EP0821331B1 - Smoke detector - Google Patents

Abstract

The smoke detector has a fixing socket in which a detector insert with an optical module is fitted. The optical module has a light source (6) and a photodetector (7) contained within a measuring chamber having a base (11). The module further has a labyrinth system provided by plates (9) which project inwards from the periphery of the measuring chamber. All the critical components of the optical module have smooth surfaces, so that the non-absorbed light is reflected in a defined direction. The optical module components may be provided by plastics injection moulding.

Description

The invention relates to a smoke detector with a detector insert which can be fastened in a base with an optics module, which is a light source, a light receiver, a Measuring chamber, a central diaphragm, a floor and a labyrinth system on the periphery the aperture arranged in the measuring chamber.

In smoke detectors of this type, which are referred to as scattered-light smoke detectors, and if necessary, in addition to the optical module, another sensor, for example one Temperature sensor, may contain, the optical module is designed such that disturbing extraneous light and smoke can easily penetrate the measuring chamber. Light source and light receiver are arranged so that no light rays on direct Can get away from the source to the receiver. In the presence of smoke particles In the beam path, the light from the light source is scattered at it and part of it this scattered light falls on the light receiver and causes an electrical signal.

The false alarm security of such scattered light smoke detectors depends, among other things, very significantly from the fact that light from the light source is actually only scattered on smoke particles the light receiver arrives, and that the so-called background light is extraneous light from the outside or on parts of the optical module or on other than smoke particles scattered light is suppressed. The background light is suppressed at the known optical smoke detectors, for example also in DE-A-44 12 212 described, by absorption of the background light on matt surfaces, to which Purpose of the corresponding parts of the optical module made of a black plastic with a matt surface. Nevertheless, it is through underground light caused signal level, the so-called basic pulse, is still relatively high, and it exists the desire for a reduction in the basic pulse.

The invention now provides a smoke detector of the type mentioned in which the basic pulse is essential compared to the smoke detectors known today is reduced.

The object is achieved according to the invention in that certain, with respect critical to the emergence of background light, parts of the optics module a shiny Have surface and are designed so that the light not absorbed into a defined direction is reflected.

The solution according to the invention brings about a drastic reduction in the basic pulse, because the specified direction can be chosen so that it reflects into it Light certainly doesn't bother you. For example, you can choose this direction so that the light that has not been absorbed is reflected several times and thus practically completely destroyed becomes. Because of the shiny black surfaces only about 5% of the striking Light is not absorbed and reflected, it only takes a few reflections or only a fraction of the original underground light that is no longer disturbing is still present is.

A first preferred embodiment of the smoke detector according to the invention is thereby characterized that the parts of the optics module mentioned the peripheral panels, include the central diaphragm and the ceiling of the measuring chamber opposite the floor. A second preferred embodiment is characterized in that other parts or the entire inside of the optics module a glossy surface exhibit.

Fig. 1

einen Querschnitt durch einen Streulichtrauchmelder im Niveau der optischen Achse von dessen Optikmodul, mit Blickrichtung gegen den Boden des Optikmoduls; und

Fig. 2

einen schematischen Schnitt nach der Linie II-II von Fig. 1 in einem gegenüber Fig. 1 verkleinerten Massstab.

In the following the invention is explained in more detail using an exemplary embodiment and the drawings; it shows:

Fig. 1

a cross section through a scattered light smoke detector in the level of the optical axis of its optics module, looking towards the bottom of the optics module; and

Fig. 2

a schematic section along the line II-II of Fig. 1 on a reduced scale compared to FIG. 1.

The scattered-light smoke detector shown consists in a known manner of a detector insert 1, which can be fastened in a base (not shown) which is preferably mounted on the ceiling of the room to be monitored, and a detector hood 2 which is placed over the detector insert 1 and which is in the area of its in the operating state of the Detector against the space to be monitored is provided with smoke inlet slots 3. The detector insert 1 essentially comprises a box-like base body, on the side facing the top of the detector an optical module 5 surrounded by a side wall 4 and on the side facing the detector base a printed circuit board with evaluation electronics (not shown) are arranged. This detector structure is known and will not be described in more detail here. In this context, reference is made, for example, to the detectors of the AlgoRex series ( AlgoRex - registered trademark of Cerberus AG) and to European patent application No. 95117405.1.

The optics module 5 essentially consists of a light source 6, a light receiver 7, a measuring chamber 8, a labyrinth system on the inside of the side wall 4 arranged peripheral panels 9, a central panel 10 and a bottom 11. The optical axes of the light source formed by an infrared light emitting diode (IRED) 6 and the light receiver 7 are not on a common straight line, but are kinked, with the central one near the intersection Aperture 10 is arranged. The side wall 4 and the bottom 11 shield the measuring chamber 8 against external light from the outside, and the peripheral panels 9 and the central Aperture 10 prevent light rays in a direct path from the light source 6 to Light receiver 7 can get. The peripheral diaphragms 9 are also used for suppression the so-called underground light, which is caused by undesirable scattering or reflections. The better the background light is suppressed, the more the basic pulse is lower, this is the signal that is detected when in the measuring chamber 8 there is no smoke. The cutting area of the emitted by the light source 6 Beams and the field of view of the light receiver 7 form the following the actual measuring range referred to as the scattering space.

The light source 6 sends short, intense light pulses into the scattering space, the light receiver 7 indeed "sees" the scattering space, but not the light source 6. The light of the Light source 6 is scattered by smoke entering the scattering space, and a part this scattered light falls on the light receiver 7. The receiver signal generated thereby is processed by the electronics. Of course, the smoke detector can be next to the optical sensor system contained in the optical module 5, further sensors, for example contain a temperature and / or a gas sensor.

If smoke arises in the room to be monitored and rises to the smoke detector, then it penetrates into the smoke inlet slots 3 and flows in the horizontal direction to the funnel-shaped bottom 11. The bottom 11 has a sieve or lattice-like structure and is on the outside with star-shaped ribs 12 provided, through which the smoke is brought to the floor. This flows the smoke in the vertical direction into the measuring chamber 8 and into the spreading space The bottom 11 of the measuring chamber has a funnel-shaped configuration larger distance than is the case with a flat floor. In the measuring chamber 8 penetrated dust particles that scatter the light from the light source 5 and therefore how Smoke particles act, are deposited in the top of the bottom 11 and are located there outside the area of incidence of the radiation from the light source 6, as a result of which the interference this smoke particle is drastically reduced.

As can be seen from the figures, the funnel-shaped area of the base 11 has the Form a pyramid or a truncated pyramid, with all side surfaces the pyramid have the sieve-like or lattice-like structure already mentioned. 1 is off For the sake of clearer recognition, only one of the pyramid surfaces lattice-like structure 13 schematically indicated. The ribs 12 on the outside of the Bottom 11 are preferably arranged along the pyramid side edges.

The probability of interference from dust particles deposited on the floor 11 is further reduced by special training of the soil. This exists in that the bottom 11 on its inner surface with a variety of vertically upwards projecting slats 14, 15 is provided, their arrangement, number, height and mutual Distance are selected so that something falling from the measuring chamber onto the floor Light hits one of the slats before reaching the floor, and that the light receiver 7 from the floor 11 sees only the lamellae 14, 15. This eliminates the risk of scatter of light on dust particles much less, since the dust is much closer to the floor remains to adhere to the vertical walls of the slats. additionally to shield the floor 11 against light from the measuring chamber 8 shield the slats 14, 15 the light receiver 7 against external light from the outside.

As shown, not all pyramid surfaces are provided with lamellas, but only that of the light source 6 and that opposite the light receiver 7 and that between pyramid surface enclosed between these two surfaces. That of the light source 6 and the light receiver 7 opposite pyramid surfaces are parallel to Base edge of the pyramid oriented longitudinal slats 14 and those between these surfaces enclosed pyramid surface is with at least one longitudinal lamella 14 and provided with several transverse lamellae 15 oriented perpendicular to this. The longitudinal slats 14 run at least approximately perpendicular to the optical axis of the opposite one Light source or the opposite light receiver. The cross slats 15 serve primarily for the optical decoupling of light source 6 and light receiver 7th

The floor 11, which is the same as the entire detector insert 1 (with the exception of the light source 6 and light receiver 7) consists of a suitable plastic and as an injection molded part is made, has at its edge several snap-in elements (not shown), the for the detachable connection of the base 11 to the side wall 4 of the optical module 5 (FIG. 2) are provided.

For even better absorption of background light, at least certain parts have of the optics module 5, in particular the peripheral diaphragms 9, the central diaphragm 10 and the the floor of the measuring chamber 8 opposite the floor 11, instead of the previously usual matt surfaces shiny, i.e. reflective, surfaces on. Of course can still other parts or the entire inside of the optics module 5 a shiny Have surface.

So far, it was believed that underground light was best absorbed can be destroyed on matt surfaces, but overlooked this consideration, that the light is diffusely scattered on the matt surfaces and uncontrolled into the measuring chamber arrives. If, on the other hand, you use glossy surfaces, then these work like black mirrors and reflect the unabsorbed light onto another one of these Surfaces, for example on the neighboring peripheral panel. Because the reflective Surfaces are black and therefore only reflect about 5% of the incident radiation, can be practically complete by repeated reflection between such surfaces be destroyed. The shiny surfaces are produced using an injection mold, at least on the surfaces that should shine, a suitable, preferably polished, surface.

Another for increasing the measurement reliability of the smoke detector shown very essential feature is that the peripheral panels 9 or at least most of them are not rotationally symmetrical but are arranged so that the Impact angle of that emitted by the light source 6 and that of the light receiver 7 received light beam on these diaphragms is constant. Arranged rotationally symmetrically Peripheral diaphragms 9 would be those that rotate by rotating an aperture around the center are formed. In Fig. 1, those of the light source 6 and the light receiver 7 are adjacent Four peripheral diaphragms 9 each are not rotationally symmetrical. The angle of incidence is chosen so that the incident and not absorbed light as often as possible is reflected between the peripheral diaphragms 9.

As shown, the peripheral panels 9 each consist of two angled partial surfaces, their mutual inclination and the distance and the length of the peripheral diaphragms 9 are selected so that the light emitted to the peripheral diaphragms 9 can not get directly onto the inner surface of the side wall 4, but in any case meets a peripheral panel 9 and from this to the adjacent peripheral panel is reflected. The non-rotationally symmetrical arrangement of the majority of the peripheral diaphragms 9 leads to better absorption of the background light and thus less stringent requirements for the positioning and component accuracy of the light source 6 and light receiver 7 and a less pollution-prone detector.

As can be seen in FIG. 1, the peripheral covers 9 are against their Central aperture 10 directed inner edge formed as sharp as possible. That has the The advantage that only a little light falls on such a sharp edge and therefore less Light is reflected in a variety of directions.

When manufacturing the injection mold by eroding, the sharpness is an edge a limit is set by the thickness of the wire used, which meets the requirements to the inner edges of the peripheral panels 9 is not sufficient. When using detector 1, the desired sharpness of the inner edges is achieved by using the injection mold a core is used, which is provided on its for forming the inner edges Periphery has a stepped (serrated or serrated) contour. The single ones Gradations of this contour lie on the inside to form the peripheral diaphragms 9 grooves formed in the injection mold and close them against the center from. This allows between the grooves of the injection mold and the gradations very sharp edges are formed of the core.

Practical tests have shown that the simultaneous use of peripheral shutters 9 with sharp inner edges and optical module parts (peripheral covers 9, Central aperture 10, ceiling of the measuring chamber 8) with a shiny surface to a striking Reduction of the basic pulse leads and that the detector is less dusty and is prone to condensation.

As can be seen from the figures, the light source 6 and the light receiver 7 each arranged in a housing 16 or 17. The two housings 16 and 17, which are worked on the ceiling of the measuring chamber 8, are open at the bottom and are covered on their open side by the floor 11. At her the central aperture 10 facing front are the housing 16 and 17 each through a window with a Light exit or light entry opening completed.

Compared to the housing windows, these windows point to known scattered light smoke detectors the difference that they are made in one piece. With the known scattered light smoke detectors The windows consist of two parts, one of which is on the ceiling of the Measuring chamber and the other is worked on the floor. When putting on the floor pass problems occur again and again and there is the formation of a light gap between the two halves of the window and thus to undesired interference of the transmitter and of the reception light. With the one-piece housing windows there are faults of this type excluded and there can be no problems with the positioning accuracy of the two Window halves occur.

As shown in Fig. 2 at window 18 of housing 16, the top and bottom are Half of the one-piece windows in the manner of the two cutting edges of scissors against each other added. As a result, the injection molding tool can be designed without side pull, that for each of the two mutually offset halves of the light output and the Light entry opening a separate shaped element is provided, so that a precisely defined Shape and a clean surface of these openings is achieved.

Claims (4)

1. Smoke alarm having an alarm insert (1) which can be secured in a pedestal and has an optical module (5) which has a light source (6), a light-receiver (7), a measuring chamber (8), a central screen (10), a base (11) and a labyrinth system having screens (9) arranged on the periphery of the said measuring chamber (8), characterised in that certain parts of the optical module (5), which are critical as regards the development of background light, have a glossy surface and are constructed in such a way that the non-absorbed light is reflected in a defined direction.
2. Smoke alarm according to claim 1, characterised in that the aforesaid parts of the optical module (5) comprise the peripheral screens (9), the central screen (10) and the cover of the measuring chamber (8), which cover lies opposite the base (11).
3. Smoke alarm according to claim 2, characterised in that further parts or the entire inner face of the optical module (5) also have a glossy surface.
4. Smoke alarm according to one of claims 1 to 3, characterised in that the peripheral screens (9) have as sharp an edge as possible on their front side which is directed towards the central screen (10).

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