JPS601529A - Surface-temperature measuring method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a surface temperature measurement method using a radiation thermometer, and in particular, to a surface temperature measurement method using a radiation thermometer. This invention relates to an improved surface temperature measurement method.

[Background of the invention]

For example, a radiation thermometer is convenient for measuring the temperature of an object being heated in an industrial continuous heating furnace while the continuous heating furnace is in operation. Temperature measurement is widely used. The operating principle of this radiation thermometer is as follows.

The radiant energy E incident on the detector of the radiation thermometer is (
1) It is approximated by Eq.

E=εKT" ... River, Old ... (1) Here, ε is the emissivity of the object whose temperature is being measured, and is a constant.

T is the absolute temperature of the object to be measured, and n is the radiation constant C1 using the measurement wavelength λ, which is usually called the n value expressed as n-=c/λT. In the radiation thermometer, in equation (1),
It measures the radiant energy E. Therefore, in order to determine the temperature T of the temperature-measuring object using a radiation thermometer, the emissivity ε of the temperature-measuring object must be known, as is clear from equation (1).

To solve this problem, a method of measuring emissivity and surface temperature simultaneously, as shown in FIG. 1, has been known. According to this conventional method, first, as shown in FIG. 1(a), a cylindrical cavity 2 with both ends open and whose inner surface is a mirror surface with high reflectance is placed at a distance above the temperature-measuring object 1. The radiation thermometer 3 measures the radiation energy E1 from the object surface.

Next, a cavity 5 is formed by covering the cavity 2 with a mirror 4 having a high reflectance, and the radiant energy E2 from the object surface is measured. In the case of Fig. 1(a), the radiant energy El incident on the radiation thermometer 3 is
It is only the radiant energy that reaches directly from the cavity 2 and is not affected by the cavity 2. On the other hand, in the case of Fig. 1(b),
Thermal radiation from the object 1 is reflected multiple times in the cavity 5,
A portion of this multiple reflected thermal radiation passes through the small hole 6 and enters the radiation thermometer 3. Therefore, the radiant energy E2 incident on the radiation thermometer 3 is much stronger than the radiant energy El in the case of FIG. 1(a), and the emissivity of the object 1 increases. If the emissivity of the object 1 whose apparent emissivity can be determined is ε, and the radiant energy of a black body having the same temperature as the object 1 is Eb, then the following equation holds true.

Et = εEb...1 river...(2) E*=gEb
...Old...river (3) Therefore, Figure 1 (a),
Letting G be the ratio of the radiant energies El and E2 measured by the measurement method shown in (b), the following equation is obtained.

G=E2/E1=g/ε...Mark/Kawa (4) The apparent emissivity g depends on both the effective reflectance γ from the cavity 5 to the object 1 and the surface roughness θ of the object 1. Parameter α
It is shown by the following formula using .

(α+1)ε 6+ke　°°“°゛°°°°old- (4), (51 formula yields the following formula.

α+1−αG. −°−°−°−°−−−−(6) Here, the correlation between the parameter α and the surface roughness θ is determined in advance by experiment. Therefore, in FIG. 1, a surface roughness measuring device (roughness meter) is attached to the radiation thermometer 3, and the surface roughness θ is first measured, and α is calculated based on the θ-α correlation diagram in advance.
Then, by taking the above-mentioned G into the radiation thermometer 3, the emissivity ε of the object 1 can be calculated according to equation (6). When El and ε are equalized, the surface temperature T of the object 1 is equalized according to equation (1). here,
The reason why the apparent emissivity g depends on the surface roughness θ will be described below.

Thermal radiation emitted from object 1 connects cavity 5 and object 1.
This is because the rate at which the light leaks out of the system while reflecting and reciprocating between the two depends on the surface roughness θ. That is, as shown in FIG. 2, part of the thermal radiation reflected from the cavity 5 to the object 1 is absorbed by the surface of the object 10, and the rest is reflected again.

At this time, a part of the reflected thermal radiation leaks out of the system through the gap 7 between the cavity 5 and the object 1.

This leakage rate depends on the state of scattering of thermal radiation on the surface of the object 1, that is, the surface condition. For this reason, the apparent emissivity g depends on the surface roughness θ, as described above.

Therefore, in the conventional temperature measurement method using a radiation thermometer, a radiation thermometer and a roughness meter are used together to determine the radiation resistance, and the surface temperature of the object to be measured is calculated based on this emissivity. procedure had to be used. In addition to the above-mentioned methods, there are several proposals regarding surface temperature measurement methods using radiation thermometers, but all of them have the problem of requiring the emissivity of the temperature-measuring object to be measured. Furthermore, these methods have the problem of not being able to measure the surface temperature continuously if the surface condition of the temperature-measuring object changes from time to time due to oxidation or adhesion of impurities, and the emissivity changes accordingly. There was a point.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a surface temperature measuring method using a radiation thermometer that can measure the surface temperature regardless of the emissivity unique to the object to be measured.

[Summary of the invention]

In order to achieve the above object, the measuring method of the present invention involves placing an artificial black body cover on the thorny surface of the object to be measured, and (1) bringing the lower edge of the artificial black body cover into almost contact with the object to be measured. The feature is that the apparent emissivity of the object to be measured is set to a constant value within a practical accuracy range, regardless of the emissivity specific to the object to be measured, and the surface temperature of the object to be measured is calculated based on this apparent emissivity. shall be.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. The artificial black body cover 8 includes a cylindrical cavity 9 with one end open and an inner surface with high reflectance (low emissivity), and an objective auxiliary cover 10 with a cylindrical shape with both ends open and also with high reflectance. . A small hole 12 is bored in the top surface of the cavity 9 facing the radiation thermometer 3), and thermal radiation from the object to be measured 1 enters the radiation thermometer 3 through the small hole 14.

A protrusion 11 attached to the side surface of the objective auxiliary cover 10 forms a groove 1 formed on the inner surface of the cavity 9 in the vertical direction in the figure.
At the same time, the weak spring 3 is structured to lightly push the objective auxiliary cover 10 downward.

With this structure, the objective auxiliary cover 10 can move up and down smoothly, and the artificial black body cover 8 and the object to be measured 1 can move smoothly up and down.
This forms a cavity 15 that is sealed except for the small hole 14 (or the gap can be ignored). Further, the objective auxiliary cover 10 is made of a heat insulating material and blocks heat from the object 1 to be measured.

The method of measuring the surface temperature using the artificial blackbody cover configured as described above cannot be called a non-contact method in the strict sense.

However, since the above-mentioned auxiliary cover 10 only lightly contacts the surface of the object to be measured 1, it does not restrict the movement of the object to be measured 1 in the horizontal direction. Moreover, it follows and fits the horizontal movement of the object to be measured 1 and performs its function as described later, so that it is equivalent to a non-contact method in terms of practical function.

The principle of the surface temperature measurement method of the present invention will be described below.

First, consider an ideal case where the reflectance γ of the inner surface of the artificial blackbody cover 8 shown in FIG. 3 is 1.0 (complete reflection), small holes can be ignored, and a sealed cavity 15 is formed. According to the principle described later with reference to FIG. 4, the apparent emissivity εf of the object to be measured 10 is 1.0 regardless of the emissivity ε of the object to be measured 1 itself. Therefore, by measuring the radiation energy E+ with the radiation thermometer 3, the temperature of the object to be measured 1 is
The temperature T of .

E+=εt KT"=KT r' ・・・・・・・・・
(In the actual case, there is absorption of thermal radiation by the inner surface of the artificial black body cover 8 and leakage of thermal radiation from the small holes 14, so that the apparent emissivity ε does not reach 1.0.

However, as will be explained later using FIGS. 5 and 6,
Within the allowable temperature measurement error range, the apparent emissivity εf of the temperature-measuring object 1 does not depend on the emissivity ε of the temperature-measuring object 11, and the space between the artificial blackbody cover 8 and the temperature-measuring object 1 It can be regarded as a constant value that depends only on the shape. Therefore, once in advance, the apparent emissivity ε! By measuring , it does not depend on the emissivity ε of the temperature-measuring object 1 (there is no need to know the emissivity of each temperature-measuring object), and the surface condition of the temperature-measuring object 10 changes during the measurement. Even if the emissivity ε changes, the temperature of the temperature-measuring object 1 can be determined by the following equation.

El-εaKT11 ・・・・・・・・・・・・(8)
Here, Et is the radiant energy measured by the radiation thermometer 3.

Figure 4 shows the case where the artificial blackbody cover is ideal, that is, the third
When the cavity 15 shown in the figure is completely sealed and the reflectance γ of the inner surface of the artificial black body cover is 1.0, the apparent emissivity εf of the object to be measured 1 is 1.0. show. Fourth
As shown in Figure (a), the cavity 15 having small holes repeatedly reflects incident light (thermal radiation) on its inner wall surface.
Again, the light is not given a chance to escape from the small hole to the outside world, and all of it is absorbed by the inner wall surface. Therefore, the inner wall surface appears to be a black body. In other words, the emissivity of the inner wall surface appears to be 1.0 above, regardless of the emissivity of the inner wall surface itself.

Of course, thermal radiation emitted by the inner wall surface is also absorbed by the inner wall surface. Such a cavity 15 is usually called an artificial blackbody. FIG. 4(b) shows the principle of the artificial black body cover of the present invention, which is an application of the principle of the artificial black body shown in FIG. 4(a). The fundamental structural difference between FIG. 4(a) and FIG. 4(b) is that the reflectance of the artificial black body cover 16 forming the cavity 15 in FIG. 4(b) is 1.0 (complete reflection). ) The advantage is that no absorption of thermal radiation occurs on this surface. therefore,
For example, as shown in Fig. 4(b), the thermal radiation emitted at point A of the temperature-measuring object 1 is reflected several times between the artificial blackbody cover 16 and the temperature-measuring object 1. However, it is eventually absorbed by the object to be measured 1 (in this case, point B).

Therefore, also in FIG. 4(b), the surface of the object to be measured 1 appears to be a black body (emissivity 1.0). That is,
It can be seen that by providing an artificial blackbody cover on the flat temperature-measuring object 1, it is possible to create an effect equivalent to creating an artificial blackbody by creating a closed cavity with only the temperature-measuring object 1. . In the present invention, an artificial black body cover is defined by a small hole 14 on the top surface as in the member 16 illustrated in FIG. 4(b) above.
Refers to an opaque cover with a

Next, consider an actual case in which absorption of thermal radiation in the artificial blackbody cover and leakage to the outside of the cavity are considered. This will be explained based on FIG.

Assuming that the effective reflectance from the artificial blackbody cover 8 side to the temperature-measuring object 1 is γl<1), the emissivity of the temperature-measuring object 1 is ε, and the temperature is T, initially, the temperature-measuring object 1 γ, (εKT″) of the radiant energy εKT″ of thermal radiation emitted from
is reflected from the artificial black body cover 8 side to the object to be measured 1 and returns. Then, εγ, (εKT ”
) absorption occurs, and the remaining γ, (1-ε) (εK
T") is again radiated to the artificial black body cover 8 side. Therefore, the radiant energies E and f that finally enter the radiation thermometer 3 are expressed by the following series.

Bat-εKT"(1+r-(1') +r,"(1'
)2+γ:(1-ε)3+・Mountain・・）・Old・・・・
(9) Equation (9) is a geometric series with common ratios γ and (1-ε), and since r and (1-ε) are multiplied by 1, the following expression is obtained.

・・・・・・・・・(10) Apparent emissivity is ε! Then, the formula (10) is...
□-7, (□-6) (11) The effective reflectance γ6 after deformation is a term (γ) that depends on the reflectance of the material of the artificial black body cover. and the probability P of surviving without leaking from the small hole 14, and can be approximated by the following equation.

γ, = γP ・・・・・・・・・・・・(13) Small hole 1
The thermal radiation reaching 4 is multiple scattered on the inner surface of the artificial black body cover 8, and the influence of the surface roughness of the temperature-measuring object 1 as explained using FIG. 2 can be ignored. . From this, γ depends only on the material and shape of the artificial blackbody cover. Therefore, 1-γ in equation (12).

γ, > (-) ・・・・・・・・・・・・(14)
If this holds true, it can be seen that the apparent emissivity εf of the object to be measured 1 has no relation to the emissivity ε. In addition, εf depends on the emissivity ε, and even if εf changes due to a change in the emissivity ε (due to a change in the type of object to be measured or a change in the surface condition), an error in the measured temperature due to the change in εf is acceptable. Within this range, fluctuations in the emissivity ε can be ignored, and the apparent emissivity εf can be kept at a constant value during this period. In this way, when the apparent emissivity εf can be considered constant from the viewpoint of temperature measurement tolerance, the apparent emissivity εf is said to be a substantially constant value. The relationship between the error Δεf caused by assuming that ε1 is constant and the error ΔT in the measured temperature T caused by this Δεf is (
From equation 8), it is approximated by the following equation.

1ΔT/TI=-1Δεf/ε11 ・・・・・・・・・
・(15) From equation (15), if an error of ΔT/T<1% is allowed, then approximately Δεt / t t
(It can be seen that an error of n% is allowed.

Next, the emissivity ε of the object to be measured 1 is ε=ε, and ε=1.0.
Calculate the value η of Δεf/εf when it fluctuates to .

According to equation (12), for example, if an error of ΔT/T<1% is allowed, then Δεf/ε, (n% is allowed, so substitute η−n into equation (17) to find gum. In particular, it can be seen that even if the emissivity of the temperature-measuring object varies from ε-ε to 1.0, the apparent emissivity εf can be assumed to remain at a substantially constant value. The ε function is a function of γ when the allowable error of ΔT/T is fixed, so when η is fixed, this situation is shown in Figure 5. In the figure, the curve shown by the solid line is (17) The following formula is satisfied.

When the emissivity ε of the temperature-measuring object is in the region (shaded area) above this curve, the apparent emissivity εf can be considered to be substantially constant. Therefore, even if the emissivity of the object to be measured is not known, the present invention can be applied if it is guaranteed that at least εmin rise is large.

FIG. 6 shows a group of curves expressed by equation (18) using the ΔT/T value as a parameter. Here, according to equation (15), ΔT/T=
i・η, and the n value is the measurement wavelength λ = 2 μm1 radiation constant C
= 1.44X10' μm IC, measured temperature km o.

°, it was set to η-12. Now, the concrete structure of the artificial blackbody cover 8 shown in Fig. 3 is such that the entire inner surface is plated with gold, the outer diameter of the cavity 9 is 30 + o + nφ, and the height of the small hole 14 is 30 m1, and the small hole is 1 m + nφ. The effective reflectance γ when The reflectance of gold for light with a measurement wavelength of 2 μm is 0.983.

On the right side of equation (13), γ is approximated by γ-0,983.

Also, the probability (1-P) of leakage from the small hole 14 is the temperature measured object 1.
Assuming that it is directly proportional to the solid angle when looking at the small hole 14 from the angle, we obtain Pki 0.9998. But two ((13)
From the formula, r, medium 0.983X0.9998=0.983
get. Accordingly, from FIG. 6, the artificial black body cover 8 of this example
When using ΔT/T=5% tolerance range,
It can be seen that the present invention is applicable as long as it is guaranteed that the emissivity ε of the object to be measured is 0.028 or more. 6th
From the figure, it can be seen that it is desirable to design the reflectance γ of the artificial blackbody cover to be as large as possible. In order to make the inner surface of the artificial black body cover highly reflective, plating the inner surface with silver, copper, or aluminum or applying magnesium oxide powder is also effective. Furthermore, since the reflectance of metal increases as the wavelength becomes longer, it is desirable to select and use the optimum measurement wavelength.

The temperature of the artificial black body cover 8 is lower than the temperature of the object to be measured and the thermal radiation emitted from the artificial black body cover 8 can be ignored, but if the measured temperature is high, the artificial black body cover 8 is cooled. That is desirable.

FIGS. 7 and 8 show an embodiment different from the above.

In FIG. 7, the effective reflectance r of the artificial black body cover 17,
An example is shown in which mirrors 18 and 18' are provided for the purpose of preventing the leakage of thermal radiation from the small hole 14 in order to increase the thermal energy. The mirror 18 is attached to the artificial black body cover 1 via the support 19.
7, and the mirror 18' is directly attached. From FIG. 7 onwards, illustration of the objective auxiliary cover 10 shown in FIG. 3 is omitted.

Furthermore, if the temperature measurement tolerance is relatively large, the method of the present invention can be carried out by omitting the installation of the objective auxiliary cover 10 and bringing the artificial blackbody cover into almost contact with the object to be measured.

The embodiment of FIG. 8 also has a small (Li2
The artificial blackbody cover 20 in this example is constructed as follows.

That is, the artificial black body cover 20 is a fan-shaped cover 20 described below.
2 and the donut-shaped cover 20b are formed into a hollow body having a shape that concentrically penetrates each other with respect to the center line Z-Z.

The fan-shaped cover 208 described above is formed by rotating a sector having an apex angle θ1 around a bisector of the apex angle.

Further, the donut-shaped cover 20b is formed by rotating a quarter circumference of the radius R2 around the center line ZZ. The shape of such an artificial black body cover 20 is named fan-shaped crown shape.

This is an example of a reflection path of thermal radiation emitted from the arrow dldD point in FIG. 8. By providing the fan-shaped crown-shaped artificial blackbody cover in this manner, it is possible to suppress thermal radiation leaking from the small holes 14 to the outside world.

FIG. 9 shows an embodiment configured to detect local temperature in order to measure temperature distribution.

The artificial black body cover 21 in this example has a fan-shaped cross section, and the bisector of the apex angle of the fan shape is perpendicular to the surface to be measured. ? c'i''L, the thermal radiation emitted from the temperature-measuring object 1 is reflected by the artificial black body cover 21 and then concentrated on the temperature-measuring object 1 again, increasing the apparent emissivity. It has a structure.

FIG. 10 shows another example of an artificial blackbody cover for measuring temperature distribution. In the one shown in FIG. 9, the artificial black body cover 21 must be moved in order to measure the temperature distribution, but in FIG. The temperature position can be scanned. - [Effects of the Invention] As detailed above, the surface temperature measurement method of the present invention places an artificial blackbody cover on the surface of the object to be measured, and places the lower edge of the artificial blackbody cover on the object to be measured. The apparent emissivity of the object to be measured is made to be a constant value within the accuracy range required for practical use, regardless of the emissivity specific to the object to be measured. By calculating the surface temperature, the surface temperature of the object to be measured can be measured regardless of the emissivity unique to the object to be measured.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are illustrations of a conventional method for measuring surface temperature, Figure 2 is an illustration of the influence of surface roughness on emissivity, and Figure 3 is an illustration of an embodiment of the method of the present invention. 4(a) and 4(b) are schematic cross-sectional views for explaining the principle of the method of the present invention. FIGS. 5 and 6 are charts showing the relationship between the emissivity of the temperature-measuring object and the reflectance of the artificial blackbody cover. FIGS. 7 to 10 are schematic cross-sectional views for explaining embodiments different from those described above. 1... Temperature measured object, 2... Cavity, 3... Radiation thermometer, 4... Lid, 5... Cavity, 6...
・Small hole, 7... gap, 8... artificial black body cover,
9... Cavity, 10... Objective auxiliary cover, 11
...Protrusion, 12...Groove, 13...Spring, 1
4...Small hole, 15...Cavity, 16...Artificial black body cover, 17...Artificial point book cover, 18.18'...
- Mirror, 19... Support, 20... Artificial black body cover, 21... Artificial black body cover, 22... Artificial black body cover, 23... Scanning mirror. Agent Patent Attorney Masami Akimoto No. 1 Ryo imitation) (b) 1,200 No. 30 Condolences 4-Haze ('2L') (b No. 5 Haze A to engineering black body force'-reflectance. In Figure 6 □ Koushii wood cover anti-Saijyu J8 No. 1 Kasumi Tsuri 10 [￥]

Claims (1)

[Claims] In a surface temperature measurement method using a 1° radiation thermometer, an artificial blackbody cover is placed on the surface of an object to be measured, and the lower edge of this artificial blackbody cover is brought into almost contact with the object to be measured. Then, the apparent emissivity of the object to be measured is set to a constant value within a precision range that is practically required, regardless of the emissivity specific to the object to be measured, and the surface temperature of the object to be measured is determined based on this apparent emissivity. A surface temperature measurement method characterized by calculating. 2. The surface temperature according to claim 1, wherein the artificial blackbody cover is composed of a cavity having an inner surface with high reflectance and an auxiliary cover in contact with the object to be measured. Measuring method. 3. The cavity of the artificial black body cover has a cylindrical shape with a top and bottom, and the auxiliary cover has a cylindrical shape that fits into the cavity in a sliding self-pressure manner. The surface temperature measuring method according to scope 2. 4. The surface temperature measuring method according to claim 2, wherein the artificial black body cover is provided with a reflecting mirror therein. 5. Claim 2, wherein the artificial black body cover has a vertical section having a fan-shaped crown shape.
Surface temperature measurement method described in section. 6. The surface temperature measuring method according to claim 2, wherein the artificial black body cover has a vertical cross section that is fan-shaped. 7. The surface temperature measuring method according to claim 1 or 2, wherein the artificial black body cover includes a cavity having a fan-shaped cross section and a scanning mirror. .