Temperature measurement method and temperature measurement device for gaseous body

Abstract

In order to measure the temperature of a gaseous body: a light source (11) that, by changing the light intensity thereof, is capable of emitting light A of a wavelength λA to be absorbed by the gaseous body, and a light sensor (16) that is capable of measuring the reception light intensity of said light A are prepared; the light source and the light sensor are placed so that the gaseous body is interposed on a light path between the light source and the light sensor; the reception light intensity at the light sensor is measured by changing the light intensity of the light source; a light intensity Imin of the light source, when a spatial or / and temporal fluctuation range of the reception light intensity becomes minimum, is obtained; an equivalent temperature TS of the light source LA with respect to the light intensity Imin when an emission spectrum of the light source is approximated with complete black body radiation is calculated; and TS is set as the temperature of the gaseous body.

Description

Method and device for measuring temperature of gaseous material

[0001] The present disclosure relates to a method and an apparatus for measuring the temperature of a gaseous medium.

[0002] As interest in environmental issues grows, there is a demand for technologies to detect and measure various gas leaks. Exhaust from exhaust stacks and chimneys that release gases into the atmosphere is generally monitored by various sensors to prevent harmful gas emissions. Meanwhile, gas leaks from pipes in natural gas plants and petrochemical plants are detected by remote monitoring systems and patrols by inspectors, and are dealt with as they occur. In particular, leaks of flammable hydrocarbon gases (VOCs) such as methane, which pose a risk of explosion and poisoning, have been detected and measured using a variety of technologies.

[0003] Carbon dioxide (CO ２ ) is becoming a problem, and it is expected that the capture and reuse of carbon dioxide will become even more popular. As a result, it is predicted that carbon dioxide leaks from pipes will also become a target for detection and measurement. In addition, ammonia (NH ３ ) and nitrogen oxides (NO ｘ ) are expected to become targets of monitoring in the future. As such, there is an increasing need to detect a variety of gases.

[0004] To detect gas leaks from pipes, portable gas sensors are typically used to inspect pipe connections. However, this method makes it difficult to thoroughly inspect the entire pipe over a long distance. Furthermore, inspecting high or difficult-to-access locations requires significant costs and poses a risk to the inspector. To solve these problems, a practical method has been developed for remote monitoring, primarily for VOCs, that utilizes the infrared absorption of gases to visualize the gases with an infrared camera.

[0005] For example, Patent Document 1 discloses a method (gas visualization technology) for detecting leaking hydrocarbon gases using an infrared camera that can observe only the absorption wavelength of the gas, and further quantitatively evaluating the concentration and amount of emissions.

[0006] However, while gas visualization technology is a convenient method for detecting gas leaks at a distance under the right conditions, it faces the problem of difficulty in quantitative measurement. This is because gas visibility is affected not only by concentration but also by temperature. Simply measuring the gas detection intensity makes it impossible to calculate the concentration without knowing the gas temperature.

[0007] Fortunately, for VOCs, which have been the subject of observation up until now, the temperature of leaked gas can generally be considered to be room temperature. In Patent Document 1, the concentration is measured on the assumption that the gas temperature can generally be considered to be the same as the ambient air temperature. Alternatively, it is assumed that the gas temperature will be determined using a separate temperature sensor if necessary.

[0008] However, gas species that will become important in the future, especially CO ２ In the case of CO, it is more common that the gas temperature cannot be considered room temperature. ２ is a gas emitted as a result of combustion of raw material gases such as VOCs. ２ The temperature of CO is often higher than room temperature. ２ CO is also contained in human exhaled breath, but in this case, it is exhaled at a temperature close to the body temperature. ２ High concentration of CO ２ Quantitative measurement of leaks from the pipes through which CO is pumped is also required. ２ The sudden expansion of CO ２ The temperature of CO2 is lower than room temperature. ２ Measurement of the above will be required.

[0009] As such, the temperature of the gas to be measured varies depending on the gas type. In the future, quantitative measurement of gases at various temperatures will be required, unlike VOCs, which can be considered room temperature. To do this, a method for determining the gas temperature is important.

[0010] Conventionally, gas temperature has been measured by inserting a temperature sensor such as a thermocouple into the airflow. However, it is difficult to accurately align the temperature sensor and obtain reliable temperature information for gas that leaks into a large space and is dispersed by the airflow. Furthermore, it is not realistic to expect a temperature sensor with a finite heat capacity to reach thermal equilibrium with a small amount of leaked gas.

[0011] Here, by making good use of the property that infrared light information of gas is also affected by temperature, it becomes possible to remotely determine the gas temperature using infrared light. For example, Patent Document 2 proposes a method of optically determining the gas temperature using a laser by focusing on multiple absorption wavelengths that have different temperature dependencies of the gas. However, using a large-scale and expensive laser system just to measure this temperature is hardly a practical method.

[0012] US Patent No. 9,225,915 Specification Japanese Patent Publication No. 2017-515117 Japanese Patent Publication No. 2022-171533

[0013] Seiichiro Koda and Yoshitaka Takubo (eds.), Spectroscopic Measurement of Flames and Its Applications: Flame Spectroscopy, Spectroscopic Society of Japan, Measurement Method Series 20, Society Publishing Center, pp. 30-32 (June 20, 1990)

[0014] An object of the present disclosure is to provide a temperature measurement device and a temperature measurement method that can easily measure the temperature of a gaseous body located at a remote location using a small, simple, portable device.

[0015] The temperature measurement method for a gaseous body according to the present disclosure includes: Ａ A method for measuring the temperature of a gaseous body that absorbs light A, comprising: a light source L capable of emitting light A with varying light intensity; Ａ and an optical sensor S capable of receiving light A and measuring the intensity of the received light. Ａ Prepare the light source L Ａ is emitted from the light sensor S Ａ The light source L is arranged so that the gaseous substance is present on the light path of the light A received by the Ａ and optical sensor S Ａ The light intensity is changed to light source LＡ When light A is emitted from the light sensor S Ａ and determining, from the measurement of the received light intensity, the light source L when the spatial and / or temporal fluctuation width of the received light intensity is minimum. Ａ The light intensity I ｍｉｎ Calculate the light source L Ａ The light intensity I when the emission spectrum of ｍｉｎ Light source L Ａ Equivalent temperature T Ｓ The equivalent temperature T Ｓ is the temperature of the gaseous body.

[0016] The temperature measuring device for a gaseous body according to the present disclosure has a wavelength λ Ａ The apparatus for measuring the temperature of a gaseous body that absorbs light A includes a camera having an image pickup element in which a plurality of optical sensors that can receive light A and measure the intensity of the received light are arranged, an imaging optical system, and a band-pass filter, a light source that emits light in a wavelength band that includes light A, a light intensity varying device that varies the light intensity of the light source, an image processing device, and an integrated control device that controls both the light intensity varying device and the image processing device, and the image processing device determines, based on a signal output from the camera, the light intensity I of the light source at which the spatial and / or temporal fluctuation width of the measured light intensity is minimized. ｍｉｎ and a function for determining the light intensity I of the light source. ｍｉｎ Equivalent temperature T of the light source Ｓ The function of calculating the above-mentioned light source emission spectrum by approximating it with perfect blackbody radiation is provided.

[0017] The temperature measuring device for a gaseous body according to the present disclosure has a wavelength λ ＡAn apparatus for measuring the temperature of a gaseous body that absorbs light A, the apparatus comprising: a light receiving device having a detection element in which an optical sensor capable of receiving light A and measuring the intensity of the received light is arranged, an imaging optical system, and a bandpass filter; a light source that emits light in a wavelength band including light A; a light intensity varying device that varies the light intensity of the light source; a signal processing device that processes signals from the light receiving device; and an integrated control device that controls both the light intensity varying device and the signal processing device; ｍｉｎ（ｔ） and a function for determining the light intensity I of the light source. ｍｉｎ（ｔ） Equivalent temperature T of the light source Ｓ The function of calculating the above-mentioned light source emission spectrum by approximating it with perfect blackbody radiation is provided.

[0018] According to the present disclosure, a temperature measurement device, a method for using the same, and a temperature measurement method are provided that can easily measure the temperature of a gaseous body located at a remote location using a small, simple, and portable device.

[0019] FIG. 1 is an explanatory diagram showing an overview of the configuration of an apparatus (measurement apparatus system) according to the present disclosure; FIG. 2 is a characteristic diagram showing the optical density spectrum of a gas; FIG. 3 is a characteristic diagram showing a perfect blackbody radiation spectrum at a typical temperature; FIG. 4 is a characteristic diagram showing the relationship between optical density and detected light intensity when the light source equivalent temperature is higher than the gas temperature; FIG. 5 is a characteristic diagram showing the detected light intensity spectrum when the light source equivalent temperature is higher than the gas temperature; FIG. 6 is a characteristic diagram showing the relationship between optical density and detected light intensity when the light source equivalent temperature is lower than the gas temperature; FIG. 7 is a characteristic diagram showing the relationship between optical density and detected light intensity when the light source equivalent temperature is equal to the gas temperature; FIG. 8 is a characteristic diagram showing the detected light intensity spectrum when the light source equivalent temperature is equal to the gas temperature; FIG. 9 is a characteristic diagram showing the relationship between the light source equivalent temperature and the difference in signal intensity of light that has passed through a gaseous body relative to light that has not passed through a gaseous body; FIG. 10 is a flowchart showing a temperature measurement method according to the present disclosure; FIG. 11 is a typical gas visualization image during an increase in the light source equivalent temperature; FIG. 12 is a typical gas visualization image during a decrease in the light source equivalent temperature; and FIG. 13 is a characteristic diagram showing the relationship between the light source equivalent temperature and the average brightness of the gas visualization image during an increase in the light source equivalent temperature (a) and a decrease in the light source equivalent temperature (b). 1A and 1B are typical gas visualization central difference images during a rise in light source equivalent temperature; FIG. 1C are typical gas visualization central difference images during a fall in light source equivalent temperature; FIG. 1D are characteristic diagrams showing the relationship between the light source equivalent temperature and the variance of gas visualization images during a rise in light source equivalent temperature (a) and a fall in light source equivalent temperature (b); FIG. 1E is a configuration diagram of a measurement system for measuring gas temperature using an intensity-variable light source and an infrared detector; FIG. 1F are characteristic diagrams showing the time change in detected intensity in a gas passage region and in the absence of gas; FIG. 1G are characteristic diagrams showing the time change in the time differential signal of the detected light intensity in a gas passage region; and FIG. 1H are characteristic diagrams showing the time change in the time differential signal of the detected light intensity in a gas passage region.

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that A to B in the text represent A or more and B or less.

[0021] 1, the temperature measuring device (temperature measuring system) 101 has a light source 11, a light source intensity variable device (intensity variable device) 12, an integrated control device 13, a light receiving device 14 consisting of a camera 15, and an image processing device 19. Alternatively, as shown in Fig. 18, the temperature measuring device 101 has, instead of the camera 15, a light receiving device 14 consisting of an optical sensor 16, a lens 17, and a bandpass filter 18, and a signal processing device 20. Here, the lens 17 is an imaging optical system that forms an image of a gaseous material 21 on the light receiving portion of the optical sensor 16.

[0022] The light source 11 and the optical sensor 16, which is part of the light receiving device 14, are arranged so that light emitted from the light source 11 reaches the optical sensor 16 via a gaseous material (gas) 21, which is the object to be measured. The gaseous material 21 only needs to be placed on the optical path from the light source 11. For this reason, by using a reflecting mirror in the optical path, it is possible to position the gaseous material 21 outside the straight line between the light source 11 and the optical sensor 16. Alternatively, the light may be transmitted through an optical fiber and emitted from the optical fiber on the other side of the gaseous material.

[0023] The size of the light source 11 may be a large-area planar light source that covers the entire area of ​​the gaseous body, or a small-area light source that illuminates only a part of the gaseous body. However, in either case, the blackbody radiation equivalent temperature (hereinafter sometimes referred to as "equivalent temperature") of the light emitted by the light source 11 must have a range that can cover an equivalent temperature higher than the temperature of the gas to an equivalent temperature lower than the temperature of the gas.

[0024] The gaseous material 21 is not particularly limited as long as it is a gas that absorbs light in a specific wavelength range. For example, methane (CH ４ ), carbon dioxide (CO ２ ), carbon monoxide (CO), nitrous oxide (N ２ O), nitric oxide (NO), nitrogen dioxide (NO ２ ), sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ), water vapor (H ２ O), ammonia (NH ３ ), sulfur hexafluoride (SF ６) and chlorofluorocarbons. These gases are particularly in high demand as measurement targets. The gaseous substance 21 may be a gas that absorbs ultraviolet light, visible light, and terahertz light.

[0025] The light source 11 is a light source that emits light in a wavelength band that includes the light absorption band of the gas in the gaseous material 21, and the light intensity can be changed by the light intensity variable device 12. Specifically, the light source 11 can be a thermal radiation light source, a cavity blackbody furnace, a light-emitting diode (LED), or a laser light source. In particular, a thermal radiation light source coated with a blackbody coating can be preferably used because it can approximate complete blackbody radiation in image and signal analysis.

[0026] The light intensity varying device 12 is a device that changes the intensity of light emitted from the light source 11 by, for example, the following (1) to (5): (1) Control of power supplied to the light source 11 (2) Variable transmittance filtering using two linear polarizing filters (3) Filtering using neutral density filters with different transmittances (4) Continuously variable neutral density filter (5) Variable aperture

[0027] For high-contrast measurements, it is preferable to limit the wavelength band of light reaching the optical sensor from the light source to the vicinity of the light absorption band of the gaseous material. Here, the vicinity of the light absorption band is the wavelength λ of the light A absorbed by the gaseous material 21. Ａ The wavelength band of the gas absorption spectrum includes the wavelength λ of the light A and is approximately the same as the wavelength band of the gas absorption spectrum of the gaseous body. Ａ The wavelength band near the light absorption band is more preferably 0.25 to 4 times the band of the gas absorption band spectrum of the gaseous substance.

[0028] The wavelength limiting means may be (1) a bandpass filter that transmits only a certain wavelength range with high efficiency, or (2) a combination of a spectroscope with a built-in diffraction grating or prism and a slit that transmits only a specific wavelength range with high efficiency. Alternatively, if the light source or the optical sensor itself is a narrow-band element, it may be used as the wavelength limiting means.

[0029] The light receiving device 14 is a device that receives light from the light source 11 and outputs a light receiving signal. Examples of the light receiving device 14 include a (2D) imaging system shown in Fig. 1 and a single pixel detection system shown in Fig. 18. The light receiving device 14 of the (2D) imaging system can be composed of a camera 15 including an image sensor (light sensor) 16, a lens 17, and a band pass filter 18, as shown in Fig. 1. The light receiving device 14 of the single pixel detection system can be composed of a photodetector (light sensor) 16, a lens 17, and a band pass filter 18, as shown in Fig. 18.

[0030] The absorption wavelength band of the gas to be measured may be any of infrared light, visible light, ultraviolet light, and terahertz light depending on the gas. Depending on the absorption wavelength band, for example, in the case of ultraviolet light, an ultraviolet imaging element, an ultraviolet lens, and an ultraviolet bandpass filter can be applied.

[0031] CO ２ , NO ｘ , CO, and NH ３ Many gaseous materials 21 that are in high demand for measurement, such as fluorine, have an absorption wavelength band in the infrared light. Therefore, the following description will focus on the infrared light band. In this case, the light receiving device 14 can be classified into a (2D) imaging system ( FIG. 1 ) and a single-pixel detection system ( FIG. 18 ). The light receiving device 14 of the (2D) imaging system ( FIG. 1 ) is composed of an infrared camera 15 including an infrared imaging element (optical sensor) 16, an infrared lens 17, and a band-pass filter 18. The light receiving device 14 of the single-pixel detection system ( FIG. 18 ) is composed of an infrared detector (optical sensor) 16, an infrared lens 17, and a band-pass filter 18.

[0032] As will be shown in the examples, a (2D) imaging system that measures spatial fluctuations is more likely to achieve measurement accuracy, whereas a single-pixel detection system has the advantage of being simple and easy to reduce costs.

[0033] <<2D Imaging System>> There are no particular restrictions on the infrared lens 17, as long as it has sufficient imaging performance as a camera. Examples of the optical system that can be used include: (1) a lens imaging system using optical lenses made of Ge, Si, ZnSe, ZnS, or sapphire; (2) a reflective optical system using mirrors; and (3) a composite optical system using both mirrors and lenses. The optical lens may be a short focal length lens or a zoom lens. There are no particular restrictions on the magnification, F-number, or allowable aberration of the optical lens, and these may be selected appropriately taking into account factors such as cost, ease of use, weight, resolution, and field of view.

[0034] The infrared imaging element (optical sensor) 16 is a pixel-shaped infrared sensor having multiple light-receiving pixels, and any light-receiving element sensitive to the above wavelength band can be used without any particular restrictions. That is, this light-receiving element is a light-receiving element that detects light tuned to the absorption wavelength of the gas to be measured. The infrared imaging element (optical sensor) 16 can be, for example, a photoelectric conversion element such as InSb, HgCdTe, InAs / GaSb superlattice, InGaAs / InAlAs quantum well, or GaAs / AlGaAs quantum well. Alternatively, the infrared imaging element 16 may be a thermal infrared light sensing element using a bolometer, thermopile, or pyroelectric element. Here, to facilitate image analysis, the pixels of the infrared imaging element 16 are preferably arranged in a matrix.

[0035] There are no particular limitations on the pixel size and number of pixels of the infrared imaging element 16. If the pixel size is reduced, the size of the infrared imaging element 16 also becomes smaller, and it becomes easier to miniaturize the infrared lens 17. If the pixel size is large, it becomes easier to improve the sensitivity and S / N ratio, and it also becomes easier to increase the resolution. The pixel size is, for example, 10×10 to 30×30 μm ２ The number of pixels is not particularly limited and may be set appropriately taking into consideration the size of the device, the required resolution, etc. Examples of the number of pixels include 64×64 to 1920×1536.

[0036] Any filter that selectively transmits light in the above wavelength bands can be used as the bandpass filter 18. For example, a multilayer film made of SiO, ZnS, Ge, etc., formed on a sapphire or germanium substrate can be used as the bandpass filter 18.

[0037] The bandpass filter may be placed in front of the infrared lens 17 or behind the infrared lens 17 when viewed from the infrared imaging element 16. Placing the bandpass filter in front of the infrared lens 17 has the advantage of making it easy to replace or remove the bandpass filter. Placing the bandpass filter behind the infrared lens 17 has the advantage that the bandpass filter can be made smaller and, when cooling as described below, can be performed, the bandpass filter can be cooled together with the infrared imaging element 16.

[0038] The infrared imaging element 16 and the bandpass filter 18 are preferably cooled. Cooling reduces noise caused by thermal radiation from the environment, components, and the like. When the bandpass filter 18 is at room temperature, thermal radiation from the bandpass filter 18 is superimposed on the signal from the infrared imaging element 16 as a large baseline. This significantly reduces the contrast of the resulting image. Examples of cooling methods include a Stirling cooler, a Peltier element, and liquid nitrogen cooling. Stirling coolers and Peltier elements are preferred because they are easy to handle. Stirling coolers are particularly preferred because they are handy, can cool to 80 K or less, and can be operated using a battery.

[0039] The cooling temperature is preferably 50 K or higher and 250 K or lower. By setting the temperature to 250 K or lower, the noise level can be improved by one order of magnitude or more. The lower the temperature, the lower the noise level. At a temperature of 50 K, the noise level drops by more than 20 orders of magnitude compared to when used at room temperature, and noise due to other factors such as voltage fluctuations becomes dominant. At extremely low temperatures, convenience and ease of handling decrease, so it is preferable to set the temperature to 50 K or higher.

[0040] The optical sensor 16, lens 17, and bandpass filter 18 (hereinafter referred to as "optical sensor 16, etc.") are described here as being for infrared light, a typical example. However, it is preferable that the optical sensor 16, etc. have a wavelength band that matches the absorption wavelength of the gas to be measured. Therefore, the optical sensor 16, etc. for at least infrared light, visible light, ultraviolet light, or terahertz light is used depending on the gas.

[0041] The image processing device 19 is a device that performs the following processes (1) to (3): (1) Processes the signal received and captured by the infrared imaging element 16 to obtain fluctuations in the spatial distribution of light intensity (image fluctuations). (2) Determines the light intensity I of the light source 11 at which the width of the spatial distribution fluctuations becomes minimum. ｍｉｎ (3) Light intensity I ｍｉｎ The equivalent temperature T of the light source 11 ｓ is calculated by approximating the emission spectrum of the light source 11 with perfect blackbody radiation.

[0042] A computer such as a mobile PC can be cited as specific hardware of the image processing device 19. A mobile PC is small, lightweight, easy to move around, and easy to handle.

[0043] <<One-Pixel System>> The infrared lens 17 and bandpass filter 18 in the one-pixel system are similar to those in the 2D imaging system.

[0044] As with 2D imaging systems, the infrared detector (optical sensor) 16 of a single-pixel system can be any light-receiving element sensitive to the above wavelength bands, without any particular restrictions. Examples of suitable infrared detectors 16 include photoelectric conversion elements such as InSb, HgCdTe, InAs / GaSb superlattices, InGaAs / InAlAs quantum wells, and GaAs / AlGaAs quantum wells. Thermal infrared sensing elements using bolometers, thermopiles, and pyroelectric elements may also be used. Because the infrared detector 16 has a single pixel, the pixel size can be increased, improving the S / N ratio. Here, a typical infrared sensor is described as an optical sensor 16. However, it is preferable that the optical sensor 16 has a wavelength band that matches the absorption wavelength of the gas to be measured. Therefore, optical sensors 16 for at least infrared light, visible light, ultraviolet light, and terahertz light are used depending on the gas.

[0045] The signal processing device 20 is a device that performs the following processes (1) to (3): (1) Processes the light reception signal of the infrared detector 16 to obtain the time fluctuation of the light intensity; (2) Determines the light intensity I of the light source 11 at which the time fluctuation width is minimized; ｍｉｎ（ｔ） (3) Light intensity I ｍｉｎ（ｔ） The equivalent temperature T of the light source 11 ｓ is calculated by approximating the emission spectrum of the light source 11 with perfect blackbody radiation.

[0046] A computer such as a mobile PC can be cited as specific hardware of the signal processing device 20. A mobile PC is small, lightweight, easy to move around, and easy to handle.

[0047] The integrated control device 13 is a device that controls the light intensity variable device 12 and the image processing device 19 or the signal processing device 20 to perform measurements. ｍｉｎ or light intensity I ｍｉｎ（ｔ） A specific example of hardware for the integrated control device 13 is a computer such as a mobile PC. A single computer can be equipped with the integrated control device 13 and the image processing device 19 or the signal processing device 20, and is small and easy to use.

[0048] <Measurement principle> As shown in FIG. 1, infrared light is emitted from a light source 11, passes through a gas, where a portion of the light is absorbed or enhanced, passes through a bandpass filter having a pass wavelength band near the absorption wavelength of the gas, and is incident on and detected by an infrared imaging element.

[0049] Infrared light is often absorbed and its intensity reduced when it passes through a gas. However, even infrared light of the same wavelength can appear to be more intense (enhanced) when it passes through a different gas (gas in a different state). This is because the light emitted from the gas is added to the infrared light.

[0050] This will be explained in detail below. The intensity of infrared light passing through the gaseous body 21 varies greatly depending on the relationship between the blackbody radiation equivalent temperature (equivalent temperature) of infrared light from the light source 11 and the temperature of the gaseous body 21. That is, if the temperature of the gaseous body 21 is lower than the equivalent temperature of the infrared light, the infrared light is absorbed by the gaseous body 21, and the intensity of the infrared light passing through the gaseous body 21 decreases. On the other hand, if the temperature of the gaseous body 21 is higher than the equivalent temperature of the infrared light, the infrared light is enhanced by the emission from the gaseous body 21. In this way, the intensity of infrared light passing through the gaseous body 21 varies greatly across the point where the equivalent temperature of the infrared light and the temperature of the gaseous body 21 become equal. Therefore, by changing the equivalent temperature of the infrared light, the temperature of the gaseous body 21 can be determined from the equivalent temperature when the intensity of the infrared light passing through the gaseous body 21 changes significantly.

[0051] In the present disclosure, the temperature of the gaseous material 21 is calculated based on the change in the intensity of infrared light corresponding to the equivalent temperature of the infrared light. Furthermore, to improve the accuracy of the temperature, the time point at which the intensity of the infrared light changes is calculated more precisely by taking into account fluctuations in the change in the intensity of the infrared light. Details of this will be described later.

[0052] The emission spectrum of the light source is ｓ Perfect blackbody radiation I ｂ (λ, T ｓ ) can be approximated by the temperature T ｓ is called the equivalent temperature of the light source. Here, changing the intensity of the light source changes the equivalent temperature T ｓThis corresponds to changing the wavelength.

[0053] Emission intensity I ｂ (λ, T ｓ When light from a gas with a density c and thickness L passes through it, the gas absorbs the light according to its absorption spectrum. At the same time, the gas itself absorbs the light at its temperature T ｇ At this time, the light intensity I detected through the gas ｄｇ (λ, T ｓ , T ｇ , c, L) are expressed by the following equations (1) and (2).

[0054] Here, the first term on the right side of equation (1) is the intensity I of the light incident on the gas from the light source. ｂ (λ, T ｓ ) is absorbed by the gas and decays exponentially.

[0055] τ ｇ (λ, T ｇ , c, L) is the optical density of the gas, which is expressed by the following equation (3):

[0056] Here, α(λ,T ｇ ) is the absorption coefficient per concentration of that gas. ｇ ) varies greatly depending on λ, and becomes large around the absorption wavelength of the gas. ｇ ) is the gas temperature T ｇ Furthermore, the absorption coefficient α(λ,T ｇ ) becomes larger as the gas concentration c becomes higher and as the gas thickness L increases.

[0057] The second term on the right side of equation (1) represents the light intensity emitted by the gas. As the optical density of the gas increases, the light intensity decreases. ｂ (λ, T ｇ ) is an exponential asymptotic function of the light intensity I ｂ (λ, T ｇ ) is the temperature T ｇ is the radiant intensity of a perfect black body.

[0058] Equation (2) represents the sum of the two terms in equation (1). As shown in equation (2), the greater the optical density of the gas, the greater the light intensity of the light source I ｓ (λ, T ｓ ) from the gas blackbody radiation I ｇ (λ, T ｇ ) gradually approaches

[0059] The intensity of light emitted from the light source that does not pass through the gas, I ｄ０ (λ, T ｓ ) is expressed by the following formula (4).

[0060] This light intensity I ｄ０ (λ, T ｓ ) is the detected intensity of light in the background area where the light source is directly visible, when the field of view of the infrared camera in Figure 1 contains a mixture of (1) a background area where the light source is directly visible and (2) a gas passage area where the light source is visible through gas.

[0061] Here, the difference in intensity of light that has passed through the gas relative to light that has not passed through the gas is expressed by the following equation (5).

[0062] The first term of equation (5) is the equivalent temperature T ｓ and the gas temperature T ｇ The second term in equation (5) is determined solely by the gas, and is close to 0 when the gas absorption is small, and increases as the optical density increases, gradually approaching 1.

[0063] Next, let us consider the behavior of Equation (2) and Equation (5) in a specific case. Consider a hypothetical gas that exhibits an absorption peak at a wavelength of 4.25 μm. Its absorption coefficient α(λ, T ｇ ) and optical density τ determined by concentration c and thickness L ｇ (λ, T ｇ , c, L) are as shown in FIG. 2. For the sake of later explanation, the wavelength λ at which gas absorption is large is a , medium wavelength λ b , small wavelength λ c Consider three representative points (wavelengths) of

[0064] FIG. 3 shows the complete blackbody radiation spectrum I at a typical temperature.ｂ (λ, T). It can be seen that the higher the temperature, the greater the light intensity. Equations (2) and (5) are the absorption coefficient α(λ, T ｇ ), and spectrum Ib(λ, T).

[0065] [1] When the light source equivalent temperature is higher than the gas temperature (T ｓ >T ｇ ) If the light source equivalent temperature is higher than the gas temperature, ｂ (λ, T ｓ )-I ｂ (λ, T ｇ )>0”, so “ΔI ｄ (λ, T ｓ , T ｇ , c, L)<0”. In other words, the light intensity in the gas passage area is lower than that in the background area.

[0066] FIG. 4 shows a schematic diagram of the behavior of equation (2) at a certain wavelength λ. The detected light intensity I ｄｇ is the light source intensity I when there is no gas absorption. ｂ (λ, T ｓ ) The detected light intensity I ｄｇ is the optical density τ ｇ The larger the value, the smaller the blackbody radiation of the gas temperature I ｂ (λ, T ｇ The positions of three representative points with different optical densities in FIG. 2 are shown in FIG. 4 as circles.

[0067] Figure 5 shows the "T ｓ = 45°C, T ｇ The spectrum is given by equation (2) for the case of "=25°C". At wavelengths where there is no absorption, the light source intensity I ｂ (λ, T ｓ ) is detected as it is, but it can be seen that the greater the absorption, the smaller the detected light intensity.

[0068] [2] When the light source equivalent temperature is lower than the gas temperature (T ｓ <T ｇ ) If the light source equivalent temperature is lower than the gas temperature, ｂ (λ, T ｓ )-I ｂ (λ, T ｇ) < 0, so "ΔI ｄ (λ, T ｓ , T ｇ , c, L)>0”. In other words, the light intensity in the gas passage region is greater than that in the background region.

[0069] FIG. 6 shows a schematic diagram of the state of equation (2) at a certain wavelength λ. The detected light intensity I ｄｇ is the light source intensity I when there is no gas absorption. ｂ (λ, T ｓ ) The light intensity I ｄｇ is the optical density τ ｇ The larger the value, the greater the blackbody radiation of the gas temperature I ｂ (λ, T ｇ The positions of three representative points with different optical densities in FIG. 2 are shown schematically by circles in FIG. 6.

[0070] In FIG. ｓ = 5 ° C., T ｇ Equation (2) is shown as a spectrum when the temperature is 25°C. At wavelengths where there is no absorption, the light source intensity I ｂ (λ, T ｓ ) is detected as is. It can be seen that the greater the absorption, the greater the detected light intensity. At first glance, it may seem odd that the greater the gas absorption, the greater the detected light intensity, but this is a consequence of Kirchhoff's law. The absorptivity, which indicates an object's ability to absorb light, is equal to the emissivity, which indicates the same object's ability to emit heat. This is Kirchhoff's law. Whether an object absorbs or emits light is determined by its relative thermal equilibrium with its surroundings. In the case of Figure 7, the gas is relatively hotter than the equivalent temperature of the light source of the incident light, so the gas's radiation is dominant.

[0071] [3] When the light source equivalent temperature and the gas temperature are equal (T ｓ =T ｇ ) What is interesting is the boundary between the two ｓ =T ｇ In this case, "I ｂ (λ, T ｓ )-I ｂ (λ, T ｇ ) = 0", so "ΔI ｄ (λ, Tｓ , T ｇ , c, L)=0. In other words, in this case, there is no difference in detection intensity between the background region and the gas passing region, and the boundary between the background region and the gas passing region is not detected.

[0072] FIG. 8 shows a schematic diagram of the state of equation (2) at a certain wavelength λ. ｓ = 25 ° C., T ｇ The optical density τ is expressed as a spectrum in the case of τ = 25 °C. ｇ Regardless of the cause, there is no difference in the detected intensity depending on whether or not the gas is present.

[0073] The actual measurement will be explained below. The signal actually obtained from the infrared camera is within a wavelength band [λ １ , λ ２ ] is obtained by integrating the light intensity of equations (2) and (5).

[0074] The difference in signal intensity between light that has passed through the gas and light that has not passed through the gas is expressed by the following formula:

[0075] where τ ｇ (λ, T ｇ , c, L) determines the function form. ｇ ) has a strong λ dependence. ｂ (λ, T ｓ ) and I ｂ (λ, T ｇ ) is, when focusing on a narrow wavelength band as in the present disclosure, α(λ, T ｇ ) can be considered to have little λ dependence.

[0076] I ｂ (λ, T ｓ ), I ｂ (λ, T ｇ ) at the center wavelength λ ０ If it can be approximated by the value in the formula (6), the following formula is established.

[0077] The second term of equation (6) becomes larger as the optical density of the gas increases. Figure 10 shows the relationship between the optical density of the gas and the T ｇThe relationship between the difference in signal intensity (Equation (6)) and the light source equivalent temperature is shown for the case of "=25°C." The gas absorption increases as the concentration c increases, the gas thickness L increases, and the wavelength band [λ １ , λ ２ ]The larger the overlap, the larger the

[0078] In Figure 10, the solid line corresponds to the case where the optical density of the gas is high, the dashed line corresponds to the case where the optical density is low, and the dashed line corresponds to the case between these two. Specifically, the solid line, dashed line, and dashed line represent the cases where the value of the second term of equation (6) is 0.16 μm, 0.09 μm, and 0.02 μm, respectively. The second term of equation (6) is given by the following equation.

[0079] Light source equivalent temperature T ｓ When the light source equivalent temperature T is low, the light intensity in the gas passage area is greater than that in the background area. As the light source equivalent temperature increases, the light intensity in the gas passage area decreases, and at a certain point, the sign of the detection intensity (difference in signal intensity) is reversed, after which the light intensity in the gas passage area decreases further. ｓ When ρ is fixed, the greater the gas absorption, the greater the change in the detected intensity of light in the gas passing region relative to the background region.

[0080] However, in all cases, regardless of the magnitude of gas absorption, "T ｓ = 25°C, that is, when "T ｓ =T ｇ ” , the gas passage area cannot be distinguished from the background area. ｓ When the change in light intensity caused by the gas is minimized (when the gas passing area cannot be distinguished from the background area), the light source equivalent temperature T ｓ As the gas temperature T ｇ can be obtained.

[0081] The intersection point (the point where the difference in signal intensity is reversed) itself does not depend on the magnitude of gas absorption. However, the greater the absorption, the greater the change in signal, and the more clearly the intersection point can be identified. The gas concentration c and thickness L are properties of the object to be measured. However, the wavelength band [λ] of the bandpass filter １ , λ ２], the absorption coefficient α(λ, T ｇ ), the integral value of the second term of Equation (6) can be increased. １ , λ ２ ] should be limited to a narrow region near the absorption peak, but if it is too narrow, the signal amount itself will decrease, resulting in a lower signal-to-noise (SN) ratio. １ , λ ２ ] will be determined.

[0082] After examining many cases, we found that the wavelength band [λ １ , λ ２ ] is the band width [λ g１ , λ g２ It has been found that a value of 0.25 to 4 times the absorption coefficient of the gas is preferable. Within this range, gas can be visualized with high contrast. Here, the measurement wavelength band refers to the full width at half maximum of the transmittance of a bandpass filter or the like. The band of the reference gas absorption band spectrum refers to 1 / 10 of the full width of the absorption coefficient of the gas.

[0083] The method disclosed herein differs from the background art in that it utilizes the equipment required for gas visualization and enables independent temperature measurement simply by adding an intensity-variable light source to it. This allows for highly accurate measurement of gas concentration from the gas visualization image and temperature information, even for gases whose temperatures are not necessarily room temperature, and enables quantitative evaluation of leaked gas emissions.

[0084] Furthermore, in the present disclosure, based on the fluctuation of light received by the optical sensor (infrared detector), the difference in detection (signal) intensity between the background area and the gas passing area is eliminated, and T ｇ and T ｓ Find the point where these coincide.

[0085] The density of a gaseous substance often fluctuates spatially and / or temporally. Therefore, the received signal intensity also fluctuates, and T ｇ and T ｓ The error in finding the point where the points coincide also seems to be large.

[0086] However, when the signal intensity is small, the fluctuations are also small. This is a general property of noise. Considering an analogy, for example, shot noise, which is the intensity fluctuation of light, is proportional to the 1 / 2 power of the light intensity. Intuitively, the weaker the light, the greater the fluctuations, and it feels as though the signal is buried in the noise. However, statistically, the stronger the light and the greater the number of photons, the greater the fluctuations in intensity and photon count. In the case of the present disclosure, the smaller the difference in detected intensity between the background region and the gas passage region, the smaller the fluctuations.

[0087] Therefore, the light source equivalent temperature T ｓ If spatial and / or temporal signal fluctuations are statistically measured during the process of changing T ｓ T ｇ As the distance approaches , the difference in light intensity becomes smaller, and therefore the fluctuation also becomes smaller. ｓ =T ｇ " and when the gas disappears, the fluctuations become minimum, and then T ｓ T ｇ Thus, by simply focusing on the statistical and mathematical objective indicators of spatial and / or temporal fluctuations, we can find the minimum point of fluctuations at T ｓ and T ｇ The points at which the two points match can be found with high accuracy.

[0088] This measurement method is the null method because the value is obtained as a minimum point. The null method is an ideal method for high-precision measurements. With this measurement method, if the equivalent temperature of the light source is properly calibrated and a range of change is secured that covers an equivalent temperature higher than the temperature of the gas to be measured to an equivalent temperature lower than the temperature of the gas to be measured, the measurement results are less likely to be affected by other factors. For example, even if the same type of gas exists in the atmosphere between the gaseous substance to be measured and the optical sensor (for example, CO in the atmosphere), the measurement results will not be affected by other factors. ２ ), and this absorption simply weakens the measurement signal light overall, but does not change the relationship between the light and dark detected intensities, so it does not affect the measurement.

[0089] On the other hand, in the null method, the reference value (in this case, the light source temperature T ｓ) must be scanned, which has the disadvantage of being time-consuming. However, when an LED is used as the light source, the light source intensity can be scanned quickly by voltage scanning. Also, when a thermal emission light source is used, the size of the light source does not need to cover the entire area of ​​the gaseous material, but a small area that illuminates only a part of it is sufficient. Therefore, high-speed measurement can be achieved by reducing the heat capacity of the thermal emission light source and scanning the temperature quickly using a large-capacity heater or large-capacity Peltier element. In this way, the temperature of a gaseous material can be measured with high reliability and high reproducibility by simply optically observing it from a distance, without inserting a temperature measuring device into the gas.

[0090] <Measurement Method> The temperature measurement method of the present disclosure is performed using a wavelength λ Ａ This method for measuring the temperature of a gaseous substance that absorbs light A will be described with reference to the process flow chart of FIG.

[0091] First, the optical sensor S Ａ A case where an infrared imaging element, that is, an infrared detector having a plurality of pixels arranged therein, is used as the infrared imaging element will be described.

[0092] First, a light source L capable of emitting light A with varying light intensity. Ａ and an optical sensor S capable of receiving light A and measuring the intensity of the received light. Ａ (Step S11). Ａ is an infrared imaging element.

[0093] Next, the light source L Ａ is emitted from the light sensor S Ａ The light source L is arranged so that the gaseous substance is present on the light path of the light A received by the Ａ and optical sensor S Ａ is placed (step S12).

[0094] Then, the light intensity is changed to Ａ When light A is emitted from the light sensor S Ａ The received light image and the received light intensity are measured (step S13).

[0095] Thereafter, from the measurement of the received light image and the received light intensity, the light source L when the spatial and / or temporal fluctuation width of the received light intensity becomes minimum is determined.Ａ The light intensity I ｍｉｎ is calculated (step S14).

[0096] Here, the spatial fluctuation of the received light intensity can be calculated from the variance of the difference image of the signal output from the infrared imaging element. On the other hand, the temporal fluctuation can be calculated from the AC component extracted by time differentiation of the received light signal output from the infrared imaging element. The difference image (for example, the central difference image I described later) ｍ ) is a differential image between images acquired at different times, so it also reflects temporal fluctuations. Therefore, strictly speaking, the fluctuation calculated from the variance of the differential image reflects not only spatial fluctuations but also temporal fluctuations, so it can be said to be "spatial fluctuations and temporal fluctuations."

[0097] In addition, when there is spatial fluctuation in the concentration of the gaseous substance to be measured, which is often the case, it is generally easier to obtain high measurement accuracy by using the spatial fluctuation. ｍｉｎ By calculating the above, more accurate information can be obtained regarding the measurement accuracy of the temperature of the gaseous body.

[0098] Then, the light source L Ａ The light intensity I when the emission spectrum of ｍｉｎ Light source L Ａ Equivalent temperature T Ｓ is calculated (step S15).

[0099] Finally, the equivalent temperature T Ｓ is set as the temperature of the gaseous material (step S16), and measurement of the temperature of the gaseous material is terminated (S02).

[0100] Next, the optical sensor S Ａ A case where a one-pixel infrared detector is used as the detector will be described.

[0101] When an infrared detector is used, the optical sensor S Ａ The light intensity measured in step S14 is the received light intensity. ｍｉｎ is the light source L when the temporal fluctuation of the received light intensity is minimum. ＡOtherwise, the temperature of the gaseous material is measured using the same steps as when using an infrared imaging element.

[0102] By measuring the temperature of a gaseous body through the above steps, it becomes possible to easily measure the temperature of a gaseous body located at a remote location using a small, simple, portable device.

[0103] Furthermore, the gas temperature can be measured optically from a distance without inserting a measuring device into the gas, making it possible to perform reliable and highly reproducible measurements.

[0104] Furthermore, in the gaseous body temperature measurement of the present disclosure, the gas temperature can be measured in a short time not only when the equivalent temperature is changed by electronically scanning the light source intensity, but also when the equivalent temperature is changed by changing the temperature of the thermal radiation light source. By reducing the heat capacity of the black body plate that emits thermal radiation and scanning the temperature at high speed using a large-capacity heater or Peltier element, the gas temperature can be changed in a short time.

[0105] Additionally, the gaseous body temperature measurement of the present disclosure can be ２ and H ２ Even if a gas of the same kind, such as O, is present in the atmosphere between the gas to be measured and the photodetector, the measurement signal light is simply weakened, and the relationship between the light and dark of the detected intensity remains unchanged, so there is no effect on the measurement.

[0106] <Applications to Concentration Measurement and Emissions Measurement> The main motivation for measuring the temperature of gaseous bodies in this disclosure was the quantitative measurement of gases using an infrared camera that visualizes specific gases by utilizing the gas's inherent infrared absorption. Gas visualization technology is a convenient method for detecting gas leaks from a distance and is an important technology for advancing the resolution of environmental issues. However, because the appearance of gas is affected not only by concentration but also by temperature, there was a problem in that quantitative measurement of concentration was not possible unless the gas temperature was known. However, this disclosure makes it possible to measure the temperature of gaseous bodies, opening up the prospect of using gas visualization technology to measure gas concentrations and emissions.

[0107] A major feature of the present disclosure is that when quantitative evaluation of gas concentration and emission amount is desired, gas temperature can be measured using almost the same optical system. Specifically, as a preliminary measurement, a variable intensity light source is placed behind the gaseous material and the temperature of the gaseous material is measured by scanning the intensity, and then the actual measurement of concentration and emission amount can be proceeded to. In some cases, a light source such as an infrared light source may be placed behind the gaseous material for highly accurate concentration measurement. In this case, the gas temperature can be measured by scanning the equivalent temperature of the light source once using the exact same optical system, and then the temperature is maintained at a temperature suitable for concentration measurement, and the concentration and emission amount can be measured.

[0108] If you want to measure the temperature as easily as possible, you can simply place a reflector, a scatterer, or the exit of an optical fiber on the other side of the gaseous medium, rather than the light source itself. In that case, since the reflector, scatterer, and optical fiber are lightweight, you can place a drone holding them on the other side of the gaseous medium only when measuring the temperature of the gaseous medium.

[0109] After the temperature of the gaseous substance has been determined, the subsequent concentration and emission measurements can be carried out as follows.

[0110] Here too, equation (6) plays an important role. First, ΔI(T ｓ , T ｇ , c, L) are known. Here, the gas temperature T ｇ is the light source equivalent temperature T at which the fluctuation width is minimized according to the present disclosure. ｓ In this measurement, a different fixed background is generally used, and the temperature of this background can be measured by using an infrared camera as a thermograph.

[0111] The infrared camera we are currently using has a limited bandwidth for gas visualization. Here, by calibrating the light intensity of the background area at a specific emissivity and temperature, we can obtain the temperature T ｓ can be obtained from the image of the moment the gas flutters. Then, the column density "c × L" can be calculated from equations (6) and (3).

[0112] To know the gas concentration c, information on the gas thickness L is required, which can be measured by observing the same gaseous body from a different direction.

[0113] When calculating the emission rate (flow rate), there is no need to divide the column density "c x L" into individual elements; the column density itself provides useful information. This represents the amount of gas integrated in the line of sight (z direction). By integrating this in the camera's line of sight (x and y directions), the total amount of gas visible on the screen can be calculated.

[0114] Furthermore, by applying a motion vector image measurement technique such as optical flow to the gas visualization image, it is possible to obtain the gas flow velocity vector at each part. Gas visualization using a vector image measurement technique is disclosed in, for example, Patent Document 3.

[0115] By applying Gauss's theorem, the volumetric flow rate (emission rate) passing through a measurement line can be calculated as the integral of the column density on the measurement line and the flow velocity component perpendicular to the measurement line. Thus, if the temperature of a gaseous body can be measured according to the present disclosure, it can be directly applied to quantitatively measuring the concentration, flow rate, and emission rate of a gas.

[0116] (Example 1) A temperature-variable thermal radiation light source having a light-emitting surface size of 130 mm square and a black coating with an emissivity of 0.96 on its surface was used as the light source. ２ The gas was sprayed at a flow rate of 1.1 SLM from a fan-shaped blower nozzle with a rectangular opening measuring 12.6 mm on the long side and 1.5 mm on the short side. The nozzle was oriented so that the long side was parallel to the surface of the light source and the short side was the thickness L of the gas. The temperature at the center of the light source was measured with a separately prepared radiation thermometer from an angle that was not affected by the gas.

[0117] The displayed temperature when the emissivity is set to 1.00 is the equivalent temperature T ｓ The accurate light source surface temperature should be calculated by correcting the emissivity of 0.96, which is the apparent measured value T ｓ However, what is required in this disclosure is the actual intensity of the emitted infrared light I ｂ (λ, T ｓ ), so here we use T ｓwas regarded as the effective light source temperature.

[0118] This situation is CO ２ The observation was made with an infrared camera that can visualize the image. The camera used was a FLIR A6796 model, which uses a 640 x 512 pixel InSb infrared imaging element and has a built-in bandpass filter for the wavelength band [4.12 μm, 4.33 μm]. This bandpass filter was cooled to 80 K or less. The infrared lens had a lens focal length of 50 mm and an F value of 2.5, and the imaging conditions were an exposure time of 40 ms and a frame rate of 25 fps. On the other hand, CO ２ The absorption spectrum band is [4.21 μm, 4.33 μm], and the wavelength band of the bandpass filter (0.21 μm) is 1.8 times the gas absorption band spectrum band (0.12 μm).

[0119] A typical image when the temperature of the light source is increased is shown in FIG. 12, and a typical image when the temperature is decreased is shown in FIG.

[0120] Specifically, the image when the temperature is rising is an image of a CO2 lamp that is rapidly heated after the light source temperature is initially set to 10°C and then changed to 40°C. ２ The image of the gas when the temperature is decreasing is the image of the CO gas that is rapidly cooled after the light source temperature is initially set to 40°C and then changed to 10°C. ２ 12 and 13, the brightness at the center of the display is adjusted to be the same as that of the background area. The brightness range is constant in both figures.

[0121] In Figure 12, when the temperature rises, the CO ２ In Figure 13, when the temperature is decreasing, the CO ２ The image gradually changes to appear brighter, but there is a moment in between when it is not visible. This moment was determined by appropriately expanding the display brightness range of the image and observing it with the naked eye. The equivalent temperature of the light source at this time is T ｓ = 23.5°C, and Ts = 23.7°C in Figure 13. ｓ= 23.6 ± 0.1 °C and just CO ２ In other words, this is the calculated gas temperature T ｇ is.

[0122] Next, for a more quantitative discussion, we will analyze the T from the information measured from the image. ｇ 14(a) and (b) show the time variation of the average brightness in FIG. 12(a) when the temperature is rising and falling, respectively, as a function of the light source equivalent temperature T ｓ The average brightness is shown as a function of . This average brightness is the average brightness within the rectangular frame (40 horizontal pixels and 32 vertical pixels located at the center of the image) in which gas is constantly observed, as shown in Figure 12(a). Note that the average brightness in Figure 14 indicates the brightness difference of the gas passage area relative to a representative location in the background area, which corresponds to equation (6) and Figure 10. In reality, the gas fluctuates violently, so a moving average of 1.0 s before and after is applied to the average brightness (brightness difference).

[0123] When the temperature rises, CO ２ appears bright at first, but T ｓ At 23.46°C, the brightness difference reversed from positive to negative. ２ When the temperature drops, the brightness difference is reversed. ｓ = 23.20°C. As with visual observation, the gas temperature is T ｇ = 23.33 ± 0.13°C (hereinafter, characteristic points representing the gas temperature are indicated by circles in the figures).

[0124] The average brightness always varies equally. Furthermore, sometimes the gas drifts, causing the gas-passing area to deviate from the measurement frame. For example, at the start of measurement (left edge) in Figure 14(a), the gas-passing area is slightly outside the rectangular frame, so the image brightness difference is observed to be small.

[0125] Therefore, we devised a different, more robust statistical index. Specifically, to focus on the parts of the image that do not change, we took a temporal difference image as a preprocessing step. Figures 15 and 16 show central difference images calculated from the images before and after the image of interest in Figures 12 and 13, respectively.

[0126] Central difference image I ｍis the image of interest I ０ Image I of the frame before and after －１ , I ＋１ The central difference image is an image obtained by averaging the brightness (luminance) of each pixel, and is calculated using the following formula. Hereinafter, the central difference image may be referred to as the "difference image." ｍ = (I －１ +I ＋１ ) / 2 I －１ : Featured image I ０ Brightness (luminance) of the image (pixel) of the previous frame I ＋１ : Featured image I ０ Brightness (luminance) of the image (pixels) in the frame one after

[0127] 15 and 16, in a rectangular region (534 pixels wide x 448 pixels high, starting from a point 32 pixels wide and 32 pixels high from the top left) that includes not only the gas passage region shown in FIG. 13(a) but also the background region, a variance value that represents the variation in values ​​(brightness) was calculated as a statistical index of image complexity.

[0128] 17(a) and 17(b) show the time variation of the variance of the difference image (central difference image) when the temperature is rising and falling, respectively, as a function of the light source equivalent temperature T ｓ The variance is shown as a function of . A moving average of 1.0 seconds before and after is applied to this variance value. It can be seen that the image fluctuates violently at first, both when the temperature is rising and when the temperature is falling, but gradually becomes uniform and then becomes complex again at a certain point. The moment when the variance value is minimum represents the moment when it is not possible to distinguish between the background region and the gas passage region. The temperature at this time is T ｓ = 23.53°C, and when the temperature drops, T ｓ = 23.12°C. Thus, the gas temperature calculated from the variance of the image is T ｇ = 23.33 ± 0.21°C, which was the same average value as when the average brightness was used.

[0129] Second Embodiment In a second embodiment, a method that does not require a special camera, unlike the first embodiment, will be described.

[0130] Light source used, method for measuring light source temperature, CO ２The gas supply conditions, nozzles used, and light source temperature settings were the same as in Example 1. However, as shown in Figure 18, an InSb detector with a pixel length of 120 μm was used as the infrared detector. A bandpass filter with a wavelength band of [4.12 μm, 4.33 μm] was placed in front of the detector. An infrared lens with a focal length of 50 mm and an F-number of 2.5 was used to image a specific point in the gas passage area onto the detector.

[0131] 19(a) and (b) show the time change of the detected intensity of the gas passage area measured during the temperature rise and the temperature fall, respectively. Note that the detected intensity is calculated by applying a moving average of 1.0 s before and after. The equivalent temperature T ｓ The detection intensity when there is no gas was also calculated separately for the same optical system. In Fig. 19, the detection intensity when there is no gas at each instant is plotted with a dashed line. At the point where the detection intensities when there is gas (gas passing region) and when there is no gas (background region) intersect, T ｇ =T ｓ The temperature at this point is T ｇ = 23.51 ° C., and when the temperature drops, T ｇ Thus, even when a single-pixel detector is used, the gas temperature can be determined from the inversion of the detected intensity depending on the presence or absence of gas. ｇ = 23.35 ± 0.16 °C.

[0132] In this example, it appears that the temperature of the same gas was determined with high accuracy. However, as can be seen from Figure 19, there is not much difference in behavior between when there is no gas (background region) and when there is gas (gas passage region), and the intersection angle is shallow, so the determination accuracy is not very high. Therefore, we also considered statistical indices similar to those in Figure 17. Due to fluctuations in the gas flow, the signal intensity in the gas passage region generally fluctuates violently. However, at the exact moment when the brightness reverses, the difference in signal intensity itself becomes small, and so the fluctuation also becomes small.

[0133] 20(a) and (b) show the time variation of the AC component extracted by time differentiation of the signal during temperature rise and fall, respectively. In both cases, the AC component becomes very small at a certain point, and it can be seen that the brightness of the background region and the gas passage region is reversed at that point.

[0134] To quantitatively evaluate this state, the variance values ​​of the differential signals in Figure 20 were calculated for intervals of 1.0 seconds before and after each point. Figures 21(a) and 21(b) show plots of the variance values ​​during temperature rise and temperature fall, respectively. These plots are indices similar to the variance values ​​of the images shown in Figure 17, and correspond to the noise density. As shown in Figure 21, the noise density becomes minimal at a certain moment, and at that moment, the noise density becomes minimal at T ｇ = 22.24°C, and when the temperature drops, T ｇ = 23.34°C.

[0135] In this way, even if a one-pixel detector is used, the time fluctuation of the detected intensity is minimized, and the gas temperature is T ｇ = 22.79 ± 0.55°C. Compared to the result obtained from Figure 19, there is a difference of 0.56°C in the average value. Compared to the first example, the second example has lower determination accuracy and there is greater variation in results depending on the signal processing method. This demonstrates the usefulness of using an image sensor as a detector.

[0136] The method of determining the temperature of a gas by inverting the detected intensity of the spectrum of the gas relative to the background light from the light source, as shown in Figure 19, using the optical system of Figure 18, has long been known as a method of measuring the temperature of a flame (spectral inversion method). The spectral inversion method is introduced, for example, in Non-Patent Document 1. This method mainly involves mixing an element such as sodium (Na) as a marker into the flame, and focusing on the visible wavelength of the emission line due to the flame color reaction from the marker element. The spectral inversion method is used to measure the temperature of a flame by detecting the CO contained in the flame. ２ and H ２ There are also cases where attention is paid to the infrared emission spectrum of O, which is equivalent to what was done in Figure 19. However, the spectrum inversion method does not take into account the method of determining the temperature from the turning point of the statistically processed value of the intensity change as shown in Figure 20.

[0137] In the above examples, the equivalent temperature of the light source is increased or decreased. However, if the equivalent temperature of the light source is periodically changed and measurements are repeated, the gas temperature can be determined with higher accuracy.

[0138] Furthermore, although the above has been described as detecting one type of gas, by using an array of bandpass filters with different center wavelengths, it is also possible to determine the concentrations and temperatures of multiple gas species using the same optical system.

[0139] Furthermore, although many gaseous substances have absorption in the infrared region, some also absorb ultraviolet light, visible light, and terahertz light. In such cases, the present disclosure can be applied as is by using a light source and optical sensor that are matched to the absorption wavelength of the gas of interest.

[0140] [Summary] The temperature measurement method for a gaseous body according to the first aspect of the present disclosure includes: Ａ A method for measuring the temperature of a gaseous body that absorbs light A, comprising: a light source L capable of emitting light A with varying light intensity; Ａ and an optical sensor S capable of receiving light A and measuring the intensity of the received light. Ａ and preparing the light source L Ａ is emitted from the optical sensor S Ａ The light source L is arranged so that the gaseous substance is present on the light path of the light A received by the Ａ and the optical sensor S Ａ and the light source L Ａ When the light intensity is changed and light A is emitted from the light sensor S Ａ and from the measurement of the received light intensity, determining the light source L when the spatial and / or temporal fluctuation width of the received light intensity is minimum. Ａ The light intensity I ｍｉｎ and the light source L Ａ The light intensity I when the emission spectrum of ｍｉｎ The light source L Ａ Equivalent temperature T Ｓ The equivalent temperature T Ｓ is the temperature of the gaseous body.

[0141] A method for measuring the temperature of a gaseous body according to a second aspect of the present disclosure is the method for measuring the temperature of a gaseous body according to the first aspect, further comprising: Ａ is a pixel sensor having a plurality of light-receiving pixels.

[0142] A third aspect of the present disclosure provides a method for measuring the temperature of a gaseous material in the second aspect, wherein the plurality of light-receiving pixels are arranged in a matrix.

[0143] A fourth aspect of the present disclosure provides a method for measuring the temperature of a gaseous body according to any one of the first to third aspects, further comprising: Ａ The imaging optical system is arranged so as to form an image on the light receiving section.

[0144] A fifth aspect of the present disclosure provides a method for measuring the temperature of a gaseous body according to any one of the first to fourth aspects, wherein the fluctuation width is Ａ The received light signal is time-differentiated and the variance of the differential signal is calculated.

[0145] A sixth aspect of the present disclosure provides a method for measuring the temperature of a gaseous body according to any one of the first to fifth aspects, further comprising: Ａ to the optical sensor S Ａ The wavelength band of the light reaching the light source L Ａ , the optical sensor S Ａ and a bandpass filter, and the width of the wavelength band is 0.25 to 4 times the width of the band of the gas absorption band spectrum of the gaseous material.

[0146] A seventh aspect of the present disclosure provides a method for measuring the temperature of a gaseous material according to any one of the first to sixth aspects, further comprising arranging a reflecting mirror on the light path.

[0147] A method for measuring the temperature of a gaseous body according to an eighth aspect of the present disclosure is any one of the first to seventh aspects, further comprising: Ａ is an infrared light source.

[0148] A ninth aspect of the present disclosure provides a method for measuring the temperature of a gaseous material according to any one of the first to eighth aspects, wherein the gaseous material is methane (CH ４ ), carbon dioxide (CO ２ ), carbon monoxide (CO), nitrous oxide (N ２ O), nitric oxide (NO), nitrogen dioxide (NO ２ ), sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ), water vapor (H ２O), ammonia (NH ３ ), sulfur hexafluoride (SF ６ ) and chlorofluorocarbons.

[0149] A tenth aspect of the present disclosure provides a method for measuring the temperature of a gaseous body according to any one of the first to eighth aspects, further comprising: Ａ emits light having a light absorption band including a plurality of types of gaseous substances, Ａ A bandpass filter array including a plurality of bandpass filters with mutually different center wavelengths is disposed in front of the light receiving surface.

[0150] The temperature measuring device for a gaseous body according to an eleventh aspect of the present disclosure has a wavelength λ Ａ 1. An apparatus for measuring the temperature of a gaseous body that absorbs light A of wavelength λ, comprising: a camera having an image pickup element including a plurality of optical sensors that can receive light A and measure the intensity of the received light, an imaging optical system, and a bandpass filter; Ａ a light source that emits light in a wavelength band including: a light intensity varying device that varies the light intensity of the light source; an image processing device; and an integrated control device that controls both the light intensity varying device and the image processing device, wherein the image processing device determines, based on a signal output from the camera, a light intensity I of the light source at which the spatial and / or temporal fluctuation width of the measured light intensity is minimized. ｍｉｎ The light intensity I of the light source is calculated. ｍｉｎ Equivalent temperature T of the light source Ｓ is calculated by approximating the emission spectrum of the light source with perfect blackbody radiation.

[0151] A temperature measuring device for a gaseous body according to aspect 12 of the present disclosure is, in aspect 11, wherein the signal output from the camera includes image information representing a temporal change in the distribution of the light intensity of light passing through the gaseous body, and the spatial fluctuation width is calculated by the variance value of a difference image (e.g., a central difference image) which is the difference between multiple images having a time difference.

[0152] The temperature measuring device for a gaseous body according to aspect 13 of the present disclosure has a wavelength λ Ａan apparatus for measuring the temperature of a gaseous body that absorbs light A, the apparatus comprising: a light receiving device including a detection element in which an optical sensor capable of receiving light A and measuring the intensity of the received light is disposed, an imaging optical system, and a bandpass filter; a light source that emits light in a wavelength band that includes light A; a light intensity varying device that varies the light intensity of the light source; a signal processing device that processes signals from the light receiving device; and an integrated control device that controls both the light intensity varying device and the signal processing device, the signal processing device being configured to: ｍｉｎ（ｔ） The light intensity I of the light source is calculated. ｍｉｎ（ｔ） Equivalent temperature T of the light source Ｓ is calculated by approximating the emission spectrum of the light source with perfect blackbody radiation.

[0153] Aspect 14 of the present disclosure provides the temperature measuring device for a gaseous material in aspect 13, wherein the temporal fluctuation width is calculated as an AC component extracted by time differentiation of the light receiving signal output from the light receiving device.

[0154] The present disclosure makes it possible to easily measure the temperature of a gaseous body located at a remote location. Here, the temperature measurement of a gaseous body according to the present disclosure is not only a fixed-point measurement, but also very convenient because the device is small and easy to carry, allowing it to be easily installed and used in various locations. Moreover, real-time measurement is possible.

[0155] Measurement of the temperature of gaseous bodies is in high demand in a variety of situations, regardless of whether it is for civilian or industrial use, such as environmental conservation (e.g., heat island improvement), combustion gas management, factory exhaust management, and gas hazard management, etc. Therefore, the present disclosure is expected to have a significant impact on society and have a significant influence on industry.

[0156] 11: Light source 12: Light intensity variable device 13: Integrated control device 14: Light receiving device 15: Camera (infrared camera) 16: Optical sensor (infrared imaging element, infrared detector) 17: Lens (infrared lens) 18: Band-pass filter 19: Image processing device 20: Signal processing device 21: Gas (gaseous substance) 101: Temperature measurement system 102: Temperature measurement system

Claims

1. Wavelength λ Ａ A method for measuring the temperature of a gaseous body that absorbs light A, comprising: a light source L capable of emitting light A with varying light intensity; Ａ and an optical sensor S capable of receiving light A and measuring the intensity of the received light. Ａ and preparing the light source L Ａ is emitted from the optical sensor S Ａ The light source L is arranged so that the gaseous material is present on the light path of the light A received by the Ａ and the optical sensor S Ａ and the light source L Ａ When the light intensity is changed and light A is emitted from the light sensor S Ａ and determining, from the measurement of the received light intensity, the light source L when the spatial and / or temporal fluctuation width of the received light intensity is minimized. Ａ The light intensity I ｍｉｎ The light source L Ａ The light intensity I when the emission spectrum of ｍｉｎ The light source L Ａ Equivalent temperature T Ｓ The equivalent temperature T Ｓ The temperature of the gaseous body is measured by the method.

2. The optical sensor S Ａ The method for measuring the temperature of a gaseous medium according to claim 1, wherein the light receiving element is a pixel sensor having a plurality of light receiving pixels.

3. The method for measuring the temperature of a gaseous medium according to claim 2, wherein said plurality of light-receiving pixels are arranged in a matrix.

4. The image of the gaseous body is detected by the optical sensor S. Ａ The method for measuring the temperature of a gaseous material according to claim 1 , further comprising disposing an imaging optical system so as to form an image on the light receiving portion of said gaseous material.

5. The fluctuation width is the optical sensor S Ａ The method for measuring the temperature of a gaseous medium according to claim 1 , wherein the temperature is calculated from a variance value of a differential signal obtained by time-differentiating the light receiving signal.

6. The light source L Ａ to the optical sensor S Ａ The wavelength band of the light reaching the light source L Ａ , the optical sensor S Ａ and a bandpass filter, and the width of the wavelength band is limited to near the light A wavelength band, and the width of the wavelength band is 0.25 to 4 times the width of the gas absorption band spectrum of the gaseous material.

7. A method for measuring the temperature of a gaseous medium according to any one of claims 1 to 6, further comprising arranging a reflecting mirror on the light path.

8. The light source L Ａ The method for measuring the temperature of a gaseous body according to any one of claims 1 to 7, wherein the light source is an infrared light source.

9. The gaseous material is methane (CH ４ ), carbon dioxide (CO ２ ), carbon monoxide (CO), nitrous oxide (N ２ O), nitric oxide (NO), nitrogen dioxide (NO ２ ), sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ), water vapor (H ２ O), ammonia (NH ３ ), sulfur hexafluoride (SF ６ 9. The method for measuring the temperature of a gaseous body according to claim 1 , wherein the gas contains one gas selected from the group consisting of fluorocarbons and fluorocarbons.

10. Said light source L Ａ emits light having a light absorption band including a plurality of types of gaseous substances, Ａ The method for measuring the temperature of a gaseous medium according to any one of claims 1 to 8, further comprising disposing a bandpass filter array in front of the light receiving surface, the bandpass filter array including a plurality of bandpass filters having mutually different center wavelengths.

11. Wavelength λ Ａ An apparatus for measuring the temperature of a gaseous body absorbing light A of wavelength λ, the apparatus comprising: an imaging element including a plurality of optical sensors capable of receiving light A and measuring the intensity of the received light, an imaging optical system, and a camera having a bandpass filter; Ａ a light source that emits light in a wavelength band including: a light intensity varying device that varies the light intensity of the light source; an image processing device; and an integrated control device that controls both the light intensity varying device and the image processing device, wherein the image processing device determines, based on a signal output from the camera, the light intensity I of the light source at which the spatial and / or temporal fluctuation width of the measured light intensity is minimized. ｍｉｎ The light intensity I of the light source is calculated. ｍｉｎ Equivalent temperature T of the light source Ｓ The temperature of a gaseous body is calculated by approximating the emission spectrum of the light source with perfect blackbody radiation.

12. A gaseous body temperature measuring device as described in claim 11, wherein the signal output from the camera includes image information representing the temporal change in the distribution of the light intensity of light passing through the gaseous body, and the spatial fluctuation width is calculated from the variance value of a differential image, which is the difference between multiple images having a time difference.

13. Wavelength λ Ａ an apparatus for measuring the temperature of a gaseous body that absorbs light A, the apparatus comprising: a light receiving device including a detection element in which an optical sensor capable of receiving light A and measuring the intensity of the received light is disposed, an imaging optical system, and a bandpass filter; a light source that emits light in a wavelength band including light A; a light intensity varying device that varies the light intensity of the light source; a signal processing device that processes signals from the light receiving device; and an integrated control device that controls both the light intensity varying device and the signal processing device, the signal processing device controlling the light intensity I of the light source at which the time fluctuation width of the measured light intensity is minimized. ｍｉｎ（ｔ） The light intensity I of the light source is calculated. ｍｉｎ（ｔ） Equivalent temperature T of the light source Ｓ The temperature of a gaseous body is calculated by approximating the emission spectrum of the light source with perfect blackbody radiation.

14. The temperature measuring device for a gaseous medium according to claim 13, wherein the width of the temporal fluctuation is calculated as an AC component extracted by time differentiation of the light receiving signal output from the light receiving device.

Images