EP2093733A1 - Smoke detection through two spectrally different light scattering measurements - Google Patents

Abstract

The device (100) has an LED (110) emitting temporal sequence of light pulses, where one of the light pulses includes spectral distribution and another light pulse includes another spectral distribution different from the former spectral distribution. A light receiver (120) receives a set of scattered lights from the light pulses, and prepares a set of output signals that are indicative for the scattered lights. An evaluation unit compares one of the output signals with another output signal. The LED and light receiver are arranged directly adjacent to one another. An independent claim is also included for a method for detecting smoke on the basis of optical scattered light measurement.

Description

The present invention relates to the technical field of danger detection technology. More particularly, the present invention relates to an apparatus for detecting smoke based on scattered light optical measurements. The present invention further relates to a method based on the principle of optical scattered light measurements for detecting smoke.

Optical or photoelectric smoke detectors usually work 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 light beam. Without smoke particles in the air, the illumination light can not reach the photosensitive sensor.

From the EP 0 472 039 A2 a fire detector is known which has a laser light source. The laser light source is set up 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 180 ° from 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. By a suitable Furthermore, the type of detected smoke can be detected by comparison with time differences obtained by reference measurements. In particular, a distinction can be made between black and white smoke. The one with the EP 0 472 039 A2 However, the fire detector described has the disadvantage that the cost of measuring and evaluating the time difference is relatively high.

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 defined by the spatial arrangement of light emitter and light receiver smoke detection area is located outside the smoke detector. The one with the EP 1 039 426 A2 However, the smoke detector described has the disadvantage that in the smoke detection area penetrating insects can distort the detection of smoke.

From the DE 10 2004 001 699 A1 a fire detector is known, which is based on the known scattered radiation principle. The fire detector has a plurality of radiation transmitters and a plurality of radiation receivers whose radiation paths define a plurality of spaced-apart scattering volumes or detection spaces. The detection spaces are spatially spaced such that small objects such as insects can not move through multiple detection spaces simultaneously. In this way, a distinction can be made between a light scattered by a small object to be measured and a case of fire, in which smoke a distinction is made between smoke distributed over all detection spaces. However, the fire detector has the disadvantage that it has several independent light paths, each with both a light transmitter and a light receiver. The equipment required for the fire alarm is thus relatively high.

The invention is based on the device-related task, a simply constructed open scattered light smoke detector to create, which is characterized on the one hand by a high reliability in the detection of smoke and on the other by a low false alarm probability of insects located in the detection room. The invention is based on the method-related object to provide a method for detecting smoke on the basis of optical scattered light measurements, which is also characterized by a high reliability in the detection of smoke and on the other hand by a low false alarm probability in insects located in the detection room.

This object is solved 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 based on scattered light optical measurements is described. The device described has (a) a light emitting device configured to emit a temporal sequence of light pulses, wherein a first light pulse has a first spectral distribution and a second light pulse has a second spectral distribution that is different from the first spectral distribution (b ) a light receiver configured to receive a first scattered light from the first light pulse and a second scattered light from the second light pulse, and to provide a first output indicative of the first stray light and a second output indicative of the second stray light , and (c) an evaluation unit configured to compare the first output signal with the second output signal.

The described apparatus for detecting smoke, which is also referred to below as a scattered light smoke detector, is based on the recognition that different Light scatterers, which may be within the detection range of the scattered light detector can be discriminated from each other by that their optical scattering properties are compared at different wavelengths.

The light receiver is preferably arranged spatially relative to the light-emitting device such that the primary illumination light emitted by the light-emitting device does not strike the light receiver. This applies to both the first and the second light pulses. Thus, in the absence of any light scatterers in the detection range of the scattered light smoke detector, no light rays reach the light receiver.

The described scattered light smoke detector may in particular be an open smoke detector. This means that a spatially separated scatter chamber, which is often referred to as a labyrinth, is not required.

By evaluating the possibly spectrally different scattering properties of possible scattering objects, a distinction can be reliably made between a detection of smoke and a detection of other light scatterers which are located in the detection range of the open scattered light smoke detector. Such other light scatterers may in particular be insects which may have entered the detection range of the scattered light smoke detector. Likewise, such light scatterers may also be typically stationary objects such as ground, wall or even side surfaces of a space monitored by the described scattered light smoke detector.

In the described scattered light smoke detector, the two output signals are each indicative of the respective scattered light. The output signals can preferably directly be proportional to the respective scattered light intensity. This means that the light receiver and the evaluation unit connected downstream of the light receiver operate linearly. A doubling of the scattered light intensity will then lead to an increase of the respective output signal by a factor of two.

According to one exemplary embodiment of the invention, the evaluation unit is set up to form a difference between the first output signal and the second output signal. This has the advantage that in a particularly simple way, smoke can be distinguished from other scattering objects. For most objects, the scattering behavior is at least to a first approximation independent of the wavelength of the light.

It should be noted that in the case of a solid object as a measurement object, the signal evaluation depending on the difference between the two output signals is particularly advantageous if this object is relatively far away from the light emitting device and / or the light receiver. For a solid object that is close to the scattered light smoke detector, the signal amplitudes can both be very large. However, whether they are in fact exactly the same size, so that the difference between two relatively large signals results in a zero signal, however, is unlikely in practice. Thus, it is quite possible that when there is a difference between two very large signals, a difference signal remains which, with regard to its signal strength, corresponds at least to the order of magnitude of a smoke difference signal.

The difference formation described is particularly suitable for a highly accurate scattered light measurement of smoke or on a relatively far from the scattered light smoke detector measuring object when the two light paths of the first light pulse and the second light pulses are adjusted with respect to the resulting output signals. When adjusting, for example, the intensity of the two light pulses can be set so that the two output signals are equal in a light scattering of the two light pulses on a Referenzstreuobjekts. The reference object may be, for example, a simple black scattering object which is introduced into the measuring range of the scattered light smoke detector during the adjustment.

In contrast to the reference scattering object or to an insect which has penetrated into the measuring area, in the case of smoke as the scattering medium, a significantly larger difference signal results than in the case of a measuring object which is located relatively far away from the light-emitting device and / or the light receiver. This is because the light scattering of smoke has a strong wavelength dependency. The dependence of the intensity I of the light scattered on Rauchaerosolen light of the wavelength λ is at least approximately described by the following relationship (1): $$\mathrm{I}\left(\mathrm{\lambda }\right)\mathrm{~}{\left(\mathrm{1}\mathrm{/}\mathrm{\lambda }\right)}^{\mathrm{n}}$$

N is typically in the range between 4 and 6.

If, after a correct adjustment of the two light pulses during operation of the scattered light smoke detector, a strong but only weakly variable difference signal results, then this is a sure indication of the presence of smoke.

It should be noted that even in the measuring range insects can lead to large single signals, the ratio is close to one. In addition, however, this ratio usually has strong temporal or abrupt fluctuations that result from a typical movement of the respective insect. Two temporally variable Accordingly, differential signals of large and approximately equal amplitude are a sure indication of the presence of insects.

According to one exemplary embodiment of the invention, the evaluation unit is set up to determine the ratio of the amplitude of the first output signal to the amplitude of the second output signal. The determination of the described amplitude ratio can also be based on the two previously determined amplitudes of the first output signal and the second output signal.

The evaluation of the amplitude ratio has the advantage that it will always give a signal ratio of approximately equal to one regardless of the distance of the object from the scattered light detector for solid objects with a weak wavelength dependence of the scattering signal. In this case, the signal ratio for a solid object, regardless of its distance from the scattered light smoke detector differs significantly from the signal ratio of smoke. From the above-mentioned relationship (1), the following relationship (2) results for the ratio of the amplitudes or the intensities of two scattered light signals: $$\mathrm{I}\left(\mathrm{\lambda }\mathrm{1}\right)\mathrm{/}\mathrm{I}\left(\mathrm{\lambda }\mathrm{2}\right)\mathrm{~}{\left(\mathrm{\lambda }\mathrm{2}\mathrm{/}\mathrm{\lambda }\mathrm{1}\right)}^{\mathrm{n}}$$

Again, n is typically in the range between 4 and 6.

Assuming that λ2 = 2 · λ1, the relationship (2) for the ratio I (λ1) / I (λ2) gives a value of about 16 to 64.

In this point, the described evaluation of the amplitude ratio differs from the subtraction described above. In the case of the difference formation described above, namely, for the case λ2 = 2 · λ1, a value I (λ1) - I (λ2) would arise, which, given the relationship (1), is approximately is equal to I (λ1). Thus, if necessary, valuable information would be lost. The evaluation of the amplitude ratio described here is therefore to be preferred to the difference formation described above for most applications.

According to a further embodiment of the invention, the light-emitting device and the light receiver are arranged directly next to one another. This has the advantage that the entire scattered light smoke detector can be realized within a particularly compact design. In particular, when using optoelectronic components for the light emitting device and the light receiver of the scattered light smoke detector can be realized for example with a maximum linear extent of about 7 mm.

All electronic and / or optoelectronic components can be mounted on a common printed circuit board. As a result, the described scattered light smoke detector can additionally be realized within a small height extent. The scattered light smoke detector can therefore be an inconspicuous object, which is suitable for many applications. Both space and aesthetic requirements can be met in a simple manner.

According to a further exemplary embodiment of the invention, the light-emitting device has a first light source and a second light source.

The two light sources may be, for example, two light-emitting diodes, which are preferably arranged directly next to each other. The two light sources can also be realized by means of a so-called. Multichip LED, which has at least two elements emitting light in different spectral ranges. In this case, the two light-emitting elements are anyway arranged in close proximity to each other.

The smallest possible distance between the two light sources has the advantage that the spatial signal paths for both light pulses are approximately equal. Thus, especially in the case of two light pulses falling in temporal succession, the scattering on an insect continues to result in two signals having at least approximately the same amplitude, which, given a separate signal detection and a subsequent amplitude comparison, provide an amplitude ratio of at least approximately one. This is true at least as long as the time difference between the two light pulses is significantly smaller than the typical time scale of movements of insects.

It should be noted that the light-emitting device can also be realized by means of a light-emitting element, from which both light pulses emerge. The light-emitting element may, for example, be the end of an optical waveguide whose other end is split into two divisional ends. One divider may then be optically coupled to the first pulsed light source, the other divisor may be optically coupled to the second pulsed light source.

According to a further exemplary embodiment of the invention, the device additionally has a microcontroller which is coupled at least to the light-emitting device and to the evaluation unit and which is set up for temporally synchronizing at least the light-emitting device and the evaluation unit.

By the described synchronization of the operation of the light emitting device and the evaluation unit can be ensured that the two output signals are actually assigned to the respective light pulse.

It should be noted that the microcontroller and the evaluation unit can also be realized within an integrated component. In this case, the evaluation unit be realized by means of software, by means of one or more special electrical circuits, ie in hardware or in any hybrid form, ie by means of software components and hardware components.

According to a further exemplary embodiment of the invention, the first light pulse lies in the near infrared spectral range and / or the second light pulse is in the visible spectral range, in particular in the blue or violet spectral range. This has the advantage that both light pulses can be realized by simple optoelectronic components. In particular, a light emitting diode in the near infrared spectral range can provide the corresponding light pulses with a high intensity. This is all the more true, since the two optoelectronic components can be acted upon in each case with a current which is higher than the current, which would result in a stationary energization to a thermal destruction of the respective light emitting diode. Between two consecutive light pulses of the same type, the respective light-emitting diode can namely at least cool somewhat.

The first light pulse may have, for example, a wavelength of 880 nm (near infrared spectral range). The second light pulse may, for example, have a wavelength of 420 nm (blue region of the visible spectrum).

According to a further exemplary embodiment of the invention, the first and / or the second light pulse has a time length in the range between 1 μs and 200 μs, in the range between 10 μs and 150 μs or in the range between 50 μs and 120 μs. Particularly preferred currently appears a pulse length of 100 microseconds for both light pulses.

The repetition rate can result from the sum of the time lengths of the individual light pulses. Likewise, after a predetermined pulse sequence with at least one The first light pulse and a second light pulse follow a rest period, so that the effective repetition rate is significantly smaller than the inverted sum of the individual pulse durations. Such a rest period can serve, for example, to reduce the effective power consumption of the described scattered light smoke detector. This is particularly advantageous in a battery-powered or battery-powered device, as this can significantly extend the life of the battery or the battery.

It should be noted that the present invention is by no means limited to the use of two types of light pulses. Rather, three or even more than three spectrally different light pulses of a given sequence can be evaluated in a suitable manner. As a result, the accuracy in the spectral discrimination of different scattering objects can be additionally improved.

It should also be noted that the number of first light pulses and the number of second light pulses within a basic cycle need not necessarily be the same. For example, it is conceivable that the first light pulse is significantly more intense than the second light pulse. The adjustment described above can also take place in that the ratio between the number of first light pulses and the number of second light pulses is not equal to one and that the respective output signals of the two light pulses are integrated within a basic cycle. By a suitable choice of this ratio, an adjustment can then take place between the corresponding integrated output signals of the different light pulses.

According to a further exemplary embodiment of the invention, the device additionally has an insect displacement device which is coupled to the evaluation unit and which can be activated in the case of temporally strong fluctuations of the first output signal and / or of the second output signal.

The insect eviscerating device may, for example, be a small "Ultra Sonic Mosquito Repeller" which, by means of an ultrasound sound that is very unpleasant for insects, sells the insects which are currently crawling over the light emitting device and / or via the light receiver and thereby causing strong fluctuations of the first output signal and / or cause the second output signal.

According to another aspect of the invention, there is provided a method of detecting smoke based on scattered light optical measurements. The method may in particular comprise a device of the above type. The specified method comprises (a) emitting a temporal sequence of light pulses by means of a light emitting device, wherein a first light pulse has a first spectral distribution and a second light pulse has a second spectral distribution that is different from the first spectral distribution, (b) receiving a first scattered light from the first light pulse and a second scattered light from the second light pulse by means of a light receiver; (c) providing a first output signal indicative of the first scattered light and a second output indicative of the second scattered light , and (d) comparing the first output signal with the second output signal by means of an evaluation unit.

The stated method for detecting smoke is also based on the knowledge that different light scatterers, which may be located in the detection range of the scattered light detector, can be discriminated from one another by comparing their optical scattering properties at different wavelengths.

According to an embodiment of the invention, the method additionally comprises matching the intensities of the two light pulses, so that when a scattering of the two light pulses to a reference scattering object, the first output signal and the second output signal are the same size.

The reference object may be, for example, a simple black scattering object which is introduced into the measuring range of the scattered light smoke detector during the adjustment.

According to another embodiment of the invention, the above-described comparison of the first output signal with the second output signal comprises forming a difference between the first output signal and the second output signal.

By forming a difference between the two output signals described, a difference signal can be generated, which is particularly indicative of the presence of smoke in the detection range of the scattered light smoke detector. This is because, unlike stationary objects such as the walls or the floor of a monitored room or moving objects such as insects, the scattered light behavior of smoke is strongly wavelength dependent. In fact, in the presence of smoke, a particularly large change in the difference signal will occur. This applies in particular to the case where the two light paths of the first light pulse and of the second light pulse are adjusted with respect to the resulting output signals, so that a difference signal of at least approximately zero normally results.

At this point it should be noted that the presence of insects can lead to a relatively large difference signal. However, this typically has relatively abrupt variations resulting from a typical movement of the respective insect. A time-varying difference signal is therefore a sure sign of the presence of insects. In contrast, is a large similarity or a correlation, especially in terms of time, another indication by means of which a smoke-based scattered signal can be discriminated by a scattered signal caused by insects.

According to a further embodiment of the invention, the method additionally comprises compensating for a slowly varying difference signal towards a zero signal. In this way, a difference signal, which is based on a slowly varying first output signal and / or second output signal, be tracked so that in the absence of smoke, the difference signal is at least approximately equal to zero. The presence of smoke can then be reliably detected, starting from a zero signal by a difference signal, which differs significantly from the usual zero signal.

Different output signals can be caused for example by a slightly wavelength-dependent attenuation of reflected at the bottom or on the side walls of a space to be monitored light pulses. Different output signals can also be caused by a time-varying and wavelength-dependent scattering behavior of the floor or the side walls. However, these effects typically occur on a very slow time scale such that they can be reliably distinguished, for example, by appropriately filtering the difference signal from a highly variable difference signal produced by the presence of smoke.

Further advantages and features of the present invention will become apparent from the following exemplary description of presently preferred embodiments.

FIG. 1 shows in a plan view of a scattered light smoke detector with a photodiode and two arranged directly adjacent to the photodiode LEDs.

FIG. 2 shows in a plan view of a scattered light smoke detector with a photodiode and a dual-chip light-emitting diode, which is seconded directly adjacent to the photodiode.

FIG. 3 shows in a cross-sectional view the in FIG. 1 shown scattered light smoke detector, in which all electronic and optoelectronic components are mounted on a common circuit board.

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 top view of a scattered light smoke detector 100. The scattered light smoke detector 100 has an in FIG. 1 not shown, on which all electronic and optoelectronic components of the scattered light smoke detector 100 are mounted.

The scattered-light smoke detector 100 has a light-emitting device 110, which comprises two light sources, a first light-emitting diode 111 and a second light-emitting diode 112. The first light-emitting diode 111 has a light-emitting chip 111a. According to the embodiment shown here, the chip 111a emits an infrared light having a wavelength of 880 nm. The second light-emitting diode 112 has a light-emitting chip 112a. According to the embodiment shown here, the chip 112a emits a blue light with a wavelength of 420 nm.

The two light-emitting diodes 111 and 112 are operated in a pulsed mode, with each light-emitting diode 111, 112 emitting light pulses with a time length of, for example, 100 μs. The pulsed operation of the two light-emitting diodes 111 and 112 is synchronized with each other so that the two light pulses are fired or activated at a very small time interval. According to the exemplary embodiment illustrated here, this time interval between an infrared light pulse and a blue light pulse is approximately 1 to 100 μs.

The described scattered light smoke detector 100 is an open smoke detector. The smoke detector 100 thus has no separated from the environment scattering chamber. The smoke detection is rather on smoke particles that are in FIG. 1 located above the drawing plane. In this case, at least part of the illumination light pulsed by the two light-emitting diodes 111, 112 is scattered at the aerosols of the smoke, and in turn a part of the scattered illumination light strikes the active surface 121 of a photodiode 120.

How out FIG. 1 As can be seen, the two light-emitting diodes 111 and 112 are arranged directly next to the photodiode 120. This means that the housing of these components connect directly to each other or flush with each other. According to the embodiment shown here, the entire arrangement has a maximum linear extent of 7 mm.

As a result of the activation of the two light-emitting diodes carried out immediately one after the other, the photodiode 120 sequentially measures a first optical scattered light signal in the near infrared spectral range and a second optical scattered light signal in the blue spectral range. By comparing the scattered light intensities of these two scattered light signals thus valuable information about the nature of the scattering object or the scattering medium can be obtained.

In evaluating the two scattered light intensities, one can take advantage of the fact that insects are not colored, but black, gray or brown to suppress the influence of insects in the scattering volume.

Their spectral reflection therefore has a very flat course. This means that they reflect or scatter equally strongly in the infrared and in the blue wavelength range.

In the following, a method is described with which 100 different scattered light signals can be distinguished from one another on the basis of their spectral signature and / or their temporal variations using the scattered light smoke detector 100.

First, the luminous fluxes of the two light sources 111 and 111a and 112 or 112a are tuned in a balancing process so that the difference of the two measured signals generated by the photodiode offset in time from the radiation reflected by a black background is equal to zero.

1. a) Signale vom Boden oder einer Seitenwand eines zu überwachenden Raumes sind wegen der unterschiedlichen Wellenlänge der zwei Leuchtdioden 111 und 112 evtl. nicht exakt gleich stark. Sie werden jedoch auf alle Fälle hinsichtlich ihrer Amplitude zumindest ähnlich stark sein. Ergibt eine Differenzbildung einen von Null verschiedenen Wert, so entsteht ein kleines Offsetsignal. Dieses hat weder mit der Detektierung von Rauch noch mit dem Einfluss von Insekten zu tun. Für einen zuverlässigen Betrieb mit einer hohen Empfindlichkeit sollte dieses Offsetsignal so nachgeführt werden, dass es stets den Signalpegel Null annimmt.
2. b) Streulicht-Messsignale von herumschwirrenden Insekten ergeben bei einer erfolgreich durchgeführten Abgleichprozedur für beide Leuchtdioden 111, 112 dasselbe Signal. Dies liegt insbesondere an den drei folgenden Umständen:
   • b1) Der oben bereits beschriebene spektral flache Verlauf des Streuverhaltens der Insekten.
   • b2) Infolge des miniaturisierten Aufbaus des Streulichtrauchmelders 100 sind für beide Arten von Lichtpulsen die relativen räumlichen Lagen der Photodiode 120, eines Insekts und der beiden Leuchtdioden 111, 112 nahezu identisch.
   • b3) Die beiden Leuchtdioden 111, 112 werden annähernd gleichzeitig aktiviert. Dies bedeutet, dass eine Bewegung des Insekts innerhalb einer Zeitspanne zwischen den beiden aufeinanderfolgenden Lichtpulsen in guter Näherung vernachlässigt werden kann.
   Die an einem Insekt reflektierten und von der Photodiode 120 empfangenen beiden Messsignale sind somit nahezu identisch für beide Leuchtdioden 111, 112. Bei der Differenzbildung fallen diese Messsignale weg.
3. c) Ist Rauch vorhanden, so ist dessen Streulichtsignal für die blaue Leuchtdiode 112 um ein Mehrfaches größer als für die infrarote Leuchtdiode 111. Dies liegt daran, dass das spektrale Streuverhalten von Rauchaerosolen seht steil ist. Das an den Rauchaerosolen reflektierte Licht hängt mit etwa (1/λ) hoch n, von der Wellenlänge λ ab. Dabei ist n abhängig von der Art und der Dichte des Rauches eine Zahl zwischen ungefähr 4 und ungefähr 6. Bei der Differenzbildung zwischen den beiden Messsignalen bleibt somit ein großes Differenzsignal bestehen. Dieses ist ein deutliches Anzeichen für das Vorhandensein von Rauch in dem Streuvolumen.
4. d) Insekten, die über die Photodiode 120 oder die Leuchtdiode 111, 112 kriechen, können über sehr starke Schwankungen der Messsignale entdeckt werden. Um die Insekten in diesem Falle zu vertreiben, kann bei Bedarf zusätzlich eine Insektenvertreibungseinrichtung verwendet werden. Die Insektenvertreibungseinrichtung kann beispielsweise ein Ultra Sonic Mosquito-Repeller sein.

When operating an open optical scattered light detector 100, there are signals from four different causes, which must be reliably distinguished from each other for a meaningful smoke detection. This is possible with described scattered light smoke detector 100.

1. a) signals from the bottom or a side wall of a space to be monitored are because of the different wavelengths of the two light-emitting diodes 111 and 112 possibly not exactly the same strength. However, they will at least be similarly strong in amplitude. If a difference formation results in a value other than zero, a small offset signal results. This has neither to do with the detection of smoke nor with the influence of insects. For reliable operation with high sensitivity, this offset signal should be adjusted so that it always assumes the signal level zero.
2. b) scattered light measurement signals from buzzing insects result in a successfully performed adjustment procedure for both LEDs 111, 112 the same signal. This is particularly due to the following three circumstances:
   • b1) The above-described spectrally flat course of the scattering behavior of the insects.
   • b2) Due to the miniaturized structure of the scattered light smoke detector 100 for both types of light pulses, the relative spatial positions of the photodiode 120, an insect and the two light-emitting diodes 111, 112 are almost identical.
   • b3) The two light-emitting diodes 111, 112 are activated approximately simultaneously. This means that movement of the insect within a time interval between the two successive light pulses can be neglected to a good approximation.
   The two measurement signals reflected by an insect and received by the photodiode 120 are thus almost identical for both light-emitting diodes 111, 112. In the case of subtraction, these measurement signals are eliminated.
3. c) If smoke is present, its scattered light signal for the blue light-emitting diode 112 is several times greater than for the infrared light-emitting diode 111. This is because the spectral scattering behavior of smoke aerosols is steep. The light reflected at the smoke aerosols depends on the wavelength λ with approximately (1 / λ) high n. In this case, depending on the type and density of the smoke, n is a number between about 4 and about 6. In the difference between the two measurement signals thus remains a large difference signal. This is a clear indication of the presence of smoke in the litter volume.
4. d) Insects that crawl across the photodiode 120 or the light emitting diode 111, 112, can be detected by very large fluctuations of the measurement signals. In order to drive off the insects in this case, if necessary, an insect expelling device can additionally be used. The insect eviscerator For example, it can be an Ultra Sonic Mosquito Repeller.

By means of the open scattered light smoke detector 100 described with this application, the scattered light signals caused by the insects in the detection range can thus be effectively masked out. In addition, the described scattered light smoke detector 100 can be realized in a miniaturized design.

FIG. 2 shows in a plan view of a scattered light smoke detector 200. The scattered light smoke detector 200 differs from that in FIG. 1 shown scattered light smoke detector 100 only in that instead of two light emitting diodes, a so-called. Multi-chip light-emitting diode 210 is used. The multi-chip light-emitting diode 210 has a chip 211a emitting in the infrared spectral range and a chip 211b emitting in the blue spectral range. The photodiode 220 is the same as the photodiode 120 of the scattered light smoke detector 100, and therefore will not be explained again. The same applies to the spatial arrangement with the directly adjacent components photodiode 220 and multi-chip LED 210. The distance from the center of the photodiode 220 to the center of the multi-chip LED 210 is less than 4 mm.

FIG. 3 shows in a cross-sectional view the in FIG. 1 shown scattered light smoke detector, which is now provided with the reference numeral 300. The scattered light smoke detector 300 has a housing 302. In the lower region of the housing 302, a groove-shaped recess is provided, which serves as a holder for a printed circuit board 305. On the circuit board 305 all electronic and optoelectronic components of the scattered light smoke detector 300 are mounted. The circuit board is thus not only used as a carrier for in FIG. 3 not shown interconnects which electrically connect the individual components of the scattered light smoke detector 300 in a suitable manner. The circuit board 3β5 thus also serves as a mechanical support for the components of the scattered light smoke detector 300th

At the bottom of the circuit board 305 are formed as a dual-chip LED light emitting device 310 and the photodiode 320. Further, located at the bottom of the common circuit board 305 designed as a US Mosquito Repeller insect eviscerating device 350. This can always be activated when at According to the signal analysis described above, an insect is located directly on the light emitting diode 310 and / or the photodiode 320 or flying around in the vicinity of these two optoelectronic components.

At the top of the circuit board 305 is a driver electronics 315 for driving the dual-chip LED 310 in a suitable manner. Further, located at the top of the circuit board 305, a photo-amplifier 322, which is connected downstream of the photodiode 320, and an evaluation unit 330, which is the photo-amplifier 322 downstream. In addition, located at the top of the circuit board 305, a microcontroller 340, which controls the entire operation of the scattered light smoke detector 300.

The microcontroller 340 and the evaluation unit 330 can also be designed as a common integrated component.

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 a multiplicity of different embodiments are to be regarded as obviously disclosed to the person skilled in the art with the embodiment variants explicitly illustrated here.

Claims (13)

Apparatus for detecting smoke based on scattered light optical measurements, comprising the apparatus (100, 200, 300) A light emitting device (110, 210, 310) arranged to emit a temporal sequence of light pulses, wherein a first light pulse has a first spectral distribution and a second light pulse has a second spectral distribution that is different from the first spectral distribution, • a light receiver (120, 220, 320), set up to receive
a first scattered light from the first light pulse and
a second scattered light from the second light pulse, and for providing
a first output signal indicative of the first stray light, and
a second output signal indicative of the second scattered light, and An evaluation unit (330) arranged to compare the first output signal with the second output signal. Apparatus according to claim 1, wherein
the evaluation unit (330) is arranged to form a difference between the first output signal and the second output signal. Device according to one of claims 1 to 2, wherein the evaluation unit (330) is arranged
for determining the ratio of the amplitude of the first output signal to the amplitude of the second output signal. Device according to one of claims 1 to 3, wherein
the light emitting device (110, 210, 310) and the light receiver (120, 220, 320) are arranged directly next to each other. Device according to one of claims 1 to 4, wherein
the light emitting device (110, 210, 310) comprises a first light source (111a, 211a,) and a second light source (112a, 212a). Device according to one of claims 1 to 5, additionally comprising A microcontroller (340) which is coupled at least to the light-emitting device (110, 210, 310) and to the evaluation unit (330) and which is set up for temporally synchronizing at least the light-emitting device (110, 210, 310) and the evaluation unit (330) , Device according to one of claims 1 to 6, wherein the first light pulse is in the near infrared spectral range and / or
the second light pulse lies in the visible spectral range, in particular in the blue and / or violet spectral range. Device according to one of claims 1 to 7, wherein the first and / or the second light pulse has a time length in the range between 1 microseconds and 200 microseconds, between 10 microseconds and 150 microseconds or between 50 microseconds and 120 microseconds. Device according to one of claims 1 to 8, additionally comprising • an insect displacement device (350) which is coupled to the evaluation unit (330) and which can be activated in the case of temporally strong fluctuations of the first output signal and / or of the second output signal. A method of detecting smoke based on optical scattered light measurements, in particular using a device (100, 20, 300) according to any one of claims 1 to 8, comprising the method Emitting a temporal sequence of light pulses by means of a light emitting device (110, 210, 310), wherein a first light pulse has a first spectral distribution and a second light pulse has a second spectral distribution that is different from the first spectral distribution, Receiving a first scattered light from the first light pulse and a second scattered light from the second light pulse by means of a light receiver (120, 220, 320), Providing a first output signal indicative of the first scattered light and a second output indicative of the second scattered light, and • Comparing the first output signal with the second output signal by means of an evaluation unit (330). The method of claim 10, further comprising • Adjusting the intensities of the two light pulses, so that when a scattering of the two light pulses on a reference scattering object, the first output signal and the second output signal are the same size. A method according to claim 11, wherein
comparing the first output signal with the second output signal
forming a difference between the first output signal and the second output signal. The method of claim 12, further comprising • Compensating a slowly varying differential signal to a zero signal.

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