EP0423489A1 - Arrangement pour la détection de fumée avec contrôle - Google Patents

Arrangement pour la détection de fumée avec contrôle Download PDF

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Publication number
EP0423489A1
EP0423489A1 EP90117759A EP90117759A EP0423489A1 EP 0423489 A1 EP0423489 A1 EP 0423489A1 EP 90117759 A EP90117759 A EP 90117759A EP 90117759 A EP90117759 A EP 90117759A EP 0423489 A1 EP0423489 A1 EP 0423489A1
Authority
EP
European Patent Office
Prior art keywords
ionization
measuring chamber
signal
voltage
current
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Withdrawn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
EP90117759A
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German (de)
English (en)
Inventor
Marc Thuillard
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.)
Cerberus AG
Original Assignee
Cerberus AG
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 Cerberus AG filed Critical Cerberus AG
Publication of EP0423489A1 publication Critical patent/EP0423489A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • G08B29/20—Calibration, including self-calibrating arrangements
    • G08B29/24—Self-calibration, e.g. compensating for environmental drift or ageing of components
    • 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
    • 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
    • G08B29/185—Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system
    • G08B29/188—Data fusion; cooperative systems, e.g. voting among different detectors

Definitions

  • the invention relates to a fire alarm system according to the preamble of claim 1, in which a number of detection lines lying ionization smoke detectors, which can assume different electrical states, are connected to a fire alarm control panel.
  • Fire alarm systems of this type are increasingly used to protect human lives and property; they consist of fire detectors that are installed in the objects to be protected and fire control panels that are connected to the detectors via a network. Ionization smoke detectors occupy a special position among fire detectors because they are able to detect fires at such an early stage that suitable means, in particular to protect human lives, can be used in good time. One therefore speaks of early warning systems.
  • the method of puncturing the ionization smoke detectors is based on the exploitation of the physical effect that the ion current flowing in an ionization chamber is caused by the presence of smoke, i.e. is influenced by aerosols.
  • the air is ionized in a measuring chamber to which the surrounding air has access using weak radioactive preparations, so that an ion current flows between the electrodes. If smoke, or generally speaking, a fire aerosol, penetrates into the measuring chamber, the air ions accumulate on the aerosol particles, which greatly reduces their mobility. The result is a decrease in the ion current. If the current change exceeds a certain limit value, an alarm signal is generated which is transmitted to the control center.
  • a problem with all fire alarm systems is the occurrence of false alarms.
  • a particular problem with ionization smoke detectors is that the detectors are sensitive to the occurrence of increased air velocities, to condensation or to the radioactive source being covered by dust or corrosion, since these phenomena have the same effect on the ion current as the occurrence of fire aerosols . Since such a change in the ion current causes the detectors to become more and more sensitive, the tendency towards false alarms is constantly increasing. The occurrence of false alarms is particularly annoying when automatic extinguishing systems are put into operation by an alarm message or external extinguishing forces are deployed.
  • EP-A1-0'070'449 it was proposed to evaluate the measured values after transmission to a signal center.
  • An idle value is formed from the individual measured values for each detector and stored in an idle value memory.
  • a current comparison value is formed from the respective detector measured value and a comparison value stored in a comparison memory and is written into the comparison memory. After comparison of the current comparison value with a limit value, either a display device is activated or a new rest value is formed from the current detector measured value and the stored rest value and written into the rest value memory. This makes it possible to compensate for a slow change in the detector, for example due to contamination, and to keep the detector sensitivity constant over a very long time.
  • a protective ring system serves to report an insulation resistance of the ionization measuring chamber which is reduced due to condensation or dust.
  • a change in the potential difference between the guard ring system and the connection point between the measuring and reference chamber is evaluated by the control center as a fault.
  • US-A-3,964,036 describes a fire detection system in which a measuring ionization chamber serving to detect smoke and a second ionization chamber serving as a reference chamber are connected in series between two lines which simultaneously serve to supply the detector with power.
  • An amplification element is connected to the common electrode of the measuring and reference chamber, which emits an amplified signal depending on the potential of the common electrode.
  • the course of the amplified signal from the ionization smoke detector is visualized on a display device and recorded by a writing device.
  • a false alarm is distinguished from a real alarm in that the signal curve obtained is compared with known curves obtained through contamination or condensation. This type of false alarm detection is technically and personnel-intensive.
  • None of the fire alarm systems described allows to immediately and immediately as well as automatically recognize whether a change in the ionization current in the ionization measuring chamber is a false alarm or a real alarm caused by a fire.
  • the object of the present invention is to provide a fire alarm system which avoids the disadvantages of the known fire alarm systems and which in particular makes it possible to distinguish between a real alarm caused by a fire phenomenon and a false alarm caused by a covering of the radioactive source.
  • a preferred embodiment of the fire alarm system according to the invention is that the means for changing the operating voltage of the ionization smoke detectors are arranged in the ionization smoke detectors.
  • Another preferred embodiment of the fire alarm system according to the invention is that the means for changing the operating voltage of the ionization smoke detectors are arranged centrally in the signal.
  • Another preferred embodiment of the fire alarm system according to the invention is that the control means for signal evaluation are provided in the ionization smoke detectors.
  • a particularly preferred embodiment of the fire alarm system according to the invention is that the output signal of the amplifier element of the ionization smoke detectors is transmitted to the signal center and that the means for changing the operating voltage of the ionization smoke detectors and the control means for signal evaluation are provided in the signal center.
  • the essential difference of the fire alarm system of the present invention compared to the known fire alarm systems is that it contains in the ionization smoke detectors instead of the reference chamber a linear resistor connected in series with the measuring chamber between two signal lines serving simultaneously for the power supply.
  • the resistance of a second ionization chamber serving as a reference chamber depends on a number of external circumstances, such as ambient temperature, air pressure and air humidity, which change the ion current; above all, however, it shows no linear current / voltage characteristic.
  • the fire alarm system according to the invention also has electronic switching elements in the evaluation circuit on, which make it possible to change the supply voltage of the ionization smoke detectors in such a way that the ionization smoke detectors can be operated at different operating voltages of the ionization measurement chamber.
  • the ionization measuring chamber of the fire alarm determines the operating point of the measuring chamber so that it is operated in an area of high sensitivity to smoke.
  • a signal is triggered which is not certain whether it is caused by the penetration of smoke into the measuring chamber or by other events which likewise reduce the ion current.
  • the operating voltage of the measuring chamber is increased by the switching elements described above, the voltage being increased so far that the measuring chamber is operated as far as possible in saturation. If it is now found that the saturation current is significantly reduced, the reduction in the ion current is not due to the penetration of smoke into the measuring chamber but to a disturbance, such as, for example, the contamination or thawing of the radioactive source.
  • FIG 1 shows the block diagram of a fire alarm system according to the prior art.
  • a number of ionization smoke detectors 7 are connected to a signaling center 6 via detection lines 8, 9, which also serve as the power supply.
  • a single ionization smoke detector is shown in the figure.
  • An ionization measuring chamber 1 and a second ionization chamber (reference chamber) 21 serving as load resistance are shown in FIG Row connected between the lines 8, 9 serving for the power supply. Changes in the measuring chamber voltage are measured with the aid of an amplifier element 3 and fed to the threshold value detector 4. If the output voltage of the amplifier element 3 exceeds the set threshold value Us, the bistable switch 5 switches to the alarm state, which is detected in the signal center 6.
  • FIG. 2 the current-voltage characteristic of an ionization measuring chamber of an ionization smoke detector according to FIG. 1 is shown in curve a.
  • the chamber current initially grows linearly and finally changes into the saturation current Is.
  • the saturation current Is is directly proportional to the number of ions generated and thus also proportional to the activity of the radioactive source.
  • Curve b of FIG. 2 shows the current-voltage characteristic in the event that a fire aerosol penetrates into the ionization measuring chamber 1.
  • the curve b lies below the curve a, but the comb current flows into the same saturation current Is as with an uninfluenced ionization measuring chamber at a higher chamber voltage.
  • the relative current change DI / IO is generally given as a measure of the smoke sensitivity of an ionization measuring chamber. As shown in curve b, it decreases with increasing chamber tension.
  • Curve c represents the current-voltage characteristic of an ionization chamber 1 in the event that the radioactive source 10 is covered. This case is explained in more detail below in connection with FIG. 3.
  • FIG. 7 An exemplary embodiment of an ionization smoke detector 7 according to the invention is shown schematically in FIG. The same reference numerals are used in FIG. 3 and the following figures for the same or analog components.
  • the ionization smoke detector 7 has an ionization measuring chamber 1 with smoke entry openings which allow the ambient air to enter the measuring chamber 1.
  • a radioactive source 10 for ionizing the air in the measuring chamber 1.
  • the ionization measuring chamber 1 is in series with a high-resistance resistor 2 between two detection lines 8, 9, which serve simultaneously for the voltage supply.
  • the load resistor 2 shows a linear current / voltage characteristic.
  • An amplifier element 3 is connected to the connection point between ionization measuring chamber 1 and load resistor 2.
  • the output of the amplifier element 3 is connected to an input of two comparators 15, 16.
  • the voltage Us1 which determines the alarm threshold of the ionization smoke detector 7, is present at the second input of the first comparator 15;
  • the voltage Us2, which determines the monitoring threshold for the saturation current Is, is present at the second input of the second comparator 16.
  • the output of the first comparator 15 is connected to a monoflop 5, the time constant of which is greater than the time required to monitor the saturation current; the output of the monoflop 5 is connected on the one hand to a voltage generator 11 connected to the signal line 8 which supplies the positive supply voltage + U, and on the other hand to an input of an AND gate 12.
  • the output of the second comparator 16 is connected to the other input of the AND gate 12.
  • the voltage generator 11 is used to generate two different voltages on the signaling line 8 serving for the voltage supply.
  • the output of the AND gate 12 is connected to a bistable switch 13 which is connected to the signal center 6 via a further signaling line 14.
  • the voltage generator 11 In the normal state, the voltage generator 11 generates a voltage U1 at its output, which defines the operating point of the measuring chamber 1. This value is chosen so that the measuring chamber 1 is operated in an area of high sensitivity to smoke.
  • the measuring chamber current generates a voltage drop U0 across the load resistor 2.
  • the logic voltages O are present at the inputs of the AND gate 12 and its output.
  • Curve a shows the course of the ionization current as a function of the chamber voltage without smoke and without source coverage.
  • Curve b shows the change in characteristic due to smoke without source coverage and curve c shows the change due to source coverage without smoke.
  • curves a and b have approximately the same saturation current Isa, i.e. the saturation current is almost independent of the smoke concentration. If, on the other hand, the ionization of the air in the ionization measuring chamber 1 is reduced by covering the radioactive source 10, the result is a greatly reduced saturation current Isc. In contrast, curves b and c hardly differ in the initial part of the current-voltage characteristic.
  • a distinction between a voltage reduction as a result of the penetration of smoke into the ionization measuring chamber 1 or as a result of covering the source 10 can be made according to the invention by measuring the chamber current at two different chamber voltages Uk1 and Uk2, the voltage Uk1 being the normal chamber voltage, which is the operating point the ionization measuring chamber 1 in a region of high sensitivity to smoke, and wherein the voltage Uk2 is a higher voltage than Uk1, which brings the ionization measuring chamber as far as possible into the range of the saturation current Is.
  • the saturation current Is can be inferred from the current Ia2 measured at the increased operating voltage. If a decrease in the saturation current Is is determined after the operating voltage has been increased, the current reduction determined at the lower operating voltage is not based on the penetration of smoke into the ionization measuring chamber 1 but has another cause, e.g. the coverage of the radioactive source 10 or a leakage current of the resistor 2.
  • the voltage Uk1 is applied to the ionization measuring chamber 1, and the current IO1 is determined. If the ion current in the ionization measuring chamber 1 changes, the output signal of the amplifier element 3 also changes accordingly. If the ion current drops to Ia1, a signal is triggered which is initially not certain whether it is an alarm signal. Now the operating voltage is increased by the voltage generator 11 and the current at this increased voltage is measured. If the current Ia2 is now determined, the penetration of smoke was the reason for the current reduction and the signal is interpreted as an alarm signal.
  • the saturation current must have decreased, and covering the radioactive source 10 by condensation or pollution must be regarded as the reason for the current reduction; the signal is therefore not interpreted as an alarm, but, if desired, displayed as a fault.
  • the voltage across the load resistor 2 drops. If the alarm threshold Us1 is undershot, the first comparator 15 triggers the monoflop 5 and applies the logic voltage 1 to the input of the AND gate 12. At the same time, the voltage generator 11 switches the operating voltage of the ionization smoke detector 7 to a higher value. As I said, this value is selected so that the measuring chamber is operated as saturated as possible.
  • the voltage drop across the load resistor 2 rises to a value that approximates the saturation current of the ionization measuring chamber 1 and, when the source 10 is uncovered, exceeds the monitoring value Us2.
  • the second comparator 16 then switches the logic voltage value 1 to the second input of the AND gate 12. Since the AND condition is now fulfilled, the bistable switch 13 switches to the alarm state.
  • the voltage across the load resistor 2 was not increased as a result of smoke entering but as a result of contamination or thawing of the radioactive source 10, the voltage at the output of the amplifier element 3 does not rise above the monitoring voltage Us2 after the operating voltage has been switched to the higher value.
  • the second comparator 16 does not switch the voltage at the second input of the AND gate 12 to the logic value 1, and consequently no alarm is triggered.
  • the monoflop 5 switches the voltage generator 11 back to the normal operating voltage, and the measuring chamber 1 operates again in the area of high sensitivity to smoke. A new measuring or monitoring cycle begins. The process described above must be repeated if the condensation or contamination of the radioactive source 10 continues.
  • a second AND gate 17 can be connected in parallel to the AND gate 12 with negation of the second input (which is connected to the second comparator 16), the output of which is connected to a fault transmission circuit 18 is connected, is switched.
  • the AND gate 17 sends a signal to the fault transmission circuit 18, which is transmitted via the detection line 14 forwards a fault signal different from the alarm signal to the signal center 6.
  • the fault transmission circuit 18 has a delay element which is dimensioned in such a way that it is ensured that the measuring or monitoring cycle has expired at least once.
  • the means for checking the signals can also be accommodated in the signal center 6.
  • the ionization smoke detector 7 contains suitable transmission electronics which transmit the voltage across the load resistor 2 digitally or analogously to the signal center 6. The switching of the chamber voltage can either take place from the signal center 6 or be triggered by a signal from the signal center 6 in the ionization smoke detector 7.
  • FIG. 4 A fire alarm system is described in FIG. 4, in which the ionization smoke detector 7 (as in the embodiment according to FIG. 3) has an ionization measurement chamber 1 with smoke inlet openings which allow the ambient air to enter the measurement chamber 1.
  • a radioactive source 10 for ionizing the air in the measuring chamber 1.
  • the ionization measuring chamber 1 is in series with a high-resistance resistor 2 between two detection lines 8, 9, which are used simultaneously for the voltage supply.
  • An amplifier element 3 is connected to the connection point between ionization measuring chamber 1 and load resistor 2. In this case, however, the output of the amplifier element 3 is connected to an analog-digital converter 19, which is connected via the detection line 14 forwards an analog signal present at the output of the amplifier element 3 in digital form to the signal center 6.
  • the digital signal is converted back into an analog signal in a digital-analog converter 20 and (as in the embodiment according to FIG. 3) fed to two comparators 15, 16.
  • the further signal processing now corresponds approximately to that of FIG. 3, the voltage generator 11 being located in the signal center 6.
  • FIG. 5 shows a further embodiment of a fire alarm system according to the invention, which essentially corresponds to the embodiment according to FIG. 4. It differs from this only in that the voltage generator 11 is not located in the signal center 6, but is respectively arranged in the fire detectors 7.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Fire-Detection Mechanisms (AREA)
EP90117759A 1989-09-15 1990-09-14 Arrangement pour la détection de fumée avec contrôle Withdrawn EP0423489A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH337289 1989-09-15
CH3372/89 1990-08-13

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EP0423489A1 true EP0423489A1 (fr) 1991-04-24

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015004458A1 (de) 2014-06-26 2015-12-31 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren für einen klassifizierenden, rauchkammerlosen Luftzustandssensor
DE102014019172A1 (de) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mit einem kompensierenden optischen Messsystem
DE102014019773A1 (de) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mittels des Displays eines Mobiltelefons

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5473314A (en) * 1992-07-20 1995-12-05 Nohmi Bosai, Ltd. High sensitivity smoke detecting apparatus using a plurality of sample gases for calibration
US5543777A (en) * 1993-07-12 1996-08-06 Detection Systems, Inc. Smoke detector with individual sensitivity calibration and monitoring
ATE362156T1 (de) * 2002-06-05 2007-06-15 Cooper Lighting And Security L Brandmelder
US7134909B2 (en) * 2004-07-28 2006-11-14 Fujitsu Limited Connector circuit board
EP2757355A4 (fr) * 2011-09-15 2015-07-29 Nec Corp Dispositif à semi-conducteur et dispositif de capture d'image infrarouge l'utilisant
CN103680043A (zh) * 2013-11-30 2014-03-26 成都国科海博信息技术股份有限公司 烟雾预警器
WO2018011232A1 (fr) 2016-07-11 2018-01-18 Autronica Fire & Security As Système et procédé de réglage de la portée dynamique d'un détecteur de fumée

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2274982A1 (fr) * 1974-06-14 1976-01-09 Cerberus Ag Installation d'avertissement d'incendie
US3964036A (en) * 1972-11-15 1976-06-15 Hochiki Corporation Ionization smoke detector co-used to issue fire alarm and detect ambient atmosphere
GB2013383A (en) * 1978-01-26 1979-08-08 Pittway Corp Warning devices
EP0248298A1 (fr) * 1986-06-03 1987-12-09 Cerberus Ag Dispositif détecteur de danger

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS529998B1 (fr) * 1969-04-25 1977-03-19
DE2454196C3 (de) * 1974-06-14 1985-02-07 Cerberus AG, Männedorf, Zürich Brandmeldeanlage
CH572644A5 (en) * 1974-06-24 1976-02-13 Cerberus Ag Ionisation chamber fire detector - with threshold cct. monitoring ionisation current connected to switch cct. for further chamber
DE2636778C3 (de) * 1976-08-16 1979-04-12 Hartwig Ing.(Grad.) 2409 Scharbeutz Beyersdorf Ionisations-Brandmelder
CH617280A5 (en) * 1976-08-16 1980-05-14 Hartwig Beyersdorf Ionisation fire detector
DE3904979A1 (de) * 1989-02-18 1990-08-23 Beyersdorf Hartwig Verfahren zum betrieb eines ionisationsrauchmelders und ionisationsrauchmelder

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3964036A (en) * 1972-11-15 1976-06-15 Hochiki Corporation Ionization smoke detector co-used to issue fire alarm and detect ambient atmosphere
FR2274982A1 (fr) * 1974-06-14 1976-01-09 Cerberus Ag Installation d'avertissement d'incendie
GB2013383A (en) * 1978-01-26 1979-08-08 Pittway Corp Warning devices
EP0248298A1 (fr) * 1986-06-03 1987-12-09 Cerberus Ag Dispositif détecteur de danger

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015004458A1 (de) 2014-06-26 2015-12-31 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren für einen klassifizierenden, rauchkammerlosen Luftzustandssensor
DE102014019172A1 (de) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mit einem kompensierenden optischen Messsystem
DE102014019773A1 (de) 2014-12-17 2016-06-23 Elmos Semiconductor Aktiengesellschaft Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mittels des Displays eines Mobiltelefons

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