EP0715744B1 - Method and apparatus for preventing false responses in optical detection devices - Google Patents

Method and apparatus for preventing false responses in optical detection devices Download PDF

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Publication number
EP0715744B1
EP0715744B1 EP94925486A EP94925486A EP0715744B1 EP 0715744 B1 EP0715744 B1 EP 0715744B1 EP 94925486 A EP94925486 A EP 94925486A EP 94925486 A EP94925486 A EP 94925486A EP 0715744 B1 EP0715744 B1 EP 0715744B1
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EP
European Patent Office
Prior art keywords
signal
source
optical radiation
optical
chaotic
Prior art date
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Expired - Lifetime
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EP94925486A
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German (de)
English (en)
French (fr)
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EP0715744A1 (en
Inventor
William Joseph Senior Hirst
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Shell Internationale Research Maatschappij BV
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Shell Internationale Research Maatschappij BV
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Priority to EP94925486A priority Critical patent/EP0715744B1/en
Publication of EP0715744A1 publication Critical patent/EP0715744A1/en
Application granted granted Critical
Publication of EP0715744B1 publication Critical patent/EP0715744B1/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
    • G08B17/12—Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions

Definitions

  • the present invention relates to a method and apparatus for preventing the occurrence of false responses in optical detection devices, which are sensitive to changes or fluctuations in optical radiation emitted from a source.
  • optical detection devices examples include flame-detectors, smoke detectors and the like.
  • the response signal of such optical detection devices can be applied to provide a fire alarm signal or, for example, to supervise operation of burners, furnaces and the like.
  • Flame detectors in which radiation from the flames is sensed have been proposed, utilizing radiation derived from the flames in the visible light range, infra-red (I.R.) range, or ultraviolet (UV) range.
  • I.R. infra-red
  • UV ultraviolet
  • Known flame detectors to provide outputs representative of presence of a flame, and operating purely within the above referred to light ranges, frequently are not reliable, since signals are derived not only from radiation due to flames, but also caused by extraneous radiation, such as daylight, artificial light sources, radiant heaters providing I.R. radiation, and the like, or interruption of such extraneous radiations although no real flame - to be sensed - is present. It is therefore necessary to provide characteristic differences which distinguish flame radiation from extraneous disturbance radiation when evaluating the signals in order to prevent erroneous signals and malfunction.
  • the different spectral composition of radiation from flames is used in order to distinguish between radiation from flames and disturbing or interfering radiation.
  • Two photoelectric sensors with different spectral sensitivity are exposed to radiation from the flame; for example, one photoelectric sensor is sensitive to blue light, and one is sensitive to red light.
  • the photo cells may be serially connected. At the junction point between the two photo cells, a d-c signal will occur which depends on the spectral composition or the colour of the light radiation to which the sensors are exposed.
  • Such a flame detector while functioning properly under most conditions may, however, react to interfering radiation which by chance has the same, or similar spectral composition as radiation from a flame.
  • the invention therefore provides a method for preventing the occurrence of false responses in optical detection devices, which are sensitive to changes or fluctuations in optical radiation emitted from a source comprising the steps of:
  • the invention further provides an apparatus for preventing the occurrence of false responses in optical detection devices, which are sensitive to changes or fluctuations in optical radiation emitted from a source comprising means for receiving optical radiation emitted by a source; means for selecting a predetermined range of wavelengths; means for detecting changes in the received optical flux and deriving therefrom a signal having time series data (signal traces) at the detector output; characterized by means for analyzing the detected signal for its chaotic (i.e.
  • aperiodic behaviour by establishing the associated fractal dimension of the signal and using the existence of this fractal property of the said time series data of the optical radiation emitted by the said source to discriminate against those sources of fluctuating optical radiation which are periodic or intermittent; and means for only providing a response at the output of the optical detection device in case of chaotic behaviour of the source.
  • the emitted and received optical radiation is in the infra-red (I.R.) range.
  • the invention is based upon the following steps:
  • the invention is further based upon the fact that certain optical radiation e.g. flame flicker is chaotic, i.e aperiodic.
  • the chaotic behaviour of the flame can be objectively quantified by applying the concept of fractal dimension to the time series data from the detector output. Rotating or vibrating sources will be periodic, i.e. non-chaotic and will not have a fractal dimension, neither will beam interrupts.
  • the roughened perimeter could be enscribed by a polygon of N sides of equal length ⁇ .
  • the key property of the detected signal is chaotic behaviour.
  • the invention is based upon the idea of using the fractal property of the time series data of the optical radiation e.g. the I.R. emitted by a flame to discriminate against those sources of fluctuating I.R. which though not flame generated, do satisfy the frequency test of existing flame detectors.
  • US-A-4,866,420 discloses a method for preventing the occurrence of false responses in the detection of fires by comparing the flicker frequency spectrum of a real fire with a theoretical fire spectrum which comparison allows a discrimination against false fire signal if a predetermined deviation is reached.
  • EP-A-525592 discloses information processing systems using fractal dimension.
  • a narrowband optical bandpass filter 1 restricts the I.R. radiation from a source entering the detection device to a narrow range of wavelengths around 4.4 microns. These wavelengths are e.g. emitted by flames 3 or hot surfaces but are sufficiently strongly absorbed by the atmosphere for no contribution to be left in sunlight at the Earth's surface. Consequently, any such wavelengths entering the detector will have been produced locally - either in a flame or from a hot surface. The detector is effectively "solar blind".
  • the transmitted I.R. radiation is then detected by an I.R. detector 2.
  • This is very sensitive and inherently suited to detecting changes in I.R. flux.
  • the detector output is passed through an electrical bandpass filter 4 that restricts the transmitted signal to components in the range of 0.5 to 15 Hz. These frequencies are characteristic of flickering flames.
  • the resulting signal trace is markedly different from that generated by a flickering flame.
  • the chaotic behaviour of the flame can be quantified by applying the concept of fractal dimension to the time series data from the detector output.
  • the vertical axes represent relative intensity, whereas the horizontal axes represent time in seconds.
  • the trace length of a signal can be measured with progressively smaller step lengths (finer discrimination) by any means suitable for the purpose for recognizing chaotic behaviour and determining fractal dimension.
  • Fig. 2 An instructive way to consider the operation is shown in Fig. 2.
  • stepping along the trace using means for measuring the trace length of a signal with progressively finer discrimination, e.g. a pair of suitable frequency dividers set to a particular step length.
  • the measured length of the trace is the number of steps times the step length; obviously for large step lengths much detailed structure is missed out.
  • progressively smaller step lengths ever smaller features of the trace can be followed and the total length measured increases.
  • a plot of log (total measured length) against log(step length) will yield a straight line graph whose slope gives the fractal dimension.
  • Fig. 3 shows such a result for a flickering flame.
  • the horizontal axis represents Log 10 (step length) whereas the vertical axis represents Log 10 (total measured length).
  • fractal dimensions of time series data are established and determined by suitable algorithms.
  • a microprocessor in the detector head efficient algorithms can be implemented.
  • a plug-in replacement head could be applied for simple retrofitting to existing systems.
  • a control card could be used to handle the processing for several detector heads, interfacing them to the existing fire-detection system.
  • the present invention is not restricted to flame detection or hot surface changes detection, but the fractal test algorithm of the invention could also be applied to detect phenomena such as smoke (where the signal fluctuations due to real smoke, are chaotic, whereas those from obscuration of the beam or beam interrupts, are not), gas or other dispersing constituents of a mixture for which the signals representing fluctuations in concentration need to be distinguished from more periodic or intermittent confusing signals.

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  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
EP94925486A 1993-08-31 1994-08-30 Method and apparatus for preventing false responses in optical detection devices Expired - Lifetime EP0715744B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP94925486A EP0715744B1 (en) 1993-08-31 1994-08-30 Method and apparatus for preventing false responses in optical detection devices

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP93306865 1993-08-31
EP93306865 1993-08-31
EP94925486A EP0715744B1 (en) 1993-08-31 1994-08-30 Method and apparatus for preventing false responses in optical detection devices
PCT/EP1994/002888 WO1995006927A1 (en) 1993-08-31 1994-08-30 Method and apparatus for preventing false responses in optical detection devices

Publications (2)

Publication Number Publication Date
EP0715744A1 EP0715744A1 (en) 1996-06-12
EP0715744B1 true EP0715744B1 (en) 1997-12-03

Family

ID=8214523

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94925486A Expired - Lifetime EP0715744B1 (en) 1993-08-31 1994-08-30 Method and apparatus for preventing false responses in optical detection devices

Country Status (8)

Country Link
EP (1) EP0715744B1 (no)
AU (1) AU7537594A (no)
CA (1) CA2170519A1 (no)
DE (1) DE69407190T2 (no)
DK (1) DK0715744T3 (no)
NO (1) NO960783L (no)
SG (1) SG97742A1 (no)
WO (1) WO1995006927A1 (no)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1236183A2 (en) * 1999-12-10 2002-09-04 Durand Technology Limited Improvements in or relating to applications of fractal and/or chaotic techniques
DE102009048739B3 (de) * 2009-07-14 2012-03-29 Deutsches Zentrum für Luft- und Raumfahrt e.V. Verfahren und Vorrichtung zur automatischen Waldbranderkennung

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4665390A (en) * 1985-08-22 1987-05-12 Hughes Aircraft Company Fire sensor statistical discriminator
US4866420A (en) * 1988-04-26 1989-09-12 Systron Donner Corp. Method of detecting a fire of open uncontrolled flames
US5051590A (en) * 1989-12-06 1991-09-24 Santa Barbara Research Center Fiber optic flame detection and temperature measurement system having one or more in-line temperature dependent optical filters
US5201321A (en) * 1991-02-11 1993-04-13 Fulton Keith W Method and apparatus for diagnosing vulnerability to lethal cardiac arrhythmias
US5185687A (en) * 1991-03-28 1993-02-09 Eaton Corporation Chaos sensing arc detection
JPH0535768A (ja) * 1991-07-26 1993-02-12 Hitachi Ltd フラクタル次元を応用した情報処理装置

Also Published As

Publication number Publication date
CA2170519A1 (en) 1995-03-09
NO960783L (no) 1996-03-12
DK0715744T3 (da) 1998-08-10
DE69407190D1 (de) 1998-01-15
EP0715744A1 (en) 1996-06-12
AU7537594A (en) 1995-03-22
WO1995006927A1 (en) 1995-03-09
SG97742A1 (en) 2003-08-20
NO960783D0 (no) 1996-02-27
DE69407190T2 (de) 1998-05-20

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