GB2437174A

GB2437174A - Measuring the conductivity of fluid flowing through a conduit

Info

Publication number: GB2437174A
Application number: GB0707040A
Authority: GB
Inventors: Jolyon Richard Tidmarsh; Lee Francis Ackrell
Original assignee: FUTURETEC TECHNOLOGIES Ltd
Current assignee: FUTURETEC TECHNOLOGIES Ltd
Priority date: 2006-04-11
Filing date: 2007-04-11
Publication date: 2007-10-17
Also published as: GB0707040D0; WO2007116223A1

Abstract

This invention relates to the measurement of the properties of liquids flowing through conduits. It is particularly, but not exclusively, concerned with measuring the properties of a beverage such as beer flowing through a dispensing system. It is known to measure the conductivity of a beverage, for example to assess its quality, to distinguish between different types of beverage, or to determine when a supply needs replenishing (which is recognised by the presence of excessive gas in the beverage). Known systems use pairs of electrodes, which may be disposed at different locations throughout the conduit, and there is a risk that there may be interference between different electrical sources, and that there will be ground loop effects, which will effect the accuracy of the measurement. The present invention has first and second electrode means within the conduit, the first electrode means comprising a first electrode, and the second electrode means comprising second and third electrodes disposed on opposite sides of the first electrode. The conductivity of the fluid is determined from a measurement of the current flowing between the first and second electrode means. The advantage of the present invention is that the second and third electrodes effectively shield the first electrode, and reduce ground loop currents.

Description

Fluid Property Measurement

Field of the Invention

This invention relates to the measurement of the properties of liquids flowing through conduits. It is particularly, but not exclusively, concerned with measuring the properties of a beverage such as beer flowing through a dispensing system.

Background to the Invention

It is known to measure the conductivity of a beverage, for example to assess its quality, to distinguish between different types of beverage and so forth. Typically, this is done by providing two electrodes which are connected to a source of alternating electric current. The use of direct current is possible but is likely to cause significant electrolysis effects. A typical frequency used when measuring the conductivity of a beverage such as beer is around 30 kHz, and current levels may be, for example, of the order of 10 j.tA rms.

In a beverage dispensing system, electrodes for different purposes may be provided at various locations. For example, measurements may be taken at one location to determine when there is excessive gas in the beverage line, indicating that a supply container such as a beer keg needs changing; and at another location to analyse the quality of the beverage. There is a risk that there may be interference between different electrical sources, and that there will be ground loop effects. Such factors may give false readings, meaning for example that beverage of an inappropriate quality may get through, kegs will be changed over prematurely, or that false alarms will be given. * * **.

Object of the Invention The present invention seeks to provide a solution to the above problems. The * present invention seeks to provide an improved beverage dispensing system which can overcome or ameliorate the above problems.

Statement of the Invention

In accordance with a first aspect of the invention, there is provided a method of measuring the conductivity of a fluid flowing through a conduit, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, an electrical current source is connected to the first and second electrode means to cause an electrical current to flow between the first and second electrode means, and the electrical current is measured; wherein the first electrode means comprises a first electrode and the second electrode means comprises second and third electrodes disposed on opposite sides of the first electrode.

In one preferred arrangement, the second electrode is disposed up stream of the first electrode and the third electrode is disposed down stream of the first electrode. In one embodiment, each electrode is an elongate conductive member, such as a metallic tube. In such an arrangement, the first, second and third electrodes may all extend across a diameter of the conduit, being spaced along the axis of the conduit and preferably being parallel to each other.

It has been found that the second and third electrodes shield the first electrode from external influences, and substantially reduce or eliminate the effects of ground loops or other electrical current sources electrically connected to the conduit.

It will be appreciated that the first electrode means may comprise other electrodes in "S addition to the first electrode, and the second electrode means may comprise other isS electrodes in addition to the second and third electrodes. *5 * S iSs

:. Preferably, the first electrode means and second electrode means are connected to a source of alternating current, preferably a low impedance signal source. Typically, : this could be, for example, around a 30 kHz source with a rated RMS value of 10 pA. The first electrode means may be connected to a high input impedance amplifier and the total RMS current is measured. From this the conductivity of the liquid can be measured.

It will be appreciated that the conductivity may not be indicated as such. For example, the system could be suitably calibrated and provide a warning if the conductivity rises above a predetermined value and / or falls below a predetermined value. Although the system may work with data indicative of, or dependent on, the conductivity of the fluid, the value of the conductivity as such may not be relevant in all circumstances.

The fluid may be a liquid such as a beverage being dispensed, for example beer. I0

In a preferred arrangement, current is only supplied to the electrode means whilst the fluid is flowing. Preferably, current is only supplied to then electrode means for a predetermined period whilst the fluid is flowing. For example, the electrode means may be energised for only about 100 ms during fluid flow. These measures reduce effects of electrolysis of the fluid, which might for example alter the taste of a beverage such as beer. In the context of the supply of beverage, flow will be intermittent depending on when it is desired to dispense the beverage. However, in the case of a constantly flowing fluid, such as in the manufacture of a beverage. The measurements may be taken for relatively short periods of time at intervals whilst the fluid is flowing.

Such arrangements are inventive in their own right, and thus viewed from another aspect the present invention provides a method of measuring the conductivity of a fluid flowing through a conduit, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, an electrical current source is connected to the first and second S..

electrode means to cause an electrical current to flow between the first and second electrode means, and the electrical current is measured; wherein the method comprises the steps of detecting fluid flow and connecting the electrical current source to the first and second electrode means for a relatively short period of time during fluid flow.

Viewed from another aspect, the present invention provides a method of measuring the conductivity of a fluid flowing through a conduit, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, a electrical current source is connected to the first and second electrode means to cause an electrical current to flow between the first and second electrode means, and the electrical current is measured; wherein the method comprises the steps of connecting the electrical current source to the first and second electrode means for relatively short periods of time during fluid flow, spaced at relatively long intervals.

In accordance with a still further aspect of the invention, there is provided an additional method step of characterising a fluid by assessment of the optical characteristics of the fluid flowing through the conduit, wherein there is provided a light source and a light receiver; the light source and light receiver being spaced apart by an optical path length within the conduit the method comprising the step of transmitting light from the light source and measuring a characteristic of the light received by the light receiver in combination with measurement of the electrical conductivity of the fluid. The optical transmitters can be wavelength specific. The optical transmitters and optical receivers can be arranged about the walls of one portion of the conduit. The optical transmitter can comprises a collimated light source and the optical receiver can comprise a sensor or sensors to determine angular deviation of the collimated beam.

In general, during the relatively short periods of time alternating current will be supplied to the electrodes. ** * ***

Brief description of the Figures

Some preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which: S.. * 30

Figure 1 shows a first embodiment according to the invention; Figure 2 illustrates how a measured parameter can vary with temperature; Figure 3 shows a variation of the arrangement disclosed in Figure I; and, Figure 4 shows the arrangement of Figure 3 with a layer 10 of bioflim built up on an inner wall of the sensor.

Figure 5 shows a first embodiment according to the invention; Figure 6 another embodiment according to the invention; Figures 6a & b show, respectively, plan and cross sectional views of a further embodiment; Figure 7 comprises a chart comparing optical transmissivitY versus electrical conductivity for a selection of liquids typically used in a beverage supply line;

Detailed Description of the Preferred Embodiments

There will now be described, by way of example only, the best mode contemplated by the inventor for carrying out the present invention. In the following description, numerous specific details are set out in order to provide a complete understanding to the present invention. It will be apparent to those skilled in the art, that the present invention may be put into practice with variations of the specific.

Figure 1 is a diagrammatic view showing first electrode 1, second electrode 2 and third electrode 3 in the form of parallel steel tubes each extending across a diameter of a conduit 4 for carrying a liquid which will flow in the direction of arrow 5, the three electrodes being spaced along the axis of the conduit. The first electrode is connected to one side of a source of alternating current, and the second and third electrodes are connected to the other side of the source. * ** S.

Most of a typical beer line is insulated in an actively cooled dispense line such that the entire dispense line is maintained at a temperature significantly lower than the 4. room ambient temperature, e.g. 3 degrees C. The final section of the line, usually within the dispense font, or the last 10cm or so before it, is usually not cooled. As a * result, the temperature of the beverage within this section usually rises towards room temperature between dispense events.

The conductivity of a beverage has been found to be a function of the temperature of the beverage. Furthermore, it has been found that the conductivity versus temperature characteristic varies between different types of beverage, e.g. between different brands of beer. The same behaviour may apply to other parameters that can bemeasured.

Figure 2 illustrates how a measured parameter can vary with temperature.

Accordingly, by measuring the conductivity or another parameter of a fluid at two or more temperatures, a "fingerprint" of the beverage can be collected. This can then be used to differentiate between different brands of lager, for example. Furthermore, it may be possible to use this measurement to determine the condition of the brand being dispensed, and to indicate whether it is fit for consumption.

This has broad application within the beverage dispense industry. It is well known that product substitution can occur -a cheap brand is served through a dispense font labelled with an expensive brand.

Such a system can be used in the context of the electrode arrangement described earlier, with other arrangements for measuring conductivity, or with arrangements for measuring other parameters such as capacitance.

Thus, view from one aspect of a further invention there is provided a method of obtaining data which is characteristic of a liquid which is cooled and dispensed through a dispensing line, comprising the steps of measuring a parameter of the liquid at a first point in the dispensing line, and measuring the same parameter of the liquid at a second point in the dispensing line where the temperature of the liquid is different from the temperature at the first point.

Preferably, the liquid is a beverage such as beer. The first point may be in a cooled portion of the dispensing line, and the second point may be in a portion of the dispensing line which is not cooled, for example adjacent the point of dispensing.

The parameter may be the conductivity of the liquid.

The values of the parameters at the two points may be compared with stored values characteristic of the liquid, or a fimction may be calculated using the parameter values, which is compared with a stored value of the function. The values of the parameters are thus used, directly or indirectly, to determine whether the liquid is substantially of the type and / or quality intended.

The quality of draught dispensed beverages is influenced by the cleanliness of the dispense lines. Since beer is a food, a bioflim will grow on any surface in contact with the beer. Over time, the bioflim will form a hard, brittle, protective coating over itself. To reduce the build up of biofllm, line cleaning must be carried out regularly. However, line cleaning is a laborious and wasteful process. The industry recommendation is that lines should be cleaned every 10 days or so. However, it is widely known that lines are frequently not cleaned correctly, and that the interval between cleaning may be extended to save costs, for example to 28 days or more.

It is desirable to be able to measure the amount or presence of biofilm growth, since this can be used to indicate when the dispense line is truly "dirty" and needs cleaning. Furthermore, it is desirable to be able to measure whether the line has been correctly cleaned.

The essence of a further invention is the realisation that the conductivity of the bioflim will be different to that of the beverage flowing through a conduit, such as beer.

Viewed from one aspect of another invention, there is provided a method of determining the extent of film built up on the inside of a conduit through which a liquid is flowing, comprising the step of measuring conductivity within the conduit at a location closely adjacent the inside surface of the conduit.

The measurement of conductivity may be carried out using surface electrodes which project from the inside surface of the conduit by a short distance, for example of the same order as the thickness of film that will be built up.

When the conduit is clean, the conductivity adjacent the surface of the conduit will be substantially the same as the bulk conductivity of the liquid in the conduit. As the bioflim builds up, it will cover the surface electrodes and so the measurement will tend towards the conductivity of the bioflim, rather than the conductivity of the bulk liquid.

Preferably, the bulk conductivity of the liquid is also measured by electrodes disposed in the bulk of the liquid. This may be at a position in the conduit which where the surface measurements are being carried out, or at least one where the temperature and flow conditions will be substantially the same.

By measuring both the surface and bulk conductivities, any variation due to the conductivity of the liquid being used can be eliminated, and the effects of temperature variations can also be reduced.

It may be possible to remove the need to measure the bulk conductivity. By measure the conductivity using the surface electrodes at two different frequencies, it may be possible to deduce the bulk and surface conductivities. This may be possible since the bioflim will have a different conductivity versus frequency characteristic from that of the bulk liquid.

Preferably the measurement of the surface conductivity is carried out using three or more electrodes, in the manner described earlier. The measurement of bulk conductivity may also be carried out as described earlier.

* 30 Viewed from another aspect, the present invention provides a method of measuring conductivity within a conduit through which fluid is flowing, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, a electrical current source is connected to the first and second electrode means to cause an electrical current to flow between the first and second electrode means, and the electrical current is measured; wherein the first electrode means comprises a first electrode and the second electrode means comprises second and third electrodes disposed on opposite sides of the first electrode.

Viewed from another aspect the present invention provides a method of measuring conductivity within a conduit through which fluid is flowing, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, a electrical current source is connected to the first and second electrode means to cause an electrical current to flow between the first and second electrode means, and the electrical current is measured; wherein the method comprises the steps of detecting fluid flow and connecting the electrical current source to the first and second electrode means for a relatively short period of time during fluid flow.

Viewed from another aspect, the present invention provides a method of measuring conductivity within a conduit through which fluid is flowing, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, an electrical current source is connected to the first and second electrode means to cause an electrical current to flow between the first and second electrode means, and the eLectrical current is measured; wherein the method comprises the steps of connecting the electrical current source to the first and second electrode means for relatively short periods of time during fluid flow, spaced at relatively long intervals. I..

I

The conductivity may the surface conductivity adjacent the inside surface of the conduit, or the bulk conductivity of the fluid within the conduit. In one preferred arrangement there is a set of first and second electrode means closely adjacent the inside surface of the conduit for measuring conductivity closely adjacent the surface, and a second set of first and second electrode means within the bulk of the fluid flowing through the conduit.

Figure 3 shows a variation of the arrangement disclosed in Figure 1, in which there are three electrodes 6, 7 and 8 provided on the inside surface 9 of the conduit 4. The inner electrode 6 is connected to one side of a source of alternating current, and the outer electrodes 7 and 8 are connected to the other side of the source. In this way, conductivity adjacent the surface 9 of the conduit 4 can be measured. Figure 4 shows the same arrangement, but with a layer 10 of bioflim built up on the inner conduit wall 9. There will be some bioflim growth on the central electrodes 1,2 and 3 which measure the bulk conductivity, but this is omitted for clarity.

Figure 5 details part of a further embodiment of the invention wherein there is an optical measurement system (in addition to the three electrodes, not shown) is comprising a fluid flow conduit with an optical transmitter 01 disposed on the wall of the conduit. The wall may have an aperture to enable the transmitter to comprise part of the wall of the conduit; alternatively the wall comprises a window operable to allow passage of required wavelengths of light from the transmitter to an optical receiver OR, similarly disposed within or upon the wall of the conduit. In conjunctiOn with measurement electronics the receiver can determine how much transmitted light has been absorbed. This can be determined in terms of the total amount of light or in relation to a range of wavelengths. Conveniently, the light source may be energised during fluid flow. I,

ConvenientlY, in a first further example, the light source comprises an LED light source at a nominal wavelength of operation of 428nm. Other LEDs operating at 4. different wavelengths can be used, for example, a 370nm LED may be more suitable. Different wavelengths are capable of providing different information with regard to a product. In conjunction with a silicon-based photodetector, placed * 30 opposite an LED source, then the transmiSSiVitY of a fluid can be determined. l0

Figure 6 shows a second further embodiment of the invention wherein there are two receivers ORI & 0R2: OR1 measures the amount of ligltt transmitted across the path length between the transmitter and the receiver (in addition to the three electrodes, not shown). Receiver 0R2 is placed such that it can determine a value for back scattered radiation. The back scattered light may be of a specific wavelength range. This information can be used in determination of the amount of cavitation within the fluid, which can be indicative of an amount of foam on beer (fob). In another embodiment, the optical receiver may comprise one unit yet is able to determine an amount of back scattered light. Two or more light sources may be used in conjunction with a single detector, which light sources may be of different wavelengths and arranged about the test space in different orientations or may be collocated or of a single wavelength and arranged about the test space in different orientations. Normal and diffracted/refracted light signals obtained from the light sources can be used to determine information about the fluid. Note that it would also be possible to provide source-detector pairs. Source-detector pairs are conveniently operated on a time multiplexed basis. The LEDs may have difference wavelengths that enable colour information to be provided. Conveniently, the light measurement is conducted only during times of fluid flow. Figures 6a & 6b show, respectively, plan and cross sectional views of a further embodiment. By replacing the LED light source with a laser, then an improved collimated beam can be used whereby to more accurately measure any angular deviation of the beam. By determining an amount of angular deviation, then the optical characteristics that can be measured are diffraction and reflection rather than scattering. I.

Figure 7 shows characteristics of a fluid which can be determined and how they relate to types of fluid or contaminant within a fluid. Simultaneous measurement of the optical transmission/recePtion and electrical conductivity of a fluid can provide robust indications whereby to differentiate between a variety of fluids, where there are known to be present only a small number of known fluids, for which the electrical and optical characteristics are known. Under certain conditions, it would be possible to determine the identity of a branded fluid. With regard to public houses and the like the risk of damage to a reputation for selling incorrect beer would be very much reduced if continuous testing was employed. I..

U

U I. U. S.

S p..

S

S S...

S

Claims

Claims 1) A method of measuring the conductivity of a fluid flowing

through a conduit, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, wherein the first electrode means comprises a first electrode and the second electrode means comprises second and third electrodes disposed on opposite sides of the first electrode, the method comprising the step of causing an electrical current to flow between the first and second electrode means, and measuring the electrical current whereby to determine the electrical conductivity of the fluid.

2) A method according to clam 1, wherein the electric current is provided by a source of alternating current.

3) A method according to claim 2, wherein the source of electrical current is a low impedance signal source.

4) A method according to any one of claims I -3, wherein the method comprises the steps of connecting the electrical current source to the first and second electrode means for relatively short periods of time during fluid flow, spaced at relatively long intervals.

5) An apparatus for measuring the conductivity of a fluid flowing through a conduit, wherein there is provided first electrode means within the conduit and second electrode means within the conduit in proximity to the first electrode means, wherein the first electrode means comprises a first electrode and the second electrode means comprises second and third electrodes disposed on opposite sides of the first electrode, the apparatus comprising means to cause an electrical current to flow between the first and second electrode means, and current measurement means whereby to determine the electrical conductivity of the fluid.

6) An apparatus according to clam 5, wherein the electric current is provided by a source of alternating current.

7) An apparatus according to claim 6, wherein the source of electrical current is a low impedance signal source; the first electrode means can be connected to a high input impedance amplifier and the total R.MS current can be measured, whereby the conductivity of the liquid can be measured.

8) An apparatus according to any one of claims 5 -7, wherein the second and third electrodes of the second electrode means are disposed, respectively, up stream and down stream of the first electrode.

9) An apparatus according to any one of claims 5 -8, each electrode is an elongate conductive member, such as a metallic tube and are spaced along the axis of the conduit.

10) An apparatus according to any one of claims 5 -9, wherein the first electrode means may comprise other electrodes in addition to the first electrode.

11) An apparatus according to any one of claims 5 -10, wherein the second electrode means may comprise other electrodes in addition to the second and third electrodes.

12) An apparatus according to any one of claims 5 -11, wherein the conductivity may not be indicated as such, and the system operates such that it provides a warning if the conductivity rises above a predetermined value and / or falls below a predetermined value.

13) An apparatus according to any one of claims 5 -11, wherein the fluid may be a liquid such as a beverage being dispensed, for example beer.

14) An apparatus according to any one of claims 5 -12, wherein the apparatus is operable to supply current to the electrode means only whilst the fluid is flowing.

15) An apparatus according to any one of claims 5 -12, wherein the apparatus is operable to supply current to the electrode means only for a predetermined period whilst the fluid is flowing.

16) An apparatus according to any one of claims 5 -15 for characterising a fluid flow through a conduit by assessment of the electrical conductivity further comprising means to determine assessment of an optical characteristic the fluid, wherein there is additionally provided a light source and a light receiver; the light source and light receiver being spaced apart by an optical path length within the conduit; the system comprising means to assess at least one characteristic of the light received by the light receiver and means to assess electrical current flow between the first and second electrode means.

17) A system according to claim 16, wherein the optical transmitter and optical receivers comprise spaced apart elongate members and may each define part of the flow conduit.

18) A system according to claim 16 or 17, wherein the optical transceivers are wavelength specific to assist in the detennination of hue, saturation and value. **

19) A method according to any one of claims 1 -4, wherein the method ::* comprises the further step of assessing the optical characteristics of the fluid flowing through a conduit, wherein there is provided a light source and a light receiver; the light source and light receiver being spaced apart by an optical path length within the conduit the method comprising the step of transmitting light from the light source and measuring a characteristic of the light received by the light receiver in combination with the electrical conductivity of the fluid.