JPH0434692B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention allows light emitted from an object to be measured to pass through a light transmitting means such as a filter or a spectroscopic prism to convert it into light of a known wavelength, and then detects the target object based on this transmitted light. This relates to a radiation thermometer that measures the temperature of a measured object.

Radiation thermometers have the advantage of being able to measure the temperature of an object to be measured without contact, and are therefore used to measure the temperature of heated steel.

First, the principle of such a radiation thermometer will be explained.

The spectral radiance L〓 _,T of the light emitted by the object is the temperature T of the object, the wavelength (hereinafter referred to as the center wavelength) at which the transmittance of the filter that transmits the light emitted by the object is at its maximum (hereinafter referred to as the center wavelength), and the emissivity of the object. It depends on ε and is given by the following formula using Wien's formula and Blank's formula.

Here, C ₁ = 1.19096×10 ^-16 [W・m ² ] C ₂ = 0.0014388 [m・K] The center wavelengths of the filter through which the emitted light from the object is transmitted are λ ₁ , λ ₂ , and the center wavelength λ ₁ , λ ₂ , _the spectral radiance L ₁ , L ₂ at each center wavelength λ ₁ , λ ₂ and emissivity ε ₁ , _{ε 2} can be calculated using equation (1). hand, becomes. Dividing equation (2) by equation (3), we get Therefore, when calculating the temperature T from this formula, T=C ₂ (1/λ ₁ -1/λ ₂ )/ _lo {L ₁ /L ₂ (λ ₁ /λ ₂
) ⁵ }+l _o ε ₂ /ε ₁ (5). This formula is the formula for determining the temperature by measuring the spectral radiances L ₁ and L ₂ .

In general, it is difficult to determine the emissivity ε ₁ and ε ₂ because they vary depending on the wavelength and temperature as well as the surface oxides and deposits of the object. From this, the emissivity ε ₁ , ε ₂ is the center wavelength λ ₁ ,
It is assumed that ε ₁ = ε ₂ without changing depending on λ ₂ . In this way, equation (5) becomes the following equation.

T=-C ₂ (1/λ ₁ -1/λ ₂ )/ _lo {L ₁ /L ₂ (λ ₁ /
λ ₂ ) ² }(6) Among radiation thermometers, the principle equation for a two-color radiation thermometer that measures temperature using light of two different wavelengths is equation (6).

Next, an example of a conventional configuration of a radiation thermometer to which such a principle is applied is shown in FIG. Here, the case of a two-color radiation thermometer among radiation thermometers is shown.

In FIG. 1, 10 is an object to be measured, 20 is a condenser lens, 30 is a filter wheel, 40 is a detection section, and 50 is a calculation section.

The object to be measured 10 is, for example, steel heated at a high temperature, and emits light.

The condenser lens 20 converges the emitted light from the object to be measured 10 .

Filters 31 ₁ and 31 ₂ having different center wavelengths λ ₁ and λ ₂ are attached to the filter wheel 30 and rotated by a motor 32 . Depending on the rotational position of the filter wheel 30, the light converged by the condenser lens 20 passes through the filter 31 ₁
and 31 ₂ can be transmitted. In this case, filters 31 ₁ and 31 ₂ are used as light transmitting means.

The detection unit 40 detects the light that has passed through the filters 31 ₁ and 31 ₂ , separates the light into signals corresponding to the spectral radiances L ₁ and L ₂ , and outputs the signals.

Based on the output of the detection unit 40, the calculation unit 50 calculates
Calculate using equation (6) to find the measured temperature.

In the radiation thermometer having such a configuration, the temperature of the object to be measured is determined as follows.

The emitted light from the object to be measured 10 is converged by the condenser lens 20 and transmitted through the filter 31 .

Of the filters 31 ₁ and 31 ₂ , the one located opposite the condenser lens 20 is used for transmission. The filter to be used is replaced by rotating the filter wheel 30 with the motor 32. Filters 31 ₁ and 31 ₂ are used alternately.

The light transmitted through the filters 31 ₁ and 31 ₂ is received by the detection unit 40 and has spectral radiance L ₁ and L ₂ respectively.
is converted into a signal according to the The calculation unit 50 performs calculation using equation (6) based on the signal from the detection unit 40 to determine the measured temperature.

However, such radiation thermometers have the following problems.

The calculation unit 50 performs the calculation using equation (6), that is, assuming that the emissivity is ε ₁ =ε ₂ . For this reason, the calculation of the calculation unit 50 does not take into account the difference between the emissivities ε ₁ and ε ₂ . Therefore, when the emissivity is ε ₁ ≠ ε ₂ , an error occurs in the measured temperature obtained using equation (6). As a result, this radiation thermometer has a problem in that measurement errors are likely to occur due to changes in emissivity.

The present invention has been made to eliminate the above-mentioned problems, and an object of the present invention is to provide a radiation thermometer that is less prone to measurement errors even when the emissivity changes.

The present invention provides a light transmitting means for transmitting light emitted from an object to be measured and converting it into light having at least a known wavelength, a detecting section for detecting each transmitted light of the light transmitting means, and a detecting section for detecting the transmitted light of the light transmitting means. In a radiation thermometer, the calculation section calculates the temperature of the object to be measured using Wien's formula or Planck's formula based on each output, and the calculation section calculates the true emissivity and the true emissivity. A memory that stores a characteristic graph representing the relationship with the approximate emissivity obtained from a functional equation including variables, and an unknown coefficient in the approximate equation representing the approximate emissivity is calculated based on the output of the detection section. a first means for obtaining an approximate emissivity from an arithmetic expression; a second means for obtaining an approximate emissivity by substituting the value of the obtained unknown coefficient into the approximation equation; If the value of The fourth step is to find an approximate value of emissivity based on
and a fifth means for determining the measured temperature from Wien's formula or Planck's formula using the approximate value determined by the fourth means.

FIG. 2 is a diagram showing the configuration of an embodiment of the radiation thermometer according to the present invention, and here, a two-color radiation thermometer is illustrated. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. In FIG. 2, 60 is an arithmetic unit.

The calculation unit 60 uniquely obtains an approximate value for the emissivity of the object to be measured according to the measurement conditions, and uses this approximate value to obtain the measured temperature from Wien's formula or Blank's formula. The calculation unit 60
- It has fifth means 61 to 65 and a memory 66, and uses these to calculate the measured temperature. The specific calculation will be described later.

In such a radiation thermometer, the measured temperature is determined as follows.

Express the emissivity ε using a predetermined approximation formula, e.g. e〓〓 ² (α is the coefficient)
Approximate by Hereinafter, the emissivity approximated in this way will be referred to as the approximate emissivity. Substituting the approximate emissivities eαλ2 ₁ and eαλ2 ₂ into equations (2) and (3) for the emissivities ε 1 and ε 2 yields the following.

Here, T _n :measured brightness temperature In equations (7) and (8), the measured brightness temperature T _n and the coefficient α are unknown quantities. From this, when equations (7) and (8) are solved for the measured brightness temperature T _n and the coefficient α, the following is obtained.

T _n = C ₂ (λ ² / ₁ / λ ₂ − λ ² / ₂ / λ ₁ ) / (λ ² _{2 lo}
L ₁ λ ⁵ / ₂ /C ₁ −λ ² ₁ l _o L ₂ λ ⁵ / ₁ /C ₁ ) (9) α=1 / λ ³ / ₁ −λ ³ / ₂ (λ ₁ l _o L ₁ λ ⁵ ／ ₁ ／C ₁ −
λ ₂ l _o L ₂ λ ⁵ / ₂ /C ₁ (10) Here, in order to compare the true emissivity ε ₁ , ε ₂ and the approximate emissivity eαλ2 1, equations (2) and (7) are used. Comparing the becomes. Using equations (2), (3), (9), and (11) to organize the relationship between the true emissivity ε ₁ , ε ₂ and the approximate emissivity eαλ2 1, we get becomes. The center wavelength of filters 31 ₁ and 31 ₂ is λ ₁ =
Assuming that 0.81×10 ^-6 [m] and λ ₂ =0.97×10 ^-6 [m], these values are substituted into equation (12) to calculate the true emissivity ε ₁ , ε ₂ and the approximate emissivity eαλ2 1. If you graph the relationship, it will look like Figure 3. In the graph of FIG. 3 (hereinafter referred to as a characteristic graph), the vertical axis represents the approximate emissivity eαλ2 1, and the horizontal axis represents the true emissivity _ε1 .

In the characteristic graph, curves A ₁ , A ₂ ...A ₇ are emissivity ε ₂
This is a graph when is 0.4, 0.5...1. In the characteristic graph, for emissivity ε ₁ and ε ₂ , 0.4 or more 1
The following range is taken. Note that the emissivities ε ₁ and ε ₂ may be set to other ranges. Regardless of the range of such emissivity ε ₁ and ε ₂ , the approximate emissivity e〓〓 ² is
It is in the range of 0.22≦eαλ2 1≦3.59.

B is a graph when the emissivity is ε ₁ =ε ₂ . Intersections C ₁ and C ₂ of graph B and graphs A ₁ and A ₇
Therefore, when the approximate emissivity is eαλ2 1>1, the true emissivity is ε ₂ >ε ₁ , and the approximate emissivity is eαλ2 1<0.75.
When , it can be seen that the true emissivity is ε ₁ > ε ₂ .

In equation (9), the measured brightness temperature T _n is calculated as eαλ2 1≈ε _1. Therefore, as the difference between the true emissivity ε ₁ and ε ₂ increases, the true emissivity ε ₁ and The difference in the approximate emissivity eαλ2 1 also increases. This causes a large measurement error in the measured brightness temperature T _n .

As an attempt, consider the case where the approximate emissivity eαλ2 1 = 2.5. As shown by the straight line D of the characteristic graph and the intersection of ε ₁ = 0.4 and the intersection D ₁ and D ₂ of the graph A ₇ , the true emissivity ε ₁ ,
ε ₂ exists in the range of 0.40≦ε ₁ ≦0.53, 0.8≦1.0. This allows the true emissivity ε ₁ and ε ₂ to be estimated within a somewhat narrow range. However, if the difference between emissivity ε ₁ and ε ₂ is small, the position of straight line D will be lower, and the distance between intersections D ₁ and D ₂ will become longer.
The range for estimating the true emissivity becomes wider.

In the case of the approximate emissivity eαλ2 1=2.5 mentioned above, the approximate emissivity greatly exceeds the range (0.4≦ε≦1.0) for the true emissivity ε ₁ and ε ₂ , so the measured luminance obtained from equation (9) The error in T _n becomes large. Therefore, when the approximate emissivity eαλ2 1 exceeds a certain value (or below a certain value), approximate values for the true emissivity ε ₁ and ε ₂ are determined using the characteristic graph shown in FIG. This reduces the error in the measured temperature.

As an example, a case where the true emissivity is ε ₁ =0.5 and ε ₂ =1 will be explained.

When the relationship between the measured brightness temperature T _n and the true temperature T is determined using equations (2), (3), (7), and (8), the following is obtained.

T=1/1/T _n −λ ² / _{2 lo} ε ₁ −λ ² / _{1 lo} ε ₂ /C ₂ (λ ²
/ ₁ /λ ₂ −λ ² / ₂ /λ ₁ ) (14) Measured brightness temperature T _n and emissivity ε ₁ = obtained from equation (9)
0.5, ε ₂ = 1 into equation (14), the true temperature is T
= 1500 [K]. These true temperature T and emissivity ε ₁ and ε ₂ are unknown values in actual measurement. From this, approximate values for the true emissivity ε ₁ and ε ₂ are obtained using the characteristic graph shown in FIG. 3, and calculations for obtaining a measured temperature close to the true temperature T using these approximate values will be explained.

Approximate emissivity eαλ2 obtained based on equation (10) 1=
Suppose it is 2.63. At this time, in the characteristic graph, the intersections of the straight line E with the approximate emissivity eαλ2 1=2.63, ε ₁ =0.4, and the graph A ₇ are designated as E ₁ and E ₂ . True emissivity ε ₁
exists on the line segments E ₁ and E ₂ , that is, within the range of 0.4≦ε ₁ ≦0.5. If we take the middle value E of ₃ points in this range, we get
The worst error for emissivity ε ₁ is 0.05.
From this, it is assumed that the approximate value of the emissivity at point E ₃ with respect to the true emissivity ε ₁ is ε ₁ ′=0.45. Furthermore, at point E ₃ , the emissivity ε ₂ found from graph A is 0.9, so the approximate value for the emissivity ε ₂ is ε ₂ '=0.9.
shall be.

Approximate values ε ₁ ′, ε ₂ ′ obtained as described above and (9)
By substituting the measured brightness temperature T _n obtained from the equation into the equation (14), the temperature T=1510 [K] is obtained, and this temperature is taken as the measured temperature. Under the aforementioned conditions, that is, true temperature T = 1500 [K], true emissivity ε ₁ = 0.5, and ε ₂ = 1, the measured temperature determined by the conventional radiation thermometer shown in Figure 1 is 1107 [K]. . Below, when the true temperature T and true emissivity ε ₁ , ε ₂ are different, the measured temperature T ₁ obtained by the conventional radiation thermometer obtained in the same way, and the approximation of the emissivity of the radiation thermometer of this example. The relationship between the values ε ₁ ', ε ₂ ' and the measured temperature T ₂ is shown in FIG. As shown in FIG. 4, the temperature measured by the radiation thermometer of this embodiment is closer to the true temperature than the temperature measured by the conventional radiation thermometer.

Here, the memory 66 in the calculation section 60 stores the characteristic graph shown in FIG.

The first means 61 uses the values of the spectral radiances L ₁ and L ₂ obtained from the output of the detection unit 40 to obtain the coefficient α from equation (10).

The second means 62 is to calculate the approximate emissivity by substituting the obtained value of α into the emissivity approximation equation e×p(αλ ₁ ² ).

If the value of the approximate emissivity e×p (αλ ₁₂ ) obtained by the second means 62 is outside a predetermined range, the third means 63 calculates the true radiation using the characteristic graph stored in the memory 66. This is to find the range in which the ratio exists.

The fourth means 64 determines an approximate value of the emissivity based on the intermediate value of the true emissivity in the range determined by the third means 63.

The fifth means 65 obtains the measured temperature by substituting the approximate value obtained by the fourth means 64 and the measured brightness temperature T _n obtained from equation (9) into equation (14).

According to the radiation thermometer having such a configuration, the following effects can be obtained.

The calculation unit 60 uses the characteristic graph to obtain approximate values for the emissivities ε ₁ and ε ₂ according to the measurement conditions, and uses these approximate values to obtain the measured temperature. As a result, as shown in Figure 4,
Even if the emissivities ε ₁ and ε ₂ change, the error in the measured temperature is prevented from increasing.

In the embodiment, a case has been described in which the filter wheel 30, the filter 31, and the motor 32 are used to convert the synchrotron radiation into light of a known wavelength. However, the present invention is not limited to this. The emitted light may be of a known wavelength. In this case, a filter 31 is used as the light transmitting means.
Instead, optical switches, spectroscopic prisms, and diffraction gratings are used. This simplifies the configuration and reduces the size. Further, when a spectroscopic prism, a diagonal grating, or the like is used, the detection unit 40 can detect light of different wavelengths simultaneously. This reduces the time required to determine the measured temperature, and can also be applied to temperature measurements of objects whose temperature changes rapidly over time. In this case, a plurality of light receiving elements are arranged dimensionally or two-dimensionally in the detection section.

As described above, according to the present invention, it is possible to provide a radiation thermometer that is unlikely to cause measurement errors even if the emissivity changes.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the conventional configuration of a radiation thermometer, Fig. 2 is a diagram showing the configuration of an embodiment of the radiation thermometer according to the present invention, and Fig. 3 is a diagram showing the true radiation of the object to be measured. Figure 4 shows the relationship between the true temperature and the temperature measured by the radiation thermometer in Figure 1 and the temperature measured by the radiation thermometer in Figure 2. This is a diagram. 10...Object to be measured, 31, 31 ₁ , 31 ₂ ...
Light transmission means, 40... detection section, 60... calculation section,
61 to 65...first to fifth means, 66...memory.

Claims (1)

[Scope of Claims] 1. A light transmitting means for transmitting light emitted from an object to be measured and converting it into light having at least two or more known wavelengths, and a detection section for detecting each transmitted light of the light transmitting means, A radiation thermometer comprising: a calculation section that calculates the temperature of the object to be measured using Wien's formula or Planck's formula based on each output of the detection section, wherein the calculation section calculates the true emissivity; A memory that stores a characteristic graph representing the relationship between the true emissivity and the approximate emissivity obtained from a functional equation that includes the true emissivity as a variable, and an unknown coefficient in the approximate equation that represents the approximate emissivity based on the output of the detection section. a first means for calculating the approximate emissivity from a predetermined calculation formula; a second means for calculating the approximate emissivity by substituting the value of the calculated unknown coefficient into the approximate equation; and an approximate emissivity calculated by the second means. If the value is outside the predetermined range, a third method is used to determine the range in which the true emissivity exists using the characteristic graph stored in the memory, and the true emissivity in the range determined by this third method is used. The fourth step is to find an approximate value of emissivity based on the intermediate value of emissivity.
A radiation thermometer characterized by comprising: a fifth means for determining a measured temperature from Wien's formula or Planck's formula using the approximate value determined by the fourth means.