DE102017223412A1 - Arrangement and automated method for non-contact temperature measurement - Google Patents

Abstract

The invention provides an arrangement for non-contact temperature measurement, comprising:
a test object (18),
a test area (1) operatively connected to the test object (18), which is designed to reflect an optical measuring signal (5), the degree of reflection (R) being dependent on the temperature (T) of the test area (1) , and
- A measuring device (16) which is adapted to radiate the optical measuring signal (5) on the test surface (1) and receive from the test surface (1) reflected optical first reflection signal (6) and to determine its intensity (R) ,
An associated method for temperature measurement is also given.

Description

Field of the invention

The invention relates to the temperature measurement of the surface of objects, in particular under adverse measurement conditions such as heat or electromagnetic radiation, from a distance. In particular, the invention relates to an arrangement and a method for non-contact temperature measurement.

Background of the invention

Continuous temperature measurement and temperature monitoring, especially in electrical equipment and devices, is of great importance. Known solutions, such as used in transformers, measure the transformer oil temperature that forms on the wall of a transformer housing. However, the temperature determined in this way says only to a limited extent and only slightly in time something about the actual state of the transformer windings and their thermal load. "Hotspots" or their environment can not be measured accurately enough.

The publication WO 2002/023562 A1 shows an example of a temperature measurement inside a transformer according to the prior art.

Summary of the invention

It is an object of the invention to provide an alternative solution that enables a robust and reliable temperature measurement even inside equipment and facilities.

According to the invention, the stated object is achieved with the arrangement and the method of the independent claims. Advantageous developments are specified in the dependent claims.

According to the invention, the temperature measurement takes place without contact mi optical means. For test objects which are not electrically contactable, e.g. galvanically isolated high voltage assemblies or similar inaccessible assemblies, a non-contact temperature measurement is beneficial. In particular, in large transformers, which are stored in oil, the selective determination of the temperature of the coil winding of great interest, for example, to be able to actively regulate electrical power to this previously inaccessible size.

• - Wird ein Körper mit Licht bestrahlt, kann von dessen Oberfläche ein Signal des reflektierten (oder transmittierten) Lichtanteiles empfangen werden.
• - Da Körper aus Molekülen und deren Verbindungen bestehen, sind deren physikalische Eigenschaften - auch die optischen - in der Regel temperaturabhängig.
• - Ist von der zu bestimmenden Oberfläche die Abhängigkeit der Reflexion (bzw. Transmission) von der Temperatur bekannt, kann dieser Zusammenhang im Umkehrschluss zur Temperaturmessung verwendet werden.
• - Wird ein Körper (eine Flüssigkeit, ein Gas) bestrahlt, wird sich bei einer Temperaturänderung desselben das Reflexions- bzw. Transmissionssignal verändern.
• - Um eine sehr hohe Temperaturauflösung zu erhalten, ist es vorteilhaft, dass die zu messende Oberfläche (= Testfläche) eine sehr hoher Temperaturabhängigkeit der optischen Eigenschaften besitzt.
• - Das kann u.a. mit optischen Spiegeln erreicht werden (z.B. durch einen dielektrischen mehrfachbeschichteten Spiegel oder einen doppelbrechende Kristalle).
• - Um messtechnisch höhere Genauigkeiten und Stabilitäten zu erzielen, ist die Nutzung eines Referenzsignals (= Referenzfläche), dessen Temperaturabhängigkeit ebenfalls bekannt ist oder gar keine Temperaturabhängigkeit aufweist, von Vorteil. Dabei muss das Referenzsignal über dieselbe Messstrecke ermittelt werden.

The idea according to the invention is based on the following considerations and findings:

• - If a body is irradiated with light, from the surface of which a signal of the reflected (or transmitted) light component can be received.
• - Since bodies consist of molecules and their compounds, their physical properties - including the optical - are usually temperature-dependent.
• If the dependence of the reflection (or transmission) on the temperature is known from the surface to be determined, this relationship can be used in reverse to the temperature measurement.
• - If a body (a liquid, a gas) is irradiated, the reflectance or transmission signal will change as the temperature changes.
• - To obtain a very high temperature resolution, it is advantageous that the surface to be measured (= test surface) has a very high temperature dependence of the optical properties.
• - This can be achieved, inter alia, with optical mirrors (eg by a dielectric multilayered mirror or a birefringent crystal).
• - To achieve metrologically higher accuracies and stabilities, the use of a reference signal (= reference surface), whose temperature dependence is also known or has no temperature dependence, is advantageous. The reference signal must be determined over the same measuring path.

• - ein Testobjekt,
• - eine mit dem Testobjekt in Wirkverbindung stehende Testfläche, die ein optisches Messsignal reflektiert, wobei der Grad der Reflexion von der Temperatur der Testfläche abhängig ist, und
• - eine Messvorrichtung, die das optische Messsignal auf die Testfläche strahlt und ein von der Testfläche reflektiertes optisches erstes Reflexionssignal empfängt und dessen Intensität ermittelt.

The invention claims an arrangement for non-contact temperature measurement, comprising:

• - a test object,
• a test area operatively connected to the test object which reflects an optical measurement signal, the degree of reflection being dependent on the temperature of the test area, and
• a measuring device which radiates the optical measuring signal onto the test surface and receives an optical first reflection signal reflected from the test surface and determines its intensity.

The arrangement also includes that the test area is part of the test object.

The invention has the advantage that a temperature measurement can be measured robustly and reliably even in the interior of equipment and devices.

In a development, the arrangement may have a control and evaluation device which determines the temperature of the test area from the intensity of the first reflection signal.

In a further embodiment, the measuring device may comprise at least one optical fiber, in particular a glass fiber, in which the optical measuring signal and the first reflection signal are optically guided.

In a further embodiment, the measuring device can have an optical light source, in particular an LED or a semiconductor laser, which emits the measuring signal.

In a further embodiment, the measuring device may have an optical first receiver which receives the first reflection signal.

• - eine mit dem Testobjekt in Wirkverbindung stehende Referenzfläche, die das optische Messsignal zu reflektiert,
• - wobei die Messvorrichtung das optische Messsignal auf die Referenzfläche strahlt und ein von der Referenzfläche reflektiertes optisches zweites Reflexionssignal empfängt und dessen Intensität ermittelt.

In a development, the arrangement may additionally include:

• a reference surface operatively connected to the test object, which reflects the optical measuring signal,
• - Wherein the measuring device radiates the optical measuring signal to the reference surface and receives a reflected from the reference surface optical second reflection signal and determines its intensity.

The arrangement also includes that the reference surface is part of the test object.

As a result, errors that relate to a change in the measuring path can be compensated in the first reflection signal.

In a development, the degree of reflection can be independent of the temperature of the reference surface.

In a further embodiment, the control and evaluation device can be designed and programmed to normalize the intensity of the first reflection signal with the intensity of the second reflection signal.

In a further embodiment, the second reflection signal can be guided in the optical fiber.

Furthermore, the test surface and / or the reference surface may be formed as a Bragg mirror.

In a development, the test object may be a transformer mounted in an oil-filled transformer tank.

• - Einstrahlen eines optischen Messsignals auf eine mit dem Testobjekt in Wirkverbindung stehende Testfläche,
• - Empfangen des von der Testfläche reflektierten optischen ersten Reflexionssignals, wobei der Grad der Reflexion von der Temperatur der Testfläche abhängig ist, und
• - Ermittlung der Intensität des ersten Reflexionssignals, wobei die Intensität ein Maß für die Temperatur ist.

The invention also claims an automated method for non-contact temperature measurement on a test object, comprising the following steps:

• Irradiating an optical measuring signal to a test area which is in operative connection with the test object,
• Receiving the optical first reflection signal reflected from the test area, wherein the degree of reflection depends on the temperature of the test area, and
• - Determining the intensity of the first reflection signal, wherein the intensity is a measure of the temperature.

• - Einstrahlen des optischen Messsignals auf eine mit dem Testobjekt in Wirkverbindung stehende Referenzfläche,
• - Empfangen des von der Referenzfläche reflektierten optischen zweiten Reflexionssignals,
• - Ermittlung der Intensität des zweiten Reflexionssignals und
• - Normierung der Intensität des ersten Reflexionssignals mit der Intensität des zweiten Reflexionssignals.

In a further development of the method, there are the following additional steps:

• Irradiating the optical measurement signal to a reference surface operatively connected to the test object,
• Receiving the reflected second optical reflection signal from the reference surface,
• - Determining the intensity of the second reflection signal and
• - Normalization of the intensity of the first reflection signal with the intensity of the second reflection signal.

In a development, the test object may be a transformer mounted in an oil-filled transformer tank.

Other features and advantages of the invention will become apparent from the following explanations of exemplary embodiments with reference to schematic drawings.

• 1: ein Blockschaltbild einer Anordnung zur berührungslosen Temperaturmessung mit einer optischen Freiraumausbreitung,
• 2: ein Blockschaltbild einer Anordnung zur berührungslosen Temperaturmessung mit einer Lichtleitfaser,
• 3: ein Schaublid des Signalverlaufs eines optischen ersten Reflexionssignals,
• 4: ein Schaubild des Signalverlaufs eines optischen zweiten Reflexionssignals,
• 5: ein Schaubild der wellenlängenabhängigen Reflexion an einem dielektrischen Spiegel bei Raumtemperatur,
• 6: ein Schaubild der wellenlängenabhängigen Reflexion an einem dielektrischen Spiegel bei 130 Grad Celsius und
• 7: ein Schaubild der temperaturabhängigen Reflexion an einem dielektrischen Spiegel und
• 8: ein Blockschaltbild einer Anordnung zur berührungslosen Temperaturmessung.

Show it:

• 1 FIG. 2 is a block diagram of a non-contact temperature measurement arrangement with free-space optical propagation. FIG.
• 2 FIG. 1 is a block diagram of a non-contact temperature measurement arrangement with an optical fiber. FIG.
• 3 FIG. 2: a diagram of the waveform of an optical first reflection signal, FIG.
• 4 FIG. 2 is a graph of the waveform of an optical second reflection signal. FIG.
• 5 FIG. 4 is a graph of wavelength dependent reflection at a room temperature dielectric mirror. FIG.
• 6 FIG. 12 is a graph of wavelength-dependent reflection at a dielectric mirror at 130 degrees Celsius and
• 7 FIG. 4 is a graph of temperature dependent reflection on a dielectric mirror and. FIG
• 8th : A block diagram of an arrangement for non-contact temperature measurement.

Detailed description of several embodiments

• - ein optisch transparenter Kanal auf Sicht (optische Freiraumausbreitung) oder
• - eine Lichtleitung durch eine Lichtleitfaser (geführte Lichtausbreitung).

There are basically two options for the beam path between a transmitter / receiver and a test object:

• - an optically transparent channel on sight (optical free space propagation) or
• - A light pipe through an optical fiber (guided light propagation).

1 shows a block diagram of an arrangement for non-contact temperature measurement by means of optical free space propagation. The block diagram shows a test object as a transformer 11 in a with transformer oil 12 filled transformer pan 10 is stored. On or in the transformer 11 There is a test area 1 as well as a reference surface 2 whose temperature-dependent reflection behavior is known. From a light source 3 in the infrared spectrum is a through the collimator 4 bundled optical measuring signal 5 through a light-transparent window 17 in the transformer tank 10 through the transformer oil 12 through to the test area 1 and the reference area 2 blasted.

From there it becomes an optical first or second reflection signal 6 or. 7 temperature-dependent reflected. Preferably, the reference surface 2 formed such that the reflection from the reference surface 2 in the temperature range of interest and wavelength range is independent of the temperature.

With an optical first detector 8th becomes the optical first reflection signal 6 detected. With an optical second detector 9 becomes the optical second reflection signal 7 detected. The aforementioned components form the measuring device 16 , The (time-resolved) intensities R the detected optical reflection signals 6 and 7 are used to determine the temperature of a control and evaluation unit, not shown 14 fed.

After correction with the intensity R the second optical reflection signal 7 can the optical first reflection signal 6 with in the control and evaluation unit 14 stored comparison data are compared and from this the current temperature T the test area 1 be determined. The second reflection signal 7 serves, for example, aging effects of the optical components or a change in the transparency of the transformer oil 12 to compensate.

The aforementioned solution needs the optically transparent window in the case of an oil bath 17 in order, if necessary, to be able to penetrate into the test object, ie transparent media are required in the optical path in the spectral range used. As a rule, this solution can only be used for surface measurements (also in bores). If the surface is semitransparent (eg polymers), test and reference surfaces can also be buried, ie hidden, formed. The solution is completely non-contact.

2 shows a block diagram of an arrangement for non-contact temperature measurement with an optical fiber 13 analogous to the arrangement according to 1 , The block diagram shows a test object as a transformer 11 in a with transformer oil 12 filled transformer pan 10 is stored. On or in the transformer 11 are the test area 1 as well as the reference surface 2 whose temperature-dependent reflection behavior must be known. From a light source 3 in the infrared spectrum is a through the collimator 4 bundled optical measuring signal 5 in an optical fiber 13 through the transformer oil 12 through to the test area 1 and the reference area 2 blasted. From there it becomes an optical first or second reflection signal 6 or. 7 temperature-dependent reflected and in the optical fiber 13 recycled. Preferably, the reflection of the reference surface 2 regardless of their temperature.

With an optical first detector 8th becomes the optical first reflection signal 6 detected. With an optical second detector 9 becomes the optical second reflection signal 7 detected. The aforementioned components form the measuring device 16 , The (time-resolved) intensities R the detected optical reflection signals 6 and 7 are used to determine the temperature of a control and evaluation unit, not shown 14 fed.

After correction with the intensity R the second optical reflection signal 7 can the optical first reflection signal 6 with in the control and evaluation unit 14 stored comparison data are compared and from this the current temperature of the test area 1 be determined. The second reflection signal 7 serves, for example, to compensate for aging effects of the optical components.

When using an optical fiber 13 (For example, a glass fiber) as an optical channel, all kinds of signal line paths (curves, internals, etc.) are possible because of their flexibility. The optical device can also be mounted on buried, ie hidden, locations. Does the signal (reflection, transmission) of the test area change? 1 in a known manner, can be from the optical Signal the temperature T be determined after the correction over the reference surface 2 is done.

Hereinafter, the application of the arrangement according to 1 in the measurement of the surface temperature of transformer windings in oil-bearing transformers. By way of example, the direct irradiation of light (= free space propagation) is explained. For the use of an optical fiber, the operation is analog, but does not need transmission through the oil.

Tests on transformer oils show that transmission in the optically visible and in the infrared spectrum can take place over several meters.

3 shows a Schaublid the waveform of an optical first reflection signal 6 that from the test area 1 is reflected. The graph shows the temperature-dependent course of the normalized intensity R the reflected signal 6 in percent depending on the temperature T in degrees Celsius. Clearly visible is the strong temperature dependence of the intensity R the reflection of the temperature T the test area 1 ,

4 shows a Schaublid the waveform of an optical second reflection signal 7 that of a reference surface 2 is reflected. The graph shows the temperature-independent course of the normalized intensity R the reflected signal 7 in percent depending on the temperature T in degrees Celsius. Clearly recognizable is the desired lack of temperature dependence of the intensity R the reflection of the temperature T the reference surface 2 ,

As a test area 1 and as a reference surface 2 Dielectric light-optical filters can be used. Due to their multiple coating, they are ideally suited for perceiving changes in optical properties (reflection, transmission) with a high effect, and Bragg mirrors in a dielectric design are preferred.

A Bragg mirror consists of alternating, thin layers of different refractive indices. Mostly the layers consist of dielectrics. Therefore, the term "dielectric mirror" is used in such reflectors. At each boundary layer, a part of the electromagnetic wave of the light is reflected according to Fresnel's formulas. When the wavelength is close to four times the optical path length of the layers, the reflected rays interfere constructively and a high quality reflector is formed. The area in which the reflection is very high is called stopband. Light whose wavelength is within the stopband can not propagate in the structure.

As the ambient temperature of the dielectric mirror changes, the optical properties of the multiple coatings (e.g., layer thickness, refractive index) change, which is perceivable as a change in reflectance.

Such dielectric mirrors are designed so that they - depending on the number of layers - release only a very small area in transmission or reflection (= bandpass characteristic!).

However, this effect is highly temperature dependent due to the internal structure of the mirror. As the mirror temperature changes, the optical properties of the dielectric layers change. For example, their layer thicknesses change as a result of the thermal expansion. Thus, the dielectric mirror is detuned, the reflected (transmitted) signal changes.

5 and 6 show diagrams of the shift of the transmission range due to a temperature increase by 100 ° C. 5 shows a graph of the wavelength-dependent normalized intensity R reflection on a dielectric mirror at room temperature. 6 shows a graph of the wavelength-dependent normalized intensity R the reflection at the dielectric mirror at 130 degrees Celsius. On the x-axis is the wavelength A in nanometers and on the y-axis the relative intensity R the reflection shown.

If a narrowing of the wavelength by means of a bandpass filter is used in the optical beam path or if a relatively monochromatic light source (for example laser diode) with an emission of 535-537 nm is used, the shaded areas in the graphs can be perceived and evaluated as integral signals.

This results in a characteristic according to the diagram of 7 for determining the temperature T in ° C as a function of normalized intensity R the reflected signal. The course clearly shows the strong change in intensity R the reflection as a function of the temperature T ,

8th shows a block diagram of an arrangement for non-contact temperature measurement. The measuring device 16 for non-contact temperature measurement ( 1 and 2 ) is with the control and evaluation unit 14 connected to the detected intensities R the reflections from the test area 1 and / or the reference surface 2 evaluates for the temperature determination. For example, the intensities R compared with previously determined and stored measured values. test area 1 and reference surface 2 stand with the test object 18 in thermal active connection. The test area 1 and the reference area 2 can thus also be part of the test object 18 his. With the display and operating unit 15 the results can be displayed and output. Likewise, an operation of the arrangement is possible.

The advantage of the solution according to the invention is that the measuring principle is independent of the selected wavelength (assuming transmission in the optical path). This means that the arrangement can be dimensioned and tuned for standard optical components. There is no need for special designs for the optical components such as LED, photodiode, dielectric mirror and optical fiber, as e.g. in the visible wavelength range (or just above) can be measured. Since the surface of the dielectric mirror can be limited to a few square millimeters, only small costs are incurred here.

Since the costs are low, it is possible in a transformer application to install several measuring sections: one or more measuring sections that measure the surface temperature of the transformer coils, and one or more measuring sections that are already integrated into the transformer windings during the manufacturing process and the internal temperature of the transformer Measure transformer. The latter variant has great potential for in-situ characterization of the condition and performance of the transformer.

The test measurement can be corrected in the presence of interference signals. Disturbing factors are as follows, for example.

The optical path can change its transmission. In the case of a direct optical path in the example transformer, this may be due to the fact that the oil changes its transmission due to heating or due to aging (suspended particles, chemical reactions, etc.). The reference measuring section with the same spectral measuring range as the test section remedies this problem. Thus, this reference signal is used to normalize the absolute values and eliminates these influences. This applies analogously to the Lichtleitaser.

The mirror elements may be attacked and aged by the environment (e.g., the oil). As a remedy, the dielectric mirrors are provided with a transparent cover layer (adhesive, film, glass embedding, etc.). In the case of optical fibers, the mirror would preferably be mounted at the end of the fiber or in the fiber.

The dielectric mirrors suffer long-term aging due to thermal stress. Aided by a burn-in test in the laboratory and / or a digital twin in the lab, which experiences the same loads, can be helped.

The influence of stray radiation can change the signal. A remedy can be the use of pulsed measuring signals and electronic filtering (choppers).

Although the invention has been further illustrated and described in detail by the embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1

test area

2

reference surface

3

light source

4

collimator

5

optical measuring signal

6

optical first reflection signal

7

optical second reflection signal

8th

optical first receiver

9

optical second receiver

10

transformer tub

11

transformer

12

transformer oil

13

optical fiber

14

Control and evaluation unit

15

Display and control unit

16

measuring device

17

window

18

test object

R

Intensity of reflection

T

temperature

A

wavelength

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

• WO 2002/023562 A1 [0003]

Claims (15)

Arrangement for non-contact temperature measurement, characterized by : a test object (18), a test surface (1) which is in operative connection with the test object (18) and is designed to reflect an optical measuring signal (5), the degree of reflection ( R) is dependent on the temperature (T) of the test area (1), and - a measuring device (16) which is designed to radiate the optical measuring signal (5) onto the test area (1) and one from the test area (1) to receive reflected optical first reflection signal (6) and to determine its intensity (R). Arrangement according to Claim 1 , characterized by : - a control and evaluation device (14) which is designed and programmed to determine from the intensity (R) of the first reflection signal (6) the temperature (T) of the test surface (1). Arrangement according to Claim 1 or 2 , characterized in that the measuring device (16) comprises at least one optical fiber, in which the optical measuring signal (5) and the first reflection signal (6) are guided. Arrangement according to one of the preceding claims, characterized in that the measuring device (16) has a light source (3) which is designed to emit the optical measuring signal (5). Arrangement according to one of the preceding claims, characterized in that the measuring device (16) has an optical first receiver (8) which is designed to receive the first reflection signal (6). Arrangement according to one of the preceding claims, characterized by : - a reference surface (2) operatively connected to the test object (18), which is designed to reflect the optical measuring signal (5), - wherein the measuring device (16) is formed to radiate optical measuring signal (5) onto the reference surface (2) and to receive an optical second reflection signal (7) reflected by the reference surface (2) and to determine its intensity (R). Arrangement according to Claim 6 , characterized in that the degree of reflection (R) of the temperature (T) of the reference surface (2) is independent. Arrangement according to Claim 2 and Claim 6 or 7 , characterized in that the control and evaluation device (14) is designed and programmed to normalize the intensity (R) of the first reflection signal (6) with the intensity (R) of the second reflection signal (7). Arrangement according to Claim 3 and one of the Claims 6 to 8th , characterized in that in the optical fiber (13), the second reflection signal (7) is guided. Arrangement according to one of the preceding claims, characterized in that the test surface (1) is designed as a Bragg mirror. Arrangement according to one of Claims 6 to 10 , characterized in that the reference surface (2) is designed as a Bragg mirror. Arrangement according to one of the preceding claims, characterized in that the test object (18) is a transformer (11) mounted in an oil-filled transformer tank (10). Automated method for contactless temperature measurement on a test object (18), characterized by : - irradiating an optical measuring signal (5) on a test surface (1) in operative connection with the test object (18), - receiving the optical reflected from the test surface (1) first reflection signal (6), wherein the degree of reflection (R) on the temperature (T) of the test surface (1) is dependent, and - determining the intensity (R) of the first reflection signal (6), wherein the intensity (R) a Measure of the temperature (T) is. Method according to Claim 13 characterized by : - irradiating the optical measuring signal (5) onto a reference surface (2) which is in operative connection with the test object (18), - receiving the second optical reflection signal (7) reflected by the reference surface (2), - determining the intensity ( R) of the second reflection signal (7) and - normalization of the intensity (R) of the first reflection signal (6) with the intensity (R) of the second reference signal (7). Method according to Claim 13 or 14 , characterized in that the test object (18) is a transformer (11) mounted in an oil-filled transformer tank (10).

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