EP0099729A1 - Suspended particle detector - Google Patents

Suspended particle detector Download PDF

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Publication number
EP0099729A1
EP0099729A1 EP83304076A EP83304076A EP0099729A1 EP 0099729 A1 EP0099729 A1 EP 0099729A1 EP 83304076 A EP83304076 A EP 83304076A EP 83304076 A EP83304076 A EP 83304076A EP 0099729 A1 EP0099729 A1 EP 0099729A1
Authority
EP
European Patent Office
Prior art keywords
radiation
detector
housing
signal
sensor
Prior art date
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.)
Withdrawn
Application number
EP83304076A
Other languages
German (de)
English (en)
French (fr)
Inventor
Christopher Davies
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.)
Chloride Group Ltd
Original Assignee
Chloride Group Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Chloride Group Ltd filed Critical Chloride Group Ltd
Publication of EP0099729A1 publication Critical patent/EP0099729A1/en
Withdrawn legal-status Critical Current

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Classifications

    • 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 present invention relates to suspended particle detectors, in particular smoke detectors, and is concerned with that type of detector including a housing, a radiation source arranged to shine a beam of radiation, typically visible light or infrared, across the housing and a sensor responsive to radiation scattered by the particles within the housing and connected to an evaluation circuit arranged to provide an alarm when the density of suspended particles reaches a predetermined value.
  • a radiation source arranged to shine a beam of radiation, typically visible light or infrared
  • a more complex detector including two sensors, one of which is responsive to particle-scattered radiation and of necessity background radiation also whilst the other is responsive only to background radiation.
  • the two sensors are coupled in opposition so that their net output is indicative of only the intensity of the particle scattered radiation and an alarm is indicated when this net output reaches a predetermined value.
  • this construction solves certain of the problems of the simpler construction it is found that in practice the output signal is not truly indicative of the intensity of the particle-scattered radiation because the two sensors are generally directed at different portions of the housing wall whose reflectivity may differ, and this difference may increase with the passage of time.
  • a suspended particle detector includes a housing containing a radiation source arranged to shine radiation across the interior of the housing, a first radiation sensor arranged to receive radiation scattered from the wall of the housing and radiation scattered from particles suspended in the housing and to produce.a first signal indicative of the total intensity of radiation incident on it and a second radiation detector arranged to produce a second signal indicative of the intensity of the radiation source, the detector also including signal combining means arranged to combine the two signals in opposition to produce a composite signal, the detector being constructed and arranged so that the composite signal has a first polarity when the density of suspended particles in the housing is less than a predetermined threshold value and the opposite polarity when the said density is greater than the threshold value and evaluation means arranged to detect when the polarity of the composite signal reverses and to produce an alarm signal.
  • the senor of the present invention operates in a very different manner to the known construction referred to above since there is no attempt to make the composite output signal independent of background radiation intensity as previously but on the other hand the threshold particle density at which an alarm is indicated is genuinely independent of the intensity of the radiation source since at this threshold density, though at no other density, the output of the two sensors is the same and thus affected equally by any change in this intensity.
  • the detector of the present invention need only detect a change in polarity of the composite signal rather than an absolute value of this signal which is inherently more simple and reliable. This latter feature means that the electrical components used in the detector can be of lower quality and thus very much cheaper than has previously been possible since variations in the characteristics of those components will cancel out at the threshold particle density.
  • the particle density at which an alarm is indicated will be dependent on the intensity of the background light. This is naturally taken account of when initially calibrating the detector but, in stark contrast to previous constructions, it is preferred that the internal surface of the wall of the housing be relatively highly reflective so that the effect of any change in reflectivity due, for instance, to dust deposits, will be proportionally reduced.
  • the second sensor may be positioned to detect the intensity of the background radiation in the manner similar to that used in the known construction since this intensity is of course proportional to that of the radiation source itself.
  • the intensity of the background radiation is relatively low and this would necessitate the use of a relatively sensitive and thus expensive sensor.
  • the second sensor is arranged to be directly subject to the radiation from the radiation source which makes possible the use of a relatively insensitive and thus cheap sensor.
  • the two sensors rely on a similar sensing principle so that any change.of sensitivity resulting from ageing ' or temperature changes will be similar for the two sensors.
  • the housing preferably includes a block of non-translucent material in which there is a first passage in which the radiation source is situated and a second passage communicating with the first passage in which the second sensor is situated. This is found to be a simple manner of ensuring that radiation from the source, e.g. visible light or infrared, impinges directly on the second sensor which is shielded from both background and particle-scattered radiation.
  • a block of non-translucent material in which there is a first passage in which the radiation source is situated and a second passage communicating with the first passage in which the second sensor is situated.
  • the detector preferably includes adjustment means arranged to vary the magnitude of the second signal at a given density of suspended particles.
  • the adjustment means may be electrical but are preferably mechanical and arranged to attenuate the radiation incident on the second sensor and in one embodiment comprises a screw arranged to obstruct a desired proportion of the area of the second passage.
  • the detector may be calibrated by introducing particles into the chamber at the desired threshold density and then adjusting the adjustment means until the composite signal at that density is zero whereas in the known constructions adjustment of the threshold density can only be effected electrically by varying the gain of the amplifier or the detection level of the comparator and there is no clear-cut relationship between the settings of these components and the threshold density of suspended particles.
  • the evaluation means includes an amplifier to the input of which the signal combining means is connected and to the output of which a logic.unit is connected, the amplifier being so arranged that if there is no input the output is of the said opposite polarity so that an alarm signal is produced.
  • the detector chamber shown in Figure 1 comprises a base 2 of non-translucent material connected to which is a cover 1 which together define a space into which no light can enter but into which air and any suspended smoke particles can enter through a tortuous passageway (not shown).
  • a pulsed radiation source 3 in this case an infrared light emitting diode, which is arranged to radiate a substantially collimated pulsed infrared beam through the passage 9 and then across the interior of the chamber.
  • a first or smoke scattered radiation sensor 5 in this case a photodiode, in front of which is an assembly 6 comprising a lens and an optical filter.
  • the sensor 5 has a field of view which extends across the interior of the chamber and intersects the path of the pulsed beam from the light-emitting diode 3 over a volume 8.
  • Communicating with the passage 9 is a further passage 10 in the base 2 within which is a second or reference sensor 4 comprising a further photodiode.
  • an adjustable radiation attenuator 7 comprising a conical tipped grubscrew received in a threaded hole in the base and accessible from the exterior of the chamber to permit a variation in the intensity of the radiation incident on the reference sensor.
  • the light emitting diode 3 is pulsed and the reference sensor 4 receives radiation whose intensity is dependent only on the position of the screw 7 and the intensity of the diode 3 and at any particular setting of the screw 7 its output signal is therefore indicative only of the intensity of the.radiation from the diode 3.
  • the sensor '5 receives two components of radiation, the first being background radiation, that is to say radiation scattered from the wall of the chamber, and the second being smoke-scattered radiation, that is to say radiation scattered by the smoke particles, if any, in the volume 8 and its output signal is thus indicative of the sum of the intensities of the background radiation and the smoke-scattered radiation.
  • the circuitry shown in Figure 2 comprises a pulse generator 21 connected to the light emitting diode 3 arranged to radiate pulses of infrared 150 microseconds in duration into the chamber.
  • the two sensors 4 and 5 are connected to a signal combining circuit 22 comprising a direct inverse parallel connection which is connected so that its output, i.e. the difference between the outputs of the sensors 4 and 5, constitutes the input of an amplifier 23.
  • the amplifier is a discrete component operational amplifier operating from a zener diode regulated 5 volt supply (not shown) and its output is connected to a logic unit 24 arranged to detect when the polarity of the output of the amplifier changes.
  • the quiescent output of the amplifier is set close to and slightly above the logic threshold of the unit 24.
  • the gain of the amplifier is such that the amplitude of the output pulses is large compared to uncertainties in the logic threshold and large compared to the difference between the quiescent output and the logic threshold and amplified signal pulse excursions are limited by the available output of the amplifier.
  • the logic unit consists of a CMOS counter which is clocked by an auxiliary output from the pulse generator 21 and connected to "reset” each time the amplifier output presents a logic “low” level during the positive transition of the clock signal and to "count” each time the amplifier presents a logic “high” level during the positive transition of the clock signal.
  • CMOS counter which is clocked by an auxiliary output from the pulse generator 21 and connected to "reset” each time the amplifier output presents a logic “low” level during the positive transition of the clock signal and to "count” each time the amplifier presents a logic “high” level during the positive transition of the clock signal.
  • the pulse generator 21 is a complementary astable oscillator operating from a current source of about 80 microamperes derived from the output terminal 26. Every 2 seconds it produces a current pulse of 1.2 amperes peak value and 150 microseconds duration into the infrared light emitting diode 3.
  • the amplifier integrates and amplifies the composite signal over the duration of the radiation pulse to produce an appropriate input for the logic unit when the positive clock transition occurs at the end of each radiation pulse.
  • the graph of Figure 3 shows the magnitude of the various signals against time, all the signals pulsing in synchronism with the radiation source with the same.duration, i.e. 150 microseconds.
  • the x axis, indicated by 30, represents the logic threshold level of the logic unit whilst the line 31 which is slightly positive with respect to it represents the amplifier output quiescent level.
  • 32 represents the output of the photodiode 4 when no smoke is present in the housing, i.e. as a result of only background radiation whilst 33 represents the output of this diode when smoke is present in the housing, i.e. as a result of both background and smoke-scattered radiation.
  • 34 represents the output of the reference sensor 5 and this is exactly the same for every pulse since the intensity of radiation does not vary.
  • 35 and 36 represent the composite signal when no smoke is present in the housing and smoke of greater than threshold density is present in the housing respectively.
  • the reference sensor 4.always produces an output represented by curve 34 at each radiation pulse whilst when no smoke is present the sensor 4 produces an output represented by curve 32 and the composite signal represented by curve 35 is negative, that is to say less than the logic threshold and no alarm is indicated.
  • the output of the sensor 4 increases to that represented by value 33 and the composite signal rises towards the curve represented by the curve 36 which is both positive and above the logic threshold.
  • the composite signal has been above the logic threshold for three pulses an alarm is indicated, though it will be appreciated that three is an arbitrary number chosen substantially to exclude the possibility of transient signals or variations in the logic threshold resulting in an alarm being incorrectly indicated.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Sampling And Sample Adjustment (AREA)
EP83304076A 1982-07-14 1983-07-13 Suspended particle detector Withdrawn EP0099729A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB08220406A GB2123548B (en) 1982-07-14 1982-07-14 Suspended particle detector
GB8220406 1982-07-14

Publications (1)

Publication Number Publication Date
EP0099729A1 true EP0099729A1 (en) 1984-02-01

Family

ID=10531663

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83304076A Withdrawn EP0099729A1 (en) 1982-07-14 1983-07-13 Suspended particle detector

Country Status (9)

Country Link
EP (1) EP0099729A1 (es)
JP (1) JPS59501283A (es)
DK (1) DK139384D0 (es)
ES (1) ES524120A0 (es)
FI (1) FI841014A0 (es)
GB (1) GB2123548B (es)
IL (1) IL69222A0 (es)
NO (1) NO840972L (es)
WO (1) WO1984000429A1 (es)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0463795A1 (en) * 1990-06-23 1992-01-02 Kidde Fire Protection Limited Smoke Particle detector
EP0547415A1 (de) * 1991-12-19 1993-06-23 Hansa Metallwerke Ag Einrichtung zur berührungslosen Steuerung einer Sanitärarmatur
EP2093733A1 (de) * 2008-02-19 2009-08-26 Siemens Aktiengesellschaft Rauchdetektion mittels zweier spektral unterschiedlicher Streulichtmessungen
WO2009103777A1 (de) * 2008-02-19 2009-08-27 Siemens Aktiengesellschaft Auswerten eines differenzsignals zwischen ausgangssignalen zweier empfangseinrichtungen in einer sensorvorrichtung

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8529585D0 (en) * 1985-11-30 1986-01-08 Casswell P H Active infra red detector
US4769504A (en) * 1987-03-04 1988-09-06 The United States Of America As Represented By The United States Department Of Energy Process for converting light alkanes to higher hydrocarbons
SE470168B (sv) * 1992-04-27 1993-11-22 Whirlpool Int Rök/ångdetektor för mikrovågsugn

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3723747A (en) * 1971-06-03 1973-03-27 Electro Signal Lab Photoelectric detector with compensating photocell
DE2856259B1 (de) * 1978-12-27 1979-12-20 Cerberus Ag Rauchdetektor
EP0015007A1 (de) * 1979-02-23 1980-09-03 Hekatron GmbH Schaltungsanordnung für einen optischen Rauchgasanzeiger

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3723747A (en) * 1971-06-03 1973-03-27 Electro Signal Lab Photoelectric detector with compensating photocell
DE2856259B1 (de) * 1978-12-27 1979-12-20 Cerberus Ag Rauchdetektor
EP0015007A1 (de) * 1979-02-23 1980-09-03 Hekatron GmbH Schaltungsanordnung für einen optischen Rauchgasanzeiger

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0463795A1 (en) * 1990-06-23 1992-01-02 Kidde Fire Protection Limited Smoke Particle detector
US5231378A (en) * 1990-06-23 1993-07-27 Kidde-Graviner Limited Particle detection which senses scattered light
EP0547415A1 (de) * 1991-12-19 1993-06-23 Hansa Metallwerke Ag Einrichtung zur berührungslosen Steuerung einer Sanitärarmatur
EP2093733A1 (de) * 2008-02-19 2009-08-26 Siemens Aktiengesellschaft Rauchdetektion mittels zweier spektral unterschiedlicher Streulichtmessungen
WO2009103777A1 (de) * 2008-02-19 2009-08-27 Siemens Aktiengesellschaft Auswerten eines differenzsignals zwischen ausgangssignalen zweier empfangseinrichtungen in einer sensorvorrichtung
WO2009103668A1 (de) * 2008-02-19 2009-08-27 Siemens Aktiengesellschaft Rauchdetektion mittels zweier spektral unterschiedlicher streulichtmessungen
US8546740B2 (en) 2008-02-19 2013-10-01 Siemens Aktiengesellschaft Evaluation of a difference signal between output signals of two receiving devices in a sensor apparatus
CN101952861B (zh) * 2008-02-19 2015-11-25 西门子瑞士有限公司 对传感器装置中的两个接收设备的输出信号之间的差信号的分析

Also Published As

Publication number Publication date
DK139384A (da) 1984-02-29
ES8405983A1 (es) 1984-06-16
WO1984000429A1 (en) 1984-02-02
ES524120A0 (es) 1984-06-16
GB2123548B (en) 1985-09-04
GB2123548A (en) 1984-02-01
FI841014A (fi) 1984-03-13
DK139384D0 (da) 1984-02-29
JPS59501283A (ja) 1984-07-19
FI841014A0 (fi) 1984-03-13
NO840972L (no) 1984-03-13
IL69222A0 (en) 1983-11-30

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Inventor name: DAVIES, CHRISTOPHER