EP0030621B1 - Ionisation smoke signaller with particular operational reliability - Google Patents

Ionisation smoke signaller with particular operational reliability Download PDF

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Publication number
EP0030621B1
EP0030621B1 EP80106923A EP80106923A EP0030621B1 EP 0030621 B1 EP0030621 B1 EP 0030621B1 EP 80106923 A EP80106923 A EP 80106923A EP 80106923 A EP80106923 A EP 80106923A EP 0030621 B1 EP0030621 B1 EP 0030621B1
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voltage
transistor
operating voltage
resistor
circuit element
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German (de)
French (fr)
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EP0030621A1 (en
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Andreas Scheidweiler
Peter Müller
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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
    • G08B17/11—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

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  • the present invention relates to an ionization smoke detector with at least one low-voltage ionization chamber with a measuring and counterelectrode sensor, to which chamber the surrounding air has practically free access and which has at least one radioactive source for generating ions, and an electrical circuit for Alarm triggering, which has a first switching element controlled by the voltage drop across the ionization chamber, which becomes conductive when a certain smoke density is exceeded, and a second switching element, which becomes conductive when the first switching element becomes conductive and triggers an alarm signal, soft detectors via lines to a detector operating voltage to the Lines emitting signal center is connected.
  • ionization smoke detectors are the most widespread early warning detectors.
  • the main advantages of this type of detector include its universal applicability and its simple and robust mechanical construction. Since the detectors must respond quickly and safely in the event of a fire, but on the other hand they must not trigger false alarms, high demands are placed on their reliability.
  • Fig. 1 shows the circuit of a typical low-voltage smoke detector, in which the mession chamber is operated in series with a load resistor, preferably a saturated reference chamber. The connection point of the two chambers is connected to the control electrode of a cold cathode tube. The voltage drop across the measuring chamber is approx. 80 V in the idle state. If smoke enters the measuring chamber, this voltage increases by approx. 50 V and thus reaches the ignition voltage of the cold cathode tube. This leads to the triggering of a current flow between the anode and cathode, which can be evaluated via a relay for triggering the alarm.
  • the chamber voltage of approx. 100 V required to operate the low-voltage ionization smoke detectors means that high electrical field strengths of a few 100 V / cm occur at the measuring electrode.
  • the dust particles that are always present in the air are therefore deposited electrostatically on the electrodes, which means that the electrodes are covered with a gradually thicker layer of dust. If these dusts are electrically non-conductive material, which is often the case especially in the dry winter periods, the ion current in the measuring chamber is blocked and a false alarm can be triggered. This means that the detectors have to be cleaned frequently, which is very expensive.
  • ionization smoke detectors that are operated with an operating voltage of ⁇ 50 V.
  • a low voltage type ionization fire detector is described, for example, in US Pat. No. 3,521,263.
  • Fig. Shows the circuit of a typical low-voltage ionization smoke detector.
  • the voltage across the measuring chamber is also the gate voltage for a field effect transistor. It is selected so that the transistor is de-energized in the idle state.
  • the controlled rectifier (SCR) is thus also blocked and the relay is not energized. If flue gases enter the measuring chamber, the chamber voltage increases and, if a certain threshold value is exceeded, the SCR is ignited, which triggers the relay alarm.
  • the object of the present invention is to remedy the above-mentioned disadvantages of the known ionization smoke detectors and, in particular, to create an ionization smoke detector with increased operational reliability, which reduces the tendency to contamination and thus the susceptibility to faults of the detectors due to a low field strength in the ionization chamber, so that the service intervals are long can be selected that requires a smaller amount of radioactive material compared to the high-voltage detectors and that is insensitive to electromagnetic interference.
  • the converter is designed such that the sensor operating voltage is at least ten times lower than the detector operating voltage.
  • the first switching element has a field effect transistor blocked in the idle state, the gate electrode of which is connected to the measuring electrode of the ionization chamber, so that the field effect transistor becomes conductive when a certain smoke density is exceeded;
  • the second switching element has a cold cathode tube as a bistable switching element, the control voltage of which is kept below the ignition voltage of the control electrode of the cold cathode tube by a switch in the idle state;
  • the ionization smoke detector has means which actuate the switch when the field effect transistor is opened such that the control voltage of the cold cathode tube slowly increases until the ignition voltage is reached and the cold cathode tube ignites.
  • the switch consists of a transistor which conducts and is saturated in the idle state, a capacitor being connected between the collector and emitter of the transistor and a resistor being connected between the collector of the transistor and the anode of the cold cathode tube , wherein the time constant R x C> 2 s, preferably> 5 s and in particular> 10 s.
  • the converter consists of a resistor, a zener diode and the base-emitter path of the transistor.
  • FIG. 3 shows an example of an ionization smoke detector according to the invention.
  • a mession chamber MK accessible to the outside atmosphere is in series with a load resistance R 6 .
  • the connection point between the mession chamber MK and load resistor R 6 is connected to the gate electrode G of a field effect transistor T 1 , the drain-source path of the FET T is connected in parallel with the Z-diode ZD 1 to the measurement chamber load resistance path.
  • the low voltage output of the converter T is connected both to one electrode of the measuring chamber MK and to a discriminator D, which is used to control a switch S which is connected to the control electrode St of the cold cathode tube KR, which is connected between the lines L, and L z , acts.
  • the control electrode St of the cold cathode tube KR is connected to the output L of the switch S via the resistor R 2 to the line L 1 and via the capacitor C to the line L z .
  • the discriminator D is designed in such a way that, when the sensor operating voltage U 2 falls below a certain threshold value, it actuates the switch S, the output of which, in the idle state, holds the control electrode voltage U St of the cold cathode tube KR below the ignition voltage (preferably more than 50 V below) in such a way that the capacitor C can charge via the resistor R 2 until the ignition voltage is reached and the cold cathode tube KR is ignited.
  • the current rise that occurs in lines L 1 and L 2 can be evaluated in the signaling center as an alarm signal.
  • FIG. 1 A preferred embodiment of a circuit of an ionization smoke detector according to the invention is explained in more detail in FIG.
  • the working resistance R a lying in series with the measuring chamber MK is designed as a reference ionization chamber RK that is difficult to access from the outside atmosphere and operates in the saturation region.
  • the detector operating voltage U 1 is supplied to a voltage stabilizer circuit consisting of a resistor R 1, a Zener diode ZD 2 and the base-emitter path of a transistor T 2 .
  • This voltage stabilizer circuit provides the for the operation of the low voltage necessary sensor operating voltage U 2 .
  • the FET T switches through and an additional current flows through the resistor R,.
  • the sensor operating voltage U 2 is reduced to such an extent that the Zener voltage of the Zener diode ZD 2 is undershot, as a result of which the base current of the transistor T 2 is interrupted so that it blocks.
  • the capacitor C is charged via the resistor R 2 . If the voltage U St across the capacitor C reaches the ignition voltage of the cold cathode tube KR, it ignites and a strong current flows through the lines L ,, L 2 ; this current flow can be evaluated in alarm center Z.
  • the time constant of the element R z , C is selected such that after the transistor T 2 is blocked, the ignition voltage of the control electrode St is only reached after approximately 2 seconds. Short-term electrical disturbances, which lead to the opening of the field effect transistor T, do not trigger an alarm since the ignition voltage of the cold cathode tube KR is not reached. While the charging of the capacitor C takes place slowly via the resistor R 2 , an immediate discharge of the capacitor C is carried out when the field effect transistor T is closed, since this is short-circuited via the transistor T 2 .
  • the time constant can be adjusted by changing the R 2 and / or C operating conditions of the smoke detector, for example, several seconds or set to about ten seconds. Repeated short bursts of smoke, such as those caused by heavy tobacco smoke, cannot lead to a false alarm, since the charges C cannot accumulate due to the immediate discharge of the charges.
  • Zener diode ZD 2 is placed between the emitter of the transistor T 2 and the line L 2 and the base of the transistor T 2 is connected directly to the point A.
  • the resistor R 5 can thus be omitted.
  • the open circuit voltage at the control electrode St of the cold cathode tube KR corresponds approximately to the Zener voltage, and a lower collector-emitter voltage at the transistor T 2 is required for the ignition of the cold cathode tube.

Abstract

An ionization smoke detector containing at least one ionization chamber operated at an extra low voltage or potential. The ionization chamber contains a sensor employing a measuring electrode and a counter electrode. Ambient air has practically free access to the ionization chamber and there are provided one or more radioactive sources for generating ions, a supply voltage source and an electrical circuit for triggering an alarm. The smoke detector possesses increased operational reliability since circuit elements are provided which enable signal reporting to a central station by means of a low-voltage of about 200 volts, however the sensor is operated at an extra low voltage.

Description

Die vorliegende Erfindung betrifft einen lonisationsrauchmelder mit einem mindestens eine mit Kleinspannung betriebene lonisationskammer mit einer Mess- und Gegenelektrode aufweisenden Sensor, zu welcher Kammer die umgebende Luft praktisch freien Zutritt hat und die wenigstens eine radioaktive Quelle zur Erzeugung von Ionen aufweist, und einer elektrischen Schaltung zur Alarmauslösung, die ein vom Spannungsabfall über der lonisationskammer gesteuertes erstes Schaltelement, welches bei Überschreiten einer bestimmten Rauchdichte leitend wird, und ein zweites Schaltelement aufweist, das beim Leitendwerden des ersten Schaltelementes leitend wird und ein Alarmsignal auslöst, weicher Melder über Leitungen an eine Melderbetriebsspannung an die Leitungen abgebende Signalzentrale angeschlossen ist.The present invention relates to an ionization smoke detector with at least one low-voltage ionization chamber with a measuring and counterelectrode sensor, to which chamber the surrounding air has practically free access and which has at least one radioactive source for generating ions, and an electrical circuit for Alarm triggering, which has a first switching element controlled by the voltage drop across the ionization chamber, which becomes conductive when a certain smoke density is exceeded, and a second switching element, which becomes conductive when the first switching element becomes conductive and triggers an alarm signal, soft detectors via lines to a detector operating voltage to the Lines emitting signal center is connected.

Unter den heute verwendeten Brandmeldern sind die lonisationsrauchmelder die am weitestverbreiteten Frühwarndetektoren. Zu den Hauptvorzügen dieses Detektortyps gehören die universelle Verwendbarkeit und die einfache und robuste mechanische Konstruktion. Da die Melder im Brandfall schnell und sicher ansprechen müssen, sie aber andererseits keine Fehlalarme auslösen dürfen, werden an ihre Zuverlässigkeit hohe Anforderungen gestellt.Among the fire detectors used today, ionization smoke detectors are the most widespread early warning detectors. The main advantages of this type of detector include its universal applicability and its simple and robust mechanical construction. Since the detectors must respond quickly and safely in the event of a fire, but on the other hand they must not trigger false alarms, high demands are placed on their reliability.

Die Wirkungsweise der bekannten lonisationsrauchmelder beruht darauf, dass sich der lonenstrom zwischen den beiden Elektroden der Messkammer stark verringert, wenn Rauch in die Messkammer eindringt. Es kommen heute hauptsächlich zwei Typen von lonisationsrauchmeldern zur Anwendung, nämlich:

  • 1. Niederspannungsrauchmelder, die mit einer Betriebsspannung von ca. 220 V arbeiten, beispielsweise die in der CH-PS Nr. 391 331 oder US-PS Nr. 3 295 121 beschriebene Vorrichtung zur Feststellung von Aerosolen in Gasen und
  • 2. Kleinspannungsrauchmelder, die mit einer Betriebsspannung von weniger als 50 V arbeiten, beispielsweise die in der-US-PS Nr. 3 521 263 beschriebene lonisationsfeuermeldeanlage.
The mode of operation of the known ionization smoke detectors is based on the fact that the ion current between the two electrodes of the measuring chamber is greatly reduced when smoke penetrates the measuring chamber. Two types of ionization smoke detectors are mainly used today, namely:
  • 1. Low-voltage smoke detectors that work with an operating voltage of approximately 220 V, for example the device described in CH-PS No. 391 331 or US-PS No. 3 295 121 for the detection of aerosols in gases and
  • 2. Low voltage smoke alarms that operate with an operating voltage of less than 50 V, for example the ionization fire alarm system described in US Pat. No. 3,521,263.

Die Niederspannungsrauchmelder verwenden als elektrisches Verstärkerelement eine Kaltkathodenröhre; sie weisen gegenüber den Kleinspannungsrauchmeldern ein wesentlich höheres Signal-zu-Rausch-Verhältnis auf. Fig. 1 zeigt die Schaltung eines typischen Niederspannungsrauchmelders, bei dem die Messionisationskammer in Serie mit einem Arbeitswiderstand, vorzugsweise einer gesättigten Referenzkammer, betrieben wird. Der Verbindungspunkt der beiden Kammern ist mit der Steuerelektrode einer Kaltkathodenröhre verbunden. Der Spannungsabfall über der Messkammer beträgt im Ruhezustand ca. 80 V. Bei Eindringen von Rauch in die Messkammer erhöht sich diese Spannung um ca. 50 V und erreicht damit die Zündspannung der Kaltkathodenröhre. Dies führt zur Auslösung eines Stromflusses zwischen Anode und Kathode, was über ein Relais zur Alarmauslösung ausgewertet werden kann.The low-voltage smoke detectors use a cold cathode tube as an electrical amplifier element; they have a significantly higher signal-to-noise ratio than low-voltage smoke detectors. Fig. 1 shows the circuit of a typical low-voltage smoke detector, in which the mession chamber is operated in series with a load resistor, preferably a saturated reference chamber. The connection point of the two chambers is connected to the control electrode of a cold cathode tube. The voltage drop across the measuring chamber is approx. 80 V in the idle state. If smoke enters the measuring chamber, this voltage increases by approx. 50 V and thus reaches the ignition voltage of the cold cathode tube. This leads to the triggering of a current flow between the anode and cathode, which can be evaluated via a relay for triggering the alarm.

Betriebsstörungen bei lonisationsrauchmeldern treten einerseits dadurch auf, dass die Detektoren Fehlalarme auslösen oder dass andererseits die Empfindlichkeit der Detektoren während des Betriebes nachlässt, was bis zum völligen Ausfall des Melders führen kann. Die Niederspannungsmelder des vorbeschriebenen Typs sind relativ unempfindlich gegenüber elektrischen Störungen, die durch das als Antenne wirkende Leitungsnetz aufgefangen werden, da diese Störungen eine beträchtliche Grösse besitzen müssen, d.h. mindestens 50 V betragen müssen, um die Kaltkathodenröhre zur Zündung zu bringen. Bei diesem Detektortyp sind daher Fehlalarme durch elektromagnetische Störungen verhältnismässig selten.Malfunctions in ionization smoke detectors occur on the one hand because the detectors trigger false alarms or on the other hand the sensitivity of the detectors decreases during operation, which can lead to the complete failure of the detector. The low voltage detectors of the type described above are relatively insensitive to electrical disturbances which are absorbed by the line network acting as an antenna, since these disturbances must be of a considerable size, i.e. must be at least 50 V to ignite the cold cathode tube. False alarms due to electromagnetic interference are therefore relatively rare with this type of detector.

Die für den Betrieb der Niederspannungs-Ionisationsrauchmelder erforderliche Kammerspannung von ca. 100 V bewirkt jedoch, dass an der Messelektrode hohe elektrische Feldstärken von einigen 100 V/cm auftreten. Die stets in der Luft vorhandenen Staubpartikeln scheiden sich daher elektrostatisch an den Elektroden ab, was dazu führt, dass die Elektroden mit einer allmählich dicker werdenden Staubschicht überzogen werden. Wenn es sich bei diesen Stäuben um elektrisch nicht leitendes Material handelt, was vor allem in den trockenen Winterperioden häufig der Fall ist, so wird der Ionenstrom in der Messkammer blockiert, und es kann zur Auslösung eines Fehlalarms kommen. Dies macht es erforderlich, dass die Melder häufig gereinigt werden, was sehr kostenintensiv ist.However, the chamber voltage of approx. 100 V required to operate the low-voltage ionization smoke detectors means that high electrical field strengths of a few 100 V / cm occur at the measuring electrode. The dust particles that are always present in the air are therefore deposited electrostatically on the electrodes, which means that the electrodes are covered with a gradually thicker layer of dust. If these dusts are electrically non-conductive material, which is often the case especially in the dry winter periods, the ion current in the measuring chamber is blocked and a false alarm can be triggered. This means that the detectors have to be cleaned frequently, which is very expensive.

Mit der Verfügbarkeit der Feldeffekttransistoren war es möglich, lonisationsrauchmelder zu entwickeln, die mit einer Betriebsspannung von < 50 V betrieben werden. Ein solcher lonisationsbrandmelder vom Kleinspannungstyp ist beispielsweise in der US-PS Nr. 3 521 263 beschrieben. Fig. zeigt die Schaltung eines typischen Kleinspannungs-lonisationsrauchmelders. Die über der Messkammer liegende Spannung ist gleichzeitig die Gatespannung für einen Feldeffekttransistor. Sie ist so gewählt, dass der Transistor im Ruhezustand stromlos ist. Der gesteuerte Gleichrichter (SCR) ist somit ebenfalls gesperrt und das Relais nicht erregt. Dringen Rauchgase in die Messkammer ein, so steigt die Kammerspannung und bewirkt beim Überschreiten eines bestimmten Schwellenwertes das Zünden des SCR, wodurch das Relais Alarm auslöst.With the availability of the field effect transistors, it was possible to develop ionization smoke detectors that are operated with an operating voltage of <50 V. Such a low voltage type ionization fire detector is described, for example, in US Pat. No. 3,521,263. Fig. Shows the circuit of a typical low-voltage ionization smoke detector. The voltage across the measuring chamber is also the gate voltage for a field effect transistor. It is selected so that the transistor is de-energized in the idle state. The controlled rectifier (SCR) is thus also blocked and the relay is not energized. If flue gases enter the measuring chamber, the chamber voltage increases and, if a certain threshold value is exceeded, the SCR is ignited, which triggers the relay alarm.

Bei diesen Kleinspannungs-lonisationsrauchmeldern beträgt der für eine Alarmauslösung erforderliche Hub der Spannung an der Messionisationskammer nur einige Volt. Da im Leitungsnetz Störimpulse dieser Grössenordnung auftreten können, besteht bei diesem Meldertyp immer die Gefahr von Fehlalarmen. Zur Kompensation dieses Nachteils ist ein erheblicher elektronischer Schaltungsaufwand erforderlich. Auf der anderen Seite wirkt sich die Tatsache äusserst positiv aus, dass infolge der wesentlich geringeren Feldstärke die Verschmutzungsgefahr erheblich kleiner ist.With these low-voltage ionization smoke detectors, the voltage swing at the mession chamber required to trigger an alarm is only a few volts. Since interference of this magnitude can occur in the line network, there is always a risk of false alarms with this type of detector. To compensate for this disadvantage, a considerable amount of electronic circuitry is required. On the other hand, the fact that the risk of contamination is significantly lower due to the much lower field strength has an extremely positive effect.

An Brandmeldeanlagen sind sehr hohe Sicherheitsanforderungen zu stellen. Es war bisher nicht gelungen, bei den lonisationsrauchmeldern vom Niederspannungstyp die Verstaubungsgefahr zu beheben oder bei den Kleinspannungsmeldern mit einfachen Mitteln die Anfälligkeit gegen elektrische Störungen zu beseitigen. Die Aufgabe der vorliegenden Erfindung besteht darin, die oben genannten Nachteile der bekannten lonisationsrauchmelder zu beheben und insbesondere einen lonisationsrauchmelder mit erhöhter Betriebssicherheit zu schaffen, der durch eine geringe Feldstärke in der Ionisationskammer die Verschmutzungstendenz und somit die Störanfälligkeit der Melder verringert, so dass die Serviceintervalle lang gewählt werden können, der gegenüber den Hochspannungsmeldern eine geringere Menge an radioaktivem Material benötigt und der gegenüber elektromagnetischen Störungen unempfindlich ist.Very high security requirements must be placed on fire alarm systems. So far it has not been possible to eliminate the risk of dust accumulation in the low-voltage type ionization smoke detectors or to remove the susceptibility to electrical interference with the low-voltage detectors using simple means. The object of the present invention is to remedy the above-mentioned disadvantages of the known ionization smoke detectors and, in particular, to create an ionization smoke detector with increased operational reliability, which reduces the tendency to contamination and thus the susceptibility to faults of the detectors due to a low field strength in the ionization chamber, so that the service intervals are long can be selected that requires a smaller amount of radioactive material compared to the high-voltage detectors and that is insensitive to electromagnetic interference.

Diese Aufgabe wird erfindungsgemäss durch die Merkmale des kennzeichnenden Teils des Patentanspruchs 1 gelöst.This object is achieved according to the invention by the features of the characterizing part of patent claim 1.

Gemäss einer bevorzugten Ausführungsform des erfindungsgemässen lonisationsrauchmelders ist der Wandler so ausgelegt, dass die Sensorbetriebsspannung mindestens zehnmal kleiner ist als die Melderbetriebsspannung. Dabei weist das erste Schaltelement einen im Ruhezustand gesperrten Feldeffekttransistor auf, dessen Gate-Elektrode mit der Messelektrode der lonisationskammer verbunden ist, so, dass bei Überschreiten einer bestimmten Rauchdichte der Feldeffekttransistor leitend wird; ferner weist das zweite Schaltelement eine Kaltkathodenröhre als bistabiles Schaltelement auf, deren Steuerspannung durch einen Schalter im Ruhezustand unterhalb der Zündspannung der Steuerelektrode der Kaltkathodenröhre gehalten wird; schliesslich weist der lonisationsrauchmelder gemäss bevorzugter Ausführungsform Mittel auf, die den Schalter beim Öffnen des Feldeffekttransistors derart betätigen, dass die Steuerspannung der Kaltkathodenröhre langsam ansteigt, bis die Zündspannung erreicht ist und die Kaltkathodenröhre zündet.According to a preferred embodiment of the ionization smoke detector according to the invention, the converter is designed such that the sensor operating voltage is at least ten times lower than the detector operating voltage. In this case, the first switching element has a field effect transistor blocked in the idle state, the gate electrode of which is connected to the measuring electrode of the ionization chamber, so that the field effect transistor becomes conductive when a certain smoke density is exceeded; Furthermore, the second switching element has a cold cathode tube as a bistable switching element, the control voltage of which is kept below the ignition voltage of the control electrode of the cold cathode tube by a switch in the idle state; finally, according to a preferred embodiment, the ionization smoke detector has means which actuate the switch when the field effect transistor is opened such that the control voltage of the cold cathode tube slowly increases until the ignition voltage is reached and the cold cathode tube ignites.

Gemäss einer weiteren bevorzugten Ausführungsform des erfindungsgemässen lonisationsrauchmelders besteht der Schalter aus einem Transistor, der im Ruhezustand leitet und gesättigt ist, wobei zwischen Kollektor und Emitter des Transistors ein Kondensator geschaltet ist und wobei zwischen den Kollektor des Transistors und die Anode der Kaltkathodenröhre ein Widerstand geschaltet ist, wobei die Zeitkonstante R x C > 2 s, vorzugsweise > 5 s und insbesondere > 10 s, ist.According to a further preferred embodiment of the ionization smoke detector according to the invention, the switch consists of a transistor which conducts and is saturated in the idle state, a capacitor being connected between the collector and emitter of the transistor and a resistor being connected between the collector of the transistor and the anode of the cold cathode tube , wherein the time constant R x C> 2 s, preferably> 5 s and in particular> 10 s.

Gemäss einer weiteren bevorzugten Ausführungsform besteht der Wandler aus einem Widerstand, einer Zener-Diode und der Basis-Emitter-Strecke des Transistors.According to a further preferred embodiment, the converter consists of a resistor, a zener diode and the base-emitter path of the transistor.

Im folgenden werden anhand von Schaltungsbeispielen bevorzugte Ausführungsformen der Erfindung näher erläutert. Es stellen dar:

  • Figur 1, die Schaltung eines bekannten Niederspannungs-lonisationsrauchmelders.
  • Figur 2, die Schaltung eines bekannten Kleinspannungs-lonisationsrauchmelders.
  • Figur 3, die Schaltung eines erfindungsgemässen lonisationsrauchmelders mit erhöhter Betriebssicherheit.
  • Figur 4, die Schaltung einer bevorzugten Ausführungsform eines erfindungsgemässen lonisationsrauchmelders.
Preferred embodiments of the invention are explained in more detail below with the aid of circuit examples. They represent:
  • Figure 1, the circuit of a known low-voltage ionization smoke detector.
  • Figure 2, the circuit of a known low-voltage ionization smoke detector.
  • Figure 3, the circuit of an ionization smoke detector according to the invention with increased operational reliability.
  • Figure 4, the circuit of a preferred embodiment of an ionization smoke detector according to the invention.

Figur 3 zeigt ein Beispiel eines erfindungsgemässen lonisationsrauchmelders. Eine der Aussenatmosphäre zugängliche Messionisationskammer MK liegt in Reihe mit einem Arbeitswiderstand R6. Der Verbindungspunkt von Messionisationskammer MK und Arbeitswiderstand R6 ist mit der Gateelektrode G eines Feldeffekttransistors T1 verbunden, die Drain-Source-Strecke des FET T, ist mit einer Z-Diode ZD1 parallel zur Messkammer-Arbeitswiderstand-Strecke geschaltet.FIG. 3 shows an example of an ionization smoke detector according to the invention. A mession chamber MK accessible to the outside atmosphere is in series with a load resistance R 6 . The connection point between the mession chamber MK and load resistor R 6 is connected to the gate electrode G of a field effect transistor T 1 , the drain-source path of the FET T is connected in parallel with the Z-diode ZD 1 to the measurement chamber load resistance path.

Die von der Zentrale her über die Leitungen L1 und Lz an den Melder angelegte Melderbetriebsspannung U1 von beispielsweise ca. 200 V wird einem Wandler T zugeführt, der die Melderbetriebsspannung U1 auf die Sensorbetriebsspannung U2 herabsetzt. Der Kleinspannungsausgang des Wandlers T ist sowohl mit der einen Elektrode der Messkammer MK als auch mit einem Diskriminator D verbunden, der zur Steuerung eines Schalters S dient, der auf die Steuerelektrode St der Kaltkathodenröhre KR, die zwischen die Leitungen L, und Lz geschaltet ist, einwirkt. Die Steuerelektrode St der Kaltkathodenröhre KR ist ausser mit dem Ausgang des Schalters S über den Widerstand R2 mit der Leitung L1 und über den Kondensator C mit der Leitung Lz verbunden.The detector operating voltage U 1, for example of approximately 200 V, applied to the detector from the control center via lines L 1 and L z is fed to a converter T, which reduces the detector operating voltage U 1 to the sensor operating voltage U 2 . The low voltage output of the converter T is connected both to one electrode of the measuring chamber MK and to a discriminator D, which is used to control a switch S which is connected to the control electrode St of the cold cathode tube KR, which is connected between the lines L, and L z , acts. The control electrode St of the cold cathode tube KR is connected to the output L of the switch S via the resistor R 2 to the line L 1 and via the capacitor C to the line L z .

Beim Eindringen von Rauch in die Messkammer MK wird deren Leitfähigkeit reduziert, die Spannung UK über der Messkammer steigt an und der Transistor T, wird leitend, wodurch die Sensorbetriebsspannung U2 verringert wird. Der Diskriminator D ist so ausgelegt, dass er bei Unterschreiten eines bestimmten Schwellwertes der Sensorbetriebsspannung U2 den Schalter S, dessen Ausgang im Ruhezustand die Steuerelektrodenspannung USt der Kaltkathodenröhre KR unterhalb der Zündspannung (vorzugsweise mehr als 50 V darunter) hält, so betätigt, dass sich der Kondensator C über den Widerstand R2 aufladen kann, bis die Zündspannung erreicht ist und die Kaltkathodenröhre KR gezündet wird. Der dadurch in den Leitungen L1 und L2 auftretende Stromanstieg kann in der Signalzentrale als Alarmsignal ausgewertet werden.When smoke enters the measuring chamber MK, its conductivity is reduced, the voltage U K across the measuring chamber rises and the transistor T becomes conductive, as a result of which the sensor operating voltage U 2 is reduced. The discriminator D is designed in such a way that, when the sensor operating voltage U 2 falls below a certain threshold value, it actuates the switch S, the output of which, in the idle state, holds the control electrode voltage U St of the cold cathode tube KR below the ignition voltage (preferably more than 50 V below) in such a way that the capacitor C can charge via the resistor R 2 until the ignition voltage is reached and the cold cathode tube KR is ignited. The current rise that occurs in lines L 1 and L 2 can be evaluated in the signaling center as an alarm signal.

In Figur 4 wird eine bevorzugte Ausführungsform einer Schaltung eines erfindungsgemässen lonisationsrauchmelders näher erläutert. Hierbei ist der in Reihe mit der Messkammer MK liegende Arbeitswiderstand Ra als eine der Aussenatmosphäre schwer zugängliche, im Sättigungsbereich arbeitende Referenzionisationskammer RK ausgebildet. Die Melderbetriebsspannung U1 wird einer Spannungsstabilisatorschaltung, bestehend aus einem Widerstand R1 einer Z-Diode ZD2 und der Basis-Emitter-Strecke eines Transistors T2, zugeführt. Diese Spannungsstabilisatorschaltung liefert die für den Betrieb des Kleinspannungsensors notwendige Sensorbetriebsspannung U2. Im Normalfall, d.h. wenn kein Rauch in die Messkammer MK eingedrungen ist, fliesst der die Z-Diode ZD2 durchfliessende Strom gleichzeitig durch die Basis-Emitter-Strecke des Transistors T2, so dass dieser leitend ist, und den Kondensator C kurzschliesst. Die Steuerspannung USt die an der Steuerelektrode St der Kaltkathodenröhre KR liegt, ist praktisch gleich 0. Parallel zu den Punkten A und B liegt ein Spannungsteiler R3, R4, der eine derartige Vorspannung U3 erzeugt, dass der Feldeffekttransistor T1 im Ruhezustand gesperrt ist.A preferred embodiment of a circuit of an ionization smoke detector according to the invention is explained in more detail in FIG. Here, the working resistance R a lying in series with the measuring chamber MK is designed as a reference ionization chamber RK that is difficult to access from the outside atmosphere and operates in the saturation region. The detector operating voltage U 1 is supplied to a voltage stabilizer circuit consisting of a resistor R 1, a Zener diode ZD 2 and the base-emitter path of a transistor T 2 . This voltage stabilizer circuit provides the for the operation of the low voltage necessary sensor operating voltage U 2 . In the normal case, ie when no smoke has entered the measuring chamber MK, the current flowing through the Zener diode ZD 2 simultaneously flows through the base-emitter path of the transistor T 2 , so that it is conductive, and short-circuits the capacitor C. The control voltage U St which is at the control electrode St of the cold cathode tube KR is practically equal to 0. In parallel with the points A and B there is a voltage divider R 3 , R 4 which generates a bias voltage U 3 such that the field effect transistor T 1 is in the idle state Is blocked.

Überschreitet die Spannung UK, die über der Messkammer MK abfällt, einen durch R3, R4 bestimmten Schwellenwert, so schaltet der FET T, durch, und es fliesst ein zusätzlicher Strom durch den Widerstand R,. Hierdurch wird die Sensorbetriebsspannung U2 so weit herabgesetzt, dass die Zenerspannung der Z-Diode ZD2 unterschritten wird, wodurch der Basisstrom des Transistors T2 unterbrochen wird, so dass dieser sperrt. Jetzt wird der Kondensator C über den Widerstand R2 aufgeladen. Erreicht die Spannung USt über dem Kondensator C die Zündspannung der Kaltkathodenröhre KR, so zündet diese und es fliesst ein kräftiger Strom über die Leitungen L,, L2; dieser Stromfluss kann in der Zentrale Z zur Alarmgebung ausgewertet werden.If the voltage U K , which drops across the measuring chamber MK, exceeds a threshold value determined by R 3 , R 4 , the FET T, switches through and an additional current flows through the resistor R,. As a result, the sensor operating voltage U 2 is reduced to such an extent that the Zener voltage of the Zener diode ZD 2 is undershot, as a result of which the base current of the transistor T 2 is interrupted so that it blocks. Now the capacitor C is charged via the resistor R 2 . If the voltage U St across the capacitor C reaches the ignition voltage of the cold cathode tube KR, it ignites and a strong current flows through the lines L ,, L 2 ; this current flow can be evaluated in alarm center Z.

Die Zeitkonstante des Gliedes Rz, C ist so gewählt, dass nach Sperren des Transistors T2 die Zündspannung der Steuerelektrode St erst nach ca. 2 Sekunden erreicht wird. Kurzzeitige elektrische Störungen, die zur Öffnung des Feldeffekttransistors T, führen, bewirken keine Alarmauslösung, da die Zündspannung der Kaltkathodenröhre KR nicht erreicht wird. Während die Aufladung des Kondensators C über den Widerstand R2 langsam erfolgt, wird beim Schliessen des Feldeffekttransistors T, eine sofortige Entladung des Kondensators C vorgenommen, da dieser über den Transistor T2 kurzgeschlossen wird. Die Zeitkonstante kann durch Veränderung von R2 und/oder C veränderten Einsatzbedingungen des Rauchmelders angepasst werden, z.B. mehrere Sekunden betragen oder auf ca. zehn Sekunden eingestellt werden. Wiederholte kurze Rauchstösse wie sie beispielsweise bei starkem Tabakrauchen entstehen, können so nicht zu einem Fehlalarm führen, da wegen der sofortigen Entladung des Kondensators C keine Kumulation der Ladungen erfolgen kann.The time constant of the element R z , C is selected such that after the transistor T 2 is blocked, the ignition voltage of the control electrode St is only reached after approximately 2 seconds. Short-term electrical disturbances, which lead to the opening of the field effect transistor T, do not trigger an alarm since the ignition voltage of the cold cathode tube KR is not reached. While the charging of the capacitor C takes place slowly via the resistor R 2 , an immediate discharge of the capacitor C is carried out when the field effect transistor T is closed, since this is short-circuited via the transistor T 2 . The time constant can be adjusted by changing the R 2 and / or C operating conditions of the smoke detector, for example, several seconds or set to about ten seconds. Repeated short bursts of smoke, such as those caused by heavy tobacco smoke, cannot lead to a false alarm, since the charges C cannot accumulate due to the immediate discharge of the charges.

Eine weitere bevorzugte Ausführungsform ergibt sich bei Vertauschung der Elemente der Spannungsstabilisatorschaltung, indem die Z-Diode ZD2 zwischen den Emitter des Transistors T2 und die Leitung L2 gelegt wird und die Basis des Transistors T2 direkt mit dem Punkt A verbunden wird. Der Widerstand R5 kann dadurch entfallen. Die Ruhespannung an der Steuerelektrode St der Kaltkathodenröhre KR entspricht ungefähr der Zenerspannung, und für die Zündung der Kaltkathodenröhre ist eine um den gleichen Betrag niedrigere Kollektor-Emitter-Spannung am Transistor T2 nötig.Another preferred embodiment results when the elements of the voltage stabilizer circuit are interchanged, in that the Zener diode ZD 2 is placed between the emitter of the transistor T 2 and the line L 2 and the base of the transistor T 2 is connected directly to the point A. The resistor R 5 can thus be omitted. The open circuit voltage at the control electrode St of the cold cathode tube KR corresponds approximately to the Zener voltage, and a lower collector-emitter voltage at the transistor T 2 is required for the ignition of the cold cathode tube.

Claims (5)

1. Ionization smoke detector containing at least one ionization chamber (MK) operated at an extra low voltage, said ionization chamber having a sensor composed of a measuring electrode and a counter electrode, the ambient air being accessible to the ionization chamber, said ionization chamber containing at least one radioactive source for generating ions and an electrical circuit for tiggering an alarm, which circuit comprises a first circuit element (ZD,, T1) controlled by a voltage drop (UK) appearing across the ionization chamber, said first circuit upon exceeding a predeterminated smoke density becoming conductive and a second circuit element (KR), which second element upon becoming conductive of the first circuit element becomes conductive and triggers an alarm signal, said smoke detector being connected by means of lines (L1, L2) with a central signal station (Z) which delivers to the lines a detector operating voltage (U1) characterized by the following features for reducing the subscep- tibility to failure of the detector in alarm conditions:
- a converter (T) is connected in series to the sensor in order to reduce the detector operating voltage (U1) being in the low voltage range to a sensor operating voltage (U2) being at least five times smaller than the detector operating voltage;
- the first circuit element (ZD,, T1) is at the sensor operating voltage (U2) and upon becoming conductive reducing the sensor operating voltage (U2) for the preparation of tiggering an alarm;
- the second circuit element (KR) is at the detector operating voltage (U1) and controlled by the sensor operating voltage (U2) in such manner that the second circuit element when the sensor operating voltage falls below a predetermined value becomes conductive.
2. lonization smoke detector according to claim 1, characterized in that to the control electrode of the second circuit element (KR) is connected a switch means (S) comprising a transistor (T2) which is conductive in its rest state and is saturated; a capacitor (C) is connected between the collector and emitter of the said transistor (T2) and a resistor (R2) is connected between the collector of the transistor (T2) and the anode of the second circuit element having a time-constant R2 × C > 2 s, preferably > 5 s.
3. lonization smoke detector according to claim 2, characterized in that the converter (T) consists of a resistor (R), a Zener diode and the base-emitter path of the transistor (T2).
4. lonization smoke detector according to claim 3, characterized in that the resistor (R) is connected at one terminal thereof directly with the line (L,) carrying a positive potential, that the Zener diode (ZD2) is connected to the other terminal of the resistor (R,) and by means of the base-emitter path of the transistor (T2) with the line (L2) carrying a negative potential; and that a further resistor (Rs) is arranged parallel to the base-emitter path of the transistor (T2).
5. Ionization smoke detector according to claim 3, characterized in that the resistor (R1) is directly connected at one terminal thereof with the line (L1) carrying a positive potential, that the base of the transistor (T2) is connected to the other terminal of the resistor (R1) and that the Zener diode (ZD2) is arranged between the emitter of said transistor and the line (L2) which carries the negative potential.
EP80106923A 1979-12-14 1980-11-10 Ionisation smoke signaller with particular operational reliability Expired EP0030621B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT80106923T ATE11345T1 (en) 1979-12-14 1980-11-10 IONIZATION SMOKE DETECTOR WITH INCREASED OPERATIONAL RELIABILITY.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH1107779 1979-12-14
CH11077/79 1979-12-14

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EP0030621A1 EP0030621A1 (en) 1981-06-24
EP0030621B1 true EP0030621B1 (en) 1985-01-16

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US (1) US4364031A (en)
EP (1) EP0030621B1 (en)
JP (1) JPS5694497A (en)
AT (1) ATE11345T1 (en)
CA (1) CA1148279A (en)
DE (1) DE3069987D1 (en)
YU (1) YU314380A (en)

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CH681932A5 (en) * 1990-12-04 1993-06-15 Cerberus Ag
JP3128633B2 (en) * 1992-05-25 2001-01-29 能美防災株式会社 Ionized smoke detector
FR2872914B1 (en) * 2004-07-07 2006-10-13 Univ Rennes I Etablissement Pu SENSOR FOR DETECTING AND / OR MEASURING A CONCENTRATION OF ELECTRICAL CHARGES CONTAINED IN AN ATMOSPHERE, USES AND METHOD FOR MANUFACTURING SAME
WO2008034080A2 (en) * 2006-09-15 2008-03-20 Nano-Proprietary, Inc. Smoke detector
DE102014019773B4 (en) 2014-12-17 2023-12-07 Elmos Semiconductor Se Device and method for distinguishing between solid objects, cooking fumes and smoke using the display of a mobile telephone
DE102014019172B4 (en) 2014-12-17 2023-12-07 Elmos Semiconductor Se Device and method for distinguishing between solid objects, cooking fumes and smoke using a compensating optical measuring system

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US3872449A (en) * 1973-03-30 1975-03-18 Cerberus Ag Fire detector and method employing assymetrical integrator
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CH489070A (en) * 1969-03-27 1970-04-15 Cerberus Ag Werk Fuer Elektron Ionization fire alarms
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US3295121A (en) * 1961-12-30 1966-12-27 Danske Securitas As Electric alarm system, preferably for fire alarms
US3872449A (en) * 1973-03-30 1975-03-18 Cerberus Ag Fire detector and method employing assymetrical integrator
FR2299879A1 (en) * 1975-02-10 1976-09-03 Hochiki Co OUTLET CIRCUIT OF AN IONIZED SMOKE DETECTOR

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DE3069987D1 (en) 1985-02-28
ATE11345T1 (en) 1985-02-15
YU314380A (en) 1983-10-31
CA1148279A (en) 1983-06-14
US4364031A (en) 1982-12-14
EP0030621A1 (en) 1981-06-24
JPS5694497A (en) 1981-07-30
JPS6242320B2 (en) 1987-09-08

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