EP0033888B2 - Ionisation fire alarm device with malfunction signalization - Google Patents

Ionisation fire alarm device with malfunction signalization Download PDF

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Publication number
EP0033888B2
EP0033888B2 EP81100552A EP81100552A EP0033888B2 EP 0033888 B2 EP0033888 B2 EP 0033888B2 EP 81100552 A EP81100552 A EP 81100552A EP 81100552 A EP81100552 A EP 81100552A EP 0033888 B2 EP0033888 B2 EP 0033888B2
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Prior art keywords
voltage
supply voltage
direct current
effect transistor
current supply
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German (de)
French (fr)
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EP0033888B1 (en
EP0033888A3 (en
EP0033888A2 (en
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Hartwig Beyersdorf
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    • 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
    • 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

Definitions

  • the invention relates to a fire alarm device according to the preamble of claim 1.
  • Such a fire alarm device is known (DE-OS 2 029 794).
  • the fault alarm circuit and the smoke alarm circuit each have a field effect transistor connected to its control electrode at the connection point of the chambers on the input side, and the source electrodes of these field effect transistors are connected to a voltage divider common to them or to a voltage divider or in such a way that the potential of this source electrode is in the undisturbed idle state approximates the potential of the connection point of the chambers.
  • the field effect transistors are of the self-conducting type, so that both are non-conductive in the undisturbed idle state.
  • the field effect transistors are of the opposite conductivity type, so that when the voltage across the measuring chamber increases as a result of smoke entering the field effect transistor of the smoke alarm circuit and when the voltage across the measuring chamber decreases as a result of lack of insulation, the field effect transistor of the fault alarm circuit becomes conductive when the control voltage, namely the Potential difference between the connection point of the chambers and the respective tap of the voltage divider exceeds the threshold voltage (pinchoff voltage) of the respective field effect transistor.
  • the potential at the connection point of the chambers on the one hand and the potential at the tap of the respective voltage divider and thus the potential of the source electrodes of the field effect transistors on the other hand change in at least approximately the same way, so that voltage changes up to the order of magnitude of 25% of the nominal value of the supply voltage do not lead to an alarm signal.
  • Contamination of the radioactive radiation source leads to an increase in the internal resistance of the measuring chamber and to a corresponding shift in the potential of the connection point between the measuring and reference chamber. Above a certain degree of contamination, this has the same effect as the entry of smoke into the measuring chamber, so that a corresponding alarm signal is generated. With the known fire detectors, it is not possible to determine the contamination even before an alarm signal is generated or to distinguish between contamination and the occurrence of smoke in the measuring chamber when an alarm signal is generated.
  • An ionization fire detector has also become known from PL-B-62 618, in which a single MOS field-effect transistor with its control electrode lies at the connection point between the measuring and reference chamber, while the drain electrode via resistors with a detector connection and the source electrode via a zener diode is connected to the other detector connection.
  • the field effect transistor therefore forms a threshold value switch, the input threshold voltage of which is largely independent of the DC supply voltage.
  • the invention is based, to monitor the functionality of the ionization fire detectors even more extensively in a fire detection device of the type mentioned.
  • a fire alarm device of the type mentioned at the outset is designed in accordance with the characterizing features of claim 1.
  • the fault alarm circuit and / or the smoke alarm circuit respond not only to a deterioration in the insulation of the measuring chamber or the smoke entering the measuring chamber, but also to such potential changes in the connection point of the chambers that result from other causes of the fault, for example to an impermissible reduction in the DC supply voltage or to one Increase in the internal resistance of the measuring chamber, which is due to contamination of the radioactive emitter that ionizes the chamber.
  • This enables an even more extensive monitoring of the parameters influencing the functional safety of the ionization fire detectors.
  • a drop in the DC supply voltage feeding the ionization fire detector can be due, for example, to the fact that the detector is arranged relatively far from a control center supplying the line with constant line voltage and that the line voltage drops along the line to the fire detector concerned, or to the fact that the battery supply is being supplied by means of a battery provided as a DC voltage source or by means of a buffer battery which is effective in the event of a power failure, the battery voltage drops as a result of exhaustion, or also that a controller provided to keep the DC supply voltage constant fails.
  • Contamination of the radioactive radiation source can be determined in that the voltage source supplying the DC supply voltage is designed to be switchable to a DC voltage that is higher than the nominal value of the DC supply voltage.
  • the thresholds The voltage of the field effect transistor of the smoke alarm circuit is selected so that the voltage occurring due to the switchover to the higher DC voltage of a control path of the field effect transistor only exceeds the threshold voltage if the measuring chamber has an increased internal resistance compared to the undisturbed idle state due to the contamination of the ionizing radiation source. In other words, an increase in the potential at the connection point between the measuring and reference chamber does not lead to the threshold circuit responding if there is no appreciable contamination of the radioactive radiation source.
  • the threshold circuit signal generated in this way is not used to generate a smoke alarm signal. It is important for the control center to know whether the signal generated can be attributed to smoke development or contamination of the measuring chamber. The smoke alarm signal generated by the pollution is therefore suppressed. Instead, a malfunction alarm signal is generated and transmitted to the evaluation circuit.
  • the fire alarm device shown in FIG. 1 comprises a control center Z and a line L connected to it with line conductors 10, 12.
  • line L is fed with a line voltage from a mains-fed, possibly battery-buffered DC voltage source 14, the nominal value of which in the exemplary embodiment Is 20 V.
  • a controller 16 is provided with it, which, depending on a setpoint / actual value comparison, effects a gate control of the thyristors provided in the DC voltage source 14.
  • the nominal value corresponding to the nominal value of the line voltage can be set on a potentiometer 18 and is fed to the controller 16 via a test switch 20.
  • the controller 16 can be given a further setpoint which can be set on a potentiometer 22 instead of the specified setpoint and which corresponds to a higher DC voltage of 24 V in the exemplary embodiment than the nominal value of the line voltage. Furthermore, a current measuring resistor 24 is switched on in the control center in the line conductor 12, at which a voltage drop proportional to the line current, with which an evaluation circuit 26 is applied. If the line current deviates from the idle state, depending on the amount of the deviation, this generates a signal S which indicates the presence of a fault alarm signal or a signal R which indicates the presence of a smoke alarm signal.
  • the evaluation circuit 26 takes into account the respective setpoint value of the controller 16 in such a way that when the higher setpoint set on the potentiometer 22 is specified, the input voltage generated by the measuring resistor 24 is correspondingly reduced in order to compensate for such current increases which result solely from the switchover from the nominal value of the line voltage to the increased DC voltage.
  • An ionization fire detector M is connected with its connections 28, 30 to the line conductor 10. Further fire detectors of the same design are connected in parallel to the line conductors 10, 12 and are not shown for the sake of simplicity.
  • the basic circuit structure of the ionization fire detector M is shown in FIG. 1, circuit details are shown in FIG. 2.
  • the ionization fire detector M comprises a measuring chamber MK with an outer electrode 32 permeable to the ambient air and a central electrode 34, and a reference chamber RK with an electrode 36, which is electrically connected to the central electrode 34 at the connection point 38, and an electrode 40 located at the connection 28
  • the series connection of the chambers MK, RK is thus due to the DC supply voltage of the ionization fire detector M formed by the line voltage.
  • the reference chamber RK is sealed much more effectively than the measuring chamber MK against the ambient air. Both chambers MK, RK are ionized by radioactive emitters 42 and 44 (FIG. 2).
  • connection point 38 an ionization current flows through both chambers MK, RK in the undisturbed quiescent state, and a quiescent potential of 10 V is established at connection point 38. If smoke enters the measuring chamber MK, its internal resistance increases, and the potential of the connection point 38 shifts towards the potential of the connection 28, as a result of which a smoke alarm signal can be generated in a known manner. Contamination of the insulation paths between the outer electrode 32 and the center electrode 34 of the measuring chamber MK, on the other hand, leads to a reduction in their internal resistance, as a result of which the potential of the connection point 38 approaches that of the connection 30, which can be used in a known manner to generate a fault alarm signal.
  • a malfunction alarm circuit which consists of a threshold amplifier 46 and an alarm transmitter 50 connected to it via an OR gate 48.
  • the threshold value switch 46 does not only produce a Ver reduction of the insulation resistance of the measuring chamber MK, but also an output signal if the DC supply voltage of the ionization fire detector M drops compared to the nominal value of this DC supply voltage and falls below a predetermined threshold value, since the threshold amplifier 46 is between the one at the connection point 38 with regard to the response required Input and a connection 28 or 38 of the DC supply voltage measured threshold voltage is approximately independent of the DC supply voltage.
  • the output signal possibly output by the threshold amplifier 46 causes the alarm signal generator 50 located between the connections 28, 30 to switch a current path reduced predetermined resistance value between the connections 28, 30, as a result of which a line current increase, which can be detected by the evaluation circuit 26, is generated, which is used to output the signal S in the central Z leads.
  • the smoke alarm circuit comprises a further threshold amplifier 62, which is connected on the input side to the connection point 38, an AND gate 64 connected downstream of the threshold amplifier 62 with an input, and an alarm signal transmitter 66 connected downstream thereof.
  • the voltage across the measuring chamber rises above the absolute value Input threshold voltage of the threshold amplifier 62, so it outputs an output signal, and since in this case a signal of L level is supplied to the inverting input of the AND gate 64, its AND condition is met, so that it is the alarm signal generator 66 starts signal.
  • the latter acts in a similar way to the alarm signal transmitter 50, but produces a different line current increase compared to it, so that the signal R can be generated by means of the monitoring circuit 26.
  • the ionization fire detector M is supplied with a DC voltage of approximately 24 V, which is higher than the nominal value of the DC supply voltage, in the manner already explained; in the case of detectors installed on line L because of control center Z, the increased DC voltage can be somewhat reduced to the same value as the line voltage due to voltage drops along line L compared to the value mentioned.
  • the threshold amplifier 62 is largely insensitive to the supply voltage and therefore detects a shift in the potential at the connection point 38 as a result of the increase in the voltage to the increased DC voltage, the increased DC voltage and the threshold voltage of the threshold amplifier 62 are selected such that the voltage increase does not increase a response of the threshold amplifier 62 leads.
  • this output signal should not lead to the generation of the signal R corresponding to a smoke alarm signal in the control center Z.
  • the forwarding of the smoke alarm signal possibly generated by the smoke alarm circuit to the evaluation circuit 26 is suppressed, depending on the switchover to the higher DC voltage, and instead the smoke alarm signal is transmitted to the evaluation circuit 26 as a fault alarm signal .
  • the ionization fire detector M has a voltage level detector 68, for example a zener diode, which emits an output signal when the voltage supplying it between the connections 28, 30 has a nominal value (20 V) of the DC supply voltage by a predetermined value Dimension exceeds, for example if the voltage between the terminals 28, 30 exceeds 21 V.
  • the output signal of the H level which is then output by the voltage level detector 68 is fed to the inverting input of the AND gate 64, as a result of which the transmission of the output signal of the threshold value amplifier 62 to the alarm signal generator 66 is blocked.
  • the inputs of a further AND gate 70 are connected to the outputs of the threshold amplifier 62 and the voltage level detector 68, the AND treatment of which is fulfilled in the case under consideration and which therefore generates an output signal.
  • This is fed to the alarm signal generator 50 via a further input of the OR gate 48, so that the latter transmits a fault alarm signal to the control center Z, on the basis of which the signal S can be generated.
  • the cheaper solution essentially depends on the number of ionization fire detectors that are connected to the control center Z in the fire detection device.
  • the solution described on the basis of the exemplary embodiment has the advantage that the fire detectors connected to line L can be equipped with mutually different alarm signal transmitters, whose different fault and smoke alarm signals can be distinguished in the control center Z, for example on the basis of different frequencies.
  • the threshold amplifier 46 of the fault alarm circuit 46, 48, 50 (FIG. 1) has on the input side a self-blocking p-channel field-effect transistor 72 connected with its control electrode to the connection point 38, the drain electrode of which via a load resistor 74 to the connection 28 of the ionization fire detector M is connected to which the reference chamber RK is located.
  • the source electrode of the field effect transistor 72 is connected to a voltage divider 76, 78 connected to the DC supply voltage.
  • the partial resistor 78 of the voltage divider 76, 78 that forms a series circuit lying parallel to the measuring chamber MK with the control path (control electrode-source electrode path) of the field effect transistor 72 has a resistance value that is several times lower than the rest of the partial resistance 76 of the voltage divider 76, 78, so that when the DC supply voltage has its nominal value and the ionization fire detector M is in the undisturbed idle state, the voltage drop across the partial resistor 78 is smaller in amount than the voltage drop across the measuring chamber MK, or in other words, the potential of the source electrode of the field effect transistor 72 is shifted relative to the potential of the connection point 38 toward the potential of the connection 30 at which the measuring chamber MK is located. This potential shift, i.e.
  • the control voltage of the field effect transistor 72 is greater than its threshold voltage.
  • the field effect transistor 72 therefore conducts in the undisturbed idle state.
  • the base of a bipolar transistor 80 which is also conductive in this state and is connected in series with a load resistor 82 between the terminals 28, 30 is connected to the drain electrode of the field effect transistor 72, and the base of a further bipolar transistor is connected to the collector of the transistor 80 84 connected, which is also in series with its load resistor 86 between the connections 28, 30, but which is non-conductive in the undisturbed idle state.
  • connection point between the transistor 84 and its load resistor 86 forms the output 88 of the threshold amplifier 46, so that the signal level generated as an output signal in the undisturbed idle state and accordingly in the unresponsive state of the threshold amplifier 46 has the potential of the connection 30, while that generated in the addressed state Signal level approximately corresponds to the potential of the connection 28.
  • the potential of the connection point 38 approaches that of the connection 30 and thus also that of the source electrode of the field effect transistor 72, until the control voltage of the field effect transistor 72 drops below when the insulation resistance falls below a predetermined threshold value whose threshold voltage (pinch-off voltage) drops, as a result of which the field effect transistor 72 and the transistor 80 become non-conductive, the transistor 84 becomes conductive and a signal which indicates the relevant state of the threshold value amplifier 46 appears at the output.
  • the voltage at the measuring chamber MK also drops approximately proportionately, i.e. the voltage amounting to 10 V in the idle state in the exemplary embodiment is now only approximately 8 V. It is further assumed that in the undisturbed idle state due to the dimensioning of the voltage divider 76, 78 and the load resistor 74, the voltage drop across the partial resistor 78 had an amount of 3 V. have, while the threshold voltage of the field effect transistor 72 is 6 V, so that the control voltage of the field effect transistor 72 was 1 V above the threshold voltage.
  • the voltage drop across the partial resistor 78 is also reduced, however, because of the low resistance value of the partial resistor 78 by only a small absolute amount. Therefore, the sum of the voltage drop across the partial resistor 78 and the threshold voltage of the field effect transistor 72, i.e. the input threshold voltage of the threshold amplifier 46 is approximately constant even when the DC supply voltage is lowered. The result is that the voltage at the measuring chamber MK (originally 10 V, now 8 V) falls below the input threshold voltage (originally 9 V, now as 8 V), that the field-effect transistor 72 becomes non-conductive and that the threshold value amplifier 46 therefore does the same An output signal is generated as is the case when the insulation resistance of the measuring chamber MK decreases.
  • the field effect transistor 72 When the field effect transistor 72 becomes non-conductive, its main current, which flowed through the partial resistor 78 in the idle state, ceases. So that the resultant reduction in the voltage drop across the partial resistor 78 does not endanger the voltage independence of the input threshold voltage from the supply voltage, as explained above.
  • the load resistor 74 must have a resistance value several times higher than the partial resistor 78. Since the input threshold voltage is composed of the sum of the voltage dropping across the partial resistor 78 and the threshold voltage of the field effect transistor 72 and the former is variable as a function of the supply voltage, while the latter is constant, the aim should be to give the field effect transistor 72 a relatively high threshold voltage. In practice, this can be between 15% and 50% of the DC supply voltage.
  • the use of a field effect transistor 72 has proven to be particularly expedient, the threshold voltage of which is approximately 30% of the DC supply voltage.
  • the threshold amplifier 62 of the smoke alarm circuit 62, 64, 66 (FIG. 1) in turn has, on the input side, a self-blocking p-channel field effect transistor 90 connected with its control electrode to the connection point 38 of the chambers MK, RK. Its drain electrode is connected via a load resistor formed by partial resistors 92, 94 to the connection 28 at which the reference chamber is located, while its source electrode is connected to a voltage divider formed by partial resistors 96,98.
  • the resistance values of the partial resistors 96, 98 are of the same order of magnitude, so that, in the undisturbed state of rest, the source electrode of the field effect transistor 90 is at a potential approximately the same as the potential of the connection point 38, but expediently at a potential relative to the potential of the connection point 38 shifted potential, and the field effect transistor 90 is non-conductive.
  • the potential of the source electrode of the field effect transistor 90 is therefore closer to that of the connection 28 than the potential of the source electrode of the field effect transistor 72 in the undisturbed idle state.
  • the output 106 of the threshold amplifier 62 is connected between the collector of the transistor 102 and its load resistor 104, so that the output signal, like that of the threshold amplifier 46, has the potential of the terminal 30 in the undisturbed idle state.
  • the statements made for the dimensioning of the threshold voltage of the field-effect transistor 72 also apply with regard to the threshold voltage of the field-effect transistor 90, but this threshold voltage must meet the additional condition that it is chosen so large that it is due to the switchover to the higher DC voltage on the control path
  • the voltage of the field-effect transistor 90 only exceeds the threshold voltage if the measuring chamber has an increased internal resistance compared to the undisturbed idle state due to the contamination of the radiator 42 ionizing it.
  • the voltage increase across the measuring chamber MK would be so great that the smoke alarm circuit 62, 64, 66 (FIG. 1) would respond to it as well as if smoke came in, even if it had to do with it Input voltage threshold would not be independent of the supply voltage.
  • the latter measure in conjunction with the switchability to the higher DC voltage provides the possibility of already detecting a relatively low level of contamination of the radiation source 42 from the control center Z, so that false alarms based on excessive contamination of the radiation source are avoided, in which case they are erroneous Smoke alarm signals are generated and evaluated as such in the control center Z.

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Abstract

1. A fire alarm means comprising: at least one ionization fire detector (M), in particular a plurality of ionization fire detectors (M) connected parallel to each other to a detecting line (L; 10, 12) and including a measuring chamber (MK) accessible to ambient air and a reference chamber (RK) more closed against the access of ambient air, the series connection of said measuring chamber and of said reference chamber being connected to a direct current supply voltage; a smoke alarm circuit (62, 64, 66) being connected at its input side to the connection point (38) of said chambers (MK, RK) and generating a smoke alarm signal when smoke enters into said measuring chamber (MK); and a fault alarm circuit (46, 48, 50) being supplied by said direct current supply voltage, being connected at its input side to the connec tion point (38) of said chambers (MK, RK), and generating a fault alarm signal when the insula tion resistance of said measuring chamber (MK) drops below a predetermined threshold value; with the smoke alarm circuit (62, 62, 66) compris ing at its input side a field- effect transistor (90) connected with its control electrode to the con nection point (38) of said chambers (MK, RK), the drain electrode of said field-effect transistor being connected through a load resistor (92, 94) to that terminal (28) of said direct current supply voltage which said reference chamber (RK) is connected to; characterized in that for the additional emis sion of an alarm signal in case of faults influenc ing the voltage drop at said measuring chamber (MK) said fault alarm circuit (46, 48, 50) and said smoke alarm circuit (62, 64, 66) are, with respect to the input thereshold voltage necessary for their actuation and being measured between their inputs and a terminal (28, 30) of said direct current supply voltage, at least approximately voltage- independent with respect to said direct current supply voltage, that the voltage source (14) pro viding said direct current supply voltage is switch able to a voltage which is increased with respect to the nominal value of said direct current supply voltage, and that the threshold voltage of said self-locking field-effect transistor (90) is such that the voltage occuring at the control path of said field-effect transistor (90) due to the switching to the increased voltage exceeds the threshold volt age only when said measuring chamber (MK), due to the contamination of the radiation source ionizing the measuring chamber shows an inter nal resistance increased with respect to the so far undisturbed status, and that in dependency from the switching to the increased voltage the trans mission of the smoke alarm signal possibly generated by said smoke alarm circuit (62, 64, 66) to an evaluating circuit (26) is suppressed and a fault alarm signal is generated instead thereof and transmitted to the evaluating circuit (26).

Description

Die Erfindung bezieht sich auf eine Brandmeldeeinrichtung nach dem Oberbegriff des Anspruchs 1.The invention relates to a fire alarm device according to the preamble of claim 1.

Eine derartige Brandmeldeeinrichtung ist bekannt (DE-OS 2 029 794). Hierbei weisen die Störungsalarmschaltung und die Rauchalarmschaltung jeweils eingangsseitig einen mit seiner Steuerelektrode an den Verbindungspunkt der Kammern angeschlossenen Feldeffekttransistor auf, und die Quellenelektroden dieser Feldeffekttransistoren sind an einen ihnen gemeinsamen Spannungsteiler oder jeweils an einen Spannungsteiler oder derart angeschlossen, dass das Potential dieser Quellenelektrode im ungestörten Ruhezustand annähernd dem Potential des Verbindungspunkts der Kammern gleicht. Die Feldeffekttransistoren sind bom selbstleitenden Typ, so dass beide im ungestörten Ruhezustand nichtleitend sind. Weiter sind die Feldeffekttransistoren von entgegengesetztem Leitfähigkeitstyp, so dass bei einer Erhöhung der Spannung über der Messkammer infolge von Raucheintritt der Feldeffekttransistor der Rauchalarmschaltung und bei Verminderung der Spannung über der Messkammer infolge von Isolationsmängeln der Feldeffekttransistor der Störungsalarmschaltung dann leitend wird, wenn die Steuerspannung, nämlich die Potentialdifferenz zwischen dem Verbindungspunkt der Kammern und dem jeweiligen Abgriff des Spannungsteilers die Schwellenspannung (Pinchoff-Spannung) des jeweiligen Feldeffekttransistors überschreitet. Bei Änderungen der Speisespannung ändert sich das Potential am Verbindungspunkt der Kammern einerseits und das Potential am Abgriff des jeweiligen Spannungsteilers und damit das Potential der Quellenelektroden der Feldeffekttransistoren andererseits in zumindest annährend gleicher Weise, so dass jedenfalls Spannungsänderungen bis zur Grössenordnung von 25% des Nennwerts der Speisespannung nicht zur Abgabe eines Alarmsignals führen.Such a fire alarm device is known (DE-OS 2 029 794). In this case, the fault alarm circuit and the smoke alarm circuit each have a field effect transistor connected to its control electrode at the connection point of the chambers on the input side, and the source electrodes of these field effect transistors are connected to a voltage divider common to them or to a voltage divider or in such a way that the potential of this source electrode is in the undisturbed idle state approximates the potential of the connection point of the chambers. The field effect transistors are of the self-conducting type, so that both are non-conductive in the undisturbed idle state. Furthermore, the field effect transistors are of the opposite conductivity type, so that when the voltage across the measuring chamber increases as a result of smoke entering the field effect transistor of the smoke alarm circuit and when the voltage across the measuring chamber decreases as a result of lack of insulation, the field effect transistor of the fault alarm circuit becomes conductive when the control voltage, namely the Potential difference between the connection point of the chambers and the respective tap of the voltage divider exceeds the threshold voltage (pinchoff voltage) of the respective field effect transistor. When the supply voltage changes, the potential at the connection point of the chambers on the one hand and the potential at the tap of the respective voltage divider and thus the potential of the source electrodes of the field effect transistors on the other hand change in at least approximately the same way, so that voltage changes up to the order of magnitude of 25% of the nominal value of the supply voltage do not lead to an alarm signal.

Eine Verschmutzung der radioaktiven Strahlungsquelle führt zu einer Erhöhung des Innenwiderstands der Meßkammer und zu einer entsprechenden Verschiebung des Potentials des Verbindungspunktes zwischen Meß- und Referenzkammer. Ab einem gewissen Verschmutzungsgrad wirkt sich dieser in gleicher Weise aus wie das Eintreten von Rauch in die Meßkammer, so daß ein entsprechendes Alarmsignal erzeugt wird. Mit den bekannten Brandmelder ist es nicht möglich, bereits vor der Erzeugung eines Alarmsignals die Verschmutzung zu ermitteln bzw. beim Entstehen eines Alarmsignals zwischen Verschmutzung und dem Eintreten von Rauch in die Meßkammer zu unterscheiden.Contamination of the radioactive radiation source leads to an increase in the internal resistance of the measuring chamber and to a corresponding shift in the potential of the connection point between the measuring and reference chamber. Above a certain degree of contamination, this has the same effect as the entry of smoke into the measuring chamber, so that a corresponding alarm signal is generated. With the known fire detectors, it is not possible to determine the contamination even before an alarm signal is generated or to distinguish between contamination and the occurrence of smoke in the measuring chamber when an alarm signal is generated.

Aus der PL-B-62 618 ist auch ein lonisations-brandmelder bekanntgeworden, bei deim ein einziger MOS-Feldeffekttransistor mit seiner Steuerelektrode an den Verbindungspunkt zwischen Meß- und Referenzkammer liegt, während die Abflußelektrode über Widerstände mit einem Melderanschluß und die Quellenelektrode über eine Zenerdiode mit dem anderen Melderanschluß verbunden ist. Die Feldeffekttransistor bildet mithin einen Schellwertschalter, dessen Eingangsschellenspannung weitgehend unabhängig von der Speisegleichspannung ist. Mit dem bekannten Brandmelder lassen sich jedoch Potentialverringerungen am Verbindungspunkt zwischen Meß- und Referenzkammer aufgrund verschlechterter Isolationsbedingungen und/oder eines Absinkens der Speisegleichspannung nicht feststellen. Ein erhöhter Innenwiderstand aufgrund einer Verschmutzung der Strahlenquelle führt zur Erzeugung eines Rauchalarmsignals, wenn der eingestellte Schwellenwert erreicht wird. Ein Unterschied zwischen Rauchalarmerzeugung im Brandfall oder als Folge einer Verschmutzung des radioaktiven Strahlers kann nicht getroffen werden.An ionization fire detector has also become known from PL-B-62 618, in which a single MOS field-effect transistor with its control electrode lies at the connection point between the measuring and reference chamber, while the drain electrode via resistors with a detector connection and the source electrode via a zener diode is connected to the other detector connection. The field effect transistor therefore forms a threshold value switch, the input threshold voltage of which is largely independent of the DC supply voltage. With the known fire detector, however, potential reductions at the connection point between the measuring and reference chamber cannot be determined due to deteriorated insulation conditions and / or a drop in the DC supply voltage. An increased internal resistance due to contamination of the radiation source leads to the generation of a smoke alarm signal when the set threshold value is reached. A difference between smoke alarm generation in the event of fire or as a result of contamination of the radioactive emitter cannot be made.

Der Erfindung liegt die Aufgabe zugrunde, bei einer Brandmeldeinrichtung der eingangs genannten Art die Funktionsfähigkeit der lonisations-Brandmelder noch weitgehender zu überwachen.The invention is based, to monitor the functionality of the ionization fire detectors even more extensively in a fire detection device of the type mentioned.

Zur Lösung dieser Aufgabe ist gemäss der Erfindung eine Brandmeldeeinrichtung der eingangs genannten Art entsprechend den kennzeichnenden Merkmalen des Anspruchs 1 ausgebildet.To achieve this object, according to the invention, a fire alarm device of the type mentioned at the outset is designed in accordance with the characterizing features of claim 1.

Bei der Brandmeldeeinrichtung sprechen die Störungsalarmschaltung und/oder die Rauchalarmschaltung ausser auf eine Isolationsverschlechterung der Messkammer bzw. den Raucheintritt in die Messkammer auch auf solche Potentialänderungen des Verbindungspunkts der Kammern an, die von anderen Störungsursachen herrühren, beispielsweise auf eine unzulässige Verminderung der Speisegleichspannung oder auf eine Erhöhung des Innenwiderstands der Messkammer, die auf eine Verschmutzung des die Kammer ionisierenden, radioaktiven Strahlers zurückzuführen ist. Damit wird eine noch weitgehendere Überwachung der die Funktionssicherheit der lonisations-Brandmelder beeinflussenden Parameter ermöglicht. Ein Abfall der den lonisations-Brandmelder speisenden Speisegleichspannung kann beispielsweise darauf beruhen, dass der Melder relativ weit von einer die Linie mit konstanter Linienspannung speisenden Zentrale angeordnet ist und dass die Linienspannung entlang der Linie bis zu dem betroffenen Brandmelder abfällt, oder darauf, dass bei Batteriespeisung mittels einer als Gleichspannungsquell vorgesehen Batterie oder mittels einer bei Netzausfall wirksamen Pufferbatterie die Batteriespannung infolge Erschöpfung abfällt, oder auch darauf, dass ein zur Konstanthaltung der Speisegleichspannung vorgesehener Regler versagt.In the case of the fire alarm device, the fault alarm circuit and / or the smoke alarm circuit respond not only to a deterioration in the insulation of the measuring chamber or the smoke entering the measuring chamber, but also to such potential changes in the connection point of the chambers that result from other causes of the fault, for example to an impermissible reduction in the DC supply voltage or to one Increase in the internal resistance of the measuring chamber, which is due to contamination of the radioactive emitter that ionizes the chamber. This enables an even more extensive monitoring of the parameters influencing the functional safety of the ionization fire detectors. A drop in the DC supply voltage feeding the ionization fire detector can be due, for example, to the fact that the detector is arranged relatively far from a control center supplying the line with constant line voltage and that the line voltage drops along the line to the fire detector concerned, or to the fact that the battery supply is being supplied by means of a battery provided as a DC voltage source or by means of a buffer battery which is effective in the event of a power failure, the battery voltage drops as a result of exhaustion, or also that a controller provided to keep the DC supply voltage constant fails.

Verschmutzungen der radioaktiven Strahlungsquelle lassen sich dadurch feststellen, daß die die Speisegleichspannung liefernde Spannungsquelle auf eine gegenüber dem Nennwert der Speisegleichspannung erhöhte Gleichspannung umschaltbar ausgebildet ist. Die Schwellenspannung des Feldeffekttransistors der Rauchalarmschaltung ist so gewählt, daß die aufgrund der Umschaltung auf die höhere Gleichspannung einer Steuerstrecke des Feldeffekttransistors auftretende Spannung nur dann die Schwellenspannung überschreitet, wenn die Meßkammer aufgrund der Verschmutzung der sie ionisierenden Strahlungsquelle einen gegenüber dem insoweit ungestörten Ruhezustand erhöhten Innenwiderstand aufweist. Mit anderen Worten, eine Erhöhung des Potentials am Verbindungspunkt zwischen Meß- und Referenzkammer führt nicht zu einem Ansprechen der Schwellwertschaltung, wenn eine nennenswerte Verschutzmung der radioaktiven Strahlungsquelle nicht besteht. Falls jedoch der durch die Verschmutzung erhöhte Innenwiderstand der Meßkammer ein bestimmtes Maß erreicht hat, reicht das Spannungserhöhung aus, die Schwellwertschaltung ansprechen zu lassen. Das auf diese Weise erzeugte Signal der Schwellwertschaltung wird jedoch nicht zur Erzeugung eines Rauchalarmsignals verwendet. Für die Zentrale ist wichtig, zu wissen, ob das erzeugte Signal auf eine Rauchentwicklung oder auf eine Verschmutzung der Meßkammer zurückzuführen ist. Das durch die Verschmutzung erzeugte Rauchalarmsignal wird deshalb unterdrückt. Statt dessen wird eine Störungsalarmsignal erzeugt und zur Auswerteschaltung übertragen.Contamination of the radioactive radiation source can be determined in that the voltage source supplying the DC supply voltage is designed to be switchable to a DC voltage that is higher than the nominal value of the DC supply voltage. The thresholds The voltage of the field effect transistor of the smoke alarm circuit is selected so that the voltage occurring due to the switchover to the higher DC voltage of a control path of the field effect transistor only exceeds the threshold voltage if the measuring chamber has an increased internal resistance compared to the undisturbed idle state due to the contamination of the ionizing radiation source. In other words, an increase in the potential at the connection point between the measuring and reference chamber does not lead to the threshold circuit responding if there is no appreciable contamination of the radioactive radiation source. If, however, the internal resistance of the measuring chamber has increased due to the contamination, the voltage increase is sufficient to make the threshold circuit respond. However, the threshold circuit signal generated in this way is not used to generate a smoke alarm signal. It is important for the control center to know whether the signal generated can be attributed to smoke development or contamination of the measuring chamber. The smoke alarm signal generated by the pollution is therefore suppressed. Instead, a malfunction alarm signal is generated and transmitted to the evaluation circuit.

Ausgestaltungen der Erfindung sind in den Unteransprüchen angegeben.Embodiments of the invention are specified in the subclaims.

Die Erfindung wird im folgenden anhand der Zeichnungen näher erläutert, in denen ein Ausführungsbeispiel dargestellt ist. Es zeigt:

  • Fig. 1 eine Brandmeldeeinrichtung gemäss der Erfindung;
  • Fig. 2 Schaltungseinzelheiten eines lonisations- Brandmelders der Brandmeldeeinrichtung nach Fig. 1.
The invention is explained in more detail below with reference to the drawings, in which an embodiment is shown. It shows:
  • 1 shows a fire alarm device according to the invention;
  • FIG. 2 circuit details of an ionization fire detector of the fire detection device according to FIG. 1.

Die in Fig. 1 dargestellte Brandmeldeeinrichtung umfasst eine Zentrale Z und eine an diese angeschlossene Linie L mit Linienleitern 10, 12. In der Zentrale Z ist die Linie L von einer netzgespeisten, ggf. batteriegepufferten Gleichspannungsquelle 14 mit einer Linienspannung gespeist, deren Nennwert im Ausführungsbeispiel 20 V beträgt. Zum Konstanthalten dieser Linienspannung ist ein mit ihr beaufschlagter Regler 16 vorgesehen, der abhängig von einem Soll-Istwertvergleich eine Anschnittsteuerung der in der Gleichspannungsquelle 14 vorgesehenen Thyristoren bewirkt. Der dem Nennwert der Linienspannung entsprechende Sollwert ist an einem Potentiometer 18 einstellbar und wird dem Regler 16 über einen Testschalter 20 zugeführt. Durch Drücken des Testschalters 20 ist dem Regler 16 anstelle des genannten Sollwerts ein an einem Potentiometer 22 einstellbarer, weiterer Sollwert vorgebbar, der einer gegenüber dem Nennwert der Linienspannung höheren Gleichspannung von im Ausführungsbeispiel 24 V entspricht. Weiter ist in der Zentrale in den Linienleiter 12 ein Strommesswiderstand 24 eingeschaltet, an dem eine dem Linientstrom proportionale Spannung abfällt, mit der eine Auswerteschaltung 26 beaufschlagt ist. Diese erzeugt bei Abweichungen des Linienstroms vom Ruhezustand je nach dem Betrag der Abweichung ein das Vorliegen eines Störungsalarmsignals bezeichnendes Signal S oder ein das Vorliegen eines Rauchalarmsignals bezeichnendes Signal R. Bei der Erzeugung der Signale S, R berücksichtigt die Auswerteschaltung 26 den jeweiligen Sollwert des Reglers 16 in der Weise, dass bei Vorgabe des höheren, am Potentiometer 22 aingestellten Sollwertes die vom Messwiderstand 24 erzeugte Eingangsspannung entsprechend vermindert wird, um solche Stromerhöhungen zu kompensieren, die allein von der Umschaltung vom Nennwert der Linienspannung auf die erhöhte Gleichspannung herrühren.The fire alarm device shown in FIG. 1 comprises a control center Z and a line L connected to it with line conductors 10, 12. In control center Z, line L is fed with a line voltage from a mains-fed, possibly battery-buffered DC voltage source 14, the nominal value of which in the exemplary embodiment Is 20 V. To keep this line voltage constant, a controller 16 is provided with it, which, depending on a setpoint / actual value comparison, effects a gate control of the thyristors provided in the DC voltage source 14. The nominal value corresponding to the nominal value of the line voltage can be set on a potentiometer 18 and is fed to the controller 16 via a test switch 20. By pressing the test switch 20, the controller 16 can be given a further setpoint which can be set on a potentiometer 22 instead of the specified setpoint and which corresponds to a higher DC voltage of 24 V in the exemplary embodiment than the nominal value of the line voltage. Furthermore, a current measuring resistor 24 is switched on in the control center in the line conductor 12, at which a voltage drop proportional to the line current, with which an evaluation circuit 26 is applied. If the line current deviates from the idle state, depending on the amount of the deviation, this generates a signal S which indicates the presence of a fault alarm signal or a signal R which indicates the presence of a smoke alarm signal. When generating the signals S, R, the evaluation circuit 26 takes into account the respective setpoint value of the controller 16 in such a way that when the higher setpoint set on the potentiometer 22 is specified, the input voltage generated by the measuring resistor 24 is correspondingly reduced in order to compensate for such current increases which result solely from the switchover from the nominal value of the line voltage to the increased DC voltage.

An die Linienleiter 10, ist mit seinen Anschlüssen 28, 30 ein lonisations-Brandmelder M angeschlossen. Weitere, gleichartig ausgebildete Brandmelder sind parallel zu diesem zwischen die Linienleiter 10, 12 geschaltet und einfachheitshalber nicht dargestellt. Der grundsätzliche Schaltungsaufbau des lonisations-Brandmelders M geht aus Fig. 1, Schaltungseinzelheiten gehen aus Fig. 2 hervor.An ionization fire detector M is connected with its connections 28, 30 to the line conductor 10. Further fire detectors of the same design are connected in parallel to the line conductors 10, 12 and are not shown for the sake of simplicity. The basic circuit structure of the ionization fire detector M is shown in FIG. 1, circuit details are shown in FIG. 2.

Der lonisations-Brandmelder M umfasst eine Messkammer MK mit einer für die Umgebungsluft durchlässigen Aussenelektrode 32 und einer Mittelelektrode 34 sowie eine Referenzkammer RK mit einer Elektrode 36, die mit der Mittelelektrode 34 am Verbindungspunkt 38 elektrisch verbunden ist, und einer am Anschluss 28 liegenden Elektrode 40. Die Reihenschaltung der Kammern MK, RK liegt somit an der von der Linienspannung gebildeten Speisegleichspannung des lonisationsbrandmelders M. Die Referenzkammer RK ist wesentlich stärker als die Messkammer MK gegenuber der Umgebungsluft abgeschlossen. Beide Kammern MK, RK sind von radioaktiven Strahlern 42 bzw. 44 (Fig. 2) ionisiert. Hierdurch fliesst im ungestörten Ruhezustand ein lonisationsstrom durch beide Kammern MK, RK, und am Verbindungspunkt 38 stellt sich ein Ruhepotential von im Ausführungsbeispiel 10 V ein. Tritt Rauch in die Messkammer MK ein, so erhöht sich deren Innenwiderstand, und das Potential des Verbindungspunkts 38 verschiebt sich zum Potential des Anschlusses 28 hin, wodurch in bekannter Weise ein Rauchalarmsignal erzeugt werden kann. Eine Verschmutzung der Isolationsstrecken zwischen der Aussenelektrode 32 und der Mittelelektrode 34 der Messkammer MK führt andererseits zu einer Verringerung von deren Innenwiderstand, wodurch das Potential des Verbindungspunkts 38 sich demjenigen des Anschlusses 30 nähert, was in bekannter Weise zur Erzeugung eines Störungsalarmsignals ausgenutzt werden kann.The ionization fire detector M comprises a measuring chamber MK with an outer electrode 32 permeable to the ambient air and a central electrode 34, and a reference chamber RK with an electrode 36, which is electrically connected to the central electrode 34 at the connection point 38, and an electrode 40 located at the connection 28 The series connection of the chambers MK, RK is thus due to the DC supply voltage of the ionization fire detector M formed by the line voltage. The reference chamber RK is sealed much more effectively than the measuring chamber MK against the ambient air. Both chambers MK, RK are ionized by radioactive emitters 42 and 44 (FIG. 2). As a result, an ionization current flows through both chambers MK, RK in the undisturbed quiescent state, and a quiescent potential of 10 V is established at connection point 38. If smoke enters the measuring chamber MK, its internal resistance increases, and the potential of the connection point 38 shifts towards the potential of the connection 28, as a result of which a smoke alarm signal can be generated in a known manner. Contamination of the insulation paths between the outer electrode 32 and the center electrode 34 of the measuring chamber MK, on the other hand, leads to a reduction in their internal resistance, as a result of which the potential of the connection point 38 approaches that of the connection 30, which can be used in a known manner to generate a fault alarm signal.

Zur Erzeugung eines Störungsalarmsignals ist eine Störungsalarmschaltung vorgesehen, die aus einem Schwellenwertverstärker 46 und einem diesem über ein ODER-Glied 48 nachgeschalteten Alarmgeber 50 besteht. Wie noch anhand von Fig. 2 näher zu erläutern sein wird, erzeugt der Schwellenwertschalter 46 nicht nur bei einer Verminderung des Isolationswiderstandes der Messkammer MK, sondern auch dann ein Ausgangssignal, wenn die Speisegleichspannung des lonisations-Brandmelders M gegenüber dem Nennwert dieser Speisegleichspannung abfällt und einen vorgegebenen Schwellenwert unterschreitet, da der Schwellenwertverstärker 46 hinsichtlich der zu seinem Ansprechen erforderlichen, zwischen dem am Verbindungspunkt 38 liegenden Eingang und einem Anschluss 28 oder 38 der Speisegleichspannung gemessenen Schwellenspannung gegenüber der Speisegleichspannung annähernd spannungsunabhängig ausgebildet ist. Das ggf. vom Schwellenwertverstärker 46 abgegebene Ausgangssignal bewirkt, dass der zwischen den Anschlüssen 28, 30 liegende Alarmsignalgeber 50 einen Strompfad verringerten vorgegebenen Widerstandswertes zwischen die Anschlüsse 28, 30 schaltet, wodurch eine mittels der Auswerteschaltung 26 erfassbare Linienstromerhöhung erzeugt wird, die zur Abgabe des Signals S in der Zentrale Z führt.To generate a malfunction alarm signal, a malfunction alarm circuit is provided, which consists of a threshold amplifier 46 and an alarm transmitter 50 connected to it via an OR gate 48. As will be explained in more detail with reference to FIG. 2, the threshold value switch 46 does not only produce a Ver reduction of the insulation resistance of the measuring chamber MK, but also an output signal if the DC supply voltage of the ionization fire detector M drops compared to the nominal value of this DC supply voltage and falls below a predetermined threshold value, since the threshold amplifier 46 is between the one at the connection point 38 with regard to the response required Input and a connection 28 or 38 of the DC supply voltage measured threshold voltage is approximately independent of the DC supply voltage. The output signal possibly output by the threshold amplifier 46 causes the alarm signal generator 50 located between the connections 28, 30 to switch a current path reduced predetermined resistance value between the connections 28, 30, as a result of which a line current increase, which can be detected by the evaluation circuit 26, is generated, which is used to output the signal S in the central Z leads.

Die Rauchalarmschaltung umfasst einen weiteren Schwellenwertverstärker 62, der eingangsseitig an den Verbindungspunkt 38 angeschlossen ist, ein mit einem Eingang dem Schwellenwertverstärker 62 nachgeschaltetes UND-Glied 64 sowie einen diesem nachgeschalteten Alarmsignalgeber 66. Steigt im ungestörten Zustand infolge Raucheintritts die Spannung an der Messkammer betragsmässig über die Eingangs-Schwellenspannung des Schwellenwertverstärkers 62 an, so gibt dieser ein Ausgangssignal ab, und da in diesem Fall dem invertierenden Eingang des UND-Glieds 64 ein Signal von L-Pegel zugeführt ist, ist dessen UND-Bedigung erfüllt, so dass es ein den Alarmsignalgeber 66 in Gang setzendes Signal abgibt. Letzterer wirkt ähnlich wie der Alarmsignalgeber 50, erzeugt jedoch eine demgegenüber unterschiedliche Linienstromerhöhung, so dass mittels der Überwachungsschaltung 26 das Signal R erzeugbar ist.The smoke alarm circuit comprises a further threshold amplifier 62, which is connected on the input side to the connection point 38, an AND gate 64 connected downstream of the threshold amplifier 62 with an input, and an alarm signal transmitter 66 connected downstream thereof. In the undisturbed state due to the occurrence of smoke, the voltage across the measuring chamber rises above the absolute value Input threshold voltage of the threshold amplifier 62, so it outputs an output signal, and since in this case a signal of L level is supplied to the inverting input of the AND gate 64, its AND condition is met, so that it is the alarm signal generator 66 starts signal. The latter acts in a similar way to the alarm signal transmitter 50, but produces a different line current increase compared to it, so that the signal R can be generated by means of the monitoring circuit 26.

Wird im ungestörten Ruhezustand der Testschalter 20 in der Zentrale Z betätigt, so wird in bereits erlaüterter Weise dem lonisations-Brandmelder M eine gegenüber dem Nennwert der Speisegleichspannung höhere Gleichspannung von annähernd 24 V zugeführt; bei an der Linie L weil von der Zentrale Z installierten Meldern kann die erhöhte Gleichspannung im selben Masse wie die Linienspannung aufgrund von Spannungsabfällen entlang der Linie L gegenüber dem genannten Wert etwas verringert sein. Obwohl der Schwellenwertverstärker 62 gegenüber der Speisespannung weitgehend spannungsunempfindlich ausgebildet ist und daher eine Verschiebung des Potentials am Verbindungspunkt 38 infolge er Erhöhung der Spannung auf die erhöhte Gleichspannung erfasst, sind jedoch die erhöhte Gleichspannung und die Schwellenspannung des Schwellenwertverstärkers 62 so gewählt, dass die Spannungserhöhung nicht zu einem Ansprechen des Schwellenwertverstärkers 62 führt. Weiter führt eine geringe Verschmutzung der radioaktiven Strahlungsquelle 42 (Fig. 2) bei nicht erhöhter Speisegleichspannung zu einer entsprechenden Erhöhung des Innenwiderstands der Messkammer MK und zu einer entsprechenden Verschiebung des Potentials des Verbindungspunkts 38 zu demjenigen des Anschlusses 28 hin, jedoch reicht auch die hierdurch bewirkte Änderung der Eingangsspannung des Schwellenwertverstärkers 62 nicht aus, dessen Eingangs- Schwellenspannung zu erreichen, so dass kein Rauchalarmsignal erzeugt wird. Wenn dagegen infolge einer Verschmutzung der radioaktiven Strahlungsquelle 42 der Innenwiderstand der Meskammer MK um ein bestimmtes Mass erhöht ist und die beschriebene Spannungserhöhung erfolgt, so reicht dann die sich insgesamt ergebende Verschiebung des Potentials des Verbindungspunkts 38 aus, den Schwellenwertverstärker 62 ansprechen zu lassen. Dieser erzeugt daher dann in gleicher Weise wie beim Eintritt von Rauch in die Messkammer MK ein Ausgangssignal. Dieses Ausgangssignal soll jedoch in der Zentrale Z nicht zur Erzeugung des einem Rauchalarmsignal entsprechenden Signals R führen. Um die Erzeugung des Signals R zu vermeiden, wird, allgemein gesagt, in Abhängigkeit von der Umschaltung auf die höhere Gleichspannung die Weiterleitung des ggf. von der Rauchalarmschaltung erzeugten Rauchalarmsignals an die Auswerteschaltung 26 unterdrückt, und stattdessen wird das Rauchalarmsignal als Störungsalarmsignal zur Auswerteschaltung 26 übertragen. Um dies zu erreichen, weist beim Ausführungsbeispiel der lonisations-Brandmelder M einen beispielsweise eine Zenerdiode umfassenden Spannungspegeldetektor 68 auf, der dann ein Ausgangssignal abgibt, wenn die ihn speisende Spannung zwischen den Anschlüssen 28, 30 den Nennwert (20 V) der Speisegleichspannung um ein vorgegebenes Mass überschreitet, beispielsweise wenn die Spannung zwischen den Anschlüssen 28, 30 21 V überschreitet. Das dann von dem Spannungspegeldetektor 68 abgegebene Ausgangssignal von H-Pegel wird dem invertierenden Eingang des UND-Gliedes 64 zugeführt, wodurch die Übertragung des Ausgangssignals des Schwellenwertverstärkers 62 zum Alarmsignalgeber 66 gesperrt ist. Andererseits sind an die Ausgänge des Schwellenvertverstärkers 62 und des Spannungspegeldetektors 68 die Eingänge eines weiteren UND-Gliedes 70 angeschlossen, dessen UND-Behandlung im betrachteten Fall erfüllt ist und das somit ein Ausgangssignal erzeugt. Dieses wird über einen weiteren Eingang des ODER-Gliedes 48 dem Alarmsignalgeber 50 zugeführt, so dass dieser ein Störungsalarmsignal zur Zentrale Z übermittelt, aufgrund dessen das Signal S erzeugbar ist.If the test switch 20 in the central Z is actuated in the undisturbed idle state, the ionization fire detector M is supplied with a DC voltage of approximately 24 V, which is higher than the nominal value of the DC supply voltage, in the manner already explained; in the case of detectors installed on line L because of control center Z, the increased DC voltage can be somewhat reduced to the same value as the line voltage due to voltage drops along line L compared to the value mentioned. Although the threshold amplifier 62 is largely insensitive to the supply voltage and therefore detects a shift in the potential at the connection point 38 as a result of the increase in the voltage to the increased DC voltage, the increased DC voltage and the threshold voltage of the threshold amplifier 62 are selected such that the voltage increase does not increase a response of the threshold amplifier 62 leads. Furthermore, a slight contamination of the radioactive radiation source 42 (FIG. 2) with a not increased DC supply voltage leads to a corresponding increase in the internal resistance of the measuring chamber MK and to a corresponding shift in the potential of the connection point 38 to that of the connection 28, but the effect caused thereby is also sufficient The input voltage of the threshold amplifier 62 does not change from reaching its input threshold voltage, so that no smoke alarm signal is generated. On the other hand, if the internal resistance of the measuring chamber MK is increased by a certain amount as a result of contamination of the radioactive radiation source 42 and the described increase in voltage occurs, then the resulting overall shift in the potential of the connection point 38 is sufficient to make the threshold amplifier 62 respond. This then generates an output signal in the same way as when smoke enters the measuring chamber MK. However, this output signal should not lead to the generation of the signal R corresponding to a smoke alarm signal in the control center Z. In order to avoid the generation of the signal R, the forwarding of the smoke alarm signal possibly generated by the smoke alarm circuit to the evaluation circuit 26 is suppressed, depending on the switchover to the higher DC voltage, and instead the smoke alarm signal is transmitted to the evaluation circuit 26 as a fault alarm signal . To achieve this, in the exemplary embodiment of the ionization fire detector M has a voltage level detector 68, for example a zener diode, which emits an output signal when the voltage supplying it between the connections 28, 30 has a nominal value (20 V) of the DC supply voltage by a predetermined value Dimension exceeds, for example if the voltage between the terminals 28, 30 exceeds 21 V. The output signal of the H level which is then output by the voltage level detector 68 is fed to the inverting input of the AND gate 64, as a result of which the transmission of the output signal of the threshold value amplifier 62 to the alarm signal generator 66 is blocked. On the other hand, the inputs of a further AND gate 70 are connected to the outputs of the threshold amplifier 62 and the voltage level detector 68, the AND treatment of which is fulfilled in the case under consideration and which therefore generates an output signal. This is fed to the alarm signal generator 50 via a further input of the OR gate 48, so that the latter transmits a fault alarm signal to the control center Z, on the basis of which the signal S can be generated.

Abweichend vom Ausführungsbeispiel wäre es ebenfalls möglich, die Teile 48, 64, 68 und 70 in den lonisations-Brandmeldern M nicht vorzusehen, andererseits aber in der Zentrale Z die Auswerteschaltung 26 derart auszubilden, dass sie in Abhängigkeit von der Betätigung des Testschalters 20 gegen eine Abgabe des Signals R gesperrt ist, dagegen bei Empfang eines Rauchalarmsignals in diesem Fall das Signal S erzeugt. Die jeweils günstigere Lösung hängt im wesentlichen von der Anzahl von lonisations-Brandmeldern ab, die bei der Brandmeldeeinrichtung an die Zentrale Z angeschlossen sind. Weiterhin hat die anhand des Ausführungsbeispiels beschriebene Lösung den Vorteil, dass die an die Linie L angeschlossenen Brandmelder mit untereinander unterschiedlichen Alarmsignalgebern ausgerüstet sein können, deren unterschiedliche Störungs- und Rauchalarmsignale in der Zentrale Z beispielsweise aufgrund unterschiedlicher Frequenz unterschieden werden können.Deviating from the exemplary embodiment, it would also be possible not to provide the parts 48, 64, 68 and 70 in the ionization fire detectors M, but on the other hand to design the evaluation circuit 26 in the central station Z in such a way that, depending on the actuation of the test switch 20, they react against one Delivery of the signal R blocked is, however, the signal S is generated when a smoke alarm signal is received in this case. The cheaper solution essentially depends on the number of ionization fire detectors that are connected to the control center Z in the fire detection device. Furthermore, the solution described on the basis of the exemplary embodiment has the advantage that the fire detectors connected to line L can be equipped with mutually different alarm signal transmitters, whose different fault and smoke alarm signals can be distinguished in the control center Z, for example on the basis of different frequencies.

Anhand von Fig. 2 seien nun Aufbau und Wirkungsweise der Schwellenwertverstärker 46, 62 näher erläutert.The structure and mode of operation of the threshold value amplifiers 46, 62 will now be explained in more detail with reference to FIG. 2.

Der Schwellenwertverstärker 46 der Störungsalarmschaltung 46, 48, 50 (Fig. 1) weist eingangsseitig einen mit seiner Steuerelektrode an den Verbindungspunkt 38 angeschlossenen, selbstsperrenden p-Kanal-Feldeffekttransistor 72 auf, dessen Abflusselektrode über einen Lastwiderstand 74 mit demjenigen Anschluss 28 des lonisations-Brandmelders M verbunden ist, an dem die Referenzkammer RK liegt. Die Quellenelektrode des Feldeffekttransistors 72 ist an einen an der Speisegleichspannung liegenden Spannungsteiler 76, 78 angeschlossen. Derjenige Teilwiderstand 78 des Spannungsteilers 76, 78, der mit der Steuerstrecke (Steuerelektroden-Quellenelektroden-Strecke) des Feldeffecttransistors 72 eine parallel zur Messkammer MK liegende Reihenschaltung bildet, hat einen mehrfach geringeren Widerstandswert als der übrige Teilwiderstand 76 des Spannungsteilers 76, 78, so dass dann, wenn die Speisegleichspannung ihren Nennwert, aufweist und sich der lonisations-Brandmelder M im ungestörten Ruhezustand befindet, die am Teilwiderstand 78 abfallende Spannung betragsmässig geringer als die an der Messkammer MK abfallende Spannung ist, oder anders gesagt, das Potential der Quellenelektrode des Feldeffekttransistors 72 gegenüber dem Potential des Verbindungspunkts 38 zum Potential desjenigen Anschlusses 30 hin verschoben ist, dan dem die Messkammer MK liegt. Diese Potentialverschiebung, d.h. die Steuerspannung des Feldeffekttransistors 72, ist grösser als dessen Schwellenspannung. Daher leitet der Feldeffekttransistor 72 im ungestörten Ruhezustand. An die Abflusselektrode des Feldeffekttransistors 72 ist die Basis eines in diesem Zustand ebenfalls leitenden, bipolaren Transistors 80 angeschlossen, der in Reihe mit einem Lastwiderstand 82 zwischen den Anschlüssen 28, 30 liegt, und mit dem Kollektor des Transistors 80 ist die Basis eines weiteren bipolaren Transistors 84 verbunden, der in Reihe mit seinem Lastwiderstand 86 ebenfalls zwischen den Anschlüssen 28, 30 liegt, der jedoch im ungestörten Ruhezustand nichtleitend ist. Der Verbindungspunkt zwischen dem Transistor 84 und seinem Lastwiderstand 86 bildet den Ausgang 88 des Schwellenwertverstärkers 46, so dass der im ungestörten Ruhezustand und demgemäss im nicht angesprochenen Zustand des Schwellenwertverstärkers 46 als Ausgangssignal erzeugte Signalpegel das Potential des Anschlusses 30 hat, während der im angesprochenen Zustand erzeugte Signalpegel annähernd dem Potential des Anschlusses 28 entspricht.The threshold amplifier 46 of the fault alarm circuit 46, 48, 50 (FIG. 1) has on the input side a self-blocking p-channel field-effect transistor 72 connected with its control electrode to the connection point 38, the drain electrode of which via a load resistor 74 to the connection 28 of the ionization fire detector M is connected to which the reference chamber RK is located. The source electrode of the field effect transistor 72 is connected to a voltage divider 76, 78 connected to the DC supply voltage. The partial resistor 78 of the voltage divider 76, 78 that forms a series circuit lying parallel to the measuring chamber MK with the control path (control electrode-source electrode path) of the field effect transistor 72 has a resistance value that is several times lower than the rest of the partial resistance 76 of the voltage divider 76, 78, so that when the DC supply voltage has its nominal value and the ionization fire detector M is in the undisturbed idle state, the voltage drop across the partial resistor 78 is smaller in amount than the voltage drop across the measuring chamber MK, or in other words, the potential of the source electrode of the field effect transistor 72 is shifted relative to the potential of the connection point 38 toward the potential of the connection 30 at which the measuring chamber MK is located. This potential shift, i.e. the control voltage of the field effect transistor 72 is greater than its threshold voltage. The field effect transistor 72 therefore conducts in the undisturbed idle state. The base of a bipolar transistor 80 which is also conductive in this state and is connected in series with a load resistor 82 between the terminals 28, 30 is connected to the drain electrode of the field effect transistor 72, and the base of a further bipolar transistor is connected to the collector of the transistor 80 84 connected, which is also in series with its load resistor 86 between the connections 28, 30, but which is non-conductive in the undisturbed idle state. The connection point between the transistor 84 and its load resistor 86 forms the output 88 of the threshold amplifier 46, so that the signal level generated as an output signal in the undisturbed idle state and accordingly in the unresponsive state of the threshold amplifier 46 has the potential of the connection 30, while that generated in the addressed state Signal level approximately corresponds to the potential of the connection 28.

Hat die Speisegleichspannung ihren Nennwert und verschlechtert sich der Isolationswiderstand der Messkammer MK, so nähert sich das Potential des Verbindungspunkts 38 demjenigen des Anschlusses 30 und damit auch demjenigen der Quellenelektrode des Feldeffekttransistors 72, bis beim Unterschreiten eines vorgegebenen Schwellenwerts des Isolationswiderstandes die Steuerspannung des Feldeffekttransistors 72 unter dessen Schwellenspannung (Pinch-off-Spannung) absinkt, wordurch der Feldeffekttransistor 72 und der Transistor 80 nichtleitend werden, der Transistor 84 leitend wird und am Ausgang ein den angesprochenden Zustand des Schwellenwertverstärkers 46 kennzeichnendes Signal erscheint.If the DC supply voltage has its nominal value and the insulation resistance of the measuring chamber MK deteriorates, the potential of the connection point 38 approaches that of the connection 30 and thus also that of the source electrode of the field effect transistor 72, until the control voltage of the field effect transistor 72 drops below when the insulation resistance falls below a predetermined threshold value whose threshold voltage (pinch-off voltage) drops, as a result of which the field effect transistor 72 and the transistor 80 become non-conductive, the transistor 84 becomes conductive and a signal which indicates the relevant state of the threshold value amplifier 46 appears at the output.

Sinkt die Speisegleichspannung des lonisations-Brandmelders gegenüber ihrem Nennwert beispielsweise um 20% ab, so sinkt auch die Spannung an der Messkammer MK annähernd proportional ab, d.h. die beim Ausführungsbeispiel betragsmässig 10 V im Ruhezustand betragende Spannung beträgt nun nur noch annähernd 8 V. Es sei weiter angenommen, dass im ungestörten Ruhezustand aufgrund der Bemessung des Spannungsteilers 76, 78 und des Lastwiderstandes 74 der Spannungsabfall am Teilwiderstand 78 einen Betrag von 3 V gehabt habe, während die Schwellenspannung des Feldeffekttransistors 72 6 V beträgt, so dass die Steurspannung des Feldeffekttransistors 72 um 1 V über der Schwellenspannung lag. Aufgrund der Spannungabsentung um 20% verringert sich nun die am Teilwiderstand 78 abfallende Spannung ebenfalls, jedoch wegen des geringen Widerstandswertes des Teilwiderstands 78 um einen nur geringen absoluten Betrag. Daher bleibt die Summe des Spannungsabfalls am Teilwiderstand 78 und der Schwellenspannung des Feldeffekttransistors 72, d.i. die Eingangs-Schwellenspannung des Schwellenwertverstärkers 46, auch bei einer Absenkung der Speisegleichspannung annähernd konstant. Die Folge ist, dass die Spannung an der Messkammer MK (ursprünglich 10 V, jetzt 8 V) die Eingangs-Schwellenspannung (ursprünglich 9 V, jetzt als 8 V) unterschreitet, das der Feldeffekttransistor 72 nichtleitend wird und dass somit der Schwellenwertverstärker 46 in gleicher Weise ein Ausgangssignal erzeugt, wie dies beim Absinken des Isolationswiderstandes der Messkammer MK erfolgt.If, for example, the DC supply voltage of the ionization fire detector drops by 20% compared to its nominal value, the voltage at the measuring chamber MK also drops approximately proportionately, i.e. the voltage amounting to 10 V in the idle state in the exemplary embodiment is now only approximately 8 V. It is further assumed that in the undisturbed idle state due to the dimensioning of the voltage divider 76, 78 and the load resistor 74, the voltage drop across the partial resistor 78 had an amount of 3 V. have, while the threshold voltage of the field effect transistor 72 is 6 V, so that the control voltage of the field effect transistor 72 was 1 V above the threshold voltage. Due to the voltage sensing by 20%, the voltage drop across the partial resistor 78 is also reduced, however, because of the low resistance value of the partial resistor 78 by only a small absolute amount. Therefore, the sum of the voltage drop across the partial resistor 78 and the threshold voltage of the field effect transistor 72, i.e. the input threshold voltage of the threshold amplifier 46 is approximately constant even when the DC supply voltage is lowered. The result is that the voltage at the measuring chamber MK (originally 10 V, now 8 V) falls below the input threshold voltage (originally 9 V, now as 8 V), that the field-effect transistor 72 becomes non-conductive and that the threshold value amplifier 46 therefore does the same An output signal is generated as is the case when the insulation resistance of the measuring chamber MK decreases.

Durch das Nichtleitendwerden des Feldeffekttransistors 72 fällt dessen Hauptstrom fort, der im Ruhezustand über den Teilwiderstand 78 floss. damit die sich hierdurch ergebende Verringerung des Spannungsabfalls am Teilwiderstand 78 nicht die vorstehend erläuterte Spannungsunabhängigkeit der Eingangs-Schwellenspannung von der Speisespannung gefährdet, muss der Lastwiderstand 74 einen mehrfach höheren Widerstandswert als der Teilwiderstand 78 haben. Da sich die Eingangs-Schwellenspannung aus der Summe der am Teilwiderstand 78 abfallenden Spannung und der Schwellenspannung des Feldeffekttransistors 72 zusammensetzt und erstere in Abhängigkeit von der Speisespannung veränderlich, letztere dagegen konstant ist, ist es anzustreben, dem Feldeffekttransistor 72 eine relativ hohe Schwellenspannung zu geben. Diese kann in der Praxis zwischen 15% und 50% der Speisegleichspannung liegen. Als besonders zweckmässig hat sich die Verwendung eines Feldeffekttransistors 72 erwiesen, dessen Schwellenspannung annähernd 30% der Speisegleichspannung beträgt.When the field effect transistor 72 becomes non-conductive, its main current, which flowed through the partial resistor 78 in the idle state, ceases. So that the resultant reduction in the voltage drop across the partial resistor 78 does not endanger the voltage independence of the input threshold voltage from the supply voltage, as explained above. The load resistor 74 must have a resistance value several times higher than the partial resistor 78. Since the input threshold voltage is composed of the sum of the voltage dropping across the partial resistor 78 and the threshold voltage of the field effect transistor 72 and the former is variable as a function of the supply voltage, while the latter is constant, the aim should be to give the field effect transistor 72 a relatively high threshold voltage. In practice, this can be between 15% and 50% of the DC supply voltage. The use of a field effect transistor 72 has proven to be particularly expedient, the threshold voltage of which is approximately 30% of the DC supply voltage.

Der Schwellenwertverstärker 62 der Rauchalarmschaltung 62, 64, 66 (Fig. 1) weist wiederum eingangsseitig einen mit seiner Steuerelektrode an den Verbindungspunkt 38 der Kammern MK, RK angeschlossenen selbstperrenden p-Kanal-Feldeffekttransistor 90 auf. Dessen Abflusselektrode ist über einen von Teilwiderständen 92, 94 gebildeten Lastwiderstand mit demjenigen Anschluss 28 verbunden, an dem die Referenzkammer liegt, während seine Quellenelektrode an einen von Teilwiderständen 96,98 gebildeten Spannungsteiler angeschlossen ist. Die Widerstandswerte der Teilwiderstände 96,98 sind grössenordnungs mässig gleich, so dass im ungestörten Ruhezustand die Quellenelektrode des Feldeffekttransistors 90 auf einem annähernd dem Potential des Verbindungspunkts 38 gleichen Potential liegt, zweckmässig jedoch auf einem gegenüber dem Potential des Verbindungspunkts 38 etwas zum Potential des Anschlusses 30 verschobenen Potential, und der Feldeffekttransistor 90 nichtleitend ist. Das Potential der Quellenelektrode des Feldeffekttransistors 90 liegt also im ungestörten Ruhezustand näher an demjenigen des Anschlusses 28 als das Potential der Quellenelektrode des Feldeffekttransistors 72. An den Verbindungspunkt der Teilwiderstände 92, 94 des Lastwiderstands sind ein parallel zum Teilwiderstand 94 liegender Glättungskondensator 100 sowie die Basis eines bipolaren Transistors 102 angeschlossen, der in Reihe mit seinem Lastwiderstand 104 zwischen den Anschlüssen 28, 30 liegt und der im ungestörten Ruhezustand vom Feldeffekttransistor 90 nichtleitend gehalten ist. Zwischen dem Kollektor des Transistors 102 und dessen Lastwiderstand 104 ist der Ausgang 106 des Schwellenwertverstärkers 62 angeschlossen, so dass das Ausgangssignal wie dasjenige des Schwellenwertverstärkers 46 im ungestörten Ruhezustand als Pegel das Potential des Anschlusses 30 hat.The threshold amplifier 62 of the smoke alarm circuit 62, 64, 66 (FIG. 1) in turn has, on the input side, a self-blocking p-channel field effect transistor 90 connected with its control electrode to the connection point 38 of the chambers MK, RK. Its drain electrode is connected via a load resistor formed by partial resistors 92, 94 to the connection 28 at which the reference chamber is located, while its source electrode is connected to a voltage divider formed by partial resistors 96,98. The resistance values of the partial resistors 96, 98 are of the same order of magnitude, so that, in the undisturbed state of rest, the source electrode of the field effect transistor 90 is at a potential approximately the same as the potential of the connection point 38, but expediently at a potential relative to the potential of the connection point 38 shifted potential, and the field effect transistor 90 is non-conductive. The potential of the source electrode of the field effect transistor 90 is therefore closer to that of the connection 28 than the potential of the source electrode of the field effect transistor 72 in the undisturbed idle state. At the connection point of the partial resistors 92, 94 of the load resistor are a smoothing capacitor 100 lying parallel to the partial resistor 94 and the base of one Bipolar transistor 102 connected, which is connected in series with its load resistor 104 between the terminals 28, 30 and which is kept non-conductive by the field effect transistor 90 in the undisturbed idle state. The output 106 of the threshold amplifier 62 is connected between the collector of the transistor 102 and its load resistor 104, so that the output signal, like that of the threshold amplifier 46, has the potential of the terminal 30 in the undisturbed idle state.

Beim Nennwert der Speisegleichspannung ebenso wie bei zulässigen Unterspannungen und auch nach Umschaltung auf die höhere Gleichspannung führt in die Messkammer MK eindringender Rauch zu einer derartigen Verschiebung des Potentials des Verbindungspunktes 38 zum Anschluss 28 hin, dass hierdurch der Feldeffekttransistor 90 und der Transistor 102 leitend werden und ein entsprechendes Ausgangssignal abgegeben wird.At the nominal value of the DC supply voltage as well as at permissible undervoltage and even after switching to the higher DC voltage, smoke entering the measuring chamber MK leads to such a shift in the potential of the connection point 38 to the connection 28 that the field effect transistor 90 and the transistor 102 become conductive and a corresponding output signal is emitted.

Wie bereits erwähnt, führt eine geringe Verstaubung der Strahlungsquelle 42 zwar zu einer Erhöhung der Spannung an der Messkammer MK, auf die der Schwellenwertverstärker 62 jedoch beim Nennwert der Speisegleichspannung nicht anspricht. Wird dagegen mittels des Testschalters 20 in der Zentrale Z (Fig. 1) auf die erhöhte Gleichspannung umgeschaltet, so erhöht sich die Spannung an der Messkammer MK proportional, während sich die Eingangs-Schwellenspannung des Schwellenwertverstärkers 62 nur geringfügig ändert, so dass letztere überschritten wird und der Schwellenwertverstärkers 62 anspricht und ein entsprechendes Ausgangssignal erzeugt. Die nur geringfügige Veränderung der Eingangs-Schwellenspannung des Schwellenwertverstärkers 62 ist wie beim Schwellenwertverstärker 46 wiederum darauf zurückzuführen, dass die Eingangs-Schwellenspannung die Summe einer relativ geringen von der Speisespannung abhängigen, hier am Teilwiderstand 98 abfallenden Spannung und einer konstanten Schwellenspannung, hier derjenigen des Feldeffekttransistors 90, ist. Dementsprechend gelten die für die Bemessung der Schwellenspannung des Feldeffekttransistors 72 gemachten Ausführungen auch hinsichtlich der Schwellenspannung des Feldeffekttransistors 90, wobei diese Schwellenspannung jedoch die zusätzliche Bedingung erfüllen muss, dass sie so gross gewählt ist, dass die aufgrund der Umschaltung auf die höhere Gleichspannung an der Steuerstrecke des Feldeffekttransistors 90 auftretende Spannung nur dann die Schwellenspannung überschreitet, wenn die Messkammer aufgrund der Verschmutzung des sie ionisierenden Strahlers 42 einen gegenüber dem insoweit ungestörten Ruhezustand erhöhten Innenwiderstand aufweist.As already mentioned, slight dusting of the radiation source 42 leads to an increase in the voltage at the measuring chamber MK, to which the threshold amplifier 62 does not respond at the nominal value of the DC supply voltage. If, on the other hand, the test switch 20 in the control center Z (FIG. 1) is used to switch to the increased DC voltage, the voltage at the measuring chamber MK increases proportionally, while the input threshold voltage of the threshold amplifier 62 changes only slightly, so that the latter is exceeded and the threshold amplifier 62 responds and generates a corresponding output signal. The only slight change in the input threshold voltage of the threshold amplifier 62, as with the threshold amplifier 46, is in turn due to the fact that the input threshold voltage is the sum of a relatively small voltage-dependent voltage, which drops here at the partial resistor 98, and a constant threshold voltage, here that of the field effect transistor 90, is. Accordingly, the statements made for the dimensioning of the threshold voltage of the field-effect transistor 72 also apply with regard to the threshold voltage of the field-effect transistor 90, but this threshold voltage must meet the additional condition that it is chosen so large that it is due to the switchover to the higher DC voltage on the control path The voltage of the field-effect transistor 90 only exceeds the threshold voltage if the measuring chamber has an increased internal resistance compared to the undisturbed idle state due to the contamination of the radiator 42 ionizing it.

Würde man eine starke Verschmutzung der Strahlungsquelle 42 zulassen, so ergäbe sich eine so starke Spannungserhöhung über der Messkammer MK, dass hierauf wie beim Eintritt von Rauch die Rauchalarmschaltung 62, 64, 66 (Fig. 1) selbst dann ansprechen würde, wenn sie hinsichtlich ihrer Eingangs-Spannungsschwelle nicht von der Speisespannung unabhängig ausgebildet wäre. Durch die letzgenannte Massnahme in Verbindung mit der Umschaltbarkeit auf die höhere Gleichspannung ist jedoch die Möglichkeit gegeben, auch bereits eine relativ geringe Verschmutzung der Strahlungsquelle 42 von der Zentrale Z aus festzustellen, so dass auf starker Verschmutzung der Strahlungsquelle beruhende Fehlalarme vermieden werden, bei denen fälschlich Rauchalarmsignale erzeugt und in der Zentrale Z als solche ausgewertet werden.If one were to allow a high level of contamination of the radiation source 42, the voltage increase across the measuring chamber MK would be so great that the smoke alarm circuit 62, 64, 66 (FIG. 1) would respond to it as well as if smoke came in, even if it had to do with it Input voltage threshold would not be independent of the supply voltage. However, the latter measure in conjunction with the switchability to the higher DC voltage provides the possibility of already detecting a relatively low level of contamination of the radiation source 42 from the control center Z, so that false alarms based on excessive contamination of the radiation source are avoided, in which case they are erroneous Smoke alarm signals are generated and evaluated as such in the control center Z.

Claims (4)

1. A fire alarm means comprising: at least one ionization fire detector (M), in particular a plurality of ionization fire detectors (M) connected parallel to each other to a detecting line (L; 10, 12) and including a measuring chamber (MK) accessible to ambient air and a reference chamber (RK) more closed against the access of ambient air, the series connection of said measuring chamber and of said reference chamber being connected to a direct current supply voltage; a smoke alarm circuit (62, 64, 66) being connected at its input side to the connection point (38) of said chambers (MK, RK) and generating a smoke alarm signal when smoke enters into said measuring chamber (MK); and a fault alarm circuit (46, 48, 50) being supplied by said direct current supply voltage, being connected at its input side to the connection point (38) of said chambers (MK, RK), and generating a fault alarm signal when the insulation resistance of said measuring chamber (MK) drops below a predetermined threshold value; with the smoke alarm circuit (62, 64, 66) comprising at its input side a field-effect transistor (90) connected with its control electrode to the connection point (38) of said chambers (MK, RK), the drain electrode of said field-effect transistor being connected through a load resistor (92, 94) to that terminal (28) of said direct current supply voltage which said reference chamber (RK) is connected to; characterized in that for the additional emission of an alarm signal in case of faults influencing the voltage drop at said measuring chamber (MK) said fault alarm circuit (46, 48, 50) and said smoke alarm circuit (62, 64, 66) are, with respect to the input threshold voltage necessary for their actuation and being measured between their inputs and a terminal (28, 30) of said direct current supply voltage, at least approximately voltage- independent with respect to said direct current supply voltage, that the voltage source (14) providing said direct current supply voltage is switchable to a voltage which is increased with respect to the nominal value of said direct current supply voltage, and that the threshold voltage of said self-locking field-effect transistor (90) is such that the voltage occurring at the control path of said field-effect transistor (90) due to the switching to the increased voltage exceeds the threshold voltage only when said measuring chamber (MK), due to the contamination of the radiation source ionizing the measuring chamber shows an internal resistance increased with respect to the so far undisturbed status, and that in dependency from the switching to the increased voltage the transmission of the smoke alarm signal possibly generated by said smoke alarm circuit (62, 64, 66) to an evaluating circuit (26) is suppressed and a fault alarm signal is generated instead thereof and transmitted to the evaluating circuit (26).
2. A fire alarm means according to claim 1, wherein said fault alarm circuit (46, 48, 50) comprises at its input side a field-effect transistor (72) connected with its control electrode to the connection point (38) of said chambers (MK, RK), the drain electrode of said field-effect transistor being connected through a load resistor (74) to a terminal (28) of said direct current supply voltage, characterized in that the drain electrode of said self-locking field-effect transistor (72) is connected to that direct current supply voltage terminal (28) which said reference chamber (RK) is connected to, and that the source electrode of said field-effect transistor (72) is held in the undisturbed status as a potential which differs from the potential of the connection point (38) of said chambers (MK, RK) by more than the threshold voltage value of said field-effect transistor (72), said differing potential being shifted with respect to the connection point (38) towards the potential of that direct current supply voltage terminal (30) which said measuring chamber (MK) is connected to.
3. A fire alarm means according to claim 2, wherein the source electrode of said field-effect transistor (72) is connected to a voltage divider (76, 78) connected to said direct current supply voltage, characterized in that that partial resistor (78) of said voltage divider (76, 78) forming with the control path of said field-effect resistor (72) a series connection in parallel relationship with said measuring chamber (MK) has a resistance value which is many times lower than the resistance value of the remaining partial resistor (76) of said voltage divider (76, 78).
4. A fire alarm means according to one of the claims 1 to 3, characterized in that the potential of the source electrode of said field-effect transistor (90) is shifted in the undisturbed status with respect to the potential of the connection point (38) of said chambers (MK, RK) toward the potential of that direct current supply voltage terminal (30) which said measuring chamber (MK) is connected to.
EP81100552A 1980-02-08 1981-01-26 Ionisation fire alarm device with malfunction signalization Expired - Lifetime EP0033888B2 (en)

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AT81100552T ATE11346T1 (en) 1980-02-08 1981-01-26 IONIZATION FIRE DETECTION DEVICE WITH FAULT SIGNALING.

Applications Claiming Priority (2)

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DE3004753A DE3004753C2 (en) 1980-02-08 1980-02-08 Fire alarm device
DE3004753 1980-02-08

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US5189399A (en) * 1989-02-18 1993-02-23 Hartwig Beyersdorf Method of operating an ionization smoke alarm and ionization smoke alarm
DE3904979A1 (en) * 1989-02-18 1990-08-23 Beyersdorf Hartwig METHOD FOR OPERATING AN IONIZATION SMOKE DETECTOR AND IONIZATION SMOKE DETECTOR
CN106741986B (en) * 2016-12-21 2023-08-29 太原航空仪表有限公司 Rod vibrator with driving function
CN114325383A (en) * 2021-12-20 2022-04-12 中国人民解放军总参谋部第六十研究所 Brushless motor winding fault detection system and method for unmanned helicopter

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CH497755A (en) * 1969-06-24 1970-10-15 Cerberus Ag Ionization fire alarms
NO129270B (en) * 1970-05-16 1974-03-18 Preussag Ag Feuerschutz
CA1019077A (en) * 1974-01-07 1977-10-11 Wilbur L. Ogden Fire detector
CH586941A5 (en) * 1975-07-25 1977-04-15 Cerberus Ag
US4138664A (en) * 1976-12-14 1979-02-06 Pittway Corporation Warning device
US4302753A (en) * 1978-01-26 1981-11-24 Pittway Corporation Multi-function combustion detecting device

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FR2475768A1 (en) 1981-08-14
EP0033888B1 (en) 1985-01-16
EP0033888A3 (en) 1982-11-03
DE3004753C2 (en) 1983-12-22
DE3004753A1 (en) 1981-08-27
FR2475768B1 (en) 1983-09-23
EP0033888A2 (en) 1981-08-19
ATE11346T1 (en) 1985-02-15

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