DE1955172A1 - Method and device for flame monitoring - Google Patents

Description

4 DÜSSELDORF,

LINDEMANNSTRASSE Sl POST BOX 4047 TELEPHONE (0211) 672246

DIPL.-ING. H. MARSCH DIPL.-ING. K. SPARING

PATENT AGENCIES

description to the patent application

Combustion Engineering, Inc., Windsor, Connecticut, U.S.A.

concerning:
"Process and device for flame monitoring"

(Addition to patent ...
Patent application P 18 15 968.7)

The invention relates to a method and an apparatus for plasma monitoring, as described in the main patent. The main patent gives a method for Flame monitoring with two electrodes penetrated by the flame and isolated from one another, in which the an electrode an alternating voltage of low amplitude is supplied and the modulation of the as a result of ionization in the flame at the second electrode detachable signal is used as a monitoring signal.

The main patent explains in more detail how the voltage amplitude of the modulated waveform is used to indicate the presence a flame is used. This is a

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gated switch arrangement provided, which only durchschäfcet, when the voltage or signal amplitude on the gate is greater than the voltage amplitude of the carrier signal alone. The gate unlock amplitude was caused by the modulation peaks.

It is true that the system protected by the main patent results in a significant improvement over this the previously customary methods and devices dealt with in more detail there, but it has been the case that in some cases Carbon and moisture become a parasitic bypass lead between the electrodes and thus reduce the amplitude of the signal modulated by the hammer, so that the detector does not show a "flame" when in reality it does Flame is still present.

The object of the present invention is the method to improve according to the main patent so that such a parasitic Shunt between the electrodes is no longer able to adversely affect the operation of the arrangement.

This object is achieved according to the invention in that the signal picked up at the second electrode is demodulated and the demodulated signal is used as a monitoring signal.

A further improvement can advantageously be made by making use of the composition of the modulation signal from many frequency components: if the modulated signal is sampled and demodulated in order to reject only the modulation signal generated by the flame, so this signal component can ultimately be used for actuation

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an output circuit can be used. It is there desirable that some particular frequency or one certain frequency range, which is located in the modulation signal generated by the flame, for the display of the Presence of the flame is used. It must be taken into account that a carrier has any frequency including Direct current can be applied to the modulation signal produced by the flame transfer. The basic requirement for the monitoring device is that the modulated signal is demodulated to give an output signal that is essentially consists of the modulating signal from the flame. Another requirement may be that the circuit in is able to filter the signal in such a way that certain frequencies, such as the carrier frequency, the meter frequency, etc., are eliminated coming from sources other than the flame itself. The demodulation and / or the filtering of the demodulated signal with blocking of all sequences in the frequency range of the carrier signal and the network frequency then provides an output signal, which necessarily indicates the presence of the flame. This output signal can be used to switch a device to actuate which the presence or absence the flame indicates. This allows alarm devices to be activated, as described in the main application.

S) S can still be mentioned that the demodulated signal without filtering also for monitoring the quality of the flame can be used, as explained in the main patent.

The invention will hereinafter be considered with reference to FIG the accompanying drawings are explained in more detail.

Figure 1 shows schematically the electrodes for determining the ionization of the flame gases

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-in

between them,

Figure Pa shows schematically the flame detector

electrodes with a device for connecting a carrier wave source,

Figure 2b shows the carrier wave signal, Figure. 2c shows the modulated signal,

Figure 3 is a block diagram of the flame detector according to the invention,

Figure 4a is a circuit diagram of the coupling circuit in a tightly coupled flame detector system;

Figure 4b is a circuit diagram of the coupling circuit

with a capacitively coupled flame detector system and

FIG. 5 is a circuit diagram of the flame detector according to FIG the invention.

Figure 1 illustrates the ionization of gas molecules in of the flame 8. The gases of the flame 8 have different Degree of ionization, depending on the thermal and electrical conditions within the flame. Within the Flame 8 there are a number of positive ions Io and free electrons 12. The rest of the flame consists of non-ionized electrons or molecules 14- of the flame gas.

V / ie shown in Figure? A, have electrodes 2 and 4, which are connected to a voltage source 6, one

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Distance from each other and the flame 8 is between them. It should be noted that the electrodes 2 and 4 are in close proximity to the area of ionization within the flame 8. This is so that a continuous conductive path is formed between the electrodes, which is not interrupted by the insulating effect of the non-ionized gases. The voltage source 6 can supply an alternating current, a pulsating direct current or a direct current. DC voltages in the order of magnitude of 150 V have proven successful as carrier signals, while AC voltage signals in the order of magnitude of 15,000 V _{ff are} required. The tension

source 6 supplies a carrier wave C, as shown in Figure 2b -

represents, to electrodes 2 and 4. The carrier wave C becomes transmitted between electrodes 2 and 4 if there is a flame. The free electrons 12 form a

conductive path for the carrier wave C and also exert a modulating effect on the carrier wave C. This modulation effect shows changes in the chemical bonds within the flame and can be seen in the modulated waveform M of FIG. 2c. This modulated waveform M consists of the carrier wave C, which is modulated by the ion pattern of the flame. It should be noted that the modulation signal comprises a large frequency and amplitude range with frequency components in the 1, lo and loo kHz range. The invention. i

makes use of the broad frequency range that this modulation signal contains to provide means for displaying the flame conditions to accomplish.

FIG. 3 shows by means of a schematic block diagram, like the principle of modulation by the flame gas ionization pattern is used for the flame test. A carrier wave source β is connected to electrodes 2 and 4 in such a way that that a carrier wave and a modulated signal between

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the electrodes when the flame is present. The electrodes 2 and 4 in this diagram can be made of metal or metal-ceramic and in close proximity to the Flame zone be arranged. In addition, the electrode can 2 are in the form of a spark plug with a housing, with an insulator within the housing and with a protruding one conductive tip that extends away from the insulator to act as both a detector probe and an ignition device to serve. Under these circumstances, the electrode 4 conveniently be the conductive portion of a chamber wall surrounding the flame. A resistor 16 in the connection between the source 6 and the electrode 2 serves as a working resistance, whereby the changing voltage drop is tapped as a flame signal. A coupling device 18 connects the signal present at the electrode 2 with a demodulation and output circuit according to the invention. Different Coupling devices for the signal to the demodulation circuit are possible, as can be explained with reference to FIGS. 4a and 4b. The demodulator 2o, which the modulated signal receives from the electrode 2, serves to demodulate this signal and provides' as an output the modulated signal, the is representative of the flame ionization pattern. The modulation signal can then be filtered to include frequency components to eliminate which could interfere with the carrier signal or are caused by it. The resulting Signal necessarily indicates the presence of a flame and, to some extent, provides one Note regarding the flame quality: the signal is only available together with the flame. This resulting signal is then used to operate an output switch 22, which acts as an electronic, mechanical or other switch " can be formed. The output switch 22 is designed so that it reacts to the presence of a modulation signal

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output from demodulator 2o responds to positive flame conditions display or represent and provide a "no flame" indication when the modulation signal is not available at the demodulator output. An alarm device 24 can be provided to acoustically or visually indicate the "no flame" condition detected by output switch 22. The output switch 22 can also to control the fuel delivery to the burner to serve.

The flame detector system shown can also be the | Serve spark detection function. The spark used to ignite the fuel can have the same modulation effect on a carrier wave as a flame. the Frequencies associated with the spark are generally essential higher than the flame modulation frequencies and if the presence of the spark is to be determined you can use filters, which both the carrier wave frequency as well as the signal frequencies generated by the flames. The signal passed through then represents the presence of the spark and can carry out a corresponding output control. ■

4a and 4b show schematically two possibilities {speeds as the modulation signal from the probe electrode? can be coupled to the detector circuit. The switch 26 applies either 5 ° or 60 Hz mains voltage to the primary winding of a standard ignition transformer J> 0 or, if the resistor 28 is provided in the circuit, a 50 or 60 Hz voltage of the order of magnitude of ~ o V to the primary winding of the transformer . The switch 26 is pressed to. to apply a high voltage to the transformer 3o for the purpose of ignition. When the switch 26 is opened, the resistor 28 becomes effective,

BATH

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to apply a lower voltage to transformer J3o lay for the purpose of flame testing.

In Figure 4a, a coupling transformer 32 is used, which inductively couples the modulated signal with the detector circuit. In this circuit, the electrode 2 is used as a spark plug shown, which is the dual function of fuel ignition and can be used for flame or spark testing. Since there is high voltage, the coupling transformer must 32 have a high insulation value (around J5o kV).

The circuit according to FIG. 4b is functionally equivalent to that according to FIG. 4a * since the only difference lies in the resistor 34 across which a voltage drop is to occur. The changing voltage drop represents the modulation signal and is coupled to the detector circuit via the capacitor 36. The use of a capacitive coupling allows the transmission of signals of lower strength than an inductive coupling device. In addition, the capacitor only couples the AC component of the modulated signal. The capacitor 36 must also be tested for high voltage (approximately 30 kV). Other coupling devices such as spark gaps, transformers with secondary windings not connected to ground and others are available to those skilled in the art.

Figure 5 shows a particular flame detector application based on the principles of the invention. Also is in Fig. 5 a particular circuit for the flame test shown. It should be understood that this circuit is only an example and that other circuits are for the same Intended use are applicable. An alternating voltage source 6, for example 50 or 6 Hz mains voltage, is applied to the primary winding of transformer 30 when the switch is turned on 26 closes, and the resistance 28 can be reduced

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Voltage amplitude reach the primary winding of the transformer 3o when the switch 26 is open. The ignition of the flame requires an operating mode in which the entire mains voltage is applied to the primary winding of the transformer, A reduced voltage of around 20 V is required on the transformer primary winding during flame testing power. The explanation of the circuit shown relates to operation during the flame test.

The secondary winding of the transformer Jo , which has a ratio of 1: loo compared to the primary winding, g supplies an alternating voltage of the order of 1500 V.

which voltage is then fed to the carrier wave, electrodes 2 and 4, the connection to electrode 2 being made via conductor j58 and electrode 4 being connected to the secondary winding of transformer J> o via the common ground connection. During the presence of a flame between electrodes 2 and 4, free electrons present in the flame form a conductive path for current to flow between the two electrodes. The resulting low current flow, reduced by the modulating influence of the flame, would appear as a soft carrier wave generated by the secondary winding of the transformer 30. As a result of the ion modulation properties, the flame has a modulation effect on the carrier wave that runs between the electrodes and thus further increases the carrier wave current considerably. The modulated signal therefore consists of a 50 or 60 Hz carrier wave with a superimposed modulation signal, which is determined by the flame characteristics The modulated signal waveform, and hence the resulting modulation waveform, indicates the presence of flame and the flame conditions

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- Io -

To filter out the signal and only the modulation signal alone to be processed as representative of the flame conditions. In addition, to avoid the possibility of a Mains frequency voltage signal can appear in the circuit except as a carrier wave and thus erroneously as a The indication of the presence of a flame could be interpreted, all frequencies including the network frequency and the carrier wave frequency are filtered out of the modulated signal. Accordingly, an alternating voltage signal for indicating the presence of a flame is only transmitted when the frequency components generated by the flame are present there. The capacitor 4o connected to the conductor 38 is connected between the electrode 2 and the secondary winding of the transformer ^ o, couples the flame-modulated signal to the detector circuit. Capacitors 4o and 42 are connected as a capacitive voltage divider, so that the voltage amplitude at their connection point 44 is strong is decreased compared to the point at which the capacitor 40 is connected to the capacitor 38. The condenser estimates a Wefct on the order of 500 pF, 20 kV, and the capacitor 42 is about o, oil i.vF, 1 kV. The capacitors 46 and 48 have such values and are connected to form a band pass filter that only filters frequencies transmits in the area in which they are only generated by the flame. The carrier wave and the network frequencies are therefore blocked. This capacitive network is used to filter the modulated signal. The ones from the capacitors 46 and 48 transmitted signal energy is then transmitted through an AC coupling capacitor 5o to the gate of the controlled silicon rectifier 52 placed. To hold it tight that that from the controlled silicon rectifier The received signal consists only of that part of the modulated signal, the frequencies of which are significantly different

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- li -

of the frequencies of the carrier wave, the network frequencies and the direct current components that have been effectively suppressed or blocked by the capacitive filter network.

The anode voltage for the controlled silicon rectifier 52 is taken from a filament transformer which is connected to the voltage source 6. The one from the capacitor Represent 5o transmitted alternating signal pulses the presence of flame and generate a forward bias at the gate of the silicon controlled rectifier 52 by means of of the voltage drop across the resistor 55 »the between the gate and the cathode of the rectifier is placed. The silicon controlled rectifier 52 amplifies the positives Signals and the ^ Iode short-circuits the negative signals, so that an amplifying demodulator results. the Forward bias allows the silicon controlled rectifier 52 to conduct during the positive half cycle of the anode voltage, where current through rectifier 52, resistor 56

fet "

and the recovery winding of a reed relay 60 flows. The current in the winding of the reed relay 60 is used to close the normally open contact of the relay. Head 62, 64 connect the contacts of the reed relay 60 with a corresponding one Output circuit which can be actuated by opening and closing the reed relay contacts 60. Jfode 58 also protects the silicon controlled rectifier against damaging reverse bias potentials at that time, while jzfer demodulates the signals.

During the controlled silicon rectifier 52 conductive the capacitor 66 is charged, and during each negative half cycle of the anode voltage, i.e. when the rectifier 52 is not conductive, the charge accumulated on capacitor 66 is discharged through the coil of the

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Reed relay, 60 so that the relay contacts during the one Half cycle of the anode voltage are kept closed, during which the controlled silicon rectifier does not is conductive. The diode 68, which is placed across the capacitor 66, - is polarized so that it prevents that destructive voltages can develop across the capacitor 66, which can result from the collapse of the Mldes are generated in the excitation winding of the reed relay 60.

When the gate of the silicon controlled rectifier 52 no longer receives an alternating signal from the capacitor 5o, the sliding preload is no longer supplied to the guide rail, and this is no longer conductive, so that the contacts of the reed relay open.

Another advantage of this particular circuit arrangement comes into play, with capacitors 42 and 48, when the arrangement is operating in the ignition mode, serve to accumulate a charge up to the point in time when the spark discharge between the electrodes 2 and 4 begins. Deliver at the same time the capacitors discharge energy in the sparks and thus amplify them.

the

It follows from the foregoing that, according to the invention, a flame detector is proposed which is less dependent is of extreme environmental conditions or the adverse electrical characteristics of the known flame detectors. The use of the ionization pattern of flanune gas themselves and in particular the high frequency components of the same ^ create a detector which has a corresponding Reading device, a reliable flame condition indicator both in quantitative and qualitative terms can deliver and thereby create a flame detection system

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allowed. The circuit arrangement shown is simple and requires little in a typical application Space. The flame detector according to the invention provides a reliable indication in a shorter response time for less Costs than all previously known detectors.

- patent claims -

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Claims (10)

Claims 1. J Procedure for flame supervision with two of the enforce wet nurses, electrodes isolated from each other, at which of the one electrode an alternating voltage lower Amplitude is supplied and the modulation of the as a result of the ionization in the flame at the second electrode detachable signal is used as a monitoring signal, according to patent ... (application P 18 15 968.7), thereby marked. shows that the one removed from the second electrode Signal is demodulated and the demodulated signal is used as a monitoring signal. 2. The method according to claim 1, characterized in that the demodulated signal is used to actuate an input gear circuit will. 3. The method according to claim 1 or 2, characterized in-v shows that a frequency range is separated from the demodulated signal as a monitoring signal, which only may have been introduced by the ionization of the flame. 4. Apparatus for performing the method according to claim 3 »characterized by frequency-selective filters for the transmission of the signal picked up at the second electrode to the demodulator. . 5. Apparatus according to claim 4, characterized in that capacitive networks are provided as frequency-selective filters. '- .. · ■. _v . - 15 - 0 0 9832/1267 6. Apparatus according to claim 5 »characterized in that that a capacitive network is designed as a voltage divider is. T. - Device according to claim 4, characterized in that a controlled silicon rectifier is used as the demodulator is provided. 8. The device according to claim J, characterized in that the gate-cathode path of the silicon rectifier is connected in parallel with a diode which derives reverse voltages at the gate-cathode path. 9. Apparatus according to claim 7 »characterized by a relay as the output circuit, the field winding of which is in series with the cathode-anode path of the silicon rectifier Moves. 10. Apparatus according to claim 4 and 7, characterized in that that the signal to be demodulated via a capacitive network to the gate electrode of the controlled silicon alignment device is laid. 009832/1267