Sniffer-type leak detection device and sniffer-type leak detection method equipped with a semiconductor gas sensor

Abstract

Provided is a sniffer-type leak detection device capable of rapidly switching between a measurement gas inlet and a reference gas inlet during gas analysis. 【Solution means】The sniffer-type leak detection device 10 includes a measurement gas inlet 28 that takes in a measurement gas to be inspected for the presence or absence of leaked gas at a measurement location at the measurement location, a reference gas inlet 30 that is separate from the measurement gas inlet 28 and takes in a reference gas from around the measurement location, a gas flow pump 16 that flows the gas taken in from the measurement gas inlet 28 and the reference gas inlet 30, and a switching valve 20 that is connected to the gas flow pump 16 by a gas conduction path 22 and is gas-conductively connected to the reference gas inlet 30 and the measurement gas inlet 28. The switching valve 20 is configured such that the gas flow pump 16 takes in gas from the measurement gas inlet 28 and / or the reference gas inlet 30 according to the switching state of the switching valve 20. The switching valve 20 and a gas sensor 18 that analyzes the gas taken in by the gas flow pump 16 are provided. The gas sensor 18 includes a gas-sensitive sensor surface 42, and the gas-sensitive sensor surface 42 has at least one physical measurable characteristic that changes according to the gas in contact with the sensor surface 42. The sensor surface 42 is arranged such that at least a part of the gas flowed by the gas flow pump 16 flows along the sensor and contacts the sensor surface 42 to change the measurable characteristic.

Description

Technical Field

[0001] The present invention relates to a sniffer-type leak detection device including a measurement gas inlet that sucks a measurement gas, which is a target for investigating the presence or absence of leaked gas at a measurement location, at the measurement location.

Background Art

[0002] Such a sniffer-type leak detection device is generally designed as a handheld probe connected by a gas conduction connection line to a gas detector for gas analysis. An air gas flow is sucked from the sniffer chip of the sniffer probe and sent to the sensor part in the gas detector. Thereby, it is examined whether or not the composite gas to be analyzed contains leaked gas that has leaked from inside the test object to the outside through the leak of the test object. For this purpose, the test object is typically filled with a test gas whose identity, such as helium, is known, or a gas or refrigerant that is already filled is used as the test gas. However, the test gas used may naturally exist in the outside air surrounding the test object. For example, air naturally contains a certain proportion of helium. Therefore, it is important to determine the natural proportion of the test gas used that is not due to the leak of the test object in the outside air surrounding the test object.

[0003] For example, it is known from EP 1 342 070 B1 (Patent Document 1) to use a reference gas inlet separate from the measurement gas inlet of the sniffer-type leak detection device together with the measurement gas inlet. The reference gas inlet is for sucking a reference gas from the periphery of the measurement location, that is, from the periphery of the test object to be investigated or the assumed leak. This is based on the idea that the proportion of the test gas used in the reference gas is not due to the leak of the test object and matches the proportion of the test gas used that occurs naturally in the composite gas to be investigated.

[0004] For switching between the reference gas inlet and the measurement gas inlet, a switching valve is used. A gas delivery pump is connected to the switching valve via a gas line path, and the gas line path can be connected to the measurement gas inlet and / or the reference gas inlet as required. That is, the switching valve can establish a gas-conducting connection between the gas sensor located on the path to the gas delivery pump and the measurement gas inlet, and / or a gas-conducting connection between the gas sensor and the reference gas inlet. Then, the gas delivery pump sucks in gas from the measurement gas inlet and / or the reference gas inlet according to the switching state of the switching valve, and the sucked gas is delivered to the gas sensor.

[0005] In a known sniffer-type leak detection device where the measurement gas inlet and the reference gas inlet are switched, typically, an optical sensor in the form of an infrared gas analyzer is used as the gas sensor. After filling the measurement cuvette with the gas to be analyzed, infrared light is irradiated. Based on the resulting absorption spectrum, conclusions can be drawn about the composition of the gas inside the measurement cuvette.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Conventional infrared gas analyzers cannot switch the measurement gas inlet and the reference gas inlet at an arbitrary frequency. Rather, the composite gas to be analyzed can only be analyzed after the measurement cell used is full, and then the composite gas of the next analysis target can finally be introduced into the same measurement cell and analyzed. For this reason, there are limitations to the switching frequency, also known as the modulation frequency, for switching the measurement gas inlet and the reference gas inlet with a switching valve. When the frequency increases, the gas in the measurement cell cannot be completely replaced, so the sensitivity of gas analysis decreases.

[0008] One object of the present invention is to provide a sniffer-type leak detection device capable of quickly switching the measurement gas inlet and the reference gas inlet during gas analysis.

Means for Solving the Problems

[0009] The sniffer-type leak detection device according to the present invention is defined by the configuration of claim 1. The method according to the present invention is defined by claim 10.

[0010] The sniffing type leak detection device includes a measurement gas inlet for sucking in a measurement gas to be investigated for the presence or absence of leaked gas at a measurement location. The leaked gas is gas that leaks from inside the test body through the leak of the test body to the outside and is collected by the sniffing type leak detection device there. Typically, a test gas whose identity is known is used as the leaked gas and the test body is filled with it, or what is already contained in the test body is taken as the leaked gas. Separately from the measurement gas inlet, a reference gas inlet is provided for sucking in a reference gas from the periphery of the measurement location, that is, from the periphery of the region where there is suspicion of a leak and gas is sucked in through the measurement gas inlet. The gas flow pump of the sniffing type leak detection device generates a gas flow in a gas line path connecting the measurement gas inlet and the reference gas inlet to the gas flow pump, thereby sucking in gas from the gas inlet being used at that time. A switching valve is used to connect the gas line to the measurement gas inlet and / or the reference gas inlet, so that the gas flow pump sucks in gas from the measurement gas inlet and / or the reference gas inlet according to the switching state of the switching valve. As the switching, it is possible to switch between the measurement gas inlet and the reference gas inlet. Alternatively, it is also possible to connect the reference gas inlet to the gas line connecting the measurement gas inlet to the gas flow pump for a short time. The gas sucked in by the gas flow pump is analyzed by a gas sensor.

[0011] The gas sensor of the sniffer-type leak detection device according to the present invention is not a conventional optical sensor such as a general infrared gas analyzer. Rather, it is a gas sensor in which at least one physically measurable characteristic of the sensor surface changes according to the gas in contact with the sensor surface, and the characteristic can be measured by the same sensor. The sensor surface is arranged such that at least a part of the gas sucked in and carried through the gas line by the gas delivery pump is guided along the sensor, comes into contact with the sensor surface, and changes the physical characteristics of the sensor surface. The physical characteristics of the same sensor surface can be measured electrically, for example, and by evaluating the measurement signal, the gas components of the composite gas to be investigated are identified.

[0012] The physical characteristics can be, for example, the electrical resistance of the sensor surface, voltage-current characteristics, etc. For example, the gas sensor can be a semiconductor-type gas sensor. Alternatively, the gas sensor may be a thermal conductivity-type sensor in which the physically measurable characteristic of the sensor surface is thermal conductivity and the thermal conductivity changes according to the contacting gas.

[0013] The present invention has a decisive advantage in that the amount of gas required to generate an electrical measurement signal suitable for gas detection is significantly less compared to optical sensors known in the prior art. For example, in an infrared absorption sensor, a meaningful measurement signal cannot be generated unless the sensor space is full, but for a gas sensor including a gas-sensitive sensor surface, it is sufficient to bring a very small amount of gas into contact with the sensor surface or simply wet the sensor surface with a very small amount of gas.

[0014] Therefore, the present invention has the advantage that the gas volume in the gas sensor or in the measurement environment of the sensor surface can be limited to a value that can speed up the signal response of the same gas sensor by the high-speed switching of the switching valve. Preferably, the gas volume in the gas sensor or in the measurement environment of the sensor surface is 1 cm 3 , preferably 500 mm 3 , most preferably 100 mm 3is limited to the value of. That is, even if the gas volume is at most 1 scc (standard state volume cm 3 ), 0.5 scc or 0.1 scc, it is possible to sufficiently generate an electrically evaluable measurement signal to increase the switching frequency of the switching valve. That is, if the switching frequency of the switching valve is, for example, 4 Hz, in order to completely replace the gas in each measurement cycle, the gas flow rate needs to be 8 sccs (standard state volume cm per second 3 ), 4 sccs or 0.8 sccs.

[0015] When increasing the suction gas flow rate to operate the sniffer type leak detector in order to speed up the replacement of the gas in the detection space, the amount of leaked gas to be sucked becomes thin, and accordingly the sensitivity is lost.

[0016] In principle, if the operating pressure in the detection space is always lowered to a lower level, the replacement of the gas in the detection space can be accelerated without changing the suction gas flow rate. As a result, the amount of gas to be replaced also decreases. However, the partial pressure of the test gas decreases, and accordingly the sensitivity decreases, so this is not convenient either.

[0017] Specifically, in the sniffer type leak detection method according to the present invention, a gas volume of less than 1 scc (standard state volume cm 3 ), less than 0.5 scc or very preferably less than 0.1 scc is guided to pass through the sensor surface while the measurement signal is being evaluated.

[0018] By reducing the amount of gas to be replaced, it is possible to increase the gas modulation frequency for completely replacing the gas in the detection space, and / or to reduce the suction gas flow rate for completely replacing the gas in the detection space to the minimum level in each modulation cycle. By reducing the suction gas flow rate, the concentration of the test gas per given leakage amount increases, and the detection sensitivity is improved.

[0019] As such semiconductor gas sensors, for example, those in the form of metal oxide type sensors having a sensor surface provided with a metal oxide film are known, although not in the field of sniffer type leak detection.

[0020] Semiconductor sensors (e.g., SnO2 type sensors, etc.) are suitable for detecting hydrogen and hydrocarbons. However, their sensor behavior is non-linear. The signal response to changes at low concentration levels is strong, but as the concentration increases, the signal change gradually flattens out, and only a slight signal change occurs in the high concentration range. At low or medium concentration levels, particularly when the reference gas concentration is low, the signal change caused by the modulation mode can be easily detected. The present invention utilizes this advantage that the signal response is strong in the low concentration range as follows. ● The higher the modulation frequency selected, the better the suppression of interfering gases during gas switching modulation. ● However, there is one constraint that when the signal fluctuation of the signal becomes incomplete during a high-speed modulation period, the sensitivity is impaired. ● In infrared absorption detection, it is required that there is a sufficient infrared absorption distance in the measurement cuvette between the infrared light emitting part and the infrared detection part. To achieve sufficient sensitivity, it is necessary to completely fill the entire measurement gas cuvette with the measurement gas or the reference gas for each modulation period. To reduce the gas volume in the cuvette, the length of the cuvette can be shortened, but at the same time, the infrared absorption distance is also shortened. As another solution to speed up the gas replacement, increasing the supply flow (gas flow) of the gas can be mentioned, but the concentration of the sample gas, that is, the leak measurement sensitivity decreases. ● Therefore, it becomes an issue to realize a high-speed modulation frequency by speeding up the complete gas replacement of the sensor while minimizing the gas flow rate. ● As a small sensing sensor element, for example, a semiconductor sensor can be mentioned. Using a semiconductor sensor in relation to gas switching modulation is not yet known. ● As other sensor elements replacing semiconductor sensors, a thermal conductivity sensor element showing gas selectivity or a Pirani gas detector may be considered.

[0021] Preferably, the switching valve is configured to switch the measurement gas inlet and the reference gas inlet at a switching frequency of 4 Hz or more, preferably 8 Hz or more, that is, a modulation frequency. In the case of a conventional infrared gas analyzer or other optical sensors, sensitivity is lost at such a high switching frequency. However, in the case of semiconductor gas analysis, such high-speed switching can be performed so as to evaluate the measurement signals of both the measurement gas and the reference gas with sufficient high sensitivity.

[0022] The switching valve may be configured to connect the reference gas inlet to the gas line connecting the measurement gas inlet to the gas flow pump at a frequency of 4 Hz or more. Also in this case, the same frequency (modulation frequency) can be 8 Hz or more. As a result, the section consisting of only the measurement gas and the section consisting of a mixture of the measurement gas and the reference gas are alternately interchanged, and the composite gas is sent to the gas sensor.

[0023] Preferably, the sensor surface of the semiconductor gas sensor has an electrical resistance or current-voltage characteristics that respond to the leakage gas or the test gas used in the test body. Preferably, the electrical resistance of the sensor surface or the current-voltage characteristics of the semiconductor change due to the test gas used. A suitable test gas is, for example, helium.

[0024] In the method according to the present invention, a gas flow is generated by the gas delivery pump, which is sucked in from the measurement gas inlet and / or the reference gas inlet according to the switching position of the switching valve and guided to pass through the gas sensor along the gas line path. When the gas component of the gas flow reacts with the sensor surface, the electrical resistance of the sensor surface or the current-voltage characteristics of the semiconductor change according to the gas type of the gas component, so that the leakage gas or the test gas sucked in from the measurement gas inlet is detected. The electrical resistance of the sensor surface is electrically measured, and the measurement signal of the measured value of the resistance is used for gas analysis.

[0025] Preferably, when the switching valve is switched to the reference gas inlet or the switching valve connects the reference gas inlet to the gas line path between the measurement gas inlet and the gas sensor, the gas sucked in from around the measurement location through the reference gas inlet is investigated for the presence or absence of leakage gas components, and the leakage gas components are considered when evaluating the gas sucked in from the measurement gas inlet. Specifically speaking, it is conceivable to obtain the ratio or concentration of the test gas originating from the leak of the test object by subtracting the ratio of the test gas or leakage gas obtained from the analyzed reference gas from the corresponding ratio of the test gas or leakage gas in the measurement gas to be analyzed.

[0026] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings.

Brief Description of the Drawings

[0027]

Figure 1

Embodiments for Carrying out the Invention

[0028] The illustrated sniffer-type leak detection device 10 includes a handheld sniffer probe 12. The sniffer probe 12 is connected to a gas delivery pump 16 by a gas communication line 13. A gas sensor 18 is provided on the sniffer probe 12. For this purpose, the sniffer probe 12 has a housing 14 that also houses the gas sensor 18. A three-way switching valve 20 is also disposed inside the housing 14, and the three-way switching valve 20 is connected to the gas sensor 18 by a gas line path 22. Another portion of the gas line path 22 connects the gas sensor 18 to the gas delivery pump 16, and the portion of the gas line path 22 that extends outside the housing 14 is constituted by the gas communication line 13.

[0029] The housing 14 has a measurement gas sniffer chip 24 and a reference gas sniffer chip 26. The two sniffer chips 24, 26 may be integrated or arranged within a common housing of a common sniffer chip. Alternatively, the reference gas sniffer chip 26 may be mounted even further spaced apart from the measurement gas sniffer chip 24 in the housing 14.

[0030] The measurement gas sniffer chip 24 has a measurement gas inlet 28 at the front end portion opposite to the housing 14. Correspondingly, a reference gas inlet 30 is provided at the end portion of the reference gas sniffer chip 26 opposite to the housing 14. Extremely importantly, the measurement gas inlet 28 is connected to the first connection portion of the switching valve 20 by a measurement gas line path 32, and the reference gas inlet 30 is also connected to the switching valve 20 by a reference gas line path 34 that is separate from the measurement gas line path 32. While the measurement gas line path 32 is connected to the first connection portion 36 of the switching valve 20, the reference gas line path 34 is connected to the second connection portion 38 of the switching valve 20, and at the same time, the gas line path 22 is connected to a third connection portion 40 of the switching valve 20 that is different from the first two connection portions 36, 38 thereof.

[0031] The switching valve 20 optionally connects the first connection portion 36 or the second connection portion 38 to the third connection portion 40 such that, in the case of the first connection portion 36, the measurement gas line 32 is connected to the gas line 22, and in the case of the second connection portion 38, the reference gas line 34 is connected to the gas line 22.

[0032] Alternatively or in addition thereto, it is also possible that the switching valve 20 connects both the first connection portion 36 and the second connection portion 38 to the third connection portion, such that in this case both the measurement gas line 32 and the reference gas line 34 are connected to the gas line 22.

[0033] The gas sensor 18 is designed as a semiconductor sensor in the form of a metal oxide type sensor. The gas sensor 18 includes a sensor surface 42 in the form of a surface of a metal oxide. The sensor surface 42 is arranged within the gas sensor 18 such that a gas flow guided along the gas line 22 within the housing 14 passes through the sensor surface 42. As a result, a part of the conveyed composite gas comes into contact with the sensor surface 42 and affects the electrical resistance of the sensor surface 42 or the current-voltage characteristics of the transistor. The resistance of the said sensor changes according to the gas species of the gas component in contact with the sensor surface 42.

[0034] The resistance of the sensor surface 42 is electrically measured in a conventionally known manner, and the gas composition at the sensor surface 42 is inferred from the measured signal of the resistance value, whereby it becomes possible to detect a specific gas component, particularly a test gas contained in the test body.

Claims

1. A measurement gas inlet (28) that sucks in a measurement gas to be investigated for the presence or absence of leakage gas at the measurement location at the measurement location, A reference gas inlet (30) that sucks in a reference gas from the periphery of the measurement location, which is different from the measurement gas inlet (28), A gas flow pump (16) that conveys the gas sucked in from the measurement gas inlet (28) and from the reference gas inlet (30), A switching valve (20) that is connected to the gas flow pump (16) by a gas conduction path (22) and is gas-conductively connected to the reference gas inlet (30) and the measurement gas inlet (28), and according to the switching state of the switching valve (20), the gas flow pump (16) is formed to suck gas from the measurement gas inlet (28) and / or the reference gas inlet (30), a switching valve (20), A gas sensor (18) that analyzes the gas sucked in by the gas flow pump (16), In a sniffer-type leak detection device (10) comprising: In the sniffer-type leak detection device (10), the gas sensor (18) includes a gas-sensitive sensor surface (42), and the gas-sensitive sensor surface (42) has at least one physical measurable characteristic that changes according to the gas in contact with the sensor surface (42). The sensor surface (42) is arranged such that at least a part of the gas conveyed by the gas flow pump (16) flows along the sensor and contacts the sensor surface (42) to change the measurable characteristic. Sniffer-type leak detection device (10).

2. In the sniffer-type leak detection device (10) according to claim 1, the gas sensor (18) is a semiconductor-type gas sensor including a sensor surface whose electrical resistance or current-voltage characteristics change according to the gas type, for example, in the form of a metal oxide type sensor. Sniffer-type leak detection device (10).

3. In the sniffer-type leak detection device (10) according to claim 1, the gas sensor is a heat conduction type sensor in which heat dissipation from the sensor surface to the gas-side environment depends on the gas type. Sniffer-type leak detection device (10).

4. In the sniffer-type leak detection device (10) according to any one of claims 1 to 3, the gas sensor (18) includes a housing (19) that limits the gas volume in contact with the sensor surface (42) to 1 cubic centimeter, preferably 0.5 cubic centimeter, and extremely preferably 0.1 cubic centimeter. A sniffer-type leak detection device (10).

5. In the sniffer-type leak detection device (10) according to any one of claims 1 to 4, the switching valve (20) is configured to switch between the measurement gas inlet (28) and the reference gas inlet (30) at a frequency of 4 Hz or more. A sniffer-type leak detection device (10).

6. In the sniffer-type leak detection device (10) according to any one of claims 1 to 5, the switching valve (20) connects the reference gas inlet (30) to the gas line (22) connecting the measurement gas inlet (28) to the gas delivery pump (16) at a frequency of 3 Hz or more. A sniffer-type leak detection device (10).

7. In the sniffer-type leak detection device (10) according to claim 5 or 6, the frequency is 5 Hz or more, for example, 10 Hz or more. A sniffer-type leak detection device (10).

8. In the sniffer-type leak detection device (10) according to any one of claims 1 to 7, the physical properties of the sensor surface (42) are electrical resistance and / or current-voltage characteristics and / or thermal conductivity. A sniffer-type leak detection device (10).

9. In the sniffer-type leak detection device (10) according to any one of claims 1 to 8, the gas sensor (18) and the switching valve (20) are arranged inside a housing (14) that constitutes a manually operated sniffer probe (12) of the sniffer-type leak detection device (10). A sniffer-type leak detection device (10).

10. In the sniffing leak detection method by the sniffing leak detection device (10) according to any one of claims 1 to 9, a gas flow is generated by the gas feed pump (16) so as to be sucked from the measurement gas inlet (28) and / or the reference gas inlet (30) according to the switching position of the switching valve (20) and guided to pass through the gas sensor (18) along the gas line path (22). When the gas component of the gas flow reacts with the sensor surface (42), the physical property of the sensor surface (42) changes according to the gas type of the gas component, and the leaked gas sucked from the measurement gas inlet (28) is detected. A method characterized by that.

11. In the method according to claim 10, the switching valve (20) is switched to the reference gas inlet (30), or the switching valve (20) connects the reference gas inlet (30) to the gas line path (22), and the gas sucked from the environment at the measurement location through the reference gas inlet (30) is investigated for the presence or absence of a leak gas component, and the leak gas component is taken into consideration in the evaluation of the gas sucked from the measurement gas inlet (28). A method characterized by that.

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