Sensor device for detecting particles or aerosols in a flowing fluid using the principle of laser-induced incandescence

Abstract

A sensor device (10) for detecting particles (24) or aerosols in a flowing fluid using the principle of laser-induced incandescence, the sensor device comprising: a first device (12) for generating laser light (14); a second device (24) for guiding the laser light (14); a third device (36) for guiding temperature radiation (28) emitted by particles (26) heated by the laser light (14); and a fourth device (34) for detecting the temperature radiation (28). It is proposed that at least parts (44, 46) of at least two of the first to fourth devices (12, 24, 36, 34) are arranged on a common carrier (48).

Description

Technical Field

[0001] The invention relates to a sensor device for detecting particles or aerosols in a flowing fluid using the principle of laser-induced incandescence according to the preamble of claim 1 . Background Art

[0002] DE 10 2017 207 402 A1 discloses a sensor device in the form of a particle sensor for detecting particles in a fluid-conducting region using the principle of laser-induced incandescence. Particles present in the exhaust-conducting region, such as soot particles, are heated to several thousand degrees Celsius by means of laser light focused onto a laser spot, causing them to emit a significant amount of thermal or temperature radiation. This thermally induced light emission of the particles is measured by means of a photodetector, which provides an output signal corresponding to the measured light intensity. Summary of the Invention

[0003] The problem on which the invention is based is solved by a sensor device having the features of claim 1. Advantageous developments are specified in the dependent claims.

[0004] According to the invention, at least some of the optical, electronic and / or optoelectronic components of the sensor device are mounted on a common carrier ("substrate") and aligned with one another. The aim is to arrange as many of these components as possible on a common carrier, fix them there, and thus create an integral part or "optical block." In particular, the optical elements required for light shaping (e.g., mirrors, lenses, beam splitters, etc.) are fixed to a common carrier. This greatly simplifies the design of the sensor device and thus also its alignment. This can be achieved actively, for example, by gluing, during the manufacture and fixing of the components. The components of the "optical block" are thus aligned with one another. Overall, the sensor topology is thus simplified. This also reduces manufacturing costs, since, in particular, smaller optical elements can also be used. The mechanical and thermal stability of the sensor device is also improved.

[0005] All of this is achieved by means of a sensor device for detecting particles or aerosols in a flowing fluid using the principle of laser-induced incandescence (LII). It should be pointed out at this point that in particular soot particles can be considered as particles and in particular exhaust gases from combustion plants or internal combustion engines can be considered as fluids. For example, the device can be used for condition monitoring of particle filters in gasoline or diesel vehicles. In principle, however, the device is generally suitable for detecting particles and aerosols in any fluid. For example, it is conceivable to use the device in other scenarios and application areas (e.g. portable exhaust emission monitoring systems, indoor air quality measurement, exhaust emissions from combustion plants). The solution makes it possible to determine the mass concentration of particles (mg / m 3or mg / mi), and can also determine the number concentration of particles (particles / m 3 or particles / mi). Measurement of particle size distribution is also possible.

[0006] In the principle of laser-induced incandescence, particles are first heated to several thousand degrees Celsius by partial absorption of laser light. The laser light is generated by a device (e.g., a laser) and focused at sufficiently high intensity into a laser spot, i.e., into a volume with minimum dimensions in the μm range. According to Planck's radiation law, these hot particles emit characteristic temperature radiation (incandescent light or thermionic emission), which serves as a measurement signal and is detected by a device (e.g., a detector).

[0007] For this purpose, for example, an optical element (for example in the form of a focusing lens) is used which is arranged in the beam path of the laser and is designed and arranged to focus the laser light emitted by the laser into a very small laser spot. In the case of a focus diameter of, for example, 10 μm, it can be assumed that: when the focus is 10 μm, the laser beam is focused. 13 / m 3 Based on the particle concentration, only one particle always flies past the laser spot at a given moment (intrinsic single-particle detectability). The detector is configured and arranged so that it detects the temperature radiation emitted by the laser spot. For example, cost-effective semiconductor laser diodes can be used as the device for generating the laser light. Detection of the temperature radiation can be performed, for example, using a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM).

[0008] Specifically, the sensor device according to the present invention comprises a first device for generating laser light, for example in the form of the aforementioned laser diode. Furthermore, the sensor device comprises a second device for guiding the laser light, wherein this device typically comprises optical components, for example in the form of lenses and / or mirrors. The sensor device also comprises a third device for guiding the temperature radiation emitted by the particles heated by the laser light in the aforementioned spot. This device also typically comprises optical components, for example in the form of lenses and / or mirrors. Finally, the sensor device according to the present invention comprises a fourth device for detecting the temperature radiation, typically in the form of a detector, for example, of the aforementioned type, for example, a photodiode.

[0009] In the sensor device according to the present invention, at least parts of at least two of the first to fourth devices are arranged on a common carrier and are thus fixedly arranged in a fixed relationship with one another in the manner of an "optical block." In this context, "common carrier" is not to be understood as meaning that the respective parts of the devices are mechanically fixed to one another in any manner or method, such as being accommodated in a common housing. A "common carrier" is preferably understood as a one-piece element to which the respective devices are fixed directly or by means of corresponding fixing devices.

[0010] In one embodiment, the carrier comprises a planar board, in particular a PCB ("Printed Circuit Board") or a ceramic board. If a PCB is used, the electronic components of the sensor device can also be integrated very simply. This is particularly advantageous with respect to the first and fourth devices. If a planar substrate made of a ceramic material is used, this offers advantages in terms of thermal conductivity, as ceramic is a good insulator and can also reliably withstand high temperatures.

[0011] In one embodiment, the sensor device has a first region facing the fluid and a second region facing away from the fluid, and only the portion of the first to fourth devices arranged in the second region is arranged on a common carrier. The carrier is thus arranged in the second region facing away from the fluid, which can also be referred to as a "cold" region, particularly when the fluid is the exhaust gas of a combustion system or an internal combustion engine, because significantly lower temperatures prevail in this second region than in the (hot) first region facing the fluid. The present invention thus enables a highly integrated embodiment of this "cold" region of the sensor device.

[0012] In one embodiment of this, the first and second regions are optically coupled to each other via a light guide, in particular a glass fiber. Due to the inventive integration of the device on a common carrier, the use of such a light guide is particularly easy to implement and allows for virtually lossless transmission of both laser light and thermal radiation, as well as for the separation of essential electronic and optical components from the typically thermally and / or chemically highly exposed first region. This significantly improves the mechanical and thermal stability of the sensor device.

[0013] However, it is also conceivable in principle to dispense with the light guide and to guide the laser light directly from the first region into the second region, and the temperature radiation directly from the second region into the first region. This allows for a very compact sensor arrangement with so-called "free-beam optics." Here, too, the goal is to implement as many or even all of the optical components of the sensor arrangement in the second, "cold" region as possible on a common carrier and thus as a monolithic, relatively large component.

[0014] In one embodiment, the carrier has at least one opening through which the laser and / or temperature radiation passes. This allows both sides of the carrier to be used for arranging optical and / or electronic components, thereby enabling a particularly compact arrangement of the devices relative to one another.

[0015] In one embodiment of this, the second and third devices include at least one common component in the form of a beam splitter, which is arranged in an opening of a common carrier such that the thermal radiation or the laser light passes through the beam splitter and the opening. Such a beam splitter can be implemented, for example, in the form of a dichroic mirror. The beam splitter makes it possible to provide a common beam path, at least partially, for both the laser light and the thermal radiation, thereby achieving a particularly compact sensor arrangement while still achieving separate beam paths for the laser light and the thermal radiation locally, i.e., between the first device and the beam splitter and between the fourth device and the beam splitter. Arranging the beam splitter in the opening of the common carrier ensures that it is relatively protected, thereby improving the mechanical stability of the sensor arrangement.

[0016] In one embodiment, the first device (e.g., a laser diode) and / or the fourth device (e.g., a detector, e.g., in the form of a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM)) are arranged on a common carrier or at least partially in a common carrier. However, the carrier is not limited to being realized by a PCB; electrical control or signal decoupling can also be realized in or on the common carrier, thereby reducing manufacturing costs and further improving the robustness of the sensor device.

[0017] In one embodiment, the first device and the fourth device are arranged at opposite ends of the carrier. In this way, mutual influence is eliminated or at least significantly reduced.

[0018] In an alternative embodiment, the first device and the fourth device are arranged adjacent to each other on opposite sides of the carrier. In this way, the electronic components of the sensor device are concentrated in a specific area of ​​the common carrier, which has advantages in production.

[0019] In one embodiment, the second and / or third device includes at least one mirror arranged on the carrier, which deflects the laser light or the temperature radiation, wherein the mirror is preferably a focusing mirror. This mirror enables simple guidance of the laser light and / or the temperature radiation, and adjustment of the mirror can be performed very simply during installation, for example, when gluing the mirror to the substrate. If the mirror is a focusing mirror, it also performs the function of a focusing lens, thereby eliminating the need for a focusing lens, thereby saving costs and reducing the required installation space. This focusing mirror can be implemented, for example, as a curved mirror. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following describes the embodiments of the present invention with reference to the accompanying drawings.

[0021] Figure 1A schematic diagram showing the structure of a sensor device for detecting particles in a flowing fluid using the principle of laser-induced incandescence;

[0022] Figure 2 Show Figure 1 A schematic cross-sectional view of a first embodiment of a first region and a second region of a sensor device;

[0023] Figure 3 Show Figure 1 A schematic cross-sectional view of a second embodiment of a first region and a second region of a sensor device;

[0024] Figure 4 Show Figure 1 A schematic cross-sectional view of a third embodiment of a first region and a second region of a sensor device;

[0025] Figure 5 Shown with Figure 3 Schematic diagram of the sensor device of the second region.

[0026] In the following description, functionally equivalent elements and regions also carry the same reference numerals in different figures and are generally not explained multiple times. DETAILED DESCRIPTION

[0027] Figure 1 A sensor device 10 for detecting particles or aerosols in a flowing fluid using the principle of laser-induced incandescence, that is, in the form of a particle sensor, is shown in highly schematic form. First, a first device 12 in the form of a laser, in the present case, by way of example, a CW laser (CW = continuous wave), which generates or emits laser light 14. First device 12 can, in particular, comprise a laser diode, which is very cost-effective. Laser light 14 is first shaped into a parallel beam by a collimating device 16 (e.g., a collimating lens or mirror), which then passes through a beam splitter 18, e.g., in the form of a beam splitter or dichroic mirror. From there, the beam reaches a focusing device 20 and further, in focused form, reaches a laser spot 22 (hereinafter referred to as simply "spot"). The term "spot" refers to a volume element with very small dimensions, in the μm range or even in the 100 nm range, in which the laser light 14 is extremely focused and therefore very energy-intensive. The collimation device 16 , the beam splitter 18 and the focusing device 20 are part of a second device 24 , by means of which the laser light 14 is guided to a light spot 22 .

[0028] High-intensity laser light 14 can be directed in spot 22 onto particles 26 present therein, such as soot particles 26 in the exhaust stream of an internal combustion engine. The intensity of laser light 14 is so high in spot 22 that the energy of laser light 14 absorbed by particles 26 heats particles 26 to several thousand degrees Celsius (only in the volume of spot 22 does the intensity of laser light 14 reach the high values ​​required for laser-induced incandescence (LII)). As a result of this heating, particles 26 spontaneously and substantially without a preferred direction emit a large amount of temperature radiation 28, also referred to as LII light and indicated by dashed arrows in the figure. Consequently, a portion of temperature radiation 28 is also emitted in a direction opposite to that of incident laser light 14. Temperature radiation 28 lies, for example, in the near-infrared and visible spectral ranges, but is not limited to these spectral ranges.

[0029] The temperature radiation 28 of the particles 26 excited by the laser light 14 in the light spot 22 passes back through the focusing device 20 to the beam splitter 18. There, it is deflected, in this case, by 90° (other angles are possible), passes through the focusing lens 30, and through the filter 32 (which is not necessarily present) to reach the detector 34. The focusing device 20, the beam splitter 18, the focusing lens 30, and the filter 32 form a third device 36, which guides the temperature radiation 28 from the light spot 22 to the detector 34. It can be seen that the beam splitter 18 and the focusing device 20 belong to both the second device 24 and the third device 36. The detector 34 in turn forms the "fourth device for detecting the temperature radiation 28." The filter 32 is designed so that it at least largely filters out the wavelength of the laser light 14, which is also reflected back to a small extent. Therefore, the filter 32 reduces interfering background. A simple edge filter (Kanten filter) is also conceivable. This improves the signal-to-noise ratio.

[0030] The size of light spot 22 is in the range of a few micrometers, in particular in the range of up to 200 μm, so that particles 26 that traverse light spot 22 are excited to emit analyzable radiation power. Consequently, it can be assumed that at most one particle 26 is always present in light spot 22 and that the instantaneous output signal of sensor device 10 originates solely from this at most one particle 26.

[0031] The detector 34 preferably comprises a multi-pixel photon counter (MPPC), a silicon photon multiplier (SiPM), or a SPAD diode (single-photon avalanche diode), which detects the temperature radiation 28 and generates a corresponding output signal. Detectors 34 of this type can even detect extremely small light signals generated by particularly small particles 26, such as those formed by a few photons. This allows the detection of particle 26 sizes down to a confirmed lower limit of 10 nm.

[0032] Laser 12 can certainly be modulated, or switched on and off (with a duty cycle of less than 100%). However, it is still preferred that laser 12 is a CW laser. This allows the use of cost-effective semiconductor laser elements (laser diodes), which makes the entire sensor device 10 cost-effective and significantly simplifies the control of laser 12 and the evaluation of output signal 34. However, the use of pulsed lasers is not excluded.

[0033] Sensor device 10 includes a first region 40, indicated by a dotted-line frame, and a second region 42, also indicated by a dotted-line frame. First region 40 faces or is adjacent to the fluid in which particles 26 are to be detected (in the present case, by way of example, the exhaust gas of an internal combustion engine), while second region 42 faces away from the fluid. Because the exhaust gas, mentioned in the present case by way of example, is hot, first region 40 may also be referred to as a hot region, and second region 42 may also be referred to as a cold region.

[0034] It can be seen that the focusing device 20, which belongs to both the second device 24 and the third device 36, represents the portion of these respective devices 24 and 36 that is arranged in a first "hot" region 40, while all other components are arranged in a second "cold" region 42. In particular, the collimating device 16 and the beam splitter 18 represent the portion 44 of the second device 24 that is arranged in the second "cold" region 42, and the beam splitter 18, the focusing lens 30, and the filter 32 represent the portion 46 of the third device 36 that is also arranged in the second "cold" region 42. In other embodiments not shown here, other, more or fewer components may also belong to the portions 44 and 46.

[0035] from Figure 1 Finally, it can be seen that the first device 12 in the form of a laser, the part 44 of the second device 24, the part 46 of the third device 36 and the fourth device 34 in the form of a detector are all arranged on a one-piece common carrier 48 and are fixed thereto firmly and immovably and ultimately adjusted relative to one another, for example by gluing. At this point, it should be noted that the common carrier 48 can be designed in a completely different manner and in Figure 1 The illustrations selected are indicative only.

[0036] Now refer to Figure 2 There, in particular, the second region 42 of the sensor device 10 is shown in greater detail. It can be seen that the common carrier 48 comprises a one-piece planar plate, which can be, for example, a PCB (“printed circuit board”) or a ceramic plate. The first device 12 in the form of a laser is inserted into a first opening 50 in the common carrier 48, so that the laser light 14 is emitted essentially orthogonally from the common carrier 48. Figure 2In an embodiment of the invention, a curved mirror is provided as focusing device 16, which ensures that the laser light 14 is emitted as a parallel beam to a beam splitter 18. The beam splitter is inserted into a second opening 52 in the common carrier 48, wherein the beam splitter 18, for example in the form of a dichroic mirror, is arranged parallel to the plane of the common carrier 48, which is designed as a flat plate.

[0037] Laser light 14 is reflected by beam splitter 18 and directed to a first "hot" region 40. This occurs directly, i.e., without an intermediate connection such as a light guide, thereby achieving a so-called "compact sensor with free-beam optics." Conversely, temperature radiation 28 passes through beam splitter 18 and is further directed via focusing lens 30 and filter 32 to detector 34.

[0038] exist Figure 3 In another embodiment shown in , not only the first device 12, the collimating device 16 belonging to the second device 24 and constructed by a collimating lens, and the beam splitter 18 belonging to both the second device 24 and the third device 36 are arranged on a common carrier 48, but also other components are arranged: for example, Figure 3 The illustration shows a curved mirror 54 on the underside of the common carrier 48, which is fixed to the common carrier 48 and reflects the temperature radiation 28 arriving through the beam splitter 18 in a direction parallel to the plane of the common carrier 48 toward another curved mirror, which has the function of the above-mentioned focusing lens 30 and therefore also has this reference numeral and can be referred to as "focusing mirror 30." The focusing mirror 30 focuses the temperature radiation 28 and directs it toward the unit formed by the filter 32 and the detector 34 (fourth device), which is also fixed directly to the underside of the common carrier 48. It can be seen that the first device 12 (laser) and the fourth device 34 (detector) are arranged at opposite ends of the common carrier 48.

[0039] On the upper side of the common carrier 48 (again see Figure 3 ), a coupling-in and output lens 58, which couples laser light 14 into a light guide 60, for example a glass fiber, and couples temperature radiation 28 emitted by particles 26 in light spot 22 out of light guide 60, is fixed to a common carrier 48 via a holding portion 56. Thus, all optical and electronic components of sensor device 10 located in second, “cold” region 42 are directly fixed to common carrier 48, which is designed as a flat plate, for example, by adhesive bonding, thereby creating a fixed, already fully adjusted unit.

[0040] Figure 4Another embodiment is shown in which the first device 12 in the form of a laser emits the laser light 14 parallel to the plane of a common carrier 48 designed as a flat plate, and the beam splitter 18 is a dichroic mirror designed to be arranged obliquely relative to the common carrier 48. The laser light 14 passes through the dichroic mirror without a change in direction, while the temperature radiation 28 is emitted, for example, at Figure 3 The radiation 28 is deflected downward by 90°, passes through the second opening 52, and strikes the straightening mirror 54 fixed there. The straightening mirror guides the temperature radiation 28 through the focusing lens 30 and parallel to the plane of the common carrier 48 to the filter 32 and further to the fourth device 34 or detector. It can be seen that the first device 12 (laser) and the fourth device 34 (detector) are arranged adjacent to each other, but on opposite sides of the common carrier 48.

[0041] exist Figure 5 FIGURE 1 shows a more detailed view of first "hot" region 40 of sensor device 10. Exhaust gas flowing in exhaust pipe 62 is symbolically represented by arrow 64. Exhaust gas 64 is generated during a combustion process, and exhaust pipe 62 may, for example, belong to the exhaust system of an internal combustion engine (diesel, gasoline, or any other fuel) in a motor vehicle. Sensor device 10 comprises an arrangement consisting of an outer protective tube 66 and an inner protective tube 68. The axes of protective tubes 66, 68 are oriented transversely to the flow of exhaust gas 64. Inner protective tube 68 protrudes axially beyond outer protective tube 66 and into flowing exhaust gas 64. At the ends of protective tubes 66, 68 facing away from flowing exhaust gas 64, outer protective tube 66 protrudes beyond inner protective tube 68. The clear width of outer protective tube 66 is preferably significantly greater than the outer diameter of inner protective tube 68 to create a first, in this case, approximately annular, flow cross section between protective tubes 66, 68. The clear width of inner protective tube 68 forms a second, in this case, circular, flow cross section.

[0042] As a result of this geometry, the exhaust gas 64 enters the arrangement of the two protective tubes 66, 68 via a first flow cross section. It then changes direction at the ends of the protective tubes 66, 68 facing away from the exhaust gas 64, enters the inner protective tube 68, and is drawn out of the inner protective tube by the exhaust gas 64 flowing through it (arrows with reference numeral 70). This creates a laminar flow in the inner protective tube 68, the flow direction of which is normally parallel to the longitudinal axis of the laser 14. This arrangement of the protective tubes 66, 68 is fixed to or in the exhaust pipe 62 transversely to the flow direction of the exhaust gas 64. The light spot 22 is located within the inner protective tube 68 in the region of the laminar flow 70.

Claims

1. A sensor device (10) for detecting particles or aerosols in a flowing fluid using the principle of laser-induced incandescence, the sensor device comprising: a) a first device (12) for generating laser light (14); b) a second device (24) for directing the laser (14); c) third means (36) for directing temperature radiation (28) emitted by particles heated by the laser (14); d) a fourth device (34) for detecting the temperature radiation (28); It is characterized in that the first device (12), at least a part (44) of the second device (24), at least a part (46) of the third device (36), and the fourth device (34) are all arranged on a common carrier (48), wherein the common carrier is a one-piece element, and the first device (12), at least a part (44) of the second device (24), at least a part (46) of the third device (36), and the fourth device (34) are all fixed to the one-piece element directly or by means of corresponding fixing devices.

2. The sensor device (10) according to claim 1, characterized in that The carrier (48) comprises a planar plate.

3. The sensor device (10) according to claim 2, characterized in that The planar board is a PCB or a ceramic board.

4. The sensor device (10) according to any one of the preceding claims, characterized in that The sensor device has a first region (40) facing the fluid and a second region (42) facing away from the fluid, and parts (44, 46) of the first to fourth devices (12, 24, 36, 34) arranged only in the second region (42) are arranged on the common carrier (48).

5. The sensor device (10) according to claim 4, characterized in that The first region (40) and the second region (42) are optically coupled to each other via a light guide (60).

6. The sensor device (10) according to claim 5, characterized in that The light guide (60) is a glass fiber.

7. The sensor device (10) according to any one of the preceding claims, characterized in that The common carrier (48) has at least one opening (52) through which the laser (14) and / or the temperature radiation (28) pass.

8. The sensor device (10) according to claim 7, characterized in that The second device (24) and the third device (36) comprise at least one common component in the form of a beam splitter (18), which is arranged in an opening (52) of the common carrier (48) such that the temperature radiation (28) passes through the beam splitter and the opening (52).

9. The sensor device (10) according to claim 1, wherein the first device (12) and the fourth device (34) are arranged at opposite ends of the common carrier (48).

10. The sensor device as claimed in claim 1, wherein the first device (12) and the fourth device (34) are arranged adjacent to one another on opposite sides of the common carrier (48).

11. The sensor device (10) according to any one of the preceding claims, characterized in that The second device (24) and / or the third device (36) comprises at least one mirror (16, 54, 30) arranged on the common carrier (48), which deflects the laser light or the temperature radiation (28).

12. The sensor device (10) according to claim 11, characterized in that The mirror is a focusing mirror (30).

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