EP0014874B1 - Fire detector using pulsed radiation - Google Patents

Fire detector using pulsed radiation Download PDF

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Publication number
EP0014874B1
EP0014874B1 EP80100508A EP80100508A EP0014874B1 EP 0014874 B1 EP0014874 B1 EP 0014874B1 EP 80100508 A EP80100508 A EP 80100508A EP 80100508 A EP80100508 A EP 80100508A EP 0014874 B1 EP0014874 B1 EP 0014874B1
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EP
European Patent Office
Prior art keywords
radiation
receiver
signal
fire alarm
alarm according
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
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EP80100508A
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German (de)
French (fr)
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EP0014874A3 (en
EP0014874A2 (en
Inventor
Walter Schnell
Jürg Muggli
Gustav Pfister
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Cerberus AG
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Cerberus AG
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Priority claimed from CH186779A external-priority patent/CH641584A5/en
Application filed by Cerberus AG filed Critical Cerberus AG
Publication of EP0014874A2 publication Critical patent/EP0014874A2/en
Publication of EP0014874A3 publication Critical patent/EP0014874A3/en
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
    • G08B17/107—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device for detecting light-scattering due to smoke
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas
    • G08B17/113—Constructional details

Definitions

  • the invention relates to a fire detector with a pulsed radiation source, the electromagnetic radiation of which is directed into a measuring chamber to which the air to be monitored for the occurrence of smoke and aerosol particles has access, and with a sensor to which an evaluation unit is connected , which triggers an alarm signal as soon as the value of the signal emitted by the transducer exceeds a predetermined threshold.
  • Such fire detectors which are also known as optical smoke detectors, evaluate the fact that the radiation emitted into a measuring room by a radiation source, e.g. B. UV, visible light or infrared radiation, in the presence of smoke particles or fire aerosol in the measuring chamber is influenced in a certain way.
  • a radiation source e.g. B. UV, visible light or infrared radiation
  • These fire detectors preferably operate according to the scattered radiation principle, with a scattered radiation receiver which is not struck by direct radiation and which receives the radiation scattered by smoke particles and triggers a fire alarm signal as soon as the scattered radiation intensity exceeds a predetermined threshold, e.g. in US Patent 4175865 or CH Patent 592 932.
  • a disadvantage of such fire detectors is that they only react to heavily scattering smoke, so-called white smoke, such as that which arises, for example, in the case of a damp material fire.
  • white smoke such as that which arises, for example, in the case of a damp material fire.
  • black smoke which often occurs in rapidly developing fires or incomplete combustion.
  • Previously known scattered-radiation fire detectors were therefore unable to report fire types which are associated with the occurrence of strongly radiation-absorbing, i.e. black, smoke. This is particularly disadvantageous in the case of rapidly developing fires in which scattered radiation detectors often only trigger an alarm signal too late.
  • Extinction fire detectors are able to detect different types of smoke with a relatively uniform sensitivity.
  • they have the disadvantage that a relatively small change in a relatively large irradiation value must be reliably detected, which in practice requires extremely good and correspondingly complicated and expensive long-term stabilization of the radiation source. Therefore, scattered light detectors have largely prevailed in practice, in which the deviation of a size of zero, which can be determined much more easily and without great stabilization effort, is determined, although the disadvantage must be accepted that such scattered light detectors do not react to all types of fire.
  • optical fire detectors Another disadvantage inherent in all known optical fire detectors is that they only respond to smoke particles whose dimensions are greater than approximately the radiation wavelength, ie greater than approximately 1 J lm. Smaller particles, which preferably occur in the early stages of a fire, cannot be detected, so that such optical fire detectors often only trigger an alarm signal at a late point in time, so that usually other, more responsive types of fire detectors, such as e.g. B. ionization fire alarm, the preference is given, but then the disadvantage must be accepted that radioactive preparations must be used, which in turn have other undesirable effects.
  • the invention has for its object to avoid the above-mentioned disadvantages of known optical fire detectors and to create a fire detector that reacts to fire products that absorb radiation pulses, safely and with faster response and higher sensitivity and which is also simple and small in size, and works reliably and is not susceptible to faults over longer periods of time.
  • this object is achieved in that, in the case of a fire detector of the type mentioned at the outset, the sensor is an acoustic sensor which picks up the air vibrations generated by the absorption of the radiation pulses by the particles.
  • the fire detector according to the invention, it can be designed such that it responds to the various types of fire occurring in practice in the manner mentioned, ie also reacts in the same way to white smoke and to invisible aerosol particles.
  • This is achieved by additionally providing a scattered radiation receiver which scatters the smoke particles in the measuring chamber in the radiation region of the radiation source Can absorb radiation, but receives no direct radiation from the radiation source.
  • air pressure pulses are generated by the absorption of the radiation pulses generated by the radiation source from particles in the radiation area.
  • the air pressure fluctuations generated during each radiation pulse are collected and summed by an acoustic transducer, at the output of which an output pulse occurs in coincidence with the radiation pulses, which is further evaluated by an evaluation unit for alarm signaling.
  • connections between the measuring chamber and the evaluation unit can be designed as electrical lines, with the acoustic transducer being an acoustic-electrical converter, e.g. a microphone.
  • connections between the measuring chamber and the evaluation unit consist exclusively of radiation-conducting elements, so-called light guides.
  • the radiation source is expediently not arranged in the measuring chamber but in the evaluation unit.
  • the radiation pulses emitted by the radiation source are transmitted to the measuring chamber by an optical fiber.
  • an acoustic-optical converter which also receives radiation from the radiation source via an optical fiber and, when air vibrations occur, redirects it to the evaluation unit in a different form via another optical fiber.
  • the changed optical signal is received by a radiation detector and converted into an electrical signal, which is further evaluated by the signal circuit for alarm signaling.
  • This development of the invention has the advantage that there are no electrical connections between the measuring chamber and the evaluation unit, and the signal transmission takes place exclusively by optical means.
  • a fire detector is therefore completely independent of electrical disturbances, for example short-term network fluctuations or voltages induced in the lines.
  • it is automatically explosion-proof, i. H. it can also be used in potentially explosive environments without restriction.
  • a radiation source 5 for example a LASER or a diode emitting light or infrared radiation, is located in the measuring chamber on the upper cover 3.
  • This radiation source is operated in pulses by an oscillator 6 and emits radiation pulses with a specific pulse frequency, for example in the range between 1 and 20 kHz, into the interior of the measuring chamber.
  • an acoustic pickup 7 is provided, e.g. B. a capacitive electret microphone with an electrically polarized film. If there is smoke or fire aerosol in the measuring chamber 1, the radiation pulses are absorbed by the particles in the radiation area. These particles heat up briefly and an air pressure wave arises from each particle. The individual pressure pulses add up and can thus be perceived by the acoustic transducer 7 as an air vibration or as a pressure pulse.
  • the acoustic pickup 7 is connected to an evaluation circuit S. First, the output signal of the acoustic pickup 7 is fed to a phase comparator 8, which is driven by the oscillator 6 in coincidence with the radiation source 5. It is thus achieved that the signal emitted by the acoustic pickup 7 is only evaluated during the pulse duration of the radiation pulses and is passed on to the downstream threshold value detector 9.
  • this threshold value detector 9 supplies an alarm signal to the signal generator 10 which it controls.
  • Integration or delay elements can be interposed in a known manner, as in the case of other optical fire suppressors, in order to avoid faulty alarm triggers by individual pulses.
  • Known measures for suppressing the transient processes for example in the phase comparator 8, can also be provided in order to avoid disturbing transient impulses.
  • the pulse frequency of the radiation pulses that is to say the frequency of the oscillator 6 and the dimensions of the measuring chamber 1
  • the pulse frequency of the radiation pulses are coordinated with one another in such a way that acoustic waves are generated in the measuring chamber.
  • the deepest cylindrically symmetrical resonance oscillation is 8.2 kHz.
  • Further resonance vibrations with other frequencies can also be excited and used, but are usually somewhat more damped and deliver a correspondingly weaker signal.
  • a substantial amplification of the signal on acoustic pickup 7 can be achieved.
  • the acoustic pickup 7 delivers such a large output signal that it can be evaluated in a simple, interference-free manner. It was therefore possible to choose the measuring chamber dimensions at least an order of magnitude smaller than was customary with extinction fire detectors without the need for a large number of sensitive, precisely adjustable and dust-prone deflection mirrors, as is usual with extinction fire detectors. Nevertheless, the arrangement described can in particular be highly absorbent, i.e. detect black smoke with surprisingly high sensitivity.
  • smoke particles which absorb less strongly and which only cause radiation scattering e.g. Detecting water vapor-containing or white smoke
  • the arrangement can be selected, for example, in accordance with the smoke detectors described in Swiss Patent No. 592932, the radiation source 5 having a cone-shaped radiation characteristic and the radiation receiver 11 being arranged in the cone axis, but outside the direct radiation range.
  • the radiation receiver 11 is shielded from the direct radiation by an aperture system B, for example to keep the radiation scattering at the edges away as a double aperture.
  • This scattered radiation receiver 11 is connected to a further phase comparator 12, likewise controlled by the oscillator 6, which, like the first phase comparator 8, amplifies the incoming signal in coincidence with the radiation pulses and forwards it to a second threshold value detector 13.
  • the threshold value detector 13 now also controls a signal transmitter.
  • This can be the same signal generator 10 as the one that is controlled by the output signals of the acoustic pickup 7, the threshold value detectors of both channels 9 and 13 being connected to the inputs of an OR gate 14 or a corresponding circuit the output of the common fire alarm signal generator 10 is connected.
  • certain signal transmitters or auxiliary devices can also be controlled separately, the triggering of which is expedient depending on the occurrence of a specific type of smoke.
  • a fire extinguishing system 15 can be controlled by the acoustic evaluation channel, which will respond preferably in the case of rapidly spreading fires, while escape route or evacuation display devices 16 can be actuated by the scattered radiation channel, which will respond preferably when white smoke occurs, because of the visual impairment associated therewith .
  • the two additional auxiliary devices 15 or 16 can also be designed as separate signal transmitters in order to be able to recognize in a signal center what type of smoke, i.e. what type of fire is reported. In this way, i.e. H.
  • a universally applicable fire detector can be created, which can detect all types of fire that occur in practice with increased sensitivity and more reliably and quickly, whereby the detector dimensions can be kept extremely small and no risk from the use of radioactive ones Substances can occur.
  • the invention can be further developed by selecting the wavelength of the radiation used in the region of the resonance radiation of a carbon oxide, for example carbon dioxide or carbon monoxide.
  • a semiconductor laser is suitable as the radiation source, which is preferably in the wavelength range of such resonance radiation, for example at 4.7 Jlm, 4.3 pm or 2.7 pm.
  • Three-element laser diodes (three-metal laser diodes) have proven particularly suitable for this purpose, e.g. B. with the composition (Pb 1-x Sn x ) Te or (Pb 1-x Sn x ) Se.
  • Other useful laser diodes are those of Composition Ga (As x P 1-x ) and (Cd x Hg 1-x ) Te, also Pb S Se has proven to be a suitable diode for the generation of radiation in the range of 4-8.5 ⁇ m.
  • the advantage of using radiation of this spectral composition is that it is also absorbed by carbon oxide molecules in the measuring chamber. It was found that when carbon oxide occurs, pressure waves are also generated synchronously with the radiation pulses in the measuring chamber, which are also registered by the acoustic pickup 7. The presence of carbon oxide in the air also triggers a signal. As a fire usually produces carbon oxide in addition to other fire secondary products, this detection of carbon oxide in a fire detector is very desirable anyway.
  • the radiation source is arranged directly in the measuring chamber and is supplied with voltage via an electrical line.
  • the acoustic sensor in the measuring chamber generates an electrical signal, which is also picked up via an electrical line and forwarded to the evaluation unit with a signal circuit.
  • the fire detector shown in FIG. 3 again consists, as in the example according to FIGS. 1 and 2, of a measuring chamber 1 and a measuring device S which is remote from it, for example in a signal center (analog elements are provided with the same reference numerals as in FIGS. 1 and 2). .
  • Measuring chamber and evaluation device are connected to one another by a number of radiation-conducting elements L 1 , L 2 ... L s .
  • These radiation-conducting elements also known as fiber optics or as light guides (for the sake of brevity hereinafter referred to as light guides), can be selected in various ways as required and in coordination with other components of the fire detector.
  • the individual light guides L 1 , L 2 , L s can either consist of a single radiation-guiding element or can also comprise several such elements, for example in the form of light guide bundles.
  • the individual light guides L 1 , L z ... L s which are shown separately in FIG. 1 for the sake of clarity, can be combined in the transmission path between the measuring chamber 1 and the evaluation device S to form a single light guide bundle.
  • a fire alarm system can be created with several measuring points distributed in a protected area. If optical fibers with particularly good transmission properties are selected, transmission lengths that are at least equivalent to those that can be achieved with electrical lines could be achieved, but have the advantage that there is no electrical connection between the measuring chamber and the evaluation device. In addition to the resulting susceptibility to interference, in particular against electrical interference, the measuring chambers can therefore also be accommodated in places where electrical lines are undesirable, in particular in potentially explosive areas.
  • the measuring chamber 1 consists of a cylindrical or slightly conical wall 22, an upper cover 3 and a lower cover 4.
  • the wall 22 is constructed from mutually offset elements, so that the outside air can penetrate into the interior, but light from the Measuring chamber is kept away. Instead, the air to be examined can also be supplied via inlet and outlet openings.
  • One of the light guides L z is introduced into the upper cover 3, via the end X of which electromagnetic radiation, ie visible light, infrared or ultraviolet radiation, is radiated into the chamber.
  • a further light guide L s is inserted into the other cover 4, with the end Y of which radiation is removed from the measuring chamber 1 and returned to the evaluation device S.
  • the exit X of the light guide L 2 and the input Y of the light guide L s are shielded from one another by a system of shutters B, so that the input Y of the light guide L s only receives scattered radiation which originates from smoke particles in the measuring chamber 1.
  • an acoustic-optical converter 17 is arranged, which is connected to the evaluation unit S by further light guides L 3 and L 4 .
  • This acoustic-optical converter 17 has the property of sound Convert vibrations into an optical signal, ie an optical signal fed to the transducer 17 via the light guide L 3 is returned in a changed form via the light guide L 4 by the recorded sound vibrations.
  • the radiation is fed to a radiation source 25 in the signal center S via the light guide L ,, L 2 of the measuring chamber 1.
  • the radiation source 25 is operated in pulses by an oscillator 6 and therefore emits radiation pulses to the light guide L z with a certain pulse frequency, for example in the range between 1 and 20 kHz.
  • the radiation pulses supplied are now absorbed by the smoke and aerosol particles in the measuring chamber 1. These particles heat up briefly and an air pressure wave is generated with each radiation pulse.
  • the pressure pulses of the individual particles add up and can be perceived by the converter 17 as an unmistakable and extraordinarily sensitive sign of the presence of radiation-absorbing particles.
  • the transducer 17 receives radiation from the radiation source 25 via the light guide L 1 and the branch L 3 on the one hand in the same rhythm as the radiation radiated into the measuring chamber 1.
  • the outgoing light guide L 4 of the converter 17 is connected in the evaluation unit S to a radiation sensor 27, the output signal of which is fed to a phase comparator 8, which is also controlled by the oscillator 6 in coincidence with the radiation source 25. This ensures that the optical signal emitted by the converter 17 is evaluated and passed on only during the pulse duration of the radiation pulses.
  • the output signal of the phase comparator 8 is again fed to a threshold value detector 9. As soon as the intensity of the output pulses of the radiation sensor 27 exceeds a certain threshold, this threshold value detector 9 supplies an alarm signal to the signal generator 10 which it controls.
  • the scattered radiation is additionally removed from the measuring chamber via the input Y of the light guide L s and fed to a further radiation sensor 21.
  • This is connected to a further phase comparator 12, likewise controlled by the oscillator 6, which likewise amplifies the incoming signal in coincidence with the radiation pulses and forwards it to a second threshold value detector 13.
  • the threshold value detector 13 controls a signal transmitter.
  • separate signal transmitters or auxiliary devices 15, 16 can also be controlled in each of the two channels.
  • any suitable lamp, a light or infrared-emitting diode or a LASER can be used as the radiation source 25.
  • Fig. 4 shows an acoustic-optical converter which is particularly suitable for operation with a single-mode light guide. It has a housing H, which is closed off by an oscillatable membrane M, so that there is a certain reference pressure inside R. A continuous light guide L 3 , L 4 is attached to the membrane M, for example cemented on. If the membrane M is slightly deformed by the action of sound vibrations, the light guide also bends, the optical transmission properties of which change. This change is particularly striking if a light guide of the monomode type is used and the spectrum of the radiation supplied via the light guide L 3 is matched to its maximum transmission. Depending on the setting, it can be achieved that the permeability either improves or deteriorates with each sound pulse. Accordingly, the evaluation unit must be adapted to the processing of positive or negative radiation inputs.
  • FIG. 5 shows an acoustic-optical converter, which can also be operated with classic or multimode light guides.
  • a housing H is provided with an interior R closed by a membrane M.
  • the membrane M is designed to be reflective or scattering on the outside, so that the radiation supplied via the light guide L 3 is reflected or scattered on the surface and can be absorbed by the light guide L 4 . If the membrane M is deformed as a result of the action of sound vibrations, the amount of radiation absorbed by the light guide L 4 changes, so that here too, any action of sound vibrations or pressure pulses causes a change in the optical signal.
  • FIG. 6 shows an autonomous piezoelectric transducer which contains a piezoelectric element P which is deformable under the action of sound and which emits an electrical charge or voltage in the event of any deformation.
  • the piezoelectric element P is provided with an element with electrically controllable transparency or reflection, e.g. B. a liquid crystal LCD, connected so that the permeability of this element is influenced by the voltage emitted by the piezoelectric element.

Description

Die Erfindung geht von einem Brandmelder mit einer impulsweise betriebenen Strahlungsquelle aus, deren elektromagnetische Strahlung in eine Messkammer geleitet wird, zu welcher die auf das Auftreten von Rauch- und Aerosolpartikeln zu überwachende Luft Zutritt hat, und mit einem Aufnehmer, an den eine Auswerteeinheit angeschlossen ist, welche ein Alarmsignal auslöst, sobald der Wert des vom Aufnehmer abgegebenen Signals eine vorgegebene Schwelle überschreitet.The invention relates to a fire detector with a pulsed radiation source, the electromagnetic radiation of which is directed into a measuring chamber to which the air to be monitored for the occurrence of smoke and aerosol particles has access, and with a sensor to which an evaluation unit is connected , which triggers an alarm signal as soon as the value of the signal emitted by the transducer exceeds a predetermined threshold.

Solche auch also optische Rauchmelder bekannten Brandmelder werten die Tatsache aus, dass die in einen Messraum von einer Strahlungsquelle ausgesandte Strahlung, z. B. UV, sichtbares Licht oder Infrarotstrahlung, bei Anwesenheit von Rauchpartikeln oder Brandaerosol in der Messkammer in bestimmter Weise beeinflusst wird.Such fire detectors, which are also known as optical smoke detectors, evaluate the fact that the radiation emitted into a measuring room by a radiation source, e.g. B. UV, visible light or infrared radiation, in the presence of smoke particles or fire aerosol in the measuring chamber is influenced in a certain way.

Vorzugsweise arbeiten diese Brandmelder nach dem Streustrahlungsprinzip, wobei ein nicht von direkter Strahlung getroffener Streustrahlungsempfänger vorgesehen ist, welcher die an Rauchpartikeln gestreute Strahlung empfängt und ein Brandalarmsignal auslöst, sobald die Streustrahlungsintensität eine vorgegebene Schwelle überschreitet, wie z.B. im US-Patent 4175865 oder CH-Patent 592 932 beschrieben.These fire detectors preferably operate according to the scattered radiation principle, with a scattered radiation receiver which is not struck by direct radiation and which receives the radiation scattered by smoke particles and triggers a fire alarm signal as soon as the scattered radiation intensity exceeds a predetermined threshold, e.g. in US Patent 4175865 or CH Patent 592 932.

Nachteilig ist bei solchen Brandmeldern jedoch, dass sie nur auf stark streuenden Rauch reagieren, sogenannten weissen Rauch, wie er beispielsweise bei einem Brand feuchten Materials entsteht. Sie reagieren jedoch nicht auf stark strahlungsabsorbierenden und daher nur wenig Streustrahlung erzeugenden Rauch, sogenannten schwarzen Rauch, wie er bei sich schnell entwikkelnden Bränden oder bei unvollständiger Verbrennung häufig auftritt. Vorbekannte Streustrahlungsbrandmelder waren daher nicht in der Lage, Brandtypen, die mit dem Auftreten von stark strahlungsabsorbierendem, also schwarzem Rauch verbunden sind, zu melden. Besonders nachteilig ist dies bei sich schnell entwickelnden Bränden, bei denen Streustrahlungsbrandmelder häufig erst zu spät ein Alarmsignal auslösen.A disadvantage of such fire detectors, however, is that they only react to heavily scattering smoke, so-called white smoke, such as that which arises, for example, in the case of a damp material fire. However, they do not react to strongly radiation-absorbing and therefore little scattered smoke, so-called black smoke, which often occurs in rapidly developing fires or incomplete combustion. Previously known scattered-radiation fire detectors were therefore unable to report fire types which are associated with the occurrence of strongly radiation-absorbing, i.e. black, smoke. This is particularly disadvantageous in the case of rapidly developing fires in which scattered radiation detectors often only trigger an alarm signal too late.

Andere vorbekannte optische Rauchmelder arbeiten nach dem Extinktionsprinzip. Dabei wird ein Strahlungsempfänger von der Strahlungsquelle direkt bestrahlt. Bei Anwesenheit von Rauch vermindert sich dessen Bestrahlung infolge der Strahlungsabsorption an Rauchpartikeln und der Strahlungsstreuung. Bei einer bestimmten Bestrahlungsverminderung wird ein Brandalarmsignal ausgelöst. Solche Brandmelder sind zwar in der Lage, auch stark absorbierenden, also schwarzen Rauch nachzuweisen, sie erfordern jedoch relativ grosse Absorptionsweglängen in der Grössenordnung eines Meters, wenn bereits, wie in der Praxis erforderlich, schon eine geringe Rauchdichte mit hinreichender Empfindlichkeit nachgewiesen werden soll. Solche Brandmelder lassen sich daher nur sehr schwer in den in der Praxis erforderlichen Abmessungen von höchstens 10 cm herstellen, wenn nicht komplizierte, empfindliche, teure und verstaubungsanfällige Umlenkspiegelsysteme verwendet werden.Other known optical smoke detectors work on the extinction principle. A radiation receiver is irradiated directly by the radiation source. In the presence of smoke, its radiation is reduced due to the radiation absorption on smoke particles and the radiation scatter. A fire alarm signal is triggered at a certain reduction in radiation. Such fire detectors are able to detect even strongly absorbing, i.e. black smoke, but they require relatively long absorption path lengths of the order of a meter if, as is necessary in practice, a low smoke density with sufficient sensitivity is already to be detected. Such fire detectors are therefore very difficult to manufacture in the dimensions of at most 10 cm required in practice if complicated, sensitive, expensive and dust-prone deflection mirror systems are not used.

Extinktionsbrandmelder sind zwar in der Lage, verschiedene Rauchtypen mit relativ gleichmässiger Empfindlichkeit nachzuweisen. Ihnen haftet jedoch der Nachteil an, dass eine relativ geringe Änderung eines relativ grossen Bestrahlungswertes sicher nachgewiesen werden muss, was in der Praxis eine extrem gute und entsprechend komplizierte und teure Langzeitstabilisierung der Strahlungsquelle erforderlich macht. Daher haben sich in der Praxis Streulichtbrandmelder weitgehend durchgesetzt, bei welchen die viel leichter und ohne grossen Stabilisierungsaufwand feststellbare Abweichung einer Grösse von Null bestimmt wird, wobei jedoch der Nachteil in Kauf genommen werden muss, dass solche Streulichtbrandmelder nicht auf alle Brandtypen reagieren.Extinction fire detectors are able to detect different types of smoke with a relatively uniform sensitivity. However, they have the disadvantage that a relatively small change in a relatively large irradiation value must be reliably detected, which in practice requires extremely good and correspondingly complicated and expensive long-term stabilization of the radiation source. Therefore, scattered light detectors have largely prevailed in practice, in which the deviation of a size of zero, which can be determined much more easily and without great stabilization effort, is determined, although the disadvantage must be accepted that such scattered light detectors do not react to all types of fire.

Ein weiterer, allen vorbekannten optischen Brandmeldern anhaftender Nachteil ist, dass sie nur auf Rauchpartikel ansprechen, deren Abmessungen grösser als etwa die Strahlungswellenlänge, d.h. grösser als etwa 1 Jlm sind. Kleinere Partikel, welche bevorzugt im Anfangsstadium eines Brandes auftreten, können nicht nachgewiesen werden, so dass solche optischen Brandmelder ein Alarmsignal häufig erst zu einem zu späten Zeitpunkt auslösen, so dass meist anderen, schneller ansprechenden Brandmeldertypen, wie z. B. lonisationsfeuermeldern, der Vorzug gegeben wird, wobei dann allerdings der Nachteil in Kauf genommen werden muss, dass radioaktive Präparate verwendet werden müssen, die wiederum andere unerwünschte Auswirkungen haben.Another disadvantage inherent in all known optical fire detectors is that they only respond to smoke particles whose dimensions are greater than approximately the radiation wavelength, ie greater than approximately 1 J lm. Smaller particles, which preferably occur in the early stages of a fire, cannot be detected, so that such optical fire detectors often only trigger an alarm signal at a late point in time, so that usually other, more responsive types of fire detectors, such as e.g. B. ionization fire alarm, the preference is given, but then the disadvantage must be accepted that radioactive preparations must be used, which in turn have other undesirable effects.

Der Erfindung liegt die Aufgabe zugrunde, die obenerwähnten Nachteile vorbekannter optischer Brandmelder zu vermeiden und einen Brandmelder zu schaffen, der auf Brandfolgeprodukte, die Strahlungsimpulse absorbieren, sicher und mit schnellerem Ansprechverhalten und höherer Empfindlichkeit reagiert und welcher zudem einfach aufgebaut ist und kleine Abmessungen aufweist, sowie funktionssicher und störunanfällig über längere Zeiträume arbeitet.The invention has for its object to avoid the above-mentioned disadvantages of known optical fire detectors and to create a fire detector that reacts to fire products that absorb radiation pulses, safely and with faster response and higher sensitivity and which is also simple and small in size, and works reliably and is not susceptible to faults over longer periods of time.

Diese Aufgabe wird erfindungsgemäss dadurch gelöst, dass bei einem Brandmelder der eingangs erwähnten Gattung der Aufnehmer ein akustischer Aufnehmer ist, welcher die durch die Absorption der Strahlungsimpulse von den Partikeln erzeugten Luftschwingungen aufnimmt.According to the invention, this object is achieved in that, in the case of a fire detector of the type mentioned at the outset, the sensor is an acoustic sensor which picks up the air vibrations generated by the absorption of the radiation pulses by the particles.

Gemäss einer bevorzugten Ausführungsform des erfindungsgemässen Brandmelders kann dieser so ausgestaltet werden, dass er auf die verschiedenen in der Praxis auftretenden Brandtypen in der genannten Weise reagiert, d.h. auch auf weissen Rauch und auf nicht sichtbare Aerosolpartikeln in der gleichen Weise reagiert. Dies wird dadurch erreicht, dass zusätzlich ein Streustrahlungsempfänger vorgesehen wird, welcher die an Rauchpartikeln in der Messkammer im Strahlungsbereich der Strahlungsquelle gestreute Strahlung aufnehmen kann, jedoch keine direkte Strahlung von der Strahlungsquelle erhält.According to a preferred embodiment of the fire detector according to the invention, it can be designed such that it responds to the various types of fire occurring in practice in the manner mentioned, ie also reacts in the same way to white smoke and to invisible aerosol particles. This is achieved by additionally providing a scattered radiation receiver which scatters the smoke particles in the measuring chamber in the radiation region of the radiation source Can absorb radiation, but receives no direct radiation from the radiation source.

Bei der vorliegenden Erfindung wird die Tatsache ausgenützt, dass durch die Absorption der von der Strahlungsquelle erzeugten Strahlungsimpulse von Partikeln im Strahlungsbereich durch die momentane Erhitzung Luftdruckimpulse entstehen. Die während jedes Strahlungsimpulses erzeugten Luftdruckschwankungen werden von einem akustischen Aufnehmer gesammelt und summiert, an dessen Ausgang also in Koinzidenz mit den Strahlungsimpulsen ein Ausgangsimpuls auftritt, welcher von einer Auswerte-Einheit weiter zur Alarmsignalgabe ausgewertet wird.In the present invention, use is made of the fact that, due to the momentary heating, air pressure pulses are generated by the absorption of the radiation pulses generated by the radiation source from particles in the radiation area. The air pressure fluctuations generated during each radiation pulse are collected and summed by an acoustic transducer, at the output of which an output pulse occurs in coincidence with the radiation pulses, which is further evaluated by an evaluation unit for alarm signaling.

Dabei können die Verbindungen zwischen der Messkammer und der Auswerte-Einheit als elektrische Leitungen ausgebildet sein, wobei der akustische Aufnehmer einen akustisch-elektrischen Wandler, z.B. ein Mikrophon, aufweist.The connections between the measuring chamber and the evaluation unit can be designed as electrical lines, with the acoustic transducer being an acoustic-electrical converter, e.g. a microphone.

Eine besonders vorteilhafte Weiterbildung der Erfindung ergibt sich, wenn die Verbindungen zwischen der Messkammer und der Auswerte-Einheit ausschliesslich aus strahlungsleitenden Elementen, sogenannten Lichtleitern besteht. Dabei ist zweckmässigerweise die Strahlungsquelle nicht in der Messkammer, sondern in der Auswerte- Einheit angeordnet.A particularly advantageous development of the invention results if the connections between the measuring chamber and the evaluation unit consist exclusively of radiation-conducting elements, so-called light guides. The radiation source is expediently not arranged in the measuring chamber but in the evaluation unit.

Die von der Strahlungsquelle emittierten Strahlungsimpulse werden von einem Lichtleiter in die Messkammer übertragen. Dort befindet sich statt eines Mikrophons ein akustisch-optischer Wandler, der ebenfalls über einen Lichtleiter Strahlung der Strahlungsquelle erhält und diese bei Auftreten von Luftschwingungen in veränderter Form über einen weiteren Lichtleiter an die Auswerte- Einheit zurückleitet. Das veränderte optische Signal wird hier von einem Strahlungsaufnehmer empfangen und in ein elektrisches Signal umgesetzt, das von der Signalschaltung weiter zur Alarmsignalgabe ausgewertet wird.The radiation pulses emitted by the radiation source are transmitted to the measuring chamber by an optical fiber. Instead of a microphone there is an acoustic-optical converter, which also receives radiation from the radiation source via an optical fiber and, when air vibrations occur, redirects it to the evaluation unit in a different form via another optical fiber. The changed optical signal is received by a radiation detector and converted into an electrical signal, which is further evaluated by the signal circuit for alarm signaling.

Diese Weiterbildung der Erfindung hat den Vorteil, dass keinerlei elektrische Verbindungen zwischen der Messkammer und der Auswerte-Einheit vorhanden sind, und die Signalübertragung ausschliesslich auf optischem Weg erfolgt. Ein solcher Brandmelder ist daher völlig unabhängig von elektrischen Störungen, beispielsweise von kurzzeitigen Netzschwankungen oder in den Leitungen induzierten Spannungen. Ausserdem ist er automatisch explosionssicher, d. h. er kann ohne Einschränkung auch in explosionsgefährdeter Umgebung verwendet werden.This development of the invention has the advantage that there are no electrical connections between the measuring chamber and the evaluation unit, and the signal transmission takes place exclusively by optical means. Such a fire detector is therefore completely independent of electrical disturbances, for example short-term network fluctuations or voltages induced in the lines. In addition, it is automatically explosion-proof, i. H. it can also be used in potentially explosive environments without restriction.

Die Erfindung sowie weitere Ausgestaltungen des Erfindungsgedankens werden anhand der in den Figuren dargestellten Ausführungsbeispiele von Brandmeldern erläutert.

  • Fig. 1 zeigt einen Längsschnitt durch die Messkammer eines Brandmelders sowie eine geeignete Signalschaltung in Blockform.
  • Fig. 2 zeigt einen Querschnitt durch die Messkammer dieses Brandmelders.
  • Fig. 3 zeigt ein weiteres Ausführungsbeispiel eines Brandmelders mit zugehörigem Blockschaltbild.
  • Fig. 4-6 zeigen dabei verwendete akustisch-optische Wandler. Der in Fig. 1 und 2 dargestellte Brandmelder weist eine Messkammer 1 auf, welche in einem Gehäuse eingeschlossen ist, welches beispielsweise aus einer zylindrischen oder leicht konischen Wand 2, einem oberen Deckel 3 und einem unteren Deckel 4 bestehen kann. Zu dieser Messkammer 1 hat die auf die Anwesenheit von Rauch- oder Brandaerosol zu untersuchende Luft Zutritt. Dies kann beispielsweise durch Zuführung der zu untersuchenden Luft über eine Eintrittsöffnung E und eine Austrittsöffnung A erfolgen oder durch Konvektion, wobei in der Kammerwand 2 oder im unteren Deckel 4 geeignete Öffnungen vorgesehen sein können, durch welche die umgebende Luft in die Messkammer 1 eintreten kann. Diese Öffnungen können in bekannter Weise lichtdicht ausgebildet sein, um das Umgebungslicht von der Messkammer 1 fernzuhalten.
The invention and further refinements of the inventive concept are explained on the basis of the exemplary embodiments of fire detectors shown in the figures.
  • Fig. 1 shows a longitudinal section through the measuring chamber of a fire detector and a suitable signal circuit in block form.
  • Fig. 2 shows a cross section through the measuring chamber of this fire detector.
  • Fig. 3 shows a further embodiment of a fire detector with an associated block diagram.
  • Fig. 4-6 show acoustic-optical converters used. The fire detector shown in FIGS. 1 and 2 has a measuring chamber 1 which is enclosed in a housing which can consist, for example, of a cylindrical or slightly conical wall 2, an upper cover 3 and a lower cover 4. The air to be examined for the presence of smoke or fire aerosol has access to this measuring chamber 1. This can be done, for example, by supplying the air to be examined via an inlet opening E and an outlet opening A or by convection, suitable openings being able to be provided in the chamber wall 2 or in the lower cover 4, through which the surrounding air can enter the measuring chamber 1. These openings can be made light-tight in a known manner in order to keep the ambient light away from the measuring chamber 1.

In der Messkammer am oberen Deckel 3 befindet sich eine Strahlungsquelle 5, beispielsweise ein LASER oder eine Licht oder Infrarotstrahlung emittierende Diode. Diese Strahlungsquelle wird von einem Oszillator 6 impulsweise betrieben und sendet in das Messkammerinnere Strahlungsimpulse mit einer bestimmten Impulsfrequenz, beispielsweise im Bereich zwischen 1 und 20 kHz aus.A radiation source 5, for example a LASER or a diode emitting light or infrared radiation, is located in the measuring chamber on the upper cover 3. This radiation source is operated in pulses by an oscillator 6 and emits radiation pulses with a specific pulse frequency, for example in the range between 1 and 20 kHz, into the interior of the measuring chamber.

An einer anderen Stelle der Messkammer 1 ist ein akustischer Aufnehmer 7 vorgesehen, z. B. ein kapazitives Elektret-Mikrophon mit elektrisch polarisierter Folie. Befindet sich nun Rauch oder Brandaerosol in der Messkammer 1, so werden die Strahlungsimpulse von den Partikeln im Strahlungsbereich absorbiert. Dabei erwärmen sich diese Partikel kurzzeitig, und es entsteht eine Luftdruckwelle von jedem Partikel. Die einzelnen Druckimpulse summieren sich und können somit vom akustischen Aufnehmer 7 als Luftschwingung oder als Druckimpuls wahrgenommen werden.At another location of the measuring chamber 1, an acoustic pickup 7 is provided, e.g. B. a capacitive electret microphone with an electrically polarized film. If there is smoke or fire aerosol in the measuring chamber 1, the radiation pulses are absorbed by the particles in the radiation area. These particles heat up briefly and an air pressure wave arises from each particle. The individual pressure pulses add up and can thus be perceived by the acoustic transducer 7 as an air vibration or as a pressure pulse.

Das Auftreten solcher Luftschwingungen während eines Strahlungsimpulses ist also ein untrügliches Zeichen, dass im bestrahlten Messraum 1 strahlungsabsorbierende Partikel vorhanden sind. Dabei zeigt sich im übrigen, dass auch Partikel, welche kleiner sind als die Wellenlänge der Strahlung, bereits einen Beitrag liefern, d.h., dass auch die im Frühstadium eines Brandes auftretenden Aerosolpartikel nachgewiesen werden können. Zur Auswertung der Luftschwingungen ist der akustische Aufnehmer 7 an eine Auswerteschaltung S angeschlossen. Zunächst wird das Ausgangssignal des akustischen Aufnehmers 7 einem Phasenkomparator 8 zugeführt, welcher in Koinzidenz mit der Strahlungsquelle 5 vom Oszillator 6 angesteuert wird. Damit wird erreicht, dass nur während der Impulsdauer der Strahlungsimpulse das vom akustischen Aufnehmer 7 abgegebene Signal ausgewertet und an den nachgeschalteten Schwellenwertdetektor 9 weitergegeben wird. Sobald die Intensität der Ausgangsimpulse des akustischen Aufnehmers 7 eine bestimmte Schwelle überschreitet, liefert dieser Schwellenwertdetektor 9 an den von ihm angesteuerten Signalgeber 10 ein Alarmsignal. Dabei können in bekannter Weise wie bei anderen optischen Brandmeidern Integrations- oder Verzögerungsglieder zwischengeschaltet sein, um fehlerhafte Alarmauslösungen durch einzelne Impulse zu vermeiden. Weiterhin können zur Vermeidung von störenden Einschwingimpulsen bekannte Massnahmen zur Unterdrückung der Einschwingvorgänge, beispielsweise im Phasenkomparator 8, vorgesehen sein.The occurrence of such air vibrations during a radiation pulse is therefore an unmistakable sign that radiation-absorbing particles are present in the irradiated measuring room 1. It also shows that particles which are smaller than the wavelength of the radiation already make a contribution, ie that the aerosol particles occurring in the early stage of a fire can also be detected. To evaluate the air vibrations, the acoustic pickup 7 is connected to an evaluation circuit S. First, the output signal of the acoustic pickup 7 is fed to a phase comparator 8, which is driven by the oscillator 6 in coincidence with the radiation source 5. It is thus achieved that the signal emitted by the acoustic pickup 7 is only evaluated during the pulse duration of the radiation pulses and is passed on to the downstream threshold value detector 9. As soon as the intensity of the output pulses of the acoustic pickup 7 exceeds a certain threshold, this threshold value detector 9 supplies an alarm signal to the signal generator 10 which it controls. Here Integration or delay elements can be interposed in a known manner, as in the case of other optical fire suppressors, in order to avoid faulty alarm triggers by individual pulses. Known measures for suppressing the transient processes, for example in the phase comparator 8, can also be provided in order to avoid disturbing transient impulses.

Als besonders zweckmässig hat es sich erwiesen, wenn die Impulsfrequenz der Strahlungsimpulse, also die Frequenz des Oszillators 6 und die Abmessungen der Messkammer 1 derart aufeinander abgestimmt sind, dass in der Messkammer stehende akustische Wellen entstehen. Bei einer zylindrischen Messkammer mit einem Durchmesser von 5 cm liegt beispielsweise die tiefste zylindersymmetrische Resonanzschwingung bei 8,2 kHz. Weitere Resonanzschwingungen mit anderen Frequenzen lassen sich ebenfalls anregen und benützen, sind aber in der Regel etwas stärker gedämpft und liefern ein entsprechend schwächeres Signal. Infolge der auftretenden Resonanz lässt sich jedenfalls eine wesentliche Verstärkung des Signales am akustischen Aufnehmer 7 erreichen.It has proven particularly expedient if the pulse frequency of the radiation pulses, that is to say the frequency of the oscillator 6 and the dimensions of the measuring chamber 1, are coordinated with one another in such a way that acoustic waves are generated in the measuring chamber. In the case of a cylindrical measuring chamber with a diameter of 5 cm, for example, the deepest cylindrically symmetrical resonance oscillation is 8.2 kHz. Further resonance vibrations with other frequencies can also be excited and used, but are usually somewhat more damped and deliver a correspondingly weaker signal. In any case, as a result of the resonance that occurs, a substantial amplification of the signal on acoustic pickup 7 can be achieved.

Besonders günstige Abmessungen, wie sie in der Praxis von einem Brandmelder gefordert werden, lassen sich also wie vorstehend erläutert beispielsweise erreichen, wenn eine Strahlungsimpulsfrequenz in der Grössenordnung von 8 kHz gewählt wird. Überraschenderweise zeigte sich, dass trotz dieser sehr kleinen Abmessungen der Messkammer der akustische Aufnehmer 7 ein so grosses Ausgangssignal liefert, das sich auf einfache Weise störsicher auswerten lässt. Somit war es möglich, die Messkammerabmessungen um mindestens eine Grössenordnung kleiner zu wählen, als dies bei Extinktionsbrandmeldern üblich war, ohne dass wie bei Extinktionsbrandmeldern üblich, eine Vielzahl von empfindlichen, genau zu justierenden und verstaubungsanfälligen Umlenkspiegeln erforderlich war. Trotzdem lässt sich mit der beschriebenen Anordnung insbesondere stark absorbierender, d.h. schwarzer Rauch mit überraschend hoher Empfindlichkeit nachweisen.Particularly favorable dimensions, as are required in practice by a fire detector, can therefore be achieved, for example, as explained above, if a radiation pulse frequency in the order of 8 kHz is selected. Surprisingly, it was found that, despite these very small dimensions of the measuring chamber, the acoustic pickup 7 delivers such a large output signal that it can be evaluated in a simple, interference-free manner. It was therefore possible to choose the measuring chamber dimensions at least an order of magnitude smaller than was customary with extinction fire detectors without the need for a large number of sensitive, precisely adjustable and dust-prone deflection mirrors, as is usual with extinction fire detectors. Nevertheless, the arrangement described can in particular be highly absorbent, i.e. detect black smoke with surprisingly high sensitivity.

Um zusätzlich auch weniger stark absorbierende Rauchpartikel, welche lediglich eine Strahlungsstreuung verursachen, z.B. wasserdampfhaltigen oder weissen Rauch nachzuweisen, hat es sich in einer Weiterbildung der Erfindung als zweckmässig erwiesen, zusätzlich einen Streustrahlungsempfänger 11 in der Messkammer 1 vorzusehen. Die Anordnung kann dabei beispielsweise entsprechend den im Schweizerpatent Nr. 592932 beschriebenen Rauchdetektoren gewählt werden, wobei die Strahlungsquelle 5 eine kegelringförmige Strahlungscharakteristik besitzt und der Strahlungsempfänger 11 in der Kegelachse, jedoch ausserhalb des direkten Strahlungsbereiches, angeordnet ist. Ausserdem wird der Strahlungsempfänger 11 von der direkten Strahlung durch ein Blendensystem B abgeschirmt, beispielsweise zur Fernhaltung der Strahlungsstreuung an den Kanten als Doppelblende ausgeführt.In addition, smoke particles which absorb less strongly and which only cause radiation scattering, e.g. Detecting water vapor-containing or white smoke, it has proven expedient in a further development of the invention to additionally provide a scattered radiation receiver 11 in the measuring chamber 1. The arrangement can be selected, for example, in accordance with the smoke detectors described in Swiss Patent No. 592932, the radiation source 5 having a cone-shaped radiation characteristic and the radiation receiver 11 being arranged in the cone axis, but outside the direct radiation range. In addition, the radiation receiver 11 is shielded from the direct radiation by an aperture system B, for example to keep the radiation scattering at the edges away as a double aperture.

Dieser Streustrahlungsempfänger 11 ist an einen weiteren, ebenfalls vom Oszillator 6 angesteuerten Phasenkomparator 12 angeschlossen, welcher ebenso wie der erste Phasenkomparator 8 das eintreffende Signal in Koinzidenz mit den Strahlungsimpulsen verstärkt und an einen zweiten Schwellenwertdetektor 13 weitergibt. Sobald die Intensität des Ausgangssignales des Streustrahlungsempfängers 11 während der Dauer der Strahlungsimpulse nun eine weitere Schwelle überschreitet, steuert der Schwellenwertdetektor 13 nun ebenfalls einen Signalgeber an. Dabei kann es sich um den gleichen Signalgeber 10 handeln, wie derjenige, der durch die Ausgangssignale des akustischen Aufnehmers 7 angesteuert wird, wobei die Schwellenwertdetektoren beider Kanäle 9 und 13 jeweils mit den Eingängen eines ODER-Tores 14 oder einer entsprechenden Schaltung verbunden sind, an dessen Ausgang der gemeinsame Brandalarm-Signalgeber 10 angeschlossen ist. In jedem der beiden Kanäle können jedoch auch separat gewisse Signalgeber oder Hilfsgeräte angesteuert werden, deren Auslösung je nach Auftreten einer bestimmten Rauchart zweckmässig ist. Beispielsweise kann durch den akustischen Auswertekanal, welcher bevorzugt bei schnell sich ausbreitenden Bränden ansprechen wird, eine Brandlöschanlage 15 angesteuert werden, während durch den Streustrahlungskanal, welcher bevorzugt bei Auftreten von weissem Rauch ansprechen wird, wegen der damit verbundenen Sichtbehinderung Fluchtweg- oder Evakuationsanzeigeeinrichtungen 16 betätigt werden. Die beiden zusätzlichen Hilfsgeräte 15 oder 16 können jedoch auch als separate Signalgeber ausgebildet sein, um in einer Signalzentrale erkennen zu können, welche Art von Rauch, d.h. welcher Brandtyp gemeldet wird. In dieser Weise, d. h. durch Einführung eines akustischen Auswertekanales in den genannten Streustrahlungsrauchdetektor lässt sich also ein universell einsetzbarer Brandmelder schaffen, welcher alle in der Praxis auftretenden Brandtypen mit erhöhter Empfindlichkeit und sicherer und schneller nachzuweisen vermag, wobei die Melderabmessungen ausserordentlich klein gehalten werden können und keine Gefährdung durch die Verwendung radioaktiver Substanzen eintreten kann.This scattered radiation receiver 11 is connected to a further phase comparator 12, likewise controlled by the oscillator 6, which, like the first phase comparator 8, amplifies the incoming signal in coincidence with the radiation pulses and forwards it to a second threshold value detector 13. As soon as the intensity of the output signal of the scattered radiation receiver 11 now exceeds a further threshold during the duration of the radiation pulses, the threshold value detector 13 now also controls a signal transmitter. This can be the same signal generator 10 as the one that is controlled by the output signals of the acoustic pickup 7, the threshold value detectors of both channels 9 and 13 being connected to the inputs of an OR gate 14 or a corresponding circuit the output of the common fire alarm signal generator 10 is connected. In each of the two channels, however, certain signal transmitters or auxiliary devices can also be controlled separately, the triggering of which is expedient depending on the occurrence of a specific type of smoke. For example, a fire extinguishing system 15 can be controlled by the acoustic evaluation channel, which will respond preferably in the case of rapidly spreading fires, while escape route or evacuation display devices 16 can be actuated by the scattered radiation channel, which will respond preferably when white smoke occurs, because of the visual impairment associated therewith . However, the two additional auxiliary devices 15 or 16 can also be designed as separate signal transmitters in order to be able to recognize in a signal center what type of smoke, i.e. what type of fire is reported. In this way, i.e. H. By introducing an acoustic evaluation channel into the stray radiation smoke detector mentioned, a universally applicable fire detector can be created, which can detect all types of fire that occur in practice with increased sensitivity and more reliably and quickly, whereby the detector dimensions can be kept extremely small and no risk from the use of radioactive ones Substances can occur.

Die Erfindung lässt sich noch dadurch weiterbilden, dass die Wellenlänge der verwendeten Strahlung im Bereich der Resonanzstrahlung eines Kohlenstoffoxids gewählt wird, beispielsweise von Kohlendioxid oder auch Kohlenmonoxid. Dazu eignet sich als Strahlungsquelle z.B. ein Halbleiter-Laser, welcher bevorzugt im Wellenlängenbereich einer solchen Resonanzstrahlung liegt, beispielsweise bei 4,7 Jlm, 4,3 pm oder 2,7 pm. Als besonders geeignet haben sich dazu Dreielement-Laser-Dioden (three metals Laser diodes) erwiesen, z. B. mit der Zusammensetzung (Pb1-x Snx) Te oder (Pb1-x Snx) Se. Weitere zweckmässige Laser-Dioden sind solche der Zusammensetzung Ga (Asx P1-x) und (Cdx Hg1-x) Te, auch Pb S Se hat sich als geeignete Diode für die Erzeugung von Strahlung im Gebiet von 4-8,5 µm erwiesen. Der Vorteil der Verwendung einer Strahlung dieser spektralen Zusammensetzung besteht darin, dass sie auch von Kohlenoxid-Molekülen in der Messkammer absorbiert wird. Es zeigte sich, dass bei Auftreten von Kohlenoxid ebenfalls synchron mit den Strahlungsimpulsen Druckwellen in der Messkammer erzeugt werden, welche ebenfalls vom akustischen Aufnehmer 7 registriert werden. Auch die Anwesenheit von Kohlenoxid in der Luft führt also zur Auslösung eines Signales. Da bei einem Brand in der Regel neben anderen Brandfolgeprodukten auch Kohlenoxid entsteht, ist dieser Nachweis von Kohlenoxid in einem Brandmelder ohnehin sehr erwünscht.The invention can be further developed by selecting the wavelength of the radiation used in the region of the resonance radiation of a carbon oxide, for example carbon dioxide or carbon monoxide. For this purpose, a semiconductor laser is suitable as the radiation source, which is preferably in the wavelength range of such resonance radiation, for example at 4.7 Jlm, 4.3 pm or 2.7 pm. Three-element laser diodes (three-metal laser diodes) have proven particularly suitable for this purpose, e.g. B. with the composition (Pb 1-x Sn x ) Te or (Pb 1-x Sn x ) Se. Other useful laser diodes are those of Composition Ga (As x P 1-x ) and (Cd x Hg 1-x ) Te, also Pb S Se has proven to be a suitable diode for the generation of radiation in the range of 4-8.5 µm. The advantage of using radiation of this spectral composition is that it is also absorbed by carbon oxide molecules in the measuring chamber. It was found that when carbon oxide occurs, pressure waves are also generated synchronously with the radiation pulses in the measuring chamber, which are also registered by the acoustic pickup 7. The presence of carbon oxide in the air also triggers a signal. As a fire usually produces carbon oxide in addition to other fire secondary products, this detection of carbon oxide in a fire detector is very desirable anyway.

Bei dem vorstehend beschriebenen Brandmelder ist die Strahlungsquelle direkt in der Messkammer angeordnet und wird über eine elektrische Leitung mit Spannung versorgt. Der akustische Aufnehmer in der Messkammer erzeugt ein elektrisches Signal, das ebenfalls über eine elektrische Leitung abgenommen und an die Auswerte-Einheit mit einer Signalschaltung weitergeleitet wird.In the fire detector described above, the radiation source is arranged directly in the measuring chamber and is supplied with voltage via an electrical line. The acoustic sensor in the measuring chamber generates an electrical signal, which is also picked up via an electrical line and forwarded to the evaluation unit with a signal circuit.

Diese elektrische Übertragung kann jedoch in gewissen Fällen auch Nachteile mit sich bringen. Elektrische Netzstörungen oder in den Leitungen induzierten Spannungen können zu Störungen führen und fehlerhafte Signale auslösen. In explosionsgefährdeter Umgebung lassen sich solche Brandmelder nur verwenden, wenn besondere, in der Regel aufwendige Explosionsschutzmassnahmen getroffen werden.However, this electrical transmission can also have disadvantages in certain cases. Electrical grid disturbances or voltages induced in the lines can lead to disturbances and trigger faulty signals. Such fire detectors can only be used in potentially explosive environments if special, usually complex explosion protection measures are taken.

Diese Nachteile lassen sich gemäss der im folgenden beschriebenen Weiterbildung der Erfindung durch Verwendung einer ausschliesslich optischen Übertragung vermeiden. Der in Fig. 3 dargestellte Brandmelder besteht wiederum wie im Beispiel nach Fig. 1 und 2 aus einer Messkammer 1 und einer entfernt davon, beispielsweise in einer Signalzentrale angebrachten Auswerteeinrichtung S (analoge Elemente sind mit gleichen Bezugszeichen versehen wie in Fig. 1 und 2). Messkammer und Auswerteeinrichtung sind miteinander durch eine Anzahl von strahlungsleitenden Elementen L1, L2 ... Ls verbunden. Diese strahlungsleitenden Elemente, auch als Fiberoptik oder als Lichtleiter bekannt (der Kürze halber in der Folge als Lichtleiter bezeichnet), können je nach Bedarf und in Abstimmung mit anderen Bauteilen des Brandmelders von verschiedener Art gewählt werden. Beispielsweise können klassische Lichtleiter vom Multimode-Typ verwendet werden oder auch, falls dies die anderen Bauteile erfordern, vom Monomode- oder Singlemode-Typ. Die unterschiedlichen Übertragungseigenschaften der verschiedenen bekannten Lichtleitertypen sind beispielsweise zusammengestellt in: TG Giallorenzi, «Optical Communications Research and Technology: Fiber optics», Proceedings of the IEEE, vol. 66, no. July 1978.According to the development of the invention described below, these disadvantages can be avoided by using exclusively optical transmission. The fire detector shown in FIG. 3 again consists, as in the example according to FIGS. 1 and 2, of a measuring chamber 1 and a measuring device S which is remote from it, for example in a signal center (analog elements are provided with the same reference numerals as in FIGS. 1 and 2). . Measuring chamber and evaluation device are connected to one another by a number of radiation-conducting elements L 1 , L 2 ... L s . These radiation-conducting elements, also known as fiber optics or as light guides (for the sake of brevity hereinafter referred to as light guides), can be selected in various ways as required and in coordination with other components of the fire detector. For example, classic light guides of the multimode type can be used or, if the other components require it, of the single-mode or single-mode type. The different transmission properties of the various known types of optical fibers are summarized, for example, in: TG Giallorenzi, "Optical Communications Research and Technology: Fiber optics", Proceedings of the IEEE, vol. 66, no.July 1978.

Es sei bemerkt, dass die einzelnen Lichtleiter L1, L2, Ls entweder aus einem einzigen strahlungsleitenden Element bestehen können auch mehrere solcher Elemente, beispielsweise in Form von Lichtleiterbündeln, umfassen können. Ausserdem können die einzelnen Lichtleiter L1, Lz ... Ls, die in Fig. 1 der Übersichtlichkeit halber getrennt dargestellt sind, in der Übertragungsstrecke zwischen der Messkammer 1 und der Auswerteeinrichtung S zu einem einzigen Lichtleiterbündel zusammengefasst sein.It should be noted that the individual light guides L 1 , L 2 , L s can either consist of a single radiation-guiding element or can also comprise several such elements, for example in the form of light guide bundles. In addition, the individual light guides L 1 , L z ... L s , which are shown separately in FIG. 1 for the sake of clarity, can be combined in the transmission path between the measuring chamber 1 and the evaluation device S to form a single light guide bundle.

Es besteht auch die Möglichkeit, statt nur einer einzigen Messkammer 1, wie in Fig. 1 dargestellt, mehrere solcher Messkammern parallel zueinander über ein einziges Lichtleiterkabel an eine Auswerteeinheit S anzuschliessen. Dazu sind in die Lichtleiter L2, L3, L4 und Ls an den Orten der Messkammern Verzweigungen angebracht, an welchen ein Teil der Strahlungsintensität abgenommen wird, bzw. wieder eingespiesen wird. Auf diese Weise lässt sich eine Brandmeldeanordnung mit mehreren in einem geschützten Bereich verteilt angeordneten Messpunkten schaffen. Bei Wahl von Lichtleitern mit besonders guten Übertragungseigenschaften könnten dabei Übertragungslängen erreicht werden, die den mit elektrischen Leitungen erreichbaren mindestens gleichkommen, jedoch den Vorteil haben, dass keine elektrische Verbindung zwischen Messkammer und Auswerteeinrichtung bestehen muss. Abgesehen von der dadurch gegebenen Störunanfälligkeit insbesondere gegen elektrische Störungen lassen sich die Messkammern daher auch an Orten unterbringen, an denen elektrische Leitungen unerwünscht sind, insbesondere in explosionsgefährdeten Bereichen.It is also possible, instead of only a single measuring chamber 1, as shown in FIG. 1, to connect a plurality of such measuring chambers to an evaluation unit S in parallel with one another via a single optical fiber cable. For this purpose, branches are attached in the light guides L 2 , L 3 , L 4 and L s at the locations of the measuring chambers, at which part of the radiation intensity is taken off or fed back in again. In this way, a fire alarm system can be created with several measuring points distributed in a protected area. If optical fibers with particularly good transmission properties are selected, transmission lengths that are at least equivalent to those that can be achieved with electrical lines could be achieved, but have the advantage that there is no electrical connection between the measuring chamber and the evaluation device. In addition to the resulting susceptibility to interference, in particular against electrical interference, the measuring chambers can therefore also be accommodated in places where electrical lines are undesirable, in particular in potentially explosive areas.

Die Messkammer 1 besteht im dargestellten Ausführungsbeispiel aus einer zylindrischen oder leicht konischen Wand 22, einem oberen Deckel 3 und einem unteren Deckel 4. Die Wand 22 ist aus gegeneinander versetzten Elementen aufgebaut, so dass die Aussenluft in das Innere eindringen kann, jedoch Licht von der Messkammer ferngehalten wird. Stattdessen kann die zu untersuchende Luft jedoch auch über Eintritts- und Austrittsöffnungen zugeführt werden.In the exemplary embodiment shown, the measuring chamber 1 consists of a cylindrical or slightly conical wall 22, an upper cover 3 and a lower cover 4. The wall 22 is constructed from mutually offset elements, so that the outside air can penetrate into the interior, but light from the Measuring chamber is kept away. Instead, the air to be examined can also be supplied via inlet and outlet openings.

In den oberen Deckel 3 ist einer der Lichtleiter Lz eingeführt, über dessen Ende X elektromagnetische Strahlung, d.h. sichtbares Licht, Infrarot-oder Ultraviolettstrahlung in die Kammer hineingestrahlt wird. In den anderen Deckel 4 ist ein weiterer Lichtleiter Ls hineingeführt, mit dessen Ende Y Strahlung aus der Messkammer 1 entnommen und zur Auswerteeinrichtung S zurückgeleitet wird. Der Austritt X des Lichtleiters L2 und der Eingang Y des Lichtleiters Ls sind durch ein System von Blenden B voneinander abgeschirmt, so dass der Eingang Y des Lichtleiters Ls nur Streustrahlung erhält, die von Rauchpartikeln in der Messkammer 1 herrühren.One of the light guides L z is introduced into the upper cover 3, via the end X of which electromagnetic radiation, ie visible light, infrared or ultraviolet radiation, is radiated into the chamber. A further light guide L s is inserted into the other cover 4, with the end Y of which radiation is removed from the measuring chamber 1 and returned to the evaluation device S. The exit X of the light guide L 2 and the input Y of the light guide L s are shielded from one another by a system of shutters B, so that the input Y of the light guide L s only receives scattered radiation which originates from smoke particles in the measuring chamber 1.

An einer anderen Stelle der Messkammer 1 ist ein akustisch-optischer Wandler 17 angeordnet, der mit weiteren Lichtleitern L3 und L4 mit der Auswerteeinheit S verbunden ist. Dieser akustisch-optische Wandler 17 hat die Eigenschaft, Schallschwingungen in ein optisches Signal umzuwandeln, d. h. ein über den Lichtleiter L3 dem Wandler 17 zugeführtes optisches Signal wird durch die aufgenommenen Schallschwingungen in veränderter Form über den Lichtleiter L4 zurückgegeben.At another location of the measuring chamber 1, an acoustic-optical converter 17 is arranged, which is connected to the evaluation unit S by further light guides L 3 and L 4 . This acoustic-optical converter 17 has the property of sound Convert vibrations into an optical signal, ie an optical signal fed to the transducer 17 via the light guide L 3 is returned in a changed form via the light guide L 4 by the recorded sound vibrations.

Zum Nachweis von Rauch- und Aerosolpartikeln in der Messkammer 1 wird die Strahlung einer Strahlungsquelle 25 in der Signalzentrale S über den Lichtleiter L,, L2 der Messkammer 1 zugeführt. Die Strahlungsquelle 25 wird von einem Oszillator 6 impulsweise betrieben und gibt an den Lichtleiter Lz daher Strahlungsimpulse mit einer bestimmtem Impulsfrequenz, beispielsweise im Bereich zwischen 1 und 20 kHz ab. In der Messkammer 1 werden die zugeführten Strahlungsimpulse nun von den Rauch- und Aerosolpartikeln absorbiert. Dabei erwärmen sich diese Partikel kurzzeitig und es entsteht bei jedem Strahlungsimpuls eine Luftdruckwelle. Die Druckimpulse der einzelnen Partikel summieren sich und können vom Wandler 17 als untrügliches und ausserordentlich empfindliches Zeichen für das Vorhandensein strahlungsabsorbierender Partikel wahrgenommen werden.To detect smoke and aerosol particles in the measuring chamber 1, the radiation is fed to a radiation source 25 in the signal center S via the light guide L ,, L 2 of the measuring chamber 1. The radiation source 25 is operated in pulses by an oscillator 6 and therefore emits radiation pulses to the light guide L z with a certain pulse frequency, for example in the range between 1 and 20 kHz. The radiation pulses supplied are now absorbed by the smoke and aerosol particles in the measuring chamber 1. These particles heat up briefly and an air pressure wave is generated with each radiation pulse. The pressure pulses of the individual particles add up and can be perceived by the converter 17 as an unmistakable and extraordinarily sensitive sign of the presence of radiation-absorbing particles.

Zur Auswertung dieser Luftschwingungen erhält der Wandler 17 einerseits von der Strahlungsquelle 25 über den Lichtleiter L1 und die Abzweigung L3 Strahlung im gleichen Rhythmus wie die in die Messkammer 1 eingestrahlte Strahlung. Der ausgehende Lichtleiter L4 des Wandlers 17 ist in der Auswerteeinheit S mit einem Strahlungsaufnehmer 27 verbunden, dessen Ausgangssignal einem Phasenkomparator 8 zugeführt wird, welcher in Koinzidenz mit der Strahlungsquelle 25 ebenfalls vom Oszillator 6 angesteuert wird. Damit wird erreicht, dass nur während der Impulsdauer der Strahlungsimpulse das vom Wandler 17 abgegebene optische Signal ausgewertet und weitergegeben wird.To evaluate these air vibrations, the transducer 17 receives radiation from the radiation source 25 via the light guide L 1 and the branch L 3 on the one hand in the same rhythm as the radiation radiated into the measuring chamber 1. The outgoing light guide L 4 of the converter 17 is connected in the evaluation unit S to a radiation sensor 27, the output signal of which is fed to a phase comparator 8, which is also controlled by the oscillator 6 in coincidence with the radiation source 25. This ensures that the optical signal emitted by the converter 17 is evaluated and passed on only during the pulse duration of the radiation pulses.

Das Ausgangssignal des Phasenkomparators 8 wird wieder einem Schwellenwertdetektor 9 zugeführt. Sobald die Intensität der Ausgangsimpulse des Strahlungsaufnehmers 27 eine bestimmte Schwelle überschreitet, liefert dieser Schwellenwertdetektor 9 an den von ihm angesteuerten Signalgeber 10 ein Alarmsignal.The output signal of the phase comparator 8 is again fed to a threshold value detector 9. As soon as the intensity of the output pulses of the radiation sensor 27 exceeds a certain threshold, this threshold value detector 9 supplies an alarm signal to the signal generator 10 which it controls.

Da der akustisch-optische Wandler vorzugsweise auf stark absorbierende Rauchpartikel reagiert, jedoch weniger auf schwach absorbierende, jedoch stark streuende Partikel, wird zusätzlich die Streustrahlung aus der Messkammer über den Eingang Y des Lichtleiters Ls abgenommen und einem weiteren Strahlungsaufnehmer 21 zugeführt. Dieser ist an einen weiteren, ebenfalls vom Oszillator 6 angesteuerten Phasenkomparator 12 angeschlossen, welcher ebenfalls das eintreffende Signal in Koinzidenz mit den Strahlungsimpulsen verstärkt und an einen zweiten Schwellenwertdetektor 13 weitergibt. Sobald die Intensität der aufgenommenen Streustrahlung während der Dauer der Strahlungsimpulse nun eine weitere Schwelle überschreitet, steuert der Schwellenwertdetektor 13 einen Signalgeber an. Dabei kann es sich um den gleichen Signalgeber 10 handeln, wie der vom Wandler 17 angesteuerte, wobei die Schwellwertdetektoren beider Kanäle 9 und 13 jeweils mit den Eingängen eines ODER-Tores 14 verbunden sind, an dessen Ausgang der gemeinsame Alarmsignalgeber 10 angeschlossen ist. In jedem der beiden Kanäle können jedoch auch separate Signalgeber oder Hilfsgeräte 15,16 angesteuert werden.Since the acoustic-optical transducer preferably reacts to strongly absorbing smoke particles, but less so to weakly absorbing but strongly scattering particles, the scattered radiation is additionally removed from the measuring chamber via the input Y of the light guide L s and fed to a further radiation sensor 21. This is connected to a further phase comparator 12, likewise controlled by the oscillator 6, which likewise amplifies the incoming signal in coincidence with the radiation pulses and forwards it to a second threshold value detector 13. As soon as the intensity of the scattered radiation picked up exceeds a further threshold during the duration of the radiation pulses, the threshold value detector 13 controls a signal transmitter. This can be the same signal generator 10 as that controlled by the converter 17, the threshold value detectors of both channels 9 and 13 each being connected to the inputs of an OR gate 14, to the output of which the common alarm signal generator 10 is connected. However, separate signal transmitters or auxiliary devices 15, 16 can also be controlled in each of the two channels.

Besonders zweckmässig ist es auch hier, die Impulsfrequenz der Strahlungsimpulse oder des Oszillators 6 und die Abmessungen der Messkammer 1 derart aufeinander abzustimmen, dass in der Messkammer 1 stehende akustische Wellen entstehen, so dass eine wesentliche Verstärkung des Ausgangssignales des akustisch-optischen Wandlers 17 erreicht werden kann.It is also particularly expedient here to coordinate the pulse frequency of the radiation pulses or the oscillator 6 and the dimensions of the measuring chamber 1 in such a way that standing acoustic waves arise in the measuring chamber 1, so that a substantial amplification of the output signal of the acoustic-optical converter 17 is achieved can.

Als Strahlungsquelle 25 lässt sich im Prinzip eine beliebige geeignete Lampe, eine Licht oder Infrarot emittierende Diode oder ein LASER verwenden. Es ist jedoch zweckmässig, das Spektrum dieser Strahlungsquelle 25 so zu wählen, dass dieses auf Übertragungseigenschaften der Lichtleiter, insbesondere bei Verwendung von Monomode-Lichtleitern, sowie an die Eigenschaften des akustisch-optischen Wandlers 17 angepasst ist.In principle, any suitable lamp, a light or infrared-emitting diode or a LASER can be used as the radiation source 25. However, it is expedient to choose the spectrum of this radiation source 25 such that it is adapted to the transmission properties of the light guides, in particular when using single-mode light guides, and to the properties of the acoustic-optical converter 17.

Fig. 4 zeigt einen akustisch-optischen Wandler, welcher speziell zum Betrieb mit einem Monomode-Lichtleiter geeignet ist. Er weist ein Gehäuse H auf, das durch eine schwingungsfähige Membran M abgeschlossen ist, so dass im Innern R ein bestimmter Referenzdruck herrscht. Auf der Membran M ist ein durchgehender Lichtleiter L3, L4 befestigt, z.B. aufgekittet. Bei geringfügigen Deformationen dieser Membran M durch Einwirkung von Schallschwingungen verbiegt sich ebenfalls der Lichtleiter, wobei dessen optische Übertragungseigenschaften sich ändern. Diese Änderung ist besonders markant, wenn ein Lichtleiter vom Monomode-Typ verwendet wird, und das Spektrum der über den Lichtleiter L3 zugeführten Strahlung auf dessen Durchlässigkeitsmaximum abgestimmt ist. Je nach Einstellung lässt sich erreichen, dass sich die Durchlässigkeit bei jedem Schallimpuls entweder verbessert oder verschlechtert. Entsprechend ist die Auswerteeinheit auf die Verarbeitung positiver oder negativer Strahlungsimputse abzustimmen.Fig. 4 shows an acoustic-optical converter which is particularly suitable for operation with a single-mode light guide. It has a housing H, which is closed off by an oscillatable membrane M, so that there is a certain reference pressure inside R. A continuous light guide L 3 , L 4 is attached to the membrane M, for example cemented on. If the membrane M is slightly deformed by the action of sound vibrations, the light guide also bends, the optical transmission properties of which change. This change is particularly striking if a light guide of the monomode type is used and the spectrum of the radiation supplied via the light guide L 3 is matched to its maximum transmission. Depending on the setting, it can be achieved that the permeability either improves or deteriorates with each sound pulse. Accordingly, the evaluation unit must be adapted to the processing of positive or negative radiation inputs.

Fig. 5 zeigt einen akustisch-optischen Wandler, welcher auch mit klassischen oder Multimode-Lichtleitern betrieben werden kann. Wiederum ist ein Gehäuse H mit einem durch eine Membran M abgeschlossenen Innenraum R vorgesehen. Die Membran M ist an der Aussenseite reflektierend oder streuend ausgebildet, so dass die über den Lichtleiter L3 zugeführte Strahlung an der Oberfläche reflektiert oder gestreut wird und vom Lichtleiter L4 aufgenommen werden kann. Bei einer Deformation der Membran M infolge von Einwirkung von Schallschwingungen ändert sich der Betrag der vom Lichtleiter L4 aufgenommenen Strahlung, so dass auch hier jede Einwirkung von Schallschwingungen oder Druckimpulsen eine Änderung des optischen Signales bewirkt.5 shows an acoustic-optical converter, which can also be operated with classic or multimode light guides. Again, a housing H is provided with an interior R closed by a membrane M. The membrane M is designed to be reflective or scattering on the outside, so that the radiation supplied via the light guide L 3 is reflected or scattered on the surface and can be absorbed by the light guide L 4 . If the membrane M is deformed as a result of the action of sound vibrations, the amount of radiation absorbed by the light guide L 4 changes, so that here too, any action of sound vibrations or pressure pulses causes a change in the optical signal.

Fig. 6 zeigt einen autonomen piezoelektrischen Wandler, der ein unter Schalleinwirkung deformierbares piezoelektrisches Element P enthält, das bei jeder Deformation eine elektrische Ladung oder Spannung abgibt. Das piezoelektrische Element P ist mit einem Element mit elektrisch steuerbarer Transparenz oder Reflexion, z. B. einem Flüssigkristall LCD, so verbunden, dass die Durchlässigkeit dieses Elementes durch die vom piezoelektrischen Element abgegeben Spannung beeinflusst wird. Bei Schalleinwirkung auf den Wandler ändert sich daher die Reflexion der über den Lichtleiter L3 zugeführten Strahlung und somit auch die Intensität der vom Lichtleiter L4 abgenommenen Strahlung.FIG. 6 shows an autonomous piezoelectric transducer which contains a piezoelectric element P which is deformable under the action of sound and which emits an electrical charge or voltage in the event of any deformation. The piezoelectric element P is provided with an element with electrically controllable transparency or reflection, e.g. B. a liquid crystal LCD, connected so that the permeability of this element is influenced by the voltage emitted by the piezoelectric element. When the transducer is subjected to sound, the reflection of the radiation supplied via the light guide L 3 and therefore also the intensity of the radiation removed from the light guide L 4 change .

Claims (16)

1. A fire alarm having a radiation source (5; 25, Lz) operated in a pulsed mode, the radiation source transmitting electromagnetic radiation to a measuring chamber (1) which is accessible to air to be examined for the presence of smoke and aerosol particles and having a receiver being connected with an evaluation unit (S) which delivers an alarm signal as soon as the signal delivered from the receiver exceeds a predetermined threshold, characterized in that the receiver is an acoustical receiver (7; 17, L4, 27) for taking-up air vibrations produced by the absorption of radiation pulses by the particles.
2. A fire alarm according to claim 1, characterized in that an electrical oscillator (6) is provided which operates the radiation source in pulsed mode with a predetermined pulse frequency and simultaneously opertes a signal circuit (8) in the evaluation circuit (S) in coincidence with the radiation pulses.
3. A fire alarm according to claim 2, characterized in that the signal circuit (8) is a phase comparator being controlled by said electrical oscillator (6), said phase comparator evaluating an output signal of the acoustical receiver essentially only during the duration of the radiation pulses and being further characterized in that a threshold value detector (9) is provided which delivers a signal to a signal transmitter (10) as soon as the intensity of the output signal of the acoustical receiver exceeds a predetermined threshold.
4. A fire detector according to any of the claims 1 to 3, characterized in that the dimensions of the measuring chamber (1) are chosen so that at the pulse frequency chosen for operation of the radiation source there are present within the measuring chamber standing acoustic waves.
5. A fire alarm according to claim 4, characterized in that the pulse frequency of the radiation source is in the range between 1 and 20 kHz, preferably in the order of about 8 kHz.
6. A fire alarm according to any of the claims 1 to 5, characterized in that additionally a scattered radiation receiver (11; Ls, 21) is provided which receives the radiation scattered by smoke particles within the measuring chamber (1) in a radiation region of the radiation source but receives no direct radiation from the radiation source, said scattered radiation receiver delivering a signal as soon as the intensity of the received scattered radiation exceeds a predetermined threshold.
7. A fire alarm according to any of the claims 3 and 6, characterized in that the scattered radiation receiver (11; L,, 21) is connected with an evaluation circuit comprising a further phase comparator (12) controlled in coincidence with the electrical oscillator (6) and a further threshold value detector (13) controlling the signal transmitter (10) as soon as the output signal of the scattered radiation receiver exceeds a predetermined value.
8. A fire alarm according to claim 7, characterized in that the evaluation circuit (S) comprises an OR-circuit (14) the inputs of said OR-circuit being controlled by respectives ones of the threshold value detectors (9, 13) and the outputs of said OR-circuit controlling the signal transmitter (10).
9. A fire alarm according to claim 7, characterized in that further auxiliary means (15, 16) are directly controllable by the output signals of the threshold value detectors (9, 13).
10. A fire alarm according to any of the claims 1 to 9, characterized in that the radiation source (5) transmits radiation in a wavelength range of the resonance radiation of a carbon oxide.
11. A fire alarm according to any of the claims 1 to 10, characterized in that the radiation source (25) and a radiation receiver (27) are disposed in an evaluation unit (S) that the radiation of the radiation source is conveyed by way of radiation-conducting elements (L,, Lz, L3) into the measuring chamber (1) and to the acoustical receiver and that the acoustical receiver comprises an acoustic-optical transducer (17) which conveyes the optical signal which is possibly modified by air oscillations by way of at least one furhter radiation-conducting element (L,) back to the radiation receiver (27).
12. A fire alarm according to claim 1, characterized in that the radiation-conducting elements (L1...L4) per se are of the monomode type.
13. A fire-alarm according to claim 12, characterized in that the acoustic-optical transducer (17) comprises an element (M) deformable by acoustic vibrations that one of the radiation-conducting elements (L3) and the further radiation-conducting element (L,) are attached to that deformabie element (M) in such manner that the optical transmission properties of both radiation-conducting elements (L3, L4) are changed simultaneously by deformation of the deformable element (M), and that the radiation-conducting elements (L3, L4) together form a single loop the one end of which is connected with the radiation source (25) and the other one with the radiation receiver (27).
14. A fire alarm according to claim 11, characterized in that the acoustic-optical transducer (17) comprises an element (M) brought into vibration by acoustic vibrations and that the radiation is directed to the vibrating element through one of the radiation-conducting elements (L3) and that the radiation reflected and scattered from the vibrating element (M) is taken up by the further radiation-conducting element (L4) and conveyed to the radiation receiver (27).
15. A fire alarm according to claim 11, characterized in that the acoustic-optical transducer (17) comprises a piezo-electric element (P) which is deformed by the action of sound and develops an electric voltage and an element (LCD) with electrically controllable transparency to which element the voltage is conveyed, and which on vibration of the piezo-electrical element (P) modifies the optical signal which is supplied by one of the radiation-conducting elements (L3) and conveyed back by the further radiation-conducting element (L4).
16. A fire alarm according to any of the claims 11 to 15, in connection with any of the claims 6 to 9, characterized in that in the evaluation unit (S) is provided a further radiation receiver (21) which is connected through a further radiation-conducting element (Ls) with the measuring chamber (1) and which receives the radiation scattered on smoke particles and conveyes the corresponding signal to the evaluation unit (S).
EP80100508A 1979-02-26 1980-02-01 Fire detector using pulsed radiation Expired EP0014874B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
CH1867/79 1979-02-26
CH186779A CH641584A5 (en) 1979-02-26 1979-02-26 FIRE DETECTORS.
CH1113779 1979-12-17
CH11137/79 1979-12-17

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EP0014874A2 EP0014874A2 (en) 1980-09-03
EP0014874A3 EP0014874A3 (en) 1980-09-17
EP0014874B1 true EP0014874B1 (en) 1983-06-08

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014019172A1 (en) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Apparatus and method for distinguishing solid objects, cooking fumes and smoke with a compensating optical measuring system
DE102014019773A1 (en) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Apparatus and method for distinguishing solid objects, cooking fumes and smoke by means of the display of a mobile telephone

Families Citing this family (3)

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Publication number Priority date Publication date Assignee Title
US4430646A (en) * 1980-12-31 1984-02-07 American District Telegraph Company Forward scatter smoke detector
DE3228802C2 (en) * 1982-08-02 1986-08-28 Kraftwerk Union AG, 4330 Mülheim Removable and remountable sealing device and a method for preparing the sealing of pipelines, in particular the main coolant nozzle of a reactor pressure vessel
GB2286667B (en) * 1994-02-15 1997-12-24 Transmould Limited Smoke detector

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US3805066A (en) * 1972-08-14 1974-04-16 T Chijuma Smoke detecting device utilizing optical fibers
CH554571A (en) * 1973-08-14 1974-09-30 Cerberus Ag PROCEDURE AND ARRANGEMENT FOR FIRE DETECTION.
IL45331A (en) * 1973-11-26 1977-12-30 Chloride Batterijen Bv Photoelectric smoke detector

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014019172A1 (en) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Apparatus and method for distinguishing solid objects, cooking fumes and smoke with a compensating optical measuring system
DE102014019773A1 (en) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Apparatus and method for distinguishing solid objects, cooking fumes and smoke by means of the display of a mobile telephone

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