WO2014009139A1

WO2014009139A1 - Led-based spectrometer probe

Info

Publication number: WO2014009139A1
Application number: PCT/EP2013/063149
Authority: WO
Inventors: Remigiusz Pastusiak; Anton Schick; Michael Stockmann; Patrick Wissmann
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-07-12
Filing date: 2013-06-24
Publication date: 2014-01-16

Abstract

The invention relates to a device, in particular a probe, and to the use thereof for spectroscopy, wherein defective spectra due to specimens for measurement which do not absorb ideally isotropically and cause scattering are avoided or effectively reduced. An emission of light in a measurement range takes place from several directions in such a way that measurement errors caused by direction-dependent scattering properties of the specimen for measurement are effectively reduced. The invention is suitable in particular for recording properties of a carbon particle stream.

Description

description

LED-based spectrometer probe The present invention relates to a device according to the preamble of the main claim and a corresponding use according to the independent claim.

Energy-efficient combustion of fossil fuels in power plants or smelting furnaces presupposes that the treatment of the fuels is effectively carried out and monitored. This also affects, among other things, the burning of coal. Coal usually has many pollutants and, depending on the pre-treatment, also has a certain degree of water, which adversely affects the combustion efficiency. Usually, the coal is dried and comminuted prior to incineration and then fed to the actual site of combustion via dust lines under high pressure and at high speed.

By means of spectroscopic methods it is possible to determine chemical impurities and the moisture content of the coals. By examining the coal dust transported through the tubes in front of the combustion chamber spectroscopically, in principle the combustion efficiency can be determined and optionally optimized via a control loop to the drying plant.

For the spectroscopic investigation it is necessary that the carbon dust transported through the tube at high speed is brought into the optical measuring field of a spectrometer probe. For optical measurement, the coal must be illuminated with a broadband light source to stimulate specific molecular vibrations of the water or chemical contaminants. The light scattered in carbon dust must then be detected and examined for its spectral composition by means of a spectrometer. Power plants usually have harsh environmental conditions. Therefore, the sensitive spectrometer, which can also be designated as an evaluation device for determining at least one state value of a test sample by means of the light received by a receiver device, is accommodated in a spatially separated manner, for example in an air-conditioned adjoining room. The feeding of the scattered light detected in the probe to the spectrometer is conventionally effected by fiber optics.

Conventional probes that operate on the basis of halogen lamp lighting are not designed for use in extreme environmental conditions. It is expected that a free space, in particular an air space, is located between the probe and the object to be measured, which is the probe of the

Object mechanically and thermally decoupled. Mechanical decoupling is required because the accelerated carbon dust is abrasive on the optical surfaces. Thermal decoupling is necessary because the temperature of a halogen lamp is very difficult to control and its life is relatively low.

It is the object of the invention to provide a device, in particular a spectrometer probe, and its use for spectroscopy, in which erroneous spectra due to non-ideal isotropically absorbing and scattering measuring samples are avoided or effectively reduced. Errors due to directionally enhanced scattering of wavelength bands in the test sample in the direction of the receiver device should be compensated.

The object is achieved by a device according to the main claim and a use according to the independent claim. According to a first aspect, an apparatus is claimed for the spectroscopy of a measurement sample to be analyzed which emits a plurality of groups each having a group in a wavelength band extending over a nominal wavelength. light emitting diodes for emitting light in the direction of a measuring sample having spatial measuring range, in which the light is focused by means of a focusing device; has a receiver device positioned at the spatial measuring range for receiving light scattered in the test sample. The device is characterized in that the number of groups, the nominal wavelength and the shape of the wavelength band per group and the spatial arrangement of the LEDs are selected such that the wavelength bands mix in the spatial measurement range to a fixed measurement spectrum and the emission Light in the measuring range in such a way from a plurality of directions that caused by directional scattering properties of the measurement sample measurement errors are effectively reduced.

According to a second aspect, a use of a device according to the first aspect for spectroscopy of a measurement sample to be analyzed, is claimed with the following steps. Emitting light by means of a plurality of groups of each group in a light emitting diode emitting wavelength band extending over a nominal wavelength toward a spatial measurement area having the measurement sample into which the light is focused by means of a focusing device; by means of a receiver device positioned at the spatial measuring range receiving light scattered in the test sample. The use is characterized in that by means of the number of groups, the nominal wavelength and the shape of the wavelength band per group of the spatial arrangement of the LEDs to each other, the wavelength bands are mixed in the spatial measurement range to a fixed measurement spectrum, the emission of light in the measuring range in such a way from a multiplicity of directions that measurement errors caused by direction-dependent scattering properties of the test sample are effectively reduced.

To solve the problem, an LED-based approach is used which reduces the narrow-band light generated. because of the different lengths of different LEDs in an ideal way. Specifically, the scope of the present invention includes spectrometer probes alone which have no evaluation device for determining at least one state value of the measurement sample by means of the light received by the receiver device and only supply the analysis light to such evaluation devices or spectrometers. The mixing of the light wave components takes place in such a way that the light is not segregated again by the scattering properties of an object or a measuring sample and thereby preferably impinges wavelength-specific scattering components on the detector and thus falsifies the true spectrum. Since LEDs (light-emitting diodes) with different wavelengths, for example seven wavelength bands, are spatially separated, their light is usually superimposed for optimal mixing at the location of the object. After passing through a focus area or overlapping area, the beam bundles with different wavelengths of light will separate again. If an object or a sample is ideally isotropic for the spectral-specific absorption, and the light always scatters isotropically into the space, then a detector with a downstream spectrometer will reproduce an unadulterated spectrogram. However, the scattering and absorbing capacity of real objects, such as coal, depends on the homogeneity of the particle sizes in a cloud of dust or the surface properties, such as purity, of a solid surface. As a result, anisotropically enhanced scattering, that is to say reflection, of individual wavelength bands can occur in the direction of the detector optics, as a result of which erroneous spectra are generated.

Further advantageous embodiments are claimed in conjunction with the subclaims.

According to an advantageous embodiment, the number of light-emitting diodes per group can be the same and the light-emitting diodes of all Groups over a starting from the sample considered the largest possible solid angle evenly distributed, be compact and arranged in a matrix. In order to avoid erroneous spectra, a multiplicity of individual LEDs with respect to the wavelength are optimally mixed in an extremely dense package in an advantageous manner. In addition, the LEDs can be distributed over the largest possible solid angle from the perspective of the material to be examined, so that the reflected-back intensity is decoupled from the reflection eigen-shafts. Matrix-shaped here means an arrangement in a tabular form.

According to a further advantageous embodiment, the light-emitting diodes can be arranged in repeating patterns of basic units in which a light-emitting diode can be arranged adjacent to one another for each group.

According to a further advantageous embodiment, the light-emitting diodes, regardless of the type of light-emitting diodes, can be arranged symmetrically with respect to an axis running through the spatial measuring range along a plate in the direction of the spatial measuring range.

According to a further advantageous refinement, the focusing device can in each case form a focusing optics for each light-emitting diode between the latter and the spatial measuring region, and the receiver device can be embodied as an optical waveguide oriented along the symmetry axis extending through the spatial measuring range by means of detector optics in the direction of the spatial measuring region be.

According to a further advantageous embodiment, the distance of the detector optics to the spatial measuring range can be smaller than the respective distance between the focusing optics and the spatial measuring range. Focusing optics and detector optics may be, for example, optical lenses. According to a further advantageous embodiment, the optical waveguide of the receiver device along the axis of symmetry from the plate to the detector optics have a Ummante- ment.

According to a further advantageous embodiment, the focusing optics may be offset in relation to the LEDs with increasing distance to them in the direction towards the axis of symmetry. As the distance from the probe axis increases, the lenses are more displaced relative to the direction of emission of the light-emitting diodes in order to generate maximum illumination intensity along the probe axis or symmetry axis and to achieve an optimum signal-to-noise ratio. In this case, the principle of the facet eye is inverted: the eye becomes the light source and all emitted rays illuminate a point in the measuring volume of the probe. Focusing optics are preferably optical lenses. According to a further advantageous embodiment, the basic units may be pairs, triangles, diamonds, trapezoids, hexagons or stretches.

According to a further advantageous embodiment, the fixed measurement spectrum can correspond to the spectrum of white light and can be at least broadband.

According to a further advantageous embodiment, the mixing components of the wavelength bands can be adjusted by means of respective electrical light-emitting diode currents.

According to a further advantageous embodiment, the nominal wavelengths can be generated in the range from 250 nm to 360 nm in 5 nm increments and at selected wavelengths from 365 nm to 637 nm. The mixing proportions of the light wavelengths can be adjusted by the respective LED currents. The lifetime of LEDs is significantly higher than that of conventional conventional halogen lamps. The lifetime of LEDs can be higher by a factor of 10 to 20.

According to a further advantageous embodiment, the measuring sample may be a particle flow flowing through a line as a spatial measuring range, wherein the line in the beam path of the light from the light emitting diodes in the spatial measuring range and from there into the receiver device may have a protective glass to which the detector optics adjoin. Zend is positioned. The detector optics advantageously has optical lenses.

In accordance with a further advantageous embodiment, the test sample may be a coal dust stream which is guided through the spatial measuring region through a pipeline, wherein the pipeline in the beam path has a protective glass consisting of sapphire or diamond. Thus, the optical properties of an abrasion-resistant protective window, for example made of diamond or sapphire, in the light paths are taken into account.

In accordance with a further advantageous refinement, an evaluation device can be designed to determine at least one status value of the measurement sample by means of the light received by the receiver device. Such an evaluation device may be a spectrometer to which the device or the probe provides access to a difficult to access and rough spatial measuring range by means of the light guide.

According to a further advantageous embodiment, the LEDs can be controlled by means of Peltier elements in terms of temperature. Since LEDs are "cold" emitters, which generate the heat loss at relatively low temperatures in the area, the temperature can be controlled by means of simple Peltier elements. The invention will be described in more detail by means of exemplary embodiments in conjunction with the figures. Show it:

1 shows a first embodiment of a device according to the invention;

Figure 2 is a representation of the principle of segregation by the obj ect; Figure 3 shows a second embodiment of a device according to the invention;

Figure 4 shows a third embodiment of a device according to the invention;

Figure 5 shows a fourth embodiment of a device according to the invention;

FIG. 6 shows an exemplary embodiment of an LED arrangement;

Figure 7 is a schematic representation of an LED arrangement according to the invention;

FIG. 8 shows further schematic representations of LED arrangements according to the invention;

FIG. 9a shows a further embodiment of an LED arrangement; FIG. 9b shows an exemplary embodiment of a lens arrangement;

10 shows an embodiment of an inventive

Use . FIG. 1 shows a first exemplary embodiment of a device according to the invention. Figure 1 shows an ideal arrangement of LEDs LEDs, here 2 different wavelength bands are used. FIG. 1 shows an entire Direction for spectroscopy of a sample to be analyzed. FIG. 1 shows two groups, wherein a wavelength band extending over a nominal wavelength is assigned to each group. Each light-emitting diode LED emits light in the direction of a measuring region having the measuring sample 5, in which the light is focused by means of a focusing device 7. A receiver device 9 positioned at the spatial measuring region 5 receives the light scattered by the measuring sample. By means of a light guide 19, the light received by the receiving device 9 is supplied to an evaluation device 11. This evaluation device 11 is preferably a spectrometer which determines at least one state value of the measurement sample by means of the light received by the receiver device 9. Basically, the scope of protection already includes a spectrometer probe according to the invention, all of which are shown in FIG

I components except for the evaluation

II. Reference numeral 17 is a plate, for example, a flex circuit board which positions and fixes them as a holder for the LEDs. FIG. 1 shows how the light of two LED groups is focused by focusing lenses 7 a onto a defined measuring range, which is the spatial measuring range 5. According to FIG. 1, the light-emitting diodes LED 1 and LED 2, which emit different wavelengths, are arranged alternately oriented along a plate 17 that is concavely curved toward the spatial measuring range in the direction of the spatial measuring range 5. Reference numeral 15 shows an axis of symmetry extending through the spatial measuring region 5, to which the spectral probe is designed to be axially symmetrical. According to FIG. 1, the emission of the light in the measuring region 5 already takes place in such a way from a multiplicity of directions that measurement errors caused by direction-dependent scattering properties of the test sample are effectively reduced.

FIG. 2 shows a representation with regard to the principle of demixing by the measurement sample 4. FIG. 2 shows that the light emitted from the LED 2 is detected by the receiver device 9 due to the direction-dependent scattering property of the measurement sample 4 shown there and is transmitted to the light guide 19. is passed. By contrast, the light emitted by the light-emitting diode LED 1 does not enter the receiver device 9 due to the direction-dependent scattering property of the test sample 4 and is therefore not forwarded in the light guide 19. FIG. 2 shows a demixing by the object or the measuring sample 4 which, as the anisotropically scattering object, preferably backscatters a wavelength band and in this way generates measuring errors. FIG. 3 shows a second exemplary embodiment of a device according to the invention. FIG. 3 shows a spectrometer probe according to the invention which supplies the spectrometer 11 with the light to be evaluated. The arrangement according to FIG. 3 shows an advantageous embodiment of an arrangement of LEDs when using a plate 17, which is designed here as a planar printed circuit board. Reference numeral 15 denotes an axis of symmetry to which the arrangement is axisymmetric. FIG. 3 shows a corresponding section. According to FIG. 3, 3 groups with respective wavelength bands of light-emitting diodes LED 1, LED 2 and LED 3 are used. According to the invention, a spectrometer probe for the measurement of a spectrum on the basis of LED light sources is proposed. In this case, the device was designed in such a way that an optimum mixture of the light wavelengths takes place from a multiplicity of individual light sources, which here can be, for example, 3 wavelength bands with 8 light sources each, through a densely packed matrix-shaped spatial arrangement. Such an arrangement prevents the light from being able to be demixed again by means of a structured, rough object and, if appropriate, the spectrum being falsified. FIG. 3 shows the light-emitting diodes oriented along a flat plate in the direction of the spatial measuring range.

FIG. 4 shows a third exemplary embodiment of an arrangement according to the invention. The scope of protection of the present application also includes all spectrometer probes which have all device features according to the invention, except for the evaluation device 11. In contrast to the device According to FIG. 3, the distance of the detector optics 9a is selected to be smaller than the respective distance of a focusing optics 7a to the spatial measuring region 5. Thus, the detector optics 9a is no longer in the plane of the focusing optics 7a. Reference symbol 21 denotes an LED luminous area of an LED 3. The receiver device 9 is preferred to avoid interference signals when using a protective glass 27 relative to the luminous plane 21. By this preference, reflections between LED luminous surfaces 21 and the protective glass 27 are directly suppressed. Reference numeral 23 denotes a carbon dust flow which flows through a pipeline 27 and the spatial measuring region 5 defined there. The protective glass 27 makes it possible to introduce the spatial measuring area 5 into the interior of the pipeline 25. The selected spatial arrangement of the receiver device 9 relative to the illumination device LED 1... LED 3 avoids reflections which can occur on the protective glass 27 , directly into the receiver device 9 and thus falsify the spectrum to be analyzed. FIG. 4 also shows a cross section of the LED arrangement.

FIG. 5 shows a fourth exemplary embodiment of an arrangement according to the invention. In contrast to FIG. 4, an optical waveguide 19 which receives light to be analyzed by the detector optics 9 a has an additional cladding 29. This jacket 29 causes a suppression of direct reflections as a result of the arrangement of the detector unit 9 between LED lighting surfaces and protective glass 27 and additionally acts as a mounting tube for easy guidance of light guides 19 and focusing optics 9a. Such a sheath 29 acts as a holder and as protection against unwanted scattered light. Furthermore, the arrangement according to FIG. 5 is similar to the arrangement according to FIG. 4. According to FIG. 5 suppression of direct reflexes takes place. The positioning of the detection optics relative to the surface on which the illumination light is emitted causes this. The closer the detection optics are spatially positioned in front of the illumination plane, the more direct light reflexes on a protective glass are avoided and at the same time The number of LEDs can be increased while maintaining the same light cone.

FIG. 6 shows an exemplary embodiment of a densely packed LED matrix using 7 wavelength bands. The

Light-emitting diodes LED numbered here, according to their group membership, are arranged in repeating patterns of basic units in which one LED is arranged adjacent to each other for each group. According to FIG. 6, the light-emitting diodes of a basic unit are arranged along a path. FIG. 6 shows a plan view of the side views shown in FIGS. Figures 7 and 8 show embodiments of repetitive patterns M of basic units in which the light-emitting diodes are arranged. A basic unit comprises one LED for each group. Figure 7 shows stretched, triangular, diamond-shaped, trapezoidal and hexagonal compact arrangements. Figures 7 and 8 show LED arrays for different numbers of wavelength bands. It is intended to effect a densest packing of light-emitting diodes in the plane. FIG. 9a shows an exemplary embodiment of an LED matrix according to the invention. FIG. 9b shows an associated lens matrix.

FIG. 10 shows an exemplary embodiment of a method for which a device according to the invention is used. With a step Sl, the emission of light by means of a plurality of groups with each group takes place in a wave band extending over a nominal wavelength

Light emitting diodes in the direction of a measuring sample having spatial measuring range in which the light is focused by means of a focusing. With a second step S2, by means of a receiver device positioned at the spatial measuring range, a reception of signals in the measuring sample takes place. scattered light. With a further step S3, an evaluation device is used to determine at least one state value of the test sample by means of the light received by the receiver device. Finally, in a step S4, the number of groups, the nominal wavelength and the shape of the wavelength band per group and the spatial arrangement of the LEDs to each other selected such that caused by directional scattering properties of the measurement sample measurement errors are effectively reduced.

The invention relates to a device, in particular a probe, and their use for spectroscopy in which erroneous spectra due to non-ideal isotropically absorbing and scattering measuring samples are avoided or effectively reduced. An emission of light into a measuring range takes place in such a way from a multiplicity of directions that measuring errors caused by direction-dependent scattering properties of the test sample are effectively reduced. The invention is particularly suitable for detecting the properties of a coal particle flow.

Claims

claims

1. Apparatus for spectroscopy of a sample to be analyzed (4), comprising

a plurality of groups each having a group in a light emitting diode (LED1, LED2) emitting a wavelength band extending over a nominal wavelength for emitting light in the direction of a spatial measuring range (5) having the test sample into which the light is directed by means of a focusing device ( 7) is focused;

a receiver device (9) positioned at the spatial measuring range for receiving light scattered in the test sample;

characterized in that the number of groups, the nominal wavelength and the shape of the wavelength band per group and the spatial arrangement of the LEDs are selected such that the wavelength bands mix in the spatial measurement range to a fixed measurement spectrum, and the emission of the light in the measuring range in such a way from a multiplicity of directions that measuring errors caused by direction-dependent scattering properties of the test sample are effectively reduced.

2. Apparatus according to claim 1, characterized in that the number of light-emitting diodes per group is the same and the

Light emitting diodes of all groups over a starting from the sample considered the largest possible solid angle evenly distributed, compact and arranged in matrix form.

3. Device according to claim 1 or 2, characterized in that the light-emitting diodes are arranged in repeating patterns (M) of basic units, in each of which a light-emitting diode are arranged adjacent to each other for each group.

4. Device according to one of the preceding claims 1 to

3. characterized in that the light emitting diodes, regardless of the type of light emitting diodes axially symmetrical to a the spatial measuring range extending axis (15), along a plate (17) oriented in the direction of the spatial measuring range are arranged.

5. Apparatus according to claim 3 or 4, characterized in that the focusing device (7) forms a focusing optics (7a) for each light-emitting diode between these and the spatial measuring range and the receiver device (9) than along the through the spatial measuring range fau- fenden Symmetry axis by means of a detector optics (9a) in

Direction to the spatial measurement range oriented toward light guide (19) is formed.

6. Apparatus according to claim 5, characterized in that the distance of the detector optics (9a) to the spatial measuring range

(5) is smaller than the respective distance of the focusing optics (7a) to the spatial measuring range.

7. Apparatus according to claim 5 or 6, characterized marked, that the optical fiber of the receiver device along the axis of symmetry from the plate to the detector optics has a sheath (29).

8. The device according to claim 5, characterized in that the focusing optics are offset in relation to the LEDs with increasing distance to them in the direction towards the axis of symmetry.

9. The device according to claim 3, characterized in that the basic units are pairs, triangles, diamonds, trapezoids, hexagons or stretches.

10. Device according to one of the preceding claims 1 to

9, characterized in that the fixed measurement spectrum corresponds to the spectrum of white light.

11. Device according to one of the preceding claims 1 to

10, characterized in that the mixing proportions of Wavelength bands are adjusted by means of respective electrical light-emitting diode currents.

12. Device according to one of the preceding claims 1 to 11, characterized in that the nominal wavelengths are generated in the range of 250nm to 360nm in 5nm increments and at selected wavelengths from 365nm to 637nm.

13. Device according to one of the preceding claims 5 to 7, characterized in that the measurement sample by a

Line is as a spatial measuring range flowing through particle flow, wherein the line in the beam path of the light from the light emitting diodes in the spatial measuring range and from there into the receiver device has a protective glass, to which the detector optics is positioned adjacent.

14. Device according to one of the preceding claims 1 to 13, characterized in that the measuring sample is a coal dust stream (23) which is passed through a pipe (25) through the spatial measuring range (5), wherein the pipeline in the beam path of a sapphire or diamond existing protective glass (27).

15. Device according to one of the preceding claims 1 to 14, characterized in that the light-emitting diodes means

Peltier elements are regulated in terms of temperature.

16. Device according to one of the preceding claims 1 to 15, characterized by an evaluation device (11) for determining at least one state value of the measurement sample by means of the received light from the receiver device;

17. Use of a device according to one of the preceding claims for the spectroscopy of a sample to be analyzed, with the steps

Emission of light by means of a plurality of groups of each group in a light emitting diode emitting in a wavelength band extending over a nominal wavelength. tion to a measuring sample having spatial measuring range, in which the light is focused by means of a focusing device;

receiving light scattered in the test sample by means of a receiver device positioned at the spatial measuring range;

characterized in that

by means of the number of groups, the nominal wavelength and the shape of the wavelength band per group and the spatial arrangement of the LEDs to each other, the wavelength bands are mixed in the spatial measurement range to a fixed measurement spectrum, wherein the emission of the light in the measuring range such from a variety of In the directions that occur, directional scattering properties of the test sample effectively reduce measurement errors.

18. The use as claimed in claim 17, characterized by determining by means of an evaluation device at least one state value of the test sample by means of the light received by the receiver device.

19. Use according to claim 17 or 18, characterized in that the mixing components of the wavelength bands are adjusted by means of respective electrical light-emitting diode currents.

20. The apparatus of claim 17, 18 or 19, characterized in that the LEDs are controlled by means of Peltier elements in terms of temperature.