EP0530723A1 - Optical smoke detector with active monitoring - Google Patents

Abstract

A scattering light smoke detector with enhanced false alarm protection has, in accordance with a first embodiment, a radiation source (2) and two radiation detectors (7, 8) which are arranged in a measuring chamber (1) so far apart from one another that radiation reflected from an arbitrary location on the walls of the measuring chamber (1) generates different electrical signals of the radiation detectors (7, 8). These signals are compared with one another in an evaluation circuit, and an alarm is triggered if the output signal of one of the radiation detectors (7, 8) overshoots a predetermined value, whilst the difference between the signals remains, however, below a predetermined value. In accordance with another embodiment, the scattering light smoke detector has two radiation sources (2, 22) and a radiation detector (7); in this case, either the two radiation sources (2, 22), which are alternately driven by a pulse generator, are arranged in the measuring chamber (1) so far apart from one another, or they have a different intensity distribution inside their radiation range that radiation reflected from an arbitrary location on the walls of the measuring chamber (1) generates different electrical signals in the radiation detector (7). The signals arriving sequentially in time are stored in a time value memory (27, 28) before evaluation and then compared with one another. <IMAGE>

Description

The invention relates to an optical smoke detector according to the preamble of claim 1. Smoke detectors of this type are generally known. They are used in particular as automatic fire detectors for the early detection of fires.

Smoke detectors occupy a special position among the multitude of types of automatic fire detectors on the market, since they are best suited to detecting fires at such an early point in time that countermeasures can still be successfully initiated.

There are two main types of smoke detectors: ionization smoke detectors and optical smoke detectors. The ionization smoke detectors take advantage of the accumulation of smoke particles in air ions; The second type of smoke detector uses the optical properties of aerosols to detect smoke. Here, one uses either the weakening of a light beam by smoke ("extinction detector") or the scattering of light on smoke particles ("scattered light smoke detector"). Since the extinction by smoke is relatively low, the measuring section must be quite long in order to enable reliable detection of smoke. The last-mentioned scattered-light smoke detectors are the most widespread, since the measuring section can be so short that they can be designed as so-called "point detectors".

The present invention relates to scattered light smoke detectors. With these detectors, care must be taken to ensure that the radiation receiver is not influenced by radiation that was not generated by scattering smoke particles. For example, to prevent radiation from the environment from striking the receiver, the detectors are provided with a light-tight housing which surrounds the radiation beam in the measuring chamber. The housing has smoke inlets that allow outside air to enter and at the same time prevent light from entering at the same time.

A prerequisite for the proper functioning of such a scattered light smoke detector is that no light is reflected on the walls limiting the measurement volume or on foreign bodies deposited there, which light hits the receiver and can thus simulate a smoke signal. Proposals have been made to influence the wall reflections by a suitable construction to reduce. These suggestions essentially concern the construction of optical labyrinths (see eg CH-A5-590'527), which largely absorb the incident light.

Since the smoke entry openings cannot be made arbitrarily small, however, it cannot be prevented that dust, fibers or insects can also penetrate into the interior of the detector and cause the detector to malfunction. The illuminated foreign bodies act like light sources; if, in the worst case, its radiation falls directly on the radiation receiver, it can generate an electrical signal there and simulate the appearance of smoke. Therefore, to avoid frequent false alarms, scattered light smoke detectors must be cleaned at regular intervals, which is associated with considerable costs.

Another, particularly annoying cause of false alarms is a mostly temporary condensation of moisture on the measuring chamber walls caused by temperature changes. This also produces reflections that are detected by the receiver. Since this can also happen with clean detectors, a revision is of no use in such cases.

To solve this problem, methods have been known which monitor the growth of the wall reflections and generate an interference signal when the secondary radiation emanating from the walls exceeds a certain value. Such methods fail, however, if the time course of the deposition is similar to that of a fire.

In order to eliminate this disadvantage, two radiation receivers were provided in a known smoke detector (JP-UM-131'052), the fields of view of which detect different parts of the radiation beam, which lie at a different distance from the radiation source and in which the scattered radiation intensity varies in the presence of smoke is. An alarm signal is only triggered by a logic circuit if the scattered radiation intensities received are in the correct relationship to one another. However, since the fields of view of the two receivers detect different wall areas, different reflection properties at these points, which can be generated, for example, by different dust deposits, cannot be eliminated.

In order to eliminate the influence of wall reflection, a scattered light smoke detector was proposed in DE-C3-27'54'139 (see the attached FIG. 1), in which a radiation source 2 is provided in a cylindrical housing 1, which radiation beam 3 extends across the beam Measuring chamber sends. At another point on the cylinder wall, a first radiation receiver 7 is attached outside the radiation beam 3 in such a way that its field of view 13 crosses the radiation beam 3 approximately in the middle and detects at least part of the radiation beam 3. Adjacent to the radiation receiver 7, a second radiation receiver 8 is provided, which is attached in such a way that its field of vision 14 does not touch the radiation beam 3, but passes by the edge thereof and is directed at the same wall area 15 that is detected by the field of view 13 of the first radiation receiver 7 . The influence of the interference radiation originating from the wall section 15 can be eliminated under certain conditions by means of an evaluation circuit which has a difference generator which forms a difference between the signals of the two radiation receivers 7, 8. However, since it is practically not possible to bundle the fields of view of the radiation receivers 7, 8 so precisely that the detected wall areas both cover one hundred percent and behave in the same way with regard to reflections, false alarms due to dust still cannot be prevented.

The main disadvantage of the known methods for preventing false alarms by dusting, however, is that there are demands on the optical systems which cannot be met in practice; this applies to both the radiation sources and the radiation receivers. By depositing foreign bodies on the lenses or diaphragms, these are influenced in such a way that they can no longer fulfill their intended tasks, i.e. the beam paths no longer run as expected.

Starting from this prior art, the invention has for its object to provide a smoke detector based on the scattered radiation principle, which does not have the disadvantages of the known scattered-light smoke detectors mentioned and in particular to create a smoke detector of the type mentioned, which makes it possible for stray light from deposited foreign bodies clearly recognizable as such and to avoid false alarms due to dust deposits.

This object is achieved in a smoke detector of the type mentioned by the characterizing features of claim 1. Preferred embodiments the invention and embodiments are defined in the dependent claims.

In search of characteristic differences between dust particles and smoke, tests were carried out on scattered-light smoke detectors that were exposed to a dusty atmosphere. It was found that, at least in the initial stage of dusting or condensation of moisture inside the smoke detectors, the distribution of the foreign bodies on the walls of the measuring chamber is very inhomogeneous, while the distribution of smoke that has entered the measuring chamber is homogeneous. There are also significant differences between smoke and dust particles in terms of size and number.

While smoke is a homogeneous distribution of a large number of very small particles, dust deposits or condensation, at least in the initial phase, are an inhomogeneous distribution of a small number of relatively large particles. A few dust particles are sufficient to cause scattered radiation that simulates a large number of smoke particles and triggers a false alarm.

The above-mentioned differences are used in a scattered-light smoke detector according to the invention in such a way that either one radiation source and several radiation receivers or several radiation sources and one radiation receiver are provided. Instead of several radiation receivers, it is also possible to use a single radiation receiver with a divided detector surface (halved or quartered).

According to a preferred embodiment of the smoke detector according to the invention, a radiation source and a plurality of radiation receivers are provided in the measuring chamber, the radiation receivers being arranged so far apart that the scattered light emanating from deposited foreign bodies travels for different distances or the fields of view of the radiation receivers are sufficiently separated from one another. In both cases, the electrical signals generated by the radiation receivers have clearly measurable differences.

According to another preferred embodiment of the smoke detector according to the invention, a plurality of radiation sources and a radiation receiver are provided in the measuring chamber, the radiation sources being operated alternately and the electrical output signals of the radiation receiver are buffered until evaluation. The radiation sources are either arranged so far apart that the light striking foreign objects has to travel different distances, or the intensity distributions of the radiation sources are sufficiently different from one another. In both cases, the scattered light emanating from the foreign bodies differs from scattered light emanating from smoke particles and the electrical signals generated in the radiation receiver differ significantly from those generated from scattered light emanating from smoke particles.

For example, if there are two radiation receivers, when smoke enters the measuring chamber of the smoke detector, the electrical output signals of the radiation receivers increase evenly due to the homogeneous distribution of the smoke particles, while the presence of foreign bodies is noticeable by the fact that the signals of the two radiation receivers grow at different rates . In the simplest case, it is therefore sufficient to form the difference between the electrical output signals of the two radiation receivers in order to determine the origin of the radiation.

Figur 1

eine perspektivische Ansicht eines Streulichtrauchmelders gemäß dem Stand der Technik,

Figur 2

einen Querschnitt durch einen erfindungsgemäßen Streulichtrauchmelder mit einer Strahlungsquelle und zwei weit voneinander entfernten Strahlungsempfängern,

Figur 3

einen Querschnitt durch einen erfindungsgemäßen Streulichtrauchmelder mit einer Strahlungsquelle und zwei Strahlungsempfängern mit unterschiedlichen Gesichtsfeldern,

Figur 4

einen Querschnitt durch einen erfindungsgemäßen Streulichtrauchmelder mit zwei weit voneinander entfernten Strahlungsquellen und einem Strahlungsempfänger,

Figur 5

einen Querschnitt durch einen erfindungsgemäßen Streulichtrauchmelder mit zwei Strahlungsquellen unterschiedlicher Intensitätsverteilung und einem Strahlungsempfänger,

Figur 5a

die Intensitätsverteilung zweier Strahlungsquellen, die räumlich nebeneneinader liegen und sich überlappen,

Figur 5b

die Intensitätsverteilung zweier Strahlungsquellen, die auf einer Achse liegen jedoch unterschiedliche Strahlungsprofile aufweisen,

Figur 6

das Blockschaltbild einer elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 2,

Figur 7

das Blockschaltbild einer weiteren Ausgestaltung der elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 2,

Figur 8

das Blockschaltbild einer elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 4,

Figur 9

das Blockschaltbild einer elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 5,

Figur 10

das Blockschaltbild einer weiteren Ausgestaltung der elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 5,

Figur 11

das Blockschaltbild einer weiteren Ausgestaltung der elektronischen Schaltung eines Streulichtrauchmelders gemäß Figur 5,

Figur 12

einen Querschnitt durch eine weitere Ausführungsform eines erfindungsgemäßen Streulichtrauchmelders mit unterteiltem Strahlungsempfänger.

The invention is explained in more detail below with reference to the preferred embodiments shown in the drawings. Show it

Figure 1

1 shows a perspective view of a scattered-light smoke detector according to the prior art,

Figure 2

2 shows a cross section through a scattered light smoke detector according to the invention with a radiation source and two radiation receivers that are far apart,

Figure 3

2 shows a cross section through a scattered light smoke detector according to the invention with one radiation source and two radiation receivers with different visual fields,

Figure 4

2 shows a cross section through a scattered light smoke detector according to the invention with two radiation sources far apart and a radiation receiver,

Figure 5

2 shows a cross section through a scattered light smoke detector according to the invention with two radiation sources of different intensity distribution and one radiation receiver,

Figure 5a

the intensity distribution of two radiation sources which are spatially adjacent and overlap,

Figure 5b

the intensity distribution of two radiation sources, which, however, lie on one axis have different radiation profiles,

Figure 6

the block diagram of an electronic circuit of a scattered light smoke detector according to Figure 2,

Figure 7

2 shows the block diagram of a further embodiment of the electronic circuit of a scattered light smoke detector according to FIG. 2,

Figure 8

the block diagram of an electronic circuit of a scattered light smoke detector according to Figure 4,

Figure 9

the block diagram of an electronic circuit of a scattered light smoke detector according to Figure 5,

Figure 10

the block diagram of a further embodiment of the electronic circuit of a scattered light smoke detector according to Figure 5,

Figure 11

the block diagram of a further embodiment of the electronic circuit of a scattered light smoke detector according to Figure 5,

Figure 12

a cross section through a further embodiment of a scattered light smoke detector according to the invention with a divided radiation receiver.

Figure 2 shows a scattered light smoke detector according to the invention in cross section in a highly simplified schematic representation. A radiation source 2 and two radiation receivers 7, 8, which are far apart from one another, are arranged in a measuring chamber 1 which is sealed off from the outside atmosphere in such a way that no radiation can fall directly from the radiation source 2 onto the radiation receivers 7, 8; this can be achieved, for example, by an appropriately arranged diaphragm system 4. The measuring chamber 1 is connected to the outside atmosphere by smoke inlet openings (not shown).

The scattering of the light emanating from a radiation source 2 on a foreign body F, which has been deposited on a wall, is the same as the scattering of the light on smoke particles R (only some of the smoke particles are indicated in FIG. 2) Strength of the light incident at the starting point of the scattered radiation proportional. However, there is a fundamental difference between the light scattering on a foreign body F and the light scattering on smoke particles R. In fact, smoke is quasi uniformly, ie homogeneously, distributed in the measuring chamber 1, whereas foreign bodies F are located at individual points on the walls of the measuring chamber 1, ie are distributed inhomogeneously in the measuring chamber 1.

In other words: the intensity of the scattered light emanating from a foreign body F is proportional to the light intensity of the radiation source 2, measured at the location of the foreign body F, while the intensity of the scattered light emanating from smoke particles R is proportional to the light intensity, measured in the entire measurement volume .

Tests on fire detectors that have been in use for a long time have shown that the foreign bodies F, e.g. Dust, very inhomogeneously distributed inside the detector. The scattered light generated by irradiation of the foreign bodies F is consequently also very inhomogeneous. The scattered light striking the receiver 7 is therefore heavily dependent on the location of the foreign bodies F. Depending on the position of the foreign bodies F, the light has to travel different distances.

In contrast, the smoke particles R acting as scattering centers are largely homogeneously distributed in the measuring chamber 1. The scattered light generated by it and impinging on the receiver 7 is only dependent on the concentration of the smoke particles R and their optical properties.

This difference is used in the smoke detector according to the invention in such a way that either several radiation receivers 7, 8 (FIGS. 2 and 3) or several radiation sources 2, 22 (FIGS. 4 and 5) are arranged in the measuring chamber 1 of the smoke detector in such a way that by comparison the electrical signals can be distinguished between the scattering of smoke particles R and the radiation emanating from deposited foreign bodies F.

If there are two spatially separate radiation receivers 7, 8 (FIG. 2), the signals can be compared directly with one another. This is explained in more detail below in exemplary embodiment 1.

If two radiation sources 2, 22, but only one radiation receiver 7 are present, as shown in FIG. 4, the two radiation sources 2, 22 must be operated alternately in a known manner, and the electrical output signals of the radiation receiver 7 are stored so that they are separated Evaluation stages (evaluation channels) can be supplied (see Figure 8). This is explained in more detail below in exemplary embodiment 2 for two radiation sources 2, 22 which are arranged far apart from one another.

FIG. 5 shows a third embodiment of the smoke detector according to the invention. Two light sources 2, 22 of different intensity distribution are arranged close to one another; With this arrangement it is possible to distinguish whether the measured signal of the radiation receiver 7 is proportional to the total light intensity of the radiation sources 2, 22, i.e. whether the measured signal was caused by smoke R or whether the signal was caused by light that was generated by scattering on a foreign body F.

worin

U1 =

Intensität des Signals, das mit dem Strahlungsempfänger 7 gemessen wird, wenn Strahlungsquelle 2 Licht aussendet,

U2 =

Intensität des Signals, das mit dem Strahlungsempfänger 7 gemessenen wird, wenn Strahlungsquelle 22 Licht aussendet,

{ =

Integralzeichen,

I1 =

Lichtintensität, wenn Strahlungsquelle 2 Licht aussendet und

I2 =

Lichtintensität, wenn Strahlungsquelle 22 Licht aussendet,

bedeuten.In other words, the following applies to stray light caused by smoke R:

wherein

U1 =

Intensity of the signal measured with the radiation receiver 7 when the radiation source 2 emits light,

U2 =

Intensity of the signal measured with the radiation receiver 7 when the radiation source 22 emits light,

{=

Integral sign,

I1 =

Light intensity when radiation source 2 emits light and

I2 =

Light intensity when radiation source 22 emits light,

mean.

This embodiment of the smoke detector according to the invention is explained in more detail below in exemplary embodiment 3.

Instead of two radiation receivers 7, 8, it is also possible to use only a single radiation receiver 7, the sensor surface of which is divided into two sensor elements (detector halves) 71, 72 (cf. FIG. 12). The radiation beam 3 emanating from the radiation source 2 crosses the field of view 13 of the radiation receiver 7; the measurement volume 6 is defined by this crossing. In front of the radiation receiver 7 there is an optical system (lens) 5 which is set up in such a way that the measurement volume 6 is imaged on the surface of the sensor 7. The division of the sensor 7, by which the sensor 7 is divided into two halves, can be done either vertically or horizontally. A fiber F on the central diaphragm 12 acts on the two sensor elements 71, 72 different. The fiber F can be distinguished from smoke R by measuring the symmetry of the signals of the two sensor halves.

If the two detector halves 71, 72 are arranged one above the other, the lower detector half 71 looks more upwards, the upper detector half 72 more downwards. Dust penetrating into the measuring chamber 1 settles mainly in the lower part of the measuring chamber. Dust F is thus primarily seen from the upper half of the detector. A symmetry measurement can be used to distinguish between dustiness of the detector and penetrating smoke.

A preferred embodiment of the above-described smoke detector with two-part sensor element 7 consists in that the sensor element 7 is divided into four sensor elements (detector quarters). A change in the radiation symmetry can thus be optimally recognized. In normal operation, the detector parts are connected in parallel. As soon as a predetermined signal threshold (pre-alarm threshold) is exceeded, the individual detector parts are queried one after the other.

In the absence of disturbing wall reflections, the signals from the individual detector elements grow to the same extent when smoke penetrates, whereas they are very different in the case of a dusty detector. The presence of disruptive foreign bodies F, whether individual fibers, insects, deposited dust or condensate, can thus be clearly recognized by comparing the output signals of the radiation receivers or sensor elements. In the simplest case, it is sufficient to form the difference between the electrical signals for checking the origin of the signals.

Figure 2 shows schematically the cross section of a scattered light smoke detector according to the invention, in which false alarms triggered by dust are suppressed. In the measuring chamber 1 there are a radiation source 2, two radiation receivers 7, 8 and an aperture system 4, by means of which radiation is prevented from falling directly from the radiation source 2 onto one of the radiation receivers 7, 8. A foreign body F is drawn on the chamber wall and is to be taken as an example of a starting point for interference radiation.

Figure 6 shows the example of an electronic circuit of an invention. optical smoke detector. The radiation source 2 is controlled periodically by a generator 9 and sends light pulses into the measuring chamber 1. The electrical output signals of the radiation receivers 7, 8 are amplified separately in associated amplifiers 10, 11 and fed separately to two operational amplifiers 16, 17.

In the event of smoke penetrating into the measuring chamber 1, both radiation receivers 7, 8 are exposed to radiation to approximately the same extent, and their output signals are therefore approximately the same size. Assuming that a foreign body F has settled on the wall of the measuring chamber 1, the different path lengths of the radiation between the foreign body F and the radiation receivers 7, 8 cause the two radiation receivers 7, 8 to receive different intensities of stray light, i.e. the electrical output signals of the amplifiers 10, 11 are different.

The first operational amplifier 16 is designed such that its output signal is proportional to the mean value of the output signals of the two amplifiers 10, 11.

The second operational amplifier 17 is designed such that its output signal is proportional to the absolute amount of the relative difference between the output signals of the two amplifiers 10, 11. This signal is a measure of the asymmetry of the scattering centers F with respect to the two radiation receivers 7, 8. In the event that smoke penetrates into the measuring chamber 1, the output signal of the second operational amplifier 17 is small, in the event that foreign bodies penetrate ( Fibers, insects) or large in the case of dust.

The outputs of the two operational amplifiers 16, 17 are connected to two threshold value detectors 18, 19, which each generate an output signal when the output signals of the associated operational amplifiers 16, or 17 exceed a predetermined limit value, ie the first threshold value detector 18 generates an output signal when the Mean value of the output signals of the two amplifiers 10, 11 (ie the output signal of the first operational amplifier 16) exceeds a predetermined value and the second threshold value detector 19 generates an output signal if the absolute amount of the relative difference of the output signals of the two amplifiers 10, 11 (ie that Output signal of the second operational amplifier 19) exceeds a predetermined limit value.

The outputs of the threshold value detectors 18, 19 are connected to a logic circuit 20, the output signal of which controls an alarm stage 21 to generate an alarm signal. The alarm stage 21 is connected to a signal center 25 via a first line 23.

The logic circuit 20 is designed such that a signal is only forwarded to the alarm stage 21 if the threshold of the first threshold value detector 18 is exceeded and, at the same time, the threshold of the second threshold value detector 19 is not exceeded. The following truth table results for the output of the logic circuit 20: Logical output of circuit 20 0 0 1 0 Logical outputs of the threshold detectors 18th 0 0 1 1 19th 0 1 0 1

• 1. Dringt Rauch in den unverstaubten Melder ein, so wird nur die Schwelle des ersten Schwellenwertdetektors 18 überschritten, und es wird ein Alarmsignal erzeugt, da die Schwelle des zweiten Schwellenwertdetektors 19 nicht überschritten wird.
• 2. Bei einer Verstaubung des Melders, ohne daß Rauch eindringt, kann zwar die Schwelle des ersten Schwellenwertdetektors 18 überschritten werden, da aber gleichzeitig die Schwelle des zweiten Schwellenwertdetektors 19 überschritten wird, wird die Alarmstufe 21 durch die logische Schaltung 20 blockiert, d.h. ein Fehlalarm durch Verstaubung wird verhindert.

By a suitable choice of the thresholds of the two threshold value detectors 18, 19 it can be achieved that a scattered light smoke detector according to the invention has the following properties:

• 1. If smoke penetrates the dust-free detector, only the threshold of the first threshold value detector 18 is exceeded and an alarm signal is generated since the threshold of the second threshold value detector 19 is not exceeded.
• 2. If the detector becomes dusty without smoke penetrating, the threshold of the first threshold detector 18 can be exceeded, but since the threshold of the second threshold detector 19 is exceeded at the same time, the alarm stage 21 is blocked by the logic circuit 20, ie a false alarm dust is prevented.

FIG. 7 shows a further example of an electronic circuit of an optical smoke detector according to the invention, in which the dust is transmitted to the signal center 25 as a fault signal. In a departure from the first example, the second threshold value detector 19 is additionally connected to a fault transmission circuit 29 which generates a fault signal when the threshold set in the second threshold value detector 19 is exceeded. This signal is transmitted to the signal center 25 by means of a second line 24. In the signal center 25, the fault signal can be evaluated as an indication of detector contamination and the replacement or cleaning of the detector can be initiated. Otherwise, the mode of operation of the circuit is the same as that described for the circuit according to FIG. 6.

Figure 4 shows a scattered light smoke detector according to the invention in cross section in a highly simplified schematic representation. With this detector, the same advantages as described above for a smoke detector with a radiation source 2 and two radiation receivers 7, 8 are achieved in that the smoke detector is equipped with only one radiation receiver 7, but instead with several radiation sources (2, 22) . The main difference to the circuit according to FIG. 6 is that the signals to be compared are generated one after the other in time. They must therefore be saved until processing. However, only one radiation receiver 7 is required for this.

In the measuring chamber 1 there are a first radiation source 2, a second radiation source 22, a radiation receiver 7 and a diaphragm system 4, by means of which radiation is prevented from falling directly from one of the two radiation sources 2, 22 onto the radiation receiver 7. A foreign body F is again drawn on the chamber wall and is to be assumed as an example of a starting point for interference radiation.

The electronic circuitry of the smoke detector according to FIG. 4 is shown schematically in FIG. The two radiation sources 2, 22 are periodically controlled alternately by a generator 9 and send light pulses into the measuring chamber 1, which, however, through the aperture system 4, the radiation receiver 7 cannot reach directly.

The output signal of the receiver 7 is amplified in the amplifier 10 and fed to the switch 26 synchronized by the generator 9, which alternately connects the first time value memory 27 and the second time value memory 28 to the amplifier 10. The output signals of the time value memories 27, 28 each correspond to the peak values of the output signals of the radiation receiver 7. In the simplest case, the two time value memories 27, 28 consist of capacitors, which are each charged or discharged via the switch 26.

As shown in FIG. 8, the outputs of the two time value memories 27, 28 are connected to two operational amplifiers 16, 17, which form the mean values or the absolute amounts of the relative difference between the output signals of the two time value memories 27, 28. The further signal processing is the same as that described in embodiment 1.

Even in the case of a scattered-light smoke detector with two radiation sources 2, 22 and a radiation receiver 7, the detection of dustiness can be signaled by a malfunction transmission circuit (not shown in FIG. 8) as a malfunction to the signal center 25.

FIG. 5 shows a further example of a scattered-light smoke detector according to the invention, in which false alarms are suppressed by dust. There are two radiation sources 2, 22 and a radiation receiver 7 in the measuring chamber 1. The radiation beam 3 emanating from the radiation sources 2, 22 and the field of view 13 of the radiation receiver 7 cross each other and the crossing area defines the measuring volume 6. A is schematically shown on the chamber wall Foreign body F is drawn in, which is to be taken as an example of a starting point for interference radiation.

The two radiation sources 2, 22 are arranged very close to one another, so that the distance to certain points on the wall and to the measuring volume 6 is practically the same. The two radiation sources 2, 22 have radiation profiles (cf. FIG. 5a) which are identical in shape but spatially side by side lie and overlap. In the embodiment shown in Figure 5, the two radiation sources 2, 22 are arranged so that their optical axes are not identical.

According to another embodiment, the two radiation sources have their main axes on the same axis, but they have differently designed radiation profiles (cf. FIG. 5b). The two radiation sources 2, 22 are controlled periodically by a generator 9 and send light pulses into the measuring chamber 1. The radiation receiver 7 is arranged in such a way that the electrical signal is very small in normal operation without smoke or interference.

The block diagram of the electronic circuit of a scattered light smoke detector according to FIG. 5 is shown in FIG. 9. The electrical signal of the radiation receiver 7 is amplified in a first amplifier 10 and fed to the switch 26 which is synchronized by the generator 9 and which alternately controls the two time value memories 27, 28. The output signals of the two time value memories 27, 28 each correspond to the peak values of the signals of the radiation receiver 7. The output signals of the two time value memories 27, 28 are fed separately to two operational amplifiers 16, 17. The first operational amplifier 16 is designed such that its output signal is proportional to the mean value of the output signal of the two time value memories 27, 28.

The second operational amplifier 17 is designed such that its output signal is proportional to the absolute amount of the relative difference between the output signals of the two time value memories 27, 28. The absolute amount of the relative difference is formed in the rectifier 31. This signal is a measure of the asymmetry of the scattering centers F. In the event that smoke enters the measuring chamber 1, the output signal of the second operational amplifier 17 is small, but it is large in the case of dust.

The outputs of the two operational amplifiers 16 and the rectifier 31 are connected to two threshold value detectors 18, 19 which generate a signal when the mean value or the absolute amount of the relative difference between the output signals of the two time value memories 27 and 28 exceeds a predetermined limit value (cf. Embodiment 1).

The outputs of the threshold value detectors 18, 19 are connected to a logic circuit 20. The logic circuit 20 is designed so that only then a signal is generated when the threshold of the first threshold detector 18 is exceeded and at the same time the threshold of the second threshold detector 19 is not exceeded.

Here, too, the thresholds of the threshold value detectors 18 and 19 can be selected such that the scattered-light smoke detector described has the properties described in exemplary embodiment 1.

FIG. 10 shows a further example of an electronic circuit of a scattered-light smoke detector according to the invention, which has the properties 1) and 2) of the scattered-light smoke detector described in exemplary embodiment 1 and in which an alarm signal is additionally triggered when smoke penetrates, even if the detector is due to dust or condensation Has displayed "Fault".

The difference from the circuit according to FIG. 9 is that the threshold value of the comparator 32 is always reset. The penultimate measured value at the output of the rectifier 31 is used as the threshold value for the comparator 32. For this purpose, the last measured values are always stored in the third 33 and fourth time value memories 34. When dust or fibers penetrate the scattered light smoke detector, the output of the logic circuit 20 is zero, so no alarm signal is forwarded. If smoke now enters the dusty detector, the relative difference between the output signals of the two amplifiers 10, 11 decreases, but the blocking of the alarm stage 20 can only be released when the threshold of the second threshold value detector 19 is again undershot. However, this is only possible if the value of the comparator is adapted to the dust. As a result, the detector is able to emit an alarm signal despite the dust. The alarm signal is transmitted to a signal center 25 by means of a first line 23 for the purpose of displaying and triggering corresponding further signals.

FIG. 11 shows a further example of an electronic circuit of a scattered light smoke detector according to the invention, in which any dust that may occur can also be transmitted to the control center as a fault signal. In a departure from the example according to FIG. 9, the second threshold value detector 19 is additionally connected to a second logic circuit 30 which generates a fault signal when the threshold set in the second threshold value detector 19 is exceeded. This signal can be obtained using a second Line 24 to the signal center 25 are transmitted. Otherwise, the mode of operation of the circuit is the same as that described in FIG. 9.

In the signal center 25, the fault signal can be evaluated as an indication of detector contamination and the replacement or cleaning can be initiated.

Zylindrisches Gehäuse, Meßkammer

1

(Erste) Strahlungsquelle

2

Zweite Strahlungsquelle

22

Strahlungsbündel

3

Blendensystem

4

Optik (Linse)

5

Meßvolumen

6

(Erster) Strahlungsempfänger

7

Detektorhälfte

71

Detektorhälfte

72

Zweiter Strahlungsempfänger

8

Generator

9

Erster Verstärker

10

Zweiter Verstärker

11

Gesichtsfeld von 7

13

Gesichtsfeld von 8

14

Wandabschnitt

15

Erster Operationsverstärker

16

Zweiter Operationsverstärker

17

Erster Schwellenwertdetektor

18

Zweiter Schwellenwertdetektor

19

(Erste) logische Schaltung

20

Alarmstufe

21

Speicher

22

Erste Leitung

23

Zweite Leitung

24

Signalzentrale

25

Schalter

26

Erster Zeitwertspeicher

27 Sample and hold circuit

Zweiter Zeitwertspeicher

28 Sample and hold circuit

Störungsübermittlungsschaltkreis

29

Zweite logische Schaltung

30

Gleichrichter

31

Komparator

32

Dritter Zeitwertspeicher

33 Sample and hold circuit

Vierter Zeitwertspeicher

34 Sample and hold circuit

Fremdkörper

F

Rauchpartikel

R

Modifications of the above-described circuits for fire detectors are possible within the scope of the invention according to the claims and are familiar to the person skilled in the art.

Cylindrical housing, measuring chamber

1

(First) radiation source

2nd

Second radiation source

22

Radiation beam

3rd

Aperture system

4th

Optics (lens)

5

Measuring volume

6

(First) radiation receiver

7

Half of the detector

71

Half of the detector

72

Second radiation receiver

8th

generator

9

First amplifier

10th

Second amplifier

11

Field of vision of 7

13

Field of view from 8

14

Wall section

15

First operational amplifier

16

Second operational amplifier

17th

First threshold detector

18th

Second threshold detector

19th

(First) logic circuit

20th

Alert level

21

Storage

22

First line

23

Second line

24th

Signaling center

25th

counter

26

First time value memory

27 Sample and hold circuit

Second time value memory

28 Sample and hold circuit

Interference transmission circuit

29

Second logic circuit

30th

Rectifier

31

Comparator

32

Third time value memory

33 Sample and hold circuit

Fourth time value memory

34 Sample and hold circuit

foreign body

F

Smoke particles

R

Claims (9)

Smoke detector with at least one radiation source (2, 22) arranged in a measuring chamber (1), at least one radiation receiver (7, arranged outside the direct radiation area of the radiation source (2, 22), which is exposed to scattered radiation in the presence of smoke and emits electrical output signals. 8), and an electronic evaluation circuit which, depending on the output signals of the radiation receivers (7, 8), emits an alarm signal and forwards it to a signal center (25), characterized in that radiation sources (2, 22) and radiation receivers (7, 8) are arranged and set up in the measuring chamber (1) in such a way that the radiation generated by scattering on fire aerosol particles distributed homogeneously in the measuring chamber (1) generates electrical signals in the radiation receivers (7, 8) which differ from electrical signals which are caused by radiation are generated, which are inhomogeneous in the measuring chamber (1) distributed foreign bodies and that in the evaluation circuit electronic means (10, 11, 16, 17, 18, 19, 20) are present, which compare these signals with one another and generate an alarm signal when the homogeneity of the output signals indicates that a Brandaersol is present in the measuring chamber (1) and generate a fault signal different from the alarm signal if the difference in the signals exceeds a predetermined value. Smoke detector according to claim 1, characterized in that a radiation source (2) and two radiation receivers (7, 8) are present in the measuring chamber (1), the radiation receivers (7, 8) being arranged so far apart from one another that they can be anywhere the walls of the measuring chamber (1) reflected radiation generates different electrical output signals of the radiation receiver (7, 8) and that in the evaluation circuit a first (10) and a second amplifier (11) for separate amplification of the output signals of the first (7) and the second Amplifier (8) are provided. (Figure 2) Smoke detector according to claim 1, characterized in that a radiation receiver (7) and two radiation sources (2, 22) are present in the measuring chamber (1), the radiation sources (2, 22) being arranged so far apart that from any place the walls of the measuring chamber (1) reflected radiation generates different electrical output signals of the radiation receiver (7) that the radiation receiver (7) is followed by an amplifier (10) and that a pulse generator (9), a switch (26), a first time value memory ( 27) and a second time value memory (28) are provided, which are electrically connected to one another and set up in such a way that the radiation sources (2, 22) alternately emit light and that the time value memory (27, 28) synchronously with the output of the amplifier (10 ) get connected. (Figure 4, 7) Smoke detector according to claim 1, characterized in that in the measuring chamber (1) there is a radiation receiver (7) and two radiation sources (2, 22) which are arranged so close to one another that their radiation areas partially overlap, and that the radiation sources ( 2, 22) have an intensity distribution that is the same in shape. (Figure 5, 5a, 9) Smoke detector according to claim 1, characterized in that a radiation receiver (7) and two radiation sources (2, 22), which have a common optical axis, are present in the measuring chamber (1) and that the radiation sources (2, 22) have a different intensity distribution have so that radiation reflected from any location on the walls of the measuring chamber (1) generates different electrical output signals of the radiation receiver (7). (Figure 5, 5b, 9) Smoke detector according to one of Claims 2 to 4, characterized in that in the evaluation circuit a first operational amplifier (16), the output signal of which is proportional to the mean value of the output signals of the amplifiers (10, 11), and a second operational amplifier (17), the output signal of which absolute amount of the relative difference in the output signals of the amplifiers (10, 11) is proportional, there are a first threshold detector (18) which is connected to the output of the first operational amplifier (16) and which generates an output signal when the mean of the Output signals of the amplifier (10, 11) exceeds a predetermined value and a second threshold detector (19), which is connected to the output of the second Operational amplifier (17) is connected and which generates an output signal when the absolute amount of the relative difference in the output signals of the amplifiers (10, 11) exceeds a predetermined limit value, and that a logic circuit (20) is provided, which of the outputs of the two threshold value detectors (18, 19) is actuated and the output signal thereof triggers an alarm stage (21) for generating an alarm signal, the logic circuit (20) being designed in such a way that an alarm signal is generated and sent to the signal center (1) via a first line (23) 25) is transmitted when the threshold value of the first threshold value detector (18) exceeds a predetermined value and the threshold value of the second threshold value detector (19) remains below a predetermined value. (Figure 6, 8) Smoke detector according to claim 6, characterized in that in the evaluation circuit, in parallel with the logic circuit (20) and the alarm stage (21), the second threshold value detector (19) is followed by a fault transmission circuit (29, 30) which is designed such that it a second line (24) of the signal center (25) transmits a fault signal when the output signal of the second threshold value detector (19) exceeds a predetermined value. (Figure 7, 11) Smoke detector according to claim 6, characterized in that in the evaluation circuit parallel to the first threshold detector (18) between the second operational amplifier (17) and the logic circuit (20) a rectifier (31), a third (33) and a fourth time value memory ( 34) and a comparator (32) which are arranged and designed such that the threshold value of the comparator (32) is set again and again depending on the output value of the rectifier (31). (Figure 10) Smoke detector according to claim 1 with a radiation source (2) arranged in a measuring chamber (1), a radiation receiver (7) arranged outside the direct radiation area of the radiation source (2), which is acted upon by stray radiation in the presence of smoke in the radiation area and emits electrical output signals, and one electronic evaluation circuit which, depending on the output signals of the radiation receivers (7, 8), emits an alarm signal and forwards it to a signaling center (25), characterized in that an optics (5) is located in front of the radiation receiver (7) and is set up in this way that the measuring volume (6) defined by crossing the radiation beam (3) emanating from the radiation source (2) with the field of view (13) of the radiation receiver (7) is imaged on the radiation receiver (7) and that the radiation receiver (7) is at least two sensor parts (71, 72), preferably four sensor parts ilt is. (Figure 12)

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