Test chamber device and method for localizing a leak in a test object

Abstract

The invention relates to a test chamber device (10) for localizing a gas leak (24) in a test object which is filled with a test gas, wherein the test chamber device (10) has a test chamber with test chamber walls (14, 16) that enclose a test volume (22), which can be hermetically sealed with respect to the external atmosphere and which is designed to receive the test object (20), and a vacuum pump (26) that is connected to the test chamber (12) in order to evacuate the test chamber. According to the invention, the test chamber device (10) has a localization device (30) which is designed to determine the temperatures of the test chamber walls (14, 16) or structures (15) adjoining the test chamber and to infer the position of a leak (24) in the test object (20) from the determined temperatures.

Description

[0001] Test chamber device and method for locating a leak in a

[0002] Examinee

[0003] The invention relates to a test chamber device and a method for locating a leak in a test object containing a test gas.

[0004] It is known to fill test objects, such as food packaging, with a test gas and place them in a film chamber which is then evacuated in order to then detect test gas escaping from the test object into the film chamber. In many cases, gas already present in the test object, e.g. a packaging bag, can be used as the test gas. This can be a protective gas or gas components of the air, such as nitrogen, oxygen or carbon dioxide. Flavorings contained in the packaging of the packaged food, for example coffee, can also be used as the test gas. Another option is to use gases that are generated in the packaging by the packaged food, such as carbon dioxide, which is generated in a coffee package after just a few hours.

[0005] Because the pressure within the foil chamber outside the test specimen is lower than inside the test specimen, test gas will escape through a potential leak in the test specimen. Conventional methods monitor the pressure increase in the foil chamber to detect a potential leak. If the pressure increase exceeds a certain level, this can be considered an indication of a leak in the test specimen.

[0006] It is also known to test test specimens containing a test gas for leaks in a test chamber with rigid test chamber walls.

[0007] Regardless of whether the test chamber has rigid walls or is designed as a film chamber with flexible test chamber walls, a leak sensor is generally connected to the test chamber. This sensor can be used to detect a leak in the test specimen after the test chamber has been evacuated to atmospheric pressure. The leak sensor can, for example, be a pressure sensor that measures the pressure within the test chamber. Common methods in this context include measuring the total pressure in the test chamber or measuring and monitoring the change in the total pressure over time ("rate of rise"). Alternatively, the partial pressure of the test gas in the test chamber can be measured, i.e., the proportion of the test gas in the gas mixture within the test chamber. The partial pressure measurement can be performed using a membrane selective for the test gas and a pressure sensor, or with a mass spectrometer.In test chambers with rigid test chamber walls, gas detectors are typically used as leak sensors that are capable of detecting the test gas.

[0008] In this specification, all these types of sensors, i.e. gas detector, pressure sensor, mass spectrometer, etc. are referred to as "leak sensor".

[0009] With conventional leak sensors in a test chamber, it is typically not possible to locate the location of a leak in the test object. Rather, they can only detect its presence. To locate the location of a leak, an additional leak detection device, such as a sniffer leak detector, must be used. Such a conventional leak detection device requires an additional measurement process independent of the actual leak detection. In this process, the test object is pressurized relative to the outside atmosphere, independent of the test chamber, and the external surface of the test object is scanned with the additional, locating leak detection device. For example, the test object surface is sniffed with a sniffer leak detector.What these localizing leak detection methods have in common is that the additional leak detector must be manually guided by an operator over the surface of the test object, and there is a risk that areas of the surface of the test object will not be examined or will not be examined sufficiently.

[0010] Against this background, the object of the invention is to provide an improved test chamber device and an improved method for locating a leak in a test specimen.

[0011] The device according to the invention is defined by the features of patent claim 1. The test chamber device is provided with test chamber walls that form a test chamber and enclose a test volume, which, when closed, are hermetically sealed from the external environment. The test chamber walls can be opened to introduce a test specimen into the test chamber. The test specimen is filled with a test gas that is either already contained in the test specimen, such as a gas present in food packaging, or that is actively introduced into the test specimen before it is introduced into the test chamber. With the "rate of rise" method, air can also be used as the test gas; the total pressure increase during the measurement is recorded using a total pressure sensor that is independent of the test gas.

[0012] The test chamber is connected to a vacuum pump which evacuates the test volume when the test chamber is closed. A leak sensor, which is not absolutely necessary for the invention, can be connected to the test volume and designed to detect a leak in the test object, for example by examining the gas extracted from the test chamber for the presence of test gas. The special feature of the invention is that the test chamber device is provided with a localization device which is designed to determine temperatures in at least one region of the test chamber walls or at least one structure adjacent to at least one of the test chamber walls, for example by measuring the temperatures or by recording parameters from which the temperature can be derived. The localization device is also designed to use the determined temperatures to deduce the location of a leak in the test object.

[0013] The idea behind this is that test gas escaping from the test object, such as air or helium, expands upon emerging from a leak and cools as a result of the expansion. The expanding, cooled test gas reaches the test chamber walls and / or the adjacent structure and cools them down in a corresponding area. By determining temperatures or temperature changes of the test chamber wall or the adjacent structure in this area, it can be determined that the test chamber wall or the structure has a lower temperature in such an area than in other areas. The localization device can then identify this area as an area near which a leak in the test object is located.

[0014] The localization device can comprise a temperature sensor. The temperature sensor can be connected to the test chamber wall or the adjacent structure, or form the structure adjacent to the test chamber wall, contact the test chamber wall, or be located outside the test chamber at a distance from the test chamber wall and detect the thermal radiation emanating from the test chamber wall. For example, the temperature sensor can be a thermographic camera that detects the thermal radiation from the outer surface of the test chamber wall. Alternatively or additionally, other types of temperature sensors are conceivable, for example, those that contact the test chamber wall.

[0015] Thermosensitive films are particularly suitable here. These are applied as structures adjacent to a test chamber wall, either inside or outside, to enable heat transfer from the test chamber wall to the film. The film changes its color in an area where the adjacent test chamber wall changes its temperature, for example, when leaking gas impinges on the test chamber wall. Alternatively or additionally, it is also conceivable for the test chamber wall to be equipped with at least one, preferably several, evenly distributed temperature sensors in the form of thermocouples. These contact the test chamber wall and generate a temperature-dependent voltage that can be recorded and evaluated to determine the temperature.

[0016] In particular, the localization device can have multiple temperature sensors, for example, by providing different temperature sensors on opposite sides of the test chamber. In particular, thermographic cameras, thermosensitive foils, and / or thermocouples can be provided on opposite sides. Furthermore, the localization device can include an analysis unit connected to the temperature sensor, which is designed to evaluate the determined temperature values ​​and, based on the temperature values, can determine an area of ​​the test chamber wall near which a leak in the test object is located. The area thus determined can be a projection of the location of a leak in the test object onto the adjacent test chamber wall. Knowing the position and orientation of the test object within the test chamber, the location of the leak in the test object can then be deduced from the determined area of ​​the test chamber wall.

[0017] For this purpose, threshold values ​​of the measured temperature can be used to infer the presence of a leak near the respective location on the test chamber wall when a threshold value is exceeded or undershot. Thus, if a test gas escaping from a leak in the test specimen cools the test chamber wall in an area adjacent to the leak, this area can be detected when the temperature of the test chamber wall falls below a corresponding threshold value.

[0018] The measured temperatures of the test chamber wall are preferably displayed to the operator on a display device of the test chamber device. The operator can then simultaneously identify the location of a potential leak in the test specimen during leak detection, without having to perform a separate measurement independent of the actual leak detection to locate the leak. In the case of a thermographic camera, for example, the image from the thermographic camera can be displayed on the display device.

[0019] In the following, an embodiment of the invention is explained in more detail with reference to the figures. In the figures: Fig. 1 shows a schematic representation of a first embodiment,

[0020] Fig. 2 is a schematic representation of a second embodiment,

[0021] Fig. 3 is a schematic representation of a third embodiment and

[0022] Fig. 4 is a schematic representation of a fourth embodiment.

[0023] The test chamber device 10 of the illustrated embodiments has a test chamber 12 in the form of a conventional foil chamber, whose test chamber walls 14, 16 consist of foil layers that are superimposed at their edges. The test chamber walls 14, 16 are hermetically connected to one another at their edges by a circumferential support frame 18, thereby hermetically sealing the test chamber 12. For removal and replacement of the test specimen 20, the support frame 18 can be opened to unfold the test chamber walls 14, 16 and thereby open the test chamber 12.

[0024] The figures show the test chamber 12 in the closed state. The test volume 22, enclosed by the test chamber walls 14, 16, contains a test specimen 20, which may, for example, be a food packaging item.

[0025] The test chamber 12 is connected to a vacuum pump 26 and is evacuated by this to a pressure lower than external atmospheric pressure. This reduces the distance between the test chamber walls 14, 16 and the test specimen 20, causing the foils of the test chamber walls 14, 16, in the case of a foil chamber, to conform to the outer contour of the test specimen 20 and contact it. For illustrative purposes only, a larger distance between the test specimen 20 and the test chamber walls 14, 16 is shown in the figures. In this respect, the figures are not to scale. The actual distance is significantly smaller in the case of a foil chamber in the evacuated state.

[0026] A leak sensor 28 in the form of a gas detector is connected to the outlet of the vacuum pump 26 as shown in Fig. 1. This gas analyzes the gas evacuated from the test chamber 12 by the vacuum pump 26. If the gas evacuated by the vacuum pump 26 contains test gas, this can be detected by the leak sensor 28. This allows the presence of a leak 24 in the test object 20 to be determined, but not its location.

[0027] As an alternative to the leak sensor 28 according to Fig. 1, a leak sensor 28 according to Fig. 4 can be provided upstream of the vacuum pump 26, i.e., between the test chamber 12 and the vacuum pump 26. The leak sensor 28 according to Fig. 4 is a total pressure sensor. After the test chamber 12 has been evacuated, a valve provided between the leak sensor 28 and the vacuum pump 26 can be closed to measure and monitor the total pressure of the gas within the test chamber 12. For example, the measurement method based on the "rate of rise" principle can be used here. This type of leak sensor 28 according to Fig. 4 is also conceivable in the embodiments according to Figs. 2 and 3. Alternatively, in each of the embodiments, it is conceivable not to use a leak sensor 28.

[0028] In order to be able to locate the location of a leak, the test chamber device 10 of each of the exemplary embodiments is provided with a localization device 30 having two temperature sensors 32, 34 on opposite sides of the test chamber 12. In the exemplary embodiment shown in Fig. 1, the temperature sensors 32, 34 are thermographic cameras, with the thermographic camera according to the temperature sensor 32 detecting the test chamber wall 14, while the thermographic camera according to the temperature sensor 34 on the opposite side detecting the test chamber wall 16. Thermal radiation 36 emanating from the test chamber walls 14, 16 is thus detected by the temperature sensors 32, 34.

[0029] The two temperature sensors 32, 34 are electronically connected to an analysis unit 38, which in the present embodiment is formed as part of the leak sensor 28. This means that the analysis unit 38 is arranged in a common housing with the leak sensor 28.

[0030] The analysis unit 38 receives the electronic measurement data generated by the temperature sensors 32, 34 and calculates corresponding thermal images of the outer surfaces of the test chamber walls 14, 16 from this measurement data. These thermal images are visually displayed on a display device 40. In the illustrated embodiment, the display device 40 is attached to the housing of the leak sensor 28 and the analysis unit 38 so that a user of the leak sensor 28 can view the display device 40.

[0031] The analysis unit 38 is configured to assign the measurement data obtained from the temperature sensors 32, 34 to spatial positions on the surface of the test chamber walls 14, 16. As a result, the analysis unit 38 is able to determine that the test chamber wall 14 has a lower temperature in one region 42 of its surface than in another region 43 and than the other test chamber wall 16.

[0032] The temperature of the test chamber wall 14 is lower in the region 42 because the test piece 20 has a leak 24 near the region 42, from which test gas flows toward the region 42 and cools as it expands while leaving the test piece 20, and cools in the region 42 upon impact with the test chamber wall 14. As a result, the region 42 can be interpreted as a projection of the location of the leak 24 onto the adjacent test chamber wall 14. Thus, the position of the region 42 on the surface of the test chamber wall 14 can be used to determine the location of the leak 24 in the underlying test piece 20.

[0033] In the embodiment in Fig. 2, the temperature sensors 32, 34 are not thermographic cameras, but rather photo cameras that record the outer surface of the test chamber walls 14, 16 and, in particular, the thermosensitive films 15 adjacent thereto. The thermosensitive films 15 according to the embodiment in Fig. 2 are placed on the outside of the respective test chamber walls 14, 16 in close contact, so that heat is transferred from the test chamber walls 14, 16 to the films 15. In the area 42, the film 15 changes color because gas escaping from the leak 24 cools the test chamber wall 14 in this area and, as a result, the temperature of the film 15 also drops, resulting in a color change in this area 42, which is recorded by the camera 32. The temperature-sensitive films thus form structures that closely adjoin the test chamber walls 14, 16 on the outside.

[0034] Another alternative is shown in Fig. 3, in which structures 15 in the form of several thermocouples are arranged adjacent to the inside of the test chamber walls 14, 16, each of which contacts the inside of the test chamber walls 14, 16. The thermocouple in region 42 cools due to the gas escaping through the leak 24 and thereby sends a different electrical voltage signal to the evaluation unit 38 than the other thermocouples. The thermocouples thus form temperature sensors 32, 34 that detect the temperatures of the test chamber walls 14, 16.

Claims

Claims 1. Test chamber device (10) for locating a gas leak (24) in a test object that is filled with a test gas, wherein the test chamber device (10) has a test chamber with test chamber walls (14, 16) that enclose a test volume (22) that can be hermetically sealed against the external atmosphere for accommodating the test object (20), and a vacuum pump (26) connected to the test chamber (12) for evacuating the test chamber, characterized in that the test chamber device (10) has a localization device (30) that is designed to determine temperatures of the test chamber walls (14, 16) or of structures (15) adjacent to the test chamber and to deduce the position of a leak (24) in the test object (20) from the determined temperatures.

2. Test chamber device (10) according to claim 1, characterized in that the localization device (30) has a temperature sensor.

3. Test chamber device (10) according to claim 1 or 2, characterized in that the localization device (30) has an analysis unit (38) which assigns the location of a measured temperature value to a location on the test chamber wall.

4. Test chamber device (10) according to claim 3, characterized in that the analysis unit (38) is designed to assign the location of the measured temperature to a leak location when a threshold value of the measured temperature is exceeded or undershot, if the leak sensor (28) has detected a leak (24) in the test object (20).

5. Test chamber device (10) according to one of the preceding claims, characterized in that the test chamber device (10) has a leak sensor (28) for detecting a possible leak (24) in the test object (20).

6. Test chamber device (10) according to one of the preceding claims, characterized in that the test chamber device (10) is a film chamber and at least one region of the test chamber walls (14, 16) consists of a flexible film which, in the evacuated state of the test chamber device (10), clings to the test object (20).

7. Method for locating a leak (24) in a test specimen (20) with a test chamber device (10) according to one of the preceding claims, characterized by the steps • Placing the test specimen (20) into the test chamber (12), • Evacuating the test chamber (12), • Determining temperatures of at least one of the test chamber walls (14, 16) or at least one structure adjacent to a test chamber wall (14, 16) with the localization device (30), • Determining the location of a leak (24) in the test specimen (20) based on the temperatures determined.

8. Method according to claim 7, characterized in that the location (42) of a temperature exceeding or falling below a threshold value is regarded as a projection of the location of a leak (24) in the test object (20) onto the test chamber wall (14).

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