JP2012127683A - Method and system for measuring surface temperature - Google Patents

Abstract

The present invention correctly measures the surface temperature of a surface to be measured without using an expensive optical element or using an apparatus having a complicated structure without being influenced by the emissivity distribution of the surface to be measured. It is an object of the present invention to provide a measurement method and a measurement system that can perform measurement.
A surface to be measured having an emissivity distribution, a radiometer for measuring a luminance distribution of the surface to be measured, and an auxiliary heat source with variable brightness installed at a specular reflection position from the radiometer with respect to the surface to be measured And changing the radiance of the auxiliary heat source so that the measured luminance of the high emissivity portion and the low emissivity portion of the measured surface are equal, and obtaining the temperature of the measured surface from the measured luminance at that time Surface temperature measuring method and measuring system characterized by the above.
[Selection] Figure 1

Description

  The present invention relates to a surface temperature measuring method and measuring system.

When a target temperature is to be measured by a radiation temperature measurement method using a two-dimensional thermal imager or a one-dimensional scanning thermometer, the target emissivity and its distribution are usually unknown, and the measurement conditions and Since it varies depending on the surface state, correct surface temperature and temperature distribution information cannot be obtained from the radiance captured by a thermal imager or a scanning radiation thermometer.
Furthermore, when there is a fine emissivity distribution, even if the material emissivity of each measurement site is known, the apparent emissivity will be different from the limit of the visual field characteristics of the thermal imaging device. There are also challenges.

In the case of non-contact measurement of the temperature of an object whose emissivity is unknown using a radiation thermometer or a thermal imager, the following method has been conventionally performed.
(1) A method of measuring the luminance distribution by heating the object to a known temperature with a heater in order to know the emissivity distribution of the measurement object.
(2) As a technique for correcting emissivity in FLA, a method of capturing two polarized lights in spot-type radiation temperature measurement, measuring a target reflectance ratio in two polarized lights, and correcting the emissivity therefrom. (See Patent Document 1)
(3) The reflected light from the black body auxiliary radiation source is superimposed on the target, and the auxiliary radiation source temperature is set so that the sum of the luminance of the thermal radiation light and the reflected light from the target is equal to the thermal radiation luminance from the auxiliary radiation source. A method of adjusting, measuring the auxiliary radiation source temperature at that time with a contact-type thermometer, and knowing the target temperature from there. (See Non-Patent Document 1)
(4) Before and after changing the ambient temperature using an infrared radiation thermometer or thermography capable of measuring two or more points simultaneously and an ambient radiation temperature switching device such as a shutter in front of the thermal infrared source as an auxiliary heat source To calculate the true target temperature from the measured brightness of the high emissivity part and low emissivity part. (See Patent Document 2)

However, each of these conventional techniques has the following problems.
The method (1) requires an additional step of heating the target with a heater and means for knowing the target temperature at this time.
Since the method (2) requires a polarizing optical element, it is expensive when applied to long-wavelength infrared light used in low-temperature radiation temperature measurement, and is not suitable for surface distribution measurement.
In the method (3), the auxiliary radiation source is required to be a black body, but it is difficult to obtain a good black body with a planar shape. If it is not a black body, correction is required, but sufficient accuracy cannot be obtained. Moreover, it is required to measure both the auxiliary radiation source and the measurement object, and the structure of the apparatus becomes complicated.
In the method (4), it is required to measure while switching the environmental temperature in a stepped manner, and thus the apparatus becomes complicated.

Japanese Patent Application No. 2009-202495 Japanese Patent No. 3939487

J. Sci. Instrum., 1963, Vol 40, 1-4.

  The present invention can measure the surface temperature of the surface to be measured correctly without using an expensive optical element or using an apparatus having a complicated structure without being affected by the emissivity distribution of the surface to be measured. It is an object to provide a method and a measurement system.

The present invention provides the following surface temperature measurement method and measurement system.
(1) A surface to be measured having an emissivity distribution, a radiometer for measuring the luminance distribution of the surface to be measured, and an auxiliary heat source with variable brightness installed at a specular reflection position from the radiometer with respect to the surface to be measured Preparing and changing the radiance of the auxiliary heat source so that the measured luminance of the high emissivity portion and the low emissivity portion of the measured surface are equal, and obtaining the temperature of the measured surface from the measured luminance at that time A characteristic method of measuring surface temperature.
(2) A surface to be measured having an emissivity distribution, a radiometer for measuring the luminance distribution of the surface to be measured, and an auxiliary heat source with variable brightness installed at a specular reflection position from the radiometer with respect to the surface to be measured Including changing the radiance of the auxiliary heat source so that the measured luminance of the high emissivity portion and the low emissivity portion of the measured surface are equal, and obtaining the temperature of the measured surface from the measured luminance at that time Surface temperature measurement system.
(3) The surface temperature measurement system according to (2), wherein the radiometer for measuring the luminance distribution is a thermal imager or a one-dimensional scanning radiometer.

According to the present invention, surface temperature distribution measurement for the purpose of heat generation site identification and heat generation measurement in semiconductor devices and circuit components using power devices, surface for the purpose of facility diagnosis and building structure defect detection In the temperature distribution measurement, the surface temperature distribution can be correctly measured without being affected by the target emissivity distribution.
Further, even in a measurement object such as an electronic device having a minute emissivity pattern that approaches the limit of the visual field characteristic of the thermal imaging apparatus, the target temperature can be measured correctly without being affected by blurring of the visual field characteristic.

Surface temperature measurement system according to the present invention Explanatory drawing of the non-contact measuring method of surface temperature concerning the present invention Image with missing pattern Image with reversed light and dark Luminance change pattern along the drawn line

(Principle of the present invention)
When the luminance distribution is measured with a thermal image device while paying attention to the portion where the change in the emissivity distribution on the surface to be measured is large, the emissivity distribution is captured as the luminance distribution. At this time, it is assumed that the temperature of the object is uniform in a certain region, or that the temperature distribution is spatially sufficient compared with the emissivity distribution. Auxiliary heat source is placed on the measurement surface at a position that is mirrored with the thermal imaging device, and the thermal radiation from the black body is reflected on the surface of the measurement target and superimposed on the thermal radiation from the measurement target and captured by the thermal imaging device .

  At this time, according to Kirchhoff's law, the relationship of reflectance + emissivity = 1 holds on the opaque surface, and therefore the low emissivity part has higher reflectivity. When the temperature of the auxiliary heat source is changed in this state, the luminance distribution changes, and the luminance increases in both the high emissivity part and the low emissivity part as the auxiliary heat source temperature rises. The low emissivity part is larger and the difference in luminance is smaller. When the auxiliary heat source temperature is further increased, the brightness difference disappears, and the pattern of the emissivity distribution of the image captured by the thermal imaging device disappears. However, the brightness becomes higher than that of the high emissivity part, and the emissivity distribution pattern is visible again. When the luminance difference disappears, that is, the luminance when the emissivity distribution pattern of the image disappears, the target temperature is obtained by assuming the emissivity as a black body and applying Planck's radiation law. As a result, the true target temperature can be known without the need to know the target emissivity distribution.

The measurement principle will be described in detail below.
Let ε _{Hi be} the emissivity of the high emissivity portion of the measurement object having the emissivity distribution, and ε _{Lo be} the emissivity of the low emissivity portion.
The thermal radiances S _Hi and S _Lo of the high emissivity part and the low emissivity part are respectively expressed by the following equations.
S _Hi = ε _Hi L (T)
S _Lo = ε _Lo L (T)
Here, L (T) is the thermal radiance of a black body at temperature T.
Next, an auxiliary heat _source with luminance L _Heat-source is installed, and the emitted light of the auxiliary heat source is superimposed on the target emitted light. The brightness captured by the thermal imaging device is given below.
S _Hi = ε _Hi L (T) + ρ _Hi L _Heat-source
S _Lo = ε _Lo L (T) + ρ _Lo L _Heat-source
Here, the reflectance of the high emissivity part is ρ _Hi, and the reflectance of _the low emissivity part is ρ _Lo .

Here, the auxiliary heat source luminance L _Heat-source is adjusted so that the high emissivity part and the low emissivity part become equal.
That is, from S _Hi = S _Lo , ε _Hi L (T) + ρ _Hi L _Heat-source = ε _Lo L (T) + ρ _Lo L _Heat-source
Both sides in the plus -L (T), ε _Hi obtained from Kirchhoff's law + ρ _Hi = 1, the deformation with ε _Lo + ρ _Lo = 1 relationship _{ρ Hi (-L (T) +} L Heat- _source ) ＝ ρ _Lo (−L (T) + L _Heat-source )
It becomes. Since ρ _Hi ≠ ρ _Lo , this equality holds when L (T) = L _Heat-source .

At this time,
S _Hi = S _Lo = ε _Hi L (T) + ρ _Hi L (T) = ε _Lo L (T) + ρ _Lo L (T) = L (T)
Therefore, the measured brightness S _Hi = S _Lo is equal to the radiation from the black body at the same temperature T as the object, and the emissivity is treated as 1, and the correct temperature T is obtained from the measured brightness S _Hi = S _Lo .
The target emissivity distribution may be, for example, a metal wiring pattern on a circuit board or device, or a pattern resulting from the fine structure distribution of the device. In addition, when there is no emissivity distribution that can be used, a paint or a metal film may be applied to or pasted on the target surface.

(Embodiment of the present invention)
The thermal imaging apparatus focuses on the measurement target surface and captures a two-dimensional thermal image. Here, the measurement object is a printed circuit board, a semiconductor device, or the like. A black body device with a blackened surface is used as an auxiliary heat source. In this state, the thermal image is measured while changing the temperature of the auxiliary heat source while keeping the target temperature approximately constant, and a condition for erasing the pattern of the thermal image due to the emissivity distribution on the measurement target is searched.
The target temperature is determined from the measured brightness at this time, assuming that the emissivity is 1. When the emissivity of the auxiliary heat source is sufficiently close to 1, the target temperature may be obtained by measuring the auxiliary heat source temperature with a contact-type thermometer or the like.

Examples of thermal images obtained when the temperature of the auxiliary heat source is raised are shown in FIGS.
In FIG. 2, the auxiliary heat source temperature is lower than the target temperature, the high emissivity part, which is a resin material of the printed circuit board, is bright with high brightness, and the pattern of the metal wiring appears dark with low brightness as the low emissivity part.
FIG. 3 is a thermal image when the auxiliary heat source temperature is raised and the luminance of the high emissivity part and the low emissivity part become equal. You can see that the pattern has disappeared.
FIG. 4 is a thermal image when the auxiliary heat source temperature is higher than the target temperature. The high emissivity part is dark and the low emissivity part is brightly shining, and the brightness and darkness are reversed compared to the image of FIG. I understand.

  FIG. 5 shows a luminance change pattern (see 2 in FIG. 5) along the line drawn in FIG. The vertical axis represents the brightness temperature. This part of the pattern includes portions (a, b) where the high emissivity part is thin and the low emissivity part is thick, and conversely, parts (c, d) where the high emissivity part is thick and the low emissivity part is thin. ing. Originally, the brightness temperature of the high emissivity part is 43 ° C., and the brightness temperature of the low emissivity part is about 35 ° C., where the thin line portion is c and the apparent emissivity is lower than a (brightness). The low emissivity part b has an apparent emissivity higher than d (brightness temperature is high). This indicates that due to imperfections in the visual field characteristics of the thermal imager, a significant brightness blur occurs for temperature measurement even at a level where the blur is not clearly recognized as an image. In this state, if the emissivity of the known high emissivity part is applied to part c to obtain the temperature, a temperature lower than the true temperature is obtained, and if the emissivity of the known low emissivity part is applied to part b, A higher temperature is measured.

  On the other hand, the luminance distribution pattern (see 1 in FIG. 5) corresponding to FIG. 3 shown in FIG. 5 is uniform, and shows a correct measurement temperature of 49 ° C. regardless of the place. Not only when the emissivity of the object to be measured is unknown, but also when measuring the temperature of an object with a minute emissivity distribution pattern that exceeds the limit of the field resolution characteristics of the thermal imager, the correct temperature is not affected. It can be seen that it can be measured.

Here, a Mokukuro device was used as the auxiliary heat source, but the auxiliary heat source is not limited to this. For example, an integrating sphere equipped with a lamp light source or a laser light source, the surface of a liquid hot bath, a flat heater, etc. Anything can be used as long as it is sufficiently large for the target and the luminance is uniform and variable.
The thermal imager may also be a camera such as a CCD that measures visible / near infrared light as long as it measures a high temperature object. Further, instead of using a two-dimensional image, measurement using a linear sensor may be used.

Claims (3)

  A surface to be measured having an emissivity distribution, a radiometer for measuring the luminance distribution of the surface to be measured, and an auxiliary heat source with variable brightness installed at a specular reflection position from the radiometer with respect to the surface to be measured, The radiance of the auxiliary heat source is changed so that the measured luminance of the high emissivity portion and the low emissivity portion of the measured surface are equal, and the temperature of the measured surface is obtained from the measured luminance at that time Method for measuring surface temperature.   A surface to be measured having an emissivity distribution, a radiometer for measuring the luminance distribution of the surface to be measured, and an auxiliary heat source having a variable brightness with respect to the surface to be measured, installed at a specular reflection position from the radiometer, A surface characterized in that the radiance of the auxiliary heat source is changed so that the measured luminance of the high emissivity part and the low emissivity part of the measured surface are equal, and the temperature of the measured surface is obtained from the measured luminance at that time Temperature measurement system. The surface temperature measurement system according to claim 2, wherein the radiometer for measuring the luminance distribution is a thermal imager or a one-dimensional scanning radiometer.