Particulate matter sensor device

Abstract

A particulate matter sensor device comprises an enclosure (21) defining a flow channel (2), a radiation source (3) for emitting radiation into the flow channel for interaction of the radiation with particulate matter in an aerosol sample in the flow channel, and a radiation detector (4) for detecting at least part of said radiation after interaction with the particulate matter. The sensor device comprises a flow modifying device (511) arranged upstream of the radiation detector and/or radiation source so as to reduce particulate matter precipitation onto the radiation detector, the radiation source and/or the channel wall sections in their proximity. The invention also relates to a method of determining parameters of particulate matter in an aerosol sample by using such a particulate matter sensor device.

Claims

1. A particulate matter sensor device for detecting or characterizing particulate matter in a flow of an aerosol sample guided through the particulate matter sensor device, comprising: an enclosure, the enclosure comprising a flow inlet and a flow outlet and defining a flow channel for guiding the flow of the aerosol sample through the particulate matter sensor device from the flow inlet to the flow outlet; a radiation source arranged and configured to emit radiation into the flow channel for interaction of the radiation with at least some of the particulate matter in the flow of the aerosol sample; a radiation detector arranged and configured to detect at least part of said radiation after interaction with the particulate matter; a circuit board, wherein the radiation detector is mounted on the circuit board; and a flow modifying device configured to at least locally modify the flow of the aerosol sample, the flow modifying device comprising a constriction in or of the flow channel, the constriction constricting the flow channel in a continuous manner to direct at least part of the flow of the aerosol sample away from the radiation detector or the radiation source, and an additional flow opening for creating an additional flow into the flow channel, wherein the additional flow opening is configured to create the additional flow in such a manner that the additional flow overflows the radiation detector or the radiation source after the additional flow has entered the flow channel, thereby sheathing the radiation detector or the radiation source.

2. The particulate matter sensor device according to claim 1, wherein the additional flow opening is arranged at a first distance of less than 8 millimetres upstream of the radiation detector or the radiation source.

3. The particulate matter sensor device according to claim 2, wherein the constriction extends over a constriction region and defines a constriction maximum, and wherein the additional flow opening is arranged upstream of the constriction maximum.

4. The particulate matter sensor device according to claim 1, wherein the additional flow opening is slit-like and extends in circumferential direction with respect to the cross-section of the flow channel.

5. The particulate matter sensor device according to claim 1, comprising a filter, the filter being associated with the additional flow opening such that the additional flow is a filtered flow.

6. The particulate matter sensor device according to claim 1, comprising a secondary inlet that is separate from the flow inlet, wherein the additional flow opening is supplied by a gas drawn into the particulate matter sensor device from the secondary inlet.

7. The particulate matter sensor device according to claim 1, wherein the particulate matter sensor device is configured such that the additional flow through the additional flow opening is suction based.

8. The particulate matter sensor device according to claim 1, wherein the circuit board has at least one through-hole, and wherein the particulate matter sensor device is configured such that the at least one additional flow traverses the circuit board through the at least one through-hole and overflows the radiation detector after the additional flow has traversed the circuit board.

9. The particulate matter sensor device according to claim 1, wherein the flow modifying device is configured for introducing into said flow channel said additional flow such that a magnitude of said additional flow, in total, equals to or is less than 30 percent of a magnitude of the flow of the aerosol sample through the flow channel upstream of said flow modifying device.

10. The particulate matter sensor device according to claim 1, wherein the constriction extends over a constriction region and defines a constriction maximum, and wherein the constriction maximum is located at a distance of less than 5 millimeters upstream of the radiation detector or the radiation source.

11. The particulate matter sensor device according to claim 1, wherein the constriction extends over a constriction region and defines a constriction maximum, and wherein said constriction constricts the flow channel such that a ratio of a constricted clear minimum width at the constriction maximum and an average flow channel diameter is in a range of from 0.2 to 0.95.

12. The particulate matter sensor device according to claim 1, wherein the constriction extends over a constriction region and defines a constriction maximum, and wherein a distance between the radiation detector and the constriction maximum is less than two thirds of a downstream half-length of the constriction.

13. The particulate matter sensor device according to claim 1, wherein said constriction defines an opening angle, the opening angle exhibiting a change per millimeter between 1? per millimeter and 10? per millimeter.

14. The particulate matter sensor device according to claim 1, wherein a maximum opening angle of said constriction is in a range between 1? and a stall angle, said stall angle being in a range of 5? to 10?.

15. The particulate matter sensor device according to claim 1, wherein the constriction extends over a constriction region and defines a constriction maximum, wherein a distance L.sub.0 between said constriction maximum and a position of a maximum opening angle ?.sub.max complies with the formula: $L_0=\frac{{?}_{\max }}{?}$ or wherein a constricted clear minimum width D1 at the constriction maximum complies with the formula: $D_1?D_0+\frac{2}{?}\log (\cos \left(?*L_0\right)$ D.sub.0 designating an average flow channel diameter, or wherein a distance L1 between said constriction maximum and a position of a stall angle SA is chosen according to the formula: $L_1=\frac{SA}{?}$ ? designating an opening angle change per millimeter of said constriction.

16. The particulate matter sensor device according to claim 1, wherein the additional flow opening is arranged in a radial wall section of the flow channel, the radial wall section radially delimiting the flow channel upstream of the radiation detector or the radiation source.

17. The particulate matter sensor device according to claim 1, wherein the constriction extends over a constriction region and defines a constriction maximum, and wherein the additional flow opening is arranged downstream of the constriction maximum.

18. A particulate matter sensor device comprising: an enclosure defining a flow channel; a radiation source for emitting radiation into the flow channel for interaction of the radiation with particulate matter in an aerosol sample in the flow channel; a radiation detector for detecting at least part of said radiation after interaction with the particulate matter; an additional flow opening for creating an additional flow into the flow channel; an environmental sensor for determining at least one environmental parameter, the environmental sensor being disposed in a flow path of the additional flow upstream from the additional flow opening; and a compensation device programmed to: read out the environmental sensor to determine an environmental parameter of the additional flow, the environmental parameter being indicative of a property of a gas in the additional flow; receive information indicative of an amount of heat ingress into the environmental sensor and/or into the gas of the additional flow before it reaches the environmental sensor; and derive a compensated environmental parameter, the compensated environmental parameter being indicative of the property of the gas before said gas entered the particulate matter sensor device, the compensation device being configured to compensate for the heat ingress when determining the compensated environmental parameter.

19. The particulate matter sensor device according to claim 18, wherein the environmental sensor is configured to determine at least one of: a humidity; and a concentration of one or more target gases.

20. The particulate matter sensor device according to claim 18, comprising a filter for filtering the additional flow, the environmental sensor being disposed in the flow path of the additional flow downstream of the filter.

21. The particulate matter sensor device according to claim 18, wherein the flow path of the additional flow is delimited by the enclosure.

22. The particulate matter sensor device according to claim 21, wherein the enclosure defines a primary flow inlet into the flow channel and a secondary flow inlet for receiving a gas that is to form the additional flow, the secondary flow inlet being separate from the primary flow inlet.

23. The particulate matter sensor device according to claim 22, wherein the particulate matter sensor device is configured to create a negative pressure at the secondary flow inlet.

24. The particulate matter sensor device according to claim 18, wherein the radiation detector is arranged in a flow path of the additional flow downstream of the environmental sensor.

25. The particulate matter sensor device according to claim 18, wherein the radiation detector and the environmental sensor are mounted on a common circuit board.

26. The particulate matter sensor device according to claim 25, wherein the circuit board comprises one or more through-holes allowing the additional flow to traverse the circuit board.

27. The particulate matter sensor device according to claim 25, wherein the radiation detector and the environmental sensor are arranged on opposite sides of the circuit board.

28. The particulate matter sensor device according to claim 18, wherein the compensation device is further programmed to receive information about a dissipated electric power of at least one of the radiation source and the radiation detector and to compensate for the heat ingress that results from the dissipated electric power.

29. The particulate matter sensor device according to claim 28, wherein the environmental sensor is configured to determine a temperature, and wherein the compensation device is further programmed to compensate for the heat ingress by employing an empirically determined lookup table that correlates the dissipated electric power with an increase of measured temperature by the environmental sensor.

30. A particulate matter sensor device comprising: an enclosure defining a flow channel; a radiation source for emitting radiation into the flow channel for interaction of the radiation with particulate matter in an aerosol sample in the flow channel; a radiation detector for detecting at least part of said radiation after interaction with the particulate matter; a circuit board, wherein the radiation detector is mounted on the circuit board; an additional flow opening for creating an additional flow into the flow channel, wherein the additional flow opening is configured to create the additional flow in such a manner that the additional flow overflows the radiation detector, thereby sheathing the radiation detector; and an environmental sensor for determining at least one environmental parameter, the environmental sensor being disposed in a flow path of the additional flow upstream of the additional flow opening, wherein the radiation detector is arranged in a flow path of the additional flow downstream of the environmental sensor.

31. The particulate matter sensor device according to claim 30, wherein the environmental sensor is configured to determine at least one of: a humidity; and a concentration of one or more target gases.

32. The particulate matter sensor device according to claim 30, wherein both the radiation detector and the environmental sensor are mounted on the circuit board.

33. The particulate matter sensor device according to claim 32, wherein the circuit board comprises one or more through-holes allowing the additional flow to traverse the circuit board, and wherein the radiation detector and the environmental sensor are arranged on opposite sides of the circuit board, such that the additional flow first passes the environmental sensor on a first side of the circuit board, is then directed to a second side of the circuit board that is opposite to the first side and there passes the radiation detector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

(2) FIG. 1(a) shows a schematic longitudinal-sectional view of an embodiment of a particulate matter sensor device;

(3) FIG. 1(b) shows, in schematic sectional top view, the embodiment of a particulate matter sensor device according to FIG. 1(a);

(4) FIG. 2(a)-(c) show, in schematic cross-sectional view, embodiments of the flow channel;

(5) FIG. 3 shows a schematic longitudinal-sectional view of an embodiment of the particulate matter sensor device with additional flow;

(6) FIG. 4 shows a schematic longitudinal-sectional view of another embodiment of the particulate matter sensor device with additional flow;

(7) FIG. 5 shows a schematic longitudinal-sectional view of yet another embodiment of the particulate matter sensor device with additional flow;

(8) FIG. 6(a) shows a schematic longitudinal-sectional view of yet another embodiment of the particulate matter sensor device with additional flow;

(9) FIG. 6(b) shows a schematic sectional top view of the embodiment of the particulate matter sensor device with additional flow according to FIG. 6(a);

(10) FIG. 7 shows a schematic longitudinal-sectional view of an embodiment of the particulate matter sensor device with a constriction;

(11) FIG. 8 shows a schematic longitudinal-sectional view of another embodiment of the particulate matter sensor device with a constriction;

(12) FIG. 9 shows, in a top view, a photograph of another embodiment of the particulate matter sensor device with a constriction;

(13) FIG. 10 shows, in a schematic lateral longitudinal-sectional view, yet another embodiment of the particulate matter sensor device with a constriction device;

(14) FIG. 11 shows a schematic lateral longitudinal-sectional view of a further embodiment of the particulate matter sensor device with a constriction and additional flow;

(15) FIG. 12(a) shows a schematic longitudinal-sectional view of another embodiment of the particulate matter sensor device with a constriction and additional flow;

(16) FIG. 12(b) shows a schematic sectional top view, of the embodiment of a particulate matter sensor device according to FIG. 12(a);

(17) FIG. 13 shows an exploded perspective view of an embodiment of a partly assembled particulate matter sensor device with from top to bottom: second enclosure (shown upside down), first enclosure, circuit board, filter and cover;

(18) FIG. 14 shows an enlarged detail view of the first enclosure of the particulate matter sensor device according to FIG. 13;

(19) FIG. 15 shows a schematic top view of an embodiment of the particulate matter sensor device with two flow channels; and

(20) FIG. 16 shows an exploded perspective view of a further embodiment of a partly assembled particulate matter sensor device.

DESCRIPTION OF PREFERRED EMBODIMENTS

(21) Preferred embodiments of the present invention are now described with reference to the figures.

(22) In the context of the figures, a particulate matter sensor device 1 for ascertaining a particulate matter concentration in an aerosol sample is exemplarily described, wherein visible light is used as radiation.

(23) FIG. 1(a) shows a schematic lateral longitudinal-sectional view of a first embodiment of a particulate matter sensor device 1. FIG. 1(b) shows this particulate matter sensor device 1 in schematic sectional top view. The device 1 comprises and enclosure 21 that delimits a flow channel 2 extending between an inlet 11 and an outlet 12 along a longitudinal axis L and having a diameter D.sub.0. A flow 20 of an aerosol sample to be measured by the sensor device 1 is guided through the flow channel 2. A fan 220, i.e. a ventilation device is arranged in the flow channel 2 for controlling the flow 20.

(24) A printed circuit board 23 is attached to the bottom of the enclosure 21.

(25) A radiation detector 4 is accommodated in a first recess 22 in a bottom section of the enclosure 21 in flow channel 2. The detector 4 may be a surface-mount photo diode. The detector 4 is arranged on or in the printed circuit board 23. The photo diode 4 has a sensitive area 40 that is directed towards the channel 2 and that extends substantially along the longitudinal axis L such that the surface 40 is substantially flush with a wall of the enclosure delimiting the channel 2. This introduces the least resistance or disturbance to the aerosol flow 20.

(26) As can be seen in FIG. 1b, a radiation source 3, here a laser, is arranged in a further first recess 22 of a lateral wall section provided by the enclosure 21. The radiation path X, here the laser light path, extends substantially perpendicularly to the longitudinal axis L of the channel 2. Moreover, the radiation path X is chosen such that is extends just above the sensitive area 40, preferably at a distance to the sensitive area by a fraction of D.sub.0, wherein preferably, the radiation path X extents in the center of the channel 2. This increases the sensitivity of the sensor device 1 since the detector 4 is closer at the reaction zone where the radiation interacts with the particulate matter in the aerosol sample.

(27) The laser device 3 emits the laser beam 32 through the flow channel 2, where the laser light interacts with the particulate matter in aerosol sample flow 20 which produces, for example, scattered light 30 that is detected by the detector 4. The laser beam fraction that does not interact is then guided into a horizontal recess 22a and onto the beam stopper 31.

(28) Opposite the laser device 3, a further recess 22a is provided, at the bottom of which a beam stopper 31 is arranged for receiving the laser light that was not (or not enough) redirected or absorbed by the aerosol sample. Providing the beam stopper 31 in the recess 22a reduces stray or spurious light that may disturb the measurement. Additionally, the recess 22a may be curved or bent while a reflecting element is arranged in the curve or bend for guiding the radiation onto the stopper 31. Back-reflections from the stopper 31 are thereby reduced.

(29) At an upstream distance d.sub.1 from the sensitive area 40, a first additional flow opening 511, here a bottom inlet opening, is arranged in a bottom wall section of the enclosure 21. The line that feeds the bottom inlet 511 extends through a through-hole 231 in the printed circuit board 23 to the bottom inlet 511 and provides the bottom inlet 511 with gas such as to produce the first additional flow 5110, which here is a bottom additional flow.

(30) At substantially the same upstream distance d.sub.1 from the sensitive area 40, a second additional flow opening 512, here a top inlet opening, is arranged in a top wall section of the enclosure 21. The top flow inlet 512 is supplied with a gas such as to produce the second additional flow 5120, which here is a top additional flow.

(31) The additional bottom and top flows 5110, 5120 are directed substantially at right angles with respect to the longitudinal axis L into the flow channel 2.

(32) Two third flow openings 513, lateral flow openings, are provided in lateral wall sections of the enclosure 21. The lateral flow inlets 513 are arranged opposite one another and are supplied with a gas such as to produce the third additional flows 5130, which here are lateral additional flows.

(33) Openings that are arranged opposite one another may be arranged directly opposite one another or may be offset in flow direction with respect to one another by a fraction of D.sub.0.

(34) As can be seen from FIG. 1b, the lateral openings 513 are angled with respect to the longitudinal axis L such that an angle between L and the extension of the final section of the supply line feeding the lateral inlet 513 is about 30? to 60?. This inclined injection of the lateral flow leads to less disturbance of the aerosol flow 20. It is also conceivable that the lateral flows 5130 are injected substantially at right angles with respect to L. Moreover, it is conceivable that any additional flow, such as the top and/or bottom flow(s) 5110, 5120 are injected in an inclined manner as explained with respect to the later flows 5130.

(35) At least some or all the additional flow openings 511, 512, 513 may be provided with a filter element or may a have an associated filter element provided preferably upstream of the opening, the filter being, e.g. an air filter, in particular a HEPA filter, or a path filter for creating a filtered additional flow. Moreover, at least some or all the additional flows 5110, 5120, 5130 may be created in that the flow 20 creates an under pressure at the respective inlet 511, 512, and 513, respectively.

(36) The device 1 is further equipped with integrated circuitry 60 and/or a microprocessor 6, here shown as integrated to the detector 4. Microprocessor(s) 6 and integrated circuits 60 may be arranged, however, on or in other elements such as the radiation source 3 of the fan 220. The device 1 is configured for carrying out a measurement under control of the integrated circuitry 60 and/or a microprocessor 6 and by means of the radiation source 3 and the detector 4.

(37) The sensor device 1 may be a PM1.0 or a PM2.5 sensor, i.e. it may measure particles that have a size of 1 micrometer and 2.5 micrometers, respectively, or smaller or it may be a PM10 device that measures particulate matter in an aerosol sample with particle sizes equal to or less than 10 micrometers.

(38) The additional flows 5110, 5120, 5130 modify the flow 20 such that precipitation of particulate matter onto the radiation detector 4 and/or the radiation source 3 and/or onto the wall surface in close proximity to radiation source and detector is reduced.

(39) An embodiment of the resulting modified flow is schematically illustrated by the three arrows B in the center of FIG. 1a and FIG. 1b. Here, peripheral flow of lower aerosol density (indicated by the thin arrows B) reduces, in comparison with a center flow (indicated by the thick center arrow) precipitation of particulate matter onto the radiation detector 4 and/or the radiation source 3 and/onto the channel wall section surface in close proximity to radiation source 3 and detector 4. Here, only a fraction of 10% or less of the flowing particulate matter in the centre of the flow channel close to the longitudinal axis 2 are hit by the radiation. The density of the aerosol in the center of the flow channel, where the measurement takes place, remains essentially unchanged and only its flow velocity may increase as compared to the inlet. If the additional flow effects the measurement, this effect is compensated for in the calibration and/or modelling of the particulate matter sensor device.

(40) The additional flow openings 511, 512, 513 may be shaped and configured such that additional flows 5110, 5120, 5130 together have a flow that is 1% to 30% (preferably 1% to 25%, more preferably 1% to 20%) of the aerosol sample flow 20 before any of said additional flows 5110, 5120, 5130.

(41) Preferable, the additional flow is limited by a dimension in the line that feeds the additional flow and not by the filter to be more robust against increased clogging of the filter and to increase longer term stability. The feed line includes the opening 231 in FIG. 13.

(42) Typical shapes of the additional flow openings 511, 512, 513 are rectangular slits or round holes with a typical width/diameter in a range of from 0.1 millimeters to 1 millimeter. Preferably, slit-like openings extend over a full width of the channel they are provided in. In some embodiments, the slit-like openings may be arranged on all channel walls, in some embodiments may be oriented along the flow direction, in some embodiments may be arranged at right or other angles thereto. In some embodiments, slit-like openings may be provided such that a circumferential opening around the entire channel is given, the circumferential opening extending either in a closed or in a spiral manner around the channel.

(43) FIGS. 2(a)-(c) show, in schematic cross-sectional view, different embodiments of the flow channel 2 and an embodiment of the position of the radiation detector 4 and the size of the detection area 40. In this embodiment, the width of the detection area 40 essentially corresponds to the width a.sub.2 of the flow channel 2. Different cross-sectional shapes with area A are shown.

(44) FIG. 2(a) shows a rectilinear cross-section with sides a.sub.1 and a.sub.2. Here, the two corners of the top wall section 215 are rounded. Moreover, lateral wall sections 216, top wall section 215, and bottom wall section 217 are indicated.

(45) FIG. 2(b) shows a triangular cross-section with base a.sub.2 and sides a.sub.1. The triangle may be an isosceles or an equilateral triangle. Moreover, lateral wall sections 216 and bottom wall section 217 are indicated. Here, the angle between the two lateral wall sections 216 is rounded.

(46) FIG. 2(c) shows a round cross-section with axes a.sub.1 and a.sub.2. The axes a.sub.1 and a.sub.2 may have the same length and the shape may preferably be circular, the axes a.sub.1 and a.sub.2 may, however, also have different lengths and the shape may preferably be elliptical. Moreover, lateral wall sections 216, top wall section 215, and bottom wall section 217 are indicated. Here, the shape of the lower half of the round cross-section is modified at the location of the radiation detector 4 to allow for a wide access angle to the detection area 40.

(47) FIG. 3 shows a schematic lateral longitudinal-sectional view of a further embodiment of the particulate matter sensor device 1 with additional flows. Differences to the previous embodiment according to FIG. 1 are described. According to FIG. 3, the printed circuit board 23 delimits the bottom section of the flow channel 2. The circuit board 23 is arranged in the enclosure 21 or the enclosure 21 is fitted onto the circuit board 23. In this embodiment, the detector 4 is not arranged in a recess in the enclosure 21 but protrudes into the channel 2 from the circuit board 23 on which it is attached. Accordingly, the average flow channel diameter D.sub.0 may be larger in this embodiment and may be constricted in the region of the detector 4. This constriction may modify the flow 20 such as to produce less precipitation of particulate matter. Alternatively, the detector 4 may be arranged in the circuit board 23 to be flush with the average channel wall which would cause less flow resistance to the flow 20.

(48) In this embodiment, bottom additional flow 5110 and lateral additional flows 5130 are provided.

(49) In this embodiment, also a slit-like inlet 514 may be provided for providing a sheet-like additional flow 5140. Here, the sheet-like additional flow is a lateral flow that produces a sheath for protecting the detector 4. Particularly preferred are slit-like flow openings on the wall section on which the element that shall be protected, i.e. the detector 4 and/or the source 3, are arranged such that this element is covered by a sheet-like flow from particulate matter deposition.

(50) FIG. 4 shows a schematic lateral longitudinal-sectional view of another embodiment of the particulate matter sensor device 1 with additional flow. In this embodiment, a top additional flow 5120 is introduced into the flow channel 2, when in use, through a second additional flow inlet 512.

(51) FIG. 5 shows a schematic lateral longitudinal-sectional view of yet another embodiment of the particulate matter sensor device 1 with additional flow. This embodiment is like the embodiment according to FIG. 1 with the difference that the detector 4 is provided in a deep first recess 22. Accordingly, the sensitive surface 40 is no longer flush with the average channel bottom wall but offset with respect to the channel centre into the recess 22. The entrance region into the recess 22 may be constricted by additional enclosure elements 24 that may be integrated to the enclosure 21 or that may be extra elements fastened to the entrance region. The constriction 24 of the entrance region is such that the radiation may exit the recess 22 without disturbance while the penetration of particulate matter into the recess 22 is reduced due to the constriction.

(52) As in the embodiment according to FIG. 1, top, bottom, and lateral flow openings 511, 512, 513 are provided according to FIG. 3 for establishing top, bottom, and lateral additional flows 5110, 5120, 5130 into the flow channel 2 for protecting the detector 4 and/or the source 3. Again, some of these additional flows may be dispensed with, e.g. only one additional flow opening may be provided, e.g. a bottom flow inlet 511.

(53) A preferred embodiment of the present invention is now described with reference to FIGS. 6 and 7.

(54) FIG. 6(a) shows a schematic lateral longitudinal-sectional view of the particulate matter sensor device 1 with additional flow according to this embodiment. FIG. 6(b) shows a schematic sectional top view this embodiment.

(55) As in the embodiment according to FIG. 5, the detector 4 is arranged in a first recess 22, the recess entrance region is constricted by additional enclosure elements 24, wherein, in the first recess 22, are provided one or more bottom additional flow openings 511, 511a that establish a gas flow channel through the circuit board 23 (through the through-holes 231) into the channel 2. Preferably, the constricted region from which flow 5110 exits into the channel 2 is just below the radiation path X.

(56) Additionally, as seen in FIG. 6(b), the first recesses 22 and 22a, in which the laser 3 and beam stopper 31, respectively, are accommodated, act as an inlet through which a lateral additional flow 5130 is established. This protects the source 3 particularly efficiently from deposition of particulate matter as particulate matter is much more unlikely to enter one of the recesses 22, 22a that act as additional flow inlets. As outlined above, the additional flow openings create a flow into or from the flow channel 2 that modify the aerosol flow 20 and that redirect the particulate matter onto trajectories that avoid deposition on detector 4 and/or source 3 or that dilute the sample locally. Instead of creating extra flow through introduction or withdrawal of gas into or from the channel, a structural element may be place in the particulate matter trajectory such that the particulate matter is diverted from the object to be protected. This is achieved a constriction that may be a bump in the channel wall or an additional element placed in the channel 2 and that basically acts like a ramp.

(57) FIG. 7 shows a schematic lateral longitudinal-sectional view of a preferred embodiment of the particulate matter sensor device 1 with a constriction device 52. In FIG. 7, the enclosure 21 forms the flow channel 2, whilst the channel 2 is constricted in the middle region of the FIG. 7 by the arrangement of the channel walls provided by the enclosure 21.

(58) FIG. 8 shows a schematic lateral longitudinal-sectional view of another embodiment of the particulate matter sensor device 1 with a constriction device 52, wherein the constriction 52 is arranged, as an additional element, on the printed circuit board 23.

(59) In both cases, the constriction 521 extends, in flow direction, over a constriction area 524 and elevates, in a smooth manner, from the channel wall at the location where the channel diameter is D.sub.0 to the axis of the channel 2 until it reaches, in flow direction, its constriction maximum 525, i.e. were the minimum clear width D.sub.1 of the channel 2 is located; thereafter the constriction 521 falls back until the channel diameter has reached its original diameter D.sub.0. The constriction 521 shown here is a smooth bump that resembles a Gaussian curve. The constriction 521 may also have a downstream half width c.sub.0 which is smaller than the upstream half width. In other words, the curve may have a positive skew. It is, however, also conceivable that the curve has a negative skew or is symmetrical.

(60) At the downstream distance d.sub.3 of the constriction maximum 525 the constriction 521 is provided with a recess 523. The recess 523 has basically the same function as the first recess 22 described in the context of the previous embodiments. The recess 523 extends, in at substantially right angles to the longitudinal direction L, down to the printed circuit board 23. It is, however, generally conceivable that the recess 523 is less deep and/or inclined or curved. The recess 523 accommodates the detector 4, which, as shown in the FIGS. 7, 8, is arranged on the printed circuit board 23.

(61) In the embodiment shown in FIG. 7, the curvature of the constriction 521 is such that, at a downstream distance L.sub.1 of the constriction maximum 525, a stall angle SA is reached. Here, L.sub.1 is larger than d.sub.3 in such a manner that the stall angle is downstream of the recess 523. Accordingly, the flow 20 stalls only behind the recess 523. A maximum angle ?.sub.max is then reached at a downstream distance of L.sub.0 from the constriction maximum 525. Here, L.sub.1 is smaller than L.sub.0.

(62) The constriction situation according to FIGS. 7/8 shows, for some embodiments and in relation to the constriction and channel 2, true relative relations between constriction 521 and channel 2 dimensions.

(63) FIG. 9 shows, in a top view, a photograph of another embodiment of the particulate matter sensor device 1 with a constriction 521. The detector 4 is arranged downstream of the constriction maximum 525 and the constriction 521 constricts the channel diameter D.sub.0 to the channel diameter D.sub.1. In this embodiment, the constriction 521 is extending circumferentially around the channel 2. Geometrical relations of different parts of the objects shown in FIG. 9 may be measured from the photograph.

(64) FIG. 10 shows a schematic lateral longitudinal-sectional view of yet another embodiment of the particulate matter sensor device 1 with a constriction device 521. In this embodiment, the constriction device 521 is a ramp-like element that is placed upstream of the detector 4. Preferably, as indicated in the figure, the ramp 521 has a height that is bigger than the height of the detector 4, i.e. the tip of the ramp 521 (which may be designated as the constriction maximum 525) is higher than the sensitive area 40. As indicated, the channel diameter D.sub.0 is larger than the constricted clear minimum width D.sub.1 of the flow channel 2. An upstream distance d.sub.4 between the tip of the constriction and the sensitive area may be 1 millimeter to 5 millimeters. Both, the ramp 521 and the detector 4 may be both arranged on the circuit board 23. It is to be understood, that the ramp 521 may have a linear slope or may follow an at least partly curved slope (see for example FIG. 8).

(65) FIG. 11 shows a schematic lateral longitudinal-sectional view of a further embodiment of the particulate matter sensor device 1 with a constriction 521 and additional flow. This embodiment is essentially the same as the embodiment according to FIG. 10, wherein, additionally, a flow opening 511 is arranged between the ramp 521 and the detector 4. Preferably, this flow opening is a bottom flow inlet as outlined above. Additionally, a top flow inlet 512 may be provided for introduction a top additional flow 5120. The top additional flow inlet 512 may be arranged opposite the bottom additional flow inlet 511. The upstream distance d.sub.4 between the ramp tip 525 and the sensitive area 40 may be in range of from 2 millimeters to 25 millimeters. The upstream distance d.sub.1 between the bottom additional inlet 511 and the sensitive area 40 may be in range of from 1 millimeter to 5 millimeters.

(66) FIG. 12(a) shows a schematic lateral longitudinal-sectional view of another embodiment of the particulate matter sensor device 1 with a constriction and additional flow. FIG. 12(b) shows a schematic sectional top view of this embodiment. Like in the embodiment according to FIG. 11, a ramp constriction device 521 a bottom additional flow 511 are arrange in the flow channel 2. In this case, however, the bottom additional flow inlet 511 is not between ramp 521 and detector 4 but the ramp 521 is arranged between the bottom additional inlet 511 and the detector 4. In other words, the bottom additional flow inlet 511 arranged upstream of the ramp 521 (not downstream as in FIG. 11). The upstream distance d.sub.4 between the ramp tip 525 and the sensitive area 40 may be in range of from 1 millimeter to 5 millimeters. The upstream distance d.sub.1 between the bottom additional inlet 511 and the sensitive area 40 may be in range of from 2 millimeters to 25 millimeters or more.

(67) FIG. 13 shows an exploded perspective top view of an embodiment of a partly assembled particulate matter sensor device 1 with from top to bottom: second enclosure 212 (shown upside down), first enclosure 211, circuit board 23, filter 213, and cover 214.

(68) The first and second enclosures 211, 212 together form the enclosure 21. The second enclosure 212 forms the top part that delimits the top half of the flow channel 2. The first enclosure 211 forms the bottom part that delimits the bottom half of the flow channel 2. In this embodiment, the flow channel 2 is essentially U shaped with a substantially rectangular cross-sectional shape. The detector 4 is directed towards the channel 2 and is arranged in a first recess 22b in the first enclosure 211 (see FIG. 14) while being attached to the printed circuit board 23. The detector 4 is arranged just downstream of the first U bend in flow direction. The laser device 3 is arranged to emit laser light just above the sensitive area 40 of the detector 4. A connector 232 provides electrical connections for powering, controlling and reading out the particulate matter sensor device 1.

(69) The aerosol sample flow 20 is drawn into the channel 2 through the inlet 11 and sucked through the flow channel 2, via the centrifugal fan 220 out through the outlet 12.

(70) In the cover 214 there is a plurality of additional inlets 13 arranged at regular distances around a peripheral wall of the cover 214 with a solid cover plate. Ambient air or another aerosol or gas is sucked into the device 1 though these additional inlets 13 and is passed through the filter 213 and then through the through-opening 231 to be guided through the additional flow openings 511 and 513 into channel 2 for establishing a filtered additional flow for modifying the aerosol sample flow 20 as outlined above.

(71) In some embodiments, an optional environmental sensor 7 is arranged in the flow path of the additional flow downstream from filter 213. The environmental sensor 7 determines an environmental parameter such as temperature, humidity or a concentration of an analyte in the filtered additional flow. By arranging the environmental sensor 7 downstream from filter 213, the environmental sensor 7 is well protected from contaminations by particulate matter, such particulate matter being filtered out by filter 213 before it can reach the environmental sensor 7.

(72) The environmental sensor 7 may comprise or be connected to a compensation device that reads out the environmental sensor and derives a compensated output parameter based on the sensor signals of the environmental sensor. The output parameter derived by the compensation device may be indicative of a property that the gas of the filtered flow had before it entered the particulate matter sensor device 1, such as the temperature, the humidity or the concentration of one or more analytes in the environment of the particulate matter sensor device 1. To this end, the compensation device can compensate for expected differences between a parameter as measured by the environmental sensor and the actual value of this parameter outside the particulate matter sensor device 1. For instance, if the environmental sensor is a temperature sensor, the compensation device may compensate for an expected temperature difference between the inside and the outside of housing 21 due to heat dissipation by the laser device 3, the radiation detector 4 and the fan 220. In this manner, a more accurate indication of the measured parameter in the environment of the particulate matter sensor device 1 is obtained.

(73) In the embodiment of FIG. 13, the environmental sensor 7 is mounted on the same circuit board 23 as the detector 4. In fact, it is mounted on the same side of the circuit board 23 as the detector 4, being laterally separated from the detector 4 only by an intermediate wall portion 71. A corresponding wall portion is also present in the bottom of first enclosure 211 so as to provide a seal between the detector 4 and the flow path of the filtered flow, which passes through through-opening 231 and past environmental sensor 7. In other embodiments, the environmental sensor 7 may be arranged on the opposite side of the circuit board 23 as compared to the detector 4.

(74) FIG. 14 shows an enlarged detail view of the first enclosure 211 of the particulate matter sensor device 1 according to FIG. 13. The laser device 3 emits the laser beam 32 through the flow channel 2, where the laser light interacts with the particulate matter in aerosol sample flow 20 which produces, for example, scattered light 30 that is detected by the detector 4. The laser beam fraction that does not interact is then guided into a horizontal recess 22a and onto the beam stopper 31. In this embodiment, it is shown that the beam stopper 31 may be arranged offset to the original beam path X. In other words, the laser light follows, after exiting the channel 2, an L-shaped path, wherein in the knee of the L-shape, the light is reflected onto the beam stopper 31. This idea may be integrated in any embodiment, as it helps to reduce disturbing stray light onto the detector 4.

(75) The detector 4 is arranged in another the first recess 22a that extends vertically. Both first recesses 22a extend substantially at right angles with the flow direction in the interaction area between laser beam 32 and particulate matter in sample flow 20.

(76) Closely upstream of the detector 4 are arranged the additional flow openings 511 and 513 for modifying the flow 20 such that less particulate matter is deposited onto the detector 4 and/or der source 3.

(77) It is to be understood that the above-mentioned embodiments are only exemplary. The different ideas of constriction, additional flow opening, and or recessing sensitive items into recesses may be combined to create further embodiments.

(78) All or some of the additional flows may be generated in a suction-based manner, i.e. the flow channel pressure situation establishes and maintains the additional flow situation. On the other hand, all or some of the additional flows may be generated by pushing gas into the additional channels associated with the inlet openings or by fan or ventilation means arranged in said additional channels.

(79) Also, for some embodiments, the flow openings 511, 512, 513, and/or 514 may be outlets, i.e. they draw gas from the channel 2. The basic principle, that, for example, a bottom additional flow inlet may divert the aerosol flow 20 upwards to the top wall section (and thereby particulate matter away from the bottom) may be achieve by a top additional opening that is an outlet and that draws gas from the gas flow.

(80) FIG. 15 shows a schematic top view of an embodiment of the particulate matter sensor device, wherein the particulate matter sensor device 1 comprises two flow channels 2 that extend separately from one another. Here, the particulate matter device comprises two radiation sources and two radiation detectors (not shown), wherein one radiation source and one radiation detector is arranged in each of the two flow channels. The enclosure 21 is arranged and configured to receive or for being connected with the circuit board 23. The two radiation detectors are mounted on the same circuit board 23.

(81) In some embodiments, the board 23 is attached to the enclosure 21 in such a manner that the board 23 delimits at least parts of the channel 2.

(82) The two channels may be used for detecting and/or characterising particulate matter of an aerosol sample or of two different aerosol samples, e.g. indoor and outdoor air samples. Alternatively or additionally, the two channels may each be especially arranged and configured for detecting and/or characterising particular particulate matter sizes such as PM10, PM2.5 or PM1.0 and/or particular types of dust such as heavy dust, settling dust or suspended atmospheric dust.

(83) FIG. 16 illustrates a further embodiment of a particulate matter sensor device 1. As in the embodiment of FIG. 13, the sensor device comprises, from bottom to top, a second enclosure 212, a first enclosure 211, a circuit board 23, a filter 213 and a cover 214. These components are mounted to one another with the aid of several screws (not shown in FIG. 16) passing, inter alia, through through-holes 233 of circuit board 23. A connector 232 is mounted on the bottom of circuit board 23.

(84) As in the embodiment of FIG. 13, a roughly U-shaped flow channel 2 is delimited by the first and second enclosures 211, 212. An aerosol sample is aspirated through an inlet 11 into the flow channel 2 by a fan 220. A laser device 3 emits laser light that crosses the flow channel 2 horizontally at a right angle to the flow direction. Laser light is scattered by the aerosol sample. Vertically above the flow channel, a photodetector (not visible in FIG. 16) is arranged in a recess 22b of the first enclosure 211 for detecting scattered light. The photodetector is mounted on the bottom side of circuit board 23 approximately in the region of the dotted rectangle 41 in FIG. 16.

(85) In order to reduce deposition of particulate matter onto the photodetector, an additional gas flow is created. To this end, an additional inlet 13 is provided in cover 214, allowing gas to enter the inside of cover 214 and to pass through sheet-like filter 213, thereby creating a filtered flow. The filtered flow passes along the top of circuit board 23 and reaches the bottom of circuit board 23 through additional through-holes 231 in circuit board 23. In this connection, it is to be noted that the additional through-holes 231 are the only openings in circuit board 23 that allow the filtered flow to pass through, since all other through-holes 233 are sealed between enclosures 211, 212 and cover 214 by the screws. Once the filtered flow has reached the bottom of circuit board 23, it passes vertically through recess 22b past the photodetector (not visible in FIG. 16) before finally entering flow channel 2. By disposing the photodetector in the flow path of the filtered flow, the photodetector is protected from excessive contamination with particulate matter.

(86) An environmental sensor 7 is mounted on circuit board 23 on the opposite side of the photodetector. As in the embodiment of FIG. 13, the environmental sensor is configured for determining an environmental parameter of the filtered flow, such as temperature, humidity or a concentration of an analyte. As in the embodiment of FIG. 13, the environmental sensor is well protected from unwanted contamination with particulate matter by being arranged in the flow path of the filtered flow behind filter 213. By mounting the environmental sensor 7 on the opposite side of the circuit board from the photodetector, thermal coupling between the photodetector and the environmental sensor 7 is reduced.

(87) The environmental sensor 7 comprises an integrated compensation device 72. The compensation device 72 derives an output parameter that is indicative of a property that the gas of the filtered flow had before it entered the particulate matter sensor device 1, i.e., an environmental parameter, by taking into account any expected differences between the conditions outside and inside the housing of the particulate matter sensor device.

(88) It is to be understood that the above-mentioned embodiments are only exemplary. In all embodiments, the particulate matter sensor device may comprise one or more additional sensors, such as temperature, humidity, gas and/or gas flow sensors, which does not necessarily need to be disposed in the flow path of the filtered flow.