Method of and an apparatus for measuring surface temperature and emmissivity of a heated material

• US 4,465,382 A
• Filed: 03/02/1981
• Issued: 08/14/1984
• Est. Priority Date: 03/04/1980
• Status: Expired due to Fees

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel Corporation
• Inventors: Iuchi, Tohru, Watanabe, Kunitoshi, Shibata, Toshihiko, Kawamura, Tetsuro
• Primary Examiner(s): Frankfort, Charles
• Assistant Examiner(s): Corr, Denis E.
• Application Number:
  US06/239,727
• Time in Patent Office: 1,261 Days
• Field of Search: 73/355 EM, 73/355 R, 374/9, 374/126
• US Class Current: 374/9
• CPC Class Codes: G01J 2005/0074 having separate detection of emissivity
• CPC Class Codes: G01J 5/0044 Furnaces, ovens, kilns G01J5/0007, G01J5/004 take precedence
• CPC Class Codes: G01J 5/0805 Means for chopping radiation
• CPC Class Codes: G01J 5/532 using a reference heater of the emissive surface type, e.g. for selectively absorbing materials

Abstract

When a steel sheet or the like is heated in a furnace to a temperature somewhat higher than the room temperature and is still or moved, its temperature can be measured by detecting the radiant energy therefrom. The measurement is normally difficult due to the influence of background noise of radiant energy from the surroundings, change of the transmittance factor of the environment or atmosphere for radiant energy, and change of the emissivity of the object to be measured. In order to remove such causes of errors and to correctly measure the temperature by detecting radiant energy, a radiometer and a black body radiator are disposed symmetrically and specularly with respect to the normal to a surface of an object to be measured, and two different amounts of radiant energies are emitted from the black body radiator, and the emissivity of the object to be measured is determined from the detected values from the radiometer, the two temperature values of the black body radiator, and the diffusely reflecting factor associated with the object to be measured, whereby correct measurement of the surface temperature of the object to be measured can be done. Embodiments for implementing this method are proposed.

Claims

1. A method for measuring the surface temperature T₁ and emissivity ε

(θ

) at an angle θ

, of an object being heated in a furnace, the surface of said object being non-specularly reflecting, said furnace having a wall temperature T₄, said method comprising the steps of;

determining a diffusely reflecting factor p for the material and surface roughness of said object where said roughness inhibits accurate measurement of T₁ should specularity of the surface be assumed, to account for the non-specularly reflecting condition of said surface;

measuring T₄ ;

positioning a radiometer and at least one black body radiator specularly and symmetrically at angles θ

with respect to a normal to said surface of said object;

with said black body radiator at a temperature T₂, emitting radiant energy E_b (T₂) toward said surface;

with said radiometer, detecting radiant energy E₂ as a result of energy emitted by and reflected from said surface;

with said black body radiator at a temperature T₃ ≠

T₂, emitting radiant energy E_b (T₃) toward said surface;

with said radiometer, detecting radiant energy E₃ as a result of energy emitted by and reflected from said surface;

determining ε

(θ

) in accordance with the relationships ##EQU32## determining T₁ in accordance with the relationship ##EQU33##

2. A method according to claim 1, wherein the optical path between said surface of said object and said radiometer has a transmittance factor K and said emissivity ε

(θ

) and temperature T₁ are determined in accordance with the relationships;

##EQU34##

3. An apparatus for measuring the surface temperature T₁ and emissivity ε

(θ

) at an angle θ

, of an object being heated in a furnace, the surface of said object being non-specularly reflecting and said furnace having a wall temperature T₄, said apparatus comprising;

a radiometer and at least one black body radiator specularly and symmetrically positioned at angles θ

with respect to a normal to said surface of said object;

means for operating said radiator at a temperature T₂ to emit radiant energy E_b (T₂) toward said surface of said object;

first means for detecting with said radiometer the radiant energy E₂ resulting from energy emitted by and reflected from said surface of said object while E_b (T₂) is emitted;

means for operating said radiator at a temperature T₃ ≠

T₂ to emit radiant energy E_b (T₃) toward said surface of said object;

second means for detecting with said radiometer the radiant energy E₃ resulting from energy emitted by and reflected from said surface of said object while E_b (T₃) is emitted;

means for determining ε

(θ

) in accordance with the ##EQU35## where p is the diffusely reflecting factor for the material and roughness of the object, where said roughness inhibits accurate measurement of T₁ should specularity of the surface be assumed;

means for measuring T₄ ; and

means for determining T₁ in accordance with the relationship ##EQU36##

4. An apparatus according to claim 3, wherein the optical path between said surface of said object and said radiometer has a transmittance factor K, and said emissivity and temperature are determined in accordance with the relationships:

##EQU37##

5. Apparatus according to claim 3, wherein said first and second means for detecting comprise switching means disposed in the optical path between said radiometer and said at least one black body radiator for selectively directing radiant energy E_b (T₂) or E_b (T₃) toward said radiometer.

6. A method for measuring the surface temperature T and emissivity ε

(θ

) at an angle θ

of an object being heated in a furnace, the surface of said object being non-specularly reflecting; and

said surface having a wall temperature T₄, said method comprising the steps of;

determining a diffusely reflecting factor p for the material and surface roughness of said object where said roughness inhibits accurate measurement of T should specularity of the surface be assumed, to account for the non-specularly reflecting condition of said surface;

positioning a radiometer and at least one reflecting surface specularly and symmetrically at angles θ

with respect to a normal to said surface of said object;

providing a sector having alternating portions respectively for absorbing and passing radiant energy;

moving said sector between said reflecting surface and said surface of said object whereby radiant energy from said surface of said object alternately is (1) absorbed by said sector or (2) passed to said reflecting surface and reflected back through said sector to said surface of said object for reflection again to said radiometer;

with said radiometer, detecting radiant energy E₁ while said sector absorbs radiant energy;

with said radiometer, detecting radiant energy E₂ while said sector passes radiant energy;

determining ε

(θ

) in accordance with the relationship ##EQU38## determining T in accordance with the relationship ##EQU39## where γ

_a is the effective reflecting factor of said reflecting surface and τ

is the transmittance factor of the radiation path between said sector and said surface of said object.

7. Apparatus for measuring the surface temperatures T and emissivity ε

(θ

) at an angle θ

of an object, the surface of said object being non-specularly reflecting, said apparatus comprising;

a radiometer and at least one reflecting surface positioned specularly and symmetrically with respect to a normal to said surface of said object;

a sector having alternating portions respectively for absorbing and passing radiant energy;

means for moving said sector between said reflecting surface and said surface of said object whereby radiant energy from said surface of said object alternately is (1) absorbed by said sector or (2) passed to said reflecting surface and reflected back through said sector to said surface of said object for reflection again to said radiometer;

means for detecting with said radiometer radiant energy E₁ while said sector absorbs radiant energy, and radiant energy E₂ while said sector passes radiant energy;

means for determining ε

(θ

) and T in accordance with the relationships ##EQU40## where γ

_a is the effective reflecting factor of said reflecting surface;

τ

is the transmittance factor of the radiation path between said sector and said surface of said object and p is the diffusely reflecting factor for the material and roughness of the object, where said roughness inhibits accurate measurement of T should specularity of the surface be assumed.

8. Apparatus according to claim 7, wherein said reflecting surface is planar.

9. Apparatus according to claim 7, wherein said reflecting surface is concave.

10. Apparatus according to claim 7, wherein said reflecting surface is diffusely reflecting.

11. Apparatus according to claim 7, wherein said radiometer and said reflecting surface are adapted to be disposed outside a furnace in which said object is to be heated.

12. Apparatus according to claim 7, wherein said object is a heated object in a furnace and said reflecting surface and said radiometer are disposed on a water cooled base plate adapted to be incorporated into a wall of said furnace.

13. A method for measuring the surface temperature T₁ and emissivity ε

(θ

) at an angle θ

, of an object being heated in a furnace, the surface of said object being non-specularly reflecting, said furnace having a wall temperature T₄, comprising the steps of;

determining a diffusely reflecting factor p for the material and surface roughness of said object, where said roughness inhibits accurate measurement of T₁ should specularity of the surface be assumed, to account for the non-specularly reflecting condition of said surface;

measuring T₄ ;

positioning a radiometer and a black body radiator specularly and symmetrically at angles θ

with respect to a normal to said surface of said object;

with said black body radiator at a temperature T₂, emitting radiant energy E_b (T₂) toward said surface of said object;

alternately absorbing said radiant energy E_b (T₂) or passing said radiant energy E_b (T₂) toward said surface of said object;

with said radiometer, detecting a radiant energy E₁ while said radiant energy E_b (T₂) is being absorbed and a radiant energy E₂ while said radiant energy E_b (T₂) is being passed;

determining ε

(θ

) in accordance with the relationship ##EQU41## determining T₁ in accordance with the relationship ##EQU42##

14. Apparatus for measuring the surface temperature T₁ and emissivity ε

(θ

) at an angle θ

, of an object being heated in a furnace, the surface of said object being non-specularly reflecting and said furnace having a wall temperature T₄, said apparatus comprising;

a radiometer and a black body radiator specularly and symmetrically positioned at angle θ

with respect to a normal to said surface of said object;

means for operating said radiator at a temperature T₂ to emit radiant energy E_b (T₂) toward said surface of said object;

means for alternately absorbing said radiant energy E_b (T₂) or passing said radiant energy E_b (T₂) toward said surface of said object;

means for detecting with said radiometer a radiant energy E₁ while said radiant energy E_b (T₂) is being absorbed and a radiant energy E₂ while said radiant energy E_b (T₂) is being passed;

means for determining ε

(θ

) in accordance with the relationship ##EQU43## where p is the diffusely reflecting factor for the material and roughness of the object, where said roughness inhibits accurate measurement of T₁ should specularity of the surface be assumed;

means for determining T₁ in accordance with the relationship ##EQU44##

15. Apparatus according to claim 14, wherein said means for alternately absorbing or passing comprises a sector having alternate portions respectively for absorbing or passing radiant energy and means for moving said sector in the optical path between said radiator and said surface of said object.