Device and method for leak testing of sealed products

Abstract

A leak detection device (1) for checking the integrity of sealed products (2) comprising a chamber (3) configured to receive at least one product that has been sealed (2) under a nitrogen-containing atmosphere, a turbomolecular vacuum pump (7), an ionized gas gauge (5), a buffer volume (8) fluidly connected to a chamber (12) of the ionized gas gauge (5), an isolation valve (9) interposed between the chamber (3) and the buffer volume (8) and configured to connect or isolate the buffer volume (8) from the chamber (3), a variable conductance restriction (10) interposed between the inlet of the turbomolecular vacuum pump (7) and the buffer volume (8) having a variable opening, and a gas injection device (11) configured to inject a variable flow rate of a substitute gas other than nitrogen into the chamber (3) containing the sealed product (2). Figure 1

Description

Title of the invention: Detection device and method for checking the tightness of sealed products Technical field of the invention

[0001] The present invention relates to a detection device for checking the tightness of sealed products such as pharmaceutical products, food products, or products from the biotechnology, automobile, watchmaking or cosmetics industries. The present invention also relates to a detection method implemented in the device. Technical background

[0002] Certain products such as sealed blisters, sachets, bottles, pouches, pharmaceutical or medical bags, syringes, are sealed in packaging at atmospheric pressure or under vacuum, to maintain their integrity.

[0003] To ensure that the seal is perfectly watertight, the leaktightness of the sealed product is tested. The test must have good sensitivity to ensure that the seal has a good leaktightness for different types of products, dry or liquid, flexible or rigid, opaque or transparent... For the pharmaceutical and food industries, this test is essential to ensure the stability of the drug or food product by protecting it from humidity, air and bacteria.

[0004] There are several methods for checking the tightness of sealed products.

[0005] Document EP2875328B1 discloses a detection method for checking the tightness of sealed products in which at least one product that has been previously sealed under an atmosphere of air, nitrogen, or argon is placed in an enclosure, the pressure in the enclosure is lowered to a secondary vacuum pressure by a turbomolecular vacuum pump and, while continuing the pumping under secondary vacuum in the enclosure, the gases contained in the enclosure are ionized to monitor the evolution in the enclosure of the concentration of at least one ionized gaseous species of the gaseous volume contained in the sealed product among nitrogen, oxygen or argon, by analysis by optical or mass emission spectrometry. The detection method uses the fact that the sealed products contain a gaseous atmosphere trapped between the element to be protected and the packaging.The search within the enclosure for the gaseous species contained in this gaseous volume therefore makes it possible to identify the presence of a leak in the sealed product. It is then no longer necessary to pierce and reseal the packaging to fill it with tracer gas. No special step is necessary between the sealing of the product in production, the leak test and the marketing of the sealed product without leaks.

[0006] However, some industries require very high sensitivity levels to detect particularly small leaks, in particular less than 0.5 pm, or 4.105 mbar.l / s, or 4.106 Pa.mVs, or even 0.2 pm, or 6.10 6 mbar.l / s, or 6.107 Pa.mVs, particularly in the pharmaceutical industry to guarantee the sterility threshold. It is then essential to lower the background noise of the test method in order to have sufficient sensitivity.

[0007] When nitrogen is the gaseous species whose evolution in the enclosure is monitored, the measured nitrogen signal may come from a leak of the sealed product that one seeks to detect but also from the degassing of the walls, in particular the walls of the enclosure, the walls of the sealed product, or even the walls of the detector chamber and the vacuum line due to their punctual communication with the enclosure, at intermediate pressure. It is possible to lower this background noise by waiting a long time in maximum pumping called ultimate vacuum. However, in ultimate vacuum, another source of parasitic nitrogen background noise comes from the back diffusion of the gases through the turbomolecular vacuum pump.

[0008] We therefore seek to reduce the nitrogen background noise that may come from degassing of the walls or backscattering through the vacuum pump to achieve sensitive detection. However, below too low a pressure, it is no longer possible to maintain an ignited plasma in the detector chamber for a sufficiently long period to carry out a leak test. Summary of the invention

[0009] An aim of the present invention is to overcome this drawback at least partially by proposing a device and a method for detecting highly sensitive leaks of products sealed under an atmosphere containing nitrogen, in particular to meet pharmaceutical standards.

[0010] To this end, the invention relates to a detection device for checking the tightness of sealed products comprising: - an enclosure configured to receive at least one product which has been sealed under an atmosphere containing nitrogen, - a turbomolecular vacuum pump, - an ionized gas gauge, characterized in that the detection device further comprises: - a buffer volume fluidly connected to a chamber of the ionized gas gauge, - an isolation valve interposed between the enclosure and the buffer volume, and configured to connect or isolate the buffer volume with the enclosure, - a variable conductance restriction interposed between the vacuum pump inlet turbomolecular and buffer volume, the variable conductance restriction having a variable opening, and - a gas injection device configured to inject a variable flow of substitute gas other than nitrogen into the enclosure containing the sealed product.

[0011] The injection of substitute gas into the enclosure combined with the reduction of flow at the suction of the turbomolecular vacuum pump makes it possible to adapt the pressure in the enclosure and therefore in the chamber of the ionized gas gauge to achieve a test pressure compatible with the generation and maintenance of a plasma. The pressure obtained is thus the lowest possible for the ignition and maintenance of a plasma, which makes it possible to obtain a high sensitivity test. The continuous injection of substitute gas into the enclosure also makes it possible to prevent the backdiffusion of nitrogen into the enclosure through the turbomolecular vacuum pump by directing the flow towards the discharge of the turbomolecular vacuum pump.The variable conductance restriction allows the pumping flow to be reduced to increase pressure while maintaining the high compression ratio of the turbomolecular vacuum pump, which also helps prevent back diffusion of gaseous species through the turbomolecular vacuum pump. It also allows less surrogate gas to be injected during the test, which avoids overwriting the nitrogen signal with that of the surrogate gas. Furthermore, the variable conductance of the restriction allows the conductance to be increased for rapid pumping of the chamber from atmospheric pressure.

[0012] The detection device may further comprise one or more of the characteristics described below, taken alone or in combination.

[0013] The detection device may comprise a control unit.

[0014] The control unit may be configured to control the variable opening of the variable conductance restriction based on a control parameter of the ionized gas gauge to ignite or maintain a plasma in the chamber.

[0015] The control unit may be configured to control the flow rate of the gas injection device based on a control parameter of the ionized gas gauge in order to ignite or maintain a plasma in the chamber.

[0016] The variable conductance restriction comprises, for example, a diaphragm.

[0017] The control parameter of the ionized gas gauge is for example the voltage of a generator of a device for generating a plasma of the ionized gas gauge.

[0018] According to an exemplary embodiment, the ionized gas gauge comprises: - a chamber, - a plasma generation device configured to generate a plasma in the chamber, - an optical emission spectrometer, - an optical window allowing the analysis of the light emitted by the plasma by the optical emission spectrometer.

[0019] According to an exemplary embodiment, the ionized gas gauge comprises a plasma generation device comprising: - a cathode comprising a cylindrical wall connected to at least one disc having a central hole and at least two peripheral holes, - a rectilinear anode arranged in the center of the cathode and crossing the cathode discs, - at least one toroidal magnet surrounding the chamber, and - a generator connected to the cathode and the anode.

[0020] The detection device may comprise a calibrated leak connected to the enclosure comprising a capillary and an isolation valve interposed between a nitrogen distributor and the enclosure.

[0021] The invention also relates to a detection method for checking the tightness of products sealed in a detection device as described above, comprising the following steps: - in a first step, at least one product which has been previously sealed under an atmosphere containing nitrogen is placed in the enclosure, - in a second step, the isolation valve is opened so as to put the enclosure in communication with the vacuum buffer volume, - in a third step, a substitute gas other than nitrogen is continuously injected into the enclosure and, while continuing the pumping under secondary vacuum in the enclosure, the gases contained in the enclosure are ionized by means of the ionized gas gauge to monitor the evolution in the enclosure of the nitrogen concentration by optical emission spectrometry analysis and to identify the presence of a leak of said sealed product, the opening of the variable conductance restriction and the flow rate of the gas injection device being controlled so as to generate and maintain an ignited plasma in the chamber of the ionized gas gauge.

[0022] According to an exemplary embodiment, in the second step, the opening of the variable conductance restriction is maximum and the flow rate of the gas injection device is minimum.

[0023] According to an exemplary embodiment, in the third step, as the pressure in the enclosure decreases, the opening of the variable conductance restriction is first reduced before increasing the flow rate of the gas injection device to keep the plasma lit.

[0024] The detection method may include a fourth step in which the isolation valve is closed while continuing to inject the replacement gas to return the enclosure to atmospheric pressure.

[0025] A substitute gas can also be injected into the enclosure in order to sweep the walls of the substitute gas enclosure during the first stage.

[0026] The substitute gas is for example chosen from argon, xenon, helium, carbon dioxide, krypton and neon.

[0027] According to an exemplary embodiment, a calibration test is carried out with an integral sealed product contained in the enclosure into which a known flow of nitrogen is injected via a calibrated leak from the detection device. Brief description of the figures

[0028] Other characteristics and advantages of the invention will emerge from the following description, given by way of example, without limitation, with reference to the appended drawings in which:

[0029] [Fig-1] [Fig.l] is a schematic view of a detection device for the leak testing of sealed products.

[0030] [Fig.2A] [Fig.2A] is a schematic front view of an exemplary embodiment of a variable conductance restriction of the detection device of [Fig.l] with a maximum aperture.

[0031] [Fig.2B] [Fig.2B] is a view similar to [Fig.2A] with a partially closed opening.

[0032] [Fig.3] [Fig.3] is a schematic sectional view of elements of an example of a sheave lization of an ionized gas gauge of the detection device.

[0033] [Fig.4] [Fig.4] shows a diagram of the steps of a detection method implemented work in the detection device.

[0034] [Fig.5A] [Fig.5A] shows an example of a spectrum obtained for a leak test of a sealed product without a substitute gas.

[0035] [Fig.5B] [Fig.5B] shows another example of a spectrum obtained for a leak test of a sealed product for which the substitute gas is argon.

[0036] In these figures, identical elements have the same reference numbers. Detailed description

[0037] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0038] [Fig.l] represents a detection device 1 for checking the tightness of sealed products 2.

[0039] The sealed products 2 are, for example, pharmaceutical or food products, such as sealed blisters, sachets, bottles, pouches, pharmaceutical bags pharmaceutical or medical products, syringes. Sealed products 2 can also be products from the biotechnology, watchmaking or automotive industries.

[0040] These products contain at least one element to be protected, for example from moisture, air or bacteria, such as a medicine or a foodstuff. The element to be protected may be in liquid or solid form. It is packaged in a sealed package. A complete seal ensures that access to the inside of the package is impossible, no gas can enter or exit the package.

[0041] The sealed product 2 contains nitrogen or a mixture of gases containing nitrogen such as air, between the element to be protected and its packaging. The pressure of the gaseous volume contained in the sealed product 2 is therefore constant. It may be atmospheric pressure or subatmospheric pressure for so-called “vacuum” packaging, depending on its packaging. It may also be an overpressure tank such as an airbag or other.

[0042] The detection device 1 comprises an enclosure 3 configured to receive at least one product which has been sealed 2 under an atmosphere containing nitrogen, a pumping group 4 and an ionized gas gauge 5.

[0043] The enclosure 3 has a volume which can contain one or more sealed products 2 and which has dimensions slightly greater than the volume of the sealed product(s) 2 to be tested, so as to limit as much as possible the absorption of gases by the surfaces of the enclosure 3 when the latter is at atmospheric pressure for loading / unloading the sealed product 2. This limits the degassing of the walls of the enclosure 3 at low pressure which could increase the background noise. In addition, a volume just slightly larger than the volume of the sealed product 2 makes it possible to lower the pressure in the enclosure 3 more quickly and therefore to improve the response time and the sensitivity of the measurement, the measurement volume being equal to the volume of the enclosure 3 from which the volume of the sealed product 2 has been subtracted.

[0044] The enclosure 3 is adapted to be able to be placed under vacuum by the pumping group 4.

[0045] The pumping group 4 comprises a primary vacuum pump 6 and a turbomolecular vacuum pump 7 which are fluidically connected in series, the inlet of the primary vacuum pump 6 being fluidically connected to the outlet of the turbomolecular vacuum pump 7. The turbomolecular vacuum pump 7 is configured to provide a secondary vacuum in the enclosure 3 in ultimate vacuum, that is to say without gas injection, less than or equal to 105 mbar (10 3Pa), such as between 10 5mbar (10 3Pa) and 10 7mbar (105Pa).

[0046] The detection device 1 further comprises a buffer volume 8, an isolation valve 9 interposed between the enclosure 3 and the buffer volume 8, a restriction at variable conductance 10 interposed between the inlet of the turbomolecular vacuum pump 7 and the buffer volume 8 and a gas injection device 11 configured to inject a variable flow rate of substitute gas other than nitrogen into the enclosure 3 containing the sealed product 2.

[0047] The variable conductance restriction 10 has a variable opening, which makes it possible to reduce the conductance between the buffer volume 8 and the turbomolecular vacuum pump 7, i.e. the dimension of the gas passage between the turbomolecular vacuum pump 7 and the buffer volume 8, while allowing continuous pumping of the buffer volume 8 by the turbomolecular vacuum pump 7.

[0048] The variable conductance restriction 10 comprises, for example, a diaphragm. The diaphragm may be, for example, completely open ([Fig.2A]) or partially closed ([Fig.2B]) with several possible degrees of closure. The variation in the size of the opening is, for example, continuous.

[0049] The isolation valve 9 can either be opened so as to put the buffer volume 8 into communication with the enclosure 3 and thus put the enclosure 3 under vacuum by means of the buffer volume 8, or closed so as to isolate the buffer volume 8 from the enclosure 3, in particular to open the enclosure 3 to atmospheric pressure for the unloading and loading of sealed products 2 to be tested and at the same time, lower the pressure in the buffer volume 8 by means of the turbomolecular vacuum pump 6.

[0050] The buffer volume 8 is thus continuously evacuated by the turbomolecular vacuum pump 7. The pressure of the buffer volume 8 does not rise to atmospheric pressure, which prevents the absorption of gases by the surfaces. The buffer volume 8 is for example between 0.5dm3 and 2dm3, such as 1dm3.

[0051] The substitute gas injection device 11 is configured to inject a variable flow rate of substitute gas other than nitrogen into the enclosure 3 containing the sealed product 2 and comprises, for example, a flow controller 25 for this purpose.

[0052] The substitute gas is injected into the enclosure 3 on the one hand during the test making it possible to identify the presence of a leak of the sealed product 2 and possibly, for the return to atmospheric pressure of the enclosure 3 and as will be seen later for the flushing of the enclosure 3 at atmospheric pressure during the loading / unloading of sealed products 2 to be tested. Alternatively, a specific additional gas injection line is used for the return to atmospheric pressure and / or for the flushing of the enclosure 3 at atmospheric pressure.

[0053] The substitute gas is a gas distinct from nitrogen in order to avoid any confusion with the nitrogen contained in the sealed product 2.

[0054] The substitute gas is, for example, argon. Argon has the advantage of facilitating the interpretation of the spectrum, in particular because the spectral lines of argon are far from the spectral lines of nitrogen. In addition, it is a neutral gas, readily available, inexpensive, and it facilitates the ignition of a plasma. Other examples include xenon, helium, carbon dioxide, krypton, or neon. The substitute gas can also include a mixture of gases other than nitrogen.

[0055] As better visible in Figures 1 and 3, according to an exemplary embodiment, the ionized gas gauge 5 comprises a chamber 12 fluidly connected to the buffer volume 8, a plasma generation device 13 configured to generate a plasma in the chamber 12, an optical emission spectrometer 14, configured to provide a spectrum from the light emitted by the plasma and an optical window 15, such as a transparent porthole, allowing the analysis of the light emitted by the plasma by the optical emission spectrometer 14.

[0056] The chamber 12 connected to the buffer volume 8 by its open end can thus be continuously evacuated thanks to the buffer volume 8.

[0057] According to an exemplary embodiment, the plasma generation device 13 of the ionized gas gauge 5 comprises an anode 16 (+ pole) and a cathode 17 (- pole) respectively connected to the positive and negative poles of a generator 21 ([Fig. 3]). The cathode 17 comprises a cylindrical wall 17a connected to at least one disc 17b, for example three distributed along the axis of the cylindrical wall 17a, each having a central hole through which the anode 16 passes and possibly having at least two peripheral holes, for example six regularly distributed around the central hole. The rectilinear anode 16 is arranged in the center of the cathode 17 with which it is insulated and passes through the discs 17b of the cathode 17.

[0058] The generator 21 of the plasma generation device 13 is configured to apply between the anode 16 (positively charged) and the cathode 17 (negatively charged) a high potential difference, for example greater than or equal to 3000 Volts which generates a radial electric field E. In practice, the generator 21 provides for example a fixed current, the voltage being a variable control parameter which depends in particular on the pressure in the chamber 12 of the ionized gas gauge 5.

[0059] This field E makes it possible to create a plasma by generating and accelerating a flow of electrons from the cathode 17 to the anode 16 in order to excite and ionize the gas molecules coming from the enclosure 3. To obtain a usable plasma, a magnetic field B of constant intensity, approximately 100 mT, and of given direction is added to it, the field lines of which are perpendicular to the electric field E and parallel to the anode 16. The magnetic field B is generated by at least one permanent toroidal magnet 18 surrounding the chamber 12. The presence of a magnetic field B coupled to the electric field E makes it possible to greatly increase the excitation of the gas molecules of the plasma.

[0060] Thus a plasma can be generated inside this chamber 12 by the plasma generation device 13 in order to be able to analyze the gaseous species present in the enclosure 3. The plasma generated on the gaseous species emits light coming from the de-excitation of the molecules characteristic of the gases present. The light which passes through the optical window 15 is collected for example by an optical collector system and analyzed spectrally by the optical emission spectrometer 14 optically connected for example by a fiber 19 which transports the light from the optical collector to the spectrometer 14 ([Fig. 1]).

[0061] In optical emission spectrometry, charged molecules (ions) are separated according to the wavelength at which they emit. The amplitude of a peak in the spectrum (or spectral line) corresponds to the relative abundance of a molecule fragment. The spectrometer 14 establishes the characteristic spectrum of the gaseous species present in the chamber 12. The wavelengths of the lines in the optical spectrum thus obtained are characteristic of the gaseous species present in the enclosure 3 (Figures 5A, 5B).

[0062] The detection method uses the fact that the sealed products 2 contain a gaseous atmosphere containing nitrogen trapped between the element to be protected and the packaging. Monitoring the evolution of nitrogen therefore makes it possible to identify the presence of a leak in the sealed product 2. A leak is detected for example by comparing at least one nitrogen line of the spectrum obtained with a nitrogen line of a spectrum of a reference sealed product 2, that is to say free of leaks or by noting the presence of a nitrogen line, in particular for example by comparing the amplitude of the nitrogen line in the spectrum obtained with a maximum threshold not to be exceeded so that the sealed product is considered to be intact.

[0063] The detection device 1 may also comprise a calibrated leak 22 connected to the enclosure 3 ([Fig.l]). By calibrated leak is meant a leak whose characteristics are known. The calibrated leak can be used to obtain the spectrum of a reference sealed product 2.

[0064] To do this, a calibration test is carried out with a sealed product 2 contained in the enclosure 3 into which a known flow of nitrogen is injected via the calibrated leak 22.

[0065] According to an exemplary embodiment, the calibrated leak 22 comprises a capillary 23 and an isolation valve 24 interposed between a nitrogen distributor and the enclosure 3. The capillary 23 allows the delivery of a constant and known flow of nitrogen. The sealed product 2 contained in the enclosure 3 at the time of this measurement makes it possible to add the degassing source from the walls of the sealed product 2 to the reference signal.

[0066] The detection device 1 may comprise a control unit 20, such as a computer, automaton or controller, connected to the optical emission spectrometer 14. to receive from the latter, signals representative of the evolution of the ionized gaseous species in the chamber 12 and to identify whether a wavelength characteristic of nitrogen is present in the spectrum to identify a leak.

[0067] According to an exemplary embodiment, the control unit 20 is configured to control the variable opening of the variable conductance restriction 10 and / or the flow rate of the gas injection device 11 as a function of a control parameter of the ionized gas gauge 5 in order to ignite or maintain a plasma in the chamber 12.

[0068] The control parameter of the ionized gas gauge 5 is for example the voltage of the generator of the plasma generation device 13.

[0069] The control unit 20 can also be configured to control the isolation valve 24 of the calibrated leak 22 if necessary.

[0070] In operation, the detection method 100 for checking the tightness of sealed products 2 in the detection device 1 comprises the following steps ([Fig.4]).

[0071] It is considered that the isolation valve 9 is initially closed, the enclosure 3 being isolated from the buffer volume 8, the buffer volume 8 being placed under vacuum by the turbomolecular vacuum pump 7, the discharge of which is maintained under primary vacuum by the primary vacuum pump 6.

[0072] In a first step 101, at least one product which has been sealed 2 beforehand under an atmosphere containing nitrogen, for example which has been sealed under air or under nitrogen, is placed in the enclosure 3. This first step 101 is carried out at the pressure of the atmosphere prevailing outside the enclosure 3, for example atmospheric pressure.

[0073] According to an exemplary embodiment, a substitution gas is injected into the enclosure 3 during the first step 101 in order to sweep the walls of the enclosure 3 with substitution gas. This sweeping of the walls with a substitution gas while the enclosure 3 is opened for the unloading / loading of a sealed product 2 to be tested makes it possible to prevent the walls of the enclosure 3 from being charged with gaseous species coming from the ambient air and increasing the background noise when the enclosure 3 is placed under vacuum. Then, the enclosure 3 is closed.

[0074] In a second step 102, the isolation valve 9 is opened so as to put the enclosure 3 in communication with the buffer volume 8 under vacuum, which lowers the pressure in the enclosure 3 and in the chamber 12 of the ionized gas gauge 5. The opening of the variable conductance restriction 10 is for example maximum and the flow rate of the gas injection device 11 is for example minimum. The secondary vacuum obtained (or test pressure) is for example between 10 2 mbars (IPa) and 107 mbars (105Pa).

[0075] The variable conductance restriction 10 makes it possible to increase the pumping flow rate. to obtain the test pressure in the enclosure 3 quickly during the first step 101 and this for different degassing rates of sealed products. Indeed, the variable conductance arranged in front of the turbomolecular vacuum pump 7 makes it possible to increase the passage section and therefore the conductance in order to lower the pressure as quickly as possible from atmospheric pressure after loading a sealed product 2 and to maintain this maximum pumping until the end of the degassing. The degassing duration can then be adapted according to the degassing rate of the sealed product 2 in order to avoid it taking several hours, for example for containers that degas a lot, such as those made of plastic material.

[0076] In a third step 103, a substitute gas other than nitrogen is continuously injected into the enclosure 3 by means of the substitute gas injection device 11, for example with an initial flow rate of 103 mbar.l / s, or 10 4 Pa.mVs and, while continuing the pumping under secondary vacuum in the enclosure 3, the gases contained in the enclosure 3 are ionized by means of the ionized gas gauge 5 to monitor the evolution in the enclosure 3 of the nitrogen concentration by analysis by optical emission spectrometry and to identify the presence of a leak of said sealed product 2.

[0077] The opening of the variable conductance restriction 10 and the flow rate of the gas injection device 11 are controlled so as to be able to generate and maintain an ignited plasma in the chamber 12 of the ionized gas gauge 5.

[0078] The continuous injection of substitution gas into the enclosure 3 combined with the reduction of flow 10 at the suction of the turbomolecular vacuum pump 7 makes it possible to adapt the pressure of the gases inside the enclosure 3 and therefore in the chamber 12 of the ionized gas gauge 5, to reach test pressures compatible with the generation and maintenance of a plasma in the chamber 12.

[0079] The continuous injection of substitute gas into the enclosure 3 makes it possible to prevent the back diffusion of nitrogen into the enclosure 3 through the turbomolecular vacuum pump 7 by directing the flow towards the discharge of the turbomolecular vacuum pump 7.

[0080] The variable conductance restriction 10 makes it possible to reduce the pumping flow while maintaining the high compression ratio of the turbomolecular vacuum pump 7, which also makes it possible to prevent backdiffusion of gaseous species through the turbomolecular vacuum pump 7. In addition, the reduction in the pumping flow compared to the maximum vacuum pumping makes it possible to inject less substitute gas to achieve the desired test pressures. The lower injection of substitute gas makes it possible not to crush the nitrogen signal with that of the substitute gas. Indeed, a smaller power is required for the generator 21 of the plasma generation device 13, which makes the nitrogen partial pressure signal visible.

[0081] The pressure obtained is thus the lowest possible for maintaining a plasma, which makes it possible to obtain high sensitivity.

[0082] In practice, for example, to keep the plasma lit, it is sought to maintain a constant current. For this, for example, as the pressure in the enclosure 3 decreases, the voltage of the generator 21 of the plasma generation device 13 is first increased. When this voltage reaches a maximum, for example 5000 Volts, the opening of the variable conductance restriction 10 is first reduced before increasing the flow rate of the gas injection device 11. The flow rate can, for example, be increased to 101 mbar.l / s, or 1 Pa.mVs.

[0083] After having carried out the leak test, in a fourth step 104, the isolation valve 9 is closed for example while continuing to inject the replacement gas for the return to atmospheric pressure in the enclosure 3. The injected replacement gas makes it possible to saturate the internal walls of the enclosure 3 and of the chamber 12 of the ionized gas gauge 5, which makes it possible to reduce the rate of adsorption of the walls by the ambient air, and in particular by nitrogen, and consequently, to reduce the time necessary for degassing between two measurements and therefore the cycle time.

[0084] The graphs shown in Figures 5A and 5B show two examples of spectra obtained by measurement by optical emission spectroscopy for the leaktightness control of sealed product packaging 2 integrated by monitoring the amplitude of the peak of a nitrogen line contained in the enclosure 3, also present in the sealed product 2.

[0085] In the spectrum of [Fig.5B] where argon is the substitute gas, the amplitude of the monitored nitrogen spectral line (around 389nm) is lower than in the spectrum of [Fig.5A] without substitute gas. The substitute gas therefore makes it possible to reduce the nitrogen background noise. Furthermore, the increase in the amplitudes of the argon spectral lines in the spectrum of [Fig.5B] due to the fact that the substitute gas is argon, does not constitute a hindrance for the monitoring of the nitrogen line because the argon lines are far from the monitored nitrogen line.

[0086] It is therefore understood that the detection device 1 makes it possible to carry out high-sensitivity leak detection of sealed products 2 meeting in particular pharmaceutical standards.

Claims

Claims

1. Detection device (1) for checking the tightness of sealed products (2) comprising: - an enclosure (3) configured to receive at least one product which has been sealed (2) under an atmosphere containing nitrogen, - a turbomolecular vacuum pump (7), - an ionized gas gauge (5), characterized in that the detection device (1) further comprises: - a buffer volume (8) fluidically connected to a chamber (12) of the ionized gas gauge (5), - an isolation valve (9) interposed between the enclosure (3) and the buffer volume (8) and configured to connect or isolate the buffer volume (8) with the enclosure (3), - a variable conductance restriction (10) interposed between the inlet of the turbomolecular vacuum pump (7) and the buffer volume (8), the variable conductance restriction (10) having a variable opening,- a gas injection device (11) configured to inject a variable flow rate of substitute gas other than nitrogen into the enclosure (3) containing the sealed product (2), and - a control unit (20) configured to control the variable opening of the variable conductance restriction (10) and / or the flow rate of the gas injection device (11) as a function of a control parameter of the ionized gas gauge (5) in order to ignite or maintain a plasma in the chamber (12).,

2. Detection device (1) according to the preceding claim, characterized in that the control parameter of the ionized gas gauge (5) is the voltage of a generator of a plasma generation device (13).

3. Detection device (1) according to one of the preceding claims, characterized in that the variable conductance restriction (10) comprises a diaphragm.

4. Detection device (1) according to one of the preceding claims, characterized in that the ionized gas gauge (5) comprises: - a chamber (12), - a plasma generation device (13) configured to generate a plasma in the chamber (12), - an optical emission spectrometer (14), - an optical window (15) allowing the analysis of the light emitted by the plasma by the optical emission spectrometer (14).

5. Detection device (1) according to the preceding claim, characterized in that the plasma generation device (13) comprises: - a cathode (17) comprising a cylindrical wall (17a) connected to at least one disc (17b) having a central hole and at least two peripheral holes, - a rectilinear anode (16) arranged in the center of the cathode (17) and passing through the discs (17b) of the cathode (17), - at least one toroidal magnet (18) surrounding the chamber (12), and - a generator (21) connected to the cathode (17) and the anode (16).

6. Detection device (1) according to one of the preceding claims, characterized in that the detection device (1) comprises a calibrated leak (22) connected to the enclosure (3) comprising a capillary (23) and an isolation valve (24) interposed between a nitrogen distributor and the enclosure (3).

7. Detection method (100) for checking the tightness of products sealed in a detection device (1) according to one of the preceding claims, characterized in that it comprises the following steps: - in a first step (101), at least one product which has been sealed (2) beforehand is placed in an atmosphere containing nitrogen, in the enclosure (3), - in a second step (102), the isolation valve (9) is opened so as to put the enclosure (3) in communication with the buffer volume (8) under vacuum (102), - in a third step (103), a substitute gas other than nitrogen is continuously injected into the enclosure and, while continuing the pumping under secondary vacuum in the enclosure (3),the gases contained in the enclosure (3) are ionized by means of the ionized gas gauge (5) to monitor the evolution in the enclosure (3) of the nitrogen concentration by optical emission spectrometry analysis and to identify the presence of a leak of said sealed product (2), the opening of the variable conductance restriction (10) and the flow rate of the gas injection device (11) being controlled so as to generate and maintain an ignited plasma in the chamber (12) of the ionized gas gauge (5).,

8. Detection method (100) according to the preceding claim, characterized in that in the second step (102), the opening of the variable conductance restriction (10) is maximum and the flow rate of the gas injection device (11) is minimum.

9. Detection method (100) according to the preceding claim, characterized in that in the third step (103), as the pressure in the enclosure (3) decreases, the opening of the variable conductance restriction (10) is first reduced before increasing the flow rate of the gas injection device (11) to keep the plasma lit.

10. Detection method (100) according to one of claims 7 to 9, characterized in that in a fourth step (104), the isolation valve (9) is closed while continuing to inject the replacement gas for the return to atmospheric pressure in the enclosure (3).

11. Detection method (100) according to one of claims 7 to 10, characterized in that a substitution gas is injected into the enclosure (3) in order to sweep the walls of the enclosure (3) with substitution gas during the first step (101).

12. Detection method (100) according to one of claims 7 to 11, characterized in that the substitute gas is chosen from argon, xenon, helium, carbon dioxide, krypton and neon.

13. Detection method (100) according to one of claims 7 to 12, characterized in that a calibration test is carried out with a sealed product (2) contained in the enclosure (3) into which a known flow of nitrogen is injected via a calibrated leak (22) of the detection device (1).

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