Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/16—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using electric detection means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/002—Investigating fluid-tightness of structures by using thermal means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
  • G01N27/128—Microapparatus
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0026—General constructional details of gas analysers, e.g. portable test equipment using an alternating circulation of another gas

Definitions

• the invention relates to a sniffer leak detection device with a measurement gas inlet for sucking in measurement gas at a measurement location, wherein the measurement gas is to be examined for the presence of a possible leakage gas at the measurement location.
• Such sniffer leak detection devices are usually designed as hand-held probes that are connected via a gas-conducting connecting line to a gas detector for gas analysis.
• a stream of air gas is sucked in via a sniffer tip of the sniffer probe and fed to a sensor unit in the gas detector. It is examined whether the analyzed gas mixture contains a leakage gas that has escaped from the inside of the test object to the outside through a leak in the test object.
• the test specimen is typically filled with a known test gas, such as helium, or is already filled with a gas or refrigerant that is used as a test gas.
• a known test gas such as helium
• the test gas contains a natural amount of helium. It is therefore important to determine the natural proportion of the test gas used in the atmosphere surrounding the test object that is not the result of a leak in the test object.
• a switchover valve is used to switch between the reference gas inlet and the sample gas inlet.
• a gas delivery pump is connected to the changeover valve through a gas line path, which in turn can optionally be connected to the measurement gas inlet and/or the reference gas inlet.
• a gas-conducting connection can be created between the measurement gas inlet and a gas sensor arranged in the path to the gas feed pump and/or a gas-conducting connection between the reference gas inlet and the gas sensor.
• the gas delivery pump then sucks gas from the measurement gas inlet and/or the reference gas inlet, depending on the situation Switching state of the switching valve and conveys the sucked gas to the gas sensor.
• an optical sensor in the form of an infrared gas analyzer is typically used as the gas sensor.
• a measuring cuvette is filled with the gas to be examined and then illuminated with infrared radiation. The resulting absorption spectrum can be used to determine the composition of the gas within the measuring cuvette.
• the invention is based on the object of providing a sniffer leak detection device which enables rapid switching between a measurement gas inlet and a reference gas inlet during gas analysis.
• the sniffer leak detection device is defined by the features of patent claim 1.
• the method according to the invention is defined by patent claim 8.
• the sniffing leak detection device has a measurement gas inlet for sucking in measurement gas at a measurement location, wherein the measurement gas is to be examined for the presence of a possible leakage gas at the measurement location.
• a leak gas is a gas that has escaped from the interior of the test object into its external environment due to a leak in a test object and is picked up there by the sniffing leak detection device.
• a known test gas is used as the leakage gas, with which the test object is filled or which is already contained in the test object.
• the gas line path is optionally connected to the measurement gas inlet and/or to the reference gas inlet in such a way that the gas feed pump sucks in gas through the measurement gas inlet and/or through the reference gas inlet, depending on the switching state of the changeover valve. Switching between the measurement gas inlet and the reference gas inlet can take place. Alternatively, the reference gas inlet can be briefly switched on to the gas line path connecting the measurement gas inlet to the gas feed pump. A gas sensor analyzes the gas drawn in by the gas pump.
• the gas sensor of the sniffing leak detection device is not a conventional optical sensor, such as a conventional infrared gas analyzer, but rather a gas sensor with a sensor surface that has at least one physically measurable property that depends on the gas contacting the sensor surface changes and can be measured by the sensor.
• the sensor surface is arranged in such a way that at least part of the Gas delivery pump of sucked gas conveyed through the gas line path is guided along the sensor and thereby contacts the sensor surface and changes the physical property of the sensor surface.
• the physical property of the sensor surface can be measured electrically, for example, with the measurement signal being evaluated to identify gas components of the gas mixture being examined.
• the physical property can be, for example, the electrical resistance of the sensor surface or the voltage-current characteristic.
• the gas sensor can be a semiconductor gas sensor.
• the gas sensor can also be a heat conduction sensor, in which the measurable physical property of the sensor surface is the thermal conductivity, which changes depending on the gas in contact.
• the invention offers the decisive advantage that, compared to the optical sensors known in the prior art, a significantly smaller amount of gas is required to generate an electrical measurement signal that is suitable for gas detection. While, for example, with optical infrared radiation absorption sensors the sensor volume must be filled before a meaningful measurement signal can be generated, with a gas sensor with a gas-sensitive sensor surface, only a much smaller gas volume is sufficient to contact or wet the sensor surface.
• the invention thus offers the advantage that the gas volume within the gas sensor or in the measuring environment of the sensor surface can be limited to a value that enables rapid switching of the switching valve with a rapid signal response from the gas sensor.
• the gas volume within the gas sensor or in the measuring environment of the sensor surface is limited to a value of 1 cm 3 , preferably 500 mm 3 and particularly preferably 100 mm 3 .
• a gas quantity of maximum 1 see, (standard cubic centimeter), 0.5 see or 0.1 see is sufficient to generate an electrically evaluable measurement signal and thereby enable a high switching frequency of the changeover valve.
• the gas delivery flow must then be 8 sees (standard cubic centimeters per second), 4 sees or 0.8 sees in order to achieve a complete gas exchange for each measuring cycle.
• a 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 the amount of leakage gas recorded being more diluted, which in turn is associated with a loss of sensitivity.
• a faster gas exchange in the detection volume can be achieved with an unchanged sniffer gas flow by lowering the working pressure in the detection volume to a constantly lower level. This also reduces the amount of gas to be exchanged. However, this leads to a reduced test gas partial pressure, which in turn is associated with reduced sensitivity and is therefore also not effective.
• a gas quantity of less than 1 scc (standard cubic centimeter), less than 0.5 scc or particularly preferably less than 0.1 scc is passed past the sensor surface while the measurement signal is evaluated.
• the reduced amount of gas to be exchanged enables a higher gas modulation frequency with complete gas exchange in the detection volume and/or enables the sniffing gas flow to be reduced to the minimum for complete gas exchange in the detection volume for each modulation cycle.
• the reduced sniffing gas flow in turn leads to a increased test gas concentration for a given leakage rate, which in turn improves the sensitivity of the detection.
• 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 not in the area of sniffer leak detection.
• Semiconductor sensors e.g. SnO2 sensors
• SnO2 sensors are suitable for detecting hydrogen or hydrocarbons.
• the sensor behavior is non-linear, the signal reaction to changes at low concentration levels is strong, the signal change flattens out more and more as the concentration increases, and at high concentrations there is only a small signal change.
• a signal change at a low or medium concentration level is easily detectable; such a signal change is generated by the modulation operation, especially if the reference gas concentration is low.
• the invention exploits this advantage of the strong signal reaction at low concentrations as follows:
• a sufficient IR absorption distance is required in the measuring cuvette between the IR emitter and the IR detector.
• the entire measuring gas cell must be completely filled with measuring gas or reference gas for each modulation cycle to ensure full sensitivity.
• the cuvette length can be shortened, but this also shortens the IR absorption path.
• An alternative solution to A faster gas exchange would result in a stronger gas delivery flow (gas flow), but this reduces the sample gas concentration and thus the sensitivity for leakage measurements.
• the task is therefore the rapid complete gas exchange at the sensor with the lowest possible gas flow in order to achieve a high modulation frequency.
• a compact and at the same time sensitive sensor element is, for example, a semiconductor sensor.
• the use of a semiconductor sensor in connection with gas alternating modulation is not yet known.
• the switching valve is preferably designed to switch between the measurement gas inlet and the reference gas inlet with a switching frequency or modulation frequency of at least 4 Hz and preferably at least 8 Hz.
• a switching frequency or modulation frequency of at least 4 Hz and preferably at least 8 Hz.
• the changeover valve can be designed to switch the reference gas inlet to the gas line path connecting the measurement gas inlet to the gas feed pump with a frequency of at least 4 Hz.
• the frequency (modulation frequency) can be at least 8 Hz.
• a gas mixture is supplied to the gas sensor at alternating intervals, which either consists only of the measurement gas or of a mixture of measurement gas and reference gas.
• the sensor surface of the semiconductor gas sensor preferably has an electrical resistance or current-voltage characteristic that reacts to the leakage gas or the test gas used in the test object.
• the electrical resistance of the sensor surface or current-voltage characteristic curve of the semiconductor is changed by the test gas used.
• a suitable test gas is, for example, helium.
• a gas flow is generated with the gas delivery pump, which, depending on the switching position of the switching valve, is sucked in through the measurement gas inlet and / or the reference gas inlet and is guided past the gas sensor along the gas line path in such a way that gas components of the gas flow react with the sensor surface in such a way that the electrical resistance of the sensor surface or current-voltage characteristic curve of the semiconductor changes depending on the gas type of the gas component in order to thereby detect a leakage gas or test gas drawn in through the measurement gas inlet.
• the electrical resistance of the sensor surface is measured electrically, with the measurement signal from the resistance measurement being used for gas analysis.
• the switching valve is switched to the reference gas inlet or connects the reference gas inlet to the gas line path between the measurement gas inlet and the gas sensor in order to examine gas drawn in through the reference gas inlet from the surroundings of the measuring location for the presence of leakage gas components and these leakage gas components when evaluating the gas drawn in through the measurement gas inlet to be taken into account.
• the determined proportions of test gas or leakage gas in the examined reference gas are subtracted from the corresponding proportions of the test gas or leakage gas in the analyzed measurement gas in order to determine the proportion of test gas or the test gas concentration that comes from a leak in the test object.
• the sniffing leak detection device 10 shown has a hand-held sniffing probe 12, which has a gas connection line is connected to a gas feed pump 16.
• a gas sensor 18 is arranged in the sniffer probe 12.
• the sniffer probe 12 has a housing 14, which also encloses the gas sensor 18.
• a three-way switching valve 20 is also arranged in the housing 14 and is connected to the gas sensor 18 by a gas line path 22.
• a further section of the gas line path 22 connects the gas sensor 18 to the gas feed pump 16, the portion of the gas line path 22 running outside the housing 14 passing through the gas line path 22
• Gas connection line 13 is formed.
• the housing 14 has a measuring gas sniffer tip 24 and a
• Reference gas sniffer tip 26 on.
• the two sniffing tips 24, 26 can also be combined or arranged in a common housing of a common sniffing tip.
• the reference gas sniffing tip 26 can alternatively also be attached to the housing 14 further away from the measuring gas sniffing tip 24.
• the measuring gas sniffer tip 24 has a measuring gas inlet 28 at its front end opposite the housing 14.
• the end of the reference gas sniffing tip 26 opposite the housing 14 is provided with a reference gas inlet 30.
• the measurement gas inlet 28 is connected to a first connection of the switching valve 20 through a measurement gas line path 32, while the reference gas inlet 30 is also connected to the switching valve 20 through a reference gas line path 34, which is different from the measurement gas line path 32.
• the measurement gas line path 32 is connected to a first connection 36 of the switching valve 20, while the reference gas line path 34 is connected to a second connection 38 of the switching valve 20, while the Gas line path 22 is connected to a third connection 40 of the switching valve 20, which is different from the first two connections 36, 38.
• the switching valve 20 selectively connects either the first connection 36 or the second connection 38 to the third connection 40, so that in the case of the first connection 36 the measurement gas line path 32 is connected to the gas line path 22, while in the case of the second connection 38 the reference gas line path 34 is connected the gas line path 22 is connected.
• the switching valve 20 connects both the first connection 36 and the second connection 38 to the third connection 40, so that in this case both the measurement gas line path 32 and the reference gas line path 34 are connected to the gas line path 22.
• 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 within the gas sensor 18 in such a way that the gas flow guided along the gas line path 22 within the housing 14 flows past the sensor surface 42.
• part of the pumped gas mixture comes into contact with the sensor surface 42 and influences the electrical resistance of the sensor surface 42 or the current-voltage characteristic of the transistor.
• the sensor resistance is changed.
• the resistance of the sensor surface 42 is measured in an electrically conventional and known manner, with the gas composition at the sensor surface 42 being deduced from the measurement signal of the resistance values and in particular specific gas components, such as test gas contained in a test specimen, being able to be detected.

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• General Physics & Mathematics (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
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• Biochemistry (AREA)
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• Pathology (AREA)
• Engineering & Computer Science (AREA)
• Electrochemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Examining Or Testing Airtightness (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2022
  • 2022-07-22 DE DE102022118431.5A patent/DE102022118431A1/de active Pending
• 2023
  • 2023-07-12 EP EP23742031.0A patent/EP4558799A2/de active Pending
  • 2023-07-12 JP JP2025501736A patent/JP2025523096A/ja active Pending
  • 2023-07-12 WO PCT/EP2023/069347 patent/WO2024017738A2/de not_active Ceased
  • 2023-07-12 CN CN202380043733.0A patent/CN119301432A/zh active Pending
  • 2023-07-12 US US18/994,873 patent/US20260016360A1/en active Pending

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