Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Reexamination Certificate
2002-10-04
2004-09-07
Fulton, Christopher W. (Department: 2859)
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
C374S124000, C374S121000
Reexamination Certificate
active
06786634
ABSTRACT:
This application is based on Japanese Patent Applications Nos. 2001-312962 and 2001-312963 both filed on Oct. 10, 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 temperature of an object body even in the case where the temperature of a wall such as a furnace wall surrounding the object body is different from that of the object body.
2. Discussion of Related Art
Temperature measuring methods of non-contact type are industrially useful and widely employed. To practice such non-contact type temperature measuring methods, there are known a radiation thermometer operable to effect a monochromatic temperature measurement, and a radiation thermometer operable to effect a dichroic temperature measruement. The former thermometer measures the temperature of an object body by comparing a radiant intensity value at one wavelength selected from an optical energy emitted from the object body with a reference value, which is a radiant intensity at the same wavelength of an optical energy emitted from a black body. Although this thermometer permits easy measurement of the temperature of the object body, it requires determination of the emissivity of the object body, and is not suitable for measuring temperature of an object body the emissivity of which changes. On the other hand, the latter thermometer can measure the temperature of an object body the emissivity of which is not unknown, since the temperature of the object body is determined on the basis of a ratio of radiant intensity values of two radiations having respective two different wavelengths selected from a radiant energy emitted from the object body, irrespective of the emissivity.
The radiation thermometers of non-contact type capable of monochromatic or dichroic temperature measurement or other non-contact type radiation thermometers may suffer from insufficient accuracy of the temperature measurement of the object body, due to a stray light noise undesirably included in the light radiated from the object body. More specifically described, the noise is a radiant energy of a stray light which is emitted toward a surface of the object body from the surroundings of the object body, e.g., inner wall surfaces of a furnace in which the object body is heated, and a heater or burner of the furnace. The stray light is reflected by the surface of the object body and incident on a photosensitive device of the radiation thermometer, so that the radiant intensity of the stray light is included in the detected radiant energy, namely, as a radiant energy as emitted from the object body itself. Thus, the detected temperature of the object body is adversely influenced by the radiant energy of the stray light. The degree of the adverse influence on the accuracy of measurement of the temperature of the object body increases with a rise in temperature of the inner wall surfaces of the furnace surrounding the object body, since the rise in the temperature of the surroundings causes an increase in the intensity of the radiant energy emitted from the inner wall surfaces of the furnace, as the stray light noise
JP-A-6-147989 discloses a radiation temperature measuring apparatus of non-contact type which is arranged to measure the temperature of an object body, by detecting a radiant energy emitted from the object body located within a furnace through an inspection opening of a water-cooled shielding plate while a radiant energy emitted from the wall surface is cut or shut off by the shielding plate. This conventional apparatus is effective when the temperature within the furnace is a relatively low near the room temperature. However, where the temperature in the furnace is relatively high, the water-cooled shielding plate cools down the object body, leading to deterioration of the temperature measurement accuracy. JP-A-6-258142 discloses another radiation temperature measuring apparatus of non-contact type. This apparatus uses two radiation thermometers for detecting radiant energies emitted from an object body and a furnace wall, respectively. The radiant energy emitted from the furnace wall, which is detected by one of the two thermometers, is multiplied by a known emissivity value of the object body, and the product is determined as a noise component derived from a stray light. The temperature of the object body is calculated based on a value of the radiant energy emitted from the object body as detected by the other thermometer minus the noise component from the radiant energy emitted from the object body as detected by the other thermometer, minus the noise component. This apparatus suffers from a drawback that the measurement accuracy is not sufficiently high when the temperature distribution within the furnace wall is uneven, since the temperature of the furnace wall is detected by the radiation thermometer at only one local portion of the furnace wall. In an electric furnace, for example, the temperature is considerably higher at a heat-generating portion than at the other portions of the furnace. Therefore, to employ a radiant energy emitted from one local portion of the entire wall surface as a radiant energy emitted from the furnace wall as a whole leads to deterioration in the accuracy of measuring the temperature of the object body.
In the above-described situation, the inventors have carried out various studies. In view of the fact that where an electric furnace is provided with an electric heater for heating an object body, a radiant energy emitted inwardly from the inner wall surface of the electric furnace increases in proportion to a drive voltage applied to the electric heater, the inventors have found that a stray light noise can be effectively removed from a detected radiant intensity of the object body according to a predetermined relationship between a radiant intensity of a stray light, which is emitted toward and reflected by the object body, and the drive voltage applied to the electric heater; upon measurement of the object body temperature, the actual radiant intensity of the stray light is obtained based on the known drive voltage actually applied to the heater and according to the above-indicated predetermined relationship. Then, the obtained radiant intensity of the stray light is removed from the radiant intensity of the radiation from the object body as detected by a suitable device, to obtain the intensity of a radiant energy which is emitted from the object body and which does not include the stray light noise.
The inventors have also found that the intensity of a radiant energy of a stray light as a noise can be easily removed from a detected intensity value of a radiant energy emitted from the object body, by providing a furnace with a shielding device operable between an open state for permitting the stray light to reach the object body and a closed state for inhibiting the stray light from reaching the object body, between the inner wall surface of the furnace and the object body. In this case, the shielding device is held in its closed state, when the intensity of the radiant energy emitted from the object body in the furnace is detected for measurement of the temperature of the object body, so that the shielding device functions to establish an even distribution of the intensity of the radiant energy of the stray light emitted from the furnace wall (provided with burners or an electric heater). That is, the intensity of the radiant energy of the stray light is determined on the basis of the temperature of the shielding device. The thus determined noise or the intensity of the radiant energy of the stray light is eliminated from the detected intensity of the radiant energy emitted from the object body, to obtain a true or net value of the radiant intensity of the radiation which is emitted from the object body and which does not include the astray light noise.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the findi
Arai Norio
Arai Satoshi
Hashimoto Miyuki
Iwata Misao
Kitagawa Kuniyuki
Arai Satoshi
Fulton Christopher W.
Jagan Mirellys
Noritake Co., Limited
Oliff & Berridg,e PLC
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