CN115060723A - Metal temperature field measuring device and measuring method - Google Patents
Metal temperature field measuring device and measuring method Download PDFInfo
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- CN115060723A CN115060723A CN202210609904.9A CN202210609904A CN115060723A CN 115060723 A CN115060723 A CN 115060723A CN 202210609904 A CN202210609904 A CN 202210609904A CN 115060723 A CN115060723 A CN 115060723A
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- 239000002184 metal Substances 0.000 title claims abstract description 66
- 238000000034 method Methods 0.000 title claims abstract description 31
- 238000012360 testing method Methods 0.000 claims description 6
- 238000005259 measurement Methods 0.000 abstract description 7
- 230000005855 radiation Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000000691 measurement method Methods 0.000 description 3
- 238000009529 body temperature measurement Methods 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
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- 239000000463 material Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B7/00—Control of exposure by setting shutters, diaphragms or filters, separately or conjointly
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Abstract
The invention discloses a metal temperature field measuring method, which adopts a heater to heat a measured metal, adopts a camera to shoot a picture of the measured metal, actively regulates and controls exposure time in the shooting process, keeps the gray level of the picture in real time, establishes a high-precision model between the gray level of the picture and the temperature, realizes high-precision measurement of the temperature of the measured metal, is not interfered by the external environment, and has low cost, higher resolution and higher accuracy. Meanwhile, the method can be suitable for measuring the temperature field of the object with uneven surface.
Description
Technical Field
The invention relates to the field of material surface temperature measurement under a high-temperature condition, in particular to a metal temperature field measuring device and a measuring method.
Background
The metal surface temperature measuring method is divided into a contact type measuring mode and a non-contact type measuring mode. The contact measurement method has high requirements on the performance of measurement devices such as a thermometer and the like, can cause interference and even damage to the metal surface in the contact process, and is difficult to obtain temperature field information of the whole surface. The non-contact measurement has certain advantages over the contact measurement, for example, the interference and the damage to the measured metal surface can not be caused, the safety of operators can be ensured by the remote measurement, and the full-surface temperature field information can be obtained.
Existing contactless temperature measurements mainly use infrared cameras, which mainly operate in the mid-infrared spectral band (3-12 μm), which also entails some disadvantages. Firstly, the interference radiation of a peripheral object to a target object needs to be measured, but because the interference radiation depends on the surface state of the object, corresponding correction is difficult to carry out; second, infrared cameras generally require a uniform surface, even a constant emissivity. However, the surfaces of most objects are non-uniform, and it is therefore difficult to measure the temperature fields of these objects with infrared cameras. In order to solve these problems, it is necessary to develop a measurement technique operating in the lower spectral range (near infrared spectrum 0.7-1.1 μm) to enable the measurement of the temperature field of objects with non-uniform surfaces.
Disclosure of Invention
Aiming at the technical defect that the existing infrared camera measures the temperature of the metal surface, the invention provides a metal temperature field measuring device and a measuring method.
The purpose of the invention is realized by the following technical scheme:
the invention has the following beneficial effects:
a metal temperature field measuring method adopts a heater to heat a measured metal, adopts a camera to shoot pictures of the measured metal, and adjusts the exposure time of each picture shot by the camera according to the following formula in the shooting process:
wherein, tau (t) and tau (t-t) 0 )、τ(t-2t 0 ) Respectively represent the t-th time of shooting, t-t 0 Time t-2t 0 Time of day exposure time, t 0 For the interval time between the shots of the camera, H (0) represents the initial time, i.e. the gray value corresponding to the 1 st picture shot by the camera, H (t-t) 0 )、H(t-2t 0 ) Respectively represent t-t of the camera 0 Time t-2t 0 Shooting the gray value of the picture at any moment;
inputting the gray value H and the exposure time tau of the picture of the metal to be detected into a formula (2) to obtain the temperature T corresponding to each gray value in the picture of the metal to be detected, so as to obtain the temperature field of the metal to be detected:
wherein k is w Is a camera parameter, C 2 1.44X 10 for the known second Planck constant -2 mK；a 0 ，a 1 Is a constant coefficient.
Further, in an off-line state, at least three pictures of the metal to be measured at different temperatures are selected, the true temperature of the metal to be measured when each picture is shot is obtained by adopting temperature measuring equipment, the three groups of gray value H and temperature T data are substituted into the formula (2) for solving, and a is obtained 0 ，a 1 And k w 。
Further, a is calculated according to formula (2) 0 ，a 1 And k w And selecting the gray value and the corresponding temperature of the position of the heater in the picture of the metal to be detected.
An apparatus for implementing the above method, the apparatus comprising:
the camera is used for shooting a picture of the measured metal;
the temperature measuring equipment is used for measuring the real-time temperature of the heated metal to be measured;
the computer is connected with the camera and the temperature measuring equipment and is used for receiving and storing pictures shot by the camera in real time and the temperature corresponding to each picture measured by the temperature measuring equipment; and adjusting the exposure time tau of each subsequent picture according to the formula (1) from the third picture taken by the camera:
then, at least three pictures of the metal to be measured at different temperatures are selected, the temperature of the metal to be measured corresponding to the pictures measured by the temperature measuring equipment, the gray value H of the pictures and the exposure time tau are input into a formula (2) to be solved, and the parameter a is obtained 0 、a 1 And k w The value of (c):
finally, inputting the gray value of the picture of the metal to be measured at a specific moment and the exposure time tau into a formula (2), and combining the known a 0 、a 1 And k w And obtaining the temperature corresponding to each gray value of the picture of the metal to be detected at a specific moment, thereby obtaining the temperature field of the metal to be detected.
Further, the device also comprises a thermocouple which is contacted with the metal to be measured and is used for measuring the temperature of the metal to be measured at a specific position.
The metal temperature field measuring method disclosed by the invention can be used for actively regulating and controlling the exposure time, keeping the image gray scale in real time, establishing a high-precision model between the image gray scale and the temperature, realizing the high-precision measurement of the temperature of the metal to be measured, and being free from the interference of the external environment, low in cost, higher in resolution and higher in accuracy. Meanwhile, the method can be suitable for measuring the temperature field of the object with uneven surface.
Drawings
Fig. 1 is a schematic three-dimensional structure diagram of a metal temperature field measuring device of the present invention, wherein 1 is a camera, 2 is a computer, 3 is an infrared thermometer, 4 is a heater, and 5 is a metal sample.
FIG. 2 is an image of the surface of a metal object under test; in the figure, a square area (i) is a real-time gray level control area which is randomly selected to prevent overexposure; the second square area is a corresponding picture gray area of the infrared thermometer; the square area is a randomly selected temperature field calculation area; the square region is a region selected for verifying the validity of the method by comparing the temperature calculated value with the thermocouple measured value;
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the objects and effects of the present invention will become more apparent, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
First, as shown in fig. 1, a method for installing a measuring device according to an embodiment of the present invention includes a camera 1, a computer 2, and an infrared thermometer 3. The camera 1 is responsible for shooting the metal to be measured, and the infrared thermometer 3 is used for accurately measuring the temperature of the metal sample 5 to be measured. The metal sample 5 to be measured is heated by the heater 4. The computer 2 is connected with the camera 1 and the infrared thermometer 3 and is used for receiving and storing pictures of the metal sample 5 to be measured, which are shot by the camera, at different temperatures in real time and storing the temperature, which is measured by the infrared thermometer 3 and corresponds to each picture, of the metal sample to be measured, converting light intensity information of each pixel point of the pictures shot by the camera 1 into a corresponding temperature value to obtain a temperature value of the whole shot picture, and finally displaying the temperature field of the metal to be measured in real time.
In the testing process, a heater 4 is adopted to heat a metal sample 5 to be tested, and a camera 1 is used for shooting according to a set shooting interval t 0 And shooting the metal sample 5 to obtain light intensity information. During the shooting process of the camera, if the exposure time τ is kept constant, the gray-scale image quickly reaches saturation as the temperature rises, and temperature information of the object is difficult to obtain, so that the device is required to actively adjust the exposure time (for example, when the temperature rises, the exposure time is reduced) so that the gray-scale value of each picture can be equal to or close to the gray-scale value of the first picture.
(1) The measurement method of the present invention adjusts the exposure time of each image by the following overexposure prevention control technique:
wherein, tau (t) and tau (t-t) 0 )、τ(t-2t 0 ) Respectively represents the t-th moment of shooting and t-t 0 Time t-2t 0 Time of day exposure time, t 0 For the interval time of the camera, H (0) represents the initial time, i.e. the gray value corresponding to the 1 st picture taken by the camera, H (t-t) 0 )、H(t-2t 0 ) Respectively represent t-t of the camera 0 Time t-2t 0 The grey value of the picture is shot at all times. That is, knowing the gray value of the 1 st picture, and the gray values and the exposure time of the two images before the current time, the exposure time of the image at the current time can be obtained.
In the off-line debugging stage, the exposure time is kept unchanged by using the camera, the previous two photos are taken, and the exposure time of the subsequent photos is predicted according to the gray value of a randomly selected area, namely a square (I) area in the graph 2, in the two photos, so that overexposure is prevented. By analogy, in the shooting and sampling process in the debugging stage, the exposure time of each picture can be dynamically controlled according to the data of the previous two pictures, so that overexposure is prevented.
(2) Meanwhile, a relationship among exposure time, temperature, and gradation is established.
According to planck's law of radiation:
t is temperature value, I (T) is light intensityH (T) is the gray value obtained by shooting with the camera 1, tau is the exposure time, lambda x Is the wavelength of the light. k is a radical of w Is a parameter of the camera 1, which needs to be determined by a radiometric calibration procedure, a 0 ，a 1 ……a n As an unknown constant, C 2 Is the known second Planck constant (1.44 × 10) -2 mK)。
Wavelength lambda of light x Can be expanded to a function related to T:
since the observable wavelength is finite, the first two terms a are used 0 And a 1 Indicating that the observed wavelength is sufficient, and thus combining the two above equations:
therefore, in the testing process, at least three groups of data of the measured temperature T of the infrared thermometer and the corresponding area of the infrared thermometer, namely the square in the graph 2, the gray value H of the area and the exposure time tau of the camera under different temperatures are input into the formula I (T) and solved to obtain the parameter a 0 、a 1 And k w And (3) realizing the establishment of a radiation model of the measured temperature.
Finally, inputting the gray value of the randomly selected area-the square in fig. 2 and the exposure time tau of the camera into the formula of I (T) at any time, and combining the known a 0 、a 1 And k w The parameter value can obtain the temperature corresponding to each gray value of the metal to be measured in the selected area, namely the square and the area III in the figure 2, thereby obtaining the temperature field of the metal in the area. In order to verify the effect of the method, the thermocouple can be used for testing the real temperature of a certain position of the metal to be tested at a specific moment, the temperature difference between the real temperature and the average temperature of a square region in the figure 2 which is the temperature region of the specific position predicted by the method is compared, and the temperature difference between the real temperature and the average temperature is within 1 percent, so that the method verifies the effect of the inventionEffectiveness of the method of (1).
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and although the invention has been described in detail with reference to the foregoing examples, it will be apparent to those skilled in the art that various changes in the form and details of the embodiments may be made and equivalents may be substituted for elements thereof. All modifications, equivalents and the like which come within the spirit and principle of the invention are intended to be included within the scope of the invention.
Claims (5)
1. A metal temperature field measuring method is characterized in that a heater is adopted to heat a measured metal, a camera is adopted to shoot pictures of the measured metal, and the exposure time of each picture shot by the camera is adjusted according to the following formula in the shooting process:
wherein, tau (t) and tau (t-t) 0 )、τ(t-2t 0 ) Respectively represents the t-th moment of shooting and t-t 0 Time t-2t 0 Time of day exposure time, t 0 For the interval time of the camera, H (0) represents the initial time, i.e. the gray value corresponding to the 1 st picture taken by the camera, H (t-t) 0 )、H(t-2t 0 ) Respectively represent t-t of the camera 0 Time t-2t 0 Shooting the gray value of the picture at any moment;
inputting the gray value H and the exposure time tau of the picture of the metal to be detected into a formula (2) to obtain the temperature T corresponding to each gray value in the picture of the metal to be detected, so as to obtain the temperature field of the metal to be detected:
wherein k is w Is a camera parameter, C 2 1.44X 10 for the known second Planck constant -2 mK；a 0 ，a 1 Is a constant coefficient.
2. The method for measuring the metal temperature field according to claim 1, wherein at least three pictures of the measured metal at different temperatures are selected in an off-line state, the true temperature of the metal to be measured when each picture is taken is obtained by adopting temperature measuring equipment, the three groups of gray value H and temperature T data are substituted into the formula (2) for solving, and a is obtained 0 ，a 1 And k w 。
3. The metal temperature field measuring method according to claim 2, wherein a is calculated according to formula (2) 0 ，a 1 And k w And selecting the gray value and the corresponding temperature of the position of the heater in the picture of the metal to be detected.
4. An apparatus for carrying out the method of any one of claims 1 to 3, characterized in that the apparatus comprises:
the camera is used for shooting a picture of the measured metal;
the temperature measuring equipment is used for measuring the real-time temperature of the heated metal to be measured;
the computer is connected with the camera and the temperature measuring equipment and is used for receiving and storing pictures shot by the camera in real time and the temperature corresponding to each picture measured by the temperature measuring equipment; and adjusting the exposure time tau of each subsequent picture according to the formula (1) from the third picture taken by the camera:
then, at least three pictures of the metal to be measured at different temperatures are selected, the temperature of the metal to be measured corresponding to the pictures measured by the temperature measuring equipment, the gray value H of the pictures and the exposure time tau are input into a formula (2) to be solved, and the parameter a is obtained 0 、a 1 And k w The value of (c):
finally, inputting the gray value of the picture of the metal to be measured at a specific moment and the exposure time tau into a formula (2), and combining the known a 0 、a 1 And k w Obtaining the metal to be measured at a specific momentAnd obtaining the temperature field of the metal to be detected according to the temperature corresponding to each gray value of the picture.
5. The apparatus of claim 4, further comprising a thermocouple in contact with the metal under test for measuring the temperature of the metal under test at a specific location.
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