JP3392936B2 - Temperature calibration device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature calibration device for a device for measuring temperature using an optical fiber. 2. Description of the Related Art In order to detect the temperature of a high-temperature liquid metal such as molten steel, a method has been proposed in which a metal tube-coated optical fiber having a tip as a temperature measuring element is inserted into the liquid metal to measure the temperature. (JP-A-2-248960). [0003] When a temperature measuring device using an optical fiber is used for measurement, it is necessary to compare and calibrate the output from the optical fiber and the actual temperature. However, when the optical fiber is inserted into a blackbody furnace in a high-temperature air of about 1500 ° C. to perform calibration, the sheath made of polymer, rubber, metal, etc.
It burns and generates light, smoke, gas, etc., causing fluctuations in output, and fouling the optical fiber, leading to measurement errors. In addition, if a sealed structure is used to prevent the exterior from burning, the structure becomes complicated and workability deteriorates. SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a temperature calibrating apparatus which can easily and highly accurately calibrate a thermometer using an optical fiber even in air in a high-temperature atmosphere. It is to be. According to the present invention, there is provided an optical fiber in which a sheath at a distal end is removed by a required length and fired, and a central bottomed portion into which the distal end of the optical fiber is inserted on one side. A black body furnace having the same, a temperature measuring means for measuring the temperature of the other side of the central bottom of the black body furnace, and a control means for controlling the heating of the black body furnace based on the output of the temperature measuring means. It is a temperature calibration device. FIG. 1 is a structural explanatory view showing an embodiment of the present invention. In the figure, reference numeral 1 denotes an optical fiber, and a tip portion 10 is inserted into one side of a central bottomed portion 20 in a cylindrical black body furnace 2. The other end of the optical fiber 1 is connected to radiation detection means 3 including a detector.
The radiant energy from the distal end portion 10 of the optical fiber 1 is detected and the temperature is measured, and a temperature output Te is output by a display or the like. A temperature sensor 4 such as a thermocouple is provided on the other side of the central bottomed portion 20 of the black body furnace 2, and the temperature is measured by a temperature measuring means 5 using the temperature sensor 4, and a temperature output T is outputted by a display or the like. . The temperature output T and the set value Tc are compared by the controller 6, the operating end 7 is driven, and the voltage, current, electric power, etc. of the heater 8 for heating the black body furnace 2 are controlled. Heating control is performed to reach the temperature. The control means is constituted by the controller 6, the operation terminal 7, and the like. When the optical fiber 1 is inserted into the black body furnace 2, the optical fiber 1 is provided at the entrance on the black body furnace 2 side or is held by the guide tube 9 provided on the optical fiber 1 side itself. It is inserted and protrudes into the cavity of the black body furnace 2 for a predetermined length. Before this insertion, as shown in FIG. 2, the sheath 1a of the optical fiber 1 is removed in advance by a predetermined length, and the exposed distal end portion 10 is burned by a burner or the like to remove the soiled portion. Perform pre-treatment for removal. In this way,
By inserting the tip 10 of the optical fiber 1 into the black body furnace 2, even if the temperature becomes as high as about 1500 ° C., unnecessary combustion does not occur and the tip 10 of the optical fiber 1 is not polluted and stably Can measure temperature. When the optical fiber 1 is inserted into the black body furnace 2,
As shown in FIG. 3, radiation detection means 3 using optical fiber 1
Output Te is first quickly, then gradually rises and equilibrates, and eventually the output decreases. The first fast rise is the reception of cavity radiation, the next slow rise is
Including self-radiation caused by heating itself,
The distal end portion 10 of the optical fiber 1 itself is exposed to a high temperature in the air, which causes a devitrification phenomenon and lowers the output. At this time, the temperature output Te of the optical fiber 1 is calibrated by comparing the balanced temperature output Te with the temperature output T of the temperature measuring means 5 and using the temperature output T as a reference. Note that the function of the temperature measuring means 5 may be provided by the controller 6, and as shown in FIG.
Instead of the thermocouple temperature sensor 4, the radiation detector 40 may detect radiant energy from the central bottomed portion 20 of the black body furnace 2 and measure the temperature by the temperature measuring means 50. Here, if the blackbody furnace 2 is formed of a high-purity alumina tube and the ratio L / D of the inner diameter D and the length L of the cavity is 4 or more, the apparent effective emissivity is 0.999. The above black body is obtained, and sufficiently stable and highly accurate measurement can be performed. This will be described below. The temperature T of the cavity of the blackbody furnace 2, the emissivity ε1,
Assuming that the temperature To of the tip 10 of the optical fiber 1 and the emissivity ε2, the spectral radiance at the measurement wavelength λ and the temperature T is L (λ, T).
Then, the output detected by the radiation detecting means 3 is expressed by the following equation. L (λ, Te) = ε ₂ L (λ, To) + (1−ε ₂ ) ε ₁ L (λ, T) (1) When the output of the optical fiber 1 is balanced, To = T Then, L (λ, Te) = ｛ε ₂ + (1−ε ₂ ) ε ₁ ｝ L (λ, T) (2) is obtained. Here, from L (λ, Te) / L (λ, T) = ε ₂ + (1−ε ₂ ) ε ₁ = εe, εe = ε ₂ + (1−ε ₂ ) ε ₁ (3) An apparent emissivity εe is obtained. Next, when the spectral radiance is approximated by an index n, the following equation is obtained when L (λ, T) = kT ⁿ and Te = T + ΔT. L (λ, Te) / L (λ, T) = (T + ΔT) ⁿ / T ⁿ = 1 + nΔT / T = εe From this, the following equation is obtained. ΔT / T = (εe−1) / n (4) where n = C2 / λT, C2 = 0.0143388 m
-It is K. From this, the calibration error is apparent emissivity ε
e and the index n. Alumina tube temperature 150
It is expected that the specific emissivity at 0 ° C. is 0.2 or more, the L / D of the cavity is 4 or more, and ε ₁ ≧ 0.9. Also, by inserting the tip 10 of the fiber into the cavity, the fiber diameter can be reduced. Since the soaking length of 10 times or more can be easily obtained and the emissivity of the fiber tip 10 can be expected to be ε ₂ ≧ 0.99, from the equation (3),
εe = 0.999. On the other hand, λ = 1.5 μm, T =
Since n = 5.4 as 1773 (K), the calibration error at this time is 0.019% from equation (4), that is, 0.34K, and sufficient calibration accuracy can be secured. According to the present invention, there is provided a temperature calibrating apparatus in which the sheath at the tip of an optical fiber is removed, the baked one is inserted into a blackbody furnace, and calibration is performed. For this reason, there is no substance that causes contamination at the tip of the optical fiber.
Even when the temperature is calibrated by heating at a high temperature in the air, the output fluctuation due to the burning of impurities and the contamination of the optical fiber are small, the workability is good, and the calibration under the high temperature atmosphere can be easily performed with high accuracy. In addition, since high-temperature calibration in air is possible, the equipment configuration is simple.By holding the optical fiber in the guide tube and inserting it into the black body furnace, the cavity of the black body furnace can be secured sufficiently and stable. Temperature measurement and calibration are possible. In addition, since the high temperature black body condition is almost the same as that in the case where the optical fiber is inserted into the molten steel, it is possible to perform calibration sufficiently corresponding to actual use.

[Brief description of the drawings] FIG. 1 is a configuration explanatory view showing one embodiment of the present invention. FIG. 2 is a configuration explanatory view showing one embodiment of the present invention. FIG. 3 is an operation explanatory diagram showing one embodiment of the present invention. FIG. 4 is a configuration explanatory view showing one embodiment of the present invention. [Explanation of symbols] 1 Optical fiber 10 Tip 2 Blackbody furnace 20 Central bottom 3 Radiation detection means 4 Temperature sensor 5 Temperature detection means 6 Controller 7 Operation terminal 8 heater 9 Guide tube

Continuation of front page (56) References JP-A 1-276032 (JP, A) JP-A 63-1923 (JP, A) JP-A 5-248960 (JP, A) JP-A 62-172228 (JP) , A) Shokai 55-57033 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01K 15/00 G01K 11/12 G01J 5/02 G01J 5/08

Claims (1)

(1) Claims: (1) An optical fiber which is obtained by removing a required length of the sheath of the end portion and fired, and a black having a central bottom portion into which the end portion of the optical fiber is inserted on one side. Body furnace, temperature measuring means for measuring the temperature of the other side of the central bottom portion of the black body furnace, and control means for controlling the heating of the black body furnace based on the output of the temperature measuring means, Temperature calibration device.