EP2093734A1 - Smoke alarm with timed evaluation of a backscattering signal, test method for functionality of a smoke alarm - Google Patents

Abstract

The smoke alarm (100) has a light transmitter (111) attached to a mounting surface of a printed circuit board (105) and transmitting an illuminating light (111a). A light receiver (112) is attached to the mounting surface adjacent to the light transmitter, and receives a measurement light (112a), which results from back-scattering of the illumination light at a measurement object located in a detection space (115). A data processing device (135) is coupled to an output of the light receiver and evaluates temporal changes of an output signal provided by the light receiver. An independent claim is also included for a method for detecting a functional capability of a smoke alarm.

Description

The present invention relates to the technical field of danger detection technology. In particular, the present invention relates to a device for detecting smoke based on the principle of optical scattered light measurements. The present invention further relates to a method for checking the operability of a scattered light smoke detector.

Smoke detectors typically operate according to the scattered light method. It is exploited that clear air reflects virtually no light. However, if smoke particles are in the air, an illumination light emitted by a light source is at least partially scattered on the smoke particles. Part of this scattered light then falls on a light receiver, which is not directly illuminated by the illumination light. Without smoke particles in the air, the illumination light can not reach the photosensitive sensor.

Scattered smoke detectors can be divided into two categories. The first category represents so-called closed smoke detectors, which have an optical chamber within a housing. In case of danger, smoke can penetrate into the optical chamber, which is then detected in the manner described above. The second category are so-called open smoke detectors. These have no optical chamber. Rather, smoke located outside the open smoke detector serves as a scattering medium.

From the EP 0 472 039 A2 is a fire detector and a method for detecting fire known. The fire alarm has one Laser light source, which is adapted to emit short laser pulses in a surveillance area. The fire detector also has a light detector which is arranged next to the laser light source and which is set up to detect laser light scattered back by approximately 180 ° of smoke or other objects located in the monitoring area. Based on the time difference between emitted and received laser pulses, the position of a backscatter object can be determined within the surveillance area.

From the EP 1 191 496 A1 a scattered light smoke detector is known, which has a light emitter and a light receiver. The light emitter and the light receiver are arranged at an angle to each other within the scattered light smoke detector such that their scattering point lies outside the scattered light smoke alarm outdoors. So this scattered light smoke detector is a so-called. Open smoke detector. A cover of transparent plastic, which is arranged between (a) light transmitter or light receiver and (b) scattering point, protects the scattered light smoke detector from moisture, aggressive gases and mechanical damage. The scattered light smoke detector also has a processor with which the light signals detected by the light receiver can be analyzed with respect to their time behavior.

From the EP 1 039 426 A2 a smoke detector is known which comprises a housing and disposed within the housing has a light emitter and a light receiver. A detection range defined by the spatial arrangement of the light emitter and the light receiver is located outside the smoke detector. In order to detect creeping contamination of the smoke detector, the light transmitter is assigned a control receiver, which is set up to detect the radiation emitted by the light emitter. Furthermore, a control transmitter assigned to the light receiver is provided, so that the sensitivity of the light receiver can be checked.

The present invention is the device-related object to provide a smoke detector, which despite a low expenditure on equipment allows reliable detection of smoke and has a low probability of triggering false alarms. A method-related object of the present invention is to provide a reliable method for checking the operability of a smoke detector.

These objects are achieved by the subject matters of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

According to a first aspect of the invention, an apparatus for detecting smoke is described, which is also referred to in the context of this application as a smoke detector. The smoke detector comprises (a) a base member having a planar mounting surface, (b) a light emitter attached to the mounting surface and configured to emit an illumination light, (c) a light receiver mounted adjacent the light emitter on the mounting surface and which is arranged to receive a measurement light resulting from a backscatter of the illumination light on a measurement object located in a detection space, and (c) a data processing device which is coupled to an output of the light receiver and which is configured to evaluate temporal changes of one of the output of the light receiver output signal.

The smoke detector described is based on the finding that the smoke detector can be realized by a planar arrangement of all optoelectronic components on a common mounting surface in a particularly flat design. The detection space is located outside the actual smoke detector, so that it is the described smoke detector is an open smoke detector.

A reliable smoke detection with a simultaneously low susceptibility to misdetections, which could be triggered, for example, by an insect penetrating into the detection space or by an object accidentally introduced into the detection space, can be achieved by careful evaluation of the time profile of the output signal. It is advantageous but not essential that the response of the light detector to the intensity of the incident measuring light is linear. This means that doubling the strength of the measuring light also doubles the level of the output signal.

Since smoke typically does not propagate abruptly within a monitored space, it can be concluded from a slow increase in the output signal to the ingress of smoke into the detection space. When a subject object is introduced into the detection space, a very rapid rise of the output signal normally takes place.

A distinction between the detection of smoke and the detection of an object introduced into the detection space can also be made by an evaluation of signal fluctuations which follow an increase of the output signal. In the detection of smoke, a comparatively slow rise is typically followed by some modulations of the measurement light intensity, which are triggered by the formation of smoke fumes. In contrast, the measurement light intensity remains at least approximately constant after the introduction of an object, which, for example, a cleaning lady accidentally leaves in the detection space. Thus, modulations in the output signal are at least a strong indication of the presence of smoke or smoke.

Due to the above-mentioned flat design, it is possible to easily integrate the described smoke detector in the walls and in particular in the ceilings of monitored areas. Even in the case of surface mounting, the described smoke detector can be easily attached to walls and / or ceilings. The smoke detector only takes up a small amount of space. In addition, the smoke detector described can be installed discreetly, so that it is not perceived by people who are in the monitored by the smoke detector room, or at least not disturbing the interior design.

As a result of the backscatter geometry used, optical elements such as lenses or mirrors for the light emitter and / or for the light receiver are advantageously not required. As a result, the smoke detector described can be made particularly cost-effective and is suitable as a low-cost mass product for monitoring private rooms.

The measurement of the scattered light takes place in the described smoke detector in Rückstreugeometrie of approximately 180 °, ie between 170 ° and 190 °. The deviation of the scattering angle from an exact backscatter and thus from exactly 180 ° results from a simple geometric consideration of (a) the spacing between the light emitter and the light receiver and (b) the distance of the location of the backscatter from the light emitter or light receiver ,

The smoke detector described differs in particular by the used backscatter geometry of conventional smoke detectors, which have either a forward scatterer a scattering angle of about 60 ° or as a back scatterer a scattering angle of about 120 ° between the illumination light and scattered light.

The optoelectronic or photoelectronic components of the smoke detector can advantageously be semiconductor diodes applied in Surface Mount Technology. The same applies to electronic components such as for the data processing device, which may also be mounted directly on the base element. In this case, the base element may be a printed circuit board or at least have a printed circuit board to which the semiconductor transmitting and semiconductor receiving diode are mounted in a known manner and electrically contacted.

It should be noted that in the context of this application, the term light basically comprises electromagnetic waves in any spectral range. These include, for example, the ultraviolet, the visible and the infrared spectral range. Also longer wavy radiation such as microwaves represent light in the context of the present application. In particular, the term light electromagnetic radiation in the near infrared spectral range meant in which light emitting diodes used as a light emitter have a particularly high light intensity. However, the described smoke detector can be operated not only with nearly monochromatic light radiation but also with light radiation which comprises two or more discrete wavelengths and / or a wavelength continuum.

According to a further exemplary embodiment of the invention, the data processing device is additionally set up to evaluate the strength of the output signal. By evaluating the strength of the output signal, which directly reflects the strength of the received backscattered measurement light, additional information on the nature of the introduced into the detection space scattering object can be obtained. In the evaluation of the strength of the output signal, it can namely be taken into account that the intensity of the measurement light scattered back by smoke particles typically is around Potencies is weaker than the measuring light scattered back from an object.

Of course, the information obtained from the strength of the output signal can also be combined with the information obtained from the time history of the strength of the output signal.

According to a further embodiment of the invention, the light emitter and the light receiver are realized by a first reflection light barrier. This has the advantage that commercially available reflection light barriers can be used. A relative adjustment between the light emitter and the corresponding light receiver for adapting the emission direction of the light emitter to the receiving direction of the light receiver is not required due to the fixed relative arrangement of these optoelectronic components within a common component or at least within a common housing. The smoke detector can therefore be constructed in an advantageous manner with a low installation cost.

According to a further embodiment of the invention, the direction of the illumination light is perpendicular to the mounting surface. The term direction in this context means the mean emission direction of the light emitter. This means that the light emitter can also have a radiation characteristic with diverging light beams which have a certain angular distribution about the central emission direction perpendicular to the mounting surface. As a result of the backscatter geometry used, this of course also applies to the measuring light, which also extends on average perpendicular to the mounting surface.

According to a further embodiment of the invention, the light emitter is arranged to emit a pulsed illumination light.

The use of pulsed illumination light allows advantageously to operate the light emitter for a short time with a particularly high current, which is greater than the maximum current that just does not result in a continuous operation of the light emitter to a thermal destruction of the light emitter. Since the light emitter can cool down in the time between two successive light pulses, such a moderately inflated current does not lead to destruction of the light emitter. Since a high current leads in particular in light emitting diodes to an increased light emission, a higher sensitivity and thus a particularly high reliability of the described smoke detector can be achieved by the use of pulsed illumination light.

It should be understood that pulsed illuminating light may also be used in conjunction with a photoreceiver having a temporal resolution greater than the transit time of the light from the source via the diffusing smoke particle and back to the receiver. As a result, additional information about the backscatter behavior and / or the spatial position of the measured objects detected by the described smoke detector can be obtained.

In the described smoke detector, the scattering volume, in which smoke is usually detected, is very close to the smoke detector. The scattering volume can have a spatial extent of less than approximately 5 cm. Then, the transit time of the measuring light for the outward and return path is typically in the range of at least a few picoseconds.

At the time of signing common simple reflection light barriers, the pulse durations are typically in the range of 1 to 100 microseconds. Therefore, the spatial distribution of smoke within the scattering volume with light barriers in the lower price segment are currently not resolved. However, in view of the rapid development in the field of optoelectronics, it seems quite possible that inexpensive short-pulse LEDs with a pulse length of only nano- or even picoseconds and corresponding photodiodes will be developed in the near future. With these information about the spatial distribution of the light scatterers can then be obtained.

Since the described smoke detector preferably detects smoke particles which are closer than approximately 10-50 mm from the light emitter or the light receiver, more distant particles provide only a vanishing, non-resolvable contribution to the smoke detection signal. In doing so, solid objects that are closer than approximately 50 mm from the smoke detector are detected over a very high backscatter signal amplitude. More distant objects may possibly be recognized as such over the term or through the associated broadening of the pulse. A distance of 30 cm corresponds to a round trip time or a pulse broadening of 2 ns. However, the easiest way to eliminate the reflections from the floor over time is to install the described smoke detector on the ceiling of a room to be monitored. A ceiling height of 3 m results in a round trip time of 20 ns.

When using very short light pulses, it is also possible to determine how far the respective scattering object is from the light emitter or the light receiver by measuring the time difference t between the emission of an illumination light pulse and the backscattered and detected by the light receiver measuring light pulse.

Although the use of pulsed illumination light offers many advantages in terms of reliable and error-free smoke detection, it is expressly stated here pointed out that the above-described smoke detector can of course be operated with a continuous illumination light.

According to a further embodiment of the invention, the light emitter and the light receiver each represent an outer boundary of the device for detecting smoke. This means that neither the light emitter nor the light receiver are located within a housing of the smoke detector described. Outside the photoelectric components light emitter and light receiver are thus no other parts of the smoke detector described. This also applies to covers or housing parts. Thus, the smoke detector can be designed such that there is no further optionally optically transparent cover between the photoelectric components and the detection space, by which the photoelectric components are protected from contamination. Such covers or dirt shields are in many applications, especially in the home but also not required.

According to a further exemplary embodiment of the invention, the smoke detector additionally has (a) a further light transmitter which is attached to the mounting surface and which is arranged to emit a further illumination light, and (b) a further light receiver which is adjacent to the further light emitter on the mounting surface is attached and which is adapted to receive a further measuring light, which results from a backscattering of the further illumination light at a measurement object located in a further detection space.

The data processing device can also be set up to jointly evaluate the output signal and a further output signal of the further light receiver. By a common evaluation of the output from the light receiver and the other light receiver output signals Additional information about the type and possibly also the position of a scattering object can be obtained.

The described smoke detector can be operated, for example, in an asymmetrical operating mode in which both light receivers are active but only one of the two light transmitters. This means that only one of the two light emitters emits an illumination light. If, in this mode of operation, both light receivers show at least approximately the same signal, then obviously this is a far-end echo. This may be due to a reflection of the illumination light emitted by the active light emitter on a faraway object such as the floor of a monitored room.

In a hazardous situation in which smoke penetrates into the monitored space or arises, the smoke will at least partially penetrate into the vicinity of the smoke detector, so that the two light receivers receive a very different measurement signal. In this case, the light receiver, which is assigned to the switched-on light transmitter, receive a measuring light of much higher intensity than the other light receiver. In this way, far away and generally strongly backscattering objects, which cause only a weak backscatter signal due to their long distance, can be reliably distinguished from a generally weakly backscattering smoke, which is located close to the smoke detector.

It should be noted that the further light emitter and the further light receiver can be designed or arranged in the same way as the light emitters and light receivers described above. This applies in particular to the combination of the further light emitter and the further light receiver in a further light barrier.

Preferably, the middle directions of both the first illumination light and the second illumination light are oriented perpendicular to the mounting surface. This means that the illumination light beam and the further illumination light beam are parallel to one another. As a result, the distance between the detection space and the further detection space essentially depends on the distance between the two light transmitters or between the two light receivers.

1. (a) ein Einbringen eines streuenden Referenzgegenstandes in den Detektionsraum, wobei der Gegenstand zumindest für eine vorgegebenen Zeitraum in der gleichen Position gehalten wird,
2. (b) ein Auswerten von zeitlichen Änderungen des von dem Lichtempfänger ausgegebenen Ausgangssignals und (c) ein Ausgeben einer Test-Alarmmeldung falls die zeitlichen Änderungen einem vorgegebenen Verlauf entsprechen.

According to another aspect of the invention, there is provided a method of checking the operability of a smoke detector of the type described above. The method has

1. (a) introducing a scattering reference object into the detection space, wherein the object is held in the same position for at least a predetermined period of time,
2. (b) evaluating temporal changes in the output signal output from the light receiver; and (c) outputting a test alarm message if the changes in time correspond to a predetermined course.

The above-mentioned method for triggering a test function of the smoke detector described above is based on the finding that the entire smoke detector, including the optical system consisting of light transmitter, light receiver and an evaluation implemented in the data processing device, can be tested by simply introducing an objective object. It can be detected by a suitable signal processing different waveforms and thus, for example, smoke from a desired triggering of the test function are clearly distinguished. In the described triggering of the test function is thus not only tested only the functionality of an alarm device such as a siren or an optical alarm indicator.

Preferably, the object is brought close to the smoke detector. The object may be any solid or liquid object which has a high light scattering surface compared to smoke. The item may also be the hand of an operator.

For example, a test bar is suitable for bringing the object into the way. This is especially true when the smoke detector is mounted on the ceiling of a room to be monitored. Also, a conventional broom with a correspondingly long state is therefore well suited as an object for triggering the test function of the smoke detector.

The triggering time for the test function or the time during which the test object must be kept in the vicinity of the smoke detector can be precisely defined. If, however, an object is located in front of the smoke detector for a considerably longer time, this means that the view of the smoke detector is obstructed by a fixed object. This is a fault and can also be detected by the implemented in the data processing device signal processing software and reported accordingly.

According to an exemplary embodiment of the invention, the method additionally comprises moving the reference object according to a predetermined time pattern, wherein the predetermined course coincides at least qualitatively with the predetermined time pattern.

This means that the triggering of the test function can additionally be coded, for example, by placing the test object in the vicinity of the smoke detector and removing it again two or three times within a defined time. By a suitable predefined coding also different test sequences can be triggered. The coding can also serve to clear the tripping function for the test from other jamming functions, as in the detection room penetrating insects to distinguish.

Figur 1

zeigt in einer schematischen Querschnittsdarstellung einen Rauchmelder mit zwei Reflexionslichtschranken, die an einer gemeinsamen Leiterplatte angebracht sind.

Figur 2

zeigt eine Querschnittsdarstellung eines Rauchmelders, welcher einen Lichtsender und zwei Lichtempfänger aufweist, die als SMD Bauelemente an einer elektronischen Leiterplatte angebracht sind.

Figur 3

zeigt ein Flussdiagramm, welches sowohl den normalen Betrieb als auch das Auslösen einer Testfunktion des in Figur 1 dargestellten Rauchmelders illustriert.

Further advantages and features of the present invention will become apparent from the following exemplary description of presently preferred embodiments. The individual figures of the drawing of this application are merely to be regarded as schematic and not to scale.

FIG. 1

shows a schematic cross-sectional view of a smoke detector with two reflection light barriers, which are mounted on a common circuit board.

FIG. 2

shows a cross-sectional view of a smoke detector, which has a light emitter and two light receivers, which are mounted as SMD components on an electronic circuit board.

FIG. 3

FIG. 3 shows a flowchart which illustrates both the normal operation and the triggering of a test function of the in FIG. 1 Illustrated illustrated smoke detector.

It should be noted at this point that in the drawing the reference numbers of identical or corresponding components differ only in their first digit.

FIG. 1 shows a smoke detector 100, which has a base plate 105. According to the embodiment shown here, the base plate is a printed circuit board 105 or a suitable circuit carrier for receiving electronic and optoelectronic components. All attached to the circuit board 105 components are contacted in a manner not shown by means of conductors or electrical wire connections in a suitable manner.

The smoke detector 100 comprises a first reflection light barrier 110 and a second reflection light barrier 120. The first reflection light barrier 110 has a first light emitter 111 and immediately adjacent thereto arranged in a common housing a first light receiver 112. The second reflection light barrier 120 has a second light transmitter 121 and immediately adjacent thereto arranged in a common housing a second light receiver 122.

The first light emitter 111 transmits a first illumination light 111a perpendicular to the plane of the printed circuit board 105. The first illumination light 111a is at least partially backscattered by approximately 180 °, ie, between 170 ° and 190 °, in a first detection space 115 in which, for example, smoke is located. The backscattered light reaches the first light receiver 112 as the first measuring light 112a.

In a corresponding manner, the second light emitter 121 transmits a second illumination light 121a perpendicular to the plane of the printed circuit board 105. The second illumination light 121a is at least partially backscattered by approximately 180 ° in a second detection space 125 in which, for example, smoke is located. The backscattered light reaches the second light receiver 122 as the second measuring light 122a.

The smoke detector 100 also has a subtraction unit 136, which forms a difference signal from the output signals of the two light receivers 112 and 122. This difference signal is supplied to a data processing device 135 of the smoke detector 100.

Furthermore, a control device 130 is provided, which is coupled to the two light transmitters 111 and 121. As a result, the two light transmitters 111 and 121 can be activated or switched on independently of each other.

All of the components 110, 120, 130, 135 and 136 of the smoke detector 100 are mounted on the circuit board 105 and electrically contacted in a suitable manner. As a result, the smoke detector 100 can be realized in a very flat design. The height of the smoke detector 100 is determined only by the thickness of the printed circuit board 105 and by the components 110, 120, 130, 135 and 136.

According to the exemplary embodiment illustrated here, all components 110, 120, 130, 135 and 136 are so-called surface mount technology (SMD) components. As a result, for example, an overall height of only 2.1 mm can be achieved. The total height results from the distance between the top of the circuit board 105 and the in FIG. 1 provided with the reference numeral 140 lower surface of the smoke detector.

According to the exemplary embodiment illustrated here, the light-active surfaces of the light emitters 111, 121 and the light receivers 112, 122 coincide with the surface 140. This means that no further parts of the smoke detector 100 are located between these light-active surfaces and the respective detection space 115, 125. This also applies to covers or housing parts. Such covers, which are often provided in known smoke detectors for the purpose of soil repellence, but are not required in many applications, especially in the home area. In addition, it is also possible to use light barriers which already have transparent protective layers for the light-active surfaces of the light emitters 111, 121 and the light receivers 112, 122, thereby providing at least some protection against soiling.

The described smoke detector 100 with two parallel reflection light barriers has the advantage that it has no optical elements such as lenses or mirrors. As a result, the smoke detector can be produced in a particularly simple manner with inexpensive components. At the Assembly or installation of the smoke detector does not require any special mounting tolerances. All components required for the smoke detector are mass-produced, which are inexpensive to procure.

According to the exemplary embodiment illustrated here, the data processing device 135 is set up such that the time profile of the output signal can be evaluated accurately. In order to achieve a high quality of the entire evaluation, the light receivers 112 and 122 have a linear response. This means that the height of the output signal is directly proportional to the respective incident light intensity.

Since smoke typically does not propagate abruptly within a monitored space, it can be concluded from a slow increase in the output signal to the ingress of smoke into the detection space. When a subject object is introduced into the detection space, a very rapid rise of the output signal normally takes place.

FIG. 2 shows a cross-sectional view of a smoke detector 200 according to another embodiment of the invention. The smoke detector 200 has a flat housing 202, in which there is a base plate 205 formed as a printed circuit board. On the circuit board 205 a plurality of electronic and optoelectronic components is mounted, which are each contacted in a suitable manner.

The most important optoelectronic component of the smoke detector 200 is a reflection light barrier 210, which comprises a light transmitter 211 and a first light receiver 212. The reflection light barrier 210 has the same structure and is operated in the same way as the reflection light barrier 110 of FIG FIG. 1 illustrated smoke detector 100.

The smoke detector 200 also has a second light receiver 222, which is also attached to the printed circuit board 205 at a certain distance from the light barrier 210. Thus, the smoke detector 200 can be operated in the asymmetrical operation mode described above. In addition, the smoke detector 200 also has a data processing device 235, by means of which the time profile of the output signal can be analyzed or evaluated.

On the circuit board 205, other electronic components are mounted in FIG. 2 Although shown but not specified. These components may be, for example, driver circuits for the light emitter 211, amplifier circuits for the two light receivers 212 and 222, hardware cast evaluation circuits such as a subtraction circuit, or any other circuits provided for the operation of the smoke detector 200.

In order to ensure a high mechanical strength of the smoke detector 200 and in particular the electronic and optoelectronic components, a potting material 245 is further provided, which at least partially encloses the components attached to the circuit board. When introducing the originally liquid potting material 245 care was taken that the optoelectronic components 211, 212 and 222 are not completely enclosed. Thus, in the smoke detector 200, the optically active surfaces of the light emitter 211, the first light receiver 212, and the second light receiver 222 at the corresponding locations constitute the outer boundary of the smoke detector 200. Thus, there are no other parts such as light emitter and light receiver outside the photoelectric components Covers or housing parts. Thus, the smoke detector can be designed such that between the optically active surfaces of the components 211, 212 and 222 and a in FIG. 2 not shown detection space no optical transparent cover, by which the components 211, 212 and 222 are protected from contamination.

FIG. 3 shows a flowchart which shows both the normal operation and the triggering of a test function in the Figures 1 and 2 illustrated smoke detector 100 and 200 illustrated.

The method illustrated in the flow chart begins with the connection of the smoke detector to a required for operation power supply, which may for example be a battery. The beginning or the start of the method is identified by the reference numeral 350.

Immediately after the beginning of the method, a first query 352 is carried out, with which it is checked whether a backscatter signal is ever received. If this is not the case, then the process begins again.

At this point it should be noted that in the in FIG. 3 The flow chart shown, the flow lines that follow a negative answer or to "no" begin with a marked on the corresponding query box circle. Flow lines that follow a positive answer or "yes" begin without a corresponding circle.

If it is determined in the query 352 that a backscatter signal is received, then the next step is followed by a query 360 in which it is determined whether the time profile of the detected backscatter signal has a slope which is greater than a predetermined reference slope. If so, then the method continues with a query 370. If the time change of the backscatter signal is less than the reference slope, then the method continues with a query 380.

The following describes the portion of the flowchart that begins with query 370.

With the query 370 is checked whether the strength of the detected backscatter signal is greater than a maximum signal of a predetermined range for smoke backscatter signals. If this is not the case, then the current scattering medium is obviously not a solid object but rather smoke. In this case, the method restarts hoping that a slower slope will be detected at re-interrogation 360 and the method continues with query 380, described below. If the magnitude of the detected backscatter signal is greater than a maximum signal associated with smoke detection, then the method continues with a query 372.

By means of the query 372 it is checked whether there are fluctuations in the backscatter signal. If fluctuations are detected, then it could possibly be a backscatter signal based on smoke detection. In this case, the procedure starts all over again. If no fluctuations in the backscatter signal are found in the query 372, then the method is continued with a query 374.

In the query 374 it is checked whether the time duration of the detected backscatter signal coincides with a predetermined specification for triggering a test function of the smoke detector. If this is the case, then a corresponding test function is triggered. This is represented by the box marked with the reference numeral 375.

If, in the context of query 374, it turns out that the time duration of the detected backscatter signal is below the specified specification for triggering the test function, then the method restarts all over again. Is that lying Duration of the detected backscatter signal above the specified specification for triggering the test function, then the cause of the detected backscatter signal can only be an object that was accidentally introduced into the detection space and leads to a time-constant backscatter. In this case, a fault message is issued by the smoke detector. This is in FIG. 3 shown with action 376.

Next, the part of the flowchart which starts with the query 380 will be described. The query 380 determines whether the amplitude or the strength of the backscatter signal is within a predetermined range, which is characteristic of a smoke backscatter. If this is not the case, then the method restarts in the hope that a larger slope will be detected on re-interrogation 360 and the method continues with query 370 described above. If it is determined at query 380 that the magnitude of the backscatter signal is within a predetermined range and typical for smoke backscatter, then the method continues with a query 382.

The query 382 determines whether the backscatter signal has fluctuations that are typical of smoke over time. If this is not the case, then the method restarts and continues with query 352 described above. However, if it is determined by query 382 that the backscatter signal has fluctuations typical of smoke detection, then an alarm message is issued by the smoke detector. This alarm message is in FIG. 3 designated by the reference numeral 383.

With the method described, three different events can thus be triggered, which depend reliably on each other due to the described plurality of queries can be distinguished. A first event is the triggering of a test function 375 with which the functionality of the smoke detector can be checked. A second event is a fault message 376 which signals that an item is in the detection room. The third event is the issuing of a smoke alarm 383.

In summary, it remains to be stated: The open optical smoke detector described has a light transmitter which optically illuminates smoke particles outside the smoke detector. The light receiver of the smoke detector is designed to receive the light scattered back by the smoke particles. If now an object is supplied instead of the smoke particles, then this can also be detected by the backscattered light. Thus, for example, by holding the hand or other object, such as an extension bar, an alarm may be triggered. In the case of smoke detectors for home use, the triggering of an alarm can generally correspond to the required test function.

• Der Rauchmelder kann in einer miniaturisierten Bauform realisiert werden.
• Die benötigte Anzahl insbesondere an optischen Bauteilen ist im Vergleich zu bekannten Rauchmeldern erheblich reduziert.
• Mittels der Testfunktion werden genau die gleichen Bauteile überprüft, welche auch für die Rauchdetektion verwendet werden. Es wird also der komplette optische Pfad getestet. Bei bekannten Rauchmeldern mit der Möglichkeit einer Testauslösung über eine Taste konnte nur eine indirekte Prüfung durchgeführt werden (Strommessung des Senders, Test des Alarmbuzzers, Test der Batterien). Der optische Pfad selbst wird bei bekannten Streulichtrauchmeldern üblicherweise nicht überprüft.
• Eine Sichtversperrung durch fixe Gegenstände kann zuverlässig erkannt werden. Dies ist auch ein entscheidender Vorteil gegenüber einem geschlossenen Rauchmelder mit Labyrinth bzw. mit einer optischen Kammer. Wird das Labyrinth bzw. die optische Kammer beispielsweise durch eine Staubschutzkappe, durch eine heruntergehängte Decke oder einen Schrank abgedeckt, dann ist der betreffende Rauchmelder nicht mehr funktionsfähig, ohne dass es von einer Überwachungsfunktion erkannt werden kann.
• Ein Test des Rauchmelders kann auf einfache Weise beispielsweise durch eine Verlängerungsstange ausgelöst werden. Ein kleiner Testknopf muss nicht betätigt werden. Vielmehr genügt es, mit einer Stange, einem Besen oder einem Wischer in die Nähe des Detektionsraumes zu kommen. Der Gebrauch einer Leiter mit der entsprechenden Unfallgefahr entfällt.
• Das optische System zur Rauchdetektion wird gleichzeitig als Auslöseeinrichtung für die Testfunktion und zur Überwachung der Sichtbehinderung eines offenen optischen Rauchmelders verwendet. Dadurch werden keine zusätzlichen Bauteile oder Vorrichtungen benötigt.

The open smoke detector described has the following advantages, for example:

• The smoke detector can be realized in a miniaturized design.
• The required number, in particular of optical components, is considerably reduced in comparison to known smoke detectors.
• The test function checks exactly the same components that are used for smoke detection. So it will test the complete optical path. In known smoke detectors with the possibility of a test release via a button, only an indirect test could be performed (current measurement of the transmitter, test of the alarm buzzer, test of the batteries). The optical path itself is usually not checked in known scattered light smoke detectors.
• A visual obstruction by fixed objects can be reliably detected. This is also a decisive advantage over a closed smoke detector with labyrinth or with an optical chamber. If the labyrinth or the optical chamber is covered, for example, by a dust cover, by a suspended ceiling or a cabinet, then the relevant smoke detector is no longer functional, without it being recognized by a monitoring function.
• A test of the smoke detector can be triggered in a simple manner, for example by an extension rod. A small test button does not have to be pressed. Rather, it is sufficient to come with a rod, a broom or a wiper in the vicinity of the detection room. The use of a ladder with the corresponding accident risk is eliminated.
• The optical smoke detection system is also used as a trigger for the test function and to monitor the visual obstruction of an open optical smoke detector. As a result, no additional components or devices are needed.

It should be noted that the embodiments described herein represent only a limited selection of possible embodiments of the invention. Thus, it is possible to suitably combine the features of individual embodiments with one another, so that for the person skilled in the art with the variants of embodiment that are explicit here, a multiplicity of different embodiments are to be regarded as obviously disclosed.

Claims (9)

A device for detecting smoke comprising the device ● a base element (105) with a planar mounting surface, ● a light transmitter (111), which
is attached to the mounting surface and
is arranged to emit an illumination light (111a), ● a light receiver (112), which
next to the light emitter (111) is mounted on the mounting surface and
is set up to receive a measuring light (112a) which results from a backscattering of the illumination light (111a) on a measuring object located in a detection space (115), ● a data processing device (135), which
is coupled to an output of the light receiver (112) and
is arranged for evaluating temporal changes of an output signal output by the light receiver (112). Apparatus according to claim 1, wherein
the data processing device (135) is additionally set up to evaluate the strength of the output signal. Device according to one of claims 1 to 2, in which
the light transmitter (111) and the light receiver (112) are realized by a first reflection light barrier (110). Device according to one of claims 1 to 3, in which
the direction of the illumination light (111a) is perpendicular to the mounting surface. Device according to one of claims 1 to 4, in which
the light emitter (111) is arranged to emit a pulsed illumination light (111a). Device according to one of claims 1 to 5, in which
the light emitter (111) and the light receiver (112) each represent an outer boundary of the device (100) for detecting smoke. Device according to one of claims 1 to 6, additionally comprising ● another light transmitter (121), which
is attached to the mounting surface and
is arranged to emit a further illumination light (121a), and ● another light receiver (122), which
next to the further light emitter (121) is mounted on the mounting surface and
is set up to receive a further measuring light (122a), which results from a backscattering of the further illumination light (121a) on a measuring object located in a further detection space (125). A method of verifying the operability of a smoke detecting device (100) according to any one of claims 1 to 7, comprising the method Introducing a scattering reference object into the detection space (115), wherein the object is held in the same position for at least a predetermined period of time, ● evaluating changes over time of the output signal output by the light receiver (112) and ● if the time changes correspond to a predefined course, output a test alarm message (375). The method of claim 8, additionally comprising ● moving the reference object according to a given temporal pattern, where the predetermined course coincides at least qualitatively with the given temporal pattern.

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