EP1783712B1 - Combined scattered light and extinction fire alarm - Google Patents

Abstract

The method involves monitoring a fire characteristic in the proximity of the ceiling according to a scattered light procedure using a sensor unit (1) of a fire alarm. A sensor unit (2) of the fire alarm transmits beam of coherent light towards a base of a structurally limited area and monitors another fire characteristic in a free area between the ceiling and a base of the limited area according to extinction procedure. An independent claim is also included for a fire alarm for a ceiling suspension, for monitoring a structurally limited area and for detecting the fire.

Description

The invention relates to a method for detecting a fire with a comprehensive at least two sensor units a structurally limited space monitoring fire alarm, in which a first fire detection unit of the fire alarm a first fire characteristic is monitored by the scattered light method.

The US 2003/020617 A1 discloses a sensor for externally incident photons is combined in a detector with one or more other sensors for detecting gas, moisture, temperature, etc. The signals of the individual sensors are evaluated and it is concluded that there is a dangerous situation, no danger situation or a false alarm.

The US 2002/0153499 A1 discloses a scattered light smoke detector with a defined measurement volume outside of the scattered light smoke detector, wherein the defined measurement volume is a few centimeters below the scattered light smoke detector, wherein the scattered light smoke detector for setting the defined measurement volume two light receiver or imaging optics for a light receiver, and with a processor, wherein the processor for Evaluation of contours of the measurement object serves to distinguish between smoke and another object.

The US 2002/0080040 A1 proposes a scattered light smoke detector having means to distinguish between smoke and other debris in the scattering point. This distinction is made, for example, by the analysis of the passage of time the received signals performed. By means of an optical system, scattered signals can be determined from different scattering ranges, so as to achieve greater safety by means of location information in order to distinguish between smoke and object. By a photoreceiver array as a light receiver is a precise spatial resolution and differentiation possible. Another alternative is a tunable light source. The scattered light smoke detector may also be combined with an ultrasonic sensor to detect an object.

Conventional point detectors, such as so-called scattered light detectors, measure almost invariably in a darkened measuring chamber, the so-called labyrinth. This greatly reduces interference caused by light. In addition, the quiescent current of the receiver diode and the associated noise are minimized. On the other hand, the labyrinth inevitably has the disadvantage that the smoke can penetrate only delayed and the smoke density inside the labyrinth at best asymptotically reaches the value of the external concentration. As a result, any fire is detected correspondingly late.

In high rooms, the smoke density generally decreases greatly toward the ceiling. Depending on the energy of the fire and the height of the room, the maximum concentration may be far from the ceiling. Conventional point detectors can therefore only delay detection of a possible fire.

The scattered light method can also be used outside a darkened measuring chamber in the room to be monitored. However, in such an application, there are significantly more environmental perturbations. For example, insects that enter the measurement area or accidental masking, for example, must be safely removed from one Covering, for example, during cleaning can be reliably distinguished from a fire or smoke. Most such disadvantages are trying to solve that the measurement or monitoring is limited to the immediate vicinity of the fire alarm. Here, a distance of 4 to 10 cm from the surface of the fire detector is generally considered typical. Unfortunately, the disadvantages can only be reduced to a limited extent.

Linear smoke detectors send a beam of light across the room to be monitored and trigger an alarm when the beam is attenuated by smoke (extinction). It is irrelevant whether transmitter and receiver are arranged in separate devices on opposite walls of the room or if they are combined in one unit. In one unit then a reflector on the opposite wall is necessary. Since the measuring distance is usually several meters, the sensitivity of linear detectors is generally greater than that of scattered light detectors. In addition, they can be positioned in high rooms at a height where smoke is expected. Of course, the influence or even a total interruption of the light beam in such arrangements is much more likely than is the case when the beam is effective only in the detector environment.

The object of the present invention is to provide a simple and efficient way to suggest the earliest possible detection of a fire.

The object is achieved in each case by the subject matters of the independent claims. Further developments of the invention are specified in the subclaims.

A core of the invention is to be seen in that for the earliest possible detection of a fire, a fire detector with a first sensor unit for monitoring a first fire characteristic according to the scattered light method and a second sensor unit for monitoring a second fire characteristic according to the extinction method is used. According to the invention, the first sensor unit consists of at least one light emitting transmitter unit and at least one receiving unit receiving the transmitted light. The second sensor unit consists of at least two strongly bundled light emitting transmitting units and at least one receiving unit receiving the emitted light. The signals of the two sensor units of the fire detector can be evaluated individually or in combination by a suitable evaluation unit such as a fuzzy processor. The fire detector is generally mounted on the ceiling of the structurally limited space. The two sensor units can partially use the same components. This means that the at least two transmitting units emitting the highly concentrated light beams can be used jointly by both sensor units. For such transmission units according to the invention, an IR laser diode, an IR diode, etc. can be used. The receiving units can then forward the received signals to a dedicated evaluation unit of the fire alarm. The highly collimated light beams emitted by the at least two transmitting units are directed from the ceiling towards the ground and may be inclined either parallel or slightly (outwardly). The angle of inclination is generally less than 10 degrees. Smoke in the immediate vicinity of the fire detector is detected by the scattered light method and by the Extinktionsverfahren, further away from the ceiling smoke only by the Extinktionsverfahren because the scattered light is too weak. To assign the measurement signals to a To receive the emitted light beams, the transmitting units are controlled shifted in time and therefore the light beams are transmitted temporally shifted. A distance measurement provides information on whether a level change involves a partially reflecting object extending in the direction of the room height. It can then be assumed that between "normal" reflection location, location in the room where the monitoring of the second fire characteristic takes place according to the invention, and the fire detector in the room is an object interfering with the measurement. If this is the case, it can usually be concluded that it is impaired by living beings (persons, animals, etc.) or moving objects. The distance measurement can, for example, with the help of in the EP 1391860 A1 revealed principle. With this principle, relative distances of a few centimeters can be detected quickly enough. In order to monitor the second fire characteristic, the received signals assigned to the individual transmission units are correlated mutually and taking into account the transmission time offset. A strong correlation with respect to time course and level with simultaneous typical course characterizes smoke or a fire, since this has no significant local concentration differences in the distance of the two transmitted beams. Receive signals, which arise due to changed reflection by moving objects, can additionally be discriminated by the temporal sequence of the signals. Large or extended objects are affected by multiple beams of light, whereas with objects smaller than beam distances (eg insects), there is always a temporal shift for all received signals and so false alarms can be avoided. In order to further reduce the risk of a false alarm, an alarm can only be triggered if a fire is detected both according to the scattered light method and according to the extinction method.

A major advantage of the method according to the invention is that a fire can be detected or detected much earlier. In this way, a fire alarm can be triggered earlier and thus risks for property damage and personal injury can be reduced to a minimum.

Another great advantage of this inventive fire alarm is that it can be integrated into the ceiling panel of a room and thus is flush with the ceiling.

The invention will be explained in more detail with reference to an exemplary embodiment shown in FIG.

Figure 1 shows a fire detector with two inventive sensor units 1, 2 and a cover plate AP. In the illustrated cover plate AP, which may consist of plastic, metal, wood, glass, etc., windows or openings for the receiving units SLE and EE, as well as for the transmitting units SE are indicated. This fire detector can be integrated into the ceiling of a room. The cover AP of the fire detector can then be flush with the ceiling or slightly protruding. The thick black lines indicate the respective measuring range. For better illustration, the two sensor units 1, 2 are shown separated from each other, but according to the invention both sensor units 1, 2 should be integrated in a fire detector and at least the transmission units SE shared by the two sensor units 1, 2. The first sensor unit 1 consists of two transmitting light emitting units SE and a scattered light receiving unit SLE. The scattered light receiving unit SLE is aligned by means of two optics so that it detects only a near-detail cutout or measuring range of the beams.

Thanks to the bundling of rays, these sections have only an extension in the direction of the beam axes, which is important for distinguishing between interfering objects and smoke or a fire. If smoke propagates in one or more of the imaged beam sections, the scattered light increases with the smoke density development characteristic of a particular fire type. The increase in smoke density development is correlated in the mean course due to the proximity to the fire detector. Device an object such as an insect, a cleaning device, etc. in one of the beam sections, so thanks to the extremely small beam cross section according to the invention, a signal jump is always measured, which differs significantly from a signal generated by smoke. The second sensor unit 2 consists of the same two transmission units SE and an extinction reception unit EE. The extinction receiving unit EE detects smoke by the extinction method. For this purpose, the extinction receiver EE with its optics forms an area at a greater distance from the ceiling, which covers all emitted light beams and lies outside the area monitored by the scattered light method. The impact points of the transmission units SE on the floor or objects that are about 2 to 5 meters from the ceiling are depicted. Thus, the reflection of the emitted light rays on the ground or at most on pieces of furniture such as tables, shelves, etc. is detected up to a ceiling height of for example 5 meters.
In an undisturbed environment, ie when the emitted light beams reach the ground unhindered, the reflected light is measured. The emitted light rays penetrate each smoke layer at any height. This not only leads to a safe but also usually to an early detection of smoke. Since the reflectance and the distance are not known in advance, the inventive fire detector adapted to the present situation at startup and later in operation. Of course, only one emitted light beam could be used for the inventive method, but then must be reckoned with significantly more interference.

• Durch die starke Lichtstrahlenbündelung wird ein Unterbruch des Strahls sehr rasch und vollständig eintreten, selbst wenn zum Beispiel ein sich bewegendes Objekt sich nur sehr langsam verschiebt. Die Geschwindigkeit einer Abnahme des Pegels unterscheidet sich deshalb deutlich von derjenigen bei Rauchentstehung.
• Eine Distanzmessung gibt Aufschluss darüber, ob bei einer Pegeländerung ein, in Richtung vom Boden zur Decke eines baulich begrenzten Raumes hin, zumindest teilweise reflektierendes Objekt beteiligt ist. Ist dies der Fall kann in der Regel auf eine Beeinträchtigung durch ein Lebewesen (Mensch, Tier etc.) oder einen sich bewegenden Gegenstand geschlossen werden. Werden gemäss dem erfindungsgemässen Verfahren mindestens zwei Sendeeinheiten SE verwendet, werden die den einzelnen Sendeeinheiten SE zugeordneten Empfangssignale gegenseitig und unter Berücksichtigung des Sendezeitversatzes korreliert. Eine starke Korrelation bezüglich Zeitverlauf und Pegel bei gleichzeitig typischem Verlauf charakterisiert Rauch, da dieser keine extrem großen lokalen Konzentrationsunterschiede aufweist. Empfangene Signale, die auf Grund einer veränderter Reflexion bei sich bewegenden Objekten (Lebewesen, ein sich bewegender Gegenstand) entstehen, können im Fall mehrerer Lichtstrahlen zusätzlich durch die zeitliche Abfolge der Empfangssignale diskriminiert werden. Bei ausgedehnten und großen Objekten können zwei Lichtstrahlen gleichzeitig beeinflusst werden. Für Objekte wie zum Beispiel Insekten etc., die kleiner sind als die Lichtstrahlenabstände, ergibt sich immer für alle Empfangssignale eine zeitliche Verschiebung.

In order to reduce false alarms to a minimum, the following measures and algorithms are used for the method according to the invention:

• Due to the strong light beam bundling an interruption of the beam will occur very quickly and completely, even if, for example, a moving object shifts only very slowly. The speed of a decrease in the level therefore differs markedly from that of smoke generation.
• A distance measurement provides information on whether a level change, in the direction from the floor to the ceiling of a structurally limited space, at least partially reflective object is involved. If this is the case can usually be closed to an impairment by a living being (human, animal, etc.) or a moving object. If at least two transmission units SE are used according to the method according to the invention, the reception signals assigned to the individual transmission units SE are correlated mutually and taking into account the transmission time offset. A strong correlation with time course and level at the same time characteristic characterizes smoke, since this does not have extremely large local concentration differences. Received signals that arise due to an altered reflection in moving objects (living beings, a moving object), in the case of multiple light beams additionally discriminated by the timing of the received signals become. For extended and large objects, two light beams can be influenced simultaneously. For objects such as insects, etc., which are smaller than the light beam distances, there is always a time shift for all received signals.

In the undisturbed state, so if no living thing or no moving object located in structurally limited space, the received signals according to the scattered light method and the received signals according to the extinction method are combined (Neuro Fuzzy processor) that a very safe statement regarding the presence of a fire the one in connection with a rather uncertain statement of the other sensor system is enough to trigger a fire alarm. Such a triggering of a fire alarm will generally occur much earlier than with point detectors that only operate according to the scattered light method.

• Die Extinktion hat brandverlaufsartig deutlich zugenommen, die Distanz vom Brandmelder zum Detektionspunkt ist jedoch unverändert.
• Eine schwache Zunahme des Streulichts zeigt an, dass erster Rauch bis zur Decke aufgestiegen ist → Alarm wird ausgelöst.

In general, the received signals are forwarded by the receiving units SLE and EE to an evaluation unit, such as a fuzzy processor for evaluation. If the analysis indicates a possible fire, an alarm is triggered. By way of example, the following states of the input variables of the fuzzy processor characterize a fire:

• The extinction has significantly increased in the course of fire, but the distance from the fire detector to the detection point is unchanged.
• A slight increase in scattered light indicates that the first smoke has risen to the ceiling → alarm is triggered.

It is obvious that it becomes difficult in the case of being affected by moving objects at the same time to measure smoke by means of extinction. The signal changes as a consequence of the moving objects are dominant. The fire detection in this state is more based on the monitoring according to the scattered light method. It is acceptable that the sensitivity is somewhat reduced under these circumstances. The open scattered light method, ie the measurement of stray light in an environment near the fire detector is superior to a classic point detector with respect to the response speed, since the smoke does not first have to penetrate into a darkened room in the fire detector.

Claims (22)

1. Method for detecting a fire by means of a ceiling-mounted fire detector that includes at least two sensor units (1, 2) and monitors a structurally limited space,
   characterised in that
   a first fire characteristic is monitored according to the scattered-light method by means of a first sensor unit (1) near the ceiling,
   a second fire characteristic is monitored according to the extinction method by means of at least one second sensor unit (2) of the fire detector emitting at least two intensely bundled light beams towards the floor of the structurally limited space and
   the at least two emitted light beams are either parallel or inclined at an angle less than 10 degrees.
2. Method according to claim 1,
   characterised in that
   the second fire characteristic is monitored according to the extinction method by the second sensor unit (2) outside the zone monitored by means of the first sensor unit (1) according to the scattered-light method.
3. Method according to claims 1 and 2,
   characterised in that
   at least two sending units (SE) each emitting an intensely bundled light beam and at least one receiving unit (SLE, EE) that receives the emitted intensely bundled light beams are used jointly for the first (1) and second (2) sensor unit.
4. Method according to claims 1 to 3,
   characterised in that
   the second fire characteristic is monitored in the open space between the ceiling and floor of the structurally limited space.
5. Method according to one of the preceding claims,
   characterised in that
   the at least two light beams emitted by the at least two sending units (SE) of the second sensor unit (2) are temporally displaced.
6. Method according to one of the preceding claims,
   characterised in that
   for monitoring the second fire characteristic the distance between the second sensor unit (2) emitting the at least two light beams and an object at least partially reflecting the emitted light beams is measured.
7. Method according to claim 6,
   characterised in that
   the object is either a living thing or a moving object.
8. Method according to one of the preceding claims,
   characterised in that
   the reflected light of the emitted light beams is evaluated by the fire detector according to the extinction method.
9. Method according to claim 8,
   characterised in that
   for monitoring the second fire characteristic the reflected light beams received by the second sensor unit (2) are assigned to the at least two emitted light beams and evaluated in terms of their temporal curve and/or level.
10. Method according to claims 8 and 9,
    characterised in that
    the received reflected light beams are assigned taking the temporal displacement of the emitted light beams into account.
11. Method according to claims 8 to 10,
    characterised in that
    a fire alarm will be triggered by the fire detector only if the temporal curve and/or level tally.
12. Method according to claims 8 to 11,
    characterised in that
    a fire alarm will be triggered only if the distance from an object reflecting the at least two emitted light beams remains constant.
13. Method according to claims 8 to 12,
    characterised in that
    a fire alarm will be triggered only if the first sensor unit (1) monitoring a first fire characteristic additionally detects a fire.
14. Method according to one of the preceding claims,
    characterised in that
    laser light is used for the intensely bundled light beams.
15. Method according to claim 1,
    characterised in that
    the at least two emitted light beams are inclined outward.
16. Method according to claim 15,
    characterised in that
    the angle of inclination is less than 10 degrees.
17. Fire detector for mounting on a ceiling, for monitoring a structurally limited space and for detecting a fire,

    - having a cover plate (AP) for covering the fire detector integrated in the ceiling of the structurally limited space,

    - having a first sensor unit (1) of the fire detector for monitoring a first fire characteristic according to the scattered-light method,

    having at least one second sensor unit (2) emitting at least two intensely bundled light beams towards the floor of the structurally limited space for monitoring a second fire characteristic according to the extinction method, with the at least two emitted light beams being either parallel or inclined at an angle less than 10 degrees.
18. Fire detector according to claim 17,
    characterised in that
    at least two sending units (SE) for emitting at least two intensely bundled light beams are provided jointly for the first (1) and second (2) sensor unit.
19. Fire detector according to claim 18,
    characterised in that
    an IR laser diode and/or IR diode are/is provided as the sending unit (SE).
20. Fire detector according to claims 17 to 19,
    characterised in that
    one receiving unit (SLE, EE) is provided in each case for the first (1) and second (2) sensor unit for receiving the intensely bundled light beams emitted by the at least two sending units (SE).
21. Fire detector according to claims 17 to 20,
    characterised in that
    an evaluation unit is provided for evaluating the light beams received by the at least one receiving unit (SLE, EE) and for triggering an alarm.
22. Fire detector according to claim 21,
    characterised in that
    a fuzzy processor is provided as the evaluation unit.

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