Calibration device for a leak testing station

Abstract

Calibration device (1) for a leak testing station, having: a closed casing (2) with a chamber (15) configured to contain a quantity of a liquid (3) and having an upper wall (4) with a through-hole (5); a wick (7) configured to convey the liquid by means of a capillary action and having a lower end (8) immersed in the liquid and an upper end (9) facing the upper wall; and a porous body (6), which is configured to be passed through by a gas generated by the evaporation of the liquid, is arranged above the upper end of the wick and occupies the through-hole of the upper wall of the casing. A dividing element (11,13) separates the chamber from the through-hole of the upper wall and defines a passage (12) occupied b at least a portion of the wick.

Description

[0001] CALIBRATION DEVICE FOR A LEAK TESTING STATION

[0002] Cross-Reference to Related Patent Applications

[0003] This patent application claims priority of the Italian patent application No. 102024000007381 filed on April 4, 2024, the content of which is incorporated by reference herein.

[0004] TECHNICAL SECTOR

[0005] The present invention relates to a calibration device for a leak testing station for testing the leak-tightness of an object.

[0006] PRIOR ART

[0007] The purpose of the leak-tightness check or test carried out on an object protected by a housing, for example a device or a component of an apparatus, is to define whether the housing is intact or has defects of a nature such as to result in the loss of (liquid or gas) substances and / or allow the unwanted infiltration thereof which, on the one hand, could negatively affect the operation thereof and, on the other hand, could have dangerous consequences both for the environment and for the safety of the operators or the users of said object.

[0008] A leak testing station comprises: a test chamber, with a known volume, capable of receiving the object(s) to be tested and able to hermetically isolate its internal volume from the external environment, once closed; a “sensor”, for example a mass spectrometer which is specially chosen depending on the substance(s) to be detected and which, when suitably connected to the test chamber and to a processing unit, firstly defines the composition of the atmosphere present inside the test chamber and then transmits a signal to the processing unit which indicates, as the system output, the possible presence of anomalous substances not present before insertion of the object. These substances, if attributable to something which is suitably introduced or is already present inside the tested object, reveal the presence of one or more leakages in the said object: the signal associated with the presence of these substances, suitably processed, is compared with a threshold value or is processed so as to quantify the degree of leakage detected, as described further below.

[0009] With the advent of electric mobility and the significant increase in “portable” applications, batteries (more generally energy storage systems) have assumed a fundamental role in the everyday life of very many persons; as a result, the requirements which characterize them, in terms of safety and performance, have become more stringent. In this context, testing the leak-tightness of batteries has assumed a fundamental role in the process for the production of these objects: in order to function properly and safely the batteries must be “leak-tight” and this requirement becomes increasingly more stringent as the production volumes of these objects increase, in particular in the motor vehicle sector. Consequently automatic or semi-automatic leak testing systems are incorporated in the production lines so as to provide immediate feedback on the process itself.

[0010] Leak testing or checking systems may be classified essentially as two types. In the systems of the first type, which carry out a so-called “attributes” check, the signal provided by the sensor is compared, in the processing unit, with a predetermined threshold signal; in this way the checked object is classified as acceptable or discarded depending on whether it is below or above the threshold signal. In the systems of the second type, which carry out a so-called “quantitative” check, the sensor sends back a measurement signal (expressed in a certain unit of measurement), the strength of which is proportional to the degree of leakage detected. In order for this second operating mode to be implemented, it is necessary to carry out a system calibration procedure in order to associate with the signal strength values provided by the sensor and suitably processed in the processing unit corresponding values of the amount of substance detected or the degree of leakage. The calibration involves the use of a calibration device or “master” which is configured to emit externally a known quantity of a substance, for example a gas, which is detected by the sensor; by knowing with precision how much gas has been emitted by the calibration device within a predetermined time interval it is possible to correlate the measurement signal provided by the sensor with the corresponding known quantity of gas.

[0011] For example, patent application No. DE102022109454A1 describes a device for testing and calibrating a leak detection station comprising a hollow housing, which can be filled with a test fluid. The test fluid can flow inside the housing and escape from there with a known leak rate thanks to the presence of a membrane.

[0012] For example, patent application No. DE102009012213A1 describes a test unit for evaluating results of leak tests comprising a housing with changing volume, which is filled with a test gas. By reducing the volume inside the housing, by moving a piston for example, the test fluid is pressurized and escapes from the housing with a defined leak rate.

[0013] DESCRIPTION OF THE INVENTION

[0014] The object of the present invention is to provide a calibration device for a leak testing station, which is able to provide an emission of a substance, in particular a gas, which is very stable over time and repeatable. Such a device moreover must be able to be used both manually and automatically and in conditions where tests are repeated frequently over time and must be easy and low-cost to produce.

[0015] According to the present invention a calibration device for a leak testing station is provided in accordance with that claimed in the attached claims.

[0016] The claims describe preferred embodiments of the present invention which form an integral part of the present description.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will now be described with reference to the attached drawings which illustrate a number of non-limiting examples of embodiment thereof, in which:

[0019] • Figure 1 is a schematic view of a calibration device provided in accordance with the present invention;

[0020] • Figure 2 is a schematic view of a first variant of the calibration device shown in Figure 1 ; and

[0021] • Figure 3 is a schematic view of a second variant of the calibration device shown in Figure 1 .

[0022] PREFERRED EMBODIMENTS OF THE INVENTION

[0023] In Figure 1 , the reference number 1 indicates overall a calibration device or “master leak” for a station for testing the leak-tightness of an object, namely the intact condition of the housing of this object. The calibration device 1 comprises a closed casing 2 configured to contain inside it a quantity of a substance in the liquid state or a liquid 3. The calibration device 1 according to the present invention is suitable in particular, but not exclusively, for the calibration of leak testing systems in which there is the presence of gas leaks generated by liquids 3 which have, at ambient temperature and pressure, a high vapour pressure (namely liquids which tend to evaporate easily).

[0024] As shown in Figure 1 , the casing 2 has an upper wall 4 which comprises a through- hole 5 and defines a chamber 15 configured to contain a quantity of the liquid 3. A porous body (or baffle) 6, of suitable size and consisting of material with known characteristics including porosity and percentage of vacuum volume, occupies the through-hole 5 of the upper wall 4 of the casing 2. The porous body 6 is configured to be passed through by a gas generated by the evaporation of the liquid 3 contained inside the casing 2.

[0025] Preferably, the porous body 6 is made of chemically inert materials (namely materials which have little or no tendency to react with other chemical elements or compounds).

[0026] The calibration device 1 further comprises a wick 7 which has a lower end 8 immersed in the liquid 3 and an upper end 9 arranged on the opposite side of the liquid 3, facing the upper wall 4 of the casing 2, preferably substantially opposite the through- hole 5 occupied by the porous body 6, and generally (but not necessarily) higher than a free surface of the liquid 3. Preferably, the wick 7 is arranged vertically. The wick 7 is configured to convey the liquid 3 by means of a capillary action; namely the wick 7 is always entirely wetted or impregnated by the liquid 3 and the liquid 3 rises up the wick 7 by means of a capillary action from the lower end 8 to the upper end 9 of the wick 7. In other words, the wick 7 is partially immersed in the liquid 3 and is always completely wetted / impregnated by the liquid 3 which rises up the wick 7 by means of a capillary action.

[0027] Preferably, the wick 7 is made of an absorbent (spongy) and chemically inert material, for example porous Teflon or carbon felt. Other materials which may be used to make the wick 7 include: glass fibre and non-woven polymers.

[0028] The calibration device 1 further comprises a pressurization valve 10 which is connected to the casing 2 opposite the chamber 15 and is configured to place in communication, when it is opened, the inside of the casing 2 with the external environment. Preferably, the pressurization valve 10 is one-way and allows an air flow only from the outside towards the inside of the calibration device 1 . Advantageously, the pressurization valve 10 is arranged above the free surface of the liquid 3 contained inside the casing 2.

[0029] According to the embodiment shown in Figure 1 , a lower surface of the porous body 6 is arranged at a non-zero distance from the upper end 9 of the wick 7, thus defining an intermediate space 14 between the porous body 6 and the wick 7. In particular, the intermediate space 14 is isolated from the liquid 3 on the outside of the wick 7; namely the intermediate space 14 is separated by means of a dividing wall or element 11 from the chamber 15 in which the liquid 3 is present in free form, and this prevents the liquid 3 from reaching directly (i.e. without passing through the wick 7) the intermediate space 14.

[0030] The function of the intermediate space 14 (i.e. of a space between the lower surface of the porous body 6 and the upper end 9 of the wick 7) is to prevent the porous body 6 from being wetted by the liquid 3 which is present in the upper end 9 of the wick 7, since the porous body 6 would be wetted by the liquid 3 in a random and uncontrolled manner, thereby making it impossible to maintain a controlled and stable condition which ensures the stability and the precision of the gaseous emission from the calibration device 1 .

[0031] Preferably, the intermediate space 14 has a small volume, namely which is as small as possible while maintaining a separation between the lower surface of the porous body 6 and the upper end 9 of the wick 7 which ensures that the porous body 6 cannot be wetted with the liquid 3 which is present in the upper end 9 of the wick 7. By reducing as far as possible the volume of the intermediate space 14 it is possible to restore quickly, after each use of the calibration device 1 , the corresponding nominal conditions and in particular obtain a rapid internal re-pressurization, thereby favouring the repeatability of the gaseous emission.

[0032] The dividing element 11 separates the intermediate space 14 from the chamber 15 where the liquid 3 is present and defines a through-hole, or passage, 12 which is occupied by at least a portion of the wick 7. In the embodiment shown in the figure, the dividing element 1 1 comprises a tubular portion or duct 13 which extends downwards, defines the passage 12 and contains the wick 7 inside it. Preferably, an entire lateral surface of the wick 7 is substantially in contact with the tubular duct 13 along the passage 12 so that only the lower end 8 of the wick 7 is directly wetted by the volatile liquid 3. In general, however, at least one portion of the wick 7 occupies (and closes) the passage 12, preventing the free liquid 3 present inside the chamber 15 from coming into contact with the porous body 6.

[0033] According to the embodiment shown in Figure 1 , the porous body 6 comprises a single body which defines two cylinders of different diameter, but alternatively it may comprise two elements arranged on top of each other and having varying diameters; preferably, the smaller element is arranged on top of the larger element and therefore the smaller element is arranged on the outside, while the larger element is arranged towards the inside (i.e. towards the wick 7). In the embodiment shown in Figure 1 , the porous body 6 has a multi-diameter cylindrical form, but the porous body 6 or the elements which make it up may have a frustoconical form. According to a different embodiment, the porous body 6 comprises a single cylindrical element, or comprises more than two elements arranged on top of each other.

[0034] According to an alternative embodiment shown in Figure 2, the wall 1 1 is not provided and the dividing element is identified only by the tubular duct 13 which defines the passage 12 and originates directly from the upper wall 4 of the casing 2. While not being shown in Figure 2, in this embodiment also shown in this Figure 2 there may also be present the intermediate space which distances the upper end 9 of the wick 7 from the lower end of the porous body 6; namely, in this embodiment also there may be present a non-zero distance (defining the intermediate space) between the upper end 9 of the wick 7 and the lower end of the porous body 6 (in the schematic representation shown in Figure 2, the passage 12 encloses in this case not only the porous body 6 and wick 7, but also the intermediate space).

[0035] According to an alternative embodiment - essentially that which is visible in the schematic representation of Figure 2 - a lower surface of the porous body 6 is in direct contact with a surface of the wick 7 and therefore there is no intermediate space.

[0036] During use, the calibration device 1 is inserted inside a sealed test chamber (the test chamber which defines a closed volume) to which there is suitably connected a sensor, for example a mass spectrometer, calibration of which is to be performed. During use, the calibration device 1 is subjected to at least one vacuum cycle in order to calibrate the sensor connected to the sealed test chamber. During a vacuum cycle, the vacuum is generated inside the sealed test chamber (for example using a vacuum pump) such that the calibration device 1 empties and releases a predefined (and therefore known) quantity of gas generated by the liquid 3 present inside the device. The quantity of released gas depends on the geometry of the porous body 6, the porosity and vacuum volume of the porous body 6, as well as the pressure inside the sealed test chamber and the vacuum time.

[0037] During the vacuum cycle, the liquid 3 contained inside the chamber 15 of the casing 2 is conveyed by means of a capillary action by the wick 7 towards the porous body 6 and the gas generated by the liquid 3 passes through the porous body 6 and is introduced into the sealed test chamber. In other words, during the vacuum cycle, the liquid 3 absorbed by the wick 7 is converted into the gaseous state and passes (in the form of a gas) through the porous body 6 into the sealed test chamber. In greater detail, before the vacuum cycle, the liquid 3 is absorbed entirely by the wick 7, and gas, generated by means of evaporation by the liquid 3, fills the intermediate space 14, in a liquid / vapour equilibrium condition. When the vacuum pump is activated, firstly all the air is drawn out from the system, namely both from the inside of the sealed test chamber and from the inside of the calibration device 1 . When the air has been eliminated, the liquid 3 which is present on the evaporation surface at the upper end 9 of the wick 7 is converted into the gaseous state and flows out through the porous body 6.

[0038] Once the quantity of substance in the form of vapour (i.e. the gas generated by the liquid 3 present in the wick 7) has emerged and the vacuum cycle is interrupted, the capillary forces tend to restore the quantity of liquid 3 present in the wick 7. This results in a slight lowering of the level of the liquid present in free form inside the chamber 15 and consequently a slight vacuum is created inside the casing 2.

[0039] At the end of a vacuum cycle, the casing 2 and in particular the chamber 15 containing the liquid 3 in free form is, as mentioned, under a slight vacuum, while the pressure of the intermediate space 14 (and of the porous body 6) is the pressure present inside the sealed test chamber. As soon as the sealed test chamber is re-pressurized to the ambient pressure, the air also enters inside the calibration device through the porous body 6. For return of the casing 2 to the ambient pressure, namely restoration of a condition in which the calibration device 1 is ready for renewed use, it is necessary to wait a relatively long time, determined by the capillary action in the wick 7, for example about several tens of minutes (said restoration time depending on the difference between the pressures and the free internal volume). If this waiting time is not compatible with the application in which the calibration device 1 is used, for example on a production line where it is required to perform multiple consecutive tests, the pressure equilibrium is restored in a decidedly more rapid manner by manually or automatically operating the pressurization valve 10.

[0040] According to a possible embodiment, the ambient pressure in the calibration device 1 at the end of a vacuum cycle is restored by manually opening the pressurization valve 10.

[0041] According to an alternative embodiment, the ambient pressure in the calibration device 1 at the end of a vacuum cycle is restored automatically (namely by orienting, when the calibration device 1 is positioned, the pressurization valve 10 so that it may be activated by an automatic actuator). According to an alternative embodiment, the pressurization valve 10, of the two-way type, could open autonomously (i.e. without any external intervention) depending on a pressure difference between the two ends of the pressurization valve 10; namely, in this case, the two-way pressurization valve 10 opens when the pressure difference between the two ends of the pressurization valve 10 exceeds a predetermined threshold value.

[0042] Advantageously, the automatic activation of the pressurization valve 10 allows the emission gas to be used in consecutive tests, with a reduced waiting time between one test and the next one, without the need for manual intervention and with a time for restoration of the nominal conditions at the end of a vacuum cycle (and therefore test cycle) shorter than the time which would be needed for manual resetting of said nominal conditions.

[0043] The pressurization valve 10 is shown in both the embodiments of Figures 1 and 2, but, in an alternative embodiment of the present invention, it may not be present if the longer waiting time for re-pressurization of the calibration device 1 does not constitute a problem for use thereof.

[0044] Figure 3 shows in schematic form an embodiment which does not comprise any pressurization valve. The alternative embodiment in Figure 3 comprises an additional element, which must not be necessarily present, but which may be useful in some cases, namely a grid 16 arranged between the upper end 9 of the wick 7 and the intermediate space 14 which prevents the uncontrolled presence of liquid - albeit in a minimum amount - inside the intermediate space 14, something which could occur in certain particular conditions such as the following two conditions mentioned only by way of example:

[0045] - ebullition of the liquid 3 retained in the wick occurs (this being possible in pressure conditions which are “stressful” for the liquid 3 itself), resulting in bubbles which reach the upper end 9 of the wick itself. The presence of the grid 16 breaks up the bubbles, preventing them from emerging into the intermediate space 14;

[0046] - an excess of vapour in the intermediate space 14 causes, as a result of condensation, the formation of liquid. The presence of the grid 16 with macroscopic holes, namely with holes which are significantly bigger than those present in the upper end 9 of the wick 7, has the effect that the vapour condenses mainly precisely on the surface of these macroscopic holes, thus avoiding the uncontrolled presence of liquid in other parts of the intermediate space 14 and preventing liquid from coming into contact with the porous body 6.

[0047] Compared to that shown in very schematic form and mainly for descriptive purposes in the attached figures, the proportions of the components may be different and have for example a more “squashed” appearance, namely a height which is smaller than the width of the casing 2. Such an appearance may result in advantages owing to the level of the liquid inside the chamber 15, which is less high and lowers only by a small amount between one test and another, and the equally smaller length of the wick, this being a favourable condition when the liquid level is at a minimum and therefore the length of the travel path of the vapour inside the absorbent material increases.

[0048] According to one possible embodiment, not shown in the figures, the calibration device 1 may be closed at the top by means of a stopper which is manually inserted on the outside so as to prevent natural evaporation of the liquid 3 through the porous body 6 and thus maximize the working life of the calibration device 1 . In this case the stopper engages externally with the upper wall 4 of the casing 2 so as to seal (ideally in a leak- tight manner) the through-hole 5 and therefore the porous body 6.

[0049] By way of example, the calibration device 1 has a gas emission which is of the order of micrograms per second and is influenced by the temperature and pressure (vacuum) to which the calibration device 1 is subject.

[0050] The above-described calibration device 1 has numerous advantages.

[0051] Firstly, the above-described calibration device 1 comprises a spacious casing 2 so as to be able to contain a large quantity of liquid 3 in free form able to generate numerous known gas emissions (or leakages); in this way, before inserting fresh liquid 3 inside the chamber 15 of the casing 2, the calibration device 1 may be used for many calibration cycles, allowing prolonged autonomy thereof.

[0052] The presence of the wick 7 and the dividing element 11 , 13 is able to maintain a constant evaporation surface of the liquid 3, which corresponds to the surface of the upper end 9 of the wick 7. If no wick 7 (and no dividing element 1 1 , 13) are present, the evaporation surface of the liquid 3 could vary when the calibration device 1 is displaced, since the liquid 3 (owing to the effect of the “waves” produced by the movement of the calibration device 1 ) could wet in a random and unpredictable manner other parts of the casing 2; instead, if the wick 7 (and the dividing element 1 1 , 13) are present, it is ensured that the evaporation surface of the liquid 3 is always the same and corresponds to the surface of the upper end 9 of the wick. The distance between the evaporation surface (the upper end 9 of the wick 7) and the surface of the porous body 6 typically facing it is also kept constant, and likewise the quantity of liquid 3 on said evaporation surface (upper end 9 of the wick 7) is kept constant, owing to the porosity of the material of the wick 7.

[0053] Furthermore, the presence of a considerable quantity of liquid 3 in free form inside the chamber 15, in addition to the aforementioned advantage with regard to autonomy, also ensures a constant quantity of liquid 3 in the wick 7 during the succession of tests in which the calibration device 1 is used, and thus prevents that variations in this quantity of liquid 3 in the wick 7 may cause undesirable and unpredictable variations in the operation of the calibration device 1 .

[0054] All these characteristics help ensure an extremely high degree of repeatability and a particularly high performance level of the calibration device 1 .

[0055] The pressurization valve 10 of the calibration device 1 provides an advantage both when qualifying the leak (allowing more stable conditions for precisely detecting the loss of weight of the liquid 3 which characterizes the calibration device) and in use, during repeated consecutive test cycles (i.e. the gas leak manages to return rapidly in each case to the same nominal initial condition). In particular, the use of the pressurization valve 10 allows the calibration device 1 to be rapidly restored to the nominal conditions cycle after cycle. As already mentioned, if no pressurization valve 10 is present, the nominal conditions may be restored only with decidedly longer waiting times (for example tens of minutes), since the air must pass through first the porous body 6 and then the wick 7. And this may not be acceptable in certain applications.

[0056] Moreover, in a preferred embodiment of the invention, the above-described calibration device 1 has, between the porous body 6 and the wick 7, an intermediate space 14 with small dimensions which is able to minimize the transient periods during emission of the gas from the calibration device 1 and restoration of the nominal conditions after each test cycle. In fact, the calibration device 1 is suitable for consecutive tests, also performed automatically.

[0057] Therefore, the calibration device 1 is able to reproduce a gas leak of known certifiable value, with an autonomy equivalent to thousands of calibration cycles.

[0058] The above-described calibration device 1 is therefore able to perform the calibration of a sensor device providing very stable and repeatable gas emission by means of certifiable tests.

[0059] The calibration device 1 according to the invention is, as already mentioned above, advantageously rechargeable, namely once the liquid contained inside the chamber 15 of the casing 2 has been used up, the latter may be opened and filled again and thus reequipped and re-qualified. Furthermore, the calibration device 1 has an architecture such as to be able operate with liquids of a different chemical nature. A particularly useful and advantageous use is for the calibration of particular systems for testing the leak-tightness of batteries in which leakages of gas generated by electrolytic components present inside the said batteries are detected. In this case, in fact, it is possible to insert in the chamber 15 of the casing 2 and use as liquid 3 the electrolytic component present in the batteries whose leak-tightness is being checked.

[0060] Finally, the above-described calibration device 1 is simple and low-cost to produce since it involves the use of components which are widely available commercially at a relatively low cost.

Claims

CLAIMS1 . Calibration device (1 ) for a leak testing station comprising:• a closed casing (2) that o incudes an upper wall (4) with a through hole (5) and o defines a chamber (15) configured for holding a quantity of a liquid (3),• a porous body (6), configured for being passed through by a gas generated by the liquid (3), that occupies the through hole (5) of the upper wall (4) of the casing (2),• a wick (7), configured for conveying by capillary action the liquid (3), including o a lower end (8) dipped in the liquid (3) and o an upper end (9) facing the upper wall (4) of the casing (2), and• a dividing element (1 1 ,13) that o separates said chamber (15) from said through hole (5) and o defines a passage (12) occupied by at least a portion of the wick (7).

2. Calibration device (1 ) according to claim 1 , wherein the wick (1 ) is vertically arranged.

3. Calibration device (1 ) according to claim 1 or claim 2, wherein said upper end (9) of the wick (7) faces the upper wall (4) substantially in correspondence of the through hole (5).

4. Calibration device (1 ) according to any one of the preceding claims, wherein the dividing element (11 ,13) comprises a tubular duct (13) defining said passage (12), a whole lateral surface of the wick (7) being substantially in contact with the tubular duct (13) at said passage (12).

5. Calibration device (1 ) according to any one of the preceding claims, wherein a lower surface of the porous body (6) is arranged at a distance different from zero from the upper end (9) of the wick (7) to define an intermediate space (14) between the porous body (6) and the wick (7).

6. Calibration device (1 ) according to claim 5, including a grid (16) arranged between the upper end (9) of the wick (7) and the intermediate space (14).

7. Calibration device (1 ) according to any one of the preceding claims and including a pressurization valve (10) that is coupled to the casing (2) at said chamber (15) and is configured to put the inside of the casing (2) in communication with an outer environment, when it is opened.

8. Calibration device (1 ) according to claim 7, wherein the pressurization valve (10) is a two-way valve and is configured for autonomously opening when the pressure difference between its two ends exceeds a predetermined threshold.

9. Calibration device (1 ) according to any one of the preceding claims, wherein the porous body (6) is made up of chemically inert materials.

10. Calibration device (1 ) according to any one of the preceding claims, wherein the wick (7) is made up of chemically inert materials.

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