Detecting test gas fluctuations during sniffer leak searching

Abstract

A method for detecting fluctuations in the amount of test gas detected by a sniffer probe of a leak detector in the gas flow from around a test piece pressurized with an oxygen-free test gas containing at least an amount of CO.sub.2, wherein an amount of oxygen in the ambient air is measured.

Claims

1. A method comprising detecting fluctuations in an amount of test gas detected by a sniffer probe of a leak detector in a gas flow from ambient air surrounding a test piece pressurized with an oxygen-free test gas containing at least an amount of CO.sub.2, wherein detecting the fluctuations in an amount of test gas comprises: measuring an amount of CO.sub.2 in the gas flow from ambient air, measuring an amount of oxygen in the gas flow from ambient air, and detecting the fluctuations in the amount of test gas based on the measured amount of CO.sub.2 and the measured amount of oxygen.

2. The method according to claim 1, wherein the amount of oxygen measured is used to determine an amount of CO.sub.2 in the ambient air that does not result from a leak in the test piece.

3. The method according to claim 1, wherein the measurement of the amount of oxygen in the ambient air surrounding the test piece is taken at atmospheric pressure.

4. The method according to claim 1, wherein the amount of oxygen in the gas flow of the sniffer probe or an exhaust gas flow of a gas-conveying pump of the leak detector connected to the sniffer probe is measured.

5. The method according to claim 1, wherein an offset c.sub.2 (t) of the amount of test gas that is contained in an intake gas flow and that does not derive from a leak in the test piece is determined using the equation: $c_2\left(t\right)=c_0+c_1\left(t\right),\mathrm{where}{c}_1\left(t\right)=\frac{a}{b}.Math.\frac{1}{I\left(t\right)},$ wherein c.sub.0 is a constant offset of CO.sub.2 in the intake gas flow, c.sub.1 (t) is a time-dependent offset amount of CO.sub.2 in the intake gas flow, a is a ratio factor between measured oxygen concentration and existing CO.sub.2 offset concentration, b is a sensitivity factor for the amount of oxygen measured by an oxygen probe, and I(t) is a change in a measurement signal of the oxygen probe.

6. A device for sniffer leak detection, comprising: a sniffer probe, wherein the sniffer probe comprises a gas-conveying pump for taking in and measuring a test gas flow that flows out of a test piece and into an ambient atmosphere surrounding the test piece, wherein the test piece is pressurized with the test gas relative to the ambient atmosphere, and wherein the test gas is oxygen-free and has at least an amount of CO.sub.2; and a CO.sub.2 sensor for measuring an amount of CO.sub.2 in the gas flow taken in by the sniffer probe; an oxygen sensor for measuring an amount of oxygen in the gas flow taken in by the sniffer probe; and a detecting unit for detecting fluctuations in an amount of CO.sub.2 in the gas flow taken in by the sniffer probe based on the measured amount of CO.sub.2 and the measured amount of oxygen, and for deriving an actual leak rate of the test piece.

7. The device according to claim 6, wherein the oxygen sensor is arranged and embodied upstream of the pump, to measure gas flowing through the sniffer probe, or is arranged and embodied downstream of the pump, to measure an exhaust gas flow of the gas-conveying pump.

8. The device according to claim 6, wherein the oxygen sensor is a lambda probe.

9. The device according to claim 6, wherein the oxygen sensor is a sensor that detects a partial pressure of oxygen.

10. The device according to claim 9, wherein the oxygen sensor is a mass spectrometer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention shall be explained in greater detail in view of the following FIGURE.

(2) FIG. 1 is a schematic representation of an exemplary embodiment of the device according to the invention.

DESCRIPTION OF THE INVENTION

(3) With reference to FIG. 1, the test piece 12 may be, for example, food packaging. The test piece 12 is pressurized with positive pressure with respect to the ambient atmosphere 14 and filled oxygen-free with at least CO.sub.2 test gas. The test gas flows out through a leak 16 due to the positive pressure relative to the ambient atmosphere 14.

(4) The leak detector 18 works according to the principle of sniffer leak detection and to this end has a sniffer probe 20 that is connected to a pump 22 or a compressor 22.

(5) The pump 22 or compressor 22 produces a gas flow that is taken in through the inlet 24 of the sniffer probe 20. The leak detector 18 furthermore has a partial pressure sensor 26, in the form of a mass spectrometer, that reacts to CO.sub.2 and that determines the amount of CO.sub.2 test gas in the intake gas flow of the sniffer probe 20. If the sniffer probe 20 is moved along the outer surface of the test piece 12 towards the leak 16, the amount of test gas in the intake gas flow increases, which may be detected using the partial pressure sensor 26.

(6) The amount of CO.sub.2 in the intake gas flow may rise for other reasons, however, for instance if the breath gas of the person moving the sniffer probe 20 is taken in by the sniffer probe or if the sniffer probe 20 is disposed in the vicinity of an exhaust gas flow of an internal combustion engine. In this case, the partial pressure sensor 26 detects a rising amount of CO.sub.2. In order to prevent this from incorrectly being understood as suggesting a leak 16 in the test piece 12, according to the invention an oxygen sensor 28 that measures the amount of O.sub.2 in the intake air flow is provided.

(7) The oxygen sensor 28 may be a sensor that detects the partial pressure of oxygen, a mass spectrometer, for example, or it may even be, for example, a conventional lambda probe.

(8) The oxygen sensor 28 in the depicted exemplary embodiment is arranged in the gas flow between the sniffer probe 20 and the pump 22. Alternatively, the oxygen sensor may be provided directly in the grip 20 or may measure the exhaust gas flow of the pump 22 at its outlet.

(9) The amount of oxygen measured is used to detect that amount of CO.sub.2 in the intake gas flow that does not derive from a leak 16 in the test piece 12, but rather results from combustion of oxygen.