JPH07270254A - Optical fiber type device for measuring temperature - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement of temperature without being affected by the length of an optical fiber, by utilizing a plurality of lights being different in wavelength. CONSTITUTION:The fore end part 10 of an optical fiber 1 covered by a metal pipe is inserted into a liquid metal 2 of high temperature in a vessel 20. The other end part 11 of the optical fiber 1 converges a radiation energy from the fore end part 10 and the energy is divided in three through the intermediary of half mirrors 51 and 52. The branched lights are passed through filters 61, 62 and 63 transmitting lights different in wavelength from one another and are detected by detecting elements 71, 72 and 73. The respective outputs of these elements are amplified by amplifying means A1, A2 and A3 and outputs of the amplifying means A1 and A2 are subjected to computation of a ratio by a ratio computing means 80. A ratio signal thereof is made a temperature signal by a converting means 81. An output of the amplifying means A3 is also made a temperature signal by a converting means 82. Based on a difference between the temperature signals of these converting means 81 and 82, a computing means 9 executes correction of the length of the optical fiber 1 and thereby a correct temperature signal is obtained. Thereby, measurement for a long time can be executed without being affected by a change in the length of the optical fiber 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring temperature using an optical fiber.

[0002]

2. Description of the Related Art In order to detect the temperature of high temperature liquid metal such as molten steel, there has been proposed one in which a metal tube-coated fiber having a temperature measuring element at its tip is inserted into molten metal to measure the temperature ( JP-A-5-248960).

[0003]

However, when the optical fiber is inserted into the molten metal having a high temperature, the tip portion is consumed, and therefore the optical fiber is sequentially fed out for use. Therefore, the length of the radiant energy from the tip of the optical fiber until it reaches the detection element at the other end is different, which may cause a difference in transmission loss and may cause a measurement error.

For this reason, Japanese Patent Application Laid-Open No. 5-142049 proposes a method in which the difference between two temperature signals is used to correct the transmission loss of the optical fiber to obtain the true temperature.

In view of the above points, an object of the present invention is to utilize three wavelengths without being affected by the length of an optical fiber,
An object of the present invention is to provide an optical fiber type temperature measuring device capable of measuring temperature with higher accuracy.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a detector element for receiving radiant energy from an object to be measured through an optical fiber and detecting light of at least three different wavelengths,
The ratio signals of the output signals for two wavelengths of the output of each wavelength of the detection element are obtained, and the correction operation is performed by the length of the optical fiber based on the difference between the ratio signal and the output signals for other wavelengths. It is an optical fiber type temperature measuring device provided with a calculating means for obtaining a temperature.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) is a structural explanatory view showing an embodiment of the present invention. In the figure, reference numeral 1 is an optical fiber coated with a metal tube or the like, and its tip 10 is attached to a container 20 or the like. It is inserted into the high temperature liquid metal 2 to be contained. This optical fiber 1
It is continuously or intermittently fed by the feeding device 3 and wound on the drum 4 by a necessary amount. Then, the other end portion 11 of the optical fiber 1 collects the radiant energy from the tip portion 10 and splits it into three directions via the half mirrors 51 and 52 to emit lights having different wavelengths λ1, λ2, and λ3. Through the filters 61, 62, 63 that pass through, the detection elements 71, 7
It is detected at 2, 73. The outputs of the detection elements 71, 72, 73 are amplified by the amplification means A1, A2, A3, the outputs of the amplification means A1, A2 are ratioed by the ratio calculation means 80, and the ratio signals are converted by the conversion means 81. A temperature signal,
The output of the amplification means A3 is also converted into a temperature signal by the conversion means 82. Based on the difference between the temperature signals of the conversion means 81 and 82, the calculation means 9 corrects the length of the optical fiber 1 to obtain a correct temperature signal.

Further, as shown in FIG. 1B, the filters 61, 62, 63 are mounted on the rotating sector 6, and the light from the other end 10 of the optical fiber 1 is made incident on one detecting element 7. Alternatively, the detection may be performed. Alternatively, after the output of the detection element 7 is amplified by the amplification means A, conversion or calculation may be digitally processed using the calculation means 90 such as a microcomputer.

Here, two different measurement wavelength bands λ
Considering a two-color thermometer for obtaining the radiance ratio of 1 and λ2, the spectral radiance L (λ, T) at the wavelength λ and the temperature T is
According to the Wien's formula, L (λ, T) = 2C1λ ⁵ exp (−C2 / λT) (1), so the ratio output R (T) is as follows.

R (T) = (λ2 / λ1) ⁵ exp {(1 / λ2-1 / λ1) · C2 / T} (2) Here, C2 = 0.014388 mK.

Focusing on the spectral absorption of the optical fiber, when the absorption coefficient is α and the length is x, the transmittance is exp (-αx).
Therefore, S1,2 (K) is obtained when a black body at temperature T (K) is measured through an optical fiber having length x and absorption coefficients α1 and α2 in the measurement wavelength bands λ1 and λ2, respectively. If the reading is obtained, the relationship of R (S1,2) = [exp (-α1x) / exp (-α2x)] R (T) (3) holds. Applying the Vienna formula to R (S1,2) and R (T) and rearranging, we obtain the following formula.

(1 / λ2-1 / λ1) C2 / S1,2 = (α2-α1) x + (1 / λ2-1 / λ1) C2 / T (4) When this is obtained for temperatures S1,2 and T , 1 / S1,2−1 / T = (α2-α1) x / {(1 / λ2-1 / λ1) C2} (5) is obtained. According to this, when α2 = α1, that is, when the spectral absorption coefficient of the optical fiber, that is, the spectral transmittances are equal to each other, T = S1,2, and no measurement error occurs regardless of the length x of the optical fiber. become.

The spectral absorption characteristics of the optical fiber are quoted from FIG. 2.3.1 (loss characteristics of ultra-sensitive optical fiber) on page 34 of "Optical Communication Manual" (published by Kagaku Shimbun, August 1984). As shown in FIG. According to this, the loss (dB) as the spectral absorption decreases as the measurement wavelength becomes longer than 0.6 μm and becomes the lowest in the 1.4 to 1.6 μm band.
When it is 6 μm or more, it increases again. In addition, as understood from the equation (2), the sensitivity of the two-color thermometer becomes larger when the two measurement wavelengths λ2 and λ1 are separated from each other. Therefore, referring to FIG. 2, it is desirable to select wavelength bands that are separated from each other and have the same loss. From such a viewpoint, for example, λ1 = 1.30 μm, λ2 =
1.62 μm, or λ1 = 1.40 μm, λ2 = 1.
Various combinations such as 60 μm can be selected. If .alpha.1 = .alpha.2 can be realized by selecting in this way, basically, an instruction error due to a change in the optical fiber length does not occur.

However, in practice, subtle variations between lots of optical fibers or lots of optical filters that control the measurement wavelength band cannot be avoided, and α1 = α2 does not always hold. When α1 ≠ α2,
As is clear from the equation (5), an instruction change is generated depending on the optical fiber length x. For example, the difference in loss between each other is 1%
When T = 1800K using an optical fiber having a length of 1 Km, λ1 = 1.30 μm and λ2 = 1.6 are obtained from the equation (5).
At 2 μm, T−S1,2 = −14.8K, similarly, λ
When 1 = 1.40 μm and λ2 = 1.60 μm, T−S
1,2 = -25.2K is obtained. Since these errors are proportional to the length, 1/2 at 500 m and 1 at 100 m
It becomes / 10. This error cannot be ignored in order to realize accurate temperature measurement.

Therefore, it is an object of the present invention to correct the length by providing a third measurement wavelength band in the wavelength band in which the loss of the optical fiber is large and measuring the spectral luminance by this.

That is, when the absorption coefficient of the optical fiber at the measurement wavelength λ3 is α3 and the length is x, the reading S3 (K) when measuring a black body at temperature T (K) is given by the Wien's formula (C1 ^{/ λ3 5) · exp (-C2} / λ3 S3) = exp (-α3x) · (C1 / λ3 5) · exp (-C2 / λ3 T) (6) is satisfied, organize this for temperature T and S3 Then, 1 / S3-1 / T-=. Alpha.3.times..lambda.3 / C2 (7) is obtained, and the reading difference of T-S3 is proportional to the length x of the optical fiber. As the measurement wavelength band, λ3 = 0.9 μm,
The absorption coefficient of the optical fiber having a length of 1 km was obtained with reference to FIG. 2 (1.7 dB, 0.324 / km), and the temperature was 1800.
When the reading difference T-S3 in K is calculated from the equation (7), T
-S3 = 65.7K is obtained.

Next, from the equations (5) and (7), the optical fiber length x is x = [1 / S1,2-1 / S3] / [{-α3λ3 + (α2-α1) / (1 / λ2 −1 / λ1)} / C2] (8) The temperature T is obtained by applying this to the equation (5).

1 / T = 1 / S1,2- (S1,2-S3) / [-α3λ3 · (1 / λ2-1 / λ1) / (α2-α1) +1] (9) where λ1, λ2 and λ3 are the respective measurement wavelength bands, α1,
Since α2 and α3 are absorption coefficients of the optical fiber at each measurement wavelength and can be treated as initial values, the temperature T is the two-color temperature reading S1,2 and the single-color temperature reading regardless of the length of the optical fiber. It can be calculated from S3.

[0019]

As described above, according to the present invention, the two-color calculation is performed from the detection output of three different wavelengths through the optical fiber, and the length of the optical fiber is corrected from the detection output of the other wavelength. Is to do. For this reason, since the two-color operation is performed, the influence of the change in the transmittance of the optical fiber is small, and the high-precision measurement can be performed. Moreover, the length can be corrected, and the influence of the change in the optical fiber length can be obtained. This enables stable and highly accurate continuous long-time measurement without receiving it.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is a characteristic explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 10 Tip part 2 Measuring object 3 Feeding device 4 Drums 51, 52, 53 Half mirrors 61, 62, 63 Filters 71, 72, 73 Detection element 80 Ratio calculation means 81, 82 Conversion means 9 Calculation means A1, A2, A3 amplification means

Claims (1)

[Claims] 1. A detection element for receiving radiant energy from an object to be measured through an optical fiber and detecting light of at least three different wavelengths, and an output for two wavelengths of each wavelength output of the detection element. Signal ratio signal,
An optical fiber type temperature measuring device, comprising: a calculating means for calculating a temperature by performing a correction calculation based on the length of the optical fiber based on the difference between the ratio signal and the output signals for other wavelengths.