JPH07270242A - Optical fiber radiation thermometer - Google Patents

Abstract

PURPOSE:To measure temperature without being affected by the optical fiber length by using two wavelegths. CONSTITUTION:Radiation energy from a measuring object 2 is detected with detection elements 71, 72 through an optical fiber 1 and two different filters 61, 62. By calculating the ratio of the outputs of the detection elements 71, 72 with a ratio operation means 80, the temperature is calculated with the operation means 80. One or both wavelength zones in the measuring wavelength zone are controlled by a control means 9 before the measurement so that the transmittances in the optical fiber 1 of each wavelength zone become equal.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A radiation thermometer using an optical fiber as an optical conductor is disclosed, for example, in "New Edition Temperature Measurement" (Measuring and Automatic Control Society, published on October 25, 1992, first edition), page 4.29 on page 231.
As described in, there are various usage forms. By using the optical fiber, not only the temperature at a narrowly bent portion can be measured but also this can be avoided even if there is a medium on the measurement optical path that obstructs the emitted light. Moreover, since the outer shape of the optical fiber is small, the optical fiber has various excellent characteristics such as easy incorporation into the device.

[0003]

However, since the optical fiber is made of high-purity quartz, even if the outer diameter is made smaller than 1 mm, the flexibility is naturally limited, and when it is strongly bent, or There is a risk of breakage when given a strong impact, and the same applies when exposed to high temperatures. Of course, by covering the outer circumference of the optical fiber with an elastic body such as rubber, plastic, or a corrugated tube, this defect can be compensated, but the outer shape becomes thick and the cost is increased.

On the other hand, when the optical fiber is broken, the end face of the optical fiber becomes jagged and the surface reflection of light increases, so it is necessary to optically polish it. It is not easy to perform this work as an emergency measure during measurement, because tools used for polishing are not generally used. Moreover, in order to correct the change in transmittance due to the change in the length of the optical fiber,
It is necessary to calibrate the scale again, which is also urgently difficult.

Therefore, an object of the present invention is to use a two-color thermometer that is not easily affected by the optical path length of a radiation thermometer, and correct the optical characteristics peculiar to the optical fiber in advance. An object of the present invention is to provide an optical fiber radiation thermometer capable of measuring temperature without influence.

[0006]

The present invention relates to a spectroscopic unit that disperses radiant energy that is incident from a measurement target through an optical fiber, and two different measurement wavelength bands of the light that is spectroscopically dispersed by the spectroscopic unit. Element for detecting the light, a calculating means for calculating the temperature by obtaining the ratio of the output signals of the two measuring wavelength bands of the detecting element, and two measuring wavelength bands which are split by the spectroscopic means and are incident on the detecting element. An optical fiber radiation thermometer having one or both of them adjusted and adjusting means for making the transmittances of the optical fibers for both wavelengths equal.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing the structure of an embodiment of the present invention. In the figure, reference numeral 1 is an optical fiber, and a tip portion 1a as a condensing portion is a lens 3 or the like from a measuring object 2 Collects radiant energy. The other end 1b of the optical fiber 1 serves as an optical connector or the like, collects the radiant energy from the tip 1a, and guides it to the radiation thermometer 4. Then, this radiant energy is split into two directions through the half mirror 5 and is passed through filters 61 and 62 as spectroscopic means that transmit light in different measurement wavelength bands λ1 and λ2, and is detected by the detection elements 71 and 72. To be detected. The outputs of the detection elements 71 and 72 are amplified by the amplification means A1 and A2, and the amplification means A
The ratios of the outputs of 1 and A2 are taken by a ratio calculating means 80, and the calculating means 8 performs a calculation based on the ratio signal to obtain a temperature signal. At this time, the filter 61 can be tilted at a desired angle θ with respect to the incident light by the adjusting means 9, and the transmitted wavelength can be variably adjusted, and the absorption coefficient of the optical fiber 1 at the wavelengths λ1 and λ2 can be adjusted. The temperature signals can be obtained without being affected by the length of the optical fiber 1 by selecting them to be equal. A microcomputer may be used for the ratio calculation means 80, the calculation means 8 and the like to digitally perform a process such as two-color calculation.

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 coefficient of the optical fiber,
When the absorption coefficient is α and the length is x, the transmittance is exp (-α
x), the absorption coefficients in the measurement wavelength bands λ1 and λ2 are α1 and α2, respectively, and S (K) is obtained when the black body at the temperature T (K) is measured through the optical fiber having the length x. If the reading is obtained, the relationship of R (S) = [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 / S = (α2-α1) x + (1 / λ2-1 / λ1) C2 / T (4) When this is obtained for the temperatures S and T, 1 / S −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 = S and the measurement error does not occur regardless of the length x of the optical fiber. .

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 reality, 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, in the case of T = 1300K using an optical fiber having a length of 1 km, the difference between the losses is ±
Even with 1%, from equation (5), λ1 = 1.30 μm, λ2 =
When 1.62 μm, the difference between T and S is ± 7.2 K, and similarly, when λ1 = 1.40 μm and λ2 = 1.60 μm,
The difference between T and S is ± 12.4K, and these errors are proportional to the length as is clear from the equation (5). Therefore, this error cannot be ignored in order to realize precise temperature measurement.

Therefore, one or both of the measurement wavelength bands λ1 and λ2 can be adjusted, and before the measurement, the absorption coefficients α1 and α2 of the optical fiber 1 of the measurement wavelength bands λ1 and λ2 are It is an object of the present invention to adjust the measurement wavelength band so that α1 = α2 holds.

That is, in FIG. 1, when the filter 61 is an interference film filter and the adjusting means 9 tilts the angle θ,
The transmission center wavelength λm is given by λm = 2nh · [1- (sin θ / n) ² ] ^1/2 / m (6). Here, the thickness is h, the refractive index is n, and the order is m. According to this, since the transmission center wavelength λm is a function of the inclination θ of the optical axis, the transmission center wavelength λm can be changed by adjusting this inclination. For example, n is 1.5 to
When 2, is adjusted by ± 45 degrees, transmission center wavelength λm
Fluctuates by 12-6%. This means that when θ is 0 degrees, for example, if the wavelength λm = 1.6 μm, then 0.19.
As a result, the transmittance can be adjusted practically as can be seen from FIG.

In this way, using the relationship of the equation (6),
The transmittances of both wavelengths are adjusted to be equal. That is,
This wavelength λm is the wavelength λ1 of the filter 61 in FIG.
And the transmittance α in the optical fiber 1 of this wavelength λ1
1 and the transmittance α2 of the filter 62 at the wavelength λ2 of the optical fiber 1 is α1 = α2, the measurement wavelength band is adjusted before the measurement is started. Disappear. The angle of the filter 62 may be adjusted in the same manner, and both wavelengths may be adjusted.

Next, FIG. 3A shows a main part of another embodiment. Radiant energy incident from an optical fiber (not shown) is branched into two via the half mirror 5, one light is incident on the detection element 72 via the filter 62 which transmits light of wavelength λ2, and the other light is Light having a predetermined wavelength λ1 is detected through the slit 10a by dispersing the light with a spectroscopic means 60 that generates a continuous spectrum such as a prism or a grating (diffraction grating), and making the angle of the spectroscopic means 60 variable and tilting with the adjusting means 91. It is incident on the element 71. The transmittance α of the optical fiber 1 having the wavelength λ1 by the spectroscopic means 60
If the measurement wavelength band is adjusted so that the relationship between 1 and the transmittance α2 of the filter 62 at the wavelength λ2 in the optical fiber 1 is α1 = α2, the influence of the length of the optical fiber 1 is eliminated.

Further, as shown in a modified example in FIG. 3 (b),
Light of incident radiant energy is dispersed by a spectroscopic means 60 such as a prism or a grating (diffraction grating) that generates a continuous spectrum, and a slit 1 is formed on a detection element 71 at a predetermined position.
The light of wavelength λ1 is made to enter via 0a, and the light of wavelength λ2 is made to enter the detection element 72 at another predetermined position via slit 10b. By adjusting and adjusting the positions of these detection elements 71 and 72 by the adjusting means 92, the spectroscopic means 60
Of the light having specific wavelengths λ1 and λ2 dispersed by the detecting element 7
It is incident on 1, 72. Wavelength λ1 by this spectroscopic means 60
If the measurement wavelength band is adjusted so that the relationship between the transmittance α1 in the optical fiber 1 and the transmittance α2 in the optical fiber 1 having the wavelength λ2 is α1 = α2, the influence of the length of the optical fiber 1 is eliminated.

Before the measurement is started, it is necessary to make adjustments so that the theoretically determined measurement wavelength band is realized. To actually make the adjustments, as shown in FIG. 4, for example, in FIG. The tip 1a of the optical fiber 1 shown is inserted into the cavity of the black body furnace 11 at a predetermined temperature T (K),
The temperature is detected by the temperature sensor 12 such as a thermocouple, the measuring means 13 measures the temperature T, and the indicating means 13a displays it. The radiant energy from the optical fiber 1 is, for example, the half mirror 5, the filters 61 and 62, the detecting elements 71 and 72, the amplifying means A1 and A2, and the ratio calculating means 8 shown in FIG.
The temperature S is measured by the measuring unit 14 corresponding to the radiation thermometer 4 including 0 and the calculating unit 8 and the temperature S is displayed on the indicating unit 14a. Then, the adjusting means 9 is adjusted so that each measuring means 13,
If the indicating temperatures T and S of the indicating means 13a and 14a of 14 are made to coincide with each other and then the optical fiber 1 is used for measurement,
The correct temperature T can be measured regardless of the length of the optical fiber 1.

Although the radiation thermometer with two wavelengths has been described above, the same can be applied to a radiation thermometer using three or more wavelengths, and correct temperature measurement can be performed regardless of the length of the optical fiber. .

[0021]

As described above, according to the present invention, the detection output of two different measurement wavelength bands is output through the optical fiber.
In addition to performing color calculation, one or both measurement wavelength bands are adjusted before the measurement so that the transmittances of the optical fibers in the respective measurement wavelength bands become equal. In this way, since the two-color calculation is performed using the measurement wavelength band having the same transmittance, it is possible to perform highly accurate temperature measurement without being affected by the transmittance of the optical fiber.
Moreover, it is not necessary to consider the length, and the measurement is stable for a long time continuously without being affected by the change of the fiber length.
It becomes possible with high accuracy.

[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.

FIG. 3 is a structural explanatory view showing an embodiment of the present invention.

FIG. 4 is a structural explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 1a Tip part 2 Measurement object 3 Feeding device 4 Radiation thermometer 5 Half mirrors 60, 61, 62 Spectral means 71, 72 Detection element 80 Ratio calculation means 8 Calculation means 9, 91, 92 Adjustment means 10a, 10b Slit 11 Blackbody furnace 12 Temperature sensor 13, 14 Measuring means A1, A2 Amplifying means

Claims (1)

[Claims] 1. A spectroscopic unit that disperses radiant energy that is incident from an object to be measured through an optical fiber, and a detection element that detects light in two different measurement wavelength bands among the light that is spectroscopically dispersed by the spectroscopic unit. , Adjusting one or both of the two measuring wavelength bands which are split by the spectroscopic means and are incident on the detecting element, and the calculating means for calculating the temperature of the output signal for the two measuring wavelength bands of the detecting element. An optical fiber radiation thermometer, comprising: an adjusting means for adjusting the transmittances of the optical fibers for wavelengths to be equal.