Sniffing leak detection device with semiconductor gas sensor and sniffing leak detection method

Abstract

A sniffing leak detection device (10) having a measurement gas inlet (28) for drawing in a measurement gas at a measurement location, the measurement gas being used to detect whether there is a possible leak gas at the measurement location; a reference gas inlet (30), different from the measurement gas inlet (28), for drawing in a reference gas from around the measurement location; a gas supply pump (16) for supplying the sucked gas through a measurement gas inlet (28) and a reference gas inlet (30); a switching valve (20) which is connected to the gas supply pump (16) via a gas conducting path (22) and to the reference gas inlet (30) and the measurement gas inlet (28) in a gas conducting manner, and which is formed in such a way that the gas supply pump (16) sucks in the gas (30) via the measurement gas inlet (28) and / or via the reference gas inlet depending on a switching state of the switching valve (20), the invention relates to a gas sensor (18) for analyzing a gas drawn in by a gas supply pump (16), characterized in that the gas sensor (18) has a gas-sensitive sensor region (42) which has at least one physical property which varies and can be measured as a function of the gas coming into contact with the sensor region (42), the sensor region (42) is arranged such that at least a portion of the gas supplied by the gas supply pump (16) passes along the sensor and thereby contacts the sensor region (42), thereby changing the measurable characteristic.

Description

[0001] The invention relates to a sniffing leak detection device with a measuring gas inlet, which is used for sucking measuring gas at a measuring position, so as to check whether there is possible leaking gas at the measuring position.

[0002] Such a sniffing leak detection device is usually designed as a handheld probe, which is connected to a gas detector via a gas conducting connection line for gas analysis. An air flow is sucked in through the sniffing tip of the sniffing probe and delivered to the sensor unit in the gas detector. This involves checking whether the gas mixture being analyzed contains leaking gas that escapes from the inside of the test sample to the outside through a leak in the test sample. To this end, the test sample is usually filled with a known test gas, such as helium, or is already filled with a gas or refrigerant used as a test gas. However, the test gas used often occurs naturally in the atmosphere around the test sample. For example, the air contains a certain proportion of helium. Therefore, it is very important to determine the natural proportion of the test gas used in the atmosphere around the test sample, which is not caused by a leak in the test sample.

[0003] For example, it is known from EP 1 342 070 B1 that in addition to the measuring gas inlet of a sniffing leak detection device, a reference gas inlet different from the measuring gas inlet is used. The reference gas inlet is intended to suck in reference gas from the vicinity of the measurement location, i.e. from the test sample being checked and the vicinity of the supposed leak. This is based on the idea that the proportion of the test gas used in the reference gas is not caused by a leak in the test sample, but corresponds to the natural occurrence of the test gas used in the mixed gas being checked.

[0004] The switching valve is used to switch between the reference gas inlet and the measurement gas inlet. The gas supply pump is connected to the switching valve via a gas pipeline path, and the switching valve can be connected to the measurement gas inlet and / or the reference gas inlet as required. This means that the switching valve can be used to establish a gas conduction connection between the measurement gas inlet and a gas sensor located in the gas supply pump path and / or a gas conduction connection between the reference gas inlet and the gas sensor. The gas supply pump then sucks gas from the measurement gas inlet and / or the reference gas inlet according to the switching state of the switching valve and delivers the sucked gas to the gas sensor.

[0005] In known sniffing leak detection devices with switching between a measuring gas inlet and a reference gas inlet, optical sensors in the form of infrared gas analyzers are usually used as gas sensors. The measuring cuvette is filled with the gas to be analyzed and then irradiated with infrared radiation. Based on the resulting absorption spectrum, conclusions can be drawn about the composition of the gas in the measuring cuvette.

[0006] Conventional infrared gas analyzers do not allow switching between the measuring gas inlet and the reference gas inlet at any frequency. Instead, the measuring cuvette used must first be filled with the gas mixture to be analyzed before the analysis can be carried out, and then the gas mixture to be analyzed must be introduced into the measuring cuvette before the analysis can be carried out. This results in a limited switching frequency (also called modulation frequency) at which the switching valve switches between the measuring gas inlet and the reference gas inlet. At higher frequencies, the sensitivity of the gas analysis decreases, because the gas in the measuring cuvette is not completely exchanged.

[0007] An object of the present invention is to provide a sniffing leak detection device which is capable of rapidly switching a measuring gas inlet and a reference gas inlet during gas analysis.

[0008] The sniffing leak detection device of the invention is defined by the features of claim 1. The method of the invention is defined by claim 10.

[0009] The sniffing leak detection device includes a measuring gas inlet for sucking the measuring gas at the measuring position, so as to check whether there is a possible leaking gas at the measuring position. The leaking gas is the gas that escapes from the inside of the test sample through the leak in the test sample, enters its external environment, and is picked up by the sniffing leak detection device there. Usually, a known test gas is used as the leaking gas, and the test sample is filled with the test gas or the test sample already contains the test gas. A reference gas inlet different from the measuring gas inlet is provided for sucking the reference gas from the vicinity of the measuring position (i.e., from the vicinity of the area suspected of leaking), and the gas is sucked from the area through the measuring gas inlet. The gas supply pump of the sniffing leak detection device generates a gas flow through the gas pipeline path connecting the measuring gas inlet and the reference gas inlet to the gas supply pump so as to suck the gas through the gas inlets used respectively. The switching valve is used to connect the gas pipeline to the measuring gas inlet and / or the reference gas inlet, so that the gas supply pump sucks the gas through the measuring gas inlet and / or the reference gas inlet according to the switching state of the switching valve. It can be switched between the measuring gas inlet and the reference gas inlet. Alternatively, the reference gas inlet can be temporarily connected to the gas pipeline connecting the measuring gas inlet and the gas supply pump. The gas sensor analyses the gas sucked in by the gas supply pump.

[0010] According to the invention, the gas sensor of the sniffing leak detection device is not a conventional optical sensor, such as a conventional infrared gas analyzer, but a gas sensor having a sensor surface having at least one physically measurable property that changes depending on the gas contacting the sensor surface and can be measured by the sensor. The sensor surface is arranged in such a way that at least a portion of the inhaled gas delivered by the gas supply pump through the gas line is guided along the sensor, thereby contacting the sensor surface and changing the physical property of the sensor surface. The physical property of the sensor surface can be measured electrically, for example, by evaluating the measurement signal to identify the gas composition of the gas mixture being examined.

[0011] The physical property can be, for example, the resistance or voltage-current characteristic of the sensor surface. For example, the gas sensor can be a semiconductor gas sensor. Alternatively, the gas sensor can also be a thermal conductivity sensor, where the measurable physical property of the sensor surface is thermal conductivity, which varies depending on the contact gas.

[0012] The invention has the decisive advantage that significantly less gas is required to generate an electrical measurement signal suitable for gas detection than is known from the prior art for optical sensors. For example, whereas the sensor volume of an optical infrared radiation absorption sensor must be filled in order to generate a meaningful measurement signal, a gas sensor with a gas-sensitive sensor surface requires only a much smaller amount of gas to contact or wet the sensor surface.

[0013] The invention therefore has the advantage that the gas volume in the measuring environment in the gas sensor or on the sensor surface can be limited to a value that enables a fast switching of the switching valve and a fast signal response of the gas sensor. Preferably, the gas volume in the measuring environment in the gas sensor or on the sensor surface is limited to a value of 1 cubic centimeter, preferably 500 cubic millimeters and particularly preferably 100 cubic millimeters. This means that a maximum gas volume of 1 standard cubic centimeter, 0.5 standard cubic centimeters or 0.1 standard cubic centimeters is sufficient to generate an electrically evaluable measurement signal, thereby achieving a high switching frequency of the switching valve. For a switching frequency of the switching valve of, for example, 4 Hz, the gas flow rate must be 8 standard cubic centimeters per second, 4 standard cubic centimeters per second or 0.8 standard cubic centimeters per second in order to achieve a complete gas exchange in each measuring cycle.

[0014] On the other hand, if the sniffing leak detector is operated with a larger sniffing gas flow in order to achieve a faster gas exchange in the detection volume, this leads to a greater dilution of the absorbed leak gas quantity, which in turn leads to a reduction in sensitivity.

[0015] In principle, a faster gas exchange in the detection volume can be achieved with a constant sniffer gas flow rate by reducing the operating pressure in the detection volume to a constant lower level. This also reduces the amount of gas to be exchanged. However, this leads to a lower test gas partial pressure, which in turn leads to a lower sensitivity and is therefore also undesirable.

[0016] In particular, in the sniffing leak detection method according to the invention, a gas volume of less than 1 standard cubic centimeter, less than 0.5 standard cubic centimeter or particularly preferably less than 0.1 standard cubic centimeter is conducted through the sensor surface when evaluating the measurement signal.

[0017] The reduced gas exchange allows for a higher gas modulation frequency to achieve complete gas exchange in the detection volume and / or for the sniffing gas flow rate to be reduced to the minimum level to achieve complete gas exchange in the detection volume during each modulation cycle. The reduced sniffing gas flow rate in turn leads to an increase in the test gas concentration for a given leak rate, which in turn increases the sensitivity of the detection.

[0018] Such semiconductor gas sensors are known, for example, in the form of metal oxide sensors, in which the sensor surface has a metal oxide coating, but are not common in the field of sniffing leak detection.

[0019] Semiconductor sensors (such as SnO2 sensors) are suitable for detecting hydrogen or hydrocarbons. However, the sensor behavior is nonlinear, with a strong signal response to changes in low concentration levels, an increasingly flat signal change as the concentration increases, and only a slight signal change at high concentrations. Signal changes at low or medium concentration levels are easily detected, and such signal changes are caused by the modulation pattern, especially when the reference gas concentration is low. The present invention takes advantage of this strong signal response at low concentrations as shown below:

[0020] The higher the selected modulation frequency, the better the interference gas suppression during gas exchange modulation.

[0021] There is a limitation here: once the signal no longer reaches the full signal swing within the fast modulation cycle, sensitivity is lost.

[0022] Optical infrared radiation absorption detection requires a sufficient infrared absorption distance between the infrared emitter and the infrared detector in the measuring cuvette. To obtain full sensitivity, the entire measuring gas cuvette must be completely filled with the measuring gas or reference gas for each modulation cycle. To reduce the gas volume in the cuvette, the cuvette length can be shortened, but this also shortens the infrared absorption distance. An alternative solution to speed up the gas exchange is a stronger gas supply flow (gas flow), but this reduces the sample gas concentration and thus the sensitivity of the leak measurement.

[0023] Therefore, the aim is to achieve a fast and complete gas exchange at the sensor with the lowest possible gas flow rate in order to achieve a high modulation frequency.

[0024] Compact and sensitive sensor elements are, for example, semiconductor sensors. The use of semiconductor sensors for the regulation of gas exchange is currently unknown.

[0025] Other sensor elements can serve as alternatives to semiconductor sensors:

[0026] -Gas selective thermal conductivity sensor element

[0027] -Pirani gas detector

[0028] The switching valve is preferably designed to switch between the measuring gas inlet and the reference gas inlet with a switching frequency or modulation frequency of at least 4 Hz, preferably at least 8 Hz. With conventional infrared gas analyzers or other optical sensors, such high switching frequencies would lead to a loss of sensitivity. However, semiconductor gas analysis enables such fast switching and has a sufficiently high sensitivity to evaluate the measurement signals of the measuring gas and the reference gas.

[0029] The switching valve can be designed to connect the reference gas inlet to the gas line connecting the measuring gas inlet to the gas supply pump at a frequency of at least 4 Hz. Here, the frequency (modulation frequency) can also be at least 8 Hz. Thus, a gas mixture consisting of the measuring gas alone or a mixture of measuring gas and reference gas is supplied to the gas sensor at alternating intervals.

[0030] The sensor surface of the semiconductor gas sensor preferably has a resistance or a current-voltage characteristic which reacts to the leaking gas or the test gas used in the test sample. Preferably, the resistance of the sensor surface or the current-voltage characteristic of the semiconductor is changed by the test gas used. A suitable test gas is, for example, helium.

[0031] According to the method of the present invention, a gas flow is generated by a gas supply pump, which is sucked in through a measuring gas inlet and / or a reference gas inlet according to the switching position of a switching valve and guided along a gas line path through a gas sensor, so that the gas components of the gas flow react with the sensor surface, so that the resistance of the sensor surface or the current-voltage characteristic of the semiconductor changes according to the gas type of the gas component, thereby detecting leaking gas or test gas sucked in through the measuring gas inlet. The resistance of the sensor surface is electrically measured, so that the measurement signal of the resistance measurement is used for gas analysis.

[0032] Preferably, the switching valve switches to the reference gas inlet or connects the reference gas inlet to the gas line path between the measuring gas inlet and the gas sensor, so that the gas sucked in from the surroundings of the measuring location via the reference gas inlet is checked for the presence of leaking gas components and these leaking gas components are taken into account when evaluating the gas sucked in via the measuring gas inlet. In particular, it is conceivable to subtract the determined proportion of the test gas or leaking gas in the analyzed reference gas from the corresponding proportion of the test gas or leaking gas in the analyzed measuring gas in order to determine the test gas proportion or the test gas concentration originating from the leak of the test sample.

[0033] Hereinafter, exemplary embodiments of the present invention will be explained in detail with reference to the accompanying drawings.

[0034] The sniffing leak detection device 10 shown has a handheld sniffing probe 12, which is connected to a gas supply pump 16 via a gas connecting line 13. A gas sensor 18 is arranged in the sniffing probe 12. To this end, the sniffing probe 12 has a housing 14, which also surrounds the gas sensor 18. A three-way switching valve 20 is also arranged in the housing 14, which is connected to the gas sensor 18 via a gas pipeline path 22. Another part of the gas pipeline path 22 connects the gas sensor 18 to the gas supply pump 16, wherein the part of the gas pipeline path 22 extending to the outside of the housing 14 is formed by the gas connecting line 13.

[0035] The housing 14 has a measuring gas sniffer tip 24 and a reference gas sniffer tip 26. The two sniffer tips 24, 26 can also be combined or arranged in a common housing of a common sniffer probe. Alternatively, the reference gas sniffer tip 26 can also be installed on the housing 14 away from the measuring gas sniffer tip 24.

[0036] The measured gas sniffer tip 24 has a measured gas inlet 28 at its front end opposite to the housing 14. In a corresponding manner, the reference gas sniffer tip 26 is provided with a reference gas inlet 30 at its end opposite to the housing 14. It is particularly important that the measured gas inlet 28 is connected to the first connection piece of the switching valve 20 via a measured gas line 32, while the reference gas inlet 30 is also connected to the switching valve 20 via a reference gas line 34 that is different from the measured gas line 32. The measured gas line 32 is connected to the first connection piece 36 of the switching valve 20, the reference gas line 34 is connected to the second connection piece 38 of the switching valve 20, and the gas line 22 is connected to the third connection port 40 of the switching valve 20, which is different from the first two connections 36, 38.

[0037] Switching valve 20 selectively connects first connection 36 or second connection 38 to third connection 40 , so that in the case of first connection 36 , measuring gas line 32 is connected to gas line 22 , and in the case of second connection 38 , reference gas line 34 is connected to gas line 22 .

[0038] Alternatively or additionally, the switching valve 20 can connect both the first connection 36 and the second connection 38 to the third connection 40 , so that in this case both the measuring gas line 32 and the reference gas line 34 are connected to the gas line 22 .

[0039] The gas sensor 18 is designed as a semiconductor sensor in the form of a metal oxide sensor. The gas sensor 18 has a sensor surface 42 in the form of a metal oxide surface. The sensor surface 42 is arranged in the gas sensor 18 so that the gas flow guided along the gas line path 22 in the housing 14 flows through the sensor surface 42. As a result, a part of the conveyed gas mixture comes into contact with the sensor surface 42 and influences the resistance of the sensor surface 42 or the current-voltage characteristic of the transistor. The sensor resistance changes depending on the gas type of the gas component in contact with the sensor surface 42.

[0040] The resistance of the sensor surface 42 is measured in an electrically customary and known manner, so that the gas composition at the sensor surface 42 can be inferred from the measurement signal of the resistance value, so that in particular specific gas components, such as test gases contained in the test sample, can be detected.

Claims

1. A sniffing leak detection device (10), comprising a measuring gas inlet (28) for sucking in measuring gas at the measuring point, wherein The measuring gas is used to detect whether there is a possible gas leak at the measured position; a reference gas inlet (30), which is different from the measurement gas inlet (28) and is used to draw in reference gas from around the measurement location; a gas supply pump (16) for supplying the sucked gas through the measurement gas inlet (28) and the reference gas inlet (30), a switching valve (20) connected to the gas supply pump (16) via a gas conduction path (22) and connected to the reference gas inlet (30) and the measurement gas inlet (28) in a gas conduction manner, and configured such that, depending on the switching state of the switching valve (20), the gas supply pump (16) draws gas through the measurement gas inlet (28) and / or the reference gas inlet (30); and a gas sensor (18) for analyzing the gas sucked in by the gas supply pump (16); It is characterized in that The gas sensor (18) has a gas sensitive sensor area (42) having at least one physical property which varies depending on the gas in contact with the sensor area (42) and which is measurable, wherein the sensor area (42) is arranged such that at least a portion of the gas supplied by the gas supply pump (16) passes along the sensor and thereby contacts the sensor area (42), thereby changing the measurable property.

2. The sniffing leak detection device (10) according to claim 1, characterized in that: The gas sensor (18) is a semiconductor gas sensor whose resistance or current-voltage characteristic at the sensor surface varies depending on the gas type, for example in the form of a metal oxide sensor.

3. The sniffing leak detection device (10) according to claim 1, characterized in that: The gas sensor is a thermal conductivity sensor, the heat emission from the sensor surface to the gas environment depends on the type of gas.

4. The sniffer leak detection device (10) according to one of the preceding claims, characterized in that The gas sensor (18) has a housing (19) which limits the volume of gas close to the sensor surface (42) to 1 cubic centimeter, preferably 0.5 cubic centimeter, particularly preferably 0.1 cubic centimeter.

5. The sniffer leak detection device (10) according to one of the preceding claims, characterized in that The switching valve (20) is designed to switch between the measurement gas inlet (28) and the reference gas inlet (30) at a frequency of at least 4 Hz.

6. The sniffer leak detection device (10) according to one of the preceding claims, characterized in that The switching valve (20) is designed to connect the reference gas inlet (30) to the gas line path (22) which connects the measurement gas inlet (28) to the gas supply pump (16) at a frequency of at least 3 Hz.

7. The sniffing leak detection device (10) according to claim 5 or 6, characterized in that: The frequency is at least 5 Hz, such as at least 10 Hz.

8. The sniffer leak detection device (10) according to one of the preceding claims, characterized in that The physical property of the sensor surface (42) is electrical resistance, current-voltage characteristic and / or thermal conductivity.

9. The sniffer leak detection device (10) according to one of the preceding claims, characterized in that The gas sensor (18) and the switching valve (20) are arranged in the housing (14) to form a manual sniffer probe (12) of the sniffer leak detection device (10).

10. A method for performing a sniffing leak detection using the sniffing leak detection device (10) according to one of the preceding claims, characterized in that: The gas supply pump (16) is used to generate a gas flow, which is sucked in through the measuring gas inlet (28) and / or the reference gas inlet (30) according to the switching position of the switching valve (20) and guided along the gas pipeline path (22) through the gas sensor (18), so that the gas components of the gas flow react with the sensor surface (42), so that the physical properties of the sensor surface (42) change according to the gas type of the gas components, thereby detecting the leaking gas sucked in through the measuring gas inlet (28).

11. The method according to claim 10, characterized in that The switching valve (20) switches to the reference gas inlet (30) or connects the reference gas inlet (30) to the gas line path (22) in order to check the gas sucked in from the environment of the measurement location via the reference gas inlet (30) for the presence of leaking gas components and to take these leaking gas components into account when evaluating the gas sucked in via the measuring gas inlet (28).

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