A method for detecting test gases leaking from a test subject using an optical sensor.

Abstract

A method for detecting a test gas cloud (16) escaping from a gas leak in a test specimen (12) comprising the steps of receiving optical radiation (20) reflected or emitted from the test specimen (12) or its background at a first time with an optical sensor (22) configured to detect at least one wavelength or range of wavelengths in the optical absorption spectrum of the test gas (16), and detecting an image point (x ij generating a first digital image (30) from the optical radiation (20) received at a first time such that the signal amplitude of the image points (x 12 ) corresponds to the amplitude of at least one absorption wavelength range of the test gas (16); receiving the optical radiation (20) reflected or emitted from the object (12) or its background at a second time using an optical sensor (22); ij generating a second digital image (30) from the optical radiation (20) received at the second time such that a signal amplitude of the reflected optical radiation (x, bar) corresponds to an amplitude of at least one absorption wavelength range of the test gas (16); and comparing the first image (30) with at least one second digital image (32) of the reflected optical radiation, the second digital image (32) being different from the first image, wherein at least a first image point (x, bar) of the first image (30) is imaged. ij At least a gas leak (14) is deemed to be detected when the difference between the signal amplitude of the first image point (xij) and the signal amplitude of at least a second image point (xij) of the second image (32) exceeds a threshold value, where i, j are natural numbers and (x ij ) is the image point at the position of the i column and j row of the first image (30), and (x ij bar) is the image point at the position of column i and row j of the second image (32).

Description

Technical Field

[0001] The present invention relates to a method for detecting a test gas leaking from a test specimen.

[0002] The detection of a test gas leaking from a test specimen is used to detect a leak in the test specimen. In particular, installed and especially large test specimens are not inspected in a test chamber but are usually inspected using a hand-held sniffer probe. The sniffer probe is guided by an operator to the test location of the test specimen to be inspected. The sniffer probe continuously sucks in air from the inlet opening of the sniffer probe. The sucked-in air is guided to a gas detector that can selectively detect the leakage gas. The leakage gas, i.e., the gas leaking from the leak part of the test specimen, is usually a known test gas filled in or already present in the test specimen. At the test location, if the test gas leaks from the leak part, the leakage gas is taken in together with the air in the environment of the test location, and a mixed gas of air and the test gas is guided to the detector. The concentration of the test gas in the sucked-in sniffer gas flow depends continuously on the leakage rate and the magnitude of the air flow continuously sucked in. The lower the leakage rate and the larger the air flow rate drawn in, the lower the concentration of the test gas in the drawn-in gas flow.

[0003] Furthermore, it is known to use a thermographic infrared camera to detect a gas cloud containing an infrared-active gas, i.e., a gas having an absorption spectrum in the infrared wavelength range. In this case, the wavelength range incident on the sensor field of the camera is restricted by an optical filter, and the passband of the filter includes the absorption spectrum or absorption band of the gas to be detected, and other wavelength ranges are blocked. When the camera is directed at the corresponding gas cloud, the radiation component transmitted through the gas cloud appears darker in the infrared absorption spectrum range than the radiation reflected from the background. As a result, the gas cloud is displayed as a darkened area in the image of the infrared camera.

[0004] For example, the FLIR GF320 camera is known to improve the display of gas cloud movement by subtracting the amplitude of individual pixels in a series of images. [Background technology]

[0005] US2003 / 0025081A describes a method for quantitatively indicating gas emissions using an infrared camera.

[0006] Imaging of gas cloud motion in infrared imaging is described in WO2018 / 45107A1, EP3392635A1, and EP3351916A1. [Overview of the project]

[0007] The object of the present invention is to provide an improved and automated method for detecting test gases leaking from a test subject.

[0008] The method according to the present invention is defined by the features of claim 1.

[0009] Therefore, the optical radiation reflected or emitted by the object being tested is first received by an optical sensor, such as a digital sensor or a CCD chip. The sensor is configured to sense at least one wavelength of the optical absorption spectrum of the test gas. Preferably, a test gas having an absorption spectrum in the infrared wavelength range is used. The sensor can be designed with a suitable optical system to detect at least one wavelength of the absorption spectrum, for example, by using a suitable optical filter in the beam path between the object and the sensor to block wavelengths outside the absorption spectrum. For example, the passband of such an optical filter may include the absorption spectrum or absorption band, and the stopband of the filter may cover a range of adjacent remaining wavelengths.

[0010] This is based on the idea of ​​receiving the light radiation reflected or emitted by the object being tested, and based on the received radiation spectrum, determining whether or not the radiation has penetrated the test gas, and concluding that the test gas is present.

[0011] Light radiation is received at a first time point and again at a second time point following the first. Two digital images are generated from the light radiation received at each of the two time points, and the pixels of these images have a signal amplitude corresponding to the amplitude of at least one absorption wavelength of the test gas at that location. Therefore, image points in locations without test gas have a larger signal amplitude than image points corresponding to locations with test gas. In locations with test gas, radiation of the absorption wavelength is absorbed, and the amplitude of radiation that passes through the test gas is smaller than the amplitude of radiation that does not pass through the test gas. Therefore, image points imaging locations with test gas have a lower signal amplitude under uniform illumination than image points in locations without test gas.

[0012] A key feature of this invention is the active movement of a potential test gas cloud, which may be leaking from a gas leak, between the time points in which two images are taken. In other words, a gas shock is released, for example, to blow away the potential test gas cloud, at the location where a gas leak is present or suspected, and at the location where the test gas cloud is present or suspected. This can be done as a compressed air pulse or with the help of a fan. It is important that the gas moving the test gas cloud is different from the test gas and does not have the same absorption band as the test gas.

[0013] In other words, the location where a gas leak exists or is suspected, and therefore the location where a test gas cloud exists or is suspected, is the location where the received light radiation is reflected or emitted, or where the image section is taken.

[0014] According to the present invention, a first image is compared with a second image of reflected and emitted light emission, and the signal amplitudes of the image points in the first and second images correspond to the amplitudes of at least one absorption wavelength range of the test gas. Here, one or more dynamically consecutive images are compared with one or more continuously captured images. Preferably, both the camera and the object are fixed so that the image sections of the continuously captured images are identical.

[0015] According to the present invention, when the difference between the signal amplitude of at least one first image point in the first image and the signal amplitude of at least one second image point in the second image exceeds a threshold, it is automatically determined that at least a gas leak has been detected. In known methods using thermographic imaging of gases, only the image of the gas is captured and illustrated, but in the method according to the present invention, automatic evaluation of the amplitude of the image points is performed to detect leaks. This makes it possible to detect gas leaks regardless of the user or distance.

[0016] The method according to the present invention allows for the integrated evaluation of the tightness of a subject by summing the differences between corresponding image points in the first and second images. This means that the amplitude of an image point in the first image, represented by the following formula (1), where i=1...n and j=1...m (n and m are natural numbers), is subtracted from the amplitude of the corresponding image point in the second image, represented by the following formula (2). Another image point in both images, for example x, is added to this difference. i+1,j or x i,j+1 The difference in amplitude is added up over multiple image points. This addition can be performed, for example, over all image points in a selected area, over all image points in the entire image, or over each nth pixel where n is a natural number. If the sum exceeds a certain threshold, a gas leak is considered to have been detected.

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number

[0017] If there is no test gas cloud at the location where the received light radiation is reflected or transmitted, then even if a gas shock is emitted at this location, the test gas cloud will not move, and the amplitude of the image points in the two images will not show a significant difference. In this case, the difference in image points will be below an appropriate threshold. However, as soon as the test gas cloud is present at that location, it will move due to the gas shock, so the test gas cloud will appear in a different position in the first image than in the second image. After subtracting the amplitude of the image points in the two images, there is still a significant amplitude value above the threshold due to the moved test gas cloud. As a result, it may be possible to detect the test gas cloud by calculating the difference in the amplitude of the image points.

[0018] The amplitude portions caused by background radiation, background noise, or reflected radiation not reflected by the test gas are reduced by subtracting each image point, leaving the amplitude portion of the absorption spectrum of the image point corresponding to the location of the test gas. As soon as the sum of these amplitudes exceeds a certain value, a leak can be automatically considered to have been detected. Thus, according to the present invention, an automatic comparison with each threshold is performed. As soon as the aforementioned threshold is exceeded, a signal containing information that "a leak is present" can be generated and / or transmitted.

[0019] Alternatively or additionally, automatic localization of gas leaks within the subject is also possible, specifically by forming the difference between the amplitude of at least one first image point (represented by formula (1) above) in the first image and the amplitude of at least one second image point in the first image that is different from the amplitude of the first image point. This difference is compared to a threshold, and if the difference exceeds the threshold, a gas leak is considered to be present at the location of the first image point. Here, the sum of the amplitudes of multiple image points in a first region of the first image can also be compared to the sum of the amplitudes of image points in a second region of the first image that is different from the first region. If the difference in the sum of the amplitudes of the image points from the two regions exceeds a preset threshold, a leak is considered to have been detected at the location of the first region. In this case as well, a signal containing information that a gas leak has been detected, or is considered to have been detected, can be automatically transmitted and / or generated.

[0020] Preferably, the test subject is irradiated with light radiation whose spectrum includes the absorption spectrum of the test gas. If the absorption spectrum of the test gas has an absorption wavelength in the infrared wavelength range, infrared radiation is used for irradiation.

[0021] When carrying out the method according to the present invention, it is advantageous that the subject and / or the measurement position on the subject are shielded from the external environment, for example by a protective wall, so that air movement from the external environment is kept away from the subject or the measurement position.

[0022] A radiation source whose emission spectrum covers most of the infrared thermal radiation, such as above 50 nm, above 100 nm, or several hundred nanometers, that is, a broadband thermal spectrum, can be used to irradiate a subject. Alternatively, a narrowband radiation source, such as a laser or LED, whose emission spectrum covers only a small portion of the thermal radiation from a few nanometers to 50 nanometers, can also be used. [Brief explanation of the drawing]

[0023] Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to the drawings.

[0024] [Figure 1] FIG. 1 is a schematic diagram of an exemplary embodiment. [Figure 2] FIG. 2 is a schematic diagram of a captured image.

Mode for Carrying Out the Invention

[0025] FIG. 1 shows a subject 12 in the form of a pipeline that transports a gas or fluid, such as a refrigerant, that contains a test gas or can itself be used as a test gas. The test gas 16 flows out from the leakage part 14 of the subject 12 and forms a cloud in the region of the leakage part 14.

[0026] The radiation source 18 is used to emit infrared rays 20 toward the subject 12. The radiation 20 is reflected by the subject 12 and the background of the subject. The reflected radiation 20 is absorbed by a sensor 22 of an infrared camera in the form of, for example, a CCD chip. The optical filter 24 is disposed in front of the sensor 22 to block the beam path of the reflected thermal radiation 20.

[0027] FIG. 2 shows a first image 30 and a second image 32 of the radiation 20 absorbed by the sensor 22. Both images 30, 32 have the same number of image points (represented by the above formula (1)), where i = 1...n is a natural number and j = 1...m is a natural number. Therefore, each of the two images 30, 32 consists of n columns and m rows. When comparing the two images, the image points in the first region 34 of the first image 30 can be compared with the image points in the region 34 of the second image 32 corresponding to the first region 34. Alternatively or additionally, the image points in the first region 34 of one image can also be compared with the image points in a second region 36 different from the first region 34. This second region can be used to identify the gas leakage position.

[0028] In particular, the comparison of the image points of two images 30 and 32 (the terms represented by formula (1) and formula (2) above) can be performed using one of the following formulas.

number

number

[0029] Here, the term represented by formula (1) above is the image point of the first image located at column i, row j, and the term represented by formula (2) above is the image point of the second image corresponding to the position of the first image point, that is, the image point of the second image located at column i, row j.

[0030] If this term exceeds a certain threshold, a gas leak is considered to have been detected. This may result in the generation and / or output of a signal indicating the presence of a gas leak or the detection of a gas leak.

[0031] Compared to prior art, the method according to the present invention offers the advantage of automated gas leak detection of a subject by capturing and evaluating digital images of the subject, without relying on a human observer to evaluate the captured images. In particular, the method according to the present invention, or at least the comparison of captured images with image points and the evaluation of image points, can be performed by computer control or a microprocessor.

Claims

1. A method for detecting a test gas cloud (16) leaking from a leak point of a subject (12), The steps include receiving light emission (20) reflected or emitted from the subject (12) or its background at a first time point with an optical sensor (22) configured to detect at least one wavelength or wavelength range of the optical absorption spectrum of the test gas (16), A step of generating a first digital image (30) from light emission (20) received at a first time point such that the signal amplitude of the image point (represented by the following formula (1)) corresponds to the amplitude of at least one absorption wavelength range of the test gas (16), The steps include receiving light radiation (20) reflected or emitted from the subject (12) or its background at a second time point using an optical sensor (22), A step of generating a second digital image (32) from light emission (20) received at a second time point, such that the signal amplitude of the image point (represented by the following formula (2)) corresponds to the amplitude of at least one absorption wavelength range of the test gas (16), The process includes the step of comparing a first image (30) with at least one second digital image (32) of reflected light emission, which is different from the first image. When the difference between the signal amplitude of at least one first image point (represented by the following formula (1)) in the first image (30) and the signal amplitude of at least one second image point (represented by the following formula (2)) in the second image (32) exceeds a threshold, it is considered that at least a gas leak (14) has been detected. Here, i and j are natural numbers, The term represented by the following formula (1) is the image point located at position i column j row in the first image (30), The term represented by the following formula (2) is the image point located at position i column j row in the second image (32). For an integrated evaluation of the sealing degree of the subject (12), the sum of the amplitude differences between the corresponding image points of the first image (30) (represented by the following formula (1)) and the image points of the second image (32) (represented by the following formula (2)) is formed, and if the sum exceeds a certain threshold, a gas leak (14) is considered to have been detected. After the first image is taken, and before the second image is taken at a second time point different from the first, a gas shock is emitted in the direction of the position from which the image section will be taken. method. [Math 1] [Math 2]

2. The positions of the optical sensor (22) and the subject (12) are fixed such that the image sections of the captured images are substantially identical. The method according to claim 1.

3. In order to identify the location of a gas leak (14) in a subject (12), a difference is formed between the amplitude of at least a first image point (represented by the above formula (1)) in the first image (30) and the amplitude of at least a second image point in the first image (30), and if the difference exceeds a certain threshold, it is considered that a gas leak (14) at the location of the first image point (represented by the above formula (1)) has been detected. The method according to claim 1 or 2.

4. The subject (12) is exposed to light emission (20) whose spectrum includes at least a portion of the absorption spectrum of the test gas (16), The method according to any one of claims 1 to 3.

5. The light radiation reflected by and received by the subject (12) is filtered by an optical filter (24) whose passband includes at least one absorption wavelength of the optical absorption spectrum of the test gas (16). The method according to any one of claims 1 to 4.

6. During measurement, the subject (12) is shielded from the external environment so that the movement of air in the external environment is kept away from the subject (12). The method according to any one of claims 1 to 5.

7. The subject (12) is irradiated by a radiation source (18) such as a halogen lamp, light bulb, radiation heater, or flash lamp, whose radiation spectrum covers the portion with high infrared thermal radiation. The method according to any one of claims 1 to 6.

8. The subject (12) is irradiated by a radiation source (18), such as a laser or LED, whose radiation spectrum covers only the portion with low infrared thermal radiation. The method according to any one of claims 1 to 7.

9. The image points (represented by the above formula (1)) of two images (30, 32) are compared with each other by the following formula: [Math 3] Here, i, j, n, and m are natural numbers. The term represented by the above formula (1) is the image point located at position i column j row in the first image (30). The term represented by the above formula (2) is the image point located at position i column j row in the second image (32). The method according to any one of claims 1 to 8.

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