JP2897496B2 - Consumable optical fiber thermometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable optical fiber which uses an optical fiber as a waveguide and measures the temperature of the optical fiber at the distal end by using an infrared detector at the other end of the radiation incident from the distal end of the optical fiber. It relates to a thermometer.

[0002]

2. Description of the Related Art A consumable immersion thermocouple has long been used as a method for measuring the temperature of molten metal. FIG. 16 is a cross-sectional view showing the configuration of a sensor probe of a consumable thermocouple. As shown, a sensor probe including a thermocouple at the tip is detachable, and is replaced every time measurement is performed. . Since this probe is disposable and expensive, it has been difficult to increase the number of measurements. Also, if the probe diameter is 30
There is also a restriction that the measurement cannot be performed in a narrow space because the measurement is as large as not less than mm and as long as not less than 1 m.

There is a strong need to continuously measure the temperature of molten metal. Recently, a method of immersing a ceramic protective tube in molten steel and continuously measuring the temperature with a thermocouple inserted in the protective tube has been put to practical use. ing. FIG. 17 is a diagram showing a configuration of an apparatus for continuously measuring a temperature with a thermocouple. The problem with this method lies in the durability of the protection tube, and the measurement time can last only about 40 to 50 hours. Melting due to heat shock or slag causes a reduction in service life. Further, the point that the protective tube is expensive is also a problem of this measuring method.

As a method for solving this problem, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 2-19727 proposes an immersion thermometer for molten metal. This thermometer continuously inserts an optical fiber into a molten metal, detects infrared light guided through the optical fiber, and continuously measures the temperature. However, this measurement method has the following problems, and it is practically difficult to measure a high temperature. a) In the case of using a general monochromatic radiation thermometer, when the length of the optical fiber becomes short, the transmission loss decreases, the indicated temperature increases, and an error occurs. Silica optical fiber GI fiber for communication with Si (0.9 μm) detector (60/125 μm)
Is about 10 ° C./100 m (1200
° C). If such a large error occurs, it is not possible to satisfy the requirement of high accuracy of ± 2 ° C. b) In the above publication, the optical fiber is, for example, 3
Although it is described that the liquid is continuously supplied at a rate of 00 mm / hour, the temperature is high near the molten steel surface, and the coating burns out with a normal vinyl-coated optical fiber, and only the core wire of the optical fiber is formed. In this case, the strength of the optical fiber is significantly reduced, and the optical fiber is easily broken. There are slag and powder on the surface of the molten steel, and it is difficult to immerse the optical fiber in the molten steel by piercing the layer and with the ordinary optical fiber. When using an optical fiber at such a relatively high temperature,
Some improvement is needed because the strength of the optical fiber is reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to eliminate the influence of the length of an optical fiber in a consumable infrared thermometer using an optical fiber. SUMMARY OF THE INVENTION An object of the present invention is to provide a consumable optical fiber thermometer capable of performing measurement with a high degree of accuracy and obtaining an optical fiber length from the progress of length correction. Another object of the present invention is to use a metal tube-coated optical fiber as a high-strength optical fiber at a high temperature so that the optical fiber can be inserted into molten steel. It is an object of the present invention to provide a consumable optical fiber thermometer capable of obtaining sufficient accuracy by basic measurement. A further object of the present invention is to provide a consumable optical fiber thermometer capable of measuring the temperature of a high-temperature molten metal or the like with high accuracy, high speed response, and low cost using an optical fiber.

[0006]

A consumable optical fiber thermometer according to one aspect of the present invention comprises: an optical fiber having a tip introduced into an object to be measured and serving as a waveguide for radiation emitted from the tip; A splitter that is disposed on the rear end side and splits the light received by the optical fiber into two lights of different wavelengths; and a second splitter that determines the indicated temperature based on the luminance of the light of the different wavelength from the splitter. 1st and 2nd thermometers, 1st and 2nd
An instruction temperature thermometer, based on the transmission loss exponent corresponding to the effective wavelength and the effective wavelength of the light demultiplexed by the demultiplexer, to correct for changes in length of the optical fiber determine the true temperature Computing means.

A consumable optical fiber thermometer according to another aspect of the present invention uses one of the following arithmetic expressions when determining the true temperature To. To = Ta− {λaDa / (λaDa−λbDb)} * (Ta−Tb) To = Tb− {λbDb / (λaDa−λbDb)} * (Ta−Tb) To = (− λbDbTa + λaDaTb) / (λaDa−λbDb) Here, Ta, Tb: indicated temperature, λa, λb: effective wavelength Da, Db: transmission loss

In a consumable optical fiber thermometer according to another aspect of the present invention, a coefficient is obtained by experiment when obtaining the true temperature To, and one of the following equations is used. To = Ta−K1 * (Ta−Tb) To = Tb−K2 * (Ta−Tb) To = K3 Ta + K4 Tb where K1, K2, K3 and K4 are coefficients obtained by experiments.

In a consumable optical fiber thermometer according to another aspect of the present invention, an optical fiber length (X) is obtained by using one of the following equations. X = Xo-C2 (Ta- Tb) / {To 2 (λaDa-λbDb)} X = Xo-K5 (Ta-Tb) where, Xo: fiber standards to calibrate the temperature length Ta, Tb: indicated temperature [lambda] a, [lambda] b : Effective wavelength Da, Db: Transmission loss To: True temperature C2: Physical constant K5: Coefficient obtained by experiment

A consumable optical fiber thermometer according to another aspect of the present invention uses a quartz optical fiber for communication as an optical fiber. In a consumable optical fiber thermometer according to another aspect of the present invention, one effective wavelength is between 1.5 μm and 1.6 μm where the transmission loss of the optical communication quartz fiber is the smallest. Then, another effective wavelength is set between 0.8 μm and 1.0 μm. A consumable optical fiber thermometer according to another embodiment of the present invention uses a quartz optical fiber for communication as a core wire of the optical fiber, and uses a metal tube-coated optical fiber using a metal tube such as SUS as a coating material. Then, the temperature of the molten metal such as molten steel is measured.

A consumable optical fiber thermometer according to another aspect of the present invention uses a quartz optical fiber for communication as a core wire of the optical fiber and a metal tube coated optical fiber using a metal tube such as SUS as a coating material. The temperature of the tip of the optical fiber and the length of the optical fiber are simultaneously determined. In a consumable optical fiber thermometer according to another aspect of the present invention, a metal tube-coated optical fiber is inserted from the top of a blast furnace, lowered at the same time as a charge, and simultaneously measures a melting position and a melting temperature of the metal tube-coated optical fiber. By doing so, it is used as a measuring device for the blast furnace melting zone level.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The measurement principle of the consumable optical fiber thermometer of the present invention can be summarized as follows. (1) The infrared light guided through the optical fiber is divided into two, and the temperature is measured using two monochromatic radiation thermometers having different wavelengths, and the true temperature is obtained from the two indicated temperatures by calculation. Further, the length of the optical fiber is also obtained by calculation. (2) By using a quartz optical fiber for communication as the optical fiber and using a metal tube coated optical fiber using a metal tube such as a SUS tube as the coating material as a sensor, the mechanical strength at high temperatures is increased, Insertion into it is possible. First, a method for eliminating the influence of the optical fiber length will be described. The spectral radiance of a black body is expressed by the following equation according to the blank rule. L (λ, T) = 2C1 / {λ 5 * (EXP (C2 / λT) -1)} (1) λT ≦ λmT (λmT = 2.8978 * 10 -3 · k)
Can be approximated by the Wien equation. L (λ, T) = 2C1 * EXP- (C2 / λT) / λ 5 (2)

FIG. 1 is a diagram showing the configuration of a consumable optical fiber thermometer. In the figure, 1 is a metal tube coated optical fiber,
2 is an optical connector, 3 is a consumable optical fiber thermometer, 4 is a demultiplexer, 5 is a photodetector (wavelength λa), 6 is a photodetector (wavelength λb), and 7 and 8 are temperature converters (Ta, Tb) and 9 are operation units, 10 is a true temperature output, and 11 is an optical fiber length output. 12 is an optical fiber supply drum, 13 is a metal tube coated optical fiber insertion device, 14 is a mold, 15 is molten steel, 1
6 is an immersion nozzle and 17 is a powder.

In the consumable optical fiber thermometer, infrared light entering from the tip of the optical fiber is attenuated by the transmission loss of the optical fiber. The attenuation characteristic is a function of wavelength. Although the transmission loss of a recent quartz optical fiber for communication has become extremely small, it is 2-3 dB / k at a wavelength of 0.9 μm.
It is said to be 0.2-0.5 dB / km for m and 1.5 μm. Published measurement examples are shown in FIGS.

FIG. 2 is a characteristic diagram of transmission loss of a quartz optical fiber for communication (Shimada, Hayashida: "Optical Fiber Cable" P52, Ohmsha, published in 1987), and FIG. 3 is also a quartz optical fiber for communication. FIG. 6 is a characteristic diagram of transmission loss (Shimada, Hayashida: "Optical Fiber Cable" P56, Ohmsha, published in 1987). As expected from this figure, the output of the consumable optical fiber thermometer is affected by the fiber length. In practice, a GI fiber (50
/ 125 μm), the indicated value was about + 10 ° C. higher at a fiber length of 10 m than a reference value of a fiber length of 100 m. In order to use the consumable optical fiber thermometer, a highly accurate temperature measurement method in which the indicated value does not fluctuate even when the fiber length becomes short must be developed.

The embodiment shown in FIG. 1 has been developed from this point of view, and uses a monochromatic radiation thermometer having two different wavelengths. In this embodiment, the fact that the transmission loss of the optical fiber differs depending on the wavelength is positively used. Using the fact that the indicated values of the two monochromatic radiation thermometers calibrated with the reference length are different as the fiber length becomes shorter, the true temperature is calculated from the two indicated values. Further, in this embodiment, the fiber length is also obtained by calculation at the same time.

The calculation method for obtaining the true temperature from the two outputs of the monochromatic radiation thermometer will be described below. Here, the effective wavelengths of the monochromatic radiation thermometer are λa and λb (μm). The spectral radiance is expressed by the Wien equation. L (λa, T) = 2C1 * EXP (-C2 / λaT) / λa 5 (3) L (λb, T) = 2C1 * EXP (-C2 / λbT) / λb 5 (4) where C1, C2 are It is a physical constant. ^{C1 = C 2 h = 5.9548 *} 10 -17 W · m 2 C2 = Ch / k = 0.014388m · k = 14388μm · k

Next, the attenuation due to the change in the optical fiber length X (km) is expressed by the following equation. R (X) = EXP (−DX) (5) In general, the transmission loss of a fiber is expressed as follows. 10 * LOGR (X) = 10 * (− DX) LOG (e) = − 10LOG (e) * DX For example, when the loss is 3 dB / km, it is as follows. −10 LOG (e) * D * 1 = −3 D = 0.3 / LOG (e) (dB / km) (6) Luminance output Va of monochromatic radiation thermometer of wavelength λa, λb at the fiber length X, Vb can be expressed by multiplying the expressions (3), (4) and (5). Va = A * {2C1 * EXP (-C2 / λaT) / λ a 5} * EXP (-DX) Va = A * 2C1 * EXP {(- C2 / λaT) -DX} / λa 5 (7) Vb = B * {2C1 * EXP (-C2 / λbT) / λb 5} * EXP (-DX) Vb = B * 2C1 * EXP {(- C2 / λbT) -DX} / λb 5 (8) where A, B Is a constant of each device, and Da and Db are transmission loss indices of wavelengths λa and λb.

Temperature calibration is performed when the fiber length is Xo (km). At this time, the indicated values Ta (Xo) and Tb (Xo) of the two monochromatic radiation thermometers are equal within the measurement temperature range. Ta (Xo) = Tb (Xo) When the fiber length is shorter than Xo, the transmission loss is reduced, and the indicated temperature becomes higher in both cases. At this time, a difference occurs between the indicated temperatures. Assuming that the true temperature is To, the indicated temperatures of both are calculated from the above-described equation by calculating the relationship between Ta, Tb and X, and the true temperature To is obtained. A * 2C1 * EXP {(- C2 / λaTo) -DaX} / λa 5 = A * 2C1 * EXP {(- C2 / λaTa) -DaXo} / λa 5 now (-C2 / λaTo) -DaX = ( - C2 / ΛaTa) −DaXo−1 / To + 1 / Ta = Da (X−Xo) * λa / C2 (Ta−To) = − TaTo * Da (X−Xo) * λa / C2 (Ta−To) compared to To When it is sufficiently small, it can be approximated by the following equation. Ta−To = −To ² * Da (X−Xo) * λa / C 2 (9)

Similarly, Tb can be approximated by equation (10). ^{Tb-To = -To 2 * Db} (X-Xo) * λb / C2 (10) (9), obtained indicated temperature difference Ta-Tb from (10). Ta−Tb = −To ² * (X−Xo) * (Daλa−Dbλb) / C2 (11) By taking the ratio of the expressions (9) and (11), (X−Xo) is eliminated. To = Ta− (Ta−Tb) * Daλa / (Daλa−Dbλb) (12) The following equation is similarly obtained from equations (10) and (11). To = Tb− (Ta−Tb) * Dbλb / (Daλa−Dbλb) (13) From expression (13), To = (Deλa * Tb−Dbλb * Ta) / (Daλa−Dbλb) (14) The true temperature To is obtained from any of the indicated temperatures of the two monochromatic radiation thermometers by any of the equations (12), (13), and (14).

As the coefficients of the equations, λa, λb, Da, and Db can be given as numerical values, and actually differ from each other.
It is also possible to measure the temperature with a blackbody furnace using a fiber with a point length and determine it from experimental values. The empirical formula is as follows. To = Ta-K1 * (Ta-Tb) (12-a) To = Tb-K2 * (Ta-Tb) (13-a) To = K3 * Tb-K4 * Ta (14-a) (9), Equation (10) shows that the indicated temperature error changes linearly with the fiber length. Although this phenomenon is difficult to understand intuitively, spectral radiance and transmission loss are represented by exponential functions of temperature and fiber length X, respectively. Next, this function will be calculated in an embodiment.

Embodiment 1 FIG. Monochromatic radiation thermometer No. 1 Si λa = 0.9 μm No. 2 Ge λb = 1.5 μm GI loss for optical fiber communication (0.9 μm) 3 dB / km Da = 0.6907 Loss (1.5 μm) 0.5 dB / km Db = 0.1151 Measurement temperature 1800K (1527 ° C) Equivalent to the molten steel temperature before solidification Calculations were made using equations (9) and (10). An indication error when the fiber reference length Xo = 0.5 km is obtained by calculation, as shown in Table 1 below.

[0023]

[Table 1]

FIG. 4 is a characteristic diagram showing the result of this calculation. From this figure also, the indication error changes linearly with the fiber length. From this relationship, without measuring the fiber length,
It can be seen that the true temperature To is required.

Next, an equation for obtaining the fiber length X will be described.
This is obtained from equation (11). (X−Xo) = − (Ta−Tb) * C 2 / {To ² (Daλa−Dbλb)} (15) X = Xo− (Ta−Tb) * C 2 / {To ² (Daλa−Dbλb)} Experimental formula The following equation is obtained. X = Xo-K5 * (Ta-Tb) (15-a) By inserting the constant of (X-Xo) =-0.009890 (Ta-Tb) X = Xo-0.009890 (Ta-Tb) From this relationship, when Ta-Tb = 1.degree.
0089 km = about 10 m shorter. Ta−Tb = 0.1 ° C.
At this time, the fiber length is about 1 m shorter. The above values are the same in terms of accuracy. If the accuracy of the indicated temperature is 0.1 ° C., the calculation accuracy of the fiber length can be expected to be 1 m. In order to improve the measurement accuracy of the fiber length, the effective wavelength of the monochromatic radiation thermometer may be a combination of a wavelength having a large transmission loss and a wavelength having a small transmission loss.

As is clear from Table 1, the indication error is smaller in the monochromatic radiation thermometer of the Ge detector having a small transmission loss. If only a short fiber length range is used, a Ge monochromatic thermometer may be sufficient if the degree of demand is low. Furthermore, Table 1 shows that two Si, G
It is expected that the use of the monochromatic thermometer e can easily achieve high accuracy even when the fiber length is 500 m.

FIG. 5 is a characteristic diagram showing an actual measurement example. This characteristic diagram is an experimental result of 10-500 m,
The value after correction over the entire length falls within the range of ± 1 ° C. This indicates that the use of an optical fiber radiation thermometer as a consumable thermometer is extremely valuable industrially. The fact that a long optical fiber of 500 m can be used reduces the frequency of replacement and improves the use efficiency of the fiber, so that its economic effect is large.

Further, it has been shown that the fiber length can be obtained by the present invention, but it is expected that a measuring method using this measuring principle will be developed in the future. For example, an electric pulse method (TDR) or a thermocouple method is currently used as a melting zone level meter of a blast furnace. The TDR method can measure the melting position but cannot measure the melting temperature. On the other hand, the thermocouple method can measure the temperature distribution of the insert and the temperature distribution during melting, but cannot measure the melting position. Further, once the hot junction has melted, it cannot be measured thereafter.

FIG. 6 is a diagram showing a configuration when the metal tube-coated optical fiber consumable thermometer of the present invention is used for a blast furnace melting zone level meter. In the drawing, 20 is a measuring roll, 21 is a charging length counter, 22 is a melting level calculator, 23 is a recorder, 24 is a blast furnace, 25 is a charging device, 26
Is a furnace interior container, and 27 is a tuyere. In the method of inserting an optical fiber according to the present invention, the measurement of the temperature of the tip of the optical fiber and the measurement of the fiber length can be performed at the same time. It is economical because measurement can be performed until the fiber runs out.

Incidentally, the optical fiber used here cannot be measured because of its insufficient mechanical strength with a normal optical fiber. Although a high-precision temperature measurement method could be developed, the measurement could not be realized without an optical fiber that can withstand high temperatures and has high mechanical strength, and would have no industrial significance.

Next, an optical fiber for realizing high temperature measurement will be described. As a method of measuring the temperature of molten metal, a method of measuring with an infrared radiation thermometer while continuously supplying an optical fiber has been proposed.However, ordinary optical fibers have insufficient heat resistance and insufficient strength. It cannot be continuously charged into the molten metal and has not been actually measured. Therefore, in order to realize an optical fiber immersion thermometer, it is necessary to increase the mechanical strength of the optical fiber. In the present invention, an optical fiber coated with a metal tube is used as a method for improving mechanical strength.

The case where the temperature of molten steel is measured with an optical fiber coated with a metal tube will be described below by way of examples. 1) Metal Tube-Coated Optical Fiber FIG. 7 is a diagram showing a cross-sectional structure of a metal tube-coated optical fiber. In the figure, reference numeral 30 denotes a metal tube, and the inner silicon is 0.7 m.
m, the outer diameter is 0.9 mm. A quartz optical fiber 31 has a core of 50 μm and a clad of 125 μm.
Reference numeral 32 denotes a coating, and the coating has an outer diameter of 150 μm.

A. Optical fiber material ・ Measurement temperature is for hot metal molten steel.
Since the temperature is as high as 650 ° C., a quartz fiber which is a material having a softening point of 1600 ° C. or higher and a melting point of 1800 ° C. or higher is used. Organic fibers have insufficient heat resistance. -Near-infrared transmission loss of optical fiber developed for communication is extremely small, and it is suitable for infrared radiation thermometer. For communication, those having a core diameter of 10 to 50 μm are usually used. Fibers for optical communication are inexpensive due to the large production volume and the smaller amount of fibers used than those with large diameters.

B. Metal clad tube optical fiber (Purpose of metal tube cladding)
No. 727, “Immersion Thermometer for Molten Metal”) describes that an optical fiber is continuously supplied during melting to measure the temperature. However, the structure as a fiber is not specified. Normal optical fibers are vinyl-coated.
If this fiber is brought close to molten steel, the vinyl coating is heated and burns out. When the coating burns, the core wire of quartz remains, but the strength is remarkably reduced, and if it is put into molten steel, it will break and it will be difficult to insert it. It can be seen that the coating of slag, roasted rice, powder, etc. often remains on the upper part of the molten steel, and it is impossible to charge the molten steel with the vinyl-coated fiber. In order to solve this problem, the present invention uses a metal tube-coated optical fiber. The metal tube has high strength and can be easily inserted into molten steel.

The properties required of the metal tube are that the hot metal temperature is close to that of the hot metal and molten steel, and that the strength is maintained at around 1400 ° C. That the melting does not affect the components to be measured. In this case, a steel pipe or a stainless steel pipe is preferable. Fortunately, a stainless steel tube-coated fiber has been developed, and a long metal tube-coated optical fiber is available and used. A stainless steel tube is used as the metal tube. The main component of stainless steel is iron, which has a melting point of about 1450 ° C. and has sufficient strength. Also, there is no problem even if stainless steel is melted and enters molten steel and hot metal. The amounts of Cr and Ni, which are alloy components, are very small and there is no problem. When the coating material is Al, Cu, or the like, the melting point is low and it is difficult to satisfy the above conditions, so that it cannot be used. If the specific temperature is higher than the molten steel in the case of a metal with a high melting temperature, if the wire breaks in the molten steel, the wire will not melt, so if it solidifies, it will remain as an inclusion in it and cause defects. Not preferred.

(Structure of Metal Tube-Coated Optical Fiber) Conditions Required for Metal Tube-Coated Fiber A. Sufficient strength. Be able to insert into molten steel. For this purpose, a thick metal tube is desirable. B. Fast response of temperature. The measurement principle of the immersion-type thermometer for metal-tube-coated optical fiber is that when the tip of the optical fiber is immersed in molten steel, the temperature of the metal-coated tube rises and becomes the same as the molten steel temperature. It will be immersed in. This situation is the same as when an optical fiber is inserted into a black body. When a metal tube-coated fiber is inserted in a black body furnace, the response speed of the thermometer is faster when the tip of the optical fiber is outside the metal tube.

FIG. 8 is a diagram showing the relationship between the shape of the tip of the metal tube coated optical fiber and the response speed when calibrating the blackbody furnace. The result is that if the optical fiber is in the metal tube or the tip positions are equal, the indicated temperature must be increased while the temperature of the metal tube is increasing to the blackbody temperature. I understand. It can be seen that the temperature rise rate of the metal tube greatly affects the temperature rate of the thermometer. For this reason, a thin metal tube having a small thickness is preferable. From the results of the above A and B, it can be seen that there is an appropriate value for the thickness and the thickness of the metal tube according to the use condition.

Next, an example of measuring the temperature of molten steel using an optical fiber coated with a metal tube will be described. Embodiment 2. FIG. Optical fiber GI fiber Core diameter: 50 μm Cladding diameter: 125 μm Metal tube: SUS Outer diameter: 0.9 mm Inner diameter: 0.7 mm Length: 150 m Infrared detector Si detector Effective wavelength: 0.9 μm Monochromatic radiation thermometer Temperature measurement Range: 800 to 1600 ° C. FIG. 9 is a diagram showing the relationship between the output voltage and the temperature when the blackbody furnace test is performed with this measuring instrument.

FIG. 10 is a measurement system diagram when the measurement is performed with a tundish of CC using an optical fiber consumable thermometer. In the figure, 40 is a tundish, 41 is an optical fiber insertion hole, and 42 is a nozzle stopper. FIG. 11 is a diagram showing the results of measurement with a tundish using an optical fiber immersion type thermometer using an optical fiber coated with a metal tube. When immersed in static molten steel, the indicated temperature shows blackout, and then the indicated temperature decreases as shown in FIG. This is considered to be because the stainless steel tube was melted, the optical fiber was disconnected, and the measurement position receded. Maximum temperature is 1555 ° C
showed that. The indicated value of the continuous thermocouple temperature measured at the same time was 1561 ° C. The measurement accuracy of the optical fiber thermometer was proved to be high. Since the indicated value drops sharply after the optical fiber is disconnected, it can be said that the intermittent measurement method is more suitable than the continuous measurement method. In the case of intermittent measurement, fast response is required. It has been proved that the metal tube-coated optical fiber having the outer diameter of the SUS tube of 0.9 mm has a sufficiently fast response.

FIG. 12 shows C under the same measurement conditions as in the tundish.
It is a figure which shows the measurement system diagram at the time of measuring by C mold, and FIGS. 13-15 is the figure which showed the measurement result.
FIG. 13 shows waveforms when the metal tube-coated optical fiber is inserted at a low speed. In this case, the indicated temperature fluctuates greatly in response to the liquid level fluctuation due to the influence of the oscillation of the mold. It is considered that the peak temperature indicates the molten steel temperature at 1510 ° C., and the low temperature side indicates the powder temperature.

FIG. 14 shows waveforms when a metal tube-coated optical fiber is inserted at a relatively high speed. The oscillating temperature indication remains the same, but the amplitude is smaller. However, the peak temperature remains unchanged at 1510 ° C. FIG. 15 shows a waveform when the insertion length is adjusted to be about 2 to 3 cm below the liquid surface and the liquid is inserted into the molten steel surface at a high speed. In this case, the peak is 1
Only one is observed. Its peak value was about 1510 ° C. as in the other cases. From the above experimental results, it was proved that the use of the metal tube-coated optical fiber makes it possible to easily insert the fiber into molten steel and to measure the temperature.

[0042]

As described above, according to the present invention, the following effects are obtained. 1) Instead of a consumable immersion thermometer using a thermocouple, inexpensive and highly accurate temperature measurement is possible, and the industrial value is extremely large. 2) Since the influence of the fiber length, which is the biggest problem of the consumable optical fiber thermometer, can be corrected, a great effect can be obtained. Reproducibility of high temperature measurement over 1500 ° C ±
The simplicity of operation at 2 ° C. has a very great effect. 3) The fiber length can be measured at the same time as the temperature measurement, which gives rise to the possibility of a new composite measurement and is expected to be used in industry in the future. 4) Since a metal tube-coated optical fiber is used, the strength is increased, and measurement in a high-temperature region is realized, which has a great effect for an industry dealing with high temperatures. 5) Also, since the outer diameter of the metal tube optical fiber is as small as about 1 mm, the number of places where the temperature can be measured increases as seen in the temperature measurement inside the CC mold, which has been difficult to measure conventionally. Conventional radiation thermometers and consumable thermocouples require a fairly long straight section for measurement, but metal tube-coated optical fibers can be bent and can be measured in a small space, which is also advantageous in this respect. . 6) Metal tube optical fiber is used in the telecommunications field, and its price is kept relatively low due to mass production effects. Use of this low-cost metal tube optical fiber has made it possible to measure temperature at a fixed price. Therefore, the number of temperature measurements in the steel process increases,
The control accuracy has been improved and the yield has been improved, contributing to the stabilization of operations with a significant effect.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of a consumable optical fiber thermometer.

FIG. 2 is a characteristic diagram showing transmission loss of a quartz optical fiber for communication.

FIG. 3 is a characteristic diagram showing transmission loss of a quartz optical fiber for communication.

FIG. 4 shows the indicated temperature difference between two monochromatic radiation thermometers (calculated value)
FIG.

FIG. 5 is a characteristic diagram showing an indicated temperature difference between two monochromatic radiation thermometers and an error (experimental value) after correction.

FIG. 6 is a configuration diagram of a blast furnace melting zone level meter using a consumable optical fiber thermometer.

FIG. 7 is a sectional view of a metal tube-coated optical fiber.

FIG. 8 is a diagram showing a relationship between a fiber tip shape and a response speed at the time of blackbody furnace calibration of a metal tube-coated optical fiber.

FIG. 9 is a characteristic diagram showing a relationship between a temperature and an output voltage of a Si monochromatic radiation thermometer.

FIG. 10 is a diagram showing a measurement system in a CC tundish.

FIG. 11 is a characteristic diagram showing a temperature measurement result in a CC tundish.

FIG. 12 is a diagram showing a measurement system in a CC mold.

FIG. 13 is a diagram showing a result of temperature measurement in a CC mold.

FIG. 14 is a diagram showing a result of temperature measurement in a CC mold.

FIG. 15 is a diagram showing a result of temperature measurement in a CC mold.

FIG. 16 is a view showing a configuration of a consumable immersion thermocouple.

FIG. 17 is a diagram showing a configuration of a continuous molten steel thermometer (thermocouple).

[Explanation of symbols]

REFERENCE SIGNS LIST 1 metal tube-coated optical fiber 2 optical connector 3 consumable optical fiber thermometer 4 splitter 5 photodetector (λa) 6 photodetector (λb) 7,8 temperature converter (Ta, Tb) 9 arithmetic unit 10 true Temperature output 11 Optical fiber length output 12 Optical fiber supply drum 13 Metal tube coated optical fiber insertion device 14 Mold 15 Molten steel 16 Immersion nozzle 17 Powder 20 Measuring roll 21 Insertion length counter 22 Melt zone level calculation 23 Recorder 24 Blast furnace 25 Insertion Device 26 Furnace insert 27 Tuyere 30 Metal tube 31 Quartz optical fiber 32 Coating 40 Tundish 41 Optical fiber insertion hole 42 Nozzle stopper

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01J 5/08 G01K 11/12

Claims (11)

(57) [Claims] 1. An optical fiber, which has a tip introduced into an object to be measured and serves as a waveguide for radiated light incident from the tip, and a light which is disposed on a rear end side of the optical fiber and receives light received by the optical fiber. A demultiplexer that divides the light into two wavelengths, first and second thermometers each for obtaining an indicated temperature based on the luminance of light of a different wavelength from the demultiplexer; and the first and second thermometers. Indicated temperature of the thermometer, and corresponded to the effective wavelength of the light demultiplexed by the demultiplexer and its effective wavelength.
A consumable optical fiber thermometer comprising: a calculating means for correcting a change in the length of the optical fiber based on the transmission loss index to obtain a true temperature. 2. The consumable optical fiber thermometer according to claim 1, wherein any one of the following arithmetic expressions is used to determine the true temperature To. To = Ta− {λaDa / (λaDa−λbDb)} * (Ta−Tb) To = Tb− {λbDb / (λaDa−λbDb)} * (Ta−Tb) To = (− λbDbTa + λaDaTb) / (λaDa−λbDb) Here, Ta, Tb: indicated temperature, λa, λb: effective wavelength Da, Db: transmission loss 3. The consumable optical fiber thermometer according to claim 1, wherein a coefficient is obtained by experiment when obtaining the true temperature To, and one of the following equations is used. To = Ta−K1 * (Ta−Tb) To = Tb−K2 * (Ta−Tb) To = K3 Ta + K4 Tb where K1, K2, K3 and K4 are coefficients obtained by experiments. 4. The consumable optical fiber thermometer according to claim 1, wherein the optical fiber length (X) is obtained by using one of the following equations. X = Xo-C2 (Ta- Tb) / {To 2 (λaDa-λbDb)} X = Xo-K5 (Ta-Tb) where, Xo: fiber standards to calibrate the temperature length Ta, Tb: indicated temperature [lambda] a, [lambda] b : Effective wavelength Da, Db: Transmission loss To: True temperature C2: Physical constant K5: Coefficient obtained by experiment 5. The consumable optical fiber thermometer according to claim 1, wherein a quartz optical fiber for communication is used as the optical fiber. 6. The consumable optical fiber thermometer according to claim 5, wherein one effective wavelength is between 1.5 μm and 1.6 μm where the transmission loss of the optical communication quartz fiber is the smallest. 7. The consumable optical fiber thermometer according to claim 6, wherein the other effective wavelength is between 0.8 μm and 1.0 μm. 8. The consumable optical fiber according to claim 1, wherein a quartz optical fiber for communication is used as a core wire of the optical fiber, and a metal tube coated optical fiber using a metal tube such as SUS is used as a coating material. thermometer. 9. The consumable optical fiber thermometer according to claim 8, wherein the temperature of the molten metal such as molten steel is measured. 10. A quartz optical fiber for communication is used as a core wire of an optical fiber, a metal tube coated optical fiber using a metal tube such as SUS is used as a coating material, and a tip temperature of the optical fiber and an optical fiber length are simultaneously obtained. Item 6. A consumable optical fiber thermometer according to Item 4. 11. A blast furnace melting zone level is measured by inserting a metal tube-coated optical fiber from the top of a blast furnace, lowering it simultaneously with the charge, and simultaneously measuring the melting position and melting temperature of the metal tube-coated optical fiber. The consumable optical fiber thermometer according to claim 9, which is used as an apparatus.