U.S. patent application number 10/910375 was filed with the patent office on 2005-01-06 for temperature measuring method and apparatus.
This patent application is currently assigned to NORITAKE CO., LIMITED. Invention is credited to Arai, Norio, Arai, Satoshi, Hashimoto, Miyuki, Iwata, Misao, Kitagawa, Kuniyuki, Yano, Kenji.
Application Number | 20050002438 10/910375 |
Document ID | / |
Family ID | 26623834 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050002438 |
Kind Code |
A1 |
Hashimoto, Miyuki ; et
al. |
January 6, 2005 |
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.
Inventors: |
Hashimoto, Miyuki;
(Ichinomiya-shi, JP) ; Yano, Kenji; (Kasugai-shi,
JP) ; Iwata, Misao; (Nagoya-shi, JP) ;
Kitagawa, Kuniyuki; (Nagoya-shi, JP) ; Arai,
Norio; (Kasugai-shi, JP) ; Arai, Satoshi;
(Kasugai-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NORITAKE CO., LIMITED
Nagoya-shi
JP
KUNIYUKI KITAGAWA
Nagoya-shi
JP
|
Family ID: |
26623834 |
Appl. No.: |
10/910375 |
Filed: |
August 4, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10910375 |
Aug 4, 2004 |
|
|
|
10263839 |
Oct 4, 2002 |
|
|
|
6786634 |
|
|
|
|
Current U.S.
Class: |
374/127 ;
374/121; 374/124 |
Current CPC
Class: |
G01J 2005/0048 20130101;
G01J 5/0044 20130101; G01J 2005/0077 20130101; G01J 5/06 20130101;
G01J 5/602 20130101 |
Class at
Publication: |
374/127 ;
374/124; 374/121 |
International
Class: |
G01N 021/00; G01J
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2001 |
JP |
2001-312962 |
Oct 10, 2001 |
JP |
2001-312963 |
Claims
What is claimed is:
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.
Description
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Discussion of Related Art
[0005] 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 measurement. 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.
[0006] 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
[0007] 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.
[0008] 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.
[0009] 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
[0010] The present invention has been developed in view of the
findings discussed above. It is a first object of the present
invention to provide a method which permits highly accurate
measurement of a surface temperature of an object body in a
furnace. A second object of the invention is to provide an
apparatus suitable for practicing the method.
[0011] The first object may be achieved according to a first aspect
of this invention, which provides 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.
[0012] According to this first aspect of the invention, the
intensity of the radiant energy of the stray light emitted from the
inner wall surface of the electric furnace toward the object body
and reflected by the object body is determined based on the drive
voltage actually applied to the heater and according to the
predetermined relationship between the radiant energy intensity and
the drive voltage, and the radiant energy intensity of the stray
light determined as a noise is removed from the detected intensity
of the radiant energy emitted from the object body, in the
stray-light noise eliminating step. Then, in the temperature
calculating step, the temperature of the object body is calculated
based on the intensity of the radiant energy from which the noise
has been removed. This arrangement assures highly accurate
measurement of the temperature of the object body in the electric
furnace.
[0013] One preferable form of the first aspect of the invention is
applicable to a dichroic measurement of a distribution of a surface
temperature of the object body in the electric furnace, 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 first and second
radiations having respective first and a second wavelengths and
selected from a light emitted from the surface of the object body.
In this preferred from of the method, the 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.
[0014] In the present method, the intensity of the radiant energy
of the stray light which is a light emitted from the inner wall
surface of the electric furnace toward the object body and
reflected by the surface of the object body and which is included
in the intensity of the radiant energy of each of the first and
second radiations is first determined at each picture element,
according to the predetermined relationship between the drive
voltage applied to the electric heater of the electric furnace and
the intensity of the radiant energy of the stray light, and based
on the actual value of the applied voltage. The intensity of the
radiant energy of the stray light is then eliminated from the
intensity of the radiant energy of each of the first and second
radiations at each picture element, which has been detected as the
intensity of the radiant energy of the first or second radiation
emitted from the object body. Based on the thus obtained intensity,
the temperature of the object body at each picture element is
calculated. Accordingly, the temperature of the surface of the
object body located inside the electric furnace can be obtained
with high accuracy. Further, in the above preferred form of the
method, 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 mutually corresponding the picture elements
of the first and second images obtained with the respective first
and second radiations having the respective first and second
wavelengths selected from the light emitted from the surface of the
object body. To select the first radiation having the first
wavelength from the light emitted from the surface of the object
body, the present method uses the first filter which permits
transmission therethrough of the first radiation having the first
wavelength which is selected according to the radiant-intensity
curve corresponding to the wavelength of the black body at the
lower limit of the range of the temperature to be measured, which
is within the high radiant-intensity range in which the radiant
intensity is higher than the radiant intensity at the normal room
temperature, and which has a half width which is not larger than
{fraction (1/20)} of the first wavelength. The present method
further uses the second filter which permits transmission
therethrough of the second radiation having the second wavelength
which is selected within the above-indicated 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 the half width of the first wavelength and the half
width of the second wavelength. Accordingly, optical signals having
sufficiently high radiation intensities can be obtained, leading to
an accordingly high S/N ratio. In addition, the first and second
wavelengths are close to each other, so that the principle of
measurement according to the present invention fully matches the
principle of measurement by a dichroic thermometer, namely, fully
meets a prerequisite that the dependency of the emissivity on the
wavelength can be ignored for two radiations the wavelengths of
which are close to each other, leading to approximation
.epsilon..sub.1=.epsilon..sub.2. Thus, the present measuring method
permits highly accurate measurement of the temperature
distribution.
[0015] The second object may be achieved according to a second
aspect of this invention, which provides 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, the
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 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 means for 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 by the
stray-light noise eliminating means.
[0016] According to this second aspect of the invention, the
intensity of the radiant energy of the stray light emitted from the
inner wall surface of the electric furnace toward the object body
and reflected by the object body is first determined based on the
drive voltage actually applied to the electric heater according to
the predetermined relationship between the radiant energy intensity
and the drive voltage, and the intensity of the radiant energy of
the stray light determined as a noise is removed from the detected
intensity of the radiant energy emitted from the object body. Then,
the temperature calculating means calculates the temperature of the
object body, based on the intensity of the radiant energy from
which the noise has been removed. This arrangement assures highly
accurate measurement of the temperature of the object body in the
electric furnace.
[0017] One preferable form of the second aspect of the invention is
a dichroic measurement of a distribution of a surface temperature
of the object body in the electric furnace, 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 first and second radiations having
respective first and second wavelengths and selected from a light
emitted from the surface of the object body. In this preferred form
of the apparatus, the radiant-energy detecting means comprises:
first-wavelength radiant-energy detecting means for detecting a
radiant intensity of the first radiation at the each picture
element, the first-wavelength radiant-energy detecting means
including selecting the first 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 of the
first 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, the first filter
permitting transmission therethrough of a radiation having a half
width which is not larger than {fraction (1/20)} of the first
wavelength; and a second-wavelength radiant-energy detecting means
for detecting a radiant intensity of the second radiation at the
each picture element, the second-wavelength radiant-energy
detecting means including 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 of the second 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 second wavelength, and wherein the
stray-light noise eliminating means comprises determining an
intensity of a radiant energy of the 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 the first-wavelength radiant-energy detecting means and the
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 the
temperature calculating means comprises calculating the temperature
of the object body at the each picture element, by obtaining, at
the 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.
[0018] In the present apparatus, the intensity of the radiant
energy of the stray light, which is a light emitted from the inner
wall surface of the electric furnace toward the object body and
reflected by the surface of the object body and which is included
in the intensity of the radiant energy of each of the first and
second radiations is first determined at each picture element,
according to the predetermined relationship between the drive
voltage applied to the electric heater of the electric furnace and
the intensity of the radiant energy of the stray light, and based
on the actual value of the applied voltage. The intensity of the
radiant energy of the stray light at each picture element is then
eliminated from the intensity of the radiant energy of each of the
first and second radiations at each picture element, which has been
detected as the intensity of the radiant energy of the first or
second radiation emitted from the object body. Based on the thus
obtained intensity, the temperature of the object body at each
picture element is calculated. Accordingly, the temperature of the
surface of the object body located inside the electric furnace can
be obtained with high accuracy. Further, in the above preferred
form of the apparatus, 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 mutually corresponding two
picture elements of the first and second images and obtained with
the respective first and second radiations having the respective
first and second wavelengths selected from the light emitted from
the surface of the object body. To select the first radiation
having the first wavelength from the light emitted from the surface
of the object body, the present apparatus uses the first filter
which permits transmission therethrough of the first radiation
having the first wavelength which is selected according to the
radiant-intensity curve corresponding to the wavelength of the
black body at the lower limit of the range of the temperature to be
measured, which is within the high radiant-intensity range in which
the radiant intensity is higher than the radiant intensity at the
normal room temperature, and which has a half width which is not
larger than {fraction (1/20)} of the first wavelength. The present
apparatus further uses the second filter which permits transmission
therethrough of the second radiation having the second wavelength
which is selected within the above-indicated 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 the half width of the first wavelength and the half
width of the second wavelength. Accordingly, optical signals having
sufficiently high radiation intensities can be obtained, leading to
an accordingly high S/N ratio of the apparatus. In addition, the
first and second wavelengths are close to each other, so that the
principle of measurement according to the present invention fully
matches the principle of measurement by a dichroic thermometer,
namely, fully meets a prerequisite that the dependency of the
emissivity on the wavelength can be ignored for two radiations the
wavelengths of which are close to each other, leading to
approximation .epsilon..sub.1=.epsilon..sub.2. Thus, the present
measuring apparatus permits highly accurate measurement of the
temperature distribution.
[0019] The first object body may be achieved according to a third
aspect of this invention, which provides a method of 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
method comprising: a heating step of heating the object body while
a shielding device disposed 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 an inner wall
surface of the heating furnace and a closed state for inhibiting
the stray light from reaching the object body, is held in the open
state; a radiant-energy detecting step of detecting an intensity of
a radiant energy emitted from the object body while the shielding
device is held in the closed state; 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
detected in the radiant-energy detecting step.
[0020] In this method, the object body is heated while the
shielding device located between the object body and the furnace
wall is held in the open state in the heating step, and then the
intensity of the radiant energy emitted from the object body is
detected while the shielding device is held in the closed state, in
the radiant-energy detecting step. In the following temperature
calculating step, the temperature of the object body is obtained,
based on the thus detected intensity of the radiant energy emitted
from the object body. According to this method, the intensity of
the radiant energy of the stray light emitted from the furnace wall
toward the object body is evenly distributed in the presence of the
shielding device held in its closed state, during the detection of
the intensity of the radiant energy emitted from the object body.
An intensity of the noise (radiant energy of the stray light) is
determined according to a predetermined relationship between the
temperature of the shielding device and the determined intensity of
the radiant energy of the stray light, and based on the intensity
of the radiant energy of the stray light. Accordingly, the stray
light noise can be easily removed from the intensity of the radiant
energy detected as the intensity of the radiant energy emitted from
the object body, enhancing the accuracy of the measurement of
surface temperature of the object body.
[0021] One preferable form of the third aspect of the invention is
applicable to a dichroic measurement of a distribution of a surface
temperature of the object body in the electric furnace, 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 first and second
radiations having respective first and a second wavelengths and
selected from a light emitted from the surface of the object body.
In this preferred from of the method, the heating step comprises
heating the object body while the shielding device disposed between
the object body and an inner wall surface of the heating furnace is
held in the open state; the radiant-energy detecting step
comprises: a first-wavelength radiant-energy detecting step of
detecting a radiant intensity of the first radiation at the each
picture element while the shielding device is held in the closed
state, the first-wavelength radiant-energy detecting step including
selecting the first 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 of the first
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, the first filter permitting transmission
therethrough of a radiation having a half width which is not larger
than {fraction (1/20)} of the first wavelength; and a
second-wavelength radiant-energy detecting step of detecting a
radiant intensity of the second radiation at the each picture
element while the shielding device is held in the closed state, the
second-wavelength radiant-energy detecting step including 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 of the second 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 second wavelength;
and wherein the temperature calculating step comprises calculating
the temperature of the object body at the each picture element, by
obtaining, at the each picture element, a ratio of the intensity of
the radiant energy of the first radiation detected in the
first-wavelength radiant-energy detecting step, to the intensity of
the radiant energy of the second radiation detected in the
second-wavelength radiant-energy detecting step.
[0022] In this preferred from of the method, the shielding device
is held open in the heating step for heating the object body, and
then brought into its closed state and held in this closed state in
the first-wavelength radiant-energy detecting step and the
second-wavelength radiant-energy detecting step for detecting the
intensities of the radiant energies of the first and second
radiations having the respective first and second wavelengths which
are selected from the light emitted from the object body. In the
following temperature calculating step, the temperature of the
object body is calculated at each picture element, based on the
thus obtained intensities of the radiant energies of the first and
second radiations, that is, a ratio of the intensity of the radiant
energy of the first radiation to the intensity of the radiant
energy of the second radiation. According to this method, the stray
light noise (the intensity of the radiant energy of the stray
light) emitted from the furnace wall toward the object body and
reflected by the surface of the object body, which noise is
included in the intensity of the radiant energy detected as the
intensity of the radiant energy emitted from the object body, is
evenly distributed by the shielding device, and the intensity of
the stray light noise is determined based on the temperature of the
shielding device. Then, the 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. This method
thus enhances the accuracy of measuring the surface temperature of
the object body. Further, in the above preferred form of method,
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 mutually corresponding two picture elements of the
first and second images and obtained with the respective first and
second radiations having the respective first and second
wavelengths selected from the light emitted from the surface of the
object body. To select the first radiation having the first
wavelength from the light emitted from the surface of the object
body, the present method uses the first filter which permits
transmission therethrough of the first radiation having the first
wavelength which is selected according to the radiant-intensity
curve corresponding to the wavelength of the black body at the
lower limit of the range of the temperature to be measured, which
is within the high radiant-intensity range in which the radiant
intensity is higher than the radiant intensity at the normal room
temperature, and which has a half width which is not larger than
{fraction (1/20)} of the first wavelength. The present invention
further uses the second filter which permits transmission
therethrough of the second radiation having the second wavelength
which is selected within the above-indicated 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 the half width of the first wavelength and the half
width of the second wavelength. Accordingly, optical signals having
sufficiently high radiation intensities can be obtained, leading to
an accordingly high S/N ratio. In addition, the first and second
wavelengths are close to each other, so that the principle of
measurement according to the present invention fully matches the
principle of measurement by a dichroic thermometer, namely, fully
meets a prerequisite that the dependency of the emissivity on the
wavelength can be ignored for two radiations the wavelengths of
which are close to each other, leading to approximation
.epsilon..sub.1=.epsilon..sub.2. Thus, the present measuring method
permits highly accurate measurement of the temperature
distribution.
[0023] The second object may be achieved according to a fourth
aspect of this invention, which provides 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 the closed state; 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 detected by the radiant-energy detecting means.
[0024] According to the fourth aspect of the invention, the
intensity of the radiant energy emitted from the object body is
detected by the radiant-energy detecting means while the shielding
device disposed between the object body and the furnace wall, and
the temperature of the object body is calculated by the temperature
calculating means, based on the thus detected intensity of the
radiant energy. According to this arrangement, the intensity of the
noise (the radiant energy of the stray light) emitted from the
furnace wall toward the object body is evenly distributed in the
presence of the shielding device held in its closed state during
the detection of the intensity of the radiant energy emitted from
the object body. The intensity of the radiant energy of the stray
light can be determined according to a predetermined relationship
between a temperature of the shielding device and the intensity of
the radiant energy of the stray light, and based on the thus
determined value of the intensity of the radiant energy of the
stray light. Accordingly, the stray light noise can be easily
removed from the intensity of the radiant energy detected as the
intensity of the radiant energy emitted from the object body,
enhancing the accuracy of the measurement of the surface
temperature of the object body.
[0025] One preferable form of the fourth aspect of the invention is
a dichroic measurement of a distribution of a surface temperature
of the object body in the electric furnace, 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 first and second radiations having
respective first and second wavelengths and selected from a light
emitted from the surface of the object body. In this preferred form
of the apparatus, the radiant-energy detecting means comprises: a
first-wavelength radiant-energy detecting means for detecting a
radiant intensity of the first radiation at the each picture
element while the shielding device is held in the closed state, the
first-wavelength radiant-energy detecting means including selecting
the first 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 of the first
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, the first filter permitting transmission
therethrough of a radiation having a half width which is not larger
than {fraction (1/20)} of the first wavelength; and a
second-wavelength radiant-energy detecting means for detecting a
radiant intensity of the second radiation at the each picture
element while the shielding device is held in the closed state, the
second-wavelength radiant-energy detecting means including
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 of the second
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 second
wavelength, and wherein the temperature calculating means comprises
calculating the temperature of the object body at the each picture
element, by obtaining, at the 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.
[0026] In this apparatus, the shielding device is held open by the
heating means during heating of the object body, and then brought
into the closed state and held in the closed state while the
first-wavelength radiant-energy detecting means and the
second-wavelength radiant-energy detecting means respectively
detect the intensities of the radiant energies of the first and
second radiations having the respective first and second
wavelengths selected from the light emitted from the object body.
Next, the temperature calculating means calculates the temperature
of the object body at each picture element, based on the thus
detected intensities of the radiant energies of the first and
second radiations, that is, a ratio of the intensity of the radiant
energy of the first radiation to the intensity of the radiant
energy of the second radiation. According to this arrangement, the
noise or intensity of the radiant energy of the stray light emitted
from the furnace wall toward the object body and reflected by the
surface of the object body, which noise is included in the
intensity of the radiant energy detected as the intensity of the
radiant energy emitted from the object body, is evenly distributed
by the shielding device, and the intensity of the stray light noise
is determined based on the temperature of the shielding device.
Then, the noise or the intensity of the radian energy of the stray
light is eliminated from the detected intensity of the radiant
energy emitted from the object body. This arrangement thus enhances
the accuracy of measuring the surface temperature of the object
body. Further, in the above apparatus, 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 mutually
corresponding two picture elements of the first and second images
obtained with the respective first and second radiations having the
respective first and second wavelengths selected from the light
emitted from the surface of the object body. To select the first
radiation having the first wavelength from the light emitted from
the surface of the object body, the present apparatus uses the
first filter which permits transmission therethrough of the first
radiation having the first wavelength which is selected according
to the radiant-intensity curve corresponding to the wavelength of
the black body at the lower limit of the range of the temperature
to be measured, which is within the high radiant-intensity range in
which the radiant intensity is higher than the radiant intensity at
the normal room temperature, and which has a half width of which is
not larger than {fraction (1/20)} of the first wavelength. The
present invention further uses the second filter which permits
transmission therethrough of the second radiation having the second
wavelength which is selected within the above-indicated 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 the half width of the first
wavelength and the half width of the second wavelength.
Accordingly, optical signals having sufficiently high radiation
intensities can be obtained, leading to an accordingly high S/N
ratio of the apparatus. In addition, the first and second
wavelengths are close to each other, so that the principle of
measurement according to the present invention fully matches the
principle of measurement by a dichroic thermometer, namely, fully
meets a prerequisite that the dependency of the emissivity on the
wavelength can be ignored for two radiations the wavelengths of
which are close to each other, leading to approximation
.epsilon..sub.1=.epsilon..sub.2. Thus, the present measuring
apparatus permits highly accurate measurement of the temperature
distribution.
[0027] In each of the preferred forms of the methods and
apparatuses according to the first to fourth aspects of the present
invention, the first and second filters are preferably arranged
such that the first filter permits transmission therethrough of the
radiation having the half width which is not larger than {fraction
(1/20)} of the first wavelength, while the second filter permits
transmission therethrough of the radiation having the half width
which is not larger than {fraction (1/20)} of the second
wavelength. According to this arrangement, the radiations having
the first and second wavelengths are considered to exhibit a
sufficiently high degree of monochromatism. Therefore, the present
invention meets the prerequisite for the principle of measurement
by a dichroic thermometer, resulting in an improved accuracy of
measurement of the temperature distribution.
[0028] The first and second filters used in the temperature
measuring methods and apparatuses according to the first to fourth
aspects of the invention are preferably arranged such that the
first and second filters have transmittance values whose difference
is not higher than 30%. This arrangement assures high sensitivity
and S/N ratio, even for one of the two radiations of the first and
second wavelengths which has a lower luminance value, permitting
accurate measurement of the temperature distribution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above and other objects, features, advantages and
technical and industrial significance of the present invention will
be better understood by reading the following detailed description
of presently preferred embodiments of the invention, when
considered in connection with the accompanying drawings, in
which:
[0030] FIG. 1 is a view schematically illustrating an arrangement
of a temperature-distribution measuring apparatus constructed
according to a first embodiment of this invention;
[0031] FIG. 2 is a view for explaining a manner of determining
wavelengths .lambda..sub.1 and .lambda..sub.2 of respective first
and second filters shown in FIG. 1;
[0032] FIG. 3 is a view for explaining first and second images
G.sub.1 and G.sub.2 formed on a light detecting surface 26 of an
image detector 32 shown in FIG. 1;
[0033] FIG. 4 is a view schematically illustrating an arrangement
of an electric furnace 42 of the apparatus of FIG. 1;
[0034] FIG. 5 is a view indicating a relationship between time and
voltage V applied to an electric heater of the electric furnace,
and a relationship between time and an intensity of a radiant
energy of a stray light, when the voltage is controlled to achieve
a target value Tm of a temperature in the furnace;
[0035] FIG. 6 is a view indicating a relationship between an
intensity of the radiant energy of the stray light and the
voltage;
[0036] FIG. 7 is a flow chart for explaining a relevant part of a
control operation performed by an arithmetic control device 40
shown in FIG. 1;
[0037] FIG. 8 is a view indicating a relationship used by the
arithmetic control device 40 to obtain a surface temperature T from
a radiant intensity ratio R in step S4 of the flow chart of FIG.
7;
[0038] FIG. 9 is a view indicating a relationship used by the
arithmetic control device 40 to determine a display color from the
surface temperature T in step S5 of the flow chart of FIG. 7;
[0039] FIG. 10 is a view corresponding to that of FIG. 1,
illustrating an arrangement of a temperature-distribution measuring
apparatus according to a second embodiment of this invention;
[0040] FIGS. 11A and 11B are fragmentary views schematically
illustrating an arrangement of a shielding device 148 of the
apparatus of FIG. 1, FIG. 11A showing the shielding device in an
open state while FIG. 11B showing the shielding device in a closed
state;
[0041] FIGS. 12A and 12B are fragmentary views schematically
illustrating an arrangement of the shielding device 148, FIG. 12A
showing the shielding device in the open state while FIG. 12B
showing the shielding device in the closed state;
[0042] FIG. 13 is a flow chart for explaining a relevant part of a
control operation performed by an arithmetic control device 140
shown in FIG. 10;
[0043] FIG. 14 is a view corresponding to FIGS. 1 and 10,
illustrating another optical system of a temperature-distribution
measuring apparatus according to a third embodiment;
[0044] FIG. 15 is a view corresponding to FIGS. 1 and 10,
illustrating an optical system according to a fourth embodiment;
and
[0045] FIG. 16 is a view corresponding to FIGS. 1 and 10,
illustrating an optical system according to a sixth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] There will be described several embodiments of the present
invention referring to the accompanying drawings.
[0047] Referring first to FIG. 1, there is shown an arrangement of
a temperature-distribution measuring apparatus 10 as a first
embodiment of this invention, wherein a light emitted or radiated
from a surface of an object body 12 in a firing furnace or a
heating furnace in the form of an electric furnace 42 is split by a
half mirror (beam splitter) 14 into a first component traveling
along a first optical path 16 and a second component traveling
along a second optical path 18. The first and second optical paths
16, 18 are bent substantially at right angles by respective mirrors
20, 22, so that the first and second components are both incident
upon a half mirror 24, and are reflected by the half mirror 24, so
as to be incident upon an image detector 32 which has a CCD device
28 and a lens device 30. The CCD device 28 has a light detecting
surface 26 on which are arranged a multiplicity of photosensitive
elements. The lens device 30 is arranged to focus images of the
object body 12 on the light detecting surface 26.
[0048] The first optical path 16 is provided with a first filter 34
which permits transmission therethrough of a radiation having a
first wavelength (band) .lambda..sub.1 (e.g., center wavelength of
600 nm) and a half width of about 10 nm, for example. The second
optical path 18 is provided with a second filter 36 which permits
transmission therethrough of a radiation having a second wavelength
(band) .lambda..sub.2 (e.g., center wavelength of 650 nm) and a
half width of about 10 nm, for example. The first and second
filters 34, 36 are so-called "interference filters" permitting
transmission of radiations in selected wavelength bands, utilizing
an optical interference.
[0049] The first and second wavelengths .lambda..sub.1 and
.lambda..sub.2 are determined in the following manner, for
instance. Initially, there is obtained according to the Planck's
law a relationship between a wavelength and a radiant intensity of
a black body at a lower limit (e.g., 500.degree. C.) of a range of
the temperature to be measured. Namely, a curve L1 shown in FIG. 2
is obtained. Then, a background radiant intensity E.sub.BG of the
object body 12 is measured at a room temperature, for example, at
25.degree. C. Next, the wavelength .lambda. at a desired point
which lies on a portion of the curve L1 and which is larger than
the background radiant intensity E.sub.BG multiplied by three, that
is, larger than a value 3.times.E.sub.BG is determined to be the
first wavelength .lambda..sub.1, so that the radiant intensity used
for the measurement is high enough to prevent an error of
measurement of the temperature. Then, the second wavelength
.lambda..sub.2 is determined to be larger or smaller than the first
wavelength .lambda..sub.1 by a predetermined difference
.DELTA..lambda., which is not larger than {fraction (1/12)} of the
first wavelength .lambda..sub.1. Where the first wavelength
.lambda..sub.1 is 600 nm, for example, the second wavelength
.lambda..sub.2 is determined to be 650 nm, which is larger than the
first wavelength .lambda..sub.1 by 50 nm. This manner of
determination of the first and second wavelengths .lambda..sub.1
and .lambda..sub.2 is intended to satisfy an approximating equation
(4) which represents the principle of measurement of a dichroic
thermometer, which will be described. It is noted that the
difference .DELTA..lambda. between the first and second wavelengths
.lambda..sub.1 and .lambda..sub.2 must be equal to or larger than a
value two times as large as a half width described below, in order
to maintain a high degree of accuracy of measurement of the radiant
intensity. For the radiations of the first and second radiations
.lambda..sub.1 and .lambda..sub.2 to maintain properties of a
monochromic light, the half widths must be equal to or smaller than
{fraction (1/20)} of the center wavelengths, for example, equal to
or smaller than about 20 nm. Further, the first and second filters
34, 36 have transmittance values whose difference is 30% or lower.
If the difference were higher than 30%, the sensitivity of one of
the two radiations of the first and second wavelengths
.lambda..sub.1, .lambda..sub.2 which has a lower luminance value
would be lowered, resulting in a reduced S/N ratio of the image
detector 32 and an accordingly reduced accuracy of display of the
temperature.
[0050] Thus, the temperature-distribution measuring apparatus 10
according to the present embodiment is arranged to select the two
radiations having the respective first and second wavelengths
.lambda..sub.1 and .lambda..sub.2 from the light emitted from the
surface of the object body 12. To this end, the first filter 34
permits transmission therethrough of the radiation having the first
wavelength .lambda..sub.1 and the first half width which is not
larger than {fraction (1/20)} of that wavelength. The first
wavelength .lambda..sub.1 is selected according to the
radiant-intensity curve L1 corresponding to the wavelength of a
black body at the lower limit of the range of the temperature to be
measured, and within a high radiant-intensity range in which the
radiant intensity is sufficiently higher than the background
radiant intensity E.sub.BG at a normal room temperature. On the
other hand, the second filter 36 permits transmission therethrough
of the radiation having the second wavelength .lambda..sub.2 and
the second half width which is not larger than {fraction (1/20)} of
the second wavelength. The second wavelength .lambda..sub.2 is
selected within the above-indicated high radiant-intensity range,
such that the second wavelength .lambda..sub.2 is different from
the first wavelength .lambda..sub.1 by a predetermined difference
which is not larger than {fraction (1/12)} of the first wavelength
.lambda..sub.1 and which is not smaller than a sum of the
above-indicated first and second half widths.
[0051] In the optical system of FIG. 1, portions of the first and
second optical paths 16, 18 between the half mirror 24 and the
image detector 32 are spaced from each other by a small distance in
a direction parallel to the light detecting surface 26 of the CCD
device 28, in order to prevent overlapping of first and second
images G.sub.1 and G.sub.2 formed on the light detecting surface
26. This spaced-apart relation of the optical paths 16, 18 is
established by suitably orienting the respective mirrors 20, 22, so
that the first and second images G.sub.1 and G.sub.2 of respective
different wavelengths are formed on the light detecting surface 26
in a spaced-apart relation with each other. Described in detail by
reference to FIG. 3, the first image G.sub.1 is formed at a first
position B.sub.1 on the light detecting surface 26 of the CCD
device 28 of the image detector 32, with the radiation having the
first wavelength .lambda..sub.1 selected by the first filter 34
from the light emitted from the surface of the object body 12,
while the second image G.sub.2 is formed at a second position
B.sub.2 on the light detecting surface 26, with the radiation
having the second wavelength .lambda..sub.2 selected by the second
filter 36 from the light emitted from the surface of the object
body 12, such that the first and second positions B.sub.1 and
B.sub.2 are spaced apart from each other in the direction parallel
to the light detecting surface 26, as indicated in FIG. 3.
According to this arrangement, the multiple photosensitive elements
arranged on the light detecting surface 26 detect the radiant
intensity values at respective picture elements of the first image
G.sub.1, and the radiant intensity values at respective picture
elements of the second image G.sub.2, such that the picture
elements correspond to the respective photosensitive elements. The
mirrors 20, 22, half mirrors 14, 24 and lens device 30 cooperate
with each other to constitute an optical imaging device capable of
performing first and second wavelength-selecting steps of selecting
the first and second wavelengths for concurrently forming
respective images of the object body 12 at respective
positions.
[0052] The arithmetic control device 40 is a microcomputer
incorporating a central processing unit (CPU), a random-access
memory (RAM), a read-only memory (ROM) and an input-output
interface. The CPU operates according to a control program stored
in the ROM, to process input signals, namely, the output signals of
the multiple photosensitive elements arranged on the light
detecting surface 26, and control an image display device 41 to
display a distribution of the surface temperature of the object
body 12.
[0053] In FIG. 4, there is schematically shown the above-indicated
electric furnace 42 for heating the object body 12. The electric
furnace 42 comprises furnace walls 44 in which the object body 12
is accommodated, an electric heater 46, and a thermometer 48 in the
form of a thermocouple for detecting a temperature Tin inside the
electric furnace 42. The furnace walls 44 are made of an inorganic
heat insulating material, such as a refractory brick. The electric
heater 46 is provided on the inner surface of the side wall 44.
Reference numeral 50 denotes a temperature adjusting device for
controlling the temperature Tin inside the electric furnace 42 by
controlling an electric control signal to be applied to a driver
circuit 52 connected to the electric heater 46, to adjust a drive
voltage V to be applied to the electric heater 46 so that the
temperature Tin as detected by the radiation thermometer 48
coincides with a predetermined target value Tm.
[0054] To control the inside temperature Tin in the electric
furnace 42, the drive voltage V to be applied to the electric
heater 46 is changed or oscillated by the temperature adjusting
device 50, as shown in FIG. 5, for example. Since an intensity of a
noise, that is, an intensity of a radiant energy of a stray light
which is emitted from the furnace walls 44 toward the object body
12 and reflected by the surface of the object body 12 changes with
the drive voltage V, a relationship between the voltage V and the
intensity of the radiant energy of the stray light at an average
temperature T inside the furnace 42, as shown in FIG. 6, is
experimentally obtained for each of the respective first and second
radiations having the respective wavelengths .lambda..sub.1 and
.lambda..sub.2. This relationship is stored in the ROM of the
arithmetic control device 40, so that the intensity of the radiant
energy of the stray light at each picture element, which is
undesirably included in the intensity of the radiant energy
detected by the image detector 32 at each picture element as an
intensity of the radiant energy emitted from the object body 12, is
obtained according to the relationship. The intensity of the
radiant energy of the stray light taken along the ordinate of the
coordinate system of FIG. 6 is obtained by multiplying an intensity
of the radiant energy emitted from the furnace walls 44 and the
electric heater 46 by a reflectivity value of the object body 12.
In this respect, it is noted that the reflectivity is obtained by
subtracting an absorptance value of the object body 12 from 1, when
the transmittance of the object body 12 is substantially 0. The
drive voltage V periodically oscillated by the temperature
adjusting device 50 may be represented by the following equation
(1):
V=f(Tin) sin .omega.t (1)
[0055] Referring to the flow chart of FIG. 7, there will be
described a relevant portion of a control operation of the
arithmetic control device 40. The control operation is initiated
with step S1 to read the output signals of the multiple
photosensitive elements arranged on the light detecting surface 26,
for obtaining radiant intensity values E.sub.1ij at respective
picture elements of the first image G.sub.1, and radiant intensity
values E.sub.2ij at respective picture elements of the second image
G.sub.2. Then, the control flow goes to step S2 corresponding to a
stray-light noise eliminating step or means, to periodically
calculate or determine, with a constant calculating cycle time, the
intensity of the radiant energy of the stray light adversely
affecting each of the first and second radiations, based on an
actual value of the drive voltage V applied from the driver circuit
52 to the electric heater 46, and according to the relationship
shown in FIG. 6, by way of example, which is stored in the ROM. The
cycle time is sufficiently shorter than the oscillating period of
the voltage V. For example, the cycle time is several milliseconds.
The intensity .DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the radiant
energy of the stray light thus obtained for each of the first and
second radiations is subtracted from the radiant intensity (the
intensity of the radiant energy) E.sub.1ij, E.sub.2ij at each
picture element in the first and second images G.sub.1, G.sub.2, as
detected in step S1, according to the following equations (2) and
(3), for example, so as to rectify or adjust the detected intensity
E.sub.1ij, E.sub.2ij of the radiant energy emitted from the object
body 12, to obtain a net value E.sub.1ijnet, E.sub.2ijnet of the
intensity of the radiant energy originated from the object body 12
only.
E.sub.1ijnet=E.sub.1ij-.DELTA.E.sub.1ij (2)
E.sub.2ijnet=E.sub.2ij-.DELTA.E.sub.2ij (3)
[0056] Then, the control flow goes to step S3 corresponding to a
radiant intensity ratio calculating step or means, to calculate a
radiant intensity ratio R.sub.ij(=E.sub.1ijnet/E.sub.2ijnet or
E.sub.2ijnet/E.sub.1ijnet) at each pair of corresponding picture
elements of the first and second images G.sub.1 and G.sub.2 which
are formed at the respective first and second positions B.sub.1 and
B.sub.2 on the light detecting surface 26. The radiant intensity
ratio R.sub.ij is a ratio of the radiant intensity value
E.sub.1jinet of the first wavelength .lambda..sub.1 which has been
detected by the photosensitive element at each picture element of
the first image G.sub.1 and from which the intensity
.DELTA.E.sub.1ij of the radiant energy of the stray light has been
subtracted, to the radiant intensity value E.sub.2jinet of the
second wavelength .lambda..sub.2 which has been detected by the
photosensitive element at the corresponding picture element of the
second image G.sub.2 and from which the intensity .DELTA.E.sub.2ij
of the radiant energy of the stray light has been subtracted. The
ratio R.sub.ij may be a ratio E.sub.2ijnet/E.sub.1ijnet. Then, step
S4 corresponding to a temperature calculating step or means is
implemented to calculate a temperature T.sub.ij at each picture
element of the image of the object body 12, on the basis of the
calculated actual radiant intensity ratio R.sub.ij at each pair of
corresponding picture elements of the first and second images
G.sub.1, G.sub.2, and according to a predetermined relationship
between the radiant intensity R and the temperature T as shown in
FIG. 8, by way of example. Data representative of the predetermined
relationship are stored in the ROM of the arithmetic control device
40. For instance, the relationship as shown in FIG. 8 may be
represented by the following equation (4), which is an
approximating equation representing the principle of measurement of
a dichroic thermometer. The equation (4) is formulated to permit
determination of the surface temperature T of the object body 12 on
the basis of the ratio R of the radiant intensity values at the
respective different wavelengths .lambda..sub.1 and .lambda..sub.2,
without having to use the emissivity of the object body 12. In the
following equations, the second wavelength .lambda..sub.2 is larger
than the first wavelength .lambda..sub.1, and "T", "C.sub.1" and
"C.sub.2" respectively represent the absolute temperature, and
first and second constants of Planck's law of radiation.
R=(.lambda..sub.2/.lambda..sub.1).sup.5 exp
[(C.sub.2/T).multidot.(1/.lamb- da..sub.2-1/.lambda..sub.1)]
(4)
[0057] The above equation (4) is obtained in the following manner.
That is, it is known that an intensity (energy) Eb of a radiation
of a wavelength .lambda. emitted from a unit surface area of a
black body for a unit time, and the wavelength .lambda. satisfy the
following equation (5), which is the Planck's equation. It is also
known that the following equation (6), which is the Wien's
approximating equation, is satisfied when exp
(C.sub.2/.lambda.T)>>1. For ordinary bodies having gray
colors, the following equation (7) is obtained by converting the
equation (6) with insertion of the emissivity .epsilon.. The
following equation (8) is obtained from the equation (7), for
obtaining the ratio R of the radiant intensity values E.sub.1 and
E.sub.2 of the two wavelength values .lambda..sub.1 and
.lambda..sub.2. Where the two wavelength values .lambda..sub.1 and
.lambda..sub.2 are close to each other, the dependency of the
emissivity .epsilon. on the wavelength can be ignored, that is,
.epsilon..sub.1=.epsilon..sub.2. Thus, the above equation (4) is
obtained. Accordingly, the temperatures T of object bodies having
different emissivity values .epsilon. can be obtained without an
influence of the emissivity.
Eb=C.sub.1/.lambda..sup.5 [expC.sub.2/.lambda.T)-1] (5)
Eb=C.sub.1 exp (-C.sub.2/.lambda.T)/.lambda..sup.5 (6)
E=.epsilon..multidot.C.sub.1 exp
(-C.sub.2/.lambda.T)/.lambda..sup.5 (7)
R=(.epsilon..sub.1/.epsilon..sub.2)(.lambda..sub.2/.lambda..sub.1).sup.5
exp [(C.sub.2/T).multidot.(1/.lambda..sub.2-1/.lambda..sub.1)]
(8)
[0058] After the temperature T.sub.ij at each picture element of
the image of the object body 12 has been calculated in step S4 as
described above, the control flow goes to step S5 corresponding to
a temperature-distribution displaying step or means, to display a
distribution of the surface temperature of the object body 12, on
the basis of the actual temperature T.sub.ij calculated at each
picture element, and according to a predetermined relationship
between the temperature T and the display color. Data
representative of the predetermined relationship are stored in the
ROM of the arithmetic control device 40. FIG. 9 shows one example
of the predetermined relationship between the temperature T and the
display color. In this case, the distribution of the surface
temperature of the object body 12 is shown in predetermined
different colors.
[0059] There will be described an experimentation conducted by the
present inventors, using the optical system shown in FIG. 1 wherein
a CCD camera (model ST-7 available from Santa Barbara Instruments
Group) comprising a telephoto lens "AF Zoom Nikkor ED 70-300 mm
F4-5.6D" available from Nippon Kougaku Kabushiki Kaisha ("Nikon"),
Japan, is employed as the image detector 32, and each of the half
mirrors 14, 24 is a half mirror of BK7 available from Sigma Koki,
Japan, which is provided with a chrome plating for a visible
radiation. The half mirror 14, 24 reflects 30% of an incident
radiation and transmits 30% of the incident radiation. The mirrors
20, 22 are aluminum plane mirrors of BK7 available from Sigma Koki,
Japan. The first filter 34 permits transmission therethrough of a
radiation having a wavelength of 600 nm and a half width of 10 nm,
while the second filter 36 permits transmission therethrough of a
radiation having a wavelength of 650 nm and a half width of 10 nm.
The object body 12 used in the experimentation is an alumina
substrate (50.times.50.times.0.8 mm). This object body 12 was
placed in a central part of the electric furnace 42 provided with a
window portion for inspecting the inside therethrough, and the
temperature of the object body 12 was repeatedly measured according
to the steps of the flow chart shown in FIG. 7, while the
temperature as detected by the thermometer 48 (thermocouple) was
held at 1000.degree. C. In the experimentation, the repeatedly
measured temperature of the object body 12 ranged from 995.degree.
C. to 1005.degree. C.
[0060] A first comparative experimentation was made by using the
same optical system and in the same steps as in the experimentation
described above, except that the first comparative experimentation
employed, in step S2 to remove the stray light noise, an average
value of the periodically oscillated drive voltage V applied to the
electric heater 46, for the purpose of determining the radiant
intensity values .DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the stray
light. In this first comparative experimentation, the repeatedly
measured temperature of the object body 12 ranged from 992.degree.
C. to 1008.degree. C. Further, a second comparative experimentation
was made by the same optical system and according to the same steps
as in the experimentation using the apparatus of the first
embodiment, except that the step S2 of removing the stray light
noise in the flow chart shown in FIG. 7 was not implemented in the
second comparative experimentation. In this second comparative
experimentation, the repeatedly measured temperature of the object
body 12 ranged from 1005.degree. C. to 1025.degree. C.
[0061] As described above, the present first embodiment is arranged
to first calculate the intensity values .DELTA.E.sub.1ij,
.DELTA.E.sub.2ij of the radiant energy of the stray light, which is
emitted from the inner wall surfaces of the electric furnace 42
toward the object body 12 and reflected by the surface of the
object body 12, at each picture element and with regard to each of
the first and second radiations having the respective first and
second wavelengths .lambda..sub.1 and .lambda..sub.2, based on the
voltage V applied to the electric heater 46 of the electric furnace
42, and according to the stored relationship shown in FIG. 6, by
way of example. Then, the temperature T.sub.ij of the object body
12 is calculated at each picture element of its image, on the basis
of the radiant intensity ratio R.sub.ij, which is a ratio of the
actual intensity E.sub.1ijnet of the radiant energy of the first
radiation, obtained by subtracting the intensity .DELTA.E.sub.1ij
of the radiant energy of the stray light (adversely affecting the
first radiation) from the intensity E.sub.1ij of the radiant energy
actually detected as an intensity of the radiant energy of the
first radiation (selected from the light emitted from the object
body 12), to the actual intensity E.sub.2ijnet of the radiant
energy of the second radiation, obtained by subtracting the
intensity .DELTA.E.sub.2ij of the radiant energy of the stray light
(adversely affecting the second radiation) from the intensity
E.sub.2ij of the radiant energy actually detected as an intensity
of the radiant energy of the second radiation (selected from the
light emitted from the object body 12). Thus, the present measuring
apparatus permits highly accurate measurement of the surface
temperature of the object body 12 in the electric furnace 42.
[0062] Further, the present embodiment is arranged such that the
radiant intensity values .DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the
stray light included in the respective first and second radiations
are periodically obtained with a cycle time sufficiently shorter
than the cycle time of oscillation of the voltage V, and the
radiant intensity values .DELTA.E.sub.1ij, .DELTA.E.sub.2ij are
eliminated from the detected radiant intensity values E.sub.1ij,
E.sub.2ij of the first and second radiations, respectively, so as
to obtain true values of radiant intensity values E.sub.1ijnet,
E.sub.2ijnet of the first and second radiations. The surface
temperature of the object body 12 in the electric furnace 42 is
obtained based on the thus obtained true values E.sub.1ijnet,
E.sub.2ijnet of the intensities of the radiant energies of the
first and second radiations. Thus, the accuracy of the measurement
is further enhanced.
[0063] As described above, the present embodiment is arranged to
calculate the temperature T.sub.ij of the object body 12 at each
picture element of its image, on the basis of the radiant intensity
ratio R.sub.ij at each pair of corresponding picture elements of
the first and second images G.sub.1 and G.sub.2 obtained with the
respective first and second radiations having the first and second
wavelengths .lambda..sub.1 and .lambda..sub.2 selected from the
light emitted from the surface of the object body 12. To select the
first radiation having the first wavelength .lambda..sub.1 from the
light emitted from the surface of the object body 12, the optical
system of the present embodiment uses the first filter 34 which
permits transmission therethrough of the radiation having the first
wavelength .lambda..sub.1 which is selected according to the
radiant-intensity curve L1 corresponding to the wavelength of the
black body at the substantially lower limit of the range of the
temperature to be measured, and which is within a high
radiant-intensity range in which the radiant intensity is higher
than the background radiant intensity E.sub.BG at a normal room
temperature. The optical system further uses the second filter 36
which permits transmission therethrough of the second radiation
having the second wavelength .lambda..sub.2 which is selected
within the above-indicated high radiant-intensity range, such that
the second wavelength .lambda..sub.2 is different from the first
wavelength .lambda..sub.1 by a predetermined difference which is
not larger than {fraction (1/12)} of the first wavelength
.lambda..sub.1 and which is not smaller than a sum of a half width
.DELTA..lambda..sub.1 of the first wavelength .lambda..sub.1 and a
half width .DELTA..lambda..sub.2 of the second wavelength
.lambda..sub.2. Accordingly, optical signals having sufficiently
high radiation intensities can be obtained, leading to an
accordingly high S/N ratio of the image detector 32. In addition,
the first and second wavelengths .lambda..sub.1 and .lambda..sub.2
are close to each other, so that the principle of measurement of
the present optical system fully matches the principle of
measurement of a dichroic thermometer, namely, fully meets a
prerequisite that the dependency of the emissivity on the
wavelength can be ignored for two radiations the wavelengths of
which are close to each other, leading to approximation
.epsilon..sub.1=.epsilon..sub.2. Thus, the present measuring
apparatus permits highly accurate measurement of the temperature
distribution.
[0064] Further, the present embodiment is arranged such that the
first filter 34 permits transmission therethrough of the radiation
having the half width .DELTA..lambda..sub.1 which is not larger
than {fraction (1/20)} of the first wavelength .lambda..sub.1,
while the second filter 36 permits transmission therethrough of the
radiation having the half width .DELTA..lambda..sub.2 which is not
larger than {fraction (1/20)} of the second wavelength
.lambda..sub.2, so that the radiations having these first and
second wavelengths .lambda..sub.1 and .lambda..sub.2 are considered
to exhibit a sufficiently high degree of monochromatism.
Accordingly, the present embodiment meets the prerequisite for the
principle of measurement by a dichroic thermometer, resulting in an
improved accuracy of measurement of the temperature
distribution.
[0065] In addition, the present embodiment is arranged such that
the first and second filters 34, 36 have transmittance values whose
difference is not higher than 30%, so that the present optical
system has high sensitivity and S/N ratio, even for one of the two
radiations of the first and second wavelengths .lambda..sub.1,
.lambda..sub.2 which has a lower luminance value, permitting
accurate measurement of the temperature distribution.
[0066] While the first preferred embodiment of the present
invention has been described in detail by reference to FIGS. 1-9,
it is to be understood that the present first embodiment may be
modified.
[0067] In step S2 of flow chart of FIG. 7 in the first embodiment,
the intensity values .DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the
radiant energies of the stray light are periodically calculated
based on the drive voltage V, with a cycle time sufficiently
shorter than the cycle time of oscillation of the voltage V applied
to the electric heater 42. However, the intensity values
.DELTA.E.sub.1ij, .DELTA.E.sub.2ij may be calculated based on a
moving average of the oscillated voltage V.
[0068] In the first embodiment, the thermometer 48 for detecting
the temperature inside the electric furnace 42 is a thermocouple.
However, the thermometer may be any other temperature sensors such
as an optical pyrometer.
[0069] There will next be described in detail a second embodiment
of the present invention, in the form of a temperature-distribution
measuring apparatus 110, which is constructed as schematically
shown in FIG. 10. Many elements of the apparatus 110 are similar to
the corresponding elements of the apparatus 10 according to the
first embodiment. Therefore, the similar elements will be denoted
with the same reference numerals and description thereof is
omitted, and only the elements specific to the apparatus 110 will
be described in detail. An optical system including mirrors 14, 24,
20, 22, an image detector 32 and a first and a second filter 34, 36
are similar to those of the first embodiment. However, in the
apparatus 110 according to the second embodiment, an object body 12
is located and heated in a heating furnace 142, which is different
in construction from the electric furnace 42 of the apparatus 10.
The heating furnace 142 will be described later.
[0070] An arithmetic control device 140 is a micro-computer
incorporating a central processing unit (CPU), a random-access
memory (RAM), a read-only memory (ROM) and an input-output
interface, similarly to the arithmetic control device 40 in the
first embodiment. However, the manner in which the arithmetic
control device 140 operates to calculate the surface temperature of
the object body 12, or to remove the stray light noise from the
detected intensity of the radiant energy of the light emitted from
the object body 12, is different from that of the first embodiment.
This different manner will be described later. The apparatus 110 of
FIG. 10 uses the same image display device 41 as used in the first
embodiment, and the description thereof is omitted.
[0071] Referring next to FIG. 11, the heating furnace 142 has the
furnace walls 44 as in the first embodiment and is provided with
burners 146 disposed in the side furnace wall 44, and a shielding
device 148 which is disposed between the burners 146 and the object
body 12 and operable between its open state and closed state. As
shown in enlargement in the fragmentary view of FIG. 12, the
shielding device 148 comprises a frame 150, a plurality of
shielding plates 152 each of which is pivotably supported by the
frame 150, and a drive device 154 for driving or pivoting the
plurality of shielding plates 152 to their open state or closed
state. FIG. 11A and FIG. 12A show the shielding device 148 placed
in the open state, while FIG. 11B and FIG. 12B show the shielding
device 148 placed in the closed state. The outer surface (on the
side of the heat source, i.e., the burners 146) of each shielding
plate 152 is provided with a coating or a thin film of a material
having a relatively high value of reflectivity, such as platinum or
silver, while the inner surface (on the side of the object body 12)
is provided with a black coating having a relatively high value of
emissivity, so that the shielding plates 152 in the closed state
reflect or absorb the noise or stray radiations which are emitted
from the burners 146 (heat source) and side furnace walls 44 and
which have respective intensities. Accordingly, the stray
radiations emitted from the burners 146 and side furnace walls 44
and reaching the object body 12 are evenly distributed around the
object body 12 in the presence of the shielding plates 152 in the
paths of traveling of the stray radiations. In other words, a local
variation in the radiant intensity of the stray light is presented
by the shielding plates 152 in its closed state. It is noted that
above-described coating having relatively high reflectivity or high
emissivity may be provided on both surfaces of the shielding plates
152.
[0072] Referring to the flow chart of FIG. 13, there will be
described a relevant portion of a control operation of the
arithmetic control device 140. The control operation is initiated
with step S11 corresponding to a light shielding step or means, in
which the shielding device 148 which has been held in its open
state (as shown in FIG. 11A and FIG. 12A) during heating of the
object body 12 in the heating furnace 142 in a heating step is
brought into its closed state (as shown in FIG. 11B and FIG. 12B).
According to this arrangement, the intensities of the radiations
emitted from the side furnace walls 44 and the burners 146 toward
the object body 12 are made uniform. The step S11 is followed by
step S12 corresponding to a radiant-energy detecting step or means
and to the step S1 of the flow chart of FIG. 7, in which the output
signals of the multiple photosensitive elements arranged on the
light detecting surface 26 are read for obtaining radiant intensity
values E.sub.1ij at respective picture elements of the first image
G.sub.1, and radiant intensity values E.sub.2ij at respective
picture elements of the second image G.sub.2, while the shielding
device 148 is held in its closed state.
[0073] Then, the control flow goes to step S13 corresponding to a
stray-light noise eliminating step or means and to the step S2 of
the flow chart of FIG. 7, to first obtain the intensity
.DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the radiant energy of the
stray light for each of the first and second radiation, based on a
temperature of the shielding device 148 and according to a
predetermined relationship between the temperature of the shielding
device 148 and the intensity of the radiant energy of the stray
light, and to subtract the intensity .DELTA.E.sub.1ij,
.DELTA.E.sub.2ij of the radiant energy of the stray light from the
radiant intensity E.sub.1ij, E.sub.2ij at the corresponding picture
element in the first and second image G.sub.1, G.sub.2, as detected
in step S12, according to the above equations (2), (3), so as to
eliminate the noise or the intensity of the radiant energy of the
stray light to obtain a net value E.sub.1ijnet, E.sub.2ijnet of the
intensity of the radiant energy originated from the object body 12
only, at each picture element in the first and second image
G.sub.1, G.sub.2. Described more specifically, the intensity
.DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the radiant energy of the
stray light, which is included in the detected intensity of the
radiant energy of the first and second radiation which is emitted
from the shielding device 148 held in its closed state toward the
object body 12 and then reflected by the surface of the object body
12, is eliminated from the detected radiant intensity E.sub.1ij,
E.sub.2ij. The predetermined relationship between the temperature
of the shielding device 148 and the intensity .DELTA.E.sub.1ij,
.DELTA.E.sub.2ij of the radiant energy of the stray light is
obtained by actually measuring the intensity of the radiant energy
at each temperature of the shielding device 148 in its closed
state, and multiplying the intensity of the radiant energy of the
stray light by the reflectivity of the object body 12. In this
respect, it is noted that the reflectivity is obtained by
subtracting the emissivity or absorptance of the object body 12
from 1, when the transmittivity of the object body 12 is
substantially 0. Data representative of the predetermined
relationship are stored in the ROM of the arithmetic control device
140.
[0074] Then, the flow chart goes to step S14 corresponding to a
radiant intensity ratio calculating step or means and to the step
S3 of the flow chart of FIG. 7, to calculate a radiant intensity
ratio R.sub.ij (=E.sub.1jinet/E.sub.2ijnet, or
E.sub.2jinet/E.sub.1ijnet) at each pair of corresponding picture
elements of the first and second images G.sub.1 and G.sub.2, in the
same manner as in the step S3. Then, step S15 corresponding to a
temperature calculating step or means and to the step S4 in the
flow chart of FIG. 7, is implemented to calculate a temperature
T.sub.ij, in the same manner as in the step S4.
[0075] After the temperature T.sub.ij at each picture element of
the image of the object body 12 has been calculated in step S15 as
described above, the control flow goes to step S16 corresponding to
a temperature distribution displaying step or means and to the step
S5 in the flow chart of FIG. 7, to display a distribution of the
surface temperature of the object body 12, in the same manner as in
step S5.
[0076] There will be described an experimentation conducted by the
present inventors, using the optical system shown in FIG. 10
wherein a CCD camera (model ST-7 available from Santa Barbara
Instruments Group) comprising a telephoto lens "AF Zoom Nikkor ED
70-300 mm F4-5.6D" available from Nippon Kougaku Kabushiki Kaisha
("Nikon"), Japan, is employed as the image detector 32, and each of
the half mirrors 14, 24 is a half mirror of BK7 available from
Sigma Koki, Japan, which is provided with a chrome plating for a
visible radiation. The half mirror 14, 24 reflects 30% of an
incident radiation and transmits 30% of the incident radiation. The
mirrors 20, 22 are aluminum plane mirrors of BK7 available from
Sigma Koki, Japan. The first filter 34 permits transmission
therethrough of a radiation having a wavelength of 600 nm and a
half width of 10 nm, while the second filter 36 permits
transmission therethrough of a radiation having a wavelength of 650
nm and a half width of 10 nm. The object body 12 used in the
experimentation is an alumina substrate (50.times.50.times.0.8 mm).
This object body 12 was placed in a central part of the heating
furnace 142 provided with a window portion for inspecting the
inside of the furnace 142 therethrough and having an electric
heater, in place of the burners 146, and the temperature within the
furnace was raised from the room temperature up to 1000.degree. C.
at a rate of 10.degree. C./min and held at 1000.degree. C. for one
hour. Then, the temperature of the object body 12 was repeatedly
measured according to the steps of the flow chart shown in FIG. 13,
while the temperature in the heating furnace 142 which was detected
by the thermometer 48 (thermocouple) was held at 1000.degree. C. In
the experimentation, the repeatedly measured temperature of the
object body 12 ranged from 995.degree. C. to 1005.degree. C.
[0077] A first comparative experimentation was made by using the
same optical system and in the same steps as in the experimentation
described just above, except that the step S13 of removing the
stray light noise was not implemented in the first comparative
experimentation. In this first comparative experimentation, the
repeatedly measured temperature of the object body 12 ranged from
1005.degree. C. to 1015.degree. C. Further, a second comparative
experimentation was made by using the same optical system and in
the same steps as in the experimentation described above, except
that the shielding device 148 was not provided and that the step
S13 was not implemented in the second comparative experimentation.
In the second comparative experimentation, the repeatedly measured
temperature of the object body 12 ranged from 1005.degree. C. to
1025.degree. C.
[0078] As described above, the second embodiment of the present
invention is arranged such that: the object body 12 is heated in
the heating step, while the shielding device disposed between the
side furnace walls 44 of the heating furnace 142 and the object
body 12 is in its open state; the intensity of the radiant energy
emitted from the object body 12 is detected in step S12
corresponding to the radiant-energy detecting step or means, while
the shielding device 148 is closed; and the temperature at each
picture element of the image of the object body 12 is calculated in
the step S15 corresponding to the temperature calculating step or
means, based on the intensity of the radiant energy emitted from
the object body 12 as detected in the step S12. Accordingly, the
stray light noise or the intensity of the radiant energy of the
stray light, which is emitted from the side furnace walls 44 and
the burners 146 toward the object body 12 and reflected by the
surface of the object body 12 and which is included in the
intensity of the radiant energy detected as the intensity of the
radiant energy emitted from the object body 12, is evenly
distributed by the shielding device 148. The even distribution of
the radiant intensity of the stray light is obtained according to
the predetermined relationship and is easily eliminated from the
detected intensity of the radiant energy emitted from the object
body 12. Thus, the surface temperature of the object body 12 in the
heating furnace 142 can be measured with high accuracy.
[0079] In addition, according to the present second embodiment, the
radiant energy emitted from the inner wall surface of the heating
furnace 142 and having a locally uneven intensity is cut or shut
off by the shielding device 148, which radiates a radiant energy
having an even intensity toward the object body 12. Based on the
temperature of the shielding device 148, the intensity
.DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the radiant energy of the
stray light which is emitted toward the object body 12 and
reflected by the surface of the object body 12 is obtained. Then,
the temperature of the object body 12 at each pair of the
corresponding picture elements is calculated based on the intensity
E.sub.1ijnet, E.sub.2ijnet which is obtained by subtracting the
intensity .DELTA.E.sub.1ij, .DELTA.E.sub.2ij of the radiant energy
of the stray light from the intensity E.sub.1ij, E.sub.2ij detected
at each pair of corresponding picture elements as the intensity of
the radiant energy emitted form the object body 12. Thus, the
surface temperature of the object body 12 can be measured with high
accuracy.
[0080] Further, according to the second embodiment, the intensity
values .DELTA.E.sub.1ij, .DELTA.E.sub.2ij are periodically
calculated with a predetermined constant cycle time, and are
eliminated from the intensity E.sub.1ij, E.sub.2ij actually
detected as the intensity of the radiant energy emitted from the
object body 12, to obtain the intensity E.sub.1ijnet, E.sub.2ijnet,
based on which the surface temperature of the object body 12 in the
heating furnace 142 is iterately determined. Thus, the accuracy of
the measurement is further improved.
[0081] The present second embodiment also exhibits some of the
advantages of the first embodiment.
[0082] It is to be understood that the illustrated embodiments of
FIGS. 1-13 may be modified. Several examples of such modifications
will be described.
[0083] In the illustrated embodiments, the apparatus 10, 110
utilizes the principle of a dichroic thermometer, according to
which two radiations having respective different wavelengths are
selected from the light emitted from the object body 12. However, a
temperature-distribution measuring apparatus utilizing the
principle of a monochromatic thermometer or the principle of a
polychroic thermometer may be employed. In the last case, three or
more radiations having respective wavelengths are selected from the
light emitted from the object body 12.
[0084] It is noted that the inspection opening of the electric
furnace 42 and the heating furnace 142, through which the radiant
intensity emitted from the object body 12 in the furnace 42, 142 is
detected, may be provided in any furnace wall, i.e., in any one of
the top, bottom and side walls of the furnace.
[0085] In place of the optical system employed in the illustrated
embodiments, any one of optical systems shown in FIGS. 14, 15 and
16 may be employed. The optical systems will be described.
[0086] In FIG. 14, there is schematically illustrated optical
system suitable for embodying the present invention. In FIG. 14, a
pair of mirrors 60, 62 are disposed such that each of these mirrors
60, 62 is pivotable about its fixed end between a first position
indicated by broken line and a second position indicated by solid
line. When the mirrors 60, 62 are placed in the first position, a
light emitted from the surface of the object body 12 is incident
upon the image detector 32 along the first optical path 16. When
the mirrors 60, 62 are placed in the second position, the light is
incident upon the image detector 32 along the second optical path
18. As in the preceding embodiments, the first optical path 16 is
provided with the first filter 34, while the second optical path 18
is provided with the second filter 36, so that the first and second
images G.sub.1 and G.sub.2 are formed by the respective two
radiations having the respective first and second wavelengths
.lambda..sub.1 and .lambda..sub.2, with a predetermined time
difference.
[0087] In still another optical system shown in FIG. 15, a rotary
disc 66 is disposed such that the rotary disc 66 is rotatable by an
electric motor 64, about an axis which is parallel to an optical
path extending between the object body 12 and the image detector 32
and which is offset from the optical path in a radial direction of
the rotary disc 66, by a suitable distance. The rotary disc 66
carries the first filter 34 and the second filter 36 such that
these first and second filters 34, 36 are selectively aligned with
the optical path by rotation of the rotary disc 66 by the electric
motor 64. The first image G.sub.1 is formed with the radiation
which has the first wavelength .lambda..sub.1 and which has been
transmitted through the first filter 34, and the second image
G.sub.2 is formed with the radiation which has the second
wavelength .lambda..sub.2 and which has been transmitted through
the second filter 36. These first and second images G.sub.1 and
G.sub.2 are successively obtained by rotating the rotary disc
66.
[0088] In a further another optical system shown in FIG. 16, the
light emitted from the surface of the object body 12 is split by
the half mirror 14 into a first component traveling along the first
optical path 16 and a second component traveling along the second
optical path 18. The first optical path 16 is provided with the
image detector 32. On the other hand, the second optical path 16 is
provided with another image detector 32'. The first and second
filters 34, 36 may be disposed in the image detector 32, 32',
respectively. In the present embodiment, too, the first image
G.sub.1 is formed with the radiation having the first wavelength
.lambda..sub.1 which is selected from the light emitted from the
surface of the object body 12, as a result of transmission of the
light through the first filter 34, and at the same time the second
image G.sub.2 is formed with the radiation having the second
wavelength .lambda..sub.2 which is selected from the light from the
object body 12 as a result of transmission of the light through the
second filter 36.
[0089] In the illustrated embodiments, the first and second
wavelengths .lambda..sub.1 and .lambda..sub.2 are selected
according to the radiant-intensity curve L1 of FIG. 2 corresponding
to the wavelength of the black body at the lower limit of the range
of the temperature to be measured, and which is within a high
radiant-intensity range in which the radiant intensity is at least
three times the background radiant intensity E.sub.BG at a normal
room temperature. However, the radiant intensity need not be at
least three times the background radiant intensity E.sub.BG, since
the principle of the present invention is satisfied as long as the
radiant intensity is sufficiently higher than the background
radiant intensity E.sub.BG at the normal room temperature.
[0090] In the illustrated embodiments, the half width
.DELTA..lambda..sub.1 of the first wavelength .lambda..sub.1 is
equal to or smaller than {fraction (1/20)} of the first wavelength
.lambda..sub.1, and the half width .DELTA..lambda..sub.2 of the
second wavelength .lambda..sub.2 is equal to or smaller than
{fraction (1/20)} of the second wavelength .lambda..sub.2. However,
the half widths need not be equal to or smaller than {fraction
(1/20)} of the wavelength values, but may be slightly larger than
{fraction (1/20)} of the wavelength values, according to the
principle of the invention.
[0091] In the illustrated embodiments, a difference of the
transmittance values of the first and second filters 34, 36 is
equal to or smaller than 30%. However, the difference need not be
equal to or smaller than 30%, but may be slightly larger than 30%,
according to the principle of the invention.
[0092] Although the surface temperature of the object body 12 is
indicated in different colors in step S5 of FIG. 7 and in step S6
of FIG. 13, the surface temperature may be indicated in any other
fashion, for example, by contour lines or in different density
values.
[0093] While the image detector 32, 32' used in the illustrated
embodiments uses the CCD device 28 having the light detecting
surface 26, the image detector may use any other light sensitive
element such as a color imaging tube.
[0094] In the illustrated embodiments, the picture elements
correspond to the respective photosensitive elements. However, a
plurality of photosensitive elements adjacent to each other may
correspond to one picture element of the images G.sub.1, G.sub.2,
or the image displayed by the display device 41.
[0095] It is noted that the relationship shown in FIG. 8 is used in
the case where the radiant intensity ratio R.sub.ij is a ratio of
the intensity E.sub.1jinet of the radiant energy of the first
radiation to the intensity E.sub.2ijnet of the radiant energy of
the second radiation. In a case where the radiant intensity ratio
R.sub.ij is a ratio of the intensity E.sub.2jinet of the radiant
energy of the second radiation to the intensity E.sub.1ijnet of the
radiant energy of the first radiation, the direction of the slope
of the graph is reversed.
[0096] It is to be understood that the present invention may be
embodied with various other changes, modifications and
improvements, which may occur to those skilled in the art, in the
light of the technical teachings of the present invention which
have been described.
* * * * *