DE19703932B4 - Thermoelectric sensor - Google Patents

Abstract

Thermoelectric sensor having at least one thermoelectric sensor element (5a) which has an active detector surface of a thin active layer (7) of a crystalline solid with anisotropic thermoelectric force and in which the surface normal of the layer (7) does not coincide with one of the main anisotropy directions Thin active layer (7) at least two contacts (10) for picking up a voltage generated by the heating of the surface of the layer (7) are present, characterized in that the thermoelectric sensor as a temperature sensor (16) with a tubular housing (17) in that the sensor element (5a) is designed in the shape of a truncated pyramid and is fastened on a carrier (3a) through which a cooling medium flows and / or flows from a thermally conductive material, and in that a back-cooling (3a, 17 ') encompassing the carrier (3a) is provided. ) is provided for the sensor element (5 a), the symm etrisch to a center plane (M) is executed, which is arranged perpendicular to the plane of the active layer (7) and to which the sensor element (5a) is mirror-symmetrical, and the sensor element (5a) on an end face of the tubular, a cooler forming housing (17) is provided

Description

The invention relates to a thermoelectric sensor according to the preamble of claim 1.

Such a sensor can be used as a fast-reacting sensor for measuring the thermal power of a radiation, in particular laser radiation. The active layer here consists of a thin anisotropic high-temperature superconductor layer grown on a monocrystalline substrate with a tilt angle. At contact surfaces, a voltage can be tapped which is proportional to the temperature gradient between the temperature at the top of the active layer and the temperature which the active layer has at the transition to the substrate. The known thermal detector basically has the advantage that the active layer can be made very thin with low mass and thereby very short time constants in the range of ns. are reachable. In a continuous load or radiation, especially in a continuous load with higher average power, however, the known thermoelectric detector or its output voltage on a pronounced drift behavior, which consists in the fact that the measurement or output voltage drops despite the same irradiation. A disadvantage of the known detector also that this signal drift is still dependent on the movement of the radiation incident on the active layer along this active layer, d. H. For example, a movement of one millimeter can increase signal drift by a factor of ten.

From the German Offenlegungsschift 2456 748 For example, a temperature sensor for measuring the temperature of metallic workpieces in a heating oven is known which has a water-cooled support or support system for cooling the sensor housing.

In order to avoid the aforementioned disadvantages and to provide a sensor which provides a power-proportional drift-free output voltage even under continuous load is in the older, but not pre-published German Patent 196 05 384 additionally proposed that in the beam path of the radiation to be measured, an optical system is provided which images this radiation on the surface of the active layer in a spot whose diameter is smaller than the dimension of the active in each axial direction lying in the plane of the surface of the active layer Layer in the respective axial direction, and that a cooling is provided for the sensor element, which is designed symmetrically to a center plane which is perpendicular to the surface of the active layer and to which the sensor element is designed mirror-symmetrically.

Object of the present invention is to provide a sensor that allows a fast temperature measurement without drift behavior.

To solve this problem, a sensor according to the characterizing part of claim 1 is formed.

An essential component of the invention is the symmetrical cooling, which ensures that in each case in the region of the two contacts in each case the same temperature conditions, in particular in the active layer, so therefore can not build up a drift of the output causing lateral temperature gradient.

Further developments of the invention are the subject of the dependent claims.

The invention will be explained in more detail below with reference to the figures of an embodiment. Show it:

1 in a simplified representation and in section an embodiment of the thermoelectric sensor according to the DE 196 05 384 C1 ;

2 in enlarged detail a section through the substrate and the active detector layer of the detector element for use in the sensor of 1 ;

3 a plan view of the detector element of 1 ;

4 in a simplified representation and in longitudinal section a suitable temperature for a sensor according to the invention;

5 in an enlarged detail the sensor element of the temperature sensor of 4 ,

The sensor shown in the figures consists essentially of a closed housing 1 with a peripheral wall 2 , with a caseback 3 and with an upper housing termination 4 , Inside the housing is the sensor element forming the active part of the sensor 5 housed, and that at the housing closure 4 opposite side of the floor 3 ,

The sensor element 5 , which in detail or in section in the 2 is reproduced again, is a thermoelectric detector, such as those skilled in the art, for example from the DE 43 06 497 C2 is known. This detector consists of the substrate 6 and the thin active layer provided on a surface side of this substrate 7 , In the sensor, this sensor element is mounted such that the layer 7 the housing closure 4 facing and lying in a plane perpendicular to an optical axis A of an optic 8th is arranged, the housing closure 4 is provided adjustable in the direction of the axis A and the radiation to be measured 9 (eg laser beam) on the layer 7 in a surface (spot), preferably in a circular area with the diameter I ', which is smaller than the corresponding dimensions of the layer 7 and also smaller than the diameter I of the measuring beam 9 before passing through the optics 8th ,

In particular, the active layer 7 a thin layer of a crystalline solid with anisotropic thermo-force, wherein the surface normal of the layer does not coincide with any of the main anisopropy-directions.

As a thermoelectrically anisotropic material, for example, a high-temperature superconductor is used, wherein the orientation of the Hauptisisopropieachsen, for example, by epitaxial growth on a suitable oriented, the substrate 6 forming crystal is achieved. As a thermoelectrically anisotropic material, for example, the high-temperature superconductor RBa ₂ Cu ₃ O _7-δ (R = rare earth) is suitable. The alignment of the anisotropy axes is then carried out by appropriate epitaxial growth on a substrate 6 forming crystal, which is cut so that its (100) surfaces emerge from the substrate surface at the angle α> 0, so that in the epitaxial growth layer also a corresponding angle between the surface normal of the layer 7 and the crystallographic c-axis of this layer.

For the production of the sensor element 5 For example, it is possible to proceed as follows:
On a SrTiO ₃ substrate tilted (100) planes at the angle α (α> 0) from the surface, a thin layer of the high temperature superconductor YBa becomes laser ablation at 680 ° C and 300 mTorr O ₂ atmosphere ₂ Cu ₃ O _7-δ (YBCO) applied. The YBCO (100) planes grow parallel to the SrTiO ₃ (100) planes ( 2 ). The crystallographic C axis of the YBCO layer thus forms the angle α with the surface normal.

Upon impact of the beam 9 on the layer 7 this is strongly heated, in particular on its exposed upper side, so that in the direction of the thickness of the layer 7 a temperature gradient arises, which due to the angle α, among others, one of this temperature gradient and thus of the thermal energy of the beam 9 dependent stress field parallel to the surface of the layer 7 generated.

For picking up by heating the surface of the layer 7 generated and the power of the beam 9 dependent output voltage serve the two contacts 10 in the illustrated embodiment, each along an edge of the square sensor element 5 on top of the layer 7 are provided and extend over the full length of a page. The contacts 10 are formed by thin layers of gold, namely by these layers or contacts 10 be sputtered with a laser. This has especially with the sensor element 5 the advantage that by sputtering material of the contacts 10 also in the shift 7 penetrates and thus a particularly high durability and liability for the contacts 10 results.

The electrical connection to the contacts 10 via contact elements 11 , which are designed as contact springs and at least at their contact surfaces made of silver. Furthermore, the contact elements 11 , especially the transition to the contacts 10 sealed to prevent corrosion.

The at the contacts 10 applied output voltage can be represented as follows: U = (Sab-Sc) × (T1-T2) × I '/ d × sin (α).

Sab/Sc:

Seebeckkoeffizienten (Materialkonstanten YBCO: Sc ca. 15 μ V/K, Sab 0 V/K)

I':

Spotdurchmesser

d:

Schichtdicke der aktiven Schicht

α:

Kippwinkel

U:

gemessene elektrische Ausgangsspannung

T1:

Temperatur an der Oberfläche der aktiven Schicht

T2:

Temperatur am Übergang zwischen der aktiven Schicht und dem Substrat.

Here are:

Sab / SC:

Seebeck coefficients (material constants YBCO: Sc approx. 15 μV / K, Sab 0 V / K)

I ':

Spot diameter

d:

Layer thickness of the active layer

α:

tilt angle

U:

measured electrical output voltage

T1:

Temperature at the surface of the active layer

T2:

Temperature at the transition between the active layer and the substrate.

With the layer 7 opposite surface side is the substrate 6 directly on the inner surface of the soil 3 attached. In the ground 3 a cooling is formed, and that symmetrical to a center plane M, to which the sensor element 5 also regarding the contacts 10 is designed mirror-symmetrical and includes the axis A with. For this symmetrical cooling is in the ground a cold room or cooling channel 12 formed, which by a cooling medium (eg., Water) can be flowed through. Of the cooling channel 12 extends perpendicular to the plane of the 1 over a length greater than the dimension of the sensor element 5 in this axial direction. Furthermore, the width of the cooling channel 12 also larger than the width of the sensor element 5 so that this in all its areas reliably by the cooling channel 12 flowing medium is cooled.

The two connections serve to supply the cooling medium 13 and 14 , which are also arranged symmetrically to the median plane M. The discharge of the cooling medium is also symmetrical to the center plane M, for example, characterized in that at one end of the cooling channel 12 an over the entire width of this channel extending outlet 15 is provided.

For a particularly good and uniform thermal contact between the substrate 6 and the floor 3 to reach is the substrate 6 polished on its back and with a thermal compound on the also polished surface of the floor 3 applied. Due to the fact that the radiation to be measured 9 with the help of optics 8th is concentrated to a spot diameter I ', which is substantially smaller in size than the dimensions of the active layer 7 , And by the symmetrical cooling is achieved that even at a high continuous load of up to 20 watts / cm ^2, the drift or deviation of the contacts 10 at most 1 to 2%.

The 4 and 5 show a temperature sensor 16 characterized by a particularly fast response with response times in the range of 10 nanoseconds and is thus suitable for very fast temperature measurements. With the currently available on the market temperature sensors, such as hot wire thermometers or thin film resistors, such response times can not be realized.

• • in der Strömungstechnik zur Untersuchung von Übergängen zwischen einer laminaren und turbulenten Strömung oder
• • in der Verbrennungsforschung, z. B. bei Verbrennungsmotoren zu sehen, wo der schnelle Temperatursensor 16 es gestattet, den zeitlichen Verlauf eines Verbrennungsvorganges exakt zu erfassen und darzustellen.

Fields of application for the temperature sensor 16 are among others

• • in flow technology to study transitions between laminar and turbulent flow or
• • in combustion research, eg. B. in internal combustion engines to see where the fast temperature sensor 16 it allows to accurately record and display the time course of a combustion process.

The temperature sensor 16 consists of a tubular housing 17 , at one end of which the sensor element 5a is provided. The latter is the same as the sensor element 5 constructed, ie it consists essentially of the substrate 6 with the active layer 7 and from the bottom or support designed as a cooling element 3a , However, the sensor element is 5a at the active layer 7 and on the substrate 6 truncated pyramid is designed so that it tapers to the side formed by the active layer and the contacts 11a starting from the active layer 7 obliquely backwards from the active layer 7 extend away. The sensor element 5a lies with the substrate 6 opposite side of its active layer 7 in a plane with the open side of the housing 17 , The between the inner surface of the housing 17 and the peripheral surface of the sensor element 5a remaining space is with a suitable, high thermal load casting compound 18 poured out, in particular also such that the contacts 11a at least as far as possible from the Eingußmasse 18 are covered.

Also the sensor element 5a has a back cooling to achieve a stable reference point. For cooling, the carrier is used 3a , which is made as a cylindrical piece of a thermally highly conductive material, namely of metal or with its and the substrate 6 opposite end in one inside the case 17 formed refrigerator 17 ' extends, which is flowed through by a cooling medium. At the other end of the cylinder 3a is the substrate 6 attached. By the on the carrier 3a provided back and symmetrical to the median plane M between the contacts 10 trained cooling also has the temperature sensor 16 a clear, fixed reference point and drifting through contact voltages is largely suppressed. This also contributes to the truncated pyramidal design of the sensor element.

At the end of the housing facing away from the sensor element 17 is a connection head 19 provided, which has an electrical connection 20 at which the electrical signal of the sensor 5a can be removed, as well as two connections 21 and 22 for the coolant, of which the connection 21 for supplying the coolant to the refrigerator 17 ' and the connection 22 for removing the coolant from the refrigerator 17 ' serves. The coolant connections between the connections 20 and 22 and the fridge 17 ' are realized, for example, that in the housing 17 and also in the head 19 a partition 23 is provided, that of the housing 17 and the head 19 formed interior divided into two sub-channels, both Känale each with the refrigerator 17 ' communicate and the one sub-channel the connection 22 and the other sub-channel connecting 22 having.

The housing 17 is at its the sensor element 5a having pressure-tight side. Furthermore, the housing has 17 on its peripheral surface an external thread 24 on which a screwing, in particular a pressure-tight screwing the temperature sensor 16 z. B. allows in the wall of a combustion chamber of an internal combustion engine. Due to the flat design on the the sensor element 5a The temperature sensor can have the 16 be arranged at the same level with a wall in flow areas, so that protruding, reaching into the flow sections are avoided.

By embedding the contacts 11a in the potting compound 18 These contacts are embedded in a temperature-stable structure with a relatively large thermal time constant, so that disturbances of the measuring signals of the active layer 7 , which result from temperature-induced contact voltages, are avoided, or are separable without problems from the fast voltage signals of the active layer. It is understood that the contacts to the carrier 3a are electrically isolated (insulator 25 ).

LIST OF REFERENCE NUMBERS

1

casing

2

peripheral wall

3

ground

3a

cylinder

4

housing end

5

sensor element

6

substratum

7

Active shift

8th

optics

9

to be measured beam

10

contact area

11, 11a

contact element

12

cooling channel

13, 14

Coolant connection

15

coolant outlet

16

temperature sensor

17

casing

17 '

refrigerator

18

sealing compound

19

connecting head

20

Meßsignalanschluß

21, 22

Coolant connection

23

partition wall

24

external thread

Claims (2)

Thermoelectric sensor with at least one thermoelectric sensor element ( 5a ), which has an active detector surface made of a thin active layer ( 7 ) of a crystalline solid with anisotropic thermo-force and in which the surface normal of the layer ( 7 ) does not coincide with one of the main anisotropy directions, wherein at the thin active layer ( 7 ) at least two contacts ( 10 ) for picking up by heating the surface of the layer ( 7 ) are present, characterized in that the thermoelectric sensor as a temperature sensor ( 16 ) with a tubular housing ( 17 ) is formed, that the sensor element ( 5a ) designed in the form of a truncated pyramid and for cooling on a carrier through which a cooling medium flows and / or flows ( 3a ) is attached from a thermally conductive material and that one of the carrier ( 3a ) comprehensive back cooling ( 3a . 17 ' ) for the sensor element ( 5a ) which is symmetrical to a median plane (M) which is perpendicular to the plane of the active layer (M). 7 ) is arranged and to which the sensor element ( 5a ) is designed mirror-symmetrically, and the sensor element ( 5a ) on a front side of the tubular, a cooler forming housing ( 17 ) is provided Sensor according to claim 1, characterized by the contacts ( 10 ) of the active layer ( 7 ) connected contact elements ( 11 ), each of which depends on the level of the active layer ( 7 ) to the rear side of the sensor element ( 5a ), preferably obliquely extend backwards.

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