EP1256763A2 - Method and device for long-term safe flame monitoring - Google Patents

Abstract

The method involves using a photo-conductive cell (6) which is connected to a two-channel monitoring circuit (7). The first channel (11) is for determining the average brightness and the second channel (12) is for monitoring variable components, i.e. flame flickering. The flame is only classed as normal when both output channels have values lying within given limits. An Independent claim is also given for a monitoring device.

Description

The invention relates to a method for flame monitoring on one or more burners, especially fan burners, and a monitoring device for flame monitoring on such burners.

For burners with gaseous or liquid Fuels must be operated during operation of the burner are monitored for safety reasons whether the fuel actually burns. To do this different monitoring devices in use. For Burners with a blue flame often become so-called ionization sensors used. In addition, there are flame sensors in use, the invisible or the visible radiation of the flame.

The security of the flame detection depends on whether the corresponding sensor element for the one to be detected Radiation works correctly. The sensor element generates a electrical signal representing the strength or power of the recorded Radiation. Here are in particular long-term (gradual) changes in continuous burner operation the properties of the sensor element dangerous. If the sensor is formed, for example, by a semiconductor can be by temperature, combustion gases or others deteriorating influences are shifted possibly the switching thresholds and detection thresholds for the radiation intensity, which is a characteristic of the Burning a flame or extinguishing it apply should.

Proceeding from this, the object of the invention is a method and a monitoring device for flame monitoring to create the malfunction due to wear of the sensor element avoids.

This task is carried out with the monitoring procedure, according to Claim 1 and the monitoring device according to claim 6 solved.

According to the method of the invention radiation-sensitive detection device supplied electrical signal in parallel through two filter devices headed with different characteristics. Both filter output signals are checked to see if they are in a Expected range. Only if this is for both Filter output signals the case is the presence a flame with a corresponding output signal. The filters can be analog filters or arithmetic blocks of a microcomputer program.

The filtering of the electrical signal of the detection device with two different filters, creeping changes in electrical properties to determine the detection device. This is because that the radiation emitted by the flame is temporal is not constant. Rather, there is usually a certain Flickering of the flame. This is especially true for fan burners, especially oil fan burners. The Flickering of the flame creates a radiation component that fluctuates sporadically. The fluctuations are in one Frequency range between 10 and 60 Hertz - depending on the burner. On the other hand, with a constantly burning flame, even if this flickers a little, a fixed mean radiation level available. The two-channel according to the invention Evaluation of the radiation signal now allows various Frequency components of the radiation signal separately capture and investigate.

For example, a temporally in the first channel weighted average of the radiation signal is evaluated become. This is e.g. through low pass filtering or obtained by numerical averaging. The so filtered Signal forms when the detection device is working properly works, the received radiation power. Becomes an optical sensor for visible light as a detection device used, the signal corresponds to the detected medium flame brightness.

For example, the alternating components can be in the other channel of the radiation signal are filtered out, the flickering mark the flame. This can be done with a High pass or with a band pass. The band pass can also serve to influence the influence of stray light sources, that can also produce alternating light, drastically to reduce. This is especially true if the band pass is sufficient detuned from the usual network frequencies (50 Hertz) is so that light fluctuations, as in the 50 or 100 Hertz rhythm occur on fluorescent lamps, irrelevant are. The bandpass is preferably at a frequency below the network frequency. Instead of the band pass a calculation block can also be used, the Sum of the amounts of differences of a number of consecutive Samples of the brightness signal determined. falls below the sum a limit, is the sporadic Brightness fluctuation (flickering) too low. So either the sensor is defective or the flame has gone out; it will an error is displayed.

Will the radiation sensitive detection device (e.g. a photo resistor) due to temperature, exposure of combustion gases or other wear influences slowly destroyed, it starts from a resistance value, that of the actual exposure to radiation (Illuminance) corresponds, gradually in the high-resistance or low impedance condition. In other words, the current resistance value of the photo resistor or other detection element, moves from its desired Value towards another value, taking the influence the illuminance with increasing destruction of the Detection element (e.g. a semiconductor) gradually decreases. Is the resistance value due to destruction of the detection device even if there is a flame failure in one area valid for the flame detection, can only by Evaluation of the mean value of the radiation signal no flame failure can be detected. However, as explained, with the destruction of the detection device also a reduction of their sensitivity, so that the Flicker content in the radiation signal even when the light is still burning Flame continued to decline. This is used in the Detection of the stochastic alternating component provided Channel registered. Falls below the detected flickering a minimum value, the output signal of this channel lies no longer in the expected range. Accordingly, no Output signal to indicate the presence of a flame generated more, and so there is a fault message.

A corresponding one reacts with the presented concept Evaluation device or monitoring device the gradual destruction of the sensor element of the detection device even before a real mistake occurs through a corresponding failure report. In practical terms Operation would result in the burner stopping, i.e. the system fails on the safe side. hazards for people and material are excluded - the Security is increased.

The concept presented is particularly suitable for long-term use Oil burners important. A review of the Functionality of the detection device of the monitoring device takes place not only at the start of operations at Ignite the flame, but through the different signal processing in both channels parallel to each other, during the operation of the burner.

The gradual destruction of a sensor component (Detection device) can also cause a electrical resistance too low or too low high values is shifted. In a preferred one Embodiment of the invention, the mean of the radiation signal, which is the resistance of the sensor component then examines whether the current Resistance value of the sensor component a minimum value below. This minimum value serving as a limit is preferably set to a value that one corresponds to over-bright lighting (radiation intensity), that cannot be applied by the flame. This Measure brings both security against short circuits on the Sensor element or in the supply lines, as well as against one creeping resistance shift. Another security measure can be as a sign of the Failure of a detection device to be assessed if that electrical signal before igniting a flame in an area in which it is expected in the presence of a flame becomes.

Occurs with a flame monitor after the one presented Method of destroying the sensor element (photo resistor) on, which leads to the resistance on a value that drifts in the valid range for there is a flame message, but the resistance is only still insufficient or not at all from the flame picture, i.e. the flickering of the flame is affected this is recognized by the alternating signal detection (second channel). The detection device can due to the destruction their semiconductor has no or only an insufficient flickering signal grasp from the flame. Through this procedure it is therefore possible to transition states of the sensor element (Photo resistors) that consist of a slow and steady Destruction of the sensor element arise and render it harmless.

The monitoring device according to the invention has two channels parallel to each other with different signal evaluation devices one, for example the signal mean and the other the alternating component of the signal evaluates. The evaluation can be done via filter devices done in hardware or software. Following that can by means of threshold switches or window discriminator circuits be examined whether the signals in the desired and expected range. The threshold switches, Window discriminators, possibly necessary rectifiers for signal rectification and the like, can both by Hardware or software.

The monitoring device according to the invention is suitable focus in particular on flame monitoring by recording the visible light with a photo resistor as a sensor element. It can be simple, inexpensive and at the same time Safe monitoring devices even when the burner is in continuous operation realize.

Advantageous details of embodiments of the Invention go from the drawing, the description below or subclaims.

Fig. 1

einen Gebläsebrenner mit optischer Flammenüberwachung in schematischer Darstellung,

Fig. 2

die Helligkeit-Widerstands-Kennlinie eines Fotowiderstands, in intaktem Zustand und in verschiedenen Verschleißzuständen,

Fig. 3

einen beispielhaften Zeitverlauf für ein von dem Fotowiderstand erzeugtes Signal,

Fig. 4

ein Ausführungsbeispiel einer Überwachungseinrichtung für einen Gebläsebrenner, als Blockschaltbild, und

Fig. 5

eine alternative Ausführungsform einer Überwachungseinrichtung als schematisiertes Schaltbild.

Exemplary embodiments of the invention are illustrated in the drawing. Show it:

Fig. 1

a fan burner with optical flame monitoring in a schematic representation,

Fig. 2

the brightness-resistance characteristic of a photo resistor, intact condition and in different wear conditions,

Fig. 3

an exemplary time course for a signal generated by the photo resistor,

Fig. 4

an embodiment of a monitoring device for a forced draft burner, as a block diagram, and

Fig. 5

an alternative embodiment of a monitoring device as a schematic circuit diagram.

In Fig. 1 is a monitoring device 1 for the Flame 2 of a forced draft burner 3 schematically illustrated. The fan burner 3 is connected to a fan 4 and one Fuel supply line 5 connected. The fuel is, for example, heating oil. The flame 2 has a turbulent flame pattern on. Their brightness changes by an average. Temporal fluctuations of the brightness L around the mean M correspond to the flickering of the flame, as shown in FIG. 3 illustrated. The fluctuations are stochastic in nature. They are often in the range of 10 - 60 Hertz.

The monitoring device 1 monitors the Flame 2 emitted visible light using a radiation sensitive Detection means. This is through a photo resistor 6 is formed, which is connected to a monitoring circuit 7 is connected. This is part of one, for example superordinate control device and thus serves, as in Fig. 1 indicated schematically, for controlling the fan burner 3 and in particular for direct and indirect shutdowns the blower 4, and the shutoff of the fuel supply by means of a corresponding controlled valve 8.

The photo resistor 6 is arranged in such a way that it collects part of the visible light emitted by the flame 2. It thus generates a signal at its output terminals, which reproduces the brightness curve illustrated in FIG. 3. The internal resistance of the photo resistor 6 depends on the illuminance. This relationship is illustrated in FIG. 2. With increasing illuminance L, the resistance R decreases more and more. In the dark or when the illuminance is low, the resistance assumes its rest resistance R ₀ . At very high illuminance levels, which are higher than any illumination that can be generated by the flame 2, the resistance R approaches its minimum value R _M. 2 shows as curve I the dependence of the resistance R on the illuminance L for an intact photoresistor 6. The characteristic curve of the photoresistor 6 can change over time as a result of temperature influences, aging and the action of combustion gases. Any damage is usually associated with the fact that the steepness of the characteristic curve decreases in the range between the resistance to rest R _o and the minimum value R _M. Curve II, shown in broken lines in FIG. 2, illustrates such a case. The rest resistance R ₀ has decreased; the minimum value has increased and the slope of the characteristic curve has decreased.

To an even greater extent, this is even further for you damaged photo resistor 6 the case, as in Fig. 2 by a third curve III is illustrated. This can be done also to higher resistance values or to lower ones overall Resistance values may have been shifted. Like the curves however they are always shifted - they have in common that the photo sensitivity of the photo resistor 6 decreases.

The monitoring circuit 7 is separate in FIG. 4 illustrated. The monitoring circuit 7 has one first channel 11 for evaluating the DC component of the photo resistor 6 generated signal and a second Channel 12 for evaluating the alternating signal component. Both Channels 11, 12 receive the same input signal that from an R / U converter 14 is output, the one of the resistor R delivers the corresponding voltage. The R / U converter is connected on the input side to the photoresistor 6 and is in the simplest case by a voltage divider (one with the photoresistor 6 ohmic resistor connected in series) educated.

The first channel 11 contains for signal evaluation (as Signal evaluation device) a low pass 15, which is used, the mean value output by the R / U converter to determine. For this purpose, the low pass 15 forms the time weighted average. Its corner frequency is, for example, 20 Hertz. This dimensioning ensures that a Loss of flame, i.e. a change in the mean of the Signals, detected very quickly and the burner 3 very much can be shut down quickly.

An analog / digital converter is at the output of the low pass 15 16 connected (A / D converter) that the Filter output signal digitized to a microcontroller 17 passes. Alternatively, the low pass 15 can be dispensed with become. The A / D converter then passes to the microcontroller 17 samples of the current time signal. The microcontroller can compute the mean of the time signal form by making a set number of the last Measured values added up. The sum thus obtained corresponds the mean.

The channel contains 12 as a signal evaluation device a band pass filter 18 (or alternatively a high pass filter). The center frequency of the bandpass 18 is, for example. at 30 Hertz, the bandwidth being relatively large can be. For example, the 3dB corner frequencies are included 10 and 40 Hertz. Network correlated alternating light components from External light sources can thus be excluded, whereby the flickering of the signal (see Fig. 3) detected broadband becomes. The filter output signal can be sent directly to the microcontroller 17 are transmitted. This keys the input signal (if necessary via an A / D converter 19) periodically ab, there will be a flickering signal as long as is to get stochastic values. So the individual lie Samples in a specified range of fluctuation. If this falls below, the alternating share is below a set limit. The microcontroller 17th can check this by constantly making differences between consecutive signal values forms and only then a flickering signal detects when the individual differences exceed a minimum value. Kick several times consecutively smaller differences, it can be assumed that the alternating component of the signal according to FIG. 3 below a predetermined limit. Alternatively, the sum on the amounts of several successive differences formed and compared with the limit.

The microcontroller 17 is programmed so that it a valid flame signal (indicating a burning flame) only releases if that recorded via channel 11 DC signal is in a predetermined range and at the same time the flicker signal detected in channel 12 is one Exceeds the minimum value. The default range for the DC signal corresponds to a resistance range B for the current resistance value of the photo resistor 6 (Fig. 1). The flicker signal provided by channel 12 must be lie above a limit value G. This is illustrated in Fig. 3.

The monitoring device 1 described so far works as follows:

When properly operated, the photo resistance is recorded 6 the light emitted by the flame 2. The brightness fluctuates according to the diagram of FIG. 3 Time course of the electrical signal at the output of the Converter 14. Channel 11 determines the short-term average this signal by low pass filtering. Has the Flame 2 such a brightness that the resistance value of the photo resistor 6 around that illustrated in FIG. 2 The value P fluctuates, which is in the area B, recognizes this the microcontroller 17. At the same time the bandpass 18 in the channel 12 the flicker portion of the channel is filtered out. The microcontroller 17 checks whether the flicker content is greater is given by the limit G (Fig. 3). If yes the microcontroller registers this. If both conditions (Channel 11, mean value in area B; channel 12 flicker percentage greater than limit G) are met, the microcontroller outputs a flame signal that indicates the presence identifies a flame or generates a corresponding one internally Signal for further processing.

If the photo resistor 6 ages or the electrical ones change Properties over time such that it e.g. receives a characteristic curve according to curve II or III, drifts Resistance value not out of range. However takes the level of the flicker signal screened by the bandpass 18 with decreasing curve steepness (curve II or Curve III). Therefore, the flickering signal soon falls below its limit G, with which the microcontroller 17 no longer recognizes both signals as valid. So he reports flame failure and thus enables the burner to be switched off Third

In addition, it can be provided that the microcontroller based on the finding that the signal of the channel 11 is in the validity range B, the flickering signal of the Channel 12 has failed, however, generates a signal that indicates the failure of the photo resistor 6.

5 is a modified embodiment of the Monitoring device 1 illustrates. The monitoring circuit 7 takes over functions that are used in the 4 by the microcontroller 17 have been taken over.

Insofar as the functionality is the same, the following Description uses the same reference numerals, as in connection with the above description, and generally to the description above directed.

The photoresistor 6 is connected with one connection to an operating voltage U _b and with its other connection to the R / U converter 14, which generates a voltage output signal which corresponds to the current flowing through the photoresistor 6. As the resistance of the photoresistor 6 decreases, the output voltage of the converter 14 increases. The output voltage is transmitted to the low-pass filter 15, which determines the time average of the converter output signal. The output signal of the low-pass filter 15 is sent to a window discriminator 21, which checks whether the low-pass filter output signal is in a predetermined switching range, which corresponds to range B in FIG. 2. The limits of the switching range are monitored by two trigger circuits 22, 23, which have control inputs 24, 25 for determining the trigger thresholds. The trigger outputs are connected to an exclusive OR gate 26, which only delivers a valid output signal at its output if only one of the two trigger circuits 22, 23 detects limit violations.

The actuating inputs 24, 25 serve the switching thresholds the trigger circuits 22, 23 to be adjusted as required and the respective operating mode of the burner 3 adapt. For example, in particular for the lower switching threshold responsible for low incidence of light Ignition operation to be set differently (lower) than after ignition during burner operation (this becomes negative Switching difference).

The channel 12 can follow the bandpass 18 Signal rectifier 27 included the flicker signal converts into a DC signal. A connected trigger circuit 28 serves to check whether the alternating signal (Flicker signal) exceeds a predetermined limit G. The two channels 11, 12 are on the output side via a Logic circuit 29, which is designed, for example, as an AND circuit is linked together to generate a flickering signal.

A continuously reliable monitoring device 1, especially for flame monitoring on oil-powered Fan burners is provided, has a photo resistor 6, which is connected to a monitoring circuit 7 is. This evaluates the output from the photo resistor 6 Two-channel signal off. A first channel 11 is used for detection the average brightness. A second channel 12 is used to record changing parts caused by flickering come from the flame. The flame will only be considered proper recognized burning when at both channel outputs of channels 11, 12 a signal is present, or that Signal is in a predetermined range. On this way you can make gradual changes in particular the characteristic of the photo resistor, as in Detect continuous burner operation and are dangerous. It ensures that the flame monitoring not made with a broken photo resistor or is tried.

Claims (15)

Method for flame monitoring on one or more burners, especially fan burners, by means of a radiation-sensitive detection device (6) which emits an electrical signal which characterizes the radiation power, wherein in the method the electrical signal is passed in parallel through at least two filter devices (15, 18) with different characteristics and both filter output signals are checked to determine whether they are within an expected range (B, G), an output signal characterizing the presence of a flame is only generated if both filter output signals are in their respective expected range (B, G). Method according to claim 1, characterized in that signal fluctuations of the electrical signal are detected by means of one of the filter devices and a signal mean value is detected by the other filter device. A method according to claim 1, characterized in that the signal fluctuations of the electrical signal are used as an indicator for the operability of the radiation-sensitive detection device (6). A method according to claim 1, characterized in that it is regarded as an indicator of a failure of the detection device (6) when its signal value is below a predetermined limit (R _k ). Method according to Claim 1, characterized in that the indicator for the failure of the detection device (6) is evaluated if the electrical signal before the ignition of a flame is in the region in which it is expected if a flame is present. Monitoring device (1) for flame monitoring on one or more burners (3), in particular fan burners, with a radiation-sensitive detection device (6) which emits an electrical signal which characterizes the absorbed radiation power, with a first channel (11) which is connected to the detection device (6) and contains a signal evaluation device (15) to which the electrical signal is fed to the detection device (6) and which outputs a flame signal at its output when the electrical signal meets a first criterion, with a second channel (12) which is connected to the detection device (6) and contains a signal evaluation device (18) to which the electrical signal is fed to the detection device (6) and which emits a flame signal at its output when the electrical signal meets a second criterion, wherein the signal evaluation devices (15, 18) of the two channels (11, 12) are set up to check different criteria, and with a logical evaluation device (17, 21, 29) which has two inputs which are connected to the channels (11, 12) and which only emits a flame detection signal if both channels (11, 12) each emit a flame signal. Monitoring device according to claim 6, characterized in that the signal evaluation devices (15, 18) are filter devices. Monitoring device according to claim 6, characterized in that a channel (11) as a signal evaluation device (15) is a device (15) for forming a time average and the other channel (12) as a signal processing device (18) is a device for detecting signal changes. Monitoring device according to claim 6, characterized in that a channel (11) contains a low-pass filter (15) as a signal evaluation device (15) for detecting the radiation power. Monitoring device according to claim 9, characterized in that the channel (11) has a window discriminator (21) following the low pass (15). Monitoring device according to claim 10, characterized in that the window discriminator (21) has at least one control input (25) for determining its switching limits. Monitoring device according to claim 6, characterized in that one of the signal evaluation devices (15, 18) is set up for the selection of flicker signals. Monitoring device according to claim 12, characterized in that the signal evaluation device (18) is a filter device with high-pass behavior. Monitoring device according to claim 12, characterized in that the signal evaluation device (18) is a filter device (18) with bandpass behavior. Monitoring device according to claim 6, characterized in that the detection device (6) is a photo resistor.

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