METHOD FOR DETECTING TEST GAS ESCAPING FROM A TEST SAMPLE USING AN OPTICAL SENSOR

Abstract

A method for detecting a cloud of test gas escaping from a leak in a test sample comprises the following steps: receiving the optical radiation reflected or emitted from the test sample or its background at a first time with an optical sensor configured to detect at least one wavelength or range of wavelengths from the optical absorption spectrum of the test gas, creating a first digital image from the optical radiation received at the first time, such that the signal amplitudes of the points xij in the image correspond to the amplitude of at least one absorption wavelength range of the test gas, receiving the optical radiation reflected or emitted by the test sample or its background at a second time using the optical sensor, creating a second digital image from the optical radiation received at the second time,so that the signal amplitudes of the image points (see Formula) correspond to the amplitude of at least one absorption wavelength interval of the test gas, compare the first image with at least a second digital image of the reflected optical radiation, which is different from the first image, wherein a leak is considered to be detected when at least the difference in amplitude of at least a first image point xij of the first image and the amplitude of at least a second image point (see Formula) of the second image exceeds a threshold value, in which i, j are natural numbers, xij is an image point located in column i and row j of the first image, and (see Formula) is an image point located in column i and row j of the second image.

Description

METHOD FOR DETECTING TEST GAS ESCAPING FROM A CQRQnn / eznz / e / YiAi TEST SAMPLE USING AN OPTICAL SENSOR Field of Invention The invention relates to a method for detecting gas leakage from a test sample. Background of the Invention The detection of escaping test gas from a test sample is used to detect a leak in the sample. In particular, stationary and especially large test samples are not examined in a test chamber, but usually with the aid of a handheld sniffing probe. The operator guides the probe into the test area of ​​the sample to be examined. The probe continuously draws air through an inlet opening. The drawn air is directed to a gas detector that can selectively detect the leaking gas. The leaking gas, i.e., the gas escaping from a leak in the test sample, is usually a known test gas with which the test sample is filled or which was previously introduced into the sample.If the test gas escapes from a leak at the test site, the leaking gas is drawn in along with the surrounding air, so that a gaseous mixture of air and test gas is directed to the detector. The concentration of the gas... Ref. 346672 The test in the aspirated gas flow depends on the leak rate and the size of the continuously aspirated airflow. The lower the leak rate and the higher the aspirated airflow, the lower the concentration of test gas in the aspirated gas flow. Furthermore, infrared thermal imaging cameras are known to be used to detect gas clouds containing an infrared-active gas—that is, a gas whose absorption spectrum includes infrared wavelengths. This means that the range of wavelengths incident on the camera's sensor field is restricted by an optical filter. The filter's passband includes the absorption spectrum, or a portion thereof, of the gas to be detected, while blocking other wavelength ranges. If the camera is then pointed at a corresponding gas cloud, the radiation components transmitted through the gas cloud appear darker in the infrared absorption spectrum range than the radiation reflected from the background. As a result, the gas cloud appears as a darkened area in the infrared camera image. For example, the FLIR GF320 camera is known to subtract the amplitudes of individual pixels from successive images, thus improving the representation of the movements of a gas cloud. CQRQnn / eznz / e / YiAi Document US 2003 / 0025081 A describes a method for the quantitative presentation of gas emissions using an infrared camera. The representation of gas cloud movements in an infrared image is described in WO 2018 / 45107 Al, EP 3 392 635 Al and EP 3 351 916 Al. Summary of the Invention The object of the invention is to provide an improved automated method for detecting the escape of test gas from a test sample. The method according to the invention is defined by the features of claim 1. Consequently, the optical radiation reflected or emitted by the test sample is first received by an optical sensor, such as a digital sensor or a CCD microcircuit. The sensor is configured to detect at least one wavelength of the optical absorption spectrum of the test gas. Preferably, a test gas with an absorption spectrum in the infrared wavelength range is used. The sensor can be designed using suitable optics to detect at least one wavelength of the absorption spectrum, for example, by using a suitable optical filter in the beam path between the test sample and the sensor to block CQRQnn / eznz / e / YiAi wavelengths outside the absorption spectrum. For example, the passband of the optical filter may include the absorption spectrum or an absorption band, while the filter's stopband covers the intervals of the remaining adjacent wavelengths. This is based on the idea that the optical radiation reflected or emitted by the test sample to be examined is received and evaluated to determine, based on the radiation spectrum received, whether the radiation is transmitted through the test gas to conclude the presence of the test gas. Optical radiation is received first and then again. Two digital images are generated from the optical radiation received at each of these two times. The pixels in these images have signal amplitudes corresponding to the amplitude of at least one absorption wavelength of the test gas at the location in question. Therefore, a point in the image at a location without test gas has a greater signal amplitude than a point in the image corresponding to a location with test gas. At locations with test gas, radiation of the absorption wavelength is absorbed; that is, the amplitude of the radiation transmitted through the test gas is less than the amplitude of the radiation not transmitted through the test gas. Therefore, image points at a location with test gas have CQRQnn / eznz / e / YiAi a lower signal amplitude under homogeneous illumination than the image points of a location without test gas. The key feature of the invention is that a potential test gas cloud, formed from the escaped gas, is actively displaced between the points during the capture of the two images. In other words, at the location where a gas leak is present or suspected, and where a test gas cloud is present or suspected, a gas discharge is emitted, for example, which expels the potential test gas cloud. This can be accomplished with a compressed air burst or with the aid of a fan. It is important that the gas used to displace the test gas cloud is different from the test gas and does not have the same absorption bands as the test gas. In other words, the location where there is or is suspected to be a gas leak, and therefore where there is or is suspected to be a test gas cloud, is the location where the received optical radiation is reflected or emitted, or from which the image section is captured. According to the invention, the first image is compared to the second image of the reflected and emitted optical radiation, wherein the signal amplitude of the image points of the first and second images corresponds to the amplitude of at least one interval of CQRQnn / eznz / e / YiAi absorption wavelength of the test gas. Here, one or more dynamically successive images are compared with one or more continuously successive images captured. When doing so, preferably, both the camera and the object are fixed so that the image section of the images captured successively is identical. According to the invention, a leak is automatically detected when the difference in signal amplitude between at least one image point in the first image and the signal amplitude of at least one image point in the second image exceeds a threshold value. Whereas known methods for obtaining thermographic images of gas only capture and display images of the gas, the method according to the invention performs an automated evaluation of the image point amplitudes to detect a leak. This allows for leak detection regardless of the user and the distance. Using the method according to the invention, a comprehensive evaluation of the airtightness of a test sample can be performed by summing the differences between the corresponding image points of the first and second images. This means that the amplitude of an image point Xij with i=l...nyj=l...m, where n, m are natural numbers, of the first image is subtracted from the amplitude of the point of CQRQnn / eznz / e / YiAi image x” of the second image corresponding to the first image point. To this difference is added the difference in the amplitudes of another image point, for example x¡+i,j or x¡,j+i of both images for several image points. This sum can be performed, for example, for all image points within a selected area, or for all image points in the entire image, or for each nth pixel, where n is a natural number. If the sum exceeds a certain threshold, a leak is considered to have been detected. If there is no test gas cloud at the location where the received optical radiation is reflected or transmitted, the gas shock emitted to this location does not displace a test gas cloud, so the amplitudes of the image points in the two images show no significant differences. The difference in image points then falls below a suitable threshold value. However, as soon as a test gas cloud is present at the location, the gas shock causes this cloud to displace, so the test gas cloud appears in a different position in the first image than in the second image. After subtracting the amplitudes of the image points from the two images, there are still significant amplitude values ​​above the threshold value due to the displacement of the test gas cloud. copQnn / eznz / B / YiAi As a result, calculating the difference in the amplitudes of the image points can allow the detection of a test gas cloud. The amplitude portion resulting from background radiation, background noise, or radiation reflected but not reflected by the test gas is reduced by subtracting the respective image points, while the amplitude portions of the absorption spectra of those image points corresponding to a location with test gas remain. As soon as the sum of these amplitudes exceeds a certain value, a leak can be considered automatically detected. Thus, according to the invention, an automatic comparison with the respective threshold value is performed. As soon as the threshold value is exceeded, a signal containing the information that a leak exists can be generated and / or transmitted. Alternatively or additionally, automatic leak detection in the test sample can also be performed by calculating the difference between the amplitude of at least one first image point xij of the first image and the amplitude of at least one second image point of the first image, which is different from the first image point. This difference is compared to a threshold value, where a leak is considered to exist at the location of the first image point if... CQRQnn / eznz / e / YiAi The difference exceeds a threshold value. Here, the sums of the amplitudes of several image points in a first area of ​​the first image can also be compared with the sums of the amplitudes of the image points in a second area of ​​the first image, which is different from the first area. If the difference between the sums of the amplitudes of the image points in the two areas exceeds a preset threshold value, a leak is considered to have been detected at the location of the first area. In this case as well, a signal containing information that a leak has been detected or is considered to have been detected can be automatically sent and / or generated. The test sample is preferably irradiated with optical radiation whose spectrum includes the absorption spectrum of the test gas. If the absorption spectrum of the test gas includes absorption wavelengths in the infrared range, the test sample is irradiated with infrared radiation. When performing the method according to the invention, it may be advantageous if the test specimen and / or the location of the measurement on the test specimen are protected from the external environment, for example by protective walls, in such a way that air movements from the external environment are kept away from the test specimen or the location of the measurement. CQRQnn / eznz / e / YiAi the measure. To irradiate the test sample, a radiation source can be used whose emission spectrum covers a large portion, such as more than 50 nm or more than 100 nm or several 100 nanometers of infrared thermal radiation—that is, whose emission spectrum is a broadband thermal spectrum. Alternatively, the radiation source can be a narrowband radiation source whose emission spectrum covers only a small portion, a few nanometers or up to 50 nm, of thermal radiation, such as a laser or an LED. Brief Description of the Figures An exemplary embodiment of the invention is explained in more detail below with reference to the Figures. In the Figures: Figure 1 is a schematic illustration of the exemplary modality, and Figure 2 is a schematic illustration of the captured images. Detailed Description of the Invention Figure 1 shows a pipe-shaped test specimen 12 carrying a gas or fluid, for example refrigerant, containing a test gas or capable of being used as a test gas. The test gas 16 flows through a leak 14 in the test specimen 12 and forms a cloud in the area of ​​the leak 14. CQRQnn / eznz / e / YiAi A radiation source 18 is used to emit infrared radiation 20 towards the test sample 12. The radiation 20 is reflected by the test sample 12 and the background of the test sample. The reflected radiation 20 is absorbed by a sensor 22, which can be a sensor of a thermal imaging camera, for example, in the form of a CCD microcircuit. An optical filter 24 is placed in front of the sensor 22 in the path of the reflected thermal radiation beam 20. Figure 2 shows a first image 30 and a second image 32 of the radiation 20 absorbed by the sensor 22. Both images 30 and 32 have the same number of image points x14, where i = l...n with n as a natural number and j = l...m with m as a natural number. Therefore, each of the two images 30 and 32 consists of n columns and m rows. When comparing the two images, the image points of a first area 34 of the first image 30 can be compared with the image points of an area 34 of the second image 32 corresponding to the first area 34. Alternatively or additionally, the image points of the first area 34 of one of the images can be compared with the image points of a second area 36 different from the first area 34. This second area can be used to locate a leak. CQRQnn / eznz / e / YiAi In particular, the comparison of the image points x¡j, of the two images 30, 32 can be performed using the term or using the term copQnn / eznz / B / YiAi Here Xij is an image point of the first image at the location of column i and row j, while is an image point of the second image corresponding to the location of the first image point, i.e., an image point of the second image at the location of column i and row j. If this term exceeds a certain threshold value, a leak is considered to have been detected. This may generate and / or emit a signal indicating that a leak exists or has been detected. Compared to the prior art, the method according to the invention offers the advantage of automated leak detection of a test sample by capturing and evaluating digital images of the test sample, without requiring a human observer to evaluate the captured images. In particular, the method according to the invention, or at least the comparison of the captured images and image points and the evaluation of the image points, can be computer-controlled or performed by a microprocessor. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A method for detecting a cloud of test gas escaping from a leak in a test sample, characterized in that it comprises the following steps: receiving optical radiation reflected or emitted from the test sample or its background at a first moment with an optical sensor configured to detect at least one wavelength or range of wavelengths of the optical absorption spectrum of the test gas, creating a first digital image from the optical radiation received at the first moment, such that the signal amplitudes of the x14 points of the image correspond to the amplitude of at least one range of absorption wavelengths of the test gas, receiving the optical radiation reflected or emitted by the test sample or its background at the second moment by means of the optical sensor, creating a second digital image from the optical radiation received at the second moment,so that the signal amplitudes of the image points correspond to the amplitude of at least one absorption wavelength interval of the test gas, compare the first image with at least a second digital image of the reflected optical radiation, which is different from the first image, in which a leak is considered to be detected when at least the difference in amplitude of at least a first image point x1:í of the first image and the amplitude of at least a second image point “ of the second image exceeds a threshold value, where i, j are natural numbers Xij is an image point located in column iy row j of the first image, and is an image point at the location of column iy row j of the second image.

2. The method according to claim 1, characterized in that a gas shock is emitted after capturing an image at the first time point and before capturing a second image at a second time point different from the first time point, in the direction of the location from which the image section is captured.

3. The method according to claim 1 or 2, characterized in that the optical sensor and the test sample are spatially fixed in such a way that the image sections of the captured images are almost identical.

4. The method in accordance with any of the preceding claims, characterized in that, for the comprehensive evaluation of the airtightness of the test sample, the sum is formed from the differences in the amplitudes of the mutually corresponding image points x1:í of the first image and ñ of the second image, a leak is considered to be detected if the sum exceeds the threshold value.

5. The method in accordance with any of the preceding claims, characterized in that, to locate a leak in the test sample, the difference is formed from the amplitude of at least a first image point xij of the first image and the amplitude of at least a second image point of the first image, a leak is considered to be detected at the location of the first image point Xij if the difference exceeds a threshold value.

6. The method in accordance with any of the preceding claims, characterized in that the test sample is irradiated with optical radiation whose spectrum includes at least a part of the absorption spectrum of the test gas.

7. The method in accordance with any of the preceding claims, characterized in that the optical radiation reflected by the test sample is filtered with an optical filter whose passband includes at least one absorption wavelength of the optical absorption spectrum of the test gas.

8. The method in accordance with any of the preceding claims, characterized in that during the measurement the test sample is protected from the environment in such a way that air movements in the environment are kept away from the test sample.

9. The method according to any of the preceding claims, characterized in that the test sample is irradiated with a radiation source whose emission spectrum covers a large part of the infrared thermal radiation, such as a halogen lamp, an incandescent lamp, a radiant heater, or a flash lamp.

10. The method according to any of the preceding claims, characterized in that the test sample is irradiated with a narrowband radiation source whose emission spectrum covers only a small part of the thermal radiation, such as a laser or an LED.

11. The method in accordance with any of the preceding claims, characterized in that the image points xgj of the two images are compared with each other using the term copQnn / eznz / B / Y 5 where i, j, n, m are natural numbers, Χΐή is an image point located in column i and row j of the first image, and “ is an image point located in column i 10 and row j of the second image.

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