EP0125485B1 - Signal suppression circuit for optical smoke detectors - Google Patents

Signal suppression circuit for optical smoke detectors Download PDF

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Publication number
EP0125485B1
EP0125485B1 EP84103961A EP84103961A EP0125485B1 EP 0125485 B1 EP0125485 B1 EP 0125485B1 EP 84103961 A EP84103961 A EP 84103961A EP 84103961 A EP84103961 A EP 84103961A EP 0125485 B1 EP0125485 B1 EP 0125485B1
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EP
European Patent Office
Prior art keywords
alarm
voltage
time
mmv1
measured value
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
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EP84103961A
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German (de)
French (fr)
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EP0125485A1 (en
Inventor
Karsten Dipl.-Ing. Poulsen
Peer Dr.-Ing. Thilo
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Siemens AG
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Siemens AG
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Priority to AT84103961T priority Critical patent/ATE25885T1/en
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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
    • G08B29/18—Prevention or correction of operating errors
    • G08B29/20—Calibration, including self-calibrating arrangements
    • G08B29/24—Self-calibration, e.g. compensating for environmental drift or ageing of components
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
    • G08B17/107—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device for detecting light-scattering due to smoke
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B26/00—Alarm systems in which substations are interrogated in succession by a central station
    • G08B26/005—Alarm systems in which substations are interrogated in succession by a central station with substations connected in series, e.g. cascade

Definitions

  • the invention relates to a circuit arrangement for suppressing interfering signals in optical smoke detectors with a light-emitting diode which emits in pulses and a photodiode receiving the scattered light from the light-emitting diode in a fire alarm system, with the individual detectors of a detection line being delayed in a chain-like manner in a predetermined sequence in a cyclical interrogation from a control center the detector line is switched on and the delay time until the subsequent detector is switched on corresponds to the respective analog detector measured value and the detector measured value and the address are determined in the control center from the time of connection.
  • electromagnetic interference e.g. interference light, interference pulses
  • shielding labele.g. metallic shielding
  • repeated scanning e.g., laser scanning
  • These multiple scans are often logically linked to the transmission signal.
  • the influence of changes in the ambient temperature on the reporting behavior is either accepted or compensated for by high-quality, temperature-constant components or by additional temperature-compensating elements.
  • the measured fire parameter is transmitted to the control center as an analog signal and processed there with high-quality evaluation algorithms.
  • the measured value determined must be available for the query for a few milliseconds. All faults that occur during this time inevitably falsify the actual detector measured value.
  • other interference can also occur.
  • an interference voltage arises which is caused by switching on the interrogation voltage. The size of the interference voltage depends on the steepness of the interrogation voltage and thus on the position of the detector on the detection line and can be larger than the useful signal.
  • the object of the invention is therefore to provide a circuit arrangement for optical smoke detectors which transmit the analog detector measured value in a fire alarm system according to the so-called pulse detector system, which reduces or eliminates such interference.
  • optical smoke detector has a voltage supply device, a transmission circuit that can be controlled with the detector interrogation, for generating transmission pulses for the light-emitting diode of a specific period of time, which is considerably shorter than the interrogation period of a detector is one of the photodiode with amplifier connected downstream, can be controlled by the transmitter circuit instantaneous value memory for the short-term storage of the analog detector measured value and a downstream voltage / time converter, which is delayed according to the detector measured value via a switching transistor, the subsequent detector to the detector line turns on.
  • an instantaneous value memory a so-called sample and hold circuit
  • the optical smoke detector has a transmission circuit for generating transmission pulses for the light-emitting diode and the above-mentioned instantaneous value storage circuit, the transmission circuit being started with the detector inquiry in order to generate only a very short light pulse of high power, so that the signal-to-noise ratio is further enlarged.
  • disturbances that occur synchronously with the pulsed measurement are damped by a time filter.
  • This time filter is implemented, for example, by a time-shifted opening of the sample and hold circuit, or in a particularly advantageous manner by delaying the measuring time and opening the sample and hold circuit together.
  • the sample and hold circuit expediently has a timing element whose time constant causes the sample and hold circuit to open at different times.
  • the transmission circuit is preceded by a delay element which is started when the interrogation voltage is applied to the optical fire detector and which controls the transmission circuit after the set delay time has expired.
  • a further embodiment of the invention avoids component-consuming and energy-consuming compensation networks to compensate for the temperature response, which preferably have electro-optical components. Rather, it advantageously uses the inevitable temperature dependency of the other functionally necessary components and also allows the use of particularly inexpensive components with normal, temperature-dependent, that is to say "apparently bad" temperature behavior. For this purpose, according to the invention, special switching measures are taken, as result from the subclaims.
  • a detection line ML is connected to a control center Z according to FIG. 1, wherein a plurality of detectors M1 to Mn can be connected to the detection line ML (two-wire line) in a predetermined order.
  • Each Mi detector has three connection terminals.
  • One line (+ UL) of the ML detection line is common to all Mi detectors.
  • the second line (-UL) of the detection line is switched in each Mi detector by the MKi detector contact.
  • All detection lines (MLi) are connected to a central detector connection module (not shown here) in the control center Z and are queried one after the other.
  • FIG. 2a shows the voltage curve and FIG. 2b shows the current profile of a detection line (ML) with four detectors (M).
  • the operation of the chain synchronization method is as follows.
  • the signal line (ML) is supplied with voltage, the idle voltage URU.
  • the detector contacts MKi according to Fig. 1 are closed in all detectors Mi.
  • the interrogation of an alarm line ML begins with a start signal TST, the line voltage UL being reduced almost to zero and to the start voltage UST.
  • the detector contacts MKi in all detectors Mi are opened.
  • the query TAB begins with the application of the query voltage UAB, which is less than the quiescent voltage URU, to the detection line ML. Since all detector contacts MKi are open, the voltage UAB is only present at the first detector M1 of this detection line ML, and only this pulls its supply current IL according to FIG. 2b over the detection line.
  • a timer not shown here, is started in detector M1, the running time T1 of which depends on the measured value of this detector M1. After the measurement-dependent delay time T1 has elapsed, the detector M1 consumes an increased current during the time t, shown in FIG. 2b with ILP, which is evaluated in the control center.
  • the known detector circuit for increased current consumption is described in DE-A-2638068.
  • the detector contact MK1 of the first detector is closed, and thus the interrogation voltage UAb is applied to the second detector M2, where the process just described is repeated.
  • the interrogation voltage UAb is applied to the second detector M2, where the process just described is repeated.
  • all detectors Mi of an ML detection line are switched on in sequence. If no further current pulse ILP is detected on the detection line ML by the control center (Z) during the time TE (FIG. 2b), which of course must be longer than the maximum delay time Ti max of a detector Mi, this means that all detector contacts MKi are switched through and the query of this line can be ended.
  • the line voltage UL is switched to the idle value URU.
  • the time intervals T1, T2, T3, ... between the successive current pulses ILP are measured and evaluated, which are dependent on measured values from the corresponding detectors M1, M2, M3, ...
  • the detector address can be determined by counting the current pulses ILP.
  • a storage capacitor is provided in the detector Mi, which is arranged in the voltage supply device SPV of the respective detector (FIG. 3 ). This capacitor, which is not specifically shown there, is almost charged to the value of the idle voltage URU during the idle state TRU and discharges during the time for the start signal TST and the query TAB.
  • This capacitor is dimensioned in such a way that it can never discharge below the interrogation voltage UAB during the stated time, so that charging currents which would interfere with the interrogation process are avoided. Reloading does not start again until the open circuit voltage URU is applied.
  • FIG. 3 An optical fire detector according to the invention for the chain synchronization principle is shown in FIG. 3 in the block diagram, but without the instantaneous value memory according to the invention.
  • the RM optical smoke detector is connected to the ML detection line, the two-wire line (+ UL) and (-UL).
  • the voltage supply device SPV is connected to the detection line ML and supplies the transmitter circuit MMV1 and the light-emitting diode LED on the one hand and the photodiode FD and the voltage / time converter VTC on the other hand via the amplifier VER.
  • the out The voltage / time converter VTC leads to the switching transistor TR, which switches depending on the detector measured value from the voltage / time converter to the next detector.
  • a light pulse of the light-emitting diode LED is caused via the transmitter device MMV1 according to FIG. 3, is scattered by smoke particles in the measuring chamber (not shown), received by the photodiode FD and a voltage / time via the amplifier VER -VC converter supplied, which in turn controls the switching transistor TR to the next detector.
  • a connection point A is drawn between the amplifier VER and the voltage / time converter VTC;
  • the sample and hold circuit according to the invention is arranged between the connection point A and the voltage / time converter VTC, as will be shown later.
  • FIG. 4 shows various voltage diagrams as a function of the time t, in order to illustrate the signal curve of a detector according to FIG. 3.
  • the transmission voltage US for the transmission pulse or the light pulse of the light-emitting diode is shown under the line voltage UL.
  • an interference level in the form of the interference voltage UST ⁇ which influences the useful voltage UN at the output of the photodiode FD or the amplifier VER according to FIG. 3, so that an effective output signal UA at the connection point A results from the sum of the interference voltage UST ⁇ and the useful voltage UN results in the output voltage UA.
  • FIG. 4 shows how a light pulse is triggered when the interrogation voltage UAB is switched on, the light is scattered and the scattered light is received. It is shown how the interference voltage UST ⁇ disturbs the useful signal UN and thus the result, i.e. falsifies the effective output signal UA. This is remedied with the sample and hold circuit according to the invention.
  • FIG. 5 shows a sample-and-hold circuit SHS (instantaneous value memory) for an optical smoke detector RM with the switching transistor TRH1, the control elements CH1 and DH and the measured value memory CH2.
  • the sample and hold circuit SHS is arranged between the amplifier VER at connection point A and the voltage / time converter VTC at connection point B. The interference signal suppression caused thereby is shown in FIG.
  • FIG. 6 shows voltage diagrams similar to FIG. 4, but with the interference signal suppression achieved.
  • the light pulse of the light-emitting diode represented by the voltage US of the transmission pulse below the line voltage UL
  • the interference, interference voltage UST ⁇ is reduced .
  • the useful signal UN at the output (connection point A) of the amplifier VER is shorter and more intensive in accordance with the transmission pulse.
  • the effective output signal UB after the sample and hold circuit SHS at connection point B clearly shows this.
  • the output voltage UB is the sum of the interference voltage UST ⁇ and the useful signal UN.
  • FIG. 7 shows the line voltage UL as the first voltage diagram, which has a steep interference edge ST ⁇ FL1 when the first detector of the detection line is switched on (application of the interrogation voltage UAB) (shown in dashed lines).
  • the interference edge ST ⁇ FLn of the last detector (Mn) of a detection line (drawn solid) is less steep.
  • the voltage diagram of the transmission signal US for the light-emitting diode and for the control of the delay-responding sample and hold circuit (SHS) is shown.
  • the measuring process i.e. the current pulses through the light-emitting diode (LED) and the opening time for the sample and hold circuit (SHS) are delayed according to the invention until the interference, d. H. experience has shown that the interference signal UST ⁇ and the transients in the amplifier have ended.
  • the transmission signal US is pending for a short time TP.
  • the interference signal UST ⁇ at connection point A according to FIG. 5 is significantly greater for the first detector M1 than for the nth detector Mn.
  • the interference signal UST ⁇ is here without the optical signal, i. H. the received signal of the photodiode shown.
  • the effective output signal UB at connection point B i.e. shown at the output of the sample and hold circuit (SHS). It can be clearly seen that after the short transmission time TP for the light pulse of the light-emitting diode (LED) the interference signals UST ⁇ have essentially subsided, so that the delayed opening of the sample and hold circuit (SHS) results in a significantly less disturbed output signal UB at connection point B.
  • FIG. 1 shows a circuit arrangement according to the invention in a block diagram for an optical smoke detector, in which the measurement process is delayed by a delay element MMV2, which is connected upstream of the transmit circuit MMV1.
  • the voltage curve at connection point A and at connection point B is shown in FIG. 9.
  • FIG. 9 This is shown in FIG. 9, below the diagram of the line voltage UL with the interference edges ST ⁇ FL1 and ST ⁇ FLn when the interrogation voltage UAB is applied, the delay (TV) of the Transmission signal US is shown.
  • the delay element MMV2 When the interrogation voltage UAB is applied, the delay element MMV2 is started in accordance with FIG. After the delay time TV has elapsed, the transmitter circuit MMV1 is activated, which in turn emits the current pulse for the light-emitting diode LED for the pulse duration TP.
  • the sample and hold circuit (SHS) is only opened after the delay time TVD and the pulse duration TP of the transmit pulse (US) have elapsed.
  • FIG. 9 shows that in this case the interference signal UST ⁇ at the time of the measurement TM, regardless of its original size, has decayed to such an extent that it can no longer falsify the measurement.
  • the profile of the interference voltage UST ⁇ is shown below the signal profile of the transmission voltage US, the interference signal UST ⁇ at connection point A having decayed to almost zero after these times (TV + TP).
  • the effective useful voltage UB at the connection point B can then reach the voltage / time converter at the time TM without influencing the interference signal.
  • 9 shows the interference voltage UST ⁇ and the output voltage UB at the connection point B without a signal voltage from the photodiode.
  • FIG. 10 shows an advantageous embodiment of the delay element MMV2 according to the invention in the optical smoke detector RM.
  • the delay element MMV2 When the interrogation voltage (UAB) is applied, the delay element MMV2 is started, which controls the downstream transmission circuit MMV1 after the delay time TV has elapsed.
  • the delay time TV arises here in that the base-emitter voltage UBE of the transistor TRV is kept below the switch-on threshold of the transistor TV by the capacitor CV until the delay time has expired.
  • CBE means the base-emitter capacitance and UBE the base-emitter voltage of the transistor TRV.
  • the delay time TV is determined not only by the time constant of the RC element from the resistor RV and the capacitor CV, but also by the base-emitter capacitance CBE.
  • a change in temperature also changes the useful signal UN at the output of the amplifier VER.
  • the useful signal becomes smaller with increasing temperature.
  • This effect is essentially due to the decreasing conversion efficiency of the electro-optical components, the light-emitting diode LED and the photodiode FD, with increasing temperature and cannot be avoided in principle.
  • advantageous temperature compensation is achieved by means of a special circuit arrangement of the transmission circuit MMV1, without having to use further, for example temperature-stabilized, components in addition to the components which are necessary anyway.
  • the circuit arrangement according to the invention, as described in FIG. 11, advantageously allows inexpensive, temperature-dependent components to be used.
  • FIG. 11 shows an exemplary embodiment of the transmission circuit MMV1 according to the invention.
  • the delay element MMV2 was also shown in accordance with FIG. 10.
  • the transistor TRV becomes conductive via the resistor RV of the delay element MMV2.
  • the transistors T1 and T2 of the transmit circuit MMV1 become conductive via the timing element R1, R2, R3, C of the transmit circuit MMV1, so that a current flows through the light-emitting diode LED.
  • the magnitude of this current is determined by the stabilized voltage Ucc and the resistor R4.
  • a Zener diode ZD with positive temperature coefficients and a carbon resistor with negative temperature coefficients are provided for the resistor R4.
  • UBE2 is the base-emitter voltage of transistor TR2 and UCE1 is the collective-emitter voltage of transistor TR2 and UCE1 is the collector-emitter voltage of transistor TR1.
  • SHS sample and hold circuit
  • FIG. 12 shows an advantageous circuit arrangement for the sample and hold circuit according to FIG. 10.
  • the sample and hold circuit SHS is again arranged between the connection points A and B and is controlled by the transmit circuit MMV 1.
  • the sample and hold circuit SHS has a field effect transistor TRH2, the gate of which is driven by the transmit circuit MMV1.
  • a resistor RH2 is arranged between the connection point A and the field effect transistor TRH2, which can also be arranged behind the transistor TRH2 or else can be the internal resistance of the amplifier (VER).
  • the capacitor CH2 is the measured value storage capacitor of the sample and hold circuit.
  • the effective useful voltage is tapped at connection point B, which reaches the voltage / time converter (VTC) and controls the switching transistor (TR) with a delay in accordance with the analog detector measured value of the optical smoke detector (RM) in order to switch on the next detector.
  • VTC voltage / time converter
  • the time constant TH for storing the measurement signal in the sample and hold circuit is determined by the RC element from the resistor RH2 and the capacitor CH2. This time constant TH is chosen so that it is the condition Fulfills.
  • TP is the transmit pulse duration according to the above equation. This ensures that the voltage with which the capacitor CH2 is recharged becomes dependent on the transmission pulse duration TP.
  • the mode of operation of the temperature compensation is explained in more detail with reference to FIG. 13.
  • the transmission signal UR4 of the light-emitting diode (LED) is shown in FIG. 13a as a function of the time t. Below this, the output voltage UA at the connection point A is shown in FIG. 13b and below the output voltage UB at the connection point B in FIG. 13c.
  • the transmission signal UR4 is proportional to the current ILD through the light-emitting diode LED and satisfies the equation
  • the sample and hold circuit SHS according to FIG. 12 is conductive for the duration TP of the transmission signal (US or UR4), otherwise it is blocked.
  • the temperature dependency which is shown for -30 ° C and + 70 ° C, affects not only the transmit signal UR4, but also the output signals at connection points A and B.
  • the output voltage UA at connection point A is equal to the received signal of the sample and hold circuit.
  • This signal is also shown for the two temperatures -30 ° C and + 70 ° C in Fig.13b.
  • the transmission pulse duration TP becomes longer as the temperature increases. With increasing temperature, the amplitude of the received signal UA before the sample and hold circuit at connection point A becomes lower, however, the received signal UA before the sample and hold circuit at connection point A is present longer with increasing temperature corresponding to the pulse duration TP.
  • the output signal UB at connection point B i.e. at the output of the sample and hold circuit (SHS), is independent of the temperature fluctuation (measurement time TM -30 ° C) or measurement time + 70 ° C), as with the one in Fig. 13c measurement signal MS is illustrated. In this way it is possible to obtain a largely temperature-independent output signal UB, ie detector measurement signal MS, at connection point B without additional elements for temperature compensation. This increases the measurement accuracy and improves fire detection.
  • SHS sample and hold circuit

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Abstract

1. A circuit arrangement in a fire alarm system, for suppressing interference signals in optical smoke detectors (RM) with a luminescence diode (LED) which transmits in pulsed fashion and with a photo-diode (FD) which receives diffused light from the luminescence diode (LED), where, during cyclic interrogation from central control (Z), the individual alarms (Mi) of an alarm line (ML) are connected in cascade to the alarm line (ML) in a predetermined sequence with a time delay and where the delay time until the connection of the following alarm corresponds to the analogue alarm measured value in question, and in the central control the alarm measured value and the alarm address are determined from the time of the connection, characterised in that the optical smoke detector (RM) comprises a voltage supply device (SPV) ; a transmitting circuit (MMV1) driven by the alarm interrogation (UAB) and serves to produce transmitted pulses (US) for the luminescence diode (LED), where the duration (TP) of the transmitted pulses is substantially shorter than the interrogation duration of an alarm ; an instantaneous value store (SHS), connected to the output of the photo-diode (FD) via the amplifier (VER), driven by the transmitting circuit (MMV1) to temporarily store the analogue alarm measured value ; and a voltage/time converter (VTC) connected to the output of the instantaneous value store, which connects the following alarm (Mi) to the alarm line (ML) via a switch-through transistor (TR) with a delay in accordance with the alarm measured value.

Description

Die Erfindung bezieht sich auf eine Schaltungsanordnung zur Störsignalunterdrückung in optischen Rauchmeldern mit einer pulsweise sendenden Leuchtdiode und einer das Streulicht der Leuchtdiode empfangenden Fotodiode in einer Brandmeldeanlage, wobei bei der zyklischen Abfrage von einer Zentrale aus, die einzelnen Melder einer Meldelinie zeitverzögert in vorgegebener Reihenfolge kettenförmig an die Meldelinie angeschaltet werden und die Verzögerungszeit bis zum Anschalten des nachfolgenden Melders dem jeweiligen analogen Meldermesswert entspricht und in der Zentrale aus dem Zeitpunkt der Anschaltung der Meldermesswert und die Meldeadresse ermittelt wird.The invention relates to a circuit arrangement for suppressing interfering signals in optical smoke detectors with a light-emitting diode which emits in pulses and a photodiode receiving the scattered light from the light-emitting diode in a fire alarm system, with the individual detectors of a detection line being delayed in a chain-like manner in a predetermined sequence in a cyclical interrogation from a control center the detector line is switched on and the delay time until the subsequent detector is switched on corresponds to the respective analog detector measured value and the detector measured value and the address are determined in the control center from the time of connection.

Bei herkömmlichen optischen Rauchmeldern werden elektromagnetische Störeinflüsse (z. B. Störlicht, Störimpulse) teils durch Abschirmung (Labyrinth, metallische Schirmung) und teils durch mehrmaliges Abtasten minimiert. Diese mehrmaligen Abtastungen werden oft mit dem Sendesignal logisch verknüpft. Der Einfluss von Änderungen der Umgebungstemperatur auf das Meldeverhalten wird entweder in Kauf genommen oder aber durch hochwertige, temperaturkonstante Bauteile oder durch zusätzliche temperaturkompensierende Elemente ausgeglichen.With conventional optical smoke detectors, electromagnetic interference (e.g. interference light, interference pulses) is minimized partly by shielding (labyrinth, metallic shielding) and partly by repeated scanning. These multiple scans are often logically linked to the transmission signal. The influence of changes in the ambient temperature on the reporting behavior is either accepted or compensated for by high-quality, temperature-constant components or by additional temperature-compensating elements.

Bei analogwertübertragenden Brandmeldern wird die gemessene Brandkenngrösse als analoges Signal zur Zentrale übertragen und dort mit hochwertigen Auswertealgorithmen bearbeitet. In dem bekannten Pulsmeldersystem (DE-B-2533382) muss dazu für die Abfrage der ermittelte Messwert für einige Millisekunden zur Verfügung stehen. Alle Störungen, die während dieser Zeit auftreten, verfälschen zwangsläufig den eigentlichen Meldermesswert. Neben einem sporadischen Störpegel, der das Nutzsignal eines optischen Rauchmelders am Ausgang der Fotodiode störend beeinflussen kann, können noch weitere Störungen auftreten. Mit dem in vorgegebener Reihenfolge zeitverzögerten Anschalten der einzelnen Melder an die Meldelinie entsteht eine Störspannung, die durch das Einschalten der Abfragespannung hervorgerufen wird. Dabei ist die Grösse der Störspannung von der Anstiegssteilheit der Abfragespannung und damit von der Lage des Melders an der Meldelinie abhängig und kann grösser als das Nutzsignal sein.In the case of fire detectors that transmit analog values, the measured fire parameter is transmitted to the control center as an analog signal and processed there with high-quality evaluation algorithms. In the known pulse detector system (DE-B-2533382), the measured value determined must be available for the query for a few milliseconds. All faults that occur during this time inevitably falsify the actual detector measured value. In addition to a sporadic interference level, which can interfere with the useful signal of an optical smoke detector at the output of the photodiode, other interference can also occur. When the individual detectors are switched on to the detection line with a time delay in a predetermined order, an interference voltage arises which is caused by switching on the interrogation voltage. The size of the interference voltage depends on the steepness of the interrogation voltage and thus on the position of the detector on the detection line and can be larger than the useful signal.

Aufgabe der Erfindung ist daher, eine Schaltungsanordnung für optische Rauchmelder, die den analogen Meldermesswert in einer Brandmeldeanlage nach dem sogenannten Pulsmeldersystem übertragen, anzugeben, die derartige Störeinflüsse reduziert bzw. eliminiert.The object of the invention is therefore to provide a circuit arrangement for optical smoke detectors which transmit the analog detector measured value in a fire alarm system according to the so-called pulse detector system, which reduces or eliminates such interference.

Diese Aufgabe wird erfindungsgemäss mit einer Schaltungsanordnung zur Störsignalunterdrückung in optischen Rauchmeldern in einer oben beschriebenen Brandmeldeanlage dadurch gelöst, dass der optische Rauchmelder eine Spannungsversorgungseinrichtung, eine mit der Melderabfrage ansteuerbare Sendeschaltung zur Erzeugung von Sendeimpulsen für die Leuchtdiode einer bestimmten Zeitdauer, die wesentlich kürzer als die Abfragedauer eines Melders ist, einen der Fotodiode mit Verstärker nachgeschalteten, von der Sendeschaltung ansteuerbaren Momentanwertspeicher zur kurzzeitigen Speicherung des analogen Meldermesswerts und einen diesem nachgeordneten Spannungs-/Zeit-Wandler aufweist, der entsprechend dem Meldermesswert zeitverzögert über einen Durchschalt-Transistor den nachfolgenden Melder an die Meldelinie anschaltet.This object is achieved according to the invention with a circuit arrangement for suppressing interference signals in optical smoke detectors in a fire detection system described above in that the optical smoke detector has a voltage supply device, a transmission circuit that can be controlled with the detector interrogation, for generating transmission pulses for the light-emitting diode of a specific period of time, which is considerably shorter than the interrogation period of a detector is one of the photodiode with amplifier connected downstream, can be controlled by the transmitter circuit instantaneous value memory for the short-term storage of the analog detector measured value and a downstream voltage / time converter, which is delayed according to the detector measured value via a switching transistor, the subsequent detector to the detector line turns on.

Erfindungsgemäss wird ein Momentanwertspeicher, eine sogenannte Sample- and Hold-Schaltung verwendet, die den analogen Meldermesswert für eine sehr kurze Zeit, z.B. 80 µs, einspeichert. Nur während dieser Zeit wird über die Sample- and Hold-Schaltung der Meldermesswertspeicher mit der eigentlichen Messeinrichtung verbunden, so dass dadurch auch nur in dieser Zeit Störsignale empfangen werden können. Daher weist der optische Rauchmelder neben einer Spannungsversorgungseinrichtung eine Sendeschaltung zur Erzeugung von Sendeimpulsen für die Leuchtdiode und die oben genannte Momentanwertspeicherschaltung auf, wobei die Sendeschaltung mit der Melderabfrage in Gang gesetzt wird, um erfindungsgemäss nur einen sehr kurzen Lichtimpuls hoher Leistung zu erzeugen, damit der Störabstand weiter vergrössert wird.According to the invention, an instantaneous value memory, a so-called sample and hold circuit, is used, which stores the analog detector measured value for a very short time, e.g. 80 µs, saved. Only during this time is the detector measured value memory connected to the actual measuring device via the sample and hold circuit, so that interference signals can only be received during this time. Therefore, in addition to a voltage supply device, the optical smoke detector has a transmission circuit for generating transmission pulses for the light-emitting diode and the above-mentioned instantaneous value storage circuit, the transmission circuit being started with the detector inquiry in order to generate only a very short light pulse of high power, so that the signal-to-noise ratio is further enlarged.

In einer weiteren Ausgestaltung der Erfindung werden Störeinflüsse, die synchron mit der pulsweisen Messung auftreten, durch ein Zeitfilter gedämpft. Dieses Zeitfilter wird beispielsweise durch eine zeitversetzte Öffnung der Sample- and Hold-Schaltung realisiert oder in besonders vorteilhafter Weise durch gemeinsame Verzögerung von Messzeit und Öffnung der Sample- and Hold-Schaltung. Dazu weist zweckmässigerweise die Sample- and Hold-Schaltung ein Zeitglied auf, dessen Zeitkonstante ein zeitversetztes Öffnen der Sample- and Hold-Schaltung bewirkt. Ferner ist der Sendeschaltung ein Verzögerungsglied vorgeschaltet, das mit dem Anlegen der Abfragespannung an den optischen Brandmelder gestartet wird und die Sendeschaltung nach Ablauf der eingestellten Verzögerungszeit ansteuert.In a further embodiment of the invention, disturbances that occur synchronously with the pulsed measurement are damped by a time filter. This time filter is implemented, for example, by a time-shifted opening of the sample and hold circuit, or in a particularly advantageous manner by delaying the measuring time and opening the sample and hold circuit together. For this purpose, the sample and hold circuit expediently has a timing element whose time constant causes the sample and hold circuit to open at different times. Furthermore, the transmission circuit is preceded by a delay element which is started when the interrogation voltage is applied to the optical fire detector and which controls the transmission circuit after the set delay time has expired.

Eine weitere Ausgestaltung der Erfindung vermeidet bauteileaufwendige und energieverzehrende Kompensationsnetzwerke zum Ausgleich des Temperaturgangs, den vorzugsweise elektrooptische Bauelemente haben. Sie nutzt vielmehr in vorteilhafter Weise die unvermeidliche Temperaturabhängigkeit der übrigen funktionsnotwendigen Komponenten und gestattet darüber hinaus die Verwendung besonders preiswerter Komponenten mit normalen, temperaturabhängigen, also «scheinbar schlechten» Temperaturverhalten. Dazu sind erfindungsgemäss besondere Schaltmassnahmen getroffen, wie sie sich aus den Unteransprüchen ergeben.A further embodiment of the invention avoids component-consuming and energy-consuming compensation networks to compensate for the temperature response, which preferably have electro-optical components. Rather, it advantageously uses the inevitable temperature dependency of the other functionally necessary components and also allows the use of particularly inexpensive components with normal, temperature-dependent, that is to say "apparently bad" temperature behavior. For this purpose, according to the invention, special switching measures are taken, as result from the subclaims.

Weitere Einzelheiten und Vorteile der Erfindung werden anhand der Zeichnungen im folgenden näher erläutert. Dabei zeigen die

  • Fig.1 eine Meldelinie mit Meldern nach dem bekannten Kettensynchronisationsprinzip,
  • Fig.2 den Spannungs- bzw. Stromverlauf gemäss Fig. 1,
  • Fig.3 ein Blockschaltbild eines erfindungsgemässen optischen Brandmelders nach dem Kettensynchronisationsprinzip, jedoch ohne die Sample- and Hold-Schaltung (Momentanwertspeicher),
  • Fig. 4 Spannungsdiagramme gemäss Fig. 3,
  • Fig.5 eine erfindungsgemässe Sample- and Hold-Schaltung in einem optischen Brandmelder gemäss Fig. 3,
  • Fig. 6 Spannungsdiagramme gemäss Fig. 5,
  • Fig.7 Spannungsdiagramme in Abhängigkeit von Störsignalen,
  • Fig.8 ein erfindungsgemässes Blockschaltbild in einer weiteren Ausführungsform eines optischen Rauchmelders,
  • Fig. 9 Spannungsdiagramme gemäss Fig. 8, bei auftretenden Störsignalen,
  • Fig.10 eine mögliche Schaltungsanordnung eines optischen Rauchmelders mit einem Verzögerungsglied,
  • Fig. 11 eine mögliche Schaltungsanordnung der Sendeschaltung gemäss Fig. 8,
  • Fig. 12 eine mögliche Ausführungsform einer Sample- and Hold-Schaltung für den optischen Rauchmelder gemäss Fig. 8, und
  • Fig. 13 Spannungsdiagramme gemäss der Fig.11 und 12 bezüglich der Temperaturkompensation.
Further details and advantages of the invention are explained in more detail below with reference to the drawings. The show
  • 1 a detection line with detectors according to the known chain synchronization principle,
  • 2 shows the voltage or current curve according to FIG. 1,
  • 3 shows a block diagram of an optical fire detector according to the invention based on the chain synchronization principle, but without the sample and hold circuit (instantaneous value memory),
  • 4 voltage diagrams according to FIG. 3,
  • 5 shows an inventive sample and hold circuit in an optical fire detector according to FIG. 3,
  • 6 voltage diagrams according to FIG. 5,
  • Fig. 7 voltage diagrams depending on interference signals,
  • 8 shows a block diagram according to the invention in a further embodiment of an optical smoke detector,
  • 9 voltage diagrams according to FIG. 8, with interference signals occurring,
  • 10 shows a possible circuit arrangement of an optical smoke detector with a delay element,
  • 11 shows a possible circuit arrangement of the transmission circuit according to FIG. 8,
  • FIG. 12 shows a possible embodiment of a sample and hold circuit for the optical smoke detector according to FIG. 8, and
  • 13 shows voltage diagrams according to FIGS. 11 and 12 with regard to the temperature compensation.

In dem bekannten Pulsmeldersystem nach dem Kettensynchronisationsprinzip ist gemäss Fig.1 eine Meldelinie ML an eine Zentrale Z angeschlossen, wobei eine Vielzahl von Meldern M1 bis Mn an die Meldelinie ML (Zweidrahtleitung) in vorgebbarer Reihenfolge anschaltbar sind. Jeder Melder Mi hat drei Anschlussklemmen. Eine Leitung (+UL) der Meldelinie ML ist gemeinsam für alle Melder Mi. Der zweite Leiter (-UL) der Meldelinie wird in jedem Melder Mi durch den Melderkontakt MKi geschaltet. Alle Meldelinien (MLi) sind an eine hier nicht dargestellte zentrale Melderanschaltbaugruppe in der Zentrale Z angeschlossen und werden von dieser nacheinander abgefragt.In the known pulse detector system based on the chain synchronization principle, a detection line ML is connected to a control center Z according to FIG. 1, wherein a plurality of detectors M1 to Mn can be connected to the detection line ML (two-wire line) in a predetermined order. Each Mi detector has three connection terminals. One line (+ UL) of the ML detection line is common to all Mi detectors. The second line (-UL) of the detection line is switched in each Mi detector by the MKi detector contact. All detection lines (MLi) are connected to a central detector connection module (not shown here) in the control center Z and are queried one after the other.

In Fig.2a ist der Spannungs- und in Fig. 2b der Stromverlauf einer Meldelinie (ML) mit vier Meldern (M) gezeigt. Die Wirkungsweise des Kettensynchronisationsverfahrens ist folgende. Im Ruhezustand TRU wird die Meldelinie (ML) mit Spannung, der Ruhespannung URU, versorgt. Die Melderkontakte MKi gemäss Fig.1 sind in allen Meldern Mi geschlossen. Die Abfrage einer Meldelinie ML beginnt mit einem Startsignal TST, wobei die Linienspannung UL nahezu auf Null, auf die Startspannung UST reduziert wird. Während des Startsignals TST, d.h., solange die Startspannung UST ansteht, werden die Melderkontakte MKi in allen Meldern Mi geöffnet. Die Abfrage TAB beginnt mit dem Anlegen der Abfragespannung UAB, die kleiner als die Ruhespannung URU ist, an die Meldelinie ML. Da alle Melderkontakte MKi geöffnet sind, liegt die Spannung UAB nur am ersten Melder M1 dieser Meldelinie ML, und nur dieser zieht seinen Versorgungsstrom IL gemäss Fig.2b über die Meldelinie. Im Melder M1 wird ein hier nicht dargestelltes Zeitglied gestartet, dessen Laufzeit T1 abhängt vom Messwert dieses Melders M1. Nach Ablauf der messwertabhängigen Verzögerungszeit T1 nimmt der Melder M1 während der Zeit t einen erhöhten Strom auf, in Fig.2b mit ILP dargestellt, der in der Zentrale ausgewertet wird. Die bekannte Melderschaltung zur erhöhten Stromaufnahme ist in der DE-A-2638068 beschrieben. Gleichzeitig mit dem zusätzlichen Stromimpuls wird auch der Melderkontakt MK1 des ersten Melders geschlossen, und somit die Abfragespannung UAb an den zweiten Melder M2 angelegt, wo sich der eben beschriebene Vorgang wiederholt. So werden der Reihe nach alle Melder Mi einer Meldelinie ML angeschaltet. Wird von der Zentrale (Z) während der Zeit TE (Fig.2b), die natürlich länger als die maximale Verzögerungszeit Timax eines Melders Mi sein muss, kein weiterer Stromimpuls ILP auf der Meldelinie ML erkannt, so heisst das, dass alle Melderkontakte MKi durchgeschaltet sind und die Abfrage dieser Linie beendet werden kann. Die Linienspannung UL wird auf den Ruhewert URU umgeschaltet.2a shows the voltage curve and FIG. 2b shows the current profile of a detection line (ML) with four detectors (M). The operation of the chain synchronization method is as follows. In the idle state TRU, the signal line (ML) is supplied with voltage, the idle voltage URU. The detector contacts MKi according to Fig. 1 are closed in all detectors Mi. The interrogation of an alarm line ML begins with a start signal TST, the line voltage UL being reduced almost to zero and to the start voltage UST. During the start signal TST, ie as long as the start voltage UST is present, the detector contacts MKi in all detectors Mi are opened. The query TAB begins with the application of the query voltage UAB, which is less than the quiescent voltage URU, to the detection line ML. Since all detector contacts MKi are open, the voltage UAB is only present at the first detector M1 of this detection line ML, and only this pulls its supply current IL according to FIG. 2b over the detection line. A timer, not shown here, is started in detector M1, the running time T1 of which depends on the measured value of this detector M1. After the measurement-dependent delay time T1 has elapsed, the detector M1 consumes an increased current during the time t, shown in FIG. 2b with ILP, which is evaluated in the control center. The known detector circuit for increased current consumption is described in DE-A-2638068. Simultaneously with the additional current pulse, the detector contact MK1 of the first detector is closed, and thus the interrogation voltage UAb is applied to the second detector M2, where the process just described is repeated. In this way, all detectors Mi of an ML detection line are switched on in sequence. If no further current pulse ILP is detected on the detection line ML by the control center (Z) during the time TE (FIG. 2b), which of course must be longer than the maximum delay time Ti max of a detector Mi, this means that all detector contacts MKi are switched through and the query of this line can be ended. The line voltage UL is switched to the idle value URU.

In der Zentrale werden die zeitlichen Abstände T1, T2, T3, ... zwischen den aufeinanderfolgenden Stromimpulsen ILP gemessen und bewertet, die abhängig von Messwerten der entsprechenden Melder M1, M2, M3, ... sind. Die Melderadresse kann durch Mitzählen der Stromimpulse ILP ermittelt werden. Um die Energieversorgung auch während des Startimpulses TST und während der Abfrage TAB solange bis der vorhergehende Melderkontakt MKi die Meldelinie ML durchgeschaltet hat, sicherzustellen, ist im Melder Mi jeweils ein Speicherkondensator vorgesehen, der in der Spannungsversorgungseinrichtung SPV des jeweiligen Melders angeordnet ist (Fig.3). Dieser dort nicht eigens gezeigte Kondensator wird während der Zeit des Ruhezustandes TRU nahezu auf den Wert der Ruhespannung URU aufgeladen und entlädt sich während der Zeit für das Startsignal TST und die Abfrage TAB. Dabei wird dieser Kondensator so dimensioniert, dass er sich während der genannten Zeit nie unter die Abfragespannung UAB entladen kann, so dass durch Ladeströme, die den Abfragevorgang störend beeinflussen würden, vermieden werden. Die Nachladung beginnt erst wieder nach Anlegen der Ruhespannung URU.In the control center, the time intervals T1, T2, T3, ... between the successive current pulses ILP are measured and evaluated, which are dependent on measured values from the corresponding detectors M1, M2, M3, ... The detector address can be determined by counting the current pulses ILP. In order to ensure the energy supply also during the start pulse TST and during the interrogation TAB until the previous detector contact MKi has switched through the detection line ML, a storage capacitor is provided in the detector Mi, which is arranged in the voltage supply device SPV of the respective detector (FIG. 3 ). This capacitor, which is not specifically shown there, is almost charged to the value of the idle voltage URU during the idle state TRU and discharges during the time for the start signal TST and the query TAB. This capacitor is dimensioned in such a way that it can never discharge below the interrogation voltage UAB during the stated time, so that charging currents which would interfere with the interrogation process are avoided. Reloading does not start again until the open circuit voltage URU is applied.

In Fig.3 ist ein erfindungsgemässer optischer Brandmelder für das Kettensynchronisationsprinzip im Blockschaltbild dargestellt, jedoch ohne den erfindungsgemässen Momentanwertspeicher. Der optische Rauchmelder RM ist an die Meldelinie ML, die Zweidrahtleitung (+UL) und (-UL) angeschlossen. An der Meldelinie ML ist die Spannungsversorgungseinrichtung SPV angeschaltet, die einerseits die Sendeschaltung MMV1 und die Leuchtdiode LED und andererseits über den Verstärker VER die Fotodiode FD und den Spannungs-/Zeit-Wandler VTC versorgt. Der Ausgang des Spannungs-/Zeit-Wandlers VTC führt zu dem Durchschalt-Transistor TR, der in Abhängigkeit des Meldermesswerts vom Spannungs-/Zeit-Wandler zum nächsten Melder durchschaltet.An optical fire detector according to the invention for the chain synchronization principle is shown in FIG. 3 in the block diagram, but without the instantaneous value memory according to the invention. The RM optical smoke detector is connected to the ML detection line, the two-wire line (+ UL) and (-UL). The voltage supply device SPV is connected to the detection line ML and supplies the transmitter circuit MMV1 and the light-emitting diode LED on the one hand and the photodiode FD and the voltage / time converter VTC on the other hand via the amplifier VER. The out The voltage / time converter VTC leads to the switching transistor TR, which switches depending on the detector measured value from the voltage / time converter to the next detector.

Nach Anlegen der Abfragespannung UAB gemäss Fig. wird über die Sendeeinrichtung MMV1 gmäss Fig.3 ein Lichtimpuls der Leuchtdiode LED verursacht, in der nicht dargestellten Messkammer an eventuell vorhandenen Rauchpartikeln gestreut, von der Fotodiode FD empfangen und über den Verstärker VER einem Spannungs-/Zeit-Wandler VTC zugeführt, der seinerseits den Durchschalt-Transistor TR zum nächsten Melder ansteuert. Zwischen dem Verstärker VER und dem Spannungs-/Zeit-Wandler VTC ist ein Anschlusspunkt A gezeichnet; zwischen dem Anschlusspunkt A und dem Spannungs-/Zeit-Wandler VTC wird die erfindungsgemässe Sample- and Hold-Schaltung, wie später noch gezeigt, angeordnet.After application of the interrogation voltage UAB according to FIG. 1, a light pulse of the light-emitting diode LED is caused via the transmitter device MMV1 according to FIG. 3, is scattered by smoke particles in the measuring chamber (not shown), received by the photodiode FD and a voltage / time via the amplifier VER -VC converter supplied, which in turn controls the switching transistor TR to the next detector. A connection point A is drawn between the amplifier VER and the voltage / time converter VTC; The sample and hold circuit according to the invention is arranged between the connection point A and the voltage / time converter VTC, as will be shown later.

In Fig. 4 sind verschiedene Spannungsdiagramme in Abhängigkeit von der Zeit t untereinander dargestellt, um den Signalverlauf eines Melders gemäss Fig.3 zu veranschaulichen. Unter der Linienspannung UL ist die Sendespannung US für den Sendeimpuls bzw. den Lichtimpuls der Leuchtdiode dargestellt. Darunter ist ein Störpegel in Form der Störspannung USTÖ dargestellt, der die Nutzspannung UN am Ausgang der Fotodiode FD bzw. des Verstärkers VER gemäss Fig. 3 beeinflusst, so dass sich ein wirksames Ausgangssignal UA am Anschlusspunkt A aus der Summe der Störspannung USTÖ und der Nutzspannung UN ergibt, nämlich die Ausgangsspannung UA. Fig.4 zeigt also, wie mit dem Einschalten der Abfragespannung UAB ein Lichtimpuls ausgelöst, das Licht gestreut und das Streulicht empfangen wird. Dabei ist gezeigt, wie die Störspannung USTÖ das Nutzsignal UN störend beeinflusst und damit das Ergebnis, d.h. das wirksame Ausgangssignal UA verfälscht. Dem wird mit der erfindungsgemässen Sample- and Hold-Schaltung abgeholfen.4 shows various voltage diagrams as a function of the time t, in order to illustrate the signal curve of a detector according to FIG. 3. The transmission voltage US for the transmission pulse or the light pulse of the light-emitting diode is shown under the line voltage UL. Below this is shown an interference level in the form of the interference voltage USTÖ, which influences the useful voltage UN at the output of the photodiode FD or the amplifier VER according to FIG. 3, so that an effective output signal UA at the connection point A results from the sum of the interference voltage USTÖ and the useful voltage UN results in the output voltage UA. FIG. 4 shows how a light pulse is triggered when the interrogation voltage UAB is switched on, the light is scattered and the scattered light is received. It is shown how the interference voltage USTÖ disturbs the useful signal UN and thus the result, i.e. falsifies the effective output signal UA. This is remedied with the sample and hold circuit according to the invention.

In Fig.5 ist eine erfindungsgemässe Sampleand Hold-Schaltung SHS (Momentanwertspeicher) für einen optischen Rauchmelder RM mit dem Schalttransistor TRH1, den Ansteuerelementen CH1 und DH sowie dem Messwertspeicher CH2 dargestellt. Die Sample- and Hold-Schaltung SHS ist zwischen dem Verstärker VER am Anschlusspunkt A und dem Spannungs-/Zeit-Wandler VTC am Anschlusspunkt B angeordnet. Die dadurch bewirkte Störsignalunterdrückung ist in Fig. dargestellt.5 shows a sample-and-hold circuit SHS (instantaneous value memory) for an optical smoke detector RM with the switching transistor TRH1, the control elements CH1 and DH and the measured value memory CH2. The sample and hold circuit SHS is arranged between the amplifier VER at connection point A and the voltage / time converter VTC at connection point B. The interference signal suppression caused thereby is shown in FIG.

Fig.6 zeigt Spannungsdiagramme ähnlich der Fig.4, jedoch mit der erzielten Störsignalunterdrückung. In Fig.6 ist zu erkennen, wie dadurch einerseits der Lichtimpuls der Leuchtdiode, dargestellt durch die Spannung US des Sendeimpulses unterhalb der Linienspannung UL, bei der Abfrage mit dem Anlegen der Abfragespannung UAB verkürzt und intensiviert und andererseits der Störeinfluss, Störspannung USTÖ, reduziert wird. Das Nutzsignal UN am Ausgang (Anschlusspunkt A) des Verstärkers VER ist entsprechend dem Sendeimpuls kürzer und auch intensiver. Das wirksame Ausgangssignal UB nach der Sample- and Hold-Schaltung SHS am Anschlusspunkt B zeigt dies deutlich. Dabei ist dieAusgangsspannung UB die Summe aus der Störspannung USTÖ und dem Nutzsignal UN. Mit dieser erfindungsgemässen Schaltungsanordnung können also die Störsignale in vorteilhafter Weise unterdrückt werden. Da jedoch weitere Störsignale, wie oben schon erläutert, auftreten können, wurden noch weitere schaltungstechnische Massnahmen getroffen.FIG. 6 shows voltage diagrams similar to FIG. 4, but with the interference signal suppression achieved. In Fig. 6 it can be seen how, on the one hand, the light pulse of the light-emitting diode, represented by the voltage US of the transmission pulse below the line voltage UL, is shortened and intensified when the query voltage UAB is applied and, on the other hand, the interference, interference voltage USTÖ, is reduced . The useful signal UN at the output (connection point A) of the amplifier VER is shorter and more intensive in accordance with the transmission pulse. The effective output signal UB after the sample and hold circuit SHS at connection point B clearly shows this. The output voltage UB is the sum of the interference voltage USTÖ and the useful signal UN. With this circuit arrangement according to the invention, the interference signals can thus be suppressed in an advantageous manner. However, since further interference signals can occur, as already explained above, further circuitry measures have been taken.

Fig. zeigt die Auswirkung einer Störspannung, die durch das Einschalten der Abfragespannung UAB hervorgerufen wird. Ihre Grösse ist von der Anstiegssteilheit STÖFL der Abfragespannung UAB und damit von der Lage des Melders an der Meldelinie abhängig und kann grösser als das Nutzsignal sein. IN Fig.7 ist als erstes Spannungsdiagramm die Linienspannung UL gezeigt, die mit dem Anschalten des ersten Melders der Meldelinie (Anlegen der Abfragespannung UAB) eine steile Störflanke STÖFL1 hat (gestrichelt gezeichnet). Die Störflanke STÖFLn des letzten Melders (Mn) einer Meldelinie (durchgezogen gezeichnet) ist weniger steil. Unter dem Diagramm der Linienspannung UL ist das Spannungsdiagramm des Sendesignals US für die Leuchtdiode und für die Ansteuerung der verzögernd ansprechenden Sample- and Hold-Schaltung (SHS) dargestellt. Um diesen Störeinfluss zu verringern, wird der Messvorgang, d.h. die Stromimpulse durch die Leuchtdiode (LED) und die Öffnungszeit für die Sample- and Hold-Schaltung (SHS) erfindungsgemäss so lange verzögert, bis der Störeinfluss, d. h. das Störsignal USTÖ und die Einschwingvorgänge im Verstärker, erfahrungsgemäss zu Ende sind. Das Sendesignal US steht für die kurze Zeit TP an. Das Störsignal USTÖ am Anschlusspunkt A gemäss Fig.5 ist für den ersten Melder M1 wesentlich grösser als für den n-ten Melder Mn. Das Störsignal USTÖ ist hierbei ohne das optische Signal, d. h. das Empfangssignal der Fotodiode, dargestellt. Unter dem Spannungsdiagramm des Störsignals USTÖ ist das wirksame Ausgangssignal UB am Anschlusspunkt B, d.h. am Ausgang der Sample- and Hold-Schaltung (SHS) dargestellt. Dabei ist deutlich zu erkennen, dass nach Ablauf der kurzen Sendezeit TP für den Lichtimpuls der Leuchtdiode (LED) die Störsignale USTÖ im wesentlichen abgeklungen sind, so dass das verzögerte Öffnen der Sample- and Hold-Schaltung (SHS) ein wesentlich geringer gestörtes Ausgangssignal UB am Anschlusspunkt B bewirkt.Fig. Shows the effect of an interference voltage, which is caused by switching on the interrogation voltage UAB. Their size depends on the steepness of rise STÖFL of the interrogation voltage UAB and thus on the position of the detector on the detection line and can be larger than the useful signal. FIG. 7 shows the line voltage UL as the first voltage diagram, which has a steep interference edge STÖFL1 when the first detector of the detection line is switched on (application of the interrogation voltage UAB) (shown in dashed lines). The interference edge STÖFLn of the last detector (Mn) of a detection line (drawn solid) is less steep. Below the diagram of the line voltage UL, the voltage diagram of the transmission signal US for the light-emitting diode and for the control of the delay-responding sample and hold circuit (SHS) is shown. To reduce this interference, the measuring process, i.e. the current pulses through the light-emitting diode (LED) and the opening time for the sample and hold circuit (SHS) are delayed according to the invention until the interference, d. H. experience has shown that the interference signal USTÖ and the transients in the amplifier have ended. The transmission signal US is pending for a short time TP. The interference signal USTÖ at connection point A according to FIG. 5 is significantly greater for the first detector M1 than for the nth detector Mn. The interference signal USTÖ is here without the optical signal, i. H. the received signal of the photodiode shown. The effective output signal UB at connection point B, i.e. shown at the output of the sample and hold circuit (SHS). It can be clearly seen that after the short transmission time TP for the light pulse of the light-emitting diode (LED) the interference signals USTÖ have essentially subsided, so that the delayed opening of the sample and hold circuit (SHS) results in a significantly less disturbed output signal UB at connection point B.

Fig. zeigt eine erfindungsgemässe Schaltungsanordnung im Blockschaltbild für einen optischen Rauchmelder, in dem der Messvorgang durch ein Verzögerungsglied MMV2, das der Sendeschaltung MMV1 vorgeschaltet ist, verzögert wird. Entsprechend dazu ist in Fig. 9 der Spannungsverlauf am Anschlusspunkt A und am Anschlusspunkt B dargestellt.1 shows a circuit arrangement according to the invention in a block diagram for an optical smoke detector, in which the measurement process is delayed by a delay element MMV2, which is connected upstream of the transmit circuit MMV1. Correspondingly, the voltage curve at connection point A and at connection point B is shown in FIG. 9.

Dies zeigt Fig.9, wobei unterhalb des Diagramms der Linienspannung UL mit den Störflanken STÖFL1 und STÖFLn beim Anlegen der Abfragespannung UAB die Verzögerung (TV) des Sendesignals US dargestellt ist. Mit dem Anlegen der Abfragespannung UAB wird das Verzögerungsglied MMV2 gemäss Fig.8 in Gang gesetzt. Nach Ablauf der Verzögerungszeit TV wird die Sendeschaltung MMV1 angesteuert, die ihrerseits für die Pulsdauer TP den Stromimpuls für die Leuchtdiode LED abgibt.This is shown in FIG. 9, below the diagram of the line voltage UL with the interference edges STÖFL1 and STÖFLn when the interrogation voltage UAB is applied, the delay (TV) of the Transmission signal US is shown. When the interrogation voltage UAB is applied, the delay element MMV2 is started in accordance with FIG. After the delay time TV has elapsed, the transmitter circuit MMV1 is activated, which in turn emits the current pulse for the light-emitting diode LED for the pulse duration TP.

Erst nach Ablauf der Verzögerungszeit TVD und der Impulsduer TP des Sendeimpulses (US) wird die Sample- and Hold-Schaltung (SHS) geöffnet. Fig.9 zeigt, dass in diesem Fall das Störsignal USTÖ zum Zeitpunkt der Messung TM, unabhängig von seiner ursprünglichen Grösse, soweit abgeklungen ist, dass es die Messung nicht mehr verfälschen kann. Der Verlauf der Störspannung USTÖ ist unter dem Signalverlauf der Sendespannung US dargestellt, wobei das Störsingal USTÖ am Anschlusspunkt A nach Ablauf dieser Zeiten (TV + TP) fast auf Null abgeklungen ist. Die wirksame Nutzspannung UB am Anschlusspunkt B kann dann zum Zeitpunkt TM ohne Störsignalbeeinflussung an den Spannungs-/Zeit-Wandier gelangen. In Fig.9 sind die Störspannung USTÖ und die Ausgangsspannung UB am Anschlusspunkt B ohne Signalspannung von der Fotodiode her dargestellt.The sample and hold circuit (SHS) is only opened after the delay time TVD and the pulse duration TP of the transmit pulse (US) have elapsed. FIG. 9 shows that in this case the interference signal USTÖ at the time of the measurement TM, regardless of its original size, has decayed to such an extent that it can no longer falsify the measurement. The profile of the interference voltage USTÖ is shown below the signal profile of the transmission voltage US, the interference signal USTÖ at connection point A having decayed to almost zero after these times (TV + TP). The effective useful voltage UB at the connection point B can then reach the voltage / time converter at the time TM without influencing the interference signal. 9 shows the interference voltage USTÖ and the output voltage UB at the connection point B without a signal voltage from the photodiode.

In Fig. 10 ist eine vorteilhafte Ausführungsform des erfindungsgemässen Verzögerungsgliedes MMV2 im optischen Rauchmelder RM dargestellt. Mit dem Anlegen der Abfragespannung (UAB) wird das Verzögerungsglied MMV2 in Gang gesetzt, das nach Ablauf der Verzögerungszeit TV die nachgeschaltete Sendeschaltung MMV1 ansteuert. Die Verzögerungszeit TV kommt hierbei dadurch zustande, dass die Basis-Emitter-Spannung UBE des Transistors TRV durch den Kondensator CV solange unter der Einschaltschwelle des Transistors TV gehalten wird, bis die Verzögerungszeit

Figure imgb0001
abgelaufen ist. Dabei bedeutet CBE die Basis-Emitter-Kapazität und UBE die Basis-Emitter-Spannung des Transistors TRV. Die Verzögerungszeit TV wird dabei nicht nur durch die Zeitkonstante des RC-Gliedes vom Widerstand RV und den Kondensator CV, sondern auch von der Basis-Emitter-Kapazität CBE bestimmt.FIG. 10 shows an advantageous embodiment of the delay element MMV2 according to the invention in the optical smoke detector RM. When the interrogation voltage (UAB) is applied, the delay element MMV2 is started, which controls the downstream transmission circuit MMV1 after the delay time TV has elapsed. The delay time TV arises here in that the base-emitter voltage UBE of the transistor TRV is kept below the switch-on threshold of the transistor TV by the capacitor CV until the delay time
Figure imgb0001
 has expired. CBE means the base-emitter capacitance and UBE the base-emitter voltage of the transistor TRV. The delay time TV is determined not only by the time constant of the RC element from the resistor RV and the capacitor CV, but also by the base-emitter capacitance CBE.

Durch eine Temperaturänderung verändert sich ebenfalls das Nutzsignal UN am Ausgang des Verstärkers VER. Bei einer Schaltungsanordnung, wie in Fig.10 dargestellt, wird mit zunehmender Temperatur das Nutzsignal kleiner. Dieser Effekt ist im wesentlichen auf den mit zunehmender Temperatur sinkenden Umsetzungs-Wirkungsgrad der elektro-optischen Bauelemente, der Leuchtdiode LED und der Fotodiode FD, zurückzuführen und ist prinzipiell nicht zu vermeiden. Erfindungsgemäss wird ein vorteilhafte Temperaturkompensation durch eine besondere Schaltungsanordnung der Sendeschaltung MMV1 erreicht, ohne zusätzlich zu den ohnehin notwendigen Bauelementen weitere, beispielsweise temperaturstabilisierte Bauteile verwenden zu müssen. Die erfindungsgemässe Schaltungsanordnung, wie sie in Fig. 11 beschrieben wird, erlaubt in vorteilhafter Weise, preisgünstige, temperaturabhängige Bauelemente zu verwenden.A change in temperature also changes the useful signal UN at the output of the amplifier VER. In the case of a circuit arrangement, as shown in FIG. 10, the useful signal becomes smaller with increasing temperature. This effect is essentially due to the decreasing conversion efficiency of the electro-optical components, the light-emitting diode LED and the photodiode FD, with increasing temperature and cannot be avoided in principle. According to the invention, advantageous temperature compensation is achieved by means of a special circuit arrangement of the transmission circuit MMV1, without having to use further, for example temperature-stabilized, components in addition to the components which are necessary anyway. The circuit arrangement according to the invention, as described in FIG. 11, advantageously allows inexpensive, temperature-dependent components to be used.

In Fig.11 ist ein erfindungsgemässes Ausführungsbeispiel der Sendeschaltung MMV1 dargestellt. Dabei wurde das Verzögerungsglied MMV2 gemäss Fig.10 mit abgebildet. Beim Anstieg der Linienspannung UL von Null auf die Abfragespannung UAB wird über den Widerstand RV des Verzögerungsgliedes MMV2 der Transistor TRV leitend. Dieser steuert die Sendeschaltung MMV1 an. Dabei werden über das Zeitglied R1, R2, R3, C der Sendeschaltung MMV1 die Transistoren T1 und T2 der Sendeschaltung MMV1 leitend, so dass ein Strom über die Leuchtdiode LED fliesst. Die Grösse dieses Stromes ist durch die stabilisierte Spannung Ucc und den Widerstand R4 bestimmt. Die stabilisierte Spannung Ucc wird aus der Versorgungsspannung US = 22V abgeleitet und über den Vorwiderstand R5 und die Zenerdiode ZD stabilisiert. Dabei ist erfindungsgemäss eine Zenerdiode ZD mit positiven Temperaturkoeffizienten und ein Karbonwiderstand mit negativen Temperaturkoeffizienten für den Widerstand R4 vorgesehen. Dadurch, und durch die mit steigender Temperatur kleiner werdenden Basis-Emitter-Spannung UBE2 des Transistors TR2 steigt der Strom durch die Leuchtdiode LED mit wachsender Temperatur und kompensiert damit einen Teil des Lichtverlustes. Eine weitere Kompensation wird durch eine Änderung der Pulsdauer erreicht. Die Sendeimpulsdauer TP lässt sich annähernd durch folgende Gleichung ausdrücken:

Figure imgb0002
11 shows an exemplary embodiment of the transmission circuit MMV1 according to the invention. The delay element MMV2 was also shown in accordance with FIG. 10. When the line voltage UL rises from zero to the interrogation voltage UAB, the transistor TRV becomes conductive via the resistor RV of the delay element MMV2. This controls the transmit circuit MMV1. The transistors T1 and T2 of the transmit circuit MMV1 become conductive via the timing element R1, R2, R3, C of the transmit circuit MMV1, so that a current flows through the light-emitting diode LED. The magnitude of this current is determined by the stabilized voltage Ucc and the resistor R4. The stabilized voltage Ucc is derived from the supply voltage US = 22V and stabilized via the series resistor R5 and the Zener diode ZD. According to the invention, a Zener diode ZD with positive temperature coefficients and a carbon resistor with negative temperature coefficients are provided for the resistor R4. As a result, and because the base-emitter voltage UBE2 of the transistor TR2, which decreases with increasing temperature, the current through the light-emitting diode LED increases with increasing temperature and thus compensates for part of the loss of light. A further compensation is achieved by changing the pulse duration. The transmission pulse duration TP can be approximately expressed by the following equation:
Figure imgb0002

Dabei ist UBE2 die Basis-Emitter-Spannung des Transistors TR2 und UCE1 die Kollektiv-Emitter-Spannung des Transistors TR2 und UCE1 die Kollektor-Emitter-Spannung des Transistors TR1. Durch Verwendung von handelsüblichen Bauelementen mit normalen Temperaturgängen wird bei dieser Schaltungsanordnung die Impulsdauer TP mit steignder Temperatur länger. Dieser Vorteil wird im Zusammenhang mit einer vorteilhaften Ausführungsform einer Sample- and Hold-Schaltung (SHS), die in Fig.12 dargestellt ist, später noch erläutert.UBE2 is the base-emitter voltage of transistor TR2 and UCE1 is the collective-emitter voltage of transistor TR2 and UCE1 is the collector-emitter voltage of transistor TR1. By using commercially available components with normal temperature responses, the pulse duration TP becomes longer with increasing temperature in this circuit arrangement. This advantage will be explained later in connection with an advantageous embodiment of a sample and hold circuit (SHS), which is shown in FIG.

Fig. 12 zeigt eine vorteilhafte Schaltungsanordnung für die Sample- and Hold-Schaltung gemäss der Fig. 10. Die Sample- and Hold-Schaltung SHS ist dabei wieder zwischen den Anschlusspunkten A und B angeordnet und wird von der Sendeschaltung MMV 1 angesteuert. Die Sample- and Hold-Schaltung SHS weist einen Feldeffekttransistor TRH2 auf, dessen Gate von der Sendeschaltung MMV1 angesteuert wird. Zwischen den Anschlusspunkt A und dem Feldeffekttransistor TRH2 ist ein Widerstand RH2 angeordnet, der auch hinter dem Transistor TRH2 angeordnet werden kann oder aber auch der Innenwiderstand des Verstärkers (VER) sein kann. Der Kondensator CH2 ist der Messwertspeicher-Kondensator der Sample- and Hold-Schaltung. Am Anschlusspunkt B wird die wirksame Nutzspannung abgegriffen, die an den Spannungs-/Zeit-Wandler (VTC) gelangt und entsprechend dem analogen Meldermesswert des optischen Rauchmelders (RM) verzögert den Durchschalt-Transistor (TR) ansteuert, um den nächsten Melder anzuschalten.FIG. 12 shows an advantageous circuit arrangement for the sample and hold circuit according to FIG. 10. The sample and hold circuit SHS is again arranged between the connection points A and B and is controlled by the transmit circuit MMV 1. The sample and hold circuit SHS has a field effect transistor TRH2, the gate of which is driven by the transmit circuit MMV1. A resistor RH2 is arranged between the connection point A and the field effect transistor TRH2, which can also be arranged behind the transistor TRH2 or else can be the internal resistance of the amplifier (VER). The capacitor CH2 is the measured value storage capacitor of the sample and hold circuit. The effective useful voltage is tapped at connection point B, which reaches the voltage / time converter (VTC) and controls the switching transistor (TR) with a delay in accordance with the analog detector measured value of the optical smoke detector (RM) in order to switch on the next detector.

Die Zeitkonstante TH für das Einspeichern des Messsignals in die Sample- and Hold-Schaltung (Momentanwertspeicher) wird vom RC-Glied aus dem Widerstand RH2 und dem Kondensator CH2 bestimmt. Diese Zeitkonstante TH ist dabei so gewählt, dass sie die Bedingung

Figure imgb0003
erfüllt. TP ist die Sendeimpulsdauer gemäss der oben genannten Gleichung. Hiermit wird erreicht, dass die Spannung, mit der der Kondensator CH2 umgeladen wird, abhängig von der Sendeimpulsdauer TP wird.The time constant TH for storing the measurement signal in the sample and hold circuit (instantaneous value memory) is determined by the RC element from the resistor RH2 and the capacitor CH2. This time constant TH is chosen so that it is the condition
Figure imgb0003
 Fulfills. TP is the transmit pulse duration according to the above equation. This ensures that the voltage with which the capacitor CH2 is recharged becomes dependent on the transmission pulse duration TP.

Anhand der Fig. 13 wird die Wirkungsweise der Temperaturkompensation näher erläutert. In Fig.13a ist das Sendesignal UR4 der Leuchtdiode (LED) in Abhängigkeit von der Zeit t dargestellt. Darunter ist in Fig. 13b die Ausgangsspannung UA am Anschlusspunkt A und darunter die Ausgangsspannung UB am Anschlusspunkt B in Fig.13c dargestellt. Das Sendesignal UR4 ist dem Strom ILD durch die Leuchtdiode LED porportional und genügt der Gleichung

Figure imgb0004
The mode of operation of the temperature compensation is explained in more detail with reference to FIG. 13. The transmission signal UR4 of the light-emitting diode (LED) is shown in FIG. 13a as a function of the time t. Below this, the output voltage UA at the connection point A is shown in FIG. 13b and below the output voltage UB at the connection point B in FIG. 13c. The transmission signal UR4 is proportional to the current ILD through the light-emitting diode LED and satisfies the equation
Figure imgb0004

Für die Dauer TP des Sendesignals (US bzw. UR4) ist die Sample- and Hold-Schaltung SHS gemäss der Fig. 12 leitend, sonst ist sie gesperrt. Dabei wirkt sich die Temperaturabhängigkeit, die für -30°C und +70°C dargestellt ist, nicht nur auf das Sendesignal UR4, sondern auch auf die Ausgangssignale am Anschlusspunkt A und B aus. Die Ausgangsspannung UA am Anschlusspunkt A ist gleich dem Empfangssignal der Sample- and Hold-Schaltung. Dieses Signal ist ebenfalls für die beiden Temperaturen-30°C und +70°C in Fig.13b dargestellt. Die Sendeimpulsdauer TP wird mit zunehmender Temperatur, wie schon erläutert, länger. Mit zunehmender Temperatur wird die Amplitude des Empfangssignals UA vor der Sample- and Hold-Schaltung am Anschlusspunkt A geringer, jedoch steht das Empfangssignal UA vor der Sample- and Hold-Schaltung am Anschlusspunkt A mit zunehmender Temperatur entsprechend der Pulsdauer TP länger an.The sample and hold circuit SHS according to FIG. 12 is conductive for the duration TP of the transmission signal (US or UR4), otherwise it is blocked. The temperature dependency, which is shown for -30 ° C and + 70 ° C, affects not only the transmit signal UR4, but also the output signals at connection points A and B. The output voltage UA at connection point A is equal to the received signal of the sample and hold circuit. This signal is also shown for the two temperatures -30 ° C and + 70 ° C in Fig.13b. As already explained, the transmission pulse duration TP becomes longer as the temperature increases. With increasing temperature, the amplitude of the received signal UA before the sample and hold circuit at connection point A becomes lower, however, the received signal UA before the sample and hold circuit at connection point A is present longer with increasing temperature corresponding to the pulse duration TP.

Das Ausgangssignal UB am Anschlusspunkt B, also am Ausgang der Sample- and Hold-Schaltung (SHS), ist dabei von der Temperaturschwankung (Messzeitpunkt TM -30° C) bzw. Messzeitpunkt +70° C) unabhängig, wie mit dem in Fig.13c gezeigten Messsignal MS veranschaulicht ist. Auf diese Weise ist es möglich, ohne zusätzliche Elemente zur Temperaturkompensation ein weitgehendes temperaturunabhängiges Ausgangssignal UB, d.h. Meldermesssignal MS, am Anschlusspunkt B zu erhalten. Dadurch wird die Messgenauigkeit vergrössert und die Branderkennung verbessert.

Figure imgb0005
The output signal UB at connection point B, i.e. at the output of the sample and hold circuit (SHS), is independent of the temperature fluctuation (measurement time TM -30 ° C) or measurement time + 70 ° C), as with the one in Fig. 13c measurement signal MS is illustrated. In this way it is possible to obtain a largely temperature-independent output signal UB, ie detector measurement signal MS, at connection point B without additional elements for temperature compensation. This increases the measurement accuracy and improves fire detection.
Figure imgb0005

Claims (9)

1. A circuit arrangement in a fire alarm system, for suppressing interference signals in optical smoke detectors (RM) with a luminescence diode (LED) which transmits in pulsed fashion and with a photo-diode (FD) which receives diffused light from the luminescence diode (LED), where, during cyclic interrogation from central control (Z), the individual alarms (Mi) of an alarm line (ML) are connected in cascade to the alarm line (ML) in a predetermined sequence with a time delay and where the delay time until the connection of the following alarm corresponds to the analogue alarm measured value in question, and in the central control the alarm measured value and the alaram address are determined from the time of the connection, characterised in that the optical smoke detector (RM) comprises a voltage supply device (SPV); a transmitting circuit (MMV1) driven by the alarm interrogation (UAB) and serves to produce transmitted pulses (US) for the luminescence diode (LED), where the duration (TP) of the transmitted pulses is substantially shorter than the interrogation duration of an alarm; an instantaneous value store (SHS), connected to the output of the photo-diode (FD) via the amplifier (VER), driven by the transmitting circuit (MMV1) to temporarily store the analogue alarm measured value; and a voltage/time converter (VTC) connected to the output of the instantaneous value store, which connects the following alarm (Mi) to the alarm line (ML) via a switch-through transistor (TR) with a delay in accordance with the alarm measured value.
2. A circuit arrangement as claimed in claim 1, characterised in that the transmitting circuit (MMV1) is preceded by a delay component (MMV2) which is set in motion with the alarm interrogation (UAB) and which drives the transmitting circuit (MMV1) with a time delay (TV).
3. A circuit arrangement as claimed in claim 1 or 2, characterised in that the instantaneous value store (SHS) comprises a timer (RH2, CH2) whose time constant (TH) determines the time at which the measurement signal (MS) is input into the instantaneous value store (SHS).
4. A circuit arrangement as claimed in one of claims 1 to 3, characterised in that the instantaneous value store (SHS) comprises a switching transistor (TRH1) arranged between the amplifier (VER) for the photo-diode (FD) and the voltage time converter (VTC), a resistor (RH1), a measured value store capacitor (CH2), and drive elements (CH1, DH).
5. A circuit arrangement as claimed in one of claims 1 to 3, characterised in that the instantaneous value store (SHS) comprises a switching transistor (TRH2) directly driven by the transmitting circuit (MMV1) and connected via a resistor (RH2) to the amplifier (VER), and by a measured value store capacitor (CH2) arranged prior to the voltage/time converter (VTC).
6. A circuit arrangement as claimed in claim 1 or 2, characterised in that the transmitting circuit (MMV1) is formed by a monostable multivibrator.
7. A circuit arrangement as claimed in Claim 6, characterised in that the transmitting circuit (MMV1) is connected to a stabilised supply voltage (Ucc) formed by a Zenerdiode (ZD) having a positive temperature coefficient and by a series resistor (R5) and consists of two transistors (TR1, TR2), a timer (R1, R2, R3, C) and a resistor (R4) having a negative temperature coefficient, where, with increasing temperature, increases occur in the current (ILD) flowing through the luminescence diode (LED), and in the pulse duration (TP).
8. A circuit arrangement as claimed in Claim 2, characterised in that the delay element (MMV2) is formed by a monostable multivibrator.
9. A circuit arrangement as claimed in Claim 8, characterised in that the delay component (MMV2) comprises a transistor (TRV) connected via a resistor (R) to a supply voltage (GV), whose collector is connected to the transmitting circuit (MMV1) and whose base is connected via a further resistor (RV) to the positive conductor (+UL) of the alarm line (ML) and is connected via a capacitor (CV) to the negative conductor (-UL) of the alarm line.
EP84103961A 1983-04-12 1984-04-09 Signal suppression circuit for optical smoke detectors Expired EP0125485B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT84103961T ATE25885T1 (en) 1983-04-12 1984-04-09 CIRCUIT ARRANGEMENT FOR INTERFERENCE SIGNAL SUPPRESSION IN OPTICAL SMOKE DETECTORS.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3313137 1983-04-12
DE19833313137 DE3313137A1 (en) 1983-04-12 1983-04-12 CIRCUIT ARRANGEMENT FOR CANCELING NOISE IN OPTICAL SMOKE DETECTORS

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EP0125485A1 EP0125485A1 (en) 1984-11-21
EP0125485B1 true EP0125485B1 (en) 1987-03-11

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DE3671120D1 (en) * 1985-07-29 1990-06-13 Siemens Ag METHOD AND DEVICE FOR THE OPERATIONAL MONITORING OF OPTICAL SMOKE DETECTORS.
EP0362798B1 (en) * 1988-10-06 1994-02-09 Siemens Aktiengesellschaft Method for the energy-saving operation of risk detectors in a risk detection arrangement
EP0362797B2 (en) * 1988-10-06 2000-05-17 Siemens Aktiengesellschaft Method for the energy-saving operation of risk detectors in a risk detection arrangement
DE58908329D1 (en) * 1989-09-19 1994-10-13 Siemens Ag Method and device for compensating for air humidity in an optical smoke detector.
EP0418411B1 (en) * 1989-09-19 1994-03-02 Siemens Aktiengesellschaft Fire alarm system with a combination sounder
EP3457369B1 (en) 2017-09-19 2021-05-19 Elmos Semiconductor SE Circuit arrangement for a smoke sensor

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FR2214189B1 (en) * 1973-01-16 1977-07-22 Silec Liaisons Elec
DE2533382C2 (en) * 1975-07-25 1980-07-03 Siemens Ag, 1000 Berlin Und 8000 Muenchen Method and device for the transmission of measured values in a fire alarm system
DE2638068C3 (en) * 1976-08-24 1986-11-13 Siemens AG, 1000 Berlin und 8000 München Fire alarm system with several detectors that can be operated via a message loop
US4149162A (en) * 1977-06-20 1979-04-10 American District Telegraph Company Battery discriminator circuit for smoke detectors

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DE3313137A1 (en) 1984-10-18
EP0125485A1 (en) 1984-11-21
DE3462637D1 (en) 1987-04-16

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