FI129497B - Air quality measuring device - Google Patents

Abstract

The apparatus for measuring the particle content of air has a laser source (701) for producing laser light and for directing it towards a target area, an air channel for controlling the air to be measured through the target area in the form of an air flow and a light detector (704) next to the target area. to detect light pulses that occur when the particles, which the air flow carries with it, scatter the laser light in the target area. The apparatus has a light trap (201) between the laser source (701) and the target area to reduce the amount of diffused light reaching the target area. In the light trap (201) there are at least two partitions (204, 205, 206) transverse to the running direction of the laser light, each of which has an opening (401, 403, 406) for releasing a desired amount of laser light through the partition in question in a desired manner. The partitions (204, 205, 206) form part of the same piece which is manufactured in an integrated manner so that each of the openings (401, 403, 406) over the entire circumference is delimited by a continuous portion of the said in an integrated manner produced paragraph.

Description

APPARATUS FOR MEASURING AIR QUALITY

FIELD OF THE INVENTION The invention relates generally to devices for measuring air quality. In particular, the invention relates to devices for measuring the concentration of particles in the air.

BACKGROUND OF THE INVENTION Small particles are solid particles floating in the air and having a diameter of up to a few micrometers. There is some variation in the use of the terms, but according to one practice, particles less than 2.5 micrometers in diameter are small particles and particles less than 10 micrometers are respirable particles. In English sources, the general terms suspended particulate matter (SPM), particulate matter (PM) or particulates are used, the subspecies of which are coarse particles (coarse particles; diameter 2.5-10 micrometers), fine particles (diameter less than 2.5 micrometers) and ultrafine particles (less than 0.1 micrometre in diameter). For the purposes of the present invention, it is not necessary to set any strict limits on the size of the particles, N, so in this text we generally speak of particles, N referring to particles floating in the air, the concentration of which is to be measured in each case. Typically, however, respirable particles, i.e., particles less than about 10 micrometers in diameter, are most important. & Figure 1 shows a known principle for measuring the particle concentration of air 3. The laser diode 101 S 35 produces a laser beam 102 which is aimed at the target area

103. An air flow is provided through the target area 103

104, with which the particles to be measured travel. The air flow can be produced, for example, by a fan. There are light detector or detectors 105 around the target area 103 in one or more directions. At least a portion of this laser light is detected as a light pulse by the light detectors 105. When the amount of flowing air per unit time is known and the light pulses detected over a period of time are calculated, the particle concentration in the air can be calculated.

The laser diode 101 may be mounted on a circuit board 106, the other components of which transmit to the laser diode 101 the operating voltage required by it. The circuit board may be housed in a housing 107 which acts as a shield and support structure. In order to limit the scattered light generated in the production and orientation of the laser beam, the light traps shown in the partitions 108 and 109 in Fig. 1 can be used.

There are problems with the prior art arrangement, especially if it is desired to be small in size and battery-powered, and to keep its manufacturing costs reasonable. One consequence of the small size requirement is that the elimination of stray light becomes more and more complex: the closer the light detector or detectors are to the light source, the more difficult it is to prevent stray light from passing through. The requirement to keep costs low has the same effect, as cheap lasers and cheap O 30 optics generally produce more stray light than expensive connectors. Battery usage means, among other things, that little electrical energy is available, making it more difficult to produce sufficient light in the target area, and at the same time there is little power available to the electronics used to detect light pulses. S Blower motors with encountered airflow

are also problematic for the adequacy of battery charging. Prior art publications that address at least somewhat similar issues include at least JP H11248628 A, JP H11248629 A, JP 2016090350 A, WO 2018032802 A1, WO 2015151502 A1, JP 2000235000 A, EP 2706516 A1, and U.S. Pat. No. 3,515,482 A.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for measuring the particle content of air so that the apparatus is small in size and inexpensive to manufacture and consumes little electricity. It is also an object of the invention that the device can be easily integrated into a larger unit, which may also have other measuring devices, so that synergy is obtained between the parts of the unit.

The objects of the invention are achieved by incorporating into the device the features of the appended independent claim.

The device according to the invention has a laser source for producing and directing laser light to the target area, an air duct for directing the measured air flow through the target area and a light detector located next to the target area for detecting light pulses generated by scattering the air 30 target areas. The device has its light between the laser source and the N target area to reduce stray light E entering the target area. The light box has at least two partitions S substantially transverse to the direction of travel of the servo, and each of them has an opening for allowing a limited amount of laser light to pass through said N partition. The partitions are part of the same piece made in one piece, so that each opening is bounded by a uniform portion of this piece made in one piece over the entire circumference of the opening.

According to an embodiment, said unitary body is produced by injection molding.

This is an advantage because injection molding is an advantageous and sufficiently dimensionally accurate manufacturing method for the production of large quantities.

According to an embodiment, said at least two partitions include a first partition and a second partition located respectively from the laser source to the target area.

The aperture in the first partition wall is conical in cross-section along the optical axis of the laser light so as to be larger on the laser source side than in the target area side, and the aperture in the second partition wall is conical in cross-section along the optical axis of the laser light so that it is larger on the target area side than on the laser source side.

This is an advantage because the design of the openings effectively limits the propagation of stray light and because the openings in the partitions can be made using suitable cores in the mold.

According to an embodiment, said at least two partitions further comprise a third partition between the laser source and the first partition.

The aperture in the third partition wall is conical in cross-section along the optical axis of the laser light, so that it is larger N from the laser source side than from the target area side.

This has the same advantage as the other two openings. z According to one embodiment, said integral piece forms a holder for the laser source to hold it in a preselected position relative to the target area.

This is an advantage because the laser source S can be mounted in a highly reproducible manner

in devices manufactured in this way and no separate part is required to hold it in place. According to an embodiment, a part of said integral body forms the edge surrounding the active area of said light detector. This is an advantage because the stray light from the sides to the light detector can be effectively limited. According to one embodiment, the distance from the laser source to the center of the target area is between 10 and 20 millimeters. This is an advantage because the appliance can be manufactured to a relatively small size, so that it can be easily integrated into a cooker or other measuring device, for example.

According to an embodiment, the active area of the photodetector is elongated in the direction of the optical axis of the laser light, and the width of the active area in the direction perpendicular to the optical axis of the laser light is less than 4 millimeters, most preferably less than 2 millimeters. This has the advantage that the appliance can be made relatively small, so that it can be easily integrated into, for example, a cooker hood or other measuring device.

According to one embodiment, the device has a circuit board to which its light and light detector are attached and to which other electronic components of the device are also attached. Said unitary unit N has one or more open areas on its side N opposite its circuit board, and O 30 one or more of said other electronic components e are arranged on the circuit board so that they are located at said one or more open areas * between the light wall partitions. . & This has the advantage of keeping the size of the device small, as its components can be packed in a relatively small space.

According to the embodiment, the laser source has a laser diode and optics housed in a common housing. The housing is mechanically supported on said integral piece. This is an advantage because the laser source can be procured as a subcontracting component and integrated into another device easily and accurately. According to an embodiment of said housing, said housing is in the form of a cylinder having a longitudinal axis, and said laser source is arranged to produce said laser light so that the optical axis of the produced laser light coincides with the longitudinal axis of said cylinder. The housing is mechanically supported by a cylindrical recess which is an extension of the light trap in a direction opposite to the direction of the target area. This is an advantage because the laser source holder can be made with the same core, which is also used to shape at least some of the openings in the partitions. Other preferred embodiments are described in the following detailed description with reference to the accompanying drawings.

LIST OF FIGURES Figure 1 shows a prior art device for measuring the concentration of airborne particles, N Figure 2 shows an S light beam according to another embodiment, = Figure 3 shows a light beam according to another embodiment 2, N Figure 4 is a more detailed representation of the structure of an E light beam according to Figure 2, LO Figure 5 shows an S light beam according to an embodiment and the cores used in its manufacture, 2 Fig. 6 shows an alternative design of the opening in the partition wall of the light beam,

Figure 7 shows a device according to an embodiment for measuring the concentration of airborne particles, Figure 8 shows a first intermediate stage of the assembly of the apparatus of Figure 7, Figure 9 shows a second intermediate stage of the assembly of the apparatus of Figure 7, Figure 10 shows the shape and shape of a laser beam, Figure 11 shows some preferred solutions for creating an air duct and sufficient air flow, Figure 12 shows some preferred solutions for creating an adequate air flow, Figure 13 shows an example of connecting a light detector and an amplifier, Figure 14 shows an example of the arrangement of components and ground plane structure , Fig. 15 shows a functional block diagram of an air particle concentration measuring device, and Fig. 16 shows a control circuit according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTS conditions. By dissolution E is meant here that the LO to be measured in the air can contain considerably more impurities S, such as gases, particles and moisture, than in ordinary outdoor or indoor air. It is understood in the invention that the behavior of a population of particles substantially like a gas is significant for the presence and measurement of particles less than about 10 micrometers in diameter. In other words, the particle population tends to diffuse into the ambient air so that the differences in concentration self-level over time. For example, in order to measure the concentration of fine particles in a room or other substantially confined space, it is sufficient to measure a relatively small sample of air, especially if the measured concentration of particles can be expected to change in minutes rather than seconds, or even slower.

This key insight has several implications. First of all, it can be stated that a relatively small air flow is sufficient to make a particle measurement, which does not necessarily require a mechanical blower at all. Secondly, when the air is “dirty”, it also tends to contaminate the structures of the measuring device, which impairs the reliability of the measurement over time - but this disadvantage can also be significantly reduced by keeping the air flow low.

Thirdly, if the air flow is small, it carries quite a few particles as a function of time, despite the dirtiness of the air, so the detection efficiency should be high, i.e. the measurement arrangement should ensure that as much of the flow-carrying particles as possible are reliably detected. Another aspect is that the measurement of a small amount of air should preferably be possible with a small-sized device whose energy consumption is so low that it is possible to make it O-operated even for a long time. The unobtrusive and relatively unrestricted placement of a small device in the room under measurement * is facilitated if any 3 35 communication connections between it and & other devices can be implemented wirelessly.

S The design factor that plays a key role in the size of a Fräs particle measuring device is the

the distance between the two. In order to be able to make it small without scattered light from a laser source interfering with the measurement, the scatter-limiting beam should be efficient and effective. The following is a first look at some of the features of the light box that have been found to be advantageous.

Figure 2 shows a light beam 201 which, if necessary, can be mounted in an air particle concentration measuring device between the laser source and the target area. The purpose of its light is to reduce stray light entering the target area. In Figure 2, the laser source used to produce and direct the laser light to the target area is thought to be located to the rear left. The light detector is thought to be located at the front right so that the target area is above the rectangular railing 202 shown at the end of the body shown in Figure 2. The direction of travel of the laser light (and at the same time its optical axis) is represented by the dotted line 203.

The light box 201 has partitions substantially transverse to the direction of travel of the laser light 203, and each of them has an opening for allowing a limited amount of laser light to pass through said partition. By way of example, the partitions 204, 205 and 206 may be considered here. - N in relation to the direction of travel of the laser light 203. From a manufacturing point of view, it may be advantageous for the partitions as a whole to be plate-shaped, so that it is easy to see how they z are transverse to the direction of travel of the laser light 203. * In an embodiment represented by the light beam shown in Figure 2, the partitions 3 35 204, 205 and 206 are part of the same unitary unit. The part in question can be produced, for example, by injection molding, which is an inexpensive and rapid method of producing large quantities of pieces with a dimensional accuracy sufficient for needs such as the device under consideration here.

There are other possible manufacturing methods, such as 3D printing and machining.

One consequence of the uniform manufacture is that each of the openings in the partitions is delimited by a uniform portion of said integral piece over the entire circumference of the opening.

The significance of the feature described by Fde can be viewed by comparing the light trap of Fig. 2 with the second embodiment shown in Fig. 3, in which the light trap 301 is not made in one piece but is made of the right and left halves to be connected to each other.

In the embodiment of Figure 3, the opening in each partition wall is delimited after the assembly step by two separate portions of the two pieces originally made separately, although they are pressed together during the assembly step.

The halves could also be the upper and lower halves, with the seam crossing each opening in the partition wall being horizontal.

From a manufacturing point of view, it is very difficult or even impossible to make the structure shown in Fig. 3 or at least two parts such that a small amount of stray light does not always leak from the seam to the other side of the partition at the point where the opening edge is sharpest.

In addition, the closer the edge of the aperture of the septum is to the actual laser beam, the more important it is that the shapes of the edge of the aperture are flawless and have no extra burrs or notches.

If its light e consists of two parts as shown in Fig. 3, the passages of the laser beam cannot in practice be completely round, because the halves cannot practically fit together perfectly.

Even a slight defect in shape causes a notch to be applied to the edge of the aperture, which is capable of reflecting unwanted light forward toward the light detector.

This also causes unit performance.

a variation in capability that increases the need for calibration both at the manufacturing stage and possibly at a later age.

From the point of view of limiting stray light, it is advantageous to shape said openings precisely so that each opening has the sharpest possible inner edge; that is, the aperture is not defined by any cylindrical surface that travels even part of the distance directly through the septum in the direction of the optical axis of the laser light.

The reason is that such a cylindrical surface defining the aperture would act as a reflector that would reflect forward light in a direction other than the exact direction of the optical axis.

In order to ensure that the light detector only detects laser light scattering particles in the target area, the light trap should be as effective as possible in preventing any laser light propagating in the non-optical axis from entering the target area and its surroundings.

Figure 4 shows in more detail some exemplary features in the same type of light trap as in Figure 2. Figure 4 follows the practice of technical drawing, in which the same object is depicted from the side (center), bottom (top), top (bottom), right (left). - on the left) and on the left (right). The direction of travel of the laser light is shown by the dotted line 203. The light trap shown in Figure 4 has partitions 204, 205 N and 206 substantially transverse to the direction of travel of the laser light.

All the partitions are part of the same piece, which is made in one piece.

As a consequence, each of said openings is bounded by a unitary portion of said unitary & fabricated body throughout the perimeter of the opening *. 3 35 Here, the partition 205 may be referred to as the first partition and the partition 206 as the second partition.

The terms “first” and “second” are used herein only to allow unambiguous reference. The target area is to the right of the side light and the laser source is to the left, so when these designations are used, the first partition 205 and the second partition 206 are located relative to each other from the laser source to the target area.

The aperture 401 in the first partition 205 is conical in cross-section along the optical axis 203 of the laser light so that it is larger on the laser source side than on the target area side. That is, the innermost, sharp edge 402 of the aperture 401 is in the portion of the aperture 401 that is on the side of the target area. Correspondingly, the aperture 403 in the second partition wall 206 is conical in cross-section along the optical axis 203 of the laser light so that it is larger on the target area side than on the laser source side. That is, the innermost, sharp edge 404 of the aperture 403 is in the portion of the aperture 403 that is on the laser source side. The aperture design described has a beneficial effect on the propagation of scattered light because the conical surface defining the aperture 401 in the first septum 205 tends to reflect back any potential scattered light and because the conical surface defining the aperture 403 in the second septum 20 anything from which it could be reflected. N The light box also most preferably has a roof surface N which delimits it from above, i.e. from the side opposite to the circuit board O 30. Some possibilities for implementing the roof surface are described in more detail below. Due to the small size of the device and the small distances between its * parts, the surface of the ceiling may be important for the design of the light barrier. Reference numeral 405 shows an area which the light detector “sees” in the ceiling of the light trap. The dotted lines illustrate how this area is determined: it is the area of its light in the ceiling,

from which it is possible to draw a straight line through the opening 403 in the second partition 206 into the active area of the light detector. In particular, it would be important to keep this area as dark as possible, ie free of stray light, so that light is not reflected from there to the light detector. The conical design of the opening 401 in the first partition 205 as described above helps to achieve this object, as it is capable of preventing the propagation of stray light towards the ceiling of the light trap between the first partition 205 and the second partition 206.

The orientation of the conical surfaces defining the openings as described above is also of a manufacturing technique, especially if their light is produced by injection molding or another method using a closable mold. Said advantage is illustrated in Figure 5, which shows the same light from the side as in Figure 4 and above the two cores 501 and 502, which could be used inside the injection mold to create the shapes of the inner parts of the light box. For example, the left core 501 has a conical portion 503 which, when injection molded, forms the conical inner surface of the opening 401 in the first septum 205. For example, the right core 502 has a conical portion 504 which, when injection molded, forms the conical inner surface of the opening 403 in the second septum 206.

N The arrows shown in Fig. 5 show how the cores N 501 and 502 are pressed towards each other during the closing step of the injection molding mold so that the ends S of the cores press against each other in the plane of the broken line 505. The directions of the conical surfaces and the other dimensions of the openings in the partitions are chosen so that the turns 501 and 502 can be easily pulled out in the step of opening the injection mold. S It should be noted that the term “conical” does not necessarily mean a straight circular cone, nor is the term used in this mathematical sense, but means that the opening is larger than one surface of the partition wall than the other.

According to the mathematical definition, a cone is a surface whose half-line draws along a closed and non-intersecting curve in the plane so that the end point of the half-line remains in place.

The surfaces delimiting the openings in the partitions are essentially in the shape of a truncated cone, and their edge lines need not be circles and the imaginary line drawn from one edge line to another need not be straight.

Figure 6 shows in detail an alternative design in which the conical surface delimiting the opening 403 in the second partition wall 206 consists of a circular cone-shaped portion 601 and a planar portion 602 intersecting it. adjacent light detector (not shown). Although the planar portion may then also reflect some stray light to the side of the second partition 206 on which the light detector is located, the reflections are directed upward, i.e. away from the light detector.

and are not harmful.

The number of partitions in the light box matters.

The larger the number of partitions, the more obstacles the diffuse light has in its path and the more effectively it is possible to prevent the diffuse light from entering the N target area.

On the other hand, the larger the number of partitions, the more complex and expensive it is to produce light.

In the embodiments e shown in Figs. 406 is conical in cross-section along the optical axis 203 of the laser light so that it is larger on the laser source side than on the target area side. Because the laser source in the embodiments shown in Figures 2-5 is intended to adhere completely to the third septum 204, and since the laser source itself may have the closest light scattering structures, a third septum 206 may not be required. On the other hand, a third septum such as that shown in Figures 2-5 may be useful even in the sense that it accurately determines the location of the end of the laser source relative to its light source.

In any case, it is advantageous if its light is shaped in such a way that it determines exactly how the laser source is positioned both in relation to the structures in the light beam which prevent the propagation of stray light and in relation to the target area. Precise positioning ensures that series-produced equipment gives exactly the same air quality measurement results and avoids errors that could be caused by purely mechanical differences between different equipment units.

In view of the precise positioning of the laser source, the unitary body shown in the light traps of Figures 2-5 forms a holder for the laser source. Here, it is assumed that the laser source has a laser diode and optics housed in a common, preferably cylindrical housing. In the embodiments shown in Figures 2-5, the holder begins flush with the third septum 204 and continues therefrom as a cylindrical recess 407 horizontal to the target area away from the target area. Such a horizontal straight cylindrical recess can be made, for example, by forming a cylindrical portion 506 in the appropriate position of the left core S 501 in Fig. 5. z - 3 35 flush with its central axis, since in this way they create natural holding nails which prevent

from a vertically mounted laser source to move vertically.

In view of the precise mutual arrangement of the parts of the device, the light trap according to Figs. If the substrate is a circuit board, it may be the same circuit board on which the light detector included in the device is mounted. Circuit boards are typically fabricated and components loaded into them, whereby the position of the holes in the circuit board - and thus the light-laser source combination attached to them - relative to the light detector stacked on the circuit board remains very precisely the same from device to device. The principles of the structure of the light trap described above, for their part, help to make it possible to make the device for measuring the concentration of particles in the air, which is described in this description, relatively small. As one example, it can be assumed that the cylindrical housing of the laser source is 3 to 6 millimeters in diameter, preferably 4 millimeters, and 6 to 15 millimeters in length, preferably 10 millimeters. As an extension of the housing, there may be circuit board portions, connectors or other parts at the end opposite to the laser light generating end. In the light trap, the cylindrical recess 407 in which the laser source is mounted corresponds in diameter to the diameter of the cylindrical housing of the laser source, and its length may be 5 to 10 millimeters, preferably 8 to 30 millimeters. Each partition 204, 205, 206 may have a thickness e of 0.5 to 2 millimeters, preferably 1 or 1.5 = millimeters. In the light detector-side terms used above, the second partition 206 may be thicker than the other partitions, for example, so that the other partitions 204 and 205 are 1 mm thick and the second S partition 206 is 1.5 mm thick. In light injection molding, the partitions may be slightly thinned in the direction in which the part of the mold that forms the planar surfaces of the partitions moves when the injection mold is opened. The distances between the partitions from the surface to the surface may be 2 to 6 millimeters, for example such that the distance between the first partition 205 and the second partition 206 is between 4 and 5 millimeters and the distance between the third partition 204 and the first part 204 is 3 to 4 millimeters. riä.

The dimensioning of the openings in the partitions depends on how thick the laser beam produced by the laser source is and how it is desired to be directed at the target area. As an example, the opening 401 in the first partition 205 is 1.5 to 2 millimeters in diameter at the edge 402 and the angle of the side of the conical surface defining it with respect to the direction of travel of the laser light 203 is 25 degrees. As another example, the aperture 403 in the second septum 206 has a minimum diameter of 1.5 to 2 millimeters at the edge 404 and the angle of the side of the conical surface defining it with respect to the direction of travel of the laser light is 20 degrees. If the conical surface delimiting the aperture 403 has a partially planar portion as in Fig. 6, the angle of the planar portion with respect to the direction of travel of the laser light 203 may be smaller, for example, 2 degrees. As a third example, the opening in the third partition wall 204 has a minimum diameter of 2.5 to 3 millimeters, and the angle of the side of the conical surface N bounding it with respect to the direction of travel of the laser light N is 2 degrees. O 30 Figure 7 shows, in the form of a single exploded view S, some parts of a device z for measuring a particle concentration according to an embodiment. The device * has a laser source 701 for producing and directing laser light to the target area. The laser source 701 has a laser diode and optics housed in a common housing 702. In this embodiment, the housing 702 is cylindrical and the laser beam exits through a circular opening 703 at one end of the housing 702. The optical axis of the produced laser light coincides with the longitudinal axis of the cylindrical housing 702. The supply voltage to the laser diode is supplied through conductors 707 visible at the opposite end of the housing 702.

The housing 702 of the laser beam 701 is mechanically supported by its light rod 201, which is a unitary body. The dashed lines indicate how the laser source 701 can be slid longitudinally into place in a cylindrical recess extending in the direction opposite to the target area as an extension of the light trap 201. The exact longitudinal position of the laser source 701 in its holder is determined by sliding it longitudinally so that its end contacts the third septum 204 in the light trap 201.

A light detector 704 is located adjacent to the target area to detect light pulses generated by the airflow particles scattering the laser light in the target area. The device has a circuit board 705 to which its light 201 and light detector 704 are attached and to which other electronic components of the device can also be attached

706. The circuit board 705 normally functions as a mechanical support structure for the components, and the electrical connections required by the components N can also be made on its surface or surfaces (and in the case of the multilayer circuit board also in the intermediate layers) in the usual way. Fig. 7 shows a preferred feature which can be utilized if the integral part forming the light trap 201 has one or more open areas on the side facing the circuit board 705. In this case, one or more of the other electronic components 706 of the device may be located on the circuit board 705 so as to be located between these open areas, located between the partitions in the light trap 201.

This saves circuit board space, as components can also be placed in those areas of the circuit board that are below the light trap 201 in the assembled structure.

In this way, it is advisable to place components that are particularly black in color, since they then act as part of their light by absorbing stray light.

In addition to or instead of the open areas, the side of the light barrier against the circuit board may have recesses that are large enough to accommodate the underlying components.

The device has an air duct for directing the air to be measured as air flow through the target area.

Figure 8 shows an intermediate stage of the assembly in which the laser source 701 is attached to its light beam 201 and the assembly formed thereon is attached to the circuit board 705. To form the air duct, this assembly is connected to a shell portion 801.

In the part of the air duct which is on the extension of the optical axis of the laser beam after the target area, it is good to have the laser beam exit opening 803. 9 shows the next step of the assembly in which the shell part 801 is in place covering the laser source.

The shell portion 801 may be a portion formed solely for the purpose of defining the air passage, or may have other functions.

The N embodiment shown in Figs.

The seam which then remains between the partition wall in the light wall 201 and the roof portion 804 of the shell part 801 does not have the same disadvantage as the seams which intersect each partition wall in this two-part light box.

This is because

that in the structure of Figure 8, the seams are far from the areas where the laser light is at its brightest. If necessary, the light fastness of the joints can be improved by using interlocking shapes that interlock in parts.

The shell portion 801 may also be part of the overall housing of the device so that a portion of the outer shell of the device acts as the shell portion 801 or at least as part of the shell portion.

It is preferable to design the air duct so that it does not contain components mounted on the circuit board 705 that are not desired to be exposed to contaminants such as grease and / or moisture. Fig. 8 shows the lines of the circuit board 705 against which the edges of the hollow portion 802 of the shell part 801 are pressed and the components outside which are thus protected from air contaminants. The portion of the surface of the circuit board 705 between the shaded areas partially defines the air duct, as does the end of the light trap 201 at the light detector side end. Depending on the design of the air duct, other structures of the light trap 201 may also contribute to delimiting the air duct. Figure 10 shows an example of the behavior of laser light in a target area. The figure shows a light detector 704 and a laser beam 1001, the direction of propagation of which is from front to back to right in the figure. The active area of the light detector 704 is the upper surface of the rectangular parallelogram shown in the figure. N Laser beam 1001 is focused. That is, O 30 here assumes that the optics of the laser source include e at least one convex lens, by the nature of which the optics form a focal point * for the laser beam 1001 at a distance f from the laser source. The focal point is not & preferably not completely point-like, but the diameter d of the focused laser beam 35 at the focal point is most preferably chosen to be between 0.2 and 0.5 millimeters. The laser beam near the focal point is thus

is so shaped that the narrowest point of the hourglass is at a distance ff from the laser source and its width is d. The size of the focal length £, i.e. the distance from the laser source to the center of the target area, is 10-20 millimeters, preferably 14 millimeters.

A particle hitting the laser beam scatters la-Servalo in substantially all directions. In order to detect light pulses, it is not necessary to define an exact length in the direction of the laser beam in the target area: the target area includes the entire three-dimensional volume that the laser beam 1001 fills as it passes through the air duct. However, the most effective detection of light pulses is in the portion of this volume perpendicular to the light detector 704, because of this portion, the distance to the light detector is the shortest and the space angle at which the advancing light impinges on the light detector is greatest. In Figure 10, the location of this portion in the longitudinal direction of the laser beam is illustrated by dashed end circles.

It is preferable to position the light detector 704 so that the center of its active region is perpendicularly below the focal point of the laser beam 1001 (X = X in Fig. 10) and the perpendicular distance is as small as possible. References above and below are to be understood only as references to directions in Figure 10. Essentially the same can be said, saying that the shortest distance between the focal point of the laser beam 1001 and the center of the active area of the light detector 704 should be kept as small as possible. In this case, the space angle O 30 covered by the active area e of the light detector 704 as viewed from the focal point of the laser beam 1001 is as large as possible. * The active area of the light detector 704 is preferably elongated in the direction of the optical axis of the laser light (2X> Y in Fig. 10). This feature is advantageous S because the target area itself is elongated: a good compromise between saving circuit board space and light pulse detection efficiency is achieved in the elongated active area of the light detector. The width Y of the active region in the direction perpendicular to the optical axis of the laser light may be less than 4 millimeters, most preferably less than 2 millimeters.

Figure 11 shows parts of an apparatus for measuring the concentration of airborne particles according to an embodiment. The assembly of the device shown in Fig. 11 corresponds to Fig. 8 above so that the shell part is not shown in Fig. 11. The device has a laser source 701 for producing and directing laser light to the target area and an air duct for directing the measured air through the target area. In the embodiment of Fig. 11, the air duct is formed in the same manner as in Fig. 8, i.e., the assembly shown in Fig. 11 is attached to the shell portion (not shown), the edges of a portion of the shell portion pressing against the circuit board 705 at dashed lines.

The beginning and end of the air duct are shown as dashed rectangles. the device also includes a light detector 704 adjacent to the target area to detect light pulses generated by the airflow particles scattering the laser light in the target area.

The device according to the embodiment of Figure 11 further has another electronic component 1101, the N characteristics of which include that it must be brought to a temperature other than ambient temperature in order to operate. As shown in Fig. 11, said electronic component 1101 is located in the air duct Ek (i.e., on the circuit board 705 in the area delimited by the dashed lines) to provide air flow convectively. | | O 35 The fact that electronic component 1101 must be brought to a temperature other than ambient temperature in order for it to function does not mean that it reaches a temperature other than ambient temperature as a by-product or as a result of its normal operation. Thus, this definition does not mean, for example, a mere resistor which heats up as the electric current passes through it, since the resistor normally acts as a resistor even before it heats up. It is a component that must be brought to a temperature other than ambient temperature before it can function as intended. An example of such a component is a metal oxide gas detector which, in order to operate, must be heated significantly above ambient temperature, preferably to 300 degrees Celsius. Another exemplary component that must be brought to a temperature other than ambient temperature in order to operate is a PIN diode or other semiconductor radiation detector that must be cooled below ambient temperature to achieve a sufficient signal-to-noise ratio.

The light detector 704 and the above-mentioned other component 1101 are mounted on the same surface of the circuit board 705, which surface of the circuit board 705 also contributes to delimiting the air duct. This simplifies the structure, as not as many other components or complex designs are needed to delimit the air duct as if it were made up entirely of, for example, the housing part or parts of the device. In order for the convective flow at the photodetector 704 to be as efficient as possible, it is preferable for the photodetector 704 and the other component 1101 N to be located quite close to each other. Their distance, measured in the direction of the channel, can be, for example, less than 20 millimeters, or even less than 10 millimeters. = In order to achieve convective flow, * it is also important how the air duct is oriented & in relation to the local vertical direction. If it is assumed that the other S component providing convective flow is a heated component such as a metal oxide gas detector, it is intended to provide a bottom-up air flow. An example of this type is illustrated in Figure 12, which is a simplified cross-section of an apparatus for measuring the concentration of airborne particles in an embodiment.

The device according to Figure 12 has an outer shell 1201, the design of which is arranged to determine the intended position of the device when installed. In Figure 12, this is done so that the outer shell 1201 has two flat and non-apertured surfaces (top surface and left side surface) which, when mounted, abut two solid horizontal and vertical surfaces. In addition to or instead of this, the outer shell may have, for example, screw holes or other such designs which in practice determine the position in which the device is intended to be in relation to the local vertical when it is installed for normal use. For example, if the appliance is a cooker hood, the installation location and position must be such that the field of view of the optical detector 1202 included in the appliance extends into the area of the hob.

The outer shell 1201 has an air duct inlet 1203 and an outlet 1204. The air duct is shown in Fig. 12 only as a schematically dashed zone within which the light detector 704 and the other component 1101 described above, which must be operated at a temperature other than ambient temperature, remain. In the air duct, next to the light detector 704, there is also a target area for the laser light, which is located towards the viewer from the visible end of the light 201. The air duct can be partially delimited by the surface of the circuit board 705 and z by a part of the outer shell 1201 which acts as a shell part as described above in Figures 7-9. & In the intended position of the device, the outlet opening 3 354 is 1204 higher than the inlet opening 1203 with respect to the local vertical direction.

by the location of the opening 1204, but also partly by the position of the circuit board 705 inside the outer shell 1201.

In the embodiment of Figure 12, a battery or accumulator 1205 or other internal DC voltage source is placed above the diagonally placed circuit board 705 to provide the operating voltage required by the device.

The inlet port 1203, the outlet port 1204, or both may simultaneously be functional openings for the operation of some other portion of the device.

This means that the sole purpose of this opening is not to direct the air to be measured into or out of the air duct, but that the opening has another purpose involving another part of the device which is not directly involved in measuring the particulate concentration of the air.

Such another device may be, for example, an optical detector, whereby another purpose of the aperture in question may be to orient and / or limit the field of view of the optical detector.

The other device may also be, for example, a loudspeaker or a microphone, in which case the other purpose of the opening in question may be to allow unobstructed sound.

Another example of another device is a switch for use by a user, the second purpose of which is to allow the movement of a moving part which forms at least part of said switch.

Figure 11 further shows the preferred feature that the air duct forms bends on either side of the light detector N 704 to reduce stray light entering the light detector from outside the device.

In the embodiment of FIG. , but the bends in the air duct can be designed in a way that best combines

their purpose and the manufacture of parts of the

its ease.

In addition to diffused light, the design of air duct openings and bends can reduce the effect of random air movements outside the device on the measurement, as the user's breathing or other random air movement cannot directly affect the air flow in the target area.

As a further feature, Figure 11 shows a reflective wall 1102 in an air duct, the purpose of which is the same as reducing the effect of bends, i.e., scattered light from outside, and / or random air currents in the target area.

One or more outgoing laser beam reflectors 1103 may also be formed on the circuit board, housing parts and / or other suitable component, the function of which is to reflect the laser light entering the target area in a direction from which its subsequent reflections and scattering do not easily find their way back to the light detector.

The reflector 1103 is preferably located so far from the laser beam exit aperture in the air duct (see reference numeral 803 in Fig. 8) that it is not possible to draw a straight line from the surface of the reflector through the laser beam exit aperture that would hit the light detector.

This ensures that the laser light self-reflecting from the reflector 1103 does not interfere with the particle measurement.

The structures of the light trap can also contribute to delimiting the air duct and prevent the passage of external stray light to the light detector.

An example of this is the N rectangular handrail 202 seen in Figures 0-30 2-5, 7-8 and 11 as part of the end of the light bar facing the target area e and forming the edge surrounding the active area of the light detector z.

Thanks to the handrail 202, the light detector is as if in a pit, so that any scattered light propagating along the air duct does not hit it very easily.

At the same time, the handrail 202 can reduce the fouling of the S light detector and improve the efficiency of particle detection because, on the one hand, it controls the air.

the airflow locally slightly higher past the light detector and on the other hand lowers the air duct locally focusing the airflow on the laser beam in the target area.

Fig. 13 is a simplified circuit diagram showing a method known per se for using a light detector to detect light pulses. In the circuit of Figure 13, the light detector is a photodiode 1301 biased in the blocking direction. The bias voltage is derived from the voltage source 1302 and its level can be changed and / or regulated by the regulator 1303. There is a preamplifier 1304 between the cathode of the photodiode 1301 and the positive terminal of the bias voltage 134. The cathode of the photodiode 1301 is connected to the inverting input of the differential amplifier 1305.

Connected to the non-inverting input of the differential amplifier 1305 is a reference potential produced from the bias voltage by the potentiometer 1306. When no light impinges on the photodiode 1301, no current passes through it and the potential of the inverting input of the differential amplifier 1305 is substantially the same as the bias voltage potential. When light hits the photodiode 1301, current begins to flow through it, which is observed as a decrease in potential at the inverting input of the differential amplifier 1305. If the potential of the inverting input drops lower than the reference potential, the output of the differential amplifier 1305 produces a positive signal. From its duration and shape it is possible to deduce how much light hit the photodiode N 1301 and for how long this light was detectable.

S When applied to a particle measuring device, the operating principle described above Ek means that the particle concentration in the air can be calculated from the number of output pulses * produced by the amplifier. In addition, from the shape and duration of a single pulse, it is possible to draw conclusions about the size and shape of the particle from which the pulse was generated. Organized

There may be several amplifiers connected to the same light detector, each of which has its own reference potential.

In this way, different amplifiers can be tuned to detect particles of different sizes, so that the relative amounts of output pulses they produce indicate the distribution of particles of different sizes in the studied air.

In addition to the example shown in Fig. 13, there are other ways known per se in which a photosensitive component can be connected as part of a detector circuit so that it can be used to detect light pulses.

When applied to particle measurement, they have in common that the initial signal produced by the photosensitive component (the increase in the blocking conductivity of photodiode 1301 in Figure 13 and the resulting decrease in potential at the cathode of photodiode 1301) is small and must be significantly amplified to an assessment of the duration would be possible.

For the evaluation to be reliable, the amplifier arrangement (shown in simplified form in Figure 13 by the differential amplifier 1305) must be as low noise as possible and the arrangement must be isolated as effectively as possible from electromagnetic interference elsewhere.

Isolation from other sources of interference in the same device, ie shorter (component-specific) EMC protection may require special protective structures, especially if the device contains N other components which, by their nature, produce a large amount of electromagnetic interference.

Such other components include, for example, relays, wireless transceivers, and switch power supplies.

Protective structures used are, for example, ground plane structures formed on the circuit board & electrically conductive EMC-S enclosures to be soldered or glued to the surface of the circuit board.

A ground plane structure is defined here as a system connected to the local ground potential,

a set of conductor areas formed on the surfaces and / or intermediate layers of the circuit board, which is formed specifically for the needs of the components to be protected by the ground plane structure in question and is not only part of the general ground plane of the device. the general ground plane of the device is typically the most uniform conductor area formed on a particular surface or intermediate layer of the circuit board that is common to all or a substantial portion of the components attached to the same circuit board, such as all analog components or all digital components. The efficiency of the ground plane structure in EMC protection is generally better the larger the area of the circuit board it can cover around the components to be protected and, in the case of a multilayer circuit board, the more layers of the circuit board it can extend.

One way in which a device for measuring the concentration of airborne particles can be made small and still maintain the good EMC protection of its key components and the straightforwardness of the design and manufacturing technique is to place two or more such key components in the area covered by the common ground plane structure. If these key components are used at different times, they do not interfere with each other, but each of them can operate the ground structure as if it were only part of the N component's own FMC protection. Fig. 14 shows an example of such an embodiment. Figure 14 shows a part of an apparatus for measuring the concentration of airborne particles. The device has a laser source 701 for producing and directing laser light to a target area marked with an image & dashed ellipse. The device has a circuit board 705 and 3 35 air ducts for directing the air to be measured as an air flow through the target area. The part of the circuit board 705 delimiting the air duct is located in a narrow line.

between the lanes indicated. The laser light forms a laser beam 1001 focused on the target area. In order to reduce stray light, the device may have its own light, the structures of which are exemplified in Figure 14 by a partition 204.

Adjacent to the target area is a light detector 704 for detecting light pulses generated by the airborne particles scattering laser light in the target area. An amplifier is connected to the light detector 704 to amplify electrical signals corresponding to the light pulses detected by the light detector. In Fig. 14, the amplifier consists of a plurality of amplifier elements included in the integrated circuits 1401 and 1402. The photodetector 704 and the components 1401 and 1402 including the amplifier are mounted on the circuit board 705.

The device has a microprocessor not shown in Figure 14 because it is located on the circuit board 705 outside the area shown in Figure 14. The microprocessor is used to perform the programmable functions of the device. In addition, the device has a communication circuit 1403 separate from the microprocessor, mounted on the circuit board 705, and connected to the microprocessor to maintain external communication links between the microprocessor and other devices outside the device. For example, the communication circuit 1403 may be equipped to maintain wireless connections such as Wi-Fi connections in accordance with the IEEE 802.11 standard N, and the antenna 1404 may be connected thereto. on circuit board 705 in the area covered by a common ground plane structure 1405 for reducing electrical interference. The ground plane structure 1405 is schematically marked in Figure 14 with a slash. The width of the circuit board 705 may be relatively small, for example 15 to 20 millimeters, and in the direction determined by the plane of the entire circuit board of the ground plane structure 1405, it may be less than 20 x 20 millimeters.

If the circuit board 705 is a multilayer circuit board, one of the surfaces of which is covered by the Leine ground plane of the device, the ground plane structure 1405 may be located inside the multilayer circuit board, separated by at least one insulating layer from the general ground plane.

The communication circuit 1403 and the amplifier are both components, for the undisturbed and efficient operation of which it is advantageous that the ground plane structure 1405 used for their EMC protection is large in relation to the size of the components and - in the case of a multilayer circuit board - covers parts of the circuit board.

The operation of the antenna 1404 of the communication circuit 1403 may also benefit from the largest and most efficient ground plane structure possible near it.

On the other hand, the communication circuit 1403 and the amplifier are components that, when operating, could produce electrical interference to each other.

In particular, the communication circuit 1403 is a component whose normal operation can produce so much interference that it would be impossible to use an amplifier to amplify electrical signals corresponding to the smallest pulse of light detected by the light detector 704 with sufficient accuracy.

Therefore, it is preferred that the microprocessor be programmed to arrange the operation of the amplifier and the communication circuit 1403 at different times.

The individual measurement time during which the micro-processor is programmed to put the amplifier into operation and the communication circuit out of operation should be chosen so that it is possible to obtain meaningful measurement results within it.

The assessment of this must z take into account the amount of air flow * through the target area and the assumed particle concentrations that the device is intended to measure.

If the cross-sectional area of the air duct is not more than a few square meters and the primary source of airflow is convection, a single measurement time may be

for example 1-10 seconds.

Said convection can be produced, for example, by placing another electronic component in the air duct, which must be brought to a temperature other than ambient temperature in order to function.

The fact that the common ground plane structure covers both the amplifier and the communication circuit 1403 and that they are on the same surface of the circuit board 705 means that it is possible to make the ground plane structure larger than if either of these components had only its own ground plane structure.

The relatively large ground plane structure means that a fairly effective EMC protection is achieved with the ground plane structure alone.

An adequate level of EMC protection can be achieved even if the device does not have an electrically conductive EMC shield on the surface of the circuit board covering either the amplifier and the communication circuit 1403. This has a cost advantage and a manufacturing advantage because the device's component list and assembly process can be completely excluded EMC enclosure and its attachment to the circuit board.

In addition to or instead of the above, other advantages can be achieved by mutually scheduling the operation of the various parts of the device.

As an example, a control circuit for processing amplified electrical signals may be considered, which in the schematic representation of Fig. 14 may be a circuit N 1406. Like the communication circuit 1403, the control circuit 1406 may be a circuit separate from but connected to the O 30 microprocessor performing programmable functions.

In one aspect, the control circuit 1406 Ek may be a simple * low power circuit compared to a microprocessor; According to another aspect, the operation of the microprocessor may be of little significance while the particle sampling itself is on.

Thus, the microprocessor may be programmed to enter a power saving mode for at least the largest ditch of the time during which the control circuit 1406 is configured to operate, i.e., to process the amplified electrical signals produced by the amplifier described above. Most of the time means more than 50% of that time. Figure 15 illustrates an exemplary functional grouping of device components. Electric power distribution lines are depicted by thicker lines and control and signal connections by thinner lines. In the arrangement of Figure 15, the source of electrical power used by all parts of the device is a battery 1501. The operating voltages required by the various parts of the device are generated and stabilized using linear regulators, such as linear regulator blocks 1502 and 1503, and / or switch power supplies 1504.

Figure 16 illustrates an exemplary control circuit 1406 that may be used to process amplified electrical signals corresponding to light pulses detected by a light detector. In this example, the control circuit has a plurality of reference circuits 1601, 1602, 1603, each of which is arranged to compare the electrical signals from the amplifier along the input line 1604 to a reference specific to that reference circuit. Each reference circuit is arranged to produce an output signal in response to N indicating that a reference has been reached or exceeded. References are shown symbolically and may refer to, for example, references to the amplitude, duration, shape, or other feature of an amplified signal. Thus, each control circuit essentially examines when the electrical signal from the amplifier satisfies a certain condition, 3 35 and produces a corresponding output signal. The reference circuits 1601-1603 may be, for example, analog reference circuits which require only a very small amount of electricity.

but it is also possible to use digital comparators.

The control circuit of Figure 16 has one or more counters, shown at 1605, 1606 and 1607. The counters are connected to receive and count the output signals of the reference circuits.

Thus, by examining the values accumulated in the counters 1605-1607, it is possible to detect how many times each reference circuit has detected features corresponding to its own reference in the electrical signal coming from the amplifier.

In the functional distribution of Figure 15, the power consumption of the microprocessor 1505 during operation may be several milliamperes, such as 5 milliamps.

If the control circuit 1406 contains only the necessary functions, its power consumption during operation may be much less than one milliampere, such as 150 microamperes.

The single measurement time during which the control circuit 1406 is in operation and most of which the microprocessor 1505 spends in the power saving mode may be between 1 and 10 seconds in length.

The time that the microprocessor 1505 then wakes up from power saving mode to read the counters 1605-1607, process and store the data it reads, and possibly communicate through the communication circuit 1403 may be only seconds or even less than a second.

Thus, with such alternation, it is possible to save a significant amount of electrical energy, N which means that the electrical energy O 30 provided by the battery 1501 is sufficient for significantly longer than if the microprocessor 1505 S were continuously operating. z As noted above, if the device has * one or more switch power supplies 1504 to provide operating voltages to at least a portion of the electronic components of the device, it is preferable to program the microprocessor 1505 to provide operation of this or these switch power supplies for a different time.

1406 activities. This ensures that the high frequency electromagnetic interference naturally produced by the switch power supplies does not interfere with the operation of the amplifier 1506 and the control circuit 1406, which are tuned to measure the presence of even the smallest particles in the test air. A device in which a particulate concentration measurement as described is carried out can be, for example, a cooker guard, ie a device in accordance with EN 50615, which monitors the safe use of the hob and, if necessary, gives an alarm and / or switches off the hob or part to prevent danger. In stove guard operation, measuring the particle concentration in the air can improve the reliability and versatility of the operation, because the measurement of the particle concentration in the air provides a lot of information that is not reported by more traditional detector types such as infrared thermometers. Other possible applications are, for example, the general measurement of indoor air quality in homes or public spaces, the monitoring of airborne particulate matter at the construction or renovation site during construction, the measurement of outdoor airborne content such as pollen content, and so on.

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Claims (10)

PATENT CLAIMS An apparatus for measuring the concentration of airborne particles, the apparatus comprising: - a laser source (701) for producing and directing laser light to a target area, generated by the scattering of said laser light in a target area by particles carried by said air flow, and a partition (204, 205, 206) substantially transverse to the direction of travel and an aperture (401, 403, 406) in each of them for passing a limited amount of laser light through said partition, said at least two partitions (204, 205, 206) being part of the same piece, made in one piece so that each of the above - the openings (401, 403, 406) are delimited by a unitary portion of said unitary body about the entire circumference of the opening, and said at least two partitions include a first partition (205) and a second partition (206) located respectively from the laser source (701) to the target area N M N, N characterized in that the aperture (401) e in the first partition wall (205) is conical in cross-section = along the optical axis (203) of the laser light so that it is * larger from the laser source (701) side than from the target area & side , and the aperture (403) in the second partition wall (206) is conical in cross-section along the optical axis (203) of the la-S servalo so as to be larger. pi from the target area side than from the laser source (701) side. Device according to claim 1, characterized in that said integral body is produced by injection molding. Device according to claim 1, characterized in that - said at least two partitions further comprise a third partition wall (204) between said laser source (701) and said first partition wall (205), and - a third partition wall (204) ) is conical in cross-section along the optical axis (203) of the laser light so that it is larger on the laser source (701) side than on the target area side. Device according to any one of the preceding claims, characterized in that said integral body forms a holder for said laser source (701) for holding it in a preselected position relative to said target area. Device according to any one of the preceding claims, characterized in that a part (202) of said integrally formed body forms an edge surrounding the active area of said light detector (704). 2 Device according to one of the preceding claims, characterized in that the distance from said laser source (701) to the center of said target area is between 10 and 20 millimeters. 5 © Device according to one of the preceding claims, characterized in that - the active area of said light detector (704) is elongated in the direction of the optical axis of the laser light, and - the width (Y) of said active area in the direction perpendicular to the optical axis of the laser light is less than 4 millimeters, most preferably less than 2 millimeters. Device according to one of the preceding claims, characterized in that - the device has a circuit board (705) to which said light emitter (201) and light detector (704) are attached and to which other electronic components of the device are additionally attached, said unitary unit has one or more open areas on its side opposite the circuit board (705), and - one or more of said other electronic components (706) are disposed on the circuit board (705) so as to be located at said open area; between the partitions (204, 205, 206). Device according to any one of the preceding claims, characterized in that - said laser source comprises a laser diode and optics housed in a common housing (702), and - said housing (702) is mechanically supported on said integral body. OF Apparatus according to claim 9, characterized in that O - said housing (702) is in the form of a cylinder with e longitudinal axis, z 30 - said laser source (701) is arranged to produce * said laser light so that the op the axial axis coincides with the longitudinal axis of said cylinder, O - said housing (702) is mechanically supported by a cylindrical recess Q as an extension of the light trap (201) in a direction opposite to the direction of the target area. OF OF O N <<Q 00 OF I and m o LO 0 K LO O TU oO OF