EP0718814B1 - Method and device for flame detection - Google Patents
Method and device for flame detection Download PDFInfo
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- EP0718814B1 EP0718814B1 EP94120083A EP94120083A EP0718814B1 EP 0718814 B1 EP0718814 B1 EP 0718814B1 EP 94120083 A EP94120083 A EP 94120083A EP 94120083 A EP94120083 A EP 94120083A EP 0718814 B1 EP0718814 B1 EP 0718814B1
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/18—Prevention or correction of operating errors
- G08B29/183—Single detectors using dual technologies
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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
- G08B17/02—Mechanical actuation of the alarm, e.g. by the breaking of a wire
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- the present invention relates to a method for detecting a flame Analysis of the change in intensity of the radiation emitted by a radiation source, an evaluation of the flicker frequency spectrum of the radiation takes place and outside signals lying in a specific frequency band are evaluated as interference signals become.
- Methods of this type use the typical flickering of the flames in one low frequency vibration range as a feature to distinguish between the radiation and interference radiation emitted by a flame.
- the definition of the frequency band in the simplest case it is carried out by the sensor for the emitted radiation upstream filter or frequency-selective amplifier connected downstream, in both cases a certain pass band of, for example, 5 to 25 Hz is obtained. Even if the frequency band is optimally matched to the flickering of flames malfunctions and false reports are relatively common because it happens again and again that random changes in intensity of the ambient radiation in the pass band lie. Such changes in intensity can be caused, for example, by shadowing or reflections from vibrating or slowly moving objects Reflections of sunlight on water surfaces or from flickering or fluctuating Light sources may be caused.
- the invention is now intended to specify a method of the type specified at the outset be what a clear and secure identification and thus elimination of interference radiation and thus has a high false alarm security, and which is also as universal as possible.
- This object is achieved according to the invention in that when evaluating the Flicker frequency spectrum determines the center and cut-off frequency and according to periodic and non-periodic signals is distinguished, and that periodic signals with a center frequency above a first and non-periodic signals with a Cut-off frequency above a second frequency value are evaluated as interference signals, the first frequency value being determined by the flickering frequency of a stationary flame a size corresponding to the minimum size to be detected is determined and the second frequency value greater than the first is selected.
- each flame can have two states, namely a steady state, which is usually then exists when the flame burns stable and undisturbed (so-called periodic Flame), and a quasi-steady state in which the flame burns unstably (so-called non-periodic flame), and that on the other hand a periodic flame Frequency spectrum with a pronounced frequency peak and a non-periodic Flame has a broadband spectrum with a maximum or limit frequency.
- the invention further relates to a flame detector with means for carrying out the mentioned method, with at least one sensor for the from the radiation source emitted radiation, and with a downstream of the at least one sensor Evaluation electronics.
- the flame detector according to the invention is characterized in that that the evaluation electronics means for analyzing the received radiation and their center and cut-off frequency and to link the radiation received corresponding sensor signals with these frequencies.
- a preferred embodiment of the flame detector according to the invention is thereby characterized in that the said means formed by a microprocessor and that this microprocessor contains a fuzzy controller.
- the fully drawn spectrum with the pronounced peak has a center frequency ⁇ mp and an upper limit frequency ⁇ gp , where: ⁇ gp ⁇ ⁇ mp
- a spectrum of this type is typical of an undisturbed and stable burning, so-called periodic flame, the center frequency ⁇ mp with a flame diameter of 10 cm being below 5 Hz and slowly decreasing with increasing diameter.
- the broadband spectrum indicated by a dashed envelope also has a center frequency and a cutoff frequency, which are denoted by ⁇ mc and ⁇ gc .
- Such a broadband spectrum is typical of a flame in an unstable or non-steady state; Such a flame is referred to below as non-periodic.
- the cutoff frequency ⁇ gc of the broadband spectrum is higher than the center frequency ⁇ mp of the periodic flame. So the following applies: ⁇ gc > ⁇ mp
- the occurrence of the cut-off frequency ⁇ gc in a non-periodic flame can be explained as follows: If a flame burns undisturbed and is in the steady state, then the convection cells forming this flame are also stationary in number and size, and the flame has a constant flickering frequency ⁇ 1 , where ⁇ 1 ⁇ ⁇ mp ⁇ ⁇ gp . If, however, the flame is exposed to external influences such as wind, the convection cells can divide or they can form aggregates of several cells, both processes being subject to a limit.
- K denotes a factor, g the gravitational pull and D the size of the flame, expressed by the diameter of the bowl-shaped container in which a liquid burns with a flame of the relevant size.
- Formula 5 gives a value of 4.7 Hz for a shell diameter of 0.1 m for ⁇ o . If you measure the flicker frequency, you get lower values.
- the minimum diameter of the fire or fire to be detected is first determined. If this is to be 10 cm, for example, then the frequency ⁇ mp ⁇ ⁇ gp of a periodic flame is below 5 Hz and the cut-off frequency ⁇ gc of the same size non-periodic flame will certainly not be above 15 Hz. Then two limit values G 1 and G 2 are set for periodic and non-periodic interference signals; the limit value G 1 for periodic interference signals preferably according to Formula 2 with G 1 > ⁇ mp , i.e. at about 5 Hz, and the limit value G 2 for non-periodic interference signals according to Formula 3 with G 2 > 3 ⁇ mp, for example at about 15 Hz.
- the signal generated by the sensor of the detector is examined for its periodicity and assigned to one of the two classes periodically or non-periodically and compared with the relevant limit value G 1 or G 2 and evaluated as an interference signal when the limit value is exceeded.
- the signal is examined for periodicity or non-periodicity, for example, by forming the difference between the cutoff frequency minus the center frequency and dividing this difference by the cutoff frequency. If the quotient is in the order of one, then it is a non-periodic signal; if it is well below one, then it is a periodic signal.
- fuzzy logic This type of signal evaluation would largely suppress potential Interference signals and thus a high level of false alarm security are guaranteed. You can do that False alarm security and reliability further improve if you evaluate the signal using fuzzy logic.
- fuzzy logic The basics of fuzzy logic will be as known (see for example the book “Fuzzy Set Theory and its Applications "by H.-J. Zimmermann, Kluver Academic Publishers, 1991 or the European patent application EP-A-646901 by Cerberus AG) which was published on April 5, 1995 and has a priority date of October 4, 1993. It is only here recalls that the central concept of fuzzy logic is the fuzzy sets or unsharp ones Are sets, with the membership of elements in a fuzzy set by the so-called membership or membership function is defined. While at sharp sets mean one belonging and zero not belonging in the fuzzy sets as values for the membership function are not just zero and one, but any values in between allowed.
- each input variable which is one of the signals mentioned above, at least one so-called membership function depicted as a matrix.
- the x scaling this function has an equivalent in the respective signal, and the y scaling corresponds to the truth content or the degree of approximation to the respective Statement and can take any value from 0 to 1.
- the determination of the frequencies ⁇ m and ⁇ g can be done with a fast Fourier transform (FFT) or with simpler and / or faster methods such as zero crossing (determination of the zero crossings) or determination of the distance between the peaks or wavelet analysis or spectral analysis (see also M. Kunt: Traitement Numérique des Signaux, Presses Polytechniques Romandes).
- FFT fast Fourier transform
- simpler and / or faster methods such as zero crossing (determination of the zero crossings) or determination of the distance between the peaks or wavelet analysis or spectral analysis
- Flame detectors are known to detect the flame radiation of possible fire locations, this flame radiation, which is heat and thus infrared radiation, reaches the detector through direct or indirect radiation.
- the detectors usually contain two pyroelectric sensors that are sensitive to two different wavelengths.
- the first sensor reacts to the infrared active flame gases in the characteristic CO 2 spectral range from 4.1 to 4.7 ⁇ m, which are formed when carbonaceous materials are burned off, and the second sensor measures the infrared energy in the wavelength range from 5 to 6 ⁇ m, which is caused by interference sources such as sunlight. artificial light or radiant heaters.
- FIG. 3 shows a highly simplified block diagram of a flame detector according to the invention, which essentially consists of an infrared-sensitive sensor 1, an amplifier 2 and a microprocessor or microcontroller 3 containing an A / D converter.
- a filter 4 is connected upstream of the sensor 1, which has an impedance converter, and is only permeable for radiation from the characteristic CO 2 spectral range mentioned, preferably for a wavelength of 4.3 ⁇ m.
- the radiation of this wavelength incident on the sensor 1 generates a corresponding voltage signal at the output of the sensor, which after amplification in the amplifier 2 reaches the microprocessor 3 and is evaluated there.
- This microprocessor now defines the three variables square signal x i 2 , center frequency ⁇ m and cut-off frequency ⁇ g and evaluates these variables, the signal evaluation being able to take place in the first way already mentioned or by means of fuzzy logic.
- the microprocessor (microcontroller) 3 contains a fuzzy controller, the rule base in a known manner with the fuzzy rules given above and includes an inference engine.
- the flame detector can also have more than one sensor, for example 2 sensors.
- the flame detector described has the advantage that the examination of the periodicity of the flicker frequency and the determination of the center and cut-off frequency and their comparison with the two frequency values G 1 and G 2 provides a simple criterion for distinguishing between useful radiation and interference radiation.
- the signal evaluation using fuzzy logic offers the additional advantage that relatively simple algorithms can be used, as a result of which the computation and storage effort remains within a modest framework.
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Abstract
Description
Die vorliegende Erfindung betrifft ein Verfahren zur Detektion einer Flamme durch Analyse der Intensitätsänderung der von einer Strahlungsquelle ausgesandten Strahlung, wobei eine Auswertung des Flackerfrequenzspektrums der Strahlung erfolgt und ausserhalb eines bestimmten Frequenzbandes liegende Signale als Störsignale bewertet werden.The present invention relates to a method for detecting a flame Analysis of the change in intensity of the radiation emitted by a radiation source, an evaluation of the flicker frequency spectrum of the radiation takes place and outside signals lying in a specific frequency band are evaluated as interference signals become.
Verfahren dieser Art benutzen also das typische Flackern der Flammen in einem sehr niederfrequenten Schwingungsbereich als Merkmal zur Unterscheidung zwischen der von einer Flamme ausgesandten Strahlung und Störstrahlung. Die Festlegung des Frequenzbandes erfolgt im einfachsten Fall durch dem Sensor für die ausgesandte Strahlung vorgeschaltete Filter oder durch diesem nachgeschaltete frequenzselektive Verstärker, wobei in beiden Fällen ein bestimmter Durchlassbereich von beispielsweise 5 bis 25 Hz erhalten wird. Selbst wenn das Frequenzband optimal auf das Flackern von Flammen abgestimmt ist, sind Störungen und Fehlanzeigen relativ häufig, weil es immer wieder vorkommt, dass zufällige Intensitätsänderungen der Umgebungsstrahlung im Durchlassbereich liegen. Derartige Intensitätsänderungen können beispielsweise durch Abschattungen oder Reflexe von vibrierenden oder sich langsam bewegenden Gegenständen, durch Reflexe des Sonnenlichts an Wasseroberflächen oder durch flackernde oder schwankende Lichtquellen verursacht sein.Methods of this type use the typical flickering of the flames in one low frequency vibration range as a feature to distinguish between the radiation and interference radiation emitted by a flame. The definition of the frequency band in the simplest case it is carried out by the sensor for the emitted radiation upstream filter or frequency-selective amplifier connected downstream, in both cases a certain pass band of, for example, 5 to 25 Hz is obtained. Even if the frequency band is optimally matched to the flickering of flames malfunctions and false reports are relatively common because it happens again and again that random changes in intensity of the ambient radiation in the pass band lie. Such changes in intensity can be caused, for example, by shadowing or reflections from vibrating or slowly moving objects Reflections of sunlight on water surfaces or from flickering or fluctuating Light sources may be caused.
In der US-A-3,739,365 ist ein Verfahren der eingangs genannten Art beschrieben, bei dem die Anfälligkeit auf Störlicht dadurch verbessert wird, dass zwei Typen von Sensoren mit unterschiedlicher spektraler Empfindlichkeit verwendet werden und die Differenz der Ausgangssignale der Sensoren in einem begrenzten niederfrequenten Schwingungsbereich gebildet wird.In US-A-3,739,365 a method of the type mentioned is described in which the susceptibility to stray light is improved by the fact that two types of sensors be used with different spectral sensitivity and the difference the output signals of the sensors in a limited low-frequency vibration range is formed.
Die praktische Erfahrung hat gezeigt, dass die Möglichkeit der Beeinflussung durch andere Strahlungsquellen und damit auch die Wahrscheinlichkeit von Fehlalarmen noch immer relativ gross ist, weil nämlich das Auftreten von Störstrahlung im kritischen Frequenzbereich nicht ausgeschlossen werden kann. Aus diesem Grund ist bei modernen Flammenmeldem der kritische Frequenzbereich auf wenige, sehr schmale Frequenzbänder beschränkt. So werden beispielsweise bei einem in der US-A-4,280,058 beschriebenen Flammenmelder nur Emissionen im Wellenlängenbereich von etwa 4,4 µm, das ist der für die Verbrennung von Kohlendioxid typische Spektralbereich, für die Alarmierung ausgewertet, was aber nicht ausschliesst, dass eine gerade in diesem Spektralbereich auftretende Störstrahlung einen Fehlalarm auslösen kann.Practical experience has shown that the possibility of being influenced by others Radiation sources and thus the probability of false alarms is always relatively large, because the occurrence of interference radiation in the critical frequency range cannot be excluded. For this reason, modern Flame detector the critical frequency range on a few, very narrow frequency bands limited. For example, one described in US-A-4,280,058 Flame detectors only have emissions in the wavelength range of around 4.4 µm, that is the spectral range typical for the combustion of carbon dioxide, for the alarm evaluated, but this does not exclude that one in this spectral range Interfering radiation can trigger a false alarm.
Bei einem in der US-A-4,866,420 beschriebenen Verfahren der eingangs genannten Art wird das Ausgangssignal eines Sensors mit dem theoretischen Flackerspektrum einer Flamme verglichen und die Entscheidung, ob eine Flamme vorliegt, erfolgt anhand des Grades der Übereinstimmung zwischen dem gemessenen und dem theoretischen Flackerspektrum. Da in der Praxis eine Flamme sehr verschiedene Flackerspektren aufweisen kann, ermöglicht auch dieses Verfahren keine sichere Ausschaltung von Störstrahlung.In a method of the type mentioned in US Pat. No. 4,866,420 the output signal of a sensor with the theoretical flickering spectrum Flame compared and the decision whether there is a flame is made using the Degree of agreement between the measured and the theoretical Flicker spectrum. In practice, a flame has very different flickering spectra can also have this method does not enable safe switching off of Interference.
Durch die Erfindung sollen nun ein Verfahren der eingangs angegebenen Art angegeben werden, welches eine eindeutige und sichere Identifizierung und damit Ausschaltung von Störstrahlung ermöglicht und somit eine hohe Fehlalarmsicherheit aufweist, und welches ausserdem möglichst universell einsetzbar ist.The invention is now intended to specify a method of the type specified at the outset be what a clear and secure identification and thus elimination of interference radiation and thus has a high false alarm security, and which is also as universal as possible.
Diese Aufgabe wird erfindungsgemäss dadurch gelöst, dass bei der Auswertung des Flackerfrequenzspektrums die Mitten- und Grenzfrequenz ermittelt und nach periodischen und nicht-periodischen Signalen unterschieden wird, und dass periodische Signale mit einer Mittenfrequenz oberhalb eines ersten und nicht-periodische Signale mit einer Grenzfrequenz oberhalb eines zweiten Frequenzwerts als Störsignale bewertet werden, wobei der erste Frequenzwert durch die Flackerfrequenz einer stationären Flamme mit einer der zu detektierenden Mindestgrösse entsprechenden Grösse bestimmt ist und der zweite Frequenzwert grösser als der erste gewählt wird. This object is achieved according to the invention in that when evaluating the Flicker frequency spectrum determines the center and cut-off frequency and according to periodic and non-periodic signals is distinguished, and that periodic signals with a center frequency above a first and non-periodic signals with a Cut-off frequency above a second frequency value are evaluated as interference signals, the first frequency value being determined by the flickering frequency of a stationary flame a size corresponding to the minimum size to be detected is determined and the second frequency value greater than the first is selected.
Das erfindungsgemässe Verfahren geht von der Tatsache aus, dass einerseits jede Flamme zwei Zustände aufweisen kann, und zwar einen stationären Zustand, der in der Regel dann vorliegt, wenn die Flamme stabil und ungestört brennt (sogenannte periodische Flamme), und einen quasistationären Zustand, in dem die Flamme unstabil brennt (sogenannte nicht-periodische Flamme), und dass andererseits eine periodische Flamme ein Frequenzspektrum mit einer ausgeprägten Frequenzspitze und eine nicht-periodische Flamme ein breitbandiges Spektrum mit einer Maximal- oder Grenzfrequenz aufweist.The method according to the invention is based on the fact that on the one hand each flame can have two states, namely a steady state, which is usually then exists when the flame burns stable and undisturbed (so-called periodic Flame), and a quasi-steady state in which the flame burns unstably (so-called non-periodic flame), and that on the other hand a periodic flame Frequency spectrum with a pronounced frequency peak and a non-periodic Flame has a broadband spectrum with a maximum or limit frequency.
Für die potentiellen Störstrahler gelten ähnliche Überlegungen: Es gibt Störquellen, wie beispielsweise Schweissapparate oder durch Blätter fallende Sonnenstrahlen, mit einem sehr breiten Fourierspektrum, und es gibt andere Störquellen, wie beispielsweise eine Lampe beim Anzünden oder von einem Ventilator bewegte heisse Luft, mit einer schmalen Frequenzspitze.Similar considerations apply to potential interference sources: There are sources of interference, such as for example welding equipment or sun rays falling through leaves, with a very wide Fourier spectrum, and there are other sources of interference, such as one Lamp when ignited or hot air moved by a fan, with a narrow Frequency peak.
Die genannten Tatsachen bilden die Basis für die Erkenntnis von der die vorliegende Erfindung ausgeht. Diese durch experimentelle Untersuchungen erhärtete Erkenntnis besteht darin, dass die Frequenz einer periodischen Flamme etwa ein Drittel bis die Hälfte der Grenzfrequenz einer nicht-periodischen Flamme von der gleichen Grösse beträgt. Ausgehend von dieser Erkenntnis wird nun sowohl für periodische als auch für nicht-periodische Signale ein Kriterium für die Unterdrückung der Störsignale festgelegt.The facts mentioned form the basis for the knowledge of the present invention going out. This knowledge, corroborated by experimental studies, exists in that the frequency of a periodic flame is about a third to a half the cutoff frequency of a non-periodic flame of the same size. Based on this knowledge, we now use both periodic and non-periodic ones Signals defines a criterion for the suppression of the interference signals.
Die Erfindung betrifft weiter einen Flammenmelder mit Mitteln zur Durchführung des genannten Verfahrens, mit mindestens einem Sensor für die von der Strahlungsquelle ausgesandte Strahlung, und mit einer dem mindestens einen Sensor nachgeschalteten Auswerteelektronik. Der erfindungsgemässe Flammenmelder ist dadurch gekennzeichnet, dass die Auswerteelektronik Mittel zur Analyse der empfangenen Strahlung und von deren Mitten- und Grenzfrequenz und zur Verknüpfung der der empfangenen Strahlung entsprechenden Sensorsignale mit diesen Frequenzen aufweist.The invention further relates to a flame detector with means for carrying out the mentioned method, with at least one sensor for the from the radiation source emitted radiation, and with a downstream of the at least one sensor Evaluation electronics. The flame detector according to the invention is characterized in that that the evaluation electronics means for analyzing the received radiation and their center and cut-off frequency and to link the radiation received corresponding sensor signals with these frequencies.
Eine bevorzugte Ausführungsform des erfindungsgemässen Flammenmelders ist dadurch gekennzeichnet, dass die genannten Mittel durch einen Mikroprozessor gebildet sind, und dass dieser Mikroprozessor einen Fuzzy-Controller enthält. A preferred embodiment of the flame detector according to the invention is thereby characterized in that the said means formed by a microprocessor and that this microprocessor contains a fuzzy controller.
Im folgenden wird die Erfindung anhand eines Ausführungsbeispiels und der Zeichnungen näher erläutert; es zeigt:
- Fig. 1
- das Spektrum der Flackerfrequenz einer periodischen und einer nicht-periodischen Flamme,
- Fig. 2
- ein Beispiel für die Fuzzy-Zugehörigkeitsfunktion der Grenzfrequenz des Spektrums von Fig. 1; und
- Fig. 3
- ein Blockschema eines erfindungsgemässen Flammenmelders.
- Fig. 1
- the spectrum of the flickering frequency of a periodic and a non-periodic flame,
- Fig. 2
- an example of the fuzzy membership function of the cutoff frequency of the spectrum of Fig. 1; and
- Fig. 3
- a block diagram of a flame detector according to the invention.
Es ist bekannt, dass die Flackerfrequenz einer Flamme in erster Näherung nur vom Flammendurchmesser abhängig ist, wobei diese Beziehung für verschiedenste Brennstoffe, wie beispielsweise alle kohlenstoffwasserhaltigen Flüssigkeiten, Festkörper (PMMA) oder Helium gilt und für Flammendurchmesser von 1cm bis zu 100m experimentell bestätigt ist. Wenn man das Fourierspektrum von Flammen bestimmt, dann erhält man eines von zwei typischen Spektren, entweder ein Spektrum mit einer ausgeprägten, schmalen Spitze oder ein breitbandiges, "verwaschenes" Spektrum ohne Spitze. Diese beiden Arten von Spektren sind in Fig. 1 dargestellt, wobei auf der Abszisse die Frequenz ω und auf der Ordinate die Amplitude F(ω) aufgetragen ist.It is known that the flickering frequency of a flame is only approximate from the first Flame diameter is dependent, this relationship for different fuels, such as all liquids containing carbon water, solids (PMMA) or helium applies and experimental for flame diameters from 1cm up to 100m is confirmed. If you determine the Fourier spectrum of flames, then you get one of two typical spectra, either a spectrum with a pronounced, narrow tip or a broadband, "washed out" spectrum without tip. These two types of spectra are shown in Fig. 1, with on the abscissa Frequency ω and on the ordinate the amplitude F (ω) is plotted.
Das voll ausgezogen eingezeichnete Spektrum mit der ausgeprägten Spitze hat eine
Mittenfrequenz ωmp und eine obere Grenzfrequenz ωgp, wobei gilt:
Ein Spektrum dieser Art ist typisch für eine ungestört und stabil brennende, sogenannte periodische Flamme, wobei die Mittenfrequenz ωmp bei einem Flammendurchmesser von 10cm unterhalb von 5 Hz liegt und mit zunehmendem Durchmesser langsam abnimmt. Das durch eine gestrichelt eingezeichnete Umhüllende angedeutete breitbandige Spektrum besitzt ebenfalls eine Mittenfrequenz und eine Grenzfrequenz, die mit ωmc beziehungsweise ωgc bezeichnet sind. A spectrum of this type is typical of an undisturbed and stable burning, so-called periodic flame, the center frequency ω mp with a flame diameter of 10 cm being below 5 Hz and slowly decreasing with increasing diameter. The broadband spectrum indicated by a dashed envelope also has a center frequency and a cutoff frequency, which are denoted by ω mc and ω gc .
Ein solches breitbandiges Spektrum ist typisch für eine Flamme in einem unstabilen
oder nicht-stationären Zustand; eine derartige Flamme wird im folgenden als nicht-periodisch
bezeichnet. Darstellungsgemäss ist die Grenzfrequenz ωgc des breitbandigen
Spektrums höher als die Mittenfrequenz ωmp der periodischen Flamme. Es gilt also:
Wie Untersuchungen der Fourierspektren einer Vielzahl von Flammen gezeigt haben,
gilt für die Grenzfrequenz ωgc ausserdem noch die Beziehung:
Das Auftreten der Grenzfrequenz ωgc bei einer nicht-periodischen Flamme kann folgendermassen erklärt werden: Wenn eine Flamme ungestört brennt und sich im stationären Zustand befindet, dann sind auch die diese Flamme bildenden Konvektionszellen nach Anzahl und Grösse stationär, und die Flamme weist eine konstante Flackerfrequenz ω1 auf, wobei gilt ω1 ≈ ωmp ≈ ωgp. Wenn aber die Flamme äusseren Einflüssen, wie zum Beispiel Wind, ausgesetzt ist, dann können sich die Konvektionszellen teilen oder sie können Aggregate aus mehren Zellen bilden, wobei beiden Vorgängen eine Grenze gesetzt sein wird.The occurrence of the cut-off frequency ω gc in a non-periodic flame can be explained as follows: If a flame burns undisturbed and is in the steady state, then the convection cells forming this flame are also stationary in number and size, and the flame has a constant flickering frequency ω 1 , where ω 1 ≈ ω mp ≈ ω gp . If, however, the flame is exposed to external influences such as wind, the convection cells can divide or they can form aggregates of several cells, both processes being subject to a limit.
Die vorstehenden Überlegungen führen zusammen mit den Formeln 1 bis 3 zum Ergebnis,
dass das (breitbandige) Spektrum einer nicht-periodischen Flamme mit hoher Wahrscheinlichkeit
keine Frequenzen enthalten wird, die höher sind als das Dreifache der
Flackerfrequenz ωo einer gleich grossen stationären Flamme. Und diese Flackerfrequenz
ωo kann für den konkreten Fall berechnet und daher als bekannt vorausgesetzt werden.
Die Berechnung erfolgt nach der Formel:
In dieser Formel bezeichnet K einen Faktor, g die Erdanziehung und D die Grösse der
Flamme ausgedrückt durch den Durchmesser desjenigen schalenförmigen Behälters, in
dem eine Flüssigkeit mit einer Flamme der betreffenden Grösse brennt. Man kann K und
g zusammenfassen und erhält dann die folgende Beziehung für ωo:
Aus Formel 5 ergibt sich für einen Schalendurchmesser von 0.1 m für ωo ein Wert von
4.7 Hz. Wenn man die Flackerfrequenz misst, dann kommt man zu tieferen Werten.
Zur Einstellung des Melders wird zuerst der minimale Durchmesser des zu detektierenden
Feuers oder Brandes bestimmt. Wenn dieser beispielsweise 10 cm betragen soll,
dann liegt die Frequenz ωmp ≈ ωgp einer periodischen Flamme unterhalb von 5 Hz und
die Grenzfrequenz ωgc der gleich grossen nicht-periodischen Flamme wird sicher nicht
oberhalb von 15 Hz liegen. Dann werden zwei Grenzwerte G1 und G2 für periodische
bzw. für nicht-periodische Störsignale festgelegt; der Grenzwert G1 für periodische
Störsignale vorzugsweise gemäss Formel 2 mit G1 > ωmp, also bei etwa 5 Hz, und der
Grenzwert G2 für nicht-periodische Störsignale gemäss Formel 3 mit G2 > 3ωmp beispielsweise
bei etwa 15 Hz.To set the detector, the minimum diameter of the fire or fire to be detected is first determined. If this is to be 10 cm, for example, then the frequency ω mp ≈ ω gp of a periodic flame is below 5 Hz and the cut-off frequency ω gc of the same size non-periodic flame will certainly not be above 15 Hz. Then two limit values G 1 and G 2 are set for periodic and non-periodic interference signals; the limit value G 1 for periodic interference signals preferably according to
Im Betrieb wird das vom Sensor des Melders erzeugte Signal auf seine Periodizität untersucht und einer der beiden Klassen periodisch oder nicht-periodisch zugeteilt und jeweils mit dem betreffenden Grenzwert G1 bzw. G2 verglichen und bei Überschreiten des Grenzwerts als Störsignal bewertet. Die Untersuchung des Signals auf Periodizität oder Nicht-Periodizität erfolgt beispielsweise dadurch, dass man die Differenz Grenzfrequenz minus Mittenfrequenz bildet und diese Differenz durch die Grenzfrequenz dividiert. Liegt der Quotient in der Grössenordnung von Einem, dann handelt es sich um ein nicht-periodisches Signal; liegt er deutlich unter eins, dann handelt es sich um ein periodisches Signal. In operation, the signal generated by the sensor of the detector is examined for its periodicity and assigned to one of the two classes periodically or non-periodically and compared with the relevant limit value G 1 or G 2 and evaluated as an interference signal when the limit value is exceeded. The signal is examined for periodicity or non-periodicity, for example, by forming the difference between the cutoff frequency minus the center frequency and dividing this difference by the cutoff frequency. If the quotient is in the order of one, then it is a non-periodic signal; if it is well below one, then it is a periodic signal.
Die Parametrierung der Sensorsignale xi erfolgt durch Festlegung der drei Grössen:
Grundsätzlich kann nun eine erste Art der Signalauswertung anhand der folgenden Kriterien erfolgen:
- Das Quadratsignal muss einen bestimmten Mindestwert übersteigen, damit die Auswertung gestartet wird.
- Untersuchung der Signale auf die Eigenschaft periodisch/nicht periodisch und entsprechende Klassierung.
- Unterdrückung aller periodischen Signale mit einer Mittenfrequenz ωm > G1 (G1 > ωmp).
- Unterdrückung aller nicht-periodischen Signale mit einer Grenzfrequenz ωg > G2 (G2 > 3ωmp).
- The square signal must exceed a certain minimum value for the evaluation to start.
- Examination of the signals for the periodic / non-periodic property and corresponding classification.
- Suppression of all periodic signals with a center frequency ω m > G 1 (G 1 > ω mp ).
- Suppression of all non-periodic signals with a cutoff frequency ω g > G 2 (G 2 > 3ω mp ).
Diese Art der Signalauswertung würde eine weitgehende Unterdrückung von potentiellen Störsignalen und damit eine hohe Fehlalarmsicherheit garantieren. Man kann die Fehlalarmsicherheit und die Zuverlässigkeit weiter verbessern, wenn man die Signalauswertung mittels einer Fuzzy-Logik vornimmt. Die Grundlagen der Fuzzy-Logik werden als bekannt vorausgesetzt (siehe beispielsweise das Buch "Fuzzy Set Theory and its Applications" von H.-J. Zimmermann, Kluver Academic Publishers, 1991 oder die europäische Patentanmeldung EP-A-646901 der Cerberus AG) welche am 5.4.1995 veröffenlicht wurde und ein Prioritäts datum vom 4.10.1993 aufweist. Es sei hier nur daran erinnert, dass der zentrale Begriff der Fuzzy-Logik die Fuzzy-Sets oder unscharfen Mengen sind, wobei die Zugehörigkeit von Elementen zu einem Fuzzy-Set durch die sogenannte Zugehörigkeits- oder Membershipfunktion definiert ist. Während bei scharfen Mengen eine Eins Zugehörigkeit und eine Null Nichtzugehörigkeit bedeutet, sind bei den Fuzzy-Sets als Werte für die Zugehörigkeitsfunktion nicht nur null und eins, sondern beliebige Werte dazwischen zugelassen.This type of signal evaluation would largely suppress potential Interference signals and thus a high level of false alarm security are guaranteed. You can do that False alarm security and reliability further improve if you evaluate the signal using fuzzy logic. The basics of fuzzy logic will be as known (see for example the book "Fuzzy Set Theory and its Applications "by H.-J. Zimmermann, Kluver Academic Publishers, 1991 or the European patent application EP-A-646901 by Cerberus AG) which was published on April 5, 1995 and has a priority date of October 4, 1993. It is only here recalls that the central concept of fuzzy logic is the fuzzy sets or unsharp ones Are sets, with the membership of elements in a fuzzy set by the so-called membership or membership function is defined. While at sharp sets mean one belonging and zero not belonging in the fuzzy sets as values for the membership function are not just zero and one, but any values in between allowed.
Die Umwandlung von scharfen Zahlen in unscharfe Mengen wird als Fuzzyfizierung bezeichnet. Bei dieser hat jede Eingangsvariable, das ist eines der oben genannten Signale, mindestens eine als Matrix abgebildete sogenannte Zugehörigkeitsfunktion. Die x-Skalierung dieser Funktion hat eine Entsprechung im jeweiligen Signal, und die y-Skalierung entspricht dem Wahrheitsgehalt oder dem Grad der Annäherung an die jeweilige Aussage und kann jeden Wert von 0 bis 1 annehmen.The conversion of sharp numbers to fuzzy quantities is called fuzzification. With this, each input variable, which is one of the signals mentioned above, at least one so-called membership function depicted as a matrix. The x scaling this function has an equivalent in the respective signal, and the y scaling corresponds to the truth content or the degree of approximation to the respective Statement and can take any value from 0 to 1.
Fig. 2 zeigt ein Beispiel für die Definition der Zugehörigkeitsfunktion der Grenzfrequenz ωg für einen Flammendurchmesser von 10 cm, basierend auf den höheren, berechneten Grenzwerten. Für das Quadratsignal xi 2 und die Mittenfrequenz ωm des Fourierspektrums werden ähnliche Zugehörigkeitsfunktionen definiert, und schliesslich werden die Fuzzy-Regeln für die Auswertung dieser drei Grössen aufgestellt. Die Fuzzy-Regeln können beispielsweise folgendermassen lauten:
- Wenn [(ωg - ωm) / ωg = gross und ωg = klein oder mittel und xi 2 = gross], dann Flamme.
- Wenn [(ωg - ωm) / ωg = gross und ωg = gross und xi 2 = gross], dann breitbandiger Störer.
- Wenn xi 2 = klein, dann Normalzustand.
- Wenn [(ωg - ωm) / ωg = klein und ωg = klein und xi 2 = gross], dann Flamme.
- Wenn [(ωg - ωm) / ωg = klein und ωg = mittel oder gross und xi 2 = gross], dann periodischer Störer.
- If [(ω g - ω m ) / ω g = large and ω g = small or medium and x i 2 = large], then flame.
- If [(ω g - ω m ) / ω g = large and ω g = large and x i 2 = large], then broadband interferer.
- If x i 2 = small, then normal state.
- If [(ω g - ω m ) / ω g = small and ω g = small and x i 2 = large], then flame.
- If [(ω g - ω m ) / ω g = small and ω g = medium or large and x i 2 = large], then periodic interferer.
Die Bestimmung der Frequenzen ωm und ωg kann mit einer schnellen Fouriertransformation (FFT) oder mit einfacheren und/oder schnelleren Verfahren wie beispielsweise Zero Crossing (Bestimmung der Nulldurchgänge) oder Bestimmung des Abstands zwischen den Spitzen oder Wavelet Analyse oder spektrale Analyse (siehe dazu M. Kunt: Traitement Numérique des Signaux, Presses Polytechniques Romandes) erfolgen.The determination of the frequencies ω m and ω g can be done with a fast Fourier transform (FFT) or with simpler and / or faster methods such as zero crossing (determination of the zero crossings) or determination of the distance between the peaks or wavelet analysis or spectral analysis (see also M. Kunt: Traitement Numérique des Signaux, Presses Polytechniques Romandes).
Flammenmelder detektieren bekanntlich die Flammenstrahlung möglicher Brandorte, wobei diese Flammenstrahlung, die eine Wärme- und damit eine Infrarotstrahlung ist, durch direkte oder indirekte Einstrahlung zum Melder gelangt. Die Melder enthalten in der Regel zwei pyroelektrische Sensoren, die auf zwei verschiedene Wellenlängen empfindlich sind. Der erste Sensor reagiert auf die infrarotaktiven Flammengase im charakteristischen CO2-Spektralbereich von 4.1 bis 4.7µm, die beim Abbrand von kohlenstoffhaltigen Materialien entstehen, und der zweite Sensor misst die Infrarotenergie im Wellenlängenbereich von 5 bis 6µm, die von Störquellen, wie beispielsweise Sonnenlicht, künstlichem Licht oder Heizstrahlern, ausgestrahlt wird.Flame detectors are known to detect the flame radiation of possible fire locations, this flame radiation, which is heat and thus infrared radiation, reaches the detector through direct or indirect radiation. The detectors usually contain two pyroelectric sensors that are sensitive to two different wavelengths. The first sensor reacts to the infrared active flame gases in the characteristic CO 2 spectral range from 4.1 to 4.7 µm, which are formed when carbonaceous materials are burned off, and the second sensor measures the infrared energy in the wavelength range from 5 to 6 µm, which is caused by interference sources such as sunlight. artificial light or radiant heaters.
Fig. 3 zeigt ein stark vereinfachtes Blockschaltbild eines erfindungsgemässen Flammenmelders,
der im wesentlichen aus einem infrarotempfindlichen Sensor 1, einem Verstärker
2 und aus einem einen A/D-Wandler enthaltenden Mikroprozessor oder Mikrocontroller
3 besteht. Dem einen Impedanzwandler aufweisenden Sensor 1 ist ein Filter 4
vorgeschaltet, das nur für Strahlung aus dem genannten charakteristischen CO2-Spek-tralbereich,
vorzugsweise für eine Wellenlänge von 4.3 µm, durchlässig ist. Die auf den
Sensor 1 auftreffende Strahlung dieser Wellenlänge, erzeugt am Ausgang des Sensors
ein entsprechendes Spannungssignal, das nach Verstärkung im Verstärker 2 in den Mikroprozessor
3 gelangt und dort ausgewertet wird. Dieser Mikroprozessor legt nun die
drei Grössen Quadratsignal xi 2, Mittenfrequenz ωm und Grenzfrequenz ωg fest und
wertet diese Grössen aus, wobei die Signalauswertung auf die schon erwähnte erste Art
oder mittels einer Fuzzy-Logik erfolgen kann.3 shows a highly simplified block diagram of a flame detector according to the invention, which essentially consists of an infrared-sensitive sensor 1, an
Im letzteren Fall enthält der Microprozessor (Mikrocontroller) 3 einen Fuzzy-Controller, der in bekannter Weise eine Regelbasis mit den weiter vorne angegebenen Fuzzy-Regeln und eine Inferenzmaschine enthält. Selbstverständlich kann der Flammenmelder auch mehr als einen Sensor, beispielsweise also 2 Sensoren, aufweisen.In the latter case, the microprocessor (microcontroller) 3 contains a fuzzy controller, the rule base in a known manner with the fuzzy rules given above and includes an inference engine. Of course, the flame detector can also have more than one sensor, for example 2 sensors.
Der beschriebene Flammenmelder hat den Vorteil, dass die Untersuchung der Periodizität der Flackerfrequenz und die Ermittlung der Mitten- und Grenzfrequenz und deren Vergleich mit den beiden Frequenzwerten G1 und G2 ein einfaches Kriterium für die Unterscheidung zwischen Nutzstrahlung und Störstrahlung liefert. Die Signalauswertung mittels Fuzzy-Logik bietet den zusätzlichen Vorteil, dass relativ einfache Algorithmen verwendet werden können, wodurch der Rechen- und Speicheraufwand in einem bescheidenen Rahmen bleibt.The flame detector described has the advantage that the examination of the periodicity of the flicker frequency and the determination of the center and cut-off frequency and their comparison with the two frequency values G 1 and G 2 provides a simple criterion for distinguishing between useful radiation and interference radiation. The signal evaluation using fuzzy logic offers the additional advantage that relatively simple algorithms can be used, as a result of which the computation and storage effort remains within a modest framework.
Claims (8)
- Method of detecting a flame by analysis of the intensity change in the radiation emitted by a radiation source, an evaluation of the flicker frequency spectrum of the radiation being made and signals lying outside a specific frequency band being evaluated as interference signals, characterized in that the frequency of the radiation is analyzed and the mid- and threshold frequency (ωmp, ωmc; ωgp, ωgc) are determined and are distinguished according to periodic and non-periodic signals and in that periodic signals with a mid-frequency (ωm) above a first frequency value (G1) and non-periodic signals with a threshold frequency (ωg) above a second frequency value (G2) are evaluated as interference signals, the first frequency value being defined by the flicker frequency of a stationary flame with a magnitude corresponding to the flame minimum magnitude to be detected and the second frequency value being selected higher than the first.
- Method according to Claim 1, characterized in that the flicker frequency of a stationary flame with said minimum magnitude is calculated for determining the first frequency value (G1) and in that the first threshold value is selected greater than this flicker frequency.
- Method according to Claim 2, characterized in that the second frequency value (G2) is selected not lower than three times said flicker frequency and therefore approximately three times as great as the first frequency value (G1).
- Method according to one of Claims 1 to 3, characterized in that the quotient is formed from the difference in the threshold frequency minus the mid-frequency (ωg - ω m) divided by the threshold frequency (ωg) to distinguish between periodic and non-periodic signals and in that the magnitude of this quotient is used as a criterion for the periodicity or non-periodicity of the signals, a value of approximately one denoting a non-periodic signal and a value clearly less than one a periodic signal.
- Method according to one of Claims 1 to 3, characterized in that the evaluation of the flicker frequency spectrum of the radiation is carried out by a rapid Fourier transform, by determining the passages through zero or by spectral analysis.
- Flame detector with means for carrying out the method according to Claim 1 with at least one sensor (1) for the radiation emitted by the radiation source and with evaluating electronics following the sensor, of which there is at least one, characterized in that the evaluating electronics comprise means for analysing the received radiation and its mid- and threshold frequency (ωmp, ωmc; ωgp, ωgc) and for linking the sensor signals corresponding to the received radiation to these frequencies.
- Flame detector according to Claim 6, characterized in that said means are formed by a microprocessor (3) and in that this microprocessor contains a fuzzy controller.
- Flame detector according to Claim 7, characterized in that the fuzzy controller contains one or more of the following fuzzy rules:Normal state when sensor signal low.Flame when [signal non-periodic and threshold frequency (ωgc) low or medium and sensor signal great].Wide-band interfering station when [signal non-periodic and threshold frequency (ωgc) high and sensor signal great].Flame when [signal periodic and threshold frequency (ωgp) low and sensor signal great].Periodic interfering station when [signal periodic and threshold frequency (ωgp) medium or high and sensor signal great].
Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE59409799T DE59409799D1 (en) | 1994-12-19 | 1994-12-19 | Method and arrangement for detecting a flame |
AT94120083T ATE203118T1 (en) | 1994-12-19 | 1994-12-19 | METHOD AND ARRANGEMENT FOR DETECTING A FLAME |
EP94120083A EP0718814B1 (en) | 1994-12-19 | 1994-12-19 | Method and device for flame detection |
AU37810/95A AU703685B2 (en) | 1994-12-19 | 1995-11-13 | Method of detecting a flame and flame detector for carrying out the method |
CZ19953218A CZ289921B6 (en) | 1994-12-19 | 1995-12-05 | Flame detection method, flame detector and flame detector operation |
CN95120895A CN1099660C (en) | 1994-12-19 | 1995-12-19 | Method of detecting flame and flame detectr for carrying out the method |
US08/574,773 US5594421A (en) | 1994-12-19 | 1995-12-19 | Method and detector for detecting a flame |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP94120083A EP0718814B1 (en) | 1994-12-19 | 1994-12-19 | Method and device for flame detection |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0718814A1 EP0718814A1 (en) | 1996-06-26 |
EP0718814B1 true EP0718814B1 (en) | 2001-07-11 |
Family
ID=8216544
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP94120083A Expired - Lifetime EP0718814B1 (en) | 1994-12-19 | 1994-12-19 | Method and device for flame detection |
Country Status (7)
Country | Link |
---|---|
US (1) | US5594421A (en) |
EP (1) | EP0718814B1 (en) |
CN (1) | CN1099660C (en) |
AT (1) | ATE203118T1 (en) |
AU (1) | AU703685B2 (en) |
CZ (1) | CZ289921B6 (en) |
DE (1) | DE59409799D1 (en) |
Cited By (1)
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CN111123423A (en) * | 2020-03-27 | 2020-05-08 | 上海翼捷工业安全设备股份有限公司 | Double-channel infrared filter combination for flame detection and preparation method and application thereof |
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US6507023B1 (en) | 1996-07-31 | 2003-01-14 | Fire Sentry Corporation | Fire detector with electronic frequency analysis |
US6515283B1 (en) | 1996-03-01 | 2003-02-04 | Fire Sentry Corporation | Fire detector with modulation index measurement |
US6518574B1 (en) | 1996-03-01 | 2003-02-11 | Fire Sentry Corporation | Fire detector with multiple sensors |
EP0834845A1 (en) * | 1996-10-04 | 1998-04-08 | Cerberus Ag | Method for frequency analysis of a signal |
US5850182A (en) * | 1997-01-07 | 1998-12-15 | Detector Electronics Corporation | Dual wavelength fire detection method and apparatus |
US5995008A (en) * | 1997-05-07 | 1999-11-30 | Detector Electronics Corporation | Fire detection method and apparatus using overlapping spectral bands |
AU768582B2 (en) * | 1998-06-02 | 2003-12-18 | Hochiki Kabushiki Kaisha | Flame detection device and flame detection method |
DE19841475C1 (en) * | 1998-09-10 | 2000-02-03 | Electrowatt Tech Innovat Corp | Flame monitoring system for gas-, oil- or coal-fired burner |
US6879253B1 (en) * | 2000-03-15 | 2005-04-12 | Siemens Building Technologies Ag | Method for the processing of a signal from an alarm and alarms with means for carrying out said method |
US6184792B1 (en) | 2000-04-19 | 2001-02-06 | George Privalov | Early fire detection method and apparatus |
WO2005111556A2 (en) * | 2004-05-07 | 2005-11-24 | Walter Kidde Portable Equipment, Inc. | Flame detector with uv sensor |
JP2010249769A (en) * | 2009-04-20 | 2010-11-04 | Oki Denki Bosai Kk | Flame monitoring device |
US8260523B2 (en) * | 2009-05-04 | 2012-09-04 | General Electric Company | Method for detecting gas turbine engine flashback |
US9251683B2 (en) | 2011-09-16 | 2016-02-02 | Honeywell International Inc. | Flame detector using a light guide for optical sensing |
CN111141504B (en) * | 2019-12-25 | 2022-04-15 | Oppo(重庆)智能科技有限公司 | Fire-break detection method and device and computer readable storage medium |
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BE759559A (en) * | 1969-12-03 | 1971-04-30 | Cerberus Ag | DEVICE TO DETECT FIRE OR FLAMES |
DE2823410A1 (en) * | 1978-04-25 | 1979-11-08 | Cerberus Ag | FLAME DETECTOR |
US4206454A (en) * | 1978-05-08 | 1980-06-03 | Chloride Incorporated | Two channel optical flame detector |
US4709155A (en) * | 1984-11-22 | 1987-11-24 | Babcock-Hitachi Kabushiki Kaisha | Flame detector for use with a burner |
JPS61178621A (en) * | 1985-02-04 | 1986-08-11 | Hochiki Corp | Flame detector |
JPS63151827A (en) * | 1986-12-17 | 1988-06-24 | Hochiki Corp | Fire judge apparatus |
US4866420A (en) * | 1988-04-26 | 1989-09-12 | Systron Donner Corp. | Method of detecting a fire of open uncontrolled flames |
US4988884A (en) * | 1988-11-22 | 1991-01-29 | Walter Kidde Aerospace, Inc. | High temperature resistant flame detector |
EP0419668B1 (en) * | 1989-01-25 | 1996-03-20 | Nohmi Bosai Kabushiki Kaisha | Fire alarm system |
US5073769A (en) * | 1990-10-31 | 1991-12-17 | Honeywell Inc. | Flame detector using a discrete fourier transform to process amplitude samples from a flame signal |
US5434560A (en) * | 1993-05-11 | 1995-07-18 | Detector Electronics Corporation | System for detecting random events |
CH686805A5 (en) * | 1993-10-04 | 1996-06-28 | Cerberus Ag | A method for processing the signals of a passive infrared detector and infrared detector for implementing the method. |
-
1994
- 1994-12-19 EP EP94120083A patent/EP0718814B1/en not_active Expired - Lifetime
- 1994-12-19 AT AT94120083T patent/ATE203118T1/en active
- 1994-12-19 DE DE59409799T patent/DE59409799D1/en not_active Expired - Lifetime
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1995
- 1995-11-13 AU AU37810/95A patent/AU703685B2/en not_active Ceased
- 1995-12-05 CZ CZ19953218A patent/CZ289921B6/en not_active IP Right Cessation
- 1995-12-19 US US08/574,773 patent/US5594421A/en not_active Expired - Lifetime
- 1995-12-19 CN CN95120895A patent/CN1099660C/en not_active Expired - Lifetime
Cited By (1)
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CN111123423A (en) * | 2020-03-27 | 2020-05-08 | 上海翼捷工业安全设备股份有限公司 | Double-channel infrared filter combination for flame detection and preparation method and application thereof |
Also Published As
Publication number | Publication date |
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DE59409799D1 (en) | 2001-08-16 |
CZ321895A3 (en) | 1996-07-17 |
EP0718814A1 (en) | 1996-06-26 |
CN1132889A (en) | 1996-10-09 |
AU3781095A (en) | 1996-06-27 |
CN1099660C (en) | 2003-01-22 |
ATE203118T1 (en) | 2001-07-15 |
AU703685B2 (en) | 1999-04-01 |
CZ289921B6 (en) | 2002-04-17 |
US5594421A (en) | 1997-01-14 |
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