EP1719947A1 - Method and device for flame monitoring - Google Patents

Method and device for flame monitoring Download PDF

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Publication number
EP1719947A1
EP1719947A1 EP05009937A EP05009937A EP1719947A1 EP 1719947 A1 EP1719947 A1 EP 1719947A1 EP 05009937 A EP05009937 A EP 05009937A EP 05009937 A EP05009937 A EP 05009937A EP 1719947 A1 EP1719947 A1 EP 1719947A1
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EP
European Patent Office
Prior art keywords
capacitor
flame
charging
phase
flame sensor
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Granted
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EP05009937A
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German (de)
French (fr)
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EP1719947B1 (en
Inventor
Klaus Obrecht
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Siemens Building Technologies HVAC Products GmbH
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Siemens Building Technologies HVAC Products GmbH
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Priority to DE502005009411T priority Critical patent/DE502005009411D1/en
Priority to EP05009937A priority patent/EP1719947B1/en
Priority to US11/429,285 priority patent/US7382140B2/en
Publication of EP1719947A1 publication Critical patent/EP1719947A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/02—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium
    • F23N5/12—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using ionisation-sensitive elements, i.e. flame rods
    • F23N5/123—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using ionisation-sensitive elements, i.e. flame rods using electronic means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/24—Preventing development of abnormal or undesired conditions, i.e. safety arrangements
    • F23N5/242—Preventing development of abnormal or undesired conditions, i.e. safety arrangements using electronic means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2227/00—Ignition or checking
    • F23N2227/12—Burner simulation or checking
    • F23N2227/16—Checking components, e.g. electronic
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2229/00—Flame sensors
    • F23N2229/12—Flame sensors with flame rectification current detecting means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2231/00—Fail safe
    • F23N2231/06—Fail safe for flame failures

Definitions

  • the invention relates to a method and a device for flame monitoring according to the preamble of claims 1 and 6.
  • the EP 1 256 763 A2 discloses a flame monitoring method in which the radiation generated by the flame is detected by a photoresistor and the sensor signal is evaluated in two channels. The first channel is used to detect the average brightness and the second channel is used to detect alternating parts resulting from the flickering of the flame. The flame is only recognized as burning if the signal is within a specified range at both channel outputs.
  • the invention has for its object to provide a method and a device for flame monitoring, which is versatile and allows a simple signal evaluation.
  • a capacitor connected to a voltage source during a charging phase is charged to a voltage value, and during a discharge phase the capacitor is discharged via a coupling member connected to the flame sensor.
  • the period of time for the charging and discharging phase of the capacitor is chosen as a function of the characteristic, in particular the impedance of the flame sensor.
  • the charging or discharging of the capacitor is cyclically repeated and the resulting voltage signal is evaluated for flame monitoring single-channel. For signal evaluation, a threshold value which is uniform for different sensor impedances is preferably used.
  • various flames for. B. pilot flame or flame at maximum load of an oil, gas, or solid fuel burner are monitored, with a variety of different flame sensors, eg. As photoresistor, ionization current electrode, UV tubes, etc. can be used for flame monitoring.
  • the invention does not require active signal amplification for evaluation.
  • the monitoring circuit can be constructed with a small number of components.
  • the capacitor provided for flame monitoring also performs the function of signal filtering with a low-pass character.
  • the method according to the invention can be used in continuous operation or in the intermittent operation of a burner, wherein different fault scenarios can be taken into account in the signal evaluation.
  • the impedance of the flame sensor can assume a static value in the event of a fault or when exposed to daylight. This can be detected at the end of the charging phase by evaluating the voltage signal obtained at the capacitor.
  • Also may be component failure of the circuit or the sensor For example, a short circuit of the flame sensor or a line break are detected to the flame sensor.
  • the flame sensor is irradiated with a fluorescent lamp or light bulb, the impedance of the flame sensor thereby changes in the rhythm of the mains frequency or its multiples.
  • the network-harmonic changes of the sensor impedance caused by the extraneous light source lead to no signal dynamics in a network-synchronous evaluation of the voltage signal.
  • the z. B. in the frequency range of 8-30 Hertz, be monitored and evaluated.
  • Fig. 1 shows the basic structure of the inventive circuit for flame monitoring, which can be adapted with little modification to different flame sensors for detecting the flame and flame existence of oil, gas and solid fuel burners.
  • the flame sensor is z. B. a photoresistor 1, which has a radiation sensitivity in the spectral range to be monitored.
  • the radiation sensitivity manifests itself by different impedance values upon irradiation of the flame sensor, with an increase in the intensity of the flame radiation resulting in a decrease in the impedance value of the photoresistor.
  • the photoresistor 1 is connected via a coupling member 19 to a capacitor 18 provided for evaluation.
  • the capacitor 18 is connected via a switch 12 to a reference voltage source 13, which has an internal resistance 11.
  • the capacitor 18 is connected via the internal resistance 11 by means of the switch 12 to the reference voltage source 13. Characterized the capacitor 18 is charged to a voltage value which is dependent on the internal resistance 11 of the reference voltage 13, the impedance of the coupling member 19 and the photoresistor 1. After a defined charging time, a measured value dependent on the impedance of the flame sensor 1 is obtained by an A / D converter 20.
  • the A / D converter 20 can be connected to the capacitor 18 via a switch 17 and a resistor 16. However, the A / D converter 20 may also be directly connected to the capacitor 18.
  • the switches 12 and 17 may, for. B. field effect transistors.
  • the connection to the reference voltage source 13 is interrupted by means of the switch 12 and the capacitor 18 is discharged via the coupling impedance 19 through the photoresistor 1.
  • the A / D converter 20 supplies a measured value which is dependent on the impedance of the flame sensor 1 and filtered by the capacitor 18.
  • the control of the charging and / or discharge phase is carried out by a control unit 21, which z. B. is designed as a microprocessor or logic device with comparator.
  • FIG. 2 shows the signal curve for the voltage Uc obtained at the capacitor as a function of the impedance of the flame sensor and the time.
  • the increase in impedance is shown by an arrow 33.
  • the voltage Uc obtained at the end of the charge phase 31 or discharge phase 32 at the capacitor assumes a higher value.
  • a uniform threshold value 34 is preferably used for evaluation of the sensor impedance-dependent voltage signal 30 for evaluation of the sensor impedance-dependent voltage signal 30, preferably used.
  • the definition of the threshold value 34 and the time duration for charging or discharging phase can be carried out by a control unit.
  • the period of time for the charging or discharging phase is selected as a function of the respective impedance or characteristic of the flame sensor.
  • FIG. 3 shows a further development of the monitoring circuit shown in FIG. 1, which additionally has a voltage divider 27 which serves to return the mains phase to the control unit 21.
  • the voltage across the capacitor 18 is thereby detected synchronously with the mains frequency.
  • the charging phase is preferably chosen so long that after charging of the capacitor 18, the switch 12 remains closed for at least one network period. During this time, by monitoring the mains phase and closing the switch 17, the voltage obtained at the capacitor 18 is detected by the A / D converter 20 cyclically and synchronously with the mains frequency. If the flame sensor is irradiated by a fluorescent lamp, for example, then the sensor impedance changes in the rhythm of the mains frequency or its multiples.
  • Fig. 4 the voltage obtained at the capacitor Uc is shown together with a network-synchronous extraneous light signal 50 as a function of time.
  • a voltage signal 40 characteristic of the respective sensor impedance, is obtained, which can be detected and evaluated in a network-synchronous manner at the times t1, t2, t3, etc.
  • identical voltage values Uc are obtained for one and the same sensor impedance in this exemplary embodiment. From these voltages z. B. an average can be formed, which is evaluated for extraneous light detection. If the mean value lies below a defined threshold value 34, then this is recognized as extraneous light error.
  • FIG. 5 shows a circuit in which the sampling can take place at arbitrary times.
  • the samples supplied by a sample-and-hold device 28 in synchronism with the line frequency are buffered in a capacitor 30.
  • a pulse shaper 29 generates from the mains frequency a control pulse which, for a short time, closes the sample-and-hold circuit 28, thereby causing the capacitor 30 to be charged with the samples.
  • FIG. 6 shows a circuit which is used for two different flame sensors 1 and 2.
  • a chemical reaction takes place during combustion, as a result of which free ions occur. These cause the flame 3 to become conductive and a current to flow when a voltage is applied. The ions move only in the direction of the flame.
  • a serial link 22 shows a simplified equivalent circuit for the rectification effect by flame ionization. An alternating voltage is applied to the ionization electrode 2 via a capacitor 25 and a resistor 26.
  • FIG. 7 shows a further development of the circuit shown in FIG. 6, which additionally has a voltage divider 27 which serves to return the mains phase to the control unit 21.
  • the detection of the voltage across the capacitor 18 is thereby synchronous to the mains frequency.
  • the evaluation can be done in the same manner as described above in connection with a photoresistor.
  • FIG. 8 shows a monitoring circuit for a UV sensor.
  • a pulsating voltage is applied to a UV sensor 4 via a capacitor 25, a resistor 26 and a diode 5.
  • the W tube When irradiated with UV light, the W tube is then ignited.
  • the cyclic firing of the W-tube drives a pulsed current through the diode 5 and leads to a potential shift at the capacitor 25.
  • Via a coupling resistor 23 and a low-pass filter 24 the charge transfer at the capacitor 25 is coupled to the capacitor 18.
  • the charge transfer at the capacitor 25 is polarized such that this leads to a discharge of the capacitor 18 during the discharge phase.
  • the evaluation of the voltage signal on the capacitor 18 for flame monitoring can be carried out in the same manner as has been described in connection with a photoresistor or ionization.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)

Abstract

The method involves having a capacitor (18) with a reference charge (13) loaded during a load phase (31) and the capacitor having an interconnection connected with a flame sensor (1) during a discharge phase (32). The length of time of the discharge phase of the capacitor is selected as a function of the characteristic of the used flame sensor and that for flame monitoring loading and or unloading the capacitor is cyclically repeated. A charging signal (30, 40) at the capacitor is evaluated with the aid of a threshold value (34) single-channel. An independent claim is included for a device for flame monitoring.

Description

Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Flammenüberwachung gemäss dem Oberbegriff der Ansprüche 1 und 6.The invention relates to a method and a device for flame monitoring according to the preamble of claims 1 and 6.

Ein Verfahren und eine Vorrichtung der eingangs genannten Art ist beispielsweise aus der EP 617 234 A1 bekannt. Diese Druckschrift offenbart einen Ionisationsflammenwächter mit einem Kondensator, der mit einer Referenzspannungsquelle und über ein Koppelglied mit dem Sekundärkreis eines Zündübertragers verbunden ist. Solange zwischen der Zündelektrode und der Masseleitung keine Flamme vorhanden ist, wird der Kondensator über einen Widerstand auf eine Betriebsspannung aufgeladen. Sobald infolge der Flammenbildung ein Ionisationsstrom fliesst, wird der Kondensator entladen. Der Kondensator ist mit einer Überwachungsschaltung verbunden, welche bei Unterschreiten eines vorbestimmten Schwellenwertes ein Ausgangssignal erzeugt, welches das Vorhandensein einer Flamme anzeigt.A method and a device of the type mentioned, for example, from EP 617 234 A1 known. This document discloses a Ionisationsflammenwächter with a capacitor which is connected to a reference voltage source and a coupling element with the secondary circuit of a Zündübertragers. As long as there is no flame between the ignition electrode and the ground line, the capacitor is charged via a resistor to an operating voltage. As soon as an ionization current flows as a result of the formation of flames, the capacitor is discharged. The capacitor is connected to a monitoring circuit which, when falling below a predetermined threshold value, generates an output signal which indicates the presence of a flame.

Die EP 1 256 763 A2 offenbart ein Flammenüberwachungsverfahren, bei dem die von der Flamme erzeugte Strahlung von einem Photowiderstand erfasst und das Sensorsignal zweikanalig ausgewertet wird. Der erste Kanal dient zur Erfassung der mittleren Helligkeit und der zweite Kanal dient zur Erfassung von Wechselanteilen, die vom Flackern der Flamme herrühren. Die Flamme wird nur dann als ordnungsgemäss brennend anerkannt, wenn an beiden Kanalausgängen das Signal jeweils in einem vorgegebenen Bereich liegt.The EP 1 256 763 A2 discloses a flame monitoring method in which the radiation generated by the flame is detected by a photoresistor and the sensor signal is evaluated in two channels. The first channel is used to detect the average brightness and the second channel is used to detect alternating parts resulting from the flickering of the flame. The flame is only recognized as burning if the signal is within a specified range at both channel outputs.

Der Erfindung liegt die Aufgabe zugrunde ein Verfahren beziehungsweise eine Vorrichtung zur Flammenüberwachung vorzuschlagen, das vielseitig einsetzbar ist und eine einfache Signalauswertung ermöglicht.The invention has for its object to provide a method and a device for flame monitoring, which is versatile and allows a simple signal evaluation.

Diese Aufgabe wird durch die in den Ansprüchen 1 und 6 angegebenen Merkmale gelöst.This object is achieved by the features specified in claims 1 and 6.

Bei dem erfindungsgemässen Verfahren wird ein während einer Ladephase mit einer Spannungsquelle verbundener Kondensator auf einen Spannungswert aufgeladen und während einer Entladungsphase wird der Kondensator über ein mit dem Flammensensor verbundenes Kopplungsglied entladen. Die Zeitdauer für die Lade- und Entladungsphase des Kondensators wird dabei in Abhängigkeit von der Charakteristik insbesondere der Impedanz des Flammensensors gewählt. Das Laden beziehungsweise Entladen des Kondensators wird zyklisch wiederholt und das dadurch erhaltene Spannungssignal wird zur Flammenüberwachung einkanalig ausgewertet.
Zur Signalauswertung wird vorzugsweise ein für verschiedene Sensorimpedanzen einheitlicher Schwellenwert verwendet.In the method according to the invention, a capacitor connected to a voltage source during a charging phase is charged to a voltage value, and during a discharge phase the capacitor is discharged via a coupling member connected to the flame sensor. The period of time for the charging and discharging phase of the capacitor is chosen as a function of the characteristic, in particular the impedance of the flame sensor. The charging or discharging of the capacitor is cyclically repeated and the resulting voltage signal is evaluated for flame monitoring single-channel.
For signal evaluation, a threshold value which is uniform for different sensor impedances is preferably used.

Durch die Erfindung können verschiedene Flammen, z. B. Pilotflamme oder Flamme bei Maximallast eines Öl-, Gas-, oder Feststoffbrenners überwacht werden, wobei eine Vielzahl unterschiedlicher Flammensensoren, z. B. Photowiderstand, Ionisationsstromelektrode, UV-Röhren, etc. zur Flammenüberwachung eingesetzt werden können.By the invention, various flames, for. B. pilot flame or flame at maximum load of an oil, gas, or solid fuel burner are monitored, with a variety of different flame sensors, eg. As photoresistor, ionization current electrode, UV tubes, etc. can be used for flame monitoring.

Die Erfindung benötigt keine aktive Signalverstärkung zur Auswertung. Dadurch kann die Überwachungsschaltung mit einer geringen Anzahl von Bauelementen aufgebaut werden. Beispielsweise übernimmt der zur Flammenüberwachung vorgesehene Kondensator auch die Funktion einer Signalfilterung mit Tiefpasscharakter.The invention does not require active signal amplification for evaluation. As a result, the monitoring circuit can be constructed with a small number of components. For example, the capacitor provided for flame monitoring also performs the function of signal filtering with a low-pass character.

Das erfindungsgemässe Verfahren kann im Dauerbetrieb oder im intermittierenden Betrieb eines Brenners zum Einsatz kommen, wobei bei der Signalauswertung unterschiedliche Fehlerszenarien berücksichtigt werden können. Beispielsweise kann die Impedanz des Flammensensors im Fehlerfall oder bei Bestrahlung mit Tageslicht einen statischen Wert annehmen. Dies kann am Ende der Ladephase durch Auswertung des am Kondensator erhaltenen Spannungssignals erkannt werden. Auch können Bauteilfehler der Schaltung oder des Sensors beispielsweise ein Kurzschluss des Flammensensors oder ein Leitungsunterbruch zum Flammensensor festgestellt werden.The method according to the invention can be used in continuous operation or in the intermittent operation of a burner, wherein different fault scenarios can be taken into account in the signal evaluation. For example, the impedance of the flame sensor can assume a static value in the event of a fault or when exposed to daylight. This can be detected at the end of the charging phase by evaluating the voltage signal obtained at the capacitor. Also may be component failure of the circuit or the sensor For example, a short circuit of the flame sensor or a line break are detected to the flame sensor.

Durch das erfindungsgemässe Verfahren kann auch Fremdlicht erkannt werden. Wird der Flammensensor mit einer Leuchtstofflampe oder Glühbirne bestrahlt, so ändert sich dadurch die Impedanz des Flammensensors im Rhythmus der Netzfrequenz oder deren Vielfache. Die durch die Fremdlichtquelle bedingten netzharmonischen Änderungen der Sensorimpedanz führen bei einer netzsynchronen Auswertung des Spannungssignals zu keiner Signaldynamik. Für eine Erkennung von Fremdlicht im Dauerbetrieb, kann auch der Flackeranteil der Flamme, der z. B. im Frequenzbereich von 8-30 Hertz liegt, überwacht und ausgewertet werden.By the inventive method, extraneous light can be detected. If the flame sensor is irradiated with a fluorescent lamp or light bulb, the impedance of the flame sensor thereby changes in the rhythm of the mains frequency or its multiples. The network-harmonic changes of the sensor impedance caused by the extraneous light source lead to no signal dynamics in a network-synchronous evaluation of the voltage signal. For detection of extraneous light in continuous operation, and the Flackeranteil the flame, the z. B. in the frequency range of 8-30 Hertz, be monitored and evaluated.

Weitere Vorteile ergeben sich aus der nachfolgenden Beschreibung der Erfindung anhand der Ausführungsbeispiele und den Figuren. Es zeigen:

Fig.1
ein prinzipielles Blockschaltbild einer Überwachungsschaltung
Fig. 2
Spannungssignalverlauf in Abhängigkeit von der Sensorimpedanz
Fig.3
eine Weiterbildung der in Fig. 1 dargestellten Schaltung zur Erkennung von Fremdlicht
Fig.4
Spannungssignalverlauf mit Fremdlichtsignal
Fig.5
bis 8 jeweils eine weitere Ausführungsform der erfindungsgemässen Überwachungsschaltung
Further advantages will become apparent from the following description of the invention with reference to the embodiments and the figures. Show it:
Fig.1
a schematic block diagram of a monitoring circuit
Fig. 2
Voltage waveform as a function of the sensor impedance
Figure 3
a development of the circuit shown in Fig. 1 for detecting extraneous light
Figure 4
Voltage waveform with extraneous light signal
Figure 5
to 8 each show a further embodiment of the inventive monitoring circuit

Fig. 1 zeigt den prinzipiellen Aufbau der erfindungsgemässen Schaltung zur Flammenüberwachung, die mit geringer Modifikation an unterschiedliche Flammensensoren zur Erfassung der Flammenbildung und Flammenexistenz von Öl-, Gas und Feststoffbrennern angepasst werden kann.Fig. 1 shows the basic structure of the inventive circuit for flame monitoring, which can be adapted with little modification to different flame sensors for detecting the flame and flame existence of oil, gas and solid fuel burners.

Der Flammensensor ist z. B. ein Photowiderstand 1, der eine Strahlungsempfindlichkeit in dem zu überwachenden Spektralbereich aufweist. Die Strahlungsempfindlichkeit äußert sich durch unterschiedliche Impedanzwerte bei Bestrahlung des Flammensensors, wobei eine Zunahme der Intensität der Flammenstrahlung eine Abnahme des Impedanzwertes des Photowiderstandes zur Folge hat.The flame sensor is z. B. a photoresistor 1, which has a radiation sensitivity in the spectral range to be monitored. The radiation sensitivity manifests itself by different impedance values upon irradiation of the flame sensor, with an increase in the intensity of the flame radiation resulting in a decrease in the impedance value of the photoresistor.

Der Photowiderstand 1 ist über ein Kopplungsglied 19 mit einem zur Auswertung vorgesehenen Kondensator 18 verbunden. Der Kondensator 18 ist über einen Schalter 12 mit einer Referenzspannungsquelle 13 verbunden, welche einen Innenwiderstand 11 aufweist.The photoresistor 1 is connected via a coupling member 19 to a capacitor 18 provided for evaluation. The capacitor 18 is connected via a switch 12 to a reference voltage source 13, which has an internal resistance 11.

Zur Aufladung ist der Kondensator 18 über den Innenwiderstand 11 mittels des Schalters 12 mit der Referenzspannungsquelle 13 verbunden. Dadurch wird der Kondensator 18 auf einen Spannungswert aufgeladen, der abhängig von dem Innenwiderstand 11 der Referenzspannung 13, der Impedanz des Kopplungsgliedes 19 und des Photowiderstandes 1 ist. Nach einer definierten Ladezeit wird ein von der Impedanz des Flammensensors 1 abhängiger Messwert durch einen A/D-Wandler 20 erhalten. Der A/D-Wandler 20 kann über einen Schalter 17 und einen Widerstand 16 mit dem Kondensator 18 verbunden. Der A/D- Wandler 20 kann jedoch auch direkt mit dem Kondensator 18 verbunden werden. Die Schalter 12 und 17 können z. B. Feldeffekttransistoren sein.For charging, the capacitor 18 is connected via the internal resistance 11 by means of the switch 12 to the reference voltage source 13. Characterized the capacitor 18 is charged to a voltage value which is dependent on the internal resistance 11 of the reference voltage 13, the impedance of the coupling member 19 and the photoresistor 1. After a defined charging time, a measured value dependent on the impedance of the flame sensor 1 is obtained by an A / D converter 20. The A / D converter 20 can be connected to the capacitor 18 via a switch 17 and a resistor 16. However, the A / D converter 20 may also be directly connected to the capacitor 18. The switches 12 and 17 may, for. B. field effect transistors.

In der Entladungsphase ist die Verbindung zur Referenzspannungsquelle 13 mittels des Schalters 12 unterbrochen und der Kondensator 18 wird über die Kopplungsimpedanz 19 durch den Photowiderstand 1 entladen. Nach einer definierten Entladungszeit liefert der A/D-Wandler 20 einen von der Impedanz des Flammensensors 1 abhängigen durch den Kondensator 18 gefilterten Messwert. Die Steuerung der Lade- und/oder Entladungsphase erfolgt durch eine Steuereinheit 21, welche z. B. als Mikroprozessor oder Logikbaustein mit Komparator ausgeführt ist.In the discharge phase, the connection to the reference voltage source 13 is interrupted by means of the switch 12 and the capacitor 18 is discharged via the coupling impedance 19 through the photoresistor 1. After a defined discharge time, the A / D converter 20 supplies a measured value which is dependent on the impedance of the flame sensor 1 and filtered by the capacitor 18. The control of the charging and / or discharge phase is carried out by a control unit 21, which z. B. is designed as a microprocessor or logic device with comparator.

Figur 2 zeigt den Signalverlauf für die am Kondensator erhaltene Spannung Uc in Abhängigkeit von der Impedanz des Flammensensors und der Zeit. Die Zunahme der Impedanz ist durch einen Pfeil 33 dargestellt. Mit zunehmender Impedanz nimmt die am Ende der Ladungsphase 31 beziehungsweise Entladungsphase 32 am Kondensator erhaltene Spannung Uc einen höheren Wert an. Durch eine zyklische Wiederholung von Ladebeziehungsweise Entladungsphase wird ein für die jeweilige Sensorimpedanz charakteristisches Spannungssignal 30 erhalten, welches zur Flammenüberwachung ausgewertet wird. Zur Auswertung des von der Sensorimpedanz abhängigen Spannungssignals 30 wird vorzugsweise ein einheitlicher Schwellenwert 34 verwendet. Die Definition des Schwellenwertes 34 und der Zeitdauer für Ladebeziehungsweise Entladungsphase kann durch eine Steuereinheit erfolgen. Die Zeitdauer für die Lade- beziehungsweise Entladungsphase wird dabei in Abhängigkeit von der jeweiligen Impedanz beziehungsweise Charakteristik des Flammensensors gewählt. Durch eine Auswertung des Spannungssignals 30 am Ende der Ladephase 31 und/oder am Ende der Entladungsphase 32, können z. B. Bauteilfehler der Überwachungsschaltung oder Fehler des Flammensensors erkannt werden.FIG. 2 shows the signal curve for the voltage Uc obtained at the capacitor as a function of the impedance of the flame sensor and the time. The increase in impedance is shown by an arrow 33. With increasing impedance, the voltage Uc obtained at the end of the charge phase 31 or discharge phase 32 at the capacitor assumes a higher value. By a cyclic repetition of charging or discharge phase, a characteristic of the respective sensor impedance voltage signal 30 is obtained, which is evaluated for flame monitoring. For evaluation of the sensor impedance-dependent voltage signal 30, a uniform threshold value 34 is preferably used. The definition of the threshold value 34 and the time duration for charging or discharging phase can be carried out by a control unit. The period of time for the charging or discharging phase is selected as a function of the respective impedance or characteristic of the flame sensor. By evaluating the voltage signal 30 at the end of the charging phase 31 and / or at the end of the discharge phase 32, z. B. component failure of the monitoring circuit or error of the flame sensor can be detected.

Figur 3 zeigt eine Weiterbildung der in Figur 1 gezeigten Überwachungsschaltung, welche zusätzlich einen Spannungsteiler 27 aufweist, der zur Rückführung der Netzphase an die Steuereinheit 21 dient. Die Spannung am Kondensator 18 wird dadurch synchron zur Netzfrequenz erfasst. Die Ladephase wird hierbei vorzugsweise so lang gewählt, dass nach Aufladung des Kondensators 18 der Schalter 12 noch für mindestens eine Netzperiode geschlossen bleibt. In dieser Zeit wird durch Überwachung der Netzphase und durch Schließen des Schalters 17 die am Kondensator 18 erhaltene Spannung durch den A/D-Wandler 20 zyklisch und synchron zur Netzfrequenz erfasst. Wird der Flammensensor beispielsweise durch eine Leuchtstofflampe bestrahlt, so ändert sich dadurch die Sensorimpedanz im Rhythmus der Netzfrequenz oder deren Vielfache.FIG. 3 shows a further development of the monitoring circuit shown in FIG. 1, which additionally has a voltage divider 27 which serves to return the mains phase to the control unit 21. The voltage across the capacitor 18 is thereby detected synchronously with the mains frequency. The charging phase is preferably chosen so long that after charging of the capacitor 18, the switch 12 remains closed for at least one network period. During this time, by monitoring the mains phase and closing the switch 17, the voltage obtained at the capacitor 18 is detected by the A / D converter 20 cyclically and synchronously with the mains frequency. If the flame sensor is irradiated by a fluorescent lamp, for example, then the sensor impedance changes in the rhythm of the mains frequency or its multiples.

In Fig. 4 ist die am Kondensator erhaltene Spannung Uc zusammen mit einem netzsynchronen Fremdlichtsignal 50 in Abhängigkeit von der Zeit dargestellt. Durch eine zyklische Wiederholung von Lade- beziehungsweise Entladungsphase wird ein für die jeweilige Sensorimpedanz charakteristisches Spannungssignal 40, erhalten, welches netzsynchron zu den Zeitpunkten t1, t2, t3, etc. erfasst und ausgewertet werden kann. Dabei werden in diesem Ausführungsbeispiel für ein und dieselbe Sensorimpedanz gleiche Spannungswerte Uc erhalten. Aus diesen Spannungswerten kann z. B. ein Mittelwert gebildet werden, der zur Fremdlichterkennung ausgewertet wird. Liegt der Mittelwert unterhalb eines definierten Schwellenwertes 34, so wird dies als Fremdlichtfehler erkannt.In Fig. 4, the voltage obtained at the capacitor Uc is shown together with a network-synchronous extraneous light signal 50 as a function of time. Through a cyclic repetition of the charging or discharging phase, a voltage signal 40, characteristic of the respective sensor impedance, is obtained, which can be detected and evaluated in a network-synchronous manner at the times t1, t2, t3, etc. In this case, identical voltage values Uc are obtained for one and the same sensor impedance in this exemplary embodiment. From these voltages z. B. an average can be formed, which is evaluated for extraneous light detection. If the mean value lies below a defined threshold value 34, then this is recognized as extraneous light error.

Figur 5 zeigt eine Schaltung bei der die Abtastung zu beliebigen Zeitpunkten erfolgen kann. Die von einem Abtast-Halteglied 28 synchron zur Netzfrequenz gelieferten Abtastwerte werden dabei in einem Kondensator 30 zwischengespeichert. Eine Impulsformerstufe 29 erzeugt aus der Netzfrequenz einen Steuerimpuls, der für eine kurze Zeit das Abtast-Halteglied 28 schliesst und dadurch eine Aufladung des Kondensators 30 mit den Abtastwerten bewirkt.FIG. 5 shows a circuit in which the sampling can take place at arbitrary times. The samples supplied by a sample-and-hold device 28 in synchronism with the line frequency are buffered in a capacitor 30. A pulse shaper 29 generates from the mains frequency a control pulse which, for a short time, closes the sample-and-hold circuit 28, thereby causing the capacitor 30 to be charged with the samples.

Figur 6 zeigt eine Schaltung die für zwei unterschiedliche Flammensensoren 1 und 2 verwendet wird. Bei einer Gasflamme 3 findet während der Verbrennung eine chemische Reaktion statt, wodurch freie Ionen auftreten. Diese führen dazu, dass die Flamme 3 leitfähig wird und beim Anlegen einer Spannung ein Strom fließen kann. Die Ionen bewegen sich dabei nur in Flammenrichtung. Legt man eine Wechselspannung zwischen Brennermasse und Ionisationselektrode 2, so erfolgt durch die Ionisation ein Gleichrichteffekt.
Ein Serienglied 22 zeigt eine vereinfachte Ersatzschaltung für den Gleichrichteffekt durch Flammenionisation. Eine Wechselspannung wird über einen Kondensator 25 und einen Widerstand 26 an die Ionisationselektrode 2 gelegt. Durch die Flammenionisation findet eine Gleichrichtung des Ionisationsstromes statt, welcher zu einer Potentialverschiebung an dem Kondensator 25 führt. Über einen Kopplungswiderstand 23 und einen Tiefpassfilter 24 wird die Ladungsverschiebung vom Kondensator 25 zum Kondensator 18 eingekoppelt. Während der Entladungsphase wird dann der Kondensator 18 in Abhängigkeit vom Ionisationsstrom entladen.FIG. 6 shows a circuit which is used for two different flame sensors 1 and 2. In the case of a gas flame 3, a chemical reaction takes place during combustion, as a result of which free ions occur. These cause the flame 3 to become conductive and a current to flow when a voltage is applied. The ions move only in the direction of the flame. If an AC voltage is applied between the burner mass and the ionization electrode 2, then a rectification effect occurs due to the ionization.
A serial link 22 shows a simplified equivalent circuit for the rectification effect by flame ionization. An alternating voltage is applied to the ionization electrode 2 via a capacitor 25 and a resistor 26. Due to the flame ionization, a rectification of the ionization current takes place, which leads to a Potential shift on the capacitor 25 leads. Via a coupling resistor 23 and a low-pass filter 24, the charge transfer from the capacitor 25 to the capacitor 18 is coupled. During the discharge phase, the capacitor 18 is then discharged in dependence on the ionization current.

Fig. 7 zeigt eine Weiterbildung der in Figur 6 gezeigten Schaltung, welche zusätzlich einen Spannungsteiler 27 aufweist, der zur Rückführung der Netzphase an die Steuereinheit 21 dient. Die Erfassung der Spannung am Kondensator 18 erfolgt dadurch synchron zur Netzfrequenz. Die Auswertung kann in der gleichen Art und Weise erfolgen, wie dies eingangs in Verbindung mit einem Photowiderstand beschrieben worden ist.FIG. 7 shows a further development of the circuit shown in FIG. 6, which additionally has a voltage divider 27 which serves to return the mains phase to the control unit 21. The detection of the voltage across the capacitor 18 is thereby synchronous to the mains frequency. The evaluation can be done in the same manner as described above in connection with a photoresistor.

Figur 8 zeigt eine Überwachungsschaltung für einen UV-Sensor. Bei dieser Schaltung wird über einen Kondensator 25, einen Widerstand 26 und eine Diode 5 eine pulsierende Spannung an einen UV-Sensor 4 gelegt. Bei Bestrahlung mit UV-Licht erfolgt dann ein Durchzünden der W-Röhre. Das zyklische Zünden der W-Röhre treibt einen Impulsstrom durch die Diode 5 und führt zu einer Potentialverschiebung am Kondensator 25. Über einen Kopplungswiderstand 23 und einen Tiefpassfilter 24 wird die Ladungsverschiebung am Kondensator 25 zu dem Kondensator 18 eingekoppelt. Die Ladungsverschiebung am Kondensator 25 ist dabei so polarisiert, dass diese zu einer Entladung des Kondensators 18 während der Entladungsphase führt. Die Auswertung des Spannungssignals am Kondensator 18 zur Flammenüberwachung kann dabei in gleicher Art und Weise erfolgen wie dies in Verbindung mit einem Photowiderstand oder Ionisationselektrode beschrieben worden ist.FIG. 8 shows a monitoring circuit for a UV sensor. In this circuit, a pulsating voltage is applied to a UV sensor 4 via a capacitor 25, a resistor 26 and a diode 5. When irradiated with UV light, the W tube is then ignited. The cyclic firing of the W-tube drives a pulsed current through the diode 5 and leads to a potential shift at the capacitor 25. Via a coupling resistor 23 and a low-pass filter 24, the charge transfer at the capacitor 25 is coupled to the capacitor 18. The charge transfer at the capacitor 25 is polarized such that this leads to a discharge of the capacitor 18 during the discharge phase. The evaluation of the voltage signal on the capacitor 18 for flame monitoring can be carried out in the same manner as has been described in connection with a photoresistor or ionization.

Claims (10)

Verfahren zur Flammenüberwachung bei dem ein Kondensator (18) während einer Ladephase (31) mit einer Referenzspannung (13) aufgeladen wird und der Kondensator über ein während einer Entladungsphase (32) mit einem Flammensensor(1) verbundenes Kopplungsglied (19) entladen wird, dadurch gekennzeichnet, dass die Zeitdauer für die Ladebeziehungsweise Entladungsphase (31, 32) des Kondensators (18) in Abhängigkeit von der Charakteristik des verwendeten Flammensensors (1) gewählt wird und dass zur Flammenüberwachung das Laden beziehungsweise Entladen des Kondensators zyklisch wiederholt wird, wodurch ein Spannungssignal (30,40) am Kondensator (18) erhalten wird, welches mit Hilfe eines Schwellenwertes (34) einkanalig ausgewertet wird.A method in which a capacitor (18) is charged during a charging phase (31) with a reference voltage (13) for flame monitoring, and the capacitor is discharged via an associate with a flame sensor (1) during a discharge phase (32) coupling member (19), characterized in that the time duration for the charge or discharge phase (31, 32) of the capacitor (18) is selected as a function of the characteristic of the flame sensor (1) used, and in that for flame monitoring the charging or discharging of the capacitor is repeated cyclically, whereby a voltage signal ( 30,40) is obtained at the capacitor (18), which is evaluated by means of a threshold value (34) single-channel. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Zeitdauer für die Lade- beziehungsweise Entladungsphase (31, 32) abhängig von der Impedanz des Flammensensors (1) ist.A method according to claim 1, characterized in that the period of time for the charging or discharging phase (31, 32) is dependent on the impedance of the flame sensor (1). Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass die Auswertung des Spannungssignals (30,40) am Kondensator (18) mit einem für verschiedene Impedanzen des Flammensensors (1) einheitlichem Schwellenwert (34) erfolgt.A method according to claim 2, characterized in that the evaluation of the voltage signal (30,40) on the capacitor (18) with a for different impedances of the flame sensor (1) uniform threshold (34). Verfahren nach Anspruch 2 oder 3, dadurch gekennzeichnet, dass durch Auswertung des Spannungssignals (30,40) am Kondensator (18) am Ende der Lade- und/oder der Entladungsphase (31,32) Bauteilfehler oder Fehler des Flammensensors erkannt werden.A method according to claim 2 or 3, characterized in that by evaluating the voltage signal (30,40) on the capacitor (18) at the end of the charging and / or the discharge phase (31,32) component errors or errors of the flame sensor are detected. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Auswertung des Spannungssignals am Kondensator (30,40) synchron mit der Netzfrequenz erfolgt.Method according to one of claims 1 to 4, characterized in that the evaluation of the voltage signal at the capacitor (30,40) takes place synchronously with the mains frequency. Vorrichtung zur Flammenüberwachung mit einem Kondensator (18), der zur Aufladung mit einer Referenzspannungsquelle (13) und zur Entladung über ein Kopplungsglied (19) mit einem Flammensensor (1) verbunden ist, dadurch gekennzeichnet, dass die Referenzspannungsquelle (13) über einen Schalter (12) mit dem Kondensator verbunden ist, der zum Aufladen des Kondensators auf Veranlassung einer Steuereinheit (21) geschlossen beziehungsweise zum Entladen des Kondensators (18) geöffnet wird, wobei die Zeitdauer für das Aufladen beziehungsweise Entladen (31,32) des Kondensators (18) in Abhängigkeit von der Charakteristik des verwendeten Flammensensors (1) von der Steuereinheit (21) bestimmt wird und dass auf Veranlassung der Steuereinheit zur Flammenüberwachung (21) das Aufladen beziehungsweise das Entladen des Kondensators zyklisch wiederholt wird, wodurch ein Spannungssignal (30,40) am Kondensator (18) erhalten wird, welches mittels eines Schwellenwertes (34) einkanalig ausgewertet wird.Flame monitoring device with a capacitor (18) which is connected to a reference voltage source (13) for charging and to a flame sensor (1) via a coupling member (19), characterized in that the reference voltage source (13) is connected via a switch (13). 12) is connected to the capacitor, which is closed for charging the capacitor on the initiative of a control unit (21) or for discharging the capacitor (18), wherein the time period for charging or discharging (31,32) of the capacitor (18) is determined by the control unit (21) as a function of the characteristic of the flame sensor (1) used, and in that the charging or discharging of the capacitor is cyclically repeated at the instigation of the flame monitoring control unit (21), whereby a voltage signal (30, 40) is generated at the Capacitor (18) is obtained, which is evaluated by means of a threshold value (34) single-channel. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, dass die Steuereinheit (21) einen A/D-Wandler (20) aufweist, der über einen Schalter (17) oder direkt mit dem Kondensator (18) verbunden ist.Apparatus according to claim 6, characterized in that the control unit (21) comprises an A / D converter (20) which is connected via a switch (17) or directly to the capacitor (18). Vorrichtung nach Anspruch 7, dadurch gekennzeichnet, dass ein Spannungsteiler (27) zur Rückführung der Netzphase an die Steuereinheit (21)vorgesehen ist.Apparatus according to claim 7, characterized in that a voltage divider (27) for returning the mains phase to the control unit (21) is provided. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, dass ein Abtast- und Halteglied (28) zur netzsynchronen Abtastung des Spannungssignals (30,40) vorgesehen ist.Apparatus according to claim 8, characterized in that a sampling and holding member (28) for the network-synchronous sampling of the voltage signal (30,40) is provided. Vorrichtung nach Anspruch 9, dadurch gekennzeichnet, dass eine Impulsformerstufe (29) einen Steuerimpuls zur Zwischenspeicherung der Abtastwerte in einem Kondensator (30) erzeugt.Apparatus according to claim 9, characterized in that a pulse shaper (29) generates a control pulse for latching the samples in a capacitor (30).
EP05009937A 2005-05-06 2005-05-06 Method and device for flame monitoring Active EP1719947B1 (en)

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DE502005009411D1 (en) 2010-05-27
EP1719947B1 (en) 2010-04-14
US7382140B2 (en) 2008-06-03

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