JPH11223554A - Temperature measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measuring instrument which can measure the temperature of an object to be measured with high accuracy in a non- contacting state. SOLUTION: A galvanometer mirror 20, a condenser lens 30, and a reflecting mirror 40 jointly position the point which is optically conjugate with a focal point that is set at the upper end of an optical fiber 51 near the position of the virtual image VI of a reflecting plate 10 when the lower surface of an object OB to be measured for temperature is a mirror surface. In addition, the mirror 20 switches the point which is optically conjugate with the upper end of the fiber 51 between the reflecting surface 10a and the inside of the through hole 10b of the reflecting plate 10. Since the radiant quantity of thermal radiation is measured by means of a radiation thermometer 50 in both states where the conjugate point is switched to the reflecting surface 10a and to the inside of the through hole 0b and the temperature of the object OB is calculated based on the measured radiant quantities, the temperature of the object OB can be measured with high accuracy in a non-contacting state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature measuring device for measuring the temperature of an object to be measured based on heat radiation.

[0002]

2. Description of the Related Art Conventionally, a temperature measuring device that measures the temperature of an object to be measured in a non-contact manner without measuring the amount of direct or indirect heat radiation from the object to be measured has been used. First, the temperature of the object to be measured is measured.

[0003]

However, in order to obtain the temperature of the object to be measured from such an amount of radiation, it is necessary to know the value of the emissivity. The emissivity is determined in advance, and the temperature is calculated using the emissivity. However, since the emissivity differs depending on the material (properties) of the object to be measured and its surface state, a plurality of materials having different materials (properties) are used. When measuring the temperature of a temperature measurement object, it is not possible to obtain an accurate emissivity of each measurement object, and the temperature measurement result has a low accuracy.

An object of the present invention is to overcome the above-mentioned problems in the prior art, and an object of the present invention is to provide a temperature measuring device capable of performing non-contact highly accurate temperature measurement.

[0005]

According to a first aspect of the present invention, there is provided a temperature measuring apparatus for measuring a temperature of an object to be measured based on heat radiation.
A reflector provided with a first reflection region having a first reflectance and a second reflection region having a second reflectance while facing the object to be measured; The surface facing the reflection plate of the object to be measured is virtually a mirror surface between the radiation amount measuring means for measuring the radiation amount of the heat radiation and the light receiving portion of the object to be measured and the radiation amount measuring means. The optical system that positions the optically conjugate position with the light-receiving part almost on the reflection plate, and the temperature of the object to be measured is detected based on the measurement result of the radiation amount obtained by the radiation amount measuring means. And a radiation path switching means for switching the position of the optical system conjugate with the light receiving section of the radiation amount measuring means between the first reflection area and the second reflection area of the reflection plate.

According to a second aspect of the present invention, there is provided the temperature measuring apparatus according to the first aspect, wherein one of the first reflection area and the second reflection area of the reflection plate has the reflection plate. It is a through hole that penetrates, and the other is a reflection surface other than the through hole.

According to a third aspect of the present invention, there is provided the temperature measuring apparatus according to the second aspect, wherein the radiation path switching means is a galvanometer mirror.

According to a fourth aspect of the present invention, there is provided the temperature measuring apparatus according to the second aspect, wherein the radiation path switching means focuses the heat radiation on the light receiving portion of the radiation amount measuring means. It is characterized by comprising a lens and lens moving means for moving the lens in a plane substantially perpendicular to its optical axis.

According to a fifth aspect of the present invention, there is provided the temperature measuring apparatus according to the fourth aspect, wherein the lens moving means comprises a lens holding means for holding the lens, and a lens holding means for holding the lens. Rotating means for rotating in a plane perpendicular to the optical axis of the lens about a position separated from the optical axis.

Further, according to a sixth aspect of the present invention, in the temperature measuring apparatus of the fourth aspect, the radiation path changing means includes a plurality of lenses, and the lens moving means includes a plurality of lenses. The lens is parallel with each optical axis,
And a lens holding means for holding the concentric circles having different radii, and a rotating means for rotating the lens holding means in a plane perpendicular to the optical axis about the center of the concentric circles having different radii. It is characterized by.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <1. Principle of the Invention> Before describing the embodiments, the principle of temperature measurement according to the present invention will be described below.

In general, when an opaque (transmittance is “0”) object is in a thermal equilibrium state, the following relational expression holds according to Kirchhoff's law.

[0013]

(Equation 1)

Here, ρ and ε are positive values of “1” or less representing the reflectance and the emissivity of the object to be measured, respectively.

Hereinafter, a case of measuring the temperature based on the heat radiation from the object to be measured will be described.

FIG. 1 is a diagram for explaining the principle of temperature measurement according to the present invention. As shown in the drawing, in the present invention, the object to be measured is held near the reflector and opposed thereto. A radiation amount measuring means for measuring the radiation amount is provided below the radiation amount measuring unit.

The amount of heat radiation at the temperature T of the black body is represented by L
When expressed as b (T), the radiation amount of the direct thermal radiation from the object to be measured having the emissivity ε is expressed as εLb (T). Further, when the heat radiation is reflected by the reflector, the amount of the radiation becomes heat radiation represented by RεLb (T) using the reflectance R of the reflector, and travels toward the object to be measured. Further, when the heat radiation is reflected again by the reflector, the amount of the radiation becomes εR (1−ε) Lb (T) using the equation of Equation 1.
In this way, when multiple reflections are sequentially repeated between the object to be measured and the reflector, the apparent radiation amount Ieff received from the object to be measured received on the reflector side becomes the first term εLb (T),
Since it is expressed as an infinite geometric series of the common ratio R (1−ε) (> 1), the following equation is obtained.

[0018]

(Equation 2)

Here, the apparent emissivity εeff is given by the following equation.

[0020]

(Equation 3)

Therefore, if the reflectance R of the reflector and the emissivity ε of the object to be measured are known, the apparent radiation amount I
By measuring eff, the temperature T of the object to be measured should be obtained from Equations 2 and 3, but in actuality, the reflectance R of the reflector and the emissivity ε of the object to be measured are various. Values may vary depending on factors such as
Since the emissivity ε of the object to be measured greatly depends on its material and surface condition, if this is measured in advance and is used in the equation (3), an accurate temperature T of the object to be measured cannot be obtained.

That is, in the equation of the equation (2) into which the equation of the equation (3) is substituted, two unknowns are the temperature T of the object to be measured and the emissivity ε.
Is not uniquely sought. Therefore, in the present invention, two regions having different reflectivities are provided on the reflector, and the expression of Equation 3 is applied to the heat radiation after multiple reflection in each region (the reflectivities R1 and R2). The accuracy of the temperature measurement is improved by obtaining the temperature T of the object to be measured by simultaneously combining the two equations for the two unknowns. That is, 2
The formula for obtaining the apparent radiation amounts I1 and I2 of the species is as follows.

[0023]

(Equation 4)

[0024]

(Equation 5)

Further, when the radiation amount Lb (T) of the black body is eliminated from the equations (4) and (5) and the emissivity ε of the object to be measured is solved, the following equation is obtained.

[0026]

(Equation 6)

As shown in FIG. 1, in the apparatus according to the present invention, the radiation path changing means (in FIG. 1, a galvanometer mirror is shown) converts the heat radiation, which has been subjected to multiple reflections by the regions having different reflectivities in the reflector, to the heat radiation. By individually leading to the radiation amount measuring means, the respective apparent radiation amounts I1 and I2 are measured, and the reflectances R1 and R2 measured in advance are used to obtain the emissivity ε using the equation (6). ,
Further, using it in Equation 4 or Equation 5, the radiation amount Lb of the black body
Find (T). Then, the temperature T of the object to be measured is determined based on the temperature distribution of the radiation amount Lb (T) of the black body known in advance based on the temperature T.

However, the equations (4) and (5) hold even when the reflectivity R1 or R2 of the reflector is substantially "0". That is, when a through-hole is provided as a region having a different reflectance from the reflection surface of the reflection plate,
Since the heat radiation from the object to be measured in the vicinity is incident on the through-hole without being reflected, multiple reflection does not occur. Therefore, the radiation amount at that time is approximately ε as described above.
It is considered that Lb (T) is obtained.
Even if = 0 (or R2 = 0 in Equation 5), the result is εLb (T), and therefore Equations 4 and 5 include such cases.

<2. First Embodiment> Hereinafter, a first embodiment will be described with reference to the drawings.

<< 2-1. Mechanical Configuration >> FIG. 2 is a diagram showing a mechanical configuration of the temperature measuring device according to the first embodiment of the present invention. Hereinafter, the mechanical configuration of the temperature measuring device will be described with reference to FIG.

As shown, the temperature measuring device 1 includes a reflector 10, a galvanometer mirror 20, a condenser lens 30, a reflector 40, and a radiation thermometer 50.

The upper surface of the reflecting plate 10 is formed as a reflecting surface 10a having a high reflectivity. When measuring the temperature, the reflecting plate 10 is installed such that the upper surface faces the object OB to be measured.

The reflecting plate 10 is provided with a through hole 10b, and the through hole 10b is formed on the reflecting surface 10a of the reflecting plate 10.
And, more specifically, a region where the reflectance R is approximately “0”, and the through hole 10 b
It also functions as a radiation path through which heat radiation reaches the upper end of the optical fiber 51 described later.

The galvanometer mirror 20 is provided so as to be rotatable around an axis as shown in the figure, and heat radiation reflected toward the condenser lens 30 (including radiation after multiple reflection with the reflector 10). Change the direction of the radiation source. The condenser lens 30 is connected to the galvanometer mirror 20 via the reflecting mirror 40.
Is condensed on the upper end of the optical fiber 51 of the radiation thermometer 50.

Here, the optical system composed of the galvanometer mirror 20, the condenser lens 30, and the reflecting mirror 40 cooperates to set the upper end of the optical fiber 51 as one focal point, and to a point optically conjugate with the focal point ("optically conjugate"). The upper surface of the reflector 10 (the surface facing the object OB) when the lower surface of the object OB (the surface facing the reflector 10) is assumed to be virtually a mirror surface. It is adjusted to be located near. In other words, with respect to the measurement surface of the object to be measured OB, the above conjugate point is located near the virtual plane optically symmetric with respect to the reflection surface 10a of the reflection plate 10.

Further, the optical system is provided with an optical fiber 51 by rotating the mirror surface of the galvanometer mirror 20.
A state in which a point optically conjugate with the upper end is located at the position CP1 in the through hole 10b of the reflection plate 10 and the reflection surface 10a of the reflection plate 10
It functions as a radiation path switching unit that switches between the state at the position CP2 in (upper surface) (hereinafter, this switching is referred to as “radiation path switching”).

In other words, a point optically conjugate with the upper end of the optical fiber 51 in the virtual image space when the lower surface of the object to be measured OB is virtually a mirror surface is referred to as a virtual image position VI of the reflector 10. , And a point optically conjugate with the upper end of the optical fiber 51 in the virtual image space is defined by the virtual image position VI1 of the through hole 10b among the virtual image positions VI of the reflection plate 10.
In the virtual image position VI2 on the reflection surface 10a of the reflection plate 10 can be switched between the state of the reflection plane 10 and the state of the reflection plane 10a.

The radiation thermometer 50 has therein an optical fiber 51 whose upper end functions as a light receiving section, a sensor section 52,
An arithmetic unit 53 having a CPU, a memory, and the like (not shown) is provided, and the reflectance of each part of the reflector 10 and the temperature T of the object to be measured OB are obtained based on heat radiation.

The optical fiber 51 guides the heat radiation incident on the upper end to the sensor section 52. The sensor unit 52 functions as a radiation amount measuring unit that captures the heat radiation, generates an electric signal indicating the radiation amounts I1 and I2, and sends the electric signal to the calculation unit 53.

The calculation unit 53 calculates the radiation amounts I1, I2 sent from the sensor unit 52 and the emissivity ε of the calibration object stored in advance.
Function as temperature calculating means for generating signals representing the temperature T of the object to be measured OB and the reflectances R1 and R2 of the respective parts of the reflector 10 based on the electric signal indicating

<< 2-2. Measurement procedure >>
A description will be given of the temperature measurement of the temperature measurement object OB by the temperature measurement device 1 according to the first embodiment.

First, an operator performs a calibration operation of the apparatus. That is, the operator installs a calibration object having a known emissivity to which a thermocouple or the like is attached so as to face the reflection surface 10a of the reflection plate 10 of this apparatus (instead of the object to be measured OB in FIG. 2). I do.

When the apparatus is activated, the radiation thermometer 50 measures the radiation amounts I1 and I2 and the thermocouple the temperature T of the calibration object. Of these, the radiation amount I
1, I2 is detected as follows. That is, the radiation thermometer 50 records the captured radiation signal of heat radiation in the memory in a time-series manner. Then, the obtained radiation amount signal shows a periodic waveform (such as a sine wave) synchronized with the radiation path switching operation by the galvanometer mirror 20. CP
U performs peak detection on the signal, and determines the maximum value of the signal as the amount of heat radiation after multiple reflection in a state where the point optically conjugate with the upper end of the optical fiber 51 is at the position CP2 described above. The minimum value of the radiation amount signal is detected as the radiation amount in the state at the position CP1 described above.

Then, the obtained measured values of the temperature T and the radiant quantities I1 and I2 of the calibration object and the value of the known emissivity ε previously stored in the memory are substituted into the above-mentioned equations (4) and (5). Then, the reflectances R1 and R2 are obtained and stored in the memory of the radiation thermometer 50.

Next, the operator removes the object for calibration, and attaches the object to be measured OB to the apparatus in the same manner as described above.

When the apparatus is started again, the radiation amounts I1 and I2 are measured in the same manner as described above, and the measured values and the reflectances R1 and R2 obtained by the above calibration work are used in the equation (6). The emissivity .epsilon. Of the object to be measured OB at that timing is obtained, and the emissivity .epsilon.
Is used in Equation 4 or Equation 5 to obtain the object to be measured O
The temperature T of B is determined.

Further, the radiation thermometer 50 has the reflectances R 1, R 1,
As described above, the emissivity ε is obtained by using R2 and the equation (6), and the temperature T of the object to be measured OB is calculated by using it in the equation (4) or (5). The temperature measurement of the object to be measured OB in the mode is ended.

As described above, according to the first embodiment, the galvanometer mirror 20 is used to determine the position optically conjugate with the upper end of the optical fiber 51 when the measurement surface of the object to be measured OB is a mirror surface. Reflection surface 10 of reflection plate 10
a and can be switched between the through hole 10b,
By measuring the temperature of the object to be measured OB while determining the emissivity of the object to be measured OB based on the measured values of the amounts of radiation I1 and I2 in each state, one measured value of the amount of radiation is measured in advance. Compared to the case where temperature measurement is performed based on the emissivity of the object to be measured OB, the temperature can be measured with high accuracy by non-contact.

Since a region having a different reflectance from the reflection surface 10a is formed as a through hole 10b penetrating the reflection plate 10,
The reflection plate 10 can be easily and inexpensively formed.

<3. Second Embodiment> Hereinafter, a second embodiment will be described with reference to the drawings.

FIG. 3 is a sectional view of a temperature measuring device 2 according to the second embodiment. In the second embodiment, the optical system including the galvanometer mirror 20, the condenser lens 30, and the reflection mirror 40 in the first embodiment is only the condenser lens 30, and the ultrasonic wave is used as a radiation path changing unit and a lens moving unit. The condenser lens 30 is provided on the rotor 61 of the motor 60.

FIG. 4 is a plan view of the rotor 61 of the ultrasonic motor 60. As shown in the drawing, the condenser lens 30 is provided slightly eccentric with respect to the rotation center RC of the rotor 61 which functions as a lens holding means, and the rotor 61 has a surface perpendicular to the optical axis of the condenser lens 30. The condensing lens 30 moves within that plane by rotating within the lens. More specifically, the condensing lens 30 moves at a maximum lens movement distance Δx
It moves only horizontally. Thereby, sufficient radiation path switching is possible as described below.

FIG. 5 is a diagram showing a state of switching the radiation path due to the horizontal displacement of the condenser lens 30. As shown, the point optically conjugate with the upper end of the optical fiber 51 is that when the condenser lens 30 is located at the first position LP1, the reflecting plate 10 Is located at a position CP1 (virtual image position VI1 when considered in a virtual image space) in the through hole 10b, and the condensing lens 30 is moved to the second position L
When located at P2, a position CP2 in the reflection surface 10a of the reflection plate 10 (a virtual image position VI2 when considered in a virtual image space).
It is in what.

Incidentally, the inner diameter r of the cross section of the upper end of the optical fiber 51, the lens moving distance Δx, the distance S1 between the upper end of the optical fiber 51 and the condenser lens 30, the reflection plate 10 formed by the condenser lens 30 and the lower surface of the object OB to be measured. Is formed such that the distance S2 from the virtual image position VI satisfies the following condition, so that the optical fiber 51 is optically connected to the upper end of the optical fiber 51 in the second embodiment as in the first embodiment. Radiation path switching for switching between a state in which the conjugate point is at the position CP1 in the through hole 10b of the reflector 10 and a state in the position CP2 in the reflection surface 10a of the reflector 10 can be performed reliably. I have.

The conditions are described below. First, an image of the cross section of the upper end of the optical fiber 51 by the condenser lens 30 at the virtual image position VI of the reflector 10 is considered. And
If the images of the cross sections at the upper end of the optical fiber 51 in the state where the condenser lens 30 is separated by the lens moving distance Δx do not overlap each other, the radiation path can be reliably switched. Hereinafter, a conditional expression for that will be obtained.

The relationship between the horizontal movement distance D of the point optically conjugate with the upper end of the optical fiber 51 due to the horizontal movement of the condenser lens 30 and the lens movement distance Δx of the condenser lens 30 is a geometric relationship. Is approximately given by

[0057]

(Equation 7)

Further, from FIG. 5, since the magnification of the condenser lens 30 is given by S2 / S1, if the inner diameter (diameter) of the cross section at the upper end of the optical fiber 51 is represented by d, the inner diameter of the image at the virtual image position VI is Since S2d / S1, the distance may be equal to or less than the conjugate point moving distance D. Therefore, the ideal condition to be obtained is as follows.

[0059]

(Equation 8)

However, this conditional expression is a conditional expression for making the maximum value and the minimum value of the amount of heat radiation captured by the sensor 52 the most different, and if this conditional expression is not always satisfied, the radiation path switching is not performed. It's not impossible.

The mechanical structure other than these is the same as that of the first embodiment, and the temperature measurement is performed except that the radiation path is switched by moving the condenser lens 30 horizontally by the rotation of the ultrasonic motor 60. Are the same as in the first embodiment. Therefore, in the second embodiment, in addition to having the same effect as the first embodiment, the radiation path can be switched by moving one condensing lens 30, so that a plurality of The device can be manufactured easily and at low cost as compared with a device such as the third embodiment described below, which requires the condenser lens 30 described above.

<4. Third Embodiment> A third embodiment will be described below with reference to the drawings.

FIG. 6 is a sectional view of a temperature measuring device 3 according to the third embodiment. In the second embodiment, the condenser lens 30 is provided on the rotor 61 of the ultrasonic motor 60 as a radiation path changing unit and a lens moving unit, whereas in the third embodiment, a motor 70 and a And a disc-shaped lens holding member 80 attached to the rotating shaft 71 and holding the condenser lens 30.

FIG. 7 shows a lens holding member 8 in this device.
0 is a plan view. As shown in the figure, the lens holding member 80 of the device according to the third embodiment has six condensing lenses 30 on concentric circles C1 and C2 having different radii. The radii of the circumferences C1 and C2 at which the condenser lenses 30 are located are different from each other by the lens movement distance Δx. Under such a configuration, the lens holding member 80 is rotated by a motor 70 in a plane perpendicular to the optical axis of the condenser lens 30 with the centers of the circumferences C1 and C2 as axes. When passing, the condenser lenses 30 are alternately shifted in the horizontal direction by the lens movement distance Δx. By such an operation, a situation similar to that of the second embodiment in which one condensing lens 30 moves above the optical fiber 51 is obtained, and the apparatus of the third embodiment is also the same as the apparatus of the second embodiment. The radiation path can be switched in the same manner as described above.

The mechanical structure other than the above is the same as that of the first embodiment, and the length of each part satisfies the conditional expression (8). The temperature measurement is the same as that of the first embodiment except that the radiation path is switched by horizontally moving the condenser lens 30 by the rotation of the motor 70 and switching. Therefore, in the third embodiment, the first
This has the same effect as that of the embodiment.

<5. Modifications> In the temperature measuring devices of the first to third embodiments, the through-hole 10b is provided as a region having a different reflectance from the reflection surface 10a of the reflection plate 10, but the present invention is not limited to this. Instead, a half mirror is provided in place of the through hole 10b, so that a different radiation amount I
1, I2 may be measured.

In the first to third embodiments, as described in the principle of the present invention, the emissivity ε of the object to be measured OB is obtained from the equation (6), and the temperature Although the temperature of the measured object OB is obtained, the emissivity ε may be eliminated from the equations of Equations 4 and 5 without obtaining the emissivity ε, and the temperature T may be directly obtained from the radiances I1 and I2.

In the first embodiment, a galvanometer mirror is used as the radiation path changing means. In the second and third embodiments, a mechanism for moving the condenser lens in a plane perpendicular to the optical axis is provided. Although used, the present invention is not limited to this, and a resonant scanner, a pentaprism, a monogon mirror, a polygon mirror, or the like can be used instead of the galvanometer mirror.

Further, in the first to third embodiments, the condenser lens 30 is used for condensing the heat radiation on the upper end of the optical fiber 51. However, the present invention is not limited to this, and the present invention is not limited to this. May be used.

[0070]

As described above, according to the first to fifth aspects of the present invention, the surface of the object to be measured facing the reflector is virtually a mirror surface by the radiation path switching means. In this case, the position optically conjugate with the light receiving section of the radiation amount measuring means can be switched between the first reflection area having the first reflectance and the second reflection area having the second reflectance on the reflector. Since the temperature of the object to be measured can be measured based on the measured value of the radiation amount in each state, the accuracy of non-contact can be improved as compared with the case where the temperature is measured based on one measured value. Temperature measurement can be performed.

Further, according to the second aspect of the present invention, one of the first reflection region and the second reflection region in the reflection plate is a through hole penetrating the reflection plate, so that the reflection plate can be formed easily and inexpensively. can do.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of temperature measurement according to the present invention.

FIG. 2 is a diagram illustrating a mechanical configuration of the temperature measuring device according to the first embodiment.

FIG. 3 is a sectional view of a temperature measuring device according to a second embodiment.

FIG. 4 is a plan view of a rotor of an ultrasonic motor according to a second embodiment.

FIG. 5 is a diagram showing a state of radiation path switching due to horizontal displacement of a condenser lens.

FIG. 6 is a sectional view of a temperature measuring device according to a third embodiment.

FIG. 7 is a plan view of a lens holding member according to a third embodiment.

[Explanation of symbols]

 1-3 Temperature measuring device 10 Reflecting plate 10a Reflecting surface (first reflecting region or second reflecting region) 10b Through hole (first reflecting region or second reflecting region) 20 Galvanometer mirror (radiation path switching unit) 30 Condensing lens Reference Signs List 50 radiation thermometer 51 optical fiber (light receiving unit) 52 sensor unit (radiation amount measuring unit) 53 arithmetic unit (temperature calculating unit) 60 ultrasonic motor 61 rotor (lens holding unit) 70 motor (rotating unit) 80 lens holding member OB Object to be measured

Claims (6)

[Claims] 1. A temperature measuring device for measuring a temperature of an object to be measured based on heat radiation, wherein the first and second reflection areas have a first reflectance and a second reflection area facing the object to be measured. A reflection plate having a second reflection region having reflectivity; radiation amount measuring means for measuring a radiation amount of heat radiation from the object to be measured on the side of the reflection plate; an object to be measured and the radiation Between the light receiving unit of the quantity measuring means and the optically conjugate position with the light receiving unit in the case where the surface of the object to be measured which faces the reflection plate is virtually a mirror surface; An optical system positioned above, and a temperature calculation unit that detects the temperature of the object to be measured based on the measurement result of the radiation amount obtained by the radiation amount measurement unit,
The optical system further includes a position conjugate with the light receiving unit of the radiation amount measuring means, the first reflection area in the reflection plate and the second reflection area.
A temperature measurement device comprising: a radiation path switching unit that switches between a reflection area and a reflection area. 2. The temperature measuring device according to claim 1, wherein one of the first reflection region and the second reflection region in the reflection plate is a through hole penetrating the reflection plate, and the other. Is a reflection surface other than the through hole. 3. The temperature measuring device according to claim 2, wherein said radiation path switching means is a galvanometer mirror. 4. The temperature measuring device according to claim 2, wherein the radiation path switching unit comprises: a lens for condensing the heat radiation on the light receiving unit of the radiation amount measuring unit; A lens moving means for moving the lens in a plane substantially perpendicular to the axis. 5. The temperature measuring apparatus according to claim 4, wherein the lens moving unit is a lens holding unit that holds the lens, and the lens holding unit is centered on a position separated from the optical axis of the lens. A rotation unit that rotates in a plane perpendicular to the optical axis of the lens. 6. The temperature measuring apparatus according to claim 4, wherein the radiation path changing unit includes a plurality of the lenses, and the lens moving unit includes a plurality of lenses each having an optical axis parallel to each other. And a lens holding means for holding the concentric circles having different radii, and a rotating means for rotating the lens holding means in a plane perpendicular to the optical axis with the center of the concentric circle having the different radius as an axis. A temperature measuring device, comprising: