Method and device for determining the absolute value of the flow rate of a particle transport medium

Abstract

The invention relates to a method for determining the absolute value of the flow velocity (v) of a particle transport medium. At least two measuring laser beams (L_i) with linearly independent, non-orthogonal measuring directions (b_i) are emitted. The measuring laser beams (L_i) scattered at the particles are detected and a measuring signal (m_i) is generated in each case for each measuring laser beam (L_i). The measuring signals (m_i) are evaluated, wherein the absolute value of the velocity component (v_i) is determined as the projection of the flow velocity (v) on the corresponding measuring direction (b_i), wherein a solid angle region is determined for the dominant direction of the flow velocity (v) and a sign assigned to the solid angle region is selected for each velocity component (v_i), and wherein the absolute value of the flow velocity (v) is determined using the determined absolute value of the velocity component (v_i) and using the selected sign for the velocity component (v_i).

Description

Technical Field

[0001] The invention relates to a method for determining the absolute value of the flow rate of a particle transport medium, and to a corresponding device. In particular, the invention relates to such a device for a portable device, in particular a smartphone, a tablet, a laptop or a wearable computer. Background Art

[0002] The measures according to the invention can advantageously be used to determine a measurement volume of a particle sensor arrangement.

[0003] Particle sensors are used in particular to determine particle pollution in the ambient air. For example, particle pollution can be quantified by determining the number of particles in a predetermined measurement volume, wherein for precise classification purposes only particles with a diameter below a predetermined size are taken into account. As a result, for example, coarse particles, fine particles and ultrafine particles can be distinguished. Such measurements are particularly important for monitoring emissions from industrial facilities. The determination of particle pollution is also necessary in the automotive sector in order to monitor compliance with predetermined limit values. In order to reduce weight and the required installation space, particle sensors with a design that is as compact as possible are required. Furthermore, even private users are interested in measuring local particle pollution independently, for example using portable devices such as smartphones, tablets, laptops or wearable computers.

[0004] The measuring methods used within the scope of particle sensors range from mechanical methods (for example using filters arranged in the stage) to optical methods. An exemplary optical particle sensor is known from WO 2017 / 198699 A1. The particle sensor comprises a laser sensor module, which comprises a plurality of lasers, which emit a measuring laser beam, which is reflected at the particles and detected by a detector in each case. The detection principle of the particle sensor is based on the self-mixing interference method (SMI method). In this method, the reflected measuring laser beam interferes with the emitted measuring laser beam. The respectively detected signals are the result of this interference. Its evaluation allows conclusions to be drawn about the presence of particles and their properties around the particle sensor. WO 2018 / 104153 A1 discloses another exemplary optical particle sensor for detecting the particle density of small particles with a particle size in the range of 0.05 μm to 10 μm. Summary of the invention

[0005] The invention relates to a method for determining the absolute value of a flow rate of a particle conveying medium, having the features of claim 1. The invention also relates to a device for determining the absolute value of a flow rate of a particle conveying medium, having the features of claim 14.

[0006] Preferred embodiments are the subject matter of the respective dependent claims.

[0007] According to a first aspect, the invention therefore relates to a method for determining the absolute value of the flow velocity of a particle transport medium, wherein at least two measuring laser beams with linearly independent, non-orthogonal measuring directions are emitted. The measuring laser beams scattered at the particles are detected and a measuring signal is generated in each case for each measuring laser beam. The measuring signals are evaluated, wherein the absolute values ​​of the velocity components are determined as the projection of the flow velocity in the respective measuring direction. A solid angle region is determined for the main directions of the flow velocity, i.e. the solid angle region containing the direction of the flow velocity, and a sign assigned to this solid angle region is selected for each velocity component. The absolute value of the flow velocity is determined using the determined absolute values ​​of the velocity components and using the selected signs for the velocity components.

[0008] According to a second aspect, the present invention therefore relates to a device for determining the absolute value of the flow velocity of a particle transport medium. The device comprises an optical transmitter device, a detector device and an evaluation device for evaluating the measurement signal. The optical transmitter device is implemented to emit at least three measurement laser beams with different measurement directions, wherein at least three of the different measurement directions are not orthogonal to each other and are linearly independent. The detector device is implemented to detect the measurement laser beam that has been scattered at the particle and to generate a measurement signal for each measurement laser beam in each case. The evaluation device is implemented to determine the absolute value of the velocity component as a projection of the flow velocity in the corresponding measurement direction. In addition, the evaluation device determines the solid angle area for the prevalent direction of the flow velocity and selects the sign assigned to the solid angle area for each velocity component. The evaluation device also uses the absolute value of the velocity component determined for the three linearly independent measurement directions and uses the sign selected for the velocity component to determine the absolute value of the flow velocity.

[0009] Advantages of the present invention

[0010] The starting point of the invention is a measuring device comprising at least two, preferably three, measuring laser beams, the measuring directions of which are linearly independent of one another; however, these measuring directions are not oriented orthogonally to one another. Such a measuring device can be realized in a substantially more space-saving manner than two or three measuring lasers aligned orthogonally to one another. However, the evaluation of the measurement signals of a non-orthogonal measuring laser device requires special measures.

[0011] The present invention relates to a measuring method in which only the absolute value of the velocity component is known along the measuring direction, but not the sign. In this case, it is generally not easy to determine the absolute value of the flow velocity if the measuring directions are not orthogonal to one another. This can be understood based on the mathematical considerations set out below. In general, the absolute value of the flow velocity for a system with three measuring laser beams It is given by the following formula:

[0012]

[0013] here, and in, and represents the normalized measurement direction, and v1, v2, and v3 represent the velocity components along the measurement direction. If the measurement directions are pairwise orthogonal, then M -1 =M T , and normalization of the measurement direction yields . Therefore, in this special case, the absolute value of the flow velocity can be determined directly from the absolute values ​​of the velocity components. However, for linearly independent measurement directions that are not pairwise orthogonal, the above formula contains an additional mixing term v i v j , where i≠j. Therefore, if the sign of the velocity component v i is unknown, it is impossible to determine the absolute value of the flow rate.

[0014] However, the present invention enables the absolute value of the flow velocity to be detected correctly. The discovery that forms the basis of the present invention is that the absolute value of the flow velocity can be well determined if the dominant direction of the flow velocity can be assigned to one of eight or four solid angle regions, which together cover the entire environment of the measuring device, i.e. the entire measuring environment. Therefore, it is not necessary to know the dominant direction of the flow velocity accurately in advance. It is sufficient if it can be assigned to one of the solid angle regions. Each of these solid angle regions is represented by a specific marking, i.e. a combination of the signs of the individual velocity components. Here, the flow velocity is considered to be a vector in a coordinate system with the measuring device, wherein the measuring laser is set at the origin of the measuring device. The alignment of this vector with the origin or away from the origin can be described by an azimuth and a zenith angle and can therefore be assigned to a solid angle region.

[0015] The solid angle region in which the flow velocity prevails can be determined by evaluating the measurement signal. As a result, the correct marker S can be determined n , which should be understood to mean the specification of the signs of the velocity components. Therefore, within the meaning of the present invention, the sign of the vector flow velocity represents a triple with entries 1 or -1, which corresponds to the signs of the respective velocity components along the measuring direction. In order to calculate the absolute value of the flow velocity, the common signs of the velocity components do not play any role, since the reversal of the flow velocity direction does not affect the calculation. Therefore, the total eight possible combinations of the signs of the three velocity components can be reduced to four relevant signs, specifically S0=diag(1,1,1), S1=diag(1,-1,-1), S2=diag(-1,1,-1) and S3=diag(-1,-1,1). The absolute value of the flow velocity is then provided by the following formula:

[0016]

[0017] In this formula, contrary to the above formula, A vector representing the absolute values ​​of the velocity components.

[0018] The invention thus allows the absolute value of the flow velocity to be determined even without initial knowledge of the prevailing direction of the flow velocity, ie without initial knowledge of the signs of the individual velocity components.

[0019] According to a variant of the method according to the invention, exactly two measuring laser beams are emitted. The absolute values ​​of the determined velocity components are used to determine the solid angle area for the dominant direction of the flow velocity. Preferably, it is further assumed that the vector of the flow velocity lies in a predetermined plane. In particular, the value of the flow velocity can be determined under the assumption that the vector of the flow velocity lies in the sensor plane or extends parallel thereto, wherein the sensor plane is given by the measuring laser beam emitted from this plane.

[0020] According to a preferred development of the method, at least three measuring laser beams with different measuring directions are emitted, wherein at least three of the different measuring directions are non-orthogonal with respect to one another and are linearly independent. The value of the flow velocity is determined using the absolute values ​​of the velocity components determined for the three linearly independent measuring directions and using the signs selected for the velocity components.

[0021] According to a preferred development of the method, in addition to the absolute value of the flow velocity, in addition to the sign, the flow velocity can also be output in vector form. For this purpose, the velocity component with the determined sign can optionally be transformed into an orthogonal coordinate system.

[0022] According to a preferred development of the method, the solid angle region for the dominant direction of the flow velocity is determined as one of eight predetermined solid angle regions, which together cover the entire measurement environment, i.e. the entire environment of the measuring device. The eight solid angle regions thus include all possible directions of the flow velocity relative to the measuring device. Two predetermined solid angle regions opposite one another are respectively assigned the same label, i.e. the sign for the individual velocity components.

[0023] Each of the eight solid angle regions corresponds to one of the eight markings. The marking changes if the projection of the flow velocity on one of the axes of the coordinate system predetermined by the measuring direction changes sign. This is the case when the angle between the flow velocity and the measuring direction exceeds or falls below the 90° value, which is the case along the plane. The solid angle region is therefore bounded by the plane and is pyramidal with the tip as the origin.

[0024] According to a preferred development of the method, each of the three linearly independent measuring directions is respectively assigned two predefined solid angle regions relative to each other. The remaining two predefined solid angle regions cover the remaining measurement environment. In the case of three measuring directions, a marker S1, S2 and S3 are assigned to each measuring direction respectively. As a result, the two solid angle regions belonging to the markers are also assigned to the measuring directions. This assignment is achieved in such a way that the sign of the velocity component relative to the corresponding measuring direction is different from the sign of the velocity components of the two other measuring directions. The remaining marker S0 is not assigned to any measuring direction.

[0025] According to a preferred development of the method, at least three absolute values ​​of the velocity components are compared with one another. The maximum absolute value of the velocity component is determined. If the difference between the maximum absolute value of the velocity component and the remaining absolute values ​​of the velocity component exceeds a predetermined first limit value, a predetermined solid angle region assigned to the measuring direction with the maximum absolute value of the velocity component is determined as the solid angle region for the dominant direction of the flow velocity. This determination of the solid angle region produces good results for flow velocities with the markings S1, S2 and S3, i.e. if the signs of the velocity components are not all the same. According to one embodiment, the first limit value can be zero.

[0026] According to a preferred development of the method, the particle count rate is determined for each measuring direction. When determining the solid angle area of ​​the dominant direction of the flow velocity, the difference between the particle count rates is taken into account. The particle count rate depends on the size of the intersection between the plane in which the flow velocity vector of the measuring laser beam and the medium are located. The larger the intersection, the more particles are detected. However, the size of the intersection depends on the angle between the emission direction of the measuring laser beam and the flow velocity vector. According to one embodiment, the three emission directions can span a pyramid, in particular a regular pyramid, whose tip is located in a plane. If the medium now moves with a vector flow velocity that is located in the plane or extends parallel to the plane, the intersection is the same. In this area, it is marked as S1, S2 or S3. If the angle between the plane and the flow velocity increases, the difference between the size of the intersection and the mark eventually also becomes S0. Only for flow velocities near the pole, that is, only when the flow velocity moves vertically toward the plane or moves away from the plane, the difference between the size of the intersection becomes smaller again and eventually disappears. Apart from these special cases which occur only rarely, it is therefore generally possible to distinguish whether the mark is equal to S0 or whether the mark is not equal to S0, i.e. one of the marks is S1, S2 or S3, based on the determination of the difference between the sizes of the intersection points. As an example, if the difference between the particle count rates exceeds a predetermined limit value, it can be identified that the mark is equal to S0. If the difference between the particle count rates is less than a predetermined limit value, it is identified that the mark is not equal to S0. The precise determination of the mark can be achieved on the basis of the above-mentioned evaluation of the absolute values ​​of the above-mentioned velocity components. Alternatively, even without further evaluation, a fixed predetermined mark can always be selected, for example if it is determined that the mark is not equal to S0, then S1 is selected.

[0027] According to a preferred development of the method, the average particle residence time in the area detected by the corresponding measuring laser beam is determined for each measuring direction. The difference between the average particle residence times is taken into account when determining the solid angle area of ​​the dominant direction of the flow velocity. Basically, the same value applies to the particle residence time as for the particle counting rate, since this likewise depends on the size of the above-mentioned intersection point.

[0028] According to a preferred development of the method, a contrast value of the associated particle count rate and / or average particle residence time is calculated for each pair of measuring directions. The solid angle area for the dominant direction of the flow velocity is determined as a predetermined solid angle area, which is not assigned to the measuring direction if at least one of the contrast values ​​exceeds a predetermined second or third limit value. Here, the second limit value refers to the limit value assigned to the particle count rate and the third limit value refers to the limit value assigned to the average particle residence time. Therefore, the solid angle area for the dominant direction of the flow velocity corresponds to the two solid angle areas corresponding to the mark S0. Whether the difference between the particle count rate and / or the particle residence time is so large that the flow velocity entering the solid angle area points to the mark S0 can be determined based on the contrast value.

[0029] According to a preferred development of the method, at least four measuring laser beams are emitted in different measuring directions. For at least two different groups of three linearly independent and non-orthogonally aligned measuring directions, a solid angle area for the dominant direction of the flow velocity and an absolute value of the flow velocity are determined in each case as an estimate. The dominant direction of the flow velocity and the absolute value of the flow velocity are determined by a consistency check. The use of at least four measuring laser beams results in a redundancy, which allows the results to be verified within the scope of the consistency check.

[0030] According to a preferred development of the method, the absolute value of at least one velocity component not belonging to the group is determined based on the corresponding measurement signal. The assumed absolute value of at least one velocity component not belonging to the group is determined based on an estimate of the solid angle area of ​​the dominant direction of the flow velocity determined for the group and an estimate of the absolute value of the flow velocity. The absolute value of at least one velocity component not belonging to the group and the assumed absolute value are compared with each other to evaluate the accuracy of the corresponding estimate. The assumed absolute value of at least one velocity component not belonging to the group can be determined by means of a flow velocity vector calculated first, wherein the entries of the vector are provided by the absolute values ​​of the velocity components with a determined sign. This vector of the flow velocity is projected onto the emission direction of at least one velocity component not belonging to the group by a projection matrix, and the absolute value is then calculated. If the difference between the absolute value and the assumed absolute value does not exceed a predetermined limit value, the determined value can be maintained, i.e. the consistency check is successful.

[0031] According to a preferred development of the method, in each case for at least three different groups of three linearly independent and non-orthogonally aligned measuring directions, a solid angle area for the dominant direction of the flow velocity is determined. To determine the absolute value of the flow velocity, the solid angle areas determined for the groups are used for the dominant direction of the flow velocity. Even if an incorrect solid angle area is determined for one or more groups, due to the resulting consistency calculation, the correct solid angle area is usually still determined, and the correct label is determined as a result thereof.

[0032] According to a preferred development of the method, the measurement signal is generated by self-mixing interference between the emitted measurement laser beam and the corresponding scattered measurement laser beam.The absolute value of the velocity component is determined based on the frequency shift between the emitted measurement laser beam and the corresponding scattered measurement laser beam, respectively.

[0033] The present invention also relates to the use of the method for determining the number of particles per unit measurement volume according to the present invention. Here, the measuring laser beam can be simply emitted directly into the surrounding environment, and therefore a closed measurement volume can be used without using it. No additional elements, such as ventilators or heating elements, are required for generating air flow, because the naturally generated air flow is sufficient under normal conditions. The measurement volume is determined based on the determined absolute value of the flow rate. In addition, particle pollution can be determined based on the number of particles per unit measurement volume. The U.S. "National Air Quality" particulate matter (PM) standard introduces the classification of suspended particles in the PMx fraction, which takes into account the size or diameter x of the dust particles, and therefore takes into account the penetration depth of these dust particles into the airway and into the individual's body. In particular, coarse particles PM10 (which include particles up to 10 μm in diameter), fine particles PM2.5 with particles up to 2.5 μm in diameter, and ultrafine particles PM1 with particles up to 1 μm in diameter are distinguished here. Based on known models of PM classification and size and mass distribution of dust particles, an estimate of particle pollution in terms of dust particle mass per unit volume can be determined based on the number of particles per unit measured volume.

[0034] According to a preferred development of the device, the optical transmitter device comprises at least three laser diodes, in particular VCSELs. The detector device comprises at least one photodiode for each of the three laser diodes, in particular a photodiode which is in each case integrated into a laser diode.

[0035] According to a preferred development of the apparatus, the evaluation device is embodied to respectively determine the absolute value of the velocity component based on a frequency shift between the emitted measuring laser beam and the corresponding scattered measuring laser beam determined by beam interference.

[0036] According to a preferred development of the apparatus, the evaluation device is also embodied to determine the particle count rate and / or the average particle residence time per measuring direction.

[0037] According to a preferred development of the device, the device comprises a first storage device for storing measurement events and measurement quantities, wherein the detection of a particle is referred to as a measurement event and in particular the occurring measurement direction, velocity component, count rate and / or residence time are stored as measurement quantities.

[0038] According to a preferred development of the device, the device comprises at least one further storage device in which at least one first limit value for the difference between the maximum velocity component and the residual velocity component and / or at least one second limit value for the contrast value of the particle counting rate and / or at least one third limit value for the contrast value of the particle residence time are stored.

[0039] The invention can advantageously be used within the scope of a device for determining the number of particles per unit of measurement volume, more precisely for determining the measurement volume on the basis of a determined absolute value of the flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The details are as follows:

[0041] Figure 1 A schematic oblique view of a device for determining the absolute value of a flow velocity of a medium according to one embodiment of the present invention is shown;

[0042] Figure 2 The relationship between the error in velocity measurement and the zenith angle and azimuth angle of the velocity under the assumption of orthogonality is shown;

[0043] Figure 3 It shows the relationship between the error in measuring the flow velocity and the zenith angle and azimuth angle of the flow velocity without considering the sign of the velocity component;

[0044] Figure 4 A diagram of the dependence of the marker on the frequency shift for the flow velocity in the plane is shown;

[0045] Figure 5 A diagram showing the dependence of the marker on the zenith angle and azimuth angle of the flow velocity;

[0046] Figure 6 shows how the error in velocity determination varies with the zenith angle and azimuth angle of the velocity when the sign is determined based on the absolute value of the velocity component;

[0047] Figure 7 A diagram showing selection of a sign S0 according to the zenith angle and azimuth angle of a flow velocity when a sign is determined based on a particle count rate using a limit value;

[0048] Figure 8A diagram showing selection of a sign S0 according to the zenith angle and azimuth angle of the flow velocity when the sign is determined based on the particle count rate using another limit value;

[0049] Fig. 9 shows the variation of the flow velocity determination error with the zenith angle and azimuth angle of the flow velocity when the sign is determined based on the particle count rate using the limiting value;

[0050] Fig.10 shows the variation of the flow velocity determination error with the zenith angle and azimuth angle of the flow velocity when the sign is determined based on the particle count rate using another limiting value;

[0051] Fig.11 shows the variation of the flow velocity determination error with the zenith angle and azimuth angle of the flow velocity when the sign is determined based on the absolute value of the velocity component and based on the particle count rate using the limiting value;

[0052] Fig.12 shows the variation of the flow velocity determination error with the zenith angle and azimuth angle of the flow velocity when the sign is determined based on the absolute value of the velocity component and based on the particle count rate using another limiting value;

[0053] Fig.13 A flow chart is shown for explaining a method for determining an absolute value of a flow velocity of a medium according to one embodiment of the present invention.

[0054] Identical or functionally equivalent elements and devices are provided with the same reference numerals in all the figures. DETAILED DESCRIPTION

[0055] Figure 1 A schematic oblique view of a device 1 for determining the absolute value of a flow velocity v of a particle transport medium 5 is shown. The flow velocity v is understood to mean a velocity relative to the device 1. For this purpose, the device 1 can be located in the medium 5, however, the device 1 can also be spaced apart from the medium 5, wherein the medium 5 can be, for example, ambient air with particles, a gas with particles flowing through the device 1 or a liquid with particles flowing through the device 1.

[0056] The device 1 comprises a light transmitter device 2 having three laser diodes 21, 22, 23 which are implemented as VCSELs and which emit a measuring laser beam L perpendicular to a sensor plane provided by a substrate of the device 1. i , i = 1, 2, 3. The lens or any other optical system steers the measuring laser beams L1, L2, L3 in three measuring directions b1, b2, b3. i Measurement direction b i different and linearly independent of each other. In addition, the measurement direction b iare pairwise non-orthogonal and preferably comprise acute angles in pairs, as a result of which a compact construction of the device 1 can be achieved. In particular, space-saving optical elements can be used and space for each individual measuring laser beam L can be saved, appropriately by using a common optical unit. i A separate optical unit.

[0057] The device 1 further comprises a detector device 3 having three photodiodes 31, 32, 33 which are integrated into the laser diodes 21, 22, 23 and detect the measuring laser beam L scattered at the particles. i The detector device 3 is provided for each measuring laser beam L i Generate the relevant measurement signal m i Preferably, if Figure 1 As shown, the light transmitter device 2 includes a corresponding measuring laser beam L i The light emitted by the laser diodes can be aligned in the corresponding measurement direction b_i by means of optical elements (such as lenses, prisms or mirrors). However, if the measurement laser beam L i is generated by splitting the emission laser beam, the number of laser diodes can also be smaller than the measurement laser beam L i The number of

[0058] like Figure 1 As shown, the detector device 3 preferably comprises a plurality of photodiodes corresponding to the laser diodes, wherein the photodiodes can preferably be integrated into the laser diodes. In this case, each photodiode detects the generated measuring laser beam L i The measuring laser beam L is scattered by the particles in the medium. i The detector device 3 measures the magnitude of the frequency shift, which depends on the particle in the measuring direction b_i (ie, in the measuring laser beam L i The velocity component v in the direction of i The detector device 3 can therefore determine the velocity component v based on the frequency shift in each measurement direction b_i. i The absolute value of the correlation can be output as the measurement signal m i In the context of the present invention, the velocity component v i It should be understood to mean the projection of the flow velocity v onto the corresponding measuring direction b_i.

[0059] The three linearly independent measurement directions form an inclined coordinate system, in which the flow velocity v can be considered as a vector pointing away from the origin of the coordinate system. Each measurement direction divides the space into two half-spaces, specifically into a positive half-space and a negative half-space, by a plane passing through the origin and perpendicular to the measurement direction. In the positive half-space, the vector of the flow velocity v has a positive velocity component v i , in the negative half space, the velocity vector v has a negative velocity component v i The planes that separate the half-spaces from one another intersect for different measuring directions, so that a total of 2·2·2=8 solid angle regions occur. For orthogonal measuring directions, i.e. the Cartesian coordinate system, these solid angle regions will correspond exactly to the octants known from geometry.

[0060] Therefore, the velocity component v is called the marker i One of the possible combinations of signs of corresponds to each solid angle region. As described above, for the calculation of the absolute value of the flow velocity v, notations that differ only in a common sign should be considered equivalent.

[0061] The evaluation device 4 of the apparatus 1 is implemented to determine the solid angle region in which the vector of the flow velocity v points, ie the solid angle region corresponding to the prevailing direction of the flow velocity v. To this end, the evaluation device 4 can calculate the velocity component v i The absolute values ​​of are compared with each other and / or the particle count rate cr is taken into account relative to the corresponding measuring direction. i and / or average particle residence time dt i . Refer to the following Figures 5 to 13 Explain these assessment methods in more detail.

[0062] The evaluation device 4 now selects the velocity component v which is assigned to the determined solid angle range. i The sign of . Therefore, the velocity component v i The absolute value and velocity component v i The signs of the velocity components v are known, i.e. the evaluation device 4 determines i The evaluation device 4 can calculate the value of the flow velocity v by means of the formula (2) specified above, where the velocity component v i The conversion to an orthogonal system can be carried out by means of a matrix M which is predetermined by the measuring direction. According to a further embodiment, the evaluation device 4 can also calculate the flow velocity v itself in addition to the absolute value of the flow velocity v; that is, it can calculate the vector form except for the sign. If the flow velocity v is to be specified in an orthogonal coordinate system, the velocity components v known relative to the measuring direction can be converted by means of the matrix M. i Transformation into an orthogonal coordinate system. Thus, in addition to the absolute value of the flow velocity v, in addition to the sign, the evaluation device 4 can also be embodied to determine the flow velocity v itself.

[0063] Figure 2It is shown that if the non-orthogonality of the measurement directions is simply ignored during the calculation, that is, if the mixing term v with unknown sign appearing in formula (1) is replaced by i v j Set to 0, the velocity measurement error is proportional to the zenith angle θ measured relative to the sensor plane and the azimuth angle of the velocity v The plotted figure is the ratio r of the calculated flow velocity v to the actual flow velocity v.

[0064] Figure 3 It shows that if the mixed term v is not taken into account in the calculation according to formula (1) i v j The correct sign of, for example, if all are set to 1 or +, the relationship between the flow velocity measurement error and the change of the zenith angle and azimuth angle of the flow velocity v.

[0065] from Figure 2 and Figure 3 As can be seen in FIG. 1 , significant errors may occur during the calculation; this is why the sign and / or relative sign (ie, label) is also determined according to the invention. The relative sign is understood to mean that the velocity component v i The product of the signs of is assigned to each pair of velocity components v i As a relative sign. In other words, it is the difference between the signs that is important, while the absolute sign is irrelevant due to the symmetry in calculating the flow velocity values.

[0066] Figure 4 The dependence of the markers on the frequency shift is shown for a flow velocity v in the xy plane extending parallel to the sensor plane. In this two-dimensional case, the planes separating the half-spaces from one another are straight lines separating the six angular regions corresponding to the solid angle regions assigned to the markers S1, S2 and S3 from one another. The maximum frequency shift Δf i Corresponding to the velocity component v i Now, for example, if the frequency shift Δf1 is maximal with respect to the first measurement direction b1, ie if said frequency shift is greater than the frequency shifts in the two other measurement directions, or equivalently, the velocity component v i is greatest with respect to the first measuring direction b1, this means that the angle between the flow velocity v and the first measuring direction b1 is smaller than the angle between the flow velocity v and the other measuring directions. For a symmetrical arrangement of the three measuring directions, i.e. if the angles between the respective two measuring directions are all of the same magnitude, this is equal to the flow velocity v pointing to the angular region assigned the marking S1. Preferably, the measuring directions are thus symmetrical with respect to one another. In the case of an asymmetrical arrangement, the boundaries of the solid angle region are shifted accordingly.

[0067] The evaluation device 4 can then be implemented to determine the velocity component v having the largest absolute valuei(max) The evaluation device 4 then selects the solid angle region of the associated measuring direction and selects the label assigned to the solid angle region, ie the velocity component v assigned to the solid angle region. i combination of marks.

[0068] Figure 5 The dependence of the marker on the zenith angle and azimuth of the flow velocity v is shown. It can be seen that the marker is equal to S0 for the zenith angle near the pole. The reason for this is that in this case the flow velocity v is always located in the positive half-space or always in the negative half-space, i.e. the flow velocity v basically always points in the same direction as the measurement direction or always points in the opposite direction to the measurement direction.

[0069] Figure 6 shows the error in the flow velocity measurement as a function of the zenith angle and azimuth angle of the flow velocity v, where the velocity component v is calculated based on the method just described. i The sign is determined by the absolute value of . This method provides very good values ​​for flow velocities v that are substantially parallel to the sensor plane. Since the marker S0 is not identified by the above method, the error is greater for more pronounced angles.

[0070] Therefore, the evaluation device 4 can alternatively or additionally be embodied as a particle counting rate cr of the particles in the measuring laser beam. i Or based on the average particle residence time dt of the particles in the measuring laser beam i to determine the mark. If for a pair of measurement directions, the particle counting rate cr i The contrast value or particle residence time dt i If the contrast value of exceeds the respective predetermined second or third limit value, the evaluation device 4 can recognize that a mark equal to S0 must be selected. Otherwise, the evaluation device 4 can select any mark S1, S2 or S3. As an example, the mark S1 can always be selected.

[0071] Based on the particle counting rate cr i The contrast ratio within the determined range depends on the particle density, since the particle density affects the particle count rate cr i About the particle count rate cr i The decision whether they are significantly different (e.g., at a 95% confidence level) can be made by hypothesis testing based on the underlying Poisson distribution for each measurement direction. i The duration of dt may depend on the particle density and may be selected to be longer for lower particle density. i There is no such dependence on particle density, so particle residence time can be used to determine labeling, especially at lower densities.

[0072] Figure 7 shows the particle count rate cr based on the use of the second limit value i The contrast value of the flow velocity v is used to select the marker S0 according to the zenith angle and azimuth angle of the flow velocity v.

[0073] Figure 8 and Figure 7 The difference is that a higher value is selected as the second limit value.

[0074] Fig. 9 The relationship between the velocity measurement error and the zenith angle and azimuth angle of the velocity is shown. The ratio of the calculated absolute value of the velocity v to the actual absolute value of the velocity v is plotted. Here, Figure 7 The second limit value is selected as shown.

[0075] Fig.10 The figure shows the relationship between the velocity measurement error and the zenith angle and azimuth angle of the velocity v. Here, Figure 8 The second limit value is selected as shown.

[0076] Furthermore, a combination of these methods is possible. Thus, initially one can base the particle count rate cr i The contrast value and / or based on the particle residence time dt i If this is not the case, the evaluation device 4 can determine, as described above, the maximum velocity component v i to determine the label S1, S2 or S3.

[0077] Furthermore, it can be provided that even if only based on the particle count rate cr i and based on the particle residence time dt i Only if both determinations based on the contrast value result in a mark that is not equal to S0 does the evaluation device 4 determine the maximum velocity component v i to determine the label S1, S2 or S3.

[0078] Fig.11 The dependence of the velocity measurement error on the zenith angle and azimuth angle of the velocity v in this combined method is shown. Figure 7 The second limit value is selected as shown.

[0079] Fig.12 The dependence of the velocity measurement error on the zenith angle and azimuth angle of the velocity v in this combined method is shown. Figure 8 The second limit value is selected as shown.

[0080] Furthermore, more than three measuring laser beams L may be emitted. iThe redundancy arising in this case can help improve the measurement result, for example by performing at least one of the above-mentioned consistency checks by means of the evaluation device 4. In particular, a fourth measuring laser beam L4 can be provided, which is for example perpendicular to the sensor plane.

[0081] Fig.13 A flow chart of a method for determining an absolute value of a flow velocity v of a medium according to one embodiment of the present invention is shown.

[0082] In a first step S1, at least two measuring laser beams L are emitted in linearly independent measuring directions b_i which are not orthogonal to each other. i , preferably at least three measuring laser beams L i .

[0083] In a second step S2, the measurement laser beam L scattered at the particle is detected. i For each measuring laser beam L i Generate measurement signal m i . For the measured signal m i For example, when the emitted measuring laser beam L i and the scattered measurement laser beam L i When interference occurs between i Frequency shifting may be included.

[0084] In the third step S3, the measurement signal m i The evaluation is performed where, based on the frequency shift, the velocity component v i The absolute value of is determined as the projection of the flow velocity v on the corresponding measuring direction b_i. In addition, the solid angle region in which the dominant direction of the flow velocity v is located is determined. The solid angle region is selected from a plurality of predetermined solid angle regions, which together cover the entire measuring environment of the measuring device. A label is assigned to each of these predetermined solid angle regions, and thus a label can be assigned to the velocity component v by determining the solid angle region in which the dominant direction of the flow velocity is located. i The absolute value of the flow velocity v can therefore also be determined.

[0085] According to a further embodiment, it may be provided that at least four measuring laser beams L are emitted. i According to the method described in each case for different sets of three measuring directions, which are linearly independent and non-orthogonal, one absolute value of the flow velocity v is calculated as an estimate. The estimated absolute values ​​of the flow velocity v are compared with one another and the final value of the absolute value of the flow velocity v is determined within the scope of a consistency check.

[0086] For example, a sign combination may be determined for one of these groups such that the velocity component v iThe absolute value of the flow velocity v is calculated in vector form. The flow velocity v is then projected onto a measurement direction that is not part of the group and the absolute value is formed in order to determine the velocity component v of this measurement direction. i This value is compared with the velocity component v determined based on interferometric measurements. i If the deviation is below a predetermined threshold, the calculation of the sign is evaluated as correct, and the absolute value of the flow velocity v determined based on the group is output. In addition, the flow velocity v itself can be output in vector form.

[0087] It is also possible to calculate the absolute value of the flow velocity v for at least three different sets of measurement directions. The most frequently occurring sign combination or the most frequently occurring solid angle region in these calculations is used to calculate the absolute value of the flow velocity v.

Claims

1. A method for determining the absolute value of the flow velocity (v) of a particle transport medium, the method comprising the following steps: emitting (S1) at least two measuring laser beams (L_i) having linearly independent, non-orthogonal measuring directions (b_i); detecting ( S2 ) the measuring laser beams (L_i) scattered at the particles and generating in each case one measuring signal (m_i) for each measuring laser beam (L_i); and evaluating ( S3 ) the measurement signal (m_i), a. wherein the absolute value of the velocity component (v_i) is determined as the projection of the flow velocity (v) in the corresponding measurement direction (b_i); b. wherein for the dominant direction of the flow velocity (v) a solid angle region associated with the dominant direction is determined, and for each velocity component (v_i) a sign assigned to the solid angle region is selected; and c. wherein the absolute value of the flow velocity (v) is determined using the determined absolute value of the velocity component (v_i) and using the selected sign for the velocity component (v_i), wherein the sign of the mixing term (v_i·v_j) of the velocity component (vi) is taken into account to determine the absolute value of the flow velocity (v).

2. The method according to claim 1, characterized in that ● emitting at least three measuring laser beams (L_i) having different measuring directions (b_i), at least three of the different measuring directions (b_i) being non-orthogonal with respect to each other and being linearly independent; and • Using the absolute values ​​of the velocity components (vi) determined for three linearly independent measurement directions (bi) and using the chosen signs for the velocity components (vi), the value of the flow velocity (v) is determined.

3. The method according to claim 1 or 2, characterized in that: The determined absolute value of the velocity component (vi) is transformed into an orthogonal coordinate system using the determined sign for the velocity component (vi) and the flow velocity (v) of the particle flow (5) is calculated in the orthogonal coordinate system, at least apart from its sign.

4. The method according to claim 1, characterized in that The solid angle region for the prevailing direction of the flow velocity is determined as one of eight predetermined solid angle regions which together cover the entire measurement environment and the same signs are respectively assigned to the individual velocity components (v_i) for two predetermined solid angle regions opposite one another.

5. The method according to claim 2, characterized in that: Two mutually opposite predetermined solid angle regions are respectively assigned to each of the three linearly independent measuring directions (b_i), and the remaining two predetermined solid angle regions cover the remaining measuring environment.

6. The method according to claim 5, characterized in that a. comparing at least three absolute values ​​of the velocity components (v_i) with each other, b. determine the maximum absolute value of the velocity component (v_i(max)), and c. determining the predetermined solid angle region assigned to the measuring direction (b_i(max)) having the maximum absolute value (v_i(max)) of the velocity component as the solid angle region for the dominant direction of the flow velocity (v) if the difference between the maximum absolute value (v_i(max)) of the velocity component and the remaining absolute values ​​of the velocity component (v_i) exceeds a predetermined first limit value.

7. The method according to claim 1, characterized in that A particle count rate (cr_i) is determined for each measuring direction (b_i) and differences between the particle count rates (cr_i) are taken into account when determining the solid angle area of ​​the dominant direction of the flow velocity (v).

8. The method according to claim 1, characterized in that An average particle residence time (dt_i) in the area detected by the corresponding measuring laser beam (L_i) is determined for each measuring direction (b_i) and differences between the average particle residence times (dt_i) are taken into account when determining the solid angle area of ​​the dominant direction of the flow velocity (v).

9. The method according to claim 4, characterized in that Contrast values ​​of the associated particle count rate (cr_i) and / or average particle residence time (dt_i) are calculated for each pair of measuring directions (b_i), and the solid angle region for the dominant direction of the flow velocity (v) is determined as a predetermined solid angle region, which is not assigned to a measuring direction (b_i) if at least one of the contrast values ​​exceeds a predetermined second or third limit value.

10. The method according to claim 1, wherein: At least four measuring laser beams (L_i) are emitted in different measuring directions (b_i), characterized in that for at least two different groups of three linearly independent and non-orthogonally aligned measuring directions (b_i), a solid angle area for the dominant direction of the flow velocity (v) and an absolute value of the flow velocity (v) are determined in each case as an estimate, and that the dominant direction of the flow velocity (v) and the absolute value of the flow velocity (v) are determined by a consistency check.

11. The method according to claim 10, characterized in that determining the absolute value of at least one velocity component (v_i) which does not belong to the group based on the corresponding measurement signal (m_i), an assumed absolute value for the at least one velocity component (v_i) not belonging to the group is determined based on an estimate of the solid angular area for the dominant direction of the flow velocity (v) and an estimate of the absolute value of the flow velocity (v) determined for the group, and The absolute value of the at least one velocity component (v_i) not belonging to the group and the assumed absolute value are compared with each other in order to assess the accuracy of the respective estimation.

12. The method according to claim 10 or 11, wherein: In each case, for at least three different groups of three linearly independent and non-orthogonally aligned measurement directions (b_i), a solid angle area for the dominant direction of the flow velocity (v) is determined, characterized in that, in order to determine the absolute value of the flow velocity (v), the solid angle areas determined for multiple groups are used for the dominant direction of the flow velocity (v).

13. The method according to claim 1, characterized in that The measurement signal (m_i) is generated by self-mixing interference between the emitted measurement laser beam (L_i) and the corresponding scattered measurement laser beam (L_i), and the absolute value of the velocity component (v_i) is determined based on the frequency shift between the emitted measurement laser beam (L_i) and the corresponding scattered measurement laser beam (L_i), respectively.

14. Use of a method according to any one of claims 1 to 13, wherein: The measurement volume is determined based on the determined absolute value of the flow velocity (v).

15. A device (1) for determining the absolute value of the flow velocity (v) of a particle transport medium, the device (1) comprising at least: An optical transmitter device (2) which is implemented to emit at least three measuring laser beams (L_i) with different measuring directions (b_i), wherein at least three different measuring directions of the different measuring directions (b_i) are not orthogonal to each other and are linearly independent; a detector device (3) which is embodied to detect the measuring laser beams (L_i) which have been scattered at the particles and to generate a measuring signal (m_i) in each case for each measuring laser beam (L_i); and An evaluation device (4) for evaluating the measurement signal (m_i), the evaluation device being embodied as follows: a. Determine the absolute value of the velocity component (v_i) as the projection of the flow velocity (v) in the corresponding measurement direction (b_i); Characterized in that the evaluation device (4) is further implemented as: b. determining for a dominant direction of the flow velocity (v) a solid angle region associated with the dominant direction and selecting for each velocity component (v_i) a sign assigned to the solid angle region; and c. determining the absolute value of the flow velocity (v) using the absolute values ​​of the velocity components (v_i) determined for three linearly independent measurement directions (b_i) and using the signs chosen for the velocity components (v_i), wherein the signs of the mixing terms (v_i·v_j) of the velocity components (vi) are taken into account to determine the absolute value of the flow velocity (v).

16. The device according to claim 15, characterized in that The optical transmitter device (2) comprises at least three laser diodes (21, 22, 23), and the detector device (3) comprises at least one photodiode (31, 32, 33) for each of the three laser diodes (21, 22, 23).

17. The device (1) according to claim 16, characterized in that The evaluation device (4) is embodied to respectively determine the absolute value of the velocity component (v_i) based on a frequency shift (Δf_i) between an emitted measuring laser beam (L_i) and a corresponding scattered measuring laser beam (L_i) determined by beam interference.

18. The device according to claim 17, characterized in that The evaluation device (4) is also implemented to determine a particle count rate (cr_i) and / or an average particle residence time (dt_i) per measuring direction (b_i).

19. The device (1) according to claim 15, characterized in that A first storage device is provided for storing measurement events and measurement quantities, wherein the detection of a particle is referred to as a measurement event and in particular the occurring measurement direction (b_i), velocity component (v_i), count rate (cr_i) and / or dwell time (dt_i) are stored as measurement quantities.

20. The device according to claim 19, characterized in that At least one further storage device is provided in which at least one first limit value for the difference between the maximum velocity component (v_i(max)) and the residual velocity component (v_i) and / or at least one second limit value for the contrast value of the particle count rate (cr_i) and / or at least one third limit value for the contrast value of the particle residence time (dt_i) is stored.

21. Use of a device according to any one of claims 15 to 20, wherein: The evaluation device (4) is further implemented to determine a measurement volume based on the determined absolute value of the flow velocity (v).

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