EP0880118B1 - Optical smoke detector - Google Patents

Abstract

The alarm has a measurement chamber (1), a light transmitter (2) with a corresp. transmission path (8) and a light receiver (3) with a corresp. light reception path (6). The transmitter and receiver are arranged so that the optical axes of their associated light paths intersect at a back-scatter angle (4) greater than 90 degrees in the measurement chamber. At least one stop (7) in the transmitter path and at least one stop (5) in the receiver path are arranged so that the paths are only superimposed in an overlap region (11) in the measurement chamber contg. small edges or surfaces on which moisture or fouling form.

Description

The invention relates to an optical smoke detector according to the backscatter principle according to the preamble of the claim 1.

Optical smoke detectors are preferably considered automatic Fire detectors used for the early detection of fires. by virtue of Their early warning features are among the many common types of automatic fire detectors are outstanding Meaning since they are best able to fire in to recognize their development phase. This can help fire fighting measures initiated early and effectively become.

With optical smoke detectors, the optical properties of particles and aerosols to identify the fire parameter Smoke used. Smoke detectors, the principle of Scattering of light from the particles in a measuring chamber and take advantage of aerosols are used as scattered light smoke detectors designated. The angle is used for scattered-light smoke detectors between the direction of propagation of a light transmitter and the optical axis of a light receiver to differentiate between types. If the angle is less than 90 °, it is a forward-scattering optical smoke detector. At a An angle that is greater than 90 ° is one backward scattering optical smoke detector. The principle of Backward scattering results compared to the principle of forward scattering a smaller one, but in terms of the type and size of the Smoke particles more evenly scattered light. This attribute makes the backward scattering optical smoke detector more practical.

Condensation in the measuring chamber of the optical smoke detector triggers on both a forward scattering and one backward scattering optical smoke detector due to an increase in stray light a false alarm.

In order to avoid the risk of false alarms, you have at locations where it is occasionally condensation of the optical smoke detector (for example production halls, Workshops, underground garages), heat detectors or the optical smoke detectors with an electrical one Detector heater equipped. Heat detectors have the disadvantage that they don't have the early warning features of the optical smoke detector have. Disadvantages of detector heating are in addition the additional costs of installing a separate power line and the non-compliant energy consumption.

In EP 0 418 410 it is described how with an optical Measuring chamber of an optical smoke detector attached Humidity sensor measured the relative humidity and thus the scattered light measured value is compensated according to a calculation rule will ensure that no false alarm is triggered when condensation occurs becomes.

An optical smoke detector is known from DE 43 07 585, at with the help of an optical measuring method the surface of the Optics of the smoke detector for condensation and contamination is examined. Compensate the measurement values obtained the scattered light measured value so that with condensation and / or contamination the optical smoke detector does not trigger a false alarm.

From WO 84/01650 an optical smoke detector is known which both according to the forward spreading and the backward spreading principle works by adding two light transmitters and one light receiver are arranged so that both principles are used can be.

A disadvantage of all three known methods and devices is that on the one hand an additional expenditure on equipment by installing a second light source or one additional moisture sensor is necessary, and on the other hand elaborate compensation procedure after the measurement to determine the parameters must be carried out.

DE-A1-32 33 368 (= EP-A1-1055199) is a radiation smoke detector according to the preamble of claim 1, in which the radiation of a radiation source via a measuring room Optical fiber is supplied and the signal to be measured via directed another light guide to a radiation receiver being, focusing in the beam path of the two light guides Elements and panels are present. As a swamp of light serving further apertures are outside the radiation cone and therefore do not lead to an increase in the scattered radiation in the best case. The sensitivity is a disadvantage on contamination of the lenses, because of the then changed optical conditions the further apertures in the radiation cone lie and therefore undesirable for scattered radiation contribute. This problem is not recognized there.

EP-A2-0213878 is also a radiation smoke detector known, in whose measuring room a labyrinth with specially designed Shielding elements is arranged. In the transmitter beam path there is an aperture, also has the receiver has a lens with an upstream Cover. The problem of changing the scattered radiation by edges in the measuring room and by precipitation of moisture or dirt on surfaces in the transmitter or receiver is not addressed there.

The object of the invention is to provide an optical smoke detector the good responsiveness of a backscatter principle working smoke detector to develop, if possible small design an improved interference immunity of the optics, especially against pollution and condensation, without to use a compensation method.

The object is achieved by an optical smoke detector with the characterizing features of the claim 1 solved.

Thereby, those belonging to the light transmitter and the light receiver become Beam paths through in front of the light transmitter and the light receiver arranged panels so restricted that the Only intersect beam paths in one area of the measuring chamber, in which there are no edges or surfaces on which condensation or dirt build up can. This condition also occurs when the lenses are dirty maintained. This ensures that in the Measuring chamber, for example, moisture drops deposited on the edge or dirt scattered light at least another reflection on an additional surface of the measuring chamber must experience to get into the light receiver. This additional reflection turns the resulting Interference signal weakened so that in the evaluation of Useful signal by scattering on one in the overlap area of the smoke particles that stop the beam paths can be and so no alarm is triggered.

In an advantageous embodiment of the invention, the optical Measuring chamber surrounded by a labyrinth made up of scattering bodies with an L-shaped cross section is arranged so that on rays of light hitting the maze are reflected in this maze and reflected back only weakly into the measuring chamber become.

Due to the insensitivity to moisture or pollution are not devices for additional Compensation mechanisms necessary. This allows the Design of the optical smoke detector very small and inexpensive realize because of the attachment of a moisture sensor or a second light source is dispensed with.

The invention is explained in more detail with reference to the single figure.

The figure shows a schematic cross section of the optical Smoke detector in top view.

In a measuring chamber 1 there are a light transmitter 2, for example an infrared emitting diode, and a light receiver 3, for example an infrared-sensitive photo detector, so attached to the edge of the measuring chamber 1 that their optical Cut axes at a backscatter angle 4 that is greater than Is 90 °. In the beam direction are in front of the light receiver 3 Apertures 5 are arranged around an assigned to the light receiver 3 Restrict the receiver beam path 6. Likewise are before the light transmitter 2 screens 7 arranged around a the light transmitter Restrict 2 assigned transmitter beam path 8. In the receiver beam path 6 is also a converging lens 9 mounted in a bracket 10, the bracket 10 together with the panels 5 of the light receiver 3 from one Piece, for example made of plastic. Thereby is an automatic adjustment of the receiver beam path 6 ensured. The transmitter beam path 8 and the receiver beam path 6 overlap both in the unpolluted as well as in the dirty case only in an overlap area 11 inside the measuring chamber 1, in which none additional edges and surfaces can be found on which dirt or moisture can precipitate. A smoke particle 12 is generated in this overlap area 11 through the backscattered on it and in the light receiver 3 detected light a useful signal. Dirt or moisture can only be reflected in the measuring chamber 1 that light backscattered thereon at least one further reflection must experience on a surface of the measuring chamber 1 in which this light is weakened to be detected in the light receiver 3 to become. The interference signal generated by this is opposite the useful signal weakened due to the additional reflection, so that through the arrangement according to the invention already a large useful / interference signal distance is ensured.

To further reduce disturbing reflections, they are circular around the measuring chamber scattering body 13 with an L-shaped Cross-section arranged in a labyrinth 14 that on the scattering bodies 13 incident light in the labyrinth 14 is reflected back and forth, and only a small part of the Light is scattered back into the measuring chamber 1.

The light transmitter 2 and the light receiver 3 are connected to a control unit 15 connected, which controls both the light transmitter 2 reads the data from the light receiver 3, evaluates and possibly an alarm message to a not represented center transmitted.

The measuring chamber 1 is in the form of an opening to the outside known smoke guide star 16 equipped for this ensure that the optical smoke detector for smoke from everyone Directions is equally sensitive.

This design makes an optical smoke detector with good Response behavior based on the backscatter principle been made insensitive to precipitation from pollution or moisture is designed.

Claims (6)

1. Optical smoke detector using the backscatter principle, having a measuring chamber (1), an optotransmitter (2) with an associated transmitter beam path (8), and an optoreceiver (3) with an associated receiver beam path (6), the optotransmitter (2) and the optoreceiver (3) being arranged such that the optical axes of the transmitter beam path (8) and of the receiver beam path (6) intersect in the measuring chamber (1) at a backscattering angle (4) of greater than 90°, at least one diaphragm (7) being arranged in the transmitter beam path (8), and at least one further diaphragm(s) being arranged in the receiver beam path (6), characterized in that the transmitter beam path (8) and the receiver beam path (6), including their scattered light ranges owing to the deposition of dirt or moisture, are limited by the diaphragms (7, 5) in such a way that no edges or surfaces at which moisture or contaminants could be deposited are present in the overlap region (11) formed by the intersection of the beam paths (8, 6) in the measuring chamber (1).
2. Optical smoke detector according to Claim 1, characterized in that a positive lens (9) is fitted in the receiver beam path (6) between the optoreceiver (3) and the at least one further diaphragm (5) assigned to the receiver beam path (6).
3. Optical smoke detector according to Claim 2, characterized in that a holding device (10) for the positive lens (9) together with the at least one further diaphragm (5) assigned to the receiver beam path (6) are made from one piece.
4. Optical smoke detector according to Claim 1, 2 or 3, characterized in that diffusers (13) of L-shaped cross section are arranged circularly around the measuring chamber (1) in a labyrinth (14) such that light incident on the diffusers (13) in the labyrinth (14) is scattered such that only a small portion is backscattered into the measuring chamber (1).
5. Optical smoke detector according to one of Claims 1 to 4, characterized in that the light source (2) is a light-emitting diode emitting in the infrared, and the optoreceiver (3) is an infrared-sensitive photodiode.
6. Optical smoke detector according to Claim 4 or 5, characterized in that the at least one diaphragm (7) assigned to the transmitter beam path (8), the at least one further diaphragm (5) assigned to the receiver beam path (6) and the diffusers (13) in the labyrinth (14) are formed from plastic.

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