JPH04216447A - Heat conduction detecting element - Google Patents

Abstract

PURPOSE:To provide a heat conduction detecting element in which a decrease of heat resistance, becoming an obstacle against making the correct measurement of the heat conductivity and shape of an object; by heat radiation from the substrate of the element is controlled, by covering at least a part of the surface of the substrate with a substance of lower emissivity than that of the substrate. CONSTITUTION:In an element to detect heat conductivity, the measure 2 heating a certain position of a substrate 1 and the measure 3 detecting the temperature of an arbitrary position of the substrate having been heated are formed on the substrate 1 of a bad conductor of heat connected thermally to a heat sink. In this element to detect heat conductivity, at least a part of the surface of the substrate is covered with a covering layer 4 of a substance of lower emissivity than that of the substrate. In this element, the substrate also in which the heat resistance by radiation is larger than the heat resistance by heat conduction of the inside of the substrate can be made.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to all kinds of thermal conduction detection elements used for measuring the thermal conductivity of substances by detecting thermal conduction, as well as for heat flow meters, thermal vacuum gauges, thickness sensors, shape measurements, and the like.

0002

[Prior Art] A conventional method for detecting thermal conduction is to bring a thermal conduction detection element into contact with a substance to be measured and measure the thermal conductivity of that substance (Japanese Patent Laid-Open No. 49-706
Publication No. 72). In other words, by placing the thermal conduction detection element in close contact with the object to be measured and passing a periodic current through the thermal conduction detection element, the side surface of the thermal conduction detection element that is in close contact with the object to be measured absorbs and generates heat, and at the same time, the side surface of the thermal conduction detection element that is in close contact with the object to be measured is brought into close contact with the object to be measured. Measure the temperature on the side,
The density and specific heat of the measured object are determined by detecting the difference in phase delay and amplitude ratio of the measured temperature waveform due to the thermal physical properties of the measured object with respect to the current waveform passed through the thermal conduction detection element, and determined in advance by some method. The value of is used to measure the thermal conductivity of the object to be measured. This method has the advantage that the measuring device is relatively lightweight.

However, with this method, it is necessary to measure the density and specific heat of the object to be measured in advance by some method, and if the density and specific heat values of the object to be measured cannot be obtained, the values of the density and specific heat of the object to be measured cannot be obtained. Thermal conductivity could not be measured.

[0004] Another method has been to sandwich an object to be measured between a low thermal conductivity substrate and a high thermal conductivity substrate and measure the thermal conductivity of the object (Japanese Patent Laid-Open Publication No. 53-107382). That is, a heat generating means is provided on a low thermal conductivity substrate, and a temperature measuring means is provided near the heat generating means, and the object to be measured is sandwiched between the low thermal conductivity substrate and the high thermal conductivity substrate, and the heat from the heating means is measured. The thermal conductivity of the object to be measured is measured by using a temperature measuring means to detect a change in temperature near the heat generating means due to passing through the object. This measurement method has the advantage of being able to measure the thermal conductivity of the object in a relatively short time because it is only necessary to measure the temperature with and without the object to be measured.

However, even with this method, the measuring devices cannot be formed on the same plane, and it is necessary to prepare a sample to be measured, and measurement is not easy because the object to be measured is sandwiched between the two.

As a thermal conduction detection method that overcomes these drawbacks, a heating heater and a thin film thermocouple are formed on a substrate of a thermally poor conductor, and the object to be measured is brought into contact with the substrate. There is a method of measuring the thermal conductivity, etc. of In this method, the thermal conductivity of the object to be measured is directly read as a change in temperature difference, so even if the density or specific heat of the object is unknown, the thermal conductivity of the object to be measured can be measured. In addition, with this method, the heat from the heater is
Because heat flows parallel to the board toward the cold junction at the edge of the board, the heat conduction detection element is integrated, compared to the conventional method of sandwiching between a high thermal conductivity board and a low thermal conductivity board, which causes heat to flow vertically. It has the advantage of being able to easily detect heat conduction, and also being able to measure the shape, thickness, etc. of piping or buried objects to be measured non-destructively and without creating a predetermined sample.

[0007] As described above, the method of measuring the thermal conductivity or shape of an object to be measured using thermal conduction is widely known.
It also has a wide range of applications.

[0008]

[Problems to be Solved by the Invention] As described above, by forming a heating heater and a thin film thermocouple on a substrate of a thermally poor conductor, and bringing the object to be measured onto the substrate,
The method of measuring the thermal conductivity of the object to be measured has the characteristics of being non-destructive, integrated, and easy to measure.

This method of bringing the object to be measured onto the substrate can be used to measure pipe objects such as gas pipes that are difficult to remove, buildings and structures such as the thickness of asphalt and concrete. Conceivable. In this case, the size of the measuring device itself becomes large depending on the object to be measured.

[0010] However, in the method of measuring by placing a thermal conduction detection element in close contact with the object to be measured, if the shape of the object to be measured becomes larger, it is necessary to increase the shape of the detection element used for measurement accordingly. It is. However, when the shape of the thermal conduction detection element becomes large, thermal resistance due to radiated heat from the substrate cannot be ignored, resulting in a decrease in the sensitivity of the thermal conduction detection element.

[0011] Therefore, it is an object of the present invention to reduce as much as possible the deterioration in detection sensitivity observed in large thermal conduction detection elements by minimizing the radiation heat from the substrate.

0012

Means for Solving the Invention In view of the above-mentioned problems, the present invention adopts the following means. A thermal conduction detection element consisting of a substrate, a heating means, and a detection means for detecting temperature uses a material (for example, platinum, nichrome, coat the substrate with iron). The thermal resistance due to heat conduction of this coating layer 4 (hereinafter also referred to as low emissivity material 4) is set to a level that does not interfere with the thermal resistance due to heat conduction within the substrate. With such a configuration, thermal resistance due to radiant heat from the substrate can be significantly increased.

[0013]

[Operation] If the thermal conduction detection element has a large shape and is not coated with a material having a low emissivity, the thermal resistance due to radiation from the substrate increases, and the influence of the radiated heat cannot be ignored. In contrast, in the present invention, since the substrate has a coating layer made of a material with low emissivity, the thermal resistance due to radiation from the substrate increases significantly. As a result, the temperature of the heat generating part increases for the same amount of heat generated by the heater, and the influence of thermal resistance due to heat radiation, which is difficult to accurately determine in measurement, decreases. Therefore, the measurement accuracy of radiation heat conduction detection is improved. In other words, a more accurate thermal conductivity is required for an object to be measured whose shape is known, and a more accurate shape is required for an object to be measured whose thermal conductivity is known.

[0014]

[Embodiment] The thermal conduction detection element according to the present invention includes a substrate 1 of a thermally poor conductor, a heating means 2 for heating a predetermined position on the substrate, and a detection means 3 for detecting the temperature at a desired position on the substrate. It is characterized in that at least a part of the surface of the substrate is coated with a material 4 having a low emissivity.

FIG. 1 is a diagram showing an embodiment of the thermal conduction detection element according to the present invention, and FIG. 1(A) is a top view of the element, and FIG.
B) is an end view in the direction of arrow E-ro. A heating thin film heater (hereinafter also referred to as a heating thin film heater 2) is provided as a heating means 2 and a thin film thermocouple (hereinafter also referred to as a thin film thermocouple 3a, 3b) as a temperature detection means 3 on a substrate 1 of a thermally poor conductor. Furthermore, a part of the substrate 1 which is a thermally poor conductor is coated with a material 4 having a low emissivity for reducing radiated heat from the substrate 1 which is a thermally poor conductor. The substrate 1, which is a thermally poor conductor, resists even a small amount of heat generated by the heater for detecting thermal conduction.
Since it is desirable to obtain a large temperature difference ΔT, the material is preferably one with low thermal conductivity. Also,
As the heating means 2, a device capable of heating a predetermined position of the substrate 1, such as a thin film heater, is used, and as the temperature detection means 3, a device capable of detecting the temperature of a desired position of the substrate 1, such as a thermocouple, is used. Pure metals such as platinum, nichrome, iron, etc. are mainly used as the low emissivity material 4 for reducing the radiated heat from the substrate 1, which is a thermally poor conductor. Note that if these low emissivity substances 4 adhere to the thermally poor conductor substrate 1, the thermal resistance of the thermally poor conductor substrate 1 will decrease, so the low emissivity substances 4 have low thermal conductivity and are It is desirable that the thickness be thin.

Here, the thermal conduction detection element according to the present invention has the following characteristics:
An example of the manufacturing method of the embodiment shown in FIG. 1 will be briefly described. After thoroughly cleaning the thermally poor conductor substrate 1 with an organic solvent or the like, it is dried in a clean atmosphere to form a thin film thermocouple 3. The thin film thermocouple 3 preferably has a large Seebeck, and is made of an amorphous semiconductor thin film such as a-Si or a-Ge. These amorphous semiconductors are deposited by a plasma CVD method, a photo CVD method, an ECRCVD method, or the like using a gas such as silane, germane, or hydrogen. Unnecessary portions of the deposited amorphous semiconductor are removed using photo-etching technology to form predetermined thin film thermocouples 3a and 3b. Subsequently, a thin film heater 2 for heating is formed. As this thin film resistor, a metal thin film of nichrome, tantalum, etc. deposited by vacuum evaporation, sputtering, etc. is used. Furthermore, a metal thin film for electrodes such as gold is deposited, and unnecessary parts are similarly removed to form ohmic electrodes for thin film thermocouples and thin film heaters. A low emissivity material 4 such as platinum, nichrome, or iron is deposited on a part of the surface of the thermally poor conductor substrate 1 by metal vapor deposition or sputtering (e.g., several nanometers).
m to 1 μm). As mentioned above, this low emissivity material 4 has a low thermal conductivity and a thin film thickness.

FIG. 2 shows a second embodiment of the present invention, and FIG.
2(A) is a top view of the element, and FIG. 2(B) is an end view in the direction of arrows E--RO. In the embodiment of the present invention shown in FIG. 1, an insulating layer 5 is formed on the thin film heater 2 and the thin film thermocouples 3a, 3b, and the insulating layer 5 is coated with a low emissivity material 4. This is an example. In the embodiment shown in FIG. 2, the entire surface of the substrate 1, which is a thermally poor conductor, is coated with a material 4 having a low emissivity, so that the thermal resistance due to radiation can be increased. and a thin film thermocouple 3,
Since the insulating layer 5 is present between the material 4 having a low emissivity, no electrical short circuit occurs. In the embodiment shown in FIG. 2, a thin film of silicon tetrafluoride, silicon dioxide, etc. is mainly used for the insulating layer 5, and its manufacturing method is as follows.
A plasma CVD method, an ECRCVD method, a photoCVD method, or the like is used.

The detection principle of the thermal conduction detection element according to the present invention will be explained with reference to FIG. FIG. 3 is a schematic diagram showing the temperature gradient inside the substrate 1 of the thermal conduction detection element shown in FIG. ) solid line). Heat generated by the heating thin film heater 2 of the thermal conduction detection element flows toward both ends of the substrate 1 which is thermally connected to a heat sink. At this time, the heating thin film heater 2 rises to a certain temperature, and the thin film thermocouple 3a near the heating thin film heater 2,
The hot junction point 3b also rises to a constant temperature. When the object to be measured 7 is brought into contact with the thermal conduction detection element in this state, part of the heat that has been flowing through the inside of the substrate 1 flows through the inside of the object to be measured 7. Therefore, the temperature of the hot junction of the thin film thermocouple 3 changes before and after contact with the object to be measured. By detecting this change, the thermal conductivity can be measured if the shape of the object to be measured 7 is known, and the shape can be measured if the thermal conductivity of the object to be measured is known.

FIG. 4 shows the embodiment shown in FIG.
This is a diagram of the temperature gradient inside the substrate when the object to be measured is not in contact with it, and when there is no coating with the low emissivity material 4 (a
) and the case (b) with a coating are shown. In a vacuum, the amount of heat supplied by the heating thin film heater 2 is due to internal heat conduction flowing inside the substrate 1, which is a thermally poor conductor, and
The heat is divided into radiant heat radiated into space and conduction, and is transmitted to cooler parts. At this time, the substrate thermal resistance Rs regarding the internal heat conduction is expressed by the following equation (1).

[0020]

[Math 1]

[0021] Also, the radiation heat resistance Rr regarding radiation heat conduction
is expressed by the following equation (2).

[0022]

[Math 2]

This radiation heat resistance Rr is proportional to the emissivity ε of the surface of the thermally poor conductor substrate 1 when the shape and temperature conditions of the thermally poor conductor substrate 1 are the same. Therefore, by covering the surface with a material having a small emissivity ε, it is possible to reduce the flow of heat due to radiation heat conduction. As is clear from FIG. 4, which shows the cases in which the substrate surface is covered with a material 4 with low emissivity (indicated by a solid line) and the case in which it is not covered (indicated by a broken line), it is clear that the surface of the substrate 1 has a low reflectivity. By coating with a substance, the thermal resistance due to radiation is significantly reduced, so a larger temperature difference ΔT can be obtained with the same amount of heat generated by the heater.

FIG. 5 shows that in the embodiment shown in FIG.
A glass substrate with substrate length L=1 (cm), substrate width W=1 (cm), and emissivity ε=0.88 has an emissivity ε=0.05.
The dependence of the thermal resistance due to conduction within the substrate and the thermal resistance due to radiation from the substrate at a temperature of 300 (K) when the entire surface of the substrate 1 is coated with platinum 100 (nm) and when it is not coated is shown. It is something. Thermal resistance is on the vertical axis,
The horizontal axis represents the thickness of the substrate. In addition, ■ is when heat is conducted inside the board and the board is not coated.
2 shows a case where heat is conducted inside the substrate and a coating is provided, 2 shows a case where heat is radiated from the substrate and there is no covering, and 2 shows a case where heat is radiated and there is a covering.

As shown in FIG. 5, platinum 100 (nm)
If there is no coating, the thermal resistance due to internal heat conduction and the thermal resistance due to radiant heat from the substrate are equal at a substrate thickness of 1 (mm). On the other hand, platinum 100 (
If there is a coating by 1 (mm), the same substrate thickness 1 (mm)
In this case, the thermal resistance due to radiant heat from the substrate is approximately 18 times the internal thermal resistance of the substrate, which can be increased by more than one order of magnitude. Furthermore, when the substrate thickness is approximately 50 (μm) or more, the thermal resistance due to radiant heat from the substrate 1 is smaller than the thermal resistance due to internal heat conduction. In this way, by coating the substrate 1, which is a thermally poor conductor, with platinum, which is a material 4 with a low emissivity, it is possible to increase the thermal resistance due to radiation, and not only increase the temperature difference △T, but also reduce the thermal resistance due to radiation. The errors that occur can be reduced, and as a result, the measurement accuracy can also be improved. That is, in the heat conduction detection element shown in FIG. 5, by coating the substrate 1, when the thermal resistance due to heat radiation is made larger than the thermal resistance due to heat conduction inside the substrate 1, it is possible to accurately and easily detect heat. It has been shown that conductivity and shape can be measured.

Furthermore, since the thermal resistance Rr due to radiation is generally determined by the exchange of heat with the surroundings, it is extremely difficult to accurately determine the thermal resistance Rr due to radiation. By applying this, it becomes possible to suppress the influence of radiation on the thermal resistance Rr, and the measurement accuracy also improves.

[0027]

[Effects of the Invention] First, the thermal conduction detection element of the present invention coats the thermally poor conductor substrate with a low emissivity material, so even if the thermal conduction detection element is large, the thermal resistance due to heat radiation can be reduced. It will not be significantly reduced. Therefore, conventional problems such as a reduction in thermal resistance due to heat radiation and a reduction in temperature difference before contact with the object to be measured, which occur due to an increase in the size of the substrate, can be solved, and measurement sensitivity is improved.

As a result, a heating heater and a thin film thermocouple are formed on a substrate of a thermally poor conductor, an object to be measured is brought into contact with the substrate, and the thermal conductivity of the object is measured. The problem of heat radiation from the substrate in the method has been solved.

[0029]

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a second embodiment of the present invention.

FIG. 3 is a diagram showing a temperature gradient in the first embodiment of the present invention.

FIG. 4 is a diagram showing a temperature gradient in a second embodiment of the present invention.

FIG. 5 is a diagram showing substrate dependence of thermal resistance in a second embodiment of the present invention.

[Explanation of symbols]

1. Board. 2 Heating means. 3 Detection means. 4 Coating layer (substance). 5 Insulating layer.

Claims (2)

[Claims] 1. A substrate (1) of a thermally poor conductor that is thermally connected to a heat sink, a heating means (2) for heating a predetermined position of the substrate, and a substrate heated by the heating means. A thermal conduction detection element comprising a detection means (3) for detecting the temperature at a desired position, a coating layer (4) made of a material having a lower emissivity than the substrate and covering at least a part of the surface of the substrate. A thermal conduction detection element characterized by comprising: 2. The thermal conduction detection element according to claim 1, wherein the substrate is made so that the thermal resistance due to heat radiation from the substrate is larger than the thermal resistance due to thermal conduction inside the substrate. A thermal conduction detection element.