Method for measuring the oxygen content of head space gas in beverage cans

Abstract

The invention relates to a method for measuring the oxygen content of head space gas in a beverage can, wherein the liquid level in the beverage can is lowered via a sampling tube such that there is a direct connection between the head space filled with head space gas and a sampling opening, wherein, after the liquid level has been lowered, the head space gas in the head space of the beverage can is supplied via the sampling tube and / or a hollow piercing or piercing head to a sensor unit, which comprises a number of sensors, and the oxygen content and / or the oxygen partial pressure and / or the head space volume of the head space gas are determined by the sensor unit. The invention also relates to a device for determining the oxygen content of head space gas in a beverage can filled with liquid.

Description

Technical Field

[0001] The invention relates to a method according to the preamble of claim 1 and to a device for carrying out the method according to the preamble of claim 13 . Background Art

[0002] For beverage fillers, knowledge of the oxygen content in containers such as beverage cans, bottles and the like is important, since this has an influence on the durability and taste of the beverage and, in the case of metal containers, on their corrosion. In order to be able to draw conclusions about the causes of any oxygen introduction, it is important to determine the oxygen content in the liquid and in the gas space above the liquid, the so-called head space, separately.

[0003] In this way it can be determined whether the oxygen arrives in the container with the liquid or as a result of a possibly poorly calibrated filling process. Measurements in the gas space are particularly important since, due to the low solubility of oxygen in aqueous liquids, a significant portion of the oxygen in the container is present in the head space or in the head space gas. The measurement of liquid samples is in most cases a common task since the liquid sample can be removed from the container via a hose line through the oxygen sensor. Generally speaking, there is enough sample to flush through the oxygen sensor until it displays stable values ​​after a certain equilibration time. A more difficult situation is when measuring the head space gas. In most cases, there are only a few milliliters of head space gas, which makes it difficult to cause this head space gas to flow through the oxygen sensor in a discarded manner.

[0004] Particularly difficult is the situation when measuring the head space gas in beverage cans. The first problem is the access to the head space gas. The can lid has a pre-engraved structure, so that the consumer can open the can. Usually, the factory logo and text are also pressed in, so it is very difficult to seal and pierce the access opening at the can lid towards the measuring device. Even if there is a suitable surface, the can must be aligned very accurately so that the surface is also reliably sealed. The cylindrical can periphery is mechanically very unstable and cannot be sealed and pierced there. Thus, only the bottom is left as a reliable position for sealing and piercing. The bottom in a beverage can containing CO2 is always strongly arched inward, which results in that when the can is inverted (or standing on the head, i.e., am Kopf stehend), the lowest point of the bottom is in the liquid and thus cannot establish access to the head space. At the same time, the lowest point of the bottom is such a point at which piercing and sealing can be performed most reliably.

[0005] The solutions known from the prior art tip the can in order to pierce the can at the upper edge region or to pierce the lid, which requires an exact alignment of the can and is not possible with all cans. The known methods described require a high expenditure on equipment and a high level of detail or good training of the operating personnel. Thus, for example, devices and methods are known from JP H04315943 (A) and JP 3405637 (B2) which open a beverage can at its edge in order to gain access to the head space gas.

[0006] The disadvantage of the method known from the prior art is that when the can is adjusted and pierced in the sampler, an increased accuracy is required. In addition, the sealing of the piercing position in the method known from the prior art is expensive and often does not reliably enough ensure measurement errors due to entering air or oxygen. Summary of the invention

[0007] The object of the present invention is therefore to provide a method which allows beverage cans to be pierced at the bottom and then to carry out a head space measurement without requiring increased requirements for accuracy during the positioning and piercing of the can in the sampler.

[0008] This object is achieved by the features of the characterizing part of claim 1. It is provided that the liquid level in the beverage can is lowered via the sampling tube in such a way that there is a direct connection between the head space filled with head space gas and the sampling opening, wherein, after the liquid level has been lowered, the head space gas in the head space of the beverage can is supplied via the sampling tube and / or a hollow piercing or piercing head to a sensor unit comprising a number of sensors, and the oxygen content and / or the oxygen partial pressure and / or the head space volume of the head space gas is determined by the sensor unit.

[0009] By piercing the beverage can at the bottom, it is possible to pierce the sampling opening independently of the exact positioning and to achieve simple sealing. In addition, the head space can be approached or the head space can be widened by lowering the liquid level to achieve simple measurement of the head space gas.

[0010] Particularly advantageous embodiments of the method according to the invention are defined in detail by the features of the dependent claims:

[0011] Advantageously, it can be provided that the liquid level in the beverage can is lowered by removing a defined portion of the sample liquid in the beverage can by means of a pump, by increasing the pressure by means of gas, in particular nitrogen, introduced into the beverage can via a piercer or a sampling tube, or by the pressure existing in the beverage can.

[0012] The oxygen content of the sample liquid can be determined simply by lowering the sampling tube into the liquid in the beverage can after measuring the oxygen content of the head space gas and then removing the liquid from the beverage can and guiding it to the sensor unit and thus determining the oxygen content in the liquid.

[0013] In order to simply determine the oxygen content and / or the oxygen partial pressure and / or the head space volume, it can be provided that an oxygen sensor is introduced, in particular via a hollow puncture device, into the head space that occurs due to the drop in the liquid level and the oxygen concentration or the oxygen partial pressure of the head space gas is determined with the aid of the oxygen sensor.

[0014] In an advantageous embodiment, it can be provided that after the liquid level has dropped, the head space gas in the head space of the beverage can is pumped by means of a pump via a sampling tube and / or a hollow piercer into a sensor unit comprising a number of sensors and then pumped back into the head space of the beverage can again, and the oxygen content and / or the oxygen partial pressure and / or the head space volume of the head space gas are thus determined by the sensor unit. This embodiment makes it possible to determine the oxygen content in the head space gas in a simple manner independently of the head space gas present and to use a large number of sensors independently of the empty volume in the head space. Likewise, there is always enough head space gas available because the head space gas is cyclically pumped or pumped back into the head space again, thereby achieving a more accurate determination of the oxygen content and / or the oxygen partial pressure and the head space volume.

[0015] According to the invention, it can be provided that, for measuring the oxygen content, in particular in the case of beverage cans with foaming liquids, foam is generated in the head space of the beverage can after the liquid level has dropped, the head space gas or a portion of the head space gas is incorporated in the foam, wherein the oxygen content and / or the oxygen partial pressure and / or the head space volume are determined in the sensor unit from the generated foam, wherein in particular the foam is subsequently introduced back into the head space of the beverage can. Thus, even if, for example, only a small portion of head space gas is present, the head space gas incorporated in the foam or the oxygen contained in this head space gas can be easily determined, since due to the poor solubility of oxygen in aqueous substances the oxygen content in the foam corresponds very well to the oxygen content in the head space.

[0016] In order to simply determine the oxygen content and / or the oxygen partial pressure and / or the head space volume, it can be provided that the sensor unit has an oxygen sensor for measuring the oxygen content and / or the oxygen partial pressure of the head space gas, wherein in particular the oxygen content and / or the head space volume is determined by additionally measuring the pressure with the aid of a pressure sensor and / or measuring the temperature with the aid of a temperature sensor, preferably in the case of a resulting change in the head space gas volume.

[0017] Since many sensors are temperature-sensitive or require temperature equilibration with the medium to be measured in order to achieve the highest accuracy, it can be provided that the head space gas is pumped from the head space into the sensor unit, in particular through the temperature sensor and then pumped back into the head space again, so frequently that the sensor unit, in particular the pressure sensor and / or the temperature sensor and / or the oxygen sensor, and / or the head space gas reaches a stable, preferably uniform temperature and / or a sensor-specific equilibration process is terminated. By pumping the head space gas through the sensor unit in multiple cycles, it is achieved that the individual sensors of the sensor unit can accept the temperature of the head space gas or equilibrate with it and can then measure the head space gas within the equilibrated temperature range. In addition, this accelerates the temperature equilibration of the sensor or the sensor unit with the temperature of the head space gas. In addition, other equilibration processes in the oxygen sensor, such as diffusion processes, must have sufficient time for complete equilibration.

[0018] Advantageously, it can be provided that the sensor unit has a certain number of further sensors, in particular CO2 sensors, alcohol sensors and / or sugar sensors, wherein the CO2 content and / or the alcohol content and / or the sugar content of the liquid in the beverage can are determined by means of the further sensors. By arranging different sensors within the sensor unit or within the measuring assembly, various parameters of the sample liquid or the head space gas can be determined, so that a complete analysis of the sample liquid and / or the head space gas can be achieved. Alternatively, it can be provided that the additional sensors are arranged outside the sensor unit in a pipeline or annular pipeline.

[0019] In order to remove any oxygen or contaminants that may be present from the sample component or to better prevent errors in the measurement results, it can be provided that before the measurement, the piercer, puncture head, sensor unit, pump, annular pipeline and / or sampling tube are purged with a purge medium, especially nitrogen, and oxygen and / or sample residues are thus removed.

[0020] Advantageously, it can be provided that the head space volume is determined by measuring the pressure in the pierced beverage can first with the sampling tube moved in and once with the sampling tube moved out, and calculating the head space volume via gas laws and the change in pressure.

[0021] Advantageously, it can be provided that before piercing the container, the pressure in the piercing device and / or the piercing head and / or in the annular line is equalized with the internal pressure of the container, in particular by introducing nitrogen gas, so as to prevent the sample liquid from foaming. This makes it possible to simply avoid the formation of foam and to prevent the undesired escape of the head space gas.

[0022] Furthermore, it is an object of the present invention to provide a device by means of which the oxygen content of the head space gas can be determined in a simple manner.

[0023] This object is achieved by the features of claim 13. According to the invention, it is provided that the device has a pipeline, in particular a ring pipeline, connected to a sampling tube, wherein a sensor unit is arranged within the pipeline, by means of which the head space gas of the beverage can can be sampled via a piercer which is designed to be hollow, wherein the device is designed such that the liquid level in the beverage can can be lowered via the sampling tube in such a way that a direct connection can be established between the head space filled with the head space gas and the sampling opening, and wherein the device also includes a control device which is designed such that the liquid level can be lowered in a defined manner via the piercer or the sampling tube until a direct connection can be established between the head space filled with the head space gas and the sampling opening. With the device according to the invention, the oxygen content or the oxygen partial pressure and / or the head space volume can be determined in a simple manner and with high measurement accuracy.

[0024] In order to be able to easily lower the liquid level, it can be provided that the device includes means for increasing the pressure in the beverage can, in particular a pump and / or a gas supply, wherein the device also includes a control device which is designed such that the liquid level can be lowered in a defined manner.

[0025] Advantageously, it can be provided that the device has a pump and an annular line, wherein the sensor unit is arranged within the annular line, and the head space gas of the beverage can is sampled by means of the sensor unit via a hollow piercer and can be fed back into the head space of the beverage can via the annular line, in particular via a sampling tube. As a result, even with low head space gas quantities, the sensor can be easily balanced and the measurement accuracy can be increased by circulating the head space gas.

[0026] Advantageously, it can be provided that the sensor unit has an oxygen sensor and / or a pressure sensor and / or a temperature sensor and / or a CO2 sensor and / or an alcohol sensor and / or a sugar sensor, wherein the oxygen sensor is in particular constructed as a photochemical sensor based on the fluorescence quenching principle or as an electrochemical oxygen sensor.

[0027] An efficient circulation of the head space gas can be achieved simply by designing the pump as a circulation pump, preferably as a diaphragm pump, hose displacement pump, piston pump, gear pump, worm pump, impeller pump or syringe pump.

[0028] In order to be able to easily introduce purge gas, for example nitrogen, into the device, it can be provided that the device has a certain number of valves integrated in the annular line, wherein the valves are arranged in the annular line such that automatic cleaning of the device, in particular the annular line, can be achieved via the valves.

[0029] Further advantages and embodiments of the invention are apparent from the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is schematically illustrated below in the drawings using particularly advantageous exemplary embodiments which are not to be understood as limiting and is described by way of example with reference to the drawings.

[0031] Figure 1 The device according to the invention is shown in a schematic diagram. DETAILED DESCRIPTION

[0032] exist Figure 1 , a schematic diagram of a device for determining the oxygen content of the head space gas of a beverage can according to the present invention is shown. The device comprises a piercing head 1, on which a hollow piercer 2 is arranged. The piercer 2 is constructed similarly to a needle in this embodiment and can be adjusted along the arrow shown within the piercing head 1. In addition, the device comprises a sample receiving portion 21, into which the beverage can 6 is brought. Here, the beverage can 6 is placed upside down on the sample receiving portion 21, so that the bottom 20 of the beverage can 6 points toward the piercer 2. The beverage can 6 can be adjusted in the direction of the piercing head 1 by means of a drive 7, whereby the piercing head 1 can be placed or mounted on the bottom 20 of the closed beverage can 6. In addition, the device comprises a sampling tube 3, which is arranged concentrically with the piercer 2 in this embodiment.

[0033] Optionally, a centering device or a stop may be provided, by means of which the beverage can and the piercer 2 can be arranged concentrically, so that the center of the bottom of the beverage can 6 is aligned with the center of the piercer 2 .

[0034] Trocar 2 Figure 1In a preferred embodiment, the sample tube 3 is configured to be hollow, so that the sample tube 3 penetrates into the puncture device 2 and can be brought into the head space 4 through the puncture device. Here, the sample tube 3 is adjusted by means of a drive 5. Optionally, it can also be arranged that the sample holding portion 21, the puncture device 2, the puncture head 1 and / or the sample tube 3 can be adjusted by hand or controlled by a drive with a control device. The annular pipeline 22 starts at the end of the sample tube 3 away from the puncture head 1, and the annular pipeline is led back to the puncture head 1 or is passed into the puncture head again. A sensor unit 8 and a pump 9 are integrated in the annular pipeline 22. By means of the pump 9, the sample liquid in the beverage can 6 or the head space gas in the head space 4 of the beverage can 6 can be taken out via the sample tube 3 and thus it can be supplied to the sensor unit 8. Via the sensor unit 8, the sample liquid or the head space gas is led back to the puncture head by the pump 9 again and thus is led back to the beverage can 6 or is led back to the head space 4 of the beverage can 6. Alternatively, it can also be provided that the head space gas and / or the sample liquid is removed via the piercing head and is fed back into the head space 4 or the sample liquid of the beverage can 6 via the sampling tube 3 .

[0035] Optionally, a pipeline may be arranged to the sampling tube 3, the puncture device 2 or the puncture head 1, which pipeline does not lead back into the head space, but leads into the surrounding environment of the device or a receiving container, into which the removed sample liquid and / or head space gas is emptied.

[0036] The sensor unit 8 is Figure 1 In the embodiment of , a temperature sensor 11 and an oxygen sensor 12 are included. In addition, the device comprises a pressure sensor 10, by means of which the pressure in the annular line 22 or in the head space 4 of the beverage can 6 can be determined.

[0037] Optionally, it can be provided that the device or the sensor unit 8 also comprises a plurality of oxygen sensors 12 , which can also be arranged outside the sensor unit.

[0038] Below with the help of Figure 1 The method according to the invention is described exemplarily by way of example:

[0039] In the method according to the invention, in a first step, a beverage can 6 is placed on the sample holder 21 and then the sample holder 21 or the piercing head 1 is adjusted so that the piercing head 1 is centered on the bottom 20 of the beverage can 6. The piercer 2 is then adjusted in the direction of the bottom of the beverage can 6, pierces the bottom and thereby creates a sampling opening in the bottom 20 of the beverage can 6. The sampling opening is covered in an airtight manner by means of a sealing element arranged at the piercer 2 and / or at the piercing head 1, so that foreign gas cannot penetrate from the surroundings into the device or the annular line 22 or the head space 4 of the beverage can 6 and the head space gas cannot escape from the beverage can 6. In this case, the sealing element of the piercing head 1 or the piercer 2 seals the beverage can 6 and the annular line 22 in an airtight manner relative to the surroundings of the device. The sampling tube 3 is then lowered into the can 6. Since in most cases there is no connection between the head space and the sampling opening in the beverage can 6 due to the curvature of the bottom 20, the sampling tube 3 is first introduced into the liquid and a portion of the liquid is removed from the beverage can 6 until there is a direct connection between the head space 4 of the beverage can and the sampling opening, so that the head space gas can be supplied to the sensor unit 8, more precisely the oxygen sensor 12, the pressure sensor 10 and the temperature sensor 11 via the sampling tube and the annular line 22. Here, it is possible to remove the sample liquid via the valve 13 and the opening 17 into the surrounding environment or the receiving container. The head space 4 is now freely accessible and can be supplied to the oxygen measuring device. By artificially increasing the head space 4, the oxygen mass in the head space 4 remains unchanged, so that the measurement result is not erroneous due to the drop in the liquid level. After the drop in the liquid level, the increased head space volume can be determined and this head space volume can be taken into account for calculating the oxygen mass or oxygen content in the head space gas from the measured oxygen partial pressure. The amount of liquid to be removed depends on the beverage can 6 and the desired filling level and can be determined, for example, empirically by removing a sample for a certain number of seconds using the method described and then checking the filling level.

[0040] In an alternative embodiment, the head space volume is measured before the liquid is removed and from this head space volume and the diameter of the beverage can 6, it is calculated how much liquid must be removed in order to determine the approach between the head space 4 and the sampling opening. The removal can be carried out in a time-controlled manner or via any form of flow measurement if the flow rate through the sampling tube 3 or the line or annular line 22 is known.

[0041] Alternatively, the head space volume can be determined in the simplest way in terms of equipment by measuring the pressure in the pierced beverage can once when the sampling tube 3 is moved in and once when the sampling tube 3 is moved out. Due to the additional volume of the sampling tube 3, the pressure of the head space gas or the pressure in the beverage can changes, and gas laws allow the head space volume to be calculated when the volume of the piercer 2 or the sampling tube 3 is known.

[0042] It has proven to be ideal if the residual filling level is lower than the lowest point of the bottom 20 of the beverage can 6 after a drop in the filling level of approximately 5 mm.

[0043] After the liquid level drops, the sampling tube 3 is positioned via the drive 5 so that it extends into the enlarged head space 4 without sinking into the liquid. The head space gas is pumped out of the head space 4 by means of the pump 9 and supplied to the sensor unit 8 via the annular line 22. In the sensor unit 8, the oxygen content and the temperature of the head space gas are determined by means of the temperature sensor 11 and the oxygen sensor 12. In addition, the pressure in the head space 4 is determined by means of the pressure sensor 10 and then the volume of the head space gas is determined, for example, via the gas equation. The head space gas is then transported back to the head space 4 of the beverage can 6 from the sensor unit 8 via the annular line 22 via the piercing head 1 by the pump 9. By circulating the head space gas via the annular line 22, the head space gas is caused to circulate within the device, so that the head space gas can be pumped through the sensor unit 8 or sensor of the device once or multiple times. By pumping the head space gas through the sensor unit 8 or the sensor once or several times, the temperature equilibrium of the sensor is improved and / or the dependence of the measurement result on the mostly gradual equilibrium behavior of the sensor, in particular the oxygen sensor 12, is reduced, so that the determination of the oxygen content, the oxygen partial pressure and / or the head space volume can be accelerated and the measured values ​​can be determined more accurately. Suitable oxygen sensors from the prior art measure the oxygen content, for example, after the oxygen diffuses through the membrane, which can require an equilibrium time of several seconds during the diffusion and can also form a passive oxygen layer in front of the corresponding sensor, which can lead to erroneous measurements. By pumping the head space gas at the sensor unit 8 or the sensor once or several times, the diffusion is improved and the formation of a passive oxygen layer is also avoided.

[0044] After determining the oxygen content of the head space gas or the head space volume or the oxygen partial pressure, the sampling tube 3 can be lowered further into the sample liquid in the beverage can from the head space 4. The sample liquid is then pumped to the sensor unit 8 and the oxygen content, temperature or pressure of the sample liquid is also determined.

[0045] Alternatively, it can be provided that the device has a line instead of the annular line 22 which opens into a receiving container or the like and allows the sample liquid to be removed via the sensor unit 8 when measuring the oxygen concentration in the liquid and / or to be discarded in the event of a drop in the liquid level.

[0046] The liquid level in the beverage can 6 can be lowered by means of a pump 9 or by increasing the pressure by means of a gas introduced into the beverage can 6 via the piercer 2 or the sampling tube 3 or the piercing head 1. Suitable gases are any gases, such as nitrogen, which do not change the oxygen concentration in the beverage can 6. Alternatively, the liquid level can be lowered by the pressure present in the beverage can, which is provided in particular in beverage cans 6 with carbonated beverages.

[0047] The problem is that beverage cans 6 with foaming liquids, such as beer, tend to foam after piercing with the aid of the piercer 2 and the liquid level is lowered, especially when quickly placed in the sample holder 21. A portion of the head space gas is locally almost fixedly incorporated in the generated foam, so that this incorporated gas portion does not participate in the measurement process via the annular line 22. Therefore, optionally, foam can be intentionally generated or foam formation can be promoted in the foaming liquid, so that the entire head space gas is uniformly incorporated in the foam. The foam can be formed, for example, in the following way: the sampling tube 3 is positioned a few millimeters below the liquid surface via the drive 5, and the head space gas is pumped from the piercing head 2 via the pump 9 and the sampling tube 3 to the liquid surface and foam is generated there. Subsequently, the generated foam can be supplied to the sensor unit 8 via the annular line 22 by means of the pump 9 and the oxygen content of the foam can be determined from this. Since the oxygen content of the foam corresponds to the oxygen content of the head space 4 or the head space gas due to the poor solubility of oxygen in the sample liquid, the oxygen content of the head space gas can be determined in this way.

[0048] The correct setting of the gas pressure in the piercer 2 when piercing the bottom 20 of the beverage can 6 varies depending on the beverage can and the sample liquid in it. In particular, in most cases, in samples that tend to form hard foam at low temperatures, the pressure of the attached gas in the piercer 2 must be coordinated with the liquid. If the piercer pressure or the pressure of the piercer 2 is selected to be significantly higher than the internal pressure of the beverage can 6, nitrogen will be injected into the head space through the liquid during piercing, and foam will form here, which will fix the oxygen in the head space and thus avoid the later measurement. Therefore, the pressure in the piercer 2 is preferably lower than the internal pressure of the can. Only when so much liquid is removed that the head space is accessible through the pierced opening can the pressure be increased via the valves 14, 15 and the storage volume 16 or the pump 9, and the liquid level can be further reduced or the head space gas can be removed.

[0049] Since the sensors in most cases have a gradual equilibrium behavior with an equilibrium time that is sensor-specific and a temperature-dependent measuring behavior, it is advantageous to equilibrate the sensors, in particular the oxygen sensor 12 and the temperature sensor 11, to the temperature or concentration of the head space gas or the sample liquid. In order to be able to carry out this equilibrium rapidly, the head space gas 4 can optionally be pumped through the sensor unit 8 or the sensor several times and the equilibrium can thereby be accelerated. By circulating the head space gas or by pumping the head space gas several times, even small amounts of head space gas can be measured by means of the sensor unit 8, or even in the case of small amounts of head space gas, a rapid equilibrium of the sensor with the head space gas and the sample liquid can be achieved. This equilibrium can include all time-dependent effects, such as temperature equilibrium and / or diffusion of the measuring gas through the sensor membrane, etc.

[0050] The device further comprises a valve 13 arranged in the annular line 22, which is connected to a line leading to the surroundings at an opening 17. Through the opening 17, for example, a purge gas such as nitrogen or a cleaning liquid can be passed into the annular line or to the sensor unit 8 or the pump 9 and the sensor and sample residues or residual oxygen can thus be swept out of the device.

[0051] Optionally, it can be set as Figure 1 As shown in , the device includes a certain number of other valves 14, 15 and a storage volume 16. The storage volume 16 is connected to the pressure sensor 10 via the valve 15 and is connected to the surrounding environment of the device via the other valve 14. Because the head space gas that was originally only in the head space 4 can be distributed in the annular pipeline 22 when the beverage can 6 is opened or after the liquid level drops through the piercer 2, a lower O2 concentration is measured compared to the O2 concentration existing in the head space 4 of the originally closed beverage can 6. Correct this system error in a calculated manner. For this purpose, it is necessary to know the volume of the pump circuit volume or the annular pipeline 22 and the volume of the components connected thereto, and it is necessary to know the head space volume. The head space volume is determined by the sensor unit 8 or the pressure sensor 10 and the temperature sensor 11 based on measurement technology and / or determined by applying gas laws during the measurement process.

[0052] In this regard, Figure 1An empty storage volume 16 is integrated into the device of the embodiment. In a first step, before piercing the beverage can 6, the valve 14 connected to the surroundings of the device via the air inlet 18 is opened and the storage volume 16 is brought to the surrounding air pressure. When the valve 15 connecting the storage volume to the annular line 22 is also open, the first air pressure p2 can be measured. At this time, the valves 14 and 15 are closed. After the beverage can 6 is pierced by the piercer 2, the pressure p1 is measured, which is obtained by the combination of the pressure of the pierced beverage can 6 and the pressure attached in the piercing head 1 and the annular line 22. The valve 15 is then opened and the mixed pressure p3 set at this time is measured. When the storage volume 16 is known, the head space volume V can be calculated by applying the Boyle-Malior law (Equation 1) at this time Headspace .

[0053] Equation 1

[0054] Since the expansion is neither purely isothermal nor purely adiabatic, the result is only a good approximation.

[0055] Expansion volume V Expansion and equipment volume V Apparat , i.e. the volume in the device or in the annular conduit 22, the sampling tube 3, the puncture device 2 and the puncture head 1 can be determined by the structure, but it is better to use different known head space volumes V Headspace A series of measurements are performed and V is calculated from them Expansion and V Apparat These two values ​​then contain, in addition to the known structural geometric information, corrections for deviations from the isothermal behavior and thus allow for even more accurate measurement results.

[0056] The measured oxygen concentration can then be corrected using the known volume with the aid of equation 2.

[0057] Equation 2

[0058] Alternatively, at the beginning of the measurement, the storage volume 16 can also be brought to a higher pressure than that present in the beverage can 6. For this purpose, the piercing head 1 is sealed before the beverage can 6 is pierced with the piercer 2. Then, the valves 14 and 15 are opened so that the same pressure is present in the entire area between the air inlet 18 and the piercing head 1. This pressure is measured by means of the pressure sensor 10. Subsequently, the valves 14 and 15 are closed and the pressure is thus "locked in" in the storage volume 16. The remaining method for measuring the oxygen concentration is then carried out in a manner similar to the method described above.

[0059] Alternatively, it can be provided that the head space gas or sample liquid is pumped out into the annular line 22 via the piercer 2 or that the sampling tube 3 is directly connected to the piercer 2. Alternatively, the piercer 2 can remain in the head space 4 after opening or piercing the bottom 20 of the beverage can 6, and the head space gas or sample liquid is pumped into the annular line 22 via the piercer or the liquid level is lowered via the piercer 2.

[0060] Optionally, the sensor unit 8 or the device may also have a certain number of additional sensors, such as CO2 sensors, alcohol sensors, sugar sensors and / or other sensors, which are integrated in the annular line 22 or the sensor unit 8. With the aid of the additional sensors, for example, the CO2 content or the alcohol content or the sugar content of the sample liquid can be determined and thus other parameters of the sample liquid can be determined. Optionally, the additional sensors can also be filled with sample liquid via the opening 17. The additional sensors can, for example, provide additional information when producing beverages such as beer or soda, so that the filling process or the quality control of the production process can be easily monitored with the aid of the device according to the invention.

[0061] The oxygen sensor 12 can be designed in particular as an optical chemical sensor based on the principle of fluorescence quenching or, for example, as an electrochemical oxygen sensor. Figure 1 Alternatively to the embodiment shown in , the sensor unit can also comprise only one oxygen sensor 12 , with the aid of which the oxygen content of the head space gas and / or of the sample liquid is determined.

[0062] Figure 1 The pump 9 in the embodiment shown in FIG. 1 can be designed, for example, as a circulation pump, in particular as a diaphragm pump, a hose displacement pump, a piston pump, a gear pump, a worm pump, a vane pump or a syringe pump.

[0063] Optionally, the drive 7 or the adjustment mechanism of the puncture device 2 and the sampling tube 3 can be driven manually or in other ways and thus cause the individual components to be adjusted relative to each other.

Claims

1. A method for measuring the oxygen content of the head space gas in a beverage can (6) having a curved bottom (20), in, The beverage can (6) is arranged in an inverted position with the bottom (20) facing away from gravity, so that the head space gas collects in the region of the bottom. wherein a sampling opening is brought into the bottom (20) of the beverage can (6) by means of a hollow piercer (2) arranged on a piercing head (1), a sampling tube (3) is inserted into the sampling opening, and wherein the sampling opening is covered in an airtight manner by means of a sealing element arranged on the piercer (2) or the piercing head (1), characterised in that the liquid level in the beverage can (6) is lowered via the sampling tube (3) in such a way that a direct connection exists between the head space (4) filled with head space gas and the sampling opening, Therein, after the liquid level drops, the head space gas in the head space (4) of the beverage can (6) is supplied to a sensor unit (8) via the sampling tube (3) and / or the hollow piercer (2) or the piercing head (1), the sensor unit comprising a certain number of sensors, and the oxygen content and / or the oxygen partial pressure and / or the head space volume of the head space gas are determined by the sensor unit (8).

2. The method according to claim 1, characterized in that The liquid level in the beverage can (6) is lowered by removing a limited portion of the sample liquid in the beverage can (6) by means of a pump (9), by increasing the pressure by means of gas introduced into the beverage can (6) via the piercer (2) or the sampling tube (3), or by the pressure existing in the beverage can.

3. The method according to claim 1 or 2, characterized in that: After measuring the oxygen content of the head space gas, the sampling tube (3) is lowered into the liquid in the beverage can (6), and the liquid is subsequently removed from the beverage can (6) and conducted to the sensor unit (8), and the oxygen content in the liquid is thus determined.

4. The method according to claim 1 or 2, characterized in that: An oxygen sensor (12) is introduced into the head space (4) which arises due to the falling filling level, with the aid of which the oxygen concentration of the head space gas is determined.

5. The method according to claim 1 or 2, characterized in that: After the liquid level drops, the head space gas in the head space (4) of the beverage can (6) is pumped by means of a pump (9) via the sampling tube (3) and / or the hollow piercer (2) into a sensor unit (8) comprising a certain number of sensors and then pumped back into the head space (4) of the beverage can (6), and in this way the oxygen content and / or the oxygen partial pressure and / or the head space volume of the head space gas are determined by the sensor unit (8).

6. The method according to claim 1 or 2, characterized in that: In order to measure the oxygen content, after the liquid level has dropped, foam is generated in the head space (4) of the beverage can (6), the head space gas or a portion of the head space gas being incorporated into the foam, wherein the oxygen content and / or the oxygen partial pressure and / or the head space volume are determined in the sensor unit (8) from the generated foam.

7. The method according to claim 1 or 2, characterized in that: The sensor unit (8) has an oxygen sensor (12) for measuring the oxygen content and / or the oxygen partial pressure of the head space gas.

8. The method according to claim 5, characterized in that The head space gas is pumped from the head space (4) into the sensor unit (8) and then pumped back into the head space again frequently until the sensor unit (8) and / or the head space gas reach a stable temperature and / or an equilibration process associated with a specific sensor is terminated.

9. The method according to claim 1 or 2, characterized in that: The sensor unit (8) has a number of further sensors, wherein the CO2 content and / or the alcohol content and / or the sugar content of the liquid in the beverage can is determined by means of the further sensors.

10. The method according to claim 1 or 2, characterized in that: Prior to the measurement, the puncture device (2), the puncturing head (1), the sensor unit (8), the pump (9), the annular line (22) and / or the sampling tube (3) are purged with a purging medium and are thus freed of oxygen and / or sample residues.

11. The method according to claim 1 or 2, characterized in that: The head space volume is determined by measuring the pressure in the pierced beverage can (6) first with the sampling tube (3) moved in and once with the sampling tube (3) moved out, and calculating the head space volume via gas laws and the change in pressure.

12. The method according to claim 1 or 2, characterized in that: Before piercing the container, the pressure in the piercer (2) and / or the piercing head (1) and / or the annular pipeline (22) is balanced with the internal pressure of the container, thereby preventing the sample liquid from foaming.

13. The method according to claim 4, characterized in that The oxygen partial pressure of the head space gas is determined with the aid of the oxygen sensor.

14. The method according to claim 1, characterized in that A sampling opening is introduced into the center of the bottom (20) of the beverage can (6) by means of a hollow piercer (2) arranged on a piercing head (1).

15. The method according to claim 2, characterized in that The gas is nitrogen.

16. The method according to claim 4, characterized in that The oxygen sensor (12) is introduced via the hollow piercing device (2) into the head space (4) which is created due to the falling liquid level.

17. The method according to claim 6, characterized in that In order to measure the oxygen content, in the case of a beverage can (6) containing a foaming liquid, foam is generated in the head space (4) of the beverage can (6) after the liquid level has dropped.

18. The method according to claim 6, characterized in that The foam is then introduced back into the head space (4) of the beverage can (6).

19. The method according to claim 7, characterized in that The oxygen content and / or the head space volume are determined by additionally measuring the pressure by means of a pressure sensor (10) and / or measuring the temperature by means of a temperature sensor (11).

20. The method according to claim 19, characterized in that The oxygen content and / or the head space volume are determined by additionally measuring the pressure by means of a pressure sensor (10) and / or measuring the temperature by means of a temperature sensor (11) with the resulting change in the volume of the head space gas.

21. The method according to claim 8, characterized in that The head space gas is pumped from the head space (4) into the sensor unit (8), pumped through the temperature sensor (11), and then pumped back into the head space again frequently until the sensor unit (8), and / or the head space gas reaches a stable temperature, and / or an equilibration process associated with a particular sensor is terminated.

22. The method according to claim 8, characterized in that The head space gas is pumped from the head space (4) into the sensor unit (8) and then pumped back into the head space again frequently until the pressure sensor (10) and / or the temperature sensor (11) and / or the oxygen sensor (12), and / or the head space gas reaches a stable temperature, and / or an equilibration process associated with a specific sensor is terminated.

23. The method according to claim 8, characterized in that The head space gas is pumped from the head space (4) into the sensor unit (8) and then pumped back into the head space again frequently until the sensor unit (8) and / or the head space gas reach the same temperature and / or the balancing process associated with the specific sensor is terminated.

24. The method according to claim 9, characterized in that The sensor unit (8) has a CO2 sensor, an alcohol sensor and / or a sugar sensor.

25. The method according to claim 10, characterized in that The cleaning medium is nitrogen.

26. The method according to claim 12, characterized in that Before piercing the container, nitrogen gas is introduced to balance the pressure in the piercer (2) and / or the piercing head (1) and / or the annular pipeline (22) with the internal pressure of the container, thereby preventing the sample liquid from foaming.

27. A device for measuring the oxygen content of the head space gas in a beverage can (6) having a curved bottom (20), wherein: The beverage can (6) is arranged in an inverted manner with the bottom (20) facing away from gravity, the device comprises a piercing head (1), a piercer (2) and a sampling tube (3) are arranged at the piercing head, characterized in that the device comprises a pipeline connected to the sampling tube (3), wherein a sensor unit (8) is arranged within the pipeline, with the aid of which the head space gas of the beverage can (6) can be sampled via the piercer (2) which is constructed as a hollow cavity, wherein the device is constructed in such a way that the liquid level in the beverage can (6) can be lowered via the sampling tube (3) so that a direct connection can be established between the head space (4) filled with the head space gas and the sampling opening, and wherein the device also includes a control device, which is constructed in such a way that the liquid level can be lowered in a defined manner via the piercer (2) until a direct connection can be established between the head space (4) filled with the head space gas and the sampling opening.

28. The device according to claim 27, characterized in that The device comprises means for increasing the pressure in the beverage can (6), wherein the device further comprises a control device which is designed in such a way that the filling level can be lowered in a defined manner.

29. The device according to claim 27 or 28, characterized in that The device comprises a pump (9) and an annular line (22), wherein the sensor unit (8) is arranged within the annular line (22), the head space gas of the beverage can (6) is sampled by means of the sensor unit via a hollow piercer (2) and can be fed back into the head space (4) of the beverage can (6) via the annular line (22).

30. The device according to claim 27 or 28, characterized in that The sensor unit (8) has an oxygen sensor (12) and / or a pressure sensor (10) and / or a temperature sensor (11) and / or a CO2 sensor and / or an alcohol sensor and / or a sugar sensor.

31. The device according to claim 27 or 28, characterized in that The pump (9) is designed as a circulation pump.

32. The device according to claim 27 or 28, characterized in that The device has a number of valves (13, 14, 15) integrated in a ring line (22), wherein the valves (13, 14, 15) are arranged in the ring line (22) such that automatic cleaning of the device can be achieved via the valves (13, 14, 15).

33. The device according to claim 27, characterized in that The measurement is carried out using a method according to any one of claims 1 to 9 .

34. The device according to claim 27, characterized in that A hollow puncture device (2) and a sampling tube (3) are arranged at the puncture head.

35. The device according to claim 27, characterized in that The device comprises an annular pipeline (22) connected to the sampling tube (3).

36. The device according to claim 28, characterized in that The means are a pump (9) and / or a gas supply.

37. The device according to claim 29, characterized in that The head space gas of the beverage can (6) is sampled by means of the sensor unit via a hollow piercer (2) and can be fed back into the head space (4) of the beverage can (6) via the sampling tube (3).

38. The device according to claim 30, characterized in that The oxygen sensor (12) is constructed as a photochemical sensor based on the fluorescence quenching principle or as an electrochemical oxygen sensor.

39. The device according to claim 31, characterized in that The pump (9) is designed as a diaphragm pump, a hose displacement pump, a piston pump, a gear pump, a worm pump, a vane pump or a syringe pump.

40. The device according to claim 32, characterized in that The valves (13, 14, 15) are arranged in the annular line (22) in such a way that automatic cleaning of the annular line can be achieved via the valves (13, 14, 15).

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