WO2005108936A1

WO2005108936A1 - Method for detecting proper functioning of an agitation device in a milk cooler

Info

Publication number: WO2005108936A1
Application number: PCT/DK2004/000331
Authority: WO
Inventors: Ole Cramer Nielsen
Original assignee: Proces-Data A/S
Priority date: 2004-05-11
Filing date: 2004-05-11
Publication date: 2005-11-17

Abstract

A method and a device for controlling and verifying that liquid in a vessel is being agitated is described, wherein the fluctuation and/or wave formation on the surface of a liquid is detected by a level sensor, and where fluctuation and/or waves indicate that the liquid is being agitated.

Description

METHOD FOR DETECTING PROPER FUNCTIONING OF AN AGITATION DEVICE IN A MILK COOLER

The present invention relates to a method for controlling and verifying that liquid in a 5 vessel is being agitated and further to a monitoring device for monitoring at least temperature, liquid level and/or impedance in a vessel containing a liquid.

It is often desirable to be able to register different characteristics relating to liquids maintained in a vessel. In the context of the present application any type of vessel for 10 holding or storing a liquid will be suitable for carrying out the monitoring with the device according to the invention. In particular, vessels or tanks in which milk is stored are especially suitable for the present invention and will below be used as an example in order to describe the inventive features and characteristics of the present invention. 15 There is a general desire in society that food stuffs and among these also diary products are treated in accordance with the highest hygienic standards and that it must be possible to document that minimum requirements either established by law, the producers or the customers are being met. Within the industry there is a growing demand 20 for documentation from soil to table.

For diary products the requirements relate to the fact that milk, after having been milked, must be stored under controlled conditions within certain temperature intervals and for a certain period of time before further processing of the milk and, finally, 25 delivery to the customer is carried out. A further aspect of the storage procedure is the fact that it is a requirement that the milk during storage in refrigerated vessels is agitated such that homogeneous conditions will prevail in the storage vessel. For this purpose agitation means such as propellers and the like are installed in these refrigerated storage tanks. 30 In order to be able to document the requirements which may be raised by customers, the manufacturer or by law, the milk farmer/producer will often store the milk in a tank built especially for this purpose, wherein built-in temperature measuring equipment is placed. Also, logs are kept for determining when batches of milk are added to the tank and when batches of milk are drained from the tank. In this connection it is also desirable to ascertain that the agitation means are functioning properly such that the milk inside the tank is in fact agitated, whereby homogeneous conditions throughout the stored milk may be maintained.

This is often done by measuring the power consumed by the agitation means which subsequently is translated into the fact that agitation is being carried out. However, the fact that power is consumed by the agitation means may only indicate that there is a short-circuit within the power means, whereby power is consumed without actually driving the shaft onto which the agitation propeller is fastened. Or the gear box, which often is installed between the power input and the axle, may have a defect such that, although power is consumed by the unit, no agitation occurs in the tank. And, finally, also rotation of the shaft may not necessarily indicate that the propeller is agitated on the shaft in that a loose mounting of the propeller on the shaft may result in no or only a very limited agitation of the milk.

Likewise, for the temperature readings the sensor built into the tank might be defective or may in another way not indicate the correct values whereby non-reliable results are obtained.

It is, therefore, an object of the present invention to alleviate these drawbacks and provide an independent and reliable system for monitoring these process parameters.

This is achieved by a method for controlling and verifying that liquid in a vessel is being agitated, wherein the fluctuation and/or wave formation on the surface of said liquid is detected by a level sensor, and where fluctuation and/or waves indicates that the liquid is being agitated. By monitoring the formation of waves or fluctuations as a consequence of the liquid being stirred, a measuring principle independent of the agitation means is provided. Hereby, a reliable indication method is provided, and at the same time, a cost effective method is provided. In principle, any type of level sensor able to detect very shallow, i.e. few millimetres, fluctuations is useable with the inventive principle. As no intervention is necessary with the existing agitation means, the sensor may be installed independently.

In a preferred embodiment, the sensor is installed by drilling a hole in the vessels for inserting the sensor in the hole such that it will be immersed in the liquid. The sensor must be isolated from contact with the vessel, for example by arranging a non- conductive gasket between the sensor and the rim of the hole in the vessel.

As this installation may be carried out in the same manner regardless of the vessel and the agitation means, a very rational installation procedure is devised, as opposed to alternative rotation detection means which has to be arranged in or on the agitation means. Often, different types and models of agitation means are provided in different vessels such that no standard procedure can be devised.

The invention also relates to a method for monitoring the liquid in a vessel where an independent monitoring device as described above is used such that the monitoring device is arranged in the vessel in a manner such that at least part of the device will be immersed in the liquid during normal operation, and that the monitoring device is electrically isolated from the vessel, and where data relating to the liquid's temperature, liquid level, liquid level fluctuation, and impedance of the liquid is collected and stored, and optionally transmitted to a separate computing unit.

By using the independent monitoring device in a way where it is electrically isolated from the vessel, the monitoring device is completely independent and is thereby not influenced by other conditions relating to the storage facility of the individual farmer. Furthermore, by being able to install the monitoring device by for example drilling an access hole in the top of the storage vessel such that the device may be immersed in the liquid, it is possible to register the temperature and whether or not the agitation means are really agitating the liquid and also the level in the tank without having to interfere with the already existing construction of the storage facility. A number of existing storage facilities do not include means for controlling or monitoring the agitation means and it may be a rather costly exercise to install the traditional means for detecting agitation in comparison to installing the inventive device according to the present application.

Traditionally, in order to detect agitation, these means have, as mentioned above, comprised measuring of the power supply to the agitation means or a conductive member placed on the axle with a corresponding receiver placed adjacent the axle such that by each rotation an impulse is generated in the receiver, indicating that the axle is being rotated. But, as described above, these ways of detecting are not necessarily 100 % correct and under any circumstances they require that somebody manu- ally installs the necessary equipment in order to be able to detect this.

In further advantageous embodiments of the method, the liquid is milk and the computing unit registers the milks level fluctuation as a change in the impedance of the tube, as an indication/parameter of whether or not an agitation device arranged in the vessel is actually agitating the liquid, and optionally registers substantial level changes as indications of batches of milk being delivered or drained from the vessel.

By these method steps it may be ascertained that the liquid, for example milk, which is stored in the vessel is being agitated and it may be verified by reading the measure- ments.

In a further advantageous embodiment of the method it may be detected and/or controlled that before the liquid is transferred from the storage vessel to a transport vessel or a further treatment device or vessel, the information collected by the monitoring device is transferred to a computing unit, where the collected information is compared to a set of pre-defined control parameters in order to determine if the liquid has been stored according to the predefined control parameters relating to agitation and/or storage time and/or temperature and/or levels in the vessel.

In this fashion it is possible to assure that the milk transferred to the collecting vessel does fulfil the requirements regarding freshness, storage etc. before it is mixed with milk which already has been collected from other suppliers or drained into the diary processing plant. As explained above, any type of level sensor will be suitable for carrying out the inventive method. In a preferred embodiment, however, the level sensor or more broadly a monitoring device suitable for carrying out the method is particular in that the device comprises a sensing unit in the shape of a tube made from a material having poor elec- trical conductive characteristics, such as for example stainless steel, where near said tube has a lower opening and an upper opening, where a closed lower end of said tube, a plug made from a material having good electrical conductive properties is provided, such as for example copper, and that further a temperature sensor, such as for example a thermocouple, is attached to the inner wall of the tube adjacent the lower opening, and further that an electrical source, preferably an AC source, is connected between the plug and the upper end of the tube, and that further the device comprises a data collection unit which unit collects and stores information originating from the temperature sensor, the variation in voltage between the upper end of the tube and the plug, and further compares the collected data with a calibrated set of data in order to determine the liquids temperature and level.

It should, however, be noted that where the monitoring device is used in environments requiring a high level of hygiene, the plug should be covered, for example by stainless steel, such that contamination is avoided.

By knowing the loss of voltage due to the low conductivity of the tube material, the sensing unit is given a reference value. Furthermore, as the material characteristics relating to conductivity and temperature are well-known for, for example stainless steel and copper, the temperature sensor provided on an inner wall of the tube will be able to correlate the reference level of the voltage in relation to any temperature. For practical purposes it has been found that a voltage drop of 100 millivolts between the plug and a tube provides for good measurements. In this connection, however, it should be noted that for other purposes or for smaller or larger vessels where it is desirable to monitor the same properties or for generally smaller or larger amounts of liquid, other voltage drops may be chosen as reference level is preferred.

As the monitoring device is immersed into the liquid, the voltage drop will change due to the change in impedance between the level sensor and the vessel. The difference in voltage drop will thereby indicate the level to which the liquid fills the vessel. When a new batch of milk is pumped into the vessel, the voltage drop will change and it will in this manner be registered that a new level is attained and, therefore, that a batch has arrived in the tank.

That the electrical sources preferably are chosen as an alternating current source is due to the fact that the tube and the block will function as two electrodes connected by a conductive medium. If a DC current was connected between the two electrodes, electrons from one electrode would travel to the other whereby erosion of one electrode would occur. It is, therefore, advantageous to use alternating currents in that no erosion of the electrodes will occur. Furthermore, by collecting the voltage drop by means of a microprocessor it is possible to average the measurements such that the average voltage drop may be assumed equal to the level. ^• ■- •

Variation in the voltage drop due to draining or filling of the tank i.e. changes in impedance will be relatively easy to detect and will be a one-off event separated by a relatively long period before the next similar event. The agitation means will, however, continuously cause small waves to occur on the surface of the liquid such that a periodical voltage drop and increase fluctuating impedance corresponding to the rota- tional speed of the agitation means, for example the propeller placed in the vessel, will be measured. By further registering this periodical voltage drop which typically will be much smaller than the voltage drop relating to draining or filling of the tank, it is possible to continuously and independent from the agitating installation to monitor that agitation of the liquid does indeed take place as the waves on the surface of the liquid stored in the tank is an indication of this agitation.

Consequently, it is therefore possible with the device according to the invention to arrange for monitoring of the above mentioned characteristics in any vessel regardless of age and shape. To monitor and document that the liquid stored in the vessel is both kept at the appropriate temperature, is being agitated and the storage time/average storage time of the liquid placed in the vessel corresponds to the pre-set requirements. In a further advantageous embodiment the data collection unit of the monitoring device further comprises a timer device and a radio transmitter for wireless transmission of data to a receiver placed in the vicinity of the device.

By providing the facilities listed above it is possible to log and store the data collected by the monitoring device and transmit this information to an outside source such as for example the vehicle collecting the milk. In this manner, it may be possible for the outside, i.e. the person collecting the milk, to ascertain that the storage of the milk has been performed according to pre-set requirements, i.e. that the milk has been agitated throughout the storage, that the temperature has been maintained at certain levels within certain predetermined intervals, and that the milk stored in the tank only has a certain age.

The monitoring device as described above will indicate a relative level, i.e. a change of level in respect to a previous level in that the voltage drop, which is an indication of the level, does not actually indicate the amount of liquid in litres, hectolitres or such. For this purpose it might be desirable to create an absolute volume measurement. This may be done by correlating the voltage drop as the tank is emptied into the collection vehicle with the flow measurement device attached on the collection vehicle which will indicated the exact amount of litres transferred from the tank/storage vessel to the collection vehicle. In this manner it is possible to establish the exact volume changes etc. for any shape of tank in relation to the voltage drop as registered by the monitoring device.

The invention will now be explained with reference to the accompanying drawings, wherein

fig. 1 schematically illustrates a milk storage facility, fig. 2 illustrates a schematic construction of a monitoring device according to the invention, fig. 3 illustrates a diagram with waves, a so-called wave diagram. In fig. 1 is illustrated a schematic storage facility. The example should illustrate a milk facility, but any storage facility where it is necessary to agitate the stored liquid may be considered within the scope of the present invention. Below, however, the invention will be explained with reference to a milk storage facility.

The storage facility 1 comprises an isolated storage vessel 2. An inlet 3 allows liquid to be pumped into the storage facility 2. The liquid which is placed in the storage facility 2, for example to the level indicated by 4 is cooled by means of the cooling aggregate 5. The liquid may be drained through the outlet 6, for example by collection by a tanker (not illustrated).

In order to keep the milk fresh, agitating means 7 is installed in the storage facility 2. The agitating means typically comprises a motor 8, an axle 9 and an agitating means 10. In the illustrated embodiment two wings 10 are illustrated as being the agitating means, but any type of agitating means may be utilised as long as they manage to agitate the entire liquid volume 4 stored in the storage facility 2. By activating the motor 8 the axle 9 will rotate and thereby the attached wings 10 will rotate. By this rotation it is achieved that a certain circulation in the liquid 4 is provided, whereby the milk will be stored under homogeneous conditions in relation to temperature.

The inventive monitoring device according the invention is illustrated as arranged through an aperture in the ceiling of the storage vessel 2. The monitoring device 11 will be explained in more detail with reference to fig. 2.

The only requirements to the installation of the inventive monitoring device is the provision of a hole in the storage vessel 2 and power supply means, for example by means of a cord 12 to be hooked up to an electrical installation. It should, however, be noted that any type of power supply such as for example a battery may be utilised in connection with the present invention.

Turning to fig. 2 a schematic illustration of the monitoring device according to the present invention is illustrated. A tube member 13, preferably made from stainless steel, constitutes one electrode. The tube is closed in a lower end by means of a plug 14. The plug may advantageously be manufactured from copper such that the plug is made from a highly electrically conductive material, whereas the tube constituting the other electrode is made from a low electrically conductive material. The plug 14 is by means of a wire 15 connected to a power source. Likewise, the low conductive tube 13 is connected by a power source by means of a wire 16. By for example connecting the wires to a AC power source providing 220 volts, the current may be adjusted such that the voltage drop between the plug 14 and the tube 13 when not immersed into a liquid is equal to 100 millivolts.

Additionally, a thermocouple 17 is provided inside the tube 13 adjacent the lower end for the tube.

In order to collect the data from the centring unit, a data collection unit 18 is provided. The data collection unit is connected to the thermocouple 17 as well as the two wires 15, 16 such that the temperature and the voltage drop may be registered depending on the liquid level 4. The data collection unit comprises at least a data storage. The data storage will collect and store the data relating to temperature and voltage drop continuously such that it at a later stage may be possible to read out the information and in this manner distinguish what has occurred inside the tank during the course of storage. Additionally, the data collection unit 18 may comprise a computing unit such that the collected data may be compared to predefined data relating to optimum storage conditions or storage intervals.

In order to install the monitoring device 11 in the storage tank 2, an aperture must be provided in the storage vessel 2. In order to isolate the storage vessel 2 from the tube

13 of the monitoring device 11, an isolation for example in the shape of a Teflon® gasket 19 may be provided. In this manner the monitoring device 11 is completely isolated from the storage vessel 2 and only influenced by the liquid maintained inside the storage vessel.

The data collected in the data collecting unit 18 may be transmitted by means of a radio transmitter 20 such that it is possible to transfer the information collected during the course of storage to for example a collection vehicle. In this manner it is possible for the personal collecting the liquid, preferably milk, to ascertain that the storage conditions have fulfilled the requirements as to agitation and temperature before commencing the draining of the tank into the tanker on the collection vehicle. Additionally, a GSM unit may be provided whereby it becomes possible from a remote position to survey and collect information by well-known wire-less equipment.

In fig. 3 is illustrated a simplified read-out from the monitoring device as described above. Along the X-axis is illustrated the course of time T and the Y-axis illustrates the drop in voltage in millivolts. During the first time period a, the liquid is at the first level aj. Then an additional batch is added at Ti, after which the level during the time period b is at bi etc. The level indications a._\ and bi are averages of the waves being the actual measurements 21.

At T₂ the storage vessel was emptied and the voltage drop was brought back to the reference level illustrated as the X axis. At T₃ a new batch of milk was added to the storage vessel and additional batches were added later. The dashed lines 23 indicate the average levels corresponding to the levels ai, bi etc. The actual wave pattern resulting in the averages ai and bi corresponds to the wave surface of the liquid indicating that the agitating means are active. The wave height indicated by 24 along with the regularity of the wave pattern is a clear indication that the agitating means are active.

By registering this regular periodical change (increase/decrease) in voltage, information is collected corresponding to the agitation means.

Claims

1. Method for controlling and verifying that liquid in a vessel is being agitated, wherein the fluctuation and/or wave formation on the surface of said liquid is detected by a level sensor, and where fluctuation and/or waves indicate that the liquid is being agitated.

2. Method according to claim 1 wherein the level sensor which is isolated from the vessel comprises a sensing unit in the shape of a tube made from a material having poor conductive characteristics such as for example stainless steel where near a closed lower end of said tube a plug made from a material having good electrical conductive properties is arranged, such as for example copper, and that further a temperature sensor, such as for example a thermocouple is attached to the inner wall of the tube adjacent the lower end, and further that an electrical source preferably an AC source is connected between the plug and the upper end of the tube and that further the device comprises a data collection unit which unit collects and stores information originating from the temperature sensor, the variation in impedance between the tube and the vessel and further compares the collected data with a calibrated set of data in order to determine the liquids temperature and level.

3. Method according to claim 1 or 2 where the liquid is milk and the computing unit registers the milks level fluctuation as a change in the impedance of the tube, as an indication/parameter of whether or not an agitation device arranged in the vessel is actually agitating the liquid, and optionally registers substantial level changes as indi- cations of batches of milk being delivered or drained from the vessel.

4. Method according to claim 1,2 or 3 c h a r a c t e r i s e d in that before the liquid is transferred from the storage vessel to a transport vessel or a further treatment device or vessel, the information collected by the monitoring device is transferred to a comput- ing unit, where the collected information is compared to a set of predefined control parameters in order to determine if the liquid has been stored according to the prede- « 12 fined control parameters relating to agitation and/or storage time and/or temperature and/or levels in the vessel.

5. Monitoring device, comprising a level sensor suitable for use in a method according 5 to any of claims 1 to 4, for monitoring at least temperature, liquid level and impedance in a vessel containing a liquid c h a r a c t e r i s e d in that the device comprises a sensing unit in the shape of a tube made from a material having poor conductive characteristics such as for example stainless steel where said tube has a lower opening and an upper opening, where near a closed lower end of said tube, a plug made from a ma- 10 terial having good electrical conductive properties is provided, such as for example copper, and that further a temperature sensor, such as for example a thermocouple is attached to the inner wall of the tube adjacent the lower opening, and further that an electrical source preferably an AC source is connected between the plug and the upper end of the tube and that further the device comprises a data collection unit which unit 15 collects and stores information originating from the temperature sensor, the variation in voltage between the upper end of the tube and the plug, and further compares the collected data with a calibrated set of data in order to determine the liquids temperature and level.

20 6. Device according to claim 1 c h a r a c t e r i s e d in that the data collection unit further comprises a timer device and a radio transmitter, for wireless transmission of data to a receiver placed in the vicinity of the device.