Method for detecting a leak on a non-rigid test specimen

Abstract

The invention relates to a simplified method for detecting leaks on a non-rigid test specimen, comprising the steps of: introducing the test specimen into a film chamber, lowering the pressure in the film chamber outside of said test specimen, and detecting a leak in the test specimen on the basis of a spatial change in the film of said film chamber.

Claims

1. A method for detecting leaks on a non-rigid test specimen, comprising the steps of: introducing the test specimen into a film chamber, lowering the pressure in the film chamber outside of said test specimen, and detecting a leak in the test specimen on the basis of a spatial change in a film of said film chamber; and wherein the pressure in the film chamber is reduced to a pressure that is lower than the pressure in the test specimen by at least 500 mbar and preferably by at least 950 mbar.

2. The method of claim 1, wherein, after the introduction of the test specimen, the closed film chamber shows a leakage rate during detection that is at least as high or at least twice as high as a leakage rate of the test specimen.

3. The method of claim 1, wherein the spatial change in the film is measured by laser-optical measurement of a position of the film surface.

4. The method of claim 3, wherein the laser-optical measurement is performed by measuring the change in deflection of a laser directed onto the film surface.

5. The method of claim 1, wherein the spatial change in the film is detected by measuring the capacitance change of a metalized film surface.

6. The method of claim 1, wherein the spatial change in the film is detected by means of a device that indicates contact or the absence of contact with the film surface.

7. The method of claim 1, wherein the leakage rate of a gas escaping through the leak in the test specimen is calculated in dependence on the measured spatial change in the film.

8. The method of claim 1, wherein the reduction of the pressure in the film chamber is performed while maintaining the atmospheric pressure in the test specimen.

Description

(1) An embodiment of the invention will be detailed hereunder with reference to the FIGURE:

(2) The FIGURE shows a measuring arrangement for the implementation of the present method.

(3) The measuring arrangement is formed by a film chamber 10 into which a non-rigid test specimen 12 in the form of a food package has been placed. After the test specimen 12 has been positioned in the film chamber 10, the film chamber is closed by laying the two films 14, 16 forming the film chamber one upon the other, with the test specimen 12 between them, and by pressing the films against each other in an airtight manner at their edge zones by means of a clamping device 18.

(4) Thereafter, the film chamber is evacuated by means of the vacuum pump 20 connected with the inside of the film chamber via a valve 22. Here, the valve 22 is opened and a ventilation valve 24, which is also connected with the inside of the film chamber 10, is closed to atmosphere. While atmospheric pressure still prevails in the test specimen 12, the pressure in the volume inside the film chamber, which surrounds the test specimen 12, is lowered by at least 1000 mbar. After the pressure in the film chamber has been lowered, the valve 22 is also closed and the pump 20 is deactivated.

(5) The distance sensor 26 is used to monitor the position of the film 14 by means of laser-optical measurement of the distance between the distance sensor 26 and the film of the film chamber 10. A change in the spatial position of the film 14 is detected as a reduced distance from the distance sensor 26 and is used as a leak indicator.

(6) A leakage rate of 10.sup.−2 mbar.Math.l/s, for instance, causes a volume change of 10.sup.−2 cm.sup.3/s in a package volume of 1 liter with a gas filling at 1000 mbar. For a cube-shaped package volume of 1 liter (cross-sectional area 100 cm.sup.2) this means a reduction in thickness of 1 μm/s. Relative distance change rates of 1 μm/s can be detected in particular with optical methods. The change in package volume is transferred to the film surface of the film test chamber.

(7) The present method is independent of the type of gas in the test specimen and in the film chamber. Leaks on the film chamber have but a negligible influence on the test method. Coarse leaks are detected quickly, due to very prominent and fast positional changes in the film surface. Only few valves are required, such as for pump connection and ventilation purposes.