WO1998003946A1

WO1998003946A1 - Smoke warning device

Info

Publication number: WO1998003946A1
Application number: PCT/CH1997/000269
Authority: WO
Inventors: Urs Riedi; Bernhard Durrer; Kurt Hess
Original assignee: Cerberus Ag
Priority date: 1996-07-22
Filing date: 1997-07-15
Publication date: 1998-01-29
Also published as: AU3332797A; CN1198236A; ATE223604T1; AU725418B2; KR100467130B1; DE59609625D1; ZA975811B; UA42086C2; EP0821330A1; ES2183899T3; PL184244B1; PL325921A1; RU2189080C2; KR20000064238A; CN1135511C; EP0821330B1

Abstract

A smoke warning device has a warning insert (1) which can be fixed in a base and is provided with an optic module which comprises a light source (6), a light receiver (7), a measurement chamber, a bottom (11) and a labyrinth system with diaphragms (9) arranged at the periphery of the measurement chamber. The bottom (11) is designed in such a way that its centre is located further away than its edge from a plane determined by the light source (6) and light receiver (7). The bottom (11) is preferably funnel-shaped with the shape of a cone or pyramid. The dust particles which deposit on the bottom are thus substantially further away from the actual measurement zone than in the prior art, substantially reducing the probability of light scattered by the dust particles reaching the measurement zone.

Description

smoke detector

The invention relates to a smoke detector with a detector insert which can be fastened in a base and has an optical module which has a light source, a light receiver, a measuring chamber, a floor and a labyrinth system with diaphragms arranged on the periphery of the measuring chamber.

In smoke detectors of this type, which are referred to as scattered-light smoke detectors, and which may optionally contain a further sensor, for example a temperature sensor, in addition to the optical module, it is known that the optical module is designed in such a way that disturbing extraneous light cannot penetrate and smoke can very easily penetrate the measuring chamber. The light source and light receiver are arranged in such a way that no light rays can get directly from the source to the receiver. In the presence of smoke particles in the beam path, the light from the light source is scattered thereon and part of this scattered light falls on the light receiver and causes an electrical signal.

It is obvious that the false alarm security of such scattered-light smoke detectors depends, among other things, on the fact that the light from the light source is scattered only on smoke particles, that is, with the exception of the smoke particles, no other particles can get into the measuring chamber, with the expression particles being the broadest The meaning is to be understood and includes insects, for example. The problem with the insects has been recognized for some time and is solved by an insect screen surrounding the measuring chamber.

A scattered-light smoke detector known from DE-A-44 12 212 contains a measuring chamber in the form of a round box, which is attached with an end face to a plate connected to the ceiling of the room to be monitored and the side wall of which by Insect screen is formed. The end of the measuring chamber facing away from the plate mentioned and facing the detector cap is covered by a flat bottom.

The practical use of such scattered light smoke detectors with a flat cylindrical measuring chamber has shown that the frequency of false alarms can increase with increasing duration of use, whereby one of the main reasons for this is that the light from the light source is scattered on dust particles deposited in the measuring chamber and thus the presence is faked by smoke particles. To rule out the occurrence of such false alarms, the detectors have to be cleaned of dust from time to time, which is an undesirable additional effort.

The invention is now to provide a smoke detector of the type mentioned at the beginning in which the triggering of false alarms due to light scattering on dust particles is avoided as far as possible or at least greatly reduced and an extension of the maintenance intervals is thereby achieved.

The object is achieved according to the invention in that the floor is designed such that it is at a greater distance in the middle from the plane determined by the light source and light receiver than at its edge.

The solution according to the invention brings about a drastic reduction in the disturbing influence of dust particles, because they are now much further away from the actual measuring zone than before, as a result of which the probability that light scattered from dust particles reaches the measuring zone has become significantly lower.

As is known, the optical axes of the light source and light receiver intersect in the area of the center of the measuring chamber and thus also the center of the floor. Because the floor is at its greatest distance from the measurement plane in the area of its tip or tip, and because dust is mainly deposited in this floor area it is very unlikely that light emitted by the light source will reach a dust particle deposited on the top of the floor and will be scattered back into the measuring chamber.

A first preferred embodiment of the smoke detector according to the invention is characterized in that the base is funnel-shaped and has the shape of a cone or a pyramid.

In a second preferred embodiment of the smoke detector according to the invention, the base has a sieve or lattice structure and acts as an insect screen. This embodiment has the advantage that the smoke detector has one component less than before, which is associated with a corresponding cost advantage.

A third preferred embodiment of the smoke detector according to the invention is characterized in that the bottom of its inner surface facing the measuring chamber is provided with a plurality of lamellae projecting vertically upwards, and in that the arrangement, number, height and mutual spacing of these lamellae are chosen such that against light falling on the floor hits one of the slats before it hits it, and the light receiver only sees the slats from the floor.

The inventive design of the floor with the slats directed upward further reduces the probability that light from the beam path in the measuring chamber is scattered on dust particles deposited on the floor. This is because the dust particles will not be deposited on the lamellae, but rather on their base on the inner surface of the floor, and this is an area that is lined up with the lamellae against light from the measuring chamber. In addition, the slats also act as a shield against external light from the outside, which further increases the measuring reliability of the smoke detector according to the invention. Another significant advantage that results from the above-mentioned absorption of the light originating from undesired secondary scattering or reflections, the so-called background light, is decreasing demands on the manufacturing tolerances. This means that with increasing absorption of the background light, the requirements for the positioning accuracy of the light source and light receiver decrease.

The invention is explained in more detail below with the aid of an exemplary embodiment and the drawings; 1 shows a cross section through a scattered light smoke detector at the optical level

Axis of its optics module, looking towards the bottom of the optics module; and FIG. 2 shows a schematic section along the line II-II of FIG. 1 on a scale reduced 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 tip of 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, and 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 6 formed by an infrared light emitting diode (IRED) and the light receiver 7 are not on a common straight line, but have a kinked course, being close the central aperture 10 is arranged at the intersection. The side wall 4 and the bottom 11 shield the measuring chamber 8 against external light from the outside, and the peripheral diaphragms 9 and the central diaphragm 10 prevent light rays from being able to reach the light receiver 7 in a direct way from the light source 6. The peripheral diaphragms 9 also serve to suppress the so-called background light, which is caused by undesired scattering or reflections. The better the background light is suppressed, the lower the basic pulse, that is the signal that is detected when there is no smoke in the measuring chamber 8. The intersection of the beam of rays emitted by the light source 6 and the field of view of the light receiver 7 form the actual measurement area, hereinafter referred to as the scattering space.

The light source 6 sends short, intense light pulses into the scattering space, the light receiver 7 "seeing" the scattering space but not the light source 6. The light from the light source 6 is scattered by smoke penetrating into the scattering space, and part of this scattered light falls on the light receiver 7. The receiver signal generated thereby is processed by the electronics. Of course, in addition to the optical sensor system contained in the optical module 5, the smoke detector can also contain further sensors, for example 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 entry slots 3 and flows in the latter in a horizontal direction to the funnel-shaped bottom 11. The bottom 11 has a sieve-like or lattice-like structure and is on its outside provided with star-shaped ribs 12 through which the smoke is brought to the floor. As a result, the smoke flows in the vertical direction into the measuring chamber 8 and into the scattering space. Due to the funnel-shaped design, the base 11 is at a considerably greater distance from the measuring chamber than is the case with a flat base. Dust particles that have penetrated into the measuring chamber 8 and scatter the light from the light source 5 and therefore act like smoke particles are deposited in the top of the base 11 and are located outside the area of incidence of the radiation from the light source 6, as a result of which the interference of these smoke particles is drastically reduced .

As can be seen from the figures, the funnel-shaped region of the base 11 has the shape of a pyramid or a truncated pyramid, all the side surfaces of the pyramid having the sieve-like or lattice-like structure already mentioned. In Fig. 1, such a lattice-like structure 13 is indicated schematically only in one of the pyramid surfaces for reasons of clearer recognition. The ribs 12 on the outside of the base 11 are preferably arranged along the side of the pyramid.

The likelihood of interference from dust particles deposited on the floor 11 is further reduced by a special design of the floor. This consists in that the bottom 11 is provided on its inner surface with a plurality of vertically upwardly projecting lamellae 14, 15, their arrangement, number, height and mutual spacing being selected such that light falling from the measuring chamber onto the floor is in front Reaching the floor meets one of the slats, and that the light receiver 7 sees only the slats 14, 15 from the floor 11. As a result, the risk of light scattering from dust particles is considerably lower, since the dust remains on the floor much sooner than that it sticks to the vertical walls of the slats. In addition to shielding the floor 11 against light from the measuring chamber 8, the lamellae 14, 15 shield the light receiver 7 against external light from the outside.

According to the illustration, not all pyramid surfaces are provided with lamellae, but only that of the light source 6 and that opposite the light receiver 7 and the pyramid surface enclosed between these two surfaces. That of the light source 6 and pyramid surfaces opposite the light receiver 7 are provided with longitudinal lamellae 14 oriented parallel to the base edge of the pyramid and the pyramid surface enclosed between these surfaces is provided with at least one longitudinal lamella 14 and with a plurality of transverse lamellae 15 oriented perpendicularly to this. The longitudinal lamellae 14 run at least approximately perpendicular to the optical axis of the opposite light source or the opposite light receiver. The transverse fins 15 serve primarily for the optical decoupling of light source 6 and light receiver 7.

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

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

Until now, it was assumed that background light could best be destroyed by absorption on matt surfaces, but overlooked the fact that the light is diffusely scattered on the matt surfaces and reaches the measuring chamber in an uncontrolled manner. If, on the other hand, glossy surfaces are used, they act like black mirrors and reflect the non-absorbed light in a defined, non-distracting direction, for example on the neighboring peripheral panel. Since the reflecting surfaces are black and therefore only about 5% of the incident radiation reflects animals, this can be almost completely destroyed by repeated reflection between such surfaces. The glossy surfaces are produced by means of an injection mold which has a suitable, preferably polished, surface, at least on the surfaces which are to be shiny.

Another feature that is very important for increasing the measurement reliability of the smoke detector shown is that the peripheral diaphragms 9 or at least most of them are not arranged rotationally symmetrically but in such a way that the angle of incidence of the light beam emitted by the light source 6 and that received by the light receiver 7 is on this aperture is constant. Peripheral diaphragms 9 arranged in a rotationally symmetrical manner would be those which are formed by rotating an aperture around the center. In FIG. 1, the four peripheral diaphragms 9 adjacent to the light source 6 and the light receiver 7 are not rotationally symmetrical. The angle of incidence is chosen such that the incident and non-absorbed light is reflected as often as possible between the peripheral diaphragms 9.

As shown, the peripheral screens 9 each consist of two angled partial surfaces, the mutual inclination and the distance and the length of the peripheral screens 9 being selected such that the light emitted to the peripheral screens 9 cannot reach the inner surface of the side wall 4 directly, but in each Case strikes a peripheral diaphragm 9 and is reflected by this on the adjacent peripheral diaphragm. The force-rotationally symmetrical arrangement of the plurality of peripheral diaphragms 9 also leads to better absorption of the background light and thus to less stringent requirements for the positioning and component accuracy of light source 6 and light receiver 7 and to a detector which is less susceptible to contamination.

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

In the production of the injection molding tool by eroding, the sharpness of an edge is limited by the thickness of the wire used, which does not meet the requirements for the inner edges of the peripheral screens 9. In the case of detector insert 1, the desired sharpness of the inner edges is achieved by inserting a core into the injection molding tool which has a stepped (serrated or serrated) contour on the periphery provided for shaping said inner edges. The individual steps of this contour lie on the inside of the grooves formed in the injection molding tool to form the peripheral diaphragms 9 and close them off from the center. As a result, very sharp edges can be formed between the grooves of the injection molding tool and the gradations of the core.

Practical tests have shown that the simultaneous use of peripheral diaphragms 9 with sharp inner edges and optical module parts (peripheral diaphragms 9, central diaphragm 10, ceiling of the measuring chamber 8) with a glossy surface leads to a marked reduction in the basic pulse, and that the detector is less dusty and becomes susceptible to condensation.

As can be seen from the figures, the light source 6 and the light receiver 7 are each arranged in a housing 16 and 17, respectively. 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. On their front facing the central panel 10, the housings 16 and 17 are each closed by a window with a light exit or light entry opening. These windows differ from the housing windows of known scattered-light smoke detectors in that they are made in one piece. In the known scattered-light smoke detectors, the windows consist of two parts, one of which is attached to the ceiling of the measuring chamber and the other to the floor. When fitting the floor, there are repeated difficulties in fitting and there is a gap between the two halves of the window, which in turn leads to undesirable interference with the transmitted and received light. With the one-piece housing windows, this type of interference is excluded and there can be no problems with the positioning accuracy of the two window halves.

As shown in Fig. 2 in the window 18 of the housing 16, the upper and the lower half of the one-piece windows are offset from one another in the manner of the two cutting edges of a pair of scissors. As a result, the injection molding tool can be designed without a side pull in such a way that a separate shaped element is provided for each of the two halves of the light exit and light entry opening which are offset with respect to one another, so that a precisely defined shape and a clean surface of these openings is achieved.

Claims

claims

1. Smoke detector with a detector insert (1) which can be fastened in a base and has an optics module (5) which has a light source (6), a light receiver (7), a measuring chamber (8), a base (11) and a labyrinth system Has diaphragms (9) arranged on the periphery of the measuring chamber (8), characterized in that the base (11) is designed such that it is at a greater distance in its center from the plane determined by the light source (6) and light receiver (7) than on its edge.

2. Smoke detector according to claim 1, characterized in that the bottom (11) is funnel-shaped and has the shape of a cone or a pyramid.

3. Smoke detector according to claim 2, characterized in that the bottom (11) has a sieve or lattice-shaped structure (13) and is designed as an insect screen.

4. Smoke detector according to one of claims 1 to 3, characterized in that the bottom (11) on its inner surface facing the measuring chamber (8) is provided with a plurality of upwardly projecting lamellae (14, 15), and that arrangement, number , Height and mutual distance of these slats are selected so that light falling against the floor (11) hits one of the slats (14, 15) before striking them, and that the light receiver (7) from the floor (11) only the slats (14, 15) sees.

5. Smoke detector according to claim 4, characterized in that the light receiver (7) is shielded by the slats (14, 15) against outside light entering the measuring chamber (8) from outside.

6. Smoke detector according to claims 2 and 4, characterized in that the lamellae (14, 15) are oriented parallel and perpendicular to the base edge of the respective pyramid side surfaces.

7. Smoke detector according to claim 5, characterized in that ribs (12) arranged in a star shape are provided on the outside of the base (11) and form the side walls of smoke guide ducts.

8. Smoke detector according to one of claims 1 to 3, characterized in that certain, critical with respect to the background light, parts of the optical module (5), preferably the peripheral diaphragm (9), the central diaphragm (10) and the floor (11) opposite the ceiling of the measuring chamber (8) have a glossy surface and are designed such that the light not absorbed is reflected in a defined direction.

9. Smoke detector according to one of claims 1 to 3, characterized in that the peripheral diaphragms (9) are arranged so that the angle of incidence of the light source (6) emitted and of the light receiver (7) received on the plurality of them constant is.

10. Smoke detector according to one of claims 1 to 3, characterized in that the peripheral diaphragms (9) on their end face directed against the central diaphragm (10) have the sharpest possible edge.