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
  • G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
  • G01M3/22—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
  • G01M3/226—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators
  • G01M3/229—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators removably mounted in a test cell
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F17/00—Methods or apparatus for determining the capacity of containers or cavities, or the volume of solid bodies
• • 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
  • G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
  • G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
  • G01M3/3236—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers
  • G01M3/3263—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers using a differential pressure detector
• • 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
  • G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
  • G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
  • G01M3/3281—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators removably mounted in a test cell

Definitions

• the invention relates to a method and a device for detecting a leak on a specimen which is contained in a test chamber.
• the filling gas in the object which is present for operational reasons, used for analysis, for example, refrigerant in the heat exchanger of a refrigerator or air conditioning.
• the object to be tested is filled with a test gas, for example with the test gas helium.
• Three different principles are used to detect the escaping test gases. 1. Vacuum leak detection
• the partial pressure of the test gas is measured in the vacuum system and serves as a measure of the leak rate.
• test specimen For accumulation, the test specimen is located in a closed measuring chamber volume and the time course of the increase in the test gas partial pressure in the measuring chamber serves as a measure of the leak rate.
• test sample is flowed around by a carrier gas.
• the gas flowing past the test piece carries test gas leaving the test piece to the measuring location, where a corresponding test gas sensor measures the test gas concentration in the carrier gas.
• the difference between the test gas concentration in the carrier gas with and without the test sample serves as a measure of the leak rate.
• test gas When selecting a suitable test gas for leak testing, it must be taken into account how high and stable the partial pressure of the test gas is in the test environment. Oxygen is actually less suitable as a test gas, because in the atmosphere, a share of about 21 percent is present.
• WO 2001/044775 A1 discloses a method in which the oxygen partial pressure is measured for localizing a leak on a test specimen.
• a first variant of the specimen is evacuated and sprayed from the outside using a spray gun with oxygen-free gas.
• the oxygen partial pressure is measured.
• a second variant of the specimen is filled with oxygen-free gas and pressurized with respect to the external atmospheric pressure with pressure. Escaping gas is absorbed with a sniffer probe and fed to a vacuum chamber containing an oxygen sensor.
• test specimen is filled with oxygen-containing gas and introduced into a test chamber, which is evacuated.
• oxygen partial pressure is measured.
• the oxygen content is measured in vacuo. It has been shown that vacuum conditions at the oxygen sensor lead to a significant signal drift and the measurement signal is difficult to evaluate.
• the invention has for its object to provide an improved method and apparatus for detecting leaks on a test specimen in a test chamber.
• the inventive method is defined by the features of claim 1.
• the inventive device is defined by claim 10.
• the test specimen is filled as exclusively as possible with an oxygen-free gas, such as nitrogen or argon, while the environment of the test specimen contains air within the test chamber.
• an oxygen-free gas such as nitrogen or argon
• the pressure in the test piece and in the test chamber is adjusted so that the pressure in the test piece is greater than the pressure in the test chamber in the area outside the test piece.
• the oxygen-free gas exits the specimen and reduces the oxygen concentration in the atmosphere surrounding the specimen.
• the reduction of the oxygen concentration serves as a measure of the leak rate.
• the oxygen concentration is measured by means of an oxygen sensor, for example in the form of a lambda probe. The measurement can be carried out by the accumulation method or by the carrier gas method.
• the oxygen partial pressure or the partial pressure of oxygen-containing gases, such as C0 2 , at the lambda probe is sufficiently high and is not measured under vacuum conditions. Under sufficiently high pressure, an oxygen partial pressure of about 10 mbar or higher is understood, which corresponds to an air pressure of about 50 mbar or higher. In this pressure range, the measuring signal of a lambda probe is particularly meaningful, whereas in vacuum conditions with a pressure p ⁇ 10 mbar the signal can not be used.
• the lambda probe can be arranged, for example, behind a test chamber evacuating pump or a compressor. A sniffer probe or a spray gun will not be used.
• test chamber A complete evacuation of the test chamber is not required, as is the case in the variant 3 described above in WO 2001/044775 Al. There, the test specimen is filled with oxygen-containing gas. Only with sufficient evacuation of the test chamber, a measurement of the oxygen partial pressure is meaningful, because only in the case of a leak on the test piece oxygen may enter the test chamber. Alternatively, if the test chamber is flooded with oxygen-free gas while the test specimen is filled with oxygen-containing gas, as also described in WO 2001/044775 A1, much more oxygen-free gas is required than in the method according to the invention.
• the operation of the lambda probe in oxygen-free gas leads to a drifting signal, as well as when operating under vacuum conditions.
• oxygen sensor (lambda probe) in pure CO 2 atmosphere.
• oxygen eg air
• the oxygen increase in the sample environment is measured.
• test chamber need not be completely evacuated. Rather, a slight negative pressure with respect to atmospheric pressure or even atmospheric pressure within the test chamber is sufficient.
• the pressure difference to the oxygen-free gas within the test sample must only be sufficiently large. For this purpose, the test specimen must be pressurized with sufficient overpressure.
• the time course of a possible increase in the oxygen partial pressure in the air of the test chamber is measured and serves as a measure of the leak rate.
• the test specimen is flowed around by air as the carrier gas, with an oxygen sensor measuring the oxygen concentration in the carrier gas downstream of the test specimen.
• the difference between the oxygen concentration in the carrier gas air with and without the test sample serves as a measure of the leak rate.
• another oxygen sensor may be arranged in the gas path to the test chamber upstream of the test specimen.
• a constant, dependent on the leakage dependent oxygen concentration In the case of the carrier gas method, a constant, dependent on the leakage dependent oxygen concentration.
• the oxygen content in the air upstream of the test specimen or before the admixture of the oxygen-free leak gas is to be kept stable. This can be made possible via a buffer or compensation volume with an additional throttle as a low-pass filter.
• the decrease of the oxygen concentration over time is measured.
• the total pressure of the gas in the test chamber and / or at the oxygen sensor is stabilized to improve the detection limit.
• the amount of gas in the test chamber volume should be kept low. This can be achieved by lowering the total pressure in the test chamber volume or by reducing the net volume (test chamber internal volume less the test specimen external volume).
• the invention offers the advantage that no expensive test gases are to be used.
• Oxygen-free operating gases such as argon or nitrogen, are readily available and inexpensive.
• the cost of an oxygen sensor is low, especially in the case of a lambda probe available as a mass product from the automotive industry.
• the measurement accuracy is improved over the pressure drop method or against the pressure increase method.
• the vacuum technical effort is lower in comparison to the helium vacuum test.
• Figure 1 shows the first embodiment in a schematic representation
• Figure 2 shows the second embodiment in a schematic representation.
• the specimen 12 is completely filled with oxygen-free test gas, so that no oxygen is contained in the test specimen.
• the test specimen is subsequently or previously introduced into a hermetically sealable test chamber 14.
• air is contained in the test chamber 14 .
• the test chamber 14 is gas-conductively connected to a carrier gas pump 16, or alternatively to a compressor.
• the test chamber 14 is gas-conductively connected to an oxygen sensor 18 in the form of a lambda probe.
• the oxygen sensor 18 and the carrier gas pump 16 are interconnected by a gas path in which a throttle 22 is provided.
• FIG. 1 is an arrangement for measurement by the carrier gas method.
• air is supplied to the test chamber 14 as carrier gas.
• a further oxygen sensor 28 in particular in the form of a lambda probe, be provided in order to determine the oxygen offset, that is, the oxygen content contained in the air without admixing the test gas 12 in the air.
• the gas path 26 further includes another flow restrictor 30 and a flow sensor 32.
• the gas path 26 opposite side of the test chamber 14 is connected to a Harmonweg 34, 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.
• the air is guided from the inlet 24 through the test chamber 14 along the surface of the test piece 12 and fed to the oxygen sensor 18.
• oxygen-free gas exits the specimen 12 and mixes with the air of the carrier gas, whereby the oxygen content in the air is reduced. This oxygen content is measured with the lambda probe (oxygen sensor 18).
• the second embodiment according to 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 another Throttle 42 between the oxygen sensor 18 and the test chamber 14.
• the two throttles 42 and 22 are disposed 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 ambient atmospheric pressure.
• the pressure in the test chamber 14 in the region outside the test piece 12 is reduced such that the oxygen-free gas in the test piece 12 flows out of a possible leak of the test piece into the test chamber 14.
• the oxygen sensor 18 the oxygen partial pressure of the air in the test chamber 14 is continuously measured. In particular, the change in the oxygen partial pressure over time is measured, wherein a decrease in the oxygen concentration indicates a leak in the test piece 12 and serves as a measure of the leak rate.
• the total pressure sensor 44 serves to be able to determine the oxygen concentration from the oxygen partial pressure signal of the lambda probe and the measured total pressure.
• the oxygen concentration C 02 is the quotient of the oxygen partial pressure Po 2 and the measured total pressure P tot :

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Examining Or Testing Airtightness (AREA)

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Citations (5)

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• 2015
  • 2015-11-16 DE DE102015222554.2A patent/DE102015222554A1/de not_active Withdrawn
• 2016
  • 2016-11-11 KR KR1020187016316A patent/KR102733784B1/ko active Active
  • 2016-11-11 EP EP16794354.7A patent/EP3377870B1/de active Active
  • 2016-11-11 JP JP2018525397A patent/JP6878425B2/ja active Active
  • 2016-11-11 US US15/776,299 patent/US10935453B2/en active Active
  • 2016-11-11 CN CN201680065738.3A patent/CN108369152A/zh active Pending
  • 2016-11-11 BR BR112018009435-8A patent/BR112018009435B1/pt active IP Right Grant
  • 2016-11-11 WO PCT/EP2016/077414 patent/WO2017084974A1/de not_active Ceased

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