned substantially the same distance from the protrusion. 12. Pressure sensor according to claims 1-11, wherein the protrusion is positioned such that substantially half the light output of the light source is blocked when the partition wall is bent substantially halfway through a maximum bending. 13. Milking system for milking a dairy animal comprising: at least one milk line connected to at least one teat cup for extracting milk from the animal; at least one pulsation air line adapted to provide varying pressure levels to the teat cup; a pressure sensor according to any of claims 1-12. 14. Milk system according to claim 13, wherein the pressure sensor is adapted to output a signal which is an indication of the pressure in one of the milk line or the air line. 15. Pressure sensor for use with a hollow body comprising an inner surface, an outer surface, and between them an opening, the pressure sensor comprising: an elastic intermediate wall that connects to the hollow body, 5. a protrusion protruding from a surface of the intermediate wall, the protrusion is arranged as an optical barrier, a light source and a light detector which are arranged with respect to the protrusion such that the output of the light detector is an indication of the bending of the partition wall, 10. a support structure that surrounds the partition wall, the support structure is made of the same material as the intermediate wall and is adapted to fit within the opening, such that the pressure sensor seals the opening, whereby bending of the intermediate wall is an indication of pressure within the body. A milking system for milking a dairy animal comprising: at least one milk line connected to at least one teat cup for extracting milk from the animal; at least one pulsation air line adapted to provide varying pressure levels to the teat cup; and 20. a pressure sensor according to claim 15, which is placed in a wall of the milk line or the air line.