EP3985631B1 - Optical smoke detector - Google Patents

Description

The present invention relates to an optical smoke detector.

Typically, an optical smoke detector comprises an optical detection chamber equipped with an LED (Light-Emitting Diode) and a photoelectric detector positioned in the chamber so as not to receive any direct light from the LED. Indeed, the operating principle of the optical detector is based on the diffusion by smoke particles of the light emitted by the LED. For example, in the event of a fire, smoke particles will enter the optical chamber via openings made in the walls of said chamber. The beam of light emitted by the LED is configured to interact with these smoke particles so as to be diffused into the optical chamber. The photoelectric detector is for its part configured and positioned to capture at least part of this scattered light, the detection of this scattered light triggering an alarm.

A problem with optical smoke detectors is linked to their aging. Indeed, over time, two phenomena can disrupt smoke detection: on the one hand, the aging of the LED which alters the intensity of the light beam emitted, and on the other hand the presence of dust which accumulates in the optical detection chamber and disrupts or prevents smoke detection. Both phenomena reduce the intensity of scattered light that can reach the photoelectric detector, preventing it from reaching a predefined intensity threshold which is configured to trigger the alarm.

Different solutions have been proposed in order to reduce or eliminate the effects of aging of the optical detector. For example, in order to estimate the pollution of the optical chamber by dust, it was proposed to measure, in the absence smoke, the signal emitted by the photoelectric detector when the LED is activated. Such a solution has proven to be unsatisfactory in the real conditions of use of the optical smoke detector. Indeed, the dust which lodges on the photodetector and/or the emitting LED results in a reduction in the light power (received or emitted respectively), while the dust located in the rest of the optical chamber tends to increase the light power received by the photodetector, so that the combination of this reduction and increase does not make it possible to detect with certainty the presence of dust, the increase/decrease phenomena being able to compensate for each other. A solution, based on the use of two light sources and two photodetectors, in which one of the two light sources is configured to emit light towards the interior of an optical detection chamber by passing through a dust-proof net has been proposed. In US 5,247,283 A . Another solution is to clean the smoke detector regularly. The cost of this cleaning operation is not negligible. Furthermore, it is not possible to know in advance, ie before opening the detection chamber, whether or not the latter is clogged with dust. Furthermore, this solution does not resolve the problem of LED aging: the decrease over time in the light intensity emitted by the LED is difficult to predict, and it is therefore not possible to predict with certainty how much moment an LED needs to be replaced. This leads in particular to replacement of detectors while they are still perfectly functional, or on the contrary, when their performance has already fallen below a critical threshold.

An aim of the present invention is to propose an optical smoke detector which makes it possible to resolve the aforementioned problem, in particular by detecting any disturbance which could come from dust and/or the aging of the LED and which could disrupt the detection of smoke particles.

For this purpose, the present invention provides an optical smoke detector as described by the independent claim. Further advantages of the invention are set forth in the dependent claims.

• une chambre optique de détection comprenant au moins une ouverture pour permettre à des particules de fumées de pénétrer dans ladite chambre optique ;
• au moins une source lumineuse, préférentiellement deux sources lumineuses, par exemple montées dans une unique LED bicolore, chaque source lumineuse étant configurée pour émettre un faisceau de lumière dans ladite chambre optique, la lumière d'au moins un, préférentiellement de chacun, desdits faisceaux de lumière étant apte à être diffusée par lesdites particules de fumée lorsque ces dernières sont présentes dans la chambre optique de détection. Le faisceau de lumière de chaque source lumineuse est préférentiellement dirigé, ou aligné optique-ment, avec un centre de détection;
• une première unité de détection comprenant au moins un détecteur photoélectrique (également appelé ci-après « premier photodétecteur »), ladite première unité de détection étant configurée pour détecter ladite lumière diffusée par les particules de fumée dans ladite chambre optique. Ladite première unité de détection est de plus configurée pour que le premier photodétecteur ne reçoive aucune lumière directe de chacune desdites sources lumineuses, i.e. qu'il soit libre d'une illumination directe par chacune desdites sources lumineuses. En particulier, ladite première unité de détection comprend ou définit une surface de collection de la lumière et est configurée pour définir dans ladite chambre optique une zone de détection. La surface de collection peut être la surface d'un objet, par exemple une lentille, ou une surface géométrique, i.e. un ensemble de points définissant à l'intérieur de la chambre optique une portion finie de l'espace, ladite surface de collection étant définie ou placée dans ladite chambre à une position libre d'une illumination directe par une ou toute source lumineuse de ladite chambre optique. Ladite zone de détection est définie de la manière suivante : une lumière directe dirigée, depuis une position située dans la zone de détection, vers ladite surface de collection, sera détectée par ledit premier photodétecteur après avoir traversé ladite surface de collection, alors qu'une lumière directe dirigée, depuis une position située hors de ladite zone de détection, vers ladite surface de collection, ne sera pas détectée par ledit premier photodétecteur. En d'autres termes, la zone de détection correspond à une zone tridimensionnelle (ou volume) dans la chambre optique caractérisée en ce que la lumière diffusée par les particules de fumée dans cette zone pourra être détectée par le premier photodétecteur, alors que la lumière diffusée par des particules situées hors de cette zone ne sera pas détectée. Préférentiellement, chaque source lumineuse est placée en dehors de ladite zone de détection;
• une seconde unité de détection comprenant au moins un détecteur photoélectrique (appelé ci-après le « second photodétecteur »), ladite seconde unité étant configurée pour que le second photodétecteur reçoive directement la lumière émise par au moins une desdites sources lumineuses- ci-après appelée la première source lumineuse -, préférentiellement par chacune desdites sources lumineuses. Le second photodétecteur est situé préférentiellement dans la chambre optique à une position libre d'une perturbation de la détection de la lumière diffusée par la première unité de détection, i.e. typiquement en dehors de ladite zone de détection. La seconde unité de détection est en particulier caractérisée en ce qu'elle comprend ou définit également une surface de collection et une zone de détection, ladite surface de collection étant placée ou définie dans la chambre optique à une position où la lumière émise par ladite première source lumineuse, ou par chacune desdites sources lumineuses, l'atteint directement. Préférentiellement, le second photodétecteur, ou plus précisément ladite surface de collection, est positionné(e) au plus proche de ladite zone de détection de la première unité de détection, i.e. à une limite extérieure de ladite zone de détection de la première unité (par limite extérieure il est fait référence à une position dudit second détecteur ou de ladite surface de collection hors de ladite zone de détection, mais aussi proche que possible de ladite zone de détection);
• une unité de contrôle du vieillissement du détecteur optique de fumée, connectée à ladite seconde unité de détection, ladite unité de contrôle étant configurée pour contrôler/piloter au moins une, en particulier ladite première source lumineuse, préférentiellement chacune, des sources lumineuses du détecteur optique de façon à ce que chaque source lumineuse contrôlée par l'unité de contrôle (notamment ladite première source lumineuse) émette, par exemple temporairement, et optionnellement périodiquement, un faisceau de lumière. Préférentiellement, l'unité de contrôle contrôle lesdites sources lumineuses de façon à ce que les faisceaux de lumière émis par une pluralité de sources lumineuses soient émis en alternance les uns avec les autres. Préférentiellement, l'unité de contrôle est apte à déterminer une absence de particules de fumées dans la chambre optique afin que chaque faisceau émis par une source lumineuse contrôlée par ladite unité de contrôle dans le but de détecter un vieillissement de la LED et/ou une présence de poussière soit émis uniquement lorsque la chambre optique est libre de toutes particules de fumée. Préférentiellement, les faisceaux de lumière émis par une pluralité de sources lumineuses pilotées par l'unité de contrôle sont émis de façon à être décalés temporellement les uns avec les autres, afin que deux sources lumineuses n'émettent jamais au même instant leur faisceau respectif de lumière. Le contrôle/pilotage par l'unité de contrôle permet notamment à cette dernière de définir pour chaque source lumineuse contrôlée l'instant (ou temps) T marquant le début d'une émission d'un faisceau de lumière et la durée D de ladite émission. En d'autres termes, l'unité de contrôle est apte à allumer et éteindre chacune des sources lumineuses qu'elle contrôle, la source lumineuse étant allumée au temps T correspondant au début de l'émission du faisceau de lumière et éteinte au temps T + D correspondant à la fin de l'émission du faisceau lumineux. L'unité de contrôle est de plus configurée pour recevoir, en réponse au faisceau émis par au moins une desdites sources lumineuses qu'elle contrôle, par exemple en réponse au faisceau émis par ladite première source lumineuse, préférentiellement en réponse à chaque faisceau de lumière émis par ladite première source lumineuse, un signal (ci-après appelé « premier signal » pour le distinguer d'un autre signal reçu) délivré par le second photodétecteur, et pour détecter à partir dudit premier signal et d'au moins un second signal généré par le détecteur optique par photo-détection (i.e. par un de ses photodétecteurs), une présence de poussières dans la chambre optique et/ou une diminution (i.e. vieillissement) de l'intensité de la lumière directe émise par la première source lumineuse. Avantageusement, l'unité de contrôle selon l'invention est capable de distinguer, à partir dudit premier signal et dudit second signal généré par le détecteur optique par photo-détection (i.e. par un de ses photodétecteurs), une présence de poussières dans la chambre optique d'une diminution (i.e. vieillissement) de l'intensité de la lumière directe émise par la première source lumineuse. Ledit second signal selon l'invention est délivré par un des photodétecteurs équipant le détecteur optique, par exemple par le second photodétecteur ou par le premier photodétecteur. Préférentiellement, ladite unité de contrôle est de plus configurée pour délivrer un signal d'alarme destiné à signaler ladite présence et/ou diminution. Préférentiellement, un premier signal d'alarme est destiné à signaler la présence de poussière et un second signal d'alarme est destiné à signaler un remplacement de la source lumineuse pour laquelle une diminution d'intensité a été détectée.

The present invention thus provides an optical smoke detector comprising:

• an optical detection chamber comprising at least one opening to allow smoke particles to enter said optical chamber;
• at least one light source, preferably two light sources, for example mounted in a single two-color LED, each light source being configured to emit a beam of light in said optical chamber, the light of at least one, preferably of each, of said beams of light being capable of being diffused by said smoke particles when the latter are present in the optical detection chamber. The light beam from each light source is preferentially directed, or optically aligned, with a detection center;
• a first detection unit comprising at least one photoelectric detector (also called hereinafter “first photodetector”), said first detection unit being configured to detect said light scattered by the smoke particles in said optical chamber. Said first detection unit is further configured so that the first photodetector does not receive any direct light from each of said light sources, ie it is free from direct illumination by each of said light sources. In particular, said first detection unit comprises or defines a light collection surface and is configured to define a detection zone in said optical chamber. The collection surface can be the surface of an object, for example a lens, or a geometric surface, ie a set of points defining inside the optical chamber a finite portion of space, said collection surface being defined or placed in said chamber in a position free from direct illumination by one or any light source of said optical chamber. Said detection zone is defined as follows: a direct light directed, from a position located in the detection zone, towards said collection surface, will be detected by said first photodetector after passing through said collection surface, while a direct light directed, from a position located outside said detection zone, towards said collection surface, will not be detected by said first photodetector. In other words, the detection zone corresponds to a three-dimensional zone (or volume) in the optical chamber characterized in that the light scattered by the smoke particles in this zone can be detected by the first photodetector, while the light scattered by particles located outside this area will not be detected. Preferably, each light source is placed outside said detection zone;
• a second detection unit comprising at least one photoelectric detector (hereinafter called the "second photodetector"), said second unit being configured so that the second photodetector directly receives the light emitted by at least one of said light sources - hereinafter called the first light source -, preferably by each of said light sources. The second photodetector is preferably located in the optical chamber at a position free from disturbance of the detection of the light scattered by the first detection unit, ie typically outside said detection zone. The second detection unit is in particular characterized in that it also comprises or defines a collection surface and a detection zone, said surface of collection being placed or defined in the optical chamber at a position where the light emitted by said first light source, or by each of said light sources, reaches it directly. Preferably, the second photodetector, or more precisely said collection surface, is positioned as close as possible to said detection zone of the first detection unit, ie at an outer limit of said detection zone of the first unit (for example outer limit reference is made to a position of said second detector or said collection surface outside said detection zone, but as close as possible to said detection zone);
• a unit for controlling the aging of the optical smoke detector, connected to said second detection unit, said control unit being configured to control/control at least one, in particular said first light source, preferably each, of the light sources of the optical detector so that each light source controlled by the control unit (in particular said first light source) emits, for example temporarily, and optionally periodically, a beam of light. Preferably, the control unit controls said light sources so that the beams of light emitted by a plurality of light sources are emitted alternately with each other. Preferably, the control unit is capable of determining an absence of smoke particles in the optical chamber so that each beam emitted by a light source controlled by said control unit with the aim of detecting aging of the LED and/or a presence of dust is emitted only when the optical chamber is free of all smoke particles. Preferably, the light beams emitted by a plurality of light sources controlled by the control unit are emitted so as to be temporally offset from each other with the others, so that two light sources never emit their respective beams of light at the same instant. The control/piloting by the control unit allows the latter in particular to define for each controlled light source the instant (or time) T marking the start of an emission of a beam of light and the duration D of said emission . In other words, the control unit is capable of turning each of the light sources it controls on and off, the light source being turned on at time T corresponding to the start of the emission of the light beam and turned off at time T + D corresponding to the end of the emission of the light beam. The control unit is further configured to receive, in response to the beam emitted by at least one of said light sources that it controls, for example in response to the beam emitted by said first light source, preferably in response to each beam of light emitted by said first light source, a signal (hereinafter called “first signal” to distinguish it from another signal received) delivered by the second photodetector, and to detect from said first signal and at least one second signal generated by the optical detector by photo-detection (ie by one of its photodetectors), a presence of dust in the optical chamber and/or a reduction (ie aging) in the intensity of the direct light emitted by the first light source. Advantageously, the control unit according to the invention is capable of distinguishing, from said first signal and said second signal generated by the optical detector by photo-detection (ie by one of its photodetectors), a presence of dust in the room optical of a reduction (ie aging) of the intensity of the direct light emitted by the first light source. Said second signal according to the invention is delivered by one of the photodetectors equipping the optical detector, for example by the second photodetector or by the first photodetector. Preferably, said control unit is further configured to deliver an alarm signal intended to signal said presence and/or reduction. Preferably, a first alarm signal is intended to signal the presence of dust and a second alarm signal is intended to signal a replacement of the light source for which a reduction in intensity has been detected.

According to the present invention, the control unit is configured to calculate a first difference and a second difference, the first difference being the difference between a value obtained for said first signal from a measurement of the latter by the control unit. control and a first reference value, and the second difference being the difference between a value obtained for said second signal from a measurement of the latter by the control unit and a second reference value, and to detect said presence of dust in the optical chamber and/or said aging of the light source from said differences. Said values obtained for said first and second signals are for example RMS values measured for the respective signals by said control unit. The reference values for said first and second signals are for example calibration values or nominal values recorded in a memory of the control unit. In order to detect the presence of dust in the optical chamber and/or an aging of the first light source, the control unit is preferably configured to compare a first ratio with a second ratio, said first ratio being equal to the value of the first difference divided by said first reference value and the second ratio being equal to the value of said second difference divided by said second reference value. Alternatively, said first ratio may be equal to the absolute value of the first
difference divided by said first reference value and the second ratio can be
equal to the absolute value of said second difference divided by said second reference value.

Depending on the embodiment of the invention, the interpretation by the control unit of the result of said comparison of the first report with the second report may be different, as may the method of detecting aging or presence of dust from the first and second difference.

For example, according to a first embodiment in the absence of smoke detection, the second signal is delivered by the first photodetector in response to said emission of the light beam by said first light source. In this case, if the value of the first difference is less than a first predefined threshold value (for example, less than 0), while the value of the second difference is less than a second predefined threshold value, then the unit of control is configured to signal aging of the first light source. On the other hand, if the value of the first difference is less than said first predefined threshold value and the value of the second difference is greater than a third predefined threshold value, then the control unit is configured to signal the presence of dust in the optical chamber. Preferably, the third predefined threshold value is greater than the second predefined threshold value. Indeed, for the same light source, the temporal comparison by the control unit of the values of said first signal with the first reference value makes it possible to detect a variation in the light emitted by the light source and directly received by the second photodetector. For example and alternatively, if the absolute value of the first difference is greater than another first predefined threshold value (which is equal to the absolute value of said first predefined threshold value), while the absolute value of the second difference is less than another second predefined threshold value, then the control unit is configured to signal aging of the first light source, while if the absolute value of the first difference is greater than said other first predefined threshold value and the absolute value of the second difference is greater than said other second predefined threshold value, then the control unit is configured to signal the presence of dust in the optical chamber.

In other words, a reduction in the light intensity, and therefore in the value of the first signal measured by the control unit, may indicate aging of the light source or the presence of dust, the distinction between aging and the presence dust being done via the second signal. To this end, each value measured by the control unit for said first signal is preferably stored in a memory of the control unit. Preferably, as long as the difference between the first reference value measured for example for a beam emitted at a time t ₀ or at a time t _j or averaged for several beams emitted in a time interval [t _j -δ; t _j ] and each of the values measured for beams emitted at respective times t _i (with in particular t ₀ being an initial time corresponding for example to the calibration of the device, with t _i > t _j > t0, and the period Δt separating t _i from t _j being predefined, for example constant, and δ being a time parameter used to define the time interval during which the beams will be taken into consideration for the calculation of the averaged reference value) remains in an interval of predefined values, then no alarm is triggered by the control unit.

• la valeur dudit second signal obtenue pour le(s) faisceau(x) qui a(ont) généré la(les) différence(s) se situant en dehors dudit intervalle et
• ladite seconde valeur de référence, qui correspond par exemple à la valeur nominale dudit second signal mesurée au temps t0 ou au temps t_j.

As soon as one, or preferably a predefined number of differences obtained by measuring temporally consecutive values, is located outside said interval, then the control unit determines a temporal variation of said second signal by measuring the difference between

• the value of said second signal obtained for the beam(s) which generated the difference(s) lying outside said interval and
• said second reference value, which corresponds for example to the nominal value of said second signal measured at time t0 or at time t _j .

If this temporal variation, i.e. the second difference, is less than the second threshold value, then the control unit will signal an aging of the first light source, and otherwise, a presence of dust.

Preferably, a processor of the control unit can be configured to periodically compare said values measured for said first and second signals with respectively said first and second threshold value in order to determine, by means of said first and second differences, the temporal variations of the light intensity measured by the first and second photodetector.

According to another embodiment, the optical detector comprises at least a second light source and is characterized in that the second signal is delivered by the second photodetector in response to an emission of a beam of light by said second light source, said emission by the second light source and said emission by the first light source being preferentially temporally offset and separated from each other (ie the control unit is configured to keep each light source on during successive time intervals which do not do not overlap with the successive time intervals for switching on the other light sources). According to this other embodiment, the control unit is configured to determine if the first light source has suffered a loss of light power greater than a predefined threshold, ie if said first difference is less than said first threshold value. If so, the control unit is then configured to determine and report the presence of dust if the absolute value of the difference between the first gear and the second gear is smaller than a fourth predefined threshold value and to determine and signal aging of the first light source if the absolute value of this difference is greater than a fifth predefined threshold value.

Preferably, said first and/or second detection unit comprises a waveguide. The waveguide is configured to guide the light from said collection surface to the photodetector (for example to the first photodetector when the waveguide equips the first detection unit, and/or to the second photodetector when the waveguide equips the second detection unit), the photodetector then being located outside said optical chamber. This embodiment notably saves space and reduces the noise of the signals delivered by the photodetector. This also makes it possible to reduce the disturbances in the detection zone which would be due to the mounting of the second photodetector in the optical chamber, the second photodetector thus being preferentially mounted outside the optical chamber and the waveguide configured to guide the light from the inside the optical chamber to the second photodetector.

Figure 1

illustration schématique d'un détecteur optique de fumée selon l'invention, vu de dessus ;

Figure 2

vue latérale schématique du détecteur optique selon figure 1 ;

Figure 3

illustration schématique d'un autre mode de réalisation d'un détecteur optique selon l'invention ; et

Figure 4

vue latérale d'un détecteur optique de fumée comprenant un guide d'onde réalisé selon l'invention.

Various aspects, advantages and characteristics of the invention will now be described in more detail with reference to the following accompanying figures, for which identical references are used for identical or similar elements/components:

Figure 1

schematic illustration of an optical smoke detector according to the invention, seen from above;

Figure 2

schematic side view of the optical detector according to figure 1 ;

Figure 3

schematic illustration of another embodiment of an optical detector according to the invention; And

Figure 4

side view of an optical smoke detector comprising a waveguide produced according to the invention.

There figure 1 schematically presents an optical smoke detector 1 according to the invention, seen from above. There figure 2 presents a schematic side view of the optical detector 1 presented in Fig. 1 and seen from section plane BB.

This optical smoke detector 1 comprises an optical detection chamber 11, at least one light source 12, for example a first light source 121 and a second light source 122, a first detection unit 13, and a second detection unit 14. According to a preferred embodiment, the first light source 121 and the second light source 122 are located in the same electronic component, for example in a two-color LED.

As illustrated in Fig. 2 , the optical chamber 11 comprises one or more openings 111, for example lateral, configured to allow smoke particles to enter the interior of the optical chamber 11, for example in the event of a fire. The optical chamber 11 is thus preferably produced in the form of a closed box comprising one or more of said openings 111. According to known embodiments, these openings are configured to allow smoke particles to penetrate, while preventing external light from entering. penetrate into the optical chamber 11 and disrupt the detection of said smoke particles. Also, according to known embodiments, the interior of the optical chamber 11 is configured to prevent light of each of the light sources is reflected and/or diffused by an internal wall of the optical chamber 11 in the direction of said first detection unit 13, or more precisely in the direction of a collection surface A1 of said first collection unit 13. To this end, the internal walls of said optical chamber 11 may comprise a structure/geometry or construction in the form of a labyrinth configured to prevent reflection and/or diffusion of light from the wall towards the first photodetector 13.

The light sources, such as the first and second light sources 121, 122, may be light-emitting diodes usually called “LEDs”. Said light sources 12 may also include a polychromatic light source whose emission spectrum covers several wavelengths. Each light source can be configured to emit radiation at one or more, preferably two, different wavelengths, for example 940 nm and 455 nm, each LED emitting for example at a different wavelength, for example alternately. . In all cases, the optical smoke detector 1 comprises at least one light source 12 emitting radiation at a wavelength capable of being diffused and/or reflected by the smoke particles when the latter are present in the optical chamber 11 The radiation from the light source 12, for example from said first and second light source 121, 122, is emitted in the form of a directed beam of light, in the optical chamber. The light beam from at least one, preferably each of said light sources 12, is directed towards a detection center C. Preferably, the optical axis of each of said light sources 12 is aligned with said detection center C.

The first detection unit 13 and the second detection unit 14 each comprise a photoelectric detector, respectively called the first photodetector 131 and the second photodetector 141. When one of the light sources 12 illuminates, by means of its beam of light, smoke particles present in the optical chamber 11, these particles diffuse and/or reflect the incident light in said optical chamber 11 and the first detection unit 13 is configured to detect this scattered and/or reflected light. Preferably, said first photodetector 131 has an optical axis configured to be directed towards or aligned with said detection center C. The first detection unit 13 is configured so that the first photodetector 131 is free from any direct illumination from each of said light sources 12. The configuration of the optical chamber and/or of said first detection unit 13 is such that said first photodetector 131 cannot be reached by direct light from each of the light sources. In other words, the first photodetector 131 is configured and/or positioned to only indirectly receive the light emitted by each of said light sources 12: it is configured not to measure any flux of light directly emitted by said light sources, but only a indirect light, ie diffused or reflected by the smoke particles inside the optical chamber. To this end, the collection surface A1 defines the single passage/opening allowing light to reach the first photodetector 131, this collection surface A1 being located in an area of the optical chamber 11 free from any direct illumination by each of the sources luminous 12.

As illustrated in Fig. 2 , the optical smoke detector 1 according to the invention further comprises a unit 15 for controlling the aging of said optical detector 1 configured to signal, by means of an alarm signal, eg light and/or sound, a decrease in the light intensity of one of said light sources 12 and/or a presence of dust in said optical chamber 11. This control unit 15 is connected on the one hand to each of said light sources 12 in order to control/control the emission of said beam of light from the latter, and on the other hand to the first and the second detection unit so as to receive from said first and second photodetector signals (electrical current or voltage) generated by the absorption of light by the photodetector. The control unit 15 is in particular configured to control said light sources 12 so that a single beam of light is emitted in the optical chamber at each instant, ie at each time t. The beams of light emitted inside the optical chamber 11 are thus preferably emitted alternately, whether for the same light source emitting for example at least two beams each at a different wavelength, or for all light beams emitted by all the light sources 12. In particular, the control unit 11 controls each light source so that only one beam of light is emitted at a time in the optical chamber 11. For example , the control unit 11 controls at least one two-color LED, so that one of the two diodes composing the two-color LED emits a beam alternately, ie never both at the same time.

Said first detection unit 13 comprises said light collection surface A1 and is configured to define a detection zone Z1 in said optical chamber. Said surface A1 is for example a surface of a lens 132 intended to collimate on the first photodetector 131 the light scattered/reflected in the optical chamber 11, this surface A1 receiving the incident light from the optical chamber and directing it towards the first photodetector 131. Said detection zone Z1 is a three-dimensional zone included in the optical chamber 11 and for which a light scattered or reflected in the direction of said surface A1 will reach the first photodetector 131 to generate a signal which can be used, according to the present invention, to detect aging or the presence of dust in the optical chamber 11. This detection zone Z1 depends on the characteristics optics of the first detection unit 13 and the optical chamber 11, such as for example the focal length of the lens 132, etc., as well as technical characteristics of the first photodetector 131. These characteristics are well known to those skilled in the art. This detection zone Z1 is typically defined symmetrically around the optical axis of the first detection unit 13 and therefore includes the detection center C aligned with said optical axis.

The second detection unit 14, and in particular said second photodetector 141, are configured as well as positioned to measure a direct light flux emitted by one, preferably each, of said light sources 12. For example, said second detection unit 14 comprises a surface A2 for collecting the direct light emitted by the light sources 12, this surface A2 being positioned in the optical chamber 11 so as to be illuminated directly by each of said light sources 12, while being outside said detection zone Z1 so as not to disturb the measurement by the first photodetector 131 of the flux of diffused/reflected light. Said second detection unit 14 is configured to transmit the flow of direct light collected/received by said collection surface A2 to said second photodetector 141, the latter being configured to generate a signal, called first signal S1, which is a function of said flow of light. direct light received by said A2 collection surface. Such a first signal S1 is thus generated for each beam of light received by the second photodetector 141. Preferably, the collection surface A2 is positioned as close as possible to the detection zone Z1, for example at its outer limit, i.e. without being located inside said detection zone Z1.

For example and as illustrated in Figure 1 or 2 , said second photodetector 141 can be positioned directly in the optical chamber 11, preferably as close as possible to the detection zone Z1 so as to be able to detect only dust likely to disrupt the measurements carried out by the first photodetector 131. Indeed, any positioning further from the detection zone Z1 could result in detection of dust located in the middle. outside the detection zone Z1, but between the latter and the second photodetector 141. This could thus generate a false alarm by said control unit 15. According to the embodiment presented in Figure 2 , the direct light flux is directly absorbed by the second photodetector 141 (considering for example the case of a photodiode), said collection surface A2 then corresponding to the light absorption surface of said second photodetector 141. absorption by the second photodetector 141 of the light flux received by said collection surface A2 is configured to generate said first signal S1, which is then transmitted to the control unit 15.

The embodiment presented in Figure 1 shows a single second detection unit 14 positioned to receive direct light from each of the light sources 12. According to another embodiment presented in Figure 3 , each light source 12 is associated with a second different detection unit 14, so that the optical smoke detector comprises as many light sources 12 as second detection units 14 as described previously, with the difference that in this case, each second detection unit 14 is configured to collect via said collection surface A2 the direct light emitted by one and only one light source 12. Preferably, each light source 12 and each second detection unit 14 all point towards said detection center C , ie have their respective optical axes aligned with the latter. Preferably, each second detection unit 14 comprises a collection surface A2 placed as close as possible to the detection zone Z1.

There Figure 4 presents an embodiment for which said second detection unit 14 comprises a waveguide 145 configured to collect the direct light emitted by one or more light sources 12 and guide it towards the second photodetector 141 in order to generate said first signal S1. In this case, the collection surface A2 corresponds to the surface of the waveguide 145 located in the optical chamber 11 is intended to collect the direct light emitted by one or more of said light sources 12. According to this embodiment, the second photodetector 141 is installed outside said optical chamber 11. Optionally, the same concept can be applied to said first detection unit 13, the latter then also comprising a waveguide with a collection surface A1 located in the optical chamber and a first photodetector 131 located outside the optical chamber 11, the waveguide collecting the light scattered/reflected by the smoke particles via said collection surface A1 and guiding this scattered/reflected light to the first photodetector in order to generate a signal making it possible to measure the flux of light absorbed by the first photodetector 131. In the case of using a waveguide for the first detection unit and/or one or more of said second units of detection, each detection unit comprising such a waveguide preferably has its photodetector installed outside the optical chamber 11 and directly fixed to a printed circuit comprising all or part of the electrical components of the control unit 15.

• la valeur V₁ obtenue ou mesurée par l'unité de contrôle 15 à partir du premier signal S1 pour un faisceau de lumière émis par la source lumineuse à temps t_i, avec
• une première valeur de référence V₁0 qui est par exemple une valeur nominale obtenue et définie pour le second photodétecteur pour un faisceau de lumière émis à un temps initial t₀ par cette même source lumineuse, par exemple lors d'une calibration du détecteur optique, ou une valeur moyenne de précédentes valeurs V₁ obtenues pour des faisceaux de ladite source lumineuse émis dans l'intervalle de temps [t_j-δ ; t_j] avec ti > t_j.

According to the present invention, the control unit 15 is configured to measure, in particular for each light source 12, the flow of direct light collected via the collection surface A2 of the second photodetector 141. Thus, for each second photodetector 141 connected to the control unit 15, the latter receives a first signal S1 delivered by the second photodetector 141 in response to the absorption of a flow of light, and determines from each of the first signals S1 a V1 value, e.g. an RMS value, configured to characterize the flow of light received by the second photodetector 141. The control unit is then configured to compare, for each light source 12,

• the value V ₁ obtained or measured by the control unit 15 from the first signal S1 for a beam of light emitted by the light source at time t _i , with
• a first reference value V ₁ 0 which is for example a nominal value obtained and defined for the second photodetector for a beam of light emitted at an initial time t ₀ by this same light source, for example during a calibration of the optical detector , or an average value of previous V ₁ values obtained for beams of said light source emitted in the time interval [t _j -δ; t _j ] with ti > t _j .

In particular, the control unit 15 is configured to calculate, for each light source 12, a first difference D1, with D1 = V ₁ -V ₁ 0- (or preferably and alternatively D1 = |V ₁ -V ₁ 0| ). This difference D1 calculated by the control unit 15 for each first signal S1 received is a measurement of a temporal variation of the flux of light received by the second photodetector 141. It in fact compares for the same light source the flux received by the second photodetector at time t _i at a nominal flux, which was for example received at time t ₀ different from t _i . This comparison is preferably carried out by the control unit 15 for each of the light sources 12 of the optical detector or for a predefined group of said light sources. The control unit 15 is further configured to determine if this difference is less than a first predefined threshold value (or alternatively if the absolute value of its difference is greater than the absolute value of said first threshold value), or if it is lies outside a range of predefined values. If this is the case, then either the light source whose beam of light is at the origin of the first signal S1 has aged and its intensity has fallen and/or dust are found in the optical chamber 11 and disrupt the light flux measurements.

In order to determine whether dust and/or aging of the first light source is/are the cause of this variation, the control unit measures a second signal S2. In order to better understand the invention, the method by which the control unit determines the presence of dust and/or aging of the LED will be explained in detail by taking the figure 1 as a non-restrictive illustration.

Let us assume that the difference D1 calculated by the control unit 15 for a first signal S1 generated by the second photodetector 141 for a flux of light emitted at time t _i by the first light source 121 is outside said interval of predefined values. In this case, said control unit 15 will take into account said second signal S2.

According to a first embodiment, this second signal S2 is the signal provided by the first photodetector 131 at time t _i , ie generated by the first photodetector 131 in response to the beam of light emitted by the first light source at time t _i . According to a second embodiment, this second signal S2 is the signal supplied by the second photodetector 141 in response to a beam of light emitted by the second light source 122 at a time t' _i different from t _i . Advantageously, the control unit 15 can use or combine the two embodiments in order to determine more precisely the cause of the variation in the flow of light received by the second photodetector 141 at time t _i .

• une valeur V₂, par ex. une valeur RMS, obtenue ou mesurée par l'unité de contrôle 15 à partir du second signal S2 délivré, selon le premier mode de réalisation, par le premier photodétecteur 131 pour le faisceau de lumière émis au temps t_i par la première source lumineuse, ou, selon le second mode de réalisation, par le second photodétecteur 141 pour le faisceau de lumière émis au temps t'_i par la seconde source lumineuse 122, avec
• une seconde valeur de référence V₂0 qui est par exemple, pour le premier mode de réalisation, une valeur nominale obtenue et définie pour le premier photodétecteur 131 pour un faisceau de lumière émis à un temps initial t₀ par la première source lumineuse 121, et pour le second mode de réalisation, une valeur nominale obtenue et définie pour le second photodétecteur 141 pour un faisceau de lumière émis à un temps initial t'₀ par la seconde source lumineuse 122, notamment lors de la calibration du détecteur optique.

As for the first signal S1, the control unit 15 is configured to compare

• a value V ₂ , e.g. an RMS value, obtained or measured by the control unit 15 from the second signal S2 delivered, according to the first embodiment, by the first photodetector 131 for the light beam emitted at time t _i by the first light source, or, according to the second embodiment, by the second photodetector 141 for the beam of light emitted at time t' _i by the second light source 122, with
• a second reference value V ₂ 0 which is for example, for the first embodiment, a nominal value obtained and defined for the first photodetector 131 for a beam of light emitted at an initial time t ₀ by the first light source 121, and for the second embodiment, a nominal value obtained and defined for the second photodetector 141 for a beam of light emitted at an initial time t' ₀ by the second light source 122, in particular during the calibration of the optical detector.

In particular, the control unit 15 is configured to calculate a second difference D2, with D2 = V ₂ -V ₂ 0 (or preferably and alternatively D2 = |V ₂ -V ₂₀ |).

The control unit 15 is then configured to compare D1 and D2 in order to determine whether dust and/or aging of the first light source is the cause of the variation measured via D1. Preferably, the control unit is configured to calculate said second difference D2 according to the second embodiment and/or according to the first embodiment for part or all of the light sources of the optical detector different from the first light source 121 and for use a dust and/or aging detection algorithm from said first difference D1 and all the second differences D2 calculated.

In particular, in the case of the second embodiment, the control unit is configured to determine whether D1/V ₁ 0 has a value comparable to D2/V ₂ 0, for example to determine whether |D1/V ₁ 0 - D2/V ₂ 0| < V ^s ₄ . If this is the case, the detection zone of the second photodetector is disturbed by dust and the control unit 15 is then configured to signal presence of dust; on the other hand, if the control unit 15 determines that D1/V ₁ 0 has a value different from D2/V ₂ 0, for example if |D1/V ₁ 0 - D2/V ₂ 0| > V ^s ₅ with V ^s ₅ ≥ V ^s ₄ , V ^s ₄ and V ^s ₅ being respectively the fourth predefined threshold value and the fifth predefined threshold value which can be stored in the control unit, then the first light source 121 has aged and the control unit 15 is configured to signal aging of the first light source 121.

According to this second embodiment and preferably, the flux of each light source 12 is compared by the control unit 15 to a nominal flux defined for the second photodetector 141 for each of the light sources 12. For each light source, the first difference D1 is calculated, normalized relative to the first reference value, then compared to the value D2 obtained for another light source and normalized relative to the second reference value defined for this other light source. In this way, the control unit 15 can compare the variations in luminous flux of each light source 12 and, by correlating the results, determine precisely the cause of a variation in flux for one of said light sources by distinguishing the presence of dust aging of the light source.

• |D1| ≤ V^s' ₁ = |V^s ₁| et |D2| ≤ V^s' ₂ : dans ce cas, l'unité de contrôle est configurée pour ne générer aucune alarme, car les variations de flux sont comprises dans des intervalles de tolérances définis par la première autre valeur seuil prédéfinie V^s' ₁ et la seconde autre valeur seuil prédéfinie V^s' ₂ , V^s ₁ étant ladite première valeur seuil; ou si
• |D1| ≤ V^s' ₁ et |D2| > V^s' ₂ : dans ce cas, l'unité de contrôle est configurée pour signaler un problème du premier photodétecteur; ou si
• |D1| > V^s' ₁ et |D2| ≤ V^s' ₂ : dans ce cas, l'unité de contrôle est configurée pour signaler un vieillissement de la première source lumineuse; ou si
• |D1| > V^s'₁ et |D2| > V^s' ₂ : dans ce cas, l'unité de contrôle est configurée pour signaler une présence de poussière.

In particular, in the case of the first embodiment, the control unit is configured to determine for each light source if:

• |D1| ≤ V ^s' ₁ = |V ^s ₁ | and |D2| ≤ V ^s' ₂ : in this case, the control unit is configured not to generate any alarm, because the flow variations are included in tolerance intervals defined by the first other predefined threshold value V ^s' ₁ and the second another predefined threshold value V ^s' ₂ , V ^s ₁ being said first threshold value; or if
• |D1| ≤ V ^s' ₁ and |D2| > V ^s' ₂ : in this case, the control unit is configured to signal a problem with the first photodetector; or if
• |D1| > V ^s' ₁ and |D2| ≤ V ^s' ₂ : in this case, the control unit is configured to signal aging of the first light source; or if
• |D1| > V ^s ' ₁ and |D2| > V ^s' ₂ : in this case, the control unit is configured to signal the presence of dust.

Preferably, said first embodiment is used in conjunction with said second embodiment by the control unit 15 in order to validate the results obtained by each of the embodiments and send an alarm signal only in the event of convergence of the results.

Preferably, the control unit 15 is configured to store in an internal memory of said optical detector 1 the different signals delivered by the first and each of said second detection units and to predict, from the recorded signals, the evolution of aging and /or the state of dustiness of the optical detector so as to automatically alert and in advance (i.e. before the state of dustiness or aging exceeds a predefined threshold value for dustiness and aging respectively) a center of maintenance or an operator. To this end, said control unit comprises in particular a prediction algorithm configured to predict the evolution of aging and/or dustiness from each of the measured signals S1 and S2.

Claims (13)

1. Optical smoke detector (1) comprising:

   - an optical detection chamber (11);

   - at least one light source (12) configured to emit a beam of light into said optical chamber (11);

   - a first detection unit (13) comprising at least one photoelectric detector - hereinafter "first photodetector" - (131) free from all direct illumination by the light source or sources (12);

   - a second detection unit (14) comprising at least one photoelectric detector - hereinafter "second photodetector" - (141), wherein said second unit (14) is configured such that the second photodetector (141) directly receives the light emitted by at least one of said light sources (12), hereinafter referred to as "first light source" (121);

   - a control unit (15) for monitoring the aging of the optical smoke detector (1), configured for controlling/managing the first light source (121) such that it temporarily emits a beam of light, wherein said control unit (15) is also configured to receive, in response to the emission of said beam of light emitted by the first light source (121), a first signal (S1) issued by the second photodetector (141), and to detect on the basis of said first signal (S1) and at least one second signal (S2) generated by one of the photodetectors of the optical detector (1) a presence of dust particles in the optical chamber and/or an aging of the first light source (121);

   wherein the optical detector (1) according to the invention is characterised in that the control unit (15) is configured to calculate a first difference and a second difference, wherein the first difference is the difference between a value obtained for said first signal (S1) on the basis of a measurement of the latter by the control unit (15) and a first reference value, and the second difference is the difference between a value obtained for said second signal (S2) on the basis of a measurement of the latter by the control unit (15) and a second reference value, and to detect said presence of dust particles in the optical chamber (11) and/or said aging of the first light source (121) on the basis of said differences.
2. Optical smoke detector (1) according to claim 1, characterised in that the control unit (15) is configured to calculate and compare a first ratio and a second ratio in order to detect said presence of dust particles in the optical chamber and/or said aging of the first light source (12), wherein said first ratio is a function of or equal to the first difference divided by said first reference value and the second ratio is a function of or equal to said second difference divided by said second reference value.
3. Optical smoke detector (1) according to claim 1, characterised in that the control unit (15) is configured to calculate and compare a first ratio and a second ratio in order to detect said presence of dust particles in the optical chamber and/or said aging of the first light source (12), wherein said first ratio is equal to the absolute value of the first difference divided by said first reference value and the second ratio is equal to the absolute value of said second difference divided by said second reference value.
4. Optical smoke detector (1) according to one of claims 1 to 3, characterised in that the second signal (S2) is issued by the first photodetector (131) in response to said emission of the beam of light by said first light source (121) .
5. Optical smoke detector (1) according to claim 4, characterised in that the control unit (15) is configured to indicate an aging of the first light source (121) if the value of the first difference is lower than a predefined first threshold value while the value of the second difference is lower than a predefined second threshold value, and to indicate a presence of dust if the value of the first difference is lower than said predefined first threshold value and the value of the second difference is higher than a predefined third threshold value.
6. Optical smoke detector (1) according to claim 4, characterised in that the control unit (15) is configured to indicate an aging of the first light source (121) if the absolute value of the first difference is higher than another predefined first threshold value while the absolute value of the second difference is lower than another predefined second threshold value, and to indicate a presence of dust if the absolute value of the first difference is higher than said other predefined first threshold value and the absolute value of the second difference is higher than said other predefined second threshold value.
7. Optical smoke detector (1) according to claims 1 to 2, comprising a second light source (122) configured to emit a beam of light into said optical chamber (11) and characterised in that the second signal (S2) is issued by the second photodetector (141) in response to an emission of a beam of light by said second light source (122), wherein said emission is separate from said emission of the beam of light by said first light source (121) and time-delayed with respect thereto.
8. Optical smoke detector (1) according to claim 7, characterised in that it comprises a bicoloured LED comprising the first and second light source.
9. Optical smoke detector (1) according to one of claims 7 or 8, characterised in that the control unit (15) is configured to determine whether the first light source has suffered a loss of luminous intensity higher than a predefined threshold and, if this is the case, to indicate a presence of dust if the absolute value of the difference between the first ratio and the second ratio is lower than a predefined fourth threshold value, and to indicate an aging of the first light source (121) if the absolute value of this difference is higher than a predefined fifth threshold value.
10. Optical smoke detector (1) according to one of claims 1 to 9, characterised in that the control unit 15 is configured to store in an internal memory of said optical detector 1 each first signal (S1) generated by the second photodetector (141) as well as each second signal (S2) and to predict, on the basis of the stored signals S1, S2, a development of the aging and/or of a state of dust contamination of the optical detector.
11. Optical smoke detector (1) according to one of claims 1 to 10, characterised in that said second detection unit (14) comprises a waveguide (145) configured to collect the direct light emitted by one or several light sources (12) and guide it towards the second photodetector (141).
12. Optical smoke detector (1) according to claim 11, characterised in that the second photodetector (141) is installed on the outside of the optical chamber 11.
13. Optical smoke detector (1) according to claim 12, characterised in that the second photodetector (141) is fastened directly to a printed circuit board comprising all or some of the electrical components of the control unit (15) .

Images