EP3374696A1

EP3374696A1 - Method and device for flame signal detection

Info

Publication number: EP3374696A1
Application number: EP16788076.4A
Authority: EP
Inventors: Martin Ries; Arno Clemens; Richard Pfüller; Sebastian Hack
Original assignee: Viessmann Werke GmbH and Co KG
Current assignee: Viessmann Werke GmbH and Co KG
Priority date: 2015-11-11
Filing date: 2016-10-26
Publication date: 2018-09-19
Anticipated expiration: 2036-10-26
Also published as: EP3374696B1; CA3004930A1; WO2017080820A1; US20180372316A1; DE102015222263B3; US10704785B2

Abstract

The invention relates to a method for flame signal detection by means of an ionisation electrode protruding into a combustion zone of a burner, comprising the steps: detecting a first signal, which is dependent upon an ionisation stream flowing off from the ionisation electrode, generating a second signal which has a predetermined periodic pattern, generating a third signal by addition of the first signal (225) and of the second signal, comparing the third signal with a first threshold value (reference 1) and generating a fourth signal (output signal 1) on the basis of the comparison of the third signal with the first threshold value (reference 2), comparing the third signal with a second threshold value (reference 2) different from the first threshold value and generating a fifth signal (output signal 1) on the basis of the comparison of the third signal with the second threshold value (reference 2), and determining an operating variable of the burner on the basis of at least one of the fourth signal and the fifth signal. The invention further relates to a corresponding device for flame signal detection.

Description

METHOD AND DEVICE FOR FLAME SIGNAL DETECTION

The invention relates to a method and a device for flame signal detection or flame resistance detection in a burner, in particular an oil or gas burner. In particular, the invention relates to a method and apparatus for adapting the signal detection of a combustion control system to the flame resistance region of a burner. Background of the invention

In the prior art, methods are known in which the determination of an operating variable of a burner, for example the air ratio λ, is effected by measuring an ionization current flowing from an ionization electrode introduced into the combustion chamber. In this case, an alternating voltage is applied to the ionization electrode and a current flowing away from the ionization electrode and rectified due to the rectifier characteristic of the flame is detected as an ionization current. By means of a control circuit, the measured ionization current is then compared with a desired value for the ionization current corresponding to the set desired value of the air ratio, and the composition of the air-fuel mixture is readjusted accordingly. Such a method is described for example in the document DE 44 33 425 AI. At the same time it is known to detect the presence of a flame in the combustion chamber by means of ionisationsstrommessung or flame resistance measurement.

In these previously known methods, however, the problem arises that the control circuit has a fixed measurement resolution, but the detected ionization current has a non-linear course over its modulation range. Therefore, it is not possible to detect the lonisationsstrom or flame resistance at the optimum operating resolution for each operating point at several operating points of the burner. Summary of the invention

It is therefore an object of the invention to provide methods and apparatus for flame signal detection which are free from the above-identified problems in the prior art. It is a particular object of the invention to provide methods and apparatus for flame signal detection, which make it possible to detect the ionisation current or flame resistance at mutually different operating points of the burner with the respectively optimum measuring resolution. It is a further object of the invention to achieve a linearization of the ionization current signal over its entire modulation range.

To solve this problem, a method for flame signal detection and a device for flame signal detection with the features of the independent claims are proposed.

According to a first aspect of the invention, a method for detecting the flame signal by means of an ionization electrode protruding into a combustion chamber of a burner is proposed. The method comprises the steps of detecting a first signal dependent on an ionization current flowing from the ionization electrode, generating a second signal having a predetermined periodic profile, generating a third signal by adding the first signal and the second signal, comparing of the third signal having a first threshold, comparing the third signal to a second threshold other than the first threshold, generating a fourth signal based on the comparison of the third signal to the first threshold (ie, generating the fourth signal by comparing the third signal to the first threshold), generating a fifth signal based on the comparison of the third signal with the second threshold (ie, generating the fifth signal by comparing the third signal with the second threshold), and Determining an operating amount of the burner based on at least one of the fourth signal and the fifth signal.

The first and second threshold values can be fixed in each case. The fourth and fifth signals may each be a signal (e.g., voltage signal) having a sequence of square pulses, in particular a pulse width modulated (PWM) signal. The operating size of the burner may be, for example, the ionization current, the flame resistance, the flame temperature, the air ratio, or the burner output.

The method described above makes it possible, by suitable selection of the curves and the first and second threshold values, to generate signals which in each case offer optimum measurement resolution (sensitivity) for the evaluation of the ionization current signal for different operating points or operating ranges of the burner. For example, on the one hand, the presence of the flame in the start-up operation of the burner, so with a large flame resistance and small ionisationsstrom, can be detected with high reliability and time resolution. On the other hand, at the same time, the flame resistance in operation near the optimum air ratio, that is, with small flame resistance and large ionization current, can be determined with high accuracy, and based on which the composition of the air-fuel mixture can be readjusted with high accuracy. The method according to the invention therefore causes a linearization of the ionisationsstromsignals on the modulation range of the burner and thus enables a safe and stable control of the burning process.

Preferably, the predetermined course of the second signal has a first portion (curve portion) with a first slope value and a second portion (curve portion) with a second slope value different from the first slope value. Preferably, the predetermined curve has a rising edge and a falling edge, and the first section and the second section are respectively arranged together in the ascending flank, or together in the descending flank. In this case, the first section and the second section can each have the shape of a straight line, that is straight line sections. Alternatively, the first and second portions may be approximate straight lines having averaged slope values. The first and second sections can adjoin one another or follow one another in the course of the curve. By suitably selecting the different slope values of the first and second sections, the respective desired measurement resolution (sensitivity) for different operating states or operating ranges of the burner can be selected independently of one another. In embodiments of the invention, the first threshold value is selected such that for a ionization current occurring in a first operating state (or in a first operating region or at a first operating point) of the burner, the d ritte signal in each case at the first time within the first threshold Period of the second signal (or within the period, the approximately periodic third signal) for which the second signal has a signal value which falls within the first portion of the periodic curve. In other words, the first threshold value is selected so that the second signal has a signal value within the first curve section at the first time. Here, the first time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the first threshold. If the first portion is within the rising edge, the first time is the time at which the third signal exceeds the first threshold. If, on the other hand, the first section is located within the descending edge, the first point in time is the point in time at which the third signal falls below the first threshold value. In embodiments of the invention, the second threshold is further selected such that for a ionization current occurring in a second operating state (or in a second operating region or at a second operating point) of the burner, the third signal the second threshold at a second time within the period of the second signal (or within the period, the approximately periodic third signal) for which the second signal has a signal value falling within the second section. In other words, the second threshold value is selected such that the second signal has a signal value within the second curve section at the second time point. In this case, the second time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the second threshold value. If the second portion is within the rising edge, the second time is the time at which the third signal exceeds the second threshold. If, on the other hand, the second section is within the descending flank, the second point in time is the time at which the third signal falls below the second threshold.

Due to the different choice of the first and second threshold values, as well as the slopes of the first and second curve sections, an optimum measurement resolution for the respective operating state can be achieved for both the first operating state and for the second operating state. For example, the selection of a smaller slope for the first curve section causes small changes in the ionization current to lead to large changes in the position of the first time point, ie a high measurement resolution is achieved. Further, for example, choosing a larger slope for the second curve section will cause large changes in the ionization current to result in only small changes in the second timing location so that changes in the ionization current can be detected and evaluated over a wide range of values. Preferably, the first slope value is less than the second slope value, and the first operation state corresponds to a higher flame resistance than the second operation state. At higher flame resistance, for example when starting the burner, the ionization is small and has seen absolutely small changes accordingly. By choosing a lower slope for the first curve section, even such relatively small changes in the ionization current can be detected, and a presence of the flame can be reliably detected. At the same time, the composition of the air-fuel mixture can be readjusted with high accuracy. With lower Flam menwiderstand, for example, in the heating operation of the burner in the vicinity of an optimal air ratio, the ionization current is correspondingly larger and has corresponding changes over a wide range of values on away. By choosing a larger slope for the second curve section changes in the ionization itself can be detected over such a large range of values, so that here too, the composition of the air-fuel mixture can be readjusted with high accuracy. As a result, a safe and stable control of the combustion system is achieved as a result.

Preferably, the value of the operating variable is determined by mathematical and / or logical combination of the fourth signal and the fifth signal (or respectively derived therefrom signals). For example, the method may include the further steps of: determining a first value of the operating amount of the burner based on the fourth signal, determining a second value of the operating amount of the burner based on the fifth signal, and determining a third value of the operating amount of the burner based on at least one the first value and the second value. In this case, the third value can be obtained by mathematical and / or logical combination of the first value and the second value. For example, depending on the first value and the second value, it may be decided output the first value as the third value, or output the second value as the third value, or output a weighted sum of the first value and the second value as the third value. The weighting can be effected as a function of an operating state derived from the first and / or second value.

By such a determination of the value of the operating variable of the burner can be used in each case to that of the fourth and fifth signals, which provides the optimal measurement resolution for the current operating state or operating range of the burner.

According to a second aspect of the invention, an apparatus for flame signal detection is proposed by means of an ionization electrode projecting into a combustion chamber of a burner. The device comprises means (eg, a measuring device) for detecting a first signal dependent on an ionization current flowing from the ionization electrode, means (eg, a signal generator) for generating a second signal having a predetermined periodic profile, means (eg an adder) for generating a third signal by adding the first signal and the second signal, means (eg, a first comparator) for comparing the third signal with a first threshold, and generating a fourth signal based on the comparison of the third signal with the first one Threshold (ie, for generating the fourth signal by comparing the third signal with the first threshold), means (eg, a second comparator) for comparing the third signal with a second threshold different from the first threshold, and generating a fifth signal based on Comparison of the third signal with the second Threshold (ie, for generating the fifth signal by comparing the third signal with the second threshold), and means (eg, an evaluation circuit) for determining an operation amount of the burner based on at least one of the fourth signal and the fifth signal. The first and second threshold values can be fixed in each case. The fourth and fifth signals can each be a signal (eg voltage signal) with a sequence of square-wave pulses, in particular a PWM signal.

Preferably, the predetermined course of the second signal has a first portion (curve portion) with a first slope value and a second portion (curve portion) with a second slope value different from the first slope value. The predetermined curve preferably has an ascending flank and a descending flank, and the first section and the second section are each arranged jointly in the ascending flank, or together in the descending flank. In this case, the first section and the second section can each have the shape of a straight line, that is straight line sections. Alternatively, the first and second portions may be approximate straight lines having averaged slope values. The first and second sections can connect to each other, or follow each other in the course of the Kurvenveriaufs. In embodiments of the invention, the first threshold value is selected such that for an ionization current occurring in a first operating state (or in a first operating range or at a first operating point) of the burner, the third signal will apply the first threshold value in each case at a first point in time within the period second signal (or, within the period, the approximately periodic third signal) for which the second signal has a signal value falling within the first portion of the periodic waveform. In other words, the first threshold value is selected so that the second signal has a signal value within the first curve section at the first time. Here, the first time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the first threshold. If the first section is within the rising edge, the first time is the time at which the third signal exceeds the first threshold. If, on the other hand, the first section is located within the descending edge, the first point in time is the point in time at which the third signal falls below the first threshold value.

In embodiments of the invention, the second threshold is further selected such that for a ionization current occurring in a second operating state (or in a second operating region or at a second operating point) of the burner, the third signal the second threshold at a second time within the period of the second signal (or within the period, the approximately periodic third signal) for which the second signal has a signal value falling within the second section. In other words, the second threshold value is selected such that the second signal has a signal value within the second curve section at the second time point. In this case, the second time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the second threshold value. If the second portion is within the rising edge, the second time is the time at which the third signal exceeds the second threshold. If, on the other hand, the second section is within the descending flank, the second point in time is the time at which the third signal falls below the second threshold.

Preferably, the first slope value is less than the second slope value, and the first operation state corresponds to a higher flame resistance than the second operation state.

In embodiments of the invention, the means for determining the operating size of the burner are configured to determine the value of the operating variable by mathematically and / or logically combining the fourth signal and the fifth signal (or signals derived therefrom). For example, the means for determining the operating quantity of the Burner to be configured to determine a first value of the operating size of the burner based on the fourth signal to determine a second value of the operating size of the burner based on the fifth signal, and a third value of the operating size of the burner based on at least one of the first value and the second value. In this case, the third value can be obtained by mathematical and / or logical combination of the first value and the second value. For example, depending on the first value and the second value, it may be decided to output the first value as the third value, or output the second value as the third value, or output a weighted sum of the first value and the second value as the third value , The weighting can be effected as a function of an operating state derived from the first and / or second value. Short description of the drawing

Further advantageous embodiments, but to which the invention is not limited in scope, will become apparent from the following description with reference to the drawing. Identical elements are provided in the figures with identical reference numerals, and it is omitted to repeat the description of elements already described. They show in detail:

FIG. 1 shows an arrangement for measuring the ionization current flowing from an ionization electrode projecting into a flame,

FIG. 2 shows an exemplary schematic representation of an example of a method according to embodiments of the invention,

3 shows an exemplary schematic representation of an example of the time characteristic of the third signal, and Figure 4 is an exemplary schematic representation of the waveform of the second signal over a period of the second signal.

Detailed description of the invention

FIG. 1 shows an arrangement 10 for measuring or detecting the ionization current flowing from an ionization electrode projecting into a flame, or a first signal which depends on the ionization current. By means of a transformer 11, a supplied supply voltage (for example mains voltage) is converted into an alternating voltage of suitable amplitude and applied to the ionisation electrode 15 via a capacitor 14. By the rectifying property of the flame, the capacitor 14 is charged with a voltage proportional to the ionization current. This results in a shift of the zero point of the AC voltage. The resulting AC voltage, ie a signal dependent on the current flowing away from the ionization electrode 15 (voltage signal), is filtered by a low-pass filter 12 and the filtered DC component is output at an output 13 of the device 10. This is due to the polarity of the rectifier property of the flame to a negative voltage. The assembly 10 may further include suitable resistors 16. The first signal is, for example, the signal output at the output 13. FIG. 2 shows schematically a block diagram of an example of the method according to the invention. The individual blocks correspond to method steps or corresponding devices and means which are designed to carry out the respective method steps. In block 205, the supply voltage (for example mains voltage) is converted into an alternating voltage of suitable amplitude, and applied to the ionization electrode 15 in block 210. Above the blocks 205, 210 are schematically illustrates the voltage applied to the ionization electrode 15 AC voltage and the resulting, tapped at the ionization voltage signal. Due to the current flowing away from the ionization electrode 15, a negative offset is impressed on the original alternating voltage signal.

The obtained signal is filtered in block 215 by using the low-pass filter 12. As a result, a first signal which is dependent on an ionization current flowing out of the ionization electrode is obtained. In other words, the low-pass filter 12 isolates the negative offset impressed on the AC signal and outputs it as the first signal. An example of the time course of the first signal is shown in FIG. 2 below block 215. It is within the scope of the above steps at the discretion of the skilled person to modify any or all of the steps accordingly, as a result of obtaining an ionization current dependent signal from the ionization electrode, and the invention is not limited to the above-described method of detecting such a signal limited.

In block 220, a second signal having a periodic waveform, such as a periodic waveform voltage signal, is generated. The periodic course during operation of the burner is fixed, but can basically be selected or adjusted according to the burner characteristics. The generation can be carried out, for example, by a curve generator or signal generator (means for generating the second signal). In this case, the second signal can be generated by using suitable software and a digital-to-analog converter, or mitteis pulse width modulation, and adapted to the respective burner characteristics. A burner-specific curve can be stored in advance in a memory. A schematic example of the curve is shown in FIG. 2 above block 220. The predetermined curve (ie, the signal value as a function of time) has in each period of the second signal a first section with a first slope value (change of the signal value per unit time, or first time derivative of the curve) and a second section with a second slope value, wherein the two slope values are different from each other. The curve also has an ascending edge and a descending edge in each period. In this case, the first section and the second section are preferably each arranged in the same flank, ie both in the ascending flank, or both in the descending flank. The two sections can connect to each other. In order to obtain PWM signals with a fixed frequency as a result, moreover, that edge in which the two sections are not arranged can run very steeply or essentially vertically. In the simplest case, the two sections each have the shape of a straight line or an approximate straight line. In the case of an approximate straight line, the respective slope value can be obtained by averaging slope values.

Examples of two possible curves of the second signal are shown in FIG. Both curves have a first portion 401 of lower slope value. The first of the two curves has a second section 402 next to it, and the second of the two curve sections has a second section 403. In both curves, the slope value of the second section 402, 403 is greater than that of the first section 401. The first section 401 and second sections 402, 403 in each case directly adjoin one another or merge into one another. Below the first section 401 and / or above the second section 402, 403, the curve may have further sections. In the example of FIG. 4, the descending edge of the curve runs essentially vertically in order to obtain fixed-frequency PWM signals in the blocks 230, 235 described below. In block 225, the first signal and the second signal are added together (mixed) to obtain a third signal. The addition or generation of the third signal may, for example, be performed by an adder (means for generating the third signal). The weighting of the two signals is determined by a mixing ratio or a mixing resistance. By a suitable choice of the mixing ratio, the sensitivity or measurement resolution of the overall system (ie equally for all operating ranges) can be determined. Higher weighting of the first signal increases the sensitivity of the measurement, but reduces the range of values covered by the measurement. On the other hand, a higher weighting of the second signal reduces the sensitivity of the measurement, but increases the range of values that can be covered by the measurement. For constant ionization current, the third signal is a periodic signal having a period equal to the period of the second signal, otherwise an approximately periodic signal.

In block 230, the resulting mixed voltage, or generally the third signal, is compared to a first reference value (first threshold) and a fourth signal (e.g., voltage signal) is generated based on the comparison. Preferably, the fourth signal is a signal (e.g., voltage signal) formed by a series of square-wave pulses, in particular a PWM signal. In this case, a first level (eg, the upper level) of the PWM signal is output if the signal value of the third signal is above the first threshold, and the second level (eg, the lower level) if the signal value of the third signal is below the first threshold. The comparison of the third signal with the first threshold value can be effected, for example, by means of a first comparator (means for generating the fourth signal). A schematic example of the time course of the fourth signal is shown in FIG. 2 above block 250.

The first reference value (threshold value) is in block 240 as a constant signal (eg voltage signal), for example by use ^' a controllable Voltage source or a DA converter (means for generating the first threshold) generated. The controllable voltage source can be controlled, for example, by means of a PWM control signal. In block 235, the mixed voltage, or generally the third signal, is compared to a second reference value (second threshold), and a fifth signal (eg, voltage signal) is generated based on the comparison. Preferably, the fifth signal is a signal (eg, voltage signal) formed by a series of rectangular pulses, in particular a PWM signal. In this case, a first level (eg, the upper level) of the PWM signal is output if the signal value of the third signal is above the second threshold, and the second level (eg, the lower level) if the signal value of the third signal is below the second level second threshold. The comparison of the third signal with the second threshold value can be effected, for example, by means of a second comparator (means for generating the fifth signal). A schematic example of the timing of the fifth signal is shown in FIG. 2 above block 255.

The second reference value is generated in block 245 as a constant signal (eg voltage signal), for example by using a controllable voltage source or a DA converter (means for generating the second threshold value). The controllable voltage source can be controlled, for example, by means of a PWM control signal. Preferably, the first threshold value for a given curve of the second signal is selected such that for a in a first operating state (or in a first operating range or at a first operating point) of the burner ionization current (or flame resistance), the third signal the first threshold each at a first time within the period of the second signal (or within the period the approximately periodic third signal) for which the second signal has a signal value falling within the first portion of the periodic waveform. With others Words, the first threshold is selected so that the second signal has a signal value within the first curve section at the first time. Here, the first time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the first threshold. If the first portion is within the rising edge, the first time is the time at which the third signal exceeds the first threshold. If, on the other hand, the first section is located within the descending edge, the first point in time is the point in time at which the third signal falls below the first threshold value.

For example, the first operating state of the burner may be the start-up mode, in which the flame resistance is correspondingly large (eg, approximately 70 to 100 Ω). Because of the large flame resistance then results in a comparatively small ionization with absolutely small changes per unit time. In this case, the slope value of the first section may be set to be small (or less than the slope value of the second section), and the first threshold may be further selected such that at the time (first point in time) at which the third signal is the first Threshold exceeds (if the first section is located in the rising edge of the second signal) or at the time when it falls below the first threshold again (if the first section is located in the falling edge of the second signal), the signal value of second signal lies within the first section. Because of the small slope of the first section, small changes in the ionization current or flame resistance already result (in absolute terms) in a clear shift in the first time point at which the third signal crosses the first threshold value. Thus, even such relatively small changes in the ionization current can be detected, and, for example, the flame can be reliably detected. In addition, the composition of the air-fuel mixture can be readjusted with high accuracy. Accordingly, the second threshold value can be chosen such that for a ionization current (or flame resistance) occurring in a second operating state (or in a second operating region or at a second operating point) of the burner, the third signal, the second threshold value in each case at a second time within the period of the second signal (or within the period the approximately periodic third signal) for which the second signal has a signal value falling within the second section. In other words, the second threshold value is selected such that the second signal has a signal value within the second curve section at the second time point. In this case, the second time is the time within the period of the second signal for which the value (signal value) of the third signal is equal to the second threshold value. If the second portion is within the rising edge, the second time is the time at which the third signal exceeds the second threshold. If, on the other hand, the second section is within the descending flank, the second point in time is the time at which the third signal falls below the second threshold.

For example, the second operating state of the burner may be operation (eg, heating operation) in the vicinity of an optimum air ratio (eg, λ "1.3) in which the flame resistance is correspondingly small (eg, about 70 to 100 kQ). Because of the small flame resistance then results in a comparatively large ionisationsstrom with absolutely great changes per unit time. In this case, the slope value of the second section may be set to be large (or greater than the slope value of the first section), and the second threshold may be further selected such that at the time (second point in time) at which the third signal is the second Threshold exceeds (if the second section is located in the rising edge of the second signal) or at the time when it falls below the second threshold again (if the second section is located in the falling edge of the second signal), the signal value of second signal lies within the second section. Because of the large slope of the second section, large changes in the ionization current or flame resistance now also result (in absolute terms) in a slight shift of the second time point at which the third signal crosses the second threshold value. Thus, relatively large changes over a wide range of values of the ionization can be detected, and the composition of the air-fuel mixture can be readjusted with high accuracy. In summary, the position of the first and second operating ranges in which a detection of the ionization current or flame resistance with a corresponding measurement resolution is desired can be predetermined for a given curve of the second signal by selecting the first and second reference voltages. Optionally, an overlap region of the operating ranges can be determined by a suitable choice of the reference voltages. By selecting the first and second slope values, however, the respective measurement resolution is predetermined. A larger slope value means a lower measurement resolution (sensitivity), and a lower slope value means a higher measurement resolution.

In other words, via the suitable choice of the curve shape of the second signal, a linearization of the ionization signal course (or flame resistance signal course) of a burner can take place over the entire modulation range. This allows a safe and stable control of the combustion system or the burning process. Overall, the method according to the invention offers five parameters (first threshold value, second threshold value, first slope value, second slope value, mixing ratio) via whose selection an ionization signal curve which is optimal for the combustion control can be achieved.

The relationship between measurement resolution (sensitivity), slope values and threshold values is shown by way of example in FIG first example, the operation in a first operating state and as a second example, the operation of the burner in a second operating state includes. The third signal shown in FIG. 3 results from a shift of the second signal to negative voltage values due to the addition of the (negative) first signal. Accordingly, the third signal also has a first section 301 and a second section 302, in which case the second section 302 has a greater gradient value than the first section 301. In the first example, if the third signal crosses the first threshold value 303 in the region of the first section 301, even small changes 304 in the ionization current (or the signal value of the third signal) result in relatively large changes 305 in the crossover time. In FIG. 3, such a small change of the signal value of the third signal is clarified for reasons of representability by a corresponding change of the first threshold value. Conversely, in the second example, if the third signal crosses the second threshold value 306 in the region of the second section 302, then changes 307 of the ionization current (or the signal value of the third signal) of the same size as in the first example result in significantly smaller changes 308 in the crossing time point. The fourth and fifth signals are, as already stated above, preferably PWM signals. The size of the ionization current determines the pulse duration (or duty cycle) of the respective PWM signals In the case described above, even small changes in the flame resistance in the first operating state result in a detectable change in the duty cycle of the fourth signal. and also large changes in the flame resistance in the second operating state are reproducible by changes in the duty cycle of the fifth signal, that is, with an appropriate choice of the threshold values and slope values, the fourth signal provides the necessary resolution for the operating range of the burner in which the flame has a high resistance (high-impedance range), and the fifth signal the necessary resolution for the operating range of the burner, in which the flame has a low resistance (low-resistance range). At block 250, the (time varying) pulse width (ie, width or duration of the square pulses) of the fourth signal is determined, and a sixth signal indicating that pulse width is generated or output. Accordingly, in block 255, the (time varying) pulse width (ie width or duration of the square pulses) of the fifth signal is determined, and a seventh signal indicating this pulse width is generated or output.

Based on at least one of the fourth signal and the fifth signal (or on the basis of at least one of the sixth signal and the seventh signal), a value of an operating variable of the burner, for example ionization current, flame resistance, flame temperature, air ratio, burner power, can now be determined. This can be done by mathematical and / or logical combination of the respective signals, so for example by mathematical and / or logical combination of the fourth and fifth signals, or by mathematical and / or logical combination of the sixth and seventh signals.

For example, for each of the sixth and seventh signals, a table can be stored in a memory which relates values of the operating variable to respectively corresponding values of the pulse duration. Based on the values of the operating variable determined by means of these tables, the value of the operating variable to be output can then be determined. For this a number of possibilities are conceivable. For example, from the two values determined by means of the tables, the operating range in which the burner is currently located can be estimated. In accordance with this estimated operating range, one of the two values determined by means of the tables can then be used in each case as the value to be output. For example, if the estimated operating range is closer to the first operating range, the value determined based on the sixth signal may be output, otherwise based on the seventh signal determined value. Further, based on the estimated operating range, weighting factors for the two values obtained by means of the tables can be derived, and a weighted sum of these values can be used as the value to be output. In general, in the context of the method according to the invention, the value of the operating variable to be output is determined by mathematical and / or logical combination of the fourth and fifth signals, or of the sixth and seventh signals.

The determination of the value of the operating variable can be done in an evaluation circuit (means for determining the operating size of the burner).

The method according to the invention has been described above on the basis of specific embodiments. Unless otherwise stated, the present disclosure is intended to cover, as it were, corresponding apparatus embodying the method which includes means and means configured to perform the respective method steps.

The invention has been explained in more detail with reference to specific embodiments, without being limited to the specific embodiments. In particular, it is possible to combine features of the different embodiments and also to use in the other embodiments.

Claims

claims

1. A method for flame signal detection by means of a projecting into a combustion chamber of a burner ionization electrode (15), comprising the steps:

Detecting a first signal from one of the

Ionisationselektrode (15) is dependent on the effluent ionization current;

Generating a second signal having a predetermined, periodic course;

Generating a third signal by adding the first signal and the second signal;

Comparing the third signal with a first threshold;

Comparing the third signal with a second threshold different from the first threshold;

Generating a fourth signal based on the comparison of the third one

Signal with the first threshold;

Generating a fifth signal based on the comparison of the third signal with the second threshold; and

Determining an operating amount of the burner based on at least one of the fourth signal and the fifth signal.

2. The method of claim 1, wherein the predetermined course of the second signal comprises a first portion having a first slope value and a second portion having a second slope value different from the first slope value.

3. The method according to at least one of the preceding claims, wherein the first threshold value is selected such that for a occurring in a first operating state of the burner ionization current, the third signal crosses the first threshold each at a first time within the period of the second signal for the the second signal has a signal value falling within the first section.

4. The method according to at least one of the preceding claims, wherein the second threshold is selected such that for a occurring in a second operating state of the burner ionization current, the third signal crosses the second threshold each at a second time within the period of the second signal for the the second signal has a signal value falling within the second section.

5. The method according to at least one of the preceding claims, wherein the operating size of the burner by mathematical and / or logical

Linking the fourth signal and the fifth signal, or from it

derived signals, is determined.

6. The method according to at least one of the preceding claims, with the further steps:

Determining a first value of the operating amount of the burner based on the fourth signal;

Determining a second value of the operating amount of the burner based on the fifth signal;

Determining a third value of the operating size of the burner

Based on at least one of the first value and the second value.

7. The method of claim 6, wherein the third value by

mathematical and / or logical combination of the first value and the second value is determined.

8. The method of claim 2, wherein the first slope value is less than the second slope value, and the first operating state corresponds to a higher flame resistance than the second operating state.

9. Apparatus for detecting flame signals by means of a projecting into a combustion chamber of a burner ionization electrode (15), the

Device comprising:

Means for detecting a first signal dependent on an ionization current from the ionization electrode (15);

Means for generating a second signal having a predetermined periodic profile;

Means for generating a third signal by adding the first signal and the second signal;

Means for comparing the third signal with a first threshold and for generating a fourth signal based on the comparison of the third signal with the first threshold;

Means for comparing the third signal with a second threshold different from the first threshold and generating a fifth signal based on the comparison of the third signal with the second one

threshold; and

Means for determining an operating amount of the burner based on at least one of the fourth signal and the fifth signal.

10. The apparatus of claim 9, wherein the predetermined course of the second signal has a first portion with a first slope value and a second portion with a second, different from the first slope value slope value.

11. The apparatus of claim 9 or 10, wherein the first threshold is selected such that for a occurring in a first operating state of the burner ionization current, the third signal crosses the first threshold each at a first time within the period of the second signal, for the second signal has a signal value that falls within the first section.

12. The device according to at least one of claims 9 to 11, wherein the second threshold value is selected such that for one in a second Operating mode of the burner occurring ionization current, the third signal crosses the second threshold each at a second time within the period of the second signal, for which the second signal has a signal value which falls within the second section.

13. The device according to at least one of claims 9 to 12, wherein said means for determining the operating size of the burner thereto

are configured to determine the operating size of the burner by mathematical and / or logical combination of the fourth signal and the fifth signal, or signals derived therefrom.

14. The apparatus of claim 9, wherein the means for determining the operating size of the burner is configured to determine a first value of the operating quantity of the burner based on the fourth signal, a second value of the operating quantity of the burner

Determine burner based on the fifth signal, and to determine a third value of the operating size of the burner based on at least one of the first value and the second value.

15. The apparatus of claim 14, wherein the means for determining the operating size of the burner are adapted to determine the third value by mathematical and / or logical combination of the first value and the second value.

16. The device of claim 10, wherein the first slope value is less than the second slope value, and the first operating state corresponds to a higher flame resistance than the second operating state.