FI20195735A1 - Air quality measuring device - Google Patents

Abstract

The apparatus for measuring the particle content in 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 defined as airborne solid particles 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. English sources use the general terms suspended particulate matter (SPM), particulate matter (PM) or particulates, the subspecies of which are coarse particles (diameter 2.5-10 micrometers), fine particles (diameter). less than 2.5 micrometers) and ultrafine particles (diameter less than 0.1 micrometers). For the purposes of the present invention, it is not necessary to set any strict limits on the size of the particles, = so in this text we generally speak of particles, N when referring to particles floating in the air, 3 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 directed at the target area

103. An air flow is arranged 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 in one or more directions around the target area 103. A particle that travels with the air flow 104 to the target area 103 and impinges on the laser beam scatters the laser light around it. 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 protective and supporting structure. In order to limit the stray light generated in the production and orientation of the laser beam, the light traps shown in Figure 1 by the partitions 108 and 109 can be used.

The arrangement according to the prior art has problems, 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 the diffuse light from passing. The requirement to keep costs low has the same effect, as cheap lasers and cheap optics generally produce more stray light than expensive ones. Battery power means, among other things, that little electrical energy is available, which makes it more difficult to produce sufficient light brightness 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 an air flow found in the product

are also problematic for the adequacy of battery charging.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for measuring the particle concentration of air in such a way 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 whole, which may also have other measuring devices, so that synergy is obtained between the parts of the whole.

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 air to be measured as air flow through the target area and a light detector located next to the target area for detecting light pulses generated by air flow scattering laser light in the target area. The device has its light between the laser source and the target area to reduce stray light entering the target area. The light trap has at least two partitions 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 partition. The partitions are part of the same piece, E, which is made in one piece, so that each of the openings LO is bounded by a uniform proportion of this piece made in one piece over the entire circumference of the opening. 2 35 According to one embodiment, said unitary piece is produced by injection molding. This has the advantage that injection molding is an advantageous and sufficiently dimensionally accurate manufacturing method for the production of large quantities of k.

According to the 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 septum is conical in cross-section along the optical axis of the laser light so that it is larger on the laser source side than on the target area side, and the aperture in the second septum 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 has the advantage that the design of the openings effectively limits the propagation of stray light and because the openings in the partitions can be made by using suitable cores in the mold.

According to the 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 on the laser source side than on the target area side. This has the same advantage as the corresponding design of the other two openings.

According to an embodiment, said integral piece forms a holder for the laser source N to hold it in a preselected position relative to the target area. This has the advantage that the laser source S can be mounted in a highly reproducible manner in all devices manufactured in this way and that no separate part is required to hold it in place.

& According to an embodiment of Frä, a part of said 3 35 integral body forms the edge surrounding the active area of said light detector. This is an advantage because the light

scattered light aimed at the sim 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 5 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, for example, a cooker or other measuring device.

According to an embodiment, the active area of the light detector 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 is an advantage because the device can be manufactured to a relatively small size, 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 integral piece has one or more open areas on its side facing the circuit board, and one or more of said other electronic components are arranged on the circuit board so as to be 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 N parts and components can be packed in a relatively small space.

S According to one embodiment, the laser source has a z laser diode and optics housed in a common + housing.

The housing rests mechanically on said integral piece.

This has the advantage that the laser source can be obtained as a subcontracting component and integrated into another device easily and dimensionally.

According to an embodiment, 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 presented in the following detailed description with reference to the accompanying figures.

LIST OF FIGURES Figure 1 shows a prior art device for measuring the concentration of airborne particles, Figure 2 shows a light beam according to one embodiment, Figure 3 shows a light beam according to another embodiment, Figure 4 is a more detailed view of the structure of a light beam according to Figure 2, Figure 5 shows an light beam according to an embodiment and Fig. 6 shows an alternative design of the opening in the partition wall of the light source, Fig. 7 shows a device © for measuring the concentration of airborne particles according to an embodiment, E Fig. 8 shows a first intermediate stage of the assembly of the device according to Fig. 7, S Fig. 9 shows a second intermediate stage of the assembly of the device according to Fig. 7, N Fig. 10 shows the shape and dimensioning aspects of the laser beam, the target area and the light detector,

Fig. 11 shows some preferred solutions for generating an air duct and sufficient airflow, Fig. 12 shows some preferred solutions for generating an adequate airflow, Fig. 13 shows an example of connecting a light detector and an amplifier, Fig. 14 shows an example of the arrangement of components and ground plane structure on a circuit board, Fig. 15 shows a functional block diagram of a device without a particle concentration measuring device, and Fig. 16 shows a control circuit according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION The solutions described in this text are suitable for all types of measurement of airborne particles, but the special features of the solutions are advantageous especially when measuring the concentration of particles smaller than about 10 micrometers in “dirty” conditions. Dirt is meant here that the air to be measured can contain considerably more impurities such as gases, particles and moisture than in normal outdoor or indoor air. It is understood in the invention that the behavior of the particle population in a substantially gaseous manner 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 LO so that the concentration differences self-level over time. For example, in order to measure the fine particulate matter content of air in a room or other substantially restricted space N, it is therefore sufficient to measure a relatively small air sample

even if the measured particle concentration can be expected to change on a schedule of minutes rather than seconds, or even more slowly.

This key insight has several consequences.

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 fan at all.

Secondly, when the air is “dirty”, it also tends to contaminate the structures of the measuring device, which over time impairs the reliability of the measurement - but even this disadvantage can 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 air dirt, so the detection efficiency should be high, i.e. the measurement arrangement should ensure that as much of the particles carried by the flow as possible are also reliably detected.

Another aspect is that it should most preferably be possible to measure a small amount of air with a small device with such a low energy consumption that it is possible to make it run even on battery power for long periods of time.

The unobtrusive and relatively unrestricted placement of a small device in the room under measurement is facilitated if the necessary data transmission connections between it and other devices can be implemented wirelessly. > One of the dimensioning factors that has a central effect on the size of the particle measuring device is the distance between the laser source and the target area.

In order to be able to make S small without the stray light from the laser source interfering with the measurement, the stray light limiting light should be efficient and effective.

In the following & first, some features of the 3 35 light traps found to be advantageous will be considered.

S Figure 2 shows a light beam 201 which, if necessary, can be mounted in an air particle 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 the laser light (and at the same time its optical axis) is represented by the dotted line 203.

The light trap 201 has partitions substantially transverse to the direction of travel of the laser light 203, and each of them has an opening to allow a desired amount of laser light to pass through said partition. By way of example, the partitions 204, 205 and 206 can be considered here. The fact that the partition is substantially transverse to the direction of travel of the laser light 203 can be considered as a feature of the opening in the partition: the closed curve of the inner edge runs in a plane substantially transverse. with respect to the direction of travel of the laser light 203. From a manufacturing point of view, it may be advantageous for the partitions to be plate-shaped in general, so that it is easy to see how they are transverse to the direction of travel of the laser light 203. In an embodiment, one of the representatives of which is the light beam shown in Figure 2, the partitions 204, 205 and 206 are part of the same, unitary piece. The body in question can be produced, for example, by injection molding, which is an inexpensive and rapid method for producing large quantities of pieces with a dimensional accuracy sufficient for needs such as the device z discussed here. There are other possible> manufacturing methods, such as 3D printing & and machining. One consequence of the uniform manufacture 3 35 is that each of the openings in the partitions is delimited by a uniform proportion of said integral piece over the entire circumference of the opening.

The significance of the feature described by Fde can be examined by comparing the light trap according to 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 interconnectable right and left halves.

In the embodiment of Figure 3, even after the assembly step, the opening in each partition wall is delimited 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 top and bottom halves, with the seam crossing each partition opening 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 between the two parts 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 consists of two parts, as shown in Figure 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 the shape causes a notch at the edge of the aperture which is liable to reflect unwanted light forward towards the light detector.

This also causes a variation in performance per piece, which increases the need for calibration both at the S manufacturing stage and possibly at a later Ek age. * From the point of view of limiting stray light, it is advantageous & to shape said apertures precisely so that each aperture has the sharpest possible inner edge; that is, the aperture is not defined by any cylindrical surface that would pass 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 light advancing in a direction other than exactly in the 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 non-optical axis propagating laser light 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 (right). - on the left) and on the left (right). The direction of travel of the laser light is indicated by a dotted line 203. The light trap shown in Figure 4 has partitions 204, 205 and 206 substantially transverse to the direction of travel of the laser light. Each partition has an aperture to allow a limited amount of laser light to pass through that partition. All partitions are part of the same piece, which is made in one piece. As a consequence, each of said openings is delimited by a unitary part of said unitary unit made of the entire circumference of the opening.

The partition 205 may be referred to herein as the first partition and the partition 206 as the second partition. The terms “first” and “second” are used herein to provide unambiguous reference. The target area is to the right of its side light b and the laser source is to the left, so that, using these designations, the first partition 205 and the second partition 206 are located relative to each other 3 35 in order from the laser source to the target area.

The aperture 401 in the first partition 205 is conical in cross section taken 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.

Accordingly, the aperture 403 in the second partition 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 any scattered light backwards and because the conical surface defining the aperture 403 in the second septum 206 provides as little laser light as possible. anything from which it could be reflected.

Most preferably, the light trap also has a roof surface which defines it from above, i.e. from the side opposite to the circuit board.

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 ceiling surface can be important for the design of the light trap.

Reference numeral 405 denotes 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, S from which it is possible to draw a straight line through the opening 403 in the second partition wall 206 to the active area of the light detector *.

In particular, it would be important to keep this area as dark as possible, i.e. free of scattered light, so that light is not reflected from there to the light detector.

In order to achieve this objective, the first

the conical opening 401 in the partition 205

design as described above because it is capable of preventing stray light from advancing toward the roof of the light trap between the first 205 and second partitions 206.

Orientation of the conical surfaces delimiting the openings as described above also has a manufacturing technical advantage, 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, two cores 501 and 502, which could be used inside the injection mold to create the shapes of the inner parts of the light trap. 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 partition 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. The arrows shown in Fig. 5 show how the cores 501 and 502 are pressed towards each other during the closing step of the injection mold so that the% ends of the cores press against each other in line with the dashed line 505. The orientations of the conical surfaces and the other dimensioning of the openings in the partitions are chosen so that the threads 501 and 502 can be easily pulled out at the stage when the injection mold is opened. N It should be noted that the term “conical” does not necessarily mean a straight circular cone, and the term S is not used in this context in its mathematical z 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 3 35 drawn by a hemisphere as it moves along a closed and non-intersecting curve in the plane S so that the end point of the hemisphere remains stationary.

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 206 consists of a circular cone-shaped portion 601 and a planar portion 602 intersecting it. The planar portion 602 is on the side of the opening closest to the second partition 206 adjacent light detector (not shown). Although the planar portion may then reflect some stray light also to the side of the second partition 206 on which the light detector is located, the reflections are directed upwards, i.e. away from the light detector, and are not detrimental.

The number of partitions in the light box matters.

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

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

In the embodiments shown in Figures 2-5, the light trap has three partitions: in addition to the first partition 205 and the second partition 206 mentioned above, there is a third partition 204 between the laser source and the first partition 205, the aperture 406 being the optical axis of the laser light. 203 is conical in cross-section so that it is larger on the laser source side than on the S side of the target area.

Since the laser source in the embodiments Ek shown in Figures 2-5 is intended to be completely attached to the third partition wall 204 and since the laser source itself may have the very closest light scattering structures, a third partition wall 206 is not necessarily required.

S On the other hand, a third intermediate, as shown in Figures 2-5,

a wall can be useful even just in the sense that

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 as to determine precisely how the laser source is positioned both in the light-emitting structures 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.

With a view to the exact 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 position shown in the figures away from the target area.

Such a horizontal cylindrical recess can be made, for example, by forming a cylindrical portion 506 at an appropriate position on the left core 501 of Fig. 5. in this way, N are formed into natural holding nails which prevent the laser source, which is mounted at an angle, from moving vertically in place. z For further precise positioning of the parts of the device *, the light trap shown in Figures 4 and 5 has fastening pins 409 through which it can be fastened to recesses or holes in a flat surface, such as a circuit board.

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.

The circuit boards are manufactured and the components 1 are typically loaded on them as robot work, whereby the position of the holes to be made in the circuit board - and thus also the light-laser source combination ---— attached to them in relation to the light detector mounted on the circuit board is fixed.

cause very closely the same device from one individual to another.

The principles of light trap structure described above, for their part, help to make the device referred to in this description for measuring the particle content of air 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 may be 5 to 10 millimeters in length, preferably 8 millimeters.

Each partition 204, 205, 206 may be 0.5 to 2 millimeters thick, preferably 1 or 1.5 millimeters.

On the light detector side, as 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 millimeter thick and the second> partition 206 is 1.5 millimeters thick.

In a light trap made by injection molding, the partitions 3 30 may be slightly thinned in the direction in which, when the injection molding mold S is opened, the part of the mold which z forms the planar surfaces of the partitions moves.

The distances between the partitions * measured from the surface to the surface may be 2-6 millimeters, for example such that the distance S between its first partition 205 and the second 206 is 4-5 millimeters and the distance between the third 204 and the first 204 and the first 204.

the distance between its partition 204 is 3-4 millimeters.

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 aim it at the target area.

As an example, the aperture 401 in the first partition 205 is 1.5-2 millimeters in diameter at the edge 402 and the side angle 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 a side angle of the conical surface defining it with respect to the direction of travel of the laser light 203.

If the conical surface delimiting the opening 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 204 has a minimum diameter of 2.5 to 3 millimeters and the side angle of the conical surface defining it with respect to the direction of travel of the laser light 203 is 2 degrees.

Figure 7 shows in the form of a single exploded view some parts of a device according to an embodiment for measuring the particle concentration.

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 la- Ek servalo coincides with the longitudinal axis of the cylindrical housing 702a.

The supply voltage is supplied to the laser diode & via wires 704 visible at the opposite end of the housing 702.

S The housing 702 of the laser beam 701 is mechanically supported on its light rod 201, which is an integral piece. The dashed lines indicate how the laser source 701 can be slid longitudinally into place in a cylindrical recess extending from the light trap 201 in a direction opposite to the direction of the target area. The exact longitudinal position of the laser source 701 in its holder is determined by the fact that it is pushed in its longitudinal direction so far that its end contacts the third partition wall 204 in the light trap 201.

The device has a light detector 704 located adjacent to the target area to detect light pulses generated by the particles carried by the air flow 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 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.

Figure 7 shows a preferred feature that can be utilized if the unitary body forming the light trap 201 has one or more open areas on the side facing its circuit board 705. In this case, one or more of the other electronic components 706 of the device can be located on the circuit board 705 so as to be at these open areas 3, located between the partitions in the light trap 201 S. This saves the circuit space of the circuit board, since the components can also be placed * in those areas of the circuit board which in the assembled structure fall below the light trap 201. In this way, it is advisable to place components which are particularly black in color, since they then contribute in part to their light by absorbing stray light. In addition to or instead of open areas, the side of the light trap 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 an 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 rod 201 and the assembly formed by these is attached to the circuit board 705.

To form the air duct, this assembly is connected to the shell part 801, a hollow part 802 of which partly delimits the air duct. In the part of the air duct which is in the extension of the optical axis of the laser beam after the target area, it is good to have a 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, light trap and light detector.

The shell portion 801 may be a portion formed solely for the purpose of defining the air passage, or may have other functions. In the embodiment shown in Figures 7-9, an example of another task is shown in that the so-called roof portion 804 belonging to the shell part 801 presses on the light trap 201 and closes the compartments between the light wall partitions from above. The seam which then remains between the partition wall in the light trap 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 trap shown in Fig. 3. This is because, in the structure of Fig. 8, the seams are far from the S areas where the laser light is at its brightest. If necessary, the light fastness of the seams can be improved * by using interlocking counter-shapes.

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

It is preferable to design the air duct so that it does not contain components mounted on the circuit board 705 which do not want to be exposed to contaminants accompanying the air to be measured, such as grease and / or moisture. Fig. 8 shows in line the parts 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 points 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 triangle shown in the figure.

The laser beam 1001 is focused. In other words, it is assumed here that the optics of the laser source include 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 2 is preferably not completely point-like, but the diameter d of the focused laser beam N at the focal point is most preferably chosen to be between 0.2 and 0.5 millimeters. Thus, near the focal point, the laser beam is in the shape of an hourglass such that the narrowest point of the hourglass is * at a distance f from the laser source and its width is d. & The magnitude of the focal length £, i.e. the distance from the laser source to the center of the deal 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, at its most effective, the detection of light pulses is in that portion of this volume which is 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 propagating light impinges on the light detector is greatest. In Figure 10, the arrangement 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 perpendicular to 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 herein only as references to directions in Figure 10. Substantially the same can be said by saying that the shortest distance between the focus 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 covered by the active area of the light detector 704 as seen from the focal point of the laser beam 1001 is as large as possible.

> The active area of the light detector 704 is preferably elongate 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 long compromise of the active area * of the light detector achieves a good compromise between saving circuit board space and light pulse detection efficiency. 3 35 The width Y of the active region in the direction perpendicular to the optical axis S 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 device of the assembly 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 generating 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 way as in Fig. 8, i.e. so that the assembly shown in Fig. 11 is attached to the shell part (not shown), the edges of a part of the shell part pressing against the circuit board 705 at dashed lines. The beginning and end of the air duct are shown as lined rectangles. the device also includes a light detector 704 adjacent to the target area for detecting light pulses generated by particles carried by the air flow scattering laser light in the target area.

The device according to the embodiment of Figure 11 further comprises another electronic component 1101, which is characterized in that it must be brought to a temperature other than ambient temperature in order to function. According to Fig. 11, said electronic component 1101 is placed in the air duct of the device> (i.e. on the circuit board 705 in the area delimited by the broken lines) to provide air flow convectively. S The fact that electronic component 1101 must be brought to a temperature other than ambient temperature in order to function does not mean that it reaches a temperature other than ambient temperature or as a by-product of normal operation. Thus, this definition does not mean, for example, a mere resistance that heats up as the electric current passes through it.

pi, because the resistor acts quite normally as a resistor even before it warms 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 significantly heated to 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, because 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, a shell 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 to place the photodetector 704 and the other component 1101 quite close together. Their distance, measured in the direction of the air duct, can be, for example, less than 20 millimeters, or even less than 10 millimeters.

> In order to achieve convective flow, N also matters how the air duct is oriented 3 30 with respect to the local vertical direction. If it is assumed that the other component z providing convective flow is a heated component such as a metal-> dioxide 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 one 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 against 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 stove guard, the installation location and position must be such that the field of view of the optical detector 1202 included in the appliance faces the area of the cooker.

The outer shell 1201 has an air duct inlet 1203 and an outlet 1204. The air duct is shown in Figure 12 only as a schematically lined 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, operate.

In the air duct, next to the light detector 704, there is also a laser light target area located from the visible end of the light beam 201 towards the viewer.

The air ducts can be partly delimited by the surface of the circuit board 705 as well as by some 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 Ek 1204 is higher than the inlet opening 1203 relative to the local vertical direction *. The direction of the air duct & can be obtained by arranging the inlet opening 1203 and the outlet opening 354, but also partly on 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 spaced circuit board 705 to provide the operating voltage required by the device. The inlet 1203, the outlet 1204, or both may at the same time be functional openings for the operation of some other part contained in 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 other device may be, for example, an optical detector, whereby another purpose of the aperture in question may be to direct 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 second purpose of the opening in question may be to allow the unobstructed flow of sound. Yet 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 movable part which forms at least part of said switch.

Figure 11 further shows the advantageous feature that the air duct forms bends on either side of the light detector 704 to reduce stray light entering the light detector from outside the device. In the embodiment of Figure 11, the bends are located symmetrically on either side of the light detector 704 so that the air duct rotates 90 degrees toward the laser source 3 immediately adjacent to the light detector 704 and again S 90 degrees to the laser source, but this is by no means necessary but the air duct bends can be * designed in a way that best combines their purpose with the ease of manufacture of the parts of the device. In addition to the diffused light, the design of the air duct openings S and bends can reduce the effect of random air movements outside the device on the measurement, since 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. diffused 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 scatterings do not easily find their way back to the light detector. It is preferable for the reflector 1103 to be 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 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 rectangular handrail 202 seen in Figures 2-5, 7-8 and 11 as part of the end of the light trap = facing the target area and forming the edge surrounding the N active area of the light detector. Due to the handrail 202, the light detector is as if in a pit, so that any stray light propagating along the air duct S does not hit it very easily. At the same time, the handrail 202 can reduce fouling of the light detector and improve the efficiency of particle detection because it directs the airflow locally from slightly higher past the light detector and lowers the air duct locally by 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 a regulator 1303. There is a preamplifier 1304 between the cathode of the photodiode 1301 and the positive terminal of the bias voltage 134. 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 strikes 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 1301 and for how long this light was detectable.

N When applied to a particle measuring device, the operating principle described above 3 30 means that the particle concentration in the air can be calculated from the number of output pulses produced by the amplifier S in time unit z. In addition, it is possible to draw conclusions about the shape and duration of a single pulse from the size and shape of the particle from which the pulse was generated. The arrangement may have 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, whereby 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 Figure 13, there are other ways known per se in which a photosensitive component can be integrated into 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 the photodiode 1301 in Fig. 13 and the resulting decrease in potential at the cathode of the photodiode 1301) is small and must be significantly amplified to an assessment of the duration would be possible.

In order for the evaluation to be reliable, the amplifier arrangement (shown simply 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 includes other components which, by their nature, produce a lot of electromagnetic interference.

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

Protective structures include, for example, ground plane structures formed on the circuit board Ek and electrically conductive EMC & shields to be soldered or glued to the surface of the circuit board.

By ground plane structure is meant here 3 35 those formed on the surfaces and / or intermediate layers of the circuit board S connected to the local ground potential.

the whole of the wired areas formed by the

specifically for the needs of the components to be protected by that ground plane structure and is not only part of the overall ground plane of the equipment. The general ground plane of a device is typically the most uniform conductor area formed on a particular surface of a circuit board or a particular intermediate layer that is common to all or a significant portion of components attached to the same circuit board, such as all analog components or all digital components. The efficiency of a ground plane structure in EMC shielding is generally better the larger the area of the circuit board it can cover around the components to be shielded 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 compact while still maintaining the good EMC protection of its key components and the straightforwardness of the structure and manufacturing technique is to place two or more such key components in a 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 in question as if it were only part of the component's own EMC protection.

Figure 14 shows an example of such an embodiment. Figure 14 shows a part of an apparatus N for measuring the concentration of airborne particles. The device has a laser source 701 for producing laser light and directing S to a target area marked with a dashed line ellipse in Fig. Ek. The device has a circuit board 705 and an * air duct for directing the air to be measured as air flow through the target area. The part of the circuit board 705 delimiting the air duct 3 35 is located between the narrow lined bands. The laser light forms a laser beam 1001 focused on the target area. Diffuse

To reduce light, the device may have its own light, the structures of which are exemplified by a partition 204 in Figure 14. A light detector 704 is located adjacent to the target area to detect light pulses generated by airflow 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 Figure 14, the amplifier consists of a plurality of amplifier elements included in integrated circuits 1401 and 1402. The light detector 704 and the amplifier include components 1401 and 140? is mounted on a 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.

A 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, for maintaining external communication connections between the microprocessor and other devices outside the device.

For example, the communication circuit 1403 may be provided to maintain wireless connections such as Wi-Fi connections in accordance with the IEEE 802.11 standard, and may be connected to an antenna 1404. = The communication circuit 1403 and the amplifier (i.e., amplifier components 1401 and 1402) are located on the circuit board 705 in the area covered by the 1405 ECE ground plane structure common to them for the reduction of 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 15-20 millimeters, and the size S of the ground plane structure 1405 in the direction determined by the plane of the circuit board may be less than 20 x 20 millimeters.

If the circuit board 705 is a multilayer circuit board, most of the surface of which is covered by the Leine ground plane of the device, the ground plane structure 704 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 smooth 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 light pulses 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 communication circuit 1403 at different times.

It is advisable to select a single measurement time during which the microprocessor is programmed to put the amplifier in operation and the communication circuit out of operation so that it is possible to obtain N meaningful measurement results during it.

In assessing this, the amount of air flow S passing through the target area and the assumed particle concentrations that the device is intended to measure must be taken into account.

If the cross-sectional area of the air duct is at most only a few square meters and the primary source of airflow is convection, the individual measurement time can 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. A sufficient level of EMC protection can be achieved even if the device does not have an electrically conductive EMC shield on the circuit board covering both 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 omitted. EMC shield and its attachment to the circuit board. In addition to or instead of that described by Fde, other advantages can be achieved by mutually scheduling the operation of different 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 include a circuit

1406. Like the communication circuit 1403, the control circuit 1406 may be separate from, but connected to, the microprocessor performing the programmable functions of the device. In one aspect, the control circuit 1406 3 30 may be a simple S and low power consumption circuit compared to the microprocessor; According to another aspect, the operation of the microprocessor may * be of little significance while the particle measurement is on. Thus, the microprocessor may be programmed to enter a power saving mode for at least S of the largest ditch of the time during which the control circuit 1406 is arranged to operate, i.e., to process the amplified electrical signals produced by the amplifier described above. Most of a certain time means more than 50% of that time.

Figure 15 illustrates an exemplary functional grouping of device components. Electrical 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 the 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 amplified by 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 the comparison 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 the amplified signal. Thus, each control circuit essentially examines when the electrical signal from the amplifier z satisfies a certain condition, + and produces a corresponding output signal. The comparator circuits 1601-1603 can be, for example, analog comparator circuits which require only a very small electrical power to operate, but the use of digital comparator circuits is also possible.

The control circuit of Figure 16 has one or more counters, indicated by reference numerals 1605, 1606 and 1607. The counters are connected to receive the output signals of the reference circuits and to count their number. 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 save 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 significant electrical energy, which means that the electrical energy provided by the battery 1501 is significantly longer than if the N microprocessor 1505 were continuously operating. As already stated above, if the device has one or more switch power supplies 1504 to supply operating voltages to at least some of the electronic components of the device, the microprocessor 1505 is & preferably programmed to arrange the operation of this or these switch power supplies for a different period of time in the control circuit 1406. activities. This ensures that the high levels of inherent power generated by switch mode power supplies

electromagnetic interference 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 particle concentration measurement of air is performed as described can be, for example, a cooker guard, i.e. a device according to EN 50615, whose function is to monitor the safe use of the hob and, if necessary, give an alarm and / or switch off the hob or part to prevent danger. In stove guard operation, measuring the particle concentration of 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 more traditional detector types such as infrared thermometers do not. Other possible applications include, for example, general measurement of indoor air quality in homes or public spaces, monitoring of airborne particle concentration at a construction or renovation site during construction, measurement of outdoor air particle content such as pollen content, and so on.

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Claims (11)

PATENT CLAIMS An apparatus for measuring the concentration of airborne particles, comprising: - a laser source for producing and directing laser light to a target area, - an air duct for directing the air to be measured as airflow through the target area, - a light detector adjacent to the target area for detecting light pulses airborne particles scattering said laser light in the target area, and - their light between said laser source and said target area to reduce stray light passing into the target area, the light jet having at least two partitions substantially transversely transverse to said laser light path and laser light to pass through said partition, characterized in that said at least two partitions are part of the same body, made integrally so that each of said openings is bounded by a uniform portion of the entire circumference of the opening s said unitary article. Device according to claim 1, characterized in that said integral piece is produced by injection molding. &> Device according to claim 1 or 2, characterized in that © 30 - said at least two partitions comprise E a first partition wall and a second partition wall silo distributed in this order from the laser source towards the target S region, 2 - in the first partition wall the aperture is conical in cross-section along the optical axis of the laser light N 35 so as to be larger on the laser source side than on the target area side, and - the aperture in the second partition is conical in cross-section along the optical axis of the laser light so as to be larger than the laser source side . Device according to claim 3, characterized in that - said at least two partitions further comprise a third partition between said laser source and said first partition, and - the opening in the third partition is conical in cross-section along the optical axis of the laser light, thus that it is larger on the laser source 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 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 of said integral body forms an edge surrounding the active area of said light detector. Device according to one of the preceding claims, characterized in that the distance from said laser source to the center of said target area is between 2 and 20 millimeters. © © Device according to any one of the preceding claims, characterized in that To) 30 - the active area of said light detector is elongated in the direction of the optical axis of the laser light and 2 - the width of said active area in the direction perpendicular to the optical N axis of the laser light is less than 4 millimeters, most preferably less than 2 millimeters. Device according to any one of the preceding claims, characterized in that - the device has a circuit board to which said light and light detector are attached and to which other electronic components of the device are additionally attached, - said integral piece has on its side opposite the circuit board one or more open areas, and - one or more of said other electronic components are arranged on a circuit board so as to be located at said one or more open areas between said partitions. Device according to any one of the preceding claims, characterized in that - said laser source has a laser diode and optics housed in a common housing, and - said housing is mechanically supported on said integral body. Device according to claim 10, characterized in that - said housing is in the form of a cylinder with a longitudinal axis, - said laser source is arranged to produce said laser light so that the optical N axis of the produced laser light coincides with the longitudinal axis of said cylinder, said housing is mechanically supported by a cylindrical O-recess extending as a light trap in the direction = 30 opposite to the direction of the target area. a & 3 &