Temperature measuring method and apparatus

Abstract

A method of measuring a temperature of an object body in an electric furnace, based on an intensity of a radiant energy emitted from the object body, the electric furnace being provided with an electric heater operable by application of a drive voltage thereto to heat the object body, the method comprising: a radiant-energy detecting step of detecting an intensity of a radiant energy emitted from the object body; a stray-light noise eliminating step of determining as a noise an intensity of a radiant energy of a stray light which is emitted from an inner wall surface of the electric furnace toward the object body and reflected by a surface of the object body, according to a predetermined relationship between the intensity of the radiant energy of the stray light and the drive voltage applied to the electric heater and based on an actually applied value of the drive voltage, and subtracting the intensity of the radiant energy of the stray light determined as the noise, from the detected intensity of the radiant energy emitted from the object body; and a temperature calculating step of calculating a temperature of the object body, based on the intensity of the radiant energy emitted from the object body from which the noise has been removed in the stray-light noise eliminating step. Also disclosed is an apparatus for practicing the method, which may include a shielding device disposed between the furnace walls and the object body.

1 . A method of measuring a temperature of an object body in an electric furnace, based on an intensity of a radiant energy emitted from the object body, said electric furnace being provided with an electric heater operable by application of a drive voltage thereto to heat the object body, the method comprising: 
 a radiant-energy detecting step of detecting an intensity of a radiant energy emitted from the object body;    a stray-light noise eliminating step of determining as a noise an intensity of a radiant energy of a stray light which is emitted from an inner wall surface of the electric furnace toward the object body and reflected by a surface of the object body, according to a predetermined relationship between the intensity of the radiant energy of the stray light and the drive voltage applied to the electric heater and based on an actually applied value of said drive voltage, and subtracting the intensity of the radiant energy of the stray light determined as said noise, from the detected intensity of the radiant energy emitted from the object body; and    a temperature calculating step of calculating a temperature of the object body, based on the intensity of the radiant energy emitted from the object body from which said noise has been removed in said stray-light noise eliminating step.    
     
     
         2 . A method according to  claim 1 , wherein a distribution of a surface temperature of said object body in said electric furnace is measured, 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 mutually corresponding two picture elements of a first and a second image which are obtained respective first and second radiations which have respective first and second wavelengths and which are selected from a light emitted from the surface of said object body, and said radiant-energy detecting step comprises: 
 a first-wavelength radiant-energy detecting step of detecting a radiant intensity of said first radiation at said each picture element, said first-wavelength radiant-energy detecting step including selecting said first radiation having said first wavelength from the light emitted from the surface of said object body, by using a first filter which permits transmission therethrough of said first radiation having said 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, said first filter permitting transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength; and    a second-wavelength radiant-energy detecting step of detecting a radiant intensity of said second radiation at said each picture element, said second-wavelength radiant-energy detecting step including selecting said radiation having said second wavelength from the light emitted from the surface of said object body, by using a second filter which permits transmission therethrough of said second radiation having said second wavelength which is selected within said high radiant intensity range, such that said second wavelength is different from said first wavelength by a predetermined difference which is not larger than {fraction (1/12)} of said first wavelength and which is not smaller than a sum of a half width of said second wavelength,    and wherein said stray-light noise eliminating step comprises determining an intensity of a radiant energy of said stray light at each picture element of each of the first and second images, and subtracting the determined intensity of the radiant energy of the stray light at each picture element of each of the first and second images, from the intensity of the radiant energy emitted from the object body at the corresponding picture element obtained in a corresponding one of said first-wavelength radiant-energy detecting step and said second-wavelength radiant-energy detecting step, so as to obtain intensities of the radiant energies of the first and the second radiation at each picture element from which the intensity of the radiant energy of the stray light has been removed and said temperature calculating step comprises calculating the temperature of the object body at said each picture element, by obtaining, at said each picture element, a ratio of the intensity of the radiant energy of the first radiation from which the intensity of the radiant energy of the stray light has been removed, to the intensity of the radiant energy of the second radiation from which the intensity of the radiant energy of the stray light has been removed.    
     
     
         3 . A method according to  claim 2 , wherein said first filter permits transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength, while said second filter permits transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said second wavelength.  
     
     
         4 . A method according to  claim 2 , wherein said first and second filters have transmittance values whose difference is not higher than 30%.  
     
     
         5 . An apparatus for measuring a temperature of an object body in an electric furnace, based on an intensity of a radiant energy emitted from the object body, said electric furnace being provided with an electric heater operable by application of a drive voltage thereto to heat the object body, the apparatus comprising: 
 a radiant-energy detecting means for detecting an intensity of a radiant energy emitted from the object body;    a stray-light noise eliminating means for determining as a noise an intensity of a radiant energy of a stray light which is emitted from an inner wall surface of the electric furnace toward the object body and reflected by a surface of the object body, according to a predetermined relationship between the intensity of the radiant energy of the stray light and the drive voltage applied to the electric heater, based on an actually applied value of said drive voltage, and subtracting the intensity of the radiant energy of the stray light determined as said noise, from the detected intensity of the radiant energy emitted from the object body; and    a temperature calculating means for calculating a temperature of the object body, based on the intensity of the radiant energy emitted from the object body from which said noise has been removed by said stray-light noise eliminating means.    
     
     
         6 . An apparatus according to  claim 5 , wherein a distribution of a surface temperature of said object body in said electric furnace is measured, 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 mutually corresponding two picture elements of a first and a second image which are obtained respective first and second radiations which have respective first and second wavelengths and which are selected from a light emitted from the surface of said object body, and said radiant-energy detecting means comprises: 
 a first-wavelength radiant-energy detecting means for detecting a radiant intensity of said first radiation at said each picture element, said first-wavelength radiant-energy detecting means including selecting said first radiation having said first wavelength from the light emitted from the surface of said object body, by using a first filter which permits transmission therethrough of said first radiation having said 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, said first filter permitting transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength; and    a second-wavelength radiant-energy detecting means for detecting a radiant intensity of said second radiation at said each picture element, said second-wavelength radiant-energy detecting means including selecting said radiation having said second wavelength from the light emitted from the surface of said object body, by using a second filter which permits transmission therethrough of said second radiation having said second wavelength which is selected within said high radiant intensity range, such that said second wavelength is different from said first wavelength by a predetermined difference which is not larger than {fraction (1/12)} of said first wavelength and which is not smaller than a sum of a half width of said second wavelength,    and wherein said stray-light noise eliminating means comprises determining an intensity of a radiant energy of said stray light at each picture element of each of the first and second images, and subtracting the determined intensity of the radiant energy of the stray light at each picture element of each of the first and second images, from the intensity of the radiant energy emitted from the object body at the corresponding picture element obtained in a corresponding one of said first-wavelength radiant-energy detecting means and said second-wavelength radiant-energy detecting means, so as to obtain intensities of the radiant energies of the first and the second radiation at each picture element from which the intensity of the radiant energy of the stray light has been removed and said temperature calculating means comprises calculating the temperature of the object body at said each picture element, by obtaining, at said each picture element, a ratio of the intensity of the radiant energy of the first radiation from which the intensity of the radiant energy of the stray light has been removed, to the intensity of the radiant energy of the second radiation from which the intensity of the radiant energy of the stray light has been removed.    
     
     
         7 . An apparatus according to  claim 6 , wherein said first filter permits transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength, while said second filter permits transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said second wavelength.  
     
     
         8 . An apparatus according to  claim 6 , wherein said first and second filters have transmittance values whose difference is not higher than 30%.  
     
     
         9 . An apparatus according to  claim 6 , further comprising: 
 a first half mirror for splitting said light emitted from the surface of said object body into two components traveling along respective first and second optical paths which are provided with said first and second filters, respectively;    a second half mirror disposed so as to receive the radiations of said first and second wavelengths from said first and second filters; and    and an image detector including a multiplicity of photosensitive elements operable in response to the radiations of said first and second wavelengths, to form two images of said object body on the basis of said radiations of said first and second wavelengths, respectively, such that said two images are spaced apart from each other.    
     
     
         10 . An apparatus according to  claim 6 , further comprising: 
 a pair of mirrors each movable between a first position in which the light emitted from the surface of said object body travels along a first path provided with said first filter, and a second position in which a corresponding one of said pair of mirrors reflects said light such that the light travels along a second optical path provided with said second filter; and    an image detector including a multiplicity of photosensitive elements operable in response to the radiations of said first and second wavelengths, to form two images of said object body on the basis of said radiations of said first and second wavelengths, respectively, such that said two images are spaced apart from each other.    
     
     
         11 . An apparatus according to  claim 6 , further comprising: 
 a rotary disc carrying said first and second filters fixed thereto and rotatable about an axis parallel to an optical path which extends from said object body, said first and second filters being disposed on said rotary disc such that said first and second filters are selectively aligned with said optical path, by rotation of said rotary disc;    an electric motor operable to rotate said rotary disc; and    an image detector including a plurality of photosensitive elements operable in response to the radiations of said first and second wavelengths, to form two images of said object body on the basis of said radiations of said first and second wavelengths, respectively, such that said two images are spaced apart from each other.    
     
     
         12 . An apparatus according to  claim 6 , further comprising: 
 a half mirror for splitting said light emitted from the surface of said object body into two components traveling along respective first and second optical paths which are provided with said first and second filters, respectively; and    a pair of image detectors disposed to receive the radiations of said first and second wavelengths, respectively, each of said pair of image detectors including a multiplicity of photosensitive elements operable in response to a corresponding one of the radiations of said first and second wavelengths, to an image of said object body on the basis of said corresponding radiation.    
     
     
         13 . An apparatus for measuring a temperature of an object body in a heating furnace, based on an intensity of a radiant energy emitted from the object body, the apparatus comprising: 
 a shielding device provided between the object body and an inner wall surface of the heating furnace and operable between an open state for permitting a stray light to be emitted from the inner wall surface to reach the object body and a closed state for inhibiting the stray light from reaching the object body;    a radiant-energy detecting means for detecting an intensity of a radiant energy emitted from the object body while the shielding device is held in said closed state;    a temperature calculating means for calculating a temperature of the object body, based on the intensity of the radiant energy emitted from the object body detected by said radiant-energy detecting means;    a pair of mirrors each movable between a first position in which the light emitted from the surface of said object body travels along a first path provided with said first filter, and a second position in which a corresponding one of said pair of mirrors reflects said light such that the light travels along a second optical path provided with said second filter; and    an image detector including a multiplicity of photosensitive elements operable in response to the radiations of said first and second wavelengths, to form two images of said object body on the basis of said radiations of said first and second wavelengths, respectively, such that said two images are spaced apart from each other;    wherein a distribution of a surface temperature of said object body in said electric furnace is measured, 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 mutually corresponding two picture elements of a first and a second image which are obtained respective first and second radiations which have respective first and second wavelengths and which are selected from a light emitted from the surface of said object body, and said radiant-energy detecting means comprises:    a first-wavelength radiant-energy detecting means for detecting a radiant intensity of said first radiation at said each picture element while the shielding device is held in said closed state, said first-wavelength radiant-energy detecting means including selecting said first radiation having said first wavelength from the light emitted from the surface of said object body, by using a first filter which permits transmission therethrough of said first radiation having said 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, said first filter permitting transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength; and    a second-wavelength radiant-energy detecting means for detecting a radiant intensity of said second radiation at said each picture element while the shielding device is held in said closed state, said second-wavelength radiant-energy detecting means including selecting said radiation having said second wavelength from the light emitted from the surface of said object body, by using a second filter which permits transmission therethrough of said second radiation having said second wavelength which is selected within said high radiant intensity range, such that said second wavelength is different from said first wavelength by a predetermined difference which is not larger than {fraction (1/12)} of said first wavelength and which is not smaller than a sum of a half width of said second wavelength,    and wherein said temperature calculating means comprises calculating the temperature of the object body at said each picture element, by obtaining, at said each picture element, a ratio of the intensity of the radiant energy of the first radiation detected by the first-wavelength radiant-energy detecting means, to the intensity of the radiant energy of the second radiation detected by the second-wavelength radiant-energy detecting means.    
     
     
         14 . An apparatus according to  claim 11 , further comprising: 
 a rotary disc carrying said first and second filters fixed thereto and rotatable about an axis parallel to an optical path which extends from said object body, said first and second filters being disposed on said rotary disc such that said first and second filters are selectively aligned with said optical path, by rotation of said rotary disc;    an electric motor operable to rotate said rotary disc; and    an image detector including a plurality of photosensitive elements operable in response to the radiations of said first and second wavelengths, to form two images of said object body on the basis of said radiations of said first and second wavelengths, respectively, such that said two images are spaced apart from each other.    
     
     
         15 . An apparatus for measuring a temperature of an object body in a heating furnace, based on an intensity of a radiant energy emitted from the object body, the apparatus comprising: 
 a shielding device provided between the object body and an inner wall surface of the heating furnace and operable between an open state for permitting a stray light to be emitted from the inner wall surface to reach the object body and a closed state for inhibiting the stray light from reaching the object body;    a radiant-energy detecting means for detecting an intensity of a radiant energy emitted from the object body while the shielding device is held in said closed state;    a temperature calculating means for calculating a temperature of the object body, based on the intensity of the radiant energy emitted from the object body detected by said radiant-energy detecting means;    a half mirror for splitting said light emitted from the surface of said object body into two components traveling along respective first and second optical paths which are provided with said first and second filters, respectively; and    a pair of image detectors disposed to receive the radiations of said first and second wavelengths, respectively, each of said pair of image detectors including a multiplicity of photosensitive elements operable in response to a corresponding one of the radiations of said first and second wavelengths, to an image of said object body on the basis of said corresponding radiation;    wherein a distribution of a surface temperature of said object body in said electric furnace is measured, 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 mutually corresponding two picture elements of a first and a second image which are obtained respective first and second radiations which have respective first and second wavelengths and which are selected from a light emitted from the surface of said object body, and said radiant-energy detecting means comprises:    a first-wavelength radiant-energy detecting means for detecting a radiant intensity of said first radiation at said each picture element while the shielding device is held in said closed state, said first-wavelength radiant-energy detecting means including selecting said first radiation having said first wavelength from the light emitted from the surface of said object body, by using a first filter which permits transmission therethrough of said first radiation having said 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, said first filter permitting transmission therethrough of a radiation having a half width which is not larger than {fraction (1/20)} of said first wavelength; and    a second-wavelength radiant-energy detecting means for detecting a radiant intensity of said second radiation at said each picture element while the shielding device is held in said closed state, said second-wavelength radiant-energy detecting means including selecting said radiation having said second wavelength from the light emitted from the surface of said object body, by using a second filter which permits transmission therethrough of said second radiation having said second wavelength which is selected within said high radiant intensity range, such that said second wavelength is different from said first wavelength by a predetermined difference which is not larger than {fraction (1/12)} of said first wavelength and which is not smaller than a sum of a half width of said second wavelength,    and wherein said temperature calculating means comprises calculating the temperature of the object body at said each picture element, by obtaining, at said each picture element, a ratio of the intensity of the radiant energy of the first radiation detected by the first-wavelength radiant-energy detecting means, to the intensity of the radiant energy of the second radiation detected by the second-wavelength radiant-energy detecting means.