EP0094534B1 - Smoke detector according to the radiation-extinction principle - Google Patents

Smoke detector according to the radiation-extinction principle Download PDF

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Publication number
EP0094534B1
EP0094534B1 EP83104219A EP83104219A EP0094534B1 EP 0094534 B1 EP0094534 B1 EP 0094534B1 EP 83104219 A EP83104219 A EP 83104219A EP 83104219 A EP83104219 A EP 83104219A EP 0094534 B1 EP0094534 B1 EP 0094534B1
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EP
European Patent Office
Prior art keywords
radiation
smoke detector
detector according
reference voltage
pulses
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EP83104219A
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German (de)
French (fr)
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EP0094534A1 (en
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Jürg Dr. sc. nat. Muggli
Martin Dr. Sc. Nat. Labhart
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Cerberus AG
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Cerberus AG
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
    • 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
    • G08B29/02—Monitoring continuously signalling or alarm systems
    • G08B29/04—Monitoring of the detection circuits
    • G08B29/043—Monitoring of the detection circuits of fire detection circuits

Definitions

  • the invention relates to a smoke detector with a pulsed operated radiation source for emitting a bundled beam into an area freely accessible to the ambient air, a radiation receiver arranged in the beam, the downstream input amplifier of which generates receive pulses proportional to the received radiation intensity and an evaluation circuit containing an element for generating one with the received pulses comparative reference voltage, an alarm level that triggers an alarm signal for a longer period of time if the received pulses weaken below a predetermined alarm threshold, and a fault level that, if the received pulses weaken faster than the alarm signal that triggers the alarm signal, falls below an alarm threshold less than the alarm threshold triggers an interference signal, and means which change a tracking variable with a time constant greater than one minute so that the difference nz between the level of the received pulses and the reference voltage is minimized, and a first device with which the ratio of the alarm threshold to the reference voltage can be changed.
  • DE-A-28 22 547 discloses a smoke detector in which, as is customary with these so-called “line extinction detectors", the radiation source and radiation receiver are accommodated in two different housings which, depending on the place of use, are at different distances from the walls of the room to be monitored be attached.
  • a fixed alarm threshold is specified.
  • this corresponds to very different smoke densities when the distance between the radiation source and receiver is different. This disadvantage leads to false alarms.
  • slow disturbances in the response behavior of the smoke detector which are caused by aging, pollution, temperature fluctuations and moisture, are eliminated by tracking the reference voltage of the output voltage of the radiation receiver.
  • GB-A-2 059128 describes an optical smoke detector according to the preamble of claim 1, in which slow disturbances due to contamination and aging are also eliminated by adapting the amplification of the output voltage of the radiation receiver to the respective state.
  • the invention has for its object to provide a smoke detector, the sensitivity of which does not depend, or only insignificantly, on the distance between the radiation source and the receiver, changes in the operating state due to contamination, aging and temperature fluctuations are to be rendered ineffective, and the smoke detector should in particular have a reduced sensitivity to interference . In the event of a fault, a fault signal should be issued reliably.
  • FIGS 1 and 2 show circuit examples of preferred embodiments.
  • the radiation source 3 in this case a light or infrared radiation emitting diode (LED), is activated by the pulse generator 1 via a driver stage 2.
  • the current is preferably regulated with the aid of the reference radiation receiver 4 in such a way that the radiation intensity of the pulses assumes a fixed value.
  • T22, R21 and R23 switch the current through LED 3, which is supplied by the capacitor C21.
  • C21 is recharged between the pulses via R24.
  • T21 and R22 regulate the radiation intensity in connection with the reference radiation receiver 4.
  • the radiation pulses falling on the radiation receiver 5 are amplified by the input amplifier 6 and fed to three comparison circuits 7, 8, 9.
  • a two-stage transistor amplifier T61, T62 whose operating point is determined by the resistors R61, R62, and R64, is sufficient as the input amplifier.
  • the differential resistance of the diode D61 together with the feedback resistor R 63 and the resistor R62 determine the gain.
  • the quiescent current through the diode D61 and thus its differential resistance is determined by the voltage U v and the resistor R65. In this way, the gain of the input amplifier 6 can be controlled.
  • the entire amplifier is separated by coupling capacitors C61 and C63.
  • the output of the input amplifier 6 is connected to the positive input of the comparison circuit 9.
  • the voltage U s (interference threshold), which is obtained with the voltage divider R1, R2, 14 from the reference voltage Uref.
  • U s interference threshold
  • a correlation pulse appears at the output of the comparison circuit 9, which is passed on to the clock inputs C of the counters 10 and 15.
  • the capacitance C161 is also discharged with the correlation pulse in the interference circuit 16 with the aid of resistor R161 and transistor T161. If there are no correlation pulses, ie if the output pulses of the input amplifier no longer reach the interference threshold U s the capacitance C161 is charged via the resistor R162 and a fault signal 19 is emitted by the logic circuit 17.
  • the comparison circuit 7 compares the signal at the output of the input amplifier 6 (receive pulses) with the reference voltage U ret . Its output controls the counting direction U / D of the V-up / down counter 11.
  • the digital value Q o ... Q I of the counter is converted in the digital-to-analog converter 12 into an analog voltage, from which a non-linear amplifier 13 the control voltage U v for the amplification of the input amplifier 6 is generated.
  • the counter reading is increased or decreased by one in accordance with the value of the output of the comparison circuit 7.
  • the gain of the input amplifier 6 is changed such that the difference between the level of the received pulses and the reference voltage is minimized, that is to say practically zero.
  • the binary counter 10 divides the frequency of the correlation pulses by a certain factor and uses them to generate the clock pulses of the up-down counter 11.
  • the tracking becomes slow enough to not or only insignificantly compensate for changes in the reception pulses due to the increase in smoke density, but nevertheless due to changes slow dusting, aging and temperature fluctuations. If the up-down counter 11 reaches its lower or upper limit (zero or 21 + 1 -1), further tracking is no longer possible.
  • a fault signal can be derived from the negated carry-out output C out , which assumes the value zero at the counter limits. This value is processed by the logic circuit 17 and a fault signal 19 is generated.
  • Another comparison circuit 8 compares the received pulses E (output of the input amplifier) with the alarm threshold U A. The output of this comparison circuit controls the reset input of the alarm delay counter 15. If the received pulses fall below the alarm threshold U A , the alarm delay counter 15 is no longer reset and the correlation pulses increase the counter reading. After a certain number of pulses, an alarm signal 18 is emitted, however, based on the logic circuit 17, only if a fault signal 19 is not also present at the same time.
  • the level of the up-down counter 11 corresponds to a certain gain of the input amplifier 6 and thus a certain radiation intensity at the radiation receiver 5.
  • This radiation intensity is in turn a good measure of the distance between the radiation source 3 and 5, since they are inversely proportional to the square of this distance behaves.
  • the counter reading Qo ... Q i is therefore characteristic of a certain distance between the radiation source and receiver.
  • the digitally controllable resistor 14 is controlled by the meter reading and thus the ratio of the alarm threshold to the reference voltage is adapted to the different distances. The functional dependence of this ratio on the distance is now preferably chosen such that the alarm threshold always corresponds to the same smoke density. This is possible by a suitable definition of the transfer function of the non-linear amplifier 13.
  • FIG. 2 shows a further circuit of a smoke detector according to the invention.
  • the pulse generator 1 controls the radiation source 3 via the driver stage 2.
  • the transistor T22 and the resistor R21 switch the current through the radiation source 3, which is supplied by the capacitance C21, which in turn is charged between the pulses via the resistor R24.
  • the current through the radiation source is regulated to a specific value with the aid of the Zener diode D21 and the resistor R23.
  • the radiation pulses falling on the radiation receiver 5 are amplified by the input amplifier 6 and fed to the three comparison circuits 7, 8, 9.
  • This amplifier 6 consists of an operational amplifier A61 and the variable feedback resistor R63, with which the gain can be set to a suitable value when the smoke detector is started up.
  • the coupling capacitance C61 separates DC components.
  • the processing of the outputs of the comparison circuits 7, 8, 9 takes place in the same way as in FIG. 1. Reference is made to their description.
  • the output of the digital-to-analog converter 12, on the other hand, is not used to control the input amplifier, but rather directly represents the reference voltage U ret .
  • the (slow) change in the counter reading of the up-down counter 11 tracks the reference voltage U ref in such a way that that the difference between the level of the received pulses and the reference voltage is minimized, i.e. practically zero.
  • the ratio of the alarm threshold to the reference voltage can be set by the variable resistor 14.
  • a switch 141 is provided, which changes the resistance value of the resistor 14 by connecting the resistors R141 or R142 in parallel to R143.
  • a continuously variable resistor eg potentiometer
  • the smoke detectors described have a significantly improved stability even over longer periods of time. Slow changes due to dust, aging of the components and temperature fluctuations are caused by a tracking mechanism is automatically compensated, without the risk of an incorrect alarm triggering and without loss of sensitivity. They are also characterized by a better defined sensitivity in that the ratio of the alarm threshold to the reference voltage is adapted to the distance between the radiation source and receiver.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Description

Die Erfindung betrifft einen Rauchdetektor mit einer impulsweisen betriebenen Strahlungsquelle zur Aussendung eines gebündelten Strahles in ein der Umgebungsluft frei zugängliches Gebiet, einem im Strahl angeordneten Strahlungsempfänger, dessen nachgeschalteter Eingangsverstärker der empfangenen Strahlungsintensität proportionale Empfangsimpulse erzeugt und einer Auswerteschaltung enthaltend ein Element zur Erzeugung einer mit den Empfangsimpulsen vergleichenden Referenzspannung, eine Alarmstufe, die bei Abschwächung der Empfangsimpulse unter eine vorgegebene Alarmschwelle länger als eine bestimmte Zeitdauer ein Alarmsignal auslöst, und eine Störungsstufe, die bei einer gegenüber der das Alarmsignal auslösenden Abschwächung der Empfangsimpulse schnelleren Abschwächung der Empfangsimpulse unter eine Störungsschwelle kleiner als die Alarmschwelle ein Störsignal auslöst, sowie Mittel, welche eine Nachführgrösse mit einer Zeitkonstante grösser als eine Minute so verändern, dass die Differenz zwischen der Höhe der Empfangsimpulse und der Referenzspannung minimalisiert wird, und eine erste Einrichtung, mit welcher das Verhältnis von Alarmschwelle zur Referenzspannung veränderbar ist.The invention relates to a smoke detector with a pulsed operated radiation source for emitting a bundled beam into an area freely accessible to the ambient air, a radiation receiver arranged in the beam, the downstream input amplifier of which generates receive pulses proportional to the received radiation intensity and an evaluation circuit containing an element for generating one with the received pulses comparative reference voltage, an alarm level that triggers an alarm signal for a longer period of time if the received pulses weaken below a predetermined alarm threshold, and a fault level that, if the received pulses weaken faster than the alarm signal that triggers the alarm signal, falls below an alarm threshold less than the alarm threshold triggers an interference signal, and means which change a tracking variable with a time constant greater than one minute so that the difference nz between the level of the received pulses and the reference voltage is minimized, and a first device with which the ratio of the alarm threshold to the reference voltage can be changed.

Bei der DE-A-28 22 547 ist ein Rauchdetektor bekannt, bei dem -wie bei diesen sogenannten "Linienextinktionsmeldern" üblich - Strahlungsquelle und Strahlungsempfänger in zwei verschiedenen Gehäusen untergebracht sind, welche je nach Einsatzort mit verschiedenem Abstand an den Wänden des zu überwachenden Raumes befestigt werden. Es ist eine feste Alarmschwelle vorgegeben. Diese entspricht aber bei unterschiedlichem Abstand zwischen Strahlungsquelle und -empfänger ganz unterschiedlichen Rauchdichten. Dieser Nachteil führt zu Fehlalarmen. Ferner werden langsame Storungen im Ansprechverhalten des Rauchdetektors, die durch Alterung, Verschmutzung, Temperaturschwankungen und Feuchtigkeit bedingt sind, durch eine Nachführung der Referenzspannung der Ausgangsspannung des Strahlungsempfängers beseitigt.DE-A-28 22 547 discloses a smoke detector in which, as is customary with these so-called "line extinction detectors", the radiation source and radiation receiver are accommodated in two different housings which, depending on the place of use, are at different distances from the walls of the room to be monitored be attached. A fixed alarm threshold is specified. However, this corresponds to very different smoke densities when the distance between the radiation source and receiver is different. This disadvantage leads to false alarms. Furthermore, slow disturbances in the response behavior of the smoke detector, which are caused by aging, pollution, temperature fluctuations and moisture, are eliminated by tracking the reference voltage of the output voltage of the radiation receiver.

In der GB-A-2 059128 ist ein optischer Rauchmelder nach dem Oberbegriff des Anspruchs 1 beschrieben, bei dem ebenfalls langsame durch Verschmutzung und Alterung bedingte Störungen beseitigt werden, indem die Verstärkung der Ausgangsspannung des Strahlungsempfängers dem jeweiligen Zustand angepasst wird.GB-A-2 059128 describes an optical smoke detector according to the preamble of claim 1, in which slow disturbances due to contamination and aging are also eliminated by adapting the amplification of the output voltage of the radiation receiver to the respective state.

Der Erfindung liegt die Aufgabe zugrunde, einen Rauchdetektor zu schaffen, dessen Empfindlichkeit nicht oder nur unerheblich vom Abstand zwischen Strahlungsquelle und Empfänger abhängt, wobei Veränderungen des Betriebszustandes durch Verschmutzung, Alterung und Temperaturschwankungen unwirksam gemacht werden sollen und wobei der Rauchdetektor insbesondere eine verringerte Störempfindlichkeit aufweisen soll. Dabei soll im Störungsfall verlässlich ein Störungssignal abgegeben werden.The invention has for its object to provide a smoke detector, the sensitivity of which does not depend, or only insignificantly, on the distance between the radiation source and the receiver, changes in the operating state due to contamination, aging and temperature fluctuations are to be rendered ineffective, and the smoke detector should in particular have a reduced sensitivity to interference . In the event of a fault, a fault signal should be issued reliably.

Die Aufgabe wird durch die Merkmale des Patentanspruchs 1 gelöst.The object is achieved by the features of patent claim 1.

Bevorzugte Ausführungsformen und weitere Ausgestaltungen der Erfindung sind in den abhängigen Ansprüchen definiert.Preferred embodiments and further refinements of the invention are defined in the dependent claims.

Die Erfindung wird im folgenden an Hand der Zeichnungen näher erläutert.The invention is explained below with reference to the drawings.

Die Figuren 1 und 2 zeigen Schaltungsbeispiele bevorzugter Ausführungsformen.Figures 1 and 2 show circuit examples of preferred embodiments.

In Figur 1 wird die Strahlugsquelle 3, in diesem Falle eine Licht oder infrarote Strahlung emittierende Diode (LED), über eine Treiberstufe 2 vom Pulsgenerator 1 angesteurt. Vorzugsweise wird der Strom mit Hilfe des Referenzstrahlungsempfängers 4 so geregelt, dass die Strahlungsintensität der Impulse einen festen Wert annimmt. T22, R21 und R23 schalten den Strom durch die LED 3, welcher von der Kapazität C21 geliefert wird. C21 wird zwischen den Pulsen über R24 wieder aufgeladen. T21 und R22 regeln in Verbindung mit dem Referenzstrahlungsempfänger 4 die Strahlungsintensität.In FIG. 1, the radiation source 3, in this case a light or infrared radiation emitting diode (LED), is activated by the pulse generator 1 via a driver stage 2. The current is preferably regulated with the aid of the reference radiation receiver 4 in such a way that the radiation intensity of the pulses assumes a fixed value. T22, R21 and R23 switch the current through LED 3, which is supplied by the capacitor C21. C21 is recharged between the pulses via R24. T21 and R22 regulate the radiation intensity in connection with the reference radiation receiver 4.

Die auf den Strahlungsempfänger 5 fallenden Strahlungsimpulse werden vom Eingangsverstärker 6 verstärkt und drei Vergleichsschaltungen 7, 8, 9 zugeführt. Als Eingangsverstärker genügt ein zweistufiger Transistorverstärker T61, T62, dessen Arbeitspunkt durch die Widerstände R61, R62, und R64 bestimmt wird. Der differentielle Widerstand der Diode D61 zusammen mit dem Rückkopplungswiderstand R 63 und dem Widerstand R62 bestimmen die Verstärkung. Der Ruhestrom durch die Diode D61 und damit ihr differentieller Widerstand, wird durch die Spannung Uv und den Widerstand R65 bestimmt. Auf diese Art kann die Verstärkung des Eingangsverstärkers 6 gesteuert werden. Der ganze Verstärker ist durch Kopplungskapazitäten C61 und C63 abgetrennt.The radiation pulses falling on the radiation receiver 5 are amplified by the input amplifier 6 and fed to three comparison circuits 7, 8, 9. A two-stage transistor amplifier T61, T62, whose operating point is determined by the resistors R61, R62, and R64, is sufficient as the input amplifier. The differential resistance of the diode D61 together with the feedback resistor R 63 and the resistor R62 determine the gain. The quiescent current through the diode D61 and thus its differential resistance is determined by the voltage U v and the resistor R65. In this way, the gain of the input amplifier 6 can be controlled. The entire amplifier is separated by coupling capacitors C61 and C63.

Der Ausgang des Eingangsverstärkers 6 wird an den positiven Eingang der Vergleichsschaltung 9 gelegt. Am negativen Eingang liegt die Spannung Us (Störungsschwelle), weiche mit dem Spannungsteiler R1, R2, 14 aus der Referenzspannung Uref gewonnen wird. Am Ausgang der Vergleichsschaltung 9 erscheint bei Anwesenheit eines Strahlungsimpulses ein Korrelationsimpuls, welcher an die Clock-Eingänge C der Zähler 10 und 15 weitergegeben wird. Ebenfalls mit dem Korrelationsimpuls wird in der Störunqsschaltung 16 mit Hilfe von Widerstand R161 und Transistor T161 die Kapazität C161 entladen. Bei Ausbleiben von Korrelationsimpulsen, d.h. falls die Ausgangsimpulse des Eingangsverstärkers die Störungsschwelle Us nicht mehr erreichen, wird die Kapazität C161 über den Widerstand R162 aufgeladen und durch die Logikschaltung 17 ein Störungssignal 19 abgegeben.The output of the input amplifier 6 is connected to the positive input of the comparison circuit 9. At the negative input is the voltage U s (interference threshold), which is obtained with the voltage divider R1, R2, 14 from the reference voltage Uref. In the presence of a radiation pulse, a correlation pulse appears at the output of the comparison circuit 9, which is passed on to the clock inputs C of the counters 10 and 15. The capacitance C161 is also discharged with the correlation pulse in the interference circuit 16 with the aid of resistor R161 and transistor T161. If there are no correlation pulses, ie if the output pulses of the input amplifier no longer reach the interference threshold U s the capacitance C161 is charged via the resistor R162 and a fault signal 19 is emitted by the logic circuit 17.

Die Vergleichsschaltung 7 vergleicht das Signal am Ausgang des Eingangsverstärkers 6 (Empfangsimpulse) mit der Referenzspannung Uret. Ihr Ausgang steuert die Zählrichtung U/D des VVorwärts-Rückwärts-Zählers 11. Der Digitalwert Qo... QI des Zählers wird im Digital-Analog-Wandler 12 in eine analoge Spannung umgewandelt, aus welcher mit einem nicht-linearen Verstärker 13 die Steuerspannung Uv für die Verstärkung des Eingangsverstärkers 6 erzeugt wird. Bei jedem Clock-Impuls des Zählers 11 wird entsprechend dem Wert des Ausganges der Vergleichsschaltung 7 der Zählerstand um Eins erhöht oder erniedrigt. Dadurch wird die Verstärkung des Eingangsverstärkers 6 so verändert, dass die Differenz zwischen der Höhe der Empfangsimpulse und der Referenzspannung minimalisiert, also praktisch null wird. Der Binärzähler 10 dividiert die Frequenz der Korrelationsimpulse durch einen bestimmten Faktor und erzeugt daraus die Clock-Impulse des Vorwärts-Rückwärts-Zählers 11. So wird die Nachführung genügend langsam, um Aenderungen der Empfangsimpulse zufolge Rauchdichteanstiegs nicht oder nur unwesentlich auszugleichen, wohl aber Aenderungen zufolge langsamer Verstaubung, Alterung und Temperaturschwankungen. Stösst der Vorwärts-Rückwärts-Zähler 11 an seine untere oder obere Grenze (Null oder 21+1 -1) ist eine weitere Nachführung nicht mehr möglich. Ein Störungssignal kann vom negierten Carry-Out-Ausgang Cout abgeleitet werden, welcher an den Zählergrenzen den Wert Null annimmt. Durch die Logikschaltung 17 wird dieser Wert verarbeitet und ein Störungssignal 19 erzeugt.The comparison circuit 7 compares the signal at the output of the input amplifier 6 (receive pulses) with the reference voltage U ret . Its output controls the counting direction U / D of the V-up / down counter 11. The digital value Q o ... Q I of the counter is converted in the digital-to-analog converter 12 into an analog voltage, from which a non-linear amplifier 13 the control voltage U v for the amplification of the input amplifier 6 is generated. With each clock pulse of the counter 11, the counter reading is increased or decreased by one in accordance with the value of the output of the comparison circuit 7. As a result, the gain of the input amplifier 6 is changed such that the difference between the level of the received pulses and the reference voltage is minimized, that is to say practically zero. The binary counter 10 divides the frequency of the correlation pulses by a certain factor and uses them to generate the clock pulses of the up-down counter 11. The tracking becomes slow enough to not or only insignificantly compensate for changes in the reception pulses due to the increase in smoke density, but nevertheless due to changes slow dusting, aging and temperature fluctuations. If the up-down counter 11 reaches its lower or upper limit (zero or 21 + 1 -1), further tracking is no longer possible. A fault signal can be derived from the negated carry-out output C out , which assumes the value zero at the counter limits. This value is processed by the logic circuit 17 and a fault signal 19 is generated.

Eine weitere Vergleichsschaltung 8 vergleicht die Empfangsimpulse E (Ausgang des Eingangsverstärkers) mit der Alarmschwelle UA. Der Ausgang dieser Vergleichsschaltung steuert den Reset-Eingang des Alarmverzögerungszählers 15. Falls die Empfangsimpulse die Alarmschwelle UA unterschreiten, wird der Alarmverzögerungszähler 15 nicht mehr zurückgestellt und die Korrelationsimpulse erhöhen den Zählerstand. Nach einer bestimmten Anzahl Pulse wird ein Alarmsignal 18 abgegeben, aufgrund der Logikschaltung 17 hingegen, nur falls nicht gleichzeitig auch ein Störungssignal 19 vorhanden ist.Another comparison circuit 8 compares the received pulses E (output of the input amplifier) with the alarm threshold U A. The output of this comparison circuit controls the reset input of the alarm delay counter 15. If the received pulses fall below the alarm threshold U A , the alarm delay counter 15 is no longer reset and the correlation pulses increase the counter reading. After a certain number of pulses, an alarm signal 18 is emitted, however, based on the logic circuit 17, only if a fault signal 19 is not also present at the same time.

Der Stand des Vorwärts-Rückwärts-Zählers 11 entspricht einer bestimmten Verstärkung des Eingangsverstärkers 6 und damit einer bestimmten Strahlungsintensität am Strahlungsempfänger 5. Diese Strahlungsintensität ist wiederum ein gutes Mass für den Abstand zwischen Strahlungsquelle 3 und -empfänger 5, da sie sich umgekehrt proportional zum Quadrat dieses Abstandes verhält. Der Zählerstand Qo... Qi ist daher charakteristisch für eine bestimmte Distanz zwischen Strahlungsquelle und -empfänger. Der digital steuerbare Widerstand 14 wird vom Zählerstand gesteuert und somit wird das Verhältnis von Alarmschwelle zu Referenzspannung den verschiedenen Distanzen angepasst. Die funktionelle Abhängigkeit dieses Verhältnisses von der Distanz wird nun vorzugsweise so gewählt, dass die Alarmschwelle immer der gleichen Rauchdichte entspricht. Dies ist durch eine geeignete Festlegung der Uebertragungsfunktion des nicht-linearen Verstärkers 13 möglich.The level of the up-down counter 11 corresponds to a certain gain of the input amplifier 6 and thus a certain radiation intensity at the radiation receiver 5. This radiation intensity is in turn a good measure of the distance between the radiation source 3 and 5, since they are inversely proportional to the square of this distance behaves. The counter reading Qo ... Q i is therefore characteristic of a certain distance between the radiation source and receiver. The digitally controllable resistor 14 is controlled by the meter reading and thus the ratio of the alarm threshold to the reference voltage is adapted to the different distances. The functional dependence of this ratio on the distance is now preferably chosen such that the alarm threshold always corresponds to the same smoke density. This is possible by a suitable definition of the transfer function of the non-linear amplifier 13.

Figur 2 zeigt eine weitere Schaltung eines Rauchmelders gemäss der Erfindung. Der Pulsgenerator 1 steuert über die Treiberstufe 2 die Strahlungsquelle 3. Der Transistor T22 und der Widerstand R21 schalten den Strom durch die Strahlungsquelle 3, welcher von der Kapazität C21 geliefert wird, welche ihrerseits über den Widerstand R24 zwischen den Pulsen aufgeladen wird. Bei dieser Ausführungsform der Treiberstufe 2 wird, im Gegensatz zur in Figur 1 dargestellten, der Strom durch die Strahlungsquelle mit Hilfe der Zenerdiode D21 und dem Widerstand R23 auf einen bestimmten Wert geregelt.Figure 2 shows a further circuit of a smoke detector according to the invention. The pulse generator 1 controls the radiation source 3 via the driver stage 2. The transistor T22 and the resistor R21 switch the current through the radiation source 3, which is supplied by the capacitance C21, which in turn is charged between the pulses via the resistor R24. In this embodiment of the driver stage 2, in contrast to that shown in FIG. 1, the current through the radiation source is regulated to a specific value with the aid of the Zener diode D21 and the resistor R23.

Die auf den Strahlungsempfänger 5 fallenden Strahlungsimpulse werden vom Eingangsverstärker 6 verstärkt und den drei Vergleichsschaltungen 7, 8, 9 zugeführt. Dieser Verstärker 6 besteht aus einem Operationsverstärker A61 und dem veränderbaren Rückkopplungswiderstand R63, mit welchem die Verstärkung bei Inbetriebnahme des Rauchmelders auf einen geeigneten Wert eingestellt werden kann. Die Kopplungskapazität C61 trennt Gleichstromkomponenten ab.The radiation pulses falling on the radiation receiver 5 are amplified by the input amplifier 6 and fed to the three comparison circuits 7, 8, 9. This amplifier 6 consists of an operational amplifier A61 and the variable feedback resistor R63, with which the gain can be set to a suitable value when the smoke detector is started up. The coupling capacitance C61 separates DC components.

Die Verarbeitung der Ausgänge der Vergleichsschaltungen 7, 8, 9 erfolgt auf dieselbe Weise wie in Figur 1. Es sei auf ihre Beschreibung verwiesen. Der Ausgang des Digital-Analog-Wandlers 12 hingegen wird nicht zur Steuerung des Eingangsverstärkers benutzt, sondern stellt direkt die Referenzspannung Uret dar. Durch die (langsame) Veränderung des Zählerstandes des Vorwärts-Rückwärts-Zählers 11 wird die Referenzspannung Uref so nachgeführt, dass die Differenz zwischen der Höhe der Empfangsimpulse und Referenzspannung minimalisiert, also praktisch null wird. Das Verhältnis von Alarmschwelle zu Referenzspannung kann durch den veränderbaren Widerstand 14 eingestellt werden. In diesem Falle ist ein Schalter 141 vorgesehen, welcher durch Parallelschaltung der Widerstände R141 oder R142 zu R143 den Widerstandswert des Widerstandes 14 verändert. Es ist aber auch möglich, diese Einrichtung durch einen kontinuierlich veränderbaren Widerstand (z.B. Potentiometer) zu ersetzen.The processing of the outputs of the comparison circuits 7, 8, 9 takes place in the same way as in FIG. 1. Reference is made to their description. The output of the digital-to-analog converter 12, on the other hand, is not used to control the input amplifier, but rather directly represents the reference voltage U ret . The (slow) change in the counter reading of the up-down counter 11 tracks the reference voltage U ref in such a way that that the difference between the level of the received pulses and the reference voltage is minimized, i.e. practically zero. The ratio of the alarm threshold to the reference voltage can be set by the variable resistor 14. In this case, a switch 141 is provided, which changes the resistance value of the resistor 14 by connecting the resistors R141 or R142 in parallel to R143. However, it is also possible to replace this device with a continuously variable resistor (eg potentiometer).

Die beschriebenen Rauchmelder weisen eine wesentlich verbesserte Stabilität auch über längere Zeiträume auf. Langsame Aenderungen durch Verstaubung, Alterung der Komponenten und Temperaturschwankungen werden durch einen Nachführmechanismus automatisch kompensiert, ohne die Gefahr einer fehlerhaften Alarmauslösung und ohne Empfindlichkeitsverlust. Weiter zeichnen sie sich durch eine besser definierte Empfindlichkeit aus, indem das Verhältnis von Alarmschwelle zu Referenzspannung der Distanz zwischen Strahlungsquelle und -empfänger angepasst wird.The smoke detectors described have a significantly improved stability even over longer periods of time. Slow changes due to dust, aging of the components and temperature fluctuations are caused by a tracking mechanism is automatically compensated, without the risk of an incorrect alarm triggering and without loss of sensitivity. They are also characterized by a better defined sensitivity in that the ratio of the alarm threshold to the reference voltage is adapted to the distance between the radiation source and receiver.

Claims (9)

1. Smoke detector comprising a pulse-like operated radiation source (3) emitting a focussed radiation beam into a region freely accessible to environmental air, a radiation receiver (5) arranged in the path of said radiation beam, said radiation receiver (5) being serially connected to an input amplifier (6) which generates received pulses (E) proportional to the intensity of the received radiation, and an evaluation circuit comprising a reference voltage generator for generating a reference voltage (Uref) for comparison with said received pulses (E); an alarm stage for triggering an alarm signal (18) when said received pulses (E) have been attenuated below a predetermined alarm threshold value (UA) for more than a predetermined period of time; a disturbance circuit (16) for triggering a disturbance signal (19) when said received pulses (E) have been more rapidly attenuated than during triggering said alarm signal (18) below a disturbance threshold (Us) being lower than said alarm threshold (UA); as well as means (7, 10, 11, 12, 13) for changing a follow-up quantity at a time constant larger than one minute such that the difference between the amplitude of said received pulses (E) and the reference voltage (Uref) is minimized, and a first device (14) for varying the ratio of said alarm threshold (UA) to said reference value (Uref), characterized in that the received pulses (E) of the input amplifier (6) and the disturbance threshold (Us) are applied to the two inputs of a comparison circuit (9) for correlating the evaluation circuit with the radiation pulses of the radiation source (3), the output of said comparison circuit (9) supplying the correlation pulses, which control the evaluation circuit and the absence of which causes delivery of the disturbance signal (19).
2. Smoke detector according to claim 1, characterized in that a counter (11) storing the follow-up quantity is changed by at most one unit for each nth pulse (n 1 1), the direction of said change being dependent on whether said received pulse(E) is greater or smaller than said reference voltage (Uref).
3. Smoke detector according to claim 2, characterized in that the gain of the input amplifier (6) is controlled by the value stored in the counter (11).
4. Smoke detector according to claim 2, characterized in that the evaluation circuit is structured such that said reference voltage (Uref) is a function of the value stored in the counter (11).
5. Smoke detector according to any of the claims 1 through 4, characterized in that the evaluation circuit is structured such that a disturbance signal (19) is transmitted whenever said follow-up quantity exceeds an upper threshold or a lower threshold.
6. Smoke detector according to any of the claims 1 through 5, characterized in that a second device is provided, which determines the distance between the radiation source (3) and the radiation receiver (5) and which automatically adjusts the ratio of the alarm threshold (UA) and the reference voltage (Ured as a function of said determined value.
7. Smoke detector according to claim 6, characterized in that the distance between said radiation source (3) and said radiation receiver (5) is determined by the intensity of said radiation pulses.
8. Smoke detector according to any of the claims 1 through 5, characterized in that a switching element is provided for manual adjustment of the ratio of said alarm threshold to said reference voltage.
9. Smoke detector according to any of the claims 1 through 8, characterized in that a flame detector is additionally arranged in the same housing, wherein the radiation source (3) or the radiation receiver (5) is arranged.
EP83104219A 1982-05-13 1983-04-29 Smoke detector according to the radiation-extinction principle Expired EP0094534B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH2973/82 1982-05-13
CH297382 1982-05-13

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EP0094534A1 EP0094534A1 (en) 1983-11-23
EP0094534B1 true EP0094534B1 (en) 1987-01-14

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US (1) US4559453A (en)
EP (1) EP0094534B1 (en)
JP (1) JPS58214997A (en)
CA (1) CA1208335A (en)
DE (1) DE3369213D1 (en)
ES (1) ES522683A0 (en)
NO (1) NO159967C (en)
ZA (1) ZA833436B (en)

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Also Published As

Publication number Publication date
EP0094534A1 (en) 1983-11-23
JPS58214997A (en) 1983-12-14
US4559453A (en) 1985-12-17
JPH0441395B2 (en) 1992-07-08
NO159967C (en) 1989-02-22
NO831682L (en) 1983-11-14
ES8404535A1 (en) 1984-04-16
ES522683A0 (en) 1984-04-16
CA1208335A (en) 1986-07-22
NO159967B (en) 1988-11-14
ZA833436B (en) 1984-01-25
DE3369213D1 (en) 1987-02-19

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