WO2015195055A1 - Apparatus and method for non-contact temperature measurement with a visible light camera - Google Patents
Apparatus and method for non-contact temperature measurement with a visible light camera Download PDFInfo
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- WO2015195055A1 WO2015195055A1 PCT/SI2015/000024 SI2015000024W WO2015195055A1 WO 2015195055 A1 WO2015195055 A1 WO 2015195055A1 SI 2015000024 W SI2015000024 W SI 2015000024W WO 2015195055 A1 WO2015195055 A1 WO 2015195055A1
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- Prior art keywords
- temperature
- camera
- visible light
- flows
- objects
- Prior art date
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- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000009529 body temperature measurement Methods 0.000 title claims abstract description 12
- 230000008569 process Effects 0.000 claims abstract description 17
- 238000004364 calculation method Methods 0.000 claims abstract description 5
- 238000003384 imaging method Methods 0.000 claims abstract description 4
- 238000012545 processing Methods 0.000 claims abstract description 4
- 230000005855 radiation Effects 0.000 claims description 3
- 230000004044 response Effects 0.000 abstract description 4
- 238000005259 measurement Methods 0.000 description 7
- 239000011490 mineral wool Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 230000002123 temporal effect Effects 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000003331 infrared imaging Methods 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000001454 recorded image Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000012800 visualization Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/0022—Radiation pyrometry, e.g. infrared or optical thermometry for sensing the radiation of moving bodies
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/30—Transforming light or analogous information into electric information
- H04N5/33—Transforming infrared radiation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J2005/0077—Imaging
Definitions
- This invention relates to an apparatus and a method for non-contact temperature measurement of high-temperature objects and flows which emit visible light due to the thermal radiation.
- Technical problem addressed is failure to measure surface temperature fields of said objects and flows with a good dynamical response and at a high spatial resolution. Said technological problem is encountered in a multitude of industrial processes, including, but not limited to the mineral wool production and hot rolling of metals.
- Hot objects and flows moving at high velocities can exhibit large spatial and temporal variations of surface temperature, consequently requiring instantaneous temperature field measurement with a good spatial resolution and dynamic response, and possibly a high sampling rate as well.
- Non-contact, nonintrusive optical methods such as the infrared imaging are most commonly employed to fulfill said temperature measurement requirements.
- Infrared cameras allow for accurate instantaneous temperature field measurements of stationary and low velocity processes.
- temperature field measurement is problematic in processes with fast moving objects or flows where available image acquisition rate of infrared cameras becomes insufficient, causing excessive temporal averaging of acquired temperature fields.
- the image acquisition rate can be improved by reduction of the acquisition window size, but the spatial resolution of computed temperature fields is reduced as a result.
- the present invention addresses the problem of non-contact temperature field measurements by employing visible light cameras.
- visible light camera refers to a camera operating in (but not necessarily limited to) the wavelength range of the light spectrum which is visible to the human eye, this is between 390nm and 700nm.
- the main advantages of temperature field measurements by employing visible light cameras instead of infrared cameras are superior image acquisition rates and spatial resolution as well as significantly lower cost of the imaging setup. Temperature measurements by a visible light camera are possible above approximately 600 °C when the signal-to-noise ratio of emitted light is sufficiently high for detection by the camera sensor.
- At least one digital camera sensitive to visible light this is light with a wavelength between 390nm and 700nm.
- Said camera can be a monochromatic camera recording grayscale images, or a color camera recording color images which are then transformed to the grayscale format.
- a computer capable of acquiring images from the camera continuously and in real time.
- a numerical computer-aided algorithm for real-time conversion of grayscale images obtained from said cameras to scalar fields of temperature is an integral part of this invention and will be presented in this section.
- Camera sensor illuminance Ev (Eq. (2)) is proportional to the product of radiating body light efficacy ( ⁇ )), and blackbody radiant exitance ( ⁇ 5 ⁇ 4 ):
- Calibration constant C is a function of distance between the camera sensor and the focal point, of the emissivity of observed hot surface, and of the sensor exposure time. Said constant is determined by calibration to a body with a known temperature.
- Light efficacy ⁇ (Eq. (3)) is defined as a ratio between luminous flux and total radiation power in the wavelength range 0 ⁇ ⁇ ⁇ .
- h is the Planck constant
- ke is the Boltzmann constant
- c is the speed of light
- ⁇ ⁇ is the spectral radiance
- ⁇ ( ⁇ ) is the normalized quantum efficiency of the camera (0 ⁇ ⁇ ( ⁇ ) ⁇ 1 ).
- Temperature dependence function ⁇ ( ⁇ ) can be obtained from Eq. (3) by computation over the temperature range of interest.
- camera sensor illuminance E v can also be defined in relation to the sensor output signal (normalized gray level G) - Eq. (4).
- Normalized gray level of each pixel in every recorded image is defined on an interval 0 ⁇ G ⁇ 1 where 0 corresponds to black color and 1 to white color. Depending on the bit depth n of the image, the interval of G is uniformly divided to 2" gray levels.
- ts is the camera sensor exposure time
- k is the sensor sensitivity with unit [lux '1 -s ⁇ 1 ] defined as the response in the normalized gray level for a given change in camera sensor illuminance.
- Temperature calibration by determination of calibration constant C. C is calculated from Eq. (5) by using temperature and corresponding image gray level data of a surface with known temperature and emissivity representative of the observed process. If the camera positioning, lens type, exposure time or the emissivity of observed objects or flows changes, temperature calibration must be repeated.
- Fig. 1 shows a schematic drawing of the apparatus and method for non-contact temperature measurement with a visible light camera. Shown is an example of application of said apparatus and method for the monitoring of the temperature fields on the first wheel of a mineral wool spinner.
- Fig. 2 A typical graph for conversion between the normalized gray level of a process image, recorded by a visible light camera, and the absolute temperature.
- Said apparatus and method for non-contact temperature field measurement with the particular application to the mineral wool production process comprises of a high-speed, visible light digital camera (6) connected to a computer (7) where continuous acquisition, processing and saving of imaging data occurs.
- Said process begins with a stream of mineral melt (4) flowing from the reservoir (3) onto the first spinner wheel (1 ) where a thin melt film (2) is formed and scattered to mineral wool fibers (5) due to the centrifugal force.
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Radiation Pyrometers (AREA)
Abstract
Apparatus and method for non-contact temperature measurement solves the technical problem of determining the temperature fields of high-temperature processes with a good dynamical response and at a high spatial resolution. The process consisting of hot objects (1) and/or hot flows (2) is recorded by a high-speed digital camera (6) with a sensor sensitive mostly to the visible light. A computer (7) is used for continuous acquisition, processing and saving of imaging data. The method of temperature calculation is based on an assumption that high-temperature objects (1) and/or flows (2) radiate as a gray body with constant emissivity and on calibration to a surface with known temperature.
Description
Apparatus and method for non-contact temperature measurement with a visible light camera
DESCRIPTION
Field of technology
Temperature measurement; Flow visualization; Image processing Technical problem
This invention relates to an apparatus and a method for non-contact temperature measurement of high-temperature objects and flows which emit visible light due to the thermal radiation. Technical problem addressed is failure to measure surface temperature fields of said objects and flows with a good dynamical response and at a high spatial resolution. Said technological problem is encountered in a multitude of industrial processes, including, but not limited to the mineral wool production and hot rolling of metals.
State of the art
Precise temperature measurement is often required for the purpose of process monitoring and control. Hot objects and flows moving at high velocities can exhibit large spatial and temporal variations of surface temperature, consequently requiring instantaneous temperature field measurement with a good spatial resolution and dynamic response, and possibly a high sampling rate as well.
Non-contact, nonintrusive optical methods such as the infrared imaging are most commonly employed to fulfill said temperature measurement requirements. Infrared cameras allow for accurate instantaneous temperature field measurements of stationary and low velocity processes. However, temperature field measurement is problematic in processes with fast moving objects or flows where available image acquisition rate of infrared cameras becomes insufficient, causing excessive
temporal averaging of acquired temperature fields. The image acquisition rate can be improved by reduction of the acquisition window size, but the spatial resolution of computed temperature fields is reduced as a result.
The present invention addresses the problem of non-contact temperature field measurements by employing visible light cameras. The term "visible light camera" refers to a camera operating in (but not necessarily limited to) the wavelength range of the light spectrum which is visible to the human eye, this is between 390nm and 700nm. The main advantages of temperature field measurements by employing visible light cameras instead of infrared cameras are superior image acquisition rates and spatial resolution as well as significantly lower cost of the imaging setup. Temperature measurements by a visible light camera are possible above approximately 600 °C when the signal-to-noise ratio of emitted light is sufficiently high for detection by the camera sensor.
Detailed description of new invention
Apparatus and method for non-contact temperature measurement which solves above referenced technical problem comprises of the following elements:
1. At least one digital camera sensitive to visible light, this is light with a wavelength between 390nm and 700nm. Said camera can be a monochromatic camera recording grayscale images, or a color camera recording color images which are then transformed to the grayscale format.
2. A computer capable of acquiring images from the camera continuously and in real time.
3. A numerical computer-aided algorithm for real-time conversion of grayscale images obtained from said cameras to scalar fields of temperature. Said algorithm is an integral part of this invention and will be presented in this section.
A hot object or flow is assumed to radiate electromagnetic waves as a gray body,
this is a body with emissivity independent of the wavelength of emitted light. Radiant exitance of a body with emissivity ε is defined by Stefan-Boltzmann law - Eq. (1 ). j = εσ3Τ4 as = 5.67 \0-*Wm~ lK- (1 )
Camera sensor illuminance Ev (Eq. (2)) is proportional to the product of radiating body light efficacy (Γ)), and blackbody radiant exitance ( σ5Τ4 ):
Ev = C ^ (fT4 (2)
Calibration constant C is a function of distance between the camera sensor and the focal point, of the emissivity of observed hot surface, and of the sensor exposure time. Said constant is determined by calibration to a body with a known temperature.
Light efficacy η (Eq. (3)) is defined as a ratio between luminous flux and total radiation power in the wavelength range 0 < λ <∞.
/z = 6.626· l(T34/ s ; kB = 1.381 W2iJ I K ; c = 2.998· 108 m/s
In Eq. (3) h is the Planck constant, ke is the Boltzmann constant, c is the speed of light, Βλ is the spectral radiance and Υ(λ) is the normalized quantum efficiency of the camera (0≤ Υ(λ)≤ 1 ). Temperature dependence function η( ~Γ) can be obtained from Eq. (3) by computation over the temperature range of interest.
Aside from the formulation in Eq. (2), camera sensor illuminance Ev can also be defined in relation to the sensor output signal (normalized gray level G) - Eq. (4). Normalized gray level of each pixel in every recorded image is defined on an
interval 0 ≤ G ≤ 1 where 0 corresponds to black color and 1 to white color. Depending on the bit depth n of the image, the interval of G is uniformly divided to 2" gray levels.
In Eq. (4), ts is the camera sensor exposure time, and k is the sensor sensitivity with unit [lux'1-s~1] defined as the response in the normalized gray level for a given change in camera sensor illuminance.
By combining Eq. (2) and Eq. (4), the relation between the normalized gray level and the absolute temperature is obtained in Eq. (6) which must be solved iteratively due to the temperature dependent value of η.
Procedure for determining the scalar temperature fields of a process includes the following steps:
1 . Recording of the process by a camera and image transfer to a computer. The exposure time must be set properly to avoid image saturation and blurring.
2. Temperature calibration by determination of calibration constant C. C is calculated from Eq. (5) by using temperature and corresponding image gray level data of a surface with known temperature and emissivity representative of the observed process. If the camera positioning, lens type, exposure time or the emissivity of observed objects or flows changes, temperature calibration must be repeated.
3. Iterative calculation of the absolute temperature by Eq. (5) and the function η( Τ). The function η{ Τ) defines the temperature dependence of the camera sensor light
efficacy and must be calculated from the sensitivity and quantum efficiency data of the particular camera.
The invention will now be described with reference to a sample embodiment illustrated in the following figures, wherein:
Fig. 1 shows a schematic drawing of the apparatus and method for non-contact temperature measurement with a visible light camera. Shown is an example of application of said apparatus and method for the monitoring of the temperature fields on the first wheel of a mineral wool spinner.
Fig. 2: A typical graph for conversion between the normalized gray level of a process image, recorded by a visible light camera, and the absolute temperature.
Said apparatus and method for non-contact temperature field measurement with the particular application to the mineral wool production process comprises of a high-speed, visible light digital camera (6) connected to a computer (7) where continuous acquisition, processing and saving of imaging data occurs. Said process begins with a stream of mineral melt (4) flowing from the reservoir (3) onto the first spinner wheel (1 ) where a thin melt film (2) is formed and scattered to mineral wool fibers (5) due to the centrifugal force.
Relation between the normalized gray level of process images, recorded by said digital camera, and the absolute temperature varies with the measurement setup (camera positioning, lens type and exposure time) and the emissivity of observed hot objects or flows. A typical graph (8) for said relation between the normalized gray level and the absolute temperature is shown in Fig. 2.
Claims
1. A method for non-contact temperature measurement of high-temperature processes, said method comprising steps of:
- gray level acquisition from images of said processes recorded by an imaging device sensitive mostly to the visible light;
- temperature calibration;
- calculation of temperature fields from image gray level data and temperature calibration data
2. A method as claimed in Claim 1 , characterized in that the algorithm for temperature field calculation from images of a high-temperature process assumes gray body thermal radiation of objects and/or flows in the said process.
3. A method as claimed in Claim 1 , characterized in that the algorithm for temperature field calculation from camera (6) images of a high-temperature process is calibrated to a surface with known temperature.
4. An apparatus for non-contact temperature measurement, characterized in that it comprises of at least one visible light camera (6) and data processing and storing means, preferably computer (7) characterized in that said camera (6) is placed in proximity to high-temperature process comprising of objects (1 ) and/or flows (2).
5. An apparatus as claimed in Claim 1 , characterized in that the sensor of the camera (6) has the maximum quantum efficiency within a wavelength range between 250nm and 1000nm, and below 10% of the maximum quantum efficiency outside of this range.
6. An apparatus according to any of claims 3 to 5 for performing a method according to any of claims 1 to 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SI201400224A SI24410A (en) | 2014-06-18 | 2014-06-18 | System and method for contactless temperature measuring with a cameraworking in the visible part of the light spectrum |
| SIP-201400224 | 2014-06-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2015195055A1 true WO2015195055A1 (en) | 2015-12-23 |
Family
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/SI2015/000024 WO2015195055A1 (en) | 2014-06-18 | 2015-06-15 | Apparatus and method for non-contact temperature measurement with a visible light camera |
Country Status (2)
| Country | Link |
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| SI (1) | SI24410A (en) |
| WO (1) | WO2015195055A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111279168A (en) * | 2017-12-11 | 2020-06-12 | 塔塔钢铁艾默伊登有限责任公司 | Method and system for measuring temperature of moving strip |
| CN113514414A (en) * | 2021-06-08 | 2021-10-19 | 中国矿业大学 | Method for establishing spectral emissivity distribution model of high-temperature single-particle coal coke thermal radiation wave band |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114509166B (en) * | 2022-01-27 | 2024-02-23 | 重庆大学 | High-transient high-temperature plasma temperature measurement system |
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2014
- 2014-06-18 SI SI201400224A patent/SI24410A/en not_active IP Right Cessation
-
2015
- 2015-06-15 WO PCT/SI2015/000024 patent/WO2015195055A1/en active Application Filing
Non-Patent Citations (2)
| Title |
|---|
| BRISLEY P M ET AL: "Three-Dimensional Temperature Measurement of Combustion Flames Using a Single Monochromatic CCD Camera", IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 54, no. 4, 1 August 2005 (2005-08-01), pages 1417 - 1421, XP011136536, ISSN: 0018-9456, DOI: 10.1109/TIM.2005.851074 * |
| JUNHONG YAN ET AL: "Research on colorimetric temperature-measurement method improved based on CCD imaging", IMAGE AND SIGNAL PROCESSING (CISP), 2010 3RD INTERNATIONAL CONGRESS ON, IEEE, PISCATAWAY, NJ, USA, 16 October 2010 (2010-10-16), pages 189 - 192, XP031810315, ISBN: 978-1-4244-6513-2 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111279168A (en) * | 2017-12-11 | 2020-06-12 | 塔塔钢铁艾默伊登有限责任公司 | Method and system for measuring temperature of moving strip |
| CN113514414A (en) * | 2021-06-08 | 2021-10-19 | 中国矿业大学 | Method for establishing spectral emissivity distribution model of high-temperature single-particle coal coke thermal radiation wave band |
Also Published As
| Publication number | Publication date |
|---|---|
| SI24410A (en) | 2014-12-31 |
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