EP1879158A1 - Method for smoke detection and optical smoke alarm - Google Patents

Abstract

The method involves arranging two optical lines (A, B) such that light of transmitters (1, 11) of one of the optical lines scattered in a scattering volume is partially utilized in receivers (5, 15) of the other optical line. Signals that are received by the receivers are combined for determining the scattering of the light that is caused by aerosol in the scattering volume. The transmitters are subjected with electrical signals (S1, S2), and electrical lines (E1, E12, E2, E21) of the receiver are detected.

Description

The present invention is in the field of fire detection and relates to a method for the detection of smoke by determining the caused by an aerosol in a scattering volume scattering of light in two optical links, each containing a transmitter, and a receiver, and an optical smoke detector with at least two optical links each having a transmitter, a receiver and a common scattering volume.

Various types of functional principles of optical smoke detectors are known. Most widespread are the so-called scattered light detectors. These contain a transmitter, preferably an LED, a spreader and a receiver, which usually consists of a PIN diode or other suitable photodiode or a phototransistor with a downstream amplifier. The light beam emitted by the transmitter illuminates the spreader room and the receiver looks in the direction of the spreader room, but is in no way within the range of the emitted light beam. As soon as smoke or another aerosol enters the spreader room, light is scattered by the transmitter and thus partially reaches the receiver. The amount of light received is a measure of the smoke density. As soon as a certain threshold value is reached, the detector triggers an alarm. Such scattered light detectors are for example in the EP-A-0 772 170 and the EP-A-0 821 331 described.

Another known type of optical smoke detector are the so-called extinction detectors, which detect the attenuation of a light beam emitted by a transmitter to a receiver, caused by smoke. A distinction is made between line and point extinction detectors, the essential difference between these being the length of the light beam between transmitter and receiver.

For the line extinction detector, this length is usually more than 10 meters and for the point extinction detector less than 10 centimeters. For the extinction detectors see for example the EP-A-1 391 860 (Line extinction detector) and the EP-A-1 017 034 (Point-Extinktionsmelder).

To enable the detection of the type of fire, scattered light detectors with multiple receivers are known, which see the scattering volume at different angles. Likewise, there may be multiple transmitters that illuminate the broadcasting room at different angles, and you can also combine multiple transmitters with multiple receivers (see, for example, FIG EP-A-1 376 504 ).

In the EP-A-1 408 469 a fire detector with two transmitters and two receivers is described, the emitters emit light of different wavelengths. Since the scattering behavior of an aerosol depends on the particle size and the wavelength of the light, with such an arrangement, additional knowledge about the distribution of the particle size and thus about the possible nature of a fire can be obtained.

It is also known to use multiple transmitters and / or multiple receivers, but not monitor the same but spatially offset scattering volumes. Such an arrangement is preferably used when an inadmissible disturbance could occur in one of the scattering volumes, which may be the case, for example, with open smoke detectors. See for example the EP-A-1 191 496 ,

In all arrangements discussed so far, the signal of the receiver depends not only on the aerosol that has entered the spreader room, but also on the physical properties of the sender and receiver, and can also be influenced by other variables such as soiling of the detector, the influencing variables in their entirety can have a very large dispersion. Thus, an adjustment of the Detectors required in the manufacture. The mentioned influencing variables can also change during the lifetime of the detector. For example, the efficiency of the transmitter diodes may drop and / or the detector may become dirty.

The invention will now be a method for detecting smoke and an optical smoke detector of the type specified are given, in which in the manufacture of the smoke detector no adjustment is required and changes in the factors during the life of the detector have no effect on its signal.

The object is achieved in the method mentioned above according to the invention that the at least two optical paths are arranged so that scattered in the scattering volume of the transmitter of an optical path can partially enter the receiver of the other optical path and vice versa and that for Determining the aforementioned scatter the signals received from the two receivers are linked.

The smoke detector according to the invention is characterized in that each transmitter sends a light beam into the scattering volume and directly to its associated receiver, that the at least two optical paths are arranged so that light from the transmitter of the one optical path which is scattered in the scattering volume, partially in can reach the receiver of the other optical path and vice versa, and that the determination of the scattering caused by an aerosol in the scattering volume by linking the received signals from the two receivers.

If at least two optical transmitters and two optical receivers are present, there are thus two direct optical paths and two paths on which light is scattered. The combination of the signals received by the two receivers can be made in such a way be that all fabrication tolerances and aging of the electronic components on the result have no effect, so it is no longer necessary to match the smoke detector in the manufacture or in the context of maintenance work.

A first preferred embodiment of the inventive optical smoke detector is characterized in that two optical paths are provided and that the transmitter and receiver of each optical path are arranged so that the optical paths intersect in the scattering volume at a certain angle.

A second preferred embodiment is characterized in that the determination of the smoke density caused by an aerosol in the scattering volume is effected by a combination of four signals, namely the signals received by both receivers from both transmitters.

A further preferred embodiment of the optical smoke detector according to the invention is characterized in that both transmitters are supplied with an electrical signal and the electrical signals of the two receivers are determined, the signal emitted by the first transmitter and received by the second receiver being transmitted by the second transmitter multiplied and multiplied by the product of the signal transmitted by the first transmitter and received by the first receiver multiplied by the signal transmitted by the second transmitter and received by the second receiver.

In the following the invention will be explained in more detail with reference to an embodiment shown in the single drawing; the drawing shows a schematic cross section through the measuring chamber of an optical smoke detector. Optical smoke detectors are assumed to be known, it is referred in this context to the following patent publications, the disclosure of which is hereby expressly incorporated by reference: EP-A-0 772 170 . EP-A-1 017 034 . EP-A-1 376 504 ,

The illustrated optical smoke detector includes two inclined optical paths A and B which intersect at the absorptive and scattering volume of the detector indicated by reference V. The volume V, referred to below as the scattering volume, is located in the measuring chamber of the detector in a known manner. The first optical path A consists of a first transmitter 1 and a first receiver 5 arranged on the opposite side of the scattering volume V, the second optical path B analogously of a second transmitter 11 and a second receiver 15 arranged on the opposite side of the scattering volume V. The angle of inclination between the two optical paths A and B is approximately 60 ° as shown, but is variable within wide limits. It should also be noted that the illustrated smoke detector and the measuring principle described also work when the optical paths A and B do not cross or intersect but are only slightly offset from each other.

At the first transmitter 1, an electrical signal S _{1 is applied} , which is converted with a certain efficiency into optical power. The corresponding optical signal passes through a path 2 in the scattering volume and propagates in this straight for the most part on a path 3, where it suffers a certain attenuation. After emerging from the scattering volume V, the light emitted by the first transmitter 1 propagates on a path 4 until it enters the first receiver 5 and is converted therein into the electrical power E ₁ with a certain degree of efficiency. The ratio of the electric power output from the first receiver 5 to the optical power entering the path 4 is hereinafter referred to as e ₁ (Table 1).

An electrical signal S ₂ is applied to the second transmitter 11, which is converted into optical power with a certain degree of efficiency. The corresponding optical signal passes through a path 12 in the scattering volume V and propagates in this straight for the most part on a path 13, wherein it suffers a certain attenuation. After emerging from the scattering volume V, the light emitted by the second transmitter 11 propagates on a path 14 until it enters the second receiver 15 and is converted therein into the electrical power E ₂ with a certain degree of efficiency. The ratio of the electrical power output from the second receiver 15 to the optical power entering the path 14 is hereinafter referred to as e ₂ (Table 1).

In the scattering volume V, a certain proportion of the light entering via the path 2 is scattered in the presence of an aerosol. This scattered light leaves the scattering volume V via a dashed path 13 and continues to propagate thereon until it enters the second receiver 15. In this it is converted with a certain degree of efficiency into an electric power E ₂₁ .

The individual components are chosen and the circuit is designed so that the ratio of the output from the second receiver 15 electrical to the path 14 entering optical power over a large range is sufficiently constant, so that this ratio even in the case of the path 13 to the path 14 reaching stray light with sufficient accuracy equal to e ₂ can be set.

In the scattering volume V, in the presence of an aerosol, moreover, a certain proportion of the light entering via the path 12 is scattered. This scattered light leaves the scattering volume V via a dashed path 16 and propagates thereon until it enters the first receiver 5. In this, it is with a certain efficiency in an electric power E ₁₂ implemented. If the above-mentioned conditions for selection of the components and design of the circuit are met, the ratio of the electrical power output from the first receiver 5 to the optical power entering the path 4 may also be in the case of passing over the path 16 to the path 4 Stray light can be set to e1 with sufficient accuracy.

The parameters mentioned in the previous description, which are used for the calculation of the smoke density, are listed in the following Table 1: Table 1 S ₁ electrical signal to first transmitter 1 S ₁ Ratio of the entering into the scattering volume V optical power to the voltage applied to the first transmitter 1 electrical power x ₁ Attenuation of light from path 2 in the scattering volume V (path 3) e ₁ Ratio of the electrical power delivered by the first receiver 5 to the optical power entering the path 4 S ₂ electrical signal to second transmitter 11 S ₂ Ratio of the entering into the scattering volume V optical power to the applied to the second transmitter 11 electrical power x ₂ Attenuation of the light from the path 12 in the scattering volume V (path 13) e ₂ Ratio of the electrical power delivered by the second receiver 15 to the optical power entering the path 14 X ₂₁ Ratio of the scattered light emerging from the path 13 to the light entering the scattering volume V on the path 2 X ₁₂ Ratio of the scattered light emerging from the path 16 to the light entering the scattering volume V on the path 12 E ₁ electric power of the first receiver 5 caused by direct light from the first transmitter 1 E ₂ electric power of the second receiver 15 caused by direct light from the second transmitter 11 E ₁₂ electric power of the first receiver 5 caused by stray light E ₂₁ caused by stray light electrical power of the second receiver 15th

Each of the two receivers 5, 15 receives direct light from the transmitter 1 or 11 of its optical path 2 or 12 and scattered light from the transmitter 11 or 1 of the other optical path 12 or 2. From the various of the two receivers 5, 15th emitted signals E ₁ , E ₁₂ ; E ₂ , E ₂₁ is now determined in the following manner, the smoke density:

und da mit geringem Fehler x1 gleich 1 gesetzt werden kann: $${\mathrm{E}}_{\mathrm{1}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{e}}_{\mathrm{1}}$$

The power of the light entering the scattering volume V from the first transmitter 1 is S ₁ s ₁ . On the straight-line path through the scattering volume V, this light is attenuated by the factor x ₁ . Since the ratio of the electrical power output by the first receiver 5 to the optical power emerging from the scattering volume V is equal to e ₁ , finally: $${\mathrm{e}}_{\mathrm{1}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{x}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{e}}_{\mathrm{1}}$$

and because with a small error x1 can be set equal to 1: $${\mathrm{e}}_{\mathrm{1}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{e}}_{\mathrm{1}}$$

The same applies to the second optical path and thus: $${\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_{\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }{\mathrm{x}}_{\mathrm{2}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_{\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_{\mathrm{2}}$$

The power of the light coming from the first transmitter 1 to the second receiver 15 can be calculated in the same way. The power of the light entering the scattering volume V from the first transmitter 1 is S ₁ s ₁ . When this light is scattered in the scattering volume V, it is attenuated by a factor of x ₂₁ . Since the ratio of the output from the second receiver 15 electrical power to that of the scattering volume If the optical power emitted is again equal to e ₂ with sufficient accuracy, the following finally applies: $${\mathrm{e}}_{\mathrm{21}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{x}}_{\mathrm{21}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_{\mathrm{2}}$$

The electrical power output by the second receiver 15 is here designated E ₂₁ to indicate that the optical power originates from the first transmitter 1 and not from the second transmitter 11. For the same reasons as above, the following applies: $${\mathrm{<figure-callout\; id="12"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_{\mathrm{12}}\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\mathrm{\cdot }{\mathrm{x}}_{\mathrm{12}}\mathrm{\cdot }{\mathrm{e}}_1$$

The smoke detector shown schematically in the drawing is constructed so that the scattering angle between the paths 3 and 13 with sufficient accuracy is the same size as the scattering angle between the paths 6 and 16. Thus, the following applies: $${\mathrm{x}}_{\mathrm{12}}\mathrm{=}{\mathrm{x}}_{\mathrm{21}}\mathrm{=}\mathrm{x}$$

To determine the smoke density, the signal S _{1 is} applied to the first transmitter 1 and the signals E ₁ and E ₂₁ emitted by the two receivers 5 and 15 are measured simultaneously or at a short distance. This ensures that emitted from the transmitter 1 optical power for both measurements to a sufficient extent agrees, even if, for example, during the measurements, the transmitter 1 forming diode should heat up and thereby changes their efficiency. Alternately to the activation of the first transmitter 1, the signal S _{2 is} applied to the second transmitter 11 and the signals E ₂ and E ₁₂ emitted by the two receivers 15 and 5 are again measured simultaneously or at a short time interval.

$${\mathrm{E}}_{\mathrm{21}}\mathrm{=}{\mathrm{S}}_2\mathrm{\cdot }{\mathrm{s}}_2\mathrm{\cdot }\mathrm{x}\mathrm{\cdot }{\mathrm{e}}_1{\mathrm{E}}_2\mathrm{=}{\mathrm{S}}_2\mathrm{\cdot }{\mathrm{s}}_2\mathrm{\cdot }{\mathrm{e}}_2$$

The following applies: $${\mathrm{e}}_{\mathrm{1}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{e}}_{\mathrm{1}}{\mathrm{e}}_{\mathrm{21}}\mathrm{=}{\mathrm{S}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{s}}_{\mathrm{1}}\mathrm{\cdot }\mathrm{x}\mathrm{\cdot }{\mathrm{e}}_2$$

$${\mathrm{e}}_{\mathrm{21}}\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\mathrm{\cdot }\mathrm{x}\mathrm{\cdot }{\mathrm{e}}_1{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\mathrm{\cdot }{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_2$$

Using a suitable processor, the following expression is calculated: $$\sqrt{\frac{e_{21}\cdot e_{12}}{e_1\cdot {\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_2}}=\sqrt{\frac{S_1\cdot s_1\cdot x\cdot {\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\cdot {\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\cdot {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\cdot x\cdot e_1}{S_1\cdot s_1\cdot e_1\cdot {\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\cdot {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\cdot {\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}}_2}}=\sqrt{x\cdot x}=x$$

The result of the calculation x is nothing more than a measure of the smoke density.

With this method of calculation, the coefficients s ₁ , s ₂ , e ₁ and e _{2 are} eliminated in the simplest manner and thus all fabrication tolerances and aging phenomena of the electronic components can be eliminated, so that it is no longer necessary to protect the detector during fabrication or in the process Framework of maintenance work.

Claims (10)

Method for detecting smoke by determining the scattering of the light caused by an aerosol in a scattering volume (V) in two optical paths (A, B) each comprising a transmitter (1; 11) and a receiver (5; 15) , characterized in that the at least two optical paths (A, B) are arranged so that in the scattering volume (V) scattered light of the transmitter (1, 11) of the one optical path (A or B) partially in the receiver (15 or 5) of the other optical path (B or A) and vice versa, and that the signals received by the two receivers (5, 15) are linked for the determination of said scattering. A method according to claim 1, characterized in that the determination of said scattering by a combination of four signals, namely of both receivers (5; 15) each of two transmitters (1, 11) received signals. Method according to Claim 2, characterized in that both transmitters (1, 11) are supplied with an electrical signal (S ₁ or S ₂ ) and the electrical signals (E ₁ , E ₁₂ , E ₂ , E ₂₁ ) of the two receivers ( 5 and 15), wherein the signal emitted by the first transmitter (1), scattered and received by the second receiver (15) is multiplied by the signal received from the second transmitter (11), scattered and received by the first receiver (5) dividing this product by the product of the signal transmitted by the first transmitter (1) and received by the first receiver (5) multiplied by the signal transmitted by the second transmitter (11) and received by the second receiver (15). Optical smoke detector with at least two optical links (A; B) each having a transmitter (1; 11), a receiver (5; 15) and a common scattering volume (V), characterized in that each transmitter (1, 11) has a Light beam into the scattering volume (V) and directly to its associated receiver (5 or 15) sends that the at least two optical paths (A, B) are arranged so that light from the transmitter (1 or 11) of the one optical path ( A or B), which is scattered in the scattering volume (V), can pass partially into the receiver (15 or 5) of the other optical path (B or A) and vice versa, and that the determination of the aerosol in the scattering volume ( V) caused by a combination of the received signals from the two receivers (5, 15). An optical smoke detector according to claim 4, characterized in that two optical paths (A, B) are provided and that the transmitter and receiver (1, 5, 11, 15) of each optical (A, B) path are arranged so that the optical paths (A, B) in the scattering volume at a certain angle. Optical smoke detector according to claim 5, characterized in that the determination of the smoke density caused by an aerosol in the scattering volume (V) by a combination of four signals, that of both receivers (5; 15) respectively of both transmitters (1, 11) received signals takes place. Optical smoke detector according to claim 6, characterized in that both transmitters (1, 11) are supplied with an electrical signal (S ₁ or S ₂ ) and the electrical signals (E ₁ , E ₁₂ , E ₂ , E ₂₁ ) of the two receivers (5 or 15) are determined, wherein the first transmitter (1) emitted, scattered and received by the second receiver (15) signal multiplied by the second transmitter (11), scattered and received by the first receiver (5) signal multiplied and this product by the Product of the signal emitted by the first transmitter (1) and received by the first receiver (5) multiplied by the signal transmitted by the second transmitter (11) and received by the second receiver (15). Optical smoke detector according to one of claims 4 to 7, characterized in that the angle at which the light beams of the at least two optical paths (A, B) intersect each other in the scattering volume (V) is between 40 ° and 90 °, and preferably about 60 ° is. Optical smoke detector according to one of claims 4 to 7, characterized in that the two transmitters (1, 11) are intermittently subjected to an electrical signal (S ₁ or S ₂ ). Optical smoke detector according to one of claims 4 to 7, characterized in that the two transmitters (1, 11) with electrical signals (S ₁ and S ₂ ) are acted upon, which differ in their frequency and / or shape so far that can be determined by suitable means, which share of the received signals (E ₁ , E ₁₂ , E ₂ , E ₂₁ ) from the transmitter (1) of the one optical path (A) and which share from the transmitter (11) of the other optical path ( B).

Images