EP2721384A1

EP2721384A1 - Method and system for emissivity determination

Info

Publication number: EP2721384A1
Application number: EP12735853.9A
Authority: EP
Inventors: Max Rothenfusser; Michael Stockmann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2011-07-20
Filing date: 2012-07-11
Publication date: 2014-04-23
Also published as: US9516243B2; WO2013010871A1; US20140152841A1; DE102011079484A1

Abstract

The invention relates to a method for determining the emissivity of an object (21), having the steps of irradiating a surface (21a) of an object (21) using an infrared light beam (20a), receiving the infrared light beams (20b) reflected at the object using an infrared camera (2), capturing a first intensity of the reflected infrared light beams (20b) on a detector (2a) of the infrared camera (2), receiving the ambient radiation reflected at the object and the characteristic radiation of the object using the infrared camera (2), capturing a second intensity of the reflected ambient radiation and of the characteristic radiation of the object on the detector (2a) of the infrared camera (2), and calculating the emissivity of the object (21) on the basis of the first intensity and the second intensity. .

Description

description

Method and system for emissivity determination The present invention relates to non-contact, infrared optical methods and systems for Emissivitäts ^¬ determination.

State of the art

The emissivity E is defined as the ratio of the radiation power of the object to that of an ideal blackbody. The value of the emissivity E for real objects lies between the extreme values 0 for perfectly specular objects and 1 for an ideal black body.

The emissivity E can be a characteristic variable for the aging of materials. Therefore, knowing the emissivity E or its changes with the time or service ^{life of} a material on the aging ^¬ behavior of the material can be deduced.

When determining the temperature of objects, it should also be taken into consideration that the radiation emitted by an object is not only dependent on the temperature but also on its emissivity E. Furthermore, in various applications of thermography, it may be necessary to know the emissivity E of the thermographed object in order to be able to determine the height of the expected signals and / or the influence of interference signals from the ambient radiation.

For example, US Pat. No. 7,133,126 B2 discloses an optical method for determining the thickness of coatings on a heat exchanger.

The document US Pat. No. 7,409,313 B2 discloses a method for determining the thickness and thermal conductivity of an insulating layer of an object in which optical pulses of the insulating layer are reflected and evaluated by an optical measuring system.

An object of the present invention is therefore to provide an apparatus, a system and a method with which the emissivity of an object can be contactless, zer ^¬ interference, wavelength-dependent and temperature-independent determined. Summary of the invention

One aspect of the present invention consists in a method of determining the emissivity of an object, comprising the steps of irradiating a surface of an object with an infrared light beam, receiving the reflected on the object beams of infrared light with an infrared camera, detecting a first intensity of the reflektier ^¬ Infrared light beams on a detector of the infrared camera, receiving the reflected radiation on the object and the intrinsic radiation of the object with the infrared camera, detecting a second intensity of the reflected ambient radiation on the detector of the infrared camera, and calculating the emissivity of the object on the Base of the first intensity and the second intensity.

According to a further aspect, the invention provides a device for determining the emissivity of an object, with egg ^¬ ner emitter device, comprising an infrared emitter, which emits infrared rays over a predetermined wavelength range, and an aperture device, which is ^¬ laid out, at least a part to focus the emitted from the infrared emitter infrared rays in a substantially parallel light beam and to send to the surface of an object ^¬ . The apparatus comprises a Auswerteein- direction to a control device, which is coupled to the emitter device and can be coupled with an infrared camera, which is adapted to the infrared camera in such a way to counteract ^¬ that the infrared camera, an intensity of the detects the surface of the object reflected infrared light beam, and which is adapted to synchronize the dispensing of Inf ^¬ Rarotstrahlen by the infrared emitter with the detection of the intensity by the infrared camera.

According to a further aspect, the invention provides a system for determining the emissivity of an object with an OF INVENTION ^¬ to the invention apparatus and an infrared camera which is coupled to the control device, and which has a de- Tektor which is adapted to the intensity of At the surface of the object reflected infrared ^¬ rays of the infrared emitter to detect.

An essential idea of the invention is to determine the emissivity of an object by reflection of an infrared ^¬ light beam on the surface thereof. Since the re ^¬ inflected portion of the infrared light characterizes the value of the emissivity according to the Kirchhoff's law, via the measurement of the intensity of the reflected infrared light rays are closed on the emissivity.

An advantage of the invention is that the method or the system can operate completely non-contact and non-destructive. This is particularly advantageous in an investigation of the emissivity of hard to reach objects, such as built-in components in machinery and equipment. Further, a determination of the emissivity of advantageously in the operation of the objects to be examined, he ^¬ follow, whereby the operating time of an object can be optimized, for example during maintenance or power ^¬ analysis of the object.

Moreover, there is the advantage that the method can be realized inexpensively in the context of thermography. With an existing infrared camera, which is usually the most expensive component of the system for determining the emissivity, an emitter device and an evaluation device can be coupled as additional components to the infrared camera to specify the thermographic measurements by calibrating for the measured emissivity.

In an advantageous embodiment, the irradiation of the object with an infrared light beam may comprise bundling an infrared radiation emitted by an infrared emitter through a diaphragm device. Thus, a nearly parallel beam can be generated, which allows a defined image of the beam cross section on the detector of the infrared camera.

Further, a lens device may be provided in an advantageous embodiment, in the infrared camera, which images the reflected infrared light rays and / or the reflected radiation oriented environment respectively to infinity on the De ^¬ Tektor. This can be achieved that the focal point of the lens apparatus is placed on the surface of the Whether ^¬ jekts. Thus, the infrared camera can be operated in such a legally advantageous ^¬ that made for each individual beam associated with a picture angle to a single point of the detector surface.

In an advantageous embodiment, the received intensity is integrated over a detection area of the detector.

Preferably, a Filtervorrich ^¬ tion can be provided in the infrared camera, by means of which a wavelength-dependent filtering of the reflected infrared light rays and / or the reflected ambient radiation is possible. In order to localize advantageously have a spectral dependence of Emissivi ^¬ ty.

In an advantageous embodiment, a lock-in amplifier may be provided in the evaluation device, wherein the output of the infrared rays by the infrared emitter is in time with a reference frequency. This has the advantage that the infrared emitter can be operated in lock-in mode. can, so that the detected by the detector measurement signal can be optimized by lock-in evaluation in the lock-in amplifier in terms of signal-to-noise ratio.

Further modifications and variations will be apparent from the features of the dependent claims.

Brief description of the figures

Various embodiments and embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which: FIG

Fig. 1 is a schematic representation of a method for

Determining the emissivity of an object according to an aspect of the invention;

FIG. 2 shows a schematic representation of the beam path of a light beam incident on an object; FIG. and

Fig. 3 is a schematic representation of a system for

Determining the emissivity of an object according to another aspect of the invention shows.

The described embodiments and developments can, if appropriate, combine with one another as desired. Further possible refinements, developments and implementations of the invention also include combinations, not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments.

The accompanying drawings are intended to provide further understanding of the embodiments of the invention. They illustrate embodiments and, together with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale ^¬ true to each other. The same reference numerals be ^¬ characterize the same or similar acting components. Detailed description of the invention

1 shows a schematic representation of a method 10 for determining the emissivity E of an object. The procedural ^¬ ren 10 may, for example, with a system 100 for determining the emissivity e of an object 21 as shown in Fig. 3 schematically be performed. In the following, the ^method 10 will be explained by way of example with reference to the components of the system 100 in FIG. 3. In a first step 11, a irradiating a Whether ^¬ jekts with an infrared light beam is carried out. In FIG. 2, the optical path of a light beam 20a is exemplified in a ^¬ to meet on a surface of an object 21 is illustrated. The light beam 20a may be reflected, absorbed or transmitted through the object 21. In this case, the light beam 20b designates the reflected component R, the arrow 22 the absorbed component A, and the arrow 23 the transmitted component T. The relative sum of the reflected component R, the trans ^¬ mediated component T and the absorbed component A is 1:

R + A + T = 1

For fully opaque objects, that is, for objects made of a material with a transmittance of 0 or nearly 0 corresponds to the absorbed portion A of the relative sum from ^¬ züglich of the reflected portion R. Further, since the degree of absorption A of an object according to the Kirchhoff's Radiation ^¬ set corresponds to the emissivity e, the emissivity e can be specified for completely or almost completely opaque objects from ^¬ dependence of the reflectance R:

E = 1 - R The irradiation of the object 21 can be effected by an emitter device 1a which has an infrared emitter 3, for example a semiconductor diode emitting light in the infrared range. Infrared emitter in the sense of constricting vorlie ^¬ invention may thereby have emitter, which can deliver in a broadband spectral range infrared light. Instead of an infrared emitter 3, a laser can be used, for example ^¬ al ternatively, which operates in the infrared red range. Preferably, this may be an infrared laser which is tunable over a predetermined wavelength range in the infrared.

The emitter device 1a can have an aperture device 4 with a multiplicity of diaphragms 4a, 4b. The diaphragm device 4 can be designed to direct infrared light emitted by the infrared emitter 3 in a nearly parallel or quasi-parallel beam as a light beam 20a onto the surface 21a of the object 21. The number of diaphragms is not limited to two diaphragms 4a, 4b, but can in principle have any number and arrangement of diaphragms.

In a second step 12 of the method 10, the infrared light beams 20b reflected by the object 21 are received by means of an infrared camera. When the incident light beam or incident light beams 20a to the object 21 is a sufficiently parallel beam depicting ^¬ len, the divergence is small 20b against the dispersion of the re- inflected light beam. The reflected light beam 20b is generally divided into a specular component, that is to say a component reflected according to the law of reflection, which has an equal projection angle to the surface normal of the surface 21a of the object 21 as the angle of incidence with respect to this surface normal of the incident light beam 20a, and a scattering portion, which due to the surface roughness of the surface 21a of the object 21 to diffuse the beam direction of the specular component is distributed. The greater the surface roughness, the greater is the angular range over which the diffusely scattered component is distributed.

For receiving the scattering lobe, particularly the diffusely scattered ge ^¬ portion of the reflected light beam 20b in the infrared camera a lens device can be provided. 6 Instead of a lens device 6, for example, a single lens can be provided with a suitable focal length. The objective device 6 can be focused on the surface 21a of the object 21, that is to say the focal point F of the objective device 6, in particular the front focal point, can be placed on the point in which the light beam 20a is scattered by the object 21 is reflected. In this case, the image on the surface 21a of the object 21 can be imaged to infinity. As a result, it is possible for each detected angle to be imaged onto a single point on a detection surface of the detector 2a. The detector 2 may be disposed insbeson ^¬ particular in a rear focal point of the lens apparatus. 6 In this case, the entire area to which the quasi-parallel beam of infrared light is incident on the Oberflä ^¬ surface 21a, are mapped in a point or a pixel on the detection surface of the detector 2a. The De ^¬ Tektor 2a can for example be a CCD or a CMOS chip or other infrared-sensitive detector.

In a third step 13, a first intensity of the reflected infrared light beams 20b is detected on the detector 2a of the infrared camera 2. The detector 2a can for this purpose have a detection surface on which the Ab ^¬ beam angle of the reflected light beams 20b can be resolved two-dimensionally. For example, in a central area of the detection surface of the detector can be detected 2a of the directly reflected light beam 20b of the incident light beam ^¬ 20a. In an outer region around the central region of the detection surface of the detector 2a In this case, the diffusely scattered light beams 20b are detected. In order to determine the intensity of all reflected light beams 20b, it may then be provided to integrate the detected intensity over the entire detection area of the detector 2a.

The detection of the intensity can be made wavelength-dependent, that is, only reflected light rays 20b ei ^¬ ner particular wavelength or wavelengths of a particular gene region are passed to the detector 2a. For this purpose, it may be provided to equip the infrared camera 2 with a filter device 5. The filter device 5 can be integrated in the infrared camera 2, for example, or mounted as an external component in front of the optical input of the infrared camera 2. The filter device 5 can be designed to filter the light beams 20b incident in the infrared camera 2 in a wavelength-dependent manner. For this purpose, the filter device 5 may, for example, have a multiplicity of individual filters 5a, which can be arranged selectively in front of the optical input of the infrared camera 2, for example bandpass filters, interference filters, blocking filters and the like. For example, the filter device 5 comprise plug-in filters, screw filters, sliding filters, turntable filters or other devices.

In fourth and fifth steps 14 and 15, the ambient radiation reflected by the object 21 and the object's own radiation with the infrared camera 2 can be received, and a second intensity of the reflected ambient radiation and own radiation of the object on the detector 2 a of the infrared camera 2 can be detected , For this purpose, in particular, the operation of the infrared emitter 3 can be adjusted, that is, the infrared emitter 3 is turned off. In this case, no light beam is incident on the surface 20a more 21a of the object 21, so that the light beam 20b only reflected To ^¬ gebungsstrahlung or interfering radiation, and the characteristic radiation of the object comprises. As a result, a zero balance of the detected first intensity can be made with the second intensity be determined by the first intensity is determined and subtracted from the first intensity of the second detected intensity. In this case can, for example, for each pixel of the Erfas ^¬ sungsfläche the detector 2a is a cleanup of the first ER summarized intensity to the second intensity. However, it may also be possible to integrate both intensities over the detection area in each case and then to subtract the integrated second intensity from the integrated first intensity.

Thus, the emissivity can be calculated E of the object 21 based on the first intensity and the two ^¬ th intensity in a fifth to step 15. For this purpose, 8 may be provided in an evaluation device 7 is a calculation ^¬ drying apparatus, which receives the detected intensities of the detector 2a of the infrared camera 2 and processed. The calculation device 8 can be, for example, a processor, a microprocessor, an ASIC, an integrated circuit or the like. The evaluation device 7 may further comprise a control device 9, which is coupled to the infrared camera 2 and the emitter device la, and which is designed to control the infrared camera 2 and the Emittervorrich ^¬ tion la. In particular, the control device 9 can be designed to synchronize the activation of the infrared camera 2 and the emitter device 1 a, so that the reflected ambient radiation and own radiation as well as the reflected infrared radiation can be correspondingly detected. For this purpose, the control device 9 can control the infrared camera 2 and the emitter device 1a in accordance with a lock-in method. The calculation device 8 can have a lock-in amplifier, which receives a time-dependent intensity signal of the detector 2a. When the controller 9, the emitter device la controls such that the Be ^¬ drive the infrared emitter 3 with a reference frequency he ^¬ follows, that is, that the infrared emitter arrival at periodic time intervals 3 and is turned off, the lock-in can Amplifier multiply the intensity signal with the optionally pha ^¬ senverschobenen reference frequency in order to improve the signal-to-noise ratio of the intensity signal considerably.

The invention relates to a method for determining the emis- sivität of an object, comprising the steps of irradiating ei ^¬ ner surface of an object with an infrared light beam, receiving the reflected on the object infrared light radiation with an infrared camera, detecting a first intensity of the reflected Infrared light rays on a detector of the infrared camera, receiving the environmental radiation reflected at the object and the object's own radiation with the infrared camera, detecting a second intensity of the reflected ambient radiation and the object's own radiation on the detector of the infrared camera, and calculating the emissivity of the object based on the first intensity and the second intensity.

Claims

Method (10) for determining the emissivity (E) of an object (21), comprising the steps:

Irradiating (11) a surface (21a) of an object (21) with an infrared light beam (20a);

Receiving (12) the infrared light beams (20b) reflected on the object (21) with an infrared camera (2); Detecting (13) a first intensity of the reflected infrared light beams (20b) on a detector (2a) of the infrared camera (2);

Receiving (14) the ambient radiation reflected at the object (21) and own radiation of the object with the infrared camera (2);

Detecting (15) a second intensity of the reflected ambient radiation and own radiation of the object on the detector (2a) of the infrared camera (2); and

Calculating (16) of the emissivity (E) of the object (21) based on the first intensity and the second Intensi ^¬ ty.

The method (10) of claim 1, wherein irradiating the object (21) with an infrared light beam (20a) comprises bundling an infrared radiation emitted by an infrared emitter (3).

Method (10) according to one of claims 1 and 2, wherein receiving the reflected infrared light beams (20b) and the reflected ambient radiation as well as the natural radiation of the object respectively bundle the reflected beams (20b) on the detector (2a) by means of an objective device (6 ).

The method (10) of claim 3, further comprising

Step:

Setting the focal point (F) of the lens device (6) on the surface (21a) of the object (21). The method (10) of any one of claims 1 to 4, wherein detecting the first intensity and the second intensity each comprises integrating the received intensity across a detection area of the detector (2a).

The method (10) according to any one of claims 1 to 5, further comprising the steps of:

wavelength-dependent filtering of the reflected infra-red light rays ^¬ (20b) by using a filter device (5) of the infrared camera (2); and

wavelength-dependent filtering of the reflected radiation and the other ^¬ bung characteristic radiation of the object by using the filter device (5).

Device (1) for determining the emissivity (E) of an object (21), comprising:

an emitter device (1a), comprising:

an infrared emitter (3) emitting infrared rays over a predetermined wavelength range; and

an aperture device (4) which is adapted to focus at least part of the infrared rays emitted by the infrared emitter (3) in a substantially parallel light beam (20a) and to transmit them to the surface (21a) of an object (21); and an evaluation device (7) having a control device (9) which is coupled to the emitter device (1a) and can be coupled to an infrared camera (2),

wherein said control means (9) is adapted to control the infrared camera (2) such that the infrared ^¬ camera (2) an intensity of from the surface (21a) of the object (21) detects the reflected infrared light beam (20b), and

wherein the control device (9) is adapted to synchronize the emission of the infrared rays by the infrared emitter (3) with the detection of the intensity by the Infrarotka ^¬ mera (2). Device (1) according to claim 7, wherein the evaluation device (7) comprises a calculating means (8) which is adapted on the basis of the information detected by the Inf ^¬ rarotkamera (2) intensity, the emissivity (E) of the object (21) to calculate.

A device (1) according to claim 8, wherein the calculating means (8) comprises a lock-in amplifier, and wherein the control means (9) is arranged to control the output of the infrared rays by the infrared emitter (3) in time with a reference frequency.

The system (100) for determining the emissivity (E) of a Whether ^¬ jekts (21), comprising:

a device (1) according to any one of claims 8 to 9; and

an infrared camera (2), which is coupled to the control device (9), and which comprises:

a detector (2a) adapted to detect the intensity of infrared rays (20b) of the infrared emitter (3) reflected on the surface (21a) of the object (21).

System (100) according to claim 10, wherein the calculating means (9) is adapted to the detected intensity on a detection surface of the detector (2a) to integ ^¬ Center.

System (100) according to one of claims 10 and 11, wherein the infrared camera (2) further comprises a lens device (6) having a front focal point (F) on the surface (21a) of the object (21), and wel ^¬ che is designed to image on the surface (21a) of the object (21) reflected infrared rays (20b) of the infrared emitter (3) to infinity on the detection ^¬ surface of the detector (2a).

13. System (100) according to claim 12, wherein the detector (2a) is arranged in a rear focal point of the objective device (6). 14. System (100) according to any one of claims 10 to 13, wherein the infrared camera (2) further comprises a filter device

(5), which is designed to the detected by the De ^¬ detector (2a) reflected infrared light rays

(20b) depending on the wavelength.