WO2020126194A1

WO2020126194A1 - Method for operating a sensor device for detecting particles or an aerosol, and sensor device

Info

Publication number: WO2020126194A1
Application number: PCT/EP2019/080352
Authority: WO
Inventors: Martin Buchholz; Radoslav Rusanov; Fabian Purkl; Panagiotis Gedeon; Enno Baars
Original assignee: Robert Bosch Gmbh
Priority date: 2018-12-21
Filing date: 2019-11-06
Publication date: 2020-06-25
Also published as: DE102018222771A1; KR20210099021A; CN113227758A

Abstract

A method for operating a sensor device (10) for detecting particles (24) or an aerosol in a flowing fluid (42) using the principle of laser-induced incandescence includes the following steps: producing laser light (14) by means of a laser (12); focusing the laser light (26) on a spot (22); capturing thermal radiation (26), emitted by a particle (24) heated in the spot (22), using a detector (32); and providing an output signal (34) by the detector (32), said output signal depending on the captured thermal radiation (26). It is proposed that the method further comprise the following steps: analyzing at least one property, in particular an intensity profile over time, of the output signal (34) by means of an evaluation device (49) and performing diagnostics on the sensor device (10) by means of the evaluation device (49) on the basis of the analysis.

Description

description

title

Method for operating a sensor device for the detection of particles or aerosol, and sensor device

State of the art

The invention relates to a method for operating a sensor device for the detection of particles or aerosol in a flowing fluid

Use of the principle of laser-induced incandescence, as well as a sensor device, each according to the preambles of the subordinate claims.

DE 10 2017 207 402 A1 discloses a sensor device for detecting particles in a fluid-carrying area using the principle of laser-induced incandescence in the form of a particle sensor. Particles present in an exhaust gas area, for example soot particles, are heated to several thousand degrees Celsius with a laser light focused on a laser light spot, so that they emit significant heat or temperature radiation. This thermally induced light emission of the particles is measured with a light detector, which provides an output signal corresponding to the measured light intensity.

Disclosure of the invention

The problem underlying the invention is solved by a method and a sensor device with the features of the subordinate ones

Expectations. Advantageous further developments are specified in the subclaims.

The method according to the invention and the sensor device according to the invention are based on the detection of particles in a fluid using the principle of laser-induced incandescence (LII). It should be pointed out at this point that particulates, in particular, soot particles and, as fluids, in particular the exhaust gas of an incinerator or internal combustion engine come into question. The device can be used, for example, to monitor the condition of a particle filter in gasoline or diesel vehicles.

Basically, however, the device is generally suitable for the detection of particles and aerosols in any fluid. For example, one

Use of the device for other scenarios and areas of application is conceivable (eg in portable emission monitoring systems, measurement of indoor air quality, emissions from incineration plants). The concept enables both the mass (mg / m ³ or mg / mi) and the number concentration (particles / m ³ or particles / mi) of the particles to be determined. Also a measurement of the

Particle size distribution becomes possible.

In the principle of laser-induced incandescence, a particle is first bundled with sufficient intensity using laser light, which emanates from a laser and is concentrated in a laser light spot, i.e. a volume range with the smallest dimensions in the pm or nm range, with sufficient intensity Laser light heated to several thousand degrees. According to the Planck law of radiation, this hot particle emits a characteristic temperature radiation (incandescence or glow emission), which serves as a measurement signal and is received with a detector.

For this purpose, for example, an optical element (for example in the form of a focusing lens) arranged in the beam path of the laser is used, which is designed and set up to bundle the laser light emanating from the laser in the very small laser light spot. With a focus diameter of e.g. 10 pm it can be assumed that at any given time only one particle will fly through the laser light spot (intrinsic single particle detectability) if one

Based on particle concentration of 10 ¹³ / m ³ . The detector is set up and arranged in such a way that it detects that emanating from the laser light spot

Temperature radiation detected. As a laser can be inexpensive

Semiconductor laser diodes are used. The detection of the temperature radiation can e.g. using a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM).

The method according to the invention specifically comprises the following steps:

a. Generating laser light using a laser;

b. Bundling the laser light in one spot; c. Detection of temperature radiation emitted by a particle heated in the spot by means of a detector; and

d. Providing a dependent on the detected temperature radiation

Output signal from the detector;

e. Analyzing at least one property, in particular a profile of an intensity over time, of the output signal using a

Evaluation device,

f. Perform a diagnosis of the sensor device using the

Evaluation device based on the analysis.

The sensor device according to the invention specifically comprises: a device for generating laser light; means for focusing the laser light in a spot; a detector for detecting temperature radiation which is emitted by a particle heated in the spot, and an evaluation device for

Evaluation of an output signal of the detector, the evaluation device being set up for this purpose, for example by means of a memory

stored computer program is programmed accordingly to carry out a method of the above type.

The method according to the invention and the sensor device according to the invention thus enable self-diagnosis, which has the advantage that a

basic function of the signal path of the sensor device can be checked, namely from the generation of the laser light to the detection of the incandescence or temperature radiation. The function is checked with a high degree of security, since the output signal of the detector on which the analysis is based can be generated with a vanishingly low probability by a malfunction of the detector itself. The output signal of the detector thus corresponds with a high degree of certainty to the temperature radiation actually arriving at the detector and therefore has certain and predictable for a specific application

Properties. This enables at least one property of the sensor that is actually obtained during operation of the sensor device to be analyzed

Compare output signal with the corresponding predicted property and on the basis of this comparison a diagnosis of

To carry out sensor device, that is to draw conclusions with regard to the correct and current function of the sensor device. This self-diagnosis can be done with very little additional component effort be carried out so that the corresponding sensor device is still very inexpensive.

For example, as mentioned above, it is possible to use the

Use sensor device for OBD monitoring (OBD = on-board diagnosis) of the state of a particle filter in the exhaust system of an incineration system, in particular an internal combustion engine of a motor vehicle. In the case of sensor devices used for OBD monitoring, a continuous check of the sensor function, i.e. a self-test, is required by law. This continuous review is carried out by the

The method according to the invention is implemented in a very simple manner.

In a further development it is provided that in step e it is analyzed whether the output signal has at least one double peak. This is based on the physical fact that by focusing the

Laser light in the spot fuses the laser light in front of and behind the spot (seen in the overall direction of the laser light), so that, when the laser light is correctly focused, the intensity distribution of the laser light has the shape of a “dumbbell” on average, one in its axial center Has constriction. This is also based on the physical fact that not all particles necessarily move exactly through the center of the spot during operation of the sensor device, but rather, within the framework of a predictable statistical distribution, a certain number of particles laterally at the center of the spot with a certain distance flies past to this center. These particles are therefore heated twice during such a flyby, namely, seen in the direction of flight or beam direction of the laser light, once shortly before and a second shortly after passing the position of the spot, so that the particles also emit a corresponding temperature radiation twice.

The detector therefore sees such a particle lighting up twice in quick succession, so that the detector provides a corresponding output signal which has a double peak. In the present case, a “double peak” is not necessarily understood to mean an analog output signal which has two high points lying immediately behind one another and a low point in between. Of course, such a double peak can also be generated by a digital output signal, for example by two "pulse clusters" that are close together in time. The The distinction between a "double peak" and a "single peak" is usually made by taking into account the period, which depends, for example, on the flow velocity and thus the flight speed of the particles, in which one and the same particles fly past two times through a usual spot to emit Thermal radiation can be excited. Only two peaks within such a time period are counted as double peaks.

As mentioned above, it can be assumed that, within the framework of a predictable statistical distribution, a certain number of particles pass the side of the center of the spot at a certain distance from the center and corresponding double peaks are generated in the output signal of the detector. If the output signal does not have a double peak, a fundamental malfunction of the signal path can be assumed. Only if the control of the laser, the focusing of the laser light on a suitable point in the fluid (spot), the supply of the fluid to this point, the detection of the temperature radiation by the detector and the signal processing function, can the said double peaks in the

Output signal can be observed. If double peaks are missing, if there are none at all, a malfunction can be assumed in at least one of the above-mentioned areas of the sensor device.

In a further development, it is provided that in step e it is analyzed whether the output signal has a number of double peaks within a certain period of time that corresponds to at least one limit value, and that if the number of double peaks within the period does not correspond to at least the limit value , in step f for an error of

Sensor device is closed, in particular an entry in a

Error memory is done. This clarification allows an even more sensitive one

Detection of a malfunction of the sensor device. Generation of one containing a plurality of characteristic double peaks

Output signal through another process is namely highest

unlikely. The existence of a number of double peaks that correspond to the

Limit value corresponds to or lies above this, can thus serve as proof of the fundamentally correct function of the signal path of the sensor device. In a further development it is provided that in step f a ratio of the number of double peaks recorded in a time period to the number of single peaks recorded in the same time period is formed and that if this ratio lies outside a predetermined range, an error of the sensor device is concluded , especially an entry in a

Error memory is done. About such a relationship between individual and

Double peaks and the comparison with typical values, for example with typical values for a specific operating point of an internal combustion engine, in the exhaust system of which the sensor device is installed, can further

Security can be gained via the sensor functionality

In a further development it is provided that if the output signal has at least one double peak, step e analyzes whether a shape of the double peak corresponds at least approximately to a predetermined shape. The shape of the double peak is also predictable for certain operating conditions or operating conditions in which the sensor device operates, and it therefore provides important information about the current functional state of individual areas of the sensor device. An analysis of the shape of the double peak can not only be used for further diagnosis

Sensor device as a whole, but specifically individual elements or areas of the sensor device. It is basically conceivable that an “average” shape is formed from a plurality of recorded double peaks, which in turn is then compared with the predetermined shape.

In a further development it is provided that in step e it is analyzed whether the double peak is symmetrical and that if an asymmetry of the double peak reaches or exceeds a certain dimension, in step f an incorrect, in particular an incorrectly oblique, flow to the spot is concluded an entry is made in an error memory in particular. This is based on the consideration that in the case of a flow of the fluid that does not occur at least essentially parallel to the overall direction of the laser light, the particles that fly just past the spot and in this respect produce a double peak in the output signal in front of the spot

Fly through the intensity range and behind the spot a second intensity range, the intensities of the two intensity ranges differing, and accordingly the temperatures and the Absolute values of the high points of the output signal of the detector

differentiate. In contrast, in a flow largely parallel to the beam axis of the laser light, the two high points of a double peak are at least approximately at the same level. A non-parallel, but oblique flow to the spot can result, for example, from partial blockage or a crack in a protective tube radially surrounding the spot, as a result of which the measuring accuracy of the sensor device is impaired or can no longer be guaranteed. This can be recognized by the analysis and evaluation or diagnosis according to the invention.

In a further development it is provided that when the output signal has at least one double peak, an analysis is carried out in step e as to whether the ratio of the two high points of the double peak to a low point between the two double peaks at least reaches a limit value and that when the ratio reached or exceeded the limit value, in step f an incorrect focusing of the laser light in the spot was concluded, in particular an entry was made in an error memory. A

Deterioration of the focus of the laser light e.g. An unwanted relative movement of optical components can be regarded as critical for the sensor device, since it is accompanied by a reduction in sensitivity.

Such an error can also be detected via the analysis of the output signal of the detector provided according to the invention. The form of the double peaks namely decreases with an enlargement (for example a broadening) of the focus area, ie the spot, since the dumbbell shape mentioned above is then less pronounced. Depending on the strength of the defocusing and design of the optics, this change can occur

Double peaks can be detected solely from the measurement signals. In other cases, the deterioration of the focusing can be detected by comparing the relative frequencies of single and double peaks and / or only with knowledge of the fluid velocity, particle concentration and size distribution. These values can be derived, for example, from an operating point of an internal combustion engine, in the exhaust system of which the sensor device is installed, using a map or by characterizing individual peaks. The characterization of individual peaks can, for example by analyzing the distribution of the intensity and the full-width-half-maxima.

In a further development it is provided that the analysis in step e involves pattern recognition by means of artificial intelligence or fitting a curve of the double peak to a pattern curve shape or the use of algorithms for finding high points and / or low points of the double peak and for evaluating a time interval between high points of the double peak. These processes are particularly efficient and reliable.

Embodiments of the invention are explained below with reference to the accompanying drawing. The drawing shows:

Figure 1 is a schematic representation of the structure of a

Sensor device for the detection of particles in a flowing fluid using the principle of laser-induced incandescence;

Figure 2 shows a schematic section through a spot of

1 with a drawn-in first trajectory of a particle;

Figure 3 is a diagram in which an output signal of a detector

Sensor device of Figure 1 for the particle of Figure 2 is plotted against time;

Figure 4 is a representation similar to Figure 2, with three drawn

second and oblique trajectories of particles;

Figures 5-7 are diagrams similar to Figure 3 for the three particles of Figure 4;

FIG. 8 shows a representation similar to FIG. 2, with a third trajectory of a particle and a spot that is slightly defocused compared to that of FIG. 2;

Figure 9 is a diagram similar to Figure 3 for the particle of Figure 8; FIG. 10 shows a representation similar to FIG. 2, with a fourth trajectory of a particle and a spot that is defocused compared to that of FIG. 2;

Figure 1 1 is a diagram similar to Figure 3 for the particle of Figure 10; and

FIG. 12 shows a flow diagram of a method for operating the

Sensor device of Figure 1.

Functionally equivalent elements and areas have the same reference symbols in the following description and are generally not explained several times.

FIG. 1 shows a possible embodiment of a sensor device for the detection of particles or aerosol in a flowing fluid beneath

Use of the principle of laser-induced incandescence, specifically in the form of a particle sensor 10. First of all, a laser 12 can be seen, in the present case, by way of example, a CW laser (CW = continuous wave) which emits laser light 14. The laser 12 can in particular have a laser diode, which is very inexpensive. The laser light 10 is first formed into a parallel beam by a lens 16 (“collimation lens”), which passes through a beam splitter 18, for example in the form of a beam splitter or a dichroic mirror. From there it arrives at a focusing lens 20 and further in a focused form to a laser light spot 22 (hereinafter referred to as “spot”). Spot 22 is a volume element with very small

Understand dimensions in the pm range or even in the nm range, in which the laser light 14 is extremely focused and thus extremely energy-tight or intense.

High-intensity laser light 14 can strike a particle 24 present in the spot 22, for example a soot particle 24 in an exhaust gas stream of an internal combustion engine. The intensity of the laser light 14 in the spot 22 is so high that the energy of the laser light 14 absorbed by the particle 24 heats the particle 24 to several thousand degrees Celsius (only in the volume of the spot 22 does the intensity of the laser light 14 reach that for laser-induced incandescence (LII ) necessary high values). As a result of the heating, the particle 24 spontaneously emits significantly and essentially without a preferred direction

Temperature radiation 26, also referred to as LII light. A part of Temperature radiation 26 is therefore also emitted in the opposite direction to the direction of the incident laser light 14. The temperature radiation 26 is, for example, in the near infrared and visible spectral range, but is not restricted to this spectral range. The laser 12, the lens 16, the beam splitter 18 and the focusing lens 20 thus form a device 27 for generating the spot 22.

The temperature radiation 26 of a particle 24 excited in the spot 22 by the laser light 14 in turn passes through the focusing lens 20 back to the beam splitter 18, where it is deflected by 90 °, passes through a focusing lens 28 and through a filter 30 (this is not mandatory) arrives at a detector 32. The filter 30 is designed so that it

Wavelengths of the laser light 14 are at least largely filtered out, which is also radiated back to a small extent. The interfering background is thus reduced by the filter 30. It is also conceivable to use a simple edge filter. This improves the signal-to-noise ratio.

The dimensions of the spot 22 are in the range of a few pm, in particular in the range of at most 200 pm, so that particles 24 passing through the spot 22 are excited to emit evaluable radiation powers. As a result, it can be assumed that there is always at most one particle 24 in the spot 22 and that an instantaneous output signal 34 of the particle sensor 10 only comes from this at most one particle 24.

The output signal 34 is generated by the detector 32, which is arranged in the particle sensor 10 in such a way that it detects radiation 26, in particular temperature radiation, emanating from the particles 24 passing through the spot 22. The detector 32 preferably comprises a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM) or a SPAD diode (single-photon avalanche diode), which detects the temperature radiation 26 and that

Output signal 34 generated. With the above-mentioned types of detectors 32, a light signal generated by a particularly small particle 24 and therefore extremely small, which is formed by a few photons, for example, can already be detected. The dimensions of particles 24, which are still just detectable, thus decrease to a lower detection limit of up to 10 nm. It is entirely possible that the laser 12 is modulated or switched on and off (duty cycle <100%). However, it remains preferred that the laser 12 is a CW laser. This enables the use of inexpensive semiconductor laser elements (laser diodes), which makes the complete particle sensor 10 less expensive and greatly simplifies the control of the laser module 12 and the evaluation of the output signal 34. However, the use of pulsed lasers is not

locked out.

Exhaust gas is also symbolized in FIG. 1 by an arrow 36, as is generated, for example, in a combustion process, for example in the exhaust system of an internal combustion engine (diesel or gasoline or any other fuel) of a motor vehicle. The sensor device 10 has an arrangement of an outer protective tube 38 and an inner protective tube 40. The axes of the protective tubes 38, 40 are aligned transversely to the flow of the exhaust gas 36.

The inner protective tube 40 projects in the direction of the axes over the outer one

Protective tube 38 and into the flowing exhaust gas 36. At the end of the two protective tubes 38, 40 facing away from the flowing exhaust gas 36, the outer protective tube 38 projects beyond the inner protective tube 40. The clear width of the outer protective tube 38 is preferably so much larger than the outer one

Diameter of the inner protective tube 40 that between the two protective tubes 38, 40 a first and in the present case approximately circular

Flow cross section results. The clear width of the inner protective tube 40 forms a second and in the present case circular flow cross section.

This geometry results in exhaust 36 over the first

Flow cross section enters the arrangement of the two protective tubes 38, 40, then changes its direction at the end of the protective tubes 38, 40 facing away from the exhaust gas 36, enters the inner protective tube 40 and is sucked out of this by the exhaust gas 36 flowing past (arrows with the reference symbol 42 ). This results in a laminar flow in the inner protective tube 40, the direction of flow of which is normally parallel to a longitudinal axis 44 of the laser light 14 shown in dash-dot lines. This arrangement of protective tubes 38, 40 is attached transversely to the flow direction of the exhaust gas 36 on or in an exhaust pipe (not shown in FIG. 1). The spot 22 is located inside the inner protective tube 40 in the area of the laminar flow 42. The particle sensor 10 preferably has a first part 46 (protective tubes 38 and 40) which is exposed to the exhaust gas 36 and a second part 48 which is not exposed to the exhaust gas 36 and which contains the optical and electronic components of the particle sensor 10. Part 46 is also referred to as the “sensor head, part 48 also as the“ SCU ”(“ sensor control unit ”). Part 48 also includes an evaluation device 49 in which the output signal 34 of the detector 32 is analyzed, in particular with regard to a course of an intensity of the output signal 34 over time. Also takes place in this

Evaluation device 49 diagnoses sensor device 10 on the basis of the analysis just mentioned. This allows the function of the

Sensor device 10, as will be explained in more detail below, can be checked in the sense of a “self-test”.

In Figure 2, the spot 22, which is formed by the focused laser light 14, is drawn in section. An example of two laser light beams focused by the lens 20 is shown in FIG. 2, these two beams are designated by 14 'and 14 ". It can be seen that the spot 22 has an elongated extension with a longitudinal extension L in the direction of the longitudinal axis 44 and a maximum extension B transverse to the longitudinal extension L. It can also be seen from FIG. 2 that due to the focusing of the laser light 14, the spot 22 has a kind of dumbbell shape with a constricted area 50 in the axial center (viewed in the direction of the longitudinal axis 44), whereby the constricted region 50 has a diameter C that is smaller than the diameter of the upper and lower axial end regions 52a and 52b, each of which has a diameter B. In FIG. 2, lines 54 of the same intensity of the laser light 14 are also drawn, of which for reasons for clarity, however, only the outermost one is provided with a reference number. It can be seen that the innermost line 5 4 has an overall substantially oval or elliptical shape, whereas the outermost line 50 drawn is the one mentioned above

Has a dumbbell shape. The intensity is highest inside the spot 22 and lowest at the edge of the spot 22.

An arrow 56 denotes the trajectory of a particle 24 (corresponding to the flow 42 in FIG. 1). In the present case, this does not lead exactly through the center of the spot 22, but past the center on the left, at such a distance from the longitudinal axis 44 and thus from the center of the spot 22 that the particle 24 initially passes through the lower region 52a moved through, then emerges from this and flies past the constricted area 50, in order to then dive into the upper area 52b and finally also to leave it again.

The intensity of the laser light 14 in the edge region of the two regions 52a and 52b, through which the particle 24 flies, is still sufficient to excite it to emit temperature radiation 26, namely twice, namely a first time when the particle 24 flies through the lower region 52a and a second time when the particle 24 flies through the upper region 52b. Accordingly, an output signal 34 is generated, which is plotted over time in FIG. A first steeply rising flank 58a can be seen, which rises to a first high point 60a, and then an equally steeply falling flank 62a, which falls to a low point 64. From there it goes along a second steeply rising edge 58b to a second high point 60b, and then again along a steeply falling edge 62b to a lower constant signal level.

The two high points 60a and 60b have approximately the same absolute value, ie are approximately at the same level. The output signal 34 thus has two high points 60a and 60b which are close to one another in time, namely within a time interval t, and in this respect one

form so-called "double peak" 66. The length of the time interval t can, among other things, depend on the speed of the fluid and thus the

Depend on the speed of particle 24. It can be seen that the double peak 66 is largely symmetrical relative to the low point 64, for example the first rising edge 58a and the second falling edge 62b are symmetrical to one another, and that the first falling edge 62a and the second rising edge 58b are also symmetrical to one another. From this, the shape of the double peak 66 can be analyzed using the

Evaluation device 49 can be closed on the one hand that the spot 22 has the dumbbell-shaped geometry described, and on the other hand it can be concluded that the particle 24 flies through the spot 22 on a trajectory 56 which is essentially parallel to the longitudinal axis 44 of the

Laser light 14 runs. This corresponds to a desired normal function of the sensor device 10. An operating situation is plotted in FIGS. 4-7, in which the trajectories 56a-c do not run parallel to the longitudinal axis 44 of the laser light 14. For example, due to a partial blockage or a crack in the inner protective tube 40, the flow 42 deviates from its ideal and parallel to the protective tube 40 or the longitudinal axis 44, whereby the measuring accuracy of the sensor device 10 is no longer guaranteed.

Here, an angle of the trajectory 56c with respect to the longitudinal axis 44 is greater than that of the trajectory 56b, and an angle of the trajectory 56b with respect to the longitudinal axis 44 is larger than that of the trajectory 56a. In Figure 5 that is

Output signal 34 is plotted for trajectory 56a. In comparison to FIG. 3, it can be seen that the shape of the double peak 66 of the output signal 34 is no longer symmetrical. This is due to the fact that the particle 24 flies through the lower region 52a further outwards and thus in a region of lower intensity, whereas it flies through the upper region 52b further inwards and therefore in a region of higher intensity. The particle 24 is therefore heated less strongly when passing through the lower region 52a than when passing through the upper region 52b. Accordingly, the absolute value of the first high point 60a of the output signal 34 is lower than that of the second high point 60b. This difference is all the more significant the more oblique the trajectory 56 is.

The larger angle of the two trajectories 56b and 56c relative to the longitudinal axis 44 is expressed in a greater asymmetry of the double peak 66, as can be seen from FIGS. 6 (corresponding to the trajectory 56b) and 7 (corresponding to the trajectory 56c). In this respect, a double peak 66 with a trajectory 56 of the particle 24 which is oblique to the longitudinal axis 44 of the laser light 14 has a characteristic asymmetrical shape, which is likewise characterized by the

Evaluation device 49 is analyzed and diagnosed by the evaluation device 49 as an oblique trajectory 56.

FIGS. 8-9 show the case in which the trajectory 56 of the particle 24 runs parallel to the longitudinal axis 44 of the laser light 14, but the spot 22 is slightly defocused, which means that the constricted area 50 has a larger diameter C. than in the stronger (and in this respect better) focusing shown in FIGS. 2 and 4. The dumbbell shape of the spot 22 of FIG. 8 is thus less pronounced than that of FIGS. 2 and 4 Spot 22 shown. Such defocusing can be caused, for example, by an unwanted relative movement of the optical components of the

Sensor device 10, for example the lens 16, the beam splitter 18, the lens 20, and the lens 28.

On the basis of the corresponding output signal 34 in FIG. 9, it can be seen that its edges 58a and 58b and 62a and 62b are less steep than that of FIG. 3, and in particular that the low point 64 is higher than that of FIG. 3. It can therefore be said that the ratio of the absolute values of the two high points 60a and 60b to the absolute value of the low point 64 in the form of the output signal 34 from FIG. 9 differs significantly from the corresponding ratio in the form of the output signal 34 from FIG. 3, namely has a significantly smaller value .

This is even more pronounced in the defocusing of the spot 22 shown in FIG. 10, which leads to the spot 22 shown in FIG. 10 having almost no dumbbell shape. Thus, in the resultant output signal 34, the absolute values of the two high points 60a and 60b hardly differ from the absolute value of the low point 64 therebetween, so that, as can be seen from FIG. 11, the characteristic shape of a double peak 66 can hardly be recognized.

This characteristic form of the output signal 34 is also analyzed by the evaluation device 49, and a defocusing of the spot 22 is diagnosed accordingly.

A method for operating the sensor device 10 will now be explained with reference to FIG. The method starts in a block 68, for example in the case of an internal combustion engine after it has started. The output signal 34 is then evaluated in a block 69 with regard to the existence of double peaks 66 with an expected frequency, both absolutely and relative to the frequency of single peaks. Accordingly, it is checked in a block 70 whether the output signal 34 of the detector 32 has a number of double peaks 66 within a certain period of time which corresponds to at least one limit value, and whether the ratio between

Double peaks and single peaks also correspond to at least one expected limit. If the answer in block 70 is “no”, optional further and independent diagnostic functions are carried out in a block 72. However, these are as I said, optional and not absolutely necessary. In a block 74, which is also merely optional, a check is carried out to determine whether an error has actually been detected. If the answer is “no”, a return is made to the start block 68. Otherwise, a (basic) error of the sensor device 10 is concluded in a block 76 and a general entry is made in an error memory. The process would then end in block 78.

If the answer in block 70 is “yes”, the double peaks 66 are evaluated in a block 80, in particular with regard to the symmetry of the high points 60a and 60b. Accordingly, it is checked in a block 82 whether the detected double peak 66 or the detected double peaks 66 is predetermined

Meet symmetry conditions, in particular whether the high points 60a and 60b are at least approximately the same height. If the answer is “No”, this is an indication of a possibly inadmissibly oblique flow 42 relative to the longitudinal axis 44. Again, in the optional block 72 already mentioned above, a further independent diagnosis can be carried out, and it can be checked in the optional block 74 whether there is actually an error. If the answer is “yes”, an error is recognized again in block 76 and a corresponding entry is made in an error memory, in which, however, the suspected impermissibly inclined flow 42 is specified compared to the above general entry.

If the answer in block 82 is “yes”, a flow 42 parallel to the longitudinal axis 44 is assumed and a block 84 then takes place

Evaluation of the double peak 66 or the double peaks 66 with regard to a generally expected shape, for example with regard to the ratio between the absolute values of the high points 60a and 60b and the low points 64 in between. If this ratio reaches or exceeds or falls below a limit value, the formation of the double peaks 66 is therefore not as expected. Thus, the answer in a test block 86 is “No” and there is again a jump to blocks 72 and 74 and, if appropriate, then to blocks 76 and 78, again specifying the error entry in the error memory in block 76 such that from an impermissible defocusing of the spot 22 is assumed. If, on the other hand, the answer in test block 86 is “yes”, correct focusing is assumed and a counter is started in block 88, which causes a return to start block 68 after a certain time.

Claims

Expectations

1. Method for operating a sensor device (10) for the detection of particles (24) or aerosol in a flowing fluid (42) under

Use of the principle of laser-induced incandescence, which has the following steps:

a. Generating laser light (14) by means of a laser (12);

b. Focusing the laser light (26) in a spot (22);

c. Detecting temperature radiation (26) emitted by a particle (24) heated in the spot (22) by means of a detector (32); and d. Providing one of the detected temperature radiation (26)

dependent output signal (34) by the detector (32);

characterized in that it further comprises the following steps:

e. Analyzing at least one property, in particular a profile of an intensity over time, of the output signal (34) by means of an evaluation device (49),

f. Carrying out a diagnosis of the sensor device (10) by means of the

Evaluation device (49) based on the analysis.

2. The method according to claim 1, characterized in that in step e it is analyzed whether the output signal (34) has at least one double peak (66).

3. The method according to claim 2, characterized in that it is analyzed in step e whether the output signal (34) has a number of double peaks (66) within a certain period of time, which corresponds to at least one limit value, and that when the number of

Double peaks (66) within the period does not at least correspond to the limit value, in step f an error of the sensor device is concluded, in particular an entry is made in an error memory.

4. The method according to at least one of claims 2 or 3, characterized

characterized in that in step f a ratio of the number of double peaks (66) recorded in a period to the number of those in the same period individual peaks is formed and that if this ratio lies outside a predetermined range, an error in the

Sensor device (10) is closed, in particular an entry is made in an error memory.

5. The method according to at least one of claims 2-4, characterized

characterized in that when the output signal (34) has at least one double peak (66), step e analyzes whether a shape of the double peak (66) corresponds at least approximately to a predetermined shape.

6. The method according to claim 5, characterized in that it is analyzed in step e whether the double peak (66) is symmetrical, and that when an asymmetry of the double peak (66) reaches or exceeds a certain dimension, in step f to a faulty, in particular a faulty, oblique flow (42) of the spot (22) is closed, in particular an entry is made in a fault memory.

7. The method according to at least one of claims 2-6, characterized

characterized in that if the output signal (64) has at least one double peak (66), step e analyzes whether the

Ratio of the two high points (60 a, 60 b) of the double peak (66) to a low point (64) between the two high points (60 a, 60 b) at least reaches a limit value, and that when the ratio reaches or exceeds the limit value , in step f an incorrect focusing of the laser light (14) in the spot (22) is concluded, in particular an entry is made in an error memory.

8. The method according to at least one of claims 2-7, characterized

characterized in that the analysis in step e involves pattern recognition by means of artificial intelligence or fitting a curve of the double peak (66) to a pattern curve shape or the use of algorithms for finding high points (60 a, 60 b) and / or low points (64 ) of the double peak (66) and for evaluating a time interval between high points (60 a, 60 b) of the double peak (66).

9. The method according to at least one of the preceding claims, characterized in that the distinction between a double peak (66) and a single peak by means of an evaluation of the time interval between high points (60 a, 60 b) in the output signal (34) of the detector (32) he follows.

10. Sensor device (10) for the detection of particles (24) or aerosol in

a flowing fluid (36, 42) using the principle of laser-induced incandescence, comprising: means (12) for generating laser light (14); a device (20) for bundling the

Laser light (14) in a spot (22); a detector (32) for detecting temperature radiation (26) emitted by a particle (24) heated in the spot (22), and an evaluation device (49) for evaluating an output signal (34) of the detector (32), characterized that the evaluation device (49) is set up to implement a method according to one of the

Execute claims 1-9.