Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Reexamination Certificate
2002-07-01
2004-11-09
Verbitsky, Gail (Department: 2859)
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
C374S130000, C356S045000, C250S208100, C250S238000, C250S559400
Reexamination Certificate
active
06814484
ABSTRACT:
This application is based on Japanese Patent Applications Nos. 2001-008573 and 2001-008574 both filed on Jan. 17, 2001, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus which permit accurate measurement of a distribution of surface temperature of an object made of a plurality of different materials the emissivity values of which are not known.
2. Discussion of Related Art
It is sometimes necessary to accurately measure a distribution of temperature, for example, a distribution of a surface temperature of an article placed within a firing or heating furnace, or a distribution of a surface temperature of a heat-generating body. There has been proposed a surface-temperature distribution, measuring apparatus which uses an image sensor operable to obtain two images of an object body with respective radiations of different wavelengths selected from an optical energy or light emitted from the object body. This measuring apparatus is arranged to obtain a ratio of radiant intensity values at each pair of corresponding local portions of the obtained two images, and measure the surface temperature of the object body, while utilizing the principle of measurement by a dichroic thermometer. JP-B2-7-6844 and JP-A-7-301569 disclose examples of such a surface-temperature distribution measuring apparatus. The apparatuses disclosed in these publications are adapted to calculate a distribution of the surface temperature of the object body, on the basis of the ratio of the actual radiant intensity values corresponding to the two different wavelengths, and according to a predetermined equation based on a known relationship between the radiant intensity ratio and the surface temperature. According to these apparatuses, the calculation is possible even where the emissivity on the surface of the object body is unknown.
The measuring apparatus disclosed in JP-B2-7-6844 uses an image receiver in the form of a television camera, to detect the radiant intensity values corresponding to the three primary colors RGB (e.g., red color of 590 nm, green color of 530 nm and blue color of 460 nm) of light from the object body, and obtain a plurality of sets of radiant intensity ratios of two colors of the three primary colors, for example, of R and G. The measuring apparatus is arranged to convert the obtained radiant intensity ratios into the surface temperature of the object body according to a predetermined theoretical curve with a compensating function, and display a distribution of the surface temperature.
The conventional surface-temperature distribution measuring apparatus described above uses the selected two colors of the three primary colors of light of the object body. However, the radiant intensity ratio of the selected two colors cannot be considered to be a ratio of the two radiations having the predetermined wavelengths, so that the principle of measurement of the conventional apparatus does not fully match the principle of measurement by the dichroic thermometer, namely, does not fully meet a prerequisite that the dependency of the emissivity value on the wavelength can be ignored for two radiations the wavelengths of which are close to each other, leading to approximation &egr;
1
=&egr;
2
. Thus, the conventional measuring apparatus suffers from a large amount of error included in the obtained surface temperature distribution.
On the other hand, JP-A-7-301569 discloses in its
FIG. 2
an apparatus for obtaining a distribution of surface temperature, comprising an image detector (image sensor) having a light detecting surface on which are arranged a multiplicity of photosensitive elements, and two filters which are respectively provided on a first optical path and second optical path along which a light emitted from an object selectively travels to be incident upon the light detecting surface of the image detector and which permit transmission of respective two radiations having respective different wavelengths. Two images, that is, a first and a second image are obtained with the respective radiations of the two wavelengths, and the temperature of the object body at each picture element of its image is calculated on the basis of the radiant intensity ratio at each pair of corresponding picture elements of the two images, while utilizing the principle of measurement by a dichroic thermometer.
In the apparatus disclosed in JP-A-7-301569, a mirror is employed to permit an incident radiation to be incident upon a selected one of the two filters, by changing its angle. According to the present apparatus, a ratio of the actual radiant intensity values corresponding to the two different wavelengths at a certain moment can not be obtained in the strict sense, since the two images corresponding to the respective radiations having the different wavelengths are not obtained simultaneously. Accordingly, there is a time lag between the moments at which the first and second images are formed. This arrangement suffers from an insufficient measuring accuracy when the measurement of distribution of surface temperature is effected on an object body whose temperature is rising or falling. The above publication also discloses in its paragraph [0020] an apparatus for dealing with this problem, namely, an apparatus in which the light emitted from the object body is split into two components which travel along respective paths, and a filter and an image detector are provided for each of the paths. However, this apparatus also does not exhibit a sufficiently high degree of measuring accuracy due to a variation in detecting sensitivity exhibited by the two image detectors.
SUMMARY OF THE INVENTION
The present invention was made in view of the background art discussed above. It is a first object of the present invention to provide a method which permits accurate measurement of a distribution of surface temperature of an object body. A second object of the invention is to provide an apparatus suitable for practicing the method.
The first object may be achieved according to a first aspect of this invention, which provides a method of measuring a surface temperature of an object body, by calculating a temperature of the object body at each picture element of its image on the basis of a radiant intensity ratio at each pair of corresponding picture elements of a first and a second image which are obtained with respective radiations having respective first and second wavelengths and selected from a light emitted from a surface of the object body, the method comprising:
a first wavelength-selecting step of selecting the radiation having the first wavelength from the light emitted from the surface of the object body, by using a first filter which permits transmission therethrough a radiation having the first wavelength which is selected according to a radiant-intensity curve corresponding to a wavelength of a black body at a lower limit of a range of the temperature to be measured, and which is within a high radiant-intensity range in which the radiant intensity is higher than a radiant intensity at a normal room temperature; and
a second wavelength-selecting step of selecting the radiation having the second wavelength from the light emitted from the surface of the object body, by using a second filter which permits transmission therethrough a radiation having the second wavelength which is selected within the high radiant-intensity range, such that the second wavelength is different from the first wavelength by a predetermined difference which is not larger than {fraction (1/12)} of the first wavelength and which is not smaller than a sum of a half width of the first wavelength and a half width of the second wavelength.
The second object indicated above may be achieved according to a second aspect of the present invention, which provides an apparatus for measuring a surface temperature of an object body, by calculating a temperature of the object body at each picture element of its image
Arai Norio
Arai Satoshi
Hashimoto Miyuki
Iwata Misao
Kitagawa Kuniyuki
Arai Satoshi
Noritake Co., Limited
Oliff & Berridg,e PLC
Verbitsky Gail
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