DE102017100433A1 - Thermal sensor for measuring a thermal transport size and method for measuring a thermal transport size - Google Patents

Abstract

The invention relates to a thermal sensor (10) for measuring a thermal transport quantity (a, λ), comprising a substrate (12) and an ohmic resistance element (14) having an extension (h) of not more than 4.5 millimeters. According to the invention, a thermal sensor element is provided, in particular a thermocouple (32) which is surrounded by the resistance element (14) of at least two sides.

Description

The invention relates to a thermal sensor for measuring a thermal transport size, comprising (a) a substrate and (b) an ohmic resistance element having a maximum extension of 4.5 mm. According to a second aspect, the invention relates to a method for measuring a thermal transport size.

A generic thermosensor is from the DE 10 2010 018 968 A1 known. Such a thermal sensor has the advantage that a thermal transport size, in particular the thermal conductivity and / or the thermal diffusivity, can be measured with a low measurement uncertainty, even if the test specimen is comparatively small. When calculating the thermal transport size, the so-called effective radius is used. The effective radius is the distance an ideal point-shaped sensor would have from an ideally punctiform heat source. It has been found that the effective radius is not a sensor constant for all materials to be measured. Rather, the effective radius for measurement on test specimens with a high thermal conductivity is smaller than for measurements on specimens with a low thermal conductivity. That is undesirable.

The invention has for its object to improve the measurement of a thermal transport size, especially when using a small sensor.

The invention solves the problem by a generic thermosensor having a thermal sensor element, in particular a thermocouple, which is surrounded by the resistance element of at least two sides. According to a second aspect, the invention solves the problem by a method for measuring a thermal transport quantity, comprising the steps of arranging such a thermal sensor in thermal contact with a test object, energizing the resistive element so that it emits a, in particular constant, heat flow, a pick-up at least one measured value which characterizes the temperature by means of the thermocouple and calculating the thermal transport quantity from the at least one measured value.

An advantage of the invention is that the effective radius is a pure sensor constant. In other words, the effective radius does not depend, at least to a very good approximation, on the material whose thermal transport size is to be measured. As a result, a lower measurement uncertainty is achieved.

It is also advantageous that the thermal sensor according to the invention is easy to produce. For example, it can be applied in the form of a printed circuit to a substrate, for example a ceramic or plastic substrate. This is possible in a cost-effective mass method.

Another advantage is that the thermal transport size of solids, liquids and gases can be determined. The thermosensor is therefore universally applicable.

It is also advantageous that the resistance element - as provided according to a preferred embodiment - can be constructed of a material whose electrical resistance changes with temperature. In this case, the temperature can be measured both by means of the thermocouple and by means of the resistive element. This gives two measured values for the temperature. For example, the resistive element may be used to measure the absolute temperature of the device under test, whereas the thermocouple is used to detect a temperature increase due to the heat flow.

In the context of the present description, the substrate is understood to be the object on which the ohmic resistance element is applied. Preferably, the substrate is thin, that is, an extension in the thickness direction is at most 1/5, more preferably at most 1/10 of the extension in the narrow directions perpendicular thereto. Preferably, the substrate has a thickness of at most 1 mm and / or at least 10 microns.

The ohmic resistance element is preferably a structure, in particular a metallic structure, whose ohmic resistance is at most 100 kilohms, preferably at most 10 kilohms and more preferably at most 1 kilohms. As suitable resistance, 100 ohms have been found. Preferably, the ohmic resistance is at least 1 ohm, in particular at least 10 ohms.

The extent of the resistance element is determined without supply. In particular, the expansion is determined on the basis of the envelope ball diameter. The envelope ball is that imaginary sphere of minimum diameter that completely surrounds the resistance element.

Alternatively, the extent of the resistance element of the diameter of the heat source ball, that of the imaginary sphere of minimum diameter, in which 90% of the heat flow are discharged when the resistance element is energized.

It is possible and advantageous, but not necessary, for the resistance element to be designed in such a way that it heats up during energization so that the isotherms in the plane of the substrate are at least substantially circular. By the feature that the isotherms are substantially circular, it is understood, in particular, that it is possible, but not necessary, for the isotherms to be circular in the strictly mathematical sense. In particular, it is possible that the isotherm associated with those temperatures which is only half the difference between the maximum temperature and the ambient temperature has a deviation from its compensation circle which is at most 15% of the radius of the compensation circle.

The thermosensor element is understood to be any element by means of which the temperature, absolute or relative to a reference temperature, can be measured. The thermosensor element is a thermocouple according to a preferred embodiment. Alternatively, the thermal sensor element may also be a resistance thermometer element whose electrical resistance changes with temperature. Such a resistance thermometer element is preferably connected to an evaluation unit which measures the resistance without current, for example by means of a Wheatstone bridge circuit.

By the feature that the thermal sensor element, in particular the thermocouple, is surrounded by the resistance element of at least two sides, it is understood that an imaginary beam extends from the center of the thermocouple, which extends in the plane in which the resistive element extends, over an angular range of at least 300 °, preferably of at least 340 °, strikes the resistive element. It is ideal if the thermocouple is surrounded on all sides by the resistive element, since then the resulting isotherms are to be described in a particularly good approximation by circles. This in turn means that in approximation of the resistive element as a punctiform represents a good approximation and thus results in a low measurement uncertainty.

The substrate is preferably electrically non-conductive. The resistive element is preferably applied as a printed circuit as the substrate. By way of example, the resistance element can be applied to the substrate in thin-film technology or in thick-film technology. It is favorable if the substrate is a foil. For example, the film may be constructed of polyimide.

According to a preferred embodiment, the resistance element is curved curved edges. This is to be understood that the outer edge of the resistive element can be described in a good approximation as non-rectilinear. Of course, the transition between a curved edge and a straight edge is fluent in that, for example, a circle can be considered to consist of an infinite number of straight sections. The decisive factor is therefore not the microstructure of the edge but its macrostructure. The outer edge of the resistive element is formed by all those points of the resistive element which, viewed from the thermocouple, have the greatest distance radially at a given azimuthal angle. For the sake of clarity, it should be noted that the thermocouple in this sense is understood to be the region in which the two different metals are in contact with one another, and not the entire structure including the feed line.

Preferably, the resistance element is at least substantially elliptical arc-shaped, in particular circular arc-shaped, bounded. By this is to be understood that it is possible, but not necessary, that the resistance element is bounded in the strict mathematical sense elliptical arc. Rather, it is also possible that the outer edge of the resistive element deviates from an ideal elliptical arc shape. Preferably, the deviation is so small that the assumption of a punctiform heat source causes a measurement uncertainty which is at most 5%.

Preferably, the thermocouple is disposed in a center of a balance circle through an outer edge of the resistive element. By the feature that the thermocouple is located in the center, it is to be understood that while it is possible, but not necessary, that the thermocouple is located at the center of the balance circle. Rather, it is also possible that the thermocouple is arranged acentric, wherein a distance of the thermocouple in the form of the geometric center of gravity of the thermocouple from the center of the compensation circle is at most 0.15 times the radius of the compensation circle.

Preferably, the resistance element surrounds the thermocouple to at least 300 °. This achieves a low measurement uncertainty.

It is favorable if the resistance element has at least one double-stranded conductor. Double-stranded conductors allow homogenous heat outputs to be achieved, which contributes to low measurement uncertainty.

It is favorable if the resistance element has at least two electrically separate conductors. It has been found that this facilitates the contacting of the thermocouple.

In order to use the resistance element for temperature measurement, it is favorable when a temperature coefficient at 20 ° C is at least 3.8 × 10 ^-3 per Kelvin, is preferably 3.9 × 10 ^-3 Kelvin. Particularly suitable nickel, rhodium, platinum or an alloy have been found that contains at least one of these metals to at least 20 weight percent.

The substrate may be a ceramic substrate. This has the advantage that the temperature sensor can be used at high temperatures.

, wobei t_m eine Eindringzeit ist, die durch Anlegen eines deltaimpulsförmigen Wärmepulses an den Prüfling und durch Messen der Zeit ermittelt wird, die dieser Wärmepuls bis an den Rand des Prüfling braucht.Preferably, the test specimen has a thickness in at least one dimension that is greater than $2\sqrt{6{\text{at}}_{\text{m}}}\text{.}$

, where t _{m is} a penetration time, which is determined by applying a delta pulse pulse heat to the specimen and by measuring the time that this heat pulse takes up to the edge of the specimen.

According to the invention is also a transport size measuring device for measuring a thermal transport size with (a) a temperature sensor according to the invention and (b) an electrical evaluation unit which is electrically contacted with the resistive element and the thermocouple, wherein the evaluation unit is adapted for automatically performing a method with the Steps (i) energizing the resistive element so that it emits a, in particular constant, heat flow, and (ii) calculating the thermal transport quantity based on at least one measured value of the thermocouple. Preferably, the evaluation unit is additionally designed for automatically calculating the temperature also from the electrical resistance of the resistance element.

wobei P die abgegebene elektrische Leistung ist, u die elektrische Spannung und i der elektrische Strom. R bezeichnet den ohmschen Widerstand des Widerstandselements. Besonders günstig ist es, wenn die elektrische Leistung P auch bei sich änderndem ohmschen Widerstand R konstant gehalten wird.According to a preferred embodiment, the method comprises the steps of calculating the heat flow Φ as the product of electric current and electric power $$\mathrm{\Phi \; =}\text{P}=\text{ui}={\text{R}}^2\text{i}$$

where P is the electrical power output, u is the electrical voltage and i is the electrical current. R denotes the ohmic resistance of the resistive element. It is particularly favorable if the electrical power P is kept constant even when the ohmic resistance R is changing.

Preferably, the method comprises calculating the thermal conductivity λ and / or a thermal diffusivity a based on an analytical solution of the thermal conductivity equation for a point source. The inventive idea is, in particular, that it is possible, when using a small heat source, to approximate these as a point source, without resulting in large measurement errors.

berechnet, wobei $$\mathrm{\Phi =}\text{ui}$$

gilt. Die Formelgröße r bezeichnet eine Gerätekonstante des Widerstandselements, die auch als effektiver Radius bezeichnet werden kann. ΔT wird mittels des Thermosensorelements gemessen.The thermal conductivity is particularly preferred on the basis of the formula $\mathrm{\lambda \; =}\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\Delta }\text{T}}$

calculated, where $$\mathrm{\Phi \; =}\text{ui}$$

applies. The formula size r denotes a device constant of the resistive element, which may also be called an effective radius. ΔT is measured by the thermosensor element.

die für kleine Argumente der komplementären Fehlerfunktion erfc(...) wie folgt genähert werden kann: $$\mathrm{\Delta }\text{T}\left(\text{r}\text{,t}\right)\approx \frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\iff \mathrm{\lambda }\approx \frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\Delta }{\text{T}}_{\text{s}}}\text{.}$$

According to a preferred embodiment, calculating the transport quantity in the form of the thermal conductivity from the thermal voltage or the ohmic resistance of the thermal sensor element comprises determining a stationary value for the thermal voltage or the ohmic resistance. Due to the fact that the resistance element has the above dimensions, it can be considered with sufficient approximation as punctiform. The heat equation is then solved by the following function: $$\mathrm{\Delta }\text{T}\left(\text{r}\text{, t}\right)=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\text{erfc}\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)\text{.}$$

which for small arguments of the complementary error function erfc (...) can be approximated as follows: $$\mathrm{\Delta }\text{T}\left(\text{r}\text{, t}\right)\approx \frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\iff \mathrm{\lambda }\approx \frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\Delta }{\text{T}}_{\text{s}}}\text{,}$$

This approximation applies to $$\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)\to \mathrm{0th}$$

It can be seen that with constant effective radius r, this term tends to quickly approach zero as time t increases. It follows that after a short waiting time ts a stationary state with sufficient accuracy occurs. The index s stands for stationary. After a waiting time t _wait ≥ t _s (for example, a maximum of 10 minutes), a stationary thermoelectric voltage U _{th, S} or a stationary ohmic resistance R _s or a stationary Thermoelectric voltage U _{th, s} measured at least once. From the value U _{th, S} or R _s or U _{th, s} , the associated temperature is calculated according to formula 3 and the stationary temperature difference ΔT _s : = ΔT (t ≥ t _s ) from this and the ambient temperature T _environment . It follows from formula 4, the thermal conductivity λ.

• 1 in Teilfigur 1a schematisch eine erfindungsgemäße Transportgrößen-Messvorrichtung mit einem erfindungsgemäßen Thermosensor und in Teilfigur 1b eine Querschnittsansicht durch ein Prüfling mit dem Thermosensor,
• 2 den Thermosensor gemäß 1 in einer schematischen detaillierteren Ansicht,
• 3 eine zweite Ausführungsform eines erfindungsgemäßen Thermosensors und
• 4 in der Teilfigur 4a eine schematische Messkurve der vom Thermoelement gemessenen Thermospannung sowie in Teilfigur 4b ein Diagramm, in dem die errechnete Temperaturdifferenz zur Umgebung über den Kehrwert der Wurzel der Zeit ausgetragen ist.
• 5 zeigt eine weitere Ausführungsform eines erfindungsgemäßen Thermosensors.

In the following the invention will be explained in more detail with reference to the accompanying drawings. It shows

• 1 FIG. 1 schematically shows a transport size measuring device according to the invention with a thermosensor according to the invention and in FIG. 1b a cross-sectional view through a test specimen with the thermosensor, FIG.
• 2 the thermal sensor according to 1 in a schematic, more detailed view,
• 3 a second embodiment of a thermal sensor according to the invention and
• 4 in the subfigure 4a a schematic measurement curve of the thermocouple measured thermoelectric voltage and in part 4b a diagram in which the calculated temperature difference is discharged to the environment on the reciprocal of the root of the time.
• 5 shows a further embodiment of a thermal sensor according to the invention.

1a schematically shows a thermal transmitter according to the invention 10 that in substrate 12 , in the present case in the form of a polyimide film, and an ohmic resistance element applied thereto 14 includes. The resistance element 14 has an extension H of 1.5 mm in the present case. The thermosensor 10 is via cable 16.1, 16.2, 16.3, 16.4 in electrical connection with an evaluation unit 18 , The expansion H Here is the diameter of an envelope ball H around the resistance element 14 , The thermosensor 10 is between a first sample part 20.1 and a second sample part 20.2 of a test object 20 arranged.

1b shows the thermosensor 10 between the two sample parts 20.1 and 20.2. It can be seen that the thermal sensor 10 is arranged with intimate thermal contact with the sample parts 20.1, 20.2 between the two. For example, the two sample parts are stretched towards each other to improve the thermal contact, but this is not necessary.

2 shows the thermosensor 10 according to 1 in a more detailed view. It can be seen that the resistance element 14 is formed from a double-stranded conductor 22 which is connected via two connecting sections 24.1, 24.2, each with a contact pad 26.1 and 26.2. The electrical current thus flows during operation from the first contact pad 26.1 to the second contact pad 26.2. The contact pads 26.1 and 26.2 are dispensable, in particular, it is also possible that the head 22 is contacted directly via wires electrically.

The double-stranded conductor 22 has a first strand 28.1 and a parallel thereto second strand 28.2. For example, the two strands have a distance of d = 0.1mm. This distance can also be smaller or larger.

2 shows that an outer edge 30 is circular arc. A thermosensor element 32 , in this case a thermocouple 32 , is at the center of a balancing circle A through the outer edge 30 arranged. It should be noted that in the case of an arcuate edge of the compensation circle A coincides with the edge itself. For better clarity, the compensation circle A enlarged drawn.

The thermocouple 32 has a first leg 34.1 of a first part or a first metal alloy and a second leg 34.2 of a second metal or a second metal alloy. The thermocouple 32 denotes the region in which the two legs 34.1, 34.2 have electrical contact with each other. As indicated above, this area is in the center of the compensation circle A , The two legs 34.1, 34.2 are electrically contacted by contact pads 26.3, 26.4.

2 shows that the thermocouple 32 at approximately 360 ° from the resistance element 14 given is. Only in the area in which the legs 34.1, 34.2 from the thermocouple 32 lead radially outward, and on the region opposite this area is the thermocouple 32 not surrounded by the resistance element 14. When the resistive element is energized via the contact pads 36.1, 36.2, this results in isotherms that can be seen in a very good approximation as circular.

3 shows a second embodiment of a thermal sensor 10 according to the invention, in which the resistance element 14 two, in the present case double-stranded, conductors 22.1, 22.2 comprises. The conductors 22.1, 22.2 are made of platinum, nickel, rhodium or an alloy of two or three of said metals. Of course, other materials are possible. The substrate 12 is a ceramic, for example corundum. The substrate 12 has, for example, a thickness of 0.01 mm and 2 mm. It is possible, but not necessary, for the substrate to be elastic.

When carrying out a method according to the invention, the evaluation unit is energized 18 the resistance element 14 so that it is a constant Heat flow Φ outputs. The heat flow Φ corresponds to the delivered electrical power P. At the same time, the evaluation unit measures 18 continuously a thermoelectric voltage U _th , which on the thermocouple 32 due to a temperature increase .DELTA.t against an ambient temperature Tu is applied.

4a shows the course of the thermoelectric voltage U _th in arbitrary units.

4b shows the calculated temperature increases .DELTA.t compared to the ambient temperature, in which is the inverse of the root of the time. It can be seen that in a time interval between the waiting time do not _wait and an end time t _end the temperature increase shows a linear course.

gilt bei einer Entwicklung der Arbeitsgleichung $$\mathrm{\Delta }\text{T}\left(\text{r}\text{,t}\right)=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\text{erfc}\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)\text{,}$$

in eine Maclaurin-Reihe: $$\mathrm{\Delta }\text{T}\left(\text{r}\text{,t}\right)=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\left[1-\frac{2}{\sqrt{\mathrm{\pi }}}\frac{\text{r}}{\sqrt{4\text{at}}}+\text{O}{\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)}^2\right]\approx \text{n}-{\text{m t}}^{\ast }$$

mit einer Steigung m und einem Achsabschnitt n. Für diese gilt $$\text{n}=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}$$

und $$\text{m}=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\frac{2}{\sqrt{\mathrm{\pi }}}=\frac{\mathrm{\Phi }}{2{\mathrm{\pi }}^{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\text{r}\mathrm{\lambda }}\text{.}$$

By applying against $${\text{t}}^{*}=\frac{1}{\sqrt{\text{t}}}$$

applies to a development of the labor equation $$\mathrm{\Delta }\text{T}\left(\text{r}\text{, t}\right)=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\text{erfc}\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)\text{.}$$

in a Maclaurin series: $$\mathrm{\Delta }\text{T}\left(\text{r}\text{, t}\right)=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\left[1-\frac{2}{\sqrt{\mathrm{\pi }}}\frac{\text{r}}{\sqrt{4\text{at}}}+\text{O}{\left(\frac{\text{r}}{\sqrt{4\text{at}}}\right)}^2\right]\approx \text{n}-{\text{m t}}^{*}$$

with a slope m and an axis section n. For these applies $$\text{n}=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}$$

and $$\text{m}=\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{r}\mathrm{\lambda }}\frac{2}{\sqrt{\mathrm{\pi }}}=\frac{\mathrm{\Phi }}{2{\mathrm{\pi }}^{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\text{r}\mathrm{\lambda }}\text{,}$$

und $$\text{a}=\frac{\mathrm{\Phi }}{2{\mathrm{\pi }}^{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\text{r m}}\iff \text{a}=\frac{{\text{n}}^2{\text{r}}^2}{{\text{m}}^2\mathrm{\pi }}$$

Dissolution delivers $$\mathrm{\lambda \; =}\frac{\mathrm{\Phi }}{4\mathrm{\pi }\text{rn}}$$

and $$\text{a}=\frac{\mathrm{\Phi }}{2{\mathrm{\pi }}^{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\text{m}}\iff \text{a}=\frac{{\text{n}}^2{\text{r}}^2}{{\text{m}}^2\mathrm{\pi }}$$

The evaluation unit 18 is set up to automatically calculate the thermal transport sizes a and or λ ,

In a method according to the invention, it is sufficient if an electrical current is applied to the ohmic resistance element, which leads to a heat flow of at most 1 watt, in particular 100 milliwatts.

The calculation of the temperature T is made on the basis of the formulas given in the DE 10 2010 018 968 A1 are delivered. As described below, from this equation, the thermal transport quantity in the form of the thermal conductivity a or the thermal conductivity λ calculated.

5 shows a further embodiment of a thermal sensor according to the invention 10 in which the thermocouple 32 contacted via a line which is relative to the substrate 12 located on the side of the side with the resistance element 14 opposite. The in accordance with the view 5 behind the substrate 12 lying conductors are shown in dashed lines. The resistance element 14 is formed as a spiral of a double-stranded conductor.

Alternatively, it is possible for the entire thermocouple 34 on one side of the substrate 12 is arranged and the resistance element 14 on the opposite, other side. In this case, the substrate should be 12 as thin as possible and preferably not more than 0.5 millimeters thick.

LIST OF REFERENCE NUMBERS

10

thermal sensor

12

substratum

14

resistive element

16

electric wire

18

evaluation

20

sample part

22

ladder

24

connecting line

26

contact pad

28

strand

30

outer edge

32

thermocouple

34

first leg

H

expansion

H

envelope sphere

a

thermal diffusivity

λ

thermal conductivity

A

balancing circuit

R

electrical resistance of the resistive element

Uth

thermovoltage

.delta.t

temperature increase

Tu

ambient temperature

do not _wait

waiting period

t _end

End Time

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010018968 A1 [0002, 0049]

Claims (10)

Thermosensor (10) for measuring a thermal transport size (a, λ), with (a) a substrate (12) and (b) a resistive element (14) having an extension (h) of at most 4.5 millimeters characterized by (C) a thermal sensor element, in particular a thermocouple (32), which is surrounded by the resistance element (14) of at least two sides. Thermosensor (10) after Claim 1 , characterized in that the resistance element (14) curved curved edges, in particular bounded elliptical arc, is. Thermosensor (10) after Claim 2 Characterized in that the thermocouple (32) is arranged in a center of a compensation circuit by an outer edge of the resistive element (14). Thermal sensor (10) according to any one of the preceding claims, characterized in that the resistance element (14) for surrounding at least the thermocouple (32) 300 °. Thermal sensor (10) according to any one of the preceding claims, characterized in that the resistance element (14) has at least one double-stranded conductor (22). Thermosensor (10) according to any one of the preceding claims, characterized in that the resistance element (14) has at least two electrically separate conductors (22.1, 22.2). Thermal sensor (10) according to one of the preceding claims, characterized in that the substrate (12) is a ceramic substrate or a plastic film. Transport-size measuring device for measuring a thermal transport quantity (a, λ) comprising (a) a thermal sensor (10) according to one of the preceding claims and (b) an electrical evaluation unit (18) connected to the resistance element (14) and the thermocouple (32 is electrically contacted (c) wherein the evaluation unit (18) is adapted to automatically perform a method comprising the steps of: (i) energizing the resistive element (14) so that it outputs a heat flow (Φ), and (ii) calculating the transport size (λ, a) based on at least one measured value (U _th ) of the thermocouple (32). Transport size measuring device according to Claim 8 Characterized in that the evaluation unit (18) is designed for automatically calculating at least one temperature (At) of an electrical resistance (R) of the resistive element (14). Method for measuring a thermal transport variable (λ, a) comprising the steps of: (i) arranging a thermal sensor (10) according to one of Claims 1 to 7 in thermal contact with a test specimen (20), (ii) energizing the resistive element (14) so that it emits a heat flow (Φ), (iii) taking at least one measured value (U _th (t)) which determines the temperature (T) characterized by the thermocouple (32) and (iv) calculating the thermal transport quantity (λ, a) from the at least one measured value (Uth (t)).

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