GB2149143A - Method and apparatus for metering milk - Google Patents

Abstract

A metering apparatus comprises a pipe (10) through which milk is fed from a farm vat (11) to a tanker mounted collection vessel (12). In the pipe (10) is arranged a meter (13), for example a turbine flow meter for metering the milk. Valves (V2, V3) are arranged downstream and upstream of the meter (13) respectively. Upstream of the valve (V3) there is arranged a reservoir vessel (14) into which is passed milk from the vat (11) by means of a hose (15). A venting pipe (16) leads, via a valve (V1) from the top region of the reservoir vessel (14) to the storage vessel (12) above an inlet (18) to the vessel (12). The apparatus and method of operation is such that the meter (13) meters only milk, and not air, the valves being controllable in response to probes (P1 to P4) to prevent milk with entrained air from being metered. <IMAGE>

Description

SPECIFICATION Method and apparatus for metering milk This invention relates to a method and appartus for metering milk.

When metering milk to be collected in a collection- vessel such as is mounted on a tanker, it is important that an accurate reading for the volume of collected milk is obtained. A frequent problem during such metering is that air entrained in the milk goes undetected and is metered as milk, causing a "high" reading to be abtained.

An apparatus for overcoming this problem is disclosed in British Patent Application No.

8323688, filed in the sole name of Flow Measurement Control but also held in trust for Milk Marketing Board, herein incorporated by reference. A copy of the description and informal drawing of Application No. 8323688 is attached to the back of the description of the present application.

The apparatus disclosed in Application No.

8323688 provides, inter alia, a vessel with sensing probes, an entrained air detector and an electronic control device for controlling the operation of a number of automatic valves.

That apparatus, although embodying a satisfactory principle, has been found to be capable of improvement, to effect more accurate metering of milk. In particular, the connection of the milk inlet pipe to the air venting pipe has been found to be undesirable.

At the commencement of milk collection, the pressure difference created in the reservoir vessel is high as the bulk collection vessel is empty. As the collection proceeds, this pressure difference decreases as the head of milk in the collection vessel increases. Since, for any air to be removed from the reservoir vessel, there must always be a sufficient pressure difference to overcome the liquid head, the system would not function when the collection vessel was filled above approximately 7,000 litres, its nominal capacity being 9,200 litres. The malfunction results in extremely low milk flow through valves V2 and V3 and the meter, causing inaccurate measurements.

The low flow is caused by the partial balancing of the system through the air venting pipe and the milk inlet pipe via valves V2 and V3, which also results in the failure of the supply hose to be emptied when a pressure difference is applied to the reservoir vessel by opening air vent valve V1.

Further, as described in Application No.

8323688, when the transfer of milk from one vessel to another is coming to an end, all the valves, that is valves V1 to V3, are open. This causes a partial balancing of the system thus slowing down the flowrate of milk to levels such that the meter performs considerably outside its calibration tolerance band.

In addition the opening of valves V1, V2 and V3 at once results in a further decrease in the pressure difference which may result in it falling below operational tolerances, and consequently the supply hose is not successfully emptied, with up to 4 litres being left in the farm vat and/or supply hose.

In accordance with one aspect of the present invention there is provided an apparatus for metering milk being transferred from a first container to a second container, the apparatus comprising: a vessel intended for communication with the first container and having a first valve at its upper end region; a pipe, for milk, connected via a second valve to a lower region of the vessel and via a third valve to an inlet of the second container; a meter means disposed in the pipe to meter milk flowing from the first to the second container; an air venting pipe connected to the second container at a region thereof above the inlet, and, via the first valve, to the vessel; one or more probe adapted to detect air in the milk; and a control unit which controls the operation of the apparatus in response to signals received from the probe(s).

In accordance with another aspect of the present invention, there is provided a method of metering milk using the apparatus defined in the immediately preceding paragraph wherein: on starting, the first valve opens to cause milk to flow from the first container to the vessel; when a predetermined volume of milk obtains in the vessel the first valve closes and subsequently the second and third valves open to allow milk to flow from the first to the second container via the metering means; and on detection of air in the milk by the or one of the probe(s), flow of the milk is stopped until the detected air has been eliminated from the milk.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which Figure 1 shows diagrammatically an apparatus in accordance with one embodiment of the present invention; Figure 2 is a flow chart illustrating the operation of the control unit; Figure 3 is a side view of one example of a reservoir vessel; Figure 4 is a front view of the vessel shown in Fig. 3; Figure 5 is an underplan view of the vessel shown in Fig. 3: and Figure 6 is a diagram of the connections to a microprocessor which may be used to control the apparatus.

Fig. 1 shows an apparatus for metering air free milk. As shown in Fig. 1, the apparatus comprises a pipe 10 through which milk is fed from a farm vat 11 to a tanker mounted collection vessel 12. In the pipe 10 are arranged a meter 13, for example a turbine flow meter for metering milk passing from the farm vat 11 to the vessel 1 2. it is important that the meter 1 3 meters only milk, and not air, and the apparatus of the present invention is thus arranged to ensure that only air-free milk is metered by the meter 1 3. Valves V2 and V3 are arranged downstream and upstream of the meter 13, respectively.

Upstream of the valve V3 there is arranged a reservoir vessel 1 4 into which is passed milk from the vat 11 by means of a hose 1 5.

The reservoir vessel 14 will be considered in more detail hereinafter. A venting pipe 16 leads, via a valve V1, from the top region of the reservoir vessel 1 4 to the storage vessel 12 above an inlet 18 to the vessel 12.

Conveniently, the venting pipe 1 6 leads to the uppermost region of the collection vessel 1 2 near an inspection hatch 17, as shown in Fig.

1. The connection of the venting pipe 1 6 between the storage vessel 1 2 and the top region of the reservoir vessel 14 results in the possibility of maintaining a suficient pressure difference, using valve V1, throughout collection of the milk, without the "partial balancing" effect mentioned herein before.

The apparatus further comprises probes P1 to P4 which are monitored by a control unit (Fig. 6) which controls the operation of valves V1 to V3. Probe P1 is arranged in the hose 1 5 leading from the farm vat 11 to the reservoir vessel 14. The probe P1 is adapted to detect small changes in conductivity of the milk to indicate the presence of air entrained in the milk, down to about 0.25% by volume.

The other probes, P2 to P4, detect the level of conductivity to deduce the presence of air or milk: of these probes, probe P2 is arranged in the reservoir vessel 14, probe P4 is arranged in the hose 1 5 and probe P3 is arranged just upstream of the meter 1 3.

The meter 1 3 includes a pick-off coil 1 9 which leads to a counting device (not shown) to meter the flow of milk through the pipe 10.

Figs. 3 to 5 illustrate one example of a suitable reservoir vessel 14. A typical vessel may be contructed with the dimensions as given below: a = 600 mm; b = 457 mm; c = 200 mm; d = 1 32 mm; e = 355 mm; f= 35 mm; g= 42 mm; h = 78 mm; = = 225 mm; j = 275 mm; k= 30 mm; I = 64 mm (internal diameter); m = 1 22 mm (outer diameter), and 100 mm (inner diameter); and n = 380 mm.

The volume of milk contained in the reservoir vessel 14 to line B-B (Fig. 4) is 23.4 litres, and to line A-A (Fig. 4) is 46.6 litres.

For a vessel constructed with the above mentioned dimensions and with the probe in the position shown in Fig. 1, the optimum length of probe P2 is p (in Fig. 1) = 256 mm. As probe P2 detects the presence or absence of milk, its length and position are important.

The length of the probe ensures that the correct level of milk is normally held in the reservoir vessel 14, the length of 256 mm giving good air separation, vortex prevention and ensuring that the tip of the probe is in the correct position with respect to the inlet of the hose 1 5 to the reservoir vessel 1 4. Further, the tip of the probe should be on the central axis of the reservoir vessel 1 4 to ensure that, despite variations in the angle of the tanker mounted vessel 12. during farm collection, the operation of the apparatus is not affected.

The operation of the apparatus will now be described with reference to Figs. 1 and 2 of the accompanying drawings. Milk collection is started manually by depressing a start button on the control unit. On starting, a pressure below atmospheric pressure (e.g. in the region of 12"-18" Hg) is caused to obtain in the collection vessel 1 2 by suitable means, and the valve V1 opens. Owing to the difference in pressure across V1 a "sucking" effect is created in the reservoir vessel 14 which causes milk to flow from the farm vat 11 through hose 1 5 towards the vessel 1 4.

Valves V2 and V3 are closed to prevent milk from flowing from the reservoir vessel 14 to the vessel 1 2. The reservoir vessel 1 4 is filled with milk until P2 goes "wet". A delay in the control logic (Fig. 2 TOP) ensures that P2 is truly wet and has not just been splashed by froth from the milk. A delay T1 of about 0.7 s is commenced to allow the correct level of milk to obtain in the vessel 14. At the end of the delay T1, V1 is closed, and a delay T2 of about 23 seconds is commenced to allow separation of the air from the milk in the vessel 14. At the end of delay T2, valve V2, and then valve V3, is opened to allow milk to flow via the pipe 10 to the vessel 1 2. The meter 1 3 will meter the milk flowing through the pipe 10 to the storage vessel 1 2 as long as probe P3 does not detect an air/milk interface. P3 is arranged to inhibit operation of the meter when sufficient air is detected.

During normal operation the only time that the meter 1 3 will be disabled in response to the probe P3 detecting air will be at the end of the collection when there will be an air/milk interface, since during normal operation all the air should have been vented from the milk in the reservoir vessel 1 4. Normal collection continues as long as the flow entering the vessel 14 equals the flow leaving it via pipe 10. If, however, the milk level in the vessel 14 drops below the tip of probe P2 for a period T3 (for example about 0.5 seconds) the control unit will shut valve V2 and then valve V3, as the fact that probe P2 has gone "dry" is an indication either that the flow of milk from the farm vat has stopped, or that the level of air in the milk is unacceptably high.This is indicated in Fig. 2 (MIDDLE) "main collection": the delays shown in the flow chart are to allow time for the valves to close (about 3s). Valve V1 is then opened, and, when P2 goes wet, assuming P4 is wet, a delay of T1, of about 0.7 seconds is commenced to allow the correct level of milk to obtain in the vessel 14, after which valve V1 closes. A period T2, as hereinbefore mentioned now commences, after which valves V2 and V3 are opened to recommence metering and flow of the milk.

The system as described in BPA No.

8323688 can suffer from a 'hunting' effect between probe P2 and valve V2 when trying to control air entrainment. This results in the control logic causig V2 to repeatedly open and close throughout the milk collection, owing to there being insufficient milk in vessel 1 4 to keep P2 'wet'.

The embodiment of the apparatus of the present invention described herein does not suffer from the hunting action described above, as the control unit is programmed to recognise and cope with the problem. After P2 has gone dry, various routes are available as shown in the flowchart of Fig. 2, including the provision of two timing periods to check the state of P2: T3, to ensure the probe state is correct; and T1 to ensure the correct milk level is obtained in the vessel 1 4 with respect to P2. As shown in the flowchart, P4 and P1 are also monitored.

A situation may occur during metered flow that a small amount of air becomes mixed with the milk due to perhaps an air leak in the pipework or between the connection between the pipework and the reservoir vessel. The quantity of air may be so small by volume compared with the milk that the level in the reservoir vessel 1 4 will not drop sufficiently to stop metered flow, and the milk/air mixture may be metered by the meter. If this occurs undetected, it will cause the meter to overread. Therefore, when probe Pi detects a significant change in conductivity when probe P4 detects all milk and when the entrained air does not cause a sufficient drop of level in vessel 14, the control unit is designed to stop the flow of milk by closing valve V2 and to simultanously trigger an alarm.An adjustable period T4, of about 2s, commences after which the state of P2 is checked. If P2 is dry, valve V3 closes and, after a delay, valve Vi opens to allow milk to be drawn into the vessel 14 as at the start of milk collection described earlier. If P2 is wet, the state of P1 is checked again. If P1 no longer detects air, valve V2 is opened and, after a delay of about 3 seconds collection of the milk continues. If P1 continues to indicate the presence of air, the monitoring cycle continues from the commencement of period T4. The system is designed to stop and start in these circumstances until all entrained air has been eliminated, by repairing the leak.If the leak or other cause of the entrainment cannot be found, a manually operated control can be activated which keeps valves V2 and V3 open to allow milk collection to proceed regardless of the state of any of the probes P1 to P4. If this action is taken an electrical signal is produced, which can be transmitted to a printing device or alarm device, to indicate that erroneous data was collected, to prevent possible misinterpretation of metered quantities.

When the collection of milk is coming to an end, air will again be detected. This will be detected firstly by probe P1 as small bubbles and then by probe P4 as larger pockets of air occur. When probe P2 becomes dry and there is no more milk to cause the level to rise sufficiently to wet it, valves V2 and then V3 close, after which valve V1 opens as described earlier to suck any remaining milk from the hose 1 5 into the vessel 14. Once P4 has gone dry continuously for a period T5, of about 5.5 s, V1 is closed and a period T6 of about 1 5 s is commenced. During this period with all valves closed the air mixed with the milk is forced to rise to the top of the reservoir vessel as the pressure in the vessel 14 approaches atmospheric pressure.When period T6 is over and with P4 still dry, V2 and V3 open again for the final collection of the remaining milk. According to the draining characteristics of the reservoir vessel 1 4 constructed as hereinbefore described, the milk to air interface will be froth free and the meter probe P3 will detect a short milk to air change. Thus the electronic counting device will be inhibited without indeterminate on/off switching, which occurs when milk drains from a badly draining farm vat.

When P3 has gone dry for a period T7 of about 3 s, the control unit will close valves V2 and V3 to inhibit further operation until the start button is reactivated.

The apparatus is conveniently controlled by a microprocessor, for example according to the flow chart illustrated in Fig. 2. One of the advantages of using a microprocessor to control the apparatus is that it is possible to meter very small amounts of milk, i.e. less than 20 litres. Thus, if the amount of milk to be metered is not sufficient to cause probe P2 to go wet, nominally 45 1, then the condition of probe P4 is monitored by the microprocessor. If P4, having been wet, goes dry for a set period of about 5.5 s, then V1 closes (with valve V2 and V3 closed) to allow air to escape to the top of the reservoir vessel 1 4 during a period of about 23 seconds, after which valves V2 and then V3 are opened to allow the small quantity of milk to flow into the storage vessel 12 and to be metered by the meter 13.

Further advantages of the control unit include: the checking of each probe on starting, after an unscheduled stop due to the detection of an unacceptable quantity of air in the milk, to ensure that the system restarts in the correct place; and, if operation of the apparatus is commenced with no milk present in the farm vat, the detection of a dry state of probe P4 for a certain period to cause the system to shut down.

At the end of the collection probes P2 and P4 are monitored. If probes P2 and P4 are wet, collection of the milk will be restarted. If probe P4 goes dry (with probe P2 dry) the end of collection sequence will comence, as hereinbefore described. If probe P4 is wet (with probe P2 dry) collection of the milk will continue (to ensure that all the milk is collected) until P4 goes dry.

While collection of milk is in progress the state of probe P3 is monitored. When this probe detects an air/milk interface upstream of the meter, the operation of the counting device attached to the meter 1 3 is inhibited and the valves V2 and V3 are closed after a period T7 of about 3 seconds to end the collection of the milk.

As an example, the microprocessor may be an 8-Bit EPROM microprocessor unit manufactured by Motorola, connected as shown in Fig. 6.

The valves V1, V2 and V3 are single acting normally closed valves, having an operating pressure of nominally 6 bar. The operating times of the valves are: from the closed to the open position about 1 second; and from the open to the closed position about 2 seconds.

The dimensions of valves V2 and V3 are 2+ (6.35 cm), and of valve V1 is 1" (2.54 cm).

Claims (11)

1. An apparatus for metering milk being transferred from a first container to a second container, the apparatus comprising: a vessel intended for communication with the first container; an air venting pipe communicating with an upper region of the vessel via a first valve and connected to the second container at a region thereof above an inlet of the second container; a pipe, for milk, connected via a second valve to a lower region of the vessel and via a third valve to the inlet of the second container; a metering means disposed in the pipe to meter milk flowing from the first to the second container; a probe adapted to detect air in the milk; and a control unit which controls the operation of the apparatus in response to signals received from the probe.

2. An apparatus as claimed in Claim 1, wherein the probe is capable of determining whether air or milk is in contact therewith and which is disposed in the vessel to determine when milk in the vessel has reached a predetermined level.

3. An apparatus as claimed in Claim 1 or 2, wherein there is a further probe capable of monitoring changes in electrical conductivity of the milk to detect bubbles of air entrained in the milk.

4. An apparatus as claimed in Claim 1, 2 or 3 which includes an additional probe which is capable of determining whether air or milk is in contact therewith and which is disposed in the pipe for milk between the second valve and the metering means.

5. An apparatus as claimed in Claim 1, 2, 3 or 4, which includes another probe which is capable of determining whether air or milk is in contact therewith and which is disposed between the first container and the vessel.

6. An apparatus for metering milk substantially as hereinbefore described with reference to, and as shown in, Figs. 1 and 3 to 6 of the accompanying drawings.

7. A method of metering milk using an apparatus in accordance with any preceding claim wherein: on starting, the first valve opens to cause milk to flow from the first container to the vessel; when milk in the vessel has reached a predetermined level the first valve closes and subsequently the second and third valves open to allow milk to flow from the first to the second container via the metering means; and the flow of milk from the first container to the second container is controlled in response to signals received from the probe so that substantially air-free milk is metered by the metering means.

8. A method as claimed in Claim 7, wherein there is a delay between the closing of the first valve and the opening of the second and third valves to allow air in the milk contained in the vessel to separate from such milk so that substantially air-free milk passes from the vessel through the pipe for milk to the second container.

9. A method of metering milk as claimed in Claim 7 or 8 which includes: detecting bubbles of air entrained in the milk between the first container and the vessel, and stopping the flow of milk, until the detected air has been eliminated, on such detection; and preventing operation of the metering means when it is determined that the flow of milk past the metering means has stopped.

10. A method of metering milk using an apparatus in accordance with Claims 2 and 5, wherein: on starting, the first valve opens to cause milk to flow from the first container to the vessel, said other probe determining that milk is in contact therewith; and when the other probe determines that air is in contact therewith, with the milk in the vessel being below said predetermined level, the second and third valves open to allow milk to flow from the first to the second container via the metering means.

11. A method of metering milk substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.