DE102013010116B4 - Method and device for measuring the directional emissivity of a component or specimen - Google Patents

Abstract

Method for measuring the directional emissivity of a component or test specimen, in which the incident light intensity Q (x, y) is determined on a reference part of known geometry and emissivity by illuminating the reference part with a light source defined in terms of radiation intensity, direction and position and is detected by an IR camera of known position connected to a computer system, the component or the test body is sequentially illuminated from at least three different positions in at least one measuring range with a light source defined in terms of radiation intensity, direction and position and the surface Z ( x, y) of the component or specimen is respectively detected by the computer connected to the IR system known position, - for each pixel at the points (x, y) of the IR camera, the intensity I (x, y) in a known direction s = (s, s, s) of the light is measured, - from the Intensit t I (x, y) and the direction of the light s = (s, s, s), then the gradient and the albedo p in each pixel are calculated by means of the equations for the three directions of illumination: where ist, - from the relation 1 = p + e then the directional emissivity e in each pixel is determined.

Description

The invention relates to a method and apparatus for measuring the directional emissivity of a component or specimen.

From the DE 28 39 107 For example, a measurement method is known in which the measurement surface is exposed to the heat radiation of a black body with a defined temperature. In this case, the heat radiator has the form of a spherical half-space in order to be able to illuminate the measuring area completely homogeneously. Part of the heat radiation reflected by the measurement surface passes through the opening in the heat radiator and is detected by a radiation sensor. In this way, the determination of the emissivity of any surface can be done with very short measurement times and also the measurement of structured or curved surfaces.

In addition, goes from the EP 1 643 225 A1 a device for measuring the emissivity as known, in which a spherical hollow body is provided with an inlet opening for the radiation energy generated by an infrared radiation source and with one of the inlet opening in the direction of the entering into the spherical hollow body radiation energy outlet opening for the latter. The spherical hollow body can be placed in a conclusive manner with the edges of the outlet opening on a test object. From a radiation detector, which is positioned by a further associated opening in the shell of the spherical hollow body and coupled on the output side with a computer system, the radiant energy reflected by the measurement object in the spherical hollow body and often scattered by the inner shell is detected and stored with a stored in the computer system downstream measurement of Emissivity of a known sample object for calculating the emissivity of the measured object compared.

Furthermore, from the DE 197 39 338 A1 a device and a method for determining the thermal emissivity, wherein a heat radiator and a sensor for measuring at least a portion of the emanating from a radiated heat source sample surface heat radiation are provided and no reference measurement by irradiation of reference surfaces is required, the same temperature as must have the sample area.

Furthermore, in the DE 10 2005 018 254 A1 discloses a method for emissivity correction in thermal images of unevenly tempered surfaces with locally fluctuating emissivity, in which a thermal image with real temperature representation is generated. Here, a thermal image of the same surface with homogeneously emitting coating is used as a reference, assuming that the temperature is known at each point.

In the case of the direct measuring methods and devices described in the prior art, heating of the surface to be measured of a component or test specimen significantly above the ambient temperature is sometimes necessary. For indirect measuring methods or measuring devices, the reflectance of the surface is used to determine the emissivity. Even small deviations of the surface topography from a flat surface can lead to errors in the emissivity calculation due to the directed part of the reflection. With the indirect measuring methods and devices, which evaluate the absorption behavior of the surface, total emission degrees are determined. A determination of the directional emissivity in the fixed wavelength band is not possible with the indirect methods.

To measure the topography of surfaces of components or specimens, the known method shape from shading (SfS) can be used. In this method, a component or specimen is illuminated in at least one measuring range with respect to radiation intensity, direction and position defined light source and detected by a camera known position. For components or specimens that reflect in the sense of a Lambertian radiator and a homogeneous albedo p can be deduced from the gray value distributions of a recording of the surface on the surface curvature.

The reflectance of a diffusely reflecting surface is determined by the albedo p described. For non-luminous flat surfaces corresponds to the albedo p the reflection coefficient r , The reflection coefficient r depends on the emissivity for an opaque body e its surface together. The relation is 1 = r + e.

The present invention has for its object to provide a method and an apparatus for measuring the directional emissivity of a component or specimen available. In this context, it is further desired to increase the accuracy of error detection in methods for nondestructive thermographic inspection of components for surface defects and / or internal defects.

• - an einem Referenzteil mit bekannter Geometrie und bekannter Emissivität die einfallende Lichtintensität Q (x, y) ermittelt wird, indem das Referenzteil mit hinsichtlich Strahlungsintensität, -richtung und -position definierter Lichtquelle beleuchtet und dabei von einer mit einem Rechnersystem verbundenen IR-Kamera bekannter Position erfasst wird (Kalibrierung),
• - das Bauteil oder der Prüfkörper in mindestens einem Messbereich mit hinsichtlich Strahlungsintensität, -richtung und -position definierter Lichtquelle sequentiell aus mindestens drei unterschiedlichen Positionen beleuchtet und dabei die Oberfläche Z (x, y) des Bauteils oder Prüfkörpers jeweils von der mit dem Rechnersystem verbundenen IR-Kamera bekannter Position erfasst wird,
• - für jeden Bildpunkt (jedes Pixel) an den Stellen (x, y) des Sensors die Intensität I (x, y) (Grauwertverteilung) bei bekannter Richtung s = (s_x, s_y, s_z) des Lichts gemessen wird,
• - aus der Intensität I (x, y) und der Richtung des Lichtes s = (s_x, s_y, s_z) anschließend die Gradienten $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{ und q}=\frac{\partial \text{Z}}{\partial \text{y}}$
  
  sowie die Albedo p in jedem Bildpunkt berechnet werden mittels der Gleichungen für die drei Beleuchtungsrichtungen: $$\text{I}\left(\text{x}\text{, y}\right)={\text{C}}_{\text{K}}\cdot \text{Q}\cdot \text{r}\cdot \text{cos}\mathrm{\Theta =\rho }\cdot n\cdot s=\mathrm{\rho }\cdot \left({\text{s}}_{\text{z}}-\text{q}\cdot {\text{s}}_{\text{y}}-\text{p}\cdot {\text{s}}_{\text{x}}\right),$$
  
  wobei $n=\frac{1}{\sqrt{1+{\text{<figure-callout id="2" label="p" filenames="DE102013010116B4\_0021.png,DE102013010116B4\_0022.png" state="{{state}}">p</figure-callout>}}^2+{\text{q}}^2}}\left(\begin{array}{c}\text{-p}\\ \text{-q}\\ 1\end{array}\right)$
  
  und C_K die Kameraempfindlichkeit ist,
• - aus dem Zusammenhang 1 = ρ + e anschließend die gerichtete Emissivität e in jedem Bildpunkt bestimmt wird.

This object is achieved by a method for measuring the directional emissivity of a component or specimen in which

• - on a reference part with known geometry and known emissivity, the incident light intensity Q (x . y) is determined by illuminating the reference part with a light source defined in terms of radiation intensity, direction and position and thereby being detected by an IR camera of known position connected to a computer system (calibration),
• - The component or the test specimen in at least one measuring range with respect to radiation intensity, direction and position defined light source sequentially illuminated from at least three different positions and thereby the surface Z (x . y) the component or specimen is in each case detected by the IR camera of known position connected to the computer system,
• - for each pixel (each pixel) in the places (x . y) measuring the intensity I (x, y) (gray value distribution) in the known direction s = (s _x , s _y , s _z ) of the light of the sensor,
• - from the intensity I (x, y) and the direction of the light s = (s _x , s _y , s _z ) then the gradients $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{and q}=\frac{\partial \text{Z}}{\partial \text{y}}$
  
  as well as the albedo p in each pixel are calculated by means of the equations for the three directions of illumination: $$\text{I}\left(\text{x}\text{, y}\right)={\text{C}}_{\text{K}}\cdot \text{Q}\cdot \text{r}\cdot \text{cos}\mathrm{\Theta \; =\; \rho }\cdot n\cdot s=\mathrm{\rho }\cdot \left({\text{s}}_{\text{z}}-\text{q}\cdot {\text{s}}_{\text{y}}-\text{p}\cdot {\text{s}}_{\text{x}}\right).$$
  
  in which $n=\frac{1}{\sqrt{1+{\text{<figure-callout id="2" label="p" filenames="DE102013010116B4\_0021.png,DE102013010116B4\_0022.png" state="{{state}}">p</figure-callout>}}^2+{\text{q}}^2}}\left(\begin{array}{c}\text{-p}\\ \text{-q}\\ 1\end{array}\right)$
  
  and C _K the camera sensitivity is,
• - from the relationship 1 = ρ + e then the directional emissivity e is determined in each pixel.

In order to minimize the error, four image recordings with a light source defined with regard to radiation intensity, direction and position are taken instead of three image recordings for calculating the albedo.

Preferably, the light sources exceed the thermal radiation of the component or specimen to be measured.

Radiant heaters are preferably used as light sources. Advantageously, lasers or broadband radiators are used as light sources.

Furthermore, a filter system is preferably used which limits the spectral range of the light sources to the sensitive spectral range of the camera and reduces the introduced energy. The filter system can be band pass filters, short pass filters, long pass filters, germanium mirrors, sapphire glass windows or combinations thereof.

To limit the time of energy input, a shutter is preferably used for each light source.

The lighting of the component or specimen is preferably carried out with homogeneous, parallel light.

The inventive method is used according to the invention for non-destructive thermographic testing of components or specimens for surface defects and / or internal defects.

• - mit einem Referenzteil mit bekannter Geometrie und bekannter Emissivität, das von einer hinsichtlich Strahlungsintensität, -richtung und -position definierten Lichtquelle zu beleuchten und dabei von einer mit einem Rechnersystem verbundenen IR-Kamera bekannter Position zur Ermittlung seiner Lichtintensität (Leuchtdichte) zu erfassen ist,
• - mit mindestens drei Beleuchtungsanordnungen, die jeweils aus einer der hinsichtlich Strahlungsintensität, -richtung und -position definierten Lichtquellen, einem Filtersystem und einem Shutter gebildet und
• - an mindestens drei unterschiedlichen Positionen der Messvorrichtung so angeordnet sind, dass das Bauteil oder der Prüfkörper sequentiell aus mindestens drei unterschiedlichen Positionen direkt oder indirekt zu beleuchten ist, wobei
• - mit der mit dem Rechnersystem verbundenen IR-Kamera bekannter Position die Oberfläche Z (x , y) des Bauteils oder Prüfkörpers in mindestens einem Messbereich bei jeder der mindestens drei sequentiellen Ausleuchtungen bildmäßig zu erfassen ist und
• - dann von dem Rechnersystem zum einen aus mindestens drei Aufnahmen der IR- Kamera (16) die Gradienten $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{ und q}=\frac{\partial \text{Z}}{\partial \text{y}}$
  
  der Oberfläche Z (x, y) des Bauteils in dem mindestens einen Messbereich mittels der Grauwertverteilungen für jeden Bildpunkt und
• - aus den mindestens drei Aufnahmen der IR-Kamera die Albedo p für jeden Bildpunkt der Oberfläche Z (x, y) des Bauteils oder Prüfkörpers zu ermitteln und
• - die gerichtete Emissivität e des Bauteils oder des Prüfkörpers aus dem Zusammenhang 1 = ρ + e für jeden Bildpunkt von dem Rechnersystem zu berechnen ist.

In addition, the object of the invention is achieved by a device for measuring the directional emissivity of a component or specimen,

• with a reference part of known geometry and known emissivity to be illuminated by a light source defined in terms of radiation intensity, direction and position, and to be detected by an IR camera of a known position for determining its light intensity (luminance) connected to a computer system,
• - With at least three lighting arrangements, each formed from one of the radiation intensity, direction and position defined light sources, a filter system and a shutter and
• - Are arranged at at least three different positions of the measuring device so that the component or the specimen is sequentially directly or indirectly to illuminate from at least three different positions, wherein
• - With the connected to the computer system IR camera known position the surface Z (x , y) of the component or specimen in at least one measuring range in each of the at least three sequential illuminations is to be detected imagewise and
• - then from the computer system on the one hand at least three images of the IR camera ( 16 ) the gradients $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{and q}=\frac{\partial \text{Z}}{\partial \text{y}}$
  
  the surface Z (x . y) of the component in the at least one measuring range by means of the gray scale distributions for each pixel and
• - From the at least three shots of the IR camera the albedo p for every pixel of the surface Z (x . y) to determine the component or specimen and
• - the directed emissivity e of the component or of the test specimen out of context 1 = ρ + e for each pixel to be calculated by the computer system.

der Oberfläche Z (x, y) des Bauteils oder Prüfkörpers auch die Albedo p ermittelt werden.The sequential use of multiple, located at different positions light sources can in addition to the gradient $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{and q}=\frac{\partial \text{Z}}{\partial \text{y}}$

the surface Z (x . y) of the component or specimen also the albedo p be determined.

berechnet werden.From the gradients p and q can for any point of the surface Z (x . y) of the component or specimen is a normal vector from the equation: $$n=\frac{1}{\sqrt{1+{\text{<figure-callout id="2" label="p" filenames="DE102013010116B4\_0021.png,DE102013010116B4\_0022.png" state="{{state}}">p</figure-callout>}}^2+{\text{q}}^2}}\left(\begin{array}{c}-\text{p}\\ -\text{q}\\ 1\end{array}\right)$$

be calculated.

The intensity thus yields the equation: $$\text{I}\left(\text{x}\text{, y}\right)={\text{C}}_{\text{K}}\cdot \text{Q}\cdot \text{r}\cdot \text{cos}\mathrm{\Theta \; =\; \rho }\cdot n\cdot s=\mathrm{\rho }\cdot \left({\text{s}}_{\text{z}}-\text{q}\cdot {\text{s}}_{\text{y}}-\text{p}\cdot {\text{s}}_{\text{x}}\right)$$

With known intensity I and known light direction s = (s _x , s _y , s _z ), the three unknowns p . q and ρ be calculated.

mit

• C_K * Q (x, y) * rho: vereinfachte Albedo bei einer Bestimmung der Oberflächengradienten
• I: von der IR-Kamera gemessene Strahldichte [W/sr * m²]
• C_K: Kameraempfindlichkeit
• Q: einfallende Strahldichte [W/sr * m²]
• rho: Reflexionsgrad der Referenzoberfläche [dimensionslose Verhältniszahl: 1 < rho < 0]
• n: Normalvektor der Refenzoberfläche [dimensionslos]
• S: Richtung des einfallenden Lichtes [m].

For the camera sensitivity C _K is usually the value 1 established. The incident radiance Q is known from calibration in which the following equalization equation has been used: $$\text{I}\left(\text{x}\text{, y}\right)={\text{C}}_{\text{K}}\cdot \text{Q}\left(\text{x}.\text{y}\right)*\text{rho}*\text{n}*\text{S}$$

With

• C _K * Q (x, y) * rho: simplified albedo for a determination of surface gradients
• I: radiance measured by the IR camera [W / sr * m ² ]
• C _K : Camera sensitivity
• Q: incident radiance [W / sr * m ² ]
• rho: Reflectance of the reference surface [dimensionless ratio: 1 <rho <0]
• n: normal vector of the reference surface [dimensionless]
• S: direction of the incident light [m].

It is thus possible to calculate by means of SfS the gradient of surfaces that do not have a homogeneous albedo.

Of importance is that in carrying out the method according to the invention a shadowing and specular reflections are avoided and only a diffuse reflection is obtained. Heights of the topography of the surface of the component or specimen must always be detected relative to a reference point, and the gradients must be defined in each pixel of the surface to be measured, ie the surface Z (x, y) to be measured must not cracks exhibit.

Significant advantages of the invention are the improved detection of defects in thermographic inspection methods. Inhomogeneous emissivities are often disturbances in non-destructive thermographic testing which make fault detection more difficult. An adjustment of the raw thermographic data for the determination of temperatures from the measured radiations is desirable and possible with known spatially resolved emissivity. The emissivity can be determined without heating the component or specimen even if the surface topology deviates from the plane.

• 1 ein Diagramm entsprechend dem Diagramm des Planckschen Strahlungsspektrums,
• 2 eine schematische Seitenansicht eines Versuchsaufbaus für die Durchführung von Vorversuchen,
• 3 eine schematische Schnittansicht einer Beleuchtungsanordnung,
• 4 eine schematische Draufsicht einer Beleuchtungsanordnung,
• 5 eine schematische Draufsicht auf eine erste Ausführungsform einer Vorrichtung zum Messen des gerichteten Emissionsgrades,
• 6 eine schematische Ansicht der Befestigung einer Beleuchtungsanordnung an einer quadratischen Grundplatte,
• 7 eine schematische Schnittansicht einer zweiten Ausführungsform der Vorrichtung zum Messen des gerichteten Emissionsgrades,
• 8 eine schematische Schnittansicht einer dritten Ausführungsform der Vorrichtung zum Messen des gerichteten Emissionsgrades,
• 9 ein schematisches Schaltbild einer einzelnen Aufnahme,
• 10 ein schematisches Blockschaltbild, aus dem der Ablauf einer ersten Ausführungsform des erfindungsgemäßen Verfahrens hervorgeht, und
• 11 ein schematisches Blockschaltbild, aus dem der Ablauf einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens ersichtlich ist.
• 1 zeigt ein Diagramm des Planckschen Strahlungsspektrums, in dem das sensitive Spektralband einer IR-Kamera 16, das den Wellenlängenbereich von 2,5 µm bis 5,1 µm umfasst, kenntlich gemacht ist.

The invention will now be explained in more detail with reference to the drawings. In these are:

• 1 a diagram corresponding to the diagram of Planck's radiation spectrum,
• 2 a schematic side view of a test setup for the implementation of preliminary tests,
• 3 a schematic sectional view of a lighting arrangement,
• 4 a schematic plan view of a lighting arrangement,
• 5 a schematic plan view of a first embodiment of a device for measuring the directional emissivity,
• 6 a schematic view of the attachment of a lighting assembly to a square base plate,
• 7 a schematic sectional view of a second embodiment of the device for measuring the directional emissivity,
• 8th a schematic sectional view of a third embodiment of the device for measuring the directional emissivity,
• 9 a schematic diagram of a single recording,
• 10 a schematic block diagram showing the sequence of a first embodiment of the method according to the invention, and
• 11 a schematic block diagram showing the sequence of a second embodiment of the method according to the invention.
• 1 shows a diagram of Planck's radiation spectrum, in which the sensitive spectral band of an IR camera 16 , which includes the wavelength range from 2.5 microns to 5.1 microns, is identified.

• c = Lichtgeschwindigkeit
• h = Plancksche Wirkungsquantum (eine Konstante)
• k = Planck-Boltzmannsche Konstante (unabhängig von der Stoffart)
• c₁, c₂ = Konstante sind.

According to Planck's Law of Radiation, the radiation power M results, which is a black body as a function of its temperature T in a wavelength range λ per unit area, from the following equation:

• c = speed of light
• h = Planck's constant of action (a constant)
• k = Planck-Boltzmann constant (regardless of the material type)
• c ₁ , c ₂ = constant.

wobei $${\text{M}}_3\left(3\mu \text{m},300\text{K},\text{ sr}\right)=\mathrm{0,057}\text{W}/\left(\mu \text{m}\cdot \text{sr}\right)$$

$${\text{M}}_5\left(5\mu \text{m},300\text{K},\text{ sr}\right)=\mathrm{2,627}\text{W}/\left(\mu \text{m}\cdot \text{sr}\right)$$

The estimation of the radiant power of a test specimen is, for example, in the frequency band between 3 μm and 5 μm at 300 K: $${\text{M}}_{\text{G}}=1/2\left({\text{<figure-callout id="3" label="M" filenames="DE102013010116B4\_0021.png,DE102013010116B4\_0023.png" state="{{state}}">M</figure-callout>}}_{\text{3}}+{\text{M}}_5\right)\cdot 2\mu \text{m}=\text{2}\text{, 684 W}/\left({\text{<figure-callout id="2" label="m" filenames="DE102013010116B4\_0021.png,DE102013010116B4\_0022.png" state="{{state}}">m</figure-callout>}}^{\text{2}}\cdot \text{sr}\right).$$

in which $${\text{M}}_3\left(3\mu \text{m}.300\text{K}.\text{sr}\right)=0.057\text{W}/\left(\mu \text{m}\cdot \text{sr}\right)$$

$${\text{M}}_5\left(5\mu \text{m}.300\text{K}.\text{sr}\right)=\mathrm{2,627}\text{W}/\left(\mu \text{m}\cdot \text{sr}\right)$$

1. 1. Die Strahlungsleistung jeder Lichtquelle 2, 3, 4, 5 muss so gering sein, dass sich der Prüfkörper 1 nur minimal erwärmt.
2. 2. Die Strahlungsleistung jeder Lichtquelle 2, 3, 4, 5 ist hoch genug, dass die Eigenstrahlung des Prüfkörpers 1 vernachlässigbar ist.

The conditions for determining the emissivity of a specimen 1 according to the method of the invention are:

1. 1. The radiation power of each light source 2 . 3 . 4 . 5 must be so small that the test specimen 1 only minimally heated.
2. 2. The radiation power of each light source 2 . 3 . 4 . 5 is high enough that the self-radiation of the specimen 1 is negligible.

• 3. Die Lichtquellen 2, 3, 4, 5 liegen im sensitiven Spektralbereich der IR-Kamera 16.

In the present example, the self-radiation of the test specimen is 1 about 2.7 W / m ² . In an over-radiation by the factor 10 , ie a lighting with about 27 W / m ² , the error lies in determining the emissivity of the specimen 1 at a maximum of 10%, caused by the emission of the test specimen 1 itself. In an overexposure to the factor 100 the error lies in the determination of the emissivity of the specimen 1 at a maximum of 1%.

• 3. The light sources 2 . 3 . 4 . 5 lie in the sensitive spectral range of the IR camera 16 ,

Out 2 schematically shows a side view of a test setup for the implementation of preliminary tests. The structure consists of a light source 2 , a filter system 6 a shutter 7 and a specimen 1 , As a light source 2 finds a conventional broadband radiator (silicon nitride) with a nominal power of 30 W use. It is also possible to use broadband radiators with up to 70 W, with nominal powers in the range of 20 W-40 W being advantageous for measurements. The emitter radiates in a wide spectral range.

To the thermal radiation of the component to be tested 1 To keep low, it is important to avoid heating the object to be tested during the lighting. For this purpose, the introduced energy must be kept to a minimum. This is done by using a filter system 6 , which is the spectral range of the light source 2 on the spectral range of the IR camera 16 limited. The filter system 6 , which limits the broad spectral range of the emitter to a desired wavelength range, is behind the light source 2 arranged, wherein a portion of the nominal power of the emitter is lost. The maximum in μm of the spectral range of the radiator should be in the range of the IR radiator of 2,5μm-5,1μm. This applies to a temperature of approx. 800 K.

As a filter system 6 Band pass filters, short pass filters, long pass filters, germanium mirrors, sapphire glass windows or combinations of these can be used.

As the emitter radiates continuously, is behind the filter system 6 a mechanical shutter 7 arranged having a shutter speed in the range of 1 ms - 20 ms. The mechanical shutter 7 limits the energy input of the emitter in time. The energy pulse can be kept low in this way in the sense of a Fotoblitzes. To warm the shutter 7 This can be prevented by a cooling device that is in 3 not shown, to be cooled.

Behind the shutter 7 the power of the introduced energy is a value of 3 W, which is above the component-dependent setpoint of approximately 2.7 W / m ² .

Out 3 schematically a sectional view of a lighting arrangement 20 out. On a base plate 18 with a circular opening is a retaining ring 17 mounted, the filter system 6 and the light source 2 circumferentially. On one side of the base plate 18 is a clamping hinge 19 for fixing the lighting arrangement 20 arranged. Below the base plate 18 is the shutter 7 arranged.

In 4 is a schematic plan view of the lighting arrangement 20 shown. The light source 2 is from the retaining ring 17 on the base plate 18 is mounted, circumferentially edged.

5 schematically shows a plan view of a first embodiment of a device for measuring the directional emissivity. In the middle of the measuring device is the base plate 18 , which is square here, with a bore for receiving the IR camera 16 arranged in 5 not shown. On the sides of the square base plate 18 are four lighting arrangements 20 according to 4 attached.

Out 6 schematically a view of the attachment of a lighting arrangement 20 at the square base plate 18 out. This is done via the clamping hinge 19 for aligning the lighting arrangement 20 , The lighting arrangement is preferred 20 pivoted by 20 ° from the horizontal, allowing the illumination of the specimen 1 with homogeneous, parallel light at an angle of 70 °.

In 7 1 is a schematic sectional view of a second embodiment of the device for measuring the directional emissivity. The test piece 1 is in at least one measuring range 23 with a light source defined in terms of radiation intensity, direction and position 2 . 3 . 4 . 5 directly to light and from the IR camera 16 known position. Illumination takes place sequentially in the sensitive spectral range of the IR camera 16 from four different positions.

Out 8th schematically shows a sectional view of a third embodiment of the device for measuring the directional emissivity. The sequential illumination of the test specimen 1 takes place indirectly via a parabolic mirror 22 in at least one measuring range 23 with a light source defined in terms of radiation intensity, direction and position 2 . 3 . 4 . 5 , Illumination takes place sequentially in the sensitive spectral range of the IR camera 16 from four different positions.

9 shows a schematic diagram of a single shot. After switching on the light source 2 becomes the shutter 7 opened, from the IR camera 16 a picture 11 the surface Z (x . y) of the test piece 1 taken and the shutter 7 then closed again. The duration for the opening of the shutter 7 , the image capture of the IR camera 16 as well as the closure of the shutter 7 total is about 20 ms. The energy input is thus limited to a short period of time, so that the surface Z (x . y) of the test piece 1 only minimally heated.

10 shows a schematic block diagram of a first embodiment of the method according to the invention. A total of four pictures will be sequential 11 . 12 . 13 . 14 from the IR camera 16 upon illumination of the component or specimen 1 with a light source defined in terms of radiation intensity, direction and position 2 . 3 . 4 . 5 taken from four different positions.

11 shows a schematic block diagram showing an automation of the method according to the invention. After switching on the first light source 2 at a first lighting position, the first shutter becomes 7 opened and from the IR camera 16 a first picture 11 the surface Z (x . y) of the component 1 added. Subsequently, the first shutter 7 closed again.

After taking the first picture 11 , becomes the first light source 2 turned off and the second light source 3 switched on at a second lighting position. This is the second shutter 8th opened, from the IR camera 16 a second picture 12 the surface Z (x . y) of the component 1 taken and the second shutter 8th closed again. Subsequently, the second light source 3 switched off and a third light source 4 switched on at a third lighting position. This is the third shutter 9 opened, from the camera 16 a third picture 13 the surface Z (x . y) of the component 1 recorded and the third shutter 9 closed again. After elimination of the third light source 4 and switching on the fourth light source 5 at a fourth illumination position, the fourth shutter can then be used 10 opened, from the IR camera 16 a fourth picture 14 the surface Z (x . y) of the component 1 recorded, the fourth shutter 10 closed again and the fourth light source 5 turned off. The duration for the opening of each shutter 7 . 8th . 9 . 10 , the image capture of the IR camera 16 as well as the closure of each shutter 7 . 8th . 9 . 10 total is about 20 ms each.

From the four pictures 11 . 12 . 13 . 14 the surface Z (x . y) of the component 1 can then from the gray value distributions of the recordings by means of the computer system 21 be concluded on the surface curvature. Next to the gradients p and q the surface Z (x , y) of the component 1 can from the recordings also the albedo p be determined. In this way it is possible to use SfS to determine the gradients of surfaces Z (x . y) to calculate that no homogeneous albedo p have. From the albedo determined during the SfS evaluation p can then over 1 = p + e the emissivity e be determined.

LIST OF REFERENCE NUMBERS

1

Component or specimen

2

first light source

3

second light source

4

third light source

5

fourth light source

6

filter system

7

first shutter

8th

second shutter

9

third shutter

10

fourth shutter

11

first picture

12

second picture

13

third picture

14

fourth picture

15

lighting arrangement

16

camera

17

retaining ring

18

baseplate

19

terminal hinge

20

lighting arrangement

21

computer system

22

parade

23

measuring range

Z (x, y)

Surface of the component

n

normal vector

r

reflection coefficient

C _K

camera sensitivity

I (x, y)

intensity

Q

Light intensity

s

Direction of the light

T

temperature

λ

wavelength

p

gradient

q

gradient

ρ

albedo

e

emissivity

Claims (11)

Method for measuring the directional emissivity of a component or specimen, in which the incident light intensity Q (x, y) is determined on a reference part of known geometry and emissivity by illuminating the reference part with a light source defined in terms of radiation intensity, direction and position and is detected by an IR camera of known position connected to a computer system, the component or the test body is sequentially illuminated from at least three different positions in at least one measuring range with a light source defined in terms of radiation intensity, direction and position and the surface Z ( x, y) of the component or specimen is in each case detected by the computer system connected to the IR camera known position, - for each pixel at the points (x, y) of the IR camera, the intensity I (x, y) in a known direction s = (s _x , s _y , s _z ) of the light is measured, - off the intensity I (x, y) and the direction of the light s = (s _x , s _y , s _z ) then the gradients $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{and q}=\frac{\partial \text{Z}}{\partial \text{y}}$

and the albedo p in each pixel are calculated by means of the equations for the three directions of illumination: $$\text{I}\left(\text{x}\text{, y}\right)=\mathrm{\rho }\cdot n\cdot s=\mathrm{\rho }\cdot \left({\text{s}}_{\text{z}}-\text{q}\cdot {\text{s}}_{\text{y}}-\text{p}\cdot {\text{s}}_{\text{x}}\right).$$

in which $$n=\frac{1}{\sqrt{1+{\text{p}}^2+{\text{q}}^2}}\left(\begin{array}{c}\text{-p}\\ \text{-q}\\ 1\end{array}\right)$$

is, from the relationship 1 = p + e then the directional emissivity e in each pixel is determined. Method for measuring the directional emissivity of a component or specimen Claim 1 , characterized in that for the minimization of errors instead of three image recordings for the calculation of the albedo four image recordings are taken with respect to radiation intensity, direction and position defined light source. Method according to Claim 1 or 2 , characterized in that the light sources exceed the thermal radiation of the component or specimen to be measured. Method according to one of the preceding claims, characterized in that are used as light sources heat radiator. Method according to one of the preceding claims, characterized in that the light sources are lasers or broadband radiators. Method according to one of the preceding claims, characterized in that a filter system is used which limits the spectral range of the light sources to the sensitive spectral range of the camera and reduces the introduced energy. Method according to Claim 6 , characterized in that are used as a filter system band pass filter, short pass filter, long pass filter, germanium mirror, sapphire crystal window or combinations thereof. Method according to one of the preceding claims, characterized in that for the time limit of the energy input for each light source, a shutter is used. Method according to one of the preceding claims, characterized in that the illumination takes place with homogeneous, parallel light. Use of the method according to the preceding claims for non-destructive thermographic testing of components or specimens for surface and / or internal defects. Device for measuring the directional emissivity of a component or specimen (1), - having a reference part of known geometry and known emissivity, to be illuminated by a light source defined in terms of radiation intensity, direction and position, and by a computer system (21) connected IR camera (16) known position for determining its light intensity, - with at least three lighting assemblies (20), each of which one of the radiation intensity, direction and position defined light sources (2, 3, 4, 5) , a filter system (6) and a shutter (7, 8, 9, 10) and are arranged at at least three different positions of the measuring device so that the component or the test body (1) sequentially from at least three different positions directly or indirectly is to illuminate, wherein - with the connected to the computer system (21) IR camera (16) known Positio n the surface Z (x, y) of the component or specimen (1) is to be imaged imagewise in at least one measuring area (23) in each of the at least three sequential illuminations and then by the computer system (21) on the one hand from at least three exposures IR camera (16) the gradients $\text{p}=\frac{\partial \text{Z}}{\partial \text{x}}\text{and q}=\frac{\partial \text{Z}}{\partial \text{y}}$

the surface Z (x, y) of the component (1) in the at least one measuring range (23) by means of the grayscale distributions for each pixel and - from the at least three images of the IR camera (16) the albedo p for each pixel of the surface Z (x, y) of the component or specimen (1) to determine and - the directional emissivity e of the component or the specimen (1) from the relationship 1 = p + e is calculated for each pixel by the computer system (21).

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