Leak Detection with Oxygen

Abstract

A method for detecting a leak in a test object, including inserting the test object into a test chamber; filling the test object with a test gas; and adjusting a pressure in the test chamber and a pressure in the test object such that the test chamber pressure is lower than the test object pressure. The test chamber contains air and the test object is filled exclusively with a gas containing no molecules with oxygen atoms. In order to detect a leak in the test object, an oxygen proportion of the air in the test chamber is measured with an oxygen sensor.

Claims

1. A method for detecting a leak in a test object, said method comprising the following steps: inserting the test object into a test chamber; filling the test object with a test gas; and adjusting a pressure in the test chamber and a pressure in the test object such that the test chamber pressure is lower than the test object pressure, wherein the test chamber contains air and the test object is filled exclusively with a gas containing no molecules with oxygen atoms, wherein, in order to detect a leak in the test object, the oxygen proportion of the air in the test chamber is measured with an oxygen sensor.

2. A method for detecting a leak in a test object, said method comprising the following steps: inserting the test object into a test chamber; filling the test object with a test gas; and adjusting a pressure in the test chamber and a pressure in the test object such that the test chamber pressure is lower than the test object pressure, wherein the test chamber holds a gas that contains molecules with oxygen atoms and that the test object is filled with gas, wherein, for the detection of a leak in the test object, the oxygen proportion in an atmosphere inside the test chamber is measured using an oxygen sensor.

3. The method of claim 2, wherein the gas that contains molecules with oxygen atoms is carbon dioxide.

4. The method of claim 1, wherein the oxygen sensor is a lambda probe.

5. The method of claim 1, wherein upon measuring the oxygen proportion, a temporal development of a change in the oxygen partial pressure in the test chamber is measured according to an accumulation approach.

6. The method of claim 1, wherein air flows as a carrier gas around the test object in the test chamber and a change in oxygen concentration in the carrier gas is measured according to a carrier gas method.

7. The method of claim 6, wherein variations in the oxygen proportion in the air flowing around the test object is reduced using a buffer volume and a throttle.

8. The method of claim 1, wherein a total pressure of the air at the oxygen sensor is maintained stable to lower a detection limit.

9. The method of claim 1, wherein a quantity of the gas in the test chamber is kept small.

10. A device for detecting a leak in a test object filled with gas containing no molecules with oxygen atoms, comprising a test chamber receiving the test object, a gas pump or compressor connected to the test chamber and a gas sensor connected to the test chamber, wherein the gas sensor is an oxygen sensor and the test chamber contains air.

11. The device of claim 10, wherein a gas path between the pump or the compressor and the oxygen sensor comprises a buffer volume for pressure surge damping.

12. The device of claim 11, wherein on a side of the test chamber opposite the oxygen sensor, the gas path connected to the test chamber comprises an additional oxygen probe.

13. The device for detecting a leak in a test object filled with air, comprising a test chamber receiving the test object, a gas pump or compressor connected to the test chamber, and a gas sensor connected to the test chamber, wherein the gas sensor is an oxygen sensor, and the test chamber or test object contains a gas containing molecules with oxygen atoms.

14. The device of claim 13, wherein a gas path between the pump or the compressor and the oxygen sensor comprises a buffer volume for pressure surge damping.

15. The device of claim 14, wherein on a side of the test chamber opposite the oxygen sensor, the gas path connected to the test chamber comprises an additional oxygen probe.

Description

[0030] The following is a detailed explanation of two embodiments with reference to the Figures. In the Figures:

[0031] FIG. 1 is a schematic illustration of the first embodiment, and

[0032] FIG. 2 is a schematic illustration of the second embodiment.

[0033] In both embodiments, the test object 12 is filled completely with an oxygen-free test gas, so that no oxygen is contained in the test object. Thereafter or before, the test object is placed in a hermetically sealable test chamber 14. The test chamber 14 contains air.

[0034] The test chamber is gas-conductively connected to a carrier gas pump 16 or, alternatively, to a compressor. In a corresponding manner, the test chamber 14 is gas-conductively connected to an oxygen sensor 18 in the form of a lambda probe.

[0035] The oxygen sensor 18 and the carrier gas pump 16 are in communication through a gas path in which a throttle 22 is provided.

[0036] The embodiment in FIG. 1 is an arrangement for measurement according to the carrier gas method. Air is supplied to the test chamber 14 as a carrier gas via the carrier gas inlet 24 and a first has path 26 connecting the carrier gas inlet 24 and the test chamber 14. A further oxygen sensor 29, in particular in the form of a lambda probe, can be provided in the gas path, so as to determine the oxygen offset, i.e. the oxygen proportion contained in the air without test gas being added thereto from the test object 12.

[0037] The gas path 26 further includes another flow throttle 30 and a flow sensor 32. The side of the test chamber 14 opposite the gas path 26 is connected to an outlet gas path 34 which includes the carrier gas pump 16, the throttle 22, the oxygen sensor 18, the buffer volume 20 and a third throttle 36 and leads to the gas outlet 38.

[0038] Using the carrier gas pump 16, the air is guided from the inlet 24 through the test chamber 14 along the surface of the test object 12 and is supplied to the oxygen sensor 18. In case of a leak in the test object 12, oxygen-free gas escapes from the test object 12 and mixes with the air of the carrier gas, whereby the oxygen proportion in the air is reduced. This oxygen proportion is measured with the lambda probe (oxygen sensor 18).

[0039] The second embodiment illustrated in FIG. 2 is provided for measurement according to the accumulation method. A gas path 40 connects two opposite sides of the test chamber 14. The gas path 40 includes the carrier gas pump 16, the throttle 22, the buffer volume 20, a total pressure sensor 44, the oxygen sensor 18 (lambda probe) and a further throttle between the oxygen sensor 18 and the test chamber 14. The two throttles 42 and 22 are arranged on opposite sides of the oxygen sensor 18. The total pressure sensor 44 may be a differential total pressure sensor that measures the differential pressure with respect to the atmospheric ambient pressure.

[0040] Using the carrier gas pump 16, the pressure in the test chamber 14 is reduced in the area outside the test object 12 such that the oxygen-free gas in the test object 12 flows from a possible leak of the test object into the test chamber 14. The oxygen sensor 18 is used to continuously measure the oxygen partial pressure of the air in the test chamber 14. Specifically, the change in the oxygen partial pressure is measured over time, wherein a decrease of the oxygen concentration indicates a leak in the test object 12 and serves as a measure for the leakage rate.

[0041] The total pressure sensor 44 serves to enable the determination of the oxygen concentration from the oxygen partial pressure signal of the lambda probe and the measured total pressure. The oxygen concentration C.sub.O2 is the quotient of the oxygen partial pressure P.sub.O2 and the measured total pressure P.sub.tot:

C.sub.O2=P.sub.O2/P.sub.tot.