Radiation thermometer and visible image acquisition method

Abstract

To obtain a fine image without halation even in an object to be measured at a high temperature.SOLUTION: The radiation thermometer 1 is provided with an ND filter 7 whose transmissivity is set to 1-10% and which reduces the quantity of light due to thermal radiation from a measuring object, an IR cut filter 8 whose cut-off wavelength is set within a prescribed wavelength range including 650 nm and which cuts off light in a wavelength region equal to or higher than the cut-off wavelength from the light due to the thermal radiation from the measuring object and transmits only visible light, and a camera module 9 which receives the light transmitted through the ND filter 7 and the IR cut filter 8 and converts it into an electric signal and processes the electric signal converted by the CMOS sensor 9b to photograph an image of the light due to the thermal radiation from the measuring object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiation thermometer that measures temperature by capturing thermal radiation from a measurement object such as a heating furnace, and a visible image acquisition method. [Background technology]

[0002] BACKGROUND ART Various types of radiation thermometers have been proposed as radiation thermometers that measure temperature by capturing thermal radiation from a measurement object, including the one disclosed in Non-Patent Document 1 below.

[0003] By the way, there is a demand from users to use this type of radiation thermometer to remotely observe high temperatures (for example, temperatures of 2000° C. or higher) in, for example, an ultra-blast furnace.

[0004] Therefore, the present inventors evaluated the visibility during high temperature visual observation using an analog radiation thermometer, IR-CZH7N, as the radiation thermometer disclosed in Non-Patent Document 1 below. The evaluation method involved placing a piece of a furnace core tube in an ultra-blast furnace and checking the visibility using the analog radiation thermometer, IR-CZH7N. Note that at 1500°C, it was impossible to see inside the furnace with the naked eye.

[0005] Using the analog radiation thermometer IR-CZH7N, the evaluation results showed that it was possible to distinguish the position of the fragments from the visible results inside the furnace at temperatures between 1500°C and 2700°C. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Chino Corporation, "High-speed Radiation Thermometer IR-CZ series, non-contact measurement for a wide range of fields" (Catalog No. CP-108-04 Jun. 23-01) Summary of the Invention [Problem to be solved by the invention]

[0007] However, when using a conventional analog radiation thermometer, the IR-CZH7N, to measure the temperature of high-temperature materials inside a furnace opening in a device with a small furnace opening, dark areas blocked by the furnace opening and bright areas inside the furnace may appear in the image. Specifically, when using the IR-CZH7N to measure an object at a high temperature of 2500°C, if half of the angle of view is hidden, the auto gain does not function properly and the image becomes overexposed.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned problems, and aims to provide a radiation thermometer and a visible image acquisition method that can obtain a fine image without whiteout even when the object to be measured is at a high temperature. [Means for solving the problem]

[0009] In order to achieve the above object, the radiation thermometer according to claim 1 of the present invention comprises an ND filter having a transmittance set to 1 to 10% and reducing the amount of light due to thermal radiation from the measurement object; an IR cut filter having a cutoff wavelength set within a predetermined wavelength range including 650 nm, which cuts out light in a wavelength range equal to or greater than the cutoff wavelength from light due to thermal radiation from the measurement object and transmits only visible light; The device is characterized by being provided with a CMOS sensor that receives light that has passed through the ND filter and the IR cut filter and converts it into an electrical signal, and a camera module that processes the electrical signal converted by the CMOS sensor and captures an image of light due to thermal radiation from the object to be measured.

[0010] The radiation thermometer according to claim 2 of the present invention is the radiation thermometer according to claim 1, The camera module is characterized in that a terminal device is connected to the camera module, which displays the image captured by the camera module and sets the exposure time for keeping light on the CMOS sensor, the white balance for correcting the influence of the color of light in the shooting environment, and the gain to the camera module.

[0011] A visible image acquisition method according to claim 3 of the present invention is a visible image acquisition method using a radiation thermometer, comprising: a step of setting the transmittance of an ND filter that reduces the amount of light due to thermal radiation from the measurement object to 1 to 10%; a step of setting a cutoff wavelength of an IR cut filter that cuts out light in a wavelength range equal to or greater than a cutoff wavelength from light due to thermal radiation from the measurement object and transmits only visible light within a predetermined wavelength range including 650 nm; receiving light transmitted through the ND filter and the IR cut filter with a CMOS sensor and converting the light into an electrical signal; and a step of processing the electrical signal from the CMOS sensor using a camera module to capture an image of light due to thermal radiation from the measurement object.

[0012] The visible image acquisition method according to claim 4 of the present invention is the visible image acquisition method according to claim 3, further comprising: a step of displaying an image captured by the camera module on a terminal device, and setting an exposure time for continuing to irradiate the CMOS sensor with light, a white balance for correcting the influence of the color of light in the shooting environment, and a gain in the camera module from the terminal device; and automatically switching exposure time, white balance, and gain in response to light due to thermal radiation from the object to be measured. [Effects of the Invention]

[0013] According to the present invention, it is possible to obtain high-resolution images without overexposure even when measuring high-temperature objects, thereby meeting the needs of users who want to remotely observe high-temperature objects such as ultra-blast furnaces (e.g., 2000°C or higher). [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an outline of the overall configuration of a radiation thermometer according to the present invention; [Figure 2]FIG. 10 is a diagram showing the superposition of the spectral sensitivities (RGB) of the CMOS sensor and the IR cut filter in the radiation thermometer according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] As shown in FIG. 1, the radiation thermometer 1 of this embodiment is a stationary type thermometer that remotely observes the temperature of an object to be measured, such as a heating furnace, and has a metal housing 2 as its main body, with a cover glass 3 attached to one end of the housing 2 in the longitudinal direction.

[0017] The cover glass 3 prevents dust and dirt from entering the housing 2 from the outside, and functions as a detection window for transmitting and detecting light due to thermal radiation from the object to be measured.

[0018] An objective lens 4 is arranged downstream of the center axis of the cover glass 3. The objective lens 4 transmits light due to thermal radiation from the measurement object that has passed through the cover glass 3, and the light enters a beam splitter 5 downstream.

[0019] The radiation thermometer 1 of this embodiment is of a variable focus type, and the objective lens 4 is focused according to the distance to the measurement object (measurement distance) so that the measurement diameter falls within the range of the field angle (horizontal x vertical).

[0020] Beam splitter 5 is placed on the optical axis after objective lens 4 and is composed of a dichroic beam splitter that separates the light incident from objective lens 4 into two lights of different wavelength bands: visible light and infrared light. Of the two lights separated by beam splitter 5, one light (visible light) travels straight in the direction of arrow A in Fig. 1 and is output, and the other light (infrared light) is reflected 90° downward in the direction of arrow B in Fig. 1 and is output.

[0021] A relay lens 6 is arranged on the optical axis after the beam splitter 5. The relay lens 6 forms an image of the light (visible light) that is split by the beam splitter 5 and output in a straight line on the light receiving surface of a CMOS sensor 9b of a camera module 9 at the later stage, which will be described later.

[0022] The light (infrared light) that is split by the beam splitter 5 and reflected and output in the direction of arrow B in FIG. 1 is received by an infrared light detection element, converted into an electrical signal, converted into a temperature, and output as a measurement value.

[0023] On the optical axis between the relay lens 6 and a CMOS sensor 9b of a camera module 9 (described later), two types of filters are arranged side by side in this order: an ND filter 7 and an IR cut filter 8. In the example of Fig. 1, the two types of filters are arranged in this order as viewed from the cover glass 3 side, but the order of the ND filter 7 and the IR cut filter 8 may be reversed.

[0024] The ND filter 7 is a neutral density filter that reduces the amount of light incident from the beam splitter 5 via the relay lens 6, and its transmittance is set within a range of 1 to 10% depending on the temperature of the object to be measured. To give a specific numerical value, when the temperature of the object to be measured is 2700°C, it is preferable to set the transmittance of the ND filter 7 to 5%.

[0025] In other words, if the temperature of the object to be measured is 2700°C as the reference temperature, the transmittance of the ND filter 7 is set to less than 5% if the temperature of the object to be measured is higher than 2700°C, and the transmittance of the ND filter 7 is set to more than 5% if the temperature is lower than 2700°C.

[0026] Since the radiation thermometer 1 of this embodiment is a visible light camera, it is necessary to illuminate the measurement target with a light or the like in a dark place.

[0027] The IR cut filter 8 cuts out light in the wavelength range equal to or greater than the cutoff wavelength contained in the light (visible light) incident from the beam splitter 5 via the relay lens 6, and transmits only visible light, with the cutoff wavelength set within a predetermined wavelength range including 650 nm (a wavelength range of 650 nm to 700 nm that takes into consideration the spectral sensitivity characteristics of the CMOS sensor 9 b and the ability to obtain images that are closer to the human eye).

[0028] In particular, as shown in FIG. 2, if the cutoff wavelength of the IR cut filter 8 is set to 650 nm, light of 650 nm or more, as indicated by the diagonal lines in FIG. 2, can be cut out, and an image closer to that seen by the human eye can be acquired by the CMOS sensor 9b of the camera module 9, which will be described later.

[0029] In Figure 2, the spectral sensitivity of the IR cut filter 8 is shown by a solid line, and the spectral sensitivity of the CMOS sensor 9b of the camera module 9 described later is shown by a dotted line for R (red), a dashed line for G (green), and a dashed line for B (blue).

[0030] A camera module 9, whose main body 9a is made of a metal case, is disposed on the optical axis after the IR cut filter 8. A heat-dissipating sheet 10 having thermal conductivity is provided between the main body 9a of the camera module 9 and the inner surface of the housing 2 in order to increase the upper limit of the operating temperature range. This allows heat generated by the camera module 9 to be dissipated from the main body 9a to the housing 2 via the heat-dissipating sheet 10.

[0031] A CMOS sensor 9b serving as an image sensor is provided inside the main body 9a of the camera module 9. The CMOS sensor 9b forms an image on the light-receiving plane of light that is caused by thermal radiation from the object to be measured and that enters through the relay lens 6, the ND filter 7, and the IR cut filter 8, photoelectrically converts the brightness of the light in the image into an amount of electric charge, and sequentially reads out the photoelectrically converted electric charges and converts them into an electric signal.

[0032] The camera module 9 captures an image corresponding to the light generated by thermal radiation from the object to be measured by converting an electrical signal generated by the CMOS sensor 9b based on the light generated by thermal radiation from the object to a signal corresponding to the temperature. When capturing this image, the CMOS sensor 9b is used, and each pixel is made up of a photodiode, an amplifier, and a switch. The charge generated by the photodiode is converted into a voltage by the amplifier for each pixel, and this voltage is transferred by turning the switch on and off in each pixel. The gain of the amplifier can be adjusted for each pixel, and the brightness of any point on the pixel can be adjusted, so that an image can be captured without overexposure even if dark and bright areas occur in the captured image.

[0033] A terminal device 11, such as a personal computer, operated by a user is connected to the output terminal of the camera module 9. The terminal device 11 displays a real-time image corresponding to the light generated by thermal radiation from the object being measured, which is video-output from the camera module 9. The terminal device 11 also sets various parameters required for capturing images corresponding to the light generated by thermal radiation from the object being measured, including the exposure time for shining light on the CMOS sensor 9b, the white balance for correcting the effects of light color in the shooting environment, the gain of the amplifier for each pixel of the CMOS sensor 9b, and the frame rate (the number of frames (images) processed per second). The terminal device 11 can also set and read various parameters for each temperature, such as the gain (for each pixel amplifier of the CMOS sensor 9b) at 1500°C, the white balance, the gain (for each pixel amplifier of the CMOS sensor 9b) at 2700°C, the white balance, etc. Furthermore, upper and lower temperature limits can be set, and various parameters can be set for each set temperature range, allowing automatic switching according to changes in the measured temperature. For example, when various parameters such as the gain (amplifier for each pixel of the CMOS sensor 9b) and exposure time at 1500°C to 2000°C and 2000°C to 2700°C are set in advance, if the measurement temperature changes from 1500°C to 2500°C, the various parameters will automatically switch, allowing you to obtain an image without whiteout.

[0034] When measuring temperature using the radiation thermometer 1 configured as described above, the transmittance of the ND filter 7, which reduces the amount of light due to thermal radiation from the measurement target, is set to 1 to 10%, and the cutoff wavelength of the IR cut filter 8, which cuts out light from the thermal radiation from the measurement target in a wavelength range above the cutoff wavelength and transmits only visible light, is set to a predetermined wavelength range including 650 nm. The light that passes through the ND filter 7 and IR cut filter 8 is received by the CMOS sensor 9b and converted into an electrical signal. The camera module 9 processes the electrical signal from the CMOS sensor 9b and captures an image of the light due to thermal radiation from the measurement target. The image captured by the camera module 9 is displayed on the terminal device 11, and various parameters, including the exposure time for shining light on the CMOS sensor 9b, white balance for correcting the influence of light color in the shooting environment, and gain (an amplifier for each pixel of the CMOS sensor 9b), can be set in the camera module 9 from the terminal device 11 for each temperature.

[0035] Here, the digital radiation thermometer 1 of this embodiment, which uses two types of filters, an ND filter 7 with a transmittance of 5% and an IR cut filter 8 with a cutoff wavelength of 650 nm, was used to evaluate visibility at high temperatures in the same manner as the analog radiation thermometer IR-CZH7N described above.

[0036] As an evaluation method, a fragment of a furnace core tube was placed in an ultra-blast furnace, and the visibility of the fragment was confirmed using the digital radiation thermometer 1 of this embodiment. As a result, the evaluation results showed that the digital radiation thermometer 1 of this embodiment can identify the fragment position from the visibility inside the furnace at temperatures between 1500°C and 2700°C, and can obtain a fine image without overexposure even when half the angle of view is hidden, particularly at high temperatures of 2500°C or higher.

[0037] As described above, according to the embodiment described above, by using two types of filters, the ND filter 7 with a transmittance of 1 to 10% and the IR cut filter 8 with a cutoff wavelength set within a predetermined wavelength range including 650 nm, and the CMOS sensor 9b as the image sensor, it is possible to obtain a fine image without overexposure even when the object to be measured is at a high temperature. Specifically, even when half of the angle of view is obscured at a temperature of 2500°C or higher, a fine image without overexposure can be obtained. As a result, it is possible to meet the needs of users who want to remotely observe high temperatures (e.g., 2000°C or higher) such as those in ultra-high-temperature blast furnaces.

[0038] Although the best mode for the radiation thermometer and visible image acquisition method according to the present invention has been described above, the present invention is not limited to the description and drawings of this mode. In other words, all other modes, examples, and operational techniques that are made by those skilled in the art based on this mode are naturally included in the scope of the present invention. [Explanation of symbols]

[0039] 1 Radiation thermometer 2. Case 3 Cover glass (detection window) 4 Objective Lenses 5 Beam splitter (light branching means) 6 relay lens 7 ND filters 8 IR cut filter 9 Camera Module 9a Main body 9b CMOS sensor 10 Heat dissipation sheet 11 Terminal equipment

Claims

1. an ND filter with a transmittance set to 1 to 10% to reduce the amount of light due to thermal radiation from the measurement object; an IR cut filter having a cutoff wavelength set within a predetermined wavelength range including 650 nm, which cuts out light in a wavelength range equal to or greater than the cutoff wavelength from light due to thermal radiation from the measurement object and transmits only visible light; a CMOS sensor that receives light that has passed through the ND filter and the IR cut filter and converts it into an electrical signal, and a camera module that processes the electrical signal converted by the CMOS sensor and captures an image of light due to thermal radiation from the object to be measured.

2. 2. The radiation thermometer according to claim 1, wherein a terminal device is connected to the camera module to display an image captured by the camera module and to set an exposure time for continuing to irradiate the CMOS sensor with light, a white balance for correcting the influence of light color in the shooting environment, and a gain in the camera module.

3. In a visible image acquisition method using a radiation thermometer, setting the transmittance of an ND filter that reduces the amount of light due to thermal radiation from the measurement object to 1 to 10%; setting a cutoff wavelength of an IR cut filter that cuts out light in a wavelength range equal to or greater than a cutoff wavelength from light due to thermal radiation from the measurement object and transmits only visible light within a predetermined wavelength range including 650 nm; receiving light transmitted through the ND filter and the IR cut filter with a CMOS sensor and converting the light into an electrical signal; and processing the electrical signal from the CMOS sensor using a camera module to capture an image of light due to thermal radiation from the object to be measured.

4. a step of displaying an image captured by the camera module on a terminal device, and setting an exposure time for continuing to irradiate the CMOS sensor with light, a white balance for correcting the influence of the color of light in the shooting environment, and a gain in the camera module from the terminal device; 4. The visible image acquisition method according to claim 3, further comprising the step of automatically switching an exposure time, a white balance, and a gain in accordance with the light due to thermal radiation from the object to be measured.

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